Ultrafast deep UV lithography using excimer lasers

Various excimer laser wavelengths have been used, both in mid- and deep-UV regions—308 nanometers (nm) from XeCl, 249 nm from KrF and 222 nm from KrCl–to delineate images in a number of resists. The quality of the images obtained with the laser exposures, the absence of speckle, and the insignificant loss of resist reciprocity make excimer laser lithography an attractive technique. The ultrafast exposures possible with this method significantly lessen the sensitivity requirements on deep UV resists, making the choice of the resist more flexible.     

Novel positive deep UV resist for KrF excimer laser lithography

A novel positive deep UV resist for KrF excimer laser lithography has been developed. The resist is composed of 1,7-bis(4-chlorosulfonyl phenyl)-4-diazo-3,5-heptanedione as the alkaline dissolution inhibitor and an alkali-soluble sytrene polymer as the main-polymer. 1,7-bis(4-chlorosulfonyl phenyl)-4-diazo-3,5-heptanedione has great capability of alkaline dissolution inhibition. High thermal stability and excellent photobleachability at 248 nm of the compound are also characterized. The alkali-soluble styrene polymer has a high transmittance of 70% in 1.0 μm thickness at 248 nm. The novel positive resist had an excellent property for dissolution kinetics and photobleaching. We achieved high aspect ratio half-micron pattern fabrication in 1.0 μm thickness using the new resist.     

A negative resist for KrF excimer laser lithography

The design and preparation of a series of negative resists for KrF excimer laser lithography are described. Each resist is composed of poly(hydroxystyrene) and an aromatic azide. The base resin shows high transmittance of 62%/μm at 248 nm, when p-ethylphenyl p-azidophenylsulfonate. 4-azido-4α-methoxy-chalcone, 1-(4 azidobenzylidene)-3-(α-hydroxy-4-azidobenzyl)-indene, 4,4α-diazido-3,3α-dimethoxybiphenyl, or 1-(4-azidostyryl)-5, 5-dimethyl-2-cyclohexen-1-one is employed as a sensitizer. These azides are obtained by red-shifting the absorption maxima to lower energy regions than the exposing wavelength of 248 nm. Transmittance of resists can be controlled from 10 to 30%. The resist is exposed with a KrF excimer laser stepper and developed in an alkaline solution. Sensitivities of about 15 mJ/cm² are observed. A good, subhalf-micron resist profile is achieved. The photochemical reaction mechanisms of poly(hydroxystyrene) and 4,4α-diazido-3,3α-dimethoxybiphenyl were studied at 248 nm and 313 nm exposure. Quantum yield for photodecomposition at 248 nm is seven times larger than that at 313 nm, but dissolution-inhibition effects are larger at 313 nm exposure. Consequently, the resist shows higher sensitivity at 313 nm than at 248 nm.     

Preparation of Ultrafine Fe–Pt Alloy and Au Nanoparticle Colloids by KrF Excimer Laser Solution Photolysis

We prepared ultrafine Fe–Pt alloy nanoparticle colloids by UV laser solution photolysis (KrF excimer laser of 248 nm wavelength) using precursors of methanol solutions into which iron and platinum complexes were dissolved together with PVP dispersant to prevent aggregations. From TEM observations, the Fe–Pt nanoparticles were found to be composed of disordered FCC A1 phase with average diameters of 0.5–3 nm regardless of the preparation conditions. Higher iron compositions of nanoparticles require irradiations of higher laser pulse energies typically more than 350 mJ, which is considered to be due to the difficulty in dissociation of Fe(III) acetylacetonate compared with Pt(II) acetylacetonate. Au colloid preparation by the same method was also attempted, resulting in Au nanoparticle colloids with over 10 times larger diameters than the Fe–Pt nanoparticles and UV–visible absorption peaks around 530 nm that originate from the surface plasmon resonance. Differences between the Fe–Pt and Au nanoparticles prepared by the KrF excimer laser solution photolysis are also discussed.     

