Gate oxide process control optimization by x-ray photoelectron spectroscopy in a semiconductor fabrication line

Abstract

X-ray photoelectron spectroscopy is a metrology technique that is used for in-line control of decoupled plasma nitridation processes in the fabrication of logic devices. This article shows XPS results of thickness and composition obtained on two types of gate oxide nitrided by a decoupled plasma nitridation process. Measurements are performed in specific test structures with an x-ray spot which can be focused down to 35μm, enabling process control directly on products. First, XPS is used to characterize and quantify the chemical composition of a SiON layer. The Results show that the nitrogen composition in a SiON layer decreases at a fast rate during the initial days after nitridation processing and stabilizes with time. Second, measurements are performed on products with the objective of transferring process control from monitor to product wafers. In this regard, comparison of nitrogen dose and thickness uniformity on monitor and pattern wafers show similar trends, indicating that measurements of nitrogen dose and thickness on monitor and product wafers give the same information. Third, different mapping protocols are studied on products to identify the best compromise between throughput and an optimized mapping representative of the process distribution. An optimized process control strategy of gate oxides with results is discussed in this article.