Effects of High-Pressure Hydrogen Gas Exposure on the Residual Stress Fields and Cracks around Vickers Indentations

Effects of high-pressure hydrogen gas exposure on the residual stress fields and cracks around the Vickers indentations introduced into {100} silicon wafers were investigated. Square chip test pieces (10 × 10 × 0.6 mm3) were cut out from a mirror-finished (001) silicon wafer that was sliced from a large crystal (diameter 300 mm, resistivity 15 Ωcm) grown using the Czochralski (CZ) method. Vickers indentations were introduced on the (001) Si wafer surface. Loads of indentations were 0.98 N and 1.96 N, and the holding time was 30 s. Upon indentation, not only was a large internal stress field formed around the indent, but small cracks were also initiated along the {110} planes from the four corners of the indent. A laser Raman microscope was used to measure the residual stress distribution before and after the hydrogen gas exposure, with four hydrogen gas pressures (from 10 to 100 MPa) applied at 270 °C for 24 h. Crack growth occurred after the hydrogen gas exposure. The crack growth ratio increased up to a hydrogen gas pressure of 35 MPa, with increasing gas pressure. However, for the hydrogen pressures above 35 MPa, the crack growth ratio was saturated, and the upper limit of the crack growth ratio was approximately 9%. Furthermore, it was found that the hydrogen gas exposure caused the compressive residual stress around the indentation to decrease. The results suggest that hydrogen may reduce the residual stress field around the crack, which is related to one of the causes of hydrogen embrittlement.