ArF Immersion Lithography Research Articles

A study of virtual lithography process for polymer directed self-assembly

For the feature size scaling down to tens of nanometers, the top-down approaches are getting more severe because the extremely ultra-violet (EUV) technique, the high-index fluid-based immersion ArF lithography, and the double patterning technology (DPT) under development may be cover one or two generations. An alternative technology to extend lithography patterning beyond current resolution limits is to combine the top-down lithography and bottom-up assembly. In this paper, an directed self-assembly lithography process of “bottom-up” block copolymer self-assembly, is modeled and simulated in molecular-scale. Impacts of block polymer components on pattern formation are analyzed and discussed.

Defect Reduction in ArF Immersion Lithography Using Particle Trap Wafers With CVD Thin Films

Particle trap wafers were applied to ArF immersion lithography to reduce the immersion-related defectivity. Interfacial free energy (gamma <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A-particle</sub> ) and work of adhesion (W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A-particle</sub> ) between particle trap wafers and particles in immersion water explain the potential of trapping particles by the particle trap wafers. It was found that the treated SiCN chemical vapor deposition wafer performed well as a particle trap wafer and can help defect reduction in immersion lithography.

32 nm Half Pitch Formation with High-Numerical-Aperture Single Exposure

According to the International Technology Roadmap for Semiconductors (ITRS), memory half pitch (hp) will reach 32 and 20 nm by 2012 and 2017, respectively. However, it is difficult to fabricate a sub-40 nm node using single-exposure technology with the currently available 1.35-numerical-aperture (NA) ArF immersion lithography. Although it is expected that either double patterning technology or extreme ultraviolet lithography will enable the realization of 32 nm hp, there are still many problems that need to be solved regarding cost reduction. Thus, the study of high-index fluid immersion technology should be pursued simultaneously. ArF water immersion systems with 1.35 NA have already been introduced for 40-nm-hp production. ArF immersion lithography using high-index materials is currently being studied for next-generation lithography. Currently, many studies are being undertaken in order to increase NA for a high-index fluid and a lens in immersion technology. The combination of LuAG (n = 2.14) and a third-generation fluid could be used to realize 1.55 NA. This combination of 0.25k1 and 32 nm hp can be obtained using single-exposure technology. In order to determine the feasibility of this process and possible process hurdles for this high-NA single-exposure technology, 32 nm hp with a 1:1 line and space pattern is tested. Various illumination conditions are tested to realize 1:1 32 nm hp, and the exposure and development conditions are varied to determine whether this single exposure can provide a processible window. As a result, 32 nm hp could be obtained by single-exposure technology with 1.55 NA.

Pattern Freezing Process Free Litho–Litho–Etch Double Patterning

Double patterning technology based on existing ArF immersion lithography is considered as the most viable option for complementary metal oxide semiconductor (CMOS) node of 32 nm and below. Most of double patterning approaches previously described requires intermediate processing step such as hard mask etching, spacer material deposition, and resist pattern freezing. The requirement of these additional steps is now leading way to requests for throughput reduction and low cost for production for double patterning technology applications. In this paper, litho–litho–etch (LLE) double patterning without any intermediate processing steps is investigated to achieve narrow pitch resist imaging. The LLE options examined in this work are combinations of positive tone-negative tone and positive tone-positive tone photoresist double patterning process. These are the alternative processes in pattern freezing process free LLE double patterning. The goals of this work are to determine witch of these approaches is the most viable for future application and to confirm the patterning potential for 32 nm and below half pitch resist imaging.

Impact of Polarization Inside a Resist for ArF Immersion Lithography

Impact of Polarization Inside a Resist for ArF Immersion Lithography

Image Formation in Chemically Amplified Resists upon Exposure to Extreme Ultraviolet Radiation

The image formation in conventional non-chemically amplified photoresists has been investigated and theorized. Image formation theories have been extended to chemically amplified KrF and ArF resists by introducing the effects of acid diffusion. After ArF immersion lithography, extreme ultraviolet (EUV) radiation is expected as an exposure tool for mass production of semiconductor devices. In EUV resists, secondary electrons play a major role in the sensitization of acid generators because the energy of EUV photons (92.5 eV) is higher than the ionization potential of resist materials. The effects of secondary electrons should be taken into account for the discussion of image formation in EUV resists. In this study, the dependence of chemical gradient on the aerial image contrast of incident photons was investigated on the basis of the sensitization mechanisms of chemically amplified EUV resists. The relationship between aerial image contrast and chemical gradient depends on the neutralization mechanisms, the rate constant for deprotection, quencher concentration, and dissolution point. To minimize line edge roughness, it is necessary to optimize not only quencher concentration but also dissolution point in accordance with the aerial image contrast.

