Search

Extreme ultraviolet lithography (EUV) materials and processes are constantly evolving and maturing, making sub-30 nm pitch single-exposure yield feasible. Characterization methodologies for stochastic variations are well-documented at this stage, with most employing critical dimension scanning electron microscopy (CDSEM) and a form of defect inspection to quantify line edge roughness (LER), local critical dimension uniformity and patterning failures. In this paper, the link between LER and stochastic defectivity is explored at a deeper level, as we probe the possibility of nucleating stochastic failures with programmed LER structures at 30 nm pitch using CDSEM, optical inspection and electrical yield data. First, we characterize LER post-develop and post-etch using unbiased LER measurements. Second, we study the defectivity and optical characteristics of the programmed LER pattern post hard mask open using optical inspection. Specifically, we measure the optical noise induced by programmed LER, the inspection performance in terms of defect capture and nuisance rate, and the predictive capability of optical inspection through a comparison of defectivity with electrical yield data.

As the industry continues to push the limits of integrated circuit fabrication, reliance on EUV lithography has increased. Additionally, it has become clear that new techniques and methods are needed to mitigate pattern defectivity and roughness at Litho and Etch together with eliminating film-related defects. These approaches require further improvements to the process chemicals and the lithography process equipment to achieve finer patterns. In particular improvements in the coater/developer hardware and process are required to enable the use of a wide variety of chemicals as well as compatibility with existing systems. This paper reviews the ongoing progress in coater/developer processes that are required to enable EUV patterning sub-30nm line and space by using MOR (Metal Oxide Resist).

Two earlier publications showed that mask defectivity contributes to the stochastics of the EUVL-printed image on wafer. The present contribution gives more insights into the methodology and resist models used therein. In addition, an extended study of two types of mask roughness is presented, comprising mask absorber line-edge roughness and rippling of the multilayer mirror on the mask. For both, it is shown that contributions to stochastics are larger than expected purely from normalized intensity log-slope considerations. As a second topic, printability of local defects is readdressed at smaller pitches and more state-of-the-art illumination settings, in preparation to a genuine study of mask defectivity contribution to wafer printing stochastics at high-NA EUV lithography. First results for one-dimensional mask patterns indicate an influence of the anamorphic characteristic of high-NA imaging, showing a different behavior for vertical and horizontal orientations.

Although several years delayed than its initial plan, extreme UV lithography (EUVL) with 13.5nm wavelength has been finally implemented into high volume manufacture (HVM) of mainstream semiconductor industry since 2018. With the delivery and installation of ASML EUV scanners in those giant Fab players like Samsung, TSMC and Intel, EUV lithography is becoming a sort of industry standard exposure metrology for those critical layers of advanced technology nodes beyond 7nm. Although ASML NXE EUVL scanner is the only commercialized EUV exposure system available on the market, its development is the concentration of all essence from worldwide industrial and academic collaboration. It is becoming more and more important not only for fab runners but also for main stream fabless design houses to understand and participate the progress of EUVL. In this review, working principles, module structures and technical challenges have been briefly discussed regarding each EUV subsystem, including light source, reflection mirrors and system, reticle module as well as photoresist development. EUV specific issues of light intensity, defectivity within reflection system, line edge roughness (LER) and mask 3D effects have been focused respectively and promising solutions have been summarized as well.

The authors present latent image characterization in photoresists by means of extreme ultraviolet (EUV) spectroscopic reflectometry. The optical constants of photoresists before and after exposure are measured in the EUV spectral range. Latent images are investigated in the form of periodic line gratings. The investigation is performed by the analysis of spectroscopic reflectance curves in the wavelength range from 5 nm to 20 nm at grazing incidence angles. Through an analysis of the reflectance curves based on rigorous electromagnetic modeling, a characterization of parameters of interest of the latent image is evaluated. This includes the latent image profile, surface topography and stochastic-related parameters such as line edge roughness.

