The demands for high resolution and issues of line edge roughness require a reconsideration of current resist design strategies. In particular, EUV lithography will provide an opportunity to examine new resist concepts including new elemental compositions and low molar mass resists or molecular resists. In the former case, resist compositions incorporating elements such as silicon and boron have been explored for EUV resists and will be described. In an example of the latter case, molecular glass resists have been designed using synthetic architectures in globular and core-arm forms ranging from one to multiple arms. Moreover, our studies include a series of ring and irregularly shaped small molecules modified to give imaging performance. These materials have been explored to improve line edge roughness (LER) compared to common polymer resists. Several examples of polymeric and molecular glass resists will be described. Several compositions showed high glass transition temperatures (T_g) of ~ 120°C and possessed no crystallinity as seen from XRD studies. Negative-tone molecular glass resists with a T-shaped phenolic core structure, 4-[4-[1,1-Bis(4-hydroxyphenyl)ethyl]]-α,α-dimethylbenzylphenol, have demonstrated feature sizes as small as 50mn. Similarly, negative-tone images made using spiro-based compounds showed feature size as small as 60nm in lines/space patterns using e-beam lithography. Most recently we have demonstrated that fully and partially tert-butoxycarbonyl (t-Boc) protected calix[4]resorcinarene derivatives can be successfully studied as a positive-tone resist using EUV and E-beam lithography. Resolution as low as 35nm was obtained by EUV exposure.

ArF immersion lithography is considered as the most promising next generation technology which enables to a 45 nm node device manufacturing and below. Not only depth of focus enlargement, immersion lithography enables to use hyper numerical aperture (NA) larger than 1.0 and achieve higher resolution capability. For 193nm lithography, water is an ideal immersion fluid, providing suitable refractive index and transmission properties. Furthermore the higher refractive index fluid is expected to provide a potential extension of optical lithography to the 32 nm node. This paper describes the material design for immersion lithography with high refractive index fluid. We have developed promising high refractive index fluids which satisfy the requirement for immersion fluid by screening wide variety of organic compounds. The physical and chemical properties of this high refractive index fluid are discussed in detail. Also the topcoat material which has good matching with high refractive index fluid is developed. While this topcoat material is soluble into aqueous TMAH developer, it does not dissolve into water or high refractive index fluid and gives suitable contact angle for immersion scan exposure. Immersion exposure experiments using high refractive index fluid with and w/o topcoat material was carried out and its lithographic performance is presented in this paper.

We have investigated the impact of water and top-coats on the resist in water immersion lithography by analyzing the dissolution behavior and the film constitution. We used a resist development analyzer (RDA) and a quartz crystal microbalance (QCM) to study the dissolution behavior. The film constitution was studied through the gradient shaving preparation (GSP) method in combination with TOF-SIMS. The GSP/TOF-SIMS method reveals the constitution of a top-coat/resist film. We found that, in a resist, the photo acid generator (PAG) anion at a depth of about 30 nm from the surface leached into water and a surface insoluble layer formed during immersion. The estimated amount of leaching was about 5% of the original content. The formation of an intermixing layer with a low dissolution rate was observed for some top-coat and resist combinations. The thickness of the intermixing layer and the formation behavior were made clear. We believe the intermixing layer was caused by the top-coat solvent eluting resist components. In a top-coat, a PAG existed within the top-coat and the PAG anion leached into the water. Top-coats blocked gaseous decomposed products from the resist film during PEB. These results are useful for estimating patterning characteristics and the defectivity due to materials for actual immersion exposure.

The emergence of immersion lithography for the extension of current lithography tools requires a fundamental understanding of the interactions between the photoresist and the immersion liquid such as water. Neutron reflectometry was used to measure the water concentration depth profile within immersed photoresist films. The bulk of the films swelled to the equilibrium water concentration. However a gradient in water concentration was observed near the polymer/substrate interface. Dependent on the relative hydrophilicity of the polymer and the substrate, either a depletion or excess of water was observed at the interface. Using HMDS treated silicon wafers as the substrate results in approximately 17% water by volume at the interface. The interfacial concentration decreases (or increases) to the bulk water solubility limit approximately 40 Å from the substrate. As the total film thickness approaches this length scale, the substrate induced concentration gradients lead to a film thickness dependent swelling; enhanced or suppressed swelling is witnessed for the excess or depleted interfacial concentrations, respectively. Variation of the substrate surface energy allows for tuning of the interfacial water concentration, ranging from 30% to less than 1% water by volume.

The interfacial mass transfer issues of resist components in ArF immersion lithography were investigated both for topcoat resist system and for non-topcoat resist system. PAGs and photoacids are known for the major components that leach out from the resist to water and topcoat has been simply expected to shut off this leaching. In this study, topcoat layer was acutally verified significantly to reduce the PAG leaching, but PAG (or photoacid) diffusion from the resist to topcoat was found as another issue. This resulted in T-top formation in the imaging due to the loss of photoacid nearby the resist surface caused by this diffusion. A material approach to reduce this interfacial diffusion was proposed through a thermodynamic consideration of the materials system. The free energy change for PAG-polymer solubilization is the key and the Solubility Parameter value was considered to represent a good measure of this free energy change. The experimental results well matched this analysis. On the other hand, a perfect suppression of the leaching without using topcoat would be more desirable if it is feasible. The influence of structural parameter of the resist component was investgiated. The hydrophobicity of PAG was found to well correlate inversely to the leaching amount of the PAG into water, and thereby a technical guideline was obtained in designing resist materials to make them resistant to the leaching. By optimizing each resist component on this bases, we actually demonstrated a resist that showed the PAG leaching level reduced down to 10^-13[mol/cm²], which we believe far below to what we are today with conventional dry resists. A resist sample was thus developed targeting the non-topcoat approach and was examined for its imaging performance with a realistic immersion lithography tool without using any topcoat. The resist actually showed good imaging results fully with the benefits that we expected with the immersion exposure.

