Selective versus non-selective growth of Si and SiGe

Selective epitaxial growth of Si and SiGe at low temperatures and reduced pressure in a single-wafer CVD reactor has been characterized with respect to its sensitivity to pattern changes. Small variations in the surface ratio of nitride (or oxide) and exposed Si cause relatively large deviations in the growth rates. The Si and SiGe growth rates are affected in opposite ways. Even worse are pattern discontinuities across the area to be deposited, unavoidable at the edge of the wafer. These discontinuities are detrimental to the deposition uniformity and are active over a long range. A sacrificial poly layer has been successfully applied to overcome these problems. An alternative solution is the deposition of a continuous Si layer which grows epitaxially on the Si in the windows and polycrystalline on the nitride or oxide fields. This offers the same advantages in suppressing the loading effects, albeit that the specific features of selective growth are lost. A limited comparison of the two growing methods in terms of process robustness was made. There is no clear winner, each method has its own share of problems.