Abstract

The etching of fine patterns on Si substrates is an important technique for the fabrication of solid capacitors and ultrahigh-density circuit integration. This technology requires high-precision depth control. Therefore, a nondestructive method of measurement suitable for mass production applications, in place of the conventional method of breakage sections with scanning electron microscopes, is an important desideratum. A nondestructive measurement technique using optical diffraction and interference was developed. When the wafer with the etched pattern is illuminated, the light reflected from the floor of a trench carries phase information that corresponds to the trench depth. Analysis demonstrated that the interference pattern formed by this light, reflected from the trench floor and from the surface of the wafer, can be observed as intensity variations in the diffracted light that correspond to the depth of the trench. From the above results, it was deduced that the zeroth-order diffracted light must be cut off by a spatial filter to permit detection of the higher-order diffraction pattern. The higher-order interferometric method was devised, which permits depth measurement of surface depressions with area dimensions 1×1µm² and a depth of 5 µm to an accuracy of ±0.2 µm.

© 1990 Optical Society of America