PEB Temperature Research Articles

Study on Fabrication Process of SU8 Photoresist Microstructures and Evaluation of Stress Gradient

A fabrication process to manufacture SU8 photoresist microstructures is presented in which BP212 positive photoresist was used as sacrifice layer and SU8 was used as structure layer. No crack has been observed in the obtained microstructures. The relation between PEB temperature and stress gradient in SU8 film has been studied by measuring radii of released SU8 cantilevers made at different PEB temperatures.

Do not always blame the photons: Relationships between deprotection blur, line-edge roughness, and shot noise in extreme ultraviolet photoresists

A corner rounding metric has been used to determine the deprotection blur of Rohm and Haas XP 5435, XP 5271, and XP 5496 extreme ultraviolet (EUV) photoresists as base wt % is varied, an experimental open platform photoresist (EH27) as base wt % is varied, and TOK EUVR P1123 and FUJI 1195 photoresists as postexposure bake temperature is varied. In the XP 5435, XP 5271, XP 5496, and EH27 resist platforms, a six times increase in base wt % reduces the size of successfully patterned 1:1 lines by over 10nm and lowers intrinsic line-edge roughness (LER) by over 2.5nm without changing deprotection blur. In TOK EUVR P1123 photoresist, lowering the PEB temperature from 100to80°C reduces measured deprotection blur (using the corner metric) from 30to20nm and reduces the LER of 50nm 1:1 lines from 4.8to4.3nm. These data are used to drive a lengthy discussion about the relationships between deprotection blur, LER, and shot noise in EUV photoresists. The authors provide two separate conclusions: (1) shot noise is probably not the dominant mechanism causing the 3–4nm EUV LER floor that has been observed over the past several years; (2) chemical contrast contributes to LER whenever deprotection blur is large relative to the printed half-pitch.

Design Consideration for Immersion 193: Embedded Barrier Layer and Pattern Collapse Margin

In immersion lithography the optical path between the lens element and the photoresist is currently water. Defects have been identified as a major roadblock for the introduction of immersion lithography to real device manufacturing. To address these immersion specific defect issues we have developed a novel additive approach for controlling the resist surface and it's interaction with water.[1] These additives have been designed to segregate within the resist film and migrate to the resist surface. Due to the high local concentration of these additives at the resist/water interface they create a very hydrophobic surface and allow control of surface properties. Data will be presented on this novel concept, illustrating the control of leaching and resist surface hydrophobicity. The use of this new technique allows control of leaching, resist surface contact angles and immersion specific defects.As critical dimensions (CDs) in the semiconductor industry shrink, pattern collapse becomes a problem. We classify pattern collapse into three classes: adhesion failure, pattern strength failure and pattern film loss failure, and relate these to the capillary forces which drive failure. In this paper, the correlation of PCM with Ψ (carbon heteroatom ratio) of polymer composition, resist profile, PEB temperature and time are discussed. Finally, mechanistic understanding of pattern failure and subsequent correlations gives us the tools to design advanced resist with excellent PCM.

Development of Novel Materials for 193-nm Dry and Immersion Lithography

We earlier developed new monocyclic fluoropolymers (FUGU) for F2 resist materials. But, it is necessary for FUGU to be improved in their characteristics, especially in the dry-etching resistance, in order to apply to ArF lithography at fine design rules. We have tried to combine FUGUs with Adamntyl methacrylates based conventional ArF resist polymer. In this paper, we have investigated the role of cyclic fluorinated unit, FUGU, in 193 nm resist polymers by analyzing the dissolution behavior. We found that FGEAM showed high sensitivity and good dissolution contrast, compared with acrylate based conventional samples at low PEB temperature (100oC). And this difference of sensitivity was clearly found when weak acidity PAGs were used. From the dissolution behaviors of FGEAM, FUGU unit can work to improve the resist sensitivity in acrylate based ArF resist polymers. These result shows that FUGU unit has a unique characteristics of the sensitivity with 193 nm exposure. We also investigated a new series of fluorinated copolymers for 193-nm lithography, combination of FUGU monomer and acrylate units which are used in conventional ArF resist. Six ter-polymers of FUGU, combination of FUGU monomers and EAdMA, GBLMA and HAdMA were prepared. We found that FUGU ter-polymers had a good dry etching resistance keeping high transparency at 193 nm. And FUGU ter-polymers showed high sensitivity toward 193 nm exposure. So we expect FUGU ter-polymers to be useful for ArF dry and immersion lithography.

PEB bake optimization for process window improvement of mixed iso-dense pattern

We have shown that process effects induced by extending the post-exposure bake temperature in the process flow of chemically amplified photoresists can lead to significant improvements in depth-of-focus (DOF) and exposure latitude (EL) and small geometry printing capability. Due to improved acid dose contrasts and a balanced optimization of acid diffusion in the presence of quencher, PEB temperature increase has enabled the printing of iso and semi-dense space of 0.2 µm and below with a large DOF, using binary masks and 248 nm lithography without expensing the iso-dense bias. The results and findings of a full patterning process in a device flow, with different PEB temperatures as a process enhancement, are presented. The main objective of this study is to demonstrate how, using KrF lithography with binary masks and no optical proximity correction (OPC) nor other reticle enhancement technique (RET), the process latitude can be improved. Lithographic process latitudes, intra-field critical dimension (CD) uniformity and resist profiles of different PEB processes are evaluated. Then, the after-etch profiles are also investigated to ensure the feasibility of this technique.

