Enhancing the dry etch resistance of polymethyl methacrylate patterned with electron beam lithography

Abstract

Acrylic resists are used for both electron beam lithography and for deep-ultraviolet (UV) lithography at 193 nm wavelength. Polymethyl methacrylate (PMMA) is the most widely used acrylic positive tone electron beam resist. While it offers superb resolution in this role, its dry etch resistance is quite poor. Here, the authors present a new technique for enhancing the dry etch resistance of PMMA. This involves adding Irgacure 651—a photo-cross-linking agent to PMMA. Irgacure-containing PMMA can be spin-coated onto substrates in exactly the same way as pure PMMA. Addition of Irgacure does not impair the chain scissioning properties of PMMA under electron beam irradiation. Electron beam lithography can be carried out with this resist in exactly the same manner as with pure PMMA, although at a higher dose. After electron beam exposure, the exposed sample can be developed in diluted methyl isobutyl ketone solvent, again just as with pure PMMA. A postlithography UV exposure step then cross-links the patterned resist; substantially enhancing its dry etch resistance. This technique enables the fabrication of deeper etched structures than is possible with PMMA alone.

Engineering Silk Protein to Modulate Polymorphic Transitions for Green Lithography Resists

“…Additionally, the Ohnishi parameter (O-parameter) of these materials was calculated as follows: O = (total number of atoms)/(number of carbon and oxygen atoms). 57,58 the low O-parameters of silk resists indicate that they are well suited for etching applications with high resistivity while also retaining mechanical strength. However, the increased etch rate at higher O 2 concentrations (1.0 to 1.7 selectivity for 2 to 5 sccm O 2 ) highlights the fact that etching gases must be carefully selected in etching applications (Figure S13).…”

“…A 1 B 4 and A 8 B 2 have O -parameter values of 2.28 and 2.34, respectively. Considering that low resistive poly­(methyl methacrylate) has an O -parameter of 5 whereas high resistive poly­(4-hydroxystyrene) has a value of 2.43, , the low O -parameters of silk resists indicate that they are well suited for etching applications with high resistivity while also retaining mechanical strength. However, the increased etch rate at higher O 2 concentrations (1.0 to 1.7 selectivity for 2 to 5 sccm O 2 ) highlights the fact that etching gases must be carefully selected in etching applications (Figure S13).…”

PMMA-Assisted Plasma Patterning of Graphene

“…erefore, we opted for a PMMA-based mask, a polymeric material employed in e-beam lithography as a resist. However, PMMA is well known to have a very low resistance to plasma oxygen [33]. For example, a double layer of PMMA (PMMA 495K A2/PMMA 950K A4) can be employed to pattern a 65 nm width graphene ribbon [15], but a metallic mask is preferred to obtain smaller ribbons with widths smaller than 50 nm [9,11,15].…”

“…Low-temperature curing is unconventional in electron-beam lithography and PMMA typically shows low resistance to oxygen plasma etching [33]. PMMA is therefore normally considered inadequate as a mask for selective plasma etching at sub-50 nm resolution.…”