EUV lithography is expected to be the main lithography option for sub-22nm device manufacturing. One of the potential issues in EUV photoresist material development is the irradiation induced outgassing of photoresist material and the related risk for optics contamination, especially when the high volume manufacturing tools are introduced. The characterization however of which resist species are important for the contamination, and their quantification, is challenging, since it involves investigation on which parts of the photoresist are outgassing, but also a study of which outgassed species will lead to contamination (and which one will not).
In this paper, we have characterized both the outgassing and the contamination using commercial and model photoresist materials. The outgassing was studied by Residual Gas Analysis (RGA), and indicated that most of the outgassing is related to PAG and protection groups. The contamination was characterized by witness sample testing, and showed that mainly the PAG cation is important for the contamination. Based on this observation several materials were tested with different cation types and loading. This has provided understanding on how to design resist chemistry to minimize the risk of optics contamination in EUV device manufacturing.

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Extreme ultraviolet (EUV) lithography is the leading candidate for the manufacture of semiconductor devices at the hp 22 nm technology node and beyond. The Selete program covers the evaluation of manufacturability for the EUV lithography process. Then, we have begun a yield analysis of hp 2x nm test chips using the EUV1 (Nikon) full-field exposure tool. However, the resist performance does not yet meet the stringent requirements for resolution limit, sensitivity, and line width roughness. We reported on Selete standard resist 4 (SSR4) at the EUVL Symposium in 2009. Although it has better lithographic performance than SSR3 does, pattern collapse limits the resolution to hp 28 nm. To improve the resolution, we need to optimize the process so as to prevent pattern collapse. An evaluation of SSR4 for the hp 2x nm generation revealed that a thinner resist and the use of a tetrabutylammonium hydroxide (TBAH) solution for the developer were effective in mitigating this problem. Furthermore, the use of an underlayer and an alternative rinse solution increased the exposure latitude by preventing pattern collapse when the resist is overexposed. These optimizations improved the resolution limit to hp 22 nm.

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Line edge roughness (LER) is the critical issue in the development of chemically amplified resists used for extreme ultraviolet (EUV) lithography. The main cause of LER in state-of-the-art resists used at 22 nm node is the chemical inhomogeneity intrinsic to chemical reactions. This LER is expressed using the chemical gradient of chemical compounds which determine the solubility of resists. However, the inhomogeneity in the initial acid distribution possibly caused by the inhomogeneous distribution of acid generators becomes a concern with the reduction of feature sizes. In this study, the effect of acid distribution on LER was theoretically investigated on the basis of the reaction mechanisms of chemically amplified EUV resists. The fluctuation of line edge originating from the initial acid distribution was compared with LER originating from the chemical gradient. The microfluctuation in the initial acid distribution was sufficiently smoothed out through catalytic chain reaction. This indicates that the smoothing effect of acid diffusion is essential to the ultrafine patterning with high sensitivity.

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Further development of a polymer-bound PAG resist system is discussed. For 28nm hp, we obtained 26% exposure latitude and 0.3 micron DOF at a sensitivity of 17.1 mj. We also obtained 20nm half pitch resolution under dipole conditions. We have undertaken to deconvolve the blur sources in EUV as well. The total diffusion blur of an EUV resist exposed under ArF exposure conditions was estimated to be 10.6nm, with 9.3nm of the blur coming from acid reaction-diffusion and 4.3nm coming from the radius of gyration of the polymer. The total diffusion blur of the same resist material under EUV exposure conditions is 11.5nm. We get an EUV-specific blur contribution of 2.5nm associated with the acid cloud generated from the electrons generated after an EUV photon hits the polymer matrix, and a presently undefined blur contribution of 3.7nm which is probably contributed from the flare of the optics, and possibly from out-of-band radiation. The polymer-bound PAG resist has effectively a 9.7nm diffusion blur contribution which should be improved to less than 8 nm for 16nm node.

