Combination photo and electron beam lithography with polymethyl methacrylate (PMMA) resist

Abstract

We describe techniques for performing photolithography and electron beam lithography in succession on the same resist-covered substrate. Larger openings are defined in the resist film through photolithography whereas smaller openings are defined through conventional electron beam lithography. The two processes are carried out one after the other and without an intermediate wet development step. At the conclusion of the two exposures, the resist film is developed once to reveal both large and small openings. Interestingly, these techniques are applicable to both positive and negative tone lithographies with both optical and electron beam exposure. Polymethyl methacrylate, by itself or mixed with a photocatalytic cross-linking agent, is used for this purpose. We demonstrate that such resists are sensitive to both ultraviolet and electron beam irradiation. All four possible combinations, consisting of optical and electron beam lithographies, carried out in positive and negative tone modes have been described. Demonstration grating structures have been shown and process conditions have been described for all four cases.

Photolithography in the vacuum ultraviolet (172 nm) with sub-400 nm resolution: photoablative patterning of nanostructures and optical components in bulk polymers and thin films on semiconductors

“…The speed and precision of the processes reported here suggest that hybrid VUV/e-beam lithography patterning, both of which accommodate PMMA photoresists, will enable the rapid patterning of nanoscale features on the same wafer without the need to strip the polymer resist when transitioning between the VUV and e-beam exposure steps. 25,26 It is our expectation that such processes will be of value in rapidly and inexpensively fabricating networks and patterns for optical wave front manipulation, 27 micro-and nano-fluidics, electronic and optical components and networks, and biomedicine and pharmacology. Not only is 172 nm photolithography appealing for advancing research in micro-and nanotechnology and physics but the affordability, precision, and speed of the exposure process expands access of academic and industrial laboratories to a lithography capable of <200-400 nm feature fabrication.…”

Emerging II-VI wide bandgap semiconductor device technologies

“…On the other hand, a combination of photolithography and electron beam lithography offers both larger and smaller features that are imaged through optical lithography and electron beam lithography, respectively. The combination of both techniques offers an effective way to make required structures with both features of large and small geometry, even in an integrated way with a much superior resolution [96].…”

Electron Energy Loss Processes in Methyl Methacrylate: Excitation and Bond Breaking

“…Methyl methacrylate (MMA) is a building block of poly­(methyl methacrylate) (PMMA), a common photoresist for both electron and photon beam lithography. − PMMA can be used as a positive photoresist, when PMMA is damaged by the action of electrons or photons and its removal by solvent is enhanced, or as a negative photoresist, when it is densified by the action of electrons or photons and the desired pattern remains on the substrate upon solvation. − The first case usually occurs via polymer chain scission at low exposures, while the second case occurs at high exposures where a high number of secondary reactive species is expected to form and induce more cross-linking in the resist . Higher exposure can lead to the formation of carbonaceous structures by PMMA “baking”. , …”