Planarization of SiGe virtual substrates by CMP and its application to strained Si modulation-doped structures

Strained Si and Ge channel high-speed devices are generally formed on strain-relaxed SiGe buffer layers (SiGe virtual substrates). However, strain-relaxed SiGe buffers grown on Si substrates usually have rough surfaces and induce the interface roughness in the strained channel layers grown on the SiGe buffers, which is thought to reduce the mobility of the carriers in the channels. To overcome this problem, surface planarization of SiGe buffers by Chemical Mechanical Polishing (CMP) is sometimes performed. Here we investigated the strain field of the CMP planarized buffers and overgrown strained Si layers by micro Raman spectroscopy and electric properties of the overgrown modulation doped (MOD) structures.