Manufacture and Metrology of 300 mm Silicon Wafers with Ultra-Low Thickness Variation

With the evolution of exposure tools for optical lithography towards larger n umerical apertures, the semiconductor industry expects continued demand for improved wafer flatness at the e xposure site. The allowable site flatness for 300 mm wafers is expected to be less than 45 nm by 2010 and it may be as low as 25 nm by 2015 according to the International Technology Roadmap for Semiconductors (ITRS 2006). This requires wafers with low thickness variation and presents a challenge for both wafer polishing and metrology tools, which must be capable of meeting the specifications. We report the results of fabricating 300 mm silicon wafers with very low thickness variation using magnetorheological finishing (MRF), a deterministic subaperture finishing process. The wafer thickness metro logy, which guided the finishing process, was provided by an infrared interferometer developed at the National Institute of Stand ards and Technology (NIST). The finishing method in combination with the interferometric wafer metrology enabled the fabrication of 300 mm silicon wafers with a total thickness variation (TTV) of about 40 nm, and between 10 nm and 15 nm thickness variation at 25 mm × 25 mm exposure sites.