To make immersion lithography a reality in manufacturing, several challenges related to materials and defects must be addressed. Two such challenges include the development of water immersion compatible materials, and the vigorous pursuit of defect reduction with respect to both the films and the processes. Suitable resists and topcoats must be developed to be compatible with the water-soaked environment during exposure. Going beyond the requisite studies of component leaching from films into the water, and absorption of water into the films, application-specific optimization of photoresists and top coats will be required. This would involve an understanding of how a wide array of resist chemistry and formulations behave under immersion conditions. The intent of this paper is to compare lithographic performance under immersion and dry conditions of resists containing different polymer platforms, protecting groups, and formulations. The compatibility of several developer-soluble top-coat materials with a variety of resists is also studied with emphasis on profile control issues. With respect to defects, the sources are numerous. Bubbles and particles created during the imaging process, material remnants from incomplete removal of topcoats, and image collapse as related to resist swelling from water infusion are all sources of yield-limiting defects. Parallel efforts are required in the material development cycle focusing both on meeting the lithographic requirements, and on understanding and eliminating sources of defects. In this paper, efforts in the characterization and reduction of defects as related to materials chemistry and processing effects will be presented.

Extraction of small molecule components into water from photoresist materials designed for 193 nm immersion lithography has been observed. Leaching of photoacid generator (PAG) has been monitored using three techniques: liquid scintillation counting (LSC); liquid chromatography mass spectrometry (LCMS); and scanning electrochemical microscopy (SECM). LSC was also used to detect leaching of residual casting solvent (RCS) and base. The amount of PAG leaching from the resist films, 30 - 50 ng/cm², was quantified using LSC. Both LSC and LCMS results suggest that PAG and photoacid leach from the film only upon initial contact with water (within 10 seconds) and minimal leaching occurs thereafter for immersion times up to 30 minutes. Exposed films show an increase in the amount of photoacid anion leaching by upwards of 20% relative to unexposed films. Films pre-rinsed with water for 30 seconds showed no further PAG leaching as determined by LSC. No statistically significant amount of residual casting solvent was extracted after 30 minutes of immersion. Base extraction was quantified at 2 ng/cm² after 30 seconds. The leaching process is qualitatively described by a model based on the stratigraphy of resist films.

We will describe our barrier coat approach for use in immersion 193 nm lithography. These barrier coats may act as either simple barriers providing protection against loss of resist components into water or in the case of one type of these formulations which have a refractive index at 193 nm which is the geometric mean between that of the resist and water provide, also top antireflective properties. Either type of barrier coat can be applied with a simple spinning process compatible with PGMEA based resin employing standard solvents such as alcohols and be removed during the usual resist development process with aqueous 0.26 N TMAH. We will discuss both imaging results with these materials on acrylate type 193 nm resists and also show some fundamental studies we have done to understand the function of the barrier coat and the role of differing spinning solvents and resins. We will show LS (55 nm) and Contact Hole (80 nm) resolved with a 193 nm resist exposed with the interferometric tool at the University of New Mexico (213 nm) with and without the use of a barrier coat.

The leaching of ionic PAGs from model resist films into a static water volume is shown to follow first order kinetics. From the saturation concentration and the leaching time constant, the leaching rate at time zero is obtained which is a highly relevant parameter for evaluating lens contamination potential. The levels of leaching seen in the model resists generally exceed both static and rate-based dynamic leaching specifications. The dependence of leaching on anion structure shows that more hydrophobic anions have lower saturation concentration; however, the time constant of leaching increases with anion chain length. Thus in our model system, the initial leaching rates of nonaflate and PFOS anions are identical. Investigation of a water pre-rinse process unexpectedly showed that some PAG can still be leached from the surface although the pre-rinse times greatly exceeded the times required for saturation of the leaching phenomenon, which are expected to correspond to complete depletion of leachable PAG from the surface. A model is proposed to explain this phenomenon through re-organization of the surface as the surface energy changes during the air/water/air contact sequence of the pre-rinse process.

Immersion lithography has already demonstrated superior performance for next generation semiconductor manufacturing, while some challenges with contact immersion fluids and resist still remain. There are many interactions to be considered with regards to the solid and liquid interface. Resist elusion in particular requires very careful attention since the impact on the lens and fluid supply system in exposure tool could pose a significant risk at the manufacturing stage. TOK developed a screening procedure to detect resist elution of ion species down to ppb levels during non and post exposure steps. It was found that the PAG cation elution is affected by molecular weight and structure while the PAG anion elution was dependent on the molecular structure and mobility. In this paper, lithographic performance is also discussed with the low elution type resist.

Polysilsesquioxane-based 193 nm positive bilayer resists are described. In this design Si for etch resistance is placed in every repeat unit and acid-labile protected and acidic groups (and polar units) are in the side chain, allowing to incorporate each lithographically critical functionality in sufficient quantity. Fluoroalcohol is employed as an acid group instead of carboxylic acid because of its more attractive dissolution properties. Polymers were carefully analyzed by ¹⁹F, ¹³C, and ²⁹Si NMR to determine composition and to quantify residual acetyl, silanol, and Q/T. Hydrogen-bonding between tertiary ester and fluoroalcohol in the polysilsesquioxanes was investigated by FT-IR and the effect of lactone incorporation on the thermal deprotection temperature elucidated. In order to better understand the dissolution behavior of exposed resist films, the silsesquioxane resist polymers were partially (ca. 30%) and fully deprotected in solution with acid and their dissolution kinetics investigated by using a quartz crystal microbalance (QCM). It has been found that the exposed areas of the silsesquioxane resists can have a very fast dissolution rate (R_max) of >20,000 A/sec (or even >100,000 A/sec). Heating the fully deprotected model polymers to 150°C did not reduce the dissolution rate much, suggesting thermal condensation of silanol end groups is insignificant. Model deprotected polymers containing triphenylsulfonium nonaflate were exposed to 254 nm radiation, baked, and subjected to QCM measurements in order to determine whether or not acid-catalyzed silanol condensation would reduce the dissolution rate. A combination of high dose and high temperature bake resulted in significant reduction of the dissolution rate in the silsesquioxane polymer containing a small trifluoroalcohol. However, the dissolution behavior of the polymer bearing a bulky norbornene hexafluoroalcohol was unaffected by exposure and bake. Chemical and development contrast curves were generated by using a temperature gradient plate and bake temperature effects investigated. While a postapply bake temperature variation from 95 to 130°C did not affect the contrast (chemical and development) and sensitivity, a postexposure bake temperature effect was quite small. The process window of the silsesquioxane bilayer resists was comparable to that of a high performance commercial 193 nm single layer resist for both isolated and nested contact hole imaging, Superior performance of our silsesquioxane resist was demonstrated in patterned etch in comparison with a COMA-based bilayer resist.