This paper extends the 2019 findings, that local defects on an EUV mask are trigger points for stochastic failures on the printed wafer, to a simulation study of non-local mask deficiencies. These relate to shortcomings of a larger area nature where the reticle deviates from an ideal reticle or fails specification. These include aspects such as global CD error, absorber slope, contamination effects, line edge roughness, and multilayer roughness. The presented results suggest that mask specifications may need refinement, specifically for roughness type deficiencies, in order to help mitigate the mask contribution in the stochastics of wafer printing by EUV lithography.

Lithographers are currently unable to generate quality patterning at tight pitches with values of k1 that are as low as have been achieved routinely using ArF immersion patterning, a situation that is largely due to the continuing pursuit of resists with low exposure doses. As a consequence, multiple patterning may be required to scale to a second node with EUV lithography, which reduces its cost-effectiveness, even if each individual exposure is done with a low exposure dose. Because of process control limitations, such multiple patterning may necessarily be triple or quadruple patterning, rather than double patterning. Processes with reduced line-edge roughness (LER) could be applied to front-end layers, increasing the value of EUV lithography. High-NA EUV lithography is in development, with a number of technical issues requiring solution, but with no apparent show-stoppers.

The ability to further shrink EUVL geometries can be facilitated using multiple lithographic approaches. Most recent proposals suggest an EUVL double patterning strategy. This path requires additional and expensive EUVL tool time. In our work, using an EUVL patterned polymer as a guide material with DSA incorporated into the lithography flow is an optional process mitigating EUVL tool time. Multiple variations of BCP (block copolymers) were successfully tested. In addition, pattern transfer through silicon containing hard mask and spin on carbon layers was demonstrated with minimum LER (line edge roughness) and good critical dimension uniformity (CDU).

Author(s): Long, L; Neureuther, AR; Naulleau, PP | Abstract: In response to the difficulties posed by the resolution, line edge roughness, sensitivity (RLS) trade-off to traditional chemically amplified resist (CAR) systems used for extreme ultraviolet lithography, a number of novel resist technologies have been proposed. In this paper, the effect of quencher loading on three resist technologies is analyzed via an error propagation-based resist simulator. In order of increasing novelty as well as complexity, they are: Conventional CAR with quencher, CAR with photodecomposable base, and PSCAR 2.0, a CAR system with photodecomposable base as well as an EUV-activated UV-sensitive resist component. Simulation finds the more complicated resist systems trade in an increase in resist stochastics for improved deprotection slopes, yielding a net benefit in terms of line width roughness.

Chemically amplified resists have been used in the EUV lithography. The basic additive, called a quencher, has been added to the resist formula to control acid diffusion. In this study, the effects of photodecomposable quencher (PDQ) concentration on the chemical gradient (an indicator for LER) in chemically amplified EUV resist processes were investigated. The chemical gradients were simulated on the basis of the sensitization and reaction mechanisms for different half-pitchs, sensitivities, photoacid generator (PAG) concentrations, PDQ concentrations, and the effective reaction radii for deprotection. The simulation results analyzed using least square, lasso, Ridge, and elastic net regressions are discussed.

Low throughput has been a critical issue in extreme ultraviolet (EUV) patterning due to the difficulty in increasing light source power. This limitation has driven the need for photoresists with better throughput which unfortunately come with higher line edge roughness (LER). In this work, the possibility of relaxing LER requirements for metal layer patterned by EUV lithography (EUVL) is studied. Single patterning and litho-etch litho-etch (LELE) patterning with EUVL are considered. To assess the impact of LER on design yield, analytical and simulation based modeling approaches are developed, which consider the LER induced metal wire shorts/opens and the enhanced time dependent dielectrics breakdown (TDDB) for metal wires with different geometries. The impact of LER on wire delay is studied by Elmore’s delay model.

As minimum lithographic size continues to shrink, the development of techniques and resist materials capable of high resolution, high sensitivity and low line edge roughness (LER) have become increasingly important for next-generation lithography. In this study we present results where the behaviour of the resist is driven towards the multi-trigger regime by manipulating the resist formulation. We also present results obtained after enhancements of the base molecule to give high resolution, better LER, and a significant sensitivity enhancement of 40% over the standard material. Finally, we present the inclusion of non-metallic high-Z elements into the formulation to allow for a further reduction in LER at the same resolution and sensitivity as seen for the enhanced MTR molecule, indicating a direction for further improvements.