Influence of resist blur on resolution of hyper-NA immersion lithography beyond &lt;inline-formula&gt;&lt;math display="inline" overflow="scroll"&gt;&lt;mrow&gt;&lt;mn&gt;45&lt;/mn&gt;&lt;mtext&gt;-&lt;/mtext&gt;&lt;mi&gt;nm&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/inline-formula&gt; half-pitch

For lithography of 45-nm half-pitch and beyond, the resist blur due to photoacid diffusion is a significant issue. On the other hand, it has been generally recognized that there is a trade-off between resist resolution and sensitivity. We study the influence of the resist blur on resolution in hypernumerical aperture ArF immersion lithography by utilizing a two-beam interferometric exposure tool. We evaluated the current photoresist performance for some of the latest commercial resists and estimated their acid diffusion lengths as 8 nm to 9 nm in sigma assuming Gaussian blur kernel. In addition, we found that the acid diffusion length, which is directly related to the resist resolution and is controllable by photoacid generator (PAG) anion size, polymer resin size, and post-exposure bake (PEB) temperature. We confirmed that there is a trade-off between resist resolution and sensitivity. Our results indicate that the resist blur is still a concern in order to extend lithography for 45 nm and beyond; however, it will not likely be a showstopper. We consider that total optimization of resists and exposure tools is important in order to achieve ultimate resolution in hyper-NA immersion lithography.

Haze Defects due to Pellicle Adhesive

The minimum feature size of a semiconductor device will be smaller and smaller because of the increasing demand for high integration of the devices. According to the recently proposed international technology roadmap of semiconductor, ArF immersion lithography will be used for 65 to 45 nm technology nodes. In the 193 nm exposure process, outgassing from the adhesive of the pellicle is a serious problem in the semiconductor industry because it causes haze to form. Various materials contribute to photomask haze including chemical residuals from mask cleaning, outgassing from pellicle adhesive/materials, and contaminants from the scanner ambient. The pellicle lifetime is important in exposure processes, is directly related to the throughput in mass production, and is affected by exposure dose and the environment surrounding the mask. The dependence of the pellicle lifetime on the dose and location of exposure is the subject of this study. The distance between the adhesive of the pellicle and the exposed area was varied to determine the direct relationship between the adhesive and the haze. A 193 nm (ArF) excimer laser was used to expose the mask with and without a pellicle. The surrounding environment of the mask with and without nitrogen purging was also varied. We compared haze formation as a function of accumulated dose. As expected, the crystal growth or haze formation increased as the accumulated dose increased. The adhesive and pellicle material contribute to haze formation; nitrogen purging can reduce haze formation.

A Mask Generation Approach to Double Patterning Technology with Inverse Lithography

Pattern reduction has generated much interest in developing effective methods of reducing the feature sizes of microelectronic and data-storage devices. For below-32-nm node technology, the bottom-up approach, namely, self-assembly, has obstacles such as the insufficient support of processes and mass production, and the top-down approaches, namely, photolithography, the extremely ultraviolet (EUV) technique, and high-index fluid-based immersion ArF lithography, are still under development. As one of the solutions for below-32 nm node technology, double patterning technology (DPT) has been researched. In this paper, we analytically report that the DPT pattern is 3/2 times denser than the double exposure technology (DET) pattern, and three times denser than the single-exposure pattern. An algorithm of the inverse lithography technology (ILT) based on not mathematical functions but pixels and the lithography model is described and simulated. An algorithm of the DPT mask design with ILT is described in terms of how to use this ILT method in an integrated computational lithography platform to handle the DPT. For its accuracy, its simulation results are compared with the simulation results obtained without ILT and with the conventional serif optical proximity correction (OPC). The ILT results are better than other results. Hence, the ILT based on pixels and the lithography model and its application algorithm of DPT can reduce the design complexity of mask design and the cost of production of DPT for below 32 nm half pitch pattern generation.

