Concept Of Chemical Amplification Research Articles

Selective Fragmentation of Radiation-Sensitive Novel Polymeric Resist Materials by Inner-Shell Irradiation.

Two key concepts in extreme ultraviolet lithography (EUVL) are important for it to be a candidate for the mass production of future integrated circuits: the polymer formulation and the photofragmentation process. In this work, both concepts were carefully studied. The design and synthesis of radiation-sensitive organic polymeric materials based on the inclusion of a radiation-sensitive tetrahydrothiophenium functional group are outlined. A 1-(4-methacryloyoxy)naphthalene-1-yl)tetrahydro-1H-thiophenium trifluoromethanesulfonate (MANTMS) monomer containing the tetrahydrothiophenium group undergoes homo- and copolymerizations using free-radical polymerization with a 2,2'-azobis(isobutyronitrile) initiator. The surface photodegradation and oxidation of these novel polymeric materials were investigated using highly monochromatized soft X-rays from synchrotron radiation at the carbon K-edge excitation region. An efficient functionalization was observed when the excitation energy was tuned to C 1s → π*C═C. A high rate of defluorination and a loss of sulfonated groups as a result of an increase in the irradiation time for the MANTMS homopolymer thin films were mainly observed under the π*C═C excitation of the naphthyl functional groups. On the contrary, excitation similar to C 1s → π*C═O or C 1s → σ*C-F did not produce important degradation, showing a highly selective process of bond breaking. Additionally, the presence of methyl methacrylate copolymer in the original MANTMS yielded a much higher degree of stability against inner-shell radiation damage. Our results highlight the importance of choosing the right polymer formulation and excitation energy to produce a sensitive material for EUVL without using the concept of chemical amplification.

Towards novel non-chemically amplified (n-CARS) negative resists for electron beam lithography applications

A novel, non-chemically amplified negative resist was synthesized and characterized for next generation lithography applications. This resist material was shown to be directly sensitive to radiation without utilizing the concept of chemical amplification (CAR) and resulted in high-resolution 20 nm features. This resist design is accomplished by copolymers that are prepared from a monomer containing a sulfonium group which is sensitive to e-beam irradiation. Under 20 keV e-beam imaging and TMAH development, a sensitivity of 2.06 μC cm−2 and contrast of 1.8 were obtained. It has an LER of 20 nm, 10 line pattern varies from 1.8 ± 0.3 to 2.3 ± 0.4 nm.

Development of New Advanced Resist Materials for Microlithography

This paper reviews development of advanced resist materials which I have been involved in for more than a quarter century. First, our attempts to increase the main chain scission susceptibility are described. Next, a simple lift-off process for fabrication of magnetoresistive heads for storage devices is presented, which became the industry-standard manufacturing technology. Then, the major focus is going to be placed on the development of chemical amplification resists. Chemical amplification resists achieve a high sensitivity through a catalytic action of a photochemically generated acid. This drastically novel imaging concept was considered laboratory curiosity initially. However, the very first chemically amplified tBOC resist was quickly implemented in mass production of 1 megabit dynamic random access memory devices by deep UV lithography at IBM. Since then the chemical amplification concept has become the paradigm of advanced resist systems, enabling the industry to continue to migrate to shorter wavelengths (from 365 to 248, and then to 193 nm) for higher resolution and to follow the Moore's law. The chemical amplification resist invented for 1 μm resolution can now resolve

Chemical Amplification Resists: Laboratory Curiosity to Paradigm

It has been a little more than a quarter century since chemical amplification resists were invented. They achieve a high sensitivity through a catalytic action of a photochemically generated acid. This drastically novel imaging concept was considered laboratory curiosity initially. However, the very first chemically amplified tBOC resist was quickly implemented in mass production of 1 megabit dynamic random access memory devices by deep UV lithography at IBM. Since then the chemical amplification concept has become the paradigm of advanced resist systems, enabling the industry to shift to shorter wavelengths (from 365 to 248, and then to 193 nm) for higher resolution and to follow the Moore's law. The chemical amplification resist invented for 1 μm resolution can now resolve 30 nm equal line/space patterns and continues to play a pivotal role in microlithography in the foreseeable future. This paper describes the inception and advancement of chemical amplification resists.

