Academic Year 2012 DISSERTATION

Novel Structure Oriented Compact Modeland Scaling Rule for Next Generation
Power Semiconductor Devices
次世代パワー半導体用高精度コンパクトモデルの開発とスケーリング則の確立

Masahiro Tanaka

Graduate School of Engineering,
Kyushu Institute of Technology
1-1 Sensui-cho, Tobata-ku, Kitakyushu-city, 804-8550, JAPANA dissertation submitted in partial fulfillment of the requirements
for the degree of Doctor of Philosophy
Copyright © 2012 by Masahiro Tanaka

i|

ACKNOWLEDGEMENTS ......................................................................................... IV
ABSTRACT ................................................................................................................ VI
和文要旨 .................................................................................................................. VIII
1BACKGROUND ..................................................................................................1
1.1

WHAT'S IGBT ..........................................................................................................1

1.2

APPLICATIONS AND MARKET TRENDS........................................................................2

1.3

ISSUES: COMPACT MODELING AND PROCESS COMPATIBILITY ..................................5

1.3.1

Compact Modeling..........................................................................................5

1.3.2

Scaling principle.............................................................................................6

1.4

SUMMARY.................................................................................................................7

2

OBJECTIVE ........................................................................................................93

STRUCTURE ORIENTED ANALYTICAL MODELING FOR MODERN TRENCHGATE IGBT ...................................................................................................................... 11
3.1

IGBT BASIC OPERATIONS ...................................................................................... 11

3.2

MODELING CONCEPT .............................................................................................15

3.3

QUASI-2D MOS-ADE MODEL................................................................................17

3.4

HOLE INJECTION MODEL FOR SHALLOW P-EMITTER .............................................21

3.4.1

NPT model ....................................................................................................21

3.4.2

PT model .......................................................................................................23

3.5

N-BASE MODEL .....................................................................................................25

3.6

SUMMARY...............................................................................................................28

4

IGBT COMPACT MODELING FOR WIDE RANGE STRUCTURE AND

TEMPERATURE .............................................................................................................. 29
4.1

IGBT CIRCUIT SIMULATION ENVIRONMENTS ........................................................29

4.2

PREVIOUS RESEARCH FOR IGBT COMPACT MODEL ...............................................30

4.2.1

Hefner’s Model .............................................................................................30

4.2.2

Palmer & Santi’s Model ...............................................................................32

4.3

MODEL FORMULATION AND IMPLEMENTATION.......................................................34

4.3.1

Voltage drop in N-Base ................................................................................35

4.3.2

Voltage drop in mesa region ........................................................................36

4.3.3

Voltage drop in MOS channel ......................................................................36

4.3.4

Built-in potential ..........................................................................................37

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4.4

IMPLEMENTATION ..................................................................................................39

4.5

VERIFICATION RESULTS .........................................................................................40

4.5.1

Structures .....................................................................................................40

4.5.2

Physical models ............................................................................................42

4.5.3

Calculation Results ......................................................................................44

4.6

DISCUSSION ...........................................................................................................62

4.6.1

Boundary condition between P-Base and N-Base ......................................62

4.6.2

Electron current via accumulation layer ....................................................63

4.7

FURTHER WORKS....................................................................................................65

4.8

SUMMARY...............................................................................................................65

5

IGBT SCALING PRINCIPLE TOWARD SHALLOW TRENCH STRUCTURE ... 66
5.1

CUTTING EDGE SILICON TECHNOLOGY AND IGBT.................................................66

5.2

PREVIOUS RESEARCH FOR IGBT PERFORMANCE LIMIT .........................................68

5.2.1

High precision process approach .................................................................69

5.2.2

Conventional process approach ...................................................................71

5.3

IGBT SCALING PRINCIPLE .....................................................................................73

5.4

SCALING THEORY ...................................................................................................75

5.5

CALCULATION RESULTS .........................................................................................78

5.6

DISCUSSION ...........................................................................................................90

5.6.1

Saturation current optimization .................................................................90

5.6.2

Electric Field in Gate Oxide ........................................................................94

5.6.3

Another Scaling Option ...............................................................................95

5.6.4

Process Flow .................................................................................................96

5.7

SUMMARY.............................................................................................................100
THE FUTURE: SHALLOW TRENCH IGBT ADVANTAGES AND RELATED

6ISSUES ........................................................................................................................ 101

7

6.1

CATHODE SIDE STRUCTURE OPTIMIZATION .........................................................101

6.2

HIGH TEMPERATURE ADVANTAGE OF SHALLOW TRENCH IGBT ...........................106

6.3

WAFER THICKNESS OPTIMIZATION .......................................................................108

6.4

LATEST SILICON PROCESS TECHNOLOGY .............................................................109

6.5

PACKAGING .......................................................................................................... 111

6.6

INTEGRATION ....................................................................................................... 112

6.7

SUMMARY: SCALED DEVICE ADVANTAGES AND ISSUES TO BE SOLVED ................... 116
CONCLUSION ................................................................................................ 117

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8

LIST OF TABLES ............................................................................................ 119

9

LIST OF FIGURES ......................................................................................... 120

10REFERENCES ................................................................................................ 126

11

RESEARCH HISTORY .................................................................................... 133
PUBLICATION ................................................................................................................133
INTERNATIONAL CONFERENCES ....................................................................................133
RELATED PAPERS ..........................................................................................................133
RELATED PATENTS ........................................................................................................134

ABOUT THE AUTHOR ............................................................................................ 135

Dissertation Committee
Supervisor Prof. Ichiro Omura
Co-advisor Prof. Akira Izumi
Prof. Satoshi MatsumotoProf. Motoi Nakao

iv |Acknowledgements
First of all I appreciate my supervisor and co-advisors. My supervisor Prof. Ichiro
Omura directed me for two years, and gave me the opportunity to study the research theme.
Without his generous treatment I could not have tackled this research theme in the firstplace.
My co-advisor Prof. Akira Izumi, Prof. Satoshi Matsumoto and Prof. Motoi Nakaogave me useful comments. Assistant Prof. Akihiko Watanabe gave me kind comments.
I would like to thank to Ms. Miyo Iwahori supported me very well for two years, a lotof documentation, payment procedure, campus life guide, coffee, etc.
I was encouraged much by my colleagues, especially Mr. Masanori Tsukuda. He
sometimes helped me a lot from official procedure to research contents. He also kindly
conducted me when we took part in the overseas conferences. I never believe I could finish
the research without his great support.
I appreciate former Prof. Kenmei Kukihara of Kagoshima University, who firstly open
the door for me toward semiconductor power device.
I appreciate former Prof. Naotsugu Nozue of The University of ElectroCommunications, who firstly open the window for me toward information science.
I thank my colleagues in Nihon Synopsys G.K., Mr. Taizo Yoshida, Dr. Hideki Takada,
Dr. Yoshinori Asahi, Dr. Wonchul Choi, Mr. Kenji Shimai, Mr. Yasuhiro Mori, Dr. Zhong
Wang, Mr. Naoki Abe, Mr. Yasushi Umezawa, Mr. Kenichi Ishikawa, Mr. Satoshi
Yamaguchi, Mr. Shiro Katsuki, Mr. Takashi Hori, Mr. Makoto Isshiki, Mr. Takashi Suzuki,
Ms. Mayumi Yutaka, Mr. Kurt Muller and many engineers and staffs. They supported andhelped for my work a lot even when I took long FTO to attend international conferences.
I also thank my former colleagues in Toshiba Cooperation and Mitsubishi Electric
Cooperation, Dr. Hiromichi Ohashi, Dr. Akio Nakagawa, Dr. Tsuneo Ogura, Mr. Tetsujiro
Tsunoda, Dr. Kaoru Imamura, Mr. Masakazu Yamaguchi, Ms. Tomoko Matsudai, Mr.
Shoichiro Kurushima, Mr. Shinichi Umekawa, Mr. Satoshi Teramae, Mr. Yasushi Takahashi,
Mr. Satoshi Nakao and a lot of engineers and researchers. They kindly taught and helped forthe research and development.
Finally I greatly thank my wife, daughter, fetus, parents, parents-in-a-law, uncle, aunt,
aunt-in-a-law, brother, brother-in-a-law, sister-in-a-law, hair stylist, wine bar’s master andv|madam, and all of my friends; Sakiko, Sakura, Kura-pon, Susumu Tanaka, Akiko Tanaka,
Noriomi Matsumoto, Masako Matsumoto, Sadao Ebisawa, Setsuko Ebisawa, Fumie
Takuma, Hirokazu, Jumpei, Takako, Makiko, Dr. Rie Irimajiri, Mr. Gordon S. Foster, Ms.
Junko Takagishi, Ms. Yukie Tokuta, Mr. Mantaro Morita and Madam Hiroko for theirpatience and supports for two years. Any of my success is also theirs.

vi |Abstract
Power electronics is one of the key technologies to realize a low emission society.
Semiconductor power devices, which are the main components of power electronics
instruments, are expected to improve in power loss. A lot of research and development havebeen done especially for IGBTs (Insulated Gate Bipolar Transistor), which are widely used
for over 600V class rated voltage, such as EV (Electric Vehicle) and HEV (Hybrid Electric
Vehicle). The annual demand for IGBTs is around 2.5 billion dollars annually in 2012,accounting for about 8% of the semiconductor market for Power Management. Itsapplication range has rapidly expanded, from IH (Induction Heating) cookers, inverter air
conditioners, and also high voltage DC transmission (HVDC) devices on behalf of several
hundred megawatts of Thyristor. Its market is growing at an annual rate of more than 10%.
Devices using new materials such as Gallium Nitride and Silicon Carbide as the next
generation power devices have been prototyped. But Silicon devices, including the Silicon
IGBTs are considered to be the mainstream for the next few decades due to its material costand ease of processing.
In the development of IGBT application systems, such as inverters, circuit simulation
is used to improve its electrical efficiency and estimate heat loss and noise. A
mathematically formulated model called the compact model that reproduces thecharacteristics of the IGBT, is used in the circuit simulation. But current IGBT compact
models do not achieve enough accuracy, especially for latest trench-gate IGBT.
In this study, accurate compact model development for the trench gate IGBT wasachieved for the first time in the world by analyzing in detail the principle operation of the
IGBT. The compact model represents high precision characteristics of the device in thesimple formula and device structure parameters. This model has been published as a

"Quasi-2D MOS-ADE" model. In addition, in the analysis of the compact model, thenewly discovered "Scaling Principle" as well as CMOS technology was also present in
the power devices. The possibility to realize the miniaturization of next-generation
power devices was demonstrated.
In Chapter 1 and Chapter 2, the background and purpose of the study is reviewed.
Discuss on the detail the operating mechanism of the IGBT, in particular, the preparation forthe construction of the model starts from Chapter 3.
In Chapter 3, a new mathematical expression for the trench-gate IGBT based on theoperation of the semiconductor device physics, was established as a compact model. Thismodel makes possible the representation of potential and carrier distribution of the Cathodeside with high accuracy. In this model, the current flows are assumed to be separated into

vii |

three portions, the electron current and the hole current flowing through the mesa region
that is sandwiched between the trenches, and the electron current flowing through theaccumulation layer of the gate sidewalls where the current in the device has been
represented as an equivalent circuit conventionally. As a result, the distribution of electrons
and holes of IGBT can be expressed accurately. In addition, because it is formulated in thedevice structure parameters only, any extraction works for fitting parameters are notnecessary.
In Chapter 4, the established compact model was verified for 600V, 1200V, and 3.3kV
rated IGBT’s. The carrier distribution profiles and I-V characteristics calculated by thecompact model and TCAD device simulation were compared. As a result of the verification,
consistent with high precision characteristics and carrier density distribution, the validity ofthe model was shown. TCAD simulation needs time-consuming calculation of more than amillion times compared to the compact model because it solves all of the basic equations of
the semiconductor.
In Chapter 5, a scaling principle for the IGBT was established for the first time. The
principle was founded from the analysis of the "Quasi-2D MOS-ADE" model. A roadmap
for achieving the next generation power devices was revealed by the principle.
Conventional IGBT uses 0.5 to 1 micron design rules, and miniaturization was notconsidered. The "scaling principle" opened the way to the adoption of large sized wafers
and high resolution semiconductor processes, and showed an explicit direction to therealization of next-generation power devices that improve the production and performance.
In Chapter 6, the future of IGBT was discussed based on the knowledge gained in thisstudy.

viii |

和文要旨
省エネルギー社会の実現に向け、パワーエレクトロニクス技術には多くの期待が寄せられている。特に、パワーエレクトロニクス機器のキーコンポーネントであるパワーデバイスには一層の低損失化が求められている。中でも、電気自動車やハイブリッド自動車などに搭載されている耐圧 600V 以上のパワーデバイスとして広く用いられている
IGBT (Insulated Gate Bipolar Transistor) に対しては多くの技術開発がなされ、低損失化を実現している。2012 年現在、IGBT は年間 2500 億円程度の需要があり、パワー
マネジメント関連半導体の約 8%の市場を占めている。また、適用範囲も急拡大しており、エアコンや IH 調理器のインバータから、最近では、サイリスタに代わって数百メガワットの直流送電 (HVDC) にまで用いられるようになってきた。この
結果年率 10%以上の勢いで市場が拡大している。次世代のパワーデバイスとして炭化シリコンや窒化ガリウムといった新素材を使用するデバイスが提案および試作されているが、加工容易性や材料コストなどの点から今後数十年はシリコン IGBT をはじめとするシリコンデバイスが主流であると考えられる。
インバータなど、IGBT の応用システムの開発では、発生する熱損失やノイズ等を事前に回路シミュレーションにより見積ることで開発効率を改善してきた。このようなシミュレーションでは IGBT 特性を再現するコンパクトモデルと呼ばれる数式モデルが用いられている。しかし現状の IGBT コンパクトモデルはデバイス特性を十分に表現できず、特に最新のトレンチゲート型 IGBT 構造への適用では精度の点で課題が大きかった。
本研究では、IGBT の動作原理を詳細に分析することにより、最新のトレンチゲート型 IGBT に対応したコンパクトモデルを開発し、素子構造パラメータと単純な数式で素子の特性を高精度に表現することに世界で初めて成功した。本モデルは「Quasi-2D MOS-ADE」モデルとして公表している。また、本コンパクトモデルによる解析で、パワーデバイスでも LSI と同様に「スケーリング則」が存在することを新たに発見し、次世代パワーデバイスが微細化により実現可能であることを明らかにした。
第 1 章、第 2 章では、研究の背景と目的を述べた。特に IGBT の動作メカニズ
ムを詳細に論じ、第 3 章以降のモデル式構築の準備とした。
第 3 章では、トレンチゲート型 IGBT の動作を半導体デバイス物理に基づいた
新たな数式表現を考案し、コンパクトモデルとして確立した。本モデルは、カソー
ド側のポテンシャルおよびキャリア分布を高い精度で表現することを可能とした。
具体的には、従来は等価回路として表現されていた素子内の電流を、トレンチで挟まれたメサ部分を流れる電子電流およびホール電流と、ゲート側壁の蓄積層を流れる電子電流との 3 つに分離して表現したことが特徴であり、その結果 IGBT 内の電ix |子およびホールの分布を正確に表すことに成功した。さらに、素子構造パラメータのみで定式化されているため、従来必要であったフィッティングパラメータの抽出作業が完全に不要となり、回路シミュレーションの自動化への道を開いた。
第 4 章では、コンパクトモデルの妥当性の検証を行った。600V, 1200V, 3.3kV の
3 種類の耐圧の IGBT をサンプルとし、半導体の基本方程式をすべて解く TCAD (デバイスシミュレーション) の結果と本コンパクトモデルの結果を比較した。検証の結果、特性およびキャリア密度分布が高い精度で一致し、モデルの妥当性が示された。なお TCAD では、本コンパクトモデルに比べ十万倍以上の計算時間を要する。
第 5 章では、IGBT のスケーリング則を世界で初めて確立した。提案した「Quasi-2D MOS-ADE」モデル式による分析から IGBT 技術における「スケーリン
グ則」の存在を発見し、次世代パワーデバイス実現のロードマップを明らかにした。
従来、IGBT では 0.5～1 ミクロン程度のデザインルールが採用されており、微細化は不可能であると判断されてきた。今回明らかにした「スケーリング則」により、
微細半導体の工程と大口径ウェーハの採用への道が開け、性能と量産性を向上した
次世代パワーデバイス実現への方向性を明示した。
第 6 章では、得られた知見を元に IGBT の将来像を議論した。大口径ウェーハへの展開、および微細 CMOS プロセスとの互換性による、量産性が高く高品質なIGBT 製品の実現に関し、素子構造の例や半導体プロセスの詳細、さらにパッケー
ジなどの周辺技術も交えて技術開発の方向性を示した。

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1 Background
1.1

What's IGBTPower device is a category of semiconductor devices. It is widely used for electrical

power conversion, for example, DC voltage converter and DC to AC converter, so called
inverter. Device type is chosen by operating frequency and output power capacity. For
Silicon device, the cover area for each device type is summarized in Figure 1.

Figure 1. Cover area for various power devices [1].

MOSFET, including vertical MOSFET (Power MOSFET) and lateral diffused
MOSFET (LDMOSFET), covers lowest power capability and fastest operating frequency
area. MOSFET is unipolar device and its on-state resistance depends on the rated voltage
because higher rated voltage needs thicker region with lower doping concentration to
expand depletion layer to support the voltage. In result, Power MOSFET has clearly
performance limit between rated voltage and on-state resistance as called “Silicon limit”.
With Silicon material, the rated voltage is actually limited up to 600V due to high on-state
resistance. By using Silicon Carbide material, the limitation expands to higher rated voltage
area due to wider band gap than Silicon. However Silicon material is considered as major

2|material for next several decades due to the material cost and the fabrication process cost,where a lot of research and development for Silicon Carbide device are performed bydevice companies and research institutes.
IGBT (Insulated Gate Bipolar Transistor) is bipolar device and it realizes lower
on-state voltage drop even with higher rated voltage than Power MOSFET by storing muchcarriers, electrons and holes, in thicker and higher resistivity region than Power MOSFET.
On the other hand switching speed is lower than Power MOSFET due to the stored carrier.
So IGBT is applied for 1 kHz to 100 kHz frequency and 1kVA to 10MVA power capacity,
especially rated voltage of 600V to 4.5kV.
In larger output capacity area than IGBT, Thyristor and GTO (Gate Turn-off Thyristor)
are still used due to lower on-state voltage drop than IGBT. But these devices havedisadvantages that their control circuits require large displacement and power consumptionof the circuit is relatively large because these devices are current controlled. IGBT is MOS
controlled device and power consumption for gate drive is very small. In future, Thyristor
and GTO should be replaced by improved Silicon IGBT, Silicon Carbide Power MOSFET
or Silicon Carbide IGBT.

1.2

Applications and market trends
There is wide range of applications for IGBT. Especially motor control is most major

field for IGBT, such as factory robot, electric train, electric vehicle (EV) and hybrid electricvehicle (HEV), air conditioner, and other home appliances. A typical motor control circuit isshown in Figure 2. The circuit converts three phase AC power to three phase AC powerwith arbitrary frequency and voltage to drive induction motor (IM). Once three phase AC
input is converted to DC by diode bridge (“Rectifier” part of Figure 2), then the DC power
is converted to AC by six IGBT chips (“Inverter” part of Figure 2). In general the circuit issimply called as “Inverter”. The circuit enables to control induction motor or synchronous
motor with arbitrary speed and torque so called “VVVF (Variable Voltage and Variable
Frequency) inverter”.

3|

Figure 2. Motor control circuit example [2]. Six IGBT chips on “Inverter” bridge
convert to three phase AC power with arbitrary frequency and voltage.

Several types of package are desined for IGBT depends on its application and power
capacity. For example, 6-in-1 (Six devices in a package) type has an inverter circuit with six
IGBTs and six diodes as “Inverter” section in Figure 2. 2-in-1 (Two devices in a package)
type has an arm in the inverter. Typical 2-in-1 packages are shown in Figure 3.

Figure 3. Photograph of IGBT modules [1].

4|Figure 4. Market share for each power devices [3]. IGBT has 8% of total power device
market.

Figure 5. Market trend for IGBT [3]. Vertical axis shows market share in Million US$.
Market is shared by mainly Industrial equipment (brown), Automotive applications (darkblue) and Consumer electronics (light blue).

5|

IGBT market shares 8% of total power device market as shown in Figure 4. The
market is forecasted to expand about 10% by a year as shown in Figure 5. One market
estimated to grow a lot is China. China’s government has encouraged fast growth in thephotovoltaic (PV) market as part of its long-term new energy development plan [4]. To that
end, total installations in China reached 1GigaWatt in capacity in 2010. It is half of theChinese government’s original 2015 target. IGBT should be used for the inverter to change
the power from photovoltaic cell (DC) to consumer power line (AC). Anotherfastest-growing application for IGBT is in new air conditioners. In order to encourage ashift to higher efficiency and power savings in air conditioning equipment, the Chinese
government released a new standard last year for room air conditioners. To support the
adoption and higher penetration rates of new air conditioners, the government has requiredthat only air conditioners able to meet higher energy efficiency standards will receive
financial subsidies. IGBT also should be used for the inverter to drive the compressor withhigh energy efficiency.

1.3

Issues: Compact Modeling and Process Compatibility
As described in previous section, IGBT is widely used for power electronics industries.

The demand of market is also high. In this dissertation, two topics will be discussed as
current issues and their solutions will be given.

