Extreme Ultraviolet Interference Research Articles

Extreme ultraviolet lithography reaches 5 nm resolution.

Extreme ultraviolet (EUV) lithography is the leading lithography technique in CMOS mass production, moving towards the sub-10 nm half-pitch (HP) regime with the ongoing development of the next generation high numerical aperture (high NA) EUV scanners. Hitherto, EUV interference lithography (EUV-IL) utilizing transmission gratings has been a powerful patterning tool for the early development of EUV resists and related processes, playing a key role in exploring and pushing the boundaries of photon-based lithography. However, achieving patterning with HPs well below 10 nm using this method presents significant challenges. In response, this study introduces a novel EUV-IL setup that employs mirror-based technology and circumvents the limitations of diffraction efficiency towards the diffraction limit that is inherent in conventional grating-based approaches. The results are line/space patterning of the HSQ resist down to HP 5 nm using the standard EUV wavelength 13.5 nm, and the compatibility of the tool with shorter wavelengths beyond EUV. Mirror-based interference lithography paves the way towards the ultimate photon-based resolution at EUV wavelengths and beyond. This advancement is vital for scientific and industrial research, addressing the increasingly challenging needs of nanoscience and technology and future technology nodes of CMOS manufacturing in the few-nanometer HP regime.

Design of an efficient illuminator for partially coherent sources in the extreme ultraviolet.

In this paper, the design of an efficient illuminator for extreme ultraviolet (EUV) applications such as photolithography, metrology, and microscopy is investigated. Illuminators are arrangements of optical components that allow us to tailor optical parameters to a targeted application. For the EUV spectral range, illuminators are commonly realized by an arrangement of several multilayer mirrors. Within this publication, design methods are developed to tailor optical parameters such as the intensity distribution, the spatial coherence, and the spectral bandwidth by using only one multilayer mirror. For the demonstration of the methods, an illuminator is designed for a compact in-lab EUV interference lithography system that is suited for industrial EUV resist qualification and large-area nanopatterning. The designed illuminator increases the wafer-throughput and improves the imaging quality.

Fabrication of high aspect ratio and tilted nanostructures using extreme ultraviolet and soft x-ray interference lithography

We demonstrate the fabrication of metal and dielectric nanostructures using interference lithography with extreme ultraviolet (EUV) and soft x-ray synchrotron radiation down to a 2.5 nm wavelength. These specific wavelengths are chosen because of the industrial relevance for EUV lithography and because they are in the vicinity of the oxygen absorption edge of the high-resolution hydrogen silsesquioxane photoresist, allowing for the exposure of thick layers. We investigate the requirements to fabricate such structures and demonstrate that tall metal nanostructures with aspect ratios up to 7 could be achieved by EUV interference lithography and subsequent electroplating. We use the unique depth-of-focus-free property of interference and achromatic Talbot lithography to fabricate uniformly tilted dielectric nanostructures.

Hybrid application of laser-focused atomic deposition and extreme ultraviolet interference lithography methods for manufacturing of self-traceable nanogratings

A novel hybrid method that combines the laser-focused atomic deposition (LFAD) and extreme ultraviolet (EUV) interference lithography has been introduced. The Cr grating manufactured by LFAD has advantages of excellent uniformity, low line edge roughness and its pitch value determined directly by nature constants (i.e. self-traceable). To further enhance the density of the Cr grating, the EUV interference lithography with 13.4 nm wavelength was employed, which replicated the master Cr grating onto a Si wafer with its pitch reduced to half. In order to verify the performance of the gratings manufactured by this novel method, both mask grating (Cr grating) and replicated grating (silicon grating) were calibrated by the metrological large range scanning probe microscope (Met.LR-SPM) at Physikalisch-Technische Bundesanstalt (PTB). The calibrated results show that both gratings have excellent short-term and long-term uniformity: (i) the calibrated position deviation (i.e. nonlinearity) of the grating is below ±1 nm; (ii) the deviation of mean pitch values of 6 randomly selected measurement locations is below 0.003 nm. In addition, the mean pitch value of the Cr grating is calibrated as 212.781 ± 0.008 nm (k = 2). It well agrees with its theoretical value of 212.7787 ± 0.0049 nm, confirming the self-traceability of the manufactured grating by the LFAD. The mean pitch value of the Si grating is calibrated as 106.460 ± 0.012 nm (k = 2). It corresponds to the shrinking factor of 0.500 33 of the applied EUV interference lithographic technique. This factor is very close to its theoretical value of 0.5. The uniform, self-traceable gratings fabricated using this novel approach can be well applied as reference materials in calibrating, e.g. the magnification and uniformity of almost all kinds of high resolution microscopes for nanotechnology.

