Analysis of high-rate a-Si:H deposition in a VHF plasma

Heintze, M.; Zedlitz, R.; Bauer, G.H.

doi:10.1088/0022-3727/26/10/036

Cited by 90 publications

(62 citation statements)

References 43 publications

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“…The increase of frequency above the usual 13.56 MHz has been proposed to be beneficial for the deposition rate, as well as for the crystallinity of the films [32][33][34][35]. However, these observations were attributed to a variety of somewhat controversial reasons ranging from the enhancement of the electron impact dissociation of SiH 4 to a higher surface reactivity owing to an increase of the ion flux.…”

Section: Frequencymentioning

confidence: 99%

Exploration of the deposition limits of microcrystalline silicon

Mataras

2005

Pure and Applied Chemistry

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The effect of various process parameters on the deposition rate of microcrystalline hydrogenated silicon is presented. The various pathways leading to high deposition rates involve the optimization of a combination of parameters, while maintaining the crystalline character of the film and avoiding the presence of particles. The deposition rate increases in conditions that enhance and at the same time "cool down" the electron population. Such conditions are: moderately higher frequencies, higher pressures, and the presence of larger molecules (like disilane) even in small quantities. There is an optimum pressure, determined by primary dissociation, for a certain silane fraction. In addition, silane fraction and power density must also increase up to the limit of transition to amorphous growth and before attachment becomes too important. In all of these cases, there is a need for optimizing the distance of the deposition substrate to the source of radical generation, especially at higher pressures, to further increase the already important contribution of higher silicon radicals. It is shown that similar deposition rates can be obtained via radical fluxes with very different compositions. In every case, there is a need for sufficient H atom fluxes to ensure crystalline growth.

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Section: Frequencymentioning

confidence: 99%

Exploration of the deposition limits of microcrystalline silicon

Mataras

2005

Pure and Applied Chemistry

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“…1,3,4 With an independent bias on this electrode with respect to the grounded substrate, ion energies can be controllably reduced. Other effective methods to reduce ion energies while maintaining high deposition rates are ͑i͒ very high frequency ͑VHF͒ excitation of the discharge, where lower peak-to-peak voltages for a given discharge power result in lower maximum-ion energies, [5][6][7][8][9] and ͑ii͒ high working pressure ͑p depo ͒ with an increased discharge power, where ion energies are reduced by multiple collisions in the plasma sheath. [10][11][12] Recently, also combinations of VHF-PECVD and high working pressure have been investigated.…”

Section: Introductionmentioning

confidence: 99%

Microcrystalline silicon solar cells deposited at high rates

Mai

Klein

Carius

et al. 2005

Journal of Applied Physics

183

123

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Hydrogenated microcrystalline silicon ͑ c-Si:H͒ thin-film solar cells were prepared at high rates by very high frequency plasma-enhanced chemical vapor deposition under high working pressure. The influence of deposition parameters on the deposition rate ͑R D ͒ and the solar cell performance were comprehensively studied in this paper, as well as the structural, optical, and electrical properties of the resulting solar cells. Reactor-geometry adjustment was done to achieve a stable and homogeneous discharge under high pressure. Optimum solar cells are always found close to the transition from microcrystalline to amorphous growth, with a crystallinity of about 60%. At constant silane concentration, an increase in the discharge power did hardly increase the deposition rate, but did increase the crystallinity of the solar cells. This results in a shift of the c-Si:H/a-Si:H transition to higher silane concentration, and therefore leads to a higher R D for the optimum cells. On the other hand, an increase in the total flow rate at constant silane concentration did lead to a higher R D , but lower crystallinity. With this shift of the c-Si:H/a-Si:H transition at higher flow rates, the R D for the optimum cells decreased. A remarkable structure development along the growth axis was found in the solar cells deposited at high rates by a "depth profile" method, but this does not cause a deterioration of the solar cell performance apart from a poorer blue-light response. As a result, a c-Si:H single-junction p-i-n solar cell with a high efficiency of 9.8% was deposited at a R D of 1.1 nm/s.

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“…Heintze et al (Heintze et al, 1993;Heintze and Zedlitz, 1996) have measured an enhanced ion flux on the growth surface at higher frequencies (see Fig. 6) which is related to the changes in both the bulk plasma and in the sheath.…”

Section: Vhf-gd Deposition Techniquementioning

confidence: 93%

Amorphous solar cells, the micromorph concept and the role of VHF-GD deposition technique

Meier¹,

Kroll²,

Vallat-Sauvain³

et al. 2004

Solar Energy

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During the last two decades, the Institute of Microtechnology (IMT) has contributed in two important fields to future thin-film silicon solar cell processing and design:(1) In 1987, IMT introduced the so-called ''very high frequency glow discharge (VHF-GD)'' technique, a method that leads to a considerable enhancement in the deposition rate of amorphous and microcrystalline silicon layers. As a direct consequence of reduced plasma impedances at higher plasma excitation frequencies, silane dissociation is enhanced and the maximum energy of ions bombarding the growing surface is reduced. Due to softer ion bombardment on the growing surface, the VHF process also favours the formation of microcrystalline silicon. Based on these beneficial properties of VHF plasmas, for the growth of thin silicon films, plasma excitation frequencies f exc in the range 30-300 MHz, i.e. clearly higher than the standard 13.56 MHz, are indeed scheduled to play an important role in future production equipment.(2) In 1994, IMT pioneered a novel thin-film solar cell, the microcrystalline silicon solar cell. This new type of thinfilm absorber material--a form of crystalline silicon--opens up the way for a new concept, the so-called ''micromorph'' tandem solar cell concept. This term stands for the combination of a microcrystalline silicon bottom cell and an amorphous silicon top cell. Thanks to the lower band gap and to the stability of microcrystalline silicon solar cells, a better use of the full solar spectrum is possible, leading, thereby, to higher efficiencies than those obtained with solar cells based solely on amorphous silicon.Both the VHF-GD deposition technique and the ''micromorph'' tandem solar cell concept are considered to be essential for future thin-film PV modules, as they bear the potential for combining high-efficiency devices with low-cost manufacturing processes.

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Analysis of high-rate a-Si:H deposition in a VHF plasma

Cited by 90 publications

References 43 publications

Exploration of the deposition limits of microcrystalline silicon

Exploration of the deposition limits of microcrystalline silicon

Microcrystalline silicon solar cells deposited at high rates

Amorphous solar cells, the micromorph concept and the role of VHF-GD deposition technique

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