Measurement of physical thicknesses in micromachined structures consistingof glass and c-Si, by Fourier transform infrared reflection

The measurement of thicknesses of micromachined structures consisting of et ched glass bonded to c-Si and multilayer structures of both etched c-Si and etched glass is presented. The peaks within the recorded interferograms ar e identified by inspecting the equation for the reflection coefficient and the corresponding equation for the reflectivity. The amplitudes of the vari ous peaks resulting from the 3-D structure underneath the spot of the beam are evaluated to be able to perform an unambiguous choice of the correct pe ak when performing automatic process monitoring. Furthermore, the peaks in the interferogram may be a strong function of wafer position (depending on device layout). In the latter case, it: is demonstrated that information ob tained directly from We interferogram can be used in wafer imaging. The die lectric dispersion functions for the glass and the c-Si wafer under investi gation are evaluated from the reflectance measurements. An anomalous shift: is observed in the interferogram peak corresponding to the glass thickness , The shift is found to be due to the strong dispersion in the refractive i ndex of glass resulting from the SiOSi asymmetric stretching frequency arou nd 1100 cm(-1). Both simulations of the interferogram, and analysis provide a 5% correction for the thickness of the glass under investigation, (C) 19 99 Society of Photo-Optical Instrumentation Engineers. [S0091-3266(99)01109 -5].