Broadband extreme ultraviolet dispersion measurements using a high-harmonic source.

We demonstrate direct dispersion measurements of various thin films at extreme ultraviolet (EUV) wavelengths, using a table-top laser-driven high-harmonic generation (HHG) source. In this method, spatially separated identical EUV pulses are generated through HHG with a pair of phase-locked infrared pulses. The EUV pulses are re-imaged to a sample plane using a single toroidal mirror, such that one pulse illuminates the target thin film, while the other pulse passes through a reference aperture. By comparing the EUV interference with and without a sample, we are able to extract the dispersion properties of the sample, integrated over the full film thickness. We have measured thin films of titanium, nickel, copper, and silicon nitride, demonstrating that this technique can be applied to a wide range of materials, only requiring a film thin, enough for sufficient EUV transmission.

Spectroscopic characterization of Si/Mo thin-film stack at extreme ultraviolet range.

A noninvasive method for characterizing Si/Mo thin-film stack thickness and its complex transfer function using common-path optical coherence tomography is proposed, analyzed, and experimentally demonstrated. A laser-produced plasma (LPP)-based extreme ultraviolet (EUV) source was excited by a four-stage nanosecond Yb:fiber laser amplifier with a pulse energy of 1.01mJ. The tabletop LPP EUV source was compact and stable for generating the EUV interference fringes. The measured complex transfer function of the Si/Mo stack was verified near the pristine 13.5-nm wavelength range.

Novel EUV Photoresist for Sub-7 nm Node

Extreme ultraviolet (EUV) lithography has been recognized as a promising candidate for the manufacturing of semiconductor devices as LS/CH pattern for 7 nm node and beyond. EUV lithography is ready for high volume manufacturing stage. For the high-volume manufacturing of semiconductor devices, significant improvement of sensitivity and line edge roughness (LWR) and Local CD Uniformity (LCDU) is required for EUV resist. It is well-known that the key challenge for EUV resist is the simultaneous requirement of ultrahigh resolution (R), low line edge roughness (L) and faster sensitivity (S). Especially sensitivity and good roughness is important for EUV lithography high volume manufacturing. We are trying to improve sensitivity and LWR/LCDU from many directions. From material side, we found that both sensitivity and LWR/LCDU are simultaneously improved by controlling acid diffusion length and efficiency of acid generation using novel resin and PAG. And optimizing EUV integration is one of the good solution to improve sensitivity and LWR/LCDU. We are challenging to develop new multi-layer materials to improve sensitivity and LWR/LCDU. Our new multi-layer materials are designed for best performance in EUV lithography system. From process side, we found that sensitivity was substantially improved maintaining LWR applying novel type of chemical amplified resist (CAR) and process. EUV lithography evaluation results obtained for new CAR EUV interference lithography. And, metal containing resist is one possibility to break through sensitivity and LWR trade off. In this paper, we will report the recent progress of sensitivity and LWR/LCDU improvement of JSR novel EUV resist and process.

