Strained Si on insulator technology: from materials to devices

摘要

SiGe-free strained Si on insulator (SSOI) is a new material system that combines the carrier transport advantages of strained Si with the reduced capacitance and improved scalability of thin film silicon on insulator (SOI). We demonstrate fabrication of 20% Ge equivalent strain level SSOI substrates with Si thicknesses of 100 and 400 A by hydrogen-induced layer transfer of strained Si layers from high quality graded SiGe virtual substrates. The substrate properties are excellent: wafer scale strained Si film thickness uniformities are better than 8%, strained Si surface roughnesses are better than 0.5 nm RMS, and robust tensile strain levels are maintained during anneals as long as 80 min at 1100℃. Fully depleted n-MOSFET electrical results show that biaxial tensile strain, and hence enhanced mobility, is fully maintained in the 400 A 20% SSOI films through the substrate and device fabrication processes, even after a generous FET fabrication thermal budget. Long channel devices exhibit nearly ideal subthreshold slopes of 66 mV/decade and exhibit 112% electron mobility enhancements at N_(inv) = 1 x 10~(13) cm~(-2), identical to devices on bulk strained Si substrates. Furthermore, a photoemission microscopy study was used to confirm that the useable SSOI layer thickness significantly exceeds the critical thickness for fabrication of bulk strained Si FETs without deleterious leakage current effects. The fabrication of epitaxially defined, thin strained Si layers directly on a buried insulator is an ideal platform for future generations of Si-based microelectronics.