A new ArF matrix based on poly(vinylsulfonamide) has been developed. Sulfonamides, whose pKa values are comparable to those of phenols, can be used as acidic functional groups in the design of chemically amplified resist (CAR) and aqueous base developable resist. Various poly(N-alkyl vinylsulfonamide)s were prepared (R=H, CH₂CF₃, Pr, 1-adanmantyl), and showed high transparency at round 193 nm region. Depending on the substituents, the dissolution rates of films in a 2.38 wt% aqueous tetraethylammonium hydroxide solution were varied from 500 to 0.0035 nm/s. The tetrahydropyranyl (THP) protected poly(vinylsulfonamide) was prepared and the deprotection of THP was easily occurred when the photoresist containing a photoacid generator was exposed to UV light, followed by post-exposure baking.

The focus of this paper is to utilize the acidity of hexafluoroalcohol (HFA) in addressing performance deficiencies associated with current 193nm methacrylate resist materials. In this study, we have designed and developed a variety of HFA pendant methacrylate monomers and the corresponding imaging polymers for ArF lithography. It was shown that typical swelling behavior observed in methacrylate resists can be substantially reduced or eliminated by replacing commonly used multicylcic lactone polar functionalities with acidic HFA side chains. The incorporation of aliphatic spacers between HFA and polymer backbone were found to be more effective than cyclic hindered moieties, in achieving linear dissolution characteristics. The typical poor etch stability associated with fluorine atoms in HFA can be substantially minimized by designing side chains with a combination of appropriate cyclic and aliphatic moieties and fine-tuning the corresponding polymer compositions. PEB sensitivity of high activation energy protecting group (e.g., methyladamentyl group) based methacrylate resists can be substantially improved through the incorporation of acidic HFA side chains (6nm/C to <1 nm/C). The key application space for HFA-methacrylate resists appears to be trench level lithography. It was also demonstrated that these HFA materials are compatible with immersion lithography and result in dramatically improved process windows for iso trench features, in addition to other lines/space features.

Recently we have developed a novel non-ionic photoacid generator (PAG), 2-[2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoro-1-(nonafluorobutylsulfonyloxyimino)-heptyl]-fluorene (DNHF), which generates a strong acid (perfluorobutanesulfonic acid) by light irradiation and is applicable to chemically amplified ArF photoresist. The studies on quantum yield of the PAG under 193 nm exposure in an ArF model formulation and in a solution comparing with the ones of ionic PAGs, triphenylsulfonium perfluorobutanesulfonate (TPSPB) and Bis(4-tert-butylphenyl)iodonium perfluorobutanesulfonate (BPIPB) revealed that this compound is superior in photo efficiency to the others. PAG leaching into water from the resist during a model immersion process was investigated in detail. No leaching of DNHF was observed under the immersion process while significant amount of TPSBP was eluted. Dissolution rate of the resist prepared under a model condition of ArF immersion exposure was monitored. No clear difference against dry condition was observed.

Of all candidate 193 nm photoresist binder resins, transition metal catalyzed vinyl addition cyclic olefin (i.e., norbornene) polymers (PCO) hold the promise of high transparency and excellent etch resistance. In order to access lower molecular weight polymers, which are typically used in photoresists, α-olefin chain transfer agents (CTAs) are used in synthesizing vinyl addition poly(norbornenes). For example, HFANB (α,α-bis(trifluoromethyl)bicyclo [2.2.1]hept-5-ene-2-ethanol) homopolymers (p(HFANB)) with molecular weights (M_n) less than 5000 have been synthesized using such chain transfer agents. However, the optical density (OD) at 193 nm of these materials was found to rise as their molecular weights decreased consistent with a polymer end group effect. Extensive NMR and MS analysis of these polymers revealed that olefinic end groups derived from the chain transfer agent were responsible for the deleterious rise in OD. Chemical modification of these end groups by epoxidation, hydrogenation, hydrosilation, etc. lowers the OD of the polymer by removing the olefinic chromophore, however, it does require a second synthetic step. Thus a new class of non-olefinic chain transfer agents has been developed at Promerus that allow for excellent control of vinyl addition cyclic olefin polymer molecular weight and low optical density without the need of a post-polymerization chemical modification. Low molecular weight homopolymers of HFANB have been synthesized using these chain transfer agents that exhibit ODs ≤ 0.07 absorbance units per micron. This molecular weight control technology has been applied to both positive tone and negative tone vinyl addition cyclic olefin binder resins. Lithographic and etch performance of positive tone photoresists based on these binder resins will be presented.

Electrostatic self-assembly (ESA) is combined with optical lithography to develop a novel process to form 70 nm space patterns to overcome the resolution limit of ArF lithography with numerical aperture (NA) of 0.75. It is proven that patterned photo resist are useful template with specific topography to undergo the subsequent ESA. Weak polyelectrolytes are shown to control the attachment amount by adjusting pH. Puddle-assembly is applied instead of spin- or dip-assembly considering pattern profile and practicality to be used in the real FAB environment. With optimized composition and assembly method, it is successful to form 70 nm spaces patterns by ESA-induced chemical attachment above 45 nm, combined with ArF lithography of 0.75 NA. Since it works at room temperature without extra process unit after exposure and development, it overcomes the disadvantages of the conventional chemical shrink processes such as thickness loss, dependence on pattern and photo resist, and throughput lowering. In addition, in-wafer uniformities are comparable to that of forming 120 nm spaces patterns with only ArF lithography, which proves that the combination of ESA and optical lithography can be a potentially and practically alternative way of forming uniform 70 nm spaces patterns over 200 nm substrates. It also means that now it is time for top-down and bottom-up approaches to meet together to access nano world.

