GaN Trench Etching andSidewall Angle Control
for Vertical Power Devices
Samco Inc. Technical Report vol.110 / July 2020

GaN Trench Etching and Sidewall Angle Control
for Vertical Power Devices
Introduction
Since gallium nitride (GaN) -based semiconductors, which are widely used in short-wavelength optical devices, haveexcellent physical properties, they are promising as materials for electronic devices such as power devices and RFdevices. Some have already been put into practical use and are already on the market. Development aimed at furtherincreasing performance is gaining momentum year by year, and it is expected that it will be widely adopted in the fieldof high frequency electronic devices.

For example, it is expected that electronic devices (trench MOS, HEMT, etc.) with high withstand voltage, low ON
resistance, and high channel mobility will be realized within the next few years. Figure 1 shows an example of a GaN
MOSFET structure adopting a trench structure and a gate recess type GaN HEMT structure.
Samco provides ICP-RIE equipment, CVD equipment and process technology for manufacturing GaN-based lightemitting devices. We also provide processes that realize trench formation, mesa formation, etc., that are 4H-SiC
high-power device manufacturing processes.

In this technical report, we will introduce a process solution that contributes to the formation of trench structures andrecess structures when creating GaN devices.

SourceOxiden+GaN
p-GaN

Sourcen+GaN

Gate

p-GaN
n-GaN
drift layer
Sourcen+GaN

Drain
Gate

Drain

AIGaN

(a) GaN trench MOSFET structure♢♢♢2DEG♢♢♢GaN(b) GaN HEMT gate recess structure
Figure 1. Schematic of GaN electronic device structure.

Page 2 of 4© Samco Inc. - GaN Trench Etching and Sidewall Angle Control for Vertical Power Device - Technical Report / vol.110 / July 2020www.samco.co.jp/en

GaN Trench Etching and Sidewall Angle Control
Samco has been developing its GaN trench processing technology. As shown in Figure 2, it is possible to control
the shape of trenches from vertical to forward taper machining. A sample created by epitaxially grown GaN on asapphire substrate was used, and etching was performed with our ICP etching system RIE-400iP.

In the conventional forward taper processing, residue is deposited on the side wall, so it is necessary to

remove this by post-treatment. On the other hand, the newly developed forward taper processing technology has
reduced residue on the side walls and does not require post-treatment. Furthermore, one point of this process tonote is that even a narrow pattern with an etching aperture width of 1 μm or less can form a forward taper of lessthan 80°. Using the conventional technique there are cases where the progress of etching is hindered by a narrow
opening width, since the opening is filled by the accumulation of residue on the side wall. Figure 3 shows the resultsof successful forward taper processing by controlling the RF power ratio between ICP and Bias and balancing ofthe etchant gases.

(a) Vertical etch(b) Conventional forward taper etch(c) New forward taper etch

Figure 2. GaN trench etching

GaN trench taper angle [°]95939189878583
8179
0.00

0.10

0.20

0.30

0.40

0.50

0.60

Etch process parameters

Figure 3. GaN trench sidewall angle control

Page 3 of 4© Samco Inc. - GaN Trench Etching and Sidewall Angle Control for Vertical Power Device - Technical Report / vol.110 / July 2020www.samco.co.jp/en

The process of forming a forward taper with this GaN trench is thought to be useful for HEMT gate recess formation.
In the gate recess structure of HEMT, it is important to design the gate length and process to control the influenceon the two-dimensional electron gas. Therefore, this process is applied to maintain the same opening width as when
the gate is formed.

Conclusion
Samco has contributed to the manufacturing process from the GaN-LED development stage, and has responded tomany customers with varying needs for etching technology for GaN-based semiconductors. In recent years, Samco has
developed several process techniques such as the recess etching of GaN-HFET, high selectivity etching of GaN / AlGaN,and GaN trench etching introduced in this report.

Samco will continue to develop processes and contribute to the practical application of GaN trench MOS. Furthermore,
Samco is proceeding with the development of gate oxide film formation (ALD, CVD) and metal CVD as well as etching,and intends to provide hardware and process expertise for gate formation.

References
Sarayama, Shoji. (2008). Shinno baruku GaN tankessho no hitsuyousei to kenkyukaihatsu doukou (Necessity andR&D Trend of True Bulk GaN Single Crystal). Kagaku Gĳutsu Doukou, November 2008.

� � Ye a rs’ E xp e r i e n ce i n T h i n Fi l m Te ch n o l o g ySamco Inc.
For more information please email: sales@samcointl.com
Japan (Headquarters, Kyoto)
Phone:+81-75-621-7841
South Korea (Suwon)
Phone:+82-70-8252-7841
TaiwanHsinchu Office
Phone:+886-3-516-5100
Tainan Service Office
Phone:+886-927-607-351

ChinaBeijing Office
Phone:+86-10-8219-4215
Shanghai Office
Phone:+86-21-6249-4662

US, Canada & Latin America
West Coast Office, California
Phone:+1-408-734-0459
East Coast Office, New Jersey
Phone:+1-631-464-0664

Singapore
Phone:+65-6465-4220

samco-ucp ltd. Liechtenstein
Phone:+423-377-5959
Email:
info@samco-ucp.com

Malaysia
Phone:+603-7629-7560

Page 4 of 4
© Samco Inc. - GaN Trench Etching and Sidewall Angle Control for Vertical Power Device - Technical Report / vol.110 / July 2020www.samco.co.jp/en