The relaxation of patterned, compressively strained, epitaxial Si0.7Ge0.3 films transferred to borophosphorosilicate (BPSG) glass by a wafer-bonding and etch-back technique was studied as an approach for fabricating defect-free Si1−xGex relaxed films. Both the desired in-plane expansion and undesired buckling of the films concurrently contribute to the relaxation. Their relative role in the relaxation process was examined experimentally and by modeling. Using x-ray diffraction, Raman scattering and atomic force microscopy, the dynamics of in-plane expansion and buckling of Si0.7Ge0.3 islands for island sizes ranging from 10 μm×10 μm to 200 μm×200 μm for anneal temperatures between 750 and 800 °C was investigated. Lateral relaxation is favored in small and thick islands, and buckling is initially dominant in large and thin islands. Raising the temperature to lower viscosity of the oxide enhances the rate of both processes equally. For very long annealing times, however, the buckling disappeared, allowing larger, flat, and relaxed islands to be achieved. Cross-sectional transmission electron microscopy observation on a relaxed Si0.70Ge0.30 island revealed no dislocations, confirming that SiGe relaxation on BPSG is a good approach to achieve high quality relaxed SiGe.
The aggressive downscaling of complementary metal-oxide-semiconductor (CMOS) technology to the sub-21-nm technology node is facing great challenges. Innovative technologies such as metal gate/high-k dielectric integration, source/drain engineering, mobility enhancement technology, new device architectures, and enhanced quasiballistic transport channels serve as possible solutions for nanoscaled CMOS. Among them, mobility enhancement technology is one of the most promising solutions for improving device performance. Technologies such as global and process-induced strain technology, hybrid-orientation channels, and new high-mobility channels are thoroughly discussed from the perspective of technological innovation and achievement. Uniaxial strain is superior to biaxial strain in extending metal-oxide-semiconductor field-effect transistor (MOSFET) scaling for various reasons. Typical uniaxial technologies, such as embedded or raised SiGe or SiC source/ drains, Ge pre-amorphization source/drain extension technology, the stress memorization technique (SMT), and tensile or comprehensive capping layers, stress liners, and contact etch-stop layers (CESLs) are discussed in detail. The initial integration of these technologies and the associated reliability issues are also addressed. The hybrid-orientation channel is challenging due to the complicated process flow and the generation of defects. Applying new highmobility channels is an attractive method for increasing carrier mobility; however, it is also challenging due to the introduction of new material systems. New processes with new substrates either based on hybrid orientation or composed of group III-V semiconductors must be simplified, and costs should be reduced. Different mobility enhancement technologies will have to be combined to boost device performance, but they must be compatible with each other. The high mobility offered by mobility enhancement technologies makes these technologies promising and an active area of device research down to the 21-nm technology node and beyond.
A cap layer was used to suppress buckling during the relaxation of compressively strained 30 nm Si 0.7 Ge 0.3 islands on borophosphorosilicate glass. The lateral expansion and buckling of a bilayer structure made of SiGe and a cap layer were studied by both modeling and experiment. Both epitaxial silicon and amorphous silicon dioxide (SiO 2) caps were investigated. Caps stiffen the islands to reduce buckling and accelerate the lateral relaxation, so that larger, flat, relaxed SiGe islands can be achieved. Using a 31 nm silicon cap, flat Si 0.7 Ge 0.3 islands up to 200 mϫ200m were achieved. However, germanium diffusion in the SiGe/Si structure took place during relaxation anneals and lowered the germanium fraction of the final fully relaxed SiGe film. Silicon dioxide caps, which are not prone to germanium diffusion, allowed suppression of SiGe buckling without lowering the germanium percentage. Full relaxation of SiGe islands was achieved by a controlled multicycle silicon dioxide removal and anneal procedure. Large, fully relaxed, smooth SiGe islands obtained using cap layers indicate that this approach could be of potential use for electronic device applications.
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