The critical dimension (CD) of contact holes for the 65-nm application specific integrated circuit (ASIC) is 100 nm according to the 2002 update of the International Technology Roadmap for Semiconductors. The common through-pitch depth of focus (DOF) of such contact holes is very small using the current ArF exposure tool. High-numerical-aperture (NA) ArF exposure tools are not expected to improve the common DOF that scales by the square of the numerical half aperture. High-transmission attenuated phase-shifting masks increase the DOF of isolated contact holes. Off-axis illumination such as annular or quadrupole illumination improves the DOF of dense contact holes. Nonetheless, both the isolated and the dense contact holes need to be printed within spec on logic circuit. To delineate 100-nm contact holes at several different pitches, we proposed the pack-and-unpack (PAU) process which employs double exposures. First, dummy holes are added to the surroundings of isolated contact holes facilitating the patterning of the resultant dense pattern with a resolution enhancement technique that favors dense contact holes. For example, dense holes are packed to 180-nm pitch and imaged with high-NA lens setting and quadrupole illumination. Then, the second image is used to open the desired holes or block the dummy contact holes. The purpose of this study was to develop new methods and new materials for the patterning of the second image. Three approaches were investigated. The first approach was forming an isolation layer to protect the first image; second, applying UV curing to harden the first image; third, using alcohol-based resists to pattern the second image. Among those three approaches of printing the second image, using resist in alcohols is the most convenient method. Even though the CD control of the second image is not so critical, resolution and process window of resists may need further improvement for 45-nm node and below. Using the second approach allows conventional ArF resists, which does not raise as many concerns as the alcohol-based resists. With the first approach, a lot more work is needed to prevent intermixing and reactions between the isolation layer and the resist for the second image. The results of this work point to the directions for material developments of the PAU process. Both the alcohol-based resists and UV curing are good approaches for PAU. Further characterizations such as DOF, exposure latitude (EL), and mask error factor (MEF) on them will be carried out in the near future.

More simple and cost-effective shrinkage techniques for contact hole (C/H) are required instead of conventional technologies such as thermal flow, RELACS, SAFIER and CONPEAT with the aggressive reduction in size of devices. We have developed a new method, Coating Assisted Shrinkage of Space (CASS) process. This process simply coats polymer over the patterned wafer. It doesn't need a bake and rinse step for shrinkage. Sub-100 nm C/H patterns were successfully defined after coating CASS material with good profile.

This paper describes an innovative approach to lithography processes using a supercritical fluid. The key idea is to improve a resist by exploiting the special properties of supercritical fluid: it is a good solvent with good diffusivity. The results of this study show that various kinds of molecules can be dissolved in supercritical carbon dioxide, and distributed uniformly throughout a resist. For example, the etch rate of ArF resist is reduced when functional molecules with a high etching durability are added to it. The unique feature of this technique is that the resist can be modified after exposure and development without damaging resist patterns. This technique constitutes a revolutionary way of enhancing resists that could have a big impact on resist composition and processes.

Patterning of sub-100nm contacts for sub-90-nm-node devices is one of the primary challenges of photolithography today. The challenge involves achieving the desired resolution while maintaining manufacturable process windows. Increases in numerical aperture and reductions in target CDs will continue to shrink process windows and increase mask error factor resulting in larger CD variation. Several techniques such as RELACS, SAFIER, and resist reflow have been developed to improve the resolution of darkfield patterns such as contacts and trenches. These techniques are all post-develop processes applied to the patterned resist. Reflow is a fast process with low cost of ownership, but has two major disadvantages of high temperature sensitivity and large proximity bias. SAFIER and RELACS both have much slower throughput and higher cost of ownership than reflow. SAFIER also is sensitive to temperature and has large proximity bias. In this paper, a novel process is described that reduces the diameter of contact holes in resist up to 25nm without proximity effects. This process uniformly swells the resist film resulting in a shrink of patterned holes or trenches. Results are shown for 248nm and 193nm single layer resists, and a 193nm bilayer resist. This process has the potential to be high throughput with low cost of ownership similar to reflow techniques but without the proximity effects and thermal sensitivity observed with reflow.

Contact hole shrink process is becoming more important option for 45nm node design rules. In general, lithography of contact hole has been harder than that of line and space application due to the low contrast of incident light. The contact hole size for 45nm node device will be around 60nm and this hole size will be the limit of 193nm lithography. High NA exposure tool for 193nm lithography achieves 60nm contact hole resolution, but both under dose margin and depth of focus will be limited. This fact results in the insufficient process window of 193nm lithography. Thus some supporting process should be necessary and a chemical shrink process is one of the possible approach to resolve 60nm contact hole with appropriate process margin. The general chemical shrink process is as follows. Chemical Shrink Material (CSM) is coated on patterned photoresist, and following bake process controls chemical cross-linking reaction and forming a layer insoluble into the developer. As a result pattern size is reduced to desired CD. However current CSM has several issues: i.e. inferior etching durability of CSM than that of 193nm resist and pattern profile degradation after the process. This will be the critical problem for pattern transfer process using CSM. From this point of view, we developed a novel CSM which has good etching durability compared with 193nm resist and does not have a pattern profile degradation. This material consists of aromatic moiety to satisfy good etching durability. Also, the shrink rate and amount are not pitch dependent.

It is becoming difficult for the lithography progress to keep pace with the acceleration of design rule shrinkage and high integration of memory devices. In order to retain the acceleration, low k1 processes beyond the limitation of wavelength are required. Various resolution enhancement techniques have been suggested for this purpose. Especially, chemical shrinkage process utilizing an additional chemical treatment upon patterned photoresist to make patterns finer has been turned out to be effective. The current chemical shrinkage materials are, however, suffering from small attachment amounts or pattern deformation. In this paper, a novel chemical shrinkage material causing large attachments without pattern deformation is suggested. The material is an aqueous solution of two kinds of polymers and its shrinkage mechanism is based on inter-polymer complex formation and gelation principle. Compositions, shrinkage properties, and application studies to contact hole patterns are presented.

The impact of wafer warpage on critical dimension (CD) control is getting larger in ArF lithography. The product wafers with stacked films are warped due to the stress caused by the difference in the film stack structure between the top side and the back side of the wafers. A typical warpage of the product wafers is of convex shape, and the amount of the warpage is larger than 50 μm for 200mm wafer. On the other hand, proximity bake method is widely used in the Post Exposure Bake (PEB). When the warped wafer is placed on the hot plate, the gap between the wafer and the hot plate varies across the wafer. That is, the temperature of the wafer center is lower than that of wafer edge. Such a temperature variation affects CD uniformity within wafer. In particular the fact is obvious in ArF chemical amplified resist because PEB sensitivity of ArF resist is larger than 5nm/degree. In this study we optimize PEB zone temperature within wafer to suit the wafer warpage. This method is based on controlling zone temperature of the PEB hot plate with concentrically divided heaters. We carry out that the CD uniformity for the warped wafer is improved by 70% compared with the conventional process.

