Dry Etch Resistance Research Articles

New Resin Systems for 157nm Lithography.

The development of sufficiently transparent resin systems is one of the key elements required for a successful and timely introduction of 157nm lithography. This paper reports on the Simple Transmission Understanding and Prediction by Incremental Dilution (STUPID) model, a quick back-of-the-envelope increment scheme to estimate the absorption of polymers at 157nm. A number of promising candidate resins based on norbornenes are discussed, and results with a first 157nm resin system developed at the University of Austin are presented. The new system is based on copolymers of norbomene-5-methylenehexafluoroisopropanol (NMHFA) and t-butyl norbornene carboxylate (BNC), formulated with an acetal additive obtained by copolymerization oftbutyl norbomene-5-trifluoromethyl-5-carboxylate (BNTC) with carbon monoxide. Lithographic performance of this system extends to 110nm dense features using standard illumination and a binary mask, or 80nm semi-dense and 60nm isolated features with a strong phase shift mas . The dry etch resistance of this resist is found to be slightly lower than APEX-E DUV resist for polysilicon but superior to it for oxide etches.

Novel linear and crosslinking polymers for nanoimprinting with high etch resistance

Aromatic polymers based on methacrylates (linear polymers) and multifunctional allylesters (crosslinked polymers) have been prepared. They feature high dry etch resistance and good imprintability in a hot embossing process. The crosslinked polymers and their prepolymers were investigated in detail. Their characteristic molecular weight distribution and thermo-mechanical behaviour were studied with respect to the crosslinking process and compared with those of linear polymers. The thermal stability of imprinted patterns has been investigated for both, linear and crosslinked aromatic polymers. The latter ones show excellent stability up to test temperatures of 200 °C directly after the imprint process.

A New Platform for ArF Lithography.

A new class of photoresist matrix polymers based on vinyl ether-maleic anhydride (VEMA) alternating copolymers were developed for ArF single-layer lithography. These polymers were synthesized by radical polymerization of alkyl vinyl ether-maleic anhydride, and acrylate derivatives having bulky alicyclic acid-labile protecting groups. They showed a good controllability of polymerization and high transmittance. Also, the resists showed a good adhesion to the substrate, high dry-etching resistance against CF4 mixture gas (1.02 times the etching rate of DUV resist), and high selectivity to the silicon oxide layer in etching. The resolution and pattern profiles were not deteriorated with the PED time, 30min. Using an ArF excimer laser exposure system with 0.6NA, 120nm L/S patterns have been resolved with conventional illumination

High etch-resistant EB resists employing adamantyl protective groups and their application for 248-nm lithography.

We developed high-etch resistant resists for electron beam (EB) lithography. The incorporation of 2-alkyl-2-adamantyl groups as cleavable protective groups in a vinylphenol-methacrylate copolymer enabled us to enhance the dry-etch resistance and obtain excellent lithographic performance. In this paper, we investigate the reactivity of 2-methyl-(MAd) and 2-ethyladamantyl (EAd) group for an acidic condition as well as the heat-flow resistance of the resist. In addition, we applied vinylphenol-2-ethyl-2-adamantyl methacrylate (VP-EAdMA)-based resist to 248-nm exposures. We found that the reactivity of the EAd group was 2.5 times higher than that of the MAd group. We also found that the resist had a 140-nm resolution at 13.2mJ/cm2 without optimization of the process conditions. We think that these resists can be used for both EB and 248-nm exposure systems.

High contrast chemically amplified 193 nm resist for gigabit dynamic random access memory generation

Four Gb dynamic access random memory (DRAM) cell patterns which have a 0.12 μm design rule were demonstrated by using a high contrast chemically amplified 193 nm positive resist and high resolution exposure. All critical layers of 4 Gb DRAM, such as isolation, word line, contact hole, bit line, and storage node, were successfully resolved with suitable focus margin. The dissolution contrast of the resist film and the slope of dissolution rate curve were much higher than those of conventional polyhydroxystyrene based chemically amplified KrF positive resist. Moreover, the dry etch resistance of the resist film for both the polysilicon etch and the oxide etch was better than those of KrF resist. These results indicated that this resist material has enough potential for practical use. Furthermore, the resist profile simulation showed that mass production of 4 Gb DRAMs can be achieved by a combination of a high contrast resist and a higher numerical aperture lens under annular illumination.

