Yu Yun-Peng

Low-Temperature Growth of Polycrystalline silicon Films by SiCl4/H2 rf Plasma Enhanced Chemical Vapour Deposition

Polycrystalline silicon film was directly fabricated at 200°C by the conventional plasma enhanced chemical vapour deposition method from SiCl4 with H2 dilution. The crystallization depends strongly on the deposition power. The maximum crystallinity and the crystalline grain size are over 80% and 200-500 nm, respectively. The results of energy dispersive spectroscopy and infrared spectroscopy measurements demonstrate that the film is mostly composed of silicon, without impurities such as Cl, N, C and bonded H. It is suggested that the crystallization at such a low temperature originates from the effects of chlorine, i.e., in-situ chemical, etching, in-situ chemical cleaning, and the detachment of bonded H.

Fast Growth of Polycrystalline Film in SiCl4/H2 Plasma

We report the discovery of fast growth of polycrystalline silicon films under low temperature of 200–300 degrees C from SiCl4/H2 mixture gases by plasma enhanced chemical vapour deposition technique. The deposition rate strongly depends not only on the rf power and the flow ratio of H2/SiCl4, but also on the substrate temperature, while the crystalline fraction is mainly affected by both the rf power and the flow ratio of H2/SiCl4. The high film-growth rate is due to the enhancement of the gas-phase reaction in SiCl4/H2 plasma. By means of adjusting the matching relation between the flow ratio of H2/SiCl4 and rf power, and optimizing the substrate temperature, we obtain the polycrystalline silicon films deposited at a higher deposition rate over 3.5 A/s, with a crystalline fraction of 75% and an average crystallite size of 400–500 nm in diameter.

The reliability of measurements on electron energy distribution function in silane rf glow discharges

Electron energy distribution function (EEDF) is a key parameter of plasmas, which 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 during the derivation process, the experimental I-V curves should be smoothed before performing the numerical derivation. This paper 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 curves 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 ne obtained by the above different methods is within about 7%. This apparently improves the reliability of the measurements of the EEDF parameters.

Spatial distribution of electron characteristic in argon rf glow discharges

The spatial distributions of the electron density and the mean electron energy of argon radio frequency (rf) glow discharge plasma in a plasma-enhanced chemical vapour deposition (PECVD) system have been investigated using an established movable Langmuir probe. The results indicate that in the axial direction the electron density tends to peak at midway between the two electrodes while the axial variation trend of mean electron energy is different from that of the electron density, the mean electron energy is high near the electrodes. And the mean electron energy near the cathode is much higher than that near the anode. This article focuses on the radial distribution of electron density and mean electron energy. A proposed theoretical model distribution agrees well with the experimental one: the electron density and the mean electron energy both increase from the centre of the glow to the edge of electrodes. This is useful for better understanding the discharge mechanism and searching for a better deposition condition to improve thin film quality.

Luminescent Properties of Nano-crystalline Silicon Films Embedded in SiO2

Nano-crystalline silicon (nc-Si) films embedded in SiO2 exhibited strong visible light luminescence at room temperature. The energies of photoluminescence peak were found to be more than 1.9eV and the peaks shifted to higher energies when nano-Si films were post-oxidized. The photoluminescence intensity depended significantly on the size of the grains and the characteristics of the oxidized surface. Microcrystalline silicon grains of 2-3 nm average size and radiation recombination centers located on the nanoscale silicon grain surfaces and located in the Si oxide layers are considered to be the source of the visible luminescence.

Room Temperature Visible Photoluminescence from Thermally Annealed Hydrogenated Amorphous Silicon Films

A visible photoluminescence from a thermally annealed boron doped hydrogenated amorphous silicon (a-Si: H) film has been observed at room temperature. The wavelength at the peak of the photoluminescent spectra is about 600 nm. The intensity of photoluminescence is dependent on the annealing temperature strongly and relative to the deposition technology parameters of the films, especially to the hydrogen dilution of the boron doped silane and the deposition rate of the films. There exists a quantum size effect of nanometer-scale porosity on the surface of the annealed a-Si: H film. The quantum-confined structures may form due to the evolution of hydrogen from the surface of the films during the annealing procedure. The density of the porosity is relative to the quantity of evolved hydrogen from the film and the evolution rate of the hydrogen.