Study on organosilicon positive resist. III. Organosilicon positive excimer laser resist (OSPR-2016)

A new alkali-developable organosilicon positive excimer laser (KrF) resist (OSPR-2016) has been developed for a bilayer resist system. OSPR-2016 is composed of poly(p-hydroxybenzylsilsesquioxane) and methyl cholate-tris (α-diazoacetoacetate). The ratio is 72.5 : 27.5 w/w. A sample of 0.5-μ thick OSPR-2016 resolved 0.35 μ L&S patterns when exposed to a dose of 320 mJ/cm² from an excimer laser projection printer (NA = 0.37).     

Effect of a deprotection group on acrylic photoresist

This study is synthesized and investigated polyacrylate single layer resist (SLR) using t-amyl alcohol as a deprotection group. The t-amyl group of the copolymer resist and dissolution inhibitor (DI) in this chemically amplified photoresist (CAMP) was deprotected by a light stimulated photoacid generator (PAG) upon post exposure bake (PEB). The polarity change of the system from a hydrophobic to a hydrophilic property made the exposed region soluble in the base developer. KrF and ArF excimer lasers were used to test resists using two components (PR and PAG) and three components (PR, DI and PAG) in the resists. This study also investigated the different effects of exposure dose, developer concentration, and content between t-amyl and t-butyl methacrylate on lithographic performance of resists.     

Polysilanes: Photochemistry and deep UV lithography

The photochemistry of poly(cyclohexylmethylsilane) (PCHMS) has been studied, and PCHMS homopolymer has been shown to be useful for high resolution, deep UV pattern generation either by using a commercial 1:1 projection printer operating in the deep UV or by an excimer laser stepper at 248 nm. In the case of the excimer laser stepper, images 0.5 μm and smaller have been printed, which represents an improvement over the 0.8 μm limit previously reported for polysilane copolymers.     

Organosilicon deep UV positive resist consisting of poly(p-disilanylenephenylene)

A new class of positive deep ultravoilet (UV) resists consisting of poly(p-disilanylenephenylene)s was developed, in which a disilanylene unit and a phenylene unit are connected alternatively in the polymer main chain. These resists had very high etching resistance against oxygen plasma. The lithographic applications of a double-layer resist system in which the poly(p-disilanylenephenylene) film was used as the top imaging layer were examined. As a result, very high resolution and high contrast were attained. The double-layer resist technique using organosilicon deep UV positive resist appears very promising for lithographic applications.     

Well‐defined diblock and triblock copolymers for KrF lithography

One of the major components of a photoresist formulation is polymer resin. Well‐defined diblock and random copolymer of tert‐butyl acrylate (tBA) and 4‐acetoxystyrene (StyOAc), as well as triblock and random tertpolymer of tBA, StyOAc, and Sty were prepared by reversible addition fragmentation chain transfer polymerization (RAFT) process. The polymers all possess M_w about ten thousand and PDI less than 1.23. After hydrolysis under basic condition, the hydroxystyrene (StyOH) analogs are obtained and then are formulated as photoresist. Lithographic evaluation under KrF excimer laser shows that random copolymer based photoresist exhibits better S/L patterns according to SEM images. However, the lithographic performance of the terpolymer based resists is similar. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Design and synthesis of new photoresist materials for ArF lithography

A new class of photoresist matrix polymers based on vinyl ether–maleic anhydride (VEMA) alternating copolymers was developed for ArF single‐layer lithography. These polymers were synthesized by copolymerization of alkyl vinyl ether and maleic anhydride alternating copolymers with acrylate derivatives containing bulky alicyclic acid‐labile protecting groups. The resulting polymers showed good control of polymerization and high transmittance. Also, these resists exhibited good adhesion to the substrate, high dry‐etching resistance against CF₄ mixture gas (1.02 times the etching rate of deep UV resist), and high selectivity to silicon oxide etching. Using an ArF excimer laser exposure system with 0.6 NA, 120‐nm L/S patterns were resolved under conventional illumination. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 165–170, 2004     

