AVS 50th International Symposium
    Vacuum Technology Wednesday Sessions
       Session VT-WeA

Paper VT-WeA3
Outgassing Characteristics of a TiN-coated SUS-316 Vacuum Chamber Developed for XHV

Wednesday, November 5, 2003, 2:40 pm, Room 323

Session: Outgassing and Large Vacuum Systems
Presenter: M. Hirata, National Institute of Advanced Industrial Science and Technology (AIST), Japan
Authors: M. Hirata, National Institute of Advanced Industrial Science and Technology (AIST), Japan
H. Akimichi, National Institute of Advanced Industrial Science and Technology (AIST), Japan
A. Kurokawa, National Institute of Advanced Industrial Science and Technology (AIST), Japan
S. Ichimura, National Institute of Advanced Industrial Science and Technology (AIST), Japan
H. Yamakawa, ULVAC Technologies, Inc.
Correspondent: Click to Email
The control of outgas from a vacuum chamber is the key issue to achieve XHV condition, since any pump has a limited pumping speed usually determined by effective connection area of the pump to the chamber. We have developed a new chamber accordingly, aiming at reducing outgas from the chamber wall as low as possible, and studied outgassing characteristic of the chamber. The chamber is made of vacuum melted stainless steel (SUS 316L) to minimize hydrogen outgassing, and treated by electrolytical polishing followed by pre-baking in vacuum and TiN coating. The outgassing rate of the chamber was measured by a throughput method after each treatment. The results are 4x10@super -9@Pa m/s, 3x10@super -12@Pa m/s and 1x10@super -13@Pa m/s, respectively.@footnote 1@ However, the ultimate pressure of the chamber (1x10@super -9@Pa) evacuated by a pump (1000 L/s) was quite higher than the pressure of 2x10@super -13@Pa estimated from the lowest value of the rate and the chamber inner area. In order to clarify the difference, the rate of the TiN coated chamber was measured by pressure rise method using an ionization (extractor) gauge and a spinning rotor gauge for several months. The results were 3x10@super -10@Pa m/s by the ionization gauge and 2x10@super -13@ to 3x10@super -12@Pa m/s by the spinning rotor gauge, respectively. The lowest value measured by the spinning rotor gauge was roughly equal to the value obtained by throughput method. These results suggest that outgas from the ionization gauge could not be ignored, and that the measured pressure of 1x10@super -9@Pa could be mainly attributed to outgas from the ionization gauge. A new method for XHV pressure measurement is inevitable. @FootnoteText@@footnote 1@S.Ichimura et. al.: Vacuum 53 (1999) 291.