Laser machining of micron-dimension rectangular holes on thin film photomasks

Hard surface photomasks consisting of thin opaque metallic or dielectric films on glass substrates are increasing in popularity as a result of the durability and high resolution they provide in the fabrication of semiconductor integrated circuits. Although in many cases the surfaces are reflective, sufficient absorption of optical radiation occurs to permit machining of these films via melting and/or evaporation, thus permitting modification or repair of processed masks using laser-based machines. The primary requirements of such systems are the ability to (1) machine the opaque film without affecting the substrate and (2) provide the precision and resolution dictated by the mask patterns.