Pulsed-Laser Annealing, a Low-Thermal-Budget Technique for Eliminating Stress Gradient in Poly-SiGe MEMS Structures

Abstract

In this paper, we demonstrate eliminating the stress gradient in polycrystalline silicon germanium films at temperatures compatible with standard CMOS (Al interconnects) backend processing. First, we study the effect of varying the germanium concentration from 40% to 90%, layer thickness, deposition pressure from 650 to 800 mtorr and deposition temperature from 400 to 450/spl deg/C, on the mechanical properties of SiGe films. Then the effect of excimer laser annealing (248 nm, 38 ns, 780 mJ/cm/sup 2/) on stress gradient is analyzed. It is demonstrated that stress gradient can be eliminated completely by depositing Si/sub x/Ge/sub 1-x/(10%<x<92%) bilayers, with the bottom film exposed to a single laser pulse, which changes the grain microstructure of both the bottom and top films. Furthermore, laser annealing seems to reduce surface roughness, significantly, which is an attractive feature for some MEMS applications.