Ilya L. Rushkin

Resist outgassing as a function of differing photoadditives

The effect of different photoadditives in high and low activation energy resist resins on resist outgassing during lithographic exposure was studied by quartz microbalance and gas chromatography/mass spectroscopy techniques. The resist outgassing was analyzed both qualitatively and quantitatively and structure-property relationships were developed between resist outgassing and the molecular structure of photoacid generators and additives. The photoadditives examined include, aryl iodonium perfluoroalkylsulfonates, triarylsulfonium perfluoroakylsulfonates, photogenerators of sulfamic acids, 2-nitrobenzyl PAGs and doxyl derivatives.

New polymers for 193-nm single-layer resists based on substituted cycloolefins/maleic anhydride resins

A series of new polymers for 193 nm single layer resist based on maleic anhydride/cycloolefin systems with minimum amount of acrylate units were synthesized. In order to minimize the acrylate content, the cycloolefin moiety of the polymers was functionalized with side groups designed to either promotes adhesion to silicon substrate and/or impart the imaging functionality. All polymers were prepared by free-radical polymerization in moderate to high yields and were characterized by variety of techniques. The initial lithographic evaluation of the new resists was carried out. It was found that acrylates can be successfully replaced with appropriately substituted cycloolefins to provide good resolution. The etch resistance of the new materials generally improves with increase in cycloolefin content. The Onishi and Kunz type plots will be discussed.

Fundamental studies of dissolution inhibition in poly(norbornene-alt-maleic anhydride) based resins

Abstract The dissolution inhibition mechanism for tert-butylcarboxylate (e.g. tert-butyl cholate) dissolution inhibitors and onium salt photoacid generators (PAGs) were examined in terpolymers of poly(norbornene-maleic anhydride-acrylic acid) (P(NB/MA/AA)). For tert-butyl carboxylates, increasing hydrophobicity increased the dissolution inhibition ability. Dissolution promotion tracked with the number of carboxylic acid moieties and the hydrophobicity of carboxylic acids moieties released upon acidolytic cleavage of the tert-butyl carboxylate. For onium salt PAGs, increasing the hydrophobicity and size of fluorinated anions decreased dissolution inhibition.

Model study by FT-IR and 13C NMR of the interaction of poly(norbornene-alt-maleic anhydride) and its derivatives with select cholate dissolution inhibitors or with select iodonium and sulfonium phot

The fundamental nature of the interactions between poly (norbornene-alt-maleic anhydride) based resins and cholate based dissolution inhibitors (DIs) were studied by FT-IR and NMR spectroscopy. We also studied the role that photo-acid generators (PAGs) play in the dissolution of these polymer resins. We attempted to disentangle the hydrophobic effects of the DIs and PAGs from the specific interactions (Van der Waals, hydrogen bonding or ionic) that these materials have within the polymer system. We employed solubility studies of DIs and PAGs using cloud point determinations and dissolution inhibition experiments on spun films to determine the extent that hydrophobicity and polymer interactions play in development. We found that for simple cholate derivatives the interactions with maleic anhydride repeating units parallel the dissolution inhibition sequence (t-butyllithocholate > t-butyldeoxycholate > t-butylcholate). For a wider range of cholate derivatives, the cloud point in water is a useful predictive tool, in that it takes into account both the hydrophobicity and the propensity to interact with other moieties. Thus for these materials, dissolution inhibition is governed by both interactions between the DI and the polymer, and the hydrophobic nature of the DIs. In contrast, for the PAGs, the cloud point is not a good predictive tool for dissolution inhibition. We found for onium salt materials, that the extent of dissolution inhibition is predicated by the size of the anion. For example, large sterically hindered anions which give rise to PAGs that exhibit poor solubility in water, paradoxically also show poor dissolution inhibition. This may be because the steric hinderance disfavors interactions with the polymer matrix.