512Mbit DRAM with 70 nm design rule was tailored using 0.31k1 ArF lithography technologies. Of the critical mask layers, four pattern layouts were demonstrated: brick wall, line/space, contact and line/contact patterns. For the sake of cost reduction, the conventional technologies were used. Results has shown that SLR (Single-Layer Resist) process, half-tone PSM and the conventional illuminations had a potential of manufacturing 70 nm DRAM. However, it was found that brick wall patterns had asymmetrical shape and total CD uniformity was out of target raging 9.2 nm through 16.3 nm depending mask layouts. We prospect that higher contrast resist and more elaborate resist process will address these problems sooner or later. In case the immersion lithography is not ready around the right time, the feasibility of 0.29k1 ArF lithography was studied through simulation and test, which represented that 0.29k1 technologies were likely to be applied for the development of 60 nm DRAM with the aid of RETs (Resolution Enhancement Technologies) including customized illumination and new hard mask process.

As linewidths continue to decrease in size, preventing smaller defects is becoming critical to maintaining yield. Defects that are caused during the development cycle and attach themselves to the BARC surface, such as water spots or photoresist residues, have always been a concern and have been usually removed at the expense of throughput. Various options are available to reduce these types of defects but each has disadvantages. One such example is a double puddle develop process. The disadvantage of this process is that the exposure dose may have to be changed. Another example is increasing the rinse time to several minutes with an associated reduction in throughput. This paper will discuss rinse alternatives that have been able to reduce develop type defects by up to 70% while also reducing the wafer-to-wafer variation by up to 80%. This process may have a dramatic increase in throughput by keeping the total rinse time under 20 seconds and may have minimal (less than 2% change) impact on measured linewidth. These rinse processes utilize a quick succession of changing spin speeds and accelerations that are acceptable for 300-mm wafer processing. Surfactant-containing rinse solutions designed to reduce line collapse in 193-nm photoresists were also investigated to determine their effectiveness in reducing post-develop defects in concert with the newly developed water rinse process. The rinse processes that will be discussed will have the flexibility of integrating the surfactant-containing rinse solution while maintaining the shortest possible cycle time. At the same time these processes will reduce defects and pattern collapse.

In this paper, surface conditioners were applied during the post-develop process to extend the capability of 248nm lithography processing below the k1= 0.30 threshold. The interaction between surface conditioner and photoresist was found to be a critical parameter in affecting pattern collapse, line width roughness (LWR), and process latitude. Tailoring the surface interaction properties required balancing between surface conditioners that had weak interactions that improved pattern collapse only marginally, to surface conditions with strong interactions that produced a considerable reduction in LWR but provided no benefit to pattern collapse or process latitude when compared to DI water. The surface conditioners with optimized resist interactions provided significant improvement in all performance parameters including reduced pattern collapse, improved LWR, and enlarged usable process latitude.

Anomalous linewidth variations of tens of nanometers have been observed for certain chemically amplified resist processes, a phenomenon we call chemical flare. These variations are highly undesirable, since they fall outside the scope of normal OPC corrective action. Experimental data is presented which clarifies the magnitude and range of chemical flare for two different 193nm resist processes. We observed that very weak background exposure, less than half the dose required to clear the resist, can have profound effects when chemical flare is strong. A TARC coating was found to completely eliminate chemical flare. In the absence of a first principles understanding of this phenomenon, we demonstrate simple screening tests for assessing resist processes.

Since their introduction in the semiconductor industry, chemically amplified resists have proven to offer very valuable benefits to lithography processes, of which improved resist contrast and higher throughput are just two examples. However, the inherent acid diffusion mechanism starts to create some issues. For instance, the reduced chemical contrast due to pronounced acid diffusion during the post-exposure bake will decrease the exposure latitudes and would impact the ultimate resolution. On the other hand, reducing the acid diffusion length will have a negative impact on line edge roughness if one wants to simultaneously keep exposure doses and shot noise effects under control. In this paper, acid diffusion lengths in present-day photoresists at different process conditions are characterized using a lithographic technique. The observed tendencies are correlated with trends in exposure latitude, resolution and the frequency spectrum of line edge roughness. The relationship between acid diffusion length and exposure latitude as well as the relationship between acid diffusion and line edge roughness are addressed in a more fundamental way. The results of this paper highlight the major impact of acid diffusion on important lithographic process characteristics, and the investigated scaling behavior gives guidelines for optimizing exposure latitude and line edge roughness for future technology nodes.

Increasing the understanding of the fundamental resist material characteristics is a necessary preamble to the development of resists with improved resolution and line edge roughness. Material characteristics will not only influence resist sensitivity and resolution, but also may influence the critical dimension control of the lithography process through its effects on line edge roughness (LER). Polymers with controlled molecular weights and polydispersities as well as several non-polymeric resist materials were prepared and studied. This entailed preparing novel derivatives of these non-polymeric materials that were compatible with photoimaging as positive acid catalyzed resists. Examples are presented where non-polymeric resist materials were isolated into single well-defined components that could be compared to mixtures of similar composition. Results are presented on materials properties such as surface roughness and resist resolution. Included in the results are examples of non-polymeric materials that are capable of sub 100-nm resolution as positive resists.

A depth profile of the base developer counterion concentration within thin photoresist films was measured in-situ using contrast variant specular neutron reflectivity to characterize the initial swelling stage of the film dissolution. We find a substantial counterion depletion near the substrate and an enrichment near the periphery of the film extending into the solution. These observations challenge our understanding of the charge distribution in photoresist and polyelectrolyte films and are important for understanding film dissolution in medical and technological applications.

The quartz crystal microbalance (QCM) method was used to obtain precise information about the dissolution behavior of resist polymers. The time evolutions of the resonance frequency and the impedance during the dissolution were measured using the QCM method. The data were simulated using the transmission line method on a four-layer model. Transmission line analysis showed Sauerbrey’s relation to be invalid during the formation and dissolution of the gel layer, although Sauerbrey’s relation was valid during the other development time with the constant thickness of the gel layer. The application of Sauerbrey’s relation in those transition areas brought out artificial changes of the dissolution or swelling rates. The rigidity of the gel layer was also analyzed from 10² to 10⁷ Pa using the transmission line method. The resonance frequency changed drastically at less than 10⁵ Pa during the formation and dissolution of the gel layer. The application of Sauerbrey’s relation in those transitional areas resulted in artificial changes of the dissolution rate from 5 nm/s to 92 nm/s and a shortening of the induction period from 5 s to 2.5 s. Transmittance analysis has shown the validity of quantitative analysis in QCM experiments.

