Characterization and reduction of pellicle degradation due to haze formation on leading edge technology photomasks

Since the adoption of deep ultraviolet lithography, time‐dependent haze defects have become an increasingly significant problem for the semiconductor industry as photomask lifetime continues to be shortened due to molecular contamination. With shorter wavelength lithography, the materials and space between the pellicle film and photomask surface can create a highly reactive environment resulting in the formation of haze defects on the photomask. One critical issue has been to understand the chemical mechanism of evolving defects on the photomask triggered by haze formation. This fundamental study was completed in a manufacturing environment in response to a sudden increase of haze defect growth during the transition to new device nodes. Time‐of‐Flight Secondary Ion Mass Spectrometry and Atomic Force Microscopy analysis techniques were essential in characterizing pellicle degradation in parallel with increased haze defect growth on the photomask surface. Extensive chemical and surface topography characterization of pellicle degradation led to a vitally important development and implementation of a design change in the pellicle frame for Flash Memory 3x and 2x nm node critical process layer photolithography. With an increased clearance between the pattern design and pellicle edge, the design modification ultimately brought an immense increase in photomask dose limitation between repell cleans and a reduction in haze growth, thus, reducing production costs and increasing wafer throughput.