A novel dielectric isolation process using molten SiGe

Using SiGe as a deposited material in the MSSD (molten silicon spraying deposition) process, the authors have lowered the substrate temperature to 1200°C while reducing the substrate curvature. The mechanism of curvature in this process is discussed. It is speculated that two kinds of stress influence the substrate curvature. One stress is caused by the thermal contraction of the SiGe layer while the temperature of the solidified SiGe layer drops to the substrate temperature. The other stress is caused by the volume expansion of the SiGe layer during solidification. The condition that enables the substrate curvature to be small is a Ge concentration between 4.3 at.% and 5 at.% at a substrate temperature of 1200°C. This process is very promising for fabricating low-cost dielectrically isolated substrates