Time-resolved layer thickness behavior of microcrystalline and amorphous silicon samples after switching on a hydrogen/silane VHF plasma

Terasa, R.; Albert, Matthias; Bartha, Johann W.; Brechtel, H. M.; Kottwitz, A.

doi:10.1016/s0022-3093(01)01177-2

Cited by 7 publications

(6 citation statements)

References 10 publications

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“…[17]. Interestingly our results gives some indication on the local growth mechanisms, as the a-Si to mc-Si transition is usually attributed either to an enhancement of the surface diffusion of the SiH x precursors [33] or to a selective etching of the weakly bonded Si atoms [34][35][36][37]. In our case, the increase of the hydrogen content at constant temperature leads to an increase of crystallinity because the selective etching mechanism start to dominate (whereas the surface diffusion remains moderate), while, for constant radical flows, the increase of temperature leads to a strong enhancement of the surface diffusion, leading both to an increase in crystallinity and to a filling of the cracks.…”

Section: Discussionmentioning

confidence: 59%

Microcrystalline silicon solar cells: effect of substrate temperature on cracks and their role in post‐oxidation

Python

Dominé

Söderström

et al. 2010

Progress in Photovoltaics

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Microcrystalline silicon (mc-Si:H) cells can reach efficiencies up to typically 10% and are usually incorporated in tandem micromorph devices. When cells are grown on rough substrates, ''cracks'' can appear in the mc-Si:H layers. Previous works have demonstrated that these cracks have mainly detrimental effects on the fill factor and open-circuit voltage, and act as bad diodes with a high reverse saturation current. In this paper, we clarify the nature of the cracks, their role in postoxidation processes, and indicate how their density can be reduced. Regular secondary ion mass spectrometry (SIMS) and local nano-SIMS measurements show that these cracks are prone to local post-oxidation and lead to apparent high oxygen content in the layer. Usually the number of cracks can be decreased with an appropriate modification of the substrate surface morphology, but then, the required light scattering effect is reduced due to a lower roughness. This study presents an alternative/complementary way to decrease the crack density by increasing the substrate temperature during deposition. These results, also obtained when performing numerical simulation of the growth process, are attributed to the enhanced surface diffusion of the adatoms at higher deposition temperature. We evaluate the cracks density by introducing a fast method to count cracks with good statistics over approximately 4000 mm of sample cross-section. This method is proven to be useful to quickly visualize the impact of substrate morphology on the density of cracks in microcrystalline and in micromorph devices, which is an important issue in the manufacturing process of modules.

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Section: Discussionmentioning

confidence: 59%

Microcrystalline silicon solar cells: effect of substrate temperature on cracks and their role in post‐oxidation

Python

Dominé

Söderström

et al. 2010

Progress in Photovoltaics

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“…In order to explain the plasma-surface interactions in the case of deposition of µc-Si : H from a silane (SiH 4 ) and hydrogen (H 2 ) discharge, three models have been proposed [13][14][15][16][17]: the surface diffusion model, the selective etching model and the chemical annealing model.…”

Section: Review Of µC-si : H Deposition Mechanismsmentioning

confidence: 99%

“…This implies that SiH 3 radicals adsorb onto the surface and diffuse until they find an adequate site to attach. The diffusion length, and thus the crystallinity are greatly improved by hydrogen coverage of the surface, which implies that a sufficient atomic hydrogen flux to the surface is necessary to saturate all surface Si dangling bonds [13][14][15].…”

Section: Review Of µC-si : H Deposition Mechanismsmentioning

confidence: 99%

“…This recombination reaction is exothermic, and the extra energy is absorbed by the film to rearrange its structure from amorphous to microcrystalline. Incoming H atoms having higher energy could also penetrate into the subsurface region and anneal the amorphous network by structural rearrangement [15]. The small decrease in film thickness under exposure to H 2 plasma implies that the rate of crystallization by etching is much lower than by chemical annealing.…”

Section: Review Of µC-si : H Deposition Mechanismsmentioning

confidence: 99%

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Plasma silane concentration as a determining factor for the transition from amorphous to microcrystalline silicon in SiH₄/H₂discharges

Strahm

Howling

Sansonnens

et al. 2006

Plasma Sources Sci. Technol.