Base additives for use in a single layer 193-nm resist based upon poly(norbornene/maleic anhydride/acrylic acid/tert-butyl acrylate)

We report on a study of the chemical and lithographic behavior of two types of base additives. One class of materials that we will report on are aminosulfonate onium salts, we report a study of both the thermal stability and the lithographic behavior imparted by these as a function of chemical structure. It will be shown that the decomposition temperature is a function of the basicity (nucleophilicity) of the counter anion but this can be countered by appropriate choice on onium cation. We will also discuss the lithographic performance of formulations containing transparent ammonium carboxylate bases. It will be shown that these materials provide for comparable lithographic to a standard formulation containing an amine additive. Since carboxylates and aminosulfonates are far less nucleophilic than amine additives these additives may be useful because they will not have the tendency to interact with electrophilic sites such as maleic anhydride derived repeat units.

Model study by FT-IR of the interaction of select cholate dissolution inhibitors with poly(norbornene-alt-maleic anhydride) and its derivatives

The fundamental nature of the interaction between the polymer matrix and the cholate based dissolution inhibitors are being studied by Fourier Transform-IR (FTIR) spectroscopy. It was found that the simple cholate derivatives undergo, in a blend with poly(norbornene-alt- maleic anhydride) and in a blend with the terpolymers poly(norbornene-alt-maleic anhydride-co-t-butylacrylate) and poly(norbornene-alt-maleic anhydride-co-acrylic acid), stronger interaction as seen by shifts in the OH region of the spectra than do blends with dimeric or oligomeric cholates.

Thermal properties of COMA materials

Glass transition measurements of cycloolefin/maleic anhydride (COMA) resist resins are complicated by the fact that their glass transitions and the thermal decomposition of their imaging groups often occur over the same temperature range. In order to gain insight into the Tg ranges of these materials, a series of model non-imaging COMA polymers was synthesized and evaluated by DSC. Among the materials thus examined were copolymers of substituted norbornenes with maleic anhydride, copolymers of nobornene with maleic anhydride and cyclohexyl acrylate, and copolymers of vinyl ethers with maleic anhydride. The effects of cholate additives on thermal properties of COMA polymers were also examined.

Optimization of 193-nm single-layer resists through statistical design

Through a series of statistical design experiments we optimized the lithographic performance of a 193 nm single layer resists based on a norbornene-maleic anhydride matrix resin. Several interesting findings were found including that having the PEB temperature improved the performance of the resist. The polymer composition was found to strongly influence the lithographic performance of the resist. Variables that we examined included acrylate loading and blocking level. By optimizing the composition of the polymer, we have obtained resist with high etch resistance, square profiles and 0.130 micron dense line ultimate resolution in 0.5 micron thick films. The resist formulations are compatible with industry standard 0.262 N TMAH. During exposure the resists does not suffer from the outgassing of volatile species.

Lithographic behavior of carboxylate-based dissolution inhibitors and the effect of blending

We report on a lithographic study of the behavior of non- cholate tert-butylcarboxylate dissolution inhibitor (DIs) formulated in a poly(norbornene/maleic anhydride/acrylic acid/tert-butyl acrylate) 193 nm single layer resin. A comparision is made between formulations containing non- cholate DIs, cholate based DIs and formulations containing blends of the two different types of DIs. It was found that formulations containing the non-cholate materials tended to give T-topped profiles while the formulations containing cholate based materials and blends containing as little as 1% cholate based DI did not.

Surface composition of a norbornene-maleic-anhydride-based 193-nm photoresists for different photoacid generators as determined by x-ray photoelectron spectroscopy

The surface composition of chemically amplified photoresists depends upon the photoacid generator used and the processing. We have used x-ray photoelectron spectroscopy to determine the surface composition of resists using four different photoacid generators: trifluoromethanesulfonate, perfluorobutanesulfonate, perfluorooctanesulfonate, and perfluorobenzenesulfonate. The fluorine in each of these PAGs was used as a tag of their presence on the surface. The surface F concentration generally increased after post- exposure bake. The F concentration tended to increase further after a short bake, but usually decreased after longer baking times. These results suggest that the surface concentration of F reflected competition between bulk diffusion of the photoacid leading to surface segregation and its volatilization.