The combination of immersion lithography and reticle enhancement techniques (RETs) has extended 193nm
lithography into the 45nm node and possibly beyond. In order to fulfill the tight pitch and small critical dimension
requirements of these future technology nodes, the performance of 193nm resist materials needs to further improve. In
this paper, a high performance 193nm photoresist system based on fluorosulfonamide (FSM) is designed and
developed. The FSM group has good transparency at 193nm. Compared to the commonly used hexafluoroalcohol
(HFA) group, the trifluoromethyl sulfonamide (TFSM) functionality has a lower pKa value and contains less fluorine
atoms. Polymers containing the TFSM functionality have exhibited improved dissolution properties and better etch
resistance than their HFA counterparts. Resists based on the FSM-containing polymers have shown superior
lithographic performance for line, trench and contact hole levels under the 45nm node exposure conditions. In
addition, FSM resists have also demonstrated excellent bright field and dark field compatibility and thereby make it
possible to use one resist for both bright field and dark field level applications. The structure, property and lithographic
performance of the FSM resist system are reported.
Reflectivity caused by topography on wafer stacks is very difficult to reduce with the use of thin antireflective bottom layers. A coating of top antireflective layer, with 1/4n wavelength of exposure source (193nm in this case), will create destructive interference between incident and reflected light. This destructive interference reduces the variation of energy deposited in resist of different thicknesses, which in turns, reduces the CD variation over topography. The optimum refractive index of this TARC layer, when coated over a resist with n value of 1.69, is around 1.3. Most currently available commercial TARCs, which are based on fluoropolymers, have an n value of 1.47 or higher. Even for TARCs with n value in this range, the swing amplitude is still in the >20% range. Besides the required low n value necessary for swing reduction, the TARC also should not affect resist image profiles. In this paper, we will discuss a newly developed TARC system which is different from the traditional approach in new TARC design. This new absorbing TARC system has demonstrated a superior capability of reducing CD swing, to less than 5%, without impacting resist image profile. This TARC system can provide a solution to the concern of CD variation over different topography on a wafer in device manufacturing.
Photoresist are commonly used in semiconductor processing as soft masks for pattern transfer into multilayer stacks using reactive ion etching. The etch performance of the photoresist during such a process is an important consideration during resist selection. Since resist composition strongly influences it's etch performance, understanding the correlation is important for resist development as well as etch optimization. In this paper, blanket etch rate of photoresist used in ArF lithography were examined as a function of polymer structure and atomic content. In particular, the impact of Fluorine content on blanket etch rate was studied. Etch results for a diverse sample of development and commercial resists were first fitted with the Ohnishi parameter [2] and ring parameter [3] models. The Ohnishi model correlates the carbon, hydrogen and oxygen atomic content of the resist to blanket etch rate whereas the ring parameter model is based on the cyclic carbon content. Since some of the evaluated resists contained fluorine which significantly influences the etch performance, both models were found to be inadequate in assessing its impact. Thus we introduce a modified Ohnishi parameter model to help examine the relative contributions due to resist fluorine content. With the new empirical model, good fits were obtained for etch rates of a fluorine containing resists. The model also enabled analysis of the etch process to determine the relative influence of oxygen versus fluorine content in the resist on etch rate. Finally, the model was utilized to design newer etch resistant materials and the improved etch performance was verified.
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.
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.
KEYWORDS: Lithography, Etching, Photomasks, Semiconducting wafers, Metals, Critical dimension metrology, Silicon, Image processing, Back end of line, Finite element methods
This paper will present results obtained during the early development of a lithography process to meet the requirements of the 65 nm node in the BEOL. For the metal levels, an IBM/JSR jointly developed trench level resist was characterized and implemented. Resist image profile, process window, through pitch performance, image shortening and the effect of illumination conditions are discussed. Results from focus - exposure monitor (FEM) wafers are shown which were characterized for minimum resolution, process window and electrical continuity through a maze structure. For the via levels, results from another IBM/JSR jointly developed resist with high resolution and process windows are described. Process windows for nested and isolated vias are given, as well as results showing the improvement in process window and resolution due to the ARC etch. The results also include FEM measurements showing the electrical continuity through simple via chain structures versus the dimension of the via.
