AVS 47th International Symposium
    Plasma Science and Technology Wednesday Sessions
       Session PS1+MS-WeA

Paper PS1+MS-WeA5
Improved Utility of Microwave Energy for Semiconductor Plasma Processing through RF System Stability Analysis and Enhancement

Wednesday, October 4, 2000, 3:20 pm, Room 310

Session: Sensors and Control in Plasma Processing
Presenter: P.W. Rummel, Michigan State University
Authors: P.W. Rummel, Michigan State University
T. Grotjohn, Michigan State University
Correspondent: Click to Email
The bulk of today’s semiconductor plasma processing equipment utilizes RF energies at frequencies from 50 KHz to 60 MHz for deposition, etching, cleaning and various other processes. One of the impediments to utilizing microwave energy for these processes is the inherent instability often encountered with systems operating at frequencies of .5 to 2.45 GHz. Systems with plasma loads excited by resonant antennas, impedance matched by resonant circuits or cavities, and powered by generators of various source impedances are invariably unstable over some operating conditions. For microwave systems, this instability typically manifests itself as a propensity for the plasma to extinguish or rapidly change to a lower density as the impedance matching device is adjusted to minimize reflected power to the microwave generator. This paper shows why this instability exists and how a microwave driven plasma system can be modified to achieve better stabilization. A Matlab Simulink model and a state-model control analysis are used to identify system parameters that affect system stability and to predict the results of modifying those parameters towards the goal of improving stability. A plasma system utilizing a microwave cavity plasma reactor operating at 2.45 GHz. is first characterized to develop the models, and then modified to improve stability and illustrate the models’ predictions. A high correlation between predicted and measured system stability validates the method of using a control analysis to model plasma system stability.