AVS 46th International Symposium
    Vacuum Technology Division Thursday Sessions
       Session VT-ThM

Paper VT-ThM8
Low-flow Measurements Techniques for Calibrating Mass Flow Controllers

Thursday, October 28, 1999, 10:40 am, Room 610

Session: Outgassing, Leaks, and Mass Flow Controllers
Presenter: S.A. Tison, Millipore Corporation
Authors: S.A. Tison, Millipore Corporation
C. Ruppert, Millipore Corporation
Correspondent: Click to Email
Many semiconductor processes require stable and known flow of a gas or multiple gases. Flows ranging from 100 slpm (7 x 10-2 mol/s) to 10 sccm (7 x 10-6 mol/s) are common. Primary standard flowmeters have been developed to measure these flows and are in common use.. The most common techniques include gravimetric and those based on volume displacement at constant pressure. Recently a significant number of processes are using much lower flows with flows as low as 0.1 sccm (7 x 10-8 mol/s) being required. Most of the traditional techniques for measuring gas flow are not well suited for measurements in this range. Becasue of this, process tuning and reproducability can be adversely affected by errors in the mass flow controllers which are induced by their calibration. Two of the most common instruments used for low-flow measurements , a constant volume flowmeter and a laminar flowmeter, were compared with a number of gases including nitrogen, hydrogen, and sulfur hexafluoride. The agreement of the techniques was generally within 0.5% over a range of 1 sccm (7 x 10-7 mol/s) to 10 sccm (7 x 10-6 mol/s) and somewhat worse for lower flows. The comparison data and attributes of these two types of standards is discussed.