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The characterization of the photoresist dissolution process after exposure has been continuously investigated in search for possible clues in the development of optimal photoresist materials and processes suit the requirements for next generation lithography. In this paper, an in-situ analysis of the photoresist's dissolution behavior is performed utilizing high-speed atomic force microscopy. Here, the physical changes in the surface of the exposed extreme ultraviolet (EUV) photoresist film is observed in real-time before, during and after the development process. This new information on the actual pattern formation of photoresists provides clues on how to better understand its mechanism and in effect further improve its performance. In this work, a comparison of the dissolution characteristics in terms of EUV photoresist platform (acryl-based polymer and fullerene-based molecular resist) in tetramethylammonium hydroxide (TMAH) developer was performed. Moreover, using the same polymer resist, the dissolution characteristic difference between the TMAH and tetrabutylammonium hydroxide (TBAH) developers was analyzed.

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In order to achieve targeted resist performance for EUV in practical applications, we have developed new materials such as molecular glass (MG), PAG, and acid amplifiers (AA). Protected NORIA, a molecular glass, was examined for extending resolution limits. The resist with protected NORIA showed 22 nm hp resolutions under EUV exposure. PAG acid diffusion effect on LWR was also investigated. It was found that acid diffusion control was one of the most important factors for LWR improvement. To improve sensitivity, application of AA (acid amplifier) was investigated. The resist with AA gained 25% sensitivity improvement over the original formulation. Elemental technologies for major progress of EUV resist were made.

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Molecular resists of Prot-2 and Prot-1 were synthesized for decomposition analysis and lithographic evaluation. After checking their structure, purity and thermal property, decomposition behavior was analyzed by high performance liquid chromatography (HPLC). From the analysis, it was found that the main reaction in an exposed area was the deprotection reaction of the protecting group in electron beam (EB) and extreme ultraviolet (EUV) lithography. The exposure dose at which the conspicuous deprotection reaction occurs coincides with the exposure dose at which the resist film thickness reduces. Furthermore, the resists which include completely deprotected group, partially deprotected group and completely protected group, which dissolution rates were different coexist at the boundary between an exposed and an unexposed region. The fundamental decomposition-analysis results indicate that the line edge roughness (LER) is caused by the existence of the different dissolution rates of resist component materials at the boundary between an exposed and an unexposed region. After confirming the fundamental analysis, these molecular resists were evaluated on a lithographic performance by EB lithography. Resist-A consisting of Prot-1 showed 20 nm hp resolution at the exposure dose of 36 μC/cm². In this paper, we will discuss about the resolution and the LER property of molecular resists at the point of their decomposition behavior.

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The synthesis and properties of noria derivatives (noria-CHVE's) with pendant acetal moieties were examined for application as extreme ultraviolet (EUV)-resist materials. The reaction of noria and cyclohexyl vinyl ether was carried out in the presence of pyridinium p-toluenesulfonate as a catalyst, to give the corresponding noria-CHVE's with various degrees of introduction (DI) of cyclohexyl acetal moieties by adjusting the feed ratio of reactant and reaction time. The physical properties (solubility, thermal stability, and film-forming ability) of noria-CHVE's were consistent with the differences in DI values. The patterning properties of noria-CHVE₅₀ (DI = 50) and noria-CHVE₅₉ (DI = 59) were investigated in an EUV-resist system, and it was found that noria-CHVE₅₀ gave higher resolution than noria-CHVE₅₉, providing a clear line and space pattern with a resolution of 37.9 nm and a line-edge roughness (LER) of 7.2 nm.

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This paper describes the synthesis of a new series of chain-scission polymers and their lithographic results in extreme ultraviolet (EUV) resist formulations. This new platform incorporates acid-catalyzed cleavable groups into the polymer backbone. Upon exposure to EUV light and bake, the polymer is transformed from high to low molecular weight segments in the exposed regions. Six polymer variations were prepared from two cleavable monomers and two aromatic linkers. Five of these polymers were formulated into resists and lithographically evaluated at Lawrence Berkeley National Laboratories. All the resists are lithographically active, and one is capable of resolving 36 nm dense lines with modulation down to 28 nm.

