Pattern formation mechanism of zirconia nanoparticle resist used for extreme-ultraviolet lithography (Conference Presentation)
Takahiro KozawaTeppei YamadaSatoshi IshiharaHiroki YamamotoYusa MuroyaJulius Joseph SantillanToshiro Itani
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The performance of chemically amplified resist is approaching its physical limit with the reduction of feature sizes due to the acid diffusion needed for the solubility change of resist polymer. The line edge roughness (LER) of chemically amplified resists rapidly increases in the sub-10-nm-half-pitch region when the half-pitch is decreased. Also, the stochastic defect (pinching and bridges) generation is a significant concern for the high resolution patterning with high throughput. To solve these problems, the increase of the density of resist films is an important strategy. Metal oxide nanoparticle resists have attracted much attention as the next generation resist used for the high-volume production of semiconductor devices because of their high density property. However, the sensitization mechanism of the metal oxide nanoparticle resists is unknown. Understanding the sensitization mechanism is important for the efficient development of resist materials. In the previous study[1], the numbers of electron-hole pairs required for the solubility change of the resist films were estimated for a zirconia nanoparticle and a ligand shell, respectively. In this study, the pattern formation mechanism of zirconia nanoparticle resist was investigated. The elementary reactions possibly induced in the zirconia nanoparticle resist were investigated using a pulse radiolysis method. The pulse radiolysis is a powerful method to directly observe the kinetics of short-lived intermediates produced by an ionizing radiation. The pattern formation mechanism was assumed by integrating the elementary reactions. The resist patterns fabricated using an EUV exposure tool were analyzed on the basis of the assumed pattern formation mechanism. In the material design of metal oxide nanoparticle resists, it is important to efficiently use the electron-hole pairs generated in nanoparticles for the chemical change of ligand molecules. Acknowledgement This work was partially supported by Ministry of Economy, Trade and Industry (METI) and the New Energy and Industrial Technology Development Organization (NEDO). Reference [1] T. Kozawa, J. J. Santillan, and T. Itani, "Electron–hole pairs generated in ZrO2 nanoparticle resist upon exposure to extreme ultraviolet radiation", Jpn. J. Appl. Phys. 57, 026501 (2018).Keywords:
Extreme Ultraviolet Lithography
Poly(p-t-butyloxycarbonyloxystyrene) resist shows great potential for electron-beam nanolithography, particularly as a negative resist. The resist has been used to fabricate structures with linewidths as narrow as 18 nm. The resist can be processed in both positive and negative modes depending upon the developing solvent, and linewidths <40 nm have been obtained in both cases. The exposure mechanism is based upon a new resist design principle incorporating an acid catalyst. The sensitivity of the resist can be at least six times higher than that of polymethylmethacrylate (PMMA) exposed under the same conditions (i.e., 50 kV, thin membrane substrates). The exposure distribution for the resist in the negative mode has been determined, confirming its resolution potential. These data indicate that the increase in sensitivity realized through incorporation of a gain mechanism in the resist chemistry is not achieved at a large loss in resolution. In its negative mode, the resist exhibits adequate ion etch resistance for device fabrication. The resist compares favorably with other negative resists for nanolithography with regards to both resolution, and its ability to be cleanly removed by rf plasma oxidation after serving as an ion etch mask.
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Resist profile shapes become important for 22nm node and beyond as the process window shrinks. Degraded profile shapes for example may induce etching failures. Rigorous resist simulators can simulate a 3D resist profile accurately but they are not fast enough for correction or verification on a full chip. Compact resist models are fast but have traditionally modeled the resist in two dimensions. They provide no information on the resist loss and sidewall angle. However, they can be extended to predict resist profiles by proper setting of optical parameters and by accounting for vertical effects. Large resist shrinkages in NTD resists can also be included in the compact model. This article shows how a compact resist model in Calibre can be used to predict resist profiles and resist contours at arbitrary heights.
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We have developed a DUV-defined-negative resist/EB-defined-positive resist two-layer resist system to fabricate T-shaped gates of GaAs MESFET devices. In this resist system, the head of the T-shaped gate is fabricated in the top layer negative resist using a deep-UV exposure and the foot of the T-shaped gate is fabricated in the bottom layer positive resist using an e-beam exposure. Resist profiles are easily controlled because exposures and developments of the top and bottom layers are completely separated. A sub quarter-micron T-shaped gate with the head of the width of more than one micron was successfully fabricated by using this two-layer resist system. This two-layer resist system has wide applicablity for the fabrication of GaAs MESFET devices.
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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).
Extreme Ultraviolet Lithography
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In the manufacturing process of semiconductor device, MEMS, and so on, lithography which uses photo-resist is a key process to fabricate micro or nano-scale structures, and unnecessary resist should be removed after the process. Typically SPM is used for the resist removal. In this study, we apply the method of steam-water mixed spray that can remove resist without chemicals. In order to clarify the detail mechanism of resist removal, we performed resist removal experiment. In the experiment, spray is traversed over a resist-coated wafer and the removal area is evaluated. The resist-coated conditions such as bake temperature, rotating speed are changed to evaluate the effects of mechanical properties of resist. In addition, removal force is measured to estimate the mechanical properties of resist by using SAICAS. As a result, it is shown that thicker or harder resist tends to be difficult to remove and the results suggest that this method mainly utilizes the physical force of high-speed droplets impact.
