PORTLAND, Ore.—A new type of annealing developed by researchers at Cornell University promises the potential to shorten processing time and improve image quality of semiconductor lithography.
Laser-spike annealing (LSA), developed by Cornell researchers backed by Semiconductor Research Corp. (Research Triangle, N.C.) , has already been tested for both 193-nanometer immersion lithography and 13-nm extreme ultra violet (EUV). The technique is currently being considered for adoption by SRC members, including IBM Corp., Texas Instruments Inc., Intel Corp., Advanced Micro Devices Inc., Freescale semiconductor Inc. and Globalfoundries Inc.
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"This new laser method delivers a breakthrough in thermal processing,” said Christopher Ober, a Cornell professor. "Faster, higher fidelity pattern transfer in the fab means better chip performance at reduced cost."
Today, thin photoresist films are annealed by heating the entire wafer for a minute or more using a hot-plate. LSA directs a pulsed laser beam to perform the same function in milliseconds, thus saving time. Testing by the researchers also revealed that line roughness caused by diffusion in the baking method is decreased, resulting in higher fidelity image quality for lithographic patterns.
SRC funded Laser Spike Annealing system at Cornell University (Ithaca, N.Y.) uses a continuous wave laser focused to a line and scanned over the silicon substrate to melting temperature in milliseconds, thus creating higher fidelity circuit patterns, more quickly than the current hotplate baking process.
Conventional baking is done at less than 300 degrees Fahrenheit to minimize diffusion. But the laser-based annealing technique can achieve temperatures of 1,450 degrees Fahrenheit in milliseconds, thereby maximizing photoresist sensitivity while minimizing pattern roughness, according to Ober, who is perfecting the laser-based annealing process with Cornell doctoral candidate Byungki Jung,
"As a next step, we anticipate creation of improved photoresists that can further leverage the benefits of this novel, more efficient annealing method,” said Bob Havemann, director of nanomanufacturing sciences at SRC.