[120] The bandwidth of EUV light reflected by a multilayer mirror used for EUV lithography is over +/-2% (>270 pm);[121] the phase changes due to wavelength changes at a given illumination angle may be calculated[122] [333], In 2015, ASML disclosed details of its anamorphic next-generation EUV scanner, with an NA of 0.55. Phys. A. Erdmann, P. Evanschitzky, T. Fuhrer, Proc. In the most recent measurement of the significant impact of secondary electrons on resolution, it was found that 93eV photoelectrons (from a gold underlayer) had a 1/e attenuation length of 28nm in resist. OoB light exposure may be alleviated by a layer coated above the resist, as well as 'black border' features on the EUV mask. [38] Consequently, there could be uncorrected variations across slit for aberration-sensitive features, which may not be obviously seen with regular line-space patterns. The polaron size can be quite large in resists, e.g., 46nm in PMMA. To help mitigate the above effects, the latest EUV tool introduced in 2017, the NXE:3400B, features a membrane that separates the wafer from the projection optics of the tool, protecting the latter from outgassing from the resist on the wafer. [207] The dose-dependent spread of secondary electrons was also known before from electron beam lithography. But EUV light is absorbed by . [51] A dose error over 2% warrants tool downtime.[51]. [147] This results in fewer photons defining smaller features (see discussion in section on shot noise). SPIE 9776, 97761R (2016). [191][192] Increasing the dose increases the number of far-reaching electrons, resulting in more extended resist loss. [194][272] The randomness of the number of secondary electrons is itself a source of stochastic behavior in EUV resist images. [200][199] The scale length of electron blur itself has a distribution. All optical elements, including the photomask, must use defect-free molybdenum/silicon (Mo/Si) multilayers (consisting of 40 Mo/Si bilayers) that act to reflect light by means of interlayer interference; any one of these mirrors absorb around 30% of the incident light. [307][308], For pitches less than half-wavelength divided by numerical aperture, dipole illumination is necessary. The process uses a laser with a 13.5 nanometer wavelength. MEMS MOEMS 18, 040501 (2019). The existing ones used traditional glass lenses to focus light onto the wafer. [245], GlobalFoundries and Lawrence Berkeley Labs carried out a Monte Carlo study to simulate the effects of intermixing between the molybdenum (Mo) and silicon (Si) layers in the multilayer that is used to reflect EUV light from the EUV mask. Lett. In other words, the less absorbing the resist, the more vertically uniform the absorption. This illumination fills at most a leaf-shaped area at the edge of the pupil. [42] As of 2016, the established EUV light source is a laser-pulsed tin plasma. SPIE 10583, 1058312 (2018). H-W Kim et al., Proc. Bulk hydrogen solutions for extreme ultra-violet lithography. Due to the varying shadowing sensitivity across the slit, the repair deposition height must be controlled very carefully, being different at different positions across the EUV mask illumination slit. S-M. Kim et al., Proc. [195] Unfortunately, hardmask layers tend to increase photoelectron emission, degrading the depth of focus. SPIE 9422, 94220A (2015). Double- or multiple-patterning would also be required if a pattern consists of sub-patterns which require significantly different optimized illuminations, due to different pitches, orientations, shapes, and sizes. Should photon-based lithography still be used for patterning smaller feature sizes, beyond EUV (BEUV) lithography at 6.x nm wavelength is an option that could potentially meet the rigid demands of . A. Narasimhan et al., "Mechanisms of EUV Exposure: Internal Excitation and Electron Blur", EUV Symposium 6/16/2016, p.11. [214], Due to the high efficiency of absorption of EUV by photoresists, heating and outgassing become primary concerns. A. Erdmann, P. Evanschitzky, and T. Fuhner, Proc. The behavior of light rays within the plane of reflection (affecting horizontal lines) is different from the behavior of light rays out of the plane of reflection (affecting vertical lines). EUV mask defect repair is also more complicated due to the across-slit illumination variation mentioned above. A lithography (more formally known as 'photolithography') system is essentially a projection system. [208], The increased secondary electron blur with increased dose makes control of stochastic defects more difficult. MEMS MOEMS 15, 021205 (2016). SPIE 10143, 101431S (2017). This wavelength is more than 14 times shorter than DUV light. Products EUV lithography systems Using EUV light, our NXE systems deliver high-resolution lithography and make mass production of the world's most advanced microchips possible Using a wavelength of just 13.5 nm (almost x-ray range), ASML's extreme ultraviolet (EUV) lithography technology can do big things on a tiny scale. 