It is expected that 193nm lithography will be introduced in manufacturing for the 100nm node. In this paper, the ArF lithography options for the 100nm node have been investigated and the status and critical issues for process implementation are reviewed. As high NA ArF step and scan systems (NA=0.75) are not yet available, exploration of the capabilities and limitations of ArF lithography at lower NA (0.63) have been carried out. Emphasis is placed on the resist process integration issues and the enhancement techniques required for 100nm and below.

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A cyclopropyl group was introduced into the photoacid generator in order to give the photobleaching property at 193nm. Cyclopropyldiphenylsulfonium trifluoromethanesulfonate (CpDP-Tf) was synthesized for this photobleaching effect. This compound is stable up to 165°C. The absorbance of CpDP-Tf at 193nm decreases upon exposure. The resist containing CpDP-Tf gave the higher resolution comparing with that containing triphenylsulfonium trifluoromethanesulfonate

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Photoacid generation is a critical step in the application of chemically amplified (CA) resist technology. During the key exposure step, a catalytic amount of a strong Brφnsted acid is released within these resists. The photoacid is subsequently used in a post-exposure bake step to catalytically react with the resist polymer. In the case of a positive tone resist, an acid sensitive polymer is deprotected to render the exposed areas soluble in dilute aqueous base thereby allowing for pattern development. As the semiconductor industry begins to focus on developing 193nm photoresists for production, it is important to identify and understand differences between prototype 193nm CA resists and current state of the art 248nm production worthy photoresists. The major difference between 193 and 248nm photoresists is the exposure wavelength, which is reduced to achieve higher resolution based on the Rayleigh equation. However, this change in wavelength has several ramifications: Firstly, the tried, tested and true phenolic polymers used in DUV resists are too absorbent to be used for 193mm application and had to be replaced by low absorbing, non-aromatic systems. Second, since even these new platforms are still more absorbing at 193 nm than the phenolic matrices are at 248nm, the PAG loading had to be lowered significantly in order to keep the overall absorbance of the resist down.
This paper describes the results of our systematic studies on understanding the reasons for observed differences in photoacid generating efficiency between 193 and 248nm chemically amplified resist systems. First, the wavelength effect is studied by comparing the relative acid generating efficiency of onium type PAGs in a prototype 193 nm and a DUV photoresist at both 193nm and 248nm exposure. Second, the photoacid generating efficiency for these PAGs at 248nm is compared in both phenolic and non-phenolic based photoresists to probe resist polymer matrix effects. Third, these experiments were repeated while varying the PAG loading in order to probe whether there is an effect of PAG loading on acid generation efficiency. Lastly, by performing all of these studies on two different onium PAG classes (iodonium and sulfonium salts), the impact of the PAG chromophore on acid generation efficiency in both sensitized and unsensitized environments was probed. In all these studies, the C-parameter method is used to determine the quantum yield of photoacid generation.
First, the exposure wavelength was found to play a significant role in determining the acid generation efficiency of both PAGs, namely efficiency significantly decreases when switching exposure wavelength from 248 to 193nm. Second, it was also found that the change in the resist matrix polymer has a profound impact on the manner in which acid is generated: The phenolic matrix enables sensitized acid generation via electron transfer from the matrix to the PAG, whereas in the acrylate polymer only direct acid generation is observed. Due to the different oxidation potential of iodonium and sulfonium PAGs, the matrix effect impacts the photoacid generation efficiency of the two PAGs very differently. This is apparent in the observed change when going from the phenolic to the methacrylate matrix. Lastly, the presence of the sensitized channel is also responsible for the observed impact of PAG loading in the phenolic polymer, which is largely absent in the acrylate matrix.

