Dow Corning targets maskless lithography with latest e-beam photoresists

by Debra Vogler, Senior Technology Editor, Solid State Technology

June 24, 2008 – Dow Corning Electronics’ silicon lithography solutions group announced the commercial availability of Dow Corning XR-1541 e-beam resists, designed to enable the development of next-generation, direct-write lithography processing technology. The family of new spin-on resists, which allows patterning with electron beams rather than conventional light, offers a maskless lithography technology capable of defining features as small as 6nm.

Available in a variety of high-purity, semiconductor-grade formulations, the resists consist of hydrogen silsesquioxane (HSQ) resin in a carrier solvent of methylisobutylketone (MIBK). These negative-tone resists can be used with standard spin-on deposition coating equipment to produce thin films ranging in thickness from 30-180nm in a single coat. Custom formulations are available for thinner or thicker films.

The product data sheet explains that variable electron beam lithography allows control of the electron penetration depth in HSQ from below 35nm to >175nm with a single exposure tool, with beam energies from 200eV to 100keV. Optimal doses depend on beam energy, resolution, and film thickness, but area doses from 400-700μmC/cm2 are typical and depend on thickness, according to the specification. A 350°C post exposure bake in N2 enhances the contrast properties of the film, which can then be developed in a standard aqueous base developer (0.26 N TMAH).

With current lithography technology becoming technically and economically difficult to extend beyond the 32nm node, these new resists will provide an economical way to directly write patterns with “some of the highest resolutions possible” and enable next-generation lithography process development for fabricating ICs, masks or nanoimprint molds, explained Jeff Bremmer, global marketing manager with Dow Corning’s silicon lithography solutions unit. He told WaferNEWS that after e-beam exposure, the new e-beam resists behave like a silicon oxide film, so they have good etch resistance.

Several universities and research groups have already used HSQ-based e-beam resists to directly write fine patterns, however the company does not have permission to identify such efforts other than what is revealed in the product specification sheet — namely Philips Research Laboratories, Cornell Center for Materials Research, and the Cornell Nanofabrication Facility.

SEM graphs of lines and spaces at 100nm, 50nm, 30nm, and 20nm pitch in 30nm thick HSQ written at 100 kV with 5000mC/cm2. (Source: Philips Research Laboratories)

It isn’t clear how soon e-beam maskless lithography can achieve the throughput needed for high-volume manufacturing, but Bremmer told WaferNEWS that Dow Corning’s new e-beam resists would enable researchers to develop the second- or third-generation e-beam technology that could be necessary to get to a high-volume solution. — D.V.

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