AVS 51st International Symposium
    Plasma Science and Technology Wednesday Sessions
       Session PS-WeA

Paper PS-WeA5
The Use of the Radio Frequency Matching Network As a Diagnostic for Plasma Processing Chambers

Wednesday, November 17, 2004, 3:20 pm, Room 213A

Session: Plasma Diagnostics
Presenter: J. Caughman, Oak Ridge National Laboratory
Authors: J. Caughman, Oak Ridge National Laboratory
G.L. Bell, Oak Ridge National Laboratory
V. Resta, Hewlett-Packard
Correspondent: Click to Email
Radio frequency (RF) power is commonly used in the plasma processing of semiconductors. As part of the RF system, many of the plasma processing chambers use RF matching networks with two variable tuning elements to transform the impedance at the chamber interface to be 50 ohms at the input of the matching network. The matching network is a highly tuned circuit, and the positions of the tuning elements are directly related to the RF impedance of the chamber. Thus, the positions of the tuning elements can be used as a diagnostic to determine processing sensitive parameters. Matching networks have been characterized to relate tuning element positions to the RF impedance and the power efficiency of the network. After characterization, the impedance and efficiency can be determined as a function of processing parameters simply by measuring the tuning element positions during processing. The technique has been demonstrated on both inductively coupled plasmas (ICP) and capacitively coupled plasmas (CCP). It has been found that the impedance is sensitive to changes in power, pressure, gas composition, and wall conditions. For example, an increase in ICP source power will cause an increase in the plasma density, which can be seen as an increase in the real part of the source impedance and a decrease in the real part of the bias impedance. The technique has been used on several different chambers and has been demonstrated to be helpful in terms of troubleshooting and chamber matching. Details of the characterization technique and the sensitivity of the impedance to processing conditions will be presented.