Critical lithographic dimensions will soon place particularly severe demands on the performance of chemically amplified (CA) resists. Although Extreme Ultraviolet (EUV) and 193 nm (immersion interferometric) lithographic results have demonstrated half pitch imaging down to 35 nm there is nonetheless a concern that image blur due to acid diffusion will begin to seriously impact the utility of CA photoresists. Previously we demonstrated that low activation energy resists and E-Beam lithography can be used to print line/space arrays with resolution approaching 20 nm. We described the factors impacting the reactivity of ketal/pHOST based resists and compared the attainable resolution under different processing conditions. In this report we describe studies on acid diffusion emphasizing the role of water in low Ea systems. We also discuss methods for the control of water absorption in low Ea resists.

Previously we have reported on the film-thickness-dependent nature of the dissolution rate of a series of model photoresist polymer resins including: novolac, poly(hydroxystyrene) (PHOST), and bis-trifluoromethyl carbinol substituted polynorbornene (i.e. HFAPNB or hexafluoroalcohol substituted polynorbornene). It was found that the dissolution rate of novolac films displayed very little dependence on the initial polymer film thickness, while the dissolution rates of both PHOST and HFAPNB films displayed a strong dependence on the initial polymer film thicknesses below a critical initial film thickness. This paper presents the results of additional experimental work that was directed at determining the underlying physical cause for the observed variation in dissolution rates with initial film thickness. Fourier transform infrared spectroscopy studies have revealed that the extent of hydrogen bonding in both PHOST and HFAPNB films exhibits a strong dependence on initial film thickness below a critical film thickness. This critical film thickness below which changes in the extent of hydrogen bonding in the film are observed correlates well with the critical film thicknesses below which changes in the film dissolution behavior are observed. In the case of novolac, no substantial dependence in the extent of hydrogen bonding in the films as a function of film thickness is observed. This new experimental evidence suggests that it is the changes in the extent of hydrogen bonding which occur as a function of the initial polymer film thickness which are responsible for the observed dissolution behavior in these materials. Further work is in progress to understand the underlying causes for these differences in the hydrogen bonding behavior of the polymer films.

Polyhedral Oligomeric Silsesquioxane (POSS) derivatives have been investigated as potential candidates for high resolution resists. POSS materials are cage compounds with defined mono-disperse molecular weights. These materials are attractive candidates for molecular resist development because of their commercial availability and the ease with which they can be derivatized. These resists are more suited for bilayer resist applications because of their high silicon content. We have developed positive bilayer resists suitable for 193-nm and other emerging lithographic applications.

The quencher mechanisms in Chemically-Amplified (CA) resists have been investigated. To explain the acid distribution with a variety of acid strengths in the presence of quencher, a new full Acid-Equilibrium-Quencher model (AEQ model) is proposed and examined in solid-model-CA-resist systems. To observe the reactions in the CA resists, real-time Fourier-Transform-Infrared Spectroscopy (FTIR) is employed during post-exposure bake (PEB). The FTIR peaks of the protection groups are detected to measure the reaction kinetics during PEB. The solid-model-CA resists used in this work consist of both a KrF-acetal-type resist with a diazomethane Photo-Acid Generator (PAG) (weaker-photoacid system) and an ArF-ester-type resist with a sulfonium-salt PAG (stronger-photoacid system). The obtained FTIR results are analyzed using conventional Full-Dissociation-Quencher model (FDQ model) and the new AEQ model. The kinetic analysis of the model resists was performed for different quencher loadings. For the weaker-photoacid system, the AEQ model much more accurately predicts the deprotection-reaction kinetics than the FDQ model with the change of quencher content. This suggests the necessity of introduction of the acid-dissociation concept in the case of the weaker photoacid. For the stronger-photoacid system, both the AEQ and conventional FDQ models adequately predict the kinetic results. This shows that the conventional FDQ model is accurate enough to simulate the super-strong photoacid system. Finally, the new AEQ model is introduced in the UC Berkeley STORM resist simulator. Some simulation examples are shown in the paper.

Computer simulators are ideal tools to study complex process spaces, but current lithography simulators are based on empirically-derived continuum approximations and thus are unsuited for investigating properties like line edge roughness (LER) because they do not incorporate molecular level details. A "mesoscale" simulation is described that enables molecular level effects to be captured. This technique is a compromise between accurate, but slow, atomic-level simulations and the less accurate, but fast, continuum models. The modeling of stochastic processes that lead to LER is enabled via use of Monte Carlo techniques. Mesoscale simulation was used to study the effects of added base quencher to overall photoresist performance. Simulations of acid/base kinetics with quencher loadings ranging from 0 to 20% show good qualitative agreement with experimental data. Results show that decreasing aerial image quality increases the root-mean-square (RMS) roughness, whereas increasing base quencher loading improves LER, up to approximately 50% base. A mechanism that explains line edge roughness stemming from acid gradients is proposed. This mechanism is supported by simulations showing that the catalytic chain length varies inversely with acid concentration. Simulation results show that base effectively limits the influence of acid in low concentration regions. A critical drawback of using base additives is significantly reduced photospeed.

Acid generation processes of chemically amplified resists for electron beam (EB) lithography are different from those of chemically amplified photoresists. In chemically amplified EB resists, the role of acid generators is to produce not protons but counter anions of acids through the reactions with low energy electrons generated at ionization events. As the distribution of counter anions determines latent acid image, the dynamics of low energy electrons is important in EB lithography. In this paper, we made clear the effects of dielectric constants of base polymers, the initial separation distances between radical cations and electrons, and the reaction radii of acid generators on the sensitivity and resolution of chemically amplified resists.

Previous work has demonstrated the dependence of photoresist line edge roughness (LER) on the image-log-slope of the aerial image over a wide range of conditions; however, this relationship does not describe the influence of other factors such as photoresist composition or processing conditions on LER. This work introduces the concept of chemical gradients in the photoresist film rather than gradients in aerial image intensity as being a governing factor in the formation of photoresist LER. This concept is used to explain how differences in acid and base concentration in the photoresist lead directly to differences in observed LER. Numerous photoresist formulations were made over a wide range of compositions using 193 nanometer photoresist polymers as the basis. Experimental results coupled with results from simulation show that increasing the gradient of photoacid and hence increasing the gradient of protected polymer and the overall chemical contrast of the system reduces printed LER.