1.3.1

Compact Modeling

Higher system level electrical efficiency and higher reliability are required
continuously in IGBT applications. It means system level optimization is strongly needed.
Accurate and fast simulation environment using simple mathematical device model, as
called compact model, is desired with capability for wide range of power and device
temperature. In the other word, simple and accurate IGBT compact model is required toperform system simulation from medium to high power applications.
Basically, electrical characteristics for IGBT are more complicated than MOSFET thathas simply resistive forward characteristic. The key point to represent IGBT’s electricalcharacteristics should be reproducing the stored carrier distribution in high resistivity region
because it affects total loss of the device, i.e. both on-state voltage drop and turn-off loss.
Physical approach should be better to cover such feature and wide range of device
temperature.
Existing IGBT compact models, such as Hefner model [5], have been widely used in6|power electronics system and circuit design as the device has expanded the application fromsmall appliances to EV/HEV and tractions etc. The compact models enable to simulate large
scale IGBT inverters and systems for many cycle of switching. Most of the IGBT compact
models have been formulated based on the combination of physics based simplified
analytical equations, equivalent circuits and behavior models with a number of fitting
parameters. As far as the models are used within the predetermined validity confirmed
operation range of the models, the circuit simulators effectively show the sufficiently
accurate results. Once the condition exceeds the validity confirmed range, such as hightemperature condition, the model requires re-fitting of the parameters so as to extend thevalidity range.
In this dissertation, a device structure based compact model for advanced trench gate
IGBTs is proposed. The model is formulated by simple equations based on physicalequations for semiconductor. Extreme conditions such as under very low or hightemperatures can be covered by the model. And only device structure parameters are used
so that no fitting parameters are required.

1.3.2

Scaling principle

CMOS technology on large diameter wafer with high resolution lithography
technologies enables to produce various digital circuits with higher performance and lower
cost. The innovation is continuing at the pace dictated by Moore’s Law as shown in Figure
6. The transistor cell structure becomes laterally smaller and smaller and verticallyshallower and shallower. On the other hand, trench gate IGBTs introduce rather deeper
trench structure to obtain lower on-state voltage drop and turn-off loss. Trench gate IGBT
was firstly proposed in 1987. The cell design had 3um width and 5um depth trench, and8um unit cell pitch [6]. After that unit cell pitch was miniaturized to 4um [7]. But rather
deeper trench is still preferred to performance improvement [8]. The technology has beenused for more than 10 years. Further miniaturization has not been believed to contribute
IGBT performance improvement. In result, currently process compatibility between CMOS
and IGBT is so limited. Manufacturing IGBT in CMOS factory is difficult due to theprocess uniformity and wafer bowing caused by deep trench. The fact can obstruct toimprove IGBT’s productivity and performance.

7|

Figure 6. Production technology capacity follwing Moore’s law [9].

A scaling principle for IGBT toward shallower structure and smaller thermal budget isalso proposed in this dissertation. The principle enables to obtain high manufacturability
and better performance that is confirmed by TCAD simulation and theoretically explainedby previously proposed compact model. The proposed scaling principle represents a
possibility of technology direction and roadmap for future IGBT for improving the device
performance consistent with high volume productivity with CMOS compatible large
diameter wafer technologies.

1.4

Summary
IGBT is widely used in power electronics system from small appliances to EV/HEV

and tractions. The market is forecasted to expand about 10% by a year. But there are someissues in system performance improvement and IGBT’s improvement. Firstly, existing
compact models have several problems about parameter extraction and validity range.
Secondly, IGBT process has poor compatibility with CMOS process that enables to improve
performance and manufacturability.
In this dissertation, a device structure based compact model for advanced trench gate

8|

IGBTs will be proposed. And a scaling principle for IGBT toward shallower structure andsmaller thermal budget will be also proposed. The compact model has superior
characteristics such that the model doesn’t need fitting parameters and parameter
extractions, and can adapt for extreme conditions such as under very low or hightemperatures. The scaling principle shows a possibility of technology direction and roadmap
for future IGBT. It predicts the device performance improvement with high volume
productivity with alignment for CMOS wafer process.

9|

2 Objective
In this dissertation, two topics will be discussed as current issue and its solutions will
be shown. From section 3 to 4, new compact model will be proposed. The model isstructure based such that no fitting parameters are required. It enables to delete parameter
extraction step as shown in Figure 7. The model is formulated by simple equations based on
physical equations for semiconductor. Extreme conditions such as under very low or hightemperatures can be covered by the model without any re-modeling process. The model canbe also used for structure optimization because it is based on only the structure parameters,
no fitting parameters.

Current solution for IGBT compact model
Deviceconcept

Structure
optimization

Devicefabrication &measurements

Proposed solution
Deviceconcept

Structure
optimization

Parameter
extraction

Compact model
for room temperature
with fitting
parameter set A
Compact modelfor high temperature
with fitting
parameter set B

Devicefabrication &measurements
Compact model for
all temperature
conditions

Figure 7. The interpretation of the contribution of this work.

In section 5, a scaling principle for IGBT toward CMOS-like shallower and narrower
structure will be proposed. The principle is based on previously proposed compact model
formulation. The principle enables to obtain high manufacturability and better performancethat is confirmed by TCAD simulation and theoretically explained by previously proposedcompact model. The proposed scaling principle represents a possibility of technology
direction and roadmap for future IGBT for improving the device performance consistent
with high volume productivity with CMOS compatible large diameter wafer technologies.

10 |Design Rule[um]10125mmΦ

CMOS
IGBT

150mmΦ

200mmΦ

1

150mmΦ
0.1

200mmΦ
0.01
1990

450mmΦ

300mmΦ
1995

2000

2005
Year

2010

2015

2020

Figure 8. IGBT process direction. Keeping process compatibility with CMOS isneeded.

11 |3 Structure Oriented Analytical Modeling for Modern Trench
Gate IGBT
3.1

IGBT Basic Operations
Generally, IGBT rated voltage is chosen to more than double of input voltage because

the device have to support surge voltage occurred by di/dt and parasitic inductance during
turn-off. The relationship between commercial power voltage and device rated voltage issummarized in Table 1. 600V and 1200V rated devices are used for home appliances, airconditioners, automotive and industrial applications. Higher rated voltage devices are used
for electric railways, iron/steel rollings, and power plants.
Table 1. Relationship between commercial power voltage and device rated voltage [2].

A cross sectional view of IGBT is shown in Figure 9. IGBT has three electrodes, Gate,
Cathode and Anode. Electrical conduction from Anode to Cathode is established when
applying a voltage between Gate to Cathode. With zero or negative gate voltage, theconduction is disappeared and high blocking voltage between Anode and Cathode isrealized.

12 |Cathode Electrode

Cathode Electrode
Gate ElectrodeN-Emitter

P-BaseGate

P-BaseGate

P-BaseN-Emitter
Gate ElectrodeP-float

N-BaseN-BaseN-Buffer
P-Emitter
Anode ElectrodeP-Emitter

Anode Electrode

Figure 9. IGBT structure. The left side figure shows old designed Planar gate thickwafer IGBT. The right side figure shows newest Trench gate thin wafer IGBT.

IGBT has basically four doping layers, N-Base, P-Base, N-Emitter and P-Emitter.
MOS gate is formed beside P-Base to establish electron conduction between N-Base and
N-Emitter. In conduction mode, applied gate voltage creates electron channel beside MOS
gate oxide. And applied forward voltage from Anode to Cathode makes IGBT act as PiN
diode. Electron injection from N-Emitter to N-Base via MOS gate channel, and hole
injection from P-Emitter to N-Base are occurred simultaneously.
During the conduction mode, N-Base conduction resistance is kept as very low
because stored carrier density of N-Base is very higher as 100x or 1000x than N-Basedoping concentration. So, N-Base carrier concentration exceeds 1e16cm-2 where N-Base13 |doping concentration is chosen for 1e13cm-2 to 1e14cm-2 depends on rated voltage. Thisphenomenon is most different point of MOSFET’s conduction mode which carrier
concentration is kept as doping concentration. The stored carriers form distribution profilesin N-Base as shown in Figure 10. The densities for electron and hole are almost same due tokeep charge neutrality, as called “conductive modulation”.

CathodeCathodeGateGatex
P-BaseP-BaseP-BaseP-BaseN-Emitter

P-BaseGate Gate

Gatex

P-float

N-BaseN-BaseN-Buffer
P-Emitterp(x)=n(x)Anodep(x)=n(x)P-Emitter

Anode

Figure 10. Carrier distribution for conduction mode. Electron and hole form same
distribution in N-Base region. The left side figure shows Planar gate IGBT. The right side
figure shows Trench gate IGBT. Carrier distribution profile is different.

On-state carrier distribution profile strongly affects power loss of IGBT. IGBT’s
conduction loss consists of MOS channel resistance, built-in potential and N-Baseconduction resistance where MOSFET on-state resistance simply consists of MOS channel
resistance and N-Base conduction resistance that clearly depends on N-Base doping
concentration. N-Base conduction resistance of IGBT is dominant of conduction loss

14 |especially high rated voltage devices which have thick N-Base region. Turn-off loss also
depends on stored carrier because turn-off is exactly exhausting operation for stored carrier.
So basically IGBT has a trade-off relationship between conduction loss and turn-off loss, i.e.
higher stored carrier enables lower conduction loss but also makes larger turn-off loss.
Improvement for the trade-off relationship is most important point for IGBT development.
In off state, i.e. Gate is biased zero or negative voltage against Cathode, applied Anodevoltage makes the junction between P-Base and N-Base as reversely biased condition anddepletion layer is formed in N-Base. It is completely same as the state of MOSFET. In
punch-through (PT) type IGBT, the extension of the depletion layer is blocked by additional
N-Buffer layer as shown in the left side of Figure 11. In non-punch-through (NPT) type
IGBT, the depletion layer is extended in thicker N-Base as shown in the right side of Figure
11. N-Base doping concentration and thickness are designed to keep rated voltage. For
example to obtain rated voltage as 600V, N-Base doping concentration should be around1.5x1014cm-3 and the thickness should be 100um for NPT-IGBT [10] [11] and 60um for
PT-IGBT [12].

15 |Electric Field
P-BaseGate Gate

GateGate

P-BaseGate Gate

GateGate

Electric Field

P-floatP-float

N-BaseN-BaseN-Buffer
P-Emitter

P-Emitter

Figure 11. Electric field distribution in off state (left: PT-IGBT, right: NPT-IGBT).

3.2

Modeling Concept
A lot of researches were performed to improve the trade-off relationship between

on-state voltage drop and turn-off loss. After that a lot of Cathode designs, such as IEGT
(Injection Enhancement Gate Transistor) or other injection enhancement structures, were
proposed to control the carrier distribution profile and improve the trade-off relationship[13] [14] [15] [16] [17] [18] [19] [20]. And low injection efficiency Anode design iscommonly used for latest IGBT to suppress parasitic operation during turn-off [10] [12][14] [21] [22] [23] [24]. By considering these technological trends, three main modelingconcepts were found as following.


Accurate on-state carrier distribution realized: the model aims to realize accurate

16 |N-Base carrier distribution. On-state carrier distribution in N-Base is most important
point to describe IGBT characteristics accurately, especially on-state voltage dropVce(sat) and turn-off loss Eoff.


Physical based: the model formulation is based on basic semiconductor equations andsome additional physical equations. It leads an advantage that the model can apply forwide range of structure and temperature with high accuracy.

Structure oriented: the model parameters consist of only structure parameters. No

P-Basex

Gate Gate

GateGatefitting parameters are needed. No parameter extraction work is required in result.

P-floatQuasi-2D MOS-ADE
model

x2

n
N-Base model

N-Basepx1

N-Buffer
P-Emitterp(x)=n(x)Anode model

Figure 12. Modeling structure.

Proposed model is formed by three parts as shown in Figure 12. The first is for
Cathode side structure named “Quasi-2D MOS-ADE model”. Electron injection efficiency
𝛾𝑛 from Cathode side to N-Base can be calculated by the structure parameters and current
density. 𝛾𝑛 is defined as𝛾𝑛 =𝐽𝑛 (𝑥2 )𝐽(1)where 𝐽𝑛 (𝑥2 ) is electron current density at Cathode side N-Base edge, 𝑥 = 𝑥2 in Figure
12. And 𝐽 is total current density. The part covers for trench gate IGBT and IEGT

17 |structures. These structures are widely used to improve trade-off relationship between
on-state voltage drop and turn-off loss by injection enhancement effect.
The second is for Anode side structure. Hole injection efficiency 𝛾𝑝 from Anode side
to N-Base can be calculated by the structure parameters and current density. 𝛾𝑝 is defined
as

𝛾𝑝 =

𝐽𝑝 (𝑥1 )𝐽(2)where 𝐽𝑝 (𝑥1 ) is hole current density at Anode side N-Base edge, 𝑥 = 𝑥1 in Figure 12.
The model covers thin wafer punch-through type IGBT which has shallow P-Emitter layerand shallow N-Buffer layer, called “Field Stop IGBT”, and thin wafer non-punch-throughtype IGBT which has only shallow P-Emitter layer. Shallow P-Emitter design is widelyused for various voltage range of IGBT to suppress parasitic operation during turn-off
period.
The last part is for N-base structure. Carrier distribution profile for electron and holecan be calculated by the structure parameters, current density, and injection efficiencies
from Cathode side and Anode side.
In result, the model can be applied for the combination of trench gate andpunch-through or non-punch-through structure with shallow doping layers. It covers various
latest IGBT structures proposed by power device manufacturers.

3.3

Quasi-2D MOS-ADE Model
Proposed Cathode side formulation is named as “Quasi-2D MOS-ADE model”. The

model formulates the relationship between Cathode side structure parameters and electron
injection efficiency for trench gate IGBT. The injection efficiency will be used to calculate
N-Base carrier distribution.
The main idea of the model is that the electron current flowing from MOS channel isdivided to two paths as shown in Figure 13. One is flowing in mesa region keeping same
carrier concentration of hole by “conductive modulation” and it holds ADE (Ambipolar
Diffusion Equation). The other is flowing along trench gate accumulation layer. In thismodel, the carrier distributions in mesa region are assumed such that carrier concentrations
are constant for horizontal direction, i.e., one-dimensional carrier distribution is assumed inmesa region. For vertical direction, the quasi-Fermi potential for electron ∅𝑛 (𝑥) affects toelectron flow of trench gate and mesa region. No carrier recombination is also assumed in18 |mesa region.

P-BaseP-BaseAccumulation layer

Gate Gate

GateGatexøn(x3)
P-Baseøn(x2)

N-BaseMesa region(n=p)

Figure 13. The main idea of the model. Current flow paths are assumed toaccumulation layer and mesa region.

This part can be calculated by ADE with considering electron current along theaccumulation layer of the trench MOS gate as a function of vertical position. ADE isdelivered by general current equation for semiconductor.

𝐽𝑛 (𝑥) = 𝑞𝜇𝑛 𝑛(𝑥)𝐸(𝑥) + 𝑞𝐷𝑛

𝑑𝑛
𝑑𝑥

(3)

𝐽𝑝 (𝑥) = 𝑞𝜇𝑝 𝑝(𝑥)𝐸(𝑥) − 𝑞𝐷𝑝

𝑑𝑝
𝑑𝑥

(4)

With Einstein's relation, they can be arranged to following.

𝐽𝑛 (𝑥) = 𝑞𝜇𝑛 𝑛(𝑥)𝐸(𝑥) + 𝑘𝑇𝜇𝑛

𝑑𝑛
𝑑𝑥

(5)

𝐽𝑝 (𝑥) = 𝑞𝜇𝑝 𝑝(𝑥)𝐸(𝑥) − 𝑘𝑇𝜇𝑝

𝑑𝑝
𝑑𝑥

(6)

In “conductive modulation” condition, 𝑛 = 𝑝 can be assumed. Equation (6) is modified to𝐽𝑝 (𝑥) = 𝑞𝜇𝑝 𝑛(𝑥)𝐸(𝑥) − 𝑘𝑇𝜇𝑝

From (5) and (7),

𝑑𝑛
𝑑𝑥

(7)

19 |

𝜇𝑝 𝐽𝑛 (𝑥) − 𝜇𝑛 𝐽𝑝 (𝑥) = 2𝜇𝑝 𝜇𝑛 𝑘𝑇

𝑑𝑛
𝑑𝑥

(8)

Equation (8) forms the relationship between the gradient of carrier density and current
densities for electron and hole.
On the other hand, the electron current flowing along the accumulation layer 𝐼𝑛𝑎𝑐𝑐 canbe calculated by the electron mobility and the accumulated carrier density of MOS gate.

𝐼𝑛𝑎𝑐𝑐 (𝑥) = −𝜎𝑎𝑐𝑐

𝑑∅𝑛
𝑑𝑥

(9)

Where ∅𝑛 (𝑥) is electron quasi-Fermi potential along mesa region. 𝜎𝑎𝑐𝑐 is sheet
conductance for the accumulation layer. So,
𝜎𝑎𝑐𝑐 = 𝜇𝑎𝑐𝑐 𝑄𝑎𝑐𝑐

(10)

𝑉𝑔𝑒
𝑇𝑜𝑥

(11)

𝑄𝑎𝑐𝑐 = 𝜀𝑜𝑥

where 𝜇𝑎𝑐𝑐 and 𝑄𝑎𝑐𝑐 are electron mobility and charge density for the accumulation layer,
respectively. 𝜀𝑜𝑥 , 𝑉𝑔𝑒 and 𝑇𝑜𝑥 are epsilon of the gate oxide, gate voltage and gate oxide
thickness, respectively. 𝜇𝑎𝑐𝑐 is degraded than bulk mobility due to carrier interaction with
the Silicon/Oxide interface by high transverse electric field. Several degradation models
were proposed [25] [26] [27] [28].
The relationship of current elements between mesa region and N-Base is shown in
Figure 14. W and S are half of cell pitch and half of mesa width, respectively.

20 |

S

W

P-BaseGate Gate

GateGatexøn(x3)

P-BaseP-Baseøn(x2)

I nacc J mesa
J nmesapcell
J cellp Jn

N-BaseFigure 14. Current elements in Trench structure

Total hole current is kept as constant at the boundary between N-Base and mesa region
due to assumed no recombination. Following equation can be formed.
𝑊𝐽𝑝𝑐𝑒𝑙𝑙 (𝑥2 ) = 𝑆𝐽𝑝𝑚𝑒𝑠𝑎 (𝑥)(12)Total electron current is kept as constant at the boundary between N-Base and sum of
mesa region and accumulation layer. Following equation can be formed for arbitrary x,
𝑊𝐽𝑛𝑐𝑒𝑙𝑙 (𝑥2 ) = 𝐼𝑛𝑎𝑐𝑐 (𝑥) + 𝑆𝐽𝑛𝑚𝑒𝑠𝑎 (𝑥)
𝑑∅𝑛
𝑑𝑥

(14)

𝐼𝑛𝑎𝑐𝑐 (𝑥)
𝜎𝑎𝑐𝑐

(15)

𝐽𝑛𝑚𝑒𝑠𝑎 (𝑥) = −𝑞𝜇𝑛 𝑛(𝑥)By (9) and (14),

𝑑∅𝑛
𝑑𝑥

(13)

can be canceled as

𝐽𝑛𝑚𝑒𝑠𝑎 (𝑥) = 𝑞𝜇𝑛 𝑛(𝑥)From (13) and (15), 𝐽𝑛𝑚𝑒𝑠𝑎 can be formed as
𝐽𝑛𝑚𝑒𝑠𝑎 (𝑥) =𝜎𝑚𝑒𝑠𝑎 (𝑛(𝑥))𝑊 𝑐𝑒𝑙𝑙𝐽 (𝑥2 )
𝜎𝑎𝑐𝑐 + 𝜎𝑚𝑒𝑠𝑎 (𝑛(𝑥)) 𝑆 𝑛

(16)

21 |

Where
𝜎𝑚𝑒𝑠𝑎 (𝑛(𝑥)) = 𝑞𝜇𝑛 𝑛(𝑥)𝑆(17)

The differential equation which expresses the relationship between structure
parameters and electron injection efficiency 𝛾𝑛 , can be obtained by substituting (12) and(16) for (8).
𝜇𝑝2𝑞𝐷𝑝 𝑆 𝑑𝑛
𝜎𝑚𝑒𝑠𝑎 (𝑛(𝑥))(+ 1) 𝛾𝑛 − 1 =𝜇𝑛 𝜎𝑎𝑐𝑐 + 𝜎𝑚𝑒𝑠𝑎 (𝑛(𝑥))𝐽 𝑊 𝑑𝑥(18)

Re-expanding 𝜎𝑚𝑒𝑠𝑎 and 𝜎𝑎𝑐𝑐 ,−1𝜀𝑜𝑥 𝜇𝑎𝑐𝑐 𝑉𝑔𝑒
𝜇𝑝
2𝑞𝐷𝑝 𝑆 𝑑𝑛((+ 1) + 1) 𝛾𝑛 − 1 =𝜇𝑛 𝑇𝑜𝑥 𝑞𝜇𝑛 𝑛(𝑥)𝑆𝐽 𝑊 𝑑𝑥(19)

In conduction mode, the junction of P-Base and N-Base is reversely biased. So theboundary condition of (18) is𝑛(𝑥3 ) = 0

3.4

(20)

Hole Injection Model for Shallow P-Emitter
Proposed model for Anode structure covers punch-through (PT) type IGBT which has

shallow P-Emitter layer and shallow N-Buffer layer, and non-punch-through (NPT) type
IGBT which has only shallow P-Emitter layer. No carrier recombination is considered inthis model because the thickness of P-Emitter and N-Buffer layers are much shorter thancarrier diffusion length. No voltage drops for majority carriers are also considered. Constant
doping concentration is assumed for P-Emitter and N-Buffer layers. Not doping profile
curve but total doping dose is dominant to calculate 𝛾𝑝 by this model.

3.4.1

NPT modelFirstly NPT type modeling is described. Cross sectional view and carrier distribution
profile is shown in Figure 15.

22 |N-baseLp

Carrier concentration

pp

hole

NA

electron=holen1npelectron0

x1

Figure 15. Structure and carrier distribution for NPT-IGBT with shallow P-Emitter

NA and Lp are P-Emitter doping concentration and thickness, respectively. np and pp,
are electron and hole concentration at P-Emitter edge of N-Base side. n1 is carrier electron
and hole concentration at N-Base edge of P-Emitter side. By considering only diffusion
current, reversely injected electron from N-Base to P-Emitter can be calculated asfollowing.