Poly(t-butyl-3α-(5-norbornene-2-carbonyloxy)-7α,12α-dihydroxy-5β-cholan-24-oate-co-maleic anhydride) for a 193-nm photoresist

A copolymer of t-butyl-3α-(5-norbornene-2-carbonyloxy)-7α,12α-dihydroxy-5β-cholan-24-oate and maleic anhydride was synthesized as a matrix polymer for ArF excimer laser lithography. The polymer has an excellent transmittance at 193nm and possesses good thermal stability up to 255°C. The resist formulated with the polymer showed better dry-etching resistance than the conventional KrF excimer laser resist for chlorine and oxygen mixed gas. A 0.15μm line and space patterns were obtained at a dose of 18mJcm−2 using an ArF excimer laser stepper.

Improvement of Dry Etching Resistance of Resists by Deep UVCure

The improvement of dry etching resistance of photoresists by the deep UV cure has been attempted. We have tried deep UV cure under N2 gas flow for KrF chemically amplified resists and obtained the same level of etching rates as novolak resists. While the rates increased under dry air. The resists after deep UV cure under both N2 and dry air were found to be cross-linked. The increase of carbonyl in Fourier transform infrared (FT-IR) spectra under dry air may suggest that oxygen atoms in the polymer structure reduce the etching resistance. For ArF resists, the combination of the incorporation of acryl unit into methacrylate polymer and deep UV cure under N2 was an effective method for improving the dry etching resistance. Using the model ArF resist consisting of acryl polymer, we obtained the same dry etching resistance as a KrF resist with inhibiting film shrinkage by optimizing the parameters of the deep UV cure.

Dissolution characteristics of chemically amplified 193 nm resists

The dissolution kinetics of two types of chemically amplified positive 193 nm resists were investigated; a ter-polymer resist consisting of poly(tricyclodecylacrylate-co-tetrahydrodpyranyl-methacrylate-co-methacrylic acid) and triphenylsulfonium triflate as a photoacid generator, and a copolymer resist consisting of poly(carboxytetracyclododecylmethacrylate-co-tetrahydro-pyranyloxy-carbonyl-tetracyclododecylmethacrylate) and triphenylsulfonium triflate as a photoacid generator. The dissolution rate contrast was higher and the slope of dissolution rate curve was steeper for the ter-polymer resist than those for the copolymer resist. However, the Arrhenius plots of the dissolution rates were straight lines for both resists irrespective of the exposure doses. This indicates that only one mechanism determines the dissolution of both resists, and it is believed that the dominant rate-determining step in both resists is the tetramethylammoniumhydroxide penetration into the resist films. The resolution capability of the ter-polymer resist was very high, 0.14 μm lines and spaces pattern. The resolution capability of the copolymer resist was moderate, 0.16 μm lines and spaces in spite of its lower dissolution contrast and smaller slope value. In addition, the dry-etch resistance of both resists was close to that of a conventional polyhydroxystyrene base KrF resist. These results indicate that both the ter-polymer and the copolymer resists are candidates for practical use.

Pd(II)-catalyzed addition polymerization and ring opening metathesis polymerization of alicyclic monomers: routes to new matrix resins for 193 nm photolithography

A series of alicyclic polymers designed for 193 nm photoresist applications have been synthesized and characterized. These polymers were synthesized by Pd(II)-catalyzed addition and ring opening metathesis polymerization techniques. Methods for removing residual metal complexes of Pd(II) and Ir(IV) from alicyclic polymers were developed. The low absorbance of these polymers at 193 nm and their high dry etch resistance make them attractive candidates for 193 nm lithography. When formulated with onium-type photoacid generators and plasticizers in propylene glycol monomethyl ether acetate, these photoresists have demonstrated high resolution and high sensitivity.

0.1-μm p/sup +/-GaAs gate HJFET's fabricated using two-step dry-etching and selective MOMBE growth techniques

