Disilane addition versus silane-hydrogen flow rate effect on the PECVD of silicon thin films (original) (raw)
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Thin Solid Films, 2010
The paper deals with the properties of silicon films obtained by low-pressure chemical vapour deposition (LPCVD). Two gaseous sources characterized by different deposition temperatures, i.e. disilane Si2H6 (420-520°C) and silane SiH4 (520-750°C), were studied in order to understand the influences of the deposition and crystallization kinetics on the silicon films properties. Thus, the deposition of amorphous, semi-crystallized and polycrystalline silicon films was related to the "volume random" and "surface columnar" crystallization phenomena, highlighting a linear relationship between the refractive index and the polysilicon volume fraction and, showing complex residual stress dependency with process conditions. Finally, by introducing the ratio Vd/Vc between the deposition and crystallization rates as a major parameter, different deposition behaviours and related semi-empirical relationships were defined in order to characterize fully the various properties of LPCVD silicon films (microstructure, polysilicon volume fraction, refractive index and residual stress) according to the chosen gaseous source, silane or disilane.
Effect of Silane flow rate on microstructure of Silicon films deposited by HWCVD
Journal of Non-Crystalline Solids, 2012
Hydrogenated silicon films ranging from pure amorphous to those containing small crystallites in large crystalline fraction are prepared using the HWCVD technique without using any hydrogen dilution which is supposed to be necessary for the deposition of nanocrystalline Si films. The only parameter that is varied is Silane flow rate. The deposition rate ranges from 6-27 Å/s. The band gap of the films (1.8-2.0 eV) is high compared to the regular films, which is attributed to the improved short and medium range order as well as the presence of low density amorphous tissues in the grain boundary regions. The films show improved stability under long term light exposure due to more ordered structure and presence of hydrogen mostly as strong Si-H bonds.
Low Temperature Growth of Hydrogenated Silicon Prepared by PECVD from Argon Diluted Silane Plasma
Crystal Structure Theory and Applications, 2012
In order to contribute to the understanding of the optoelectronics properties of hydrogenated nanocrystalline silicon thin films, a detailed study has been conducted. The samples were deposited by 13.56 MHz PECVD (Plasma-Enhanced Chemical Vapor Deposition) of silane argon mixture. The argon dilution of silane for all samples studied was 96% by volume. The substrate temperature was fixed at 200˚C. The influence of depositions parameters on optical proprieties of samples was studied by UV-Vis-NIR spectroscopy. The structural evolution was studied by Raman spectroscopy and X-ray diffraction (XRD). Intrinsic-layer samples depositions were made in this experiment in order to obtain the transition from the amorphous to crystalline phase materials. The deposition pressure varied from 400 mTorr to 1400 mTorr and the rf power from 50 to 250 W. The structural evolution studies show that beyond 200 W, we observed an amorphous-nanocrystalline transition, with an increase in crystalline fraction by increasing rf power and working pressure. Films near the amorphous to nanocrystalline transition region are grown at reasonably high deposition rates (~10 Å/s), which are highly desirable for the fabrication of cost effective devices. The deposition rate increases with increasing rf power and process pressure. Different crystalline fractions (21% to 95%) and crystallite size (6 -16 nm) can be achieved by controlling the process pressure and rf power. These structural changes are well correlated to the variation of optical proprieties of the thin films.
2004
A pulsed PECVD system was developed from a modification of the existing d.c. PECVD system with a modulation frequency of 10KHz. In this work, the effects of silane flow-rate on the structural properties of films prepared by both techniques were investigated. These films were analysed using X-ray diffraction (XRD), Fourier Transform infrared (FTIR) absorption and Raman spectroscopy. The results presented here are only initial results from the pulsed PEVCD system since the deposition conditions are fixed to the optimized deposition conditions for the d.c. PECVD system which are 200 degree Celsius, 0.45 mbar and 1.4 W for the deposition temperature, pressure and power respectively. The ON-time and OFF-time was set at 30 seconds for the pulsed PECVD system. The FTIR absorption spectroscopy results showed that films produced by pulsed PECVD technique were comparatively more homogeneous and had lower H content at most flow-rates than the d.c. PECVD films. Evidence of nanocrystallites presence in the film structure was observed at high silane flow-rate in the pulsed PECVD films. The Raman spectroscopy results were used to confirm this effect.