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This paper describes the properties of our new alkylsulfonium salts for use as photoacid generators in ArF excimer laser lithography; 2-oxobutylthiacyclopentanium trifluoromethanesulfonate, 2-oxobutyithiacyclopentanium nonafluorobutanesulfonate, 2-oxobutylthiacyclohexanium trifluoromethanesulfonate, and 2-oxobutylthiacyclohexanium nonafluorobutanesulfonate. These compounds were thermally stable at more than 200°C in air and at more than 170°C in methacrylate-polymer film. They showed low absorption at 193.4nm and high sensitivity with an ArF-excimer-laser dose. The PAGs were also expected to be applicable to resists for use in F₂-excimer-laser lithography because of their transparency at 157.6nm, the wavelength of the laser. A resist composed of 2-oxobutylthiacyclopentanium trifluoromethanesulfonate and an alicyclic terpolymer achieved the resolution of a 0.13-μm line-and-space pattern by using an ArF scanner (NA=0.6, annular illumination) at a 20-mJ/cm2 dose.

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ArF lithography, in combination with chemically amplified resists, has been investigated as one of the most promising technologies for producing patterns below 100nm. In considering the polymer matrix for 193nm photoresist applications, factors such as sensitivity, transparency to 193nm radiation, adhesion to substrate, dry etch resistance, ease of synthesis, and availability of monomers are very critical. In these respects, remarkable progress has been made in development of ArF resist material. Polymers of acrylic and methacrylic esters show good imaging performance at 193nm, but have insufficient dry-etch resistance under oxide or nitride etch condition. On the other hand, cyclic olefin-maleic anhydride (COMA) alternating copolymers exhibit good dry etch resistance, but have poor resolution capability. We previously reported a new platform, based on a vinyl ether-malefic anhydride (VEMA) alternating polymer system, that demonstrated both good resolution and high dry etch resistance.
In this paper, VEMA systems with improved lithographic performance are presented. The new platform (VEMA) showed good performance in resolution, depth of focus (DOF), isodense bias, and post-etch roughness. With conventional illumination (NA=0.6, sigma=0.7), 120nm dense line/space patterns with 0.4μM DOF were resolved. And 90nm L/S patterns 0.6μM DOF were resolved with off axis illumination (NA=0.63). Another important factor to be considered for the dry-etch process is post-etch roughness. In the case of VEMA system a clean surface was observed after etch under oxide, nitride, and poly conditions. The VEMA resist system is regarded as one of the most production-worthy material for real device manufacture.

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We report on a study of the chemical and lithographic behavior in a 193nm single layer resist of two types of base additives, aminosulfonates opium and tetrabutylammonium carboxylate salts. These additives were examined because of their low potential for undesirable reaction with maleic anhydride or acrylic acid repeat units in norbonene/maleic anhydride/acrylate based 193nm resins. For ammonium carboxylate additives it will be shown that using these gives comparable lithographic performance to a standard formulation containing an amine additive. For aminosulfonate onium salts a study was done of the relationship between chemical structure of these additives and their thermal stability and the lithographic performance imparted by these to a 193nm single layer resist system. It will be shown that the decomposition temperature is a function of the basicity (nucleophilicity) of the counter anion decreasing with increasing basicity but can be improved by going from an iodonium to a sulfonium chromophore. Cyclamate and cysteate opium salts will be shown to provide good lithographic performance with good post-exposure bake delay latitude.

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In previous papers we have reported on the lithographic and etch performance of IBM's internally developed 193nm single layer photoresist system which is based on functionalized poly(norbornenes). These polymers are unique in that they offer potentially superior etch resistance when compared to other polymer systems being investigated for 193nm lithography, and in addition, have the requisite transparency which could lead to superior imaging performance as well. However, this class of polymers is unusual in that the dissolution properties are very different when compared to 248nm or other 193nm polymer platforms as has been previously reported by Ito. This paper will focus on the design, properties and lithographic performance of functionalized norbornene polymers we used for 193nm resist materials development.