𝐽𝑛 (𝑥1 ) = 𝑞𝐷𝑛

𝑛𝑝
𝑑𝑛
= 𝑞𝐷𝑛
𝑑𝑥
𝐿𝑝

(21)

where Dn is diffusion coefficients for hole and electron, respectively. It can be calculated bycarreir lifetimes. Carrier lifetime degradation model due to higher doping concentration
should be applied [29] [30] [31] [32].
By p-n power continuity across N-Base / P-Emitter junction and charge neutrality in
P-Emitter,

𝑛𝑝 =

𝑛12
𝑛12
=
𝑝𝑝 𝑛𝑝 + 𝑁𝐴

(22)

23 |

By solving the quadratic equation,−𝑁𝐴 ± √𝑁𝐴2 + 4𝑛12
𝑛𝑝 =
2

(23)

The electron current density can be obtained by substituting (22) for (20). Only the plus sidesolution of (22) can be applied.

𝐽𝑛 (𝑥1 ) = 𝑞𝐷𝑛−𝑁𝐴 + √𝑁𝐴2 + 4𝑛12
2𝐿𝑝

(24)

The relationship between structure parameters and hole injection efficiency 𝛾𝑝 , can beobtained by (2) and (23)𝛾𝑝 = 1 − 𝑞𝐷𝑛

3.4.2−𝑁𝐴 + √𝑁𝐴2 + 4𝑛12
2𝐽𝐿𝑝

(25)

PT modelNext, PT type modeling is described. Cross sectional view and carrier distribution
profile is shown in Figure 16. NA, Lp, ND and Ln are P-emitter concentration, thickness,N-buffer concentration and thickness, respectively.

24 |N-baseLp

Ln

Carrier concentration

pp

hole

NA
p1 ' N D
p1  N D
n1
p1 '
p1
np

0

electron=hole

electronx1 'x1

Figure 16. Structure and carrier distribution for PT-IGBT with shallow P-Emitter andshallow N-Buffuer

By considering only diffusion current, the current densities Jn and Jp at N-base edge
can be calculated by
𝑛𝑝
𝑑𝑛
= 𝑞𝐷𝑛
𝑑𝑥
𝐿𝑝

(26)

𝑑𝑝
𝑝1 ′ − 𝑝1
= 𝑞𝐷𝑝
𝑑𝑥
𝐿𝑛

(27)

𝐽𝑛 (𝑥1 ) = 𝑞𝐷𝑛
𝐽𝑝 (𝑥1 ) = 𝑞𝐷𝑝

Following boundary conditions can be obtained by power continuity across P-Emitter /N-Buffer junction and N-Buffer / N-Base boundary.
(𝑝1 + 𝑁𝐷 )𝑝1 = 𝑛12
𝑝𝑝 𝑛𝑝 = (𝑁𝐴 + 𝑛𝑝 )𝑛𝑝 = (𝑝1′ + 𝑁𝐷 )𝑝1′
Equations (25)-(28) can be modified with process parameters as following.

(28)
(29)

25 |

𝐽𝑛 (𝑥1 ) = 𝑞𝐷𝑝√𝑁𝐷2 + 4(𝑁𝐴 + 𝑛𝑝 )𝑛𝑝 + √𝑁𝐷2 + 4𝑛12

(30)

2𝐿𝑛

The relationship between structure parameters and hole injection efficiency 𝛾𝑝 , can beobtained by (2) and (29)𝛾𝑝 = 1 − 𝑞𝐷𝑝

(31)

2𝐽𝐿𝑛

P-BaseGate Gate

N-Base Model

GateGate

3.5√𝑁𝐷2 + 4(𝑁𝐴 + 𝑛𝑝 )𝑛𝑝 + √𝑁𝐷2 + 4𝑛12

P-floatxn(x)x2N-Basex1

N-Buffer
P-Emittern(x)Figure 17 Cross sectional view of Trench gate IGBT

A cross-sectional view of Trench gate IGBT is shown in Figure 17. N-base carrier
concentration n(x) can be delevered by carrier transport equations (5)(6) and following
continuity equations.

26 |

𝑑𝑛
1 𝑑𝐽𝑛
=−
+ 𝐺𝑛 − 𝑅𝑛
𝑑𝑡
𝑞 𝑑𝑥

(32)

𝑑𝑝 1 𝑑𝐽𝑝=+ 𝐺𝑝 − 𝑅𝑝
𝑑𝑡 𝑞 𝑑𝑥(33)

Where Gn and Gp are generation rate for electron and hole. Rn and Rp are recombination rate
for electron and hole. In the model Gn=Gp=0 is assumed. For Rn and Rp, only Shockley–Read–Hall (SRH) recombination is assumed in the model.

𝑅𝑛 = 𝑅𝑝 =𝑝𝑛 − 𝑛𝑖2
𝜏𝑝 (𝑛 + 𝑛1 ) + 𝜏𝑛 (𝑝 + 𝑝1 )(34)

where 𝜏𝑛 and 𝜏𝑝 are carrier lifetime for electron and hole.
𝐸𝑡𝑟𝑎𝑝

𝑛1 = 𝑛𝑖 𝑒 𝑘𝑇
𝑝1 = 𝑛𝑖 𝑒−𝐸𝑡𝑟𝑎𝑝
𝑘𝑇

(35)
(36)

where Etrap is the difference between the defect level and intrinsic level.
In high injection condition, (34) can be approximated as

𝑅𝑛 = 𝑅𝑝 =𝑛𝑛=𝜏𝑝 + 𝜏𝑛 𝜏(37)

where 𝜏 is carrier lifetime in high injection condition.
𝜏 = 𝜏𝑝 + 𝜏𝑛(38)With using 𝜏 and n=p, (32) and (33) can be rewritten as
𝑑𝐽𝑝
𝑑𝐽𝑛
𝑛 𝑑𝑛
=−
= 𝑞( + )𝑑𝑥
𝑑𝑥
𝜏 𝑑𝑡
By differentiating (8) with respect to x,

(39)

27 |

𝑑𝐽𝑝
𝑑𝐽𝑛
𝑑2𝑛
− 𝜇𝑛
= 2𝜇𝑝 𝜇𝑛 𝑘𝑇 2
𝑑𝑥
𝑑𝑥
𝑑𝑥

(40)

𝑛 𝑑𝑛
𝑑2𝑛
𝑞(𝜇𝑝 + 𝜇𝑛 ) ( + ) = 2𝜇𝑝 𝜇𝑛 𝑘𝑇 2
𝜏 𝑑𝑡
𝑑𝑥

(41)

𝜇𝑝

By substituting (39) for (40),

Finally carrier distribution function n(x) is formed as

𝐿2𝐴

𝑑 2𝑛
𝑑𝑛
=𝑛+𝜏
2
𝑑𝑥
𝑑𝑡

(42)

Where LA is diffusion length of high injection condition.

𝑘𝑇 2𝜇𝑝 𝜇𝑛
𝐿𝐴 = √
𝜏𝑞 𝜇𝑝 + 𝜇𝑛(43)

For the steady state conditions, time dependent term is omitted and the solution can beformed as

𝐿2𝐴

𝑑 2𝑛
=𝑛
𝑑𝑥 2

(44)

The solution of the differential equation (44) can be𝑛(𝑥 ) = 𝐿𝐴

𝑑𝑛
𝑥 −𝑥
𝑑𝑛
𝑥−𝑥
− 𝑑𝑥 (𝑥1 ) cosh ( 2𝐿 ) + 𝑑𝑥 (𝑥2 ) cosh ( 𝐿 1 )𝐴𝑥 −𝑥sinh ( 2 𝐿 1 )

𝐴

(45)

𝐴

where x1 and x2 are positions of Anode edge and Cathode edge of N-Base region asshown in Figure 17. Equation (45) means that N-Base carrier distribution depends on the
differentials of the carrier distribution at both edges.
The differentials of the carrier distribution at N-Base edges can be obtained by (8).

28 |

𝜇𝑝
)
𝜇𝑝 + 𝜇𝑛𝑑𝑛(𝑥1 ) = −𝜇𝑝 𝜇𝑛𝑑𝑡
2 𝜇 + 𝜇 𝑘𝑇
𝑝𝑛
𝜇𝑛
𝐽 (𝛾𝑛 −)𝜇𝑑𝑛𝑝 + 𝜇𝑛(𝑥 ) = −𝜇𝑝 𝜇𝑛
𝑑𝑡 22 𝜇 + 𝜇 𝑘𝑇𝑝𝑛
𝐽 (𝛾𝑝 −

(46)

(47)

where 𝛾𝑝 and 𝛾𝑛 are hole injection efficiency at Anode side and electron injection
efficiency at Cathode side, respectively.

3.6

Summary
IGBT structure has thick and high resistive N-Base layer. Electron and hole are stored

in the layer in conduction mode. The shape of stored carrier concentration profile is mostimportant for IGBT characteristics. To reproduce accurate carrier concentration profile,
three models were established. Firstly, “Quasi-2D MOS-ADE” Cathode side model was
created to calculate electron injection efficiency from trench gate structure. It can be applied
for conventional trench gate structures and injection enhancement structures such as IEGT.
Secondly, Anode side model was also created to calculate hole injection efficiency fromshallow P-Emitter and N-Buffer structure. It can be applied to for PT-IGBT and NPT-IGBT
with shallow P-Emitter and N-Buffer layer. Finally N-Base model is formulated by using
Cathode side injection efficiency and Anode side injection efficiency. All models aredescribed by semiconductor basic equations and structure parameters. No fitting parameteris used for proposed model.

29 |4 IGBT Compact Modeling for Wide Range Structure andTemperature
4.1

IGBT Circuit Simulation Environments
In power electronics system development, circuit simulation must be required forsystem optimization, such as checking output waveforms and estimating power loss andheat generation. Two approaches exist currently, compact model and TCAD (Technology
CAD).
On the compact model approach, semiconductor device electrical characteristics are
expressed by simple equations. And circuit topology is written as “Netlist” in a text file.
Then circuit simulator such as SPICE (Simulation Program with Integrated Circuit
Emphasis) solves them. The advantage and disadvantages of this approach is following.
Computing cost: Calculation time is much shorter than TCAD approach because
the number of nodes to be solved is much smaller.



Capability: The number of circuit nodes and devices can be over 10 million and 9
million, respectively [33]. It is enough to describe power electronics circuit.

Modeling complexity: Compact model consists of a lot of parameters which stands
on physical meaning and for fitting. Parameter extraction is required andparameters strongly affect calculation results.



Accuracy: Accuracy depends on the quality of the compact model itself andparameter extraction.

On the other approach, calculation by TCAD simulator, semiconductor geometricalstructure is written in FEM (Finite Element Method) model with a lot of nodes. The
simulator solves the FEM model with a lot of basic semiconductor physical models, andconnected circuits. The advantage and disadvantages of this approach is following.
Computing cost: It consumes much longer calculation time than compact model
approach due to large node number for FEM model.

Capability: The number of the circuit nodes solved with FEM model should be
limited by computing cost and convergence issue.

Modeling complexity: Good quality mesh is necessary to avoid convergence30 |problem and to get accurate results.


Accuracy: In general, much better accuracy than compact model approach isrealized even if using default physical parameter set. With physical calibration,
extremely accurate result can be obtained.

The comparison of these two approaches is summarized in Table 2.

Table 2. Pros and cons of compact model and TCAD approach.
Compact Model

TCAD

Computing cost

Smaller

LargerCapability for circuit node

LargerSmallerModeling complexity

Needs parameter extraction Needs FEM model creation

Accuracy

Depends on the compact

Bettermodel and its parameters

4.2

Previous Research for IGBT Compact Model
A lot of researches were performed for IGBT compact model. Existing models are

categorized into three types.
Physics based model: Based on semiconductor basic equations. Better to express
complex characteristics of IGBT.



Combination model by MOSFET model and Bipolar Transistor model: A
limitation exists due to wide base PNP transistor in IGBT. Bipolar Transistor
model is designed for narrow base transistors.



Behavior model: Electrical characteristics are written in the combination ofmathematical formula. Once the condition is changed, re-fitting is required.

Two physics based models will be reviewed in this section.

4.2.1

Hefner’s Model

Dr. Allen R. Hefner Jr. proposed his first IGBT compact model in 1988 [5]. It was very
early because IGBT had been firstly founded as IGR in 1982 and non-latch up IGBT had
been produced by Nakagawa in 1985. He wrote his modeling approach in his Ph. D. thesis1
1

A. R. Hefner, “Characterization and Modeling of the Power Insulated Gate Bipolar Transistor.” Ph. D. Dissertation,

University of Maryland. Ann Arbor, MI: University Microfilms International, 1987.

31 |in 1987. He seemed to research this topic from very early of IGBT history. From the firstresearch, load circuit was considered to calculate device-circuit interaction. Then gate drive
condition dependencies also took into account [34]. Implementation for Saber simulator[35] and IG-SPICE [36] were also reported. Furthermore, model extension toward
considering self-heating effect [37] and thermal calculation approach on IGBT module [38],were reported. For model validation with load circuit, PWM inverter case [39] and soft
switching case [40] were reported.
Hefner model is physics based and the motif structure is NPT-IGBT with thick
P-Emitter as shown in Figure 18. High injection efficiency from Anode side and low
injection efficiency from Cathode side are assumed to represent Planar gate NPT-IGBT atthat time. N-Base on-state carrier distribution profile is linearly decreasing from Anode to
Cathode as shown in Figure 19. After that the model was extended to consider N-Buffer
layer [41].
Hefner model is still most popular IGBT compact model and widely used in industrial
applications. Even in 2009, regarding report was published for pulse power application [42].

Figure 18. IGBT structure for Hefner model [5]. Cell structure is planar gate type.
Thick P+ substrate layer exists and act as P-Emitter.

32 |Figure 19. Assumed carrier distribution in Hefner model [5]. Horizontal axis shows
distance from P-Emitter. The profile is linearly decreasing from Anode to Cathode.

4.2.2

Palmer & Santi’s Model

Dr. Patrick R. Palmer and Associate Prof. Enrico Santi’s group in the University ofSouth Carolina proposed several physical models for IGBT and Diode [43] [44] [45]. ADE
is solved by Fourier based calculation. The second-order partial differential equation isconverted into an infinite set of first-order linear differential equations in time with seriescoefficients p0,…, pk,…,pn forming equivalent RkCk components. In earlier articles themodel assumed zero carrier concentration at Cathode side N-Base edge as Hefner’s model.
From [43], the model started taking into account Cathode side electron injection.
The motif structure is shown in Figure 20. In this model, no electron current in mesa
region is assumed. The main idea of Cathode side treatment is considering hole horizontal
distribution profile observed by two-dimensional TCAD simulation as shown in Figure 21.
The vertical hole current density in mesa region is assumed as linearly increasing from
center of mesa to trench edge as shown in Figure 22. And the horizontal hole current density
under the trench gate is also assumed as linearly increasing from center of trench gate to
trench edge as shown in Figure 22. By these assumption, horizontal hole distribution profile
can be calculated. Finally the average of the hole concentration is used for the boundary
condition of ADE in N-Base.

33 |Figure 20. Motif structure for Palmer & Santi’s model [43]. Cutline C1 to Cn iscorresponding hole distribution in Figure 21.

Figure 21. Hole horizontal distribution calculated by two-dimentional TCAD
simulation [43]. A gradient is observed at cutline Cn, just below the trench gate.

34 |Figure 22. Assumed hole current distributions and hole distribution for Palmer &Santi’s model [43].

4.3

Model Formulation and Implementation
By combining “Quasi-2D MOS-ADE” Cathode model, Anode model, and N-Basemodel described in previous section, new IGBT compact model is established. By
reviewing modeling concept:

35 |



Accurate on-state carrier distribution realized: the model aims to realize accurate
N-Base carrier distribution. On-state carrier distribution in N-Base is most important
point to describe IGBT characteristics accurately, especially on-state voltage dropVce(sat) and turn-off loss Eoff.



Physical based: the model formulation is based on basic semiconductor equations andsome additional physical equations. It leads an advantage that the model can apply forwide range of structure and temperature with high accuracy.

Structure oriented: the model parameters consist of only structure parameters. No
fitting parameters exist. No parameter extraction work is required in result.
In this implementation, on-state voltage drop is divided to following elements.


Voltage drop in N-Base

Voltage drop in mesa region

Voltage drop in MOS channel



Built-in potential.

The voltage drop in N-Emitter, P-Emitter and N-Buffer were ignored because these arevery small due to very thin layers.

4.3.1

Voltage drop in N-Base

N-Base carrier distribution can be calculated by following equations, Cathode side
injection efficiency formed as
𝜇𝑝
2𝑞𝐷𝑝 𝑆 𝑑𝑛(𝑥)𝜎𝑚𝑒𝑠𝑎 (𝑛(𝑥))(+ 1) 𝛾𝑛 − 1 =𝜇𝑛 𝜎𝑎𝑐𝑐 + 𝜎𝑚𝑒𝑠𝑎 (𝑛(𝑥))𝐽 𝑊 𝑑𝑥(48)

Anode side injection efficiency formed as,−𝑁𝐴 + √𝑁𝐴2 + 4𝑛12
𝛾𝑝 = 1 − 𝑞𝐷𝑛
2𝐽𝐿𝑝

(49)

and N-Base carrier distribution formed as𝑛(𝑥 ) = 𝐿𝐴

−

𝑑𝑛
𝑥 −𝑥
𝑑𝑛
𝑥 − 𝑥1(𝑥 ) cosh ( 2)+(𝑥 ) cosh (
)
𝑑𝑥 1
𝐿𝐴
𝑑𝑥 2
𝐿𝐴
𝑥 −𝑥
sinh ( 2 𝐿 1 )
𝐴

(50)

36 |

𝜇𝑝
)
𝜇𝑝 + 𝜇𝑛𝑑𝑛(𝑥1 ) = −𝜇𝑝 𝜇𝑛𝑑𝑡
2 𝜇 + 𝜇 𝑘𝑇
𝑝𝑛
𝜇𝑛
𝐽 (𝛾𝑛 −)𝜇𝑑𝑛𝑝 + 𝜇𝑛(𝑥 ) = −𝜇𝑝 𝜇𝑛
𝑑𝑡 22 𝜇 + 𝜇 𝑘𝑇𝑝𝑛
𝐽 (𝛾𝑝 −

(51)

(52)

The voltage drop in the N-base can be calculated based on the above stored carrier
concentration.
𝑥2
𝜇𝑝 − 𝜇𝑛 𝑘𝑇 𝑥2 1 𝑑𝑛
𝐽
1𝑉𝑁−𝐵𝑎𝑠𝑒 =
∙
∫
𝑑𝑥 +
∫
𝑑𝑥
𝜇𝑝 + 𝜇𝑛 𝑞 𝑥=𝑥1 𝑛 𝑑𝑥
𝑞(𝜇𝑝 + 𝜇𝑛 ) 𝑥=𝑥1 𝑛

4.3.2

(53)

Voltage drop in mesa region

Carrier distribution profile in mesa region can be calculated by
𝜇𝑝
2𝑞𝐷𝑝 𝑆 𝑑𝑛(𝑥)𝜎𝑚𝑒𝑠𝑎 (𝑛(𝑥))(+ 1) 𝛾𝑛 − 1 =𝜇𝑛 𝜎𝑎𝑐𝑐 + 𝜎𝑚𝑒𝑠𝑎 (𝑛(𝑥))𝐽 𝑊 𝑑𝑥(54)

The voltage drop in mesa region can be calculated based on the above stored carrier
concentration.

𝑉𝑚𝑒𝑠𝑎 = −𝐽𝛾𝑛 𝑊 𝑥3 1
𝜎𝑚𝑒𝑠𝑎 (𝑛(𝑥))
𝑑𝑛(𝑥)
∙ ∫
𝑑𝑥
𝑞𝜇𝑛 𝑆 𝑥=𝑥2 𝑛(𝑥) 𝜎𝑎𝑐𝑐 + 𝜎𝑚𝑒𝑠𝑎 (𝑛(𝑥)) 𝑑𝑥(55)

where 𝑥3 is the junction position between P-Base and N-Base.

4.3.3

Voltage drop in MOS channel

The voltage drop of the channel can be calculated by power of electron current via
MOS gate, which is calculated by Cathode side electron injection efficiency, and channel
conductance, which is calculated by surface potential along the channel.
To simplify the model, strong inversion condition is assumed for the channel region.
Surface potential 𝜑𝑆 (𝑥 ) can be calculated by following.
𝜑𝑆 (𝑥 ) = 2𝜑𝑃 (𝑥 ) + 𝑉𝑑𝑠 (𝑥)

(56)

37 |

where 𝜑𝑃 (𝑥 ) is the difference of intrinsic Fermi potential and P-base Fermi potential.
𝑉𝑑𝑠 (𝑥) is the potential drop from source side. The charge concentration of gate oxide canbe calculated by
𝑄𝐺 (𝑥 ) = 𝐶𝑜𝑥 (𝑉𝑔𝑒 − 𝜑𝑆 (𝑥 ))(57)

where 𝐶𝑜𝑥 is the capacitance per unit area of gate oxide, and 𝑉𝑔𝑒 is gate-emitter voltage.
The charge concentration of channel region can be calculated by
𝑄𝐶 (𝑥 ) = −(𝑄𝐺 (𝑥 ) + 𝑄𝐴 (𝑥 ))= −𝐶𝑜𝑥 (𝑉𝑔𝑒 − 𝜑𝑆 (𝑥 )) − 𝑄𝐴 (𝑥 )(58)

where 𝑄𝐴 (𝑥 ) is acceptor concentration of P-Base region. We can modify it by using
acceptor concentration of P-Base region 𝑁𝐴 (𝑥),𝑄𝐶 (𝑥 ) = −𝐶𝑜𝑥 (𝑉𝑔𝑒 − (2𝜑𝑃 (𝑥 ) + 𝑉𝑑𝑠 (𝑥)))+ √2𝜀𝑆𝑖 𝜀0 (2𝜑𝑃 (𝑥 ) + 𝑉𝑑𝑠 (𝑥))𝑞𝑁𝐴 (𝑥)(59)

Finally the channel conductance can be calculated by𝜎𝑐ℎ𝑎𝑛𝑛𝑒𝑙 (𝑥) = 𝜇𝑐ℎ𝑎𝑛𝑛𝑒𝑙 (𝑥)𝑄𝐶 (𝑥 )(60)𝜇𝑐ℎ𝑎𝑛𝑛𝑒𝑙 (𝑥) is the electron mobility in the channel. As mentioned before, it is muchdegraded than bulk mobility due to carrier interaction with the Silicon/Oxide interface byhigh transverse electric field. Degradation model [25] [26] [27] [28] must be applied toestimate accurate 𝜇𝑐ℎ𝑎𝑛𝑛𝑒𝑙 (𝑥).

