An important aspect ofsingle-layer resist use at 193-nm is the inherently poor etch resistance ofthe polymers currently under evaluation for use. In order to provide the information necessary for resist process selection at 1 93 urn, we have projected the ultimate etch resistance possible in 193-nm transparent polymers based on a model we have developed. First, a data base ofetch rates was assembled for various alicyclic methacrylates. This data base has been used to develop an empirical structure-property relationship for predicting polymer etch rates relative to novolac-based resist.This relationship takes the functional form NormalizedRate -3.8Or +6.71r -4.42r+ 2.10, where r is the mass fraction ofpolymer existing as cyclic carbon. From this analysis, it appears as though methacrylate resists equal in etch resistance to deep UV resists will be possible. Early generations of methacrylate-based 1 93-nm resists were also evaluated in actual IC process steps, and those results are presented with a briefdiscussion ofhow new plasma etch chemistries may be able to further enhance resist etch selectivity.
An investigation of the thermal cure reactions and the hydrolysis reactions involved in the degradation of polyimide films under temperature and humidity stress using nitrogen-15 solids nuclear magnetic resonance (NMR) is herein reported. Nitrogen-15 labeling was used in combination with dipolar decoupled, cross polarization magic angle spinning (CPMAS) NMR techniques as a means of monitoring chemical reactions as these occur in solid state polyimide. The relative concentration of each nitrogen-containing functional group was calculated using standard NMR methods based on determination of the values of the cross polarization time constant, Thn. the proton rotating frame time constant, , , and observed spectral line intensities. The polyimides were derived from an oligomeric poly(amic acid) precursor [pyromellitic dianhydride (PMDA) and 4,4'-oxydianiline (ODA)], a high molecular weight poly(amic acid ester) precursor (PMDA m-diacyl chloride diethyl ester and ODA), and a polyisoimide oligomer [3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) and l,3-bis(3-aminophenoxy)benzene (APB) endcapped with (3-aminophenyl)acetylene (APA)]. The number of "defect sites" or imide-precursor groups where imidization does not occur was estimated to be between 6 and 9% of the total nitrogen and varies with the type of precursor used. The degree of imidization or cure was found to vary between 91 and 94% following a cure at 400 °C. Residual isoimide groups were detected after an extended 400 °C bake of the polyisoimide precursor. Cured films were subjected to temperature and humidity stress at 85 °C and 81% relative humidity for 450 h. Estimates of hydrolysis range from as little as 1 % of total nitrogen for the BTDA-APB-APA derived material to approximately 13 % for the PMDA-ODA poly(amic acid ester) precursor. About 30% of the amide acid groups formed during stress react with water in a second hydrolysis reaction with chain cleavage to yield a terminal diacid and a terminal amine group. Hydrolysis from temperature and humidity stress is almost completely reversed if the stressed polyimide is heated at 400 °C after stress. The data obtained in this study are consistent with previously reported macroscopic observations in which polymer properties degrade during temperature and humidity stress and are recovered after post temperature and humidity bakes.
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