Chemically enhanced FIB repair of opaque defects on molybdenum silicide photomasks

Abstract

The characteristics of an ideally repaired opaque defect on a molybdenum silicide (MoSi<SUB>a</SUB>O<SUB>b</SUB>N<SUB>c</SUB>) photomask are: (1) the total removal of the MoSi<SUB>a</SUB>O<SUB>b</SUB>N<SUB>c</SUB> defect, leaving no residual MoSi<SUB>a</SUB>O<SUB>b</SUB>N<SUB>c</SUB>; (2) a smooth, level quartz surface (no over-etch) after the MoSi<SUB>a</SUB>O<SUB>b</SUB>N<SUB>c</SUB> is removed; (3) minimal riverbedding of the quartz at the perimeter of the MoSi<SUB>a</SUB>O<SUB>b</SUB>N<SUB>c</SUB> defect; and (4) maximum light transmission (%T) at the i-line (365 nm) and DUV (248 nm) lithographic wavelengths. Achieving these ideal repair characteristics is becoming increasingly difficult as the patterned features become smaller, as the lithographic wavelength becomes shorter and as phase shifting mechanisms are implemented. A chemical process has been developed to enhance the FIB (focused ion beam) etching of MoSi<SUB>a</SUB>O<SUB>b</SUB>N<SUB>c</SUB> defects. Using this chemical process, a FIB protocol has been developed which enhances the removal of a MoSi<SUB>a</SUB>O<SUB>b</SUB>N<SUB>c</SUB> defect while inhibiting the removal of quartz. AFM (atomic force microscopy) indicates that (1) MoSi<SUB>a</SUB>O<SUB>b</SUB>N<SUB>c</SUB> is totally removed, (2) the quartz remains smooth and level (no over-etch), and (3) the riverbends are, at this time, 10 - 45 nm; our target is 1 - 15 nm. The MoSi<SUB>a</SUB>O<SUB>b</SUB>N<SUB>c</SUB> etch process reduces optical staining due to implanted gallium