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Extreme ultraviolet interference lithographic exposure tool was installed at the long undulator beamline in NewSUBARU for the resist evaluation in 25 nm node and below. It was confirmed that the spatial coherence length is 1.1 mm using a 10-μm-wide slit in the Young's double slit experiment. The transmission grating was the key component to decide the resist pattern size and contrast for EUVIL. To obtain the high contrast of the interference fringes of the two window transmission grating on the wafer, the transmission grating was designed. The window size of the transmission grating optimized to be 300X30 μm² in size to avoid Fresnel diffraction which reduces the contrast of the interference fringes on the wafer. In addition, to obtain highest diffraction efficiency, TaN employed as the absorber material, and the thickness of the absorber was optimized to be 70 nm. Furthermore "Center stop" layer was design to reduce the transmitted light from the region between two diffraction grating windows to obtain high contrast of the interference fringes on the wafer. A 25-nm half pitch (hp) resist pattern was successfully replicated by extreme ultraviolet interference lithography (EUV-IL) utilizing a two-window transmission grating pattern of a 50-nm line and space (L/S). As results, the transmission grating design can be applied for the resist patterning of 25 nm and below in EUV-IL.

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Exposure tool of EUV interference lithography (EUV-IL) has been developing for the EUV resist evaluation for 22 nm and 16 nm nodes below. The fabrication of the transmission grating is a key technology for EUV-IL. The transmission grating for EUV-IL which has no crack and no crumple in the membrane region was fabricated by controlling film stresses of SiO₂ and TaN layers. In addition, applying SiO,sub>2 hard mask process, diffraction grating pattern of 50 nm L/S was fabricated. Furthermore, the center stop process was added to the transmission grating fabrication. And using this transmission grating 25 nm hp pattern was replicated on a wafer using EUV-IL. It is confirmed that the SiO₂ hard mask process is significant process for the fabrication of 40 nm hp grating which corresponding to 20 nm hp resist pattern on a wafer.

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Non-conventional chemically amplified (CA) resist was designed. Photo-induced thiol/ene radical reaction was used to insolubilize the resist based on difunctional thiol and poly(4-hydroxystyrene) (PHS) derivatives. Hydroxy groups of PHS were modified with allyl or propargyl moiety. Dissolution property of the modified-PHS in TMAHaq solution was affected by the modification degree. Resist was prepared by mixing the modified-PHS, difunctional thiol compound, and photoradical generator. Photosensitivity of the resist was studied using 254- and 13.5-nm light. The sensitivity was strongly affected by the modification degree of PHS, molecular weight of PHS, molecular weight distribution of PHS, and amounts of thiol compound and photoradical generator added. Outgassing of the present system was studied by the pressure rise analysis. It was found that the present resist system was highly sensitive to EUV exposure.

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Several methods to improve sensitivity of EUV resist, with a couple of key points of acid generation efficiency and de-protection reaction efficiency. Larger loading of PAG to increase the secondary electron absorption possibility, cation unit design to lower the lowest unoccupied molecular orbital of cation, and lowering ionization potential of polymer to enable efficient secondary electron generation, were discussed in the viewpoint of acid generation efficiency. Larger size of anion structure design on PAG was applied to special formulation of small loading of quencher to minimize necessary generated acid concentration to give enough de-protection reaction amount, and to higher PEB temperature resist process to maximize de-protection reaction efficiency.

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The physical characterization of extreme ultraviolet (EUV) ultra-thin underlayers (ULs) and their effects on photoresist EUV lithographic performance was investigated. UL polymer compositions were modeled to identify polymer compositions that would encompass a range of glass transition temperatures (Tg) and surface polarities. Eight UL polymers compositions were synthesized and characterized, demonstrating that polymer composition can dictate the surface polarity and Tg properties of cross-linked UL films. The Tg of UL films drops significantly for film thicknesses below ~30 nm. EUV imaging of open source and commercial resists on the eight UL films was evaluated. Resist adhesion improved when the surface polarity of the underlayers decreased. It was discovered that the coefficient of thermal expansion (CTE) plays an important role in determining the adhesion of resist to underlayers.

