༤ ኈ ㄽ ᩥ㸦Doctoral Thesis㸧
Investigation on the Mechanism of Millisecond
Solid Phase Crystallization of Silicon Films
Formed by Micro-Thermal-Plasma-Jet and Their
Application to Bottom-Gate Thin Film
Transistors኱Ẽᅽ࣐࢖ࢡࣟ⇕ࣉࣛࢬ࣐ࢪ࢙ࢵࢺ↷ᑕ࡟ࡼࡿࢩࣜࢥࣥⷧ
⭷ࡢ࣑ࣜ⛊⤖ᬗ໬࣓࢝ࢽࢬ࣒ࡢゎ᫂࡜࣎ࢺ࣒ࢤ࣮ࢺᆺⷧ⭷ࢺࣛࣥࢪࢫࢱ࡬ࡢᛂ⏝Hoa Thi Khanh Nguyenᗈᓥ኱Ꮫ኱Ꮫ㝔ඛ➃≀㉁⛉Ꮫ◊✲⛉
Graduate School of Advanced Sciences of Matter
Hiroshima University
2021 ᖺ 9 ᭶
㸦September 2021㸧

Contents
Chapter 1: Introduction..........................................................................................................1
1.1.Background..........................................................................................................................2
1.1.1.

Introduction to thin film transistors.....................................................................2

1.1.2.

Review about conventional TFT channel’s material...........................................6

1.1.3.

Published researches on mechanism of solid phase crystallization...................10

1.1.4.

Micro thermal plasma jet irradiation.................................................................13

1.1.5.

Direct observation phase transformation..........................................................14

1.1.6.

Contactless temperature measurement..............................................................16

1.2.Overview of thesis..............................................................................................................171.2.1.

Motivation and purpose....................................................................................17

1.2.2.

Composition.....................................................................................................18

References ......................................................................................................................20
Chapter 2: Simultaneous Observation of the Phase Transformation and Temperature of
Silicon Film during Millisecond Annealing..........................................................................23
2.1. Principle of measurement...................................................................................................24
2.2. Experimental procedure.....................................................................................................25
2.3. Results and discussion.......................................................................................................27
2.3.1.

HSC snapshots and transient reflectivity of Si film during μ - TPJ irradiation.27

2.3.2.

Crystallinity......................................................................................................30

2.4. Summary............................................................................................................................31
References.......................................................................................................................33iChapter 3: Temperature Calculation and Growth Mechanism of Millisecond Solid Phase
Crystallization Silicon Film....................................................................................................34
3.1. Introduction.......................................................................................................................35
3.2. TOC measurement experiment..........................................................................................38
3.3. Results and discussion.......................................................................................................39
3.3.1.

TOC measurement............................................................................................39

3.3.2.

Estimation of nucleation temperature...............................................................423.3.3.

Characteristic crystallization time....................................................................45

3.3.4.

Grain size..........................................................................................................48

3.3.5.

Growth mechanism...........................................................................................50

3.4. Summary............................................................................................................................54
References.......................................................................................................................55
Chapter 4: Characteristics of Millisecond Solid Phase Crystallization of Phosphorous
Doped Silicon films.................................................................................................................56
4.1. Introduction.......................................................................................................................57
4.2. Experimental procedure.....................................................................................................57
4.3. Results and discussion.......................................................................................................59
4.3.1.

Phase diagram...................................................................................................59

4.3.2.

Surface roughness.............................................................................................61

4.3.3.

Crystallinity......................................................................................................62ii

4.3.4.

Hall effect measurement’s results.....................................................................63

4.4. Summary............................................................................................................................65
References.......................................................................................................................66
Chapter 5: Application of Millisecond Solid Phase Crystallization Silicon Film for
Bottom-Gate Thin Film Transistors.....................................................................................67
5.1. Introduction.......................................................................................................................68
5.2. Experimental procedure.....................................................................................................68
5.3. Results and discussion.......................................................................................................70
5.3.1.

Cross-sectional image of bottom-gate TFTs.....................................................70

5.3.2.

Transfer characteristics.....................................................................................72

5.4. Summary............................................................................................................................76
References.......................................................................................................................77
Conclusion...............................................................................................................................78
Publications and Awards........................................................................................................80
Acknowledgement..................................................................................................................83iii

Chapter 1: Introduction

Chapter 1
Introduction

1Chapter 1: Introduction

1.1. Background1.1.1. Introduction to thin film transistors (1,2,3)
A thin film transistor (TFT) is a key technology for developing active-matrix flat panel
displays (AMFPDs). It is a special type of field effect transistor formed by placing thin filmsof the dielectric layer as well as an active semiconductor layer and metallic contacts onto a
supporting substrate (1,2,3).
Thin film transistor differs from metal oxide semiconductor field effect transistor(MOSFET) in certain way. Firstly, TFT works in accumulation layer while MOSFET works
under inversion layer. Secondly, TFT is amorphous in nature as compared to MOSFET, whichis crystalline in nature. Thirdly, TFT is undoped while MOSFET is mostly Si-doped (1). The
applied gate voltage (VG) controls the electrons flow from source to drain. For positive gate
voltage, electrons attract towards the bottom side of the semiconductor layer and conduct achannel. Then, the voltage applied between the two terminals results in current flow. The
current flow occurs from drain to source.
Thin film transistor can be worked in depletion mode or enhancement mode dependingon whether it requires a gate voltage to induce the channel conduction. When no gate voltage
is applied, the channel conductance is low for enhanced mode of operation. Therefore, a low
carrier density in the channel is essential to achieve this mode. A channel has to be induced incase of enhancement mode. In this mode, channel enhances on increasing the gate source
voltage. Then applying voltage between the drain and source terminals causes the drain current
to flow. While in case of depletion mode, if we apply the drain source voltage, the drain current
will flow for zero gate source voltage. In this type of MOSFET, there is an implanted channel(1).
Based on position of the electrodes, we can classify to four basis configurations of TFT
as: top gate bottom contact, top gate top contact, bottom gate top contact, and bottom gatebottom contact. Although using the exact same materials, different TFT structures can display
2

Chapter 1: Introduction

quite different device characteristics. The illustrations of TFT configurations are shown in Fig.
1.1.

Fig. 1.1. TFT configuration: (a) top gate bottom contact, (b) top gate top contact, (c) bottom
gate top contact, and (d) bottom gate bottom contact.
Different processes taken for the TFT fabrication typically determines the selection of aparticular structure. The deposition of semiconductor channel layer is firstly made in coplanar
top gate structure, while deposition on insulator layer is firstly made in the bottom gate
structure. Both of them can fabricate in self-aligned structure, therefore the parasitic overlap
capacitance between the gate and source/drain terminals is reduced. However, bottom gate
structure needs smaller masks number for photolithography process. As a result, in view ofmass production, it will help to reduce the production’s cost.
There are two common bottom-gate TFT structures as back-channel-etched (BCE) andetch-stop (ES). These have different fabrication processes which is discussed below. Figure
1.2. shows an example of the main steps in fabricating BCE hydrogenated amorphous silicon(a-Si:H) TFT. The first stage is gate formation: metal deposition, photolithography and etching3

Chapter 1: Introduction

by using mask M1. The gate is coated by a stack of three consecutively deposited films of aSiNx : H, intrinsic a-Si:H, and doped a-Si:H by using plasma enhanced chemical vapor
deposition (PECVD). The film thicknesses for commercial TFTs are typically 300 nm a- SiNx :H, 200 nm intrinsic a-Si:H, and 50 nm doped a-Si:H (4). In the second patterning stage, M2, thetriple stack is defined into the individual TFT islands. Next is the deposition of the source anddrain contact metals and photolithography by mask stage M3. The gate is used as an etch mask
to remove the doped layer from those areas of the TFT island stack where it is not protected by
the metal. The fabrication process is completed by the deposition of a final capping/passivation
layer of a-SiNx : H, which is patterned by mask M4 into contact holes down to the source, drain
and gate pads. In summary, the BCE process consists of four mask stages, two PECVD
depositions, and two metal sputter deposition stages (2).

Fig. 1.2. Illustration of main steps in BCE a-Si:H TFT fabrication.

4

Chapter 1: Introduction

Similarly, Fig. 1.3 shows an example of the main steps in ES a-Si:H TFT fabrication.
The main difference between two structure is the present of an a-SiNx : H pack above the edgesof the doped regions. It gives better etch selectivity between the etching of the doped region
and the underlying a-SiNx : H, therefore avoiding the need to use a critical etching time.
However, by using this way, the fabrication process is more complex. In summary, the ES
process requires 5 mask stages, and three PECVD depositions. It is clear that, providing theback channel etch is well controlled, the BCE process is simpler, with fewer steps. As theconsequence, it can take higher manufacturing throughput and lower overall cost and isextensively implemented in production facilities (2).

Fig. 1.3. Illustration of main steps in ES a-Si:H TFT fabrication.

5

Chapter 1: Introduction

1.1.2. Review about conventional TFT channel’s material
In the past several years, the TFT technology has progressed intensely, especially in the
low temperature, large-area, high throughput fabrication process (2). To date, difference typesof TFTs with the improved mobility, novel structures or flexible material properties have beenreported for application in displays, sensors, imagers, detectors, flexible electronics, etc (2). In
this section, we will review some conventional TFT channel’s materials.
1.1.2.1.Hydrogenated amorphous siliconHydrogenated amorphous silicon (a-Si:H) is an alloy of Si with ~10% hydrogen.
Hydrogen plays a key role both in defect passivation within the material, by reducing thedangling bond density from ~ 1020 cm-3, in H-free a-Si, to ~ 1016 cm-3 (5) and in the a-Si:H
deposition process itself.
Hydrogenated amorphous silicon is well suited for active-matrix liquid crystal displays(AMLCDs) because it is easy to deposit over large areas at low temperature that are fullycompatible with glass or plastic substrates by using plasma enhanced chemical vapor
deposition (PECVD). Because of a high dark resistivity, it makes TFTs having low leakage
currents. It can be made n- or p – doped a-Si:H, therefore the fabrication of low-resistancecontacts is available. The processing of a-Si:H TFTs is similar to the crystalline silicon metaloxide-semiconductor (MOS) integrated circuited technologies, which make AMLCDs moremature than other technologies, for example organic displays based on light-emitting devices.
Finally, a-Si:H technology benefits from the tremendous investment in a-Si:H solar cells madeseveral years ago, and so has become the dominant player in the active-matrix display world.
However, its low mobility, < 1 cm 2/Vs,(6,7) is perfectly suitable to TFTs within each pixel but
is unsuitable for the faster switching circuits needed for addressing the rows and columns in
the display itself.
6

Chapter 1: Introduction

1.1.2.2.Transparent amorphous oxide semiconductors
Transparent amorphous oxide semiconductors, in particularly a-InGa-aZnO (a-IGZO),
are attracting increasing attention as TFT material for large sized active-matrix organic lightemitting diode (AMOLED) displays. Because of an electron mobility ~ 10 times higher thana-Si:H (8,9), it is more easily able to deliver the large drive currents needed for OLEDs. Due toamorphous material, devices show good uniformity and promise a simpler processing schedule.
However, the current TFTs are only n-channel, and integrated logic circuits made in thismaterial will be slower and consume more power than the complementary pair circuits
available with polycrystalline silicon (poly-Si) TFTs. The device structure is typically either
inverted staggered ES or inverted coplanar, which can be made with a 5 or 4 mask process,respectively. In principle, this is a low temperature process, including the deposition of a-IGZO
by DC sputtering at room temperature, although post-deposition anneals are required tostabilize the material. Device performance is sensitive to ambient oxygen and water, andeffective passivation of the structure is essential for the fabrication of high quality TFTs withstable long-term operation.
1.1.2.3.Polycrystalline silicon
The interest in poly-Si as an alternative TFT material started soon after a-Si:H TFTs
became recognized as the most promising technology for the large-scale production of activematrix LCDs. In contrast to the carrier mobility in a-Si:H, which does not change to much overlast 20 years or so, the electron mobility in poly-Si has increased, over the same period, from
<5 to ~ 120 cm2/Vs with routine processing, and up to ~ 900 cm2/Vs with innovative techniques
yielding quasi-single-crystal large-grain material (10). Several ways have been examined for theformation of these TFTs such as direct deposition methods as well as conversion using a-Si
film.

7

Chapter 1: Introduction

The principal technique for the direct deposition of poly-Si is by low-pressure chemical
vapor deposition (LPCVD) using silane in nitrogen carrier gas. Practical deposition rates of 1
– 10 nm/min are obtained over temperature range 540 – 620 °C. For typical silane pressures of
100 – 200 mTorr, films will be deposited at upper temperature in a fine grain columnar form.
The grain size is typically 100 nm and with a preferred (110) orientation. At the lower
temperature the films are more likely to be amorphous, but the precise structure of the film
depends upon both pressure and temperature. Films deposited in the amorphous state and thencrystallized into poly-Si have been shown to have higher carrier mobilities due to larger grain
size compared with film deposited in the polycrystalline state. The use of amorphous films asprecursor material has meant that large-area plasma-enhanced CVD is also used.
Crystallization of the amorphous material is achieved either by solid-phase crystallization(SPC) at temperature of ~ 600 °C or by the use of a laser.
Directly deposited columnar poly-Si was the material of initial interest in this area.
However, columnar structure with typical grain size as 100 nm limited the electron field effectmobility μFE of 5 cm2/Vs (11,12). Meakin et al. (6) reported that deposited at a reduced pressureof < 10 mTorr at 630 °C can yield larger-grain material, with fewer intragrain defects and ahigher μFE of ~ 10 cm2/Vs. The interrelationship between silane pressure, growth mechanism,grain structure and surface morphology has been comprehensively studied. In the lowerpressure regime (< 10 mTorr), the large high-quality grains are only obtained in films thicker
than ~ 0.5 μm, which is likely to result in large TFT off-currents. In addition, these largegrained films also show considerable surface roughness which has been demonstrated todegrade carrier mobility as well as the long-term stability of the devices. Although this work
has considerably increased the understanding of the grain growth mechanisms, the filmroughness has limited its application.

