Against the backdrop of remarkable strides in recent EUVL research, EUV chemically amplified resists were discussed as a critical issue in last year's International EUVL Symposium. Important concerns involving resists include improvements in resolution and sensitivity and reductions in outgassing and roughness. One important factor in improving resolution and sensitivity is understanding the behavior of the de-protection reaction of a photoresist during EUV exposures. We examined a system to analyze de-protection reactions in an ultra-thin-film process suitable for the EUV resist process.
A system for photo-chemical analysis of EUV lithography processes has been
developed. This system has consists of 3 units: (1) an exposure that uses the Z-Pinch
(Energetiq Tech.) EUV Light source (DPP) to carry out a flood exposure, (2) a
measurement system RDA (Litho Tech Japan) for the development rate of photo-resists,
and (3) a simulation unit that utilizes PROLITH (KLA-Tencor) to calculate the resist
profiles and process latitude using the measured development rate data. With this
system, preliminary evaluation of the performance of EUV lithography can be
performed without any lithography tool (Stepper and Scanner system) that is capable of
imaging and alignment. Profiles for 32 nm line and space pattern are simulated for the
EUV resist (Posi-2 resist by TOK) by using VLES that hat has sensitivity at the 13.5nm
wavelength. The simulation successfully predicts the resist behavior. Thus it is
confirmed that the system enables efficient evaluation of the performance of EUV
This paper describes a study of a cross-linking reaction model for chemically amplified negative-type thick-film resists. Profile simulation is a major technique used to acquire experimental indicators. For this reason, numerous reports address simulation techniques, and many studies have focused in particular on chemically amplified positive-type resists, due to their role as mainstream resist materials used in the production of ICs. However, virtually no research has been performed on the profile simulation of chemically amplified negative-type thick-film resists. We measured the cross-linking reaction of a chemically amplified negative-type thick-film resist and created a new cross-linking reaction model. Our study demonstrates that this new model is more effective for thick-film resists than conventional models.
SU-8 (Kayaku Microchem Co., Ltd.) provides well-defined resist profiles with high aspect ratios, and is also suitable for use as a permanent resist. SU-8 has been widely used for many years in the MEMS (Micro Electro Mechanical System), IC package (bump, insulator, encapsulation), micro fluid (inkjet, micro reactor, biochips), and optical device (waveguide, optical switch) fields. SU-8 is a chemically amplified negative resist based on epoxy resin. This resist generates a strong acid during exposure, and PEB (Post Exposure Baking) induces the crosslinking reaction of the resin with the acid working as a catalyst to insolubilize the resist. In our study, we sought to investigate the potential application of SU-8
3000NIL, the most commonly used resist for the MEMS process, to imprint lithography. The results we obtained indicate that SU-8 3000NIL can indeed be applied to imprint lithography after optimizing
process conditions for imprinting.
Numerous methods are available for lithography below the 100 nm node scale, including F2, 193 nm immersion, EB, EUV, and imprint lithography. Among these methods, imprint lithography has attracted significant attention because it does not require expensive exposure equipment. Imprint lithography can be performed by one of two primary methods: the thermal method or the UV curing method. In thermal imprinting, the resin is softened above Tg before being formed by a mold. In UV imprinting, a transparent mold is applied to a liquid resin, which is then exposed to UV light for curing. Thermal imprinting requires a pressure of 10 MPa and consumes throughput (to increase and reduce the temperature) time ["requires time for throughput (i.e., time required to increase and reduce temperatures)"]. In contrast, UV imprinting does not require high pressure, since the resin is basically a viscous liquid and soft enough to be deformed. However, since the resin is in liquid form, the UV imprinting process is sensitive to the flatness of the substrate and mold. Problems of non-uniformity (i.e., interference patterns) have been noted in residual film distribution. In response, we developed what we call the PEP method, which combines the advantages of both thermal and UV imprinting. We have performed various experiments to examine the consequences of the PEP approach. The Pre-Exposure Process method essentially consists of a type of UV imprinting, but one in which the resin is subject to extremely weak exposed prior to the pressing ["exposed to very weak UV radiation before pressing"], which slightly hardens the resist and increases rigidity. The mold is then pressed to shape the resin, followed by the primary exposure. This process allows the resin to maintain softness equivalent to that at or above Tg in thermal imprinting, while allowing processing, as in UV imprinting. We also examined the relationship between exposure and crosslinking ratios, using FT-IR equipment with an exposure function, to determine the optimal crosslinking ratio for the PEP method. The results of these examinations are also reported.
The quencher mechanisms in Chemically-Amplified (CA) resists have been investigated. To explain the acid distribution with a variety of acid strengths in the presence of quencher, a new full Acid-Equilibrium-Quencher model (AEQ model) is proposed and examined in solid-model-CA-resist systems. To observe the reactions in the CA resists, real-time Fourier-Transform-Infrared Spectroscopy (FTIR) is employed during post-exposure bake (PEB). The FTIR peaks of the protection groups are detected to measure the reaction kinetics during PEB. The solid-model-CA resists used in this work consist of both a KrF-acetal-type resist with a diazomethane Photo-Acid Generator (PAG) (weaker-photoacid system) and an ArF-ester-type resist with a sulfonium-salt PAG (stronger-photoacid system). The obtained FTIR results are analyzed using conventional Full-Dissociation-Quencher model (FDQ model) and the new AEQ model. The kinetic analysis of the model resists was performed for different quencher loadings. For the weaker-photoacid system, the AEQ model much more accurately predicts the deprotection-reaction kinetics than the FDQ model with the change of quencher content. This suggests the necessity of introduction of the acid-dissociation concept in the case of the weaker photoacid. For the stronger-photoacid system, both the AEQ and conventional FDQ models adequately predict the kinetic results. This shows that the conventional FDQ model is accurate enough to simulate the super-strong photoacid system. Finally, the new AEQ model is introduced in the UC Berkeley STORM resist simulator. Some simulation examples are shown in the paper.