45 nm/32 nm CMOS – Challenge and perspective

Production of 45nm node CMOS has already started. However, difficulty of new technology development is increasing and some company dropped off from the competition. The big challenge for 45nm node is the introduction of ArF immersion lithography. Most of the other technologies used for 45nm node are the extension of those used for 65nm node. On the other hand, there will be a big jump for 32nm node technology. The biggest item is metal gate and high-k gate insulator system. Self barrier layer formation for BEOL is also the promising item. Variability is the biggest concern for 32nm node SRAM. To overcome these difficulties, collaboration between device and circuit engineer is important.

Feasibility Study on Immersion System Using High-Index Materials

ArF water immersion systems with a numerical aperture (NA) of more than 1.3 have already been introduced for the node up to 45-nm half-pitch production. For next-generation lithography, we focus on ArF immersion lithography using high-index materials. At present, LuAG (n=2.14) is the most promising candidate as a high-index lens material. Second-generation fluids (n=1.64) have the sufficient performance as a high-index immersion fluid. The combination of LuAG and a second-generation fluid can enhance the NA up to 1.55 and the exposure system would be available for the 34-nm half-pitch node when k1 is 0.27. Although high-index immersion lithography is attractive because it is effective in improving the resolution, there are some issues not encountered in a water immersion system. The issues associated with LuAG are its availability and intrinsic birefringence. Fluid degradation induced by dissolved oxygen or laser irradiation, lens contamination, and residual fluid on a wafer are the specific issues associated with second-generation fluids. In this article, we describe the current status of the above issues and discuss the feasibility of an ArF immersion system using high-index materials.

Impact of polarized illumination on high NA imaging in ArF immersion lithography at 45 nm node

Immersion lithography has been considered as the mainstream technology to extend the feasibility of optical lithography to further technology nodes. Using proper polarized illumination in an immersion lithographic tool is a powerful means to enhance the image quality and process capability for high numerical aperture (NA) imaging. In this paper, the impact of polarized illumination on high NA imaging in ArF immersion lithography for 45 nm dense lines and semi-dense lines is studied by PROLITH simulation. The normalized image log slope (NILS) and exposure defocus (ED) window are simulated under various polarized illumination modes, and the impact of polarized illumination on image quality and process latitude is analyzed.

Study of PAG Material Design for ArF Immersion Photoresist

One of some critical issues for ArF immersion lithography was leaching of resist components to water fluid. To decrease the leaching amount, increase hydrophobicity of Photo Acid Generator (PAG) was one of the most effective methods. The hydrophobicity of PAG was detected by simulating Log-P value and measuring Retention Time (RT) on reversed phase chromatography. However, simple high hydrophobic PAG indicated high defect number. The improvement of this issue was achieved by introducing acid cleavable group into PAG cation frame. It may suggest that PAG material proposed on this study showed low leaching amount and low defect risk as new concept for ArF immersion resist.

Development of Materials and Processes for Double Patterning toward 32nm Node ArF Immersion Lithography

A new negative tone imaging with application of new developer to conventional ArF immersion resist materials is proposed for narrow trench pattern formation, which is effective to the double trench process that is one of the candidates of double patterning process for 32 nm node semiconductor devices. No swelling property was realized in the developing step, in which the dissolution mechanism was discussed. Significantly better line width roughness (LWR) and resolution on narrow trench pattern were observed with this negative tone development compared to positive tone development. These results suggest that this negative tone development process is one of the promising candidates for double trench process.

Proposed single layer composite film used as high transmission phase shifting masks for the 32, 45, and 65nm technology nodes

The optical constants of composite films are linearly dependent on their mole fraction. The (Al2O3)x–(TiO2)1−x composite films prepared by using rf unbalanced magnetron sputtering are completely oxidized using an O2∕Ar flow rate ratio of 2.0. By tuning the Al2O3 mole fraction of (Al2O3)x–(TiO2)1−x composite films, the optical constants can be made to meet the optical requirements for a high transmittance attenuated phase shifting mask (HT-AttPSM) blank. It can be seen that the Al2O3 mole fraction in (Al2O3)x–(TiO2)1−x composite films which would best meet the optical requirements of a HT-AttPSM blank in ArF (immersion) lithography is calculated to be between 78% and 86%. In order to obtain a HT-AttPSM blank with an optimized transmittance of 20%, one Al2O3–TiO2 composite film is fabricated. All the films meet the requirements of the adhesion test and surface roughness for HT-AttPSM applications. Therefore, a single layer composite film of Al2O3–TiO2 could be applied to HT-AttPSM blanks, which can be utilized to design fine patterns with dimensions as small as 65, 45, and 32nm.