143, 91101 (2015). Die Size Tradeoff Due to EUV Pupil Rotation", "Horizontal, Vertical, and Slanted Line Shadowing Across Slit in Low-NA and High-NA EUV Lithography Systems", "Adaptive Optics to Counteract Thermal Aberrations: System Design for EUV-Lithography with Sub-nm Precision", "Mentor Graphics Director Details Challenges for Edge Placement Control in 2020", "Nonideal Imaging in EUV Lithography Systems", "Out-of-band exposure characterization with the SEMATECH Berkeley 0.3-NA microfield exposure tool", "Measurement and characterization of EUV mask performance at high-NA | EECS at UC Berkeley", "Carl Zeiss SMT GMbH, Semicon Europa, Nov. 16 2018", "[PDF] Properties of broadband depth-graded multilayer mirrors for EUV optical systems. This can be correlated with the phase difference between the zero and first diffraction orders. [105][106][101] Annular illumination nonuniformity and asymmetry also significantly impact the imaging. L. van Look et al., Proc. J. M. Bayraktar et al., Opt. Spec. [76], The off-axis illumination of the reticle is also the cause of non-telecentricity in wafer defocus, which consumes most of the 1.4nm overlay budget of the NXE:3400 EUV scanner[77] even for design rules as loose as 100nm pitch. SPIE 4754, 1 (2002). For the k1 approaching 0.5, some weak resolution enhancement including attenuated phase shift masks has been used as essential to production with the ArF laser wavelength (193nm),[172][173][174][175][176][177] whereas this resolution enhancement is not available for EUV. For the 40nm pitch vertical lines, an 18nm nominal tip-to-tip drawn gap resulted in an actual tip-to-tip distance of 29nm with OPC (optical proximity correction),[105] while for 32nm pitch horizontal lines, the tip-to-tip distance with a 14nm nominal gap went to 31nm with OPC. EUV lithography is a fabrication method that produces light with a 13.5-nm wavelength, which is short enough to produce large features on a chip. [252] At target 250W levels, the pellicle is expected to reach 686 degrees Celsius,[253] well over the melting point of aluminum. and Rel. Aside from the resolution impact, higher dose also increases outgassing[297] and limits throughput, and crosslinking[298] occurs at very high dose levels. [240] Defects can be buried underneath or within the multilayer stack[241] or be on top of the multilayer stack. ASML has followed the guidelines of Dutch export controls and until further notice, will have no authority to ship the machines to China. The sun produces EUV; humans create it through synchrotrons, or from plasma. 22, 30623 (2014). 123, 063301 (2018). After enabling the EUV wavelength, the industry is looking into increasing the NA. [183] At sufficient doses 40eV electrons are known to penetrate 180nm thick resist leading to development. 241, 146824 (2020). [129], A narrower bandwidth would increase sensitivity to mask absorber and buffer thickness on the 1nm scale.[130][131]. [72] More significantly, mask defocus has been found to result in large overlay errors. We have designed and studied a high-power EUV free-electron laser (FEL) based on energy-recovery linac (ERL) for future lithography. [190], The process of electron penetration through a resist is essentially a stochastic process; there is a finite probability that resist exposure by released electrons can occur quite far from the point of photon absorption. A key challenge for EUV is the counter-scaling behavior of the line tip-to-tip (T2T) distance as half-pitch (hp) is scaled down. The coupling between the primary image and the self images is too strong for the asymmetry to be eliminated by assist features; only asymmetric illumination can achieve this. These challenges arise from smaller fields, additional mirrors, and shot noise. This study aims to identify EUV specific challenges regarding NA scaling beyond 0.55. Labs in the US and the Netherlands soon also began to explore this potential new development in lithography. Depth of focus[337] being reduced by increasing NA is also a concern,[338][333] especially in comparison with multi-patterning exposures using 193nm immersion lithography: High-NA EUV tools also suffer from obscuration, which can cause errors in the imaging of certain patterns. Rice, in Nanolithography, 2014 2.1.2 EUV lithography: the basics To print ever smaller features at high contrast projection lithography technology has evolved to shorter wavelength light and larger NA. Ionization must precede EUV emission in matter. A. Narasimhan et al., Proc. SPIE 10450, 1045008 (2017). SPIE 2726, 146 (1996). Quantum yield makes the resist response comparable for chemically amplified resists for both ArF and EUV wavelengths, but ArF resists also allow larger blur, enabling further smoothing. L. C. Choo et al., Proc. [53] A state-of-the-art ArF immersion lithography 120 W light source requires no more than 40kW[54] while EUV sources are targeted to exceed 40kW. SPIE 11328, 113280V (2020). [288] It is worse for EUV than DUV wavelengths due to lower photon density at commonly used doses, as well as smaller feature sizes being represented by smaller pixels. [138] More conventionally, optical proximity correction (OPC) is used to address the corner rounding and line-end shortening. SPIE 9048, 90480Q (2014). [255] Hydrogen plasmas can also etch silicon as well. [76] With the blank