Dopant Effects on the Kinetics of Formation of Platinum Silicides
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ABSTRACT We have investigated the growth kinetics of platinum silicide compounds on undoped and heavily arsenic doped polycrystalline silicon. The results are compared with published data on the growth kinetics of these silicides on other silicon substrate materials. From this comparison we conclude that dopants and the microstructure of the substrate material do not affect the activation energy of the growth kinetics which means that the growth mechanism of these silicides is not altered. Only the preexponential factor is lowered in some cases, pointing to a slowing of the speed of growth.
INTRODUCTION In the past the kinetics of formation of platinum silicides have been studied mainly on lightly doped (ý-10'5 cm- 3 ) single crystal silicon substrates. However, in advanced silicon device technology silicides are formed on a number of different silicon materials. These include highly doped (= 102 cm-3) single crystal as well as polycrystalline silicon layers. High doping levels are required to form low resistance ohmic contacts. Both the microstructure of the silicon substrate and the high doping levels are known to influence the kinetics of silicide formation. Arsenic implanted to a concentration of 5 x 102"cm-1 into single crystal silicon has been shown to reduce the preexponential factor but not the activation energy of the PtSi growth kinetics")•. The change in preexponential factor is independent of single crystal silicon substrate orientation. In a similar investigation, phosphorous concentrations of 8 x 1021cm- 3 in polycrystalline silicon were found to have no effect on the activation energy and only a small effect on the preexponential factor of the growth kinetics of PtSi and PtSi'2). There are contradicting reports on the influence of the microstructure of the silicon substrate on the sequence of platinum silicide compound formation in thin films up to 100A thickness. It has been reported that PtSi and PtSi grow simultaneously on amorphous silicon"' . This is in contrast to the general trend observed in silicides that only one compound grows at any given timel 4 l. Also, in another study the formation of a welldefined primary phase of PtSi was found to be absent on UIHV cleaned silicon substrates"' . The findings of Ref.3 and 5 are at variance with the results of a recent study which shows that the silicon substrate material, whether it is single crystal, polycrystalline or amorphous, has no effect on the sequence of compound formation of platinum silicides'. It is clear from the above excerpts of the existing literature that the roles of dopants and substrate crystallinity in the sequence and kinetics of platinum silicide formation is
Mat. Res. Soc. Symp. Proc. Vol. 54. , 1986 Materials Research Society
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