8

Chapter 1: Introduction

The poly-Si film via SPC using precursor a-Si film increase μFE comparing with directly
deposited poly-Si film. For film deposited at temperatures below 600

oC, thermal

crystallization for 20 h at 600 oC was required to convert them into their final polycrystalline
form. The grains resulting from this process are generally elliptical in shape due to preferential
growth in the <112> direction, and dendritic dur to the formation of twins along boundaries.
Grain size dimension in excess of 1 μm have been obtained by this technique. Due to the lowtemperatures used (in order to keep the process compatible with the use of glass substrates)
long crystallization times of several hours are necessary. Grain size has been reported toincrease with film thickness in crystallized amorphous LPCVD silicon, probably due to grain
nucleation occurring at the back of the film. In addition to the use of LPCVD a-Si precursor
material, similar results have been obtained from use of PECVD a-Si:H deposited atsignificantly lower temperatures, such as 250 oC. This exploits the use of large-area deposition
equipment available for a-Si:H TFTs and also benefits from the higher deposition rates
achievable with this technique compared with LPCVD a-Si (typically hundreds of angstroms
per minute and tens of angstroms per minute respectively). Large dendritic grains are obtained
after SPC, the major difference from LPCVD a-Si being a longer regrowth time due to a
combination of a lower degree of inherent structural order in the film (due to the lower
deposition temperature) and to the effect of the higher impurity density found in PECVD
material. One of the practical limitations to the SPC process to the SPC process at ~ 600 oC has
been the long thermal anneal cycles necessary for the regrowth of the films. Some techniques
are introduced to reduces this cycle time such as the use of metal induced crystallization (13-15).
However, film contamination by either the metal itself or the metal silicide are their issue.
Excimer laser annealing (ELA) has been widely utilized and provides high-crystallinity Si
films with low thermal damage to substrate by melting and crystallizing Si films within
nanoseconds (16). However, the high density of Si films crystallized by ELA results in large

9Chapter 1: Introduction

variation of TFTs characteristics. In addition, the application of ELA to large area processing
leads to difficulties in reducing the process cost due to high initial investment and operating
costs.
The content of this section is summarized in Table 1.
Table 1. The summary of properties of some conventional bottom gate TFTs channelmaterials.
Material
a-Si:H-

Properties
Large scale production of AMLCDs-

μFE < 1 cm2/Vs, not suitable for faster switching circuit.

Amorphous transparent oxide-

Better overall performance than a-Si:H(especially a-InGaZnO)-

μFE only around 10 cm2/Vs, ES bottom gate architecture

is preferred, therefore it not good for mass production.
Poly-Si-

Direct deposition (LPCVD): μFE = 5 ~ 7 cm2/Vs but

crystallized film has columnar structure.
-

Advance process as excimer laser annealing, μFE > 100

cm2/Vs, large grain size. However, the devices show nonuniformity and have difficulty in large area application
because of high initial investment and operating costs.
-

Solid phase crystallization using precursor a-Si film:

μFE ~ 20 cm2/Vs, devices show good uniformity, easy forlarge area application but long thermal cycle is limited its
application in technology.

1.1.3. Published researches on mechanism of solid phase crystallization(20)Completed research on the kinetics of SPC based on classical nucleation theory has been
carried out since the 70s of the last decade (17-21). These publications only focused on the low
crystallization temperature region of a-Si, from 550 to 700 oC (22-25). Hong et al. studied the
kinetics of SPC by annealing a-Si films in a tube furnace when the temperature changed from10

Chapter 1: Introduction

560 to 1000 °C (26). Because of the heating-rate-limitation of the conventional method, they did
not give the evidence for SPC crystallization at temperatures higher than 800 oC.
In this section the classical theory of solid-phase nucleation and growth in a
homogeneous amorphous material is reviewed. The activation energies associated withtransient time, nucleation rate, and growth velocity are found in relation to thermodynamic
parameters of the classical theory.
According to classical theory, micro-crystallites (containing only a few atoms) will
nucleate frequently. Because of a large surface-to-volume ratio, these tend to shrink. Fromthermodynamic considerations, however, a few will become large enough that further growthis energetically favorable. Growth in the microcrystalline regime occurs by the same basic
mechanism as growth in the macrocrystalline regime: the rate at which each atom at an
amorphous-crystalline interface makes a transition between the amorphous state and the
crystalline state is a function of the energy levels of the two stages. Growths is energeticallyfavorable when the free energy of the system is lowered by the transition of an interface atomfrom the amorphous to the crystalline state. In the classical model of nucleation, the Gibbsfree-energy ΔG, the barrier energy an atom must pass across to transfer from amorphous phaseto crystalline phase, as a function of number of atoms in the cluster is given by:∆G= - ∆gv

4π
+σca ,
3a(1.1)

where Δgv is the difference of free energy between amorphous phase and crystal phase, σca is
the interfacial free energy at the crystal – amorphous interface, r is the cluster radius, and a isthe average atomic distance (0.27 nm). The maximum free energy, denoted as ΔG*, occurs ata critical grain radius of r*. The smaller clusters, with r < r*, tend to shrink, and the larger
clusters, with r > r*, tend to grow.

11

Chapter 1: Introduction

The forward reaction rate is the rate that a cluster grows from n to n + 1 atoms. The
reverse reaction rate is the rate that a cluster shrink from n + 1 to n atoms. These rates are foundby defining an unbiased atomic jump frequency ν at the amorphous phase, it can becharacterized by the activation energy of self-diffusion in amorphous silicon Ed. Because all
reaction rates are proportional to ν, Ed enters into the activation energies for transient time to(time before the onset of nucleation), steady-state nucleation rate rn, a characteristic
crystallization time tc (measured from to) and growth velocity vg.
In each case a characteristic time tt associated with transient nucleation was found to havethe same temperature dependence. By assuming that the free energy of formation is a weak
function of temperature, the form is
~ / ∗
where

∗

(1.2)

is the forward (or reverse) reaction rate at the critical cluster size. Kashchiev’s

theoretical results, which are in good agreement with experiment, indicate that to is proportional
to tt:(1.3)~ exp( )The linear temperature term in Eq. 1.3 contributes kT to Eto (defined here as the slope of to on
an Arrhenius plot.
=

(1.4)

−

The theorical temperature dependence of the steady state nucleation rate is~(1/ )

[−(

+∆

∗

(1.5)

]

)/

activation energy for nucleation rate is the absolute slope of rn on an Arrhenius plot.
The growth rate can be found from the net forward reaction rate for a large cluster.
Addition of one atom to a large cluster will not significantly change the surface energy. Thechange in free energy is – ΔG’.
~

[−(

−∆

/2)/

(1.6)

]
12

Chapter 1: Introduction

The Gibbs-free-energy difference between the amorphous and crystalline phases is
∆
where

=2

(1.7)

−

is the activation energy of the growth velocity.

A number of analyses of activation energies for to, rn, tc, vg of SPC Si film at low
temperature regime (500 – 700 °C) have been published(22-25). According to Iverson et al. (23) ,activation energy for transient time is 2.7± 0.15 eV. Activation energy for nucleation rate is
5.1 ± 0.15 eV following research of Iverson et al. (23); Zellama et al. (24) and Koster et al. (25)show an activation energy of 4.9 eV at 570 oC. The characteristic crystallization time is also
the function of temperature. The activation energy is 3.9 ± 0.25 eV from Iverson et al. (23), 3.1
eV from Blum and Feldman(22). This activation energy is not related to a particular
crystallization process, but rather, is the result of number of processes. The growth velocity
also depends on temperature. Iverson et al. (23) shows activation energy as 3.3 ± 0.35 eV. Also,
some data from several sources as 2.9 eV from Koster (25), 2.4-4.9 eV from Zellama et al. (24).
1.1.4. Micro thermal plasma jet irradiation
As we mentioned before, it is required a lower cost crystallization technique for large
area electronics. We previously proposed the application of an atmospheric-pressure direct
current (DC) arc discharge micro thermal plasma jet (μ-TPJ) to the millisecond crystallizationof a-Si films on quartz substrate (27). Figure 1.4 shows the experimental set up. The wolfram W
cathode and the water – cooled copper Cu anode separated 2 mm each other is connected to a
supplied power. Arc discharge was performed by supplying DC bias between electrodes withan argon Ar gas flow. The thermal plasma is blown out through an orifice with diameter ϕ as
600μm. The substrate was moved linearly by a motion stage with a scanning speed v.

13

Chapter 1: Introduction

Fig. 1.4. Schematic of μ-TPJ experimental set-up.
The crystallized Si films formed by μ-TPJ shows good quality. The crystalline volume
fraction Rc estimated from Raman spectra reaches 100 % in case of recrystallized from liquid
phase and 70% in case of solid phase crystallization (28).
Surface morphologies were observed by atomic force microscopy (AFM) (29). The typicalgrain size and root mean square (RMS) were ~ 20 and 0.5 nm, respectively, are obtained when
Si films crystallized in SPC. In contrast, the melting and solidification that occurred in the Si
film resulted in large grains 300 – 600 nm in size. This crystallization was called “liquid phasecrystallization (LPC)” in a previous study (29) because it was induced via a liquid phase. The
grain size in LPC is close to that of Si films formed by ELA.
1.1.5. Direct observation of phase transformation
We introduced a new in situ observation technique of phase transformation using highspeed camera (HSC) with a microsecond time resolution (30). The substrate was linearly moved
by a motion stage in front of the μ-TPJ with a scanning speed v changing from 500 to 2500
14

Chapter 1: Introduction

mm/s. The distance between the plasma source and substrate (d) was varied from 1.0 to 1.5
mm. For the in-situ observation of grain growth of a-Si film during μ-TPJ irradiation, an optical
microscope and a HSC was set on the motion stage on the backside of the substrate. The frame
rate ( Rf ) was varied from 3000 to 1650000 frames per second (fps) (30).
Phase transformation of the Si film induced by μ-TPJ irradiation was very clearlyobserved. Figure 1.5 shows the HSC snapshots during μ-TPJ irradiation under conditions of fAr= 1.6 L/min, P = 1.12 kW, v = 1500 mm/s, d = 1.0 mm, ES = 2.0 mm.

Fig.1.5. HSC snapshots of Si film taken by HSC during μ-TPJ irradiation. μ-TPJ
conditions were fAr = 1.6 L/min, P = 1.12 kW, v = 1500 mm/s, d = 1.0 mm, ES = 2.0 mm.

15Chapter 1: Introduction

Since liquid Si shows very high reflectivity due to free carriers, which called the molten
region (MR). A SPC formed in front of the molten Si was clearly distinguished from
amorphous phase. Following the movement of MR, grains grew perpendicularly to a liquidsolid interface, called high speed lateral crystallization (HSLC). It should be noted that a region
showing a wave-like pattern exists between MR and SPC region. In previous research, it iscalled leading wave crystallization (LWC) because it exhibits a periodic and repeating structure
like waves (30).
Furthermore, a new crystallization mechanism named LWC was discovered. Grain
growth with a velocity measured as high as 4500 mm/s intermittently propagates into SPC
regions. As a result, LWC formed periodic and repeating-structure-like waves, and LWC-Si
films showed a very high crystalline volume fraction of 100%. The length of LWC increased
with the increase of thickness of Si film and scanning speed v. This result suggests that not
only heat conducted from μ-TPJ but also latent heat plays a very important role in LWC. The
growth mechanism in LWC is well understood on the basis of a model including the explosive
propagation of a thin liquid layer driven by released latent heat at the liquid-solid interface.
1.1.6. Contactless temperature measurement
By obtaining the transient reflectivity of quartz substrate during μ-TPJ irradiation, wedeveloped the method for measuring its temperature (31). The transient reflectivity wasmeasured by irradiating the quartz substrate with He-Ne laser (633 nm) or yttrium aluminum
garnet (YAG) laser (532 nm) from the backside of the substrate and detecting the reflected
light intensity using a photodiode through a band pass filter. Other route was used to investigate
the phase transformation of Si films. The oscillating transient reflectivity of He-Ne laser light
relates to sample temperature. The number of oscillations increases with decreasing v, whichsuggests that the increase in the number of oscillations reflects an increasing surface

16Chapter 1: Introduction

temperature. The transient reflectivity oscillates by the interface of the incident light reflected
multiple times between the top and bottom surfaces of the substrate. The oscillation was
reproduced in numerical simulation of heat diffusion and optical interference (31). The
simulation was based on a two-dimensional heat diffusion equation (32),
( , )

=

( , )

+

( , )

