Satoshi Takechi

Alicyclic polymer for ArF and KrF excimer resist based on chemical amplification

We designed a new chemical amplification resist for ArF and KrF excimer lithography. The resist comprises alicyclic the copolymer of adamantylmethacrylate and tert-butylmethacrylate, with triphenylsulfonium hexafluoroantimonate as a photo acid generator. This resist is highly transparent at KrF and ArF wavelengths because it has no aromatic and its dry etch resistance is comparable to that of a Novolac resist. The lithographic performance of this resist was evaluated using a KrF excimer laser stepper. A less than 0.5 micron line and space pattern profile was obtained with our resist.

Evaluation of chemically amplified resist based on adamantyl methacrylate for 193-nm lithography

An ArF single layer resist based on alicyclic polymer has been developed. Our work centers on improving the solubility of the base polymer in an aqueous base solution. The solubility is the most significant point in using alicyclic polymer. A suitable developer is obtained by adding isopropyl alcohol to the standard TMAH solution with a proper mixing ratio. This mixture greatly enhances the dissolution rate and allows the alicyclic polymer to act as a highly sensitive resist. Over-top coating has also been used to improve the pattern profile. We applied these processes to a resist based on a copolymer of 3-oxocyclohexyl methacrylate and adamantyl methacrylate. The results of ArF lithography are encouraging. There is a high sensitivity of about 10 mJ/cm2, and a high resolution of 0.17 micrometers lines and spaces is achieved. This shows that by enhancing the solubility the lithographic characteristics of the resist based on the alicyclic polymer are effectively improved.

Overcoat materials for acrylate resists to enhance their resolution

We have developed a series of water developable overcoat materials to enhance the resolution of acrylate resists. The overcoat materials are water solutions that consist of a water-soluble polymer, a cross-linker, and non-ionic surfactant with a small amount of IPA (2-propanol). They exhibit affinity for acrylate resists that make them penetrate and react at the surface of the patterned resists. The resolution of the resist can be improved below the resolution limit of the exposure wavelengths by using the optimized materials. Additionally, the line edge roughness of the resist patterns can be reduced with only a small change in the pattern size when a low baking temperature (<95°C) and/or a small change of the composition of the material is applied. These materials are compatible with both acrylate-based 193-nm chemically amplified resists and PMMA (poly(methyl methacrylate)) resists. This indicates that the reaction can proceed even without acids, which are generally generated from photo acid generators (PAGs). The opitimized material affords sub 100-nm patterns for hole and L/S (line and space) with an alicyclic acrylate resist. A 28-nm shrinkage is also obtained with a PMMA resist to formulate the 68-nm trench pattern.

193 nm phase-shifting lithography with single layer resist for VLSIs beyond 1 G-bit DRAM

We have demonstrated the usefulness of ArF lithography with single layer resist based on adamantyl copolymer. Using the alternating phase shifting mask, 0.12 /spl mu/m L&S patterns has been achieved, and we are looking forward to applying it to VLSIs larger than 1 G-bit DRAM.

New trilayer resist process using a phenol-capped siloxane-based middle-layer for ArF resist process

We have developed a new tri-layer resist process to meet requirements related to etching durability and aspect ratio of ArF process. The new phenol capped siloxane-based middle-layer does not change thickness and does not increase particles even after six months. Additionally no footing pattern formation occurs. Our middle-layer has a function as anti-reflect and simulated reflectivity in a top ArF resist layer is less than 1.0% at the tri-layer structure by controlling middle-layer and under-layer thickness. The critical dimension (CD) uniformity of 140 nm contact hole pattern is less than 6 nm (3 sigma) intra wafer. This new middle layer gives high etching sensitivity relative to under-layer and we can demonstrate pattern transfer using a contact hole pattern. We have applied this system to a dual damascene process and successfully completed a 280-nm pitch multilevel copper interconnection. We conclude that our new tri-layer resist process is suitable for use in mass production of 90-nm node LSI and below.

Approach to high-aspect-ratio patterning using cleavable adamantyl resist

We tested 2-methyl-2-adamantylmethacrylate-mevalonic lactone methacrylate (2MAdMA-MLMA) resist on thick films and found that the pattern collapse determined the resist performance in high aspect ratio patterning. To solve this problem, we investigate the effects of modifying the softbake-PEB (post exposure bake) condition, the developer, and the photo acid generator (PAG). We replaced the 2.38% (0.27N) TMAH developer with a 0.27N TBAH (tetrabutylammonium hydroxide) developer, which functioned as a surfactant, and the collapse was reduced markedly for thicker films. As a result, the exposure and focus latitudes improved. These results suggest that good solubility in an exposed region reduces the collapse, allowing high aspect ratio patterning to be achieved.