In this manuscript, various fluorine-containing BCPs were synthesized by living anionic polymerization or reversible addition−fragmentation chain-transfer (RAFT) polymerization. The resulted BCPs showed high χ value > 0.2. With similar χ value, we observed that PS-typed BCPs formed microdomains of 5 nm within 1 min at 80°C, whereas polymethacrylate-typed ones required 1 h annealing at 160°C. When rigid side chain was incorporated into the polymethacrylate block, the annealing time can be shortened to 5 min at 160°C. However, the poor film formation of the such BCP with rod-like side chain resulted in rough line pattern after the thermal annealing process. The polymethacrylate-typed BCPs generally requires high boiling point solvents for better film formation and better line patterning.
In recent years, high-χ block copolymers (BCPs) have been reported to achieve sub-5 nm resolution. These BCPs always require long annealing time at high annealing temperature, which may limit their implementation into semiconductor process. Since hot baking time in conventional semiconductor process is normally less than 3 minutes, how to shorter the thermal annealing time at lower temperature becomes a new topic for the sub-5 nm high-χ BCPs. In this manuscript, various fluoro-containing BCPs are synthesized by living anionic polymerization or atom transfer radical polymerization. The best BCP formed thermal equilibrium sub-5 nm nano domains after mere 1 min annealing at temperature lower than 100 °C, which is the fastest thermal annealing process reported so far. BCPs with various morphology and domain size are obtained by precise control of both the length and the molar ratio of the two blocks. The resulted smallest half-pitch of the BCPs are less than 5 nm in lamella and hexagonal morphologies. Linear and starshaped BCPs containing PMMA and fluoro-block are also synthesized, which also shows best phase separation into ca. 6 nm half-pitch, however, the annealing time is 1 hour at 180 °C.
KEYWORDS: Line edge roughness, Monte Carlo methods, Diffusion, Lithography, Chemically amplified resists, Image processing, Electron beams, Extreme ultraviolet, Electron beam lithography, Extreme ultraviolet lithography
It is well-known that line edge roughness (LER) of patterned features in chemically amplified (CA) resists is formed in
the acid generation stage and expected to be moderated by the acid diffusion and development process. To provide an
insight into the limit of LER is essential for the realization of next-generation lithographies such as electron beam or
extreme ultraviolet. Based on the results of Monte Carlo simulation which reproduces dynamics of chemical
intermediates in positive-tone CA resist, we discuss the possibility of low LER (high frequency) after development. It is
found that low LER is achievable; however, the process condition is still strict.
KEYWORDS: Line edge roughness, Monte Carlo methods, Lithography, Molecules, Diffusion, Image enhancement, Electron beam lithography, Ionization, Electron beams, Polymers
Of great importance in post-optical lithographies, such as electron beam (EB) and extreme ultraviolet, is the improvement of line edge roughness or line width roughness of patterned resists. We provide an exposure dose dependence on LER of a latent image in chemically amplified EB resist from 1 to 50 µC/cm2. By using a Monte Carlo simulation and empirical equations, the effects of exposure dose and amine concentration on LER are investigated in terms of shot noise and image contrast. We make clear the correlation between LER and the fluctuation of the initial number of acid molecules generated in resists.
In this contribution, we describe our efforts to develop novel chemically amplified molecular glass (MG) photoresists
based on bulky phenol structures. In contrast to conventional polymeric materials, MG resists possess distinct
advantages, such as smaller molecular size and uniformity in composition. A number of compounds which possess rigid
aromatic backbones were synthesized in our laboratories and evaluated for electron beam lithography. Herein, two new
MG photoresists are discussed in terms of their physical and lithographic properties. In the first section, we introduce
tert-butoxycarbonyl (t-Boc) protected 'Noria-Boc' photoresists as a promising candidate for next generation
lithographic technique. Noria-Boc was synthesized through a condensation reaction between resorcinol and 1,5-
pentanedial. After protection with di-tert-butyl dicarbonate [(t-Boc)2O], the cyclic, bulky and amorphous material was
characterized by a high glass transition temperature (Tg > 120 °C) and excellent film-forming properties. Post-exposure
bake at 140 °C was necessary to ensure complete development of the exposed area and produced sub-100 nm lines. In
the second part, we describe the synthesis and lithographic evaluation of partially t-Boc-protected bulky phenol 'CR1'.