+

(1.8)

where x is the position along the plasma jet scanning direction, y is the depth from the substratesurface, T is the temperature, t is the time, κ, ρ and c are the thermal conductivity, the density
and the specific heat of the quartz substrate, respectively, and S is the thermal incidence. The
details of the analysis have been reported elsewhere (32). Using the analysis of transient changes
in optical reflectivity of quartz substrates, the temperature during TPJ process is measured
within 30K error. In this analysis, we can well reproduce the observed waveforms with doubleGaussian shapes of the TPJ profile. From the analysis of transient changes in optical reflectivityof quartz substrates exposing to the Ar TPJ, the maximum surface temperature and theannealing duration were evaluated under different annealing conditions. We have found thatmaximum surface temperature can be controlled in the range of 980 to 1780K with almost
constant annealing duration at ~ 3 ms by changing the Ar gas flow rate and distance between
the plasma source and the substrate d. This technique was also applied to Si wafers andconventional glass substrate (33,34).
1.2. Overview of thesis
1.2.1. Motivation and purpose
Bottom gate TFTs fabricated with SPC – Si films show high mobility as 20 cm²/Vs(35)and good uniformity. Hence, it is suitable for large area applications. However, theconventional methods for SPC film fabricating as LPCVD, PECVD or furnace need long17

Chapter 1: Introduction

thermal cycle which is main drawback when applying in industry. By using metal induced
crystallization, this annealing time is reduced, but the film is contaminant by metallic. Basedon experience to make SPC-Si film with good characteristics by μ-TPJ irradiation, we propose
millisecond SPC Si film formed by μ-TPJ is an alternative material for TFT’s channel.
Based on our knowledge, due to the limitations of conventional method, the millisecond
SPC Si films formed in at temperature around 1000 oC have not been studied in detail. In thisthesis, we will propose a new method for observing the phase transformation and temperature
SPC Si film formed in millisecond region by μ-TPJ at temperature around 1000 oC. The
characteristics of millisecond SPC Si film are investigated by optical microscopy, Raman
spectra, Hall effect measurement, atomic force microscopy (AFM), and high-resolution
transmittance electron microscopy (HRTEM). Then, bottom gate TFTs fabricated withmillisecond SPC film are prepared. Our target is TFTs mobility as high as 20 cm 2/Vs and small
variation in transfer characteristics.
1.2.2. Composition
My thesis consists of two main points. First is about mechanism of millisecond SPC Si
film annealed by μ-TPJ at high temperature. Second is characteristics of millisecond SPC Si
film and its application to bottom gate TFTs. Beside the background presented in chapter 1,
my research is presented in four chapters with title listed as below,
Chapter 2: Simultaneous Observation of Phase Transformation and Temperature of
Silicon Film during Millisecond Annealing
Chapter 3: Temperature Calculation and Growth Mechanism of Millisecond Solid Phase
Crystallization Silicon Film
Chapter 4: Characteristics of Millisecond Solid Phase Crystallization Phosphorous
Doped Silicon Films
18

Chapter 1: Introduction

Chapter 5: Application of Millisecond Solid Phase Crystallization Silicon Film for
Bottom-Gate Thin Film Transistors Fabrication
Content of chapter 2 and 3 mainly comes from Main Paper 1 and that of chapter 4 and 5comes from Main Paper 2.
In the last, some conclusions are presented.

19

Chapter 1: Introduction

References(1) A. Sharma, C. Madhu, and J. Singh: Int. J. Comput. Appl. 89 (2014) 36.
(2) S. D. Brotherton: Introduction to Thin Film Transistors, Physic and Technology of TFTs,
Springer International Publishing Switzerland (2013).
(3) S. D. Brotherton: Semicond. Sci. Technol. 10 (1995) 721.
(4) Y. T. Yang, T. K. Won, S. Y. Choi, T. Takehara, Y. Nishimura, J. M. White: IEEE J. Disp.
Tech. 3 (4) (2007) 386.
(5) A. J. Flewitt, W. I. Milne: a-Si:H TFT thin film and substrate materials. In: Kuo Y (ed)Thin film transistors, materials and processes, Vol. 1. Amorphous silicon thin film transistors.
Kluwer Academic Publishers, Norwell, Massachusetts, (2004).
(6) D. B. Meakin, A. P. Coxon, P. Migliorato, J. Stoemenos, and A. N. Ecconomou: Appl.
Phys. Lett. 50 (1987) 1894.
(7) M. J. Powell: IEEE Trans. ED 36 (1989) 2753.
(8) Y.G. Mo, M. Kim, C. K. Kang, J. H. Jeong, Y. S. Park, C. G. Choi, H. D. Kim, and S. S.
Kim: J SID 19 (2011) 16.
(9) M. Ito, C. Miyazaki, M. Ishizaki, M. Kon, N. Ikeda, T. Okubo, R. Matsubara, K. Hatta, Y.
Ugajin, and N. Sekine: J Non-Cryst. Solids 354 (2008) 2777.
(10) M. Mitani, T. Endo, Y. Taniguchi, T. Katou, S. Shimoto, T. Ohno, S. Tsuboi, T. Okada,K. Azuma, G. Kawachi, M. Matsumura: Jpn. J. Appl. Phys. 47 (2008) 8707.
(11) S. D. Brotherton, J. R. Ayres, and N. D. Young: Solid State Electron. 34 (1991) 671.
(12) A. Mimura, N. Konishi, K. Ono, J.I. Ohwada, Y. Hosokawa, Y.A. Ono, T. Suzuki, K.
Miyata, and H. Kawakami: IEEE Trans. 36 (1989) 351.
(13) C.P. Lin, Y.H. Hsiao, and B.Y. Tsui: IEEE Trans. Electron Devices 53 (2006) 3086.
(14) C.C. Tsai, H.H. Chen, B.T. Chen, and H.C. Cheng: IEEE Electron Device Lett. 28 (2007)
599.

20

Chapter 1: Introduction(15) M. Wong, Z. Jin, G.A. Bhat, P.C. Wong, and H.S. Kwok: IEEE Trans. Electron Devices
47 (2000) 1061.
(16) K. Sera, F. Okumura, H. Uchida, S. Itoh, S. Kaneko, and K. Hotta: IEEE Trans. Electron
Devices 36 (1989) 2868.
(17) G. L. Olson: Symposium A – Energy Beam – Solid Interactions and Transient Thermal
Processing 35 (1984) 25.
(18) R. Bisaro, J. Magario, K. Zellama, S. Squelard, P. Germain, and J. F. Morhange: Phys.
Rev. B 31 (1985) 3568.
(19) L. Haji, P. Joubert, M. Guendouz, N. Duhamel, and B. Loisel: Symposium R – Phasetransformation kinetics in thin films 230 (1991) 177.
(20) T. Sontheimer, C. Becker, U. Bloeck, S. Gall, and B. Rech: Appl. Phys. Lett. 95 (2009)
101902.
(21) R. Bisaro, J. Magarino, Y. Pastol, P. Germain, and K. Zellama: Phys. Rev. B 40 (1989)
7655.
(22) N. A. Blum and C. Feldmann: J. Non-Cryst. Solids 11 (1972) 242.
(23) R. B. Iverson and R. Reif: J. Appl. Phys. 62 (1978) 1875.
(24) K. Zellama, P. Germain, S. Squelard, J. C. Bourgoin, and P. A. Thomas: J. Appl. Phys. 50(1979) 6995.
(25) U. Koster: phys. stat. sol. 48 (1978) 313.
(26) W.E.Hong and J.S.Ro: J. Appl. Phys. 114 (2013) 073511.
(27) H. Kaku, S.Higashi, H. Taniguchi, H. Murakami, and A. Miyazaki: Appl. Surf. Sci. 244(2005) 8.
(28) S. Hayashi, Y. Fujita, T. Kamikura, K. Sakaike, M. Akazawa, M. Ikeda, and S. Higashi:
Jpn. J. Appl. Phys. 52 (2013) 05EE02.

21

Chapter 1: Introduction(29) S. Higashi, H. Kaku, H. Taniguchi, H. Murakami, and S. Miyazaki: Thin Solid Films 487(2005) 122.
(30) S. Hayashi, Y. Fujita, T. Kamikura, K. Sakaike, M. Akazawa, M. Ikeda, H. Hanafusa, S.
Higashi: Appl. Phys. Lett. 101 (2012) 172111.
(31) T. Okada, S. Higashi, H. Kaku, N. Koba, H. Murakami, and S. Miyazaki: Thin Solid Films
515 (2007) 4897.
(32) T. Okada, S. Higashi, H. Kaku, N. Koba, H. Murakami, and S. Miyazaki, Jpn. J. Appl.
Phys. 45 (2006) 4355.
(33) H. Furukawa, S. Higashi, T. Okada, H. Kaku, H. Murakami, and S. Miyazaki: Jpn. J. Appl.
Phys. 47 (2008) 2460.
(34) K. Tanaka, S. Hayashi, S. Morisaki, and S. Higashi: Jpn. J. Appl. Phys. 54 (2015) 01AE05.
(35) M. K. Hatalis and D. W. Greve: J. Appl. Phys. 63 (1988) 2260.

22

Chapter 2: Simultaneous Observation of the Phase Transformation and Temperature of Silicon Film during
Millisecond Annealing

Chapter 2
Simultaneous

Observation

of

the

Phase

Transformation and Temperature of Silicon
Film during Millisecond Annealing23

Chapter 2: Simultaneous Observation of the Phase Transformation and Temperature of Silicon Film during
Millisecond Annealing

2.1. Principle of measurement
The temperature dependence of the optical properties of solids has been the focus ofmany studies(1, 2).
As known, the refractive index n of material depends on temperature, called thermooptic-coefficient (TOC), in details:
=

+

=

=

×

(2.1)

(2.2)

When a light comes through interface between two media, the reflectivity appears withthe reflectivity coefficient r depends on refractive index n as following equation:
=

−
+

(2.3)

with n1, n2 are the refractive index of media when the light come in and come out, respectively.
It is cleared that the changing in reflectivity depends on temperature of sample. Hence, by
obtaining the transient reflectivity of Si film during μ-TPJ irradiation, the transient temperature
can be extract by applying inference phenomena inside the thin film.
Based on our experienced, an idea for direct observation phase transformation andtemperature of Si film at high temperature simultaneously is supposed. A laser light isintroduced to objective lens of HSC and focuses on the a-Si films surface during μ-TPJ
annealing. The Fig. 2.1 shows the illustration of optical path inside the sample.

24

Chapter 2: Simultaneous Observation of the Phase Transformation and Temperature of Silicon Film during
Millisecond Annealing

Fig. 2.1. Illustration of optical path inside the thin film
The interference phenomenon inside quartz substrate is neglected. The reflectivity whichcomes from interference of multiply reflected light at the top and the bottom surfaces of a-Si
film is collected by an oscilloscope. From the reflected signal during annealing and TOC of aSi film, we can extract the temperature. In this chapter, we present the phase transformationand transient reflectivity of Si film during μ-TPJ irradiation. The temperature extracted fromreflectivity is presented in Chapter 3.
2.2. Experimental procedure
150-nm-thick a-Si films were deposited on 525-μm-thick quartz substrate by PECVD
using SiH4 and H2 at 250 oC. Dehydrogenation was performed by N2 annealing at 450 oC for 1
h. Before the μ-TPJ annealing experiments, the samples were cleaned simply by acetone for10 minutes to remove inorganic contaminants on the sample surface. Figure 2.2 shows theschematic diagram of the experimental setup. The system is consisted of μ-TPJ to irradiate thesamples and HSC set on a motion stage which moved linearly with a sample in front of μ-TPJ
with v ranging from 350 to 2020 mm/s. The distance between two electrodes (ES) was 2.0 mm,
P was from 0.5 to 1.2 kW, fAr was 1.0 L/min, and d was 1.0 mm. The μ-TPJ was generated byblowing out the thermal plasma through an orifice with 600 μm in diameter. He-Ne laser light25

Chapter 2: Simultaneous Observation of the Phase Transformation and Temperature of Silicon Film during
Millisecond Annealing

with 632.8 nm in wavelength was introduced to the objective lens of HSC, focused on thesurface of a-Si film and located at the center of crystallization area. The changes in reflectivityℛ of the sample during μ-TPJ irradiation was detected by a photodiode connected with a fast
oscilloscope. Strong light from the μ-TPJ was cut off by a bandpass filter. In addition, a partof reflected light from top surface of Si film comes to CCD of HSC, the phase transformation
will be collected. By this method, we can observe the phase transformation and transient ℛ of
Si film during μ-TPJ irradiation simultaneously.

Fig. 2.2. Experimental setup for direct observation of phase transformation and non-contact
temperature measurement of Si films during μ-TPJ irradiation (3).

