Chemically Amplified Resist Research Articles

Thermal treatment for optical proximity correction

For 32-nm technology node, thermal treatment is one of the process extension techniques with 193-nm ArF lithography equipment and chemically-amplified resist (CAR). However, it is difficult to use these techniques in the manufacture process because the optical proximity effect of thermal effects is quite severe. In this paper, thermal processes, such as softbake, post-exposure bake and thermal reflow, are described and modeled to investigate the property changes of a positive type, 193-nm CAR. The simulated results agree well with the experimental results. For the optical proximity correction (OPC) of the thermal effects, an orthogonal functional method is introduced. Due to contact hole (C/H) pattern, the underbake of post-exposure bake (PEB) and thermal reflow are performed for the 45-nm critical dimension (CD) by using the OPC simulated images, to demonstrate the possibility of controlling these thermal processes for the formation of 32-nm CD.

Chemical Amplification Resists: Laboratory Curiosity to Paradigm

It has been a little more than a quarter century since chemical amplification resists were invented. They achieve a high sensitivity through a catalytic action of a photochemically generated acid. This drastically novel imaging concept was considered laboratory curiosity initially. However, the very first chemically amplified tBOC resist was quickly implemented in mass production of 1 megabit dynamic random access memory devices by deep UV lithography at IBM. Since then the chemical amplification concept has become the paradigm of advanced resist systems, enabling the industry to shift to shorter wavelengths (from 365 to 248, and then to 193 nm) for higher resolution and to follow the Moore's law. The chemical amplification resist invented for 1 μm resolution can now resolve 30 nm equal line/space patterns and continues to play a pivotal role in microlithography in the foreseeable future. This paper describes the inception and advancement of chemical amplification resists.

Electron-beam patterning and process optimization for magnetic sensor fabrication

Electron-beam lithography has been widely applied to define critical features in magnetic recording thin-film heads. To be a viable resist candidate for read sensor fabrication, e-beam resists need to be optimized in three major aspects—resolution, etching resistance, and strippability. Here the authors investigated four typical resists for their applicability in the production of sub-50nm read sensors and extendibility into sub-30nm regime, including a negative-tone chemically amplified resist (CAR), a negative-tone non-CAR, a positive-tone CAR, and a positive-tone non-CAR. Pattern design for positive-/negative-tone resists, resist resolution capability, sloped resist pole profile, underlayer preparation for Si-containing imaging layer, hybrid lithography for low-sensitivity non-CARs, and process issues in ion-beam etching of sensor stacks are discussed in detail. Finally, 20nm giant magnetoresistive sensor fabrication was demonstrated.

Photosensitive resists for optical lithography

Optical lithography relies on photosensitive materials to transfer the aerial image into the substrate. These photoresists have been steadily improved to keep up with the innovations in the lithography tools targeting a higher fidelity in the pattern transfer. After describing the resist process and the photolithographic criteria for such materials, this article will focus on the Chemically Amplified Resists (CAR) especially for the 193 nm lithography. The added challenges of the immersion lithography will then be addressed and some perspectives will be given. To cite this article: B. Mortini, C. R. Physique 7 (2006).

Line edge roughness of a latent image in post-optical lithography

The progress of electronic devices has been supported by advances in ‘top-down’nanotechnology, namely lithography, which reached a scale of 90 nm on the mass productionstage in 2005. The energy of the exposure source would exceed the ionization potential ofthe resist materials at the 32 nm scale with the deployment of extreme ultraviolet (EUV)light or an electron beam (EB). Among the issues of nanoscale fabrication with chemicallyamplified (CA) resists, line edge roughness (LER) is the most serious concern. Here, wereport a Monte Carlo simulation of a latent image LER caused by ionization, in terms ofproton dynamics, acid diffusion, and the effect of amine additives. The minimum LER(defined as three times the standard deviation) after post-exposure baking was∼9.5 nmfor a 5 µC cm−2 exposure dose with 0.5 wt% amine. Although the deployment of a high-energy exposuresource is the only method that allows further miniaturization after ArF immersionlithography, the acid generation mechanism, clarified for the first time in this paper, willemerge as a critical factor in limiting the availability of post-optical lithography.