Sub-50nm half-pitch imaging with a low activation energy chemically amplified photoresist

Critical lithographic dimensions are rapidly approaching the sub-50nm regime where there is a concern that image blur due to acid diffusion will impose a practical limit to the resolution of chemically amplified (CA) resists. Although recent EUV and 193- and 157nm immersion interferometric experiments have reportedly resolved line-space arrays with individual dimensions on the order of ∼40nm, smaller nested features are likely to prove problematic. Numerous reports suggest that conventional photoresist performance degrades rapidly at half-pitch dimensions in this range. New approaches to processing and materials development of photoresists will likely be required if the concept of chemical amplification is to be extended to the 32nm node and beyond. In this article we show that through materials choice and proper processing, image blur can be controlled to an extent where dense features below 40nm can routinely be resolved in CA resists. We describe our studies on high-sensitivity resists of differing activation energies and demonstrate the effect of postexposure bake conditions on the ultimate resolution. Most notably, electron-beam exposure of a CA resist that requires no postexpose bake has demonstrated half-pitch resolution down to 30nm with reasonable process latitude. Acid diffusion measurements performed on the same systems using a 193nm top surface-imaging-technique correlate with the observed resolution of the different resists and processing conditions. Additionally, this system has been probed to explore the effect of humidity on the rate of the resist deprotection reactions in order to determine the impact this might have on resolution.

A chemically amplified calix649arene-based electron-beam resist

The concept of chemical amplification via cationic polymerization was applied to the novel class of calixarenes as nonpolymeric negative-tone electron-beam resist materials for the first time. By using a calix[4]arene bearing epoxid residues and a photoacid generating triphenylsulfonium salt (PAG) as nonpolymeric chemical amplified resist system (npCAR) a tremendous increase of resist sensitivity was achieved. The high resolution capability of this npCAR is promising. Etching resistances of the npCAR and the commonly used novolak resins are comparable.

Effects of Ester Groups on Proton Generation and Diffusion in Polymethacrylate Matrices

The control of acid generation and diffusion is essential for the improvement of resist performance based on the chemical amplification concept. Polymethacrylates are excellent matrices to study resist reaction mechanisms. The dependence of polymer structure on acid generation and diffusion was investigated using polymethacrylate matrices. The ester groups of the polymers strongly affect the yield and diffusion of protons. This suggests that the yield and the diffusion constant of the acid can be controlled in chemically amplified resists based on a polymethacrylate copolymer by changing the composite ratio of the units.

A chemically amplified calix[4]arene-based electron-beam resist

The concept of chemical amplification via cationic polymerization was applied to the novel class of calixarenes as nonpolymeric negative-tone electron-beam resist materials for the first time. By using a calix[4]arene bearing epoxid residues and a photoacid generating triphenylsulfonium salt (PAG) as nonpolymeric chemical amplified resist system (npCAR) a tremendous increase of resist sensitivity was achieved. The high resolution capability of this npCAR is promising. Etching resistances of the npCAR and the commonly used novolak resins are comparable.

Chemical amplification resists: Inception, implementation in device manufacture, and new developments

AbstractThe chemical amplification concept aimed at dramatically boosting the resist sensitivity was invented at IBM Research in San Jose, CA, in 1980. The sensitivity enhancement is achieved by generating acid by irradiation, which induces a cascade of chemical transformations in a resist film. A chemically amplified resist based on acid‐catalyzed deprotection was quickly employed in the mid‐80s in manufacture of 1 megabit (Mbit) dynamic random access memory (DRAM) devices by deep ultraviolet (UV) (∼250 nm) lithography in IBM. The unexpectedly high‐resolution capability of chemical amplification resists promoted their acceptance in the resist community and the microelectronics industry. All the advanced lithographic technologies (current workhorse 248 nm, maturing 193 nm, and emerging 157 nm, extreme UV, and projection electron beam) depend on chemical amplification resists. This article describes the invention, implementation in device manufacturing, current status, and future perspective of chemical amplification resists. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3863–3870, 2003

A Novel Diphenylmaleimide Dye for Fluorescence Photopatterned Images

Abstract A novel fluorescent diphenylmaleimide dye, 1–BOC, can be converted into non–fluorescent 1–OH by the deprotection of the tert–butyloxycarbonyl group of 1–BOC with photogenerated acid, which makes 1–BOC of an useful material for fluorescence images patterned by a photolithographic method based on chemical amplification concept.

