Modeling and correction of global CD uniformity caused by fogging and loading effects in 90-nm-node CAR process

Abstract

As critical dimensions (CDs) continue to approach the 90 nm node, it is inevitable that the industry has employed the use of chemically amplified resist (CAR) with 50 kV e-beam writing tool. However, the fogging effect by re-scattered incident electron at a high acceleration e-beam writer and the loading effect at dry etching step due to pattern density are critical issues since these effects make the variation of CD mean to target (MTT) and the degradation of CD uniformity. Tracking the CD error sources in CD uniformity and minimizing the error are very important task for high technology node mask production. In this paper, we focus on finding the source of the radial error in CD uniformity for each process step since the radial error occupy the main part of total CD uniformity. Also we present the radial error modeling using convolution equation between Gaussian CD error distributions with pattern densities. Finally, we describe the radial error correction method by phantom exposure with rectangle representing local pattern density. Fogging effect at writing process is one of the main sources of the radial error in global CD uniformity. The error by fogging effect is linearly proportional to mask pattern density, whereas loading effect at dry etch process increases the radial error in the case of the higher pattern density. The correction method using defocused beam based on our CD uniformity model effectively reduces the radial error and total error to 50% of their original value.