Polymer-bound Photoacid Generator Research Articles

Molecular Layer Deposition of Nanoscale Organic Films for Nanoelectronics Applications

The trend toward nanoelectronics motivates the development of new materials and processes. Novel organic materials are of interest for various applications, and this talk will focus on the development of nanoscale organic films for lithography and patterning. Current photoresist materials are facing many challenges introduced by advanced lithography, particularly the need for excellent compositional homogeneity and ultrathin film thickness. Traditional spin-on polymeric resists have inherent limitations in achieving a high level of control over the chemical composition, leading to interest in alternative methods for making photoresists. In this work, we demonstrate that molecular layer deposition (MLD) is a promising method for synthesizing photoresists because it allows for precise control over organic film thickness and composition. As an analogue to atomic layer deposition (ALD), MLD utilizes sequential, self-limiting reactions of organic precursors to build a thin film directly on a substrate surface. An advantage of MLD is that it grows organic films by depositing only one molecular layer at each precursor dose, which in turn allows for fine tuning of the position and concentration of various functionalities in the deposited film. In our study, we use bifunctional precursors, diamine and diisocyanate, to build polyurea resist films via urea coupling reaction. Acid-labile groups are embedded in the backbone of the diamine precursor and incorporated into the resist film with a highly uniform distribution. Two methods of incorporating photo acid generator (PAG) are employed. The first method is to soak a PAG into the resist film after deposition and the second approach is to form in-situ polymer-bound PAG. By this novel synthetic approach, both aromatic and aliphatic polyurea films were successfully deposited by MLD and characterized for both materials properties and resist response. Electron-beam lithographic tests are carried on the MLD photoresists. Among the various MLD films studied, the aliphatic film performed best as a photoresist material, with a good sensitivity of 30 µC/cm2 with 100kV e-beam exposure, and a patterned line resolution of sub-100 nm. Other uses of MLD for advanced patterning methods, as well as fundamental studies into the mechanism of MLD, will also be described.

Synthesis of triphenylsulfonium triflate bound copolymer for electron beam lithography.

Photoacid generator (PAG) has been widely used as a key component in photoresist for high-resolution patterning with high sensitivity. A novel acrylic monomer, triphenylsulfonium salt methyl methacrylate (TPSMA), was synthesized and includes triphenylsulfonium triflate as a PAG. The poly(MMA-co-TPSMA) (PMT) as a polymer-bound PAG was synthesized with methyl methacrylate (MMA) and TPSMA for electron beam lithography. Characterization of PMT was carried out by NMR and FTIR. The molecular weight was analyzed by GPC. Thermal properties were studied using TGA and DSC. Thecharacterization results were in good agreement with corresponding chemical compositions and thermal stability. PMT was subsequently employed in electron beam lithography and its lithographic performance was confirmed by FE-SEM. This PMT was accomplished to improve the lithographic performance including sensitivity, line width roughness (LWR) and resolution. We found that PMT was capable of 20 nm negative tone patterns with better sensitivity than hydrogensilsesquioxane (HSQ) which is a conventional negative tone resist.

Study on Resist Performance of Polymer-Bound and Polymer-Blended Photo-Acid Generators

In the fabrication beyond a 16 nm node, the uniform distribution of acid generators in a resist matrix is a serious concern. The incorporation of acid generators into polymers via covalent bonds has attracted much attention in overcoming the compatibility problem of acid generators with polymers and reducing the diffusion lengths of acids, which leads to a high resolution and a low line edge roughness (LER). Therefore, the resist performance characteristics of a polymer-bound photo-acid generator (PAG) and a polymer-blended PAG were investigated and compared. The numbers of acid molecules generated in the polymer-bound and polymer-blended PAGs upon exposure to extreme ultraviolet (EUV) were almost the same at both 5 and 10 mol % acid generator contents. However, the sensitivity of the polymer-blended PAG was higher than that of the polymer-bound PAG. Although the etching durabilities of the developed polymer-blended and polymer-bound PAGs were lower than that of conventional resist materials, the surface roughness of the polymer-bound PAG was lower than that of the polymer-blended PAG. The developed polymer-bound PAG resist showed an excellent performance (30 nm line and 80 nm pitch). Thus, it was proved that polymer-bound PAG resists are promising candidates for the resist materials of nanolithography, such as electron beam and EUV lithography.