peak-to-valley spec of 50nm, ~1.25nm image placement error is possible. The situation is specifically challenging for logic devices, where multiple pitches have critical requirements at the same time. SPIE 11327, 113270X (2020). The entire system is about one and a half meters high, weighs about 3.5 tons and consists of more than 35,000 individual parts. [212] Such large electric fields have been observed to lead to dielectric breakdown. [328][322], Multiple exposures of the same mask are also expected for defect management without pellicles, limiting productivity similarly to multiple-patterning. M. Muller et al., Appl. However, graphite, graphene or other carbon nanomaterials (nanosheets, nanotubes) are damaged by EUV due to the release of electrons[254] and also too easily etched in the hydrogen cleaning plasma expected to be deployed in EUV scanners. SPIE 4691, 476 (2002). [51], The EUV light source limits tool uptime besides throughput. EUV generation An 18nm metal linewidth has a k1 of 0.44 for 13.5nm wavelength, 0.33 NA, for example. Comment. SPIE 9661, 96610G (2015). SPIE 2726 (1996)", "EUV pattern shift compensation strategies - art. [1][2] At IEDM 2020, TSMC reported its 5nm node minimum metal pitch to be reduced 30% (to ~28nm) from that of its 7nm node,[3] which was 40nm. [206] This is associated with fewer trapping sites as dose is increased and the reactions depleting the trapping sites proceed. SPIE 10583, 105830U (2018). Due to the stochastic variations in arriving photon numbers, some areas designated to print actually fail to reach the threshold to print, leaving unexposed defect regions. In a two-week period, for example, over seven hours downtime may be scheduled, while total actual downtime including unscheduled issues could easily exceed a day. The thermal production of multicharged positive ions is only possible in a hot dense plasma, which itself strongly absorbs EUV. 108, 263 (2012). As SRAFs are smaller features than primary features and are not supposed to receive doses high enough to print, they are more susceptible to stochastic dose variations causing printing errors. [68][69] Ultimately, this results in different positions of best focus for different pitches and different illumination angles. Simulations as well as experiments have shown that pupil imbalances in EUV lithography can result in pitch-dependent pattern placement errors. Despite greater transparency of the resist, the incident photon flux is about 14 times larger (193/13.5) for the same energy dose per unit area. The parts to be excluded depend on the pattern. The coexistence of stochastically underexposed and overexposed defect regions leads to a loss of dose window at a certain post-etch defect level between the low-dose and high-dose patterning cliffs. The two issues of shot noise and EUV-released electrons point out two constraining factors: 1) keeping dose high enough to reduce shot noise to tolerable levels, but also 2) avoiding too high a dose due to the increased contribution of EUV-released photoelectrons and secondary electrons to the resist exposure process, increasing the edge blur and thereby limiting the resolution. | Semantic Scholar", "The Very Different Wavelengths of EUV Lithography", Fundamental Principles of Optical Lithography, Thin Half-tone Phase Shift Mask Stack for Extreme Ultraviolet Lithography, "Stochastic Printing of Sub-Resolution Assist Features", The Need for Low Pupil Fill in EUV Lithography. [125] Conversely, the peak reflected wavelength varies across the pupil due to different incident angles. [260], Self-aligned litho-etch-litho-etch (SALELE) is a hybrid SADP/LELE technique whose implementation has started in 7nm[329] and continued use in 5nm. [210] The trapping of secondary electrons leads to a reduction of secondary electrons emitted from the film;[210] however, the trap sites may themselves be depleted, resulting in effectively extended secondary electron blur for larger doses. R. Capelli et al., Proc. [84][85], The direction of illumination is also highly dependent on slit position, essentially rotated azimuthally. SPIE 9776, 97762D (2016). The EUV technology was considered impossible by many. [235], Hydrogen also reacts with resists to etch[236][237] or decompose[238] them. Alternative materials need to allow sufficient transmission as well as maintain mechanical and thermal stability. The peak reflectance wavelength increases for smaller incident angles. In fact, for the application to the two-bar asymmetry case, the optimum assist feature placement may be less than or exceed the two-bar pitch. Extreme ultraviolet (sometimes also called XUV) denotes soft x-rays with wavelengths between 124 and 10 nm or photon energies between 10 eV and 124 eV. Blank thickness variations up to 80nm also contribute, which lead to up to 2nm image shift. The scanner uses Zeiss optics, which that company calls "the most precise mirrors in the world" and are produced by locating imperfections and then knocking off individual molecules with techniques such as ion beam figuring. This led MIT Technology Review to name it 'the machine that saved Moore's law'. X. Liu et al., Proc. I. V. Fomenkov, Proc. [159] At 