This paper reports the first successful fabrication of high-performance, 0.1-/spl mu/m p/sup +/-gate pseudomorphic heterojunction-FET's (HJFET's). By introducing the two-step dry-etching technique which compensates for the poor dry-etching resistance of PMMA, 0.1-/spl mu/m or less gate-openings with a high aspect-ratio of 3.5 in SiO/sub 2/ film are achieved. In addition, by using the gate electrode filling technique with selective MOMBE p/sup +/-GaAs growth, 0.1-/spl mu/m voidless p/sup +/-GaAs gate electrodes with a high aspect-ratio are achieved for the first time. The fabrication technology leads to a reduction of external gate fringing capacitance (Ce/sup ext//sub f/) in a T-shaped gate-structure and an improvement in gate turn-on voltage. The fabricated 0.1-/spl mu/m, T-shaped, p/sup +/-gate n-Al/sub 0.2/Ga/sub 0.8/As/In/sub 0.25/Ga/sub 0.75/As HJFET exhibits a high gate turn-on voltage (V/sub f/) of about 0.9 V, and a good gm/sub max/ of 435 mS/mm. Also, an excellent microwave performance of f/sub T/=121 GHz and f/sub max/=144 GHz is achieved due to the C/sup ext//sub f/ reduction. The technology and device show great promise for future high-speed applications, such as in power devices, MMIC's, and digital IC's.

Cyclization Reaction in Acrylonitrile-Contained Acrylic Copolymers and Its Possible Application for the Improvement of Dry Etch Resistance for Photoresists.

Acrylonitrile (AN)/methacrylic acid (MAA) copolymer and AN/tert-butyl methacrylate (tBMA)/MAA terpolymer were prepared, and their dry etch resistance were measured. The excellent dry etch resistance found in these materials were attributed to the contribution of some induced chemical reactions. To further understand their roles in the improvement of dry etch resistance, the reactions especially the thermally induced cyclization reaction were investigated in detail. It was found that thermally induced cyclization of the nitrile groups in carboxyl acid-contained copolymers closely depended on the content of the acidic component. Protection of the acid moiety through esterfication thus suppressed the occurrence of the reaction. Conversely, cleavage of the protection groups led to the resumption of the reaction. Attempt was made to correlate the increase of fry etch resistance upon thermal treatment with theformation of cyclized structures.

5690747 Method for removing photoresist with solvent and ultrasonic agitation

A series of alicyclic polymers designed for 193 nm photoresist applications have been synthesized and characterized. These polymers were synthesized by Pd(II)-catalyzed addition and ring opening metathesis polymerization techniques. Methods for removing residual metal complexes of Pd(II) and Ir(IV) from alicyclic polymers were developed. The low absorbance of these polymers at 193 nm and their high dry etch resistance make them attractive candidates for 193 nm lithography. When formulated with onium-type photoacid generators and plasticizers in propylene glycol monomethyl ether acetate, these photoresists have demonstrated high resolution and high sensitivity.

Lithographic performance of 193 nm single and bi-layer materials.

For 193nm lithography several resist options are available such as single layer in combination with anti-reflective layers, bi-layer and top surface imaging. Single layer resist materials are preferred by the industry because of their limited complexity. A bi-layer resist process however has its inherent resolution and processing latitudes advantage as the imaging takes place in a thin top resist layer. Both single layer and bi-layer resists havebeen evaluated in terms of lithographic performance such as resolution, linearity, process windows and proximity effect. While satisfactory results are obtained with the single layer resist, the bi-layer results are still superior. Critical step in the bi-layer process is the dry development in an oxygen plasma. The dry development step has been optimised. The bi-layer resist shows a resolution down to 0.12μm with wide processing latitudes, adequatereflection control and good dry etch resistance. The resolution and processing windows were even further increased by the use of off-axis illumination.

5691117 Method for stripping photoresist employing a hot hydrogen atmosphere

A series of alicyclic polymers designed for 193 nm photoresist applications have been synthesized and characterized. These polymers were synthesized by Pd(II)-catalyzed addition and ring opening metathesis polymerization techniques. Methods for removing residual metal complexes of Pd(II) and Ir(IV) from alicyclic polymers were developed. The low absorbance of these polymers at 193 nm and their high dry etch resistance make them attractive candidates for 193 nm lithography. When formulated with onium-type photoacid generators and plasticizers in propylene glycol monomethyl ether acetate, these photoresists have demonstrated high resolution and high sensitivity.

High-Aspect-Ratio Nanometer-Pattern Fabrication Using Fullerene-Incorporated Nanocomposite Resists for Dry-Etching Application

This paper presents the improved performance of a nanocomposite resist system that incorporates an unseparated mixture of fullerenes C60 and C70 into ZEP520, a positive electron-beam resist, particularly focusing on the enhancement of mechanical strength and dry-etching resistance. This system exhibits similar improvements to that of a pure C60-incorporated system; 90-nm-pitch high-aspect-ratio (>5) resist patterns without pattern collapse and a 10-% enhancement of dry-etching resistance are obtained in a 10-wt% fullerene mixture-incorporated system due to the reinforcement effect induced by the fullerene incorporation. In addition, 80-nm-pitch resist patterns are successfully transferred to SiN film by C2F6-reactive ion etching without any harmful effects. The use of an unseparated mixture of C60 and C70, which is commercially available at a much lower price than pure C60, will greatly facilitate the practical application of the nanocomposite resist system from the economic point of view.