Fabrication of ultrahigh resolution metal nanowires and nanodots through EUV interference lithography

We demonstrate the fabrication of high-resolution (sub-100nm) nanowires and nanodots using HSQ/PMMA bilayer resists for a negative-tone lift-off process. The high resolution patterning on HSQ layers was performed using EUV (extreme ultraviolet) interference lithography at the Swiss Light Source (SLS). The thicknesses of HSQ and of the sacrificial PMMA layers were optimized for different resolutions. We succeeded in transferring periodic HSQ nanoline structures with resolution as high as 16nm half-pitch into PMMA layers by O2 plasma etching and then into Cr/Au nanowires by metallization and lift-off. The duty cycles of the nanowires are varied by controlling the exposure doses of the irradiation light. HSQ nanodots and nanoholes are obtained by exposing the resist layer using a two-dimensional mask. After subsequent treatment, Cr/Au nanodots with sizes of 25nm–60nm are obtained.

Nearly amorphous Mo-N gratings for ultimate resolution in extreme ultraviolet interference lithography

We present fabrication and characterization of high-resolution and nearly amorphous Mo1 − xNx transmission gratings and their use as masks for extreme ultraviolet (EUV) interference lithography. During sputter deposition of Mo, nitrogen is incorporated into the film by addition of N2 to the Ar sputter gas, leading to suppression of Mo grain growth and resulting in smooth and homogeneous thin films with a negligible grain size. The obtained Mo0.8N0.2 thin films, as determined by x-ray photoelectron spectroscopy, are characterized to be nearly amorphous using x-ray diffraction. We demonstrate a greatly reduced Mo0.8N0.2 grating line edge roughness compared with pure Mo grating structures after e-beam lithography and plasma dry etching. The amorphous Mo0.8N0.2 thin films retain, to a large extent, the benefits of Mo as a phase grating material for EUV wavelengths, providing great advantages for fabrication of highly efficient diffraction gratings with extremely low roughness. Using these grating masks, well-resolved dense lines down to 8 nm half-pitch are fabricated with EUV interference lithography.

Broadband transmission masks, gratings and filters for extreme ultraviolet and soft X-ray lithography

Lithography and patterning on a nanometre scale with extreme ultraviolet (EUV) and soft X-ray radiation allow creation of high resolution, high density patterns independent of a substrate type. To realize the full potential of this method, especially for EUV proximity printing and interference lithography, a reliable technology for manufacturing of the transmission masks and gratings should be available. In this paper we present a development of broadband amplitude transmission masks and gratings for extreme ultraviolet and soft X-ray lithography based on free-standing niobium membranes. In comparison with a standard silicon nitride based technology the transmission masks demonstrate high contrast not only for in-band EUV (13.5nm) radiation but also for wavelengths below Si L-absorption edge (12.4nm).The masks and filters with free standing areas up to 1000×1000μm2 and 100nm to 300nm membrane thicknesses are shown. Electron beam structuring of an absorber layer with dense line and dot patterns with sub-50nm structures is demonstrated. Diffractive and filtering properties of obtained structures are examined with EUV radiation from a gas discharge plasma source.

Generation of extreme ultraviolet vortex beams using computer generated holograms

We fabricate computer generated holograms for the generation of phase singularities at extreme ultraviolet (EUV) wavelengths using electron beam lithography and demonstrate their ability to generate optical vortices in the nonzero diffraction orders. To this end, we observe the characteristic intensity distribution of the vortex beam and verify the helical phase structure interferometrically. The presented method forms the basis for further studies on singular light fields in the EUV frequency range, i.e., in EUV interference lithography. Since the method is purely achromatic, it may also find applications in various fields of x ray optics.