36nm pitch, horizontal and vertical darkfield features have more than 30nm difference of focus. In a system, an EUV light source makes use of a high power laser to create a plasma. G. J. Stagaman et al., Proc. Pellicles are normally expected to protect the mask from particles during transport, entry into or exit from the exposure chamber, as well as the exposure itself. MEMS MOEMS 9, 023001 (2010). SPIE 10583, 1058321 (2018). Finders et al., Proc. Then leading producers of steppers Canon and Nikon stopped development, and some predicted the end of Moore's law. H. J. Levinson and T. A. Brunner, Proc. [234] These are essentially the blister defects which arise after a sufficient number of EUV mask exposures in the hydrogen environment. Wafer defocus also leads to image placement errors due to deviations from local mask flatness. In this case, the lower limit is around 30nm. On the other hand, for EUV, this conflicts with the goal of increasing absorption for more sensitivity at current EUV power levels. 55, 095108 (2016). Reducing defects on extreme ultraviolet (EUV) masks is currently one of the most critical issues to be addressed for commercialization of EUV lithography. Phase-Shifting Masks for NILS Improvement - A Handicap for EUV? [249], Heating of the EUV mask pellicle (film temperature up to 750K for 80W incident power) is a significant concern, due to the resulting deformation and transmission decrease. [196], The generation of photoelectrons in the photoresist itself is a fundamental part of the image formation, and is marked by a random spread which increases with dose. MEMS MOEMS 2, 2733 (2003). SPIE 8322, 832229 (2012). Tech. SPIE 10959, 1095904 (2019). T. E. Brist and G. E. Bailey, Proc. 191194, 439 (1992). [184] At a dose of 160C/cm2, corresponding to 15mJ/cm2 EUV dose assuming one electron/photon, 30eV electrons removed 7nm of PMMA resist after standard development. 28, 1268 (1981). EUV Lithography. The demagnification is increased from 4x to 8x only in one direction (in the plane of incidence). Masks are then inspected and later repaired using an electron beam. While state-of-the-art 193nm ArF excimer lasers offer intensities of 200W/cm2,[52] lasers for producing EUV-generating plasmas need to be much more intense, on the order of 1011 W/cm2. The dose variation leads to a variation of the feature edge position, effectively becoming a blur component. [49] The membrane contains layers which absorb DUV and IR radiation, and transmits 8590% of the incident EUV radiation. In the semiconductor industry, EUV refers to extreme ultraviolet lithography, a technology that is expected to bring a radical progress to one of the most important steps in semiconductor manufacturing, photolithography. ASML ASML reported first-quarter results ahead of our expectations thanks to strong system sales. [127] Aperiodic multilayers have been proposed to reduce the sensitivity at the cost of lower reflectivity but are too sensitive to random fluctuations of layer thicknesses, such as from thickness control imprecision or interdiffusion. S-S. Yu et al., Proc. [55], The power target for EUV lithography is at least 250W, while for other conventional lithography sources, it is much less. [95] The reason for this is a mirror is used to transform straight rectangular fields into arc-shaped fields. J. Fu et al., Proc. EUV lithography, a technology entirely unique to ASML, uses light with a wavelength of 13.5 nanometers. T. Van de Ven et al., J. Appl. [144] Generally, there is still a focus-exposure tradeoff as the dose window is constrained by the need to have the assist features not print accidentally. D. M. Williamson, Proc. Y. Wang and Y. Liu, Proc. This article is a basic primer on this important yet complex technology. SPIE 9776, 97762O (2016). Low-energy electron-induced events also increase in number at a given distance from the photon absorption site, as dose is increased. [44] A higher dose requires a slower stage motion (lower throughput) if pulse power cannot be increased. The pattern is defined in a tantalum-based absorbing layer over the multilayer. [210] An EUV exposure with less blur leads to more pronounced charge differences at the feature edge,[211] which can lead to larger electric fields. We show that the EUV-FEL light source has many advantages, such as . SPIE 5900, 59000G (2005). [260] These wafers are inspected after printing for repeating defects indicating a dirty mask; if any are found, the mask must be cleaned and another set of inspection wafers are exposed, repeating the flow until the mask is clean. Thus enables structures with dimensions of less than 20 nanometers. B. Bilski et al., Proc. Computer modeling of contamination and cleaning of EUV source optics, The Denitridation of Nitrides Under Hydrogen, "C. G. van de Walle and B. Tuttle, THEORY OF HYDROGEN INTERACTIONS WITH AMORPHOUS SILICON in, "Hydrogen-induced blistering in thin film multilayers", "Ruthenium gate electrodes on SiO2 and HfO2: Sensitivity to hydrogen and oxygen ambients", "Screening of oxidation-resistance capping layers", "Hydrogen plasma for photoresist stripping", "Getting up to speed with roadmap