Fast etching of amorphous and microcrystalline silicon by hot-filament generated atomic hydrogen
A hot tungsten wire effectively dissociates H{sub 2} into atomic hydrogen and thereby facilitates etching and hydrogenation of silicon. Hot filament generated atomic hydrogen etches amorphous silicon (a-Si:H) at a rate of up to 27 {angstrom}/s and microcrystalline ({micro}c) Si at rates up to 20 {angstrom}/s. A large laminar gas flow is the key to high etch rates. It provides for a fast transport of the etch products out of the reaction zone and thereby avoids redeposition. The etch rate increases with pressure and with H{sub 2} gas flow. Likewise, the etch rate rises with the filament temperature and saturates at a filament temperature of approximately 2,150 C when approaching the maximum H{sub 2} dissociation probability. The decrease of the etch rate at higher substrate temperatures is attributed to the loss of the surface coverage by atomic hydrogen. The etch selectivity between a-Si:H and {micro}c-Si drops at elevated substrate temperatures. Boron doping decreases the etch rates both for a-Si:H and {micro}c-Si, whereas phosphorous doping does not significantly affect it. This etch selectivity is caused by a catalytic effect of BH{sub 3} on the surface hindering the formation of the main etch product silane. Even for highest etch rates no surface roughening of a-Si:H occurs, however, a bond structure modification of the near surfaces arises, an effect which results in the formation of a nanocrystalline surface layer. The increase of the {micro}c-Si etch rate close to the film substrate interface characterizes the film thickness at which the coalescence of the microcrystalline nuclei starts.
- Research Organization:
- Univ. Stuttgart (DE)
- OSTI ID:
- 20085545
- Resource Relation:
- Conference: Amorphous and Microcrystalline Silicon Technology - 1997, San Francisco, CA (US), 03/31/1997--04/04/1997; Other Information: PBD: 1997; Related Information: In: Amorphous and microcrystalline silicon technology--1997. Materials Research Society symposium proceedings, Volume 467, by Wagner, S.; Hack, M.; Schiff, E.A.; Schropp, R.; Shimizu, I. [eds.], 999 pages.
- Country of Publication:
- United States
- Language:
- English
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