A Common-Path Heterodyne Interferometer for Surface Profiling in Microelectronic Fabrication

Articles you may be interested in Improved common-path fast-scanning heterodyne interferometer system as potential dense-plasma diagnostics Rev. Power spectral densities: A multiple technique study of different Si wafer surfaces A prototype imaging second harmonic interferometer Rev. We describe the design of a common-path heterodyne laser interferometer for the surface profiling of micron-sized photopatterned features during the microelectronic fabrication process. The common-path design of the interferometer's reference and measurement arms effectively removes any path length difference in the measurement which can be attributed to the movement of the target surface. It is shown that repeated surface profiling during the ion milling process allows the difference in etch rates between the photoresist layer and the exposed portions of the underlying substrate layer to be monitored online. A prototype apparatus has been assembled and results demonstrating the usefulness of the device are reported. The surface profiles of both a photopatterned nickel–iron trench and an unmasked aluminum trench are measured and compared to those obtained using a stylus-based scanning profiler and an atomic force microscope.