High reliable Al-Si alloy/Si contacts by rapid thermal sintering

As device size reduces, the Si in A1-Si alloy In conclusion, rapid thermal annealing technology causes serious problems on reliability. One of them is has been applied for sintering process. Low contact contact resistance increase due to Si precipitation at resistance has been maintained even afcer postcontact holes. It is difficult to solve this problem sintering heat treatments. A d e l t'mt explains chis by conventional furnace annealing process and a new effect with nmber of Si nodules was proposed. It is annealing technology is desired. Rapid thermal clarified that RTS is an effective technique for annealing technology has been applied for sintering metallization process. process (Rapid Thermal Sintering : RTS) and high reliable contact characteristics has been obtained. Contact resistance measurement samples were prepared using conventional VLSI fabrication processes. Surface carrier concentration for n+ Si and pt Si were 3~1O~~cm-3 and 2x1OZ0 cm-! respectively. Al-lYSi was used for metallization material. Contact resistance for lw@ contacts was measured by Kelvin's pattern. Samples for Si nodule observation were prepared as follows. BPSG film ( 3 O h ) was deposited on 6-inch Si(100) wafers. Al-lYSi ( 7 O O m ) was deposited by mgnetron sputtering method. After heat treatments, Si was delineated by phosphorus acid and Si nodules were observed by scanning electron microscope. In both evaluation, heat treatments were carried out by furnace or rapid thermal annealing equipnent. Furthemre, additional annealing considering post-sintering heat treatments were performed by furnace. Contact resistance of furnace-sintered (FS) samples increases with post-sintering heat treatment. On the other hand, RTS samples has no increase on contact resistance. In order to analyze this result, relationship between contact resistance and the nmber of Si nodules has been investigated. The nmber of Si nodules can be controlled easily by RTS. Si nodules formed by RTS is larger in nmber than those f o m d by FS. Si nodules formed by FS and WS has a drastic difference in nmber. Its tendency is kept even after post anneal. This phenomenon can be explained by the theory of classical homogeneous nucleation considering heat treatment time. Contact resistance is kept low in the region where the nmber of Si nodules is large. While, as the nmber of Si nodules decreases, contact resistance increases drastically. In order to explain this result, we propose a d e l here. The Si contained in A1-Si alloy continues dissolving and precipitating during heat treatments. The dissolved Si in A1-Si' precipitates to nuclei after heat treatment. Si nodules and the Si at contact holes are considered to be nuclei for precipitating Si. After all, the dissolved Si are shared by these nuclei. When the number of Si nodules existed around a contact hole is large, the amount of Si precipitated at the contact hole is small and the contact resistance is kept small. On the other hand, contact resistance increases when the n m k r of Si nodules existed around a contact hole is small. RTS realizes low contact resistance by making the nmber of Si nodules large.