Three-dimensional image processing for acoustic microscopy

The authors have built a scanning acoustic microscope operating in the 3- to 10-MHz range that measures both amplitude and phase. Using the additional information available with an acoustic microscope that measures phase as well as amplitude allows image processing that cannot be done with amplitude alone. The effective resolution can be increased in the transverse resolution and doubled in the vertical direction by Fourier deconvolution of experimental images taken at a single frequency. By combining images taken at closely-spaced frequencies, a significant further increase in effective depth resolution can be obtained. These techniques were applied to images of a deep trench designed as a scale model of vertical capacitors in integrated circuits. The effects of the surface on the overall image can be removed, leaving only the image of the bottom of the trench. The reflection from the top surface of a block of aluminium was numerically removed, providing better contrast of substrate defects