4.3.4

Built-in potential

The built-in potential is the difference between quasi-Fermi potential and electro static
potential. In case of high injection device, such as PiN diode, it can be illustrated as Figure
23. Hole quasi-Fermi potential ∅𝑝 is equal to Anode potential connected to P-Emitter
because hole is majority carrier in P-Emitter. Similarly, electron quasi-Fermi potential ∅𝑛
is equal to Cathode potential. In on-state, N-Base potential φ is lower than holequasi-Fermi potential and higher than electron quasi-Fermi potential. The definitions for38 |quasi-Fermi potential are following.
𝑞𝑛(𝑥 ) = 𝑛𝑖 𝑒 𝑘𝑇(𝜑−∅𝑛)

(61)

𝑞

𝑝(𝑥 ) = 𝑛𝑖 𝑒 𝑘𝑇(∅𝑝−𝜑)(62)

where ni is intrinsic carrier density. Band gap narrowing model [46] [47] [48] should beconsidered to apply effective intrinsic carrier density.
Vbuilt-in1

CathodeN-Emitter

N-BaseP-Emitter

Vbuilt-in2

Anode

Figure 23. Built-in potential for high injection devices.

In proposed IGBT model, the built-in potential is calculated as the sum of thedifference between hole quasi-Fermi potential and potential at x1 and the difference between
electron quasi-Fermi potential and potential at x2 as shown in Figure 24. They can becalculated by (53) and (54).

𝑉𝑏𝑢𝑖𝑙𝑡−𝑖𝑛 (𝑥1 ) =𝑘𝑇𝑛(𝑥1 )
log
𝑞
𝑛𝑖

(63)

39 |

𝑉𝑏𝑢𝑖𝑙𝑡−𝑖𝑛 (𝑥2 ) =𝑘𝑇𝑛(𝑥2 )
log
𝑞
𝑛𝑖

(64)

Gate Gate

GateGate

Vbuilt-in1

P-BaseP-floatx2

N-Basex1

N-Buffer
P-Emitter
Vbuilt-in2

Figure 24. Built-in potential definition for the model.

4.4

Implementation
The established model was implemented on Microsoft Excel spreadsheet application

software as shown in Figure 25. A solution between current density, Anode side hole
injection efficiency, and Cathode side electron injection efficiency is found by genuine
newton solver add-on of the software. GRG non-linear method is used due to good
convergence.
The equations mentioned above are described on the spreadsheet. The solution for eachcurrent density is found by least squares method with varying electron injection efficiency
from Cathode side and hole injection efficiency from Anode side. Carrier distribution
profiles for N-Base and mesa region is also calculated. The step is repeated from small

40 |current density to rated current density. Finally, Jc-Vce characteristic is formed. Typicalcalculation time is several seconds for each current density by standard performance laptop
PC (Lenovo ThinkPad X121e; AMD E-300 processor 1.30GHz).
Injection efficiencies
N-Base model
Anode model
Cathode model
Physical constants
Built-in potentials
N-Base carrier distribution
Mesa carrier distribuion

Figure 25. Model implementation on Microsoft Excel.

4.5

Verification Results
Established model was verified by comparing with two-dimensional TCAD calculation

results. Synopsys Sentaurus Process and Sentaurus Device version E-2010.12 was used for
TCAD calculation. Process simulation was performed to create FEM models of IGBT. Then
voltage boundary conditions were applied in device simulation.

4.5.1

Structures

Three types of trench gate IGBT are used for the validation; 600V rated NPT-IGBT,
1200V rated PT-IGBT and 3.3kV rated IEGT. Cross sectional views and structure
parameters for these structures are summarized in Figure 26 and Table 3. For 3.3kV IEGT
structure, cell pitch and trench depth were varied to confirm the model could follow
injection enhancement effect.
The 600V NPT-IGBT has shallow P-Emitter and no N-Buffer. Wafer thickness is100um. Cell structure is standard trench gate IGBT with 2um half cell pitch. No dummy

41 |cell for injection enhancement is used. Rated current density is 200A/cm2.
The 1200V PT-IGBT has shallow P-Emitter and shallow N-Buffer. Wafer thickness is120um. Cell structure is standard trench gate IGBT with 2um half cell pitch. No dummycell for injection enhancement is used. Rated current density is 150A/cm2.
The 3.3kV IEGT has also shallow P-Emitter and shallow N-Buffer. Wafer thickness is
350um. Cell structure is trench gate IEGT type. It has dummy cell with P-float layer for

8um

2um

2um

injection enhancement. Rated current density is 50A/cm2.

Gate

Gate
Gate

Gate

Base

P-float

120um

Gate

Gate
Gate

N-base100um

P-floatN-buffer
P-emitter(b) 1200V
PT-IGBTN-buffer
P-emitterAnode(c) 3300V PT-IEGT

Figure 26. Structures used for verifications.

350um(a) 600V
NPT-IGBT

Base

N-baseP-emitter

Gate

Gate
Gate

Base

N-baseGate

Cathode42 |Table 3. Parameters using model verification.
600V

1200V

3.3kV

NPT-IGBT

PT-IGBTPT-IEGT

N-Base concentration [1/cm3]

1.5 x1014

8x10132x1013

N-Base thickness [um]

93

112

342

Half-cell pitch: W [um]

2.0

2.0

8.0(center)

Half mesa width: S [um]

1.5

1.5

1.5

P-Base surface concentration[1/cm3]

2x10172x10172x1017

P-Base thickness: Db [um]

3.0

3.0

3.0

Trench depth: DT [um]

6.0

6.0

6.0(center)

Gate oxide thickness: Tox [angstrom]

1000

1000

1000

P-Emitter concentration: NA [1/cm3]

1x10171x10172x1017

P-Emitter thickness: Lp [um]

1.0

1.0

1.0

9x10169x10161.0

1.0

Parameters

N-Buffer concentration: ND [1/cm3]
No N-Buffer
N-Buffer thickness: Ln [um]4.5.2

Physical models

Several physical models were commonly applied for the proposed model and TCAD.
Especially temperature dependences were taken into account to follow device temperature.
The device temperature is varied from 300K, 400K and 450K in the validation.
Physical constants for room temperature are summarized in Table 4. For carrier
mobility, doping concentration dependence and temperature dependence are considered.
And Electron mobility degradation by normal electric field in MOS channel is considered to
calculate electron current through MOS channel.
For carrier lifetime, doping concentration dependence and temperature dependence areconsidered.
For effective intrinsic carrier density, doping concentration dependence [47] andtemperature dependence [49] band gap narrowing model are applied.

43 |Table 4. Physical constants for 300K.
Constants

For electron

For hole

Carrier mobility [cm2/Vs]

1417

470.5

Carrier lifetime [usec]

10.0

3.0

Intrinsic carrier density [1/ cm3]

1.18x1010

44 |

4.5.3

Calculation Results

Forward Jc-Vce characteristics and on-state carrier distribution profiles were
calculated and compared with TCAD results. TCAD carrier distribution profile wasmeasured at the center of trench MOS cell as Figure 27.

N-base

Gate

Base

Gate
Gate

P-float

Gate

Gate

CathodeP-floatCutlineN-buffer
P-emitter
Anode
Figure 27. Carrier distribution profile measurement.

Forward Jc-Vce characteristics for 600V NPT-IGBT are summarized in Figure 28.
These calculation results show good agreement with TCAD results. On-state N-Base carrier
distribution profiles for 600V NPT-IGBT are calculated at Jc=50A/cm2, 100A/cm2,
150A/cm2 and 200A/cm2 as shown in Figure 29, Figure 30, Figure 31, and Figure 32,
respectively. These calculation results show good agreement with TCAD results. It means
the model can be applied to low rated voltage IGBT from room temperature to extremely
high temperature, perfectly.
Forward Jc-Vce characteristics for 1200V NPT-IGBT are summarized in Figure 33.
These calculation results also show good agreement with TCAD results. On-state N-Basecarrier distribution profiles for 1200V PT-IGBT are calculated at Jc=50A/cm2, 100A/cm2,
and 150A/cm2 as shown in Figure 33, Figure 34, and Figure 35, respectively. These
calculation results show good agreement with TCAD results. It means the model can beapplied to medium rated voltage IGBT from room temperature to extremely high45 |temperature, perfectly.
Forward Jc-Vce characteristics for 3.3kV IEGT are summarized in Figure 37. These
calculation results also show better agreement with TCAD results but slight difference isobserved in T=450K case. On-state N-Base carrier distribution profiles for 3.3kV IEGT are
calculated at Jc=10A/cm2, 30A/cm2, and 50A/cm2 as shown in Figure 38, Figure 39, andFigure 40, respectively. These calculation results show better agreement with TCAD results
but slight differences are observed especially N-Base both edges.
For trench depth variation for 3.3kV IEGT, trench depth-Vce(sat) relationship with
8.0um of half-cell pitch is summarized in Figure 41. For cell pitch variation for 3.3kV IEGT,
cell pitch-Vce(sat) relationship with 6.0um of trench depth is summarized in Figure 42.
These calculation results show better agreement with TCAD results. They indicate themodel can predict device improvement accurately.

46 |600V NPT-IGBT Jc-Vce characteristics
200
Model

TCAD

T=300K

Jc[A/cm2]

150

100

50

0

0.0

0.5

1.0

1.5

2.0

1.5

2.0

1.5

2.0

Vce[V]
200
Model

TCAD

T=400K

Jc[A/cm2]

150

100

50

0

0.0

0.5

1.0

Vce[V]
200
Model

TCAD

T=450K

Jc[A/cm2]

150

100

50

0

0.0

0.5

1.0

Vce[V]

Figure 28. Calculated Jc-Vce characteristic comparison between proposed compact
model and TCAD simulator for 600V NPT-IGBT.

47 |600V NPT-IGBT carrier distribution at 50A/cm2
Carrier Concentration[1/cm3]

1.0E+17
Model

TCAD

1.0E+16

T=300K

1.0E+15

1.0E+14

0

20

40

60

80

100

Distance from Anode[um]Carrier Concentration[1/cm3]

1.0E+17
Model

TCAD

1.0E+16

T=400K

1.0E+15

1.0E+14

0

20

40

60

80

100

Distance from Anode[um]Carrier Concentration[1/cm3]

1.0E+17
Model

TCAD

1.0E+16

T=450K

1.0E+15

1.0E+14

0

20

40

60

80

100

Distance from Anode[um]Figure 29. Calculated carrier distribution comparison between proposed compact
model and TCAD simulator for 600V NPT-IGBT at 50A/cm2.

48 |600V NPT-IGBT carrier distribution at 100A/cm2
Carrier Concentration[1/cm3]

1.0E+17
Model

TCAD

1.0E+16

T=300K

1.0E+15

1.0E+14

0

20

40

60

80

100

Distance from Anode[um]Carrier Concentration[1/cm3]

1.0E+17
Model

TCAD

1.0E+16

T=400K

1.0E+15

1.0E+14

0

20

40

60

80

100

Distance from Anode[um]Carrier Concentration[1/cm3]

1.0E+17
Model

TCAD

1.0E+16

T=450K

1.0E+15

1.0E+14

0

20

40

60

80

100

Distance from Anode[um]Figure 30. Calculated carrier distribution comparison between proposed compact
model and TCAD simulator for 600V NPT-IGBT at 100A/cm2.

49 |600V NPT-IGBT carrier distribution at 150A/cm2
Carrier Concentration[1/cm3]

1.0E+17
Model

TCAD

1.0E+16

T=300K

1.0E+15

1.0E+14

0

20

40

60

80

100

Distance from Anode[um]Carrier Concentration[1/cm3]

1.0E+17
Model

TCAD

1.0E+16

T=400K

1.0E+15

1.0E+14

0

20

40

60

80

100

Distance from Anode[um]Carrier Concentration[1/cm3]

1.0E+17
Model

TCAD

1.0E+16

T=450K

1.0E+15

1.0E+14

0

20

40

60

80

100

Distance from Anode[um]Figure 31. Calculated carrier distribution comparison between proposed compact
model and TCAD simulator for 600V NPT-IGBT at 150A/cm2.

50 |600V NPT-IGBT carrier distribution at 200A/cm2
Carrier Concentration[1/cm3]

1.0E+17
Model

TCAD

1.0E+16

T=300K

1.0E+15

1.0E+14

0

20

40

60

80

100

Distance from Anode[um]Carrier Concentration[1/cm3]

1.0E+17
Model

TCAD

1.0E+16

T=400K

1.0E+15

1.0E+14

0

20

40

60

80

100

Distance from Anode[um]Carrier Concentration[1/cm3]

1.0E+17
Model

TCAD

1.0E+16

T=450K

1.0E+15

1.0E+14

0

20

40

60

80

100

Distance from Anode[um]Figure 32. Calculated carrier distribution comparison between proposed compact
model and TCAD simulator for 600V NPT-IGBT at 200A/cm2.

51 |1200V PT-IGBT Jc-Vce characteristics
150
Model

TCAD

T=300K

Jc[A/cm2]

100

50

0
0.0

0.5

1.0

1.5

2.0

2.5

2.0

2.5

2.0

2.5

Vce[V]
150
Model

TCAD

T=400K

Jc[A/cm2]

100

50

0

0.0

0.5

1.0

1.5

Vce[V]
150
Model

TCAD

T=450K

Jc[A/cm2]

100

50

0

0.0

0.5

1.0

1.5

Vce[V]

Figure 33. Calculated Jc-Vce characteristic comparison between proposed compact
model and TCAD simulator for 1200V PT-IGBT.

52 |1200V PT-IGBT carrier distribution at 50A/cm2
Carrier Concentration[1/cm3]

1.0E+17
Model

TCAD

1.0E+16

T=300K

1.0E+15

1.0E+14
0

20

40

60

80

100

120

Distance from Anode[um]Carrier Concentration[1/cm3]

1.0E+17
Model

TCAD

1.0E+16

T=400K

1.0E+15

1.0E+14
0

20

40

60

80

100

120

Distance from Anode[um]Carrier Concentration[1/cm3]

1.0E+17
Model

TCAD

1.0E+16

T=450K

1.0E+15

1.0E+14
0

20

40

60

80

100

120

Distance from Anode[um]Figure 34. Calculated carrier distribution comparison between proposed compact
model and TCAD simulator for 1200V PT-IGBT at 50A/cm2.

53 |1200V PT-IGBT carrier distribution at 100A/cm2
Carrier Concentration[1/cm3]

1.0E+17
Model

TCAD

1.0E+16

T=300K

1.0E+15

1.0E+14
0

20

40

60

80

100

120

Distance from Anode[um]Carrier Concentration[1/cm3]

1.0E+17
Model

TCAD

1.0E+16

T=400K

1.0E+15

1.0E+14
0

20

40

60

80

100

120

Distance from Anode[um]Carrier Concentration[1/cm3]

1.0E+17
Model

TCAD

1.0E+16

T=450K

1.0E+15

1.0E+14
0

20

40

60

80

100

120

Distance from Anode[um]Figure 35. Calculated carrier distribution comparison between proposed compact
model and TCAD simulator for 1200V PT-IGBT at 100A/cm2.

54 |1200V PT-IGBT carrier distribution at 150A/cm2
Carrier Concentration[1/cm3]

1.0E+17
Model

TCAD

1.0E+16

T=300K

1.0E+15

1.0E+14
0

20

40

60

80

100

120

Distance from Anode[um]Carrier Concentration[1/cm3]

1.0E+17
Model

TCAD

1.0E+16

T=400K

1.0E+15

1.0E+14
0

20

40

60

80

100

120

Distance from Anode[um]Carrier Concentration[1/cm3]

1.0E+17
Model

TCAD

1.0E+16

T=450K

1.0E+15

1.0E+14
0

20

40

60

80

100

120

Distance from Anode[um]Figure 36. Calculated carrier distribution comparison between proposed compact
model and TCAD simulator for 1200V PT-IGBT at 150A/cm2.

55 |3.3kV IEGT Jc-Vce characteristics
50
Model

T=300K

Jc[A/cm2]

40

TCAD

30
20
10
0
0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

2.5

3.0

3.5

4.0

2.5

3.0

3.5

4.0

Vce[V]
50
Model

T=400K

Jc[A/cm2]

40

TCAD

30
20
10
0
0.0

0.5

1.0

1.5

2.0

Vce[V]
50
Model

T=450K

Jc[A/cm2]

40

TCAD

30
20
10
0
0.0

0.5

1.0

1.5

2.0

Vce[V]

Figure 37. Calculated Jc-Vce characteristic comparison between proposed compact
model and TCAD simulator for 3.3kV IEGT.

56 |T=300K

Carrier Concentration[1/cm3]

3.3kV IEGT carrier distribution at 10A/cm2
1.0E+17
Model

TCAD

1.0E+16

1.0E+15

1.0E+14
0

50

100

150

200

250

300

350

T=400K

Carrier Concentration[1/cm3]

Distance from Anode[um]1.0E+17
Model

TCAD

1.0E+16

1.0E+15

1.0E+14
0

50

100

150

200

250

300

350

T=450K

Carrier Concentration[1/cm3]

Distance from Anode[um]1.0E+17
Model

TCAD

1.0E+16

1.0E+15

1.0E+14
0

50

100

150

200

250

300

350

Distance from Anode[um]Figure 38. Calculated carrier distribution comparison between proposed compact
model and TCAD simulator for 3.3kV IEGT at 10A/cm2.

57 |T=300K

Carrier Concentration[1/cm3]

3.3kV IEGT carrier distribution at 30A/cm2
1.0E+17
Model

TCAD

1.0E+16

1.0E+15

1.0E+14
0

50

100

150

200

250

300

350

T=400K

Carrier Concentration[1/cm3]

Distance from Anode[um]1.0E+17
Model

TCAD

1.0E+16

1.0E+15

1.0E+14
0

50

100

150

200

250

300

350

T=450K

Carrier Concentration[1/cm3]

Distance from Anode[um]1.0E+17
Model

TCAD

1.0E+16

1.0E+15

1.0E+14
0

50

100

150

200

250

300

350

Distance from Anode[um]Figure 39. Calculated carrier distribution comparison between proposed compact
model and TCAD simulator for 3.3kV IEGT at 30A/cm2.

58 |

3.3kV IEGT carrier distribution at 50A/cm2
Carrier Concentration[1/cm3]

1.0E+17
Model

TCAD

1.0E+16

T=300K

1.0E+15

1.0E+14
0

50

100

150

200

250

300

350

T=400K

Carrier Concentration[1/cm3]

Distance from Anode[um]1.0E+17
Model

TCAD

1.0E+16

1.0E+15

1.0E+14
0

50

100

150

200

250

300

350

T=450K

Carrier Concentration[1/cm3]

Distance from Anode[um]1.0E+17
Model

TCAD

1.0E+16

1.0E+15

1.0E+14
0

50

100

150

200

250

300

350

Distance from Anode[um]Figure 40. Calculated carrier distribution comparison between proposed compact
model and TCAD simulator for 3.3kV IEGT at 50A/cm2.

59 |Vce(sat) [V] @ Jc=50A/cm2

2.5
Model

TCAD

2.0

1.5
5.0

6.0
7.0
Trench depth [um]8.0

Figure 41. Trench depth-Vce(sat) relationship comparison between proposed modelVce(sat) [V] @ Jc=50A/cm2

and TCAD for 3.3kV IEGT.

3.0
Model

TCAD

2.5

2.0

1.5
2.0

4.0

6.0

8.0
10.0 12.0
Half cell pitch [um]

14.0

16.0

Figure 42. Cell pitch-Vce(sat) relationship comparison between proposed model and
TCAD for 3.3kV IEGT.

60 |

5um

Carrier Concentration[1/cm3]

3.3kV IEGT carrier distribution at 50A/cm2, trench depth dependencies
1.0E+17
Model

TCAD

1.0E+16

1.0E+15

1.0E+14
0

50

100

150

200

250

300

350

6um(ref.)

Carrier Concentration[1/cm3]

Distance from Anode[um]1.0E+17
Model

TCAD

1.0E+16

1.0E+15

1.0E+14
0

50

100

150

200

250

300

350

7um

Carrier Concentration[1/cm3]

Distance from Anode[um]1.0E+17
Model

TCAD

1.0E+16

1.0E+15

1.0E+14
0

50

100

150

200

250

300

350

8um

Carrier Concentration[1/cm3]

Distance from Anode[um]1.0E+17
Model

TCAD

1.0E+16

1.0E+15

1.0E+14
0

50

100

150

200

250

300

350

Distance from Anode[um]Figure 43. On-state carrier distribution profiles with varied trench depth for 3.3kV
IEGT at 50A/cm2. Electron injection efficiency from Cathode side depends on the depth.

61 |

2um

Carrier Concentration[1/cm3]

3.3kV IEGT carrier distribution at 50A/cm2, cell pitch dependencies
1.0E+17
Model

TCAD

1.0E+16

1.0E+15

1.0E+14
0

50

100

150

200

250

300

350

4um

Carrier Concentration[1/cm3]

Distance from Anode[um]1.0E+17
Model

TCAD

1.0E+16

1.0E+15

1.0E+14
0

50

100

150

200

250

300

350

8um(ref.)

