Fast Etching of Amorphous and Microcrystalline Silicon by Hot-Filament Generated Atomic Hydrogen

Abstract

A hot tungsten wire effectively dissociates H2 into atomic hydrogen and thereby facilitates etching and hydrognation of silicon. Hot filament generated atomic hydrogen etches amorphous silicon (a-Si:H) at a rate of up to 27 Å/s and microcrystalline (μc) Si at rates up to 20 Å/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 H2 gas flow. Likewise, the etch rate rises with the filament temperature and saturates at a filament temperature of approximately 2150°C when approaching the maximum H2 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 μc-Si drops at elevated substrate temperatures. Boron doping decreases the etch rates both for a-Si:H and μc-Si, whereas phosphorous doping does not significantly affect it. This etch selectivity is caused by a catalytic effect of BH3 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 μc-Si etch rate close to the film substrate interface characterizes the film thickness at which the coalescence of the microcrystalline nuclei starts.

Characterization of silicon nitride thin films deposited by hot-wire CVD at low gas flow rates

“…The increasing number of defects results in the observed decreasing FTIR bonding densities and the observed disordering within the Si Si http://repository.uwc.ac.za regions as shown by Raman spectroscopy. Wanka and Schubert [45] reported on the effective etching of a native oxide film on silicon by atomic hydrogen generated by a heated filament. In line with the findings by Wanka and Schubert [45] the reduction in the oxide thickness between the SiNx/c-Si interface as the NH 3 flow rate increases is attributed to an enhancing etching by atomic hydrogen.…”

Hydrogen plasma treatment of very thin p-type nanocrystalline Si films grown by RF-PECVD in the presence of B(CH3)3

“…The standard a-Si : H deposition method is based on the dissociation of silane (SiH 4 ) in radio-frequency plasma enhanced chemical vapor deposition (RF-PECVD) reactors and production of SiH X radicals. The growth of nc-Si : H by PECVD requires a very high hydrogen dilution of silane, as the hydrogen radicals assist in the formation of nc-Si : H via (a) hydrogen surface coverage [7,8], (b) creation of surface dangling bonds, (c) chemical etching (creation of dangling bonds and breakage of weak Si-Si bonds) [9] and (d) relaxation of Si network by hydrogen propagation into the bulk [10].…”

High‐Throughput Chemical Vapor Deposition System and Thin‐Film Silicon Library

“…This behavior can be explained by the etching rate associated with the number of atomic H, which will increase when more hydrogen molecules flow into the reaction region. [16] The increased etching rate causes a decrease in deposition rate and the structure changes from a-Si:H to mc-Si. Figure 4 shows the c-Si volume fraction (X c ) as a function of R (the ratio of H 2 /SiH 4 ) at four SiH 4 flow rates of 3, 8, 16, and 22 sccm, while keeping the TVP at 50%.…”