The effects of low-angle off-axis substrate orientation on MOSFET performance and reliability

The effects of low-angle off-axis substrate orientation on MOSFET performance and reliability are examined. When <100> wafers are tilted off axis from 0 degrees to 8 degrees around the <011> axis, two principal effects are observed. First, for current flow normal to the axis of rotation, inversion-layer mobility is lower than for current flow in the parallel direction. This mobility difference is due to anisotropy in the inversion-layer effective mass as well as increased surface roughness in the normal compared with the parallel direction. Second, as the substrate is rotated off axis, the susceptibility of gate oxide to defect-related breakdown is enhanced. The off-axis surface exhibits increased surface roughness, which promotes nonuniform oxidation and can significantly degrade VLSI reliability.<
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