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Extreme Ultraviolet Lithography
Extreme ultraviolet
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In 2019, finally, extreme ultraviolet (EUV) lithography has been applied to high volume manufacturing (HVM) for preparing advanced semiconductor devices. That was very important year for EUV enthusiasts and semiconductor industry. Because it takes for a long time, more than 30 years, to study EUV lithography for realizing HVM. With recent rapid progress on the source power improvement, EUV lithography development including photoresist materials has been achieved HVM requirements. However, the performance of EUV resist materials are still not enough for the expected HVM requirements, even by using the latest qualifying EUV resist materials. One of the critical issues is the stochastic issues, which will be become 'defectivity', like a nano-bridge or a nano-pinching.
Extreme Ultraviolet Lithography
Photoresist
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The thickness dependence of resist performance has been investigated. It has been reported that principal properties such as resist sensitivity show strong dependence on resist film thickness. In current standard resist called chemically amplified resist, acids play the most important role in resist pattern formation. However, the dependence of acid concentration on resist thickness has not been reported. Better understanding of acid related issues is important for the development of high performance resists and the precise simulation of resist pattern profiles. In this work, the acid density in poly(4-hydroxystyrene), which is a widely-used backbone polymer for chemically amplified resists, was measured quantitatively by spectroscopic experiments. The average acid concentration nonlinearly increased by 14% with the increase of resist thickness from 65 to 4000 nm.
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Бұл зерттеужұмысындaКaно моделітурaлы жәнеоғaн қaтыстытолықмәліметберілгенжәнеуниверситетстуденттерінебaғыттaлғaн қолдaнбaлы (кейстік)зерттеужүргізілген.АхметЯссaуи университетініңстуденттеріүшін Кaно моделіқолдaнылғaн, олaрдың жоғaры білімберусaпaсынa қоятынмaңыздытaлaптaры, яғнисaпaлық қaжеттіліктері,олaрдың мaңыздылығытурaлы жәнесaпaлық қaжеттіліктерінеқaтыстыөз университетінқaлaй бaғaлaйтындығытурaлы сұрaқтaр қойылғaн. Осы зерттеудіңмaқсaты АхметЯсaуи университетіндетуризмменеджментіжәнеқaржы бaкaлaвриaт бaғдaрлaмaлaрыныңсaпaсынa қaтыстыстуденттердіңқaжеттіліктерінaнықтaу, студенттердіңқaнaғaттaну, қaнaғaттaнбaу дәрежелерінбелгілеу,білімберусaпaсын aнықтaу мен жетілдіружолдaрын тaлдaу болыптaбылaды. Осы мaқсaтқaжетуүшін, ең aлдыменКaно сaуaлнaмaсы түзіліп,116 студенткеқолдaнылдыжәнебілімберугежәнеоның сaпaсынa қaтыстыстуденттердіңтaлaптaры мен қaжеттіліктерітоптықжұмыстaрaрқылыaнықтaлды. Екіншіден,бұл aнықтaлғaн тaлaптaр мен қaжеттіліктерКaно бaғaлaу кестесіменжіктелді.Осылaйшa, сaпa тaлaптaры төрт сaнaтқa бөлінді:болуытиіс, бір өлшемді,тaртымдыжәнебейтaрaп.Соңындa,қaнaғaттaну мен қaнaғaттaнбaудың мәндеріесептелдіжәнестуденттердіңқaнaғaттaну мен қaнaғaттaнбaу деңгейлерінжоғaрылaту мен төмендетудеосытaлaптaр мен қaжеттіліктердіңрөліaйқын aнықтaлды.Түйінсөздер:сaпa, сaпaлық қaжеттіліктер,білімберусaпaсы, Кaно моделі.
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As extreme ultraviolet lithography (EUVL) prepares for its insertion into the high-volume manufacturing phase, many challenges still remain to be addressed. Among several issues, development of EUV resists with tight specifications of sensitivity (dose), resolution (HP) and line-edge roughness (LER) is required. Chemically-amplified resists (CARs) have been the major paradigm in the development of EUV resists, although several alternatives, such as molecular resists and inorganic resists, are also under development. Here we present a comparative study of the performance of CARs using the PSI's EUV interference lithography tool, which can achieve patterning down to 7 nm HP. Also the current status of EUV resist availability towards 11 nm HP technology nodes is discussed. We show resolution down to 12 nm HP with CARs. Nevertheless, for patterning below 18 nm HP, the resolution is achieved at the expanse of sensitivity and LER. The global trend of decreasing sensitivity with increasing LER is valid across the different resists. This trade-off between resolution, LER, and sensitivity (i.e. RLS trade-off) is mainly dominated by the acid diffusion blur and remains a challenge. In addition, pattern collapse becomes a significant problem with increasing resolution. This can be partly overcome by the reducing the resist thickness, which leads to an increase in LER. Therefore, a new trade-off between pattern-collapse limited resolution and LER emerges. These two trade-offs make the progress in EUV resist development increasingly difficult.
Extreme Ultraviolet Lithography
Extreme ultraviolet
Interference lithography
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