Chemically amplified resists have been used for the fabrication of semiconductor devices. With the miniaturization of circuits, the performance of chemically amplified resists approaches their limit due to the acid diffusion. The development of a novel platform without acid diffusion becomes important. In this study, we proposed a negative-type polymer resist used for extreme ultraviolet (EUV) and electron beam (EB) lithography. The proposed resist utilizes polarity change and radical crosslinking triggered by EUV/EB exposure. Polymers having triarylsulfonium cations and 2,2,2-trisubstitued acetophenone as side chains were designed for realizing the dual insolubilization property. 2,2,2- trisubstitued acetophenone was incorporated for the efficient radical generation on the polymer structure for the crosslinking. An onium salt was incorporated for the efficient use of thermalized electrons for the polarity change and the radical generation of the side chain. In addition, triphenyl-(4-vinyl-phenyl)-stannane (StTPSn) was incorporated into the resist polymer as the EUV/EB absorber to enhance sensitivity. The highly sensitive property of the designed polymers was demonstrated.
In EUV lithography (EUVL), the most critical issue has been low intensity of the EUV light source. Light-source intensity and resist sensitivity have a complementary relationship. Therefore, the sensitization of EUV resist is very important to compensate the low intensity of the EUV light source. However, dramatically improving the resist sensitivity of chemically amplified resist (CAR) is very difficult because of the resolution/line-width roughness/sensitivity (RLS) trade-off. Therefore, we propose a very new process: high resist sensitization by the combination lithography of EUV or EB pattern exposure with UV flood exposure (PF combination lithography) of photosensitized chemically amplified resist (PS-CAR). The combination lithography of EB pattern exposure with UV flood exposure achieved a sensitivity enhancement of more than a factor of 10 with respect to conventional EB single-exposure lithography, without loss in space resolution of line/space of 75 nm<sup>1</sup>. The breakthrough of RLS trade-off by PF combination lithography of PS-CAR is explained based on RLS trade-off simulation method2 and acid generation mechanism of PF combination lithography of PS-CAR. One of the problems of the PF combination lithography of PS-CAR is postexposure delay (PED) effects suffered from airborne contamination. The present paper describes forming of 75 nm contact hole and PED effects in the PF combination lithography of PS-CAR. The sensitization of EUV resists by new method accelerates EUVL implementation.
Extreme ultraviolet lithography (EUVL) at 13.5 nm will soon be applied in high-volume manufacturing of
semiconductors, as a replacement to the ArF excimer laser immersion lithography. Recently, the potential application of
exposure wavelengths of 6.x nm (particularly 6.6-6.8 nm) has been discussed as EUVL extension. The 6.x nm exposure
source is currently under development, therefore screening of resists with conventional exposure tools will accelerate the
selection or novel development of high sensitivity resists for 6.x nm EUVL. In the present study, the sensitivities of a
chemically amplified (CA) resist (OEBR-CAP112) and non-CA resists (ZEP520A and poly(methyl methacrylate)) were
evaluated with 30 keV and 75 keV electron beam lithography (EBL) tools. In terms of radiation chemistry, the obtained
dose/sensitivities (μC cm<sup>-2</sup>) were converted into the absorbed doses (Gray; Gy = J kg<sup>-1</sup>). If EB- and EUV-induced
chemical reactions are the same, the required absorbed doses for EB and EUV would be similar values. The sensitivities
for EUV/soft X-rays including 6.x nm were predicted assuming the required absorbed doses in a resist would show
similar values for both EB and EUV. We investigated precise sensitivities of the resists for EUV/soft X-rays including
6.7 nm using highly-monochromated synchrotron radiation. For both CA and non-CA resists, the predicted and
experimentally obtained sensitivities agreed well with each other. These results suggested that almost the same chemical
reactions are induced in resists for both EUVL and EBL. Hence, it was found that we can predict the resist sensitivities
for EUV/soft X-rays at any exposure wavelength from the exposure results for EBL.
Recently, polymer-bound PAGs (anion bound) are actively investigated as Extreme ultra violet (EUV) resist. Some
experimental results showed, in case of shot diffusion length acid generator bounded polymer showed lower sensitivity comparing with long diffusion length acid generator. In our previous investigation, short diffusion length PAG reactivity is changed due to binding to polymer by pulse radiolysis method. However, shot diffusion PAG bound to polymer showed lower LWR than long diffusion length PAG. Therefore, acid diffusion length difference originate in
PAG is important to resist performance. The diffusion length difference influence deprotection reaction in PEB process.
In this paper, we evaluated polymer-bound PAGs and polymer blend PAGs by electron beam (EB) exposure tool employing various PEB temperature and PEB time to conform the influence of acid diffusion regulation about polymer-bound PAGs for resist performances. As the result, even if acid generator bound polymer applied as a resist, acid diffusion regulation isn’t so strict that acid can migrate in the polymer matrix during PEB.
We synthesized three type polymers 1) Poly hydroxyl-styrene (PHS resist). 2) hydroxyl-styrene methacrylate copolymer (Hybrid resist). 3) methacrylic acid tertiary aliphatic esters copolymer (Methacrylate resist). These polymers have been used in ArF, KrF lithography. Recently, these resists have been investigated to employ for Extreme ultra violet (EUV) lithography because absorption of EUV doesn’t depend on the molecular structure. But EUV has very higher energy
than ArF, KrF and it is exceed ionization potential of resist materials. Thus, polymer behavior under the EUV exposure is different from ArF, KrF exposure. For analyzing difference between ArF, KrF and EUV, we conducted to exposed resist materials (PHS, Hybrid, Methacrylate resist) using electron beam (EB) radiation source. As the results, we observed PHS resist showed crosslinking behavior less than 5μ C/cm<sup>2</sup> , Hybrid resist showed cross-linking behavior more than 20μ C/cm<sup>2</sup>, Methacrylate resist showed moderate main chain scission behavior less than 20μ C/cm<sup>2</sup> respectively.