In recent years, silicon germanium (SiGe) has become one of the most promising materials for the fabrication of heterojunction bipolar transistor, metal-oxide-semiconductor (MOS) field-effect transistor (FET), and optoelectronic devices [1-3]. Among these devices, the MOS device is the most interesting because it is compatible with Si technology and the possibility of ultra large scale integrated (ULSI) circuit fabrication. Moreover, the hole mobility [4] of SiGe is higher than that of Si; therefore, SiGe-based complementary MOSFET (CMOS) can provide a faster switching speed and a larger driving capacity than conventional Si CMOS.
However, the benefits of SiGe-based MOS transistors have been limited mainly due to the difficulty in achieving high-quality gate oxides (SiO 2 ) on SiGe strained layer. It had been shown previously that SiGe wet oxidation and rapid-thermal oxidation [4,5] in pure oxygen or in steam to produce SiO 2 will cause Ge to be rejected completely out of the SiO 2 layer to form a Ge-rich layer at the SiO 2 / SiGe interface. The resulting Ge-rich layer is responsible for the high fixed oxide charge, interface state densities and poor breakdown characteristics of MOS devices with SiGe oxides.
To overcome these problems, low-temperature radio-frequency (RF) plasma [6] and electron-cyclotron resonance (ECR) [7,8] techniques were proposed for SiGe oxidation.