Carrier Concentration[1/cm3]

Distance from Anode[um]1.0E+17
Model

TCAD

1.0E+16

1.0E+15

1.0E+14
0

50

100

150

200

250

300

350

12um

Carrier Concentration[1/cm3]

Distance from Anode[um]1.0E+17
Model

TCAD

1.0E+16

1.0E+15

1.0E+14
0

50

100

150

200

250

300

350

16um

Carrier Concentration[1/cm3]

Distance from Anode[um]1.0E+17
Model

TCAD

1.0E+16

1.0E+15

1.0E+14
0

50

100

150

200

250

300

350

Distance from Anode[um]Figure 44. On-state carrier distribution profiles with varied half cell pitch for 3.3kV
IEGT at 50A/cm2. Electron injection efficiency from Cathode side depends on the cell
pitch.

62 |4.6

Discussion
By the results shown in previous paragraph, the basic feasibility of the model is proved.

The model can be applied for wide range of rated voltage and device temperature. Three
topics will be discussed in this paragraph.

4.6.1

Boundary condition between P-Base and N-BaseIn this model, zero carrier concentration is assumed as a boundary condition at thejunction between P-Base and mesa region (N-type) to calculate carrier distribution in mesa
region. However, there is depletion layer extended from the junction toward mesa region asshown in Figure 45 for 600V NPT-IGBT and Figure 46 for 3.3kV IEGT. Carrier distribution
profile is different from TCAD calculation results. It affects the boundary condition
between N-Base and mesa region. Especially in 3.3kV IEGT case, the width of thedepletion layer is about 0.8um and it is considerable by comparing mesa length of 3.0um. It
is equivalent to shallower trench depth.

Carrier Concentration[1/cm3]

5.0E+15

Model
TCAD(Electron)

4.0E+15

Mesa

3.0E+15

P-Base2.0E+15

Depletion
Layer

1.0E+15

0.0E+00
94

96

98

100

Distance from Anode[um]Figure 45. Carrier distribution in mesa region of 600V NPT-IGBT at 200A/cm2.

63 |Carrier Concentration[1/cm3]

5.0E+15
Model
TCAD(Electron)

4.0E+15

Mesa

3.0E+15

P-Base2.0E+15

Depletion
Layer

1.0E+15
0.0E+00

344

346

348

350

Distance from Anode[um]Figure 46. Carrier distribution in mesa region of 3.3kV IEGT at 50A/cm2.

4.6.2

Electron current via accumulation layer

Electron current via accumulation layer acts an important role. Carrier concentration inmesa region, electron current density in mesa region and electron current via accumulation
layer are shown in Figure 47. The structure is 1200V PT-IGBT. The current density is
150A/cm2.

64 |Inacc(x)Gate

JncellJnmesa(x)Gatex2Electron current density
Electron current
in mesa region
via accumulation layer
Jnmesa(x)Inacc(x) (per trench)

P-BaseJpmesa(x)JpcellGate
x3

5.00E-

0.005A02

4.00E-

0.004A02
3.00E0.003A02
2.00E0.002A02
1.00E0.001A02
0.00E+00-0.00 -0.00 -0.00
032
02
01
1.00E+0
2
cm
2

0A

x

x03

x

x03

100A/

8.00E+02
80A/cm1

6.00E+02
60A/cm1

4.00E+02
40A/cm1

2.00E+02
20A/cm1

0.00E+02
0A/cm
0-0.00 -0.00 -0.00
032
02
01

Carrier concentrationn(x)=p(x)1.00E+1

3
1016/cm
6

1.00E+1

3
1015/cm
5

1.00E+1

3
1014/cm4

3
10131.00E+1
/cm
3

x

-0.00 -0.00 -0.00
032
02
01

x30

Figure 47. Relationship for carrier concentration in mesa region, electron current
density in mesa region and electron current via accumulation layer. The structure is 1200V
PT-IGBT. The current density is 150A/cm2.

In this condition, the electron current density in N-Base region is 111A/cm2 by
𝛾𝑛 = 0.74. On the other hand, the electron current density at position x2 is about 44.4A/cm2

65 |as shown in Figure 47. So, 40% of electron current at N-Base edge, position x2, flows frommesa region. And 60% of that flows from the accumulation layer. Therefore, the mobility of
the accumulation layer 𝜇𝑎𝑐𝑐 strongly affects the balance of each electron current element.
Moreover, electron injection efficiency 𝛾𝑛 can be improved by increasing 𝜇𝑎𝑐𝑐 . The
proposed compact model formulates this aspect accurately.

4.7

Further works
In this work, accurate on-state modeling for modern trench gate IGBT is realized.

Accurate carrier distribution can be obtained by the established model. For further works,compact modeling for turn-off characteristics can be considered. Several works werereported for PiN diode reverse recovery characteristics calculation by on-state carrier
distribution [50]. The carrier distribution of PiN diode is similar to IGBT’s because PiN
diode and IGBT has both high resistivity N-Base layer and their stored carrier keep
“conductive modulation” status. And turn-off process of IGBT is also similar to reverse
recovery process of PiN diode because they are exhausting operations for stored carrier byapplied electric field. The difference is that IGBT has P-Emitter region and it acts as hole
injection source during turn-off process. The phenomena can be explained by the Anodemodel previously described in section 3.4. So, accurate turn-off characteristics should be
calculated by these models. Some parasitic capacitances, they affect turn-off characteristics,
should be also modeled by structure parameters.

4.8

Summary
New compact model for Trench gate IGBT was established. The model is formulated

by only physical parameters. Based on previously proposed structure oriented design model,
calculation program to write Jc-Vce characteristics and carrier distribution profiles was
implemented. Modeling is easier than existing compact models because parameter
extraction is not required. And also no fitting parameter exists for the modeling. The model
is validated by comparing with two-dimensional TCAD simulation results for three IGBT
structures. The forward characteristics and the internal carrier distributions of 600V thin
wafer NPT-IGBT, 1200V thin wafer PT-IGBT and 3.3kV IEGT show superior agreementwith TCAD results with temperature range from 300K to 450K. The model capability forstructure parameter dependencies was also confirmed.

66 |5 IGBT Scaling Principle toward Shallow Trench Structure
5.1

Cutting Edge Silicon Technology and IGBTThe 300mm to 450mm “More Moore” field semiconductor technology based on highresolution lithographic techniques enhances significant performance and mass-productivity
improvements in digital integrated circuits by Moore’s Law as a scaling by a factor of 0.7
every 2 years for critical dimension [51] as shown in Figure 48. On the other hand, theimportance of “More than Moore” field like that analog and mixed signal processors,
sensors and actuators, micro-mechanical devices, and power devices, is increased a lot. And
these “More than Moore” devices also will be forced to be designed in the compatibility of
the large diameter wafer process technology to realize better performance andmanufacturability as shown in Figure 49.

Figure 48. Technology node shrinking [52].

67 |Figure 49. “More Moore” field and “More than Moore” field [9].

The basic principle of “More Moore” technological trend is the scaling principle
proposed by Dr. Robert H. Dennard in 1974 [53]. The concept is shown in Figure 50.
Reducing the channel length of MOSFET leads to undesirable changes in the device
characteristics. These changes become significant when the depletion layer surrounding the
Source and Drain extend over a large portion of the region in the Silicon substrate under theGate electrode. And most undesirable short-channel effect reduces Vth. MOSFET. In the
Dennard’s scaling, to decrease channel length the device is scaled by a transformation inthree variables: dimension, voltage and doping. First, all linear dimensions are reduced by aunitless scaling factor k, i.e. Gate oxide thickness Tox’=Tox/k, where primed parametersrefer to the new scale down device. This reduction includes vertical dimensions such as gateinsulator thickness, junction depth, etc., as well as the horizontal dimensions of channel
length and width. Second, the voltages applied to the device are reduced by the same factor(e.g., Vds’ = Vds/k). Third, the substrate doping concentration is increased, again using thesame scaling factor (i.e., NA’= k NA). After that the depletion layer wd, Vth, and drain current
Id are reduced as wd’≈wd/k, Vth’ ≈Vth/k, and Id’ ≈Id/k, respectively.

68 |Figure 50. MOSFET scaling principle [53]. The principle scales channel length L, Gate
oxide thickness Tox, and substrate doping concentration NA to L’=L/k, Tox’=Tox/k, andNA’= k NA, respectively.

Trench gate IGBTs are currently mass produced on the wafers of ~200mm diameter.
Current structures have several microns of deep trench gate to obtain better trade-off
relationship between on-state voltage drop Vce(sat) and turn-off loss. Miniaturization has
not been believed to contribute IGBT performance improvement. However, to improve its
manufacturability, certain process compatibility to “More Moore” field semiconductor must
be required i.e. IGBT process have to follow “More Moore” process technology. To apply
such technology for IGBT fabrication, Cathode side cell structure should be shallower as
CMOS structure to keep process uniformity and avoid wafer warpage.
In this section, a scaling principle for trench gate IGBT will be proposed toward
CMOS process compatibility. As Dennard’s scaling principle, a unitless scaling factor k is
introduced into “Quasi-2D MOS-ADE” model described before. With CMOS process, highresolution lithographic techniques enable very small trench-trench spacing for IGBT cellstructure and it leads significant performance improvement.

5.2

Previous Research for IGBT Performance Limit
Before establishing scaling principle, two researches mentioned about IGBT

performance limit are reviewed. One is a theoretical prediction. The other includes
experimental results. Both researches show increasing Cathode side injection efficiency

69 |improves IGBT performance.

5.2.1

High precision process approach

Dr. Akio Nakagawa proposed a theory for IGBT performance limit in [54]. In the paper,
asymmetrical conduction is assumed to get lowest on-state voltage drop. All of the current
flows by electrons and holes contribute only to the conductivity modulation. The
phenomenon is realized under the condition that hole diffusion current is equal to hole drift
current, and they are flowing opposite direction. In this condition, N-Base carrier
distribution is linearly decreasing from Cathode to Anode as shown in Figure 51. The
relationship between Cathode side electron injection efficiency and Vce(sat) is shown in
Figure 53. With extremely high electron injection efficiency case, proposed device design
has 40nm mesa width. The channel inversion layer is connected to opposite side channel
layer, and they form a barrier for holes. The author predicted Silicon IGBT will realize low
on-resistance even below Silicon Carbide material limit for over 2kV range as shown in
Figure 54.

Figure 51. N-Base carrier distribution profile for lowest on-state voltage drop [54].
N-Base carrier distribution is linearly decreasing from Cathode to Anode (in this figure,“Collector” to “Emitter”).

70 |Figure 52. Simulated Ic-Vc characteristic of IGBT performance limit [54].

Figure 53. The relationship between Cathode side injection efficiency and on-statevoltage drop [54].

71 |Figure 54. IGBT performance limit prediction [54]. The author predicted Silicon IGBT
will realize low on-resistance even below SiC limit for over 2kV range.

5.2.2

Conventional process approach

Mr. Manabu Takei developed experimental device which put previous Nakagawa’s
theory into concrete shape [55]. The device called as DB (Dielectric Barrier)-IGBT has
buried layer between P-Base and N-Base as shown in Figure 55. The proposed DB-IGBT
structure is equivalent to the trench IGBT with wide and deep trench, and with very narrowmesa width. It enables extreme electron injection efficiency from Cathode side. Simulated
N-Base carrier distribution is linearly decreasing from Cathode to Anode as shown in Figure
56, and as Nakagawa’s proposal.
Lateral selective epitaxial growth is selected to fabricate experimental device. The
epitaxial layer is grown from 1um width Silicon window in buried oxide. After the growth,
unnecessary portion is removed by CMP (Chemical Mechanical Polishing). Other thanthese processes, the device can be fabricated by older planar gate process without

72 |submicron technologies.
Fabricated device shows much better trade-off relationship between on-state voltage
drop and turn-off loss as shown in Figure 57.

Figure 55. Cross sectional view of DB-IGBT [55]. Internal oxide layer is inserted
between P-Base and N-Base.

Figure 56. Calculated hole distribution in N-Base [55]. Hole concentration is linearlydecreased from Cathode side to Anode side.

73 |Figure 57. Trede-off relationship between on-state voltage drop and turn-off loss for
DB-IGBT [55].

In addition, Mr. Sumitomo showed another concept of the structure with high injection
efficiency in ISPSD 2012 [56]. The structure is similar with latest deep trench gate IGBT
but very narrow mesa width is realized. Trial fabrication results were also demonstrated.

5.3

IGBT Scaling Principle
In this section, a scaling principle for trench gate IGBT will be proposed toward

CMOS process compatibility. The principle is based on general CMOS scaling principle
and the formulation of Cathode side injection efficiency described before. Beside highmanufacturability, the principle also predicts that scaled down IGBT shows lower Vce(sat)even with shallower Cathode structure; shallower trench gate and shallower P-base. The
principle shows the design trends for shallower Cathode structure with the compatibility forthe large diameter wafer process technology, but keeping low on-state voltage drop as
current products.

74 |

3.0um
6.0um

P-BaseGate Gate

GateGate

3um

P-float

Tox=100nm

N-Base16um(a) k=1

1.5um

1.5um

3.0um

Tox=50nm
16um(b) k=2
0.6um
P-Base0.6um

P-Base1.2um
Tox=20nm
16um(c) k=5
Figure 58. Proposed scaling principle for trench gate IGBT.

Table 5. Proposed scaling principle for trench gate IGBT.
Parameters

Scaling factor

Half cell pitch: W

1

Half mesa width: S

1/kTrench depth: DT

1/k

P-Base depth: Db

1/kGate oxide thickness: Tox

1/kGate Voltage: Vge

1/k, 1/k2

75 |The concept of IGBT scaling is shown in Figure 58. Figure 58(a) shows commerciallyavailable IGBT that has 6um depth trench gate and 3um depth P-Base. Trench-trench
spacing is 3um and cell pitch is 16um. It uses 1000 angstrom gate oxide thickness and
P-Base concentration is chosen to give suitable gate threshold voltage Vth of around 5V. A
unitless scaling factor “k” is introduced for some of IGBT structure parameters. Figure58(b) and (c) show scaled IGBT with k=2 and 5 respectively. They have shallower trenchgate, shallower P-base, narrower trench-trench spacing and thinner gate oxide scaled by k,
but keeping unit cell pitch as original to enable same electron injection efficiency from
Cathode side. Moreover, scaled IGBT is operated lower gate voltage as “Constant Field”
CMOS scaling principle. There are no arrangements in Anode side. Scaled structure
parameters are summarized in Table 5.
The basic idea of keeping low on-state voltage drop is that N-Base carrier distribution
depends on only Cathode and Anode side injection efficiency. The principle is toward
shallower Cathode structure that has same injection efficiency of conventional structure. By
applying the principle, the device is scaled by a transformation in two variables: dimension
and operation voltage.
About dimension, four parameters are reduced by scaling factor k; trench-trench
spacing S, gate oxide thickness Tox, trench depth DT and P-base depth Db. In the otherwords, S’=S/k, Tox’=Tox/k, DT’=DT/k and Db’=Db/k where the primed parameters refer tothe scaled device. They are toward shallow structure produced by high resolution
lithography technique and smaller thermal budget. Unlike CMOS scaling principle, the
P-Base doping concentration is unchanged to keep similar saturation current level ofconventional structure. As a power device of IGBT needs to conduct large current in MOS
channel.
About gate voltage, two type scaling is considered. First, with Vge’=Vge/k, higher
electron injection efficiency from Cathode side and performance improvement is estimated.
In this case applied electric field for gate oxide is same as conventional structure. Second,with Vge’=Vge/k2, same electron injection efficiency from Cathode side can be obtained.

5.4

Scaling Theory
The theory for the principle is delivered from (19).
−1𝜀𝑜𝑥 𝜇𝑎𝑐𝑐 𝑉𝑔𝑒
𝜇𝑝
2𝑞𝐷𝑝 𝑆 𝑑𝑛(𝑥)((+ 1) + 1) 𝛾𝑛 − 1 =𝜇𝑛 𝑇𝑜𝑥 𝑞𝜇𝑛 𝑛(𝑥)𝑆𝐽 𝑊 𝑑𝑥

(19)

76 |

Equation 19 indicates that the scaled device has same injection efficiency of original
device with following conditions:
𝜀𝑜𝑥 𝜇𝑎𝑐𝑐 𝑉𝑔𝑒= 𝑐𝑜𝑛𝑠𝑡.
𝑇𝑜𝑥 𝑞𝜇𝑛 𝑛(𝑥)𝑆(65)

𝑆 𝑑𝑛(𝑥)= 𝑐𝑜𝑛𝑠𝑡.
𝑊 𝑑𝑥

(66)

In (65), the gate voltage Vge, the gate oxide thickness Tox and the trench-trench
spacing S are scaled by the principle. By applying the scaling principle as Figure 58 and
Vge’=Vge/k2 of Table 1, (65) keeps constant with varied k. By applying the scaling principlewith Vge’=Vge/k of Table 1, (65) becomes smaller with increasing k. Thus,
𝜀𝑜𝑥 𝜇𝑎𝑐𝑐 𝑉𝑔𝑒 ′𝑉𝑔𝑒= 𝑐𝑜𝑛𝑠𝑡. (𝑉𝑔𝑒 ′ = 2 )𝑇𝑜𝑥 ′𝑞𝜇𝑛 𝑛(𝑥)𝑆′𝑘𝜀𝑜𝑥 𝜇𝑎𝑐𝑐 𝑉𝑔𝑒 ′𝜀𝑜𝑥 𝜇𝑎𝑐𝑐 𝑉𝑔𝑒
𝑉𝑔𝑒>(𝑉𝑔𝑒 ′ =)𝑇𝑜𝑥 ′𝑞𝜇𝑛 𝑛(𝑥)𝑆′ 𝑇𝑜𝑥 𝑞𝜇𝑛 𝑛(𝑥)𝑆𝑘(67)

In (66), the trench-trench spacing S is scaled but cell pitch W is not changed by thescaling. And the divergence of carrier concentration in mesa region dn/dx is increased byfactor k, (dn/dx)’=k(dn/dx) as shown in Figure 59. So the right hand side of (19) is
unchanged by the scaling principle.
𝑆′ 𝑑𝑛′(𝑥) 𝑆 𝑑𝑛(𝑥)
=
𝑊 𝑑𝑥
𝑊 𝑑𝑥

(68)

By applying (67) and (68) into (19), following results are obtained.

𝛾𝑛 ′ = 𝑐𝑜𝑛𝑠𝑡. (𝑉𝑔𝑒 ′ =

𝑉𝑔𝑒
)
𝑘2

𝑉𝑔𝑒
𝛾𝑛 ′ > 𝛾𝑛 (𝑉𝑔𝑒 ′ =
)
𝑘

(69)

Formulas (69) mean that higher 𝛾𝑛 than original device can be obtained by increasing
k by applying Vge’=Vge/k. It leads higher carrier concentration in N-Base Cathode side andlower on-state voltage drop. It means device characteristic improvement can be done by77 |P-float

P-BaseGate Gate

GateGate

scaling down Cathode structure and applying same electric field for gate oxide.

n(x)

mesa

N-Basex(a) Conventional structure
P-BaseP-Basen(x)x(b) Shallow structure
Figure 59. Comparison of mesa region carrier distribution.

Other electrical characteristics are changed by introducing scaling factor k as Table 2:
Gate-emitter capacitance Cge is unchanged because Tox’=Tox/k and Db’=Db/k. Gate charge
Qg is reduced by factor k, Qg’=Qg/k. Contact metal current density JMetal is increased byfactor k, JMetal=k JMetal because contact hole width is reduced by factor k. Electro migration
should be considered for large k.
One characteristic that the principle fails to scale is threshold voltage. Thresholdvoltage Vth can be calculated as following𝑉𝑡ℎ =√2𝜀0 𝜀𝑆𝑖 𝑞𝑁𝐴 𝜑𝑆
+ 𝜑𝑆
𝐶𝑜𝑥

(70)

Where Cox is gate capacitance per unit area, NA is acceptor concentration in P-Baseand 𝜑𝑆 is surface potential of MOS channel. Vth is reduced because gate capacitance perunit area is increased by the scaling principle as Cox’=kCox. But Vth is not scaled by kexactly even if NA and 𝜑𝑆 are unchanged.
Therefore, saturation current is not also scaled. MOS gate saturation current is formed
approximately as following

78 |𝐼𝑛,𝑠𝑎𝑡 =𝑊𝐶ℎ𝑎𝑛𝑛𝑒𝑙
1
2
𝐶𝑜𝑥 (𝑉𝑔𝑒 − 𝑉𝑡ℎ )
𝐷𝑏
2

(71)

Vge and Db are scaled as Vge’=Vge/k and Db’=Db/k, respectively. From (70) and (71),saturation current is slightly increased by the scaling.
Finally, the scaling factors are summarized in Table 6.

Table 6. Scaling factors by proposed scaling principle.
Parameters
Gate voltage: Vge

Scaling factor
1/k

2

Half cell pitch: W

1

Half mesa width: S

1/kN-Emitter width: We

1/kTrench depth: DT

1/k

P-Base depth: Db

1/k

N-Emitter depth: De

1/kHalf contact width: Wc

1/k

Gate oxide thickness: Tox

1/kGate-Emitter capacitance: Cge

1

Gate-Collector capacitance: Cgc

1

Collector-Emitter capacitance: Cce

1/kk

Current density in contact hole: JMetal

5.5

1/k

2

Gate charge: Qg

1/k

1/k

Electron injection efficiency: 𝛾𝑛1>1Stored carrier density: n=p1>1

Calculation Results
Established scaling principle was verified by TCAD calculation. Two types of scaling

principle were compared as shown in Figure 60. In the “simple scaling” approach, scaling isapplied for all structure dimensions including the cell pitch W. The channel density is
increased in “simple scaling” approach, as Power MOSFET improvement direction. On theother hand, the cell pitch W is constant in the proposed scaling principle. The channel
density is constant in the proposed scaling principle.