114

131

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In this work, the microstructure transition from amorphous to microcrystalline silicon is defined in terms of the silane concentration in the plasma as opposed to the silane concentration in the input gas flow. In situ Fourier transform infrared absorption spectroscopy combined with ex situ Raman spectroscopy has been used to calibrate and validate this approach. Results show that a relevant parameter to obtain µc-Si : H from SiH 4 /H 2 mixtures is the plasma composition, which is determined not only by the gas dilution ratio but also by the silane depletion fraction. It is also shown that µc-Si : H can only be deposited efficiently, in terms of gas utilization, at a high rate by using high input concentration and depletion of silane.

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“…For the purposes of this study, we will use the term microcrystalline. The mechanisms involved in the deposition of mc-Si:H are complex and not completely understood, however there is a general consensus on the key role of atomic hydrogen in the crystallization of the growing film [33][34][35][36]. So far, most efforts have been devoted to the development of PECVD processes at low silane (SiH 4 ) concentration, on the order of a few percent of the total gas mixture.…”

Section: Process Conditions For Lc-si:h Deposition At 10 å /Smentioning

confidence: 99%

High‐rate deposition of microcrystalline silicon in a large‐area PECVD reactor and integration in tandem solar cells

Parascandolo

Bugnon

Feltrin

et al. 2010

Progress in Photovoltaics

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We study the high-rate deposition of microcrystalline silicon in a large-area plasma-enhanced chemical-vapor-deposition (PECVD) reactor operated at 40.68 MHz, in the little-explored process conditions of high-pressure and high-silane concentration and depletion. Due to the long gas residence time in this process, the silane gas is efficiently depleted using moderate feed-in power density, thus facilitating up-scaling of the process to large surfaces. As observed in more traditional deposition processes, the deposition rate and performance of device-quality material are limited by the inter-electrode gap of the reactor. We significantly increase the cell performances by reducing this gap. X-ray diffractometry (XRD) and secondary ion mass spectroscopy (SIMS) are used to characterize the microcrystalline material deposited in the modified reactor at a rate of 1 nm/s. Comparison with a microcrystalline process at a low deposition rate demonstrates that the crystallographic orientation of the absorbing layer of the cell and the concentrations of contaminants are strongly correlated and dependent on the process. We use microcrystalline cells with absorber layer grown at a rate of 1 nm/s integrated as bottom cells in amorphous-microcrystalline (micromorph) tandem solar cells using the superstrate configuration. We report an initial efficiency of 10.8% (9.6% stabilized) for a tandem cell with 1.2 cm 2 surface.

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Time-resolved layer thickness behavior of microcrystalline and amorphous silicon samples after switching on a hydrogen/silane VHF plasma

Cited by 7 publications

References 10 publications

Microcrystalline silicon solar cells: effect of substrate temperature on cracks and their role in post‐oxidation

Microcrystalline silicon solar cells: effect of substrate temperature on cracks and their role in post‐oxidation

Plasma silane concentration as a determining factor for the transition from amorphous to microcrystalline silicon in SiH₄/H₂discharges

High‐rate deposition of microcrystalline silicon in a large‐area PECVD reactor and integration in tandem solar cells

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Time-resolved layer thickness behavior of microcrystalline and amorphous silicon samples after switching on a hydrogen/silane VHF plasma

Cited by 7 publications

References 10 publications

Microcrystalline silicon solar cells: effect of substrate temperature on cracks and their role in post‐oxidation

Microcrystalline silicon solar cells: effect of substrate temperature on cracks and their role in post‐oxidation

Plasma silane concentration as a determining factor for the transition from amorphous to microcrystalline silicon in SiH4/H2discharges

High‐rate deposition of microcrystalline silicon in a large‐area PECVD reactor and integration in tandem solar cells

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Plasma silane concentration as a determining factor for the transition from amorphous to microcrystalline silicon in SiH₄/H₂discharges