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The laser-based mask repair system has progressed from an attractive high-return investment to a critical production tool necessary for manufacturing defect-free reticles. In fact, since the early 1980s Quantronix' DRS I and DRS II laser repair systems have become the industry standards for the production of defect-free reticles.
As the semiconductor industry moves into the 1990's, a new generation of photomasks, both conventional and phase-shift types with smaller critical dimensions and multiple layers, requires that more information be encoded onto the masks. Increased mask production cost and tighter defect tolerances have created the critical need for new high sensitivity pattern inspection and defect repair equipment for chrome and phase-shift masks. We are actively investigating new and improved technologies to meet the future repair demands of the maskmaking community, including methods and devices to improve chrome repair, to modify phase-shift materials and to increase overall system utility and throughput.
The strengths of laser mask repair systems are well known, although misconceptions may exist about the limitation of the laser technique, especially concerning repair accuracy which is currently specified in the DRS II as ±0.15 um (2 sigma). Recent experimental results in our laboratory indicate that a laser micromachining technique should be able to achieve an edge accuracy for the repair of opaque defects on feature edges of ±0.05 um (3 sigma). This capability will satisfy the edge defect specifications for future generations of 5x optical reticles which will be used for manufacture of 64M and beyond DRAM chips.
In this paper the laser processing results for chrome and candidate phase-shift materials will be discussed; the discussion will begin with some background information on Quantronix' activities with lasers and laser repair systems.
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