An inorganic anti-reflective coating for use in photolithography

In this work, we discuss the design of an inorganic anti-reflective coating for use in photolithography at a wavelength of 3650 Å (I line). We consider the effect of the optical constants on the reflectance and show that when the extinction coefficient, k, of the film has a value near 0.8, the reflectance will be very small for a range of values of the thickness and the index of refraction, n. We illustrate the principle with one example where we use a combination of TiW and the oxide of TiW. Reflectance is measured for a range of thicknesses of both the TiW and the oxide of TiW. Values less than 5% were obtained.