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A negative resist system utilizing acid-catalyzed intramolecular esterification of δ-hydroxy acid has been developed for ArF phase-shifting lithography. The system is made up of an acrylate polymer with pendant structure of androsterone derivative with δ-hydroxy acid and a photo-acid generator. We investigated the effect of the comonomer and found that it changes the affinity of the resist polymer to the aqueous base developer. The change of the polarity of the comonomer was found to drastically affect the dissolution properties and the resolution capability. Optimization of the δ-hydroxy acid content and the developer concentration prevented pattern deformation such as "winding lines" and scum between the lines. The improved resist formulation combined with an ArF excimer-laser stepper with a phase-shifting mask produced a clearly resolved 100-nm line-and-space patterns.

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Copolymers containing basic monomers such as 3-(t-butoxycarbonyl)-1-vinyl caprolactam (BCVC) and piperidyl 5-norbornene-2-carboxylate (PNC) were synthesized for postexposure delay (PED) stability. The evaporation of a photogenerated acid in a basic polymer film-was measured by a spectral change of tetrabromophenol blue sodium salt and the diffusion of the photogenerated acid in the film was investigated using Fick's law and the transport equation of internal diffusion and surface evaporation. As the content of the basic monomer increases in the resist composition, the evaporation and diffusion of the photogenerated acid are reduced since only acids surviving the deactivation by the basic units diffuse and evaporate. Also, the sterically hindered aliphatic basic additive, cis-2, 6-di-t-butylpiperidine (DBPi), was synthesized and evaluated for PED stability. With these methods, the control of diffusion and evaporation of the photogenerated acid was accomplished without severe deterioration of the sensitivity. These new resist systems enable us to form fine patterns even after PED under an ammonia atmosphere.

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Pattern deformation during SEM inspection has been investigated for different types of 193nm positive resists. The mechanism of the CD changes is discussed based on the slimming rate analyses as well as on the e-beam penetration depth. As a general tendency, the methacrylate resists exhibit faster line width reduction than the cycloolefin-maleic anhydride (COMA) systems; however, other resist components as well as CD SEM settings play an important role. Based on the exposure time vs. CD loss, the line width slimming (LWS) is found to proceed in three steps, which are assigned as: (1) chemical change of outer resist layer, (2) evaporation of volatiles and (3) bulk chain scission or deprotection. Countermeasures for CD degradation are proposed from both the formulation and process sides. A calculation of e-beam penetration depth suggests that deprotection, chain scission and other reactions occur in the first 20-40nm, and these reaction rates combined with thermal effects determine LWS. The CD SEM measurement method has been improved to minimize e-beam exposure and to spread out the thermal load over a larger period of time. An optimized formulation exhibits less than 0.2% LWS per measurement with the improved CD measurement program.

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To accomplish sub-100nm minimum feature size to sub 100nm, new light sources for photolithography are emerging, such as ArF(λ=193nm), F2(λ=157nm), EPL(E-beam Project Lithography) and EUV(Extremely Ultraviolet, 13nm). Among these lithography technologies, ArF lithography will be used for sub 100nm lithography at first. For a few years, ArF resist development has been the key issue for the success of ArF lithography. For this ArF lithography, we have developed COMA (cyclo-olefin/maleic anhydride) type ArF resists in which the base resin consists of cycloolefin and maleic anhydride. Now, this COMA type resist is strong candidate for primary ArF resist. From the patterning results, we can say that the ArF resist is enough to start real device production except contact hole patterning. For the sub 100nm contact hole patterning, more intensive research must be performed in the field of RFP (Resist Flow Process) or RELACS (Resolution Enhancement Lithography Assisted by Chemical Shrink). From the etch resistance point of view, COMA type ArF resists have some problems under oxide etch condition. To solve this oxide etch problem, additional E-beam curing is required. For the more fundamental solution for the oxide etch, new etch equipment or hard mask must be developed for implementation of ArF process. E-beam curing also solves the line slimming due to E-beam attack during SEM measurement.

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We investigated resist profile change caused by re-sticking acid from exposed area during PEB. Using high activation energy type chemically amplified positive resist, the profile changed from T-top to rounded profile with increasing Exposed Area Ratio (EAR). We thought that this profile change was caused by acid evaporation from exposed area and its re-sticking on patterned area. To estimate the effect of re-sticking acid, we performed resist sandwich tests and observed resist profile change caused by re-sticking acid. The results thereby obtained support the model we propose.
To reduce the effect of re-sticking acid, we tried to use an OverCoat Layer (OCL). The effect of OCL was certified to be useful during PEB not during exposure.

