The main difference between e-beam lithography and photolithography is the exposure phase. In photolithography, light shines through a patterned stencil called a mask, striking the whole surface of the chip at once. With e-beam lithography, on the other hand, a beam of electrons scans across the surface of the resist, row by row, a more time-consuming operation.
One way to improve the efficiency of e-beam lithography is to use multiple electron beams at once, but there’s still the problem of how long a beam has to remain trained on each spot on the surface of the resist. That’s the problem the MIT researchers address
Two tricks were used to improve the resolution of high-speed e-beam lithography. The first was to use a thinner resist layer, to minimize electron scattering. The second was to use a solution containing ordinary table salt to “develop” the resist, hardening the regions that received slightly more electrons but not those that received slightly less.
Pieter Kruit, a professor of physics at the Delft University of Technology in the Netherlands and co-founder of Mapper, a company that has built lithographic systems with 110 parallel e-beams, says that in addition to being faster, e-beam systems that deliver smaller doses of electrons are much easier to build. The larger the dose of electrons, the more energy the system consumes, and the more insulation it requires between electrodes. “That takes so much space that it’s impossible to build an instrument,” Kruit says.
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