<title>Novel design of WIS-free overlay measurement mark</title>

Abstract

The Wafer-Induced-Shift (WIS) is the overlay measurement error due to the reflection trick of the metal film by Physical Vapor Deposition, specially sputtering. The WIS happens to the wide open type mark because this sputtering method can cause a non-symmetric edge deposition by the self-shadowing of mark depth. But the marks with a wide width and space, which are currently used in the industry, have not detected the WIS. It is the modification of overlay measurement mark that has to be primarily improved to solve this problem. So we suggest the new methodology using the overlay mark with the narrow space. The concept of this mark is to use the geometrical property of deposition and detect the optical contrast signal of the space-type mark instead of the edge contrast signal of wide bar-type mark. This will reduce the non-symmetric deposition property by the self-shadowing. In this paper, we conformed the WIS using the overlay errors after and before etching film, and reported the effectiveness of our new mark by using the sputtered Pt film being one of the electrodes of BST capacitor. Several marks with a space 0.2 micrometer up to 0.5 micrometer were examined for the various thicknesses of the film by comparing the overlay measuring error between the standard mark and the new mark, and correlating the degree of the metal filing into the narrow space of overlay mark with the wafer scale factor. From the experimental results, we can find that the major component of WIS is the wafer magnification factor, and the new mark had a good feasibility for the WIS and might be called the WIS-free mark. Additionally we will discuss more details of our experimental results.