Evaluation of advanced epoxy novolac resist, EPR, for sub 100nm synchrotron x-ray proximity lithography

The performances of the advanced cresol epoxy novolac-based resist, EPR, were characterized for use of synchrotron x-ray proximity lithography at PALC (Postech Advanced Lithography Center). Although the high sensitivity and resolution capability of the EPR in e-beam lithography had been reported [1], its performances in the x-ray lithography have not been well investigated yet. We compared EPR to TDUR-N908 [2] of TOK, which is commercially available high sensitive negative tone resist used in x-ray lithography. The Experiments showed about 8 times higher sensitivity of EPR than that of TDUR-N908. The fine-line resolution capability of EPR was proven down to double spaced 80 nm dense lines. The contrast of EPR depends more on PEB temperature within the ranges of 90° C ∼ 100° C rather than PAB temperature of 130° C ∼ 150° C. But the sensitivity was not much changed by those variations of PEB and PAB temperature. In addition, we optimized the resist process of EPR for sub 100 nm regime in this work.

Advances in Resist Materials for 193 nm Lithography.

The performance of a 193nm single layer resist based on a norbornene-malefic anhydride matrix resin has been optimized through a series of statistical design experiments. The SDE demonstrated the importance of setting the PEB temperature above the SB temperature with optimum performance being observed at a SB of 150°C and a PEB of 160°C. The lithographic performance of the resist was also strongly influenced by polymer composition, specifically acrylate loading and blocking level. Optimizing the composition of the polymer, gave resists with high etch resistance, square profiles and 0.130 micron dense line ultimate resolution in 0.5 micron thick films. The resist formulations are compatible with industry standard 0.262N TMAH. During exposure the resist does not suffer from the outgassing of volatile species (less than 1e12 molecules/cm2 x sec). A new thermally curable undercoat for bi-layer application has also been developed whose optical properties have been optimized to reduce reflectivity at the desired wavelength. The reflectivity has been reduced by a factor of eight over an earlier UV-cured version.

Towards a better understanding of positive chemically amplified systems.

The phenomena involved in positive chemically amplified resists are the result of intricate chemical and physical mechanisms. This complexity is observed from spin-coating to development. The physical properties of the lithographic layer are strongly influenced by the chemistry used. In turn, the deprotection reaction can exhibit different kinetics depending on the physical properties and thermal history of the film. The deprotection reaction generates an expanded matrix that can collapse and densify when the PEB temperature is higher than the transition temperature. This work shows that both deprotection and dissolution rate are not related to exposure dose by simple relationships. This new approach provides a deeper understanding for good control, design and modeling of these systems.

KRS: An Environmentally Robutst Resist Based on Fast Reaction kinetics.

An environmentally stable resist with high contrast, sensitivity and resolution is presented. Delay stability in excess of 24hr. has been achieved with insignificant change in linewidth. The resist also demonstrates extreme insensitivity to PEB, showing insignificant linewidth changes over a PEB temperature variation between 20°C-100°C. The resist is sensitive to DUV, X-ray and e-beam radiation. Linearity down to 0.25μ m using 0.5NA MSII (248nm) tool has been demonstrated. The resist shows better than 0.8μm DOF and 15% DL at 0.25μm line and space pairs. Resolution down to 75nm line and space pairs has been demonstrated with 100KeV e-beam tool. We have discussed a new approach to achieving an environmentally-stable, chemically-amplified resist. The resist system, KRS, combines the advantages of conventional and chemically-amplified resists. The resist exhibits high contrast, sensitivity and resolution and at the same time is environmentally-robust and extremely insensitive to PEB temperature variation. The resist demonstrated linearity down to 0.25μm with acceptable DOF and DL using 0.5NA MSII stepper. The ultimate resolution is 0.225μm, limited only by the smallest feature on the mask at the current time. The resist attributes make it compatible with current 0.25μm DUV lithography requirements and extendible to future needs with an improved DUV tool set. The resist is also sensitive to e-beam and X-ray radiation. High resolution imaging, 75nm line and space pairs in 0.75μm thick resist, has been demonstrated using 100KeV e-beam tool.

Diffusion of acid and activation energy of positive chemical amplification resist.

A new simple method of measuring diffusion range of acid in chemical amplification resist has been designed. With this method, PEB temperature and PEB time dependence of diffusion range were investigated, and apparent activation energy of diffusion was estimated. Comparing this and activation energy of decomposition of inhibitor, decomposition was revealed to be rate-determining reaction during PEB. This is thought to be the reason for PEB dependence on the pattern profile of the resist.