Abstract
AbstractUltrathin refractory metal silicide films, such as tungsten silicide (WSix) offer a wide range of applications in VLSI and ULSI circuits such as local interconnects, bit lines and wordlines. One practical way of depositing WSix is by a CVD technique in which WF6, is reduced by either silane (SiH4) or dichlorosilane (SiH2 Cl2 ). In this investigation, step coverage characteristics of silane based and dichlorosilane based tungsten silicide films, deposited by low pressure chemical vapour deposition method will be compared. WSix films of various thicknesses (1200–2000 Å) were deposited on topographies created by patterning poly-Si layers. WSix, step coverage was evaluated as a function of deposition temperature, poly-Si layer thickness and poly-Si line spacing. Field emisssion scanning electron microscopy was used to characterize step coverage profiles. It is clearly shown that, silane based WSix films deposited on poly-Si lines with sub 0.5 micron spacings result in poor step coverage which could lead to higher localized stress, cracking and higher line resistance. Dichlorosilane based WSix, on the other hand showed more conformal step coverage, which results in better process marhin for subsequent patterning steps. Finally, it was also observed that, the final silicide profile is highly dependent on the thickness of the underlying poly-Si layer, as well as poly patterning process margin.
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