論文の要旨（Thesis Summary）
氏名 Hoa Thi Khanh Nguyen（Name）
論文題目
Investigation on the Mechanism of Millisecond Solid Phase Crystallization of Silicon Films Formedby Micro-Thermal-Plasma-Jet and Their Application to Bottom-Gate Thin Film Transistors（大気圧マイクロ熱プラズマジェット照射によるシリコン薄膜のミリ秒結晶化メカ
ニズムの解明とボトムゲート型薄膜トランジスタへの応用）
Bottom-gate thin film transistors (TFTs) have attracted much attention because of theiradvantages in industry. With only four masks for fabrication process, the production cost isreduced. Hydrogenated amorphous silicon (a-Si:H) TFTs are suitable for current sources, onpixel amplifier, and peripheral driver circuits. However, faster switching circuits are out of theirreach because of their low mobility as ~ 1 cm2/Vs and their insufficient hole mobility for pchannel operation. In addition, being a photoconductor, they have a large leakage current when
exposed to light. Polycrystalline silicon (poly-Si) is an alternative material for TFTs fabrication.
Small grain poly-Si films with smooth surface make good uniformity devices. Several ways havebeen examined for the formation of these TFTs such as direct deposition methods as well as
conversion using amorphous silicon (a-Si) film. The principal technique for the direct depositionof poly-Si is by low-pressure chemical vapor deposition (LPCVD). However, columnar structurewith typical grain size as 100 nm and low field effect mobility µFE of 5 ~7 cm2/Vs are main weak
points. The poly-Si film via solid phase crystallization (SPC) using precursor a-Si film increaseµFE comparing with columnar poly-Si film. This could be done by LPCVD at 550-600 oC, plasma
enhanced chemical vapor deposition PECVD at 350 oC, or furnace ambient at typical temperatureof 600 oC. However, a long thermal crystallization, up to tens of hours, is required to transfer
films to polycrystalline. Some techniques are introduced to reduces this cycle time such as theuse of higher temperatures in a rapid thermal annealing cycle and the use of metal induced
crystallization. However, large grain size formation and film contamination by either the metal
itself or the metal silicide are their issue.
For these issues, we have proposed a new crystallization technique for making SPC film in
millisecond region at high temperature, called “millisecond SPC”, using micro-thermal-plasmajet (µ-TPJ). It has a simple structure and high output energy. In this work, we attempted todirectly observe the phase transformation, to investigate the growth mechanism, thecharacteristics of millisecond SPC films induced by µ-TPJ as well as their abilities in bottom gate
TFTs fabrication.
My thesis consists of 5 chapters, which are listed below.

In chapter 1, the evolution of thin film transistor technology, the introduction of microthermal plasma jet irradiation, and the objective of this research are discussed.
In chapter 2, a new method to directly observe the transient reflectivity of a-Si film and thephase transformation simultaneously during µ-TPJ irradiation is presented. The SPC-Si film is
produced in millisecond region, calling millisecond SPC. Optical microscopy shows the different
morphology of crystallization area when film is melted and millisecond SPC state. Phasetransformation is observed in real time by using high speed camera (HSC) which moved withsample during µ-TPJ irradiation. By introducing the He-Ne laser to objective lens of HSC, weobtained the transient reflectivity of Si film during µ-TPJ annealing. (Main paper 1)
In chapter 3, based on the reflectance and transmittance phenomenon, the transient variationof Si film temperature during µ-TPJ irradiation is investigated from obtained reflectivity inchapter 2. The nucleation temperature is around 1000 oC, heating rate is as high as 106 K/s. Bothincrease with the increase of scanning speed v. In addition, according to classical nuclear
theorical, I suggested a simple physical model to explain the growth mechanism of millisecond
SPC at high temperature region around 1000 oC. (Main paper 1)
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. Based on that, characteristics of millisecond SPC film isinvestigated by Hall effect measurement, Raman spectra microscopy, and atomic force
microscopy. Millisecond SPC films formed at near melted condition show high 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. (Main paper 2)
In chapter 5, bottom gate TFTs fabricated with millisecond SPC film under different
conditions of µ-TPJ

are prepared. Electrical characteristics of devices are investigated toevaluate the ability of millisecond SPC in TFTs fabrication. The devices show high field effectmobility of 28 cm2/Vs and a small variation in transfer characteristic. (Main paper 2)
From the achievement of this research, millisecond SPC Si film is a good candidate for small
grain bottom-gate TFTs fabrication.