Hydrogen-plasma etching of thin amorphous silicon layers for heterojunction interdigitated back-contact solar cells
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Hydrogen-plasma etching of thin amorphous silicon layers for heterojunction interdigitated back-contact solar cells Stefano. N. Granata1, 2, Twan Bearda1, Ivan Gordon1, Jef Poortmans1,2, Robert Mertens1,2 1
IMEC, Kapledreef 75, B-3001 Heverlee, Belgium
2
KU Leuven ESAT Kasteelpark Arenberg 10 B-3001 Heverlee Belgium
ABSTRACT In this study, A H2-plasma is studied as a dry method to etch thin layers of amorphous silicon aSi:H(i) deposited on a crystalline wafer. It is found that H2-plasma etches aSi:H(i) selectively toward silicon nitrides hard masks with an etch rate below 3nm/min. Depending on power density and temperature of the substrate during the H2-plasma, the energy bandgap, the hydrides distribution and the void concentration of the aSi:H(i) layers are modified and the amorphous-to-crystalline transition is approached. At high temperature (>250C) and low plasma power (250°C) the film tends towards crystalline transition and at low temperature the film is etched. This change in regime is mainly due to the temperature dependent diffusion of the hydrogen incorporated in the a-Si:H network. As such, hydrogen plasma can be used to remove thin layer of amorphous silicon from a crystalline substrate, since it respects criteria of low etch rate and selectivity toward hard masks. However, the integration of this step in a solar cell process flow would be possible only if the amorphous/silicon interface is damage free after H2 etching of the full layer. Surface damage and interface defects induced by H2–plasma will be object for future investigations.
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