26

Chapter 2: Simultaneous Observation of the Phase Transformation and Temperature of Silicon Film during
Millisecond Annealing

2.3. Results and discussions
2.3.1. HSC snapshots and transient reflectivity of Si film during μ - TPJ irradiation
To have full sight of what happens with Si film during μ-TPJ irradiation, Fig. 2.3 shows(a) a typical example of HSC snapshots and (b) the transient ℛ of a-Si film when the film is
totally melted during μ-TPJ annealing under the conditions of P = 1.06 kW, d = 1.0 mm, fAr =1.0 L/min, and v = 1680 mm/s. The He-Ne laser spot can be seen in a bright spot which is about
20 μm in diameter in Fig. 2.3 (a). The phase transformation of a-Si film during annealing wasobserved comprehensively. The SPC was formed before the leading wave crystallization(LWC) (2) which part had a wave-like form. It is clearly different from SPC and a-Si. Molten
region (MR) went after the LWC. The part that has dendritic morphology following MR iscalled high-speed lateral crystallization (HSLC) (4). The transient ℛ waveform of a-Si film
during μ-TPJ irradiation taken simultaneously with Fig. 2.2 (a) is shown in Fig. 2.2 (b) andarrows (i) to (v) correspond to the HSC captures of Fig. 2.2 (a) (i) to (v). Before the onset of
SPC, ℛ of a-Si gradually increases during the annealing process ((i) to (ii)). It is related to thechanging of a-Si film temperature because the refractive index of a-Si depends on temperature,
called the thermal-optic coefficient (TOC). From (ii) to (iii), the decrease of ℛ relates to thephase transformation process from amorphous to crystalline. The trending between (iii) and(iv) relates to the appearance of LWC. A significant increase in ℛ was perceived after LWC,
the maximum ℛ reached around 70 % (at point (iv)). It comes from the free carrier generationin molten Si. When the laser spot touches the HSLC region (at point (v)), ℛ moves downward.
It relates to the solification of molten silicon.

27Chapter 2: Simultaneous Observation of the Phase Transformation and Temperature of Silicon Film during
Millisecond Annealing

(a)

(b)

Fig. 2.3. (a) HSC snapshots of 150-nm-thick Si film during μ-TPJ irradiation under conditionsof P = 1.06 kW, d = 1.0 mm, fAr= 1.0 L/min, and v = 1680 mm/s, respectively and (b)its transientℛ during μ-TPJ irradiation taken simultaneously with Fig. 2.3(a). (i) to (v) corresponds to the
HSC snapshots shown in (a) (3).

28

Chapter 2: Simultaneous Observation of the Phase Transformation and Temperature of Silicon Film during
Millisecond Annealing

Next, the millisecond SPC film is focused on. A typical example of transient ℛ
waveforms observed during μ-TPJ irradiation to a 150-nm-thick a-Si film under annealing
conditions of P = 0.61 kW, d = 1.0 mm, fAr = 1.0 L/min, and v = 500 mm/s is shown in Fig.2.4.
The points (i), (ii), and (iii) correspond to point (i), (ii), and (iii) of HSC snapshots in the inset.
Under this condition, a-Si film is crystallized in solid phase because we see no abrupt increasein ℛ due to melting.

Fig. 2.4. The transient ℛ of 150-nm-thick a-Si film observed during μ - TPJ irradiation (P =0.61 kW, fAr = 1.0 L/min, d = 1.0 mm, v = 500 mm/s) when SPC occurs (3).
As mentioned in Section 2.1, the increase in transient ℛ from (i) to (ii) is due to thechanging of refractive index, meaning as the changing in film temperature in amorphous phase.
Nucleation occurs at (ii) and phase transformation from amorphous to crystalline proceed until
29Chapter 2: Simultaneous Observation of the Phase Transformation and Temperature of Silicon Film during
Millisecond Annealing(iii). We can interpret the decrease in ℛ from (ii) to (iii) as the change in crystalline volume
fraction (Rc). Therefore, by obtaining the temperature variation of a-Si from (i) to (ii), we candetermine Tc. In addition, we can extract the transient variation of Rc from (ii) to (iii) and candetermine tc. It will be discussed in detail in Chapter 3.
2.3.2. Crystallinity
Micro-Raman spectroscopy analysis was performed to determine Rc of crystallized
silicon films. The Ar laser with wavelength as 514.5 nm was used for measurement. Figure 2.5
indicates the micro-Raman scattering spectra of μ-TPJ crystallized films under conditions of P
= 0.61 kW, d = 1.0 mm, fAr = 1.0 L/min, and v from 480 – 520 mm/s together with precursor
a-Si and single crystalline Si.
In our experiments, d was kept constant and v was changed 20 mm/s for SPC condition,
the heating rate is not too different between three Raman samples (1). Rc is extracted from
Raman spectra by using the equation shown as=++(2.4).

+

Here, Sc, Sm, and Sa are transverse optical (TO) phonon peak area of crystalline-Si (c-Si)(~ 520 cm-1), microcrystalline-Si (μc-Si) (~ 500 cm-1), and a-Si (~ 480 cm-1).
As can be seen in Fig. 2.5, when v = 520 mm/s, SPC–Si film shows a peak position of
514.8 cm-1, full width half maximum (FWHM) of 7.6 cm-1, and Rc of 65 %. When we decreased
v to 500 mm/s, SPC – Si film displays a peak at 515.3 cm-1, FWHM of 7.4 cm-1, and Rc of 82 %.
HSLC film formed under v at 480 mm/s shows a peak position of 515.4 cm-1, FWHM of 6.3
cm-1, and Rc of almost 100 %. The result is suitable with our previous publications (5,6). The cSi TO phonon peak of both crystallized Si shifted to lower wavenumber because of tensilestress, grain size, and the composition of crystalline and microcrystalline phase. By decreasingv, FWHM gradually decreased and the peak positions were close to that of single c-Si at 520
30

Chapter 2: Simultaneous Observation of the Phase Transformation and Temperature of Silicon Film during
Millisecond Annealing

cm-1. From these results, the crystallinity of millisecond SPC-Si film was improved by μ-TPJ
crystallization with slow v because of the low nucleation temperature Tc and larger grain size
as discussed in the following sections.

Fig. 2.5. Micro-Raman scattering spectra obtained from 150-nm-thick crystallized films
formed by different experiment conditions (3).
2.4. Summary
This work gives a new method to directly observe the phase transformation and measure
the transient ℛ of Si film during μ-TPJ irradiation simultaneously. The phase transformationof a-Si film during annealing was observed clearly. When film is melted, the millisecond SPC
comes before LWC, next is MR, and HLSC follows MR. In case of 150-nm-thick Si film, ℛ
31

Chapter 2: Simultaneous Observation of the Phase Transformation and Temperature of Silicon Film during
Millisecond Annealing

gradually increases before the onset of SPC. When phase transformation process from
amorphous to crystalline occurs, the decrease of ℛ is observed. The significant increase in ℛ
appeared when film was melted and recrystallized from liquid phase. Micro-Raman
spectroscopy analysis indicates the crystallinity of millisecond SPC films is higher than 65 %and it grows up with the decreasing of v.

32

Chapter 2: Simultaneous Observation of the Phase Transformation and Temperature of Silicon Film during
Millisecond Annealing

References(1) H. G. Dreehsen, C. Hartwich, J. H. Schaefer, and J. Uhlenbusch: J. Appl. Phys. 56 (1984),
238.
(2) O. Yavas, N. Do, A. C. Tam, P. T. Leung, W. P. Leung, H. K. Park, C. P. Grigoropoulos,
J. Boneberg, and P. Leiderer: Optics Letters 18 (1993) 540.
(3) H. T. K. Nguyen, H. Hanafusa, Y. Mizukawa, S. Hayashi, and S. Higashi: Mater. Sci.
Semicond. Process. 121 (2021) 105357.
(4) S. Hayashi, Y. Fujita, T. Kamikura, K. Sakaike, M. Akazawa, M. Ikeda, H. Hanafusa, and
S. Higashi, Appl. Phys. Lett. 101 (2012) 172111.
(5) A. H. M. Smets, D. C. Schram, and M. C. M. van de Sanden, J. Appl. Phys. 88 (2000)
6388.
(6) S. Hayashi, S. Higashi, H. Murakami, and S. Miyazaki, Appl. Phys. Express 3 (2010)
061401.

33

Chapter 3: Temperature Calculation and Growth Mechanism of Millisecond Solid Phase Crystallization Silicon
Film

Chapter 3
Temperature
Mechanism

CalculationofMillisecond

Crystallization Silicon Film

34

and
Solid

GrowthPhase

Chapter 3: Temperature Calculation and Growth Mechanism of Millisecond Solid Phase Crystallization SiliconFilm

3.1. Introduction
As we mentioned in Chapter 2, from the TOC of a-Si combined with transient reflectivity
obtained during μ-TPJ irradiation, the transient temperature will be calculated. Moreover,based the changing of transient reflectivity during phase transformation process, characteristic
crystallization time is found out. In this section, theory for calculation is introduced.
3.1.1. Optical interference
In addition, when a light passed an interface between two media, it is affected byreflectance and transmittance. The optical model is shown in Fig.3.1.

Fig. 3.1. Reflection and transmission phenomena when a light passed through two media.
The Fresnel’s equation for these phenomena as below was applied:-

Reflectivity coefficient
=

-

−
+

(3.1)

Transmittance coefficient35

Chapter 3: Temperature Calculation and Growth Mechanism of Millisecond Solid Phase Crystallization Silicon
Film

2
+

=

(3.2)

The phase difference 2δf between a reflection from interface 1 and a transmission fromthe film following reflection from interface 2 is represented by the following equation

2

=

4

(3.3)

This equation is based on Snell’s law and a simple geometrical consideration.
Considering the phase difference, amplitude reflectance and amplitude transmittance arecalculated from a summation of reflectance or transmittance.
Amplitude reflectance

=

+
1+

exp (−2 )exp (−2 )(3.4)

exp (−2 )exp (−2 )(3.5)

Amplitude transmittance

=

+
1+

By multiple with complex conjugation of amplitude reflectance and amplitudetransmittance, we can calculate the energy reflectance and energy transmittance as follow,
Energy reflectance

=1−

8
(

+

)(

+

)+4

+(

−

)(

−

) cos 2−)(−) cos 2

(3.6)

Energy transmittance

=

8
(

+

)(

+

)+4

+(

36

(3.7)

Chapter 3: Temperature Calculation and Growth Mechanism of Millisecond Solid Phase Crystallization SiliconFilm

In case of no absorptance, the total of energy reflectance and transmittance need to beequal 1.
When consider an absorptance, the complex refractive index of medium is:.

=−, with ni is the refractive index, ki is extinction coefficient. Fresnel coefficients in Equation(3.1) and (3.2) become:

=

−
+

(3.8)

=

2
+

(3.9)

3.1.2. The usage of time-resolved reflectivity in studies of random nucleation and growth
Because the indices of refraction of a-Si and c-Si are different, reflectivity measurement
can be used to detect to formation of crystalline material in an amorphous matrix, even in theabsence of epitaxy. In the present work, time-resolved reflectivity (TRR) was used to study the
random nucleation and solid phase growth of crystalline grains within amorphous films
deposited onto quartz. The measured reflectivity as a function of time was used to calculate thevolume fraction of crystallized material as a function of time. From this information, the kinetic
parameters governing random crystallization, such as crystallization time and activation energy
were determined. To extract the kinetics of random crystallization from the reflectivity data we
modelled the crystallizing films as a homogeneous mixture of amorphous and crystalline
material, and its index of refraction was treated as a linear combination of the amorphous andcrystalline indices. In a more accurate treatment, the polarizabilities rather than the indices ofrefraction would be treated as linear in the volume fraction, but for the purpose of extracting
crystallization times, it is not significant different between the two approaches.

37

Chapter 3: Temperature Calculation and Growth Mechanism of Millisecond Solid Phase Crystallization Silicon
Film

In this chapter, the TOC of our a-Si film is measured, from that we determine therelationship between the reflectivity and temperature. Combined with transient reflectivity of
Si films obtained during μ-TPJ irradiation in Chapter 2, we estimate the nucleation temperature
Tc and characteristic crystallization time tc. In the last part, we will suggest a simple theoricalmodel for explain mechanism of millisecond SPC formed at high temperature region.
3.2. TOC measurement experiment
We have measured the TOC of our a-Si films which used in experiments in Chapter 2.
Figure 3.2 shows the experimental set-up of TOC measurement.

Fig. 3.2. Schematic of TOC measurement experimental set-up.
A He-Ne laser with wavelength as 632.8 nm is used to irradiate sample and thetransmissivity T is measured. The chamber is evacuated to 1 Pa and the 1 x 1 cm2 a-Si film ( orquartz ) is heated gradually at 5 K/min by a plate heater while maintaining thermal equilibrium
and the transmissivity and sample temperature are measured at 0.25 s intervals. A 0.05-mmdiameter type-R thermal couple is used to avoid effects due to the heat capacity and conductionof the wire. The chamber windows are covered by aluminum heat shields to prevent a thermal

38

Chapter 3: Temperature Calculation and Growth Mechanism of Millisecond Solid Phase Crystallization Silicon
Filmradiation wave from the heater, and the TOC is extracted from the measured waveform of thetransmissivity (1). In this time of experiment, we performed measure the TOC of quartz substrate
and a-Si film deposited on the quartz substrate separately.
3.3. Results and discussion
3.3.1. TOC measurement
The measured T (T) value is converted to n (T) and k(T) by using the Fresnel formula
when considering the interference phenomena of quartz substrate and a-Si film. In thissimulation, we introduced the thermal expansion coefficient of a-Si and quartz as 3 x 10-6 and5 x 10-7 oC-1 (2, 3), respectively.
The T (T) and simulated optical model of quartz is shown in Fig.3.3 (a) and those of a-Si
deposited on a quartz substrate is shown in Fig.3.3 (b). The oscillation in Fig.3.3 (a) comesfrom the interference of multiply reflected light at the top and the bottom surfaces of quartz. In
Fig. 3.3 (b), the number of oscillation and amplitude of T are slightly changed, which is theeffect of TOC of quartz. By applying the optical interference equation as described in section
1, the refractive index of quartz and a-Si film is found as= 1.457 + 1.12 × 10

+ 0.7 × 10

+ 21 × 10

×(3.10)(3.11)= 4.19 + 7 × 10

We extracted the TOC of a-Si as dn⁄dT =7×10-4 ℃-1 . This value is suitable with the
publication of Smets et al. (4).
According to Hong et al., when the annealing time comes to around 800 oC, a-Si films
crystallize in less than 1 s (5). It is impossible to measure the TOC at a temperature higher than
800 oC by the present method. Therefore, we estimated TOC of a-Si film at high-temperatureby extrapolating the measured value at the low-temperature regime.

