New advance in confocal microscopy

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 mu m. The procedure is direct by the integration of the measurement of intensity and phase, hereby faster than a normal scanning microscope. For the line-width 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.