Real-time feedback for etch rate and sidewall profile control in reactive ion etching.

Abstract

The purpose of this dissertation is to explore how real-time feedback control may be used to improve the reactive ion etching process. A control strategy was developed based on conceptually decomposing the etching process into a plasma generation process and a wafer etch process. The research was performed on an Applied Materials Precision Etch 8300 using a CF$\sb4$ chemistry. This etcher was first reconfigured to allow implementation of the real-time control strategy. Several of the actuators and sensors on the etcher were upgraded. This included the addition of an optical emission spectroscopy system to estimate fluorine concentration in the plasma. A data acquisition and control system was also developed to allow the implementation of real-time control algorithms. Control-oriented models of the plasma generation process were developed based on empirical data. These models were then used to develop a real-time controller to regulate plasma characteristics. It was shown that the real-time control strategy was effective in attenuating disturbances to etch rate. Finally, a feasibility study was performed for a sidewall profile control strategy based upon the process decomposition. A method was developed to relate desired sidewall profiles the plasma conditions during the etch. These conditions can then be regulated using the plasma generation process controller. The potential of this strategy was investigated by relating plasma characteristics to a sidewall profile at a single operating point.