Research On Relaxation Of SiGe/SOI And Fabrication Of SSOI Materials

Strained silicon was a new type electronic material. It was been fabricated by hetero-epitaxial growth of ultra-thin silicon layer on relaxed SiGe substrates. The strained silicon layer was under a biaxial compress stress. In its conduction band, six valleys degenerated without strained are split into 2-fold valleys with low energy and 4-fold valleys with high energy by strain. Since strained Si provided both large conduction and valence band offsets, a significant improvement in hole and electron mobility can be achieved. Strained Si is becoming one of the most promising materials for MOSFETs channels, because the compatibility with Si LSI technology. It was very important for development of VLSI to fabricate high quality strained silicon materials.In general, it need relaxed SiGe layer with low threading dislocation density as the substrates to epitaxial grow strained silicon. However, alloy scattering in SiGe film degradated carriors mobility, and several micrometers thick SiGe buffer layer was hard for photolithography. Strained silicon on insulator was combination of SOI technology and strained silicon technology. It was not suffer from alloy scattering (hence mobility degradation). Photolithography was easily without several micrometers thick SiGe buffer layer. There were both virtues of SOI and strained silicon in SSOI materials. In recent years, it was the hotspot and emphasis of semiconductor research field.In recent years, SSOI layers without intermediate relaxed SiGe layers were fabricated by a combination of wafer bonding and Smart Cut. The strained silicon layer epitaxial grown on relaxed SiGe substrates was bonding with SiO₂ layer oxidated on Si surface. Smart Cut was done by ion implantation for removing SiGe films. This method was still inexperimental discussion.In research of the relaxation of strained SiGe film epitaxial grown on ultra-thin SOI substrates, people found that there was low threading dislocation density in SiGe film with high degree relaxed and there was some partial strain in the SOI substrates. From this result, we discussed the relaxation mechanism of strained SiGe film on ultra-thin SOI substrates. There was a strain distribution and transfer process between SiGe film and top silicon layer. The strain in each side of the bilayer is determined by the thickness and composition of two layers. Strain in SiGe film was relaxed through strain distributed and transfer from SiGe film to SOI layer. The strain transferred to SOI layer was relaxed through two ways: 1, dislocation nucleated and propagation, 2, gliding of SOI layer on SiO2 interface. However, the Si/SiO2 interface has covalent bonds, the layer would have to more macroscopic distance to accommodate the lattice mismatch over a wafer, and the viscosity of SiO2 is too low and these temperatures to have this mechanism work. The SOI layer relaxed through dislocation formation not gliding on Si/SiO2 interface. If the Si/SiO2 interface was weaked by sub process, the SOI layer could glid on SiO2 layer to relax the strain distributed from SiGe film. New strain was formed in SOI layer during gliding process to resisted the strain transfer form SiGe film to top silicon layer. Strain formed in SOI layer was keeped after SiGe film removed.In this article, strained SiGe film was epitaxial grown on ultra-thin SOI substrate. N+ ions were implanted into SOI substrate above Si/SiO2 interface. Si/SiO2 interface was weaked by the ion implanted in it. In later annealing, strain transfer from strained SiGe film to SOI layer. SOI layer glided on SiO2 layer to relax the strain distributed from SiGe film. The SOI layer was partial strain after annealing. The residual strain in SSOI layer was 7%. It was a new idea for fabrication of SSOI materials.