Polymer-Inorganic High Contrast and High Sensitivity Resists for Nanolithography
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Abstract Polyhedral oligosilsesquioxane methacrylate (POSSMA)/methyl methacrylate(MMA)/tert-butyl methacrylate(TBMA)/tert-butyl acrylate(TBA) copolymers were synthesized by solution polymerization. Their preliminary lithographyrelated properties were studied. It is shown that the mass ratio of MMA/POSSMA=85.8/14.2 leads to an X-ray resist with a high contrast of 23.5 without sacrificing the sensitivity(1350 mJ/cm 2) which remains comparable to that of standard PMMA. By careful manipulation of components and compositions, this generic type of polymer could potentially be utilized as a DUV or e-beam resist as well.
Introduction For the past few decades, tremendous efforts have been expended for developing new resist materials for DUV, X-ray and electron beam lithography." 2' 3 Ultra large Scale Integration should lead to 100 nm production circuits by 2006 as predicted by the Semiconductor Industry Association. This challenge imposes a formidable pressure on lithographic processes in terms of dimension tolerances (10 nm or less) and positioning accuracy (1 nm or less), to quote only a few specifications. For sub-100 nm lithography it is crucial to synthesize higher performance and especially higher contrast resists4 . It has already been shown that inorganic resists are capable of exhibiting higher contrast than organic resists5, but their intrinsically lower sensitivity and complex deposition methods make them suitable primarily for ion lithography. A combination of high contrast necessary for sub-100 nm resolution and high sensitivity necessary for industrial throughput could be reached by carefully engineering organic/inorganic nanocomposites, acting as optimum resists for a given lithographic technology. The scope of our investigation is to develop and broaden this concept into a "general resist" for next generation lithographies (NGL). Polyhedral oligosilsesquioxane methacrylate (POSSMA, 1) are structurally welldefined macromers that have an inorganic silica-like core as shown in Figure 1. The core is surrounded by seven inert organic groups for solubility and one polymerizable vinyl group. These POSSMA macromers have similar reactivity as common methacrylate monomers and can easily copolymerize with the latter. 6 We therefore anticipated that incorporation of POSSMA into polymeric resist materials might generate higher-
121 Mat. Res. Soc. Symp. Proc. Vol. 584 © 2000 Materials Research Society
resolution and higher-contrast resists. This paper reports the synthesis and characterization of POSSMA-containing polymethacrylate copolymers. It is anticipated that these polymers may have potential applications as thin layer resists in 157 nm and EUV lithography. Also we anticipate that these copolymers are potential resists for nanolithography at 193 nm DUV wavelength, X-ray and electron beam exposure tools. CH3
CH3
I
OHO3
0 AJN,6 CI
CH + 2 =C~~ H=CCH
2 --C ---
Ili H CH2 -c-A-
Sc=o 000
0 OH3
OH3
si
R-f4 •R
si
/7i.R
2
o-4R 0
1. (R=cyclopentyl)
3
Figure 1. Scheme for the synthesis of POSSMA/MMA copo
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