INTERFACIAL REACTIONS AND SILICIDE FORMATION IN SI NI/SI AND SI/CR/SISANDWICH LAYERS/

The preparation of well-characterized silicide thin films for microele ctronics needs a control of interfacial reactions and diffusion proces ses during heat treatment of metal/semiconductor systems. Two sandwich structures of Si(33 nm)/Me(50 nm)/Si(33 nm), where Me = Ni or Cr, wit h a total thickness of each structure of 116 nm were sputter deposited onto smooth silicon-(111) substrates. The reactions of both metals wi th amorphous silicon thin films were activated in a differential scann ing calorimeter (DSC), at a heating rate of 40-degrees-C/min-1, betwee n room temperature and different higher temperatures. Auguer electron spectroscopy depth profiles showed that the Si/Ni/Si sandwich structur e reacted almost completely during heat treatment up to 320-degrees-C and formed reaction products with a composition close to Ni3Si2. Selec ted area diffraction patterns revealed that this is a mixture of Ni2Si and NiSi silicides. A much less pronounced reaction between Si and Cr was observed in the Si/Cr/Si sandwich structure, even with heating to 630-degrees-C, resulting in CrSi2 silicide and different Cr-Si solid solutions. The results of AES depth profiling studies of the thermally treated sandwich structures are discussed in terms of diffusion proce sses, movement of interfaces and formation of silicides. The additiona l information obtained with differential scanning calorimetry and tran smission electron microscopy enables a detailed identification of reac tion products formed in the early stage of the thermally treated Si/Me /Si structures.