Abstract
A new surface profilometry technique is proposed for profiling a wafer surface with both diffuse and specular reflective properties. Most moiré projection scanning techniques using triangulation principle work effectively on diffuse reflective surfaces, on which the reflected light beams are assumed to be well captured by optical sensors. In reality, this assumption is no longer valid when measuring a semiconductor wafer surface having both diffuse and specular reflectivities. To resolve the above problem, the proposed technique uses a dual optical sensing configuration by engaging two optical sensors at two different viewing angles, with one acquiring diffuse reflective light and the other detecting at the same time specular surface light for achieving simultaneous full-field surface profilometry. The deformed fringes measured by both sensors could be further transformed into a 3-D profile and merged seamlessly for full-field surface reconstruction. Several calibration targets and industrial parts were measured to evaluate the feasibility and accuracy of the developed technique. Experimental results showed that the technique can effectively detect diffuse and specular light with repeatability of one standard deviation below 0.3 µm on a specular surface and 2.0 µm on a diffuse wafer surface when the vertical measuring range reaches 1.0 mm. The present findings indicate that the proposed technique is effective for 3-D microscale surface profilometry in in-situ semiconductor automated optical inspection (AOI).
Highlights
Measuring the 3-D profile of an object surface has become increasingly important in industrial automation, in in-situ product inspection. 3-D surface measurement could be generally classified into two major categories: tactile and non-contact measuring conditions
Optical techniques often require uniform surface light reflection to ensure reliable sensing. The absence of such condition would pose difficulty for using optical triangulation techniques to measure a surface with both diffuse and
phase shifting profilometry (PSP) is widely employed in industrial inspection because of its promising accuracy and high spatial resolution [4]
Summary
Measuring the 3-D profile of an object surface has become increasingly important in industrial automation, in in-situ product inspection. 3-D surface measurement could be generally classified into two major categories: tactile and non-contact measuring conditions. For obtaining the object shape, the common 3-D measurement techniques include mainly phase shifting profilometry (PSP) [1] and Fourier transform profilometry (FTP) [2] These techniques project structured light patterns, called fringes, onto the object surface. PSP is widely employed in industrial inspection because of its promising accuracy and high spatial resolution [4] It uses a time-resolved wrapping strategy to extract phase information for reconstruction of object profiles. Some light separation strategies using light property analysis were developed, including separation specular reflection using color analysis [3], examining chromaticity and intensity value of specular and diffuse pixels [16], employing polarization to separate reflection components [24] or using environmental structured illumination [25] techniques These methods have been effective to some extents in separating diffuse from specular light, they basically assume either uniform surface reflectance or specific surface light reflectance conditions, which may not be applicable for many in-situ testing applications.
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