5. Stability: thermal and mechanical Thermal stability At elevated temperatures, metals can react with Si or SiO2 to produce unwanted phases, e. g silicides, eutectics or intermetallics This limits the maximum processing temperature (Typically quite low compared to temperatures needed for oxidation, dopant diffusion: hence the metal is done last Max temperatures Al on si <450°C Won s <600°C Effects can be predicted from the phase diagrams I/I703 3.l55J/6.152J Al-Si has a eutectic at 577 203040506070 C,1.59%Si During processing 57 The al unde co moras .o Mahaar a rg can diffi 1200 forms spikes into which can destroy any junction underneath SI Alon Si T>450°C barrier layers eg. PtSi, TiSi,, TiW, TIN 3.155J6.152J5. Stability: thermal and mechanical Thermal stability: At elevated temperatures, metals can react with Si or SiO2 to produce unwanted phases, e.g. silicides, eutectics or intermetallics. This limits the maximum processing temperature (T typically quite low compared to temperatures needed for oxidation, dopant diffusion: hence the metal is done last). Max. temperatures: Al on Si <450˚C W on Si <600˚C Effects can be predicted from the phase diagrams. 11/17/03 3.155J/6.152J 16 8 Al-Si has a eutectic at 577˚ C, 1.59%Si. During processing, Si can diffuse into the Al. The Al under compression, which can destroy any junction underneath. Al Si forms spikes into the Si Al on Si @ T > 450˚C Solution: add ~1%Si to metal; use barrier layers eg. PtSi, TiSi2, TiW, TiN 11/17/03 3.155J/6.152J 17