A high-resolution non-contact thickness test method of ultra-thin silicon diaphragm

This paper reported a high-resolution non-contact thickness test method of ultra-thin silicon diaphragm fabricated by KOH cavity erosion. For the first time, the test sensitivity increases when film thickness decreases, so the novel method is especially suitable for ultra-thin film measurement. Traditional test methods, like optical microscope, step profiler and optical profiler, are incapable of measuring thin films due to silicon wafer total thickness variation (TTV). Employing the deformation mechanism for multi-layer materials, a film thickness and film deformation curvature radius (Curve) relationship model is established and optimized to realize high-resolution and non-contact thickness measurement. Only by measuring membrane curvature radius, film thickness will be handily got. The stress release structure (SRS) on KOH mask is the key to the thickness measurement. For 5.01 μm thickness thin film (480 μm × 480 μm), Curve is measured as −18.77 mm. In addition to the high precision (3 nm) of vertical deformation measurement of optical profiler, the resolution of the film thickness measurement method is very high (< 0.1 μm).