Hideo Hada

Spectral analysis of line-edge roughness in polyphenol EB-resists and its impact on transistor performance

Resists using polyphenol resin are introduced to reduce line-edge roughness (LER), and the spatial frequency characteristics of LER are evaluated. It is found that the long-period components of LER are suppressed in our low molecular-weight polyphenol resists. Device simulation using the measured LER shows that our polyphenol-based resist can drastically reduce the number of low-threshold-voltage (Vth) transistors compared with a conventional resist due to reduced long-period LER. Because LER impact is more serious as the transistor width shrinks, our results suggest that the use of the polyphenol-type resist will be more effective in improving device performance in future lithography process. In addition, it is shown that spectral analysis is a powerful tool for LER evaluation, especially from the viewpoint of device performance estimation.

Photoinduced outgassing from the resist for extreme ultraviolet lithography by the analysis of mass spectroscopy

Extreme ultraviolet lithography (EUVL) requires the vacuum environment for exposing the resist. The contamination in the vacuum environment decreases the reflectivity of the reflective mask and that of the imaging optics. The photoinduced outgassing from the resist becomes the contamination in the vacuum environment. Therefore, the outgassing detection investigation is very important. The outgassing from the chemically amplified (CA) resists EUV001 for EUVL, EUV006N for EUVL, UV5 for KrF lithography and the nonchemically amplified resists OEBR2000 and ZEP520 for electron beam lithography were investigated. Based on the photoinduced reactions of the resist, the fragment ions species that were measured by the quadrupole mass spectrometer were identified. It is found that the amount of the photoinduced outgassing such as hydrocarbons from the DQN resist and annealing-type CA positive-tone resist is small.

Studies of the Photo Acid Generator Material Design for Chemically Amplified Photoresists

In current optical lithography, resolution is required to reach for 45 nm half-pitch and a chemically amplified resist (CAR) is used for a wide variety of applications. For ArF lithography beyond the 45 nm half-pitch, it is important to control pattern quality. The molecular design of a photo acid generator (PAG) is very important in the study to control not only acid strength but also acid diffusion length. Various novel PAGs that have different characteristics were synthesized for resist performance improvement. Acid molecular size was determined by molecular orbital (MO) calculation, and the acid diffusion coefficients (D) of these PAGs were evaluated by a bilayer method. As a result, it was found that acid diffusion coefficient (D) could not be controlled simply by adjusting anion molecular size. It may be presumed that the molecular interaction between acid generated by the exposure and polymer matrix areas is one of the most important key factors for controlling acid diffusion.

Cleaning of extreme ultraviolet lithography optics and masks using 13.5nm and 172nm radiation

Under extreme ultraviolet (EUV) exposure, the surfaces of the imaging optics and mask, which are coated with a Mo∕Si multilayer, become contaminated with organic compounds. Thus, an efficient method of removing carbon contamination from masks and the imaging optics is required. Then, we propose two methods as a removal method of contamination: one is in situ cleaning method without heating a sample by synchrotron radiation irradiation that is mainly targeted at the imaging optics, and another is cleaning method without heating a sample using by 172nm light irradiation that is targeted at an EUV lithography finished mask. For in situ cleaning so called online cleaning, the contamination removal rate is 0.24nm∕min in the condition of O2-rich-vacuum environment at a pressure of 5.0×10−2Pa and an electron beam current of 130mA of 1.0GeV electron storage ring. For offline cleaning using 172nm light, the contamination removal rate is 2nm∕min in the O2-rich-vacuum environment at the pressure of 2×10−3Pa. Both tw...

Distribution control of protecting groups and its effect on LER for EUV molecular resist

We have designed and synthesized a molecular resist material, which has no distribution of the protecting groups and have evaluated its performance as a molecular resist with EB and EUV exposure tool. The molecular resist attained a resolution of sub-45 nm patterning at an exposure dose of 12 mJ/cm2. It was found that controlling the distribution of the protecting groups in a molecular resist material has a great impact on improving Line Edge Roughness (LER). Low LER values of 3.1 nm (inspection length: L = 620 nm) and 3.6 nm (L = 2000 nm) were achieved with this molecular resist using Extreme UltraViolet (EUV) lithography tool.

Fine pattern replication on 10 x 10-mm exposure area using ETS-1 laboratory tool in HIT

Utilizing ETS-1 laboratory tool in Himeji Institute of Technology (HIT), as for the fine pattern replicated by using the Cr mask in static exposure, it is replicated in the exposure area of 10 mm by 2 mm in size that the line and space pattern width of 60 nm, the isolated line pattern width of 40 nm, and hole pattern width of 150 nm. According to the synchronous scanning of the mass and wafer with EUVL laboratory tool with reduction optical system which consisted of three-aspherical-mirror in the NewSUBARU facilities succeeded in the line of 60 nm and the space pattern formation in the exposure region of 10mm by 10mm. From the result of exposure characteristics for positive- tone resist for KrF and EB, KrF chemically amplified resist has better characteristics than EB chemically amplified resist.

