TiN as a Phosphorus Outdiffusion Barrier Layer for WSi_x/Doped-Polysilicon Structures (Special Issue on Sub-Half Micron Si Device and Process Technologies)

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Phosphorus-doped amorphous or polycrystalline silicon can yield a conformal, low resistance, thermally-stable plug for the high-aspect-ratio, sub-half-micron contact-holes found in current development prototypes of future 64 and Mega-bit DRAMs. When directly contacted to a silicide layer, however, such as WSi_x found in polycide gate or bit line metallization / contact structures, the outdiffusion of phosphorus from the doped-silicon layer into the silicide can occur, resulting in an increase in resistance. The characteristics of both the doped-silicon and WSi_x layers influence the outdiffusion. The grain size of the doped silicon appears to control diffusion at the WSi_x / doped-silicon interface while the transition of WSi_x from an as-deposited amorphous to a post-annealed polycrystalline state appears to help cause uniform phosphorus diffusion throughout the silicide film. The results of phosphorus pre-doping of the silicide to reduce the effects of outdiffusion are dependent upon the relative material volumes and interfacial areas of the layers. Due to the effectiveness of the TiN barrier layer / Ti contact layer structure used in Al-based contacts, Ti and TiN were evaluated on their ability to prevent phosphorus outdiffusion. Ti reacts easily with doped silicon and to some extent with WSi_x, thereby allowing phosphorus to outdiffuse through the TiSi_x into the overlying WSi_x. TiN, however, is very effective in preventing phosphorus outdiffusion and preserving polycide interface smoothness. A WSi_x / TiN / Ti metallization layer on an in situ-doped (ISD) silicon layer with ISD silicon-plugged contact-holes yields contact resistances comparable to P^+-implanted or non-implanted WSi_x layers on similar ISD layers / plugs for contact sizes greater than approximately 0.5 μm but for contacts of 0.4 μm or below the trend in contact resistance is lowest for the polycide with TiN barrier / Ti contact interlayers. A 20 nm-thick TiN film retains its barrier characteristics even after a -hour 850℃ anneal and is applicable to the silicide-on-doped-silicon structures of future DRAM and other ULSI devices.
社団法人電子情報通信学会の論文
1993-04-25

TiN as a Phosphorus Outdiffusion Barrier Layer for WSi_x/Doped-Polysilicon Structures (Special Issue on Sub-Half Micron Si Device and Process Technologies)

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