requirements for extreme-UV lithography", "Fast Simulation Methods for Non-Planar Phase and Multilayer Defects in DUV and EUV Photomasks for Lithography", "EUVL activities in South Korea (including Samsung and SKHynix)", "EUV Pellicle, Uptime And Resist Issues Continue", "TSMC Manufacturing Update: N6 to Match N7 Output by EOY, N5 Ramping Faster, Better Yields Than N7", "Samsung to develop 'Pellicle', an essential EUV process product - ETNews", Visualizing EUV Stochastics for a 14nm DRAM Example, EUV Resist Absorption Impact on Stochastic Defects, CD-pitch combinations disfavored by EUV stochastics, The Stochastic Impact of Defocus in EUV Lithography, "Localized and cascading secondary electron generation as causes of stochastic defects in extreme ultraviolet projection lithography", Hot Spots for Stochastic Defects in EUV Lithography, Sub-Resolution Assist Features and Stochastic EUV Sidelobe Printing, Visualizing EUV's Stochastic Valley of Death, "S. Bhattarai, PhD Thesis,"Study of Line Edge Roughness and Interactions of Secondary Electrons in Photoresists for EUV Lithography," U. Calif. Berkeley, 2017", "From Shot Noise to Stochastic Defects: Dose-Dependent Gaussian Blur in Lithography", A Demonstration of Stochastic Edge Placement Error (EPE), Stochastic Origins of EUV Feature Edge Roughness, Stochastic Behavior of Shape Edges in EUV Lithography, Stochastic Effects from Photon Distribution Entropy in High-k1 EUV Lithography, Contrast Reduction vs. Photon Noise in EUV Lithography, Revisiting EUV Lithography: Post-Blur Stochastic Distributions, "Reduction of Line Edge Roughness (LER) in Interference-Like Large Field Lithography", "2013 Nissan Chemical Industries, 2013 International Workshop on EUV Lithography", Resolution, LER, and Sensitivity Limitations of Photoresist, "Samsung 18 nm DRAM cell integration: QPT and higher uniformed capacitor high-k dielectrics", "Prices for DRAMs Continue to Climb while NAND Flash ASPs Drop", "SemiWiki.com - Top 10 Highlights from the TSMC Open Innovation Platform Ecosystem Forum", "Cadence Achieves EDA Certification for TSMC 5nm and 7nm+ FinFET Process Technologies to Facilitate Mobile and HPC Design Creation", "Synopsys Digital and Custom Design Platforms Certified on TSMC 5-nm EUV-based Process Technology", "Intel presentation on Complementary Lithography at 2012 International Workshop on EUV Lithography", "EUV was never going to be single patterning", SALELE double patterning for 7nm and 5nm nodes, Intel's Xeon E5-2600 V4 Chips Feature An Insane 7.2 Billion Transistors on a 456mm2 Die, Idiosyncrasies of Obstructed High-NA EUV Imaging, Stochastic Sidelobe Risks and Tradeoffs in High-NA EUV Systems With the Central Pupil Obscuration, Pitches Forbidden by the Central Obscuration in High-NA EUV Lithography, Obscuration-Induced Pitch Incompatibilities in High-NA EUV Lithography, 36 nm Pitch on High-NA EUV: Obscured Diffraction Across Slit, Printing of Stochastic Sidelobe Peaks and Valleys in HIgh NA EUV Lithography, High NA EUV Design Limitations for 1 x nm Nodes, Reality Checks for High-NA EUV for 1.x nm Nodes, "ASML presentation at 2010 International Workshop on Extreme Ultraviolet Sources", "Beyond EUV lithography: a comparative study of efficient photoresists' performance", "Extreme Ultraviolet Lithography: Towards the Next Generation of Integrated Circuits", Radio-frequency microelectromechanical systems, Biological microelectromechanical systems, https://en.wikipedia.org/w/index.php?title=Extreme_ultraviolet_lithography&oldid=1157056240, Articles with dead external links from December 2019, Articles with permanently dead external links, Short description is different from Wikidata, Articles containing potentially dated statements from 2023, All articles containing potentially dated statements, Articles with unsourced statements from May 2023, Creative Commons Attribution-ShareAlike License 3.0, Reflective multilayers (~40% absorbing per mirror), This page was last edited on 26 May 2023, at 00:43. 69211B", "Rutgers University Department of Physics and Astronomy", "H. Mizoguchi et al., 2017 EUV-FEL Workshop, p. 4", "Polarization by Reflection in EUV Lithography Systems", "The Growing Significance of Polarization in EUV Lithography", "The Uncertain Phase Shifts of EUV Masks", "Pattern Shifts Induced by Dipole-Illuminated EUV Masks", "Double Diffraction in EUV Masks: Seeing Through The Illusion of Symmetry", "Defocus Induced Image Shift in EUV Lithography", "Multiple Monopole Exposures: The Correct Way to Tame Aberrations in EUV Lithography? 4000, 1193 (2000). 