On the way to 1 Gb: demonstration of e-beam proximity effect correction for mask making

Abstract

The e-beam proximity effect is well known as one of the limiting factors in e-beam lithography. As features get smaller the need for e-beam proximity effect correction increases. There exist different approaches to cover these effects by varying dose or shape of the pattern layout during the exposure step. Whichever algorithm is used, the question of proximity effect correction gets more and more a performance problem for forefront applications like the 256 megabit and 1 gigabit chips. The correction approach has to handle large data volume in reasonable time. Key to overcome this hurdle is to include hierarchial data handling into the proximity correction algorithm, which involves hierarchical data structures as well as hierarchy reorganization methods. The goal of the present work is to perform all necessary steps in order to guarantee the accuracy of the exposure result for the 1 gigabit memory chip. One step of the preparation is the e-beam proximity correction for raster scan machines. With respect to proximity effect correction, raster scan machines have a severe drawback. The scanning speed is constant while writing the layout, i.e., dose variation is not applicable to compensate for the proximity effect. There is, however, the geometry which can be exploited as degree of freedom. Geometrical variations of the layout underlie many constraints such as neighboring features, the exposure grid of the e-beam tool and, but not least, writing time. The paper presents how to solve some of the major problems occurring when proximity effect correction becomes an unavoidable step in the mask making process. Power and application limits of proximity effect correction for raster scan machines are investigated. The exposure has been carried out on a MEBES 4500 system. Process latitude and line width linearity are presented. In addition, practical questions like file size increase due to proximity correction are investigated. Exposure results of uncorrected and corrected pattern are compared to demonstrate the necessity of the correction as well as the improvement in pattern fidelity.