The Study On Heterodyne Interferometric Microscope For Profiles Of Microelectronic Mask Surfaces Measurement

Focusing the developing tendency of both international and internal microelectronic industry, the measuring methods for the surface features of the mask plate by the heterodyne interferometric are researched in this dissertation. A Common-Path Heterodyne Interferometric Confocal Measuring System (CHICM) and a Polarization Heterodyne Interferometric Confocal Measuring System (PHICM) are proposed to measure the step height and the linewidth of a microelectronic mask. The two measuring system are detailedly investigated by the theory, experimentation and errors analyse.A novel CHICM system is presented to measure the step height of a mask. This measuring system keeps all the advantage of the Dual-frequency Interferometric Confocal Microscope (DICM): both high resolution (sub-nanometer) by heterodyne interferometry and relatively large measurement range (over 5 micron) by confocal method. Otherwise, the system has strong ability of overcoming environmental disturbance because it realizes the common path design by a birefringent lens. Moreover, the theory of the heterodyne interferometric and a dual-differential phase discrimination are studied in the dissertation; a low beat frequency transverse Zeeman laser and a FPGA phase measurement card were built. Otherwise, lock-in amplifier is used to measure the light intensity of the confocal microscope system; the relationship between the intensity and the distance from focus and specimen is analyzed.This dissertation proposes a novel PHICM system to accurately aim at the edge of the step, in order to measure the linewidth of a mask. The measurement system combines polarization interferometry with confocal microscopy. It focuses precisely using confocal technique to get best beam spot, which contains two orthogonal linear-polarized components, for measurement. The phase shifts of two components differ from each other when reflected by the edge of a step. The difference is measured using heterodyne interferometric technique and the edge is then positioned. This system satisfies common-path rule and is highly resistant to environmental disturbance. The principle is validated by simulations with the rigorous coupled-wave theory applied.Experimental results show that, under regular laboratorial condition (temperature variation is 1 degree Centigrade), the phase drift in CHICM system is less than 8 degrees within three hours. Its stability is better than that of a DICM system, which gives phase drift of 15 degrees within 1 hour under the same condition. From experiments, the uncertainty in edge positioning of the PHICM system is 15nm and the uncertainty of line width measurements is 21nm. The measurement of an international standard line-width specimen from the PHICM system accords well with the result from the Atom Force Microscope (AFM).