CR1 is also characterized by high glass transition temperature (Tg ≈ 130 °C) and good film-forming properties. Postapply
bake at 130 °C and post-exposure bake above 130 °C were necessary to ensure good contrast under deep UV
(DUV) exposure conditions.
In order to meet the growing demand of the electronics industry for smaller, higher resolution features much recent attention has focused on next generation lithographic techniques, such as Extreme Ultraviolet (EUV) or e-beam lithography. Complementary to this field of research is the design of the next generation of photoresists to produce sub 50 nm feature sizes. Chemically amplified molecular glass resists are among the most promising alternatives to traditional polymeric materials. These materials are monodisperse, amorphous organic molecules which lead to high resolution patterns with low line edge roughness owing to their small size and lack of chain entanglement. In this submission, we describe our work in the development of molecular glass resists. The materials are designed with rigid cores, to ensure high Tg, and with bulky side groups to inhibit crystallization. We show that these materials are capable of producing high resolution feature sizes and show great promise in meeting the demands of emerging next-generation lithographic techniques.
More demanding requirements are being made of photoresist materials for fabrication of nanostructures as the feature critical dimensions (CD) decrease. For extreme ultraviolet (EUV) resists, control of line width roughness (LWR) and high resist sensitivity are key requirements for their success. The observed LWR and CD values result from many factors in interdependent processing steps. One of these factors is the deprotection interface formed during the post-exposure bake (PEB) step. We use model EUV photoresist polymers to systematically address the influence of exposure-dose on the spatial evolution of the deprotection reaction at a model line edge for fixed PEB time using neutron reflectivity. The bilayer consists of an acid feeder layer containing photoacid generator (PAG) and a model photoresist polymer, poly(hydroxystyrene-co-tert-butylacrylate) with perdeuterated t-butyl protecting group. The deuterium labeling allows the protection profile to be measured with nanometer resolution. The evolution of two length scales that contribute to the compositional profile is discussed.
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 (Tg) 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.
The uniqueness in extreme ultraviolet (EUV) Lithography is encouraging the development of new polymer platform as a resist material. The absorbance characteristic of materials at the EUV region demands the use of polymers containing highly transparent silicon atoms. Also very low level of outgassing is required due to the vacuum environment during exposure and the extremely high cost of the EUV tools. To fulfill those requirements, two types of silicon backbone polymers were studied; chemically amplifiable polysilanes and polysilsesquiazanes. In the former case, the direct incorporation of acid sensitive groups into the polymer backbone allows for a solubility switch upon exposure. In the later system, this nitrogen-containing silicon polymer can be cleaved upon exposure to induce a solubility switch. These polymers possess many essential properties including low absorbance, low outgassing, and high sensitivity. Polymers having different substituents and branching ratios were synthesized. The properties of the polymers will be discussed relating to their lithographic performances.
To fulfill industry requirements for EUV resists, the development of entirely new polymer platforms is needed. In order to address transparency issues, we have been studying low absorbance materials, specifically silicon based resist platforms. In this approach, we have synthesized and studied resist materials based on polysilanes, polycarbosilane, and polysilsesquiazanes. Poly(methylphenylsilane) was chemically modified to incorporate polar groups to enhance solubility in polar solvents and developer solution. Copolymerization of the modified polysilane with an acid sensitive monomer has been used to produce chemically amplified copolymers. Preliminary studies have shown promising behavior. Polysilsesquiazanes-based resist were synthesized and tested using a 248 nm stepper. They showed excellent lithographic performance but some issues, including long term stability, are presently unknown. Our strategy to produce silicon-based resist together with outgassing and lithography issues will be discussed.
Performance requirements for EUV resists may require the development of entirely new polymer platforms. In the first approach, we have synthesized norbornene-based copolymers using ring-opening metathesis polymerization (ROMP). Silicon containing norbornenes were synthesized and copolymerized with a series of monomers having acid sensitive and polar groups, including nitrile, carboxylic acid, hydroxyl, and anhydride functions to achieve random copolymers with suitable properties to be applied as resist materials. Using well-characterized metal alkylidene complexes, we could prepared polymers having controlled molecular weights and low polydispersities. From initial exposure studies using an EUV interferometer, we were able to pattern 150 nm pitchs without additional optimization. In the second approach, polysilane has been copolymerized with acid sensitive monomers (acrylate and styrene derivatives) to produced chemically amplified polysilane-copolymers.
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