Silicon Wafer Thickness Variation Measurements Using the NIST Infrared Interferometer
Angela Davies, Tony L. Schmitz, R E. Parks, Christopher J. Evans
?creasing depths of focus, coupled with increasing silicon wafer diameters, place greater restrictions on chucked wafer flatness in photolithography processes. In this work, a measurement device is described that measures thickness variation of double side polished wafers using an infrared source and vidicon detector. Various possible instrument configurations are described with the focus on a setup which uses a collimated wavefront to produce interference fringes between the front and back surfaces of the plane parallel wafer. Experimental results are presented, including a drift test; comparisons between measurements performed using different collimators and, subsequently, wavefronts; an exploration of the impact of phase change on reflection due to the clamping method; and an intercomparison with thickness measurements recorded by a capacitance gage-based instrument and surface measurements obtained using a separate visible wavelength interferometer.