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The effect of developer alkaline concentration variation during development on CD was investigated. It was observed that alkaline concentration variation during development affected CD. The influence appeared as CD differences between scan directions in the scanning development method. The amount of CD differences depended on resist material. The order of the CD differences corresponded to that of the sensitivity of dissolution rate to alkaline concentration. Sensitivity of dissolution rate to alkaline concentration is one of the factors that cause the CD differences among resists.

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Dry etch resistance and antireflective performance were studied for a spun-on carbon film containing 90.4wt% of carbon. The refractive index of the spun-on carbon film at KrF wavelength (248nm) is n=2.17, k=0.37 and that at ArF wavelength (193nm) is n=1.44, k=0.39. The bilayer BARC system composed of upper spun-on glass (SOG) and lower spun-on carbon was evaluated. It reduces the reflectivity to 1% for KrF wavelength and 0.5% for ArF wavelength and the variation of the substrate thickness can be ignored. Resist profiles are obtained without any footing, residue, or standing-wave. The etch resistance of the spun-on carbon film is 1.3 times greater than that of the thermally oxidized novolak film (i.e., conventional under-layer for trilayer resist process).

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An increasing number of nowadays advanced lithographic technologies require photoresist film thickness of at least 50μm. The patterning of high aspect ratio structures in ultra thick photoresist films is extremely challenging and the photoresists should provide low absorption in order to achieve vertical sidewalls and easy stripping after the pattern transfer processing. In the current work a novel resist platform is presented and applied in the case of film thicknesses up to 65μm. The resist formulation consists of a mixture of an epoxy novolac oligomer and poly(hydroxy styrene) and onium salt photoacid generators. Since the resist is rich in hydroxyl groups the unexposed regions can be developed in industrial aqueous solutions (TMAH 0.27N). Additionally since the required crosslink density is limited, the crosslinked regions can be easily removed by commercial wet photoresist strippers. First experimental data reveal a promising lithographic performance with resolution down to 30μm.

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Thick film ceramic microstructures with cross sectional areas of 5 by 10μm² were fabricated by casting aqueous colloidal suspensions of fine ceramic powders into photoresist structures. In order to anneal the ceramic microstructures without damaging, the dissolving behaviour of novolak resist was empirically assessed for different solvents. As a result, the resist was dissolved in tetrahydrofurane before pyrolysis. The processing of ceramic powders in the form of suspensions as used for bulk ceramic parts is new to the field of microfabrication.

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A new thin film optical wave guide to cross over the other waveguide was proposed with using polystyrene micro-sphere array. Light propagation characteristics of linear and curvilinear polystyrene micro-sphere array on the flat surface of spin coated PMMA film for 1O-1μmφ polystyrene spheres were measured. An optical waveguide mixed with polystyrene sphere and thin film bank was fabricated in order to confirm the possibility of practical waveguide fabrication.

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An adhesion problem is one of the most significant problems in nano imprint lithography. A mold should be released from a resist polymer without adhesion. We investigate a surface coating of a mold by fluorine polymers to reduce surface tension and making it easy to release the mold from the resist polymer. Evaporation of a FEP polymer in vacuum atmosphere and surface treatment for a mold by a silane-coupling agent with perfluoropolyether (PFPE-S) is examined. The releasing characteristics of molds are quantitatively evaluated by a contact angle for a water droplet. Durability of the fluorine polymers is also evaluated by continuous imprinting and the abrasion examinations.