79 |Ic-Vce, Ic-Vge, turn-off with inductive load, and short circuit calculation were
performed. 1200V PT-IGBT structure was used for the motif. Cross sectional view of basestructure i.e., structure for k=1, is shown in Figure 61. Base structure parameters are shownin Table 7. Scaled structure parameters are shown in Table 8. The thickness from trenchbottom to Anode electrode is 120um for all devices. Total device thickness is different by
the scaling factor k because trench depth depends on k. For example, wafer thickness are
126um and 121.2um for k=1 and k=5, respectively.
As previous section, Synopsys Sentaurus Device version E-2010.12 was used for
TCAD calculation. In this verification, structure generation tool Sentaurus Structure Editor
was used to create the FEM structure instead of process simulator. Same physical models as
section 4.5 were used and lattice self heating effect was taken into account for short circuit
calculation.

P-float

Tox=100nm

N-BaseGate Gate

P-Base

3.0um
6.0um

P-float

GateGate

P-Base

3.0um
6.0um

3um

Gate Gate

GateGate

3um

Tox=100nm

N-Base16um

16um(a) Original structure k=1(a) Original structure k=1

1.5um

3.0um

Tox=50nm

3.0um

Tox=50nm
8um

16um(b) Proposed scaling k=2
0.6um
P-Base

1.5um

1.5um

1.5um

(b’) Simple scaling k=2
0.6um

0.6um

P-Base

1.2um

1.2um

Tox=20nm
16um(c) Proposed scaling k=5

0.6um

P-BaseTox=20nm
3.2um(c’) Simple scaling k=5

Figure 60. Proposed scaling (Left side) and Simple scaling (Right side). In proposed
scaling, cell pitch is constant. In simple scaling, cell pitch is also scaled.

80 |

3.0um
6.0um

P-Base

Gate

Gate

3um

P-float

N-Base120um

Tox=100nm

N-Buffer
P-Emitter

Figure 61. Base structure for scaling principle verification. 1200V PT-IGBT structureis used for the motif.

Table 7. Base structure parameters used for the verification.
Parameters
N-base concentration

8x1013/cm3

N-base thickness

120um

Half cell pitch: W

8.0um

Half mesa width: S

1.5um

P-base surface concentration

1x1017/cm2

P-base thickness: Dp

3.0um

Trench depth: DT

6.0um

Gate oxide thickness: Tox

1000angstrom

P-emitter concentration

1x1017/cm3

P-emitter thickness

1.0um

N-buffer concentration

9x1016/cm3

N-buffer thickness

1.0um

81 |

Table 8. Structure parameters used for the scaling principle verification.

Half cell pitch: W[um]

k =1

k =2

k =3

k =4

k =5

8.0

8.0

8.0

8.0

8.0

(4.0)

(2.67)

(2.0)

(1.6)

(Half cell pitch for simple scaling[um])Half mesa width: S[um]

1.5

0.75

0.5

0.375

0.3

Trench depth: DT[um]

6.0

3.0

2.0

1.5

1.2

1000

500

333

250

200

Gate Voltage: Vge[V] for 1/k scaling

15.0

3.75

1.67

0.94

0.60

Gate Voltage: Vge[V] for 1/k scaling

15.0

7.5

5.0

3.75

3.0

Gate oxide thickness: Tox[angstrom]
2

Ic-Vge characteristics of scaled devices are shown in Figure 62. Vth is decreased byscale down. gm is increased due to thinner gate oxide and shorter channel length.
Ic-Vc characteristics of scaled devices with scaled gate voltage Vge’=Vge/k2, i.e.
scaled electric field in gate oxide Eox’=Eox/k, are shown in Figure 63. In proposed scaling,
the curves for k=1 and 2 show complete agreement but more scaled devices show smaller
saturation current. It is due to scaling induced Vth shift as (70) and saturation current dropas (71). On the other hand, in simple scaling, Vce(sat) becomes higher with scale down.
In proposed scaling, N-Base carrier distribution for k=2 is kept as k=1 as shown in
Figure 64. Without saturation current drop, proposed scaling rule is proved very well. In
simple scaling, Cathode side carrier concentration becomes lower with scale down.
Ic-Vc characteristics with scaled gate voltage Vge’=Vge/k, i.e. constant electric field ingate oxide Eox’=Eox, are shown in Figure 65 and Figure 66. In proposed scaling, lower
Vce(sat) is obtained by scale down. On the other hand, in simple scaling, Vce(sat) becomes
higher with scale down. In proposed scaling, Vce(sat) improvement is observed especially
under high temperature condition.
On-state carrier distribution in N-Base region is shown in Figure 67 and Figure 68. In
proposed scaling, N-Base carrier distribution is improved, so that Cathode side carrier
concentration is increased, by scale down. Higher n and lower Vce(sat) are achieved byscale down even with shallower trench, as mentioned in previous section. In simple scaling,
Cathode side carrier concentration becomes lower with scale down.
Turn-off waveforms of scaled devices with constant electric field in gate oxide as
Eox’=Eox, are shown in Figure 69. External gate resistance is constant. Scaled devices
show slight delays because the difference of gate voltage and threshold voltage, Vge-Vth, is
not scaled by k exactly. Because of Cge and Cgc are constant, the length of miller plateau isconstant too.
Short-circuit waveforms of scaled devices are shown in Figure 70. In this calculation,

82 |half of rated gate voltage was applied to avoid thermal runaway. Scaled device showsslightly higher saturation current because Vge-Vth is not scaled by k exactly. Oscillation isobserved in larger k.

140

k=1

120

k=2

Jc[A/cm2]

k=3

100

k=4

80

k=5

60
40
20
0
0.0

2.0

4.0

6.0

8.0

10.0

Vge[V]

Figure 62. Ic-Vge characteristics for scaled devices. Scaled devices show lower Vthand higher gm.

83 |Vge’=Vge/k2

k=1 Vge=15.0V
k=2 Vge=3.75V
k=3 Vge=1.67V
k=4 Vge=0.94V
k=5 Vge=0.6V

140
120

Proposed scaling
T=300K

Jc[A/cm2]

100
80
60
40
20
0
0.0

120

Jc[A/cm2]

100

T=300K

1.0
Vce[V]

1.5

2.0

1.0
Vce[V]

1.5

2.0

k=1 Vge=15V
k=2 Vge=3.75V
k=3 Vge=1.67V
k=4 Vge=0.94V
k=5 Vge=0.6V

140

Simple scaling

0.5

80
60
40
20
0
0.0

0.5

Figure 63. Calculated Ic-Vc characteristics of scaled devices with scaled electric fieldin gate oxide as Eox’=Eox/k. In proposed scaling, k=1 and 2 show good agreement but morescaled devices show lower saturation current. In simple scaling, Vce(sat) becomes higher
with increasing scaling factor k.

84 |Vge’=Vge/k2

Proposed scaling
T=300K

Carrier Concentration[1/cm3]

4.0E+16
k=1 Vge=15.0V
k=2 Vge=3.75V

3.0E+16

2.0E+16

1.0E+16

0.0E+00
-10

10
30
50
70
90
Distance from mesa/N-Base boundary[um]110Simple scaling
T=300K

Carrier Concentration[1/cm3]

4.0E+16
k=1 Vge=15V
k=2 Vge=3.75V
k=3 Vge=1.67V
k=4 Vge=0.94V
k=5 Vge=0.6V

3.0E+16

2.0E+16

1.0E+16

0.0E+00
-10

10
30
50
70
90
Distance from mesa/N-Base boundary[um]110Figure 64. Calculated carrier distribution in N-Base region of scaled devices withscaled electric field in gate oxide as Eox’=Eox/k. The zero point of horizontal scale is set tomesa/N-Base boundary. In proposed scaling, similar carrier distribution is obtained insteadof scale down. In simple scaling, Cathode side carrier concentration becomes lower withincreasing scaling factor k.

85 |Vge’=Vge/k140

k=1 Vge=15.0V
k=2 Vge=7.5V
k=3 Vge=5.0V
k=4 Vge=3.75V
k=5 Vge=3.0V

120

Proposed scaling
T=300K

Jc[A/cm2]

100
80
60

40
20
0
0.0

140

Jc[A/cm2]

100

T=300K

1.0
Vce[V]

1.5

2.0

1.0
Vce[V]

1.5

2.0

k=1 Vge=15V
k=2 Vge=7.5V
k=3 Vge=5.0V
k=4 Vge=3.75V
k=5 Vge=3.0V

120

Simple scaling

0.5

80
60

40
20
0
0.0

0.5

Figure 65. Calculated Ic-Vc characteristics of scaled devices with constant electricfield in gate oxide as Eox’=Eox. In proposed scaling, Vce(sat) is improved by increasing
scaling factor k. In simple scaling, Vce(sat) becomes higher with increasing scaling factor k.

86 |Vge’=Vge/k140

k=1 Vge=15.0V
k=2 Vge=7.5V
k=3 Vge=5.0V
k=4 Vge=3.75V
k=5 Vge=3.0V

120

Proposed scaling
T=300K

Jc[A/cm2]

100
80
60

40
20
0
0.0

140

Jc[A/cm2]

100

T=450K

1.0
Vce[V]

1.5

2.0

1.0
Vce[V]

1.5

2.0

k=1 Vge=15.0V
k=2 Vge=7.5V
k=3 Vge=5.0V
k=4 Vge=3.75V
k=5 Vge=3.0V

120

Proposed scaling

0.5

80
60

40
20
0
0.0

0.5

Figure 66. Calculated Ic-Vc characteristics of proposed scaling devices with constantelectric field in gate oxide as Eox’=Eox. In higher temperature condition, Vce(sat) improved
especially.

87 |Vge’=Vge/k

Proposed scaling
T=300K

Carrier Concentration[1/cm3]

4.0E+16
k=1 Vge=15.0V
k=2 Vge=7.5V
k=3 Vge=5.0V
k=4 Vge=3.75V
k=5 Vge=3.0V

3.0E+16

2.0E+16

1.0E+16

0.0E+00
-10

10
30
50
70
90
Distance from mesa/N-Base boundary[um]110Simple scaling
T=300K

Carrier Concentration[1/cm3]

4.0E+16
k=1 Vge=15V
k=2 Vge=7.5V
k=3 Vge=5.0V
k=4 Vge=3.75V
k=5 Vge=3.0V

3.0E+16

2.0E+16

1.0E+16

0.0E+00
-10

10
30
50
70
90
Distance from mesa/N-Base boundary[um]110Figure 67. Calculated carrier distribution in N-Base region for scaling factor k=1 to 5.
The zero point of horizontal scale is set to mesa/N-Base boundary. In proposed scaling,
Cathode side carrier concentration is increased by scale down. In simple scaling, Cathodeside carrier concentration becomes lower with increasing scaling factor k.

88 |Vge’=Vge/k

Proposed scaling
T=300K

Carrier Concentration[1/cm3]

4.0E+16
k=1 Vge=15.0V
k=2 Vge=7.5V
k=3 Vge=5.0V
k=4 Vge=3.75V
k=5 Vge=3.0V

3.0E+16

2.0E+16

1.0E+16

0.0E+00
-10

10
30
50
70
90
Distance from mesa/N-Base boundary[um]110Proposed scaling
T=450K

Carrier Concentration[1/cm3]

4.0E+16
k=1 Vge=15.0V
k=2 Vge=7.5V
k=3 Vge=5.0V
k=4 Vge=3.75V
k=5 Vge=3.0V

3.0E+16

2.0E+16

1.0E+16

0.0E+00
-10

10
30
50
70
90
Distance from mesa/N-Base boundary[um]110Figure 68. Calculated carrier distribution in N-Base region for proposed scaling device
with T=300K and 450K. The zero point of horizontal scale is set to mesa/N-Base boundary.
In proposed scaling, Cathode side carrier concentration is increased by scale down
especially in high temperature condition.

89 |

16.0
k=1 Vge=15.0V
k=2 Vge=7.5V
k=3 Vge=5.0V
k=4 Vge=3.75V
k=5 Vge=3.0V

14.0
12.0

Vge[V]

10.0

8.0
6.0
4.0
2.0

0.0
-2.0
0.0

1.0

2.0

3.0
time[us]

4.0

5.0

200

Jc[A/cm2]150

k=1 Vge=15.0V
k=2 Vge=7.5V
k=3 Vge=5.0V
k=4 Vge=3.75V
k=5 Vge=3.0V

100

400

Vce[V]

600

200

50

0

0
0.0

1.0

2.0

3.0
time[us]

4.0

5.0

Figure 69. Calculated Turn-off characteristics of proposed scaling devices withconstant electric field in gate oxide as Eox’=Eox. Device active area is 1cm2. Same external
gate resistance of 10ohm is used.

90 |

16.0

14.0

k=1 Vge=7.5V
k=2 Vge=3.75V
k=3 Vge=2.5V
k=4 Vge=1.875V
k=5 Vge=1.5V

12.0
Vge[V]

10.0
8.0
6.0
4.0
2.0
0.0
-2.0
0.0

5.0

10.0
time[us]

15.0

20.0

5000
4500
k=1 Vge=7.5V
k=2 Vge=3.75V
k=3 Vge=2.5V
k=4 Vge=1.875V
k=5 Vge=1.5V

Jc[A/cm2]

3500
3000
2500
2000

400

1500

Vce[V]

600

4000

200

1000
500
0

0
0.0

5.0

10.0
time[us]

15.0

20.0

Figure 70. Calculated short-circuit waveforms of proposed scaling devices withconstant electric field in gate oxide as Eox’=Eox. Lower gate voltage was applied to avoid
thermal runaway in this calculation.

5.6

Discussion
5.6.1

Saturation current optimization

In previous calculation, Vth was set to lower than usual to confirm the scaling principlewith scaled electric field in gate oxide as Eox’=Eox/k as Figure 63. Moreover, Vth isreduced as less than Vth/k due to surface potential 𝜑𝑆 . In result, saturation currents werehigher especially scaled devices and rated short-circuit calculation could not be finishedwithout thermal runaway. To apply the proposed scaling principle to actual device, Vthshould be set to limit saturation current but not increase channel resistance for rated current.

91 |Vth can be scaled by following calculation from (70).

𝑉𝑡ℎ =√2𝜀0 𝜀𝑆𝑖 𝑞𝑁𝐴 𝜑𝑆
+ 𝜑𝑆
𝐶𝑜𝑥

(70)

𝐶𝑜𝑥 2 (𝑉𝑡ℎ − 𝜑𝑆 )22𝜀0 𝜀𝑆𝑖 𝑞𝜑𝑆

(72)

𝑁𝐴 =

By applying the scaling rule,(𝑘𝐶𝑜𝑥 )2 (𝑉𝑡ℎ /𝑘 − 𝜑𝑆 )2𝑁𝐴 ′ =
2𝜀0 𝜀𝑆𝑖 𝑞𝜑𝑆(73)

Another calculation was performed with adjusted Vth to realize optimized saturation
current around 1000-1500A/cm2. Optimized P-Base surface concentration is shown in Table
9.

Table 9. P-Base surface concentration for Vth adjustment.
k =1
P-Base surface concentration[1/cm3]

k =2

k =3

k =4

k =5

2.8x1017 3.5x1017 4.0x1017 4.4x1017 4.8x1017

Ic-Vge characteristics of scaled devices are shown in Figure 71. Vth is just scaled as
scaling factor k. gm is still higher due to thinner gate oxide and shorter channel length.
Ic-Vc characteristics with scaled gate voltage Vge’=Vge/k, i.e. constant electric field ingate oxide Eox’=Eox, are shown in Figure 72. Lower Vce(sat) is achieved by scale downeven with higher and just scaled Vth.
Turn-off waveforms of scaled devices with constant electric field in gate oxide as
Eox’=Eox, are shown in Figure 73. External gate resistance is constant. All devices show
almost same turn-off characteristics by Vth adjustment.
Short-circuit waveforms of scaled devices are shown in Figure 74. Same saturation
current is realized among all scaled devices, and no oscillation is appeared even for higher
scaled devices.

92 |

140
120
Jc[A/cm2]

100
80
k=1

60

k=2

40

k=3
k=4

20

k=5

0
0.0

2.0

4.0

6.0
Vge[V]

8.0

10.0

12.0

Figure 71. Ic-Vge characteristics for scaled devices with Vth adjustment. Scaled
devices show higher gm.

140

k=1 Vge=15.0V
k=2 Vge=7.5V
k=3 Vge=5.0V
k=4 Vge=3.75V
k=5 Vge=3.0V

120
Jc[A/cm2]

100
80
60
40
20
0

0.0

0.5

1.0
Vce[V]

1.5

2.0

Figure 72. Calculated Ic-Vc characteristics of scaled devices with Vth adjustment andconstant electric field in gate oxide as Eox’=Eox. Vce(sat) is improved by increasing scaling
factor k.

93 |

16.0
14.0

k=1 Vge=15.0V
k=2 Vge=7.5V
k=3 Vge=5.0V
k=4 Vge=3.75V
k=5 Vge=3.0V

12.0

Vge[V]

10.0
8.0
6.0
4.0

2.0
0.0
-2.0
0.0

1.0

2.0

3.0
time[us]

4.0

5.0

200

Jc[A/cm2]150

k=1 Vge=15.0V
k=2 Vge=7.5V
k=3 Vge=5.0V
k=4 Vge=3.75V
k=5 Vge=3.0V

100

400

Vce[V]

600

200

50

0

0
0.0

1.0

2.0

3.0
time[us]

4.0

5.0

Figure 73. Calculated Turn-off characteristics of scaled devices with Vth adjustment.
Device active area is 1cm2. Applied gate voltage is scaled by keeping constant electric fieldin gate oxide as Eox’=Eox. All devices show almost same turn-off characteristics by Vthadjustment.

94 |

16.0
k=1 Vge=15.0V
k=2 Vge=7.5V
k=3 Vge=5.0V
k=4 Vge=3.75V
k=5 Vge=3.0V

14.0
12.0

Vge[V]

10.0
8.0
6.0
4.0

2.0
0.0
-2.0
0.0

5.0

10.0
time[us]

15.0

20.0

2000

Jc[A/cm2]

1500

1000

400

Vce[V]

600
k=1 Vge=15.0V
k=2 Vge=7.5V
k=3 Vge=5.0V
k=4 Vge=3.75V
k=5 Vge=3.0V

200

500

0

0
0.0

5.0

10.0
time[us]

15.0

20.0

Figure 74. Calculated short-circuit waveforms of scaled devices with Vth adjustment.
Applied gate voltage is scaled by keeping constant electric field in gate oxide as Eox’=Eox.
Lower and similar saturation current are realized. No thermal runaway was occurred.

5.6.2

Electric Field in Gate Oxide

One concern for the scaled device is the reliability of thinner gate oxide. To confirm it,
maximum electric field values were measured with static breakdown simulation between
Anode and Cathode as shown in Figure 75. No critical increasing for the electric field wasobserved.
Another scaling option keeping gate oxide thickness as original can be applied as
discussed in the next paragraph.

95 |2.5E+06

Maximum Electric Fieldin gate oxide[V/cm]

k=1

k=2

2.0E+06k=3

k=4

1.5E+06k=5

1.0E+06
5.0E+05
0.0E+00
0

200

400

600

800 1000 1200 1400 1600
Vce[V]

Figure 75. Simulated maximum electric field in gate oxide for static breakdown.

5.6.3

Another Scaling Option

In highly scaled device, thinner gate oxide and lower gate voltage could be issues ofreliability. For example, tunneling current must be concerned via very thin gate oxide lessthan 5nm. And lower gate voltage could cause malfunction due to parasitic capacitances andexternal noise. Another scaling option might be effective to avoid these issues. By Quasi-2D
MOS-ADE model of (19), another scaling principle can be delivered without decreasinggate oxide thickness and gate voltage.
−1
𝜀𝑜𝑥 𝜇𝑎𝑐𝑐 𝑉𝑔𝑒
𝜇𝑝
2𝑞𝐷𝑝 𝑆 𝑑𝑛(𝑥)((+ 1) + 1) 𝛾𝑛 − 1 =𝜇𝑛 𝑇𝑜𝑥 𝑞𝜇𝑛 𝑛(𝑥)𝑆𝐽 𝑊 𝑑𝑥(19)

With keeping gate oxide thickness and gate voltage, the left hand side of (19) ischanged by scaled trench-trench spacing S.
𝜀𝑜𝑥 𝜇𝑎𝑐𝑐 𝑉𝑔𝑒
𝜀𝑜𝑥 𝜇𝑎𝑐𝑐 𝑉𝑔𝑒>
𝑇𝑜𝑥 𝑞𝜇𝑛 𝑛(𝑥)𝑆′ 𝑇𝑜𝑥 𝑞𝜇𝑛 𝑛(𝑥)𝑆(74)

By applying (74) into (19), following results are obtained.
𝛾𝑛 ′ > 𝛾𝑛

(75)

96 |

This scaling principle is summarized in Table 10.

Table 10. Another scaling factors by proposed scaling principle.
Parameters

Scaling factor

Gate voltage: Vge

1

Half cell pitch: W

1

Half mesa width: S

1/kN-Emitter width: We

1/kTrench depth: DT

1/k

P-Base depth: Db

1/k

N-Emitter depth: De

1/kHalf contact width: Wc

1/k

Gate oxide thickness: Tox

1

Gate-Emitter capacitance: Cge

1

Gate-Collector capacitance: Cgc

1

Collector-Emitter capacitance: Cce

1/kCurrent density in contact hole: JMetalk

Gate charge: Qg

1/kElectron injection efficiency: 𝛾𝑛>1Stored carrier density: n=p

>1

5.6.4

Process Flow

By applying the scaling principle, the trench gate and doping layers become shallower.
It enables to eliminate thermal budget. For k=5 or more, P-Float layer and P-Base layer canbe formed by ion implantation and very short thermal process such as laser anneal or flash
anneal. Following list and Figure 76 show an example of “cell first” process flow.
1. Preparing N- doped wafer. Resistivity is chosen by the rated voltage.
2. Oxidation to protect contamination by next deposition.
3. (Edge termination structure formation)
4. Deposition thick oxide as masking material for trench etching.
5. Photolithography for trench gate pattern.
6. Masking layer formation by anisotropic etching for oxide.
7. Stripping photoresist.

