Metallization on Si-Ge Alloys

Abstract

Silicides are used as low resistivity contacts in VLSI circuits. As devices dimension starts to shrink, the existing silicides used have their drawbacks.

For this report, the silicidation or germanization reaction of nickel film on (100)Si, polycrystalline Si/Ge/Si79Ge21 was investigated.

It was found that when the substrate is Si(100), a low sheet resistance(3~5 ?/? ) corresponding to the low resistivity phase, NiSi was obtained, depending on what temperature the samples were annealed. However at higher temperature, the surface morphology was degraded, agglomerated resulting in high sheet resistance values (45 ?/?). When the substrate is polySilicon, the low resistivity phase existed for a lower temperature range, and the surface start to invert at a lower temperature resulting in high sheet resistance values (9~95 ?/?).

For the germanium type substrate, low sheet resistance values(2~3 ?/? ) were obtained due to the presence of NiGe. This occurred at low temperature ranges, and starts to invert at a lower temperature than the polySi samples. At even higher temperature, the surface starts to form bead-like structure and the sheet resistance increases significantly.

As for the Si79Ge21 type substrate, the low sheet resistance values of 3~4 ?/? was because of the Ni(Si1-yGey) solid mixture and existed at a higher temperature range than both the polysilicon and polygermanium samples. However at high temperatures, the surface formed bead-like structure rather than invert as in the case of the polysilicon sample and causes the sheet resistance to increase substantially.

The sheet resistance values will thus depends on the phases present and the surface morphology.