Subcritical Crack Growth in Single-crystal Silicon Using Micromachined Specimens

A micromachined specimen with a test section only 150-μm thick was developed for investigating subcritical crack growth in silicon. Crack growth rates in the range 10⁻⁴–10⁻¹⁰m/s were measured as a function of applied stress intensity (v–Kcurves) during tests in humid air and dry nitrogen lasting up to 24 h. The fracture toughness,K_Icof {110} silicon was also measured at 1.15 ± 0.08 MPa m^1/2. While some evidence MPa-m^1/2of subcritical crack growth appeared to occur in the region 0.9K_Ic 0.98K_Ic, the extremely high crack growth exponent (n100) and the high ratio of the apparent stress corrosion threshold,K_Iscc, to the fracture toughness,K_Iscc/K_Ic> 0.9, suggests that no clear evidence exists for a stress corrosion process in silicon exposed to humid air.