AVS 47th International Symposium
    Vacuum Technology Thursday Sessions
       Session VT-ThA

Paper VT-ThA8
Intelligent Flow Measurement and Control

Thursday, October 5, 2000, 4:20 pm, Room 201

Session: Pressure and Flow Measurements
Presenter: G.H. Leggett, Millipore Corporation
Authors: G.H. Leggett, Millipore Corporation
S.A. Tison, Millipore Corporation
K. Tinsley, Millipore Corporation
Correspondent: Click to Email
Vacuum processes typically use mass flow controllers for delivery of stable and known flow of gas to the process chamber. A variety of techniques are used for gas measurement and control, but the most prevalent is based on thermal transfer between a heated tube wall and the gas stream. This class of mass flow controller is referred to as a thermal mass flow controller. These instruments have been in use for over 20 years and have evolved with time. Most recent versions are digital controllers which allow for digital setpoints and digital outputs. While advances have been made, MFCs are still custom manufactured for a particular gas and flow range, and their accuracies with process gases is typically no better than +/-5%. A new thermal based MFC has been developed which is capable of operating over extended ranges (500 to 1 flow ratios) and is able to achieve accuracies with process gases to within 1% of the MFC full scale. These accuracies are attained by using theoretical and empirical based techniques for relating the flow of the calibration gas to that of the process gas. Similar techniques are used for tuning of the MFC to ensure typical response times of one second. This paper describes the design, control techniques, calibration processes, and verification data for a thermal based mass flow controller with typical semiconductor process gases.