Yin, C., Lin, D., Liu, Z. and Jiang, Xiang (2006) New advance in confocal microscopy. Measurement Science and Technology, 17 (3). pp. 596-600. ISSN 0957-0233

Step height and line-width are two key parameters in the metrology
of micro-electronic masks. A novel common-path heterodyne interferometric
confocal measuring system is presented to measure the step height of masks. It
combines both the methods of heterodyne interferometry and confocal
microscopy. The resolution is 0.01 nm and the measurement range is around 8
μm. The procedure is direct by the integration of the measurement of intensity
and phase, hereby faster than a normal scanning microscope. For the linewidth
measurement of masks, a polarization heterodyne interferometric
confocal microscope is proposed, which combines a polarization
interferometer with a confocal microscope. An ideal beam spot is obtained and
precise focus is realized by using the confocal technique. The phase shifts of
the two orthogonal polarization beams differ from each other when they are
reflected at the edge of a sample. The experimental results show that the
uncertainty of line-width measurement is 21 nm. Both of the systems satisfy
the common-path principle, so as to get high ability of resistance to
environment disturbances.

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