Dissolution Inhibitors for 193-nm Chemically Amplified Resists

Dissolution characteristics and adhesion of 193-nm resists have been investigated by using molecular orbital calculations. The calculation indicated that naphthalene compound had better adhesion than alicyclic compounds by a factor of 1.2. Another calculation result obtained indicated that naphthalene was more hydrophilic than alicyclic compounds. In order to improve the adhesion and dissolution characteristics of the alicyclic resist, introduction of the naphthalene backbone into alicyclic resists was attempted in the form of additives (dissolution inhibitors) or copolymer components. Dissolution inhibitors that have simultaneously a naphthol novolak backbone and a characteristic generate carboxylic acid, such as tetrahydropyranyl ester of naphthol novolak compound condenced with glyoxlic acid (NV4THP), were the most effective dissolution inhibitors increasing dry etch resistance of base polymer by 14% and pattern resolution of original resist by 10%. The naphthalene dissolution inhibitor also largely improves pattern adhesion. These results were consistent with above-mentioned calculation results. 193-nm resists containing vinyl naphthalene in the copolymer structure were also investigated and fundamental resist requirements were satisfied with this polymer by adding adamantane dissolution inhibitor di-tert-butyl 2-((1-adamanthyl)carbonylmethyl) malonate (ADTB).

Fabrication of microlens arrays by direct electron beam exposure of photoresist

A novel process has been developed for the fabrication of dry-etch masks capable of defining diffractive structures in quartz. Shipley S1805 and UVIII photoresists have been patterned by electron beam lithography to exploit the high dry-etch resistance of photoresist and the attributes of electron beam lithography. The yield, linewidth fidelity, uniformity, verticality and resolution of the diffractive structures demonstrate that the process is suitable for submicron optics and avoids process repeatability problems often encountered in fabrication procedures involving metallization followed by lift-off or wet etching.

New ArF Single-Layer Resist for 193-nm Lithography.

A new class of photoresist matrix polymer based on alicyclic cyclopolymer was developed for use in ArF single-layer lithography. A novel polymer was synthesized by terpolymerization reaction between tert-butyl methacrylate and alicyclic-malefic anhydride alternating copolymer, which has a hydroxy substituent on the alicyclic group. The polymer showed good adhesion property to Si- substrate and adequate dissolution behavior in a 2.38wt% TMAH aqueous solution, high thermal stability up to 180°C, and a good dry-etch resistance against CF4 mixture gas (1.14 times the etching rate of novolak resist). Using an ArF excimer laser exposure system, a 140nm line and space patterns have been resolved.

Synthesis and Dissolution Characteristics of Novel Alicyclic Polymers with Monoacid Ester Structures.

We have developed novel alicyclic polymers having monoacid ester structures by alcoholysis of non-conjugated cyclic diene and malefic anhydride copolymers. This polymer, named ALPHA, exhibited good solubility (10-50nm/sec) in 0.113% aqueous tetramethyl-ammonium hydroxide solution without swelling. Absorbance was around 0.6 μm-1 at 193nm. Dry-etching resistance for Cl2/BCl3 gas was the same as that of polyhydroxystyrene. A two-component resist system, consisting of 1-ethoxyethyl-protected ALPHA polymer and onium salt, produced 0.20-μm line-and-space patterns using a KrF excimer laser stepper with a phase-shifting mask. Consequently, we believe ALPHA is suitable as a base polymer for ArF excimer laser resists.

Chemically Amplified Silicon Containing Resist for ArF Excimer Laser Lithography.

A new positive chemically amplified resist which consists of novel methacrylate terpolymer with bis(trimethylsilyl)isopropyl group and a photoacid generator has been developed for ArF excimer laser photoresists. The polymer structure and properties was evaluated by 1H-NMR, UV, FT-JR. DSC, TGA and GPC. This new terpolymer demonstrates good thermal stability up to 135°C, good dry-etching resistance, high transparency (75%) for a ArF excimer laser exposure. Preliminary line and space patterns were obtained using an ArF excimer laser exposure system.