Piloting epitaxy through ellipsometric feedback

This research explores the synthesis of feedback controllers for gas-source molecular beam epitaxy, and the related processes, using spectroscopic ellipsometry as a sensor technology. The objective in these processes is to deposit a spatially uniform film that has certain properties with respect to thickness. We approach this objective of synchronizing film properties with thickness as a relaxation of tracking with a natural separation in the feedback design. This paper surveys some of the key issues associated with the modeling, tracking, and synchronization of this system. Simulations indicate previously ungrowable structures, such as quaternary films with arbitrary graded compositions, can be realized