47, 4944 (2008). Q. Lin, Proc. no. M. Burkhardt et al., Proc. SPIE 11323, 113231L (2020). [citation needed]. [160] For the 3448nm pitch range, the best focus position shifts roughly linearly in the opposite direction as a function of pitch. The larger absorption leads to larger, more significant differences between the absorbed doses at the top and the bottom of the resist. Tech. Opt. R-H. Kim et al., Proc. Intel, Canon and Nikon (leaders in the field at the time), as well as ASML and Silicon Valley Group (SVG) all sought licensing, however Congress denied Japanese companies the necessary permission as they were perceived as strong technical competitors at the time, and should not benefit from taxpayer-funded research at the expense of American companies. The lower part of the resist layer is more susceptible to underexposure, due to absorption in the upper part. Other lithography machines use lenses to focus light. In actuality, the reflected power is distributed mostly in the 13.3-13.7nm range. The multilayer is also responsible for image shifting due to phase shifts from diffracted light within the multilayer itself. [334] However, the 0.55 NA has a much smaller depth of focus than immersion lithography. [71], The use of reflection causes wafer exposure position to be extremely sensitive to the reticle flatness and the reticle clamp. [349] With current technology, BEUV wavelengths would have worse shot noise effects without ensuring sufficient dose.[350]. With 11 reflections, only ~ 2% of the EUV source light is available at the wafer. [14] The multilayer may be protected by a thin ruthenium layer. [8], By 2018 Dutch company ASML succeeded in deploying the EUV-LLC IP after several decades of developmental research, with incorporation of European-funded EUCLIDES (Extreme UV Concept Lithography Development System) and long-standing partner German optics manufacturer ZEISS and synchrotron light source supplier Oxford Instruments. Light is projected through a blueprint of the pattern that will be printed (known as a 'mask' or 'reticle'). "Resolution vs. In the 4864nm pitch range, the best focus position shifts roughly linearly as a function of pitch, by as much as 1020nm. SPIE 4691, 1537 (2002). [19] The exposed photoresist is developed (removed) and the unprotected areas are etched. SPIE 10809, 1080903 (2018). [47] The carbon contamination is known to affect multilayer reflectivity[218] while the oxygen is particularly harmful for the ruthenium capping layers on the EUV multilayer optics.[219]. These photoelectrons in turn generate secondary electrons, which slow down before engaging in chemical reactions. [140] With OPC, these become 39nm and 28nm for 24nm half-pitch and 32nm half-pitch, respectively.[142]. Mat. [132] However, the layer coating inevitably absorbs EUV light, and the black border adds EUV mask processing cost. [9] The first prototype in 2006 produced one wafer in 23 hours. As of 2022, a scanner produces up to 200 wafers per hour. Chem. EUV light occurs naturally in outer space. [141], For larger pitches, where conventional illumination can be used, the line tip-to-tip distance is generally larger. The throughput is tied to the source power, divided by the dose. [153] This would necessitate the use of different source-mask combinations at each slit position, i.e., multiple mask exposures per layer.[115][158]. The tin vaporizes into plasma which emits EUV radiation. A. V. Pret et al., Proc. Due to stochastic considerations, the IRDS 2022 lithography roadmap now acknowledges increasing doses for smaller feature sizes. SPIE 8679, 867923 (2013). However, for EUV, the feasibility of pellicle use is severely challenged, due to the required thinness of the shielding films to prevent excessive EUV absorption. The above-mentioned chromatic aberrations, due to mask-induced apodization,[124] also lead to inconsistent source-mask optimizations for different wavelengths. M. Burkhardt and A. Raghunathan, Proc. [59] Additionally, the different polarizations (TE and TM) have different phase shifts. What is EUV? The EUV machine pushes Moore's Law forward and chip makers cannot produce leading-edge chips without it. Even if the defect height is shallow, the edge still deforms the overlying multilayer, producing an extended region where the multilayer is sloped. Self-aligned litho-etch-litho-etch (SALELE) has become an accepted form of double-patterning to be used with EUV, starting at the 5nm node, where some layers are 28nm pitch. TSMC reported starting limited use of its own pellicle in 2019 and continuing to expand afterwards,[261] and Samsung is planning pellicle introduction in 2022.[262]. D. Rio et al., Proc. The next step, going even smaller, was dubbed Extreme UV or EUV. [290], Another approach to dealing with stochastic issues is to use directional etching to smooth sidewall edges.[291]. D: Appl. SPIE 11323, 113232H (2020). Atomic hydrogen is produced by EUV light directly photoionizing H2: Electrons generated in the above reaction may also dissociate H2 to form atomic hydrogen: The reaction with tin in the light source or resist or on an optical surface to form volatile SnH4 proceeds via the reaction: The SnH4 can reach the coatings of other EUV optical surfaces, where it redeposits Sn via the reaction: Redeposition may also occur by other intermediate reactions. [281], Photon shot noise can be linked to stochastic defects through the presence of dose-dependent blur (modeled as Gaussian). SPIE 9235, 92350J (2014). [109], The slit position dependence is particularly difficult for the tilted patterns encountered in DRAM. D. Civay et al., Proc. D. De Simone et al., Advanced Lithography 2019, 10957-21. SPIE 10957, 1095710 (2019). [70] This is inevitable due to light passing twice through the