39

Chapter 3: Temperature Calculation and Growth Mechanism of Millisecond Solid Phase Crystallization Silicon
Film(a) Quartz(b) a-Si deposited on quartz

Fig. 3.3. The transient T of quartz (a) and a-Si films deposited on quartz substrate (b) withrespect to the sample temperature (6).
Based on the TOC, we calculated the reflectivity as a function of temperature ℛ( ) for
150-nm-thick a-Si film as shown in Fig.3.4.
40

Chapter 3: Temperature Calculation and Growth Mechanism of Millisecond Solid Phase Crystallization Silicon
FilmFig. 3.4. ℛ of 150-nm-a-Si/quartz sample as a function of temperature calculated based oninterference phenomena inside the a-Si film. The inset shows the optical model of calculation(6).
Because the laser light is focused on the surface of a-Si film deposited on quartz substratein the in-situ measurement (see Fig. 2.2), we only consider the multiple reflection andinterference inside the a-Si film. The interference effect in quartz substrate can be neglected.
The optical model to calculate ℛ ( )of a-Si films is shown in inset figure of Fig. 3.4. Since
thickness of a-Si film is very thin, we obtain only a small portion of the oscillation in Fig. 3.4.
ℛ( ) follows the equation as below:ℛ(T)=9.26 − 2.15 ×10-3 ×T +10-4 ×T2 − 10-7 ×T3 +4×10-4 ×T4
41(3.12),

Chapter 3: Temperature Calculation and Growth Mechanism of Millisecond Solid Phase Crystallization Silicon
Filmwhere T is expressed in degree Celsius and ℛ is in percentage.
3.3.2. Estimation of nucleation temperature
Equation 3.12 combined with the transient ℛ as a function of time from Fig. 2.3 (i) to (ii)gives us the dependence of a-Si film temperature on time.
Figure 3.5 shows the transient variation of ℛ and temperature of a-Si before the onset of
SPC deducted from Fig. 2.4 (i) to (ii). The μ-TPJ conditions were P = 0.61 kW, fAr = 1.0 L/min,d = 1.0 mm, and v = 500 mm/s. From this result, we can estimate the Tc to be 991 °C. The time
for temperature increases from room temperature to Tc was 1.708 ms, namely, the average Rh
was 5.66×105 K/s. As mentioned above, the laser spot size is 20 μm, the distribution oftemperature inside the laser spot can be neglected.

Fig.3.5. Transient variation of temperature and the transient ℛ of a-Si film depend on heatingtime before the onset of SPC deducted from Fig. 2.4 (i) to (ii). The μ-TPJ conditions were P =0.61 kW, fAr = 1.0 L/min, d = 1.0 mm, and v = 500 mm/s (6).

42

Chapter 3: Temperature Calculation and Growth Mechanism of Millisecond Solid Phase Crystallization SiliconFilm

We applied the present temperature analysis method to millisecond SPC samples
crystallized at different v and P, the dependence of Tc on Rh are summarized in Fig. 3.6.
(a)

(b)

Fig.3.6. (a) the transient variation of a-Si temperature measured under different v and P
depends on heating time, ■ marks indicate the Tc, (b) dependence of Tc on Rh (6).
43

Chapter 3: Temperature Calculation and Growth Mechanism of Millisecond Solid Phase Crystallization Silicon
Film

The Fig. 3.6 (a) shows the transient variation of a-Si temperature measured under v from
350 to 2020 mm/s. It is clearly seen that the Tc increases from 985 to 1071 oC with thedecreasing heating time from 2.155 to 0.458 ms. In other words, the Rh increases from
4.45×105 to 2.28×106 K/s. For our knowledge, this is the first experiment result reporting thetemperature of nucleation in millisecond annealing.
As we know, SPC of a-Si involves two distinct processes, namely the nucleation of seeds(formation of clusters of crystalline silicon) and their growth to polycrystalline films (7).
According to classical nucleation theory, only seed nuclei increase to critical sizes can transfer
to polycrystalline, other nuclei come back to amorphous phase. The time for nuclei gets criticalsizes called incubation time. The incubation time reduces with the increase of heating rate.
As reported in other publications, the concentration of hydrogen also effects on
crystallization process (8). Budini et al. (8) claimed that a higher hydrogen concentration leads
to a faster crystallization. The presence of Si-Hn bonds leads to the production of atomic H
during the SPC process. The interaction between H and Si-H bonds gives as a result minusculecrystallites in a very high density which prevent grains to grow to a considerable size, resulting
in a nanocrystalline material with grain sizes in the rage of 24 - 28 nm(8). In our experiments,
a-Si films were prepared by using PECVD with SiH4 and H2 at 250 oC, then dehydrogenation
was carried out in N2 ambient at 450 oC in 1 hour. According to Budini et al.(8), after
dehydrogenation process, hydrogen concentration in samples is lower than 5 %. However, thefurther research about the influence of hydrogen concentration on crystallization process athigh temperature is not carried out in this thesis.

44

Chapter 3: Temperature Calculation and Growth Mechanism of Millisecond Solid Phase Crystallization SiliconFilm

3.3.3. Characteristic crystallization time
Characteristic crystallization time tc is the time required to crystallized 67 % volume ofsample.
In Fig. 2.3, the transient ℛ from point (ii) to (iii) reflects the phase transformation of
amorphous to crystalline. We consider the film as a homogeneous optical medium with an
optical constant equal to a linear combination between amorphous and crystalline Si values (9).
We assumed that at point (ii), the total volume is in an amorphous state, at point (iii) all thevolume is transferred to polycrystalline. Based on the above assumption, the measured ℛ canbe converted into volume fraction of crystalline. Figure 3.7 (a) and (b) show examples of ℛ
and Rc as functions of time during phase transformation when SPC film was formed by μ-TPJ
irradiation under v at 500 mm/s and 800 mm/s, respectively. From these figures, we can findthe tc as 60 and 36 μs when v as 500 and 800 mm/s, respectively.

45

Chapter 3: Temperature Calculation and Growth Mechanism of Millisecond Solid Phase Crystallization SiliconFilm(a) v = 500 mm/s(b) v = 800 mm/s

Fig. 3.7. ℛ and Rc as a function of time during phase transformation when the a-Si film wasannealed by μ-TPJ under v as 500 mm/s (a) and 800 mm/s (b), respectively. Solid lines showtransient ℛ shown in Fig. 2. 3 (ii) to (iii) and extracted crystalline volume fraction Rc. The
dotted line is the calculation data of Rc based on the proposed model in section 3.3.3 (6).
46

Chapter 3: Temperature Calculation and Growth Mechanism of Millisecond Solid Phase Crystallization Silicon
Film

The tc as a function of Tc, determined in the same way, is plotted in Fig. 3.8. The valueof tc decreases from 95 to 20 μs when the Tc increases from 985 to 1071 oC. It is extremely
shorter than that at 600oC. The activation energy E (solid line) is 2.9 eV. According to thedefinition of tc in classical nucleation theory, it is proportional with the product of nucleation
rate (rn) and growth velocity (vg) as tc ~ rn ×v2g

-1/3 (9). Therefore, the E found from Fig. 3.8

relates to both nucleation and crystal growth.
According to Iverson et al., at low temperatures regions the maximum free energy ΔG* for thecluster formation is 2.4 eV and activation energy for growth process is 3.3 eV (9). Therefore, athigh temperature region, the nucleation process with high nucleation frequency is a primaryprocess. As a result, the final grain size will be small.

Fig. 3.8. Characteristic crystallization time tc as a function of Tc. The solid line was fit to thedata of this work and corresponds to an activation energy of 2.9 eV (6).
47

Chapter 3: Temperature Calculation and Growth Mechanism of Millisecond Solid Phase Crystallization SiliconFilm

3.3.4. Grain size
HRTEM observation was performed to investigate the grain size of millisecond SPC
films. To perform HRTEM measurement, the area of 1.0 x 1.0 cm 2 was crystallized byoverlapping the scanning steps with a 50 μm pitch. Two samples with v as 500 and 800 mm/s
were prepared. Figure 3.9 (a) shows the HRTEM image of SPC films when v is 500 mm/s (Rh= 5.66 x 105 K/s) and Fig. 3.9 (b) show that of sample when v is 800 mm/s (Rh = 8.86 x 105
K/s).

From the HRTEM images, we can observe very small grains, however, it isdifficult to determine exactly the average value of grain size from these images. Whenv is 500 mm/s, a rough estimation of grain size distribution from 30 to 60 nm. When v
increases to 800 mm/s, the most of grain is smaller than 20 nm. It is clearly seen thatthe decrease in grain size is related to increasing of v.

48

Chapter 3: Temperature Calculation and Growth Mechanism of Millisecond Solid Phase Crystallization SiliconFilm(a) v = 500 mm/s(b) v = 800 mm/s

Fig. 3.9 HRTEM images of solid-phase crystallized a-Si films annealing by μ-TPJ at v of 500
mm/s (a) and 800 mm/s (b), respectively (6).
Figure 3.10 shows the selected area electron diffraction patterns for SPC film crystalized
at v of 500 mm/s (a) and precursor a-Si film (b).

49

Chapter 3: Temperature Calculation and Growth Mechanism of Millisecond Solid Phase Crystallization Silicon
FilmFig. 3.10. The selected area electron diffraction patterns for SPC film crystalized at v of 500
mm/s (a) and precursor a-Si film (b) (6).
We can confirm many bright spots in Fig. 3.10 (a) reflecting diffraction from eachcrystalline grain. Here we see no halo rings. This means the film is in crystalline at least froma microscopic viewpoint. Because the heat flow from μ-TPJ is the highest in a center part anddecreases when going to the edges of the crystallization area, there is a distribution of
crystallinity. Due to very small beam spot, HRTEM can concentrate on the sample surface
position which has the highest crystallinity. However, the Raman measurement with the laser
spot size as 10 μm, which is much larger than electron beam spot, the spectra reflect both thearea with low crystallinity and amorphous phase outside the 100-μm-crystallization area. Thisis reason why the Raman and HRTEM result indicate different crystallinity.
3.3.4. Growth mechanism
We suppose a simple physical model to estimate the crystal grain size based on theclassical nucleation theory. Iverson et al. (9) gave the equation showing the dependence of rn
on temperature T as rn =1037exp(-5.1 eV/kT) (events/cm3s), where k is Boltzmann constant. In
50Chapter 3: Temperature Calculation and Growth Mechanism of Millisecond Solid Phase Crystallization SiliconFilmaddition, vg as function of temperature was indicated by Zellama et al.

(11)

,

vg =1013 exp(-2.4 eV/kT) (nm/s). We assume that Rh will be constant during the phasetransformation process. The time for completed crystallization is divided into small fractions
with step Δt. At the to = 0 μs, the temperature of a-Si film reaches Tc (corresponds to Fig. 3.6),
no crystal inside the volume. After Δt μs, temperature increases, the number of nuclei N1
appears inside the volume and grows with velocity vg1, and the volume of a-Si reduces. After
2Δt μs, the temperature raises up, N2 nuclei additionally appear and grow with velocity vg2. In
addition, N1 nuclei in the previous time step continue to grow with the same velocity vg2. The
volume of a-Si keeps on reducing. This process will be continued until the crystal grains fillout the considering volume and no appearance of a-Si.
The volume of crystal (Vc) is calculated as follows
At t = to = 0: temperature To = Tc: before the onset of nucleation.
At t1 = to + Δt: temperature T1 = To + RhΔt: nucleation starts.
The length of crystal growth or grain size l10 = vg1Δt (nm).
During this time, the number of nuclei N1 in considering volume V is rn1VΔt (nuclei).
The Vc1 at t1 is
4
= π
2
3

3

N1

(3. 13).

At t2 = to + 2Δt: temperature T2 = To + 2RhΔt,
The length of crystal growth or grain size l20 is vg2Δt (nm).
The number of nuclei N2 in the rest of considering volume V is rn2(V – Vc1)Δt (nuclei).
N2 nuclei occupies a volume as
4
π
2
3

3

N2

(3. 14).

51

Chapter 3: Temperature Calculation and Growth Mechanism of Millisecond Solid Phase Crystallization SiliconFilm

In addition, N1 nuclei in the previous time step continue to grow with vg2 and reach thesize l11 =l01 +vg2×∆t.
The Vc2 is
3

4

= 3π

2

3

4

N2 + 3 π

2N1(3. 15).

.………
The crystalline volume is calculated as
Vc = Vcn =V(3. 16).