Decomposition Analysis of Chemically Amplified Resists for Improving Critical Dimension Control

We have designed and synthesized a molecular resist material, which has only two protecting groups per molecule (prot-mad-2). Resists with this material can resolve a sub-30-nm half pitch (hp) pattern. We quantitatively analyzed a decomposition reaction using prot-mad-2 at the exposed and unexposed areas by taking advantage of its properties of high purity and simple structure. From the high performance liquid chromatography (HPLC) results, it was found that the main decomposition reaction was deprotection of prot-mad-2. The ratio of partly deprotected material (deprot-1-prot-mad-1) and fully deprotected material (deprot-2) increased with exposure dose. It was found that the exposure dose resulting in maximum surface roughness coincided with the exposure dose where fully protected, partly deprotected, and fully deprotected materials were present in equal quantities in the resist film. Furthermore, dissolution rates of prot-mad-2, deprot-1-prot-mad-1 and deprot-2 were completely different. It is considered that high surface roughness was generated by the different dissolution rates of prot-mad-2, deprot-1-prot-mad-1 and deprot-2. The results suggest that reducing the range of dissolution rates at the boundary between exposed and unexposed regions is key to improving line edge roughness (LER).

Development of fast-photospeed chemically amplified resist in extreme ultraviolet lithography

In a high-annealing type resist system that employs polyhyodroxy styrene as a base resin, we found that tri-phenysulfonium cyclo(1,3-perfluoropropanedisulfone) imidate when employed as a photoacid generator (PAG) is more sensitive than tri-phenysulfonium nonaflate under extreme ultraviolet (EUV) exposure. However, their sensitivities are almost the same under KrF and EB exposures. As results of both outgassing species and FT-IR measurements, the EUV-induced reaction of cyclo(1,3-perfluoropropanedisulfone) imidate employed as an anion of PAG occurred more efficiently than that of nonaflate employed as an anion of PAG. Therefore, the anion of PAG contributes to achieve a fast photospeed under EUV exposure. Furthermore, from the sensitivity curve measurements, it is found that tri-phenylsulfonium employed as a cation increases the developing rate more than diphenyl-naphthylsulfonium employed as a cation of PAG. As a result, we have succeeded in developing a fast photospeed chemically amplified resist that has a sensitivity of 1.1 mJ/cm2 and a partial pressure displacement accumulated in the total exposure time between after and before exposures on the order of 10-6 Pa s.

Development of amorphous polyphenol resists with low molecular weight and narrow dispersion for EB lithography

Minimum feature size in LSI circuit geometry will reach 20 nm in the coming 45 nm technology node. In order to achieve this, various new lithography technologies, such as EB and EUV lithography, are now being intensively developed. Furthermore, accuracy to within 10% of the feature size is required to guarantee the performance of LSI systems. In many cases, this requires controlling feature size with accuracy of one molecule in circuit geometry with sizes corresponding to ten molecules. The aim of this study is to develop a new resist material platform, which achieves this molecular level accuracy with high productivity, We confirmed the effects of suppressing material dispersion by using amorphous low molecular weight polyphenols as resist resin.[] -61 To investigate the possibility of amorphous low molecular weight polyphenols as a chemically amplified positive-tone electron-beam (EB) resist, two low molecular weight polyphenols, 4,4‘-methylenebis[2-[di(2-methyl-4-hydroxy-5-cyclohexylphenyl)]methyl] phenol (3M6C-MBSA), and 4,4’-methylenebis[2-[di(4-hydroxy-2,5-dimethylphenyl)~methyl]phen~l (25X-MBSA), and poly@-hydroxystyrene) (PHS) as a control with an average molecular weight of 8400 were prepared. The phenol groups were protected by 1-ethoxyethyl groups to control the dissolution rate of these materials in 0.26 N tetramethylammonium hydroxide (TMAH) aq. developer. The structures for polyphenols and PHS protected by l-ethoxyethyl (EE) groups are shown in Figure 1. As shown in Table 1 , three model resists based on 3M6C-MBSA, 25X-MBSA and PHS were prepared for the lithographic evaluation with EB exposure. EB imaging evaluation of resists A, B and C with I50 nm film thickness was performed. The results are shown in Figure 2. Resist A indicated an excellent pattern profile and resolution of 60 nm lines and spaces (lines/spaces=l/l). Furthermore, 50 nm lines and spaces pattern were partially resolved. The surface roughness of resist A and C following EB exposure at various doses and development were measured by AFM. The increase in roughness is apparent as the dose increases from 10 to 20 pCcm*’ and 10 to 13 pCcnf2 for resist A and C respectively. (Figure 3) Although the shapes of the curves are similar to one another, resist C showed higher roughness maximum value than that of resist A. Figure 4 shows the AFM images of the film surfaces of resists A and C at the doses which indicated the maximum roughness. Larger grain size was observed in Figure 4(b) as compared to Figure 4(a). We therefore conclude that surface roughness could be suppressed by low molecular weight and narrow polydispersity. We also expect that these low molecular weight materials will indicate lower LER as compared to typical polymers. ’

Molecular resists based on cholate derivatives for electron-beam lithography

We have reported the characteristics and LER properties of molecular resists based on low molecular weight polyphenols as a chemically amplified (CA) positive-tone EB resist (Hirayama et al., 2004; Hirayama et al., 2005). In this paper, new molecular resist based on cholate derivatives for EB lithography was reported.