Sub-10 nm patterning using EUV interference lithography

Extreme ultraviolet (EUV) lithography is currently considered as the leadingtechnology for high-volume manufacturing below sub-20 nm feature sizes. In parallel,EUV interference lithography based on interference transmission gratings hasemerged as a powerful tool for industrial and academic research. In this paper,we demonstrate nanopatterning with sub-10 nm resolution using this technique.Highly efficient and optimized molybdenum gratings result in resolved line/spacepatterns down to 8 nm half-pitch and show modulation down to 6 nm half-pitch.These results show the performance of optical nanopatterning in the sub-10 nmrange and currently mark the record for photon-based lithography. Moreover,an efficient phase mask completely suppressing the zeroth-order diffraction andproviding 50 nm line/space patterns over large areas is evaluated. Such efficient phasemasks pave the way towards table-top EUV interference lithography systems.

Development of interference lithography for 22nm node and below

An extreme ultraviolet (EUV) interference lithographic exposure tool was installed at the long undulator beamline in NewSUBARU to evaluate EUV resists for 25nm node and below. The two-window transm...

Transmission Grating Fabrication for Replicating Resist Patterns of 20 nm and Below

We proceed to develop the extreme ultraviolet (EUV) interference lithographic exposure tool to determine whether the obtained resist could satisfy the requirement for the 20 nm node and below down to the 11 nm node. Transmission grating fabrication is a key technology in EUV interference lithography (EUV-IL). To replicate a 20 nm line and space resist pattern, a 40 nm line and space (L/S) pattern is required for the transmission grating. In the hard mask process, by optimizing the resist thickness to 60 nm and the dry etching conditions, and improving the alignment procedure for back-side etching, the 40 and 35 nm L/S patterns of the transmission grating were successfully fabricated. In addition, by applying a chemically amplified resist to adopt the center stop process in the transmission fabrication process and optimizing the resist thickness to attenuate completely the 0th order light, which was transmitted through the absorber and membrane, we succeeded in increasing the light intensity of the interference fringes and in replicating the 20 nm L/S resist pattern on a wafer. Furthermore, the chemically amplified molecular resist in the positive tone was confirmed to have a 20 nm resolution.

Development of interference lithography for 22 nm node and below

An extreme ultraviolet (EUV) interference lithographic exposure tool was installed at the long undulator beamline in NewSUBARU to evaluate EUV resists for 25nm node and below. The two-window transmission grating of 40 and 50nm half pitch (hp) were fabricated with techniques of spattering, electron beam lithography, dry etching and wet etching. hp patterns (20 and 25nm) of chemically amplified resist (CAR) and non-CAR were successfully replicated using the EUV interference lithographic exposure tool.

Chain scission resists for extreme ultraviolet lithography based on high performance polysulfone-containing polymers

A series of polymers with a comb architecture were prepared where the poly(olefin sulfone) backbone was designed to be highly sensitive to extreme ultraviolet (EUV) radiation, while the well-defined poly(methyl methacrylate) (PMMA) arms were incorporated with the aim of increasing structural stability. It is hypothesized that upon EUV radiation rapid degradation of the polysulfone backbone will occur leaving behind the well-defined PMMA arms. The synthesized polymers were characterised and have had their performance as chain-scission EUV photoresists evaluated. It was found that all materials possess high sensitivity towards degradation by EUV radiation (E0 in the range 4–6 mJ cm−2). Selective degradation of the poly(1-pentene sulfone) backbone relative to the PMMA arms was demonstrated by mass spectrometry headspace analysis during EUV irradiation and by grazing-angle ATR-FTIR. EUV interference patterning has shown that materials are capable of resolving 30 nm 1 : 1 line : space features. The incorporation of PMMA was found to increase the structural integrity of the patterned features. Thus, it has been shown that terpolymer materials possessing a highly sensitive poly(olefin sulfone) backbone and PMMA arms are able to provide a tuneable materials platform for chain scission EUV resists. These materials have the potential to benefit applications that require nanopattering, such as computer chip manufacture and nano-MEMS.

