The Improved Infrared Interferometer (IR3) at the National Institute of Standards and Technology (NIST) is a phase-measuring interferometer, operating at a wavelength of 1550 nm, which is being developed for measuring the thickness and thickness variation of low-doped silicon wafers with diameters up to 300mm. The purpose of the interferometer is to produce calibrated silicon wafers, with a certified measurements uncertainty, which can be used as reference wafers by wafer manufacturers and metrology tool manufacturers. We give an overview of the design of the interferometer and discuss its application to wafer thickness measurements. The conversion of optical thickness, as measured by the interferometer, to the wafer thickness requires knowledge of the refractive index of the material of the wafer. We describe a method for measuring the refractive index which is then used to establish absolute thickness and thickness variation maps for the wafer.
Conference Dates: July 20-22, 2005
Conference Location: Middletown, CT
Conference Title: ASPE (American Society for Precision Engineering) 2005 Summer Topical Meeting - Precision Interferometric Metrology
Pub Type: Conferences
300 mm silicon wafers, Infrared interferometer, Interferometry, wafer thickness, wafer thickness variation (TTV)