Vis‐sensitive photopolymer containing vinyl ether compound and pyrromethene dye

AbstractA visible light(vis)‐sensitive photoresist based on the concept of chemical amplification was developed utilizing poly(p‐hydroxystyrene) (PHS), 2,2‐bis[4‐(2‐(vinyloxy)‐ethoxy)phenyl]propane (BPA‐DEVE) as a crosslinking agent, N‐trifluoromethylsulfonyloxy‐1,8‐naphthalimide (NIT) as a photoacid generator (PAG) and pyrromethene dyes such as 1,3,5,7,9‐pentamethylbipyrromethene difluoroborate (PRH) and 2,8‐diethyl‐1,3,5,7,9‐pentamethylbipyrromethene difluoroborate (PRE) and 3,3′‐carbonylbis(7,7′‐diethylaminocoumarin) (KCD). On irradiation with an argon ion laser, the photopolymer comprising PRH and PRE exhibited a high sensitivity of 65 and 46 mJ cm−2, respectively. It is suggested that the sensitization mechanism of the pyrromethene dye/PAG system involves singlet electron transfer. The sensitivity of the photoresist increased with the decreasing molecular weight of PHS because of the high dissolution rate. Copyright © 2002 John Wiley & Sons, Ltd.

Norbornene-Derived Quinizarin Dye Molecules for Photoimaging in Polymer Film Based on Chemical Amplification

Abstract A novel photoimaging process in thin films has been disclosed by taking advantage of photolithographic techniques based on chemical amplification concept. The key materials utilized in the process are norbornene-derived quinizarin dye molecules protected with acid-labile tert-butoxycarbonyl (t-Boc) blocking groups.

Digression on chemical electromagnetic field effects in membrane signal transduction — cooperativity paradigm of the acetylcholine receptor

There is ongoing public concern on potential hazards and risks of even small electromagnetic fields (EMFs) such as those emanating from electrical appliances. Evolution and persistence of life in the natural geofields and basic scientific experience in using technical EMFs ( F) suggest that, in general, living matter is remarkably stable against external field perturbations within the technical safety limits of the EM field strengths. Besides the trivial primary effects of EMF on ionic charges and dipolar matter, it is explicitly elaborated that cellular biochemical reactivity and channel transport processes are field dependent. However, equilibrium ( K) and rate ( k) constants are only sensitive to F if the reaction moments Δ M are finite, as seen in the general van't Hoff relationship d ln K/d F=Δ M/ RT. Indeed, it is the difference (Δ M) in the electric or magnetic moments ( M), representing the difference in the field forces on the reaction partners, that determines the extent of the field-induced transitions, say from an inactive conformer of a macromolecule to an active one. If small EM fields, which locally can only cause small shifts in K and k, are to become effective for chemical reactivity, amplification is required. A widely encountered concept of chemical amplification is structural, and thus functional, cooperativity, realized in many biopolymers. The cooperation of n units of such a polymer yields a larger Δ M( n)= nΔ M and exponentially increases the field sensitivity of the overall equilibrium constant K( n)= K n . Using the acetylcholine receptor protein as an example for signal amplification by structural cooperativity, explicit proposals are specified for the presumed amplification of small local field effects on proteins of the classical signal transduction cascades. Electric membrane field amplification by interfacial polarization in external fields is discussed in the context of using electric field pulses to transiently permeabilize cells and tissue for the direct transfer of effector substances and genes in cancer and gene therapy.

Chemical amplification resists: History and development within IBM

The chemical amplification concept was invented at IBM Research and quickly brought into use in the production of dynamic random access memory devices in the company. It has remained as an important foundation for the design of advanced resist systems for use in short-wavelength (<300-nm) lithographic technologies.

Etch resistance enhancement and absorbance optimization with polyaromatic compounds for the design of 193 nm photoresists

The O 2 and SF 6 plasma etch rate reduction of poly methyl methacrylate films provided by a series of adamantane and anthracene derivatives at different loadings was examined. The improvement is substantial at loadings up to 10 %, but further reduction by increasing loading is not easily achieved. Anthracenes have distinctly better performance especially with SF 6 plasmas. Spectral characteristics of anthracene compounds at the 193 nm region allow loadings of 5–10% to produce single layer model resists. The loadings amount depends on the specific compound used and the spectrum of the base polymer. Good sensitivities for 193 nm imaging have been obtained only with acrylate/anthracene formulations based on the concept of chemical amplification with onium salts.

