Low coherent Linnik interferometer optimized for use in nano-measuring machines**This article was presented at the 56th International Scientific Colloquium on ‘Precision Engineering and Precision Measurement Technology’ held at Ilmenau University of Technology, Germany, and submitted for publication in the July 2012 special issue of this journal devoted to papers from that meeting.

Abstract

The precise acquisition of three-dimensional geometrical data in micro- and nanotechnologies plays a crucial role in advanced fabrication processes. Scanning white-light interferometry achieves nanometer resolution in the axial direction, but the lateral resolution is far more critical. The requirements for an area-based optical sensor in a nano-measuring machine are very high. The resolution in every dimension and the working distance have to be as high as possible. In contrast to a Mirau interferometer, a Linnik interferometer does not need any optical components in front of the objective lens. This benefit permits both a long working distance and a high lateral resolution. In the EC-funded project ‘NanoCMM’ we developed a Linnik interferometer providing a working distance of more than 5 mm and a lateral resolution of 0.44 µm. This is achieved by near-UV illumination. The interferometer measures the full modulation depth and the rectangular shape of a pitch standard with 0.6 µm pitch length.