Owing to the worldwide efforts, the development of extreme ultraviolet (EUV) lithography has significantly progressed during the past decade. The resolution of chemically amplified resists has reached sub-16-nm region. From the viewpoint of the extendibility of EUV lithography, the development of resist materials capable of resolving sub-10-nm is an urgent task. In this review, the resist material options for EUV lithography are discussed on the basis of the EUV sensitization mechanisms after reviewing the problems for the sub-10-nm fabrication.

The optimization problem of reducing EUV line edge roughness (LER) of a given feature, subject to the tolerance constraints on a CD of this feature at nominal EUV process conditions and several off-nominal conditions, is formulated. A stochastic rigorous Monte-Carlo EUV resist model is employed to solve this stochastic optimization problem. Several options for optimization algorithms, suitable for the solution of the formulated EUV LER optimization problem, are presented and discussed, along with the results of their tests.

With the extreme ultraviolet (EUV) lithography, the performance limit of chemically amplified resists has recently been extended to 16-and 11-nm nodes. However, the line edge roughness (LER) and the line width roughness (LWR) are not reduced automatically with this performance extension. In this paper, to investigate the impacts of the EUVL mask and the EUVL exposure process on LER, EUVL is modeled using multilayer-thin-film theory for the mask structure and the Monte Carlo (MC) method for the exposure process. Simulation results demonstrate how LERs of the mask transfer to the resist and the exposure process develops the resist LERs.

We developed and evaluated a photoacid generator (PAG)-bonded resist, a chemical amplified (CA) resist for decreasing line edge roughness (LER) and increasing sensitivity in extreme ultraviolet lithography (EUVL) and electron beam (EB) lithography. We investigated many samples to find an effective for the PAG-bonded resist. Under EB exposure, the LERs and resolutions of the PAG-bonded resist and PAG-blended resist which uses the same PAG and base polymer were compared. It was confirmed that the LER and resolution of the PAG-bonded resist are better than those of the PAG-blended resist. An LER of 3.5 nm in 75 nm line-and-space (L/S) and a resolution of 25 nm space were achieved. Under EUV exposure, a sensitivity of 5.0 mJ/cm2 was achieved.

The resolution of chemically amplified extreme ultraviolet (EUV) resists has reached sub-30 nm. However, the sensitivity and the reduction in the line edge roughness of such resists is still inadequate for the realization of EUV lithography. The pattern formation of chemically amplified resists is based on chemical reactions, which start with energy deposition from exposure tools and are terminated by quenchers or by cutting the heat supply for chemical reactions. In this study, the effects of rate constant for deprotection on latent image formation in chemically amplified EUV resists were investigated from the viewpoint of the difference between high- and low-activation-energy (Ea)-type resists. In chemically amplified resists, neutralization and deprotection competitively proceed. In high-Ea-type resists, in which neutralization proceeds before deprotection, the contrast of pattern edges is improved by suppressing deprotection in the low-dose region. In low-Ea-type resists, in which a fast deprotection is expected, the difference in the extent of deprotection between the high- and low-dose regions can be enhanced by promoting deprotection over neutralization. For the improvement in high- or low-Ea-resist performance, it is effective to enhance or balance all advantages of chemical reactions.

In order to reduce line edge roughness and to increase sensitivity, PAG-bonded chemically amplified resist was developed and was evaluated in extreme ultraviolet lithography (EUVL) and electron beam (EB) lithography. We investigated various kinds of photo acid generators (PAGs) which are on the basis of the sulfonium salts to find the beneficial photo acid generator (PAG) for our designed PAG-bonded resist. It was confirmed that not only the structure of anion of PAG but also the structure of cation of PAG are important to achieve the resist specification. It is confirmed that by a selected PAG system, high E0 sensitivity was achieved under the EUV exposure. In addition, LER of 3.5 nm (3σ) was achieved by an EB writing tool.