Study on Resist Performance of Polymer-Bound and Polymer-Blended Photo-Acid Generators

In the fabrication beyond a 16 nm node, the uniform distribution of acid generators in a resist matrix is a serious concern. The incorporation of acid generators into polymers via covalent bonds has attracted much attention in overcoming the compatibility problem of acid generators with polymers and reducing the diffusion lengths of acids, which leads to a high resolution and a low line edge roughness (LER). Therefore, the resist performance characteristics of a polymer-bound photo-acid generator (PAG) and a polymer-blended PAG were investigated and compared. The numbers of acid molecules generated in the polymer-bound and polymer-blended PAGs upon exposure to extreme ultraviolet (EUV) were almost the same at both 5 and 10 mol % acid generator contents. However, the sensitivity of the polymer-blended PAG was higher than that of the polymer-bound PAG. Although the etching durabilities of the developed polymer-blended and polymer-bound PAGs were lower than that of conventional resist materials, the surface roughness of the polymer-bound PAG was lower than that of the polymer-blended PAG. The developed polymer-bound PAG resist showed an excellent performance (30 nm line and 80 nm pitch). Thus, it was proved that polymer-bound PAG resists are promising candidates for the resist materials of nanolithography, such as electron beam and EUV lithography.

Novel chemically amplified resists incorporating anionic photoacid generator functional groups for sub-50-nm half-pitch lithography

A series of chemically amplified resists based on polymers of 4-hydroxystyrene, 2-ethyl-2-adamantyl methacrylate and a monomer-bound anionic photoacid generator (PAG) were prepared and characterized. Specifically, the following PAGs were separately incorporated into the main-chain of the polymers: the isomers triphenylsulfonium salt 2-(methacryloxy)-4-trifluoromethyl benzenesulfonate and triphenylsulfonium salt 4-(methacryloxy)-2-trifluoromethyl benzenesulfonate (CF3 PAG); triphenylsulfonium salt 4-(methacryloxy)-3-nitro-benzenesulfonate (NO2 PAG); and triphenylsulfonium salt of 1,1,2-trifluorobutanesulfonate methacrylate (MTFB PAG). Triphenylsulfonium salt 4-(methacryloxy)-2,3,5,6-tetrafluorobenzenesulfonate (F4 PAG) was used as the reference PAG. The intrinsic lithography performance of these polymer-bound PAG resists showed sub-50-nm half-pitch resolution and <5 nm LER (3σ) under 100 keV electron beam patterning. The relative sensitivity of these materials under 100 keV e-beam exposure was MTFB PAG ≥ F4 PAG > CF3 PAG > NO2 PAG. Resolved pattern sizes of 40 and 32.5 nm half-pitch were obtained for fluorinated PAGs (such as MTFB PAG and F4 PAG) bound polymer resists under EUV interference lithography. The surface roughness was inspected with AFM.

The effect of direct PAG incorporation into the polymer main chain on reactive ion etch resistance of 193 nm and EUV chemically amplified resists

The incorporation of photoacid generator (PAG) functional groups directly into the resist resin polymer backbone has shown improved lithographic performance in achieving high resolution, high sensitivity, and low line edge roughness (LER) simultaneously in chemically amplified resists. However, the effect of direct PAG incorporation into the resist polymer on the reactive ion etch (RIE) performance in such materials was not previously studied. This paper discusses the dependence of the etch performance of such polymer-bound PAG materials on PAG structure and composition. Increased PAG loadings in both 193nm and EUV polymer-bound PAG resist platforms shows significant improvement in polymer etch resistance. Current polymer etch rate correlations and models were not able to accurately predict the trend of etch behavior within each polymer-bound PAG resist family.

Incorporation of ionic photoacid generator (PAG) and base quencher into the resist polymer main chain for sub-50 nm resolution patterning

Previous research has shown that polymer-bound PAG resists exhibit improved lithographic performance in both 193 nm and extreme ultraviolet lithography (EUVL) applications as compared to their more traditional blended PAG analogs. The further incorporation of base directly into the resist polymer backbone is a potential route for improving the resist performance and processing window. In this work, a new series of chemically amplified resists (CARs) that incorporate both PAG and base quencher functional groups into the polymer main chain are reported. The lithographic performance of these materials was investigated using electron-beam lithography (EBL). The polymer-bound PAG cation resist showed higher photospeed than the polymer-bound PAG anion resists. Base quencher incorporation slightly decreased the photospeed but improved the resolution in the case of resists with the polymer-bound PAG cation and pyridine base. Base quencher incorporation showed no improvement on the lithographic performance of polymer-bound PAG anion resists.