Strain relaxation in patterned strained silicon directly on insulator structures

Abstract

Strain relaxation is studied in strained silicon directly on insulator (SSDOI) substrates patterned with nanoscale features. Using interference lithography, biaxially strained SSDOI substrates with 30nm thick strained Si on insulator films were patterned into grating structures with 90nm wide stripes, and arrays of 80nm×170nm pillars. The strain profiles of these patterned structures were examined by ultraviolet Raman spectroscopy. Raman analysis of the SSDOI gratings indicates strain relaxation in the 90nm wide stripes, compared to the strain measured in unpatterned portions of the SSDOI wafer. Three-dimensional finite-element modeling of the stress distributions in the grading structures predicts that 95% of the strain is maintained in the direction along the length of the stripes. These simulations are used to decouple the strain components along the width and length of the SSDOI grating structure, inferred from Raman measurements. The results are consistent with substantial stress relaxation across the width of the stripes and very little stress relaxation along the length of the stripes.