Photoresist line edge roughness (LER) has been highlighted to have an adverse impact on device performance whereas post-etch LER is probably the more relevant metric. Post-etch LER can be reduced by migrating to thicker photoresist films or developing etch processes that are accompanied with lower energy ion bombardment. However, the photoresist and etching processes chosen might have desirable attributes and therefore cannot be changed, e.g. large process window or minimal nested-isolated feature etch bias. In this paper, we demonstrate the reduction of LER at the polysilicon gate level by an inexpensive treatment prior to etch. This HBr plasma treatment can be performed in the main etch chamber with minimal impact on wafer throughput. As a result, during the following etch steps, the photoresist mask is more homogeneous from an etch perspective which in turn helps lower the final LER. In addition, results from blanket etch studies on the various photoresist component films are shown. FTIR spectra of unetched and etched films are compared to demonstrate the preferential etching of certain photoresist/polymer components. The large differences observed in the unetched and etched film surface roughness values for certain photoresist components is postulated as an important source of final LER.

We have studied several factors having an effect on LER in terms of resist chemistry, resist process, CD-SEM metrology, numerical aperture and sigma settings of the exposure tool, and the mask pattern. LER is extracted from the developed resist profile. In ArF lithography process, development and rinse process is very critical because ArF resist is relatively hydrophobic compared to KrF resist. It causes heterogeneous interaction at interface of resist and aqueous solution (developer or deionized water). We improved roughness at contact hole pattern by the introduction of wetting process prior to development. Clear and homogeneous rinsing is also needed to remove scum and swelled resist generated at development step. On the other hand, the roughness of mask pattern is one of the important factors of LER on wafer. We confirmed that this global dislocation is a potent influence but local edge roughness of mask is insignificant to wafer LER. This dislocation of pattern is originated from the lack of shot accuracy in E-beam writer using variable shaped beam.

Recently, gate length variation such as Line Width Roughness (LWR) is severe problem in MPU. The LWR of resist pattern is mainly due to resist material and optical contrast. However it is hard to improve these factors. Many techniques have reported to decrease LWR, but there were no reports which process was more effective for improvement on LWR. Some methods were considered to improve resist roughness. This paper discusses about LWR of ArF resist in gate layer of 65 nm node device. We tied post bake process after development to smooth resist pattern surface by its surface tension. Recess process of resist roughness by using a pattern shrink film was also investigated. LWR’s were 36% and 26% decreased by post baking process and recess process, respectively. Post bake temperature was near resist melting point. From the consideration of thermal flow process, distance of smoothing force by surface tension is considered about several hundreds nm. Pattern shrink film is using acid catalysis reaction, so its distance of smoothing by acid diffusion is considered about one hundred nm. It is considered that effect of post development process is caused by distance of smoothing force. Moreover influence of those processes for lithographic performance will be evaluated.

Electron Beam Direct Write (EBDW) lithography represents a low cost and a rapid way to start basic studies for advance devices and process developments. Patterning for sub-45nm node technology requires the development of high performance processes. Different alternatives for the improvement of EBDW lithography are investigated in this paper for the ASIC manufacturing on 300mm wafer size. Among them, process development has been tuned for clear field equivalent level to improve both line width roughness by monitoring post applied bake conditions, and both process window by specific design correction. Concerning dark field level, process resolution has been improved by a shrinkage technique.

Extending the resolution capability of 193nm lithography through the implementation of immersion has created new challenges for ArF B.A.R.C.s. The biggest of which will be controlling reflectivity over a wider range of incident angles of the incoming imaging rays. An optimum B.A.R.C. thickness will depend on the angle of incidence of the light in the B.A.R.C. and will increase as the angle increases. At high angles different polarization have different optimum thicknesses. These confounding effects will make it increasingly difficult to control reflectivity over a range of angles through interference effects within a single homogenous B.A.R.C. Unlike single layer B.A.R.C.s, multilayer B.A.R.C.s are capable of suppressing reflectivity through a wide range of incident angles. In fact, remarkable improvements in antireflective properties can be achieved with respect to CD control and through angle performance with the simplest form of a multilayer B.A.R.C., a dual layer. Here we discuss the attributes of an all organic dual layer B.A.R.C. through simulations and preliminary experiments. One attribute of an organic over inorganic B.A.R.C. in high-NA lithography is its ability to planarize topography. ArF scanners designed to meet the needs of the 45nm node will have a very small depth-of-focus (DOF) which will require planar surfaces.

Spin on bottom anti-reflective coatings were introduced to the semiconductor industry about 20 years ago to help control substrate reflectivity, improve critical dimension (CD) control, and, most importantly, improve depth of focus window, thus improving throughput and yields. Bottom anti-reflective coating (BARC) materials are either inorganic or organic in nature. Inorganic BARCs are chemical vapor deposition (CVD) films that work on the principal of destructive interference to eliminate reflectivity and demand tight thickness control in the BARC layer. In contrast, organic BARCs are generally spin-on polymeric materials that reduce substrate reflectivity by absorbing exposure radiation to provide greater latitude in thickness control. As an added benefit, organic spin-on BARCs also provide a level of planarization efficiency prior to photoresist deposition to improve depth of focus and process window in the photolithography step. As the feature sizes continue to shrink, etching becomes very challenging due to thin ArF photoresist (PR) layers which are much less etch resistant compared to KrF photoresists. The reduced thickness, as well as the reduced etch resistance, of the PR makes it nearly impossible to use the PR as both an imaging and a pattern transfer layer. This has lead to the development of a new class of spin-on “hybrid” BARC materials which not only have improved etch selectivity to the PR due to inorganic functionality but also have the absorbing properties, and hence offer greater process latitude. Hybrid BARC (H-BARC) materials enable the BARC layer to act as both an anti-reflective coating and as a pattern transfer layer in standard etch-back integration schemes. Due to the polymeric functionality associated with H-BARCs, these materials have exceptional gap-fill and planarization properties and can also be used in via-first dual damascene applications where similar etch characteristics between interlayer dielectric materials and the via-fill BARC enable better CD control. This paper will focus on the benefits of ENSEMBLE ARC materials, a new class of spin-on hybrid BARC materials, which can be used in either standard BARC applications or in via-first dual damascene applications which require that the BARC act both as an anti-reflective coating and as a via-fill material to assist in CD control during trench etch processes. This paper demonstrates lithography with 193-nm resists, resist compatibility, via-fill performance, optical properties, and etch rates with different plasma recipes.