We developed a novel chemically amplified resist to increase sensitivity and reduce line edge roughness (LER) in extreme ultraviolet (EUV) lithography. This resist consists of a base resin of which a photochemical acid generator (PAG) is bonded to the side chain this is called the PAG-bonded resist. Under EUV exposure, an E0 sensitivity of 1.9 mJ/cm2 and a low outgassing pressure of 2.5×10-6 Pa were achieved. Resolution and LER were obtained by electron beam (EB) exposure. Under EB exposure, an LER of 2.1 nm (3σ) for a 100 nm line and space (L/S) pattern was achieved by the PAG-bonded base resin. In addition, we improved this resist and an LER of 4.0 nm (3σ) for a 50 nm L/S pattern was achieved under EB exposure. These results demonstrate that the novel resist system has a good advantage in terms of high sensitivity and low LER.

We have designed and synthesized a molecular resist material, which has no distribution of the protecting groups and have evaluated its performance as a molecular resist with EB and EUV exposure tool. The molecular resist attained a resolution of sub-45nm patterning at an exposure dose of 12mJ/cm^2. It was found that controlling the distribution of the protecting groups in a molecular resist material has a great impact on improving line edge roughness (LER). Low LER values of 3.1nm (inspection length: L=620nm) and 3.6nm (L=2000nm) were achieved with this molecular resist using Extreme UltraViolet (EUV) lithography tool.

We developed and evaluated PAG bonded resist which is chemically amplified (CA) resist to reduce line edge roughness (LER) in extreme ultraviolet lithography (EUVL). Under electron beam (EB) exposure, it is compared that LER and resolution of photo acid generator (PAG) bonded resist and PAG blended resist which using same PAG and base polymer. It was found that LER and resolution of PAG bonded resist are better than that of PAG blended resist. LER of 3.5 nm in 75 nm L/S and resolution of 25 nm space were achieved. Under EUV exposure, sensitivity of 5.0 mJ/cm2 is achieved.

It is reviewed that research and development of resist for extreme ultraviolet lithographic in University of Hyogo. It is focused on the mitigation of the development of high sensitive and low line edge roughness EUV resist. To achieve high sensitivity, it is found that cyclo(1,3-per-fluoropropanedisulfone) imidate employed as an anion of PAG is beneficial in EUV exposure to achieve high sensitivity. To achieve low LER and high sensitivity simultaneously, PAG bonded resist is proposed. We demonstrate Eo sensitivity of higher than 2 mJ/cm2 under EUV exposure. PAG bonded resist which has LER of around 2.0 nm and 6.8 μC/c2 are demonstrated. Furthermore, design concept of low outgassing resist is introduced.

Extreme ultraviolet lithography (EUVL) is considered to be the most promising option to continue with the aggressive scaling required in high-volume manufacturing (HVM) of integrated circuits. One of the main challenges, however, is the development of EUV resists that fulfill the strict sensitivity, resolution, and line-edge roughness specifications of future nodes. Here, we present our EUV resist screening results of a wide range of EUV resists in their developmental phase from our collaborators from around the world. Furthermore, we have carried out extensive experiments to improve the processing parameters of the resists as well as to identify the optimal wafer pre-treatment methods in order to optimize the adhesion of the resist to the substrate. We show that even though significant improvements in performance of chemically amplified resists have been achieved, pattern collapse is still the major process-limiting factor as the resolution decreases below 14 nm half-pitch (HP).

New photoresist compositions containing tert-butyloxycarbonyl group protected C-4-hydroxyphenyl calix [4] resorcinarene molecular glasses and perfluorooctylsulfonate (PFOS) free photoacid generators (PAG) composed of a triphenylsulfonium aryloxyperfluoroalkylsulfonate was developed. The patterning performance of PFOS free photoresist compositions was examined using extreme ultraviolet (EUV or 13.4 nm) lithography and compared with photoresist compositions containing conventional perfluorobutanesulfonate (PFBS) PAGs. Features as small as 30 nm with low line edge roughness (LER) were readily obtained for both formulations. The non-PFOS photoacid generator forms acid that contains fewer fluorine atom than found in PFOS or in PFBS. The newly developed non-PFOS PAGs may find application in chemically amplified resists that address the environmental concerns raised by the widely used PFOS containing PAGs.