Image formation in photosensitive layers on top of highly conductive substrates

The distribution of the average electric energy density defines which part of an exposed photosensitive resist layer is affected by the light beam. The image, which is formed by using optical projection systems, cannot be described by the standard Fresnel-Kirchhoff theory if highly reflective substrates are used. The theory has to take full account of the vectorial character of the light that accomplishes the exposure of the resist. It is shown that, even when objectives with a high numerical aperture are used, the standing wave effects will strongly affect the image. Especially in the region very close to the metal-resist interface, large deviations from scalar diffraction theory have been observed. These conclusions are supported by experimental evidence. The relevance of the theory is discussed by considering the consequences for the realization of microelectronic circuits.