97 |8. Trench formation by anisotropic etching for Silicon.
9. Stripping mask oxide.
10. (If required) Sacrificed oxidation to remove etching damage.
11. Gate oxidation.
12. Gate electrode formation by PolySilicon deposition.
13. Removing surface PolySilicon by etching or CMP (Chemical Mechanical
Polishing).
14. Photolithography for P-Float pattern.
15. P-Float layer formation by Boron implantation (High energy).
16. Stripping photoresist.
17. Photolithography for P-Base pattern.
18. P-Base layer formation by Boron implantation (Medium energy).
19. Stripping photoresist
20. P-Float and P-Base activation by RTA (Rapid Thermal Anneal), flash anneal, or
laser anneal.
21. Photolithography for N-Emitter pattern.
22. N-Emitter formation by Arsenic or Phosphorus implantation.
23. N-Emitter activation by RTA (Rapid Thermal Anneal), flash anneal, or laser anneal.
24. Deposition BPSG or PSG for inter layer.
25. (If required) Gettering to recover the bulk carrier lifetime.
26. Photolithography for contact pattern.
27. Contact hole formation by anisotropic etching.
28. Stripping photoresist
29. P+ layer formation by Boron or BF2 implantation (Low energy).
30. P+ activation by RTA (Rapid Thermal Anneal), flash anneal, or laser anneal.
31. Front metal formation.
32. Photolithography for metal pattern.
33. Etching metal to divide Gate, Emitter electrode and edge termination.
34. Passivation formation.
35. Wafer thinning by backside grinding, polishing and/or etching.
36. N-Buffer formation by Phosphorus implantation for backside (High energy).
37. P-Emitter formation by Boron implantation for backside.
38. N-Buffer and P-Emitter activation by RTA (Rapid Thermal Anneal), flash anneal,or laser anneal.
39. Back metal formation.

98 |2. Oxidation

6. Masking

8. Trench etching 11. Gate oxidation

12. Gate PolySilicon 15. P-Float

24. Inter layer

31. Front Metal

18. P-Base

22. N-Emitter

37. Backside

38. Back Metal

Figure 76. An example of “cell first” process flow.

Because of smaller thermal budget for cell formation process, P-Emitter and N-Buffer
can be formed in advance. Following list and Figure 77 show an example of “cell last”
process flow.
1. Preparing N- doped wafer. Resistivity is chosen by the rated voltage.
2. Wafer thinning by backside grinding, polishing and/or etching.
3. N-Buffer formation by Phosphorus implantation for backside (High energy).
4. P-Emitter formation by Boron implantation for backside.
5. N-Buffer and P-Emitter activation by RTA (Rapid Thermal Anneal), flash anneal,or laser anneal.
6. (Flip the wafer for cell formation process. If needed, supporting material is attached
to backside.)
7. Oxidation to protect contamination by next deposition.
8. (Edge termination structure formation)
9. Deposition thick oxide as masking material for trench etching.
10. Photolithography for trench gate pattern.
11. Masking layer formation by anisotropic etching for oxide.

99 |12. Stripping photoresist.
13. Trench formation by anisotropic etching for Silicon.
14. Stripping mask oxide.
15. (If required) Sacrificed oxidation to remove etching damage.
16. Gate oxidation.
17. Gate electrode formation by PolySilicon deposition.
18. Removing surface PolySilicon by etching or CMP (Chemical Mechanical
Polishing).
19. Photolithography for P-Float pattern.
20. P-Float layer formation by Boron implantation (High energy).
21. Stripping photoresist.
22. Photolithography for P-Base pattern.
23. P-Base layer formation by Boron implantation (Medium energy).
24. Stripping photoresist
25. P-Float and P-Base activation by RTA (Rapid Thermal Anneal), flash anneal, or
laser anneal.
26. Photolithography for N-Emitter pattern.
27. N-Emitter formation by Arsenic or Phosphorus implantation.
28. N-Emitter activation by RTA (Rapid Thermal Anneal), flash anneal, or laser anneal.
29. Deposition BPSG or PSG for inter layer.
30. (If required) Gettering to recover the bulk carrier lifetime.
31. Photolithography for contact pattern.
32. Contact hole formation by anisotropic etching.
33. Stripping photoresist
34. P+ layer formation by Boron or BF2 implantation (Low energy).
35. P+ activation by RTA (Rapid Thermal Anneal), flash anneal, or laser anneal.
36. Front metal formation.
37. Photolithography for metal pattern.
38. Etching metal to divide Gate, Emitter electrode and edge termination.
39. Passivation formation.
40. Back metal formation.

100 |

5. Backside

11. Masking

13. Trench etching

20. P-Float

23. P-Base

36. Front Metal

40. Back Metal

7. Oxidation

16. Gate oxidation 17. Gate PolySilicon

27. N-Emitter

29. Inter layer

Figure 77. An example of “cell last” process flow.

5.7

Summary
New scaling principle for Trench gate IGBT was proposed. The structure oriented

analytical model previously discussed in this dissertation was extended to the scaling
principle. The principle is theoretically established and can apply to wide range of device
structures. By the principle, IGBT cell structure becomes shallow so that its diffusion layers
and trench depths is diminished to 1/k where current depths are several microns. The
principle was proved by two-dimensional TCAD simulation. Same on-state characteristic asconventional design can be obtained even by shallow structure except lower saturation
current. On-state characteristic can be also improved by applying higher gate voltage where
electric field is same as conventional design. After adjusting Vth, turn-off and short circuit
characteristics are not affected by scale down at all.
The principle has large impact for new IGBT development. Scaled IGBT can bealigned for CMOS wafer process with highly reduced thermal budget, and mass produced in
CMOS manufacturing line with high productivity.

101 |

6 The Future: Shallow Trench IGBT Advantages and Related
IssuesIn this section, further performance improvement of IGBT is discussed with aiming
higher power density. A design methodology based on the proposed compact model and thescaling principle will be shown.

6.1

Cathode Side Structure Optimization
Ic-Vce characteristic of 1200V PT-IGBT calculated by the proposed compact model isshown in Figure 78. Currently the rated current density of 1200V IGBT is about
100-150A/cm2. With aiming higher current density, for example 450A/cm2, higher voltage
drop should be a problem. Higher on-state voltage drop generates large heat and it have to
be exhausted toward ambient via heat sink.

600

Jc[A/cm2]

500
400
300

200
100
0

0.0

0.5

1.0

1.5
Vce[V]

2.0

2.5

3.0

Figure 78. Ic-Vce characteristic for 1200V PT-IGBT calculated by the proposedcompact model. To improve power density, Vce(sat) must be reduced in high current
density region.

As described in section 4, on-state voltage drop consists of four portions, N-Base,mesa region, MOS channel, and built-in potential. The potions depend on the current
density as shown in Figure 79. N-Base voltage drop is dominant in high current density
region.

Portions of voltage drop

102 |

100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%

N-BaseMesa
ChannelBuilt-in2
Built-in1

50

150

250
350
Jc[A/cm2]

450

550

Figure 79. Portions of voltage drop at 300K for 1200V PT-IGBT calculated by the
proposed compact model. N-Base voltage drop is dominant in high current density region.

For example, at 450A/cm2, the total voltage drop is 2.29V and the N-Base voltage dropis 1.43V. The portion of the N-Base voltage drop is 62% of the total voltage drop. Now, let’s
consider reducing the N-Base voltage drop as half as current structure. Higher stored carrier
concentration should be required. The estimated carrier concentration can be calculated byfollowing sequence.

𝐽𝑛 = 𝑞𝜇𝑛 𝑛𝐸 + 𝑞𝐷𝑛

𝑑𝑛
𝑑𝑥

(3)

𝐽𝑝 = 𝑞𝜇𝑝 𝑝𝐸 − 𝑞𝐷𝑝

𝑑𝑝
𝑑𝑥

(4)

In high current region, carrier distribution profile becomes to be flat. So,
𝑑𝑛 𝑑𝑝
=
=0
𝑑𝑥 𝑑𝑥

(76)
𝑉

𝐽 = 𝐽𝑛 + 𝐽𝑝 = 𝑞(𝜇𝑝 + 𝜇𝑛 )𝑛𝐸= 𝑞(𝜇𝑝 + 𝜇𝑛 )𝑛 𝑁−𝐵𝑎𝑠𝑒𝑡𝑁−𝐵𝑎𝑠𝑒(77)

By (77), n=2.51x1016cm-3 is delivered to obtain VN-Base=0.715V for J=450A/cm2 at

103 |

300K.
Next, move to design the Cathode structure. In high current region, 𝛾𝑝 and 𝛾𝑛 can beassumed to 0.25 and 0.75 respectively. By Quasi-2D MOS-ADE model, estimated carrier
concentration at N-Base edge can be calculated comprehensively with various values of W
and k because the model formulation is simple. Following graphs can be drawn.

1.0E+17

1.0E+17

7.5E+16

5.0E+16
2.5E+1620 18 16
14 12 10
8
W[um]

6

1
4

5
4
3
2

k

0.0E+00

2

7.5E+16
5.0E+16

2.5E+1620 18 16
14 12 10
8
W[um]

6

1
4

5
4
3
2

k

0.0E+00

2

7.5E+16

5.0E+16
2.5E+16

0.0E+00
20 18 16
14 12 10
8
W[um]

6

1
4

5
4
3
2

k

T=450K

Carrier Concentration[1/cm3]

T=400K

Carrier Concentration[1/cm3]

T=300K

1.0E+17

Carrier Concentration[1/cm3]

104 |

2

Figure 80. Relationship between cell pitch W, scaling factor k and carrier concentrationn at N-Base/mesa boundary for 450A/cm2. The electron injection efficiency is assumed as
0.75.

105 |

7.5E+16-1.0E+17
2.5E+16-5.0E+16

5.0E+16-7.5E+16
0.0E+00-2.5E+16

53T=300K

k

4

2
1

20

18

16

14

12
10
W[um]

7.5E+16-1.0E+17
2.5E+16-5.0E+16

8

6

4

2

5.0E+16-7.5E+16
0.0E+00-2.5E+16

53

T=400K

k

4

2
1
20

18

16

14

12
10
W[um]

7.5E+16-1.0E+17
2.5E+16-5.0E+16

8

6

4

2

5.0E+16-7.5E+16
0.0E+00-2.5E+16

53

T=450K

k

4

2
1

20

18

16

14

12
10
W[um]

8

6

4

2

Figure 81. Relationship between cell pitch W, scaling factor k and carrier concentrationn at N-Base/mesa boundary for 450A/cm2. The electron injection efficiency is assumed as
0.75.

106 |The graphs show clear designing guidelines. By Figure 80 and Figure 81, Cathodestructure parameter relationship for n=2.51x1016cm-3 can be delivered. The line is about theboundary between blue area (less than 2.5 x1016cm-3) and brown (more than 2.5 x1016cm-3)
area. For example, with scaling factor k=1, W should be more than 12um. With scaling
factor k=5, W should be more than 6um.

6.2

High Temperature Advantage of Shallow Trench IGBTBy Figure 80 and Figure 81, a relationship between carrier concentration andtemperature, i.e., injection efficiency and temperature is observed. Higher injection
efficiency can be obtained by higher temperature, especially with large k. The temperaturedependency is summarized in Figure 82. The phenomena can be explained by Quasi-2D
MOS-ADE model.
−1𝜀𝑜𝑥 𝜇𝑎𝑐𝑐 𝑉𝑔𝑒
𝜇𝑝
2𝑞𝐷𝑝 𝑆 𝑑𝑛(𝑥)((+ 1) + 1) 𝛾𝑛 − 1 =𝜇𝑛 𝑇𝑜𝑥 𝑞𝜇𝑛 𝑛(𝑥)𝑆𝐽 𝑊 𝑑𝑥(19)

S is trench-trench spacing which is scaled as S’=S/k. For large k, (19) can be modified
as follows.

𝛾𝑛 =2𝑞𝐷𝑝 𝑆 𝑑𝑛(𝑥)
𝜇𝑛
(1 +
)
𝜇𝑝
𝐽 𝑊 𝑑𝑥(78)

Equation (73) leads that Cathode side electron injection efficiency 𝛾𝑛 depends on holediffusion constant Dp. The thermal coefficient of Dp is negative (Dp is degraded by higher
temperature). In result higher 𝛾𝑛 can be obtained by higher temperature, especially withlarge k.

W

[um]

[um]

2

Carrier Concentraiton[1/cm3]

W
1.0E+17

300K
400K
450K

8.0E+16
6.0E+1612

4.0E+16
2.0E+16

Carrier Concentraiton[1/cm3]

107 |0.0E+003k

4

8.0E+16
6.0E+1614

4.0E+16

2.0E+16

3
k

4

2

3
k

4

5

2

3
k

4

5

2

3
k

4

5

2

3
k

4

5

2

3
k

4

5

300K
400K
450K

8.0E+16

6.0E+16
4.0E+16
2.0E+16

1

300K
400K
450K

8.0E+16

6.0E+1616

4.0E+16
2.0E+16

1.0E+17

300K
400K
450K

8.0E+16
6.0E+16
4.0E+16

2.0E+16
0.0E+00

1.0E+17

2

3
k

4

1

5

300K
400K
450K

8.0E+16

6.0E+1618

4.0E+16
2.0E+16

Carrier Concentraiton[1/cm3]

Carrier Concentraiton[1/cm3]

1.0E+17

5

Carrier Concentraiton[1/cm3]

Carrier Concentraiton[1/cm3]

1.0E+171

1.0E+17300K
400K

8.0E+16450K

6.0E+16
4.0E+16

2.0E+16
0.0E+00

0.0E+00

1.0E+17

2

3
k

4

1

5

1.0E+17

300K
400K
450K

8.0E+16
6.0E+1620

4.0E+16
2.0E+16

Carrier Concentraiton[1/cm3]

1

Carrier Concentraiton[1/cm3]

2.0E+16

0.0E+002

0.0E+00

10

4.0E+16

1

300K
400K
450K

1

8

6.0E+16

5

Carrier Concentraiton[1/cm3]

Carrier Concentraiton[1/cm3]

1.0E+172

0.0E+00

6

300K
400K
450K

8.0E+16

0.0E+00
14

1.0E+17

300K
400K
450K

8.0E+16
6.0E+16
4.0E+16
2.0E+16
0.0E+00

0.0E+00
1

2

3
k

4

5

1

Figure 82. Relationships between carrier concentraion and scaling factor k. higher
temperature makes higher injection efficiency especially with large k. The electron injection
efficiency is assumed as 0.75.

108 |

6.3

Wafer Thickness Optimization
Scaled devices show higher breakdown voltages as shown in Figure 83. In thiscalculation, as previous section, the thickness from Anode to trench bottom was set to120um for all devices. The reason for higher breakdown voltage is larger curvature ofequipotential line as shown in Figure 84. Narrow trench-trench spacing and shallower
trench improves potential distribution such that the electric field is relaxed around trenchbottom.

1.0E-03k=1
k=2

1.0E-04

k=3

Jc[A/cm2]

k=4

1.0E-05k=5

1.0E-06

1.0E-07
1.0E-08

0

200

400

600

800 1000Vce[V]

1200

1400

1600

Figure 83. Breakdown characteristics for scaled devices.

k=5

k=1

Figure 84. Potential distribution comparison between original device (k=1) and scaled
device (k=5) at breakdown.

109 |

By this improvement, the wafer thickness should be reduced for scaled devices. It
leads to reduce on-state voltage drop. Further scaled devices should have diode-likejunction structure. It also contributes to improve Diode characteristics of RC (Reverse
Conductive)-IGBT [57].

6.4

Latest Silicon Process Technology
In this dissertation, the scaling principle toward high productivity and highperformance was found out. The principle predicts that shrinking mesa width is mandatory
to apply shallower trench.

Figure 85. Transistor innovations in “More Moore” field [52].

In 2012, the latest transistor cell structure in CMOS world is FinFET. Intel just starts
mass production of FinFET, named “Tri-Gate”, first of the world. The cell structure is three
dimensional. The current flows from front to back in Figure 86. The minimum width of the
Silicon pillar “Fin” is 22nm. According to the Dr. Nakagawa’s theoretical prediction for
IGBT performance limit reviewed in section 5.2, the proposed design has 40nm of mesa
width. Therefore, the ultimate performance IGBT design can be realistic in terms of thedimension.

110 |

Figure 86. Latest transistor cell in 2012 [52]. Three dimensional structure, called“Tri-Gate”, is used to prevent off-state leakage current, keeping enough on-state current
level.

One issue which would prevent IGBT’s scale down is current density around Cathodecontact. At Cathode contact, the metal needs to contact to both N-Emitter and P-Base.
Planar contact and trench contact are used as illustrated in the left side of Figure 87. There
are two issues to be considered. First, the contact area between metal and Silicon becomesso limited. It causes high contact resistance between them and increases on-state voltage
drop. Second, electro migration can be occurred in the narrow width metal layer with highcurrent density. It can cause reliability problem.
One idea to solve the issues is independently designing mesa width and contact area as
illustrated in the right side of Figure 87. According to the proposed principle, P-Base andcontact layer don’t need to be shrank, where mesa width must be decreased. Similar idea
was proposed by Mr. Sumitomo in ISPSD 2012 [56].

111 |

P-Float

P-Float

N-Basemesa width

Gate

P-Float

P-BaseGate

P-BaseContact hole width

GateGate

GateGate

Contact hole width

P-Float

N-BaseNarrowermesa width

Figure 87. A structure to keep lower contact resistance and avoid electro migration(right side). Mesa width limitation is exist in conventional cell design (left side).

6.5

Packaging
One of the restrictions for IGBT operations is temperature limit. Joule heating by

carrier conduction rises chip temperature. Once the temperature exceeds a limit, carriers are
generated due to higher intrinsic carrier density than N-Base doping concentration. It iscalled thermal breakdown. Even with lower temperature than thermal limit, many kinds ofdegradations can be occurred. So the heat has to exhaust to ambient via package and heatsink, effectively.
One movement toward effective heat spreading is double sided cooling as illustrated in
Figure 88. For extra high voltage applications, such as power plants and electrical trains,
double sided cooling package has been used as called “press pack”. However the package is
not used in general industrial equipment or home appliances because it requires expensive
parts and very tough structure. Recently some companies proposed double sided coolingpackages as extension from conventional package. And they are already produced for HEV(Hybrid Electric Vehicle).

112 |

Figure 88. Double sided cooling pakage [58].

6.6

Integration
In latest IGBT products, vertical device is major than lateral device due to its handlinglarger current per chip. Vertical device can integrate only a few components on a chip suchas current sensing cell and temperature detector diode, where lateral device is embedded
onto large scale integrated circuit as called Power IC. In currently produced IGBT modules,
some functions such as gate drive, over current protection, and over temperature protection,
are implemented by additional IC chips installed in the modules as illustrated in Figure 89.
However, shorter distance between IGBT and IC is preferable to decrease parasitic elements,
prevent malfunction by noise and save the footprint. Especially, noise should be taken carefor highly scaled IGBT which has higher gm as simulated in previous section. An oscillation
example is shown in Figure 90. The waveform shows that less than 0.5V oscillation for gate
voltage can cause collector current oscillation.

113 |

Figure 89. Cross sectional view of IPM (Intelligent Power Module) [1]. IC chip isinstalled separatelly.

6000

3.0
Ic
Vge

2.0

4000

1.0

3000

0.0

2000

-1.0

1000

-2.0

0

Vg[V]

Ic[A]

5000

-3.0
0

5

10
time[us]15

20

Figure 90. Oscillation waveform during short circuit for scaled device of k=5. Applied
gate voltage=1.5V. Collector current oscillation is caused by the gate voltage.

One solution is proposed as illustrated in Figure 91. In this idea, firstly a lamination
film is formed covering IGBT chip. Then contact holes are formed by laser drilling. Finallymetal layer is formed by electro-plating. After the technology established, some IC chips
can be embedded on IGBT chip. Wire bonding will be used to connect IC chips and IGBT
chips.

114 |

Figure 91. One approach for integration [59].

Another solution can be introduced from TSV (Through Silicon Via) technology. TSVtechnology is under developing for three dimensional LSI stack integration. Connectionlines are formed inside Silicon vertically and connected to another LSI chip as illustrated in
Figure 92. To form TSV, firstly via holes are formed by RIE (Reactive Ion Etching), thenoxide layers are formed the surfaces of the via holes, finally the via holes are filled by ametal. TSV technology has advantages to suppress parasitic inductance than wire bonding
method.

115 |

Figure 92. TSV (Through Silicon Via) technology [60].

116 |

6.7

Summary: Scaled device advantages and issues to be solved
As described above, proposed scaling principle gives great potential for further

performance improvement to Silicon IGBT. On the other hand, several issues to beconsidered are alive. The advantages and issues are summarized in Table 11 and Table 12.

Table 11. Advantage of scaled device.
Device Performance
On state voltage drop

Improved. Power loss is reduced. More improved in hightemperature than room temperature.

Gate charge

Decreased as 1/k. The power consumption of gate drive isdecreased. The capacity of gate drive circuit can be smaller.
Manufacturability

Gate etching

Improved. Etching time can be reduced and the uniformity
should be improved for shallower trench.

Gate oxidation

Improved. Oxidation time can be reduced by thinner oxide.

P-Base formation

Improved. Diffusion time can be reduced by shallower depth.
Process controllability should be improved because final
profile can be close to as-implantation profile.

N-Emitter formation

Improved. Diffusion time can be reduced by shallower depth.
Process controllability should be improved because final
profile can be close to as-implantation profile.

Backside processing

Improved. The warpage of the wafers can be reduced byshallower trench.

117 |

Table 12. Issues to be solved for scaled device.
Device Performance
On state voltage drop

Low contact resistance techniques are required between
Cathode electrode and P-Base/N-Emitter because contact
current density becomes higher.

Malfunction

Higher stability for Gate-Emitter voltage is required tosuppress oscillation and malfunction. The potential variation of
Cathode electrode should be reduced.

Reliability

Electro-migration must be considered for Cathode electrodedue to higher current density.
Reliability of thinner gate oxide must be checked under severe
conditions such as breakdown and short-circuit.
Manufacturability

Wafer

300-450mm diameter FZ (Floating Zone) wafer must be
developed.