Study of X-ray lithographic conditions for SU-8 by Fourier transform infrared spectroscopy

There is growing interest in the use of chemically-amplified resists (CARs) such as SU-8 in the field of microelectromechanical systems (MEMS) research. This is due to its outstanding lithographic performance and its ability for use in the fabrication of stable structures with very high aspect ratio. However, it is important to control the processing conditions for optimum results in the desired application. In this investigation, the thickness (10–25 μm) of SU-8 resist film, due to different spin coating speeds on silicon wafers, was measured using Fourier transform infrared (FT-IR) spectroscopy. The effect of thermal-initiated cross-linking at various temperatures (95–160 °C) for 15 min baking time on the 25 μm SU-8 resist was studied by monitoring the 914 cm −1 absorption peak in the FT-IR spectrum. Results of the experiments showed that the onset of thermal-initiated cross-linking begins at about 120 °C. Furthermore, 25 μm SU-8 resist was optimized for X-ray lithographic applications by studying the cross-linking process of the resist under different conditions of post-exposure bake (PEB) temperatures. The exposure dose of soft X-ray (SXR) irradiation with energies about 1 keV from a dense plasma focus (DPF) device was fixed at 2500 mJ/cm 2 on the resist surface. Results showed that the optimum processing conditions consisted of an intermediate PEB at 65 °C for 5 min, with the PEB temperature ramped up to 95 °C over 1.5 min and then followed by a final PEB at 95 °C for 5 min. The scanning electron microscopy (SEM) images showed SU-8 test structures successfully imprinted, without affecting the resolution, and with aspect ratios of up to 20:1 on 25 μm SU-8 resist.

Simulation of material and processing effects on photoresist line-edge roughness

Sub-100 nm device fabrication rules require extremely tight control of Line-Edge Roughness (LER) of patterned structures. During lithographic processes the resist film introduces an initial LER due to its chemical structure and processing. This initial LER evolves during the subsequent etching step. A stochastic simulator is presented which takes into account material and process effects on photoresist LER. Its application in model cases reveals that LER decreases with lower degree of polymerisation, but is sensitive on the acid diffusion process during post exposure bake in Chemically Amplified Resists (CARs). Further simulations confirm that LER can be reduced during etch patterning, at the expense of critical dimension control.

New stochastic post-exposure bake simulation method

A new method for simulating the post-exposure bake (PEB) of optical lithography is presented and applied to modeling the reaction-diffusion processes in a chemically amplified resist (CAR). The new approach is based on a mesoscopic description of the photoresist, taking into account the discrete nature of resist molecules and inhibitor groups that are attached to the resist polymers, but neglecting molecular details on an atomistic (microscopic) level. As a result, the time- and space-dependent statistical fluctuations of resist particle numbers, the correlations among them, and their effect on the printing result can be accounted for. The less molecules that are present in the volume of interest, the more important these fluctuations and correlations will become. This is the case for more and more shrinking critical dimensions (CD) of the lithographic structures but unchanged molecular sizes of the relevant resist species. In particular, the new PEB simulation method allows us to predict the behavior of statistical defects of the printed lithographic structures, which may strongly contribute to printing features like line edge roughness (LER).

Effect of a surface inhibition layer on line edge roughness

Line edge roughness (LER) is one of the most important issues in sub-100nm lithography. We have designed and implemented an experiment to study the coupled effect from acid depletion and percolation property of development process of Chemically Amplified Resist (CAR) on Line Edge Roughness (LER). The resist selected is UV-5 (a positive tone CAR from Shipley), known to be fairly sensitive to acid loss. After development, the resist is analyzed using high-resolution SEM (LEO 1550 VP), and an in-house made software is used for LER measurements. Our results indicate that the effect on LER and Critical Dimension (CD) variation depends on image modulation, and that aggressive lithography (low modulation image) will be more sensitive to the environment. In addition, it is shown that percolation development with stochastic energy deposition model can explain all the observed phenomena.

Study of a Chemically Amplified Resist for X-Ray Lithography by Fourier Transform Infrared Spectroscopy

