Strain-Free Ultra High Vacuum Windows
Monitor Thin Film Deposition In Real Time With Bomco's UHV Windows
"This is as close as anyone has come to windowless, optical access to an ultrahigh vacuum chamber."*
As the demand for higher performance materials for semiconductors increases, so does the need for real-time information about crystal growth by molecular beam epitaxy (MBE). Optical access to the vacuum environment of this process is essential to determine such data as sample temperature, tolerances of layer thicknesses and composition. Engineers at Bellcore and Bomco worked together to develop a UHV window suitable for this environment. This UHV window permits the use of optical pyrometry, elliposometry, light scattering and reflectance-difference spectoscopy (RDS) to obtain data in real time. . . "this is as close as anyone has come to windowless, optical access to an ultra high vacuum chamber."*
Advantages over conventional glass viewports
Unlike conventional viewports, Bomco UHV windows can be heated to 400 degrees Celsius to remove typical MBE growth deposits without venting the station for disassembly and cleaning. By eliminating deposit-induced inaccuracies in optical pyrometry, the Bomco UHV window allows highlight influences to be transmitted with minimum attenuation.
Tests have also shown that retardations of the Bomco UHV windows are consistently and substantially less than those of conventional viewports. In the measurement of strain homogeneity, the Bomco UHV windows were homogeneous to within 0.1 degree, while conventional viewports were inhomogeneous by more than 1 degree. Access to the window periphery allows the window to be loaded mechanically to tune residual strain birefringence to negligible values.*
The design of the Bomco UHV window
This low-strain, fused quartz window assembly is mounted on a UHV flange. The window is made by fusing a 1/16" thick synthetic quartz disc to a quartz tube. The open end of the tube is fused to a quartz-to-molybdenum seal that is brazed to the UHV flange.
"Double-Thick" flanges
Double-thick flanges of approximately 1 inch are now available for UHV windows, part numbers 5935 and 5936. Consult Bomco engineers for details.
Two Ways To Protect UHV Windows And Preserve Optical Access To MBE Chambers
Protective shields for UHV windows
Constructed of stainless steel, the protective shields slip easily over the UHV flange and the clamp is tightened with a screw driver. The shields are available for all window sizes shown below.
New Re-Entrant UHV Window
These new re-entrant style UHV windows are mounted on CF flanges with a window located inside the outer surface of the flange (as shown below). This new re-entrant window is available in two sizes as shown below.
The use of this new re-entrant window saves space and provides protection for MBE applications.
Pricing for UHV window assemblies**
UHV WINDOW ASSEMBLIES Part Number Description 1 - 4 pcs 5 - 10 pcs Over 10 pcs B5935 1.50" Window (2.75" Flange) $1,326.00 $1,199.00 $1,122.00 B5936 2.00" Window (2.75" Flange) $1,352.00 $1,224.00 $1,148.00 (Add $160.00 for double think flange - B5936 & B5935 only) B6456 2.00" Window (4.5" Flange) $1,530.00 $1,377.00 $1,173.00 B7172 0.75" Window (1.33" Flange) $816.00 B7396 1.00" Window (1.33" Flange) $1,020.00
RE-ENTRANT UHV WINDOWS B6874 1.50" Re-Entrant Window (4.5" Flange) $1,683.00 B7485 2.00" Re-Entrant Window (6.0" Flange) $1,989.00 $1,785.00
PROTECTIVE SHIELDS FOR UHV WINDOW B6869 (Fits B5935 Window) $97.00 B6869 (Fits B5936 Window) $97.00 B6875 (Fits B6456 Window) $112.00
* "Low-Retardance Fused-Quartz Window for Real-Time Optical Applications in Ultrahigh Vacuum," A.A. Studna, D.E. Aspnes, L.T. Florez, B.J. Wilkens, J.P. Harbison and R.E. Ryan. Journal of Vacuum Science Technology. A, Volume 7, Number 6, Nov/Dec 1989. Copy available on request.
** Prices subject to change without notice. Export orders require prepayment unless other terms are arranged.
Here the Bomco UHV window permits the measurement of film growth by spectroscopic elliposometry in a MBE chamber. Photo courtesy of the J.A. Woolam Co., Lincoln, NB.
Bomco, Inc.
125 Gloucester Avenue
Gloucester, MA 01930-2254
Phone: 978-283-9000
Fax: 978-283-2882
E-Mail: custserv@bomco.com
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