Finally, we have a distribution of grain size. The final grain size r is average of grain size
as following calculation
=

×

+

×
+

+
+

×
+ ⋯+
+⋯+

×

(3. 17),n-20with ln-1
1 , l2 ,…, ln is the grain size of N1 , N2 ,…,Nn nuclei at the final time step, respectively.

In addition,(3. 18).

=Figure 3.11 shows an illustration of this model.

Fig. 3.11. Physical model of grain size estimation (6).
52

Chapter 3: Temperature Calculation and Growth Mechanism of Millisecond Solid Phase Crystallization Silicon
Film

Based on the calculation, it is easy to obtain that Rc and r do not depend on the value ofconsidering volume. In our experiments, a-Si films thickness was 150 nm, the length ofcrystallization region is 1 cm and its width is 100 μm due to the size of sample and diameterof μ-TPJ orifice. Thus, we consider the 1.5 x 1014-nm3-volume of sample. First, when v as 500
mm/s (Rh = 5.66 x 105 K/s) is considered. The chosen Δt is 5 μs. Using the equation of Iverson
and Zellama, at t1 is 5 μs, N1 and l10 are 683 nuclei and 0.01 nm, respectively. However, at thistemperature, the critical radius of nuclei r* at a critical cluster size i* is

r* =

3

3×i*× 3 3 3 32 σ3ca 3=× π×a =0.63 (nm)4π
4π 3 ∆g3v(3.19)

with σca = 0.105 eV/atom [25], Δgv = 0.09 eV/atom (12-14). Therefore, l10 is much smaller thanr*. According to classical nucleation theory, the crystal with this size does not exist. Thus, theclassical model needs to be modified in our cases. In this study, we increase the pre-exponential
factors in rn and vg equation as rno = 3.3 x 1040 nuclei/(cm3s) and vgo = 4.2 x 1015 nm/s,
respectively. In addition, when the volume of the sample is filled with crystal, the velocity
growth will be decreased because of the collision between the crystals. Since we introduce thefactor (1 - Rc ) to vg equation to describe the reducing of velocity. The dots in Fig. 3.7 shows
the calculation results of Rc as a function of time when v is 500 mm/s (a) and 800 mm/s (b),respectively. The time step is 5 and 2 μs when v is 500 and 800 mm/s, respectively. These
values are the same as the sampling time of transient ℛ in two cases. As can be seen from thesefigures, the assuming vgo and rno give the best fitting between experimental and simulation data.
Moreover, these values are so sensitive. For example, if we keep the same value of Δt and rno,
only vgo is changed to 4.0 x 1015 or 4.5 x 1015 nm/s, the error increases significantly and thefitting to the experimental curve obviously degrades.

53

Chapter 3: Temperature Calculation and Growth Mechanism of Millisecond Solid Phase Crystallization Silicon
Film

From the theoretical calculation, when v is 500 mm/s (Rh = 5.66 x 105 K/s,) the grain size
varies from 3 nm to 36 nm, and r is 20 nm. In case v is 800 mm/s (Rh = 8.86 x 105 K/s), thegrain size varies from 1 nm to 20 nm, and r is 16 nm. The r decreases with the increase of Rh.
In our assumption, the Δt can be explained as incubation time because it is the time required
for the growing of nucleation, during Δt the nucleation is prohibited. When Rh increases, theΔt decreases. It is explained by the required time for nuclei growing decreases at hightemperature. This estimated r is fairly agreed with HRTEM observation shown in Fig.3.9.
3.4. Summary
Based on the transient reflectivity obtained in Chapter 2, we succeed in estimate the Tcof a-Si films and tc. When Rh increases from 4.45×105 to 2.28×106 K/s the Tc increases from
985 to 1071 o C. The small size of the laser spot, 20 μm, makes the results more confident. The
tc was pointed out by using the TRR method as the function of Tc corresponds to activationenergy 2.9 eV. A simple theorical model is suggested to explain the kinetics of millisecond
SPC film formed by μ-TPJ at high temperature. The calculated results from our model are quite
suitable with experimental results.

54

Chapter 3: Temperature Calculation and Growth Mechanism of Millisecond Solid Phase Crystallization Silicon
FilmReferences(1) A. Kameda, Y. Mizukawa, H. Hanafusa, and S. Higashi: J. Appl.Phys. 127 (2020) 203302.
(2) O. Yavas, N. Do, A. C. Tam, P. T. Lueng, W. P. Leung, H. K. Park, C. P. Grigoropoulos,
J. Boneberg, and P. Leiderer: Optics Letters 18 (1993) 540.
(3) N. Do, L. Klees, P. T. Lueng, F. Tong, W. P. Leung, and A. C. Tam: Appl. Phys. Lett. 60(1992) 2186.
(4) A.H.M. Smets, D. C. Schram, and M.C.M. van de Sanden: J. Appl. Phys. 88 (2000) 6388.
(5) W. E. Hong and J. S. Ro: J. Appl. Phys. 114 (2013) 073511.
(6) H. T. K. Nguyen, H. Hanafusa, Y. Mizukawa, S. Hayashi, and S. Higashi: Mater. Sci.
Semicond. Process. 121 (2021) 105357.
(7) K. Pangal, J. C. Sturm, S. Wagner, and T. H. Buyuklimanli: J. Appl. Phys. 85 (1999) 1900.
(8) N. Budini, P. A. Rinaldi, J. A. Schmidt, R. D. Arce, R. H. Buitrago: Thin Solid Films 518(2010) 5349.
(9) R. B. Iverson and R. Reif: J. Appl. Phys. 62 (1978) 1875.
(10) N. A. Blum and C. Feldmann: J. Non-Cryst. Solids 11 (1972) 242.
(11) K. Zellama, P. Germain, S. Squelard, J. C. Bourgoin, and P. A. Thomas: J. Appl. Phys. 50(1979) 6995.
(12) C. W. Ow-Yang and D. Spinner: J.Appl.Phys. 83 (1998) 145.
(13) E. P. Donovan, F. Spaepen, D. Turnbull, J. M. Poate and D. C. Jacobson: J. Appl. Phys.
57 (1985) 1795.
(14) E. P. Donovan, F. Spaepen, J. M. Poate, and D. C. Jacobson: Appl. Phys. Lett. 55 (1989)
1516.

55

Chapter 4: Characteristics of millisecond solid phase crystallization of phosphorous doped silicon films

Chapter 4
Characteristics of Millisecond Solid Phase
Crystallization of Phosphorous Doped Silicon
films

56

Chapter 4: Characteristics of millisecond solid phase crystallization of phosphorous doped silicon films

4.1. Introduction
In chapter 2 and 3, the mechanism of millisecond SPC film formed by μ-TPJ at hightemperature was investigated. Based on that, when films are annealed at high v, rn and vg are
high, it makes the smaller grain size. Therefore, we can control the grain size of the crystallized
films by controlling experimental conditions such as v. The average grain size of millisecond
SPC film is smaller than 50 nm (1).
A μ-TPJ annealing technique was applied to activate dopants for the source/drain (S/D)
region of TFTs (2). The crystallization and activation can be performed simultaneously by μTPJ irradiation to intrinsic Si films on heavy-doped S/D island. In previous studies(2), 60-nmthick phosphorous-doped a-Si films were prepared by PECVD using SiH4 and PH3 gases
diluted with H2. The doped a-Si films were annealed by μ-TPJ under different conditions. By
this method, the dopant activation efficiency achieved 82 % at a 1 % PH3 concentration of 31 %(2)

. It suggested that many phosphorous atoms with above the thermal equilibrium solid soluble

limit were activated by non-equilibrium phase transformation of Si film. The cooling rate after
annealing affected the carrier concentration accompanying with the activation rate (2). The
results indicate that TPJ millisecond annealing is very effective for activating dopants in S/Dregions of TFTs.
In this chapter, the characteristics of millisecond SPC of double layer structure as
phosphorous doped silicon (P-doped-Si) deposited on a-Si films induced by μ-TPJ will be
investigated.
4.2. Experimental procedure
In our research, sample structure is 30-nm-thick of a-Si film deposited on 30-nm-thickof phosphorous-doped a-Si film (a-Si/P-doped a-Si) deposited on 525-μm-thick quartz
substrate. After the wet chemical cleaning of quartz substrate, 30-nm-thick of P-doped a-Si was
57

Chapter 4: Characteristics of millisecond solid phase crystallization of phosphorous doped silicon films

deposited by using PECVD with SiH4, H2, and PH3 at a substrate temperature of 200 oC. Then,PECVD was performed once more to make 30-nm-thick non-doped a-Si film using SiH4 andH2 at a substrate temperature of 250 oC. After dehydrogenation in N2 ambient at 450oC for 1
hour, the samples were crystalized by μ-TPJ under different experimental conditions. The
illustration of experimental set-up for annealing samples is indicated in Fig. 4.1. The samples
were fixed in a motion stage which moved linearly in front of μ-TPJ. The P changed from 0.73
to 1.05 kW. The ES was 2.0 mm and the d was fixed at 1.0 mm. The fAr was 1.0 L/min. The
thermal plasma was blowing out through an orifice with the diameter (߶) of 600 μm. The
crystallized films were formed by overlapping the scanning steps with a 50 μm pitch. Then,the characteristics were investigated by optical microscopy, micro-Raman spectra, atomic force
microscopy (AFM), and Hall effect measurement.

Fig. 4.1. Illustration of experimental set-up for annealing samples by μ-TPJ (3). (Copyright(2021) The Japan Society of Applied Physics)

58

Chapter 4: Characteristics of millisecond solid phase crystallization of phosphorous doped silicon films

4.3. Results and discussion
4.3.1. Phase diagram
The phase diagram of μ-TPJ irradiated a-Si/P-doped a-Si film with respect to P and v isindicated in Fig. 4.2.

Fig. 4. 2. Phase diagram of μ-TPJ irradiated a-Si/P-doped a-Si films with respect to P and v (3).
(Copyright (2021) The Japan Society of Applied Physics)
As can be seen, with an increase in annealing temperature, namely increase P or
decreased v, the phase of the film changes in the order of amorphous, millisecond SPC, melt
and regrowth, and stripped. The millisecond SPC is always formed in between conditions ofamorphous and melt and regrowth. It is easily to obtain that each crystallized Si film was
independently formed by control of μ-TPJ irradiation conditions such as P and v. According to
Nguyen et al. (1), the millisecond SPC film formed under slow v gives us better quality of59

Chapter 4: Characteristics of millisecond solid phase crystallization of phosphorous doped silicon films

crystallinity and grain size. Therefore, in this research, we focused on crystallized film underconditions of μ-TPJ as P of 0.73 kW and v changed from 400 to 900 mm/s. Based on phase
diagram, when v as 400 mm/s, the film was melted. When condition of v changed from 500 to
900 mm/s, the crystalized film was formed by millisecond SPC. The films are a-Si when
crystallized under condition of v larger than 900 mm/s.
The optical microscopy images of crystallized film formed by conditions of v as 400 and
500 mm/s are shown in Fig. 4.3(a) and (b) respectively. We confirmed dendritic morphology,
which is frequently observed when the grain growth is induced by lateral movement of themolten region as show in Fig. 4.3(a) (4). In contrast, millisecond SPC film show no remarkable
morphology because of the small grain size as shown in Fig. 4.3(b).

Fig. 4. 3. Optical microscopy images of crystallized samples annealed by μ-TPJ irradiation
under v of (a) 400 mm/s and (b) 500 mm/s (3). (Copyright (2021) The Japan Society of Applied
Physics)

60

Chapter 4: Characteristics of millisecond solid phase crystallization of phosphorous doped silicon films

4.3.2. Surface roughness
AFM images of crystallized samples under the condition of v as 400, 500, and 600 mm/s
are indicated in Fig. 4.4 (a), (b), and (c), respectively. Root mean square (RMS) roughness was
obtained using 5x5μm2 scan window size. When v as 400 mm/s, film was melted, and the valueof RMS is 2.56 nm. When v = 500 and 600 mm/s, namely that millisecond SPC film wasformed, RMS values is largely decreased to 0.61 and 0.31 nm, respectively. The maximum
heights of the surface feature were 19, 5, and 3 nm when condition of v as 400, 500, and 600
mm/s, respectively. It can be easily to obtain, millisecond SPC samples surface reduces morethan 76 % roughness compared to the case of melted sample. The evolution of the surface
morphology of thin film can show scaling characteristics that are directly related to the growth
processes occurring during film growth. When v is 400 mm/s, film is melted and recrystallized
from liquid phase. A long grain growth was caused by a strong lateral temperature gradient of
the molten region. Therefore, the sample surface is rough. As mentioned before, the increaseof v makes the increase of nucleation temperature. For that reason, the final grain size of
crystallized films induced at high v is smaller and surface is smoother. As reported in ourprevious work (1), in case of v = 500 mm/s, the grain size distribution was from 30 to 60 nm.

