Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

Differential Pumping of Gas Mixtures

IP.com Disclosure Number: IPCOM000109053D
Original Publication Date: 1992-May-01
Included in the Prior Art Database: 2005-Mar-23
Document File: 1 page(s) / 49K

Publishing Venue

IBM

Related People

Coffey, KR: AUTHOR [+2]

Abstract

When gas mixtures (such as H2 dilute in Ar) are supplied to a vacuum chamber (e.g. sputter deposition chamber) under viscous flow conditions and pumped under molecular flow conditions, different pumping speeds for the two gas species can be realized, which will affect the partial pressure ratio of the gases in the vacuum chamber. For example, the use of a 4% H2 in Ar gas supply will result in a 1% H2 in Ar partial pressure ratio if conductance limited pumping is used. The same supply gas can result in 60% H2 in Ar partial pressure ratio in the vacuum chamber if compression ratio limited turbomolecular pumping is used.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 80% of the total text.

Differential Pumping of Gas Mixtures

      When gas mixtures (such as H2 dilute in Ar) are supplied to a
vacuum chamber (e.g. sputter deposition chamber) under viscous flow
conditions and pumped under molecular flow conditions, different
pumping speeds for the two gas species can be realized, which will
affect the partial pressure ratio of the gases in the vacuum chamber.
For example, the use of a 4% H2 in Ar gas supply will result in
a 1% H2 in Ar partial pressure ratio if conductance limited pumping
is used.  The same supply gas can result in 60% H2 in Ar partial
pressure ratio in the vacuum chamber if compression ratio limited
turbomolecular pumping is used.  While most turbomolecular pumping
systems commercially available are designed for nearly equal pumping
speeds of all gases, compression ratio limited pumping is readily
induced for lower compression ratio gas species.  For example, large
reductions in H2 pumping speed with minimal change in Ar pumping
speed may be easily achieved by increasing turbomolecular pump
backing pressure or by reducing the rotational frequency of the
turbomolecular pump.  Thus, a pumping system consisting of a
turbomolecular pump with variable foreline pressure and/or variable
rotational frequency downstream of a variable conductance orifice
allows independent control of total pressure and Ar/H2 partial
pressure ratio in a vacuum chamber.  The 1 to 60 percent variation
readily observed with Ar and H2 is an extreme example in part b...