The mask fabrication industry is slowly migrating to chemically amplified (CA) resists to take the advantages of their high contrast, resolution, and sensitivity. During this migration process, the industry has encountered several problems associated with CA resists such as baking homogeneity of thick mask plates on hot plates, footing on Cr masks, and storage stability of mask blanks. In addressing these issues, we have adopted a low Ea CA resist platform to overcome the bake latitude issue. The resist formulation has been reformulated to reduce the footing and a new package method has been introduced to extend the storage of the blanks. In addition, we will also discuss our studies on two major areas, such as sensitivity and etch resistance, which we think is extremely important for E-beam resists in the future. The mask industry started with 248nm DUV CA resist systems and then found out that there was a need for even higher sensitivity resist systems to address the throughput issue. In our early study, we have observed that by simply increasing photoacid generator loading in the resist formulation we were able to increase the sensitivity, but there was a significant reduction in the dose latitude. After studying the dissolution and inhibition properties of different PAGs, we have been able to optimize PAG and base loading in combination with proper choice of PAGs to achieve high sensitivity and large dose latitude. The new resist formulation exhibits a large dose latitude of 38% for 100 nm l/s images with high sensitivity of 4.4μC/cm2 at 100 kV. Due to the electron scattering effect and the image collapse issues with thicker resists, thinner imaging layer is desirable. Sufficient etch selectivity is needed to compensate the insufficient resist thickness. Therefore, there is a need to develop a high Cl2/O2 RIE (used in Cr etch process) etch resistant resist system for mask making. We have reported earlier that a resist formulation based on blending KRS-XE with SSQ polymer has resolved 50nm l/s resist images with etch rate 20% better than conventional novolak I-line resist systems. Since then, we have investigated a few new SSQ polymers and found some lithographic improvement in this new blending systems due to better compatibility of the SSQ polymer to the KRS-XE.
While evaluating 193 nm, and early versions of 157 nm and EUV resists, the lithography community has focused on post-develop LER values derived from image analysis of top-down SEM micrographs. These numbers, however, do not capture the tendency of a resist to facet and roughen during plasma etching processes. They also do not convey any information about the role of the anti-reflective coatings/hard masks in the transfer of resist roughness into the underlying substrate. From a manufacturing perspective, it is the "LER" of the final etched substrate that is more important. This paper systematically studies the impact of resist polymer platform and thickness, etching conditions, and presence of organic and inorganic anti-reflective coatings/hard masks on substrate roughening. An AFM technique, previously developed by Reynolds and Taylor, is used to measure the feature sidewall roughness as a function of etch depth. This technique enables us to calculate the sidewall roughness of the resist, ARC/hard mak and substrate surfaces simultaneously, and determine correlations that may exist between these values. The paper identifies and demonstrates patterning methodologies that can be used to achieve "smooth" substrate surfaces even when the resist is "thin".
In an effort to design our next generation resist materials for sub-100nm lithography, we have introduced the hexafluoroisopropanol (HFA) functionality into the cyclic olefin (CO) polymer structure. It is found that the fluorine-containing HFA group not only helps reduce the 157nm optical density (O.D.) of the polymer and makes it suitable for 157nm application, but also dramatically improves the dissolution properties of the resulting CO polymer. Copolymers with a wide range (20-80%) of norbornene HFA (NBHFA) concentrations show little swelling behavior in aqueous base developer. The dissolution properties of the CO polymer could be further improved by combining the HFA and lactone structures in the CO polymers. This new version of CO polymers maintain a good etch resistance and excellent surface roughness after etch despite the fluorine content. Lithographic evaluation of resists based on these polymers (Cobra 5K) using a 193nm exposure tool (0.75 NA) reveals that Cobra 5K has a low post exposure bake (PEB) sensitivity (<0.5 nm/°C), good process window for both line/space (L/S) and contact holes patterns, and outstanding resolution capabilities especially for contacts application (<100nm).