Gate oxide

High-k material should be applied for highly scaled design toprevent tunneling current. The process uniformity applied fortrench gate structure is unknown.

7 Conclusion
IGBT is widely used in middle to larger capacity power electronics system by higher
rated voltage capability than MOSFET, and easier gate drive than Thyristor. The market size
is about 2.5 billion dollars annually, and forecasted to expand about 10% by a year.
Performance improvements for the whole systems and IGBT are continuously required.
This dissertation targets two topics that obstruct to the improvements.
First, the issue about the limitation of existing compact models was discussed. In
typical usage for three phase inverter circuit, six IGBTs and diodes are used to convert DC
to three phase AC power. Compact models are used for such system simulation for
performance improvement or failure analysis. It enables to simulate many cycle ofswitching with short calculation time. With existing compact model, as far as the models areused within the predetermined validity confirmed operation range of the models, the circuit

118 |

simulators effectively show the sufficiently accurate results. Once the condition exceeds thevalidity confirmed range, such as high temperature condition, the model requires re-fittingof the parameters so as to extend the validity range.
Second, the issue about poor process compatibility between IGBT and CMOS device
was discussed. “More Moore” field semiconductor technology based on high resolution
lithographic

techniques

enhancessignificant

performanceandmass-productivity

improvements in digital integrated circuits by Moore’s Law as a scaling by a factor of 0.7
every 2 years. On the other hand, IGBTs introduce rather deeper trench structure to obtainlower on-state voltage drop and turn-off loss. The technology trend continues for more than
10 years and miniaturization has not been believed to contribute IGBT performance
improvement. In result, currently process compatibility between CMOS and IGBT islimited. IGBT mass production in CMOS factory is difficult.
For the first issue, a device structure based compact model for advanced trench gate
IGBTs was proposed for the first time. The compact model has superior characteristics sothat the model doesn’t need fitting parameters and parameter extractions, and can adapt for
extreme conditions such as under very low or high temperatures. The model should havelarge impact to be used for system analysis under wide range temperature condition.
For the second issue, a scaling principle for IGBT toward shallower structure andsmaller thermal budget was also proposed for the first time by extension of the first topic.
The scaling principle shows a possibility of technology direction and roadmap for future
IGBT. It predicts the device performance improvement with high volume productivity withalignment for CMOS wafer process. The principle should have large impact to be used for
new IGBT development designed for CMOS compatible wafer process, and mass producedin CMOS manufacturing line.
The most important topics required to achieve higher efficiency power electronics
system were discussed and the solutions were provided. This dissertation contributes todesign the systems and IGBT chips by providing new compact model and new scaling
principle.

119 |

8

List of Tables

Table 1. Relationship between commercial power voltage and device rated voltage [2].
.......................................................................................................................... 11
Table 2. Pros and cons of compact model and TCAD approach. .................................30
Table 3. Parameters using model verification. ............................................................42
Table 4. Physical constants for 300K. ........................................................................43
Table 5. Proposed scaling principle for trench gate IGBT. ..........................................74
Table 6. Scaling factors by proposed scaling principle. ..............................................78
Table 7. Base structure parameters used for the verification. ......................................80
Table 8. Structure parameters used for the scaling principle verification. ...................81
Table 9. P-Base surface concentration for Vth adjustment. .........................................91
Table 10. Another scaling factors by proposed scaling principle. ................................96
Table 11. Advantage of scaled device....................................................................... 116
Table 12. Issues to be solved for scaled device. ........................................................ 117

120 |

9 List of Figures
Figure 1. Cover area for various power devices [1]. .................................................... 1
Figure 2. Motor control circuit example [2]. Six IGBT chips on “Inverter” bridge
convert to three phase AC power with arbitrary frequency and voltage. ............... 3
Figure 3. Photograph of IGBT modules [1]. ................................................................ 3
Figure 4. Market share for each power devices [3]. IGBT has 8% of total power device
market. ............................................................................................................... 4
Figure 5. Market trend for IGBT [3]. Vertical axis shows market share in Million US$.
Market is shared by mainly Industrial equipment (brown), Automotive
applications (dark blue) and Consumer electronics (light blue). ........................... 4
Figure 6. Production technology capacity follwing Moore’s law [9]. ........................... 7
Figure 7. The interpretation of the contribution of this work. ...................................... 9
Figure 8. IGBT process direction. Keeping process compatibility with CMOS isneeded. ..............................................................................................................10
Figure 9. IGBT structure. The left side figure shows old designed Planar gate thickwafer IGBT. The right side figure shows newest Trench gate thin wafer IGBT. ..12
Figure 10. Carrier distribution for conduction mode. Electron and hole form same
distribution in N-Base region. The left side figure shows Planar gate IGBT. The
right side figure shows Trench gate IGBT. Carrier distribution profile is different.
..........................................................................................................................13
Figure 11. Electric field distribution in off state (left: PT-IGBT, right: NPT-IGBT). ...15
Figure 12. Modeling structure. ...................................................................................16
Figure 13. The main idea of the model. Current flow paths are assumed toaccumulation layer and mesa region...................................................................18
Figure 14. Current elements in Trench structure .........................................................20
Figure 15. Structure and carrier distribution for NPT-IGBT with shallow P-Emitter ...22
Figure 16. Structure and carrier distribution for PT-IGBT with shallow P-Emitter andshallow N-Buffuer .............................................................................................24
Figure 17 Cross sectional view of Trench gate IGBT .................................................25
Figure 18. IGBT structure for Hefner model [5]. Cell structure is planar gate type.
Thick P+ substrate layer exists and act as P-Emitter. ..........................................31
Figure 19. Assumed carrier distribution in Hefner model [5]. Horizontal axis shows
distance from P-Emitter. The profile is linearly decreasing from Anode to Cathode.
..........................................................................................................................32
Figure 20. Motif structure for Palmer & Santi’s model [43]. Cutline C1 to Cn is121 |

corresponding hole distribution in Figure 21. .....................................................33
Figure 21. Hole horizontal distribution calculated by two-dimentional TCAD
simulation [43]. A gradient is observed at cutline Cn, just below the trench gate.33
Figure 22. Assumed hole current distributions and hole distribution for Palmer &Santi’s model [43]..............................................................................................34
Figure 23. Built-in potential for high injection devices...............................................38
Figure 24. Built-in potential definition for the model. ................................................39
Figure 25. Model implementation on Microsoft Excel. ..............................................40
Figure 26. Structures used for verifications. ...............................................................41
Figure 27. Carrier distribution profile measurement. ..................................................44
Figure 28. Calculated Jc-Vce characteristic comparison between proposed compact
model and TCAD simulator for 600V NPT-IGBT. .............................................46
Figure 29. Calculated carrier distribution comparison between proposed compact
model and TCAD simulator for 600V NPT-IGBT at 50A/cm2. ...........................47
Figure 30. Calculated carrier distribution comparison between proposed compact
model and TCAD simulator for 600V NPT-IGBT at 100A/cm2. .........................48
Figure 31. Calculated carrier distribution comparison between proposed compact
model and TCAD simulator for 600V NPT-IGBT at 150A/cm2. .........................49
Figure 32. Calculated carrier distribution comparison between proposed compact
model and TCAD simulator for 600V NPT-IGBT at 200A/cm2. .........................50
Figure 33. Calculated Jc-Vce characteristic comparison between proposed compact
model and TCAD simulator for 1200V PT-IGBT. ..............................................51
Figure 34. Calculated carrier distribution comparison between proposed compact
model and TCAD simulator for 1200V PT-IGBT at 50A/cm2. ............................52
Figure 35. Calculated carrier distribution comparison between proposed compact
model and TCAD simulator for 1200V PT-IGBT at 100A/cm2. ..........................53
Figure 36. Calculated carrier distribution comparison between proposed compact
model and TCAD simulator for 1200V PT-IGBT at 150A/cm2. ..........................54
Figure 37. Calculated Jc-Vce characteristic comparison between proposed compact
model and TCAD simulator for 3.3kV IEGT. .....................................................55
Figure 38. Calculated carrier distribution comparison between proposed compact
model and TCAD simulator for 3.3kV IEGT at 10A/cm2. ..................................56
Figure 39. Calculated carrier distribution comparison between proposed compact
model and TCAD simulator for 3.3kV IEGT at 30A/cm2. ..................................57
Figure 40. Calculated carrier distribution comparison between proposed compact
model and TCAD simulator for 3.3kV IEGT at 50A/cm2. ..................................58122 |

Figure 41. Trench depth-Vce(sat) relationship comparison between proposed modeland TCAD for 3.3kV IEGT. ...............................................................................59
Figure 42. Cell pitch-Vce(sat) relationship comparison between proposed model and
TCAD for 3.3kV IEGT. .....................................................................................59
Figure 43. On-state carrier distribution profiles with varied trench depth for 3.3kV
IEGT at 50A/cm2. Electron injection efficiency from Cathode side depends on thedepth. ................................................................................................................60
Figure 44. On-state carrier distribution profiles with varied half cell pitch for 3.3kV
IEGT at 50A/cm2. Electron injection efficiency from Cathode side depends on thecell pitch. ...........................................................................................................61
Figure 45. Carrier distribution in mesa region of 600V NPT-IGBT at 200A/cm2. .......62
Figure 46. Carrier distribution in mesa region of 3.3kV IEGT at 50A/cm2. ................63
Figure 47. Relationship for carrier concentration in mesa region, electron current
density in mesa region and electron current via accumulation layer. The structureis 1200V PT-IGBT. The current density is 150A/cm2. ........................................64
Figure 48. Technology node shrinking [52]. ...............................................................66
Figure 49. “More Moore” field and “More than Moore” field [9]. ..............................67
Figure 50. MOSFET scaling principle [53]. The principle scales channel length L, Gate
oxide thickness Tox, and substrate doping concentration NA to L’=L/k, Tox’=Tox/k,and NA’= k NA, respectively. ...............................................................................68
Figure 51. N-Base carrier distribution profile for lowest on-state voltage drop [54].
N-Base carrier distribution is linearly decreasing from Cathode to Anode (in thisfigure, “Collector” to “Emitter”). .......................................................................69
Figure 52. Simulated Ic-Vc characteristic of IGBT performance limit [54]. ...............70
Figure 53. The relationship between Cathode side injection efficiency and on-statevoltage drop [54]. ..............................................................................................70
Figure 54. IGBT performance limit prediction [54]. The author predicted Silicon IGBT
will realize low on-resistance even below SiC limit for over 2kV range. ............71
Figure 55. Cross sectional view of DB-IGBT [55]. Internal oxide layer is inserted
between P-Base and N-Base. .............................................................................72
Figure 56. Calculated hole distribution in N-Base [55]. Hole concentration is linearlydecreased from Cathode side to Anode side. ......................................................72
Figure 57. Trede-off relationship between on-state voltage drop and turn-off loss for
DB-IGBT [55]. ..................................................................................................73
Figure 58. Proposed scaling principle for trench gate IGBT. ......................................74
Figure 59. Comparison of mesa region carrier distribution. ........................................77

123 |

Figure 60. Proposed scaling (Left side) and Simple scaling (Right side). In proposed
scaling, cell pitch is constant. In simple scaling, cell pitch is also scaled. ...........79
Figure 61. Base structure for scaling principle verification. 1200V PT-IGBT structureis used for the motif. ..........................................................................................80
Figure 62. Ic-Vge characteristics for scaled devices. Scaled devices show lower Vthand higher gm. ...................................................................................................82
Figure 63. Calculated Ic-Vc characteristics of scaled devices with scaled electric fieldin gate oxide as Eox’=Eox/k. In proposed scaling, k=1 and 2 show good
agreement but more scaled devices show lower saturation current. In simple
scaling, Vce(sat) becomes higher with increasing scaling factor k.......................83
Figure 64. Calculated carrier distribution in N-Base region of scaled devices withscaled electric field in gate oxide as Eox’=Eox/k. The zero point of horizontal
scale is set to mesa/N-Base boundary. In proposed scaling, similar carrier
distribution is obtained instead of scale down. In simple scaling, Cathode side
carrier concentration becomes lower with increasing scaling factor k. ................84
Figure 65. Calculated Ic-Vc characteristics of scaled devices with constant electricfield in gate oxide as Eox’=Eox. In proposed scaling, Vce(sat) is improved byincreasing scaling factor k. In simple scaling, Vce(sat) becomes higher withincreasing scaling factor k. .................................................................................85
Figure 66. Calculated Ic-Vc characteristics of proposed scaling devices with constantelectric field in gate oxide as Eox’=Eox. In higher temperature condition, Vce(sat)improved especially. ..........................................................................................86
Figure 67. Calculated carrier distribution in N-Base region for scaling factor k=1 to 5.
The zero point of horizontal scale is set to mesa/N-Base boundary. In proposed
scaling, Cathode side carrier concentration is increased by scale down. In simple
scaling, Cathode side carrier concentration becomes lower with increasing scaling
factor k. .............................................................................................................87
Figure 68. Calculated carrier distribution in N-Base region for proposed scaling device
with T=300K and 450K. The zero point of horizontal scale is set to mesa/N-Baseboundary. In proposed scaling, Cathode side carrier concentration is increased byscale down especially in high temperature condition. .........................................88
Figure 69. Calculated Turn-off characteristics of proposed scaling devices withconstant electric field in gate oxide as Eox’=Eox. Device active area is 1cm2.
Same external gate resistance of 10ohm is used. ................................................89
Figure 70. Calculated short-circuit waveforms of proposed scaling devices withconstant electric field in gate oxide as Eox’=Eox. Lower gate voltage was applied124 |

to avoid thermal runaway in this calculation. .....................................................90
Figure 71. Ic-Vge characteristics for scaled devices with Vth adjustment. Scaled
devices show higher gm. ....................................................................................92
Figure 72. Calculated Ic-Vc characteristics of scaled devices with Vth adjustment andconstant electric field in gate oxide as Eox’=Eox. Vce(sat) is improved byincreasing scaling factor k. .................................................................................92
Figure 73. Calculated Turn-off characteristics of scaled devices with Vth adjustment.
Device active area is 1cm2. Applied gate voltage is scaled by keeping constantelectric field in gate oxide as Eox’=Eox. All devices show almost same turn-off
characteristics by Vth adjustment. ......................................................................93
Figure 74. Calculated short-circuit waveforms of scaled devices with Vth adjustment.
Applied gate voltage is scaled by keeping constant electric field in gate oxide as
Eox’=Eox. Lower and similar saturation current are realized. No thermal runaway
was occurred......................................................................................................94
Figure 75. Simulated maximum electric field in gate oxide for static breakdown. ......95
Figure 76. An example of “cell first” process flow. ....................................................98
Figure 77. An example of “cell last” process flow. ................................................... 100
Figure 78. Ic-Vce characteristic for 1200V PT-IGBT calculated by the proposedcompact model. To improve power density, Vce(sat) must be reduced in highcurrent density region. ..................................................................................... 101
Figure 79. Portions of voltage drop at 300K for 1200V PT-IGBT calculated by the
proposed compact model. N-Base voltage drop is dominant in high current
density region. ................................................................................................. 102
Figure 80. Relationship between cell pitch W, scaling factor k and carrier concentrationn at N-Base/mesa boundary for 450A/cm2. The electron injection efficiency is
assumed as 0.75. .............................................................................................. 104
Figure 81. Relationship between cell pitch W, scaling factor k and carrier concentrationn at N-Base/mesa boundary for 450A/cm2. The electron injection efficiency is
assumed as 0.75. .............................................................................................. 105
Figure 82. Relationships between carrier concentraion and scaling factor k. higher
temperature makes higher injection efficiency especially with large k. The
electron injection efficiency is assumed as 0.75................................................ 107
Figure 83. Breakdown characteristics for scaled devices. ......................................... 108
Figure 84. Potential distribution comparison between original device (k=1) and scaled
device (k=5) at breakdown. .............................................................................. 108
Figure 85. Transistor innovations in “More Moore” field [52].................................. 109

125 |

Figure 86. Latest transistor cell in 2012 [52]. Three dimensional structure, called“Tri-Gate”, is used to prevent off-state leakage current, keeping enough on-state
current level. .................................................................................................... 110
Figure 87. A structure to keep lower contact resistance and avoid electro migration(right side). Mesa width limitation is exist in conventional cell design (left side).
........................................................................................................................ 111
Figure 88. Double sided cooling pakage [58]. .......................................................... 112
Figure 89. Cross sectional view of IPM (Intelligent Power Module) [1]. IC chip isinstalled separatelly. ......................................................................................... 113
Figure 90. Oscillation waveform during short circuit for scaled device of k=5. Applied
gate voltage=1.5V. Collector current oscillation is caused by the gate voltage. . 113
Figure 91. One approach for integration [59]. .......................................................... 114
Figure 92. TSV (Through Silicon Via) technology [60]. ........................................... 115

126 |

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11 Research History
Publication
1. M. Tanaka and I. Omura, “Structure Oriented Compact Model for Advanced Trench
IGBTs without Fitting Parameters for Extreme Condition: part I”, Microelectronics
Reliability 51, pp. 1933-1937, 2011.

International Conferences
1. Masahiro Tanaka, Satoshi Teramae, Yasushi Takahashi, Toru Takeda, Masakazu
Yamaguchi, Tsuneo Ogura, Tetsujiro Tsunoda and Satoshi Nakao: “600V Trench-gate
NPT-IGBT with Excellent Low On-State Voltage”, Proceedings of the 12th
International Symposium on Power Semiconductor Devices & ICs (ISPSD), pp.
279-282, 2000.
2. Masahiro Tanaka and Ichiro Omura, “Scaling Rule for Very Shallow Trench IGBT
toward CMOS Process Compatibility”, Proceedings of the 24th International
Symposium on Power Semiconductor Devices & ICs (ISPSD), pp. 177-180, 2012.

Related Papers
1. H. Nakanishi, M. Kobayashi, T. Chaki, Y. Yamakawa, T. Tanaka, M. Kuwahara, S.
Kurushima, Y. Miyazaki, M. Yamaguchi, M. Tanaka, G. Tchouangue: “Designs andPerformance of Trench Gate IGBTs for Induction Heating, Switching Power Supply andMotor Control Applications”, Proceedings of PCIM 1999, pp. 247-253, 1999.
2. Tomoko Matsudai, Hideki Nozaki, Shinichi Umekawa, Masahiro Tanaka, Motoshige
Kobayashi, Hidetaka Hattori and Akio Nakagawa: “Advanced 60um Thin 600V
Punch-Through IGBT Concept for Extremely Low Forward Voltage and Low Turn-off
Loss”, Proceedings of the 13th International Symposium on Power Semiconductor
Devices & ICs (ISPSD), pp. 441-444, 2001.

134 |

3. Shin’ichi Umekawa, Masahiro Tanaka, Takahiro Okuno, Tetsujiro Tsunoda, Nobutatsu
Kimura, Sho-ichiro Kurushima, Tomoko Matsudai, Akio Nakagawa: “600V Trench
Gate PT type IGBT Development Utilizing Ultra Thin Wafer Technology”, EPE-PEMC
2002, 2002.
4. S. Kurushima, T. Tsunoda, S. Umkawa, M. Tanaka, M. Kitagawa, M. Oomichi, G.
Tchouangue: “Toshiba’s newest 1200V devices equipped with UTPT technology”,
Proceedings of PCIM 2003, PE13-6, 2003.
5. Tomoko Matsudai, Masanori Tsukuda, Shinichi Umekawa, Masahiro Tanaka and Akio
Nakagawa: “New Anode Design Concept of 600V Thin Wafer PT-IGBT with Very Low
Dose P-buffer and Transparent P-emitter”, Proceedings of the 15th International
Symposium on Power Semiconductor Devices & ICs (ISPSD), pp. 75-78, 2003.
6. Masakazu Yamaguchi, Ichiro Omura, Satoshi Urano, Shinichi Umekawa, Masahiro
Tanaka, Takahiro Okuno, Tetsujiro Tsunoda and Tsuneo Ogura: “IEGT Design Criterion
for Reducing EMI Noise”, Proceedings of the 16th International Symposium on Power
Semiconductor Devices & ICs (ISPSD), pp. 115-118, 2004.
7. Masahiro Tanaka, “Status and Examples of Power Device Simulation: Past Present andFuture”,

Companion

Workshop,International

Conferenceon

Simulationof

Semiconductor Processes and Devices (SISPAD) 2011, 2011.(Invited Paper)
8. T. Matsudai, M. Tsukuda, S. Umekawa, M. Tanaka and A. Nakagawa: “New Anodedesign concept of 600V thin wafer PT-IGBT with very low dose P-buffer andtransparent P-emitter”, IEE Proceedings of Circuits Devices & Systems, Vol. 151, No.3,
pp. 255-258, 2004.

Related Patents
Japanese Patent, No. 4762663, 4703138, 3984227, 3906181, 3727827.
Japanese Unexamined Patent Application Publication, 2012-195347, 2011-82585,
2004-79988, 2003-69019, 2001-274400, H11-345969, H11-307785.
United States Patent, No. 7560773, 7211861, 7095079, 6936893, 6992340, 7271040.
Chinese Patent, No. 1949533, 1402356.

135 |

Korean Patent, No. 20030712.

About the Author
Masahiro Tanaka was born in Yokohama, Japan on July 13, 1969. He received
Bachelor degree in electrical engineering from the Kagoshima University, Japan in 1994
and Master’s degree in information systems engineering from Graduate School ofInformation Systems, the University of Electro-Communications, Japan in 1996. He was apower device design specialist at Toshiba Cooperation from 1996 to 2005, where he was
responsible for the development of thin wafer IGBTs for industrial applications. From 2004
to 2005, he was responsible for IGBT product migration from Toshiba Cooperation to
Mitsubishi Electric Cooperation. Since 2005, he has been a TCAD senior II cooperateapplication engineer at Nihon Synopsys G.K. Since 2010, he has been a doctor student in
Graduate School of Engineering, Kyushu Institute of Technology, Japan. His interests areadvanced power semiconductor devices, process-device simulations, and compact modelingfor them.