MULTIPLE-LAYER BLANK STRUCTURE FOR PHASE-SHIFTING MASK FABRICATION

A multiple-layer blank structure with two shifter layers coated on a q uartz substrate is proposed for the fabrication of phase-shifting mask s. The thickness of these shifter layers is such that they induce a 18 0 degrees phase shift of light compared to air. On top of these shifte r layers, an opaque layer is coated. The top shifter layer is patterne d during the fabrication of the phase-shifting mask. The bottom shifte r layer is patterned only to repair missing shifter defects. But the m ain purpose of this bottom layer is to act as an etch layer or give an end point during the repair of the phase defects or during the fabric ation of the mask. Using yttrium fluoride etch stop/end point layer (b ottom shifter layer), we have demonstrated the feasibility of multiple -layer blanks. This layer acts as an etch stop during the patterning o f the main shifter layer and has a good refractive index match to that of quartz. The phase-shifting masks made using this multiple-layer bl ank structure have shown lithographic performances comparable to those of standard phase-shifting masks. (C) 1996 American Vacuum Society.