ISSN:
0021-8995
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
Notes:
Copolymers of itaconic acid with methyl methacrylate, P(ItA-MMA), have been synthesized as promising positive working electron beam resists.1,2 However, attempts to obtain greater electron beam sensitivity by increasing the itaconic acid content and initial molecular weight of these copolymers have been hindered by difficulties in synthesizing itaconic acid copolymers with an ItA content greater than 50 mol% or with a molecular weight above 250,000. The usefulness of the MMA-ItA copolymers is also limited by their susceptibility to anhydride formation which makes this resist very sensitive to prebake conditions and aging times. To overcome these limitations and to develop resist materials with improved sensitivity, alkyl ester derivatives of itaconic acid have been synthesized, both as homopolymers and as copolymers with methyl methacrylate. The electron-beam chain scissioning yields, G(s), of these derivatives have been determined, and the most promising of these copolymers and homopolymers have been evaluated for lithographic performance. The G(s) values of the alkyl itaconate copolymers depend greatly on the structure of the alkyl group. The mono-alkyl itaconate copolymers exhibit G(s) values 2-3 times greater than the corresponding dialkyl itaconate copolymers. In particular, copolymers of monomethyl itaconate (MeI) with methyl methacrylate are found to be promising resist materials with high sensitivities and compatability with processing conditions. A trend in sensitivity is observed for a series of MMA-MeI copolymers ranging from 20 to 85 mol % MeI, with a maximum sensitivity observed for the 57 and 73% MeI compositions. These copolymers exhibit improved sensitivity over that of the itaconic acid copolymers. Anhydride is formed less readily from the MeI copolymers than from the ItA copolymers, improving the stability of the resist for process conditions. Areas exposed in P(MMA-73 mol % MeI) at 4 μC/cm2 (20 kV) were developed with less than 10% thinning of unexposed resist and with a contrast (γ) of 2. Vertical walls were observed for 1 μm wide lines using P(MMA μ73% MeI) at a dose of about 6 μC/cm2.
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/app.1985.070301210
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