Sidewall profile reconstruction of microstructures with high aspect ratio based on near-infrared light scanning interferometry

Sidewall profile reconstruction of microstructures with the high aspect ratio is a problem urgently to be solved in MEMS field. In this paper, a measuring method based on near-infrared light scanning interferometry (NILSI) is presented according to the transmission principle of semiconductor materials in the infrared light region. The NILSI is extended from the white light to near-infrared light and from surface profile reconstruction to sidewall profile reconstruction. The NILSI system is constituted by a near-infrared light source, an interference microscope, infrared CCD, piezoelectric ceramics (PZT) with high accuracy and the data acquisition system. The test sample is taken from GaAs microstructures with high aspect ratio and made by two different height steps for measuring with different typical testing equipment. Near-infrared light vertical scanning interference (NILVSI) is improved to compensate optical path difference (OPD) and the large surface roughness. The sidewall profile of the sample is obtained and compared with that of scanning electron microscopy (SEM) and white light scanning interferometry (WLSI). Test results demonstrate that the steps have 2.115 μm and 0.762 μm relative heights and 1.34 % and 2.14% relative errors respectively. There is a good agreement with the results of SEM and WLSI. The system can reconstruct the sidewall profile of microstructures with high aspect ratio.