mask pattern. SPIE 10809, 108090A (2018). [250] ASML developed a 70nm thick polysilicon pellicle membrane, which allows EUV transmission of 82%; however, less than half of the membranes survived expected EUV power levels. The mirror responsible for collecting the light is directly exposed to the plasma and is vulnerable to damage from high-energy ions[24][25] and other debris[26] such as tin droplets, which require the costly collector mirror to be replaced every year. [161] Assist features, if they can fit within the pitch, were found not to reduce this tendency much, for a range of intermediate pitches,[162] or even worsened it for the case of 1827nm and quasar illumination. SPIE vol. R. K. Ali et al., Proc. [222], The redeposited Sn[46][47] might be subsequently removed by atomic hydrogen exposure. L. Wisehart et al., Proc. [246] The results indicated high sensitivity to the atomic-scale variations of layer thickness. J-H. Franke et al., J. Micro/Nanopatterning, Materials, and Metrology 21, 030501 (2022). The results of this successful effort were disseminated via a public/private partnership Cooperative R&D Agreement (CRADA) with the invention and rights wholly owned by the US government, but licensed and distributed under approval by DOE and Congress. [194] On the other hand, for doses >500 uC/cm2, the resist begins to thicken due to crosslinking. M. van de Kerkhof et al., Proc. To address this scientific challenge, researchers at several United States Department of Energy (DOE) national laboratories (specifically Livermore, Berkeley, and Sandia) were funded in the 1990s to perform basic research into the technical obstacles. 42, 2301 (2003). The resist underlayer also plays an important role. The main uses of extreme ultraviolet radiation are photoelectron spectroscopy, solar imaging, and lithography. SPIE 7969, 79690H (2011). ", "Preparing for the Next Generation of EUV Lithography at the Center for X-ray Optics". Because it is such a key technology for development in many fields, the United States licenser pressured Dutch authorities to not sell these machines to China. [265] This could be due to the secondary electrons generated by the underlayer. Proc. SPIE 9422, 942208 (2015). Despite the potential of the optics to reach sub-20nm resolution, secondary electrons in resist practically limit the resolution to around 20nm (more on this below).[41]. MEMS MOEMS 16(4), 041013 (2017). Rev. A. N. Broers, IEEE Trans. EUV lithography uses light with an extremely short wavelength of 13.5 nanometers. World, 94, 25 (2000). S. Nagahara et al., Proc. D. Hellweg et al., Proc. [49], EUV is anticipated to use double-patterning at around 34nm pitch with 0.33NA. E. van Setten et al., Proc. Language links are at the top of the page across from the title. [186] These indicate the distances the electrons can travel in resist, regardless of direction.[187]. K. Lee et al., J. Microlith/Nanolith. Chem. Due to the effects of non-telecentricity, standard illumination pupil shapes, such as disc or annular, are not sufficient to be used for feature sizes of ~20nm or below (10nm node and beyond). Light is projected through a blueprint of the pattern that will be printed (known as a 'mask' or 'reticle'). This is primarily done using steppers and scanners, which are equipped with optical light sources. R. Socha, Proc. SPIE 7379, 73790P (2009). [133][134] The rounding of the corners of the line end leads to line end shortening,[135] and this is worse for binary masks. 177, 35 (2017). The NXE:3600D is equipped . [287] Since the blur is less than the feature size, the feature's total enclosed area can still have fluctuations. [206] Electron trapping is predicted to occur as part of polaronic behavior,[213][214] which confines the electron's final energy deposition to trap site locations. Generally, the image shift is balanced out due to illumination source points being paired (each on opposite sides of the optical axis). M.I.Jacobs et al., Phys. It is currently applied only in the most advanced semiconductor device fabrication. Direct photocurrent measurements have been used to obtain secondary electron yields in response to EUV radiation. S-Y. [200], Some patterns are more vulnerable to stochastic defects, due to pinching between corners,[273] or sidelobes.[274]. [80] For a depth of focus of 100nm, a small local deviation from flatness of 2.5 mrad (0.14) can lead to a pattern shift of 1nm. D. Rio et al, Proc. SPIE 10957, 1095719 (2019). [5], In the 1960s, visible light was used for IC-production, with wavelengths as small as 435 nm (mercury "g line"). [94] The rotating plane of incidence (azimuthal range within -25 to 25) is confirmed in the SHARP actinic review microscope at CXRO which mimics the optics for EUV projection lithography systems. Jang et al., Proc. An extension of the two-bar case to a grating consisting of many horizontal lines shows similar sensitivity to defocus. K. Hooker et al., Proc. The second pulse heats these to 220,000Celsius, 40 times hotter than the surface of the sun. [286], The photon shot noise is removed to some degree by blurring factors such as secondary electrons or acids in chemically