A spin-on sacrificial 193 nm UV absorbing organosiloxane film was developed to facilitate ArF photoresist (PR) patterning. To improve lithographic compatibility with acrylate based photoresists, different performance additives were evaluated as photoresist adhesion promoter. The results suggested that the type and loading of the photoresist adhesion promoter had a large impact on the profile and focus latitude of the patterned photoresist features. An efficient photoresist adhesion promoter candidate was identified, which has minimum impact on other solution and film properties. This work has led to the development of DUO 193 organosiloxane based bottom anti-reflective coating. Application of this film as a blanket level bottom anti-reflective coating or as a fill material for via first trench last (VFTL) dual damascene patterning is possible. The SiO structure intrinsic to this film provides a high degree of plasma etch selectivity to the thin ArF photoresists in use today. Furthermore, an equivalent plasma etch rate between DUO 193 and the low dielectric constant SiOCH films used as the dielectric layer in the backend Cu interconnect structure is possible without compromising the photoresist etch selectivity. Equivalent etch rate is necessary for complete elimination of the “fencing” or “shell” defects found at the base of the etched trench feature located at the perimeter of the top of the via. Advanced ArF PR features of 100 nm in width (and smaller) have been routinely patterned on DUO 193 film. Via fill, plasma etch rate, wet etch rate, ArF PR patterning and shelf life data will be discussed in this presentation.

The patterning targets for EUV resists at the 32 nm node are stringent, and will require significant resist development in order to meet these targets. In this paper, we benchmark the patterning performance of current EUV resists against Intel targets. Resolution data for dense L/S structures, isolated lines, and contact hole structures show that current resists are close to meeting Intel requirements for the 32 nm node, though further optimization is needed. A trade-off is seen between LWR and sensitivity (6.0 nm LWR and 6.8 mJ/cm² for resist A versus 11.1 nm LWR and 2.7 mJ/cm² for resist C). However even at the higher dose, the LWR target is far from Intel’s spe. At best dose and focus sidewall angles of 85° were measured, decreasing by as much as 10° - 12° as the resist moved out of focus by 400 nm.

A chemically amplified resist, Poly(4-hydroxystyrene-co-tertiarybutylmethacrylate-co-MethacrylphenylPOSS) with different Polyhedral oligosilsesquioxane (POSS) loading has been synthesized by free radical polymerization. The incorporation of POSS units into the resist matrix has been found to affect their RIE resistance in O₂ plasma. The thickness of the films were monitored using ellipsometry at various etch intervals to determine the etch rate and selectivity. It was observed that etch rate of these nanocomposite resists were comparable to the standard PHOST and Novolac based resists. HRTEM and HAADF studies showed that the POSS units exhibit a morphology of rectangular crystallites that are responsible for the plasma etch behavior. We have obtained 120 nm (1:1) (Line/Space) feature using 248 nm lithography. The protecting group, tertiary butyl protecting group exhibits acceptable outgassing. Using e-beam lithography, 70nm pattern feature was obtained.

Atomic layer deposition (ALD) is a promising method for depositing high quality, conformal, ultra-thin films. The ability to perform area selective ALD would provide a number of benefits including a reduction in the cost and number of process steps required for patternwise deposition of materials, elimination of possible substrate and device damage induced by plasma etching of thin films, and ability to direct pattern materials that are difficult to etch. Previous attempts have been made to develop area selective ALD processes based on the use of self-assembled monolayers (SAMs). In these schemes, the SAM layers were used to selectively passivate specific regions of a substrate surface and thus prevent ALD. However, the process times required for SAM deposition and problems with SAM defectivity have limited the practical application of such methods. This paper presents a new approach to area selective atomic layer deposition techniques (ASALDT) based on the use of lithographically definable polymeric masking layers that allow deposition only in selected areas of a substrate. It is shown that there are a number of factors that must be considered in designing such patternable polymeric masking materials and processes including: reactivity of the polymer with the ALD precursor species, diffusion of ALD precursors through the polymer mask, and remnant precursor content in the masking film during ALD cycling. Finally, successful direct patterned deposition of TiO₂ is demonstrated using a poly(methyl methacrylate) masking layer that has been patterned using deep-UV lithography.

Multifunctional films have the potential to reduce the number of processing steps to prepare various complex electronic devices and thereby reduce the cost of manufacturing the device and increase the throughput of the process. By combining low dielectric thin film and photoresist technologies into one material, such an advantage could be provided to electronics device markets. Air Products and Chemicals has discovered negative tone photodefinable films having dielectric constant values less than 3.0 that are developable in water and/or aqueous TMAH solutions. The low dielectric films produced via a novel reaction pathway involving the use of photoacid generators (PAGs) provides a versatile link to various feature sizes depending on the choice of radiation source and PAG used. Specific examples of film properties and processing latitude will be presented for these developmental materials.

The 38nm and 32nm lithography nodes are the next major targets for optical lithography on the Semiconductor Industry Roadmap. The recently developed water-based immersion lithography using ArF illumination will be able to provide an optical solution for lithography at the 45nm node, but it will not be able to achieve the 38nm or the 32nm nodes as currently defined. To achieve these next lithographic nodes will require new, very high refractive index fluids to replace the water used in current immersion systems. This paper describes tests and experiments using an interference immersion lithography test jig to develop key technology for the 32nm node. Interference imaging printers have been available for years, and with the advent of Immersion Lithography, they have a new use. Interference immersion image printing offers users a rapid, cost-effective way to develop immersion lithography, particularly at extremely high resolutions. Although it can never replace classical lens-based lithography systems for semiconductor device production, it does offer a way to develop resist and fluid technology at a relatively low cost. Its simple image-forming format offers easy access to the basic physics of advanced imaging. Issues such as: Polarization of the image forming light rays; Fluid/resist interaction during exposure; Topcoat film performance; and the Line Edge Roughness (LER) of resists at extremely high resolutions can all be readily studied. Experiments are described and results are provided for work on: 32nm imaging tests; high refractive index fluid testing using 193nm wavelength at resolutions well beyond current lens-based system capabilities; and polarization configuration testing on 45nm, 38nm, and 32nm L/S features. Results on the performance of resists and topcoats are reported for 32nm L/S features.

An all i-line 0.22 um T-gate process is demonstrated. A resist structure suitable for metal deposition and lift-off is constructed sequentially with two different resist materials. The lithographic process is described in details in this paper.