A new technique for multiple overlay check

Abstract

A new concept of overlay multiple mark is presented in this paper. The new kind of mark meets the increasing request to have multiple overlay check in a faster and precise method. The proposed technique is based on the usage of a reference mark composed by multiple layers. The purpose of this technique is to check the misalignment to multiple reference levels in one run minimizing the error due to overlay machine stage repeatability and saving mark detection time. In the specific application that is discussed, we use a box in ring in ring mark printed on real production wafer. Such a technique has shown to be a faster way to gather multiple overlay data in a reliable way meeting the ULSI request to have a better control of the misalignment related to more than a couple of levels. Experiments run on production material have confirmed the validity of this novel technique, by reducing data acquisition time and overlay error. Moreover, this technique application in real production environment meets the ULSI request to have more scribe line room in order to better control device sanity through in line checks. Future possible applications of such a technique are also discussed.