The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Jun. 17, 2008
Filed:
Apr. 03, 2006
Gunars Indars, Littleton, MA (US);
Anatoliy E. Rzhanov, Westford, MA (US);
Gunars Indars, Littleton, MA (US);
Anatoliy E. Rzhanov, Westford, MA (US);
Valley Design Corporation, Shirley, MA (US);
Abstract
An interferometer for measuring the flatness, variation of thickness and parallelism of large, thin transparent wafers held vertically and undistorted by gravitational forces. A sodium lamp provides monochromatic light that is diffusely reflected off a background screen towards the wafer. A reference flat surface is positioned sufficiently closely to the wafer that an interference fringe pattern is formed that is a measure of the air gap between the reference flat surface and the surface of the wafer being measured. The background screen is angled so that the fringe pattern, which is localized at the air gap can be viewed at an angle to a normal to the wafer. The background screen has trapezoidal markings that, when viewed at the angle required to see the fringes, appear as a grid. This allows counting of the number of fringes visible within a fixed distance to characterize the surface flatness.