A NEW TECHNIQUE FOR MULTIPLE OVERLAY CHECK

A new concept of overlay multiple mark is presented in this paper. The new kind of mark meets the increasing request to have multiple overla y check in a faster and precise method. The proposed technique is base d on the usage of a reference mark composed by multiple layers. The pu rpose of this technique is to check the misalignment to multiple refer ence levels in one run minimizing the error due to overlay machine sta ge repeatability and saving mark detection time. In the specific appli cation 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 req uest to have a better control of the misalignment related to more than a couple of levels. Experiments run on production material have confi rmed the validity of this novel technique, by reducing data acquisitio n time and overlay error. Moreover, this technique application in real production environment meets the ULSI request to have more scribe lin e room in order to better control device sanity through in line checks . Future possible applications of such a technique are also discussed.