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.