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Deprotection reactions of chemically amplified resists during exposure are observed by using the in-situ FT-IR with the 248nm light source, and resist profiles are simulated using the activation energy and the prefactor calculated. The resists used in this experiment are poly(p-hydroxystyrene) (PHS) protected by Ethoxyethyl (EOE) group, by tert-Butoxycarbonyl (t-BOC) group and by these heterogeneous protection groups. The activation energy for the EOE resist is much lower than that for the t-BOC resist. The existence of heterogeneous protection groups affect mutually deprotection reactions; the EOE group additions to t-BOC resist reduce the activation energy for the deprotection reaction of t-BOC group. It is confirmed that existences of heterogeneous protection groups affect the formation of resist pattern profile by lithography simulator.

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A material and process development for tri-level resist process is carried out in terms of both lithography and RIE processes. The goal is to introduce the tri-level resist process into 0.13μm DRAM fabrication. The film stack of the tri-level resist process consists of thermally cross-linked novolak resin (I-line photo resist) as a bottom layer (500-900nm thickness), spin-on-glass (SOG) as a middle layer (70-90nm thickness) and an environmentally stable chemical amplified positive (ESCAP) type KrF photo resist as a top layer (200-300nm thickness). The lithographic process window for 130nm L/S structure using the KrF photo resist is determined to be 0.6um depth of focus (DOF) and 16% exposure latitude, under the exposure condition of 0.68NA, 0.75 sigma and 2/3 annular illumination. The resist pattern of the top layer is transferred to the middle layer and the bottom layer using conventional RIE techniques.
A WSi gate structure (nested and isolated lines) capped with SiN film in 0.13um DRAM is formed using the tri-level resist processing.

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The primary benefits of bottom anti-reflective coating (BARC) in photolithography are focus/exposure latitude improvement, enhanced CD control and the elimination of reflective notching. As the semiconductor industry demands higher chip functionality, the drive to reduce linewidths and increase die density per wafer is intense. The introduction of BARC technology can postpone the necessity to introduce new equipment needed for these shrinks by enhancing the capability of existing equipment, thus reducing product development time and also eliminating qualification of new material and tool sets. This paper reviews substrate reflectivity, and discusses and reports on material requirements for advanced organic BARCs. Some of the new BARC products based on the design requirement will also be discussed.

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Polymers based on biphenyl methacrylate as chromophore were synthesized with different compositions for use as anti-reflective coating (ARC) in KrF lithography. These polymers were formulated with a melamine cross-linker and a thermally activated acidic catalyst. The absorption characteristics of these polymers were adjusted by changing the monomer composition. The optimum ranges of n and k for the ARC were found to be 1.56 to 1.76 and 0.125 to 0.275, respectively. The curing properties of the coatings were studied by appropriate thermal analytical techniques. The desired degree of cross-linking was achieved by varying the amount of curing agent and temperature of curing. Fine lithographic patterns could be printed with no footing and scum at imaging layer-ARC interface.

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Three different silylation chemistries and processes are presented. The highly sensitive epoxy resist (EPR) can be silylated with chlorosilanes while the hydroxyl functionalized SAL601 and AZPN114 are silylated with the standard silyl amine chemistry (positive tone, single layer, top surface imaging (TSI), liquid or gas phase silylation processes). The process developed for epoxy functionalized resists is applied effectively to 193 nm and high energy (50KeV) electron-beam lithography. Process issues are discussed. In addition, a novel bilayer silylation process for an experimental 157nm chemically amplified positive (CAP) resist is presented in which the silylation reaction takes place after the wet development following the standard silyl amine chemistry. Alternatively, the acrylate moieties can be silylated with diamino siloxanes in alcoholic solutions.

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This work describes several novel Si-containing polymers with low optical densities at 193nm and acid labile protecting groups. These materials are evaluated at 193nm lithography as one of the top surface imaging techniques to enhance lithography performance. Additionally, norbornene/maleic anhydride copolymers containing silicon side chains are synthesized. Experimental results indicate that the unexposed and exposed regions differ in terms of silicon content to the extent that patterns are formed using oxygen reactive ion etching. Moreover, a polymer with at least 3.5%wt of Si content can provide effective etch resistance in this study. 0.11μm line/space patterns are also obtained using conventional developer with an ArF excimer laser stepper.

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