Xuanying Lin

Low temperature fast growth of nanocrystalline silicon films by rf-PECVD from SiH4/H2 gases: microstructural characterization

Hydrogenated nanocrystalline silicon thin films were deposited at a high rate of 0.8 nm s−1 by conventional (13.56 MHz) plasma enhanced chemical vapour deposition from SHi4/H2 gas mixture at a low temperature of 200 °C. The effects of hydrogen dilution, radio frequency power density, substrate temperature and deposition pressure on the crystalline volume fraction and the deposition rate of films were systematically investigated. The results show that the high hydrogen dilution and the substrate temperature are favourable for improving the crystallinity properties. The high deposition rate requires high power density over 0.7 W cm−2 in combination with high deposition pressure above several hundreds of Pa to overcome the degradation of film quality.

Growth mechanism of polycrystalline silicon films from hydrogen-diluted SiCl4 at low temperature

The growth process of polycrystalline silicon films fabricated at 200 °C by radio-frequency glow discharge plasma-enhanced chemical-vapor deposition technique from hydrogen-diluted SiCl4 has been investigated. We analyze the changes of crystallinity and crystalline grain size with the depth from the top surface of the film through studying the depth profiles of the Raman spectra. The results show that the top surface is composed of silicon nanometer crystalline grains and the clustered amorphous silicon. The component of crystalline phase increases with the increase in depth. Moreover, the film crystallization structure depends strongly on the power. On the other hand, it is almost independent of the substrate temperature and the annealing temperature. Comparing with the growth processes of polycrystalline silicon films from hydrogen-diluted SiH4, it is considered that the formation of nanometer size grains occurs in the gas phase reaction process at the initial stage of film growth, while the grain growt...

Investigation on the initial growth of nanocrystalline silicon prepared from hydrogen-diluted SiCl4 at low temperatures

Ultrathin nanocrystalline silicon films have been fabricated by plasma enhanced chemical vapour deposition from hydrogen-diluted SiCl4 at a low temperature of 250??C. The Raman spectra measurements and high resolution transmission electron microscopy observations reveal that nanocrystalline silicon can be directly grown on an insulator glass substrate at the initial growth of the deposition process. The crystallinity and the grain size increase with the increase in the deposition period. Furthermore, the crystalline fraction as well as the grain size also increase with the decrease in the hydrogen dilution ratio. The I?V characteristic curves measured by a tuned Langmuir probe in the SiCl4/H2 plasma region at a substrate temperature of 100??C show that silicon films with higher conductivity were deposited on the probe surface in the deposition process. This behaviour is completely different from that observed in the SiH4/H2 system. It is considered that the formation of nanometre size grains occurs in the gas phase reaction process at the initial stage of film growth, while the growth of grains is mainly governed by the surface reaction process where chlorine and hydrogen play an important role. The direct growth of nanocrystalline Si on the insulator surface at low temperatures using SiCl4/H2 opens up the possibility of directly fabricating nc-Si/SiO2 or nc-Si/a-SiNx systems at low temperatures.

Light-induced changes in the photoconductivity of rapidly-deposited hydrogenated amorphous silicon films

Abstract The temperature dependence of steady-state photoconductivity in hydrogenated amorphous silicon films prepared at high deposition rates have been measured in thermally-annealed states (state A) and light-soaked states (state B). The light-induced changes (the Staeble-Wronski effect) in the photoconductivity were studied using a computer simulation calculation process. The Simmons-Taylor theory and occupation statistics of correlated defects were used to describe the exponential distribution band tail states and the dangling bond states. Tunneling recombination of excess carriers was taken into account at low temperature. It was found that the density of dangling bond states increases after light soaking, but there is no change in the density and distribution of band tail states. A discussion of the experimental and simulation results is given.

Effects of hydrogen dilution on deposition process of nano-crystalline silicon film by SiCl4/H2 plasma

Growth of nano-crystalline silicon (nano-Si) films from hydrogen-diluted SiCl4 by the plasma enhanced chemical vapour deposition technique at 250 °C has been studied through mass spectrometry, Langmuir probe diagnostic techniques and Raman spectra measurements. The effects of the hydrogen dilution ratio on the relative densities of SiCln (n = 0–2) in SiCl4/H2 plasma are investigated. The average electron energy (Ee) and electron density (Ne) in SiCl4/H2 plasma increase with the hydrogen dilution ratio till their maxima at 9.25 eV and 3.7 × 109 cm−3, respectively. A suitable hydrogen dilution ratio R (0.4–0.67) is beneficial for the formation of SiCln (n = 0–2) radicals because Ee and Ne both have maxima in this range. More SiCln (n = 0–2) radicals will improve the deposition rate and film quality. In addition, hydrogen radicals play an important role in the surface reaction process. The reaction of H and SiCln (n = 0–2) on the growing surface is beneficial for creating dangling bond sites and prompting the film growth, and the exothermic reaction exothermic energy of H with Cl on the film-growing surface results in the increase of the effective temperature of the film growth.