Future applications of microelectromechanical systems (MEMS) require lithographic performance of very high aspect ratio. Chemically amplified resists (CARs) such as the negative tone commercial SU-8 provide critical advantages in sensitivity, resolution, and process efficiency in deep ultraviolet, electron-beam, and X-ray lithographies (XRLs), which result in a very high aspect ratio. In this investigation, an SU-8 resist was characterized and optimized for X-ray lithographic applications by studying the cross-linking process of the resist under different conditions of resist thickness and X-ray exposure dose. The exposure dose of soft X-ray (SXR) irradiation at the average weighted wavelength of 1.20 nm from a plasma focus device ranges from 100 to 1600 mJ/cm(2) on the resist surface. Resist thickness varies from 3.5 to 15 mum. The cross-linking process of the resist during post-exposure bake (PEB) was accurately monitored using Fourier transform infrared (FT-IR) spectroscopy. The infrared absorption peaks at 862, 914, 972, and 1128 cm(-1) in the spectrum of the SU-8 resist were found to be useful indicators for the completion of cross-linking in the resist. Results of the experiments showed that the cross-linking of SU-8 was optimized at the exposure dose of 800 mJ/cm(2) for resist thicknesses of 3.5, 9.5, and 15 microm. PEB temperature was set at 95 degrees C and time at 3 min. The resist thickness was measured using interference patterns in the FT-IR spectra of the resist. Test structures with an aspect ratio 3:1 on 10 microm thick SU-8 resist film were obtained using scanning electron microscopy (SEM).

Challenges to Ultra-thin Resist Process for LEEPL

An ultra-thin resist process is indispensable for low-energy electron-beam proximity projection lithography (LEEPL) because it uses 2-kV-accelerated electrons with small penetration depth. 70- nm-thick chemically-amplified resists for a tri-layer process were developed with the consideration of the interaction of a polymer with a spin-on-glass material, showing the resolution of 140-nm- pitch contact holes. Application of the tri-layer process developed for LEEPL to making via holes in a 90-nm-node back-end-of-line process proved that the ultra-thin resist was lithographically useful in terms of resolution and etching tolerance. Exploring the resolution performance of electron beam lithography showed that line edge roughness and resolution limit of resist patterns was in linear relation with blur of latent image profile. Reducing the resist thickness is effective in enhancing the resolution of LEEPL because 47 % of the blur is attributed to electron scattering. A Monte Carlo simulation shows that the blur caused by the electron scattering decreases 41 %, to 20 nm from 34 nm, by reducing the resist thickness to 30 nm from 70 nm.

Line edge roughness of sub-100 nm dense and isolated features: Experimental study

The nanoscale roughness in patterned images has become a crucial problem in advanced lithography. We have designed and implemented an experiment to study the line edge roughness (LER) for both dense line and space (DEN) and isolated (ISO) lines. The resist selected is UV-6 (a positive tone chemically amplified resist (CAR) from Shipley), and as a comparison, non-CAR such as poly(methylmethacrylate) (PMMA) is also measured. After development, the resist is analyzed using high resolution scanning electron microscopy (SEM) (LEO 1550 VP). An in-house made software is used for LER estimations. Our results indicate that DEN lines appear to be rougher than ISO lines given the same dose and nominal modulation. This is fully accounted by the lower modulation of DEN patterns caused by proximity effects. In addition, CAR resists like UV-6 are much rougher than non-CARs such as PMMA. A simple percolation model based on stochastic modeling predicts the observed trends.

