Development of a 5-kHz solid state 193-nm actinic light source for photomask metrology and review

Attaining acceptable yields in the manufacture of advanced photomasks will require higher performance optical metrology tools. Key to improving these tools is the development of new ultraviolet light illumination sources that operate at the actinic wafer exposure wavelength, which is now projected to be 193 nm for the 65 and 45 nm device nodes. The use of an actinic light source for metrology facilitates imaging of photomask phase structures, and ensures that optical path difference measurements and printing simulations are performed in-band and are not subject to off-wavelength accuracy errors. We review the solid-state laser technologies that have been employed to generate 193 nm, and describe the development of a new solid-state 193 nm laser platform tailored specifically for high resolution photomask phase metrology. This source operates at a repetition rate of five-kilohertz, produces 2.5 mW average power with a spectral bandwidth of 10 pm and has excellent mode quality. Additionally, we present high-resolution, 200X-magnification photomask images obtained using this new illumination source.