An INSPECT Measurement System for Moving Objects

Noncontact optical imaging is frequently used in the inspection and metrology of stationary objects, including in particular the reconstruction of the 3-D surface profile. A technique, known as phase-measuring profilometry, involves projecting a sinusoidal pattern and then inferring the height of various points on the object by measuring the resulting phase changes at the respective locations. However, this method cannot be directly applied to systems involving moving objects, as the translation and the perspective geometry effect manifest as errors in the height calculations. In this paper, we report on an imaging and numerical surface profilometry with error compensation technology (INSPECT) measurement system that is tailored for moving objects. We model the imaging system that considers the nonlinear perspective geometry effect, and simplify to a first-order equation using Taylor series expansion. With this, we generalize the conventional phase shift algorithm, and develop the optimization procedures that can compute the height information effectively. We apply this technology to the INSPECT measurement system in semiconductor manufacturing and show significant improvement in accuracy and robustness.