Chemical amplification resists: History and development within IBM

The chemical amplification concept was invented at IBM Research and quickly brought into use in the production of dynamic random access memory devices in the company. It has remained as an important foundation for the design of advanced resist systems for use in short-wavelength (<300-nm) lithographic technologies.

Chemically amplified resists: Chemistry and processes

AbstractContinued advances in mocroelectronic device fabrication are trying the limits of conventional lithographic techniques. In particular, conventional photoresist materials are not appropriate for use with the new technologies that will be necessary for sub‐0.5 μm lithography. One approach to the desing of new resist chemistries involves the concept of chemical amplification, where one photochemical event can lead to a cascade of subsequent reactions that effect a change in solubility of the parent material. The most well‐known chemically amplified resists utilise photchemically generated acid to catalyse crosslinking or deprotection reactions. This paper reviews the acid generator, crosslinking, deprotection and depolymerisation chemistries that have been evaluated for chemical amplification resist processes. Additionaly, process characteristics and resist performance relative to the process environment are addressed.

Resist system based on the cationic photocrosslinking of poly(4‐hydroxystyrene) and polyfunctional electrophiles

AbstractNew resist systems based on acid‐catalyzed, electrophilic aromatic substitution are described. These new resists show high sensitivity to deep UV and E‐beam radiation with values approaching 2 mJ/cm2 and 2 μC/cm2, respectively. The resists are based on a three component system consisting of poly(4‐hydroxystyrene), a polyfunctional, low molecular weight, latent electrophile, and a photoactive onium salt used as an acid generator. Irradiation of the resist film produces a latent image of acid dispersed in the matrix. During the postbaking step the photo‐generated acid reacts with the latent polyfunctional electrophile and releases a reactive carbocationic intermediate with concomitant liberation of acetic acid. The carbocationic intermediate then reacts with neighboring phenolic moieties in a crosslinking reaction. The substitution reaction liberates a proton, making the process catalytic in nature, thus incorporating the concept of chemical amplification. These highly sensitive materials can be used as nonswelling negative multipurpose resists that function in deep‐UV, x‐ray or E‐beam modes. © 1993 John Wiley &amp; Sons, Inc.

Advances in Chemical Amplification Resist Systems

The chemical amplification concept proposed in 1982 to boost resist sensitivities is now well accepted by the lithography community, which stems not only from high sensitivities that chemical amplification resist systems can offer but also from additional benefits of high contrasts and unexpectedly high resolution capabilities. The design flexibility and versatility that the use of acid as a catalytic species offers are another attractive feature of chemical amplification, giving rise to a birth of an entire family of advanced resist systems. Manufacture and prototype fabrication of DRAM's by deep UV lithography have been accomplished with use of chemical amplification resists. However, some process problems uniquely associated with chemical amplification resists have surfaced recently, which include their latent image instability due to their sensitivity toward minute amounts of air-borne contaminants. This paper reviews recent advances made in our laboratory in the field of chemical amplification resist systems and discusses 1) influence of residual casting solvent on absorption of NMP by polymer films, 2) effects of polymer end groups on resist sensitivity, and 3) new imaging mechanisms based on acid-catalyzed dehydration.

Novolak Based Resists for X-ray and Electron Beam Lithography.

X-ray and elctron beam lithography is expected to be leading candidates for the future VLSI's having a minimum dimension below the resolution limit of optical lithography. Since the concept of chemical amplification has been introduced, tremendous progress has been achieved in designing resists for deep-UV, x-ray and electron beam lithography. Recently three component resist systems which contain polymer matrix, photoacid generator and dissolution inhibitor have shown the enhanced sensitivity and excellent resolution. Novel novolak based positive resist containing three components has been developed. The properties of novolak resins with solvent treatment was characterized by GPC, TGA and DSC. The results suggest that the solvent extraction influences the thermal stability and molecular weight of novolak resins. Preliminary synchrotron x-ray lithography shows that KXPR resist containing 0.3 wt% PAG is capable of ca. 0.4μm resolution and 60mJ/cm2 sensitivity . The KXPR resist is also sensitive to electon beam exposure. The resist containing 0.7 wt% PAG has a high sensitivity of ca. 3μC/cm2 with γ 5.1, and is capable of 0.3μm resolution. Etch resistance was evaluated and reported on silicon dioxide and polysilicon layers.