Which Mask is Preferred for Sub-60 nm Node Imaging?

ArF immersion lithography may be the best candidate for sub-60 nm device patterning. However, the polarization effect is the most prominent root cause for the degradation of the image quality in high numerical aperture (NA) immersion lithography as the feature size shrinks. Therefore, it is important to understand the polarization effect in the mask. It is common knowledge that a small mask pattern is considered as the wave guide of transmission light. The induced polarization effect shows the different aspects between the conventional mask and the attenuated phase-shift mask (PSM). In this paper, we considered the effects of polarization state as a function of mask properties. The aerial image depends on the polarization states induced by the mask. We evaluated the performances of the conventional mask and the attenuated PSM by using the Solid-ETM simulation and AIMSTM (Aerial Image Measurement System) tool along with real wafer printing.

Effect of Resolution Enhancement Techniques on Aberration Sensitivities of ArF Immersion Lithography at 45 nm Node

The impact of resolution enhancement technologies (RET) on aberration sensitivities are studied in the conditions of different pattern density, numerical aperture (NA) and polarized light with ArF immersion lithography at 45 nm node. The results show that the aberration sensitivity of all order astigmatism, coma, and spherical aberration is much small when the dense line is printed. The aberration sensitivities are higher when strong alternating phase shift mask (altPSM) and chrome-less (Cr-less) PSM are employed. The low order aberration sensitivity is much bigger when polarization effect is no longer neglected in hyper NA system. RET and aberration should be accounted in conjunction with polarization effect during the design stage since minimization of negative effects is a primary goal. These results reveal that RET, pattern type, size, NA and polarized illumination impact the aberration sensitivity significantly in hyper NA lithography. Tool designer and device maker should pay more attention on this for 45 nm node and below.

The optical properties of monolayer amorphous Al 2O 3–TiO 2 composite films used as HT-APSM blanks for ArF immersion lithography

Amorphous (Al 2O 3) x –(TiO 2) 1− x composite films are prepared using r.f. unbalanced magnetron sputtering in an atmosphere of argon and oxygen at room temperature. The optical constants of (Al 2O 3) x –(TiO 2) 1− x composite films are linearly dependent on the Al 2O 3 mole fraction in the Al 2O 3–TiO 2 composite film. The optical constants of these Al 2O 3–TiO 2 composite films can be made to meet the optical requirements for a high transmittance attenuated phase shift mask (HT-APSM) blank by tuning the Al 2O 3 mole fraction. The Al 2O 3 mole fraction range that would allow the films to meet the optical requirements of an HT-APSM blank for ArF immersion lithography is calculated to be between 76% and 84%. One π-phase-shifted Al 2O 3–TiO 2 composite thin film to be used as an HT-APSM blank for ArF immersion lithography is fabricated and is shown to satisfy the optical requirements.

Evaluation of Next Generation Fluids for ArF Immersion Lithography Beyond Water

Evaluation of Next Generation Fluids for ArF Immersion Lithography Beyond Water

Influence of resist blur on ultimate resolution of &lt;inline-formula&gt;&lt;math altimg="none" display="inline" overflow="scroll"&gt;&lt;mrow&gt;&lt;mi&gt;ArF&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/inline-formula&gt; immersion lithography

The chemical amplification provides high sensitivity of resists for deep-uv and extreme-uv (EUV) lithography. On the other hand, the chemical amplification involves photoacid diffusion that causes contrast degradation of the latent image or, in other words, resist blur. We study the influence of the resist blur in high-numerical aperture ArF immersion lithography by using an interferometric exposure tool. The contrast ratio between the resist latent image and the original aerial image was measured for half pitches from 45 to 80 nm. Acid diffusion length for a high-resolution ArF resist was determined as 11 nm in sigma (26 nm in full width at half maximum) assuming a Gaussian blur kernel. The results revealed that the influence of the resist blur is a significant issue for the 45-nm half-pitch node. The reduction of acid diffusion length is highly desirable. Given the tradeoff between the resist resolution and sensitivity, increasing illumination intensity in exposure tools can be an effective means to overcome the challenge of the resist blur. We also demonstrate resist imaging of 30-nm line-and-space pattern with a high-index fluid. While our focus is on ArF immersion lithography, our findings are also relevant to EUV lithography.