Development of a combined interference microscope objective and scanning probe microscope

Abstract

A compact sensor head combining optical interference and scanning probe microscopy in a single instrument has been developed. This instrument is able to perform complementary quantitative measurements, combining fast nondestructive three-dimensional surface analysis with high lateral resolution imaging. A custom interference microscope sensor head has been designed as the optical microscope objective and integrated within the architecture of a commercial interference microscope. The combined instrument makes available both the acquisition software and the hardware interface of the commercial microscope. The latter is able to function as a phase-shift interferometer or white light interferometer. Furthermore, the use of an optical fiber to transmit light from an external laser: (i) removes a major heat source from the measurement environment and (ii) makes aperture correction unnecessary. The lateral resolution of the instrument has been extended by the addition of a previously developed compact scanning probe microscope (SPM) module to the custom interference microscope objective. This SPM unit is based upon piezoresistive cantilever technology. The “piezolevers” are self-sensing and therefore require no additional systems, such as optical beam deflection or fiber interferometry, to monitor their displacement. The mechanical simplicity of the piezolever SPM unit allows for a small physical size and can thus be added to the custom optical sensor head without violating constraints on the working distance defined by the optics. A major benefit of the system, in terms of a quantitative nanometrology, is the possibility to perform a traceable and direct calibration of the SPM module. This calibration is achieved practically by measuring an appropriate sample at a common location using both techniques. Results are presented here for the measurement of two calibration standards and a test sample to demonstrate the increased lateral resolution of the instrument.