Start-up Company Exploits Maskless Photolithography
Technique
Aaron Hand, Managing Editor -- Semiconductor International, 8/1/2001
Armed with a maskless technique called Smart Filter Technology, a new company has entered the photolithography arena. Intelligent Micro Patterning LLC (St. Petersburg, Fla.) plans to commercialize the technique, targeting such applications as microelectromechanical systems (MEMS), high-density packaging, multi-chip modules (MCMs), optoelectronic devices, microfluidics and other thin-film devices.The company's SF-100 exposure system makes use of a technique originally developed at the University of South Florida. The patented subsystem — with the optics, broadband white light source and electronics — directly generates exposure patterns into photoresists and other photoimageable materials.
The necessary exposure energy comes from the high-intensity light source, which is filtered and optimized by various integrated optics, including spatial light modulation. The image is thereby imposed in the light path, creating the final exposure pattern on the substrate surface.
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As shown in this schematic, the SF-100 uses a PC to
send exposure images through the Smart Filter assembly to the substrate,
aligning with an optical microscope and alignment stages. (Source:
Intelligent Micro
Patterning)
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Intelligent Micro Patterning has incorporated this subsystem into the SF-100. The subsystem connects to a PC, which provides the exposure image. From the subsystem, the pattern is transferred to the wafer surface, aligned through the use of an optical microscope, and course and fine alignment stages (
Figure). The exposure system
uses a step and repeat method.
The system can expose features as small as 20 µm, on substrates up to 200 mm2. Using a standard Novolac positive photoresist, exposure time is <60 sec/µm. Although the technology will certainly not be competing for rights to print the fine linewidths of next-generation integrated circuits, its exposure capabilities offer much over competing maskless technologies, which have resolutions of about 300 µm, according to Jay Sasserath, CEO of Intelligent Micro Patterning.
It offers other advantages as well. Competing ink-jet techniques have generally not offered the resolution that the Smart Filter Technology does, although at least one group has achieved finer resolutions (see Semiconductor International, November 2000). However, the technique requires changing the entire resist system, Sasserath noted. The SF-100, on the other hand, is basically a drop-in replacement for standard lithography systems, able to use existing resists (it processes all standard Novolac photoresist materials, as well as other photosensitive materials), coaters, etc. What it offers over standard techniques, of course, is a significant reduction in operating costs by eliminating the need for photomasks.
Within a few days after its introduction last month, the company was already getting inquiries about the SF-100. "Microfluidics is big. I've seen a lot of interest already," Sasserath said, noting that MEMS and micro-optics also would be important applications, and the relatively fine linewidth would encourage limited applications in advanced packaging as well. A couple of demo units are up and running, he said, including a MEMS-related program at General Dynamics and a bioMEMS program at the University of Florida.
The technology has been worked on for about a year and a half at the University of South Florida's College of Ocean Technology, which continues to offer the company support, Sasserath said. Much of the research money for the project came from marine interest in MEMS, he noted. The technology's inventor, David Fries, founded Intelligent Micro Patterning along with Sasserath, and is now the company's chief technical officer.
For additional information on lithography, go to www.semiconductor.net/lithography
