Repair of transparent defects on photomasks by laser-induced metal deposition from an aqueous solution

Abstract

This paper describes a newly developed technique for repairing transparent defects on photomasks. After the uniform application of a thin transparent TiO2 film on the entire mask, a noble metal is photodeposited locally on the mask from an aqueous plating solution. The rate of photodeposition, and thereby, the structure and adherence of the deposited metal, depend on the preparation conditions of the TiO2 film, the composition of the plating solution and the incident light flux. These parameters can be selected in such a way that opaque metal metal pads can be deposited in sufficiently short illumination times (∼5 s). By means of laser projection through a variable rectangular aperture, it is possible to deposit rectangular metal pads with micron-sized dimensions and sharp edges and corners in a controlled and reproducible way. Since deposition is induced photochemically, thermal broadening of the deposit does not occur. It is shown that the repair process meets the requirements with respect to spot definition, photolithography, mask cleaning, and laser trimming.

Universal behavior of photochemical deposition in liquid solutions driven by a one-photon transition

“…At the same time, some authors developed an alternative method using condensed phase precursors for the photodeposition of conducting materials in the form of films 7 or spots 8 . The technique uses UV or visible light sources to efficiently break molecular bonds, generate a new species and induce its rapid deposition in the illuminated area 9 .…”