The introduction of photomask laser pattern generators presents new challenges to system designers and manufacturers. One of the laser pattern generator's environmental operating challenges is Airborne Molecular Contamination (AMC), which affects both chemically amplified resists (CAResist) and laser optics. Similar challenges in CAResist protection have already been addressed in semiconductor wafer lithography with reasonable solutions and experience gained by all those involved. However, photomask and photomask equipment manufacturers have not previously had a comparable experience, and some photomask AMC issues differ from those seen in semiconductor wafer lithography. Culminating years of AMC experience, the authors discuss specific requirements of Photomask AMC. Air sampling and material of construction analysis were performed to understand these particular AMC challenges and used to develop an appropriate filtration specification for different classes of contaminates. The authors portray the importance of cooperation between tool designers and AMC experts early in the design stage to assure goal attainment to maximize both process stability and machine productivity in advanced mask making. In conclusion, the authors provide valuable recommendations to both laser tool users and other equipment manufacturers.
Atmospheric pressure deep UV lithography using fast chemically amplified photoresists (CAR) will be the mainstay of photomask production into the foreseeable future. Issues surrounding the sensitivity of chemically amplified photoresists to molecular bases such as ammonia, NMP, TMA and related compounds, have been the sources of intensive study and numerous publications1,2,3. Photoresist sensitivity issues challenge photoresist suppliers' abilities to improve resistance to airborne molecular contamination, equipment suppliers' abilities to control molecular bases within the tool and photomask/reticle manufacturers' capability to adapt their cleanroom environments and lithography processes for CAR.
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