Fig. 4.4. Atomic force microscopy results of crystallized samples under the conditions of v as(a) 400 mm/s, (b) 500 mm/s, and (c) 600 mm/s (3). (Copyright (2021) The Japan Society ofApplied Physics)
61

Chapter 4: Characteristics of millisecond solid phase crystallization of phosphorous doped silicon films

4.3.3. Crystallinity
The crystallinity of film is estimated from micro-Raman spectroscopy which was shownin Fig. 4.5. We used Ar laser with wavelength at 514.5 nm, laser power of 23 mW and laser
spot size of 10 μm. The melted film under v of 400 mm/s shows a peak position of 511.4 cm-1,
a FWHM of 8.87 cm-1, and Rc of 72 %. It is easily observed that the Raman peak intensity isdecrease, more asymmetric, and the width is larger with the increase of v. Therefore, the Rc
degrades with the increase of v. It is caused by millisecond SPC films composed of
microcrystalline grain with the typical size of ~ 20 nm (5, 6). However, when millisecond SPC
film formed under condition of v of 500 mm/s, Rc still reached up to 61% with peak positionof 511.7 cm-1 and FWHM of 9.14 cm-1. This result suggests that millisecond SPC film formed
at slow v have good crystalline quality. Comparing with conventional SPC at typicaltemperature as 630 oC, it takes 5 hours to make SPC film with crystalline fraction of 28% (7).
According to results in Chapter 3, the nucleation temperature of millisecond SPC films formedby μ - TPJ is very high as 1000 oC.

62

Chapter 4: Characteristics of millisecond solid phase crystallization of phosphorous doped silicon films

Fig. 4.5. Raman scattering spectra obtained from crystallized films formed by μ-TPJ under thedifferent conditions of v (3). (Copyright (2021) The Japan Society of Applied Physics)
As our knowledge, SPC Si films formed in millisecond annealing at high temperature
have not been studied in detail. Therefore, present study gives us a new insight that millisecond
SPC Si films formed at high temperature could have high crystallinity closer to that of Si films
formed by melting and solidification process. Millisecond SPC is a new approach and a new
finding that we can obtain fairly high crystallinity.
4.3.4. Hall effect measurement’s results
Resistivity, carrier concentration and carrier mobility were obtained from Hall effectmeasurement. Resistivity measurements confirm the high activation level of dopant element.
The evolution of the resistivity with v is shown in Fig. 4.6 (a).

63

Chapter 4: Characteristics of millisecond solid phase crystallization of phosphorous doped silicon films

Fig. 4.6. (a) resistivity (b) carrier concentration and carrier mobility of melted sample andmillisecond SPC samples obtained from Hall effect measurement. The μ-TPJ conditions wereP = 0.73 kW, fAr = 1.0 L/min, d = 1.0 mm, ES = 2.0 mm, v = 400 – 900 mm/s (3). (Copyright(2021) The Japan Society of Applied Physics)
The resistivity significantly increases with the increase of v. This behavior is caused by
the diffusion and subsequent activation of phosphorus atoms into silicon. However, it is easily
observed that there is not significant different in resistivity when crystallized films were formed
under melted condition with v at 400 mm/s and millisecond SPC condition with v at 500 mm/s.
The value of resistivity is 9.6 x 10-4 and 1.36 x 10-3 Ωcm when condition of v as 400 and 500
mm/s, respectively. These values are a little higher than resistivity of poly-Si film formed byother low temperature poly-silicon process. For instance, according to T. Noguchi (8), the lowest
resistivity of P-doped -Si film formed by excimer laser annealing with pulse energy density of
350 mJ/cm2 is 4.2 x 10-4 Ω.cm. In principle, these values are suitable for transistor fabrication.
Carrier concentration and carrier mobility are shown in Fig. 4.6 (b). Both increase with thedecrease of v. This behavior can be attributed to an increase in the solubility of phosphorous
into silicon and the increase in activation efficiency. The value of carrier concentration was
6.09 x 1020 cm-3 when v as 400 mm/s and 4.61 x 1018 cm-3 when v as 900 mm/s. In case of64

Chapter 4: Characteristics of millisecond solid phase crystallization of phosphorous doped silicon films

carrier mobility, it is 16.3 cm2/Vs when v as 400 mm/s, and comes to 1.15 cm 2/Vs when v as
900 mm/s. However, both of quantities is still high when millisecond SPC film was formed
under v as 500 mm/s, carrier concentration is also around 3.41 x 1020 cm3 and carrier mobility
is 12.2 cm2/Vs. Based on these results, the millisecond SPC film formed under v as 500 mm/s
is potential material for small grain poly-Si TFTs.
4.4. Summary
We succeed in activation doped element in millisecond SPC film by μ - TPJ. The
crystallized films formed under conditions closed with melted conditions shows high carrier
concentration as 3.41 x 1020 cm-3, high mobility as 12.2 cm2/Vs , low resistivity as 1.36 x 10-3
Ωcm , and high crystallinity as 60%. When the v increases, the characteristics of crystallized
films are worst.

65

Chapter 4: Characteristics of millisecond solid phase crystallization of phosphorous doped silicon films

References(1) H. T. K. Nguyen, H. Hanafusa, Y. Mizukawa, S. Hayashi, and S. Higashi: Mater. Sci.
Semicond. Process. 121 (2021) 105357.
(2) H. Kaku, S. Higashi, H. Furukawa, T. Okada, H. Murakami, and S. Miyazaki: Dig. Tech.
Pap. AM-FDP 07 (2007) 33.
(3) H. T. K. Nguyen, H. Hanafusa, R. Kawakita, S. Hayashi, and S. Higashi: Jpn. J. Appl.
Phys., In press. (DOI: https://doi.org/10.35848/1347-4065/ac18ac)(4) S. Hayashi, Y. Fujita, T. Kamimura, K. Sakaike, M. Akazawa, M. Ikeda, H. Hanafusa, and
S. Higashi: Appl. Phys. Lett. 101 (2012) 172111.
(5) S. Higashi, H. Kaku, H. Taniguchi, H. Murakami, and S. Miyazaki: Thin Solid Films 487(2005) 122.
(6) S. Higashi, K. Sugakawa, H. Kaku, T. Okada, and S. Miyazaki: Jpn. J. Appl. Phys. 49(2010) 03CA08.
(7) R. B. Iverson and R. Reif: J. Appl. Phys. 62 (1987) 1675.
(8) T. Noguchi: J. Inf. Disp. 11 (2010) 12.

66

Chapter 5:Application of Millisecond Solid Phase Crystallization Silicon Film for Bottom-Gate Thin Film
Transistors

Chapter 5
ApplicationofMillisecond

Solid

Phase

Crystallization Silicon Film for Bottom-GateThin Film Transistors

67

Chapter 5:Application of Millisecond Solid Phase Crystallization Silicon Film for Bottom-Gate Thin Film
Transistors

5.1. Introduction
Bottom-gate TFTs have attracted much attention because of their advantages in industry(1-5). As mentioned in Chapter 1, by using backside exposure of photoresist on the top of theplate, bottom gate acts as a mask to define the channel length (6,7). With this approach, it only
needs four masks which is the smallest mask number for TFTs fabrication process. Moreover,
it is possible to fabricate bottom-gate TFTs, without ion implantation, by sequentiallydepositing doped amorphous silicon (a-Si) and intrinsic a-Si and removing the doped a-Si fromthe channel region (8-10). Therefore, the product cost is reduced.
Based on our knowledge about millisecond SPC from previous chapters, in this chapter,the bottom-gate TFTs with millisecond SPC film as S/D and channel are fabricated. Our
objective is that μFE of devices is larger than 20 cm2/Vs and transfer characteristics show asmall variation.
5.2. Experimental procedure
N-type bottom-gate TFTs were fabricated using millisecond SPC Si film crystallized by
μ-TPJ irradiation by the procedure as shown in Fig. 5.1. 525-μm-thick quartz was used as thesubstrate. After RCA cleaning process, Mo film as gate was deposited by sputtering system.
Its thickness was 100 nm. The gate pattern was formed by photolithography and wet etchingby H3PO4 : HNO3 : CH3COOH : H2O solution. Next, 200-nm-thick SiO2 as an insulator layer
was formed by remote PECVD at 350 oC. Then, 30-nm-thick of P-doped a-Si was depositedby PECVD using SiH4, H2 and PH3 with substrate temperature as 200 oC. After back exposure
with gate as a mask, chemical dry etching (CDE) using CF 4 and O2 was done to remove Pdoped a-Si film in the channel path. An intrinsic a-Si film with thickness of 10 nm wasdeposited by PECVD with SiH4 and H2 at 250 oC. Photolithography and CDE were performed
to make channel patterns. After dehydrogenation in N2 ambient at 450 oC for 1 h, a-Si/P-doped
68Chapter 5:Application of Millisecond Solid Phase Crystallization Silicon Film for Bottom-Gate Thin Film
Transistors

a-Si was transferred to millisecond SPC by using μ-TPJ under conditions of P = 0.73 kW, fAr= 1.0 L/min, ES = 2.0 mm, d = 1.0 mm, and v from 400 to 900 mm/s. The electrodes of gate,
source, and drain were formed by Al evaporation and wet etching after opening the contact
holes.

Fig. 5.1 Bottom-gate TFTs fabrication process and structure diagram of transistors (11).
(Copyright (2021) The Japan Society of Applied Physics)

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Chapter 5:Application of Millisecond Solid Phase Crystallization Silicon Film for Bottom-Gate Thin Film
Transistors

5.3. Results and discussion
5.3.1. Cross-sectional image of bottom-gate TFTs
A cross sectional transmittance electron microscopy (TEM) of bottom gate TFT
fabricated with millisecond SPC formed under v as 500 mm/s is shown in Fig. 5.2 (a) and (b).
Figure 5.2 (a) shows the channel position and Fig. 5.2 (b) shows the S/D position as indicatedin Fig. 5.1. The upper Pt and C layers are for antistatic and surface protection of the sample
during TEM observation. According to TEM observation, the thickness of each layer is asfollowing: Mo layer as 132 nm, SiO2 layer as 210 nm, P-doped Si layer as 27.8 nm, and intrinsic
Si layer as 7.7 nm at source/drain position. As can be seen in Fig. 5.2(a), the Mo surface is notflat, therefore the roughness of SiO2 and millisecond SPC film is large. In the in-surface
direction of millisecond SPC film, the contrast caused by the diffraction of crystals such as
black and white part can be confirmed. There is no doubt that it is a crystalline Si film. Since
the film thickness is very thin, we suggest that the crystallinity in the depth direction in the
millisecond SPC film is very uniform. Due to very thin millisecond SPC - Si layer, it is very
difficult to observe the interface by TEM.

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Chapter 5:Application of Millisecond Solid Phase Crystallization Silicon Film for Bottom-Gate Thin Film
Transistors

Fig. 5.2. A cross sectional TEM image of (a) channel position and (b) source/drain position ofbottom gate TFT fabricated with millisecond SPC film formed under v of 500 mm/s (11).
(Copyright (2021) The Japan Society of Applied Physics)
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Chapter 5:Application of Millisecond Solid Phase Crystallization Silicon Film for Bottom-Gate Thin Film
Transistors

5.3.2. Transfer characteristics
Transfer characteristics, μFE, and output characteristics of bottom-gate TFT withdimension as L/W = 80/40 μm fabricated with millisecond SPC film are indicated in Fig. 5.3(a) and (b).
The millisecond SPC film was formed by μ-TPJ under v of 500 mm/s. The millisecond
SPC-Si TFTs show high μFE of 28 cm2/Vs, which is ~ 4 times higher than direct deposition
poly-Si by using LPCVD method(12,13). The mobility changes in inverse proportion to theimpurity concentration. In case of Hall effect measurement, millisecond SPC film formed
under v = 500 mm/s has high carrier concentration, around 10 20 cm-3. However, channel of
TFTs is intrinsic Si layer, the carrier concentration is small. Therefore, μFE is higher than carrier
mobility obtained from Hall effect measurement. The ratio between the on-state drain current(measured at a gate voltage of 35V) and the off-state drain current (minimum current) is definedas the on/off ratio. As can be seen in Fig. 5.3(a), the devices show the ratio of on/off current as
106, threshold voltage Vth were 14 V.

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Chapter 5:Application of Millisecond Solid Phase Crystallization Silicon Film for Bottom-Gate Thin Film
Transistors

(a)

(b)

Fig. 5.3. (a) transfer characteristic and field effect mobility and (b) output characteristic
obtained by bottom-gate TFTs fabricated with millisecond SPC film formed under v of 500
mm/s (11). (Copyright (2021) The Japan Society of Applied Physics)73

Chapter 5:Application of Millisecond Solid Phase Crystallization Silicon Film for Bottom-Gate Thin Film
Transistors

The characteristics of bottom-gate TFTs with millisecond SPC film as source-drain andchannel annealed by μ-TPJ under different experimental conditions are shown in Fig. 5.4 (a)and (b). Figure 5.4 (a) shows the transfer characteristics of 50 devices fabricated withmillisecond SPC film. The millisecond SPC films were formed under v as 500 mm/s, and TFT’s
dimension as L/W = 80/40 μm. The average μFE were 28.6 cm2/Vs and the average thresholdvoltage Vth were 13.5 V. As shown in Fig. 5.4 (a), there is small variation among devices. The
variations of μFE and Vth from the average value were 0.49 cm2/Vs and 0.57 V, respectively.
For these reasons, TFTs show good uniformity. It is the result of small grain size and randomorientation of millisecond SPC film. Figure 5.4 (b) show the Id - Vg curve of transistor withdimensions as L/W = 80/20 μm when the millisecond SPC formed under different condition ofv. The performance of devices is worst when v increases. The maximum value of on current
decreases 4 order in magnitude when v increases from 500 to 900 mm/s. This result is suitablewith electrical characteristics of crystallized films collected from Hall effect measurement
shown in Chapter 4. This result suggests millisecond SPC film formed close to melted
condition is a good candidate for small grain bottom-gate TFTs fabrication.

