High-efficiency, energy-recycling exposure system

Abstract

A system is described for recycling radiation reflected by an illuminated patterning mask in a via-hole drilling or exposure tool. The mask is illuminated by high-energy laser radiation, and the illuminated region is imaged onto a substrate by a projection, proximity, or contact method. The source radiation is suitably shaped by a lens assembly and focused into an optical intensity homogenizer with the desired numerical aperture. The homogenizer has the base function of converting the focused beam to self-luminous light required for drilling of via-holes or other processes accomplished by the tool, while maintaining the numerical aperture of the beam. The homogenizer also participates in the radiation-recycling function. An apertured reflector allows radiation from the source to enter the homogenizer. The radiation passing through and exiting the homogenizer is image by a lens to illuminate a portion of the mask. Radiation incident on transparent areas of the mask coming propagates to the substrate, but radiation incident upon reflective regions of the mask coating is reflected back into the homogenizer. The apertured reflector at the entry port of the homogenizer has a reflective back surface which returns the majority of the light re-entering the homogenizer to the patterning mask. The effective illumination intensity is greatly increased by the recycling of the back-reflected radiation, allowing for a reduction in source power or decrease in exposure time for the drilling of via-holes or other exposure processes.