Use of Cyclopolysilanes for Silicon Films Deposition
Publication Date: 2013-Jan-03
The IP.com Prior Art Database
A method of forming silicon films layer on a substrate, the method comprising: providing a substrate; providing a mixture of hydrogen, silane and a cyclopolysilane; and forming a silicon layer on the substrate.
It is proposed to use cyclopolysilanes, preferably polyhexasilane, as an activator or accelerant to promote excess electron concentration and enhance radical formation in the plasma. The cyclopolysilanes gases are promising source gases for high growth rate due to their low dissociation threshold. High growth rate (2 nm/sec) for a-Si films using Si2H6 as a source gas has been reported (“Microcrystalline silicon solar cells deposited at high rates” J. Appl. Phys. 97 (2005) 114913) but they had inferior electronic quality.
It is proposed to use a small fraction of cyclopolysilanes in SiH4 + H2 plasma as a source of additional electrons due to their enhanced ionization probability. Thus small concentrations (~ 1%) of cyclopolysilanes can stimulate much higher concentrations of low energy electrons. They would be a negligible source of Si precursors in a largely SiH4 plasma so does not adversely affect the film properties.
The preferred cyclopolysilane is cyclohexasilane, a molecule that can be produced in a cost effective manner (a single digit of dollar per gram; US Patent 5,550,269; 5,942,637), as opposed to trisilane (> $20/g) and higher polysilanes (>$40/g, and even >$100/g for some of them).
An approach to increase the deposition rate while maintaining the uniformity and the optical properties was described (“Ele...