The metrology of a miniature FT spectrometer MOEMS device using white light scanning interference microscopy

Micro-optical electro-mechanical systems (MOEMS) technology, making use of existing silicon based fabrication techniques shows great potential for making complete miniaturized hybrid devices. Such technology has been used to make a Fourier transform spectrometer based on a time-scanning Michelson interferometer. An electrostatic comb drive actuator moves the scanning mirror over a distance of 40 μm. The measured resolution of the spectrometer is 6 nm at a wavelength of 633 nm. The dimensions of the device are 5×5×0.5 mm, and the depth of feature is 75 μm. During quality control of such devices it is necessary to check the dimensions of micron wide structures that are tens of microns deep, over areas of tens of square millimeters. In this work we have investigated the use of white light scanning interference (WLSI) microscopy for making rapid, non-destructive precision three-dimensional measurements. While a high axial precision can be achieved, an artifact has been observed with classical configurations that tend to extend the location of deep step discontinuities by up to 3 μm and so broaden narrow structures. With certain modifications in the optical configuration, this error can be considerably reduced. The results of this work demonstrate that WLSI shows great potential for the rapid and precise quality control of MOEMS devices.