Optical Flatness Metrology for 300 mm Silicon Wafers

The National Institute of Standards and Technology (NIST) is developing two interferometric methods for measuring the thickness, thickness variation, and flatness of free-standing and chucked silicon wafers with diameters up to 300 mm. The "eXtremely accurate CALIBration InterferometeR" (XCALIBIR) is a precision phase measuring interferometer with an operating wavelength of 633 nm and a test beam of 300 mm diameter. XCALIBIR is used to evaluate the flatness of chucked wafers. NIST's Infrared Interferometer (IR2) is a phase measuring interferometer that operates at 1.55 gm and is used to measure the thickness variation of free-standing 300 mm silicon wafers.