Preparation of nanocrystalline silicon thin film at high pressure and fast rate by PECVD technique

Hydrogenated Nano-crystalline silicon thin films with deposition rate of 0.4nm/s were prepared by conventional plasma enhanced chemical vapor deposition technique under the high deposition pressure (133∼266Pa), which were characterized and analyzed by Raman spectra and IR spectra. The results showed the average grain size is about 6nm, dark-conductivity value is about 10−4 10−3 Ω−1. cm−1; The FTIR spectra showed that the bonds of Si-C, Si-O, or Si-N have not been found, the Si-H bond disappears gradually with the crystallinity increasing.

Low-Temperature Fast Growth of Polycrystalline Silicon Thin Film from SiCl4 Light-Diluted Hydrogen by PECVD

The polycrystalline silicon films deposited at a high deposition rate over 3.5Aring/S along with a crystalline fraction of 80% have been obtained using decomposing SiCl4 gas lightly diluted in hydrogen under low temperature of 200-300 by plasma enhanced chemical vapor deposition technique. The deposition rate and the crystalline fraction strongly depend not only on the if power, but also on the hydrogen dilution ratio. It is found that the higher growth rate crystalline fraction can be achieved using light-hydrogen dilution in contrast to SiH4/H2 gases and through the enhancement of the gas-phase reaction in SiCl4/H2 plasma by the optimum radio frequency power

Structure character of fast growth polycrystalline silicon film from SiCl/sub 4//H/sub 2/

The polycrystalline silicon films with the deposition rate over 4.5 /spl Aring//s prepared at low temperature of 250 /spl deg/ were obtained from the hydrogen dilution of tetrachlorine silicon using PECVD technique. The results show that the growing surface of film contains a large amount of silicon crystalline grains with 30-100 nm in diameter. The crystalline fraction and the crystalline grain size strongly depend on the RF power and the hydrogen dilution ratio. The optimum RF power and the optimum hydrogen dilution ratio for the best crystalline character are related to the deposition rate. On the other hand, the crystalline fraction and the crystalline grain size are almost independent on the substrate temperature. It is considered that the space reaction processes and the Cl element play an important role in the initial stage of the crystalline formation and in the crystalline grain growth for the low-temperature crystallization of the films.

The Reliability of Measurements on Electron Energy Distribution Function in Silane rf Glow Discharges

Electron energy distribution function (EEDF) is directly proportional to the second derivative of the probe I-V characteristics. Because of an amplifying effect of unavoidable noises in the experimental probe I-V curves on the derivation process, the experimental I-V curves should be smoothed before performing the numerical derivation. This article investigates the effect of adjustable factors used in the smoothing process on the deduced second derivative of the I-V curves, and an optimum group of the adjustable factors is selected to make the rms deviation of the smoothed I-V curves from the measured ones less than 1 %. A simple differentiation circuit is designed and used to measure the EEDF parameter straightforwardly. It is the first time, so far as we know, to measure the EEDF parameters simultaneously by means of both numerical and circuit derivative methods under the same discharge conditions and on the same discharge equipment. The deviation between two groups of mean electron energy ( E ) and electron density ( n e ) obtained by the above different methods is within about 7 %. This apparently improves the reliability of the measurements on the EEDF parameters.

Low-temperature growth of poly-crystalline silicon films using SiCl/sub 4/ and H/sub 2/ mixture

Polycrystalline silicon thin films were deposited at 200 degC using a SiCl/sub 4//H/sub 2/ mixture by conventional plasma enhanced chemical vapor deposition technology. The effect of deposition power on grain size and crystallinity has been determined. The maximum grain size measured by SEM is 1.5 /spl mu/m. The crystallinity of films estimated from Raman spectroscopy is more than 90% and it depends strongly on the deposition power. The measurements of energy dispersion spectroscopy shows that the films are composed of pure silicon, without impurities such as Cl, H, C, N, and O, etc.. The low-temperature growth mode is discussed.