Method of reducing heat-induced distortion of photomasks during lithography

摘要

The present invention relates generally to methods, apparatus and materials to reduce or minimize the heating of a substrate (and associated distortions of the photomask) caused by electron-beam energy deposited in the substrate during patterning. Heating of the substrate is exacerbated by radiative transfer of infrared energy from the substrate to other nearby components of the e-beam apparatus followed by reflection or re-radiation of a portion of the energy back to the substrate. The present invention provides useful materials and methods for reducing such reflection or re-radiation effects, leading to temperature stability of the substrate, reduced thermal distortion and the possibility of increased patterning accuracy. The infrared absorbing materials of the present invention also possess sufficient electrical conductivity to dissipate scattered electrons residing on the material, and sufficient thermal conductivity to dissipate heat rapidly and not result in local heating or significant temperature rise of the absorber. The semiconducting material silicon carbide (SiC) is satisfactory for the practice of the present invention. Doped SiC having altered electrical conductivity may also be used. It is shown that emission and re-absorption from the uncoated face of the substrate dominates the substrate's temperature rise.