Electrical measurement of submicrometer contact holes

A technique to measure submicrometer-sized isolated features electrically is described. P.M. Hall's formula (1967-8) modified with an experimentally determined coefficient is used to obtain the hole diameter and the hole area from the electrically measured linewidth with a higher precision than the precision of the linewidth itself. By incorporating a large number of features in a single test structure, a gain in precision of better than 3 nm is shown analytically. The contact hole diameter and the area of the isolated features obtained in this way, were found to be accurate when compared with physical measurements using a scanning electron microscope. The test pattern used is a combination of two basic four-point probe linewidth-measuring structures and two modified ones. The modified structures contain a large number of contact holes in the 10-μm lines running in the horizontal and vertical directions, which reduce the apparent electrical linewidth. Subtracting the reduced linewidth from that of a solid reference line removes the other contributions to linewidth variation. The size of the contact holes can then be derived from these results. The special test pattern, an analytic expression for interpretation of the results, and hole size data from a variety of exposure dosages are discussed