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.
The impact of alicyclic protective groups on acid-labile substituents in a vinylphenol-methacrylate-based chemically amplified positive resist was investigated. The resist consists of the copolymer of vinylphenol and adamantyl methacrylate (VP/AdMA) with triflate onium salt as a photo- acid generator. The alicyclic protective groups in our system show a higher reactivity and higher hydrophobicity than those of the tert-butyl group, which is widely used in chemically amplified resists. The resists containing the alicyclic protective group resolved 0.09-micrometer hole patterns at 6 (mu) C/cm<SUP>2</SUP>, and a resist with a base additive resolved 0.12-micrometer line and space patterns at 9.0 (mu) C/cm<SUP>2</SUP> using a 50-keV EB lithography system with a 2.38% TMAH aqueous solution as the developer. The dry etching durability of resists containing the alicyclic group was also compared with resists containing the tert-butyl group and with polyvinylphenol (PVP). The dry etching durability of our resists for a C<SUB>4</SUB>F<SUB>8</SUB> plasma was 1.3 times superior to that of resist containing the tert-butyl group, and 1.1 times better than that of PVP. This means the thickness of film in pattern fabrication can be reduced to obtain a higher sensitivity and higher resolution.
Incorporation of organic salt additives consisting of an organic acid and organic base improves the resist stability. The sensitivity of a t-BOC resist without the salt decreased to 1/4 after standing for one hour after deep-UV exposure. Typical T-top patterns were obtained on this resist by a KrF excimer laser stepper (NA equals 0.45), and a half-micron resolution was barely obtained. On the other hand, a t-BOC resist, with an organic salt, consisting of p- toluenesulfonic acid and dicyclohexylamine (PTS/DCHA), showed no change in sensitivity after one hour. The resist with the PTS/DCHA achieved a 0.3-micrometers resolution line-and- space pattern without environmental control or a protective topcoat.
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/cm<SUP>2</SUP>, 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.
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.