Feedback control of growth rate and surface roughness in thin film growth

In this work, we present an approach for multivariable feedback control of surface roughness and growth rate in thin film growth using kinetic Monte-Carlo (MC) models. We use the process of thin film growth in a stagnation flow geometry and consider atom adsorption, desorption and surface migration as the three processes that shape film micro-structure and determine film growth rate. A multiscale model is used to simulate the process. Following the methodology presented in, a roughness and growth rate estimator is constructed that allows computing estimates of the surface roughness and growth rate at a time-scale comparable to the real-time evolution of the process. The interactions between the inputs and outputs in the closed-loop system are studied and found to be significant. A multivariable feedback controller, which uses the state estimator and explicitly compensates for the effect of input/output interactions, is designed to simultaneously regulate the growth rate and surface roughness by manipulating substrate temperature and inlet precursor mole fraction. Application of the proposed control system to the multiscale process model demonstrates successful regulation of the surface roughness and growth rate to the desired set-point values. The proposed approach is found to be superior to control of the growth rate and surface roughness using two independent feedback control loops.