A variety of N-substituted maleimide monomers have been synthesized and copolymerized with styrene derivatives(XSt) and/or 1-vinyl-2-pyrrolidinone (VP). The resulting copolymers were subjected to deep UV(DUV) irradiation to evaluate them as potential photoresists. The facile deprotection of the silyl protecting groups in the silicon-containing copolymer P(SiOMI/XSt) by DUV irradiation in the presence of a photoacid generator brought a signifiant change in solubility properties. Accordingly, a clean positive image pattern with 0.7-㎛ line and space was obtained.
Since the silicon containing copolymer P(SiOMI/XSt) requires a photoacid generator, next phase of our efforts has focused on the development of a single-component resist system. Thus, a maleimide monomer CSOMI having 10- camphorsulfonyl group was prepared and copolymerized with styrene derivatives to provide copolymers P(CSOMI/XSt).
The releasing of a strong camphorsulfonic acid(CSA) upon DUV irradiation from copolymers P(CSOMI/XSt) was confirmed by spectroscopic analysis of the resulting polymer and of the released camphorsulfonic acid. Accordingly, the copolymers P(CSOMI/XSt) were found to possess the capability of a single-component resist system based on the chemical amplification concept in the absence of an externally added PAG. This type of resist system should be free of the compatibility problem arising from addition of a crystalline PAG due to its low solubility in the resist media.
For the improvement of the resist properties from the copolymers P(CSOMI/XSt), we then moved into a terpolymer system, in which 1-vinyl-2-pyrrolidinone (VP) was employed as a new monomer. The weakly basic VP units are particularly incorporated into the polymer backbone for enhancing solubility, adhesion and furthermore improving post-exposure delay (PED) stability. The terpolymer P(CSOMI/t-BOCMI/VP) have a good film-forming property with a very low optical density of $0.08μm^{-1}$ at 250 nm.
Indeed, a clean positive resist image of 0.3-㎛ line and space patterns was obtained by irradiation with 30 KeV electron beam, PEB, and development in a 2.38% aqueous TMAH solution.
