A method for inspecting near-right-angle V-groove surfaces based on dual-probe wavelength scanning interferometry

摘要

High-angled structured surfaces such as micropyramidal arrays, V-grooves and lenslet arrays are widely used in industries. However, there is currently no effective way to inspect these microstructures, resulting in very high scrap rates. This paper presents a proof-of-principle demonstration of an optical system capable of measuring V-groove structures in a single measurement acquisition. The dual-probe wavelength scanning interferometry (DPWSI) system comprises dual probes, with orthogonal measurement planes. The calibration of the DPSWI system is the key to registering the relative locations of the dual measurement planes and allowing the surface topography to be correctly reconstructed. In order to achieve this, a custom calibration artefact was manufactured comprising focused ion beam etched features on two faces of a precision cube. The procedures for the characterisation of the artefact to generate reference topography, and the subsequent calibration of the DPWSI are described in full. A measurement example from a metallised saw tooth sample featuring near-right-angles grooves having a peak-to-valley height of 32 mu m and nominal pitch of 25 mu m is presented and compared with a result obtained using stylus profilometry. DPWSI is shown to obtain an areal dataset in a single acquisition and is able to better resolve peak/valley points compared with the stylus, which is limited by a 2-mu m tip radius. Some lateral scale error is apparent in the final DPWSI results and a discussion of this in terms of the limitations surrounding the current calibration artefact is presented.