Synthesis and Radical Polymerization of Pyrocarbonate Functionalized Monomers: Application to Positive-Tone Photoresists
- PDF / 830,435 Bytes
- 6 Pages / 396 x 630 pts Page_size
- 36 Downloads / 201 Views
ABSTRACT The synthesis of two new tert-butyl carbonic anhydride monomers, 4-vinylbenzoic and methacrylic tert-butyl carbonic anhydride was achieved successfully. Radical polymerization at 450 C yielded tert-butyl pyrocarbonate protected materials. Thermographic analysis showed that both polymers decompose cleanly at 135 0 C. The lithographic performance of both materials was evaluated in presence of 2,4,6-tris-(trichloromethyl)-s-triazine as photoacid generating species. It was demonstrated that the large polarity change resulted in a chemically amplified positive photoresist system. INTRODUCTION The chemical amplification concept proposed by Ito and coworkers [1,2] has been an important contribution to the design of advanced photolithographic imaging systems. In chemically amplified processes, a cascade of acid-catalyzed deprotection steps is light-induced by conversion of photoacid generating species (PAGs). The most widely used acid-labile protecting group is the tert-butyloxycarbonyl (tert-BOC) group which is readily removed by H+-catalyzed thermolysis. This process is accompied by a large polarity shift from a nonpolar to a polar state, inducing the necessarily solubility changes required for practical imaging applications. Poly[4(tert-butyloxycarbonyl)oxystyrene] (PBOCSt) has been studied extensively as the model for tertBOC-resist systems [3-6]. Acidolysis of the latter material results in the formation of polar phenol moieties, easily developed in alkaline medium, affording a positive working resist sytem. tert-Butyl esters such as tert-butyl methacrylate or 4-tert-butylcarboxystyrene also have been evaluated successfully as photoresist materials [7]. They offer an even larger shift in polarity, but only at higher temperature as compared to the tert-butyl carbonate analogues. Moreover, the latter polymers are often characterized by a high glass transition temperature Tg, requiring elevated processing temperatures. Therefore, in this study a synthetic route was devised yielding the tert-butyl carbonic anhydrides of 4-carboxystyrene and methacrylic acid. This new class of thermo- and acid labile tert-butyl protected monomers and corresponding polymers retains a high thermosensitivity while still resulting in a carbonic acid after deprotection, providing a significant polarity change. In this paper we report the results of the polymer synthesis as well as an evaluation of the performance of poly(4-vinylbenzoic tert-butylcarbonic anhydride) and poly(methacrylic tert-butylcarbonic anhydride) as novel positive working UV-photoresist materials. Their thermal properties as well as their lithographic application as compared to tert-butyl ester and carbonates are discussed.
199 Mat. Res. Soc. Symp. Proc. Vol. 624 © 2000 Materials Research Society
EXPERIMENT Measurements The average molecular weights Mw and M" of the copolymers were determined by gel permeation chromotography (GPC) on a PL-Gel Mixed D-51i 7.8x600 mm column, calibrated without correction by polystyrene standards, using chloroform as eluent and a MEL
Data Loading...
