Improving resistance of metal-silicide layers to heat treatment - when deposited on previously sputter-cleaned surface in layer with adequate thickness

摘要

Thin layers of silicides of refractory metals, used in Si processes, are formed by siliciding of metal layers deposited in a sputtering process immediately after sputter cleaning in an inert gas the surface of the substrate. The metal deposition pref. Ti, is made in the same equipment with a layer thickness of at least 50 nm, pref. 60 nm, to allow heat treatments at temps. of at least 900 deg. C. The silicide formation is then carried out, using rapid thermal annealing in N2, in 2 steps at a temp. in the range 600-850 deg. C sepd. by a wet etching step to remove the unreacted metal or metal-nitride. Following high temp. processes are then carried out at a min. temp. of 900 deg. C., e.g. to flow an intermediate oxide layer. The siliciding process is carried out pref. in N2 over a time of 20 secs. at 650 deg. C for the first step and for 10 secs. at 850 deg. C for the second step. The intermediate oxide is formed by a deposition of SiO2, pref. 150 nm thick from thermal decomposition of tetratethylortho-silicate, followed by deposition of BP-silicate glass, pref. a 650 nm thick layer. USE/ADVANTAGE - The process of restructuring of the silicide layer, which currently causes resistance increase of the contacts, is significantly reduced by the process changes. This results in contact resistance values of 2.0 ohm/sq. and 1.7 ohm/sq. for contact between Ti-silicide and respectively an n(+)- and a p(+)-Si-layer with a surface concn. of 5 x 10 power 19 and of 3.2 ohm/sq. to an n(+)-polysilicon layer with a concn. of 10 power 21.