Anisotropic stress observation of 4H-SiC trench metal-oxide semiconductor field-effect transistor test structures by scanning near-field optical Raman microscope

We prepared two types of trench-test metal-oxide semiconductor field-effect transistor (MOSFET) structures on m- and a-faces in 4H silicon carbide (4H-SiC) and investigated the anisotropic stress distribution of small trenches with a depth of 1 μm using a scanning near-field optical Raman microscope (SNOM) that we developed. The stress distributions of σ₁₁ (a-axis) under the bottom of the trench for m-face were approximately 100 MPa larger than those for a-face, and the stress distributions of σ₃₃ (c-axis) under the bottom of the trench for m-face were almost the same as those for a-face. The experimental result agrees well with that calculated by the finite element method (FEM). These results indicate that the anisotropic stress distributions of σ₁₁ components around the apex of the trenches of 4H-SiC trench-test MOSFET occur in m- and a-faces. Thus, it is possible that the differences in mobilities for m- and a-faces might be caused by the anisotropic stresses.