3D STRUCTURES FORMATION IN A SINGLE LAYER SU-8 CAR USING DUAL UV AND ELECTRON-BEAM LITHOGRAPHY

International Journal of Computational Engineering ScienceVol. 04, No. 03, pp. 719-723 (2003) Poster PapersNo Access3D STRUCTURES FORMATION IN A SINGLE LAYER SU-8 CAR USING DUAL UV AND ELECTRON-BEAM LITHOGRAPHYV. A. KUDRYASHOV, X. -C. YUAN, T. L. TAN, P. LEE, S. F. A. KARIM and B. L. TANV. A. KUDRYASHOVSchool of Electrical & Electronic Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798, Singapore Search for more papers by this author , X. -C. YUANSchool of Electrical & Electronic Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798, Singapore Search for more papers by this author , T. L. TANNatural Sciences, National Institute of Education, Nanyang Technological University, 1 Nanyang Walk, Singapore 637616, Singapore Search for more papers by this author , P. LEENatural Sciences, National Institute of Education, Nanyang Technological University, 1 Nanyang Walk, Singapore 637616, Singapore Search for more papers by this author , S. F. A. KARIMNatural Sciences, National Institute of Education, Nanyang Technological University, 1 Nanyang Walk, Singapore 637616, Singapore Search for more papers by this author and B. L. TANChartered Semiconductor Manufacturing Ltd., Fab 3 Operations-Thin Film, 60, Woodlands Industrial Park D, Street 2, Singapore 738406, Singapore Search for more papers by this author https://doi.org/10.1142/S1465876303002131Cited by:0 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail AbstractA self-supporting 3D structure in SU-8 chemical amplified resist (CAR) using dual e-beam and ultraviolet (UV) exposure technique was fabricated. A single 15-micron thick layer of the negative tone SU-8 was firstly exposed with a mask using 365-nm UV to produce a latent image of the supporting structure. An additional structure was then exposed in its upper layer only with an electron beam. The dual exposed resist layer was then baked (PEB) and developed to give a 3D structure with self-supporting elements formed in the upper resist layer. This novel Dual Exposure Technique (DET) was based on the difference in the penetration depth in resist for UV photons and low-energy electrons. The 15-micron thick resist was spin-coated on Si wafer at a speed of 2000 rpm, soft-baled at 95°C for 5 min, and epxosed with UV dose of 500mJ/cm2> the resist was further irradiated with low-energy (5 keV) electrons with a relatively high dose of 5 μC/cm2 to provide a reasonable acid concentration in the upper layer of about 0.5-micron thick. The resist was then postexposure baked at 95°C at an optimum time of at least 2 min, and developed for 3 min by immersion in a standard SU-8 developer. The cross-linking process in SU-8 was monitored using Fourier transform infrared (FTIR) spectroscopy to optimize the process conditions. The infrared absoprtion peak at 914 cm-1 was found to be a useful indicator to study cross-linking in SU-8.Keywords:UV and e-beam lithographicschemically amplified resistSU-8infrared spectroscopy References N. C. LaBiancaet al., Proc. 4th Int. Symp. on Magnetic Materials, Processes, and Devices, The Electrochem. Soc. 95-18, 386 (1995). Google ScholarJ. M. Shawet al., IBM Journal of Research and Development 41, 81 (1997). Crossref, Google ScholarH. Lorenzet al., Sens. & Act. A64, 33 (1998). Google ScholarW. H. Wong and E. Y. B. Pun, J. Vac. Sci. Technol. B 19(3), 732 (2001). Google ScholarA. L. Bogdanov and S. S. Peredkov, Microelectronic Engineering 53, 493 (2000). Crossref, Google ScholarV. A. Kudryashov and P. Lee, Materials & Process Integration for MEMS, ed. F. E. H. Tay (Kluwer Academic Publ, Boston, 2002) pp. 187–202. Google ScholarF. E. H. Tay, J. Microm. and Microeng. 8, 27 (2001). Google ScholarD. F. Westonet al., J. Vac. Sci. Technol. B 19(6), 2846 (2001). Google ScholarT. L. Tan, V. A. Kudryashov and B. L. Tan, Materials & Process Integration for MEMS, ed. F. E. H. Tay (Kluwer Academic Publ, Boston, 2002) pp. 99–111. Google ScholarP. M. Dentinger and J. W. Taylor, J. Vac. Sci. Technol. B 15(6), 2632 (1997). Google Scholar FiguresReferencesRelatedDetails Recommended Vol. 04, No. 03 Metrics Downloaded 11 times History KeywordsUV and e-beam lithographicschemically amplified resistSU-8infrared spectroscopyPDF download

Cr photomask etch

Theoretical and experimental Cr photomask etch studies are carried out using different resists [ZEP, chemically amplified resists (CAR), and optical resists] and different brand etch tools. The effects of chrome loading are analyzed, and theoretical equations are developed for etch time calculations and endpoint determinations of extremely low Cr load photomasks. It was found that these equations agreed well with experimental data. Etch critical dimension (CD) movement data are analyzed and calculated, showing agreement with experimental data. Metrology measurement and characterization tools include a profilometer, an optical film measurement system, and SEM and optical CD measurement systems. Significant etch performance differences are noted across etch tools, irrespective of the resist type used. An etch property number method is proposed, which is found to accurately describe the etch process analysis and the extent to which etch performance can be expected to be improved. Etch properties are focused on etch CD movement, isolated/dense etch CD bias, radial CD etch contribution, and Cr load effects.

FT-IR study of a chemically amplified resist for X-ray lithography.

