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Several methods have been investigated which improve the processability of polyimide homo-or copolymer systems. In particular, the utilization of a solution imidization technique in converting the poly(amic acid) intermediate to the fully cyclized polyimide has been successfully exploited. The solution imidization was conducted in Nmethylpyrollidone (NMP) and an azeotroping agent, such as cyclohexylpyrollidone (CHP), at approximately 160°C for 24 hours. This technique has been shown to yield more soluble products than the corresponding bulk thermal imidization which is conducted at higher temperatures of ∼300°C. Another important method of improving melt as well as solution processability involves the incorporation of a monofunctional reagent to obtain nonreactive end groups and controlled molecular weights. Structural modification by copolymerization with more flexible oligomers such as poly(arylene ether)s may also enhance processability and possibly provide improved impact strength. In this paper, the effects of incorporating varying concentrations of poly(arylene ether) sulfone and ketone oligomers into the polyimide backbone are reported. The overall copolymer molecular weight was consistently controlled to —25,000 g/mole, with the use of small molar quantities of the monofunctional reagent phthalic anhydride. Very tough, transparent films were obtained in all cases by compression molding copolymers at 340°C. Thermal analysis indicated that microphase separation is achievable in some cases as judged by the presence of two glass transition temperatures.

Optimization of the deep‐UV and electron‐beam lithographic properties of a copolymer of trimethylsilylmethyl methacrylate (SI) and chloromethylstyrene (CMS), P(SI‐CMS), within a weight average molecular weight range of 1.4 to 4.1 × 105 and 90 to 93 mole percent SI composition has been achieved. The solubility behavior of P(SI‐CMS) resist was examined using the Hansen 3‐dimensional solubility parameter model and dissolution rate measurements. Swelling of the resist has been minimized through the identification of a single component developer (2‐propanol) and rinse (water) system. For the material containing 90 mole percent SI (14.9 weight percent Si) and M̄ω = 1.4 × 105, the sensitivity to 248 nm radiation is 65 mJ/cm2 and to electron‐beam exposure is 3.4 μC/cm2 at 20 kV. This material Is applicable to bilevel lithographic processes, and the O2 reactive ion etching (RIE) rate is 16 times slower than standard hard‐baked photoresist. Using a He/O2(60/40) RIE pattern transfer process, 0.4 μm line/space patterns have been resolved in a 1.3 μm bilayer structure for deep‐UV exposures, and 0.25 μm imaging has been demonstrated in a 0.7 μm thick planarizing layer using electron beam irradiation. The loss in linewidth associated with the 0.25 μm process is ∼0.04 μm.

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