In this paper we describe the lithographic behavior and related material properties of a new class of chemically amplified, positive tone, silicon-containing methacrylate photoresists incorporating the polyhedral oligomeric silsesquioxane (POSS) group as the etch-resistant component. POSS-bearing monomers were copolymerized with methacrylic acid (MA), tertbutyl methacrylate (TBMA), tert-butyl trifluoro methacrylate (TBTFMA), itaconic anhydride (IA), and 2-(trifluoromethyl) acrylic acid (TFMA), in various compositions. A perfluorooctylsulfonate-based photoacid generator (PAG) was used to deprotect TBMA (or TBTFMA) to base soluble carboxylic acid by heating after exposure. XPS and angular XPS analysis were used to examine possible surface segregation phenomena. It was proven that POSS surface enrichment occurs for the POSS-TBMA copolymers while surface segregation may be reduced if suitable additional resist components are selected. The POSS-based resists were studied for 157-nm lithographic applications and found to have high sensitivity (<10 mJ/cm 2 under open field exposure), no silicon outgassing, and sub-100-nm resolution capabilities. Ninety nanometer patterns in 100-nm thick films were resolved. At present, their absorbance is high (∼4 µm -1 ) for single-layer lithographic applications at 157 nm; however, high etch resistance in oxygen plasma makes them suitable for bilayer schemes.

Siloxane and silsesquioxane copolymers have been synthesized and first evaluated as potential components of 157 nm resist materials. In block copolymers of dimethylsiloxane and tert-butyl methacrylate negative imaging chemistry dominates at 157 nm, due to the presence of the siloxane component, although positive imaging in aqueous base developers via chemical amplification was obtained at longer wavelengths ͑248 nm͒. The same behavior is observed in graft copolymers of dimethylsiloxane and tert-butyl methacrylate. On the other hand, random copolymers of polymerizable polyhedral oligomeric silsesquioxane monomers with various acrylates, including partially fluorinated, can be used as components of resist formulations that provide positive imaging at 157 nm, aqueous base development, and physicochemical properties which resemble those of conventional poly͑meth͒acrylates. Pattern transfer properties depend on the selection of the silsesquioxane component. Polymers containing 30% or higher w/w ethyl-substituted silsesquioxane cages provide the necessary etch resistance as well as low surface roughness to oxygen plasma at 100 nm film thickness, allowing bilayer 157 nm lithography, even without further absorbance optimization.

Novel polymers containing polyhedral oligomeric silsesquioxane (POSS) pendant groups have been synthesized and evaluated as components of I 57 nm resist formulations. Random copolymers of polymerizable, ethyl-POSS containing monomers with various acrylates, including tert-butyl methacrylates, were first used in positive, aqueous basedevelopable resist formulations and evaluated at thicknesses in the range of 100 nm. Copolymers with optimized monomer composition do not present strong self-organization phenomena and provide materials with good film forming properties, and high sensitivity at 157 nm (1-10 mJ/cm2 under open field exposure). Process studies reveal strong influence of thermal processing conditions and development concentrations on swelling of unexposed and underexposed resist areas. Similar results are obtained from Dissolution Rate Monitoring (DRM) studies. A typical process selected for swelling reduction includes pre-exposure and post-exposure bake steps at 160°C (2minutes) and selection of low strength developers. High resolution patterning under these conditions has shown potential for sub 130 11111 lithography upon further material optimization. On the other hand, pattern transfer studies have shown that 100 nm thick films ofPOSS containing materials, having the same silicon content as the ones evaluated for high resolution 157 nm lithography, provide the necessary oxygen plasma resistance for use as bilayer resists. X-ray photoelectron spectroscopy (XPS) was used for surface characterization before plasma etching. Both XPS and angular XPS characterization have revealed that the POSS moieties tend to segregate preferentially on the free surface ofthe films.

Thin films of ethyl polyhedral oligomeric silsesquioxane (ethyl-POSS) containing polymers at different compositions were chemically modified using laser irradiation at 157 nm. The irradiation caused photodissociation of C–O and C–H bonds followed by the formation of new chemical bonds. The content of Si–O and C–O bonds increased, as did the surface hardness. Vacuum ultraviolet (VUV) absorption, mass spectrometry, x-ray photoelectron spectroscopy, and atomic force microscopy imaging and indentation were used to evaluate the effects of the 157 nm irradiation. The chemical modification was restricted to a thin surface layer. The layer depth was determined by the penetration depth of the 157 nm VUV photons inside the thin copolymer layer. With prolonged VUV irradiation, the absorbance of the polymers increased, eventually becoming saturated. The chemical changes were accompanied by surface hardening, as evidenced by the increase in the Young’s modulus from 4 to 24 GPa due to glassification of the irradiated parts. The chemically modified layer acts as a shield against photodissociation and degradation of the deeper portion of the POSS polymer by VUV radiation. Applications include the protection of solar cells on low orbit satellites from solar VUV photons.

No abstract

Study of 193 nm photoresist degradation during short time fluorocarbon plasma exposure III. Effect of fluorocarbon film and initial surface condition on photoresist degradation

No abstract

No abstract