amplified resists, but when too significant the blur also reduces the image contrast at the edge. W. Gillijns et al., Proc. A known significant contribution to this effect is the dose used to print. [322][326], In 2020, ASML reported that for the 3nm node, center-to-center contact/via spacings of 40nm or less would require double- or triple-patterning for some contact/via arrangements. [99] This is preferred, as reflective systems must use off-axis paths, which aggravate aberrations. SPIE 9422, 94220X (2015). [234][226] Hydrogen may also react with the capping layer, resulting in its removal. The best focus for a given feature size varies as a strong function of pitch, polarity, and orientation under a given illumination. [21], The tool consists of a laser-driven tin (Sn) plasma light source, reflective optics comprising multilayer mirrors, contained within a hydrogen gas ambient. Elec. [166] Critical layers often contain lines at one minimum pitch of one polarity, e.g., darkfield trenches, in one orientation, e.g., vertical, mixed with spaces of the other polarity of the other orientation. DUV vs. EUV Tool Energy Consumption (measured 2020):[31] EUV tools consume at least 10x more energy than immersion tools. [139], In unidirectional metal layers, tip-to-tip spacing is one of the more severe issues for single exposure patterning. SPIE 10809, 108090M (2018). T. Winkler et al., Prod. SPIE 8679, 86791L (2013). SPIE 5037, 494 (2003). [11], EUV photomasks work by reflecting light,[12] which is achieved by using multiple alternating layers of molybdenum and silicon. SPIE 7640, 76401H (2010). O. Yu et al., J. Elec. Z. G. Song et al., J. Phys. In air, EUV is the most highly absorbed component of the electromagnetic spectrum, requiring high vacuum for transmission. So if a new lithography tech requires vacuum, mirrors and a new source, you might as well do it right and jump down to 13.5nm. Tin-plasma sources used for lithography emit at 13.5nm, and other EUV applications are also adopting this wavelength as the standard. [45] This could be due to the accumulating Sn residue mentioned above which is not completely cleaned off. Even with annular or circular illumination, the rotational symmetry is destroyed by the angle-dependent multilayer reflectance described above. [165] The best focus position vs. pitch is also dependent on resist. SPIE 10143, 1014306 (2017). [292], In Intel's complementary lithography scheme at 20nm half-pitch, EUV would be used only in a second line-cutting exposure after a first 193nm line-printing exposure. J. Appl. The world's most powerful pulsed industrial laser To produce light with this wavelength, a special light source is needed. The EUV mask absorber, due to partial transmission, generates a phase difference between the 0th and 1st diffraction orders of a line-space pattern, resulting in image shifts (at a given illumination angle) as well as changes in peak intensity (leading to linewidth changes)[66][67] which are further enhanced due to defocus. SPIE 9048, 90483D (2014). As of 2023[update], ASML Holding is the only company who produces and sells EUV systems for chip production, targeting 5nm and 3nm process nodes. [310][311] This resolution is equivalent to '1Y' for DRAM. In EUV systems, this light can be EUV or out-of-band (OoB) light that is also produced by the EUV source. Today's EUV scanners enable resolutions down to 22nm half-pitch. However, due to 3D effects in the EUV mask,[309] smaller pitches require even smaller portions of this leaf shape. O. Adan and K. Houchens, Proc. Wood et al., Proc. SPIE 9776, 97761O (2015). L. Meli et al., J. Micro/Nanolith. SPIE 11325, 113251P (2020). SPIE 9776, 977617 (2016). It can be estimated that the contribution of mask non-flatness to overlay error is roughly 1/40 times the peak-to-valley thickness variation. Dev. [6] The CRADA consisted of a consortium of private companies and the Labs, manifested as an entity called EUV-LLC. J. G. Garofalo et al., Proc. SPIE 9231, 923109 (2014)", "M. van den Brink et al., Proc. [96][97] In order to preserve a fixed plane of incidence, the reflection from the previous mirror would be from a different angle with the surface for a different slit position; this causes non-uniformity of reflectivity. SPIE 10143, 101430R (2017). [46][47] On the other hand, conventional immersion lithography tools for double-patterning provide consistent output for up to a year. D. D. Simone et al., Proc. missing holes or bridging lines. [50] Source-mask optimization that is based on line-space gratings and tip-to-tip gratings only does not entail improvements for all parts of a logic pattern, e.g., a dense trench with a gap on one side. [163] 50nm contact holes on 100nm and 150 pitches had best focus positions separated by roughly 25nm; smaller features are expected to be worse. SPIE 6151, 615137 (2006). The Extreme Ultraviolet (EUV) Flat Mirrors are designed for use at 13.5nm because 13.5nm is one of the most commonly used EUV wavelengths. With the pattern encoded in the light, the system's optics shrink and focus the pattern onto a photosensitive silicon wafer.

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