A self-aligned silicide technology with the Mo/Ti bilayer system

Abstract

Self-aligned silicide (SALICIDE) with TiSi2 is the most widely used metallisation process that is based on the utilisation of metal silicides in the Si VLSI technology. One important issue with the TiSi;! SALICIDE process is the ever increased difficulties in phase formation on polycrystalline Si (poly-Si) lines, as the line width is scaling down continuously. It is more so on heavily doped poly-Si lines below 0.5 pm width.Despite numerous studies, the formation of TiSi2 remains as a technological challenge. Important advances in this specific subject have been made recently : The temperature needed for the formation of the C54 phase of TiSi2 is shown to be lowered by 100-150", either by ion implantation of MO or W into Si prior to Ti sputter-deposition [l], or by deposition of a thin MO layer between Ti films and Si substrates [2]. It has hrther been demonstrated [2,3] that a template mechanism is operative, at least for the case with the interposition of a thin MO layer.In this work, the formation of Ti& from the T M o bilayers on both blanket and patterned poly-Si substrates during rapid thermal annealing (RTA) was first studied by means of electrical measurements on van der Pauw test structures. Then, ohmic contacts between the silicide and both p-and n-type Si, as well as electrical shorts between the gate and sourceldrain electrodes were investigated. The MO layer was 0.5 nm thick (nominal), and the Ti layer 60 nm. The silicide formation was camed out in N? atmosphere at 700" or 800°C for 30 seconds. Sheet resistance ( R , )measurements of the TiSi2 films formed on blanket substrates show that the presence of MO enhances the formation of the C54 phase resulting in lower R, values at 7OOOC fig. l), in accordance with our previous results on <loo> Si and poly-Si substrates [2.3]. On submicron lines, the comparison between the silicide formed from the TiMo bilayers and that from pure Ti (reference) is presented infigure 2. Generally, R, is lower and the spreading in R, is smaller for the samples with MO, under otherwise the same conditions for silicide formation. For the TiSiz formed without MO, it is mainly the C49 phase that is formed at 700°C. Increasing the formation temperature to 800°C reduces R, substatially. but Rsqr increases considerably with decreasing linewidth presumably because of the uncompleted C49 to C54 phase transformation. With MO, R, is not only lower but also much less sensitive to linewidth, which is a consequence of the direct formation of the C54 phase already at 700°C [2,3]. For the samples with the silicide formed from the TiMo bilayers at 800"C, a constant value of R, around 2 0 per square is obtained down to 0.35 pm linewidth. Additional results on contact resistance measurement with Kelvin structures and bridging test with long gates will be presented, showing, probably for the first time, an approach towards the SALICIDE technology using TiMo bilayers. MAM'97 -Materials for Avanced Metallization 116