Line-edge roughness (LER) continues to be one of the biggest challenges as the CD size shrinks down to sub 100 nm. It is shown that resist components as well as illumination conditions play a big role. Influence of resist components in both 248 and 193nm chemically amplified resist formulations has been reported but the root cause is not fully understood and may be platform or even specific formulation dependent. This paper attempts to tackle the issue from the processing side. Effects of a simple hard bake process on the LER were studied. In the hard bake process, a given resist pattern was typically baked close to the glass-transition temperature after the development process. LER improved dramatically due to melting down of the rough surface. However, the wall angle of the edge lines also started to degrade at the optimum hard bake temperature. Studies on the effects of polymer Tg, hard bake temperature and time and the issues of the process are discussed.
Keeping post exposure bake (PEB) sensitivity low has become one of the most crucial factors for implementing the 193nm resist process into mass production. In a previous report, we have demonstrated that the nature of the photo acid generator (PAG) has a strong effect on the PEB sensitivity of 193 resists. Based on our findings, we decided to extend our studies to the other important resist components, such as polymers prepared with various monomer compositions, and casting solvents. Also, in an effort to investigate whether PEB sensitivity can be reduced by process optimization, the influence of soft bake and post exposure bake conditions was studied. This paper describes our new findings on some of the important factors that affect the PEB sensitivity of 193 resists.
The performance of a new class of photoacid generators (PAGs) made from the onium salts of bis(perfluoroalkylsulfonyl)imide and tris(perfluoroalkylsulfonyl)methide anions were studied in 193nm formulations. The lithographic properties such as sensitivity, resolution, pattern profiles, footing, I-D bias and PEB sensitivity were investigated in methacrylate and COMA/methacrylate hybrid type matrix resins. In general the iodonium PAGs were about three times slower than the sulfonium PAGs. Methide and imide PAGs possessing similar fluoroalkylgroups showed comparable performance in terms of exposure latitude, I-D bias. And PEB sensitivity. Compared to the reference PAG, the profiles exhibited T-tops and sum. Among the new PAGs studied bis(perfluorobutanesulfonyl)imide exhibited close performance to that of the reference PAG except for the scum. Details on the exposure results of these PAGs in both methacrylate type and COMA/methacrylate hybrid type polymer based 193nm resist formulations are provided.
In an effort to develop a production-worthy 193-resist, it is important to understand the critical factors that impacts the CD variation during a routine photo lithographic process. A comprehensive investigation was done on factors affecting PEB sensitivity in ArF resist system. The areas of interest are polymer components, PAGs, bases, and photo lithographic process. In order to understand effects of the PAGs on PEB sensitivity, a number of PAGs possessing different types of cations and anions were investigated. Sulfonium type cations and acids with longer alkyl chains were found to be effective in reducing the PEB sensitivity. Influence of lithography process conditions was also studied on the PEB sensitivity. Increasing the soft bake (SB) temperature and decreasing the post exposure bake (PEB) temperature reduced the PEB sensitivity but mostly at the expense of line-edge roughness (LER). This paper presents our findings of the critical factors affecting PEB sensitivity and describes improved lithographic results of an optimized experimental formulation. In addition, delay effects after coating, soft bake, exposure, and post exposure bake (PEB) were also investigated and these results are included.
Electron beam (e-beam) curing techniques are known to improve etch and CD-SEM stability of 248 and 193nm resists. The effects of three different e-beam curing processes (standard, LT and ESC) on the methacrylate and hybrid type 193nm resists were studied with respect to resin chemistry changes, resist film shrinkage, pattern profiles, etch rates, and CD SEM stability. Both methacrylate and hybrid type 193nm resists lose carbonyl groups from the resins, with possibly a reduction in the free volume leading to improved etch resistance/selectivity. Methacrylate resist films shrink ca. 22-24% and hybrid resist films shrink ca. 23-27%. The LT process shrinks the least compared to the ESC and standard process. The ESC and LT processes were found to stabilize the patterns uniformly compared to the standard process. Etch rate, selectivity and resist surface roughness after etch of both methacrylate and hybrid resists were improved using the e-beam curing process. E-beam curing drastically reduces the CD SEM shrinkage (from ca. 15% to 2- 5%); however, considerable shrinkage occurs during the curing process itself.
A high performance 193 nm resist has been developed from a novel hybrid copolymer based on a cycloolefin-maleic anhydride and methacrylate (COMA/Methacrylate) polymer system. A variety of copolymers have been synthesized from t-butyl norbornene carboxylate (BNC), t-butyl tetracyclo [18.104.22.168.<SUP>2,6</SUP>1<SUP>7,10</SUP>]dodec-8-ene-3-carboxylate (BTCDC), and 5-[2-trifluoromethyl-2,1,1-trifluoro-2-hydroxypropyl]-2- norbornene (F1) with different types of methacrylate monomers and maleic anhydride (MA). The effect of the monomers and the ratio of monomers in the copolymer on lithographic performance and etch rate has been studied. Lithographic evaluation of some of these polymers has shown resolution down to 80 nm using conventional 193 nm illumination and standard development conditions, particularly for semi and fully isolated lines. This paper will report the chemistry of the polymer platform and relative advantages of having certain monomers in terms of lithographic performance and line edge roughness.
The copolymerization reaction between methyl cyanoacrylate (MCA) and a variety of cycloolefins (CO) was investigated. Cycololefin/cyanoacrylate (COCA) copolymers were obtained in good yields and with lithographically interesting molecular weights for all cycoolefins studied. Anionic MCA homopolymerization could be largely suppressed using acetic acid. Based on NMR data, the copolymerization may tend to a 1:1 CO:MCA incorporation ratio but further work with better suppression of the anionic component is needed to confirm this. Lithographic tests on copolymers of appropriately substituted norbornenes and MCA showed semi-dense and isolated line performance down to 90 nm.
We have studied 193 nm contact hole resists in view of resist components, process conditions and optical settings. Sidewall roughness was improved by optimizing photoacid generators. Side lobes were eliminated by applying higher post exposure bake temperature or modification of polymers. The influence of optical settings, types of masks and mask bias was discussed with simulation and lithographic results and guidelines for better resolution and iso-dense bias were proposed. The optimized formulation, AZAX1050P has a high resolution combined with a large depth of focus and an iso- dense overlap window (130 nm(NA=0.63) DOF 0.38micrometers Exposure latitude 10%).