Critical Factors for Enhancement of Compressive Strain in SGOI Layers Fabricated by Ge Condensation Technique

Strained SiGe has been regarded as one of the promising channel materials of p-channel MOSFETs. Here, high Ge contents over 0.85 and high compressive strain are effective in significantly increasing the hole mobility [1]. In addition, ultrathin SiGe-On-Insulator (SGOI) structures are suitable for scaled MOSFETs, because of the immunity against short channel effects. One of the promising techniques to fabricate the compressive-strain SGOI structures is the Ge condensation technique [2, 3]. In the conventional Ge condensation using unstrained SOI substrates, the strain relaxation occurs around the Ge fraction of 0.6. However, the effects of the oxidation process and the substrate structures before oxidation on the strain in the SGOI layers have not been studied yet. In this paper, we have examined the effects of the oxidation recipe and the initial substrate structures before oxidation on the strain relaxation properties for realizing the SGOI channel layers with higher Ge fraction and higher strain. (100)-oriented strained-SOI (sSOI) and SOI substrates were used. SiGe layers and 8 nm Si cap layers were epitaxially grown on sSOI and SOI substrates by a low-temperature MBE. The SiGe thickness was 33, 40, 54 and 69 nm and the Ge fraction, x, was 0.16, 0.22 and 0.28. A Si layer of the sSOI substrate had 0.83 % bi-axial tensile strain, corresponding to the strain in sSi on SiGe with the Ge fraction of 0.2. The Ge fractions and in-plane strain in the SGOI layers were evaluated by Raman spectroscopy. Fig. 1 shows the change in the compressive strain for the SOI substrate during the Ge condensation under two oxidation recipes. In the recipe A, the samples were oxidized at 1100 C for x < 0.49, at 1050 C for 0.49 < x < 0.6, at 1000 C for 0.6 < x < 0.74, at 950 C for 0.74 < x &lt