Bulletin of the American Physical Society
63rd Annual Gaseous Electronics Conference and 7th International Conference on Reactive Plasmas
Volume 55, Number 7
Monday–Friday, October 4–8, 2010; Paris, France
Session SF3: Plasma Processing for Photovoltaic Applications |
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Chair: Hajime Shirai, Saitama University, Japan Room: 151 |
Friday, October 8, 2010 8:30AM - 8:45AM |
SF3.00001: Effect of radical density for high rate deposition of microcrystalline silicon film in UHF and RF hybrid PECVD Youn J. Kim, Yoon S. Choi, In S. Choi, Jeon G. Han Hydrogenated microcrystalline silicon ($\mu $c-Si:H) thin films were deposited on glass substrates by additional ultra high frequency (UHF, 314 MHz) plasma source in conventional RF (13.56 MHz) plasma enhanced chemical vapor deposition (PECVD) system. The effect of radical density on the deposition rate and the crystalline volume fraction of films were systematically investigated at different UHF antenna position comparing without UHF plasma source. The results show the controlling of radical density is a crucial factor for design and improving the deposition rate and microstructure of $\mu $c-Si:H film. The main reasons for the improved deposition rate and crystallinity of the $\mu $c-Si:H thin films are discussed in terms of radicals control. [Preview Abstract] |
Friday, October 8, 2010 8:45AM - 9:00AM |
SF3.00002: Control of Microcrystalline Silicon Deposition by RF Waveform Tailoring Erik Johnson, Jean-Paul Booth, Jean-Charles Vanel, Thomas Verbeke Deposition of microcrystalline silicon thin films at an adequate rate is a key challenge in the fabrication of thin film silicon tandem photovoltaic modules for viable large-scale power generation. Conventionally films are deposited using sinusoidal RF excitation of parallel plate reactors containing lean H$_{2}$-SiH$_{4}$ mixtures. Higher voltage increases deposition rates, but also increases the ion bombardment energy which degrades the film, thus limiting the deposition rate of high quality films to $\approx $1 nm/s for RF excitation at 13.56 MHz. We have investigated plasma excitation using non-sinusoidal waveforms to decouple the injected RF power from the ion bombardment. Various waveforms were generated using a function generator and wide-band power amplifier. Film deposition in Ar/SiF$_{4}$/H$_{2}$ plasmas was characterised using in-situ spectroscopic ellipsometry. Certain waveforms allow the deposited film structure to be switched from amorphous to microcrystalline, simply by changing from the original waveform to its complement. [Preview Abstract] |
Friday, October 8, 2010 9:00AM - 9:15AM |
SF3.00003: SiH$_{4}$ and SiF$_{4}$ dissociation in MDECR plasmas and consequences for material properties Samir Kasouit, Pavel Bulkin, Laurent Kroely, Pere Roca i Cabarrocas Depositing at higher rates and on larger areas are important objectives for the reduction of thin film silicon modules costs. High deposition rates have been obtained using different plasma sources but uniformity over large areas is still problematic. Matrix distributed electron cyclotron resonance (MDECR) systems consist of individual plasma sources, which could be arranged in arrays with virtually no size limitations. Deposition rate of silicon alloys, exceeding 10 nm/s, has been demonstrated, but little is known so far about the precursors' dissociation and species fluxes onto the surface. We study here the dissociation of SiH4 and SiF4, and its dependence on the process parameters such as the power density and pressure. SiH4 is found to be completely depleted within a wide range of powers and pressures, and no gas phase polymerization is observed. This leads to high deposition rates from species such as atomic Si. Such behavior is compared to SiF4 mixtures, and correlated to the properties of the deposited material. [Preview Abstract] |
Friday, October 8, 2010 9:15AM - 9:30AM |
SF3.00004: High rate and high yield silicon deposition under mesoplasma condition for a next generation Siemens technology Makoto Kambara, Junichi Fukuda, Sudong Wu, Liwen Chen, Toyonobu Yoshida Silicon thick films have been deposited by mesoplasma CVD with trichlorosilane (TCS) as source gas. The deposition rate of the Si films is found to increase linearly with the TCS flow rate, epitaxial films are deposited at a maximum rate of 200 nm/sec on silicon wafer as a substrate at low TCS flow rate up to 80 sccm. In contrast, when the TCS flow rate increases to 100 sccm, polycrystalline films were deposited instead at a rate of $\sim $500 nm/sec. It is noteworthy that the deposition efficiency of such films reaches roughly $>$20{\%} for epitaxy and $>$80{\%} for polycrystalline films, which has proven the expectation from the thermodynamic consideration under mesoplasma condition. [Preview Abstract] |
Friday, October 8, 2010 9:30AM - 9:45AM |
SF3.00005: Measurement of surface loss probabilities of hydrogen radicals in plasma-enhanced Si CVD process for solar cell Yusuke Abe, Keigo Takeda, Kenji Ishikawa, Hiroki Kondo, Makoto Sekine, Masaru Hori Microcrystalline silicon ($\mu $c-Si:H) thin films are promising materials for the bottom cell of a tandem solar cell, because they absorb light with higher wavelength towards the infrared region of solar spectrum and have excellent stability against light soaking with respect to top cell in which amorphous silicon thin films are used. It is known that hydrogen radicals play an important role in the deposition of $\mu $c-Si:H thin films by plasma enhanced chemical vapor deposition (PECVD). Film structures of $\mu $c-Si:H, such as crystallinity and crystal orientation, are decided by the flux ratio of hydrogen radicals to film precursors. The process margin to get a high qulity $\mu $c-Si:H thin film for solar cells is very narrow. Therefore, it is important to recognize the behavior of hydrogen radicals in plasma. However, the basic data such as a surface loss probability have not been sufficient. In this study, the surface loss probabilities of hydrogen radical on chamber walls were estimated by measuring the decay time constants of H radicals in H$_{2}$ plasma afterglow. The surface loss probability of hydrogen radicals on the stainless-steel was estimated to be 0.12. When the stainless-steel was heated to 465 K, it decreased to 0.022. [Preview Abstract] |
Friday, October 8, 2010 9:45AM - 10:00AM |
SF3.00006: Plasma Modeling of Microcrystalline Silicon Thin Film Deposition Process Eleftherios Amanatides, Spyridon Sfikas, Dimitrios Mataras, Aurel Salabas PECVD of thin films from SiH$_{4}$-H$_{2}$ discharges is a widely used technique for deposition of hydrogenated amorphous as well as microcrystalline silicon. All plasma parameters strongly affect the plasma chemistry, the characteristics and quality of the deposited films. A well tuned discharge model can serve as a reliable laboratory tool. We present a model for PECVD of mc-Si:H, using a self consistent fluid approach. All simulations were performed in CCP discharge sustained at 40.68 MHz. Process conditions have been chosen so that the obtained films are close to the a-Si:H to mc-Si:H transition. The geometry corresponds to a bench chamber similar with plasma reactors used for solar panel manufacturing. The effect of plasma power on the deposition process was investigated; the other plasma parameters were kept constant. The contribution of precursor fluxes to the film growth rate is discussed in the context of film thickness uniformity. The main reasons that favor the growth of mc-Si:H instead of a-Si:H under relatively high power conditions are also analyzed. [Preview Abstract] |
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