An optical metrology system for lithography process monitoring and control

As the semiconductor industry approaches the first sub-100 nm technology node on the SIA roadmap, process equipment and materials are stretched toward their limits, thus making the process very sensitive to even small perturbations of process conditions. At the same time, building and maintaining a semiconductor production fab has become increasingly expensive, and lithography alone can account for as much as one third of the overall chip manufacturing cost. Therefore, it is very important to monitor and control the lithography process in order to enhance the production yield. This thesis presents a framework for lithography process monitoring and control using the full line-edge profile information obtained from scatterometry, and discusses in detail the performance issues of scatterometry as they pertain to lithography control.; In this thesis we review various optical configurations of optical metrology tools that have been used for scatterometry, and analyze some related theoretical problems. The results show that signal matching with weighting based on signal noise or in the domain close to the raw detector signal can yield a greatly improved CD and thickness precision. These results provide ample evidence that full-profile scatterometry is easily scalable for use on the 70 nm technology node on the International Technology Roadmap for Semiconductors.; Some experimental results on characterizing a scatterometry system used in a production environment are also presented. The accuracy and precision of the system are demonstrated on various applications. The scatterometry profiles and line widths of shallow trench isolation and polysilicon gate structures are sufficiently close to those measured with cross-section SEM and CD-SEM. Most importantly, however, the long-term precision of scatterometry is several times better than that of the CD-SEM.; It is still a big challenge to integrate scatterometry into the advanced process control (APC) framework. Research and development on using the wafer level and full-profile information of scatterometry is still in the early stages. A framework on lithography process monitoring and control using scatterometry is proposed first in this thesis. The simulation results show significant benefits in using CD and sidewall angle information obtained from scatterometry as controlled variables. Namely, the resulting CD and sidewall angle variations are more than 30% smaller than those with the traditional CD-based control method. The requirements and challenges in applying scatterometry in a real production environment are also discussed.