Masatoshi Wakagi

Change in crystalline morphologies of polycrystalline silicon films prepared by radio‐frequency plasma‐enhanced chemical vapor deposition using SiF4+H2 gas mixture at 350 °C

Polycrystalline silicon films have been deposited on glass substrates at 350 °C by radio‐frequency plasma‐enhanced chemical vapor deposition using a SiF4+H2 gas mixture. Crystalline fraction decreased abruptly with increasing gas flow ratio. Film structure drastically changed by increasing gas pressure from 0.4 to 2.0 Torr. At lower gas pressure, columnar crystals 30 nm in diameter grew from the glass substrates, while at higher gas pressure larger columnar crystals with a maximum diameter of approximately 100 nm grew on an amorphous Si layer approximately 170 nm thick.

Crystalline Fraction of Microcrystalline Silicon Films Prepared by Plasma-Enhanced Chemical Vapor Deposition Using Pulsed Silane Flow

Microcrystalline silicon (?c-Si) films have been prepared at 200?C by radio-frequency (rf: 13.56 MHz) plasma-enhanced chemical vapor deposition using pulsed silane flow. The crystalline fraction, Xc(Raman), of ?c-Si films approximately 200 nm thick is quantitatively determined by decomposing Raman spectra into three peaks: crystalline, intermediate (small-grain-size-crystalline), and amorphous. The effects of rf power on Xc(Raman) and hydrogen content, CH, have been studied. Xc(Raman) increases with increasing rf power and tends to saturate; the maximum value of Xc(Raman) is 71%. With increasing rf power CH decreases to a minimum value of 4.5% and then increases. Hydrogen introduction into Si films overlapped with hydrogen elimination is responsible for the increase and saturation of Xc(Raman) with rf power.

Ge K-Edge Extended X-Ray Absorption Fine Structure Study of the Local Structure of Amorphous GeTe and the Crystallization

The local structure and crystallization of amorphous GeTe (a-GeTe) were examined by means of Ge K-edge EXAFS. In a-GeTe, both Ge-Ge and Ge-Te bonds were observed to exist in nearest neighbors of Ge. The average coordination number around Ge is 3.7, which is close to the tetrahedral structure. A random covalent network (RCN) model seems to be suitable for the local Structure. After a-GeTe crystallizes at 129°C, the Ge-Ge bond disappears and the Ge-Te bond length increases considerably. As temperature rises, in a-GeTe the Debye-Waller factor of the Ge-Te bond increases greatly, while that of the Ge-Ge bond increases only slightly. At the crystallization, it is found that the fluctuation of the Ge-Te bond length plays a major role in the change of the local structure and bonding state around Ge.

Real time spectroscopic ellipsometry for characterization of the crystallization of amorphous silicon by thermal annealing

Abstract We have applied real time spectroscopic ellipsometry (RTSE) to characterize the formation of polycrystalline silicon (poly-Si) films by a rapid thermal annealing process at relatively low temperatures, ranging from 580 to 625°C. A gradual transition of the silicon films from amorphous to polycrystalline with annealing time at constant temperature was quantified by RTSE using the Bruggeman effective medium theory (EMT). Grain growth processes were studied by critical point (CP) analyses applied to the deduced poly-Si dielectric functions. The resulting CP broadening parameter provides information on the average grain size within the top∼0.3 μm of the film. The EMT and CP analyses suggest that crystallization occurs from isolated nuclei uniformly distributed within the film. RTSE analysis results for poly-Si formation at different temperatures, further provides information on the crystallization kinetics. We found that poly-Si having a somewhat larger grain size was generated at the lower crystallization rates obtained under lower annealing temperatures.

Effects of Back-Channel Etching on the Performance of a-Si:H Thin-Film Transistors

Thickness of the a-Si:H layer in the back-channel etched thin film transistor (TFT) was successfully reduced to less than 100 nm, with an accompanying increase in the field effect mobility. The thinning was realized by reducing surface defects of the a-Si:H layer generated in the back-channel overetching step. The relationships between the TFT performance and surface defects, analyzed by spectroscopic ellipsometry, were investigated as a function of a-Si:H thickness and back-channel etching depth.

46.3: A 2.2″ QVGA a-Si TFT LCD with High Reliability Integrated Gate Driver

A 2.2″ QVGA a-Si TFT-LCD with a novel integrated gate driver has been developed. High reliability is achieved by assigning pull-down and retention processes to two individual TFTs and by stabilizing the gate voltages of the pull-up TFTs. The developed LCD shows sufficient performance even at −35°C after a 5000hour operation test at 55°C.

Novel 3.3-kV advanced trench HiGT with low loss and low dv/dt noise

Novel 3.3-kV trench IGBT with low loss and low dv_AK/dt noise was developed. The structural feature of the IGBTs is deep p-WELL layers separated from trench gates. This structure suppresses excess V_GE overshoot and then reduces recovery dv_AK/dt. Moreover, this effect is enhanced by reducing the resistance of the deep p-WELL layers (R_FP). It was found that, for the first time, the trade-off characteristics between V_CEsat and recovery dv_AK/dt were drastically improved by separating p-WELL layers from trench gates and decreasing R_FP. The recovery dv_AK/dt could be reduced by 79% more than that for the conventional trench IGBT, maintaining a small V_CEsat and E_on equal to the conventional one.

Rapid heat treatment for spin coated ITO films by electron plasma annealing method

Abstract A method of Electron Plasma Annealing (EPA) is developed. The EPA method allows a lower substrate temperature to be used in spin-coating-type ITO film fabrication. Using the EPA method is expected to have beneficial sample surface heating and plasma treatment effects. The ITO films which are treated in an N 2 gas atmosphere by EPA exhibit lower resistivity and higher transmittance than ITO films fabricated with a thermal treatment at 550 °C. The ITO films obtained by N 2 EPA treatment also show higher density and purity, although they have finer grain compared to the thermal annealing films. These structural features should be the reason for the good electrical and optical characteristics of ITO films.

Nanocrystalline Silicon Film Prepared by Laser Annealing of Organosilicon Nanocluster.

A novel process for the formation of nanocrystalline silicon film using an organosilicon nanocluster as a precursor was developed. A thin-film coating of the organosilicon nanocluster, soluble in common organic solvents, is preheated and then annealed by an excimer laser to yield a film of nanocrystalline silicon with approximately 10 nm in size. The structural changes of the precursor film caused by preheating and excimer laser annealing were investigated by Raman spectroscopy.

Structural study of amorphous Ge using extended X-ray absorption fine structure

Extended X-ray absorption fine structure measurements were made on amorphous germanium, a-Ge, and hydrogenated amorphous germanium, a-Ge:H, both prepared at the substrate temperature of 50°C by sputtering. The first nearest neighbor distances of a-Ge and a-Ge:H are longer than that of crystalline germanium, c-Ge, by 0.016 A and 0.011 A, respectively. The Debye-Waller factor, Δ σ, and the third moment of the first nearest neighbor distribution, , were also determined. The relationships among the first nearest neighbor distance, Δ σ and are in agreement with theoretical results derived from thermodynamics. These results suggest the existence of states corresponding to several hundred degrees quenched in a-Ge and a-Ge:H. Furthermore, the state of a-Ge is estimated to be about one hundred degrees higher than that of a-Ge:H.