Morphological Instability of High Ge Percent SiGe Films Grown by Ultra-High Vacuum Chemical Vapor Deposition

The Ge content in SiGe bipolar transistors (HBTs) has been steadily increasing for the past few decades in order to meet higher Fmax targets. Problems exist with higher Ge content films due to the strain from the pseudomorphic growth on Si substrates. In addition to relaxation by misfit dislocation at high Ge contents, SiGe films have been observed to exhibit morphological instability or surfaces waves. This phenomena, known for some time, produces surface corrugations several nm in height that can have detrimental effects on SiGe HBTs. While historic solutions to the problem involved lowering the growth temperature, hot-wall UHVCVD presents a unique challenge due to the inability to quickly change temperatures during growth. In this report, the process parameters including film growth rate, temperature, and H2 pressure will be described in their effect on reducing and eliminating the surface waves. These results will be presented with regards to the total hydrogen coverage of the surface and the adatom mobility during growth.