Photon-beam lithography reaches 12.5nm half-pitch resolution

We have printed dense line/space patterns with half-pitches as small as 12.5nm in a negative-tone calixarene resist using extreme ultraviolet (EUV) interference lithography. The EUV interference setup which is based on transmission diffraction gratings is illuminated with spatially coherent radiation from a synchrotron source. The results show the extendibility of EUV lithography to printing features measuring less than 15nm in size. We discuss the potential impact of effects such as photoelectron blur and shot noise in high-resolution EUV lithography.

High performance resist for EUV lithography

As the semiconductor industry moves to the 32 nm node, it becomes apparent that new lithography technology will be needed. One possibility for fabricating this feature size is extreme ultraviolet (EUV) technology. With the advent of EUV, new high performance resist materials will need to be developed. This study looks at the use of a poly[4-hydroxystyrene- co-2-(4-methoxybutyl)-2-adamantyl methacrylate] system as a possible candidate material for extreme ultraviolet lithography (EUVL). This material was synthesized and evaluated as an EUV chemically amplified resist. This resist system showed reasonable sensitivity and contrast compared to conventional PMMA resist. This resist system exhibits both negative and positive tone behavior at high and low dose, respectively. A negative pattern of 35 nm L/S (70 nm pitch) was printed using the transmission-grating EUV Interference Lithography (EUV-IL) tool [J.K. Chen, F.H. Ko, H.L. Chen, F.C. Chang, Jpn. J. Appl. Phys. 42 (2003) 3838]. A positive pattern of 50 nm (pitch 180 nm) was achieved using the EUVL tool at Sandia National Laboratory [Synchrotron Radiation Center website www.src.wisc.edu & Center for Nanotechnology website www.nanotech.wisc.edu]. Resist patterns were characterized in detail using scanning electron microscopy and atomic force microscopy. Both showed similar characteristics of the pattern lines.

Exploring the ultimate resolution of positive-tone chemically amplified resists: 26 nm dense lines using extreme ultraviolet interference lithography

Interference lithography (IL) [Yen et al., Appl. Opt. 31, 2972 (1992)] based on reflective optics, and utilizing extreme ultraviolet (EUV) light from an electron storage ring, can be used to pattern structures with periods below 70 nm [Solak et al., Appl. Phys. Lett. 75, 2328 (1999); Ali et al., Microelectron. Eng. 65, 454 (2003)]. Previously achromatic interferometers with EUV transmission diffraction gratings were also used for this purpose [Wei et al., J. Vac. Sci. Technol. B 12, 3648 (1994)], and recently we have printed sub-50 nm high quality periodic structures in poly(methylmethacrylate) exposed with transmission-grating EUV interference lithography (EUV-IL) [Solak et al., Microelectron. Eng. 61, 77 (2002); Solak et al., ibid. 67-68, 56 (2003)]. With this technique, two-dimensional patterns are easily achievable using multiple diffraction gratings. Both types of EUV-IL have been implemented on one of the undulator beam lines at the University of Wisconsin-Madison Synchrotron Radiation Center electron storage ring because this undulator source provides a tunable and coherent beam of radiation well suited for IL studies. In this article, both exposure methods were applied to explore the ultimate resolution of two positive-tone chemically amplified resists supplied by the Shipley Corporation. We have demonstrated the printing of features as small as 26 nm line and space in Shipley XP9947W-100 resist. The present results demonstrate the fine quality of the above-mentioned EUV-IL techniques to test resist formulations for high-resolution patterning, and we provide the experimental setup and discuss the observed results.

Four-wave EUV interference lithography

We have developed a multiple beam Extreme Ultraviolet (EUV) interference lithography system to create two-dimensional periodic structures. A spatially coherent EUV beam from an undulator source is diffracted by several transmission gratings, which were written by electron beam lithography. Interference pattern due to the diffracted beams is recorded on a photoresist coated substrate. Square array of holes with a 141-nm periodicity were written in initial tests. In this paper, we discuss the potential of this technique for extremely high-resolution patterning and issues related to illumination coherence and polarization.