The performance of KRS-XE, a low activation energy, chemically amplified resist designed specifically for mask making with electron beam lithography, has been extended in terms of its sensitivity, coated-film stability and etch resistance. By careful manipulation of resist composition, high sensitivity formulations have been generated that will allow exposure doses of less than 10 mC/cm2 with 50 keV electron beam tools. This sensitivity enhancement has been achieved without sacrificing the robust process latitude previously reported for this resist. The performance of this resist can be maintained, even in coated film form, for prolonged periods of time by careful packaging of the coated films. Additionally, formulations with etch resistance versus chlorine/oxygen plasma in excess of that of novolak-based resists have been generated by the incorporation of organometallic additives. The combination of these improvements leads to resist formulations that will allow the high resolution and throughput that is demanded for state-of-the art mask making applications.
The objective of this report will be to clarify the maturity of the current 193 SLR materials. We are going to report on all major platform chemistries, i.e.,(meth) acrylate system, ROMP system, cyclic olefin addition system, cyclic olefin/maleic anhydride system, vinyl ether/maleic anhydride system, and cyclyzed system at the same time. We are going to discuss maturity of each platform from several viewpoints such as polymerization process, physical properties of the resins, lithographic performances of the resists, and process latitude of the resists including etch performances. We are also referring to several critical issues such as etch resistance, surface roughness after etch, line slimming, etc. Three major platform chemistries, (meth)acrylate, COMA, and addition, are selected in order to cover the whole spectra of layer requirements. Those three systems respectively show characteristics lithographic performances.
Monomer components and composition of a resist polymer have large influence on its lithographic performance. Finding the right components and composition for a resist polymer involves laborious systematic synthesis of different polymers. On the other hand, post-modification offers a convenient way to incorporate desired functional groups into an existing polymer and hence improve its lithographic performance and mechanical properties. Using this method, different groups could be quickly tested and the results could direct the future design of new resist materials. Another advantage of this method is that functional groups which are sensitive to the polymerization condition could also be incorporated. In this paper, we demonstrated the feasibility of using the post-modification method. Through a simple esterification reaction in which the acid groups react with alkyl halides in the presence of 1,8- diazobicyclo[5.4.0]undec-7-ene(DBU) or trialkylamine, three different functional groups were incorporated into the existing Ibm Version 2 (V2) methacrylate polymer. The post- modification reaction gave high yield and it is possible to control the percentage of the acid groups modified by the initial feeding ratio fo the alkyl halide and the carboxylic acid. Depending on the structures of the added groups, the post-modified resist materials demonstrated improved lithographic performances such as better compatibility towards 0.26 N developer and better etch-resistance than the precursor materials. The synthesis, characterization and lithographic performance of the modified polymers are presented.
In this paper, we have shown the progress we have made in improving reactive-ion-etch stability and lithographic performance of IBM 193 nm resist materials. Using selectively functionalized cyclicolefins, we have developed 193 nm resists with etch stability and post-etch surface roughness comparable to those of the matured, state-of-the-art DUV resists. Furthermore, we have also demonstrated dramatically improvement in dense line (100 nm 1:1 L/S) and semi-dense line (< 100 nm 1:2, 1:3 L/S) resolution using resolution enhancement techniques such as alternate phase shift mask.
A MEMS micro-cooling system which comprises microchannel, micropump and pin-fin fan-sink technologies is proposed to meet the need of innovative and advanced IC cooling techniques for the microelectronics industry. An analytical study is conducted by employing a self-developed computer code. This study shows that the closed-loop MEMS micro- cooling system under the steady-state condition with water as the coolant has a capacity to remove heated flux as high as 100 W/cm2 from the flip chip into the ambient. This can be done while maintaining the maximum temperature on the surface of the flip chip below 100 degrees C. Simulation and analysis of flow and heat transfer performance on this single-phase forced convection MEMS micro-cooling system are performed in both laminar and turbulent flows. The design parameters which include the coolant inlet pressure, the geometry of the silicon microchannel, the ambient temperature as well as the variety of the aluminum pin-fin fan-sink coolers show that these variables all have significant effect on the working performance of the system. The simulation results validated this new compact and highly efficient MEMS micro-cooling system.
The phase-change media, such as GeSbTe and AglnSbTe, are widely applied in rewritable DVD-RAM, CD-RW, and PD optical disks. Before information can be recorded on these disks, the initialization process that changes phase-change media from as-deposited amorphous state to crystalline state must be completed.
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