Strain relaxation of silicon-germanium on compliant borophosphosilicate glass and its applications

We have studied the strain relaxation of SiGe on compliant borophosphosilicate glass (BPSG). Through modeling and experiments it has been shown that strain relaxation in the SiGe film can be induced by lateral expansion and buckling of the SiGe film. Stress balance of a bilayer on the compliant oxide has been observed for the first time. Geometry has been successfully utilized to realize uniaxial and orthorhombic strain. Buckling on large islands can be suppressed using stress balance of SiGe/Si or SiGe/SiO2 bilayers. Fully-relaxed, flat SiGe islands with edge width as large as 100 mum have been achieved.; We have explored two methods to achieve high Ge-content relaxed SiGe films: SiGe oxidation and stress balance of SiGe films on BPSG. We have demonstrated Ge content as high as 70%. Strain resulting from the increased Ge content has been found to relax by lateral expansion, which makes dislocations unnecessary.; To achieve tensile silicon, stress balance between Si and SiGe layers has been employed. Ten nm strained silicon on BPSG with low doping levels has been obtained by removing the top SiGe film after stress balance. Fully-depleted strained-Si n-channel MOSFETs on BPSG were fabricated and strain-induced electron mobility enhancement of 50% has been observed. The absence of SiGe in the final device structure overcomes any potential process or device drawbacks due to existence of a SiGe layer.