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Homopolymers of a bis-trifluorocarbinol substituted norbornene (1) (α,α-bis(trifluoromethyl)bicyclo[2.2.1]hept-5-ene-2-ethanol or HFANB) were produced using a palladium catalyst and hydrogen as a chain transfer agent to control molecular weight. As the hydrogen pressure increased, the molecular weight of poly(1) decreased. Spectroscopic analysis of these polymers by 1H NMR and MALDI-TOF MS confirmed that the hydrogen chain transfer agent generated hydrogen-terminated vinyl addition homopolymers of 1. The optical density of these polymers is extremely low at 193 nm and is independent of molecular weight.

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Developable BARC (DBARC) technology is presently being considered for use in semiconductor device manufacture. The unique ability of a DBARC to offer substrate reflection control without the need for a BARC open etch is attractive for application in two large segments of device manufacture. Firstly, implant lithography may benefit from DBARC technology as these layers cannot withstand a BARC open etch but improved reflection control is needed over existing TARC and dyed resist schemes.
The other area of potential interest is to reduce cost of ownership by replacing a conventional BARC with a DBARC thereby eliminating the BARC open etch step in conventional lithographic applications.
In this paper, we describe recent improvements in Developable BARC (DBARC) technology for advanced lithography. The general design concepts used to create high performing DBARC materials are reviewed and fundamental characterization data are presented. Thereafter, data on key performance metrics is shared for implant and non-implant applications. For KrF implant applications, the key metrics include CD swing and CD control over varying oxide thickness and active to filed CD bias. In the case of ArF implant, data on performance over topography is included. Based on the implant application data, our DBARC technology is surpassing the capability of a traditional TARC process for both KrF and ArF implant applications. In the non-implant application, we demonstrate our DBARC is competitive with conventional BARC in an aggressive immersion ArF application. In this application the DBARC offers leading edge lithography without the need for a BARC open etch step. This suggests a DBARC may help reduce cost of ownership even in critical applications.

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Developable bottom anti-reflective coatings (DBARCs) are useful for implant layers because they eliminate the plasma etch step avoiding damage to the plasma sensitive layers during implantation. It is expected that DBARC will also be used for non-implant layers and double exposure technology. AZ has pioneered DBARCs based on photosensitive cleave as well as crosslink/decrosslink mechanisms.
In this paper, we focus on the challenges and advances in the photosensitive DBARCs, including DBARC/resist matching and the influence of various process factors on lithographic performance, such as prewet, thickness, topography and substrates. DBARC/resist mismatching was addressed both from process and formulation sides. Prewet of DBARC before resist coating deteriorated performance, however, it was overcome by modifying DBARC formulations. The optimized DBARC showed both optical and lithographic performance comparable to conventional BARCs. DBARCs minimized reflection from the substrates and notching of patterns was improved on silicon oxide topography. This paper includes simulation, DBARC contrast curve analyses, recent 248 nm, 193 nm dry and immersion exposure results of DBARC.

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This paper gives examples of the connection of new research on water purificiation membranes to earlier research on resist chemistry. Two new membrane materials are reported here. The first is a reverse osmosis desalination membrane material based on a new hexafluoro alcohol-modified aromatic polyamide. This polymer is made in a reactive casting operation using interfacial polycondensation. The membrane has intriguing performance with pH-dependent properties. The second membrane presented here is designed to have fouling resistance. We found through the course of this work that the material had intrinsic nanofiltration properties and data is presented that supports this finding. Research experiences in high performance functional materials can accelerate new efforts in other areas of technology, in this case sustainability.

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Step and Flash imprint lithography (SFIL) has reached a critical point in its development life cycle. Resolution and image fidelity have been well established, and progress is being made on both the process and template fronts. This simple technique has the potential to become the next generation lithography (NGL) choice for semiconductor manufacturing. Yet, despite the positive outlook, SFIL has very little industry support. Concerns about defectivity, throughput, overlay, template cost, infrastructure, and a host of other critical issues are legitimate. More important, however, is the severe shortage of publicly available data on SFIL for semiconductor applications, giving the false impression that it is still in its infancy. This paper discusses the current status of SFIL and shows where industry collaboration is needed to solve the critical issues and demonstrate that it is a viable NGL technology.

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