Microelectronic devices for future applications demand lithographic performance that falls within the 0.10 microm region and below. Chemically amplified resists (CARs), such as the positive tone commercial UVIII resist, offer a substantial gain in sensitivity, resolution, and process efficiency in deep ultraviolet, e-beam, and X-ray lithographies. In this work, the UVIII resist is characterized for X-ray lithographic applications by studying the "deprotection" or acid generation-diffusion process of the resist under different conditions of post-exposure bake (PEB) temperature and time, and of X-ray exposure dose. The X-ray irradiation from a copper anode at a wavelength of 1.33 nm was at an intensity of 30 microW/cm2 on the resist surface. The deprotection process of the resist during PEB was accurately monitored by using Fourier transform infrared (FT-IR) spectroscopy. The infrared absorption peaks at 1151, 1369, and 2977 cm(-1) in the spectrum of the UVIII resist were found to be useful indicators for the completion of deprotection. Results of the experiments showed that the performance of UVIII could be optimized at the PEB temperature of 140 degrees C, a time of 2 min, and X-ray exposure dose of 12 mJ/cm2. The change in resist thickness after PEB was also measured. The results were confirmed by scanning electron microscopy (SEM) in which a test structure as small as 0.12 microm was obtained in a 1-microm-thick UVIII resist layer.

Analysis of Line Edge Roughness Using Probability Process Model for Chemically Amplified Resists

Line edge roughness (LER) in chemically amplified resists (CARs) is understood to be fluctuations in the acid catalyzed reaction that determine molecular solubility and developer percolation. Two probability processes that cause LER are modeled: one is local acid generation with diffusion process, and the other is the main reaction and developer percolation process. A typical fluctuation size in these processes is significantly larger than the molecular size and depends on various parameters, such as acid concentration, diffusion length, molecular size, protection ratio and variation, and image conditions. Careful scaling for these parameters is required to reduce LER with certain shrinking design feature sizes. Our results suggest various factors that dominate LER in several resist systems. Reliable metrology for LER requires a sufficient sample size due to the random nature of origin. High contrast exposure characteristics of the dissolution rate in CARs today are also explained with the model.

Negative tone chemically amplified resist formulation optimizations for ultra high-resolution lithography

Starting from the Sumitomo commercial platform NEB-33 resist, three new experimental negative tone chemical amplified resist (CAR) formulations have been developed, to push resolution below 40 nm in direct electron beam lithography. PEB temperatures and times have been optimized between 60 and 100 °C and, respectively, 20 and 120 s. Fourier transform infra red spectra have been performed and allowed us to follow the solvent and PAG concentration in order to optimize processes on all samples. As a consequence, 25-nm isolated lines have been resolved with these new chemical amplified resists.

Probabilistic gel formation theory in negative tone chemically amplified resists used in optical and electron beam lithography

In this article a probabilistic model able to describe gel formation in negative tone chemically amplified resists (CARs) is developed. This model is a continuation and development of previous work on polymer cross-linking and on gelation of negative tone nonchemically amplified resists. The relation between gel fraction and exposure dose in negative tone CARs is obtained. A new parameter called inhibition activity with a vital role in the quantification of the cage effect (i.e., acid species trapping) is analyzed. The description of cage effect evolution with exposure dose, postexposure temperature, and time in CARs is accomplished through this parameter. The theory is tested against two negative tone CARs. The first one is EPR, an experimental CAR with known chemistry and the other is SAL-601, a commercial CAR from Shipley.

Edge Roughness Study of Chemically Amplified Resist in Low-Energy Electron-Beam Lithography Using Computer Simulation

We investigated the line edge roughness (LER) of chemically amplified resist (CAR) in the high-sensitivity resist process in low-energy electron beam lithography (LEEBL). We have confirmed that a sub-100 nm pattern having a small line edge roughness could be obtained at the exposure dose below sub-1 µC/cm2 for LEEBL. In order to explain the experimental results, we have proposed a resist exposure model, considering the generation yield and diffusion of secondary electrons (SEs). Based on the proposed model, we analyzed the LER for LEEBL using a simulation. When the beam blur and the acceptable LER were 30 nm (σ) and 2 nm (σ), the acceptable exposure doses for 2–5 keV and 50 keV were 0.3 µC/cm2 and 2.5 µC/cm2, respectively. This means that a high-sensitivity CAR process at the exposure dose below 0.5 µC/cm2 can be achieved in LEEBL.

Sensitivity of Simulation Parameter for Critical Dimension

In this study, lithography processes were modeled and simulated for the optimized parameters of 365 nm, 248 nm, and 193 nm resists. Also, sensitivity of those parameters for the critical dimension (CD) and side wall angle of simulated profiles was analyzed using the response surface methodology (RSM). Through the quantization of sensitivity of these easy-to-optimize simulation parameters, we quantified lithography processes and discussed the different phenomenon of the chemically amplified resist (CAR) compared to the non-CAR. To validate our results, the quantitative comparison between our results and those of a commercial tool was shown.