Title: Selective RTLPCVD of TiSi2 without substrate consumption
Abstract: Abstract Among the various materials likely to be used as substitutes for polysilicon, TiSi 2 appears to offer a greater number of advantages compared to other silicides used in VLSI devices. It has, indeed, the lowest resistivity (15μω· cm) and can be selectively deposited through chemical vapor deposition techniques. Whatever the starting gaseous phase, TiCl 4 -H 2 or TiCl 4 -SiH 4 -H 2 , selectivity never fails even in the case of submicronic lines. The problem, however, originates from an undesirable etching of the silicon substrate even through the use of the TiCl 4 -SiH 4 -H 2 gaseous phase. Different reaction mechanisms have been recently proposed by J.L. Regolini, D. Bensahel, G. Bomchil and J. Mercier [Appl. Surf. Sci. 38 (1989) 408], which involve: (i) silicon substrate etching by chlorinated species, (ii) silicon substrate consumption to form TiSi 2 , (iii) TiSi 2 deposition from the gaseous species, (iv) silicon deposition from SiH 4 cracking, and which show that TiSi 2 selectively deposited layers can be achieved at 800°C without any silicon substrate consumption through a careful control of the various gas flow ratios. In particular, they pointed out that the TiCl 4 thermal diffusivity is about one order of magnitude lower than the SiH 4 . Hydrogen is thus used in excess allowing a faster thermallization of the gas mixture [J. Mercier, J.L. Regolini and D. Bensahel, J. Electron. Mater. 19-3 (1990) 253]. As far as we are concerned, TiSi 2 selectively deposited films are obtained on 4 inch silicon wafer from the TiCl 4 -SiH 4 -H 2 gaseous phase by using a RTLPCVD reactor where gas mixture is injected all around the substrate. Thickness measurements show great differences between the edge and the center of the wafer. These differences can be interpreted as variations in the gas mixture composition: TiCl 4 , a heavy molecule, is too slow to reach the wafer center, and mainly reacts at the edge of the substrate leading to the formation of a thick TiSi 2 layer with silicon consumption and silicon etching. On the contrary, at the center of the substrate, the gas mixture becomes impoverished in TiCl 4 , and produces a silicon pedestal under a thin TiSi 2 film. Between the center and the edge of the wafer, the gas mixture composition achieves the right balance, allowing for TiSi 2 to deposit with neither silicon etching and consumption, or silicon pedestal deposition. Regarding our reactor, the solution allowing for deposition of TiSi 2 films with a proper thickness homogeneity on a 4 inch diameter silicon substrate should be obtained through a special geometry of gas mixture injectors. Mention is made of recent results achieved through different gas introduction systems.
Publication Year: 1991
Publication Date: 1991-11-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 15
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