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Chapter 5:Application of Millisecond Solid Phase Crystallization Silicon Film for Bottom-Gate Thin Film
Transistors

(a)

(b)

Fig. 5.4. (a) Transfer characteristic of 50 TFTs fabricated with millisecond SPC film annealed
under v of 500 mm/s and (b) comparison of transfer characteristics of TFTs fabricated withmillisecond SPC film annealed under different value of v (11). (Copyright (2021) The Japan
Society of Applied Physics)
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Chapter 5:Application of Millisecond Solid Phase Crystallization Silicon Film for Bottom-Gate Thin Film
Transistors

In this time of fabrication, the TFTs fabricated at v = 400 mm/s did not work at all
although the device showed normal appearance. We do not know the reason why at thismoment. In future work, we will investigate the characteristic of bottom gate TFTs fabricatedwith melted film and compare with that of bottom gate TFTs fabricated with millisecond SPC
film.
5.4. Summary
We succeed in make bottom gate TFTs with millisecond SPC film as S/D and channel.
The devices fabricated with millisecond SPC film formed under conditions closed with melted
condition show good performance as on/off ratio as high as 106 , high mobility as 28 cm2/Vs
and small variation in transfer characteristics. The performance become worst when the v isfaster.

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Chapter 5:Application of Millisecond Solid Phase Crystallization Silicon Film for Bottom-Gate Thin Film
Transistors

References(1) Z. Xia, L. Lu, J. Li, H. S. Kwok, and M. Wong: IEEE Trans. Electron Devices 65 (2018)7.
(2) C. Y. Han, Y. X. Ma, W. M. Tang, X. L. Wang, and P. T. Lai: IEEE Electron Device Lett.
38 (2017) 6.
(3) H. J. Chae, K. Y. Song, and S. K. Joo: Thin Solid Films 661 (2018) 128.
(4) S. Jeon, J. Cho, and S. M. Cho: Mater. Sci. Semicond. Process. 121 (2021) 105417.
(5) K. Kandpal, N. Gupta, J. Singh, and C. Shekkar: Surf. Interfaces 23 (2021) 100996.
(6) J. Li, L. Lu, Z. Xia, H. S. Kwok, and M. Wong: IEEE Electron Device Lett. 39 (2017) 1.
(7) S. K. Lee, K. H. Seok, H. J. Chae, Y. H. Lee, J. S. Han, H. A. Jo, and S. K. Joo: Solid StateElectron. 129 (2017) 6.
(8) R. Sinha, P. Bhattacharya, S. Sambandan, and M. Shrivastava: J. Appl. Phys. 126 (2019)135706.
(9) R. E. I. Schropp, B. Stannowski, and J. K. Rath: J. Non-Cryst. Solids 299-302 (2002) 1304.
(10) H. N. Lee, H. J. Kim, and C. K. Kim: Jpn.J.Appl.Phys., 49 (2010) 020202.
(11) H. T. K. Nguyen, H. Hanafusa, R. Kawakita, S. Hayashi, and S. Higashi: Jpn. J. Appl.
Phys., In press. (DOI: https://doi.org/10.35848/1347-4065/ac18ac).
(12) S. D. Brotherton, J. R. Ayres, and N. D. Young: Solid State Electron. 34 (1991) 671.
(13) A. Mimura, N. Konishi, K. Ono, J. I. Ohwada, Y. Hosokawa, Y. A. Ono, T. Suzuki, K.
Miyata, and H. Kawakami: IEEE Trans. 36 (1989) 351.

77

CONCLUSION
The main objective of this research is investigation on the mechanism of millisecond
SPC Si films formed at high temperature region by using μ-TPJ. After that, the ability of using
it for bottom gate TFTs fabrication with high mobility as 20 cm2/Vs and small variation intransfer characteristics.
A new method to directly observe the transient reflectivity of a-Si film and the phasetransformation simultaneously during μ-TPJ irradiation is introduced. The SPC-Si film is
produced in millisecond region, calling millisecond SPC. Phase transformation is observed inreal time by using HSC which moved with sample during μ-TPJ irradiation. By introducing
the He-Ne laser to objective lens of HSC, we obtained the transient reflectivity of Si film during
μ-TPJ annealing. Raman spectra show high crystallinity as higher as 65%. HRTEM images
show the distribution of grain size. In general, it is smaller than 60 nm and decreases with theincrease of v.
In chapter 3, based on the interference phenomenon, the transient variation of Si film
temperature during μ-TPJ irradiation is investigated from obtained reflectivity in chapter 2.
The nucleation temperature is around 1000 oC, heating rate Rh is as high as 106 K/s. Bothincrease with the increase of scanning speed v. In addition, according to classical nuclear
theorical, we suggested a simple physical model to explain the growth mechanism of
millisecond SPC at high temperature region around 1000 oC. The results calculated from ourtheorical model are suitable with experimental results.
In chapter 4, phase diagram of μ-TPJ irradiated a-Si/P-doped a-Si films with respect tosupplied power P and v is shown. Optical microscopy shows the different morphology of
crystallization area when film is melted and millisecond SPC state. Characteristics of78

millisecond SPC film is investigated by Hall effect measurement, Raman spectra microscopy,
and atomic force microscopy. Millisecond SPC films formed at near melted condition showhigh crystallinity as 61%, low resistivity as 1.36 x 10 -3 Ωcm, high concentration carrier as
3.41 x 1020 cm-3, the carrier mobility as 12.2 cm2/Vs and smooth surface. So, we succeed in
dopants activation by μ-TPJ irradiation.
In chapter 5, we succeed in make bottom gate TFTs with millisecond SPC film as S/D
and channel. The devices fabricated with millisecond SPC film formed under conditions closedwith melted condition show good performance as on/off ratio as high as 106, high mobility as
28 cm2/Vs and small variation in transfer characteristics. The performance become worst whenthe v is faster.
Based on our achievements in this research, we can conclude that millisecond SPC films
formed by μ-TPJ are suitable for bottom-gate TFTs.

79

Publications and Awards
Academic papers
1. H.T.K. Nguyen, H. Hanafusa, Y. Mizukawa, S. Hayashi and S. Higashi: “Direct
Observation of Ultra-Rapid Solid Phase Crystallization of Amorphous Silicon Films Irradiatedby Micro-Thermal-Plasma-Jet”, Materials Science in Semiconductor Processing, 121 (2021)
105357-1 – 105357-9.
2. H.T.K. Nguyen, H. Hanafusa, R. Kawakita, S. Hayashi, T. Sato and S. Higashi:“Investigation on Chracteristics of Millisecond Solid Phase Crystallized Silicon FIlms
Annealed by Atmospheric Pressure DC Arc Discharge Micro-Thermal-Plasma-Jet and Their
Application to Bottom-Gate Thin Film Transistors Fabrication”, Japanese Journal of Applied
Physics, In press (DOI: https://doi.org/10.35848/1347-4065/ac18ac)

International Conference
1. H.T.K Nguyen, H. Hanafusa, R. Kawakita, K. Segawa, and S. Higashi: “Chracteristics
of Millisecond Solid Phase Crystallized Silicon Films Formed by Micro-Thermal-Plasma-Jet
and Their Application to Bottom-Gate Thin Film Transistors”, 2021 International Conference
on Solid State Devices and Materials (SSDM2021), (Online, Sept. 6-9, 2021), Peer-Reviewed,
Oral Presentation
2. H.T.K. Nguyen, H. Hanafusa, Y. Mizukawa, S. Hayashi and S. Higashi: “Characteristicof Rapidly Solid Phase Crystallized Amorphous Silicon Films Formed by Micro-TermalPlasma Jet Irradiation”, 2020 International Conference on Solid State Devices and Materials(SSDM2020), (Online, Sept.27-30, 2020) Peer-Reviewed, Oral Presentation.

80

Domestic Conference
1. H.T.K.Nguyen, H. Hanafusa, and S. Higashi: “Application of Millisecond Solid Phase
Crystallization of Silicon Films Induced by Micro-Thermal-Plasma-Jet to Bottom-Gate ThinFilm Transistors”, The 82nd JSAP Autumn Meeting 2021 23a-P06-3, Poster (2021.09.21-23,
Hybrid)2. H.T.K. Nguyen, H. Hanafusa, and S. Higashi: “Characteristics of Millisecond Solid
Phase Crystallization of Phosphorus Doped Silicon Film Annealed by Thermal-Plasma-Jet
Irradiation”, The 68th JSAP Spring Meeting 18p-Z24-7, Oral Presentation (2021.03.16-19,
Online)3. H.T.K. Nguyen, H. Hanafusa, Y. Mizukawa, S. Hayashi, and S. Higashi: “Investigation
on millisecond solid phase crystallization of amorphous silicon films induced by microthermal-plasma jet”, Silicon Device and Materials SDM 2020-18, Oral Presentation(2020.10.22, Online)
4. H.T.K. Nguyen, Y. Mizukawa, H. Hanafusa, and S. Higashi: “Investigation on Rapid
Solid Phase Crystallization of Amorphous Silicon Films Induced by Micro-Thermal-PlasmaJet”, The 81st JASP Autumn Meeting 10p-Z10-7, Oral Presentation (2020.9.8-11, Online)
5. H.T.K. Nguyen, Y. Mizukawa, H. Hanafusa, S. Higashi: “Investigation the Solid phase
Crystallization kinetics at the high-temperature region by annealing amorphous silicon using
micro-thermal-plasma jet”, The 67th JSAP Spring Meeting 15a-PB3-1, Oral Presentation(2020.3.12-15, Sophia University, Yotsuya Campus)
6. H.T.K. Nguyen, Y. Mizukawa, H. Hanafusa, S. Higashi: “ Direct Observation of Phase
Transformation and Transient Reflectivity of Amorphous Silicon Film During Micro-ThermalPlasma-Jet Irradiation”, The 80th JASP Autumn Meeting, 18p-C309-6, Oral Presentation81

(2019.9.18-21, Hokkaido University, Sapporo Campus)

Awards
1. Hiroshima University Excellent Student Scholarship in 202082

Acknowledgement
First and foremost, I would like to express my heartfelt gratitude to my supervisor,
Professor Seiichiro Higashi for his invaluable advice, continuous support, and patience during
my Ph.D. course. His immense knowledge and plentiful experience have encouraged me in all
the time of my academic research and daily life.
My sincere appreciation is extended to Associate Professor Hiroaki Hanafusa for giving
me his kind guidance. He always gave freely of his time to help me perform experiments aswell as discuss about my research. I have learned a lot from his vast knowledge and experience.
I also want to give many thanks to Prof. Akinobu Teramoto and Prof. Shin-Ichiro Kuroki for
their valuable comments to improve my thesis as well as my research.
I give special thanks to Dr. Yuri Mizukawa for her support and encouragement for bothmy studies and my life in Japan. She helped me whenever I had problems. The experiments
performed with her support are utmost important to my work in this thesis.
I owe many thanks to Dr. Shohei Hayashi, who assisted with the high-resolution
transmission electron microscopy observation. His measurement helped me expand myknowledge of crystalline mechanism. In addition, part of this work was supported by the
Research Institute for Nanodevice and Bio Systems (RNBS), Hiroshima University. I would
like to acknowledge the staffs of this outstanding facility.
From the bottom of my heart, I would like to say big thank you for all the members in
the Semiconductor Electronics Laboratory for their very kind assistant.
Last but not the least, I would like to give special thanks to my family for theiroutstanding, support and encouragement that always keep me going.
September 2021,
Hoa Thi Khanh Nguyen

83

බ⾲ㄽᩥ
㸦Articles㸧(1) Direct Observation of Ultra-Rapid Solid Phase Crystallization of Amorphous Silicon Films
Irradiated by Micro-Thermal-Plasma-Jet
H.T.K. Nguyen, H. Hanafusa, Y. Mizukawa, S. Hayashi and S. Higashi
Materials Science in Semiconductor Processing 121, 105357 (2021)(2) Investigation on Characteristics of Millisecond Solid Phase Crystallized Silicon Films Annealedby Atmospheric Pressure DC Arc Discharge Micro-Thermal-Plasma-Jet and Their Application to
Bottom-Gate Thin Film Transistors Fabrication
H.T.K. Nguyen, H. Hanafusa, R. Kawakita, S. Hayashi, T. Sato and S. Higashi
Japanese Journal of Applied Physics, In press

ཧ⪃ㄽᩥ㸦Thesis Supplements㸧
(1) Characteristics of Millisecond Solid Phase Crystallized Silicon Films Formed by MicroThermal-Plasma-Jet and Their Application to Bottom-Gate Thin Film Transistors.
H.T.K Nguyen, H. Hanafusa, R. Kawakita, K. Segawa, and S. Higashi
2021 International Conference on Solid State Devices and Materials, (Online, Sept. 6 – 9, 2021)
Peer-Reviewed, Oral Presentation.
(2) Characteristic of Rapidly Solid Phase Crystallized Amorphous Silicon Films Formed by MicroTermal-Plasma Jet Irradiation.
H.T.K. Nguyen, H. Hanafusa, Y. Mizukawa, S. Hayashi and S. Higashi
International Conference on Solid State Devices and Materials, (Online, Sept.27-30, 2020) PeerReviewed, Oral Presentation.