Vacuum, 2009
Thin film silicon Medium-range order Grain size Hydrogen dilution Microstructure X-ray diffraction Raman analysis FTIR spectrometry a b s t r a c t Plasma enhanced chemical vapour deposition (PECVD) has been used to prepare hydrogenated amorphous silicon (a-Si:H) thin films at different hydrogen dilution of silane source gas. The films were deposited on Corning glass 1737 substrate and on (100) oriented c-Si wafers and characterized by XRD diffraction, micro-Raman and FTIR spectrometry. Experimental data show evolution from amorphous to nanocrystalline silicon and contain the medium-range order (MRO) with varying hydrogen dilution during deposition. From X-ray diffraction and Raman analysis, it is found that the presence of crystalline phase depends on the kind of substrate and on the dilution scale.
The European Physical Journal Applied Physics, 2004
Fully microcrystalline silicon, µc-Si, thin films (<100 nm) have been deposited at low temperature (60 • C) on Corning glass and plastic flexible polyimide substrates by plasma enhanced chemical vapor deposition (PECVD) using SiF4-H2-He. The effect of deposition temperature on the structure, i.e., crystallinity and density, of µc-Si films is investigated by spectroscopic ellipsometry in the 1.5−5.5 eV energy range. Modeling of spectroscopic ellipsometry data is used for highlighting crystallinity of the substrate/film interface, i.e., the absence of any amorphous incubation layer. It is found that film crystallinity does not depend on film thickness, and it increases with the decrease of deposition temperature. The temperature dependence is explained on the basis of a like-Arrhenius kinetic analysis of the etching process by atomic fluorine and hydrogen of both µc-Si and a-Si phases.
Structural and transport properties near the amorphous to microcrystalline transition region of Si:H samples deposited from a silane-hydrogen mixture have been studied. The gas pressure during the plasma enhanced chemical vapor deposition process has been varied from 1.0 to 0.1 Torr. The defect density in the subband gap region measured by modulated photocurrent and constant photocurrent methods vary asymmetrically above and below midgap with changes in pressure. The transport properties of the electrons and holes studied by measurement of mobility lifetime product (ls) and diffusion length (L D ), respectively, change in the opposite direction with pressure. The sample deposited at 0.2 Torr exhibits high L D but low ls product. Moreover, an increase of the band gap was observed with decreasing pressure. These unusual behaviors have been explained on the basis of quantum confinement effect. The changes in plasma chemistry observed by optical emission spectroscopy present an interesting perspective in understanding the evolution of the structural and electronic properties with the changes in pressure.
Special features of the growth of hydrogenated amorphous silicon in PECVD reactors
Technical Physics, 2000
A model has been developed to calculate the growth parameters of silicon films in diode-and triodetype PECVD reactors and to analyze the factors affecting the deposition of silicon-containing radicals. Mechanisms of the effect of diluting silane with molecular hydrogen on the film growth process have been explained.
Amorphous-Nanocrystalline Transition in Silicon Thin Films Obtained by Argon Diluted Silane PECVD
Crystal Structure Theory and Applications, 2012
The Plasma-Enhanced Chemical Vapor Deposition (PECVD) method is widely used compared to other methods to deposit hydrogenated silicon Si:H. In this work, a systematic variation of deposition parameters was done to study the sensitivities and the effects of these parameters on the intrinsic layer material properties. Samples were deposited with 13.56 MHZ PECVD through decomposition of silane diluted with argon. Undoped samples depositions were made in this experiment in order to obtain the transition from the amorphous to nanocrystalline phase materials. The substrate temperature was fixed at 200˚C. The influence of depositions parameters on the optical proprieties of the thin films was studied by UV-Vis-NIR spectroscopy. The structural evolution was also studied by Raman spectroscopy and X-ray diffraction (XRD). The structural evolution studies show that beyond 200 W radio frequency power value, we observed an amorphous-nanocrystalline transition, with an increase in crystalline fraction by increasing RF power and working pressure. The deposition rates are found in the range 6-10 Å/s. A correlation between structural and optical properties has been found and discussed.