Recent resist developments in Japan—a review

Several kinds of resist materials for microlithography have been developed in Japan. Poly(4-vinyl phenol) sensitized with 3,3′-diazidodiphenyl sulfone has been proved to be a high resolution negative deep UV resist with high sensitivity and good resistance to dry etching. The use of this resist enables a 1:1 projection printer to replicate fine patterns with 1 micrometer (μm) minimum feature size at the rate of 90 wafers per hour. Poly(methyl isopropenyl ketone) (PMIPK) has been investigated as a positive deep UV resist. Several resists composed of PMIPK with or without sensitizers are commercially available. Dry-developable photo- and deep UV resists comprising PMIPK and aromatic bisazides have been developed. Poly(glycidyl methacrylate) having the sensitivity of 0.4 micro Coulomb (μC)/per square centimeter (cm²) is now being routinely used as a negative electron beam resist in the fabrication of chromium masks. Recently, aromatic polymers such as chloromethylated polystyrene, iodinated polystyrene, chloromethylated poly(α-methylstyrene), poly(vinylnaphthalene) and its copolymers have been investigated as dry-etching resistant electron beam resists.     

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 193 nm 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 0.15 μm line and space patterns were obtained at a dose of 18 mJ cm⁻² using an ArF excimer laser stepper.     

Characterization of low-temperature solution-processed indium–zinc oxide semiconductor thin films by KrF excimer laser annealing

We have employed KrF excimer laser annealing (ELA) treatment on sol–gel derived indium–zinc oxide (IZO) precursor films to develop a method of low thermal-budget processing. As-coated IZO sol–gel film was dried at 150 °C and then annealed using KrF excimer laser irradiation under ambient air. The laser irradiation energy density was adjusted to 150, 250, 350, and 450 mJ/cm² to investigate the effects of laser irradiation energy density on the microstructure, surface morphology, optical transmittance, and electrical properties of laser annealed IZO thin films. Results of GIXRD and TEM-SAED indicated that the ELA IZO thin films had an amorphous phase structure. The surface characteristics and electrical properties of laser annealed IZO thin films were significantly affected by the laser irradiation energy density. It was found that the dried IZO sol–gel films irradiated with a laser energy density of 350 mJ/cm² exhibited the flattest surface, the highest average optical transmittance in the visible region, and the best electrical properties among all ELA samples.     

248nm深紫外光刻胶

本文从化学增幅技术的产生，深紫外248nm胶主体树脂及PAG发展历程、溶解抑制剂、存在的工艺问题及解决途径多个方面综述了深紫外248nm胶的发展与进步．     

Simultaneous Laser‐Induced Reduction and Nitrogen Doping of Graphene Oxide in Titanium Oxide/Graphene Oxide Composites

Titanium oxide/graphene oxide nanocomposite thin films were grown by ultraviolet (UV) matrix‐assisted pulsed laser evaporation (MAPLE) technique in controlled oxygen or nitrogen atmospheres. The effect of graphene oxide addition and laser‐induced reduction as well as nitrogen doping on the wetting behavior and photoactive properties of titanium oxide thin films was investigated. Hydrophobic to hydrophilic conversion of titanium oxide films takes place progressively as the relative amount of graphene oxide in the MAPLE composite target increases. Nitrogen doping leads to further decrease of the static contact angle of the composite films. The photoactive properties of the synthesized materials were investigated through the evolution of contact angle under UV light irradiation. Wetting properties of both TiO₂ and TiO₂/GO nanocomposite thin films improved upon exposure to UV light.     

Excimer Laser Induced Removal of Particles from Hydrophilic Silicon Surfaces

A pulsed KrF excimer laser was used to remove several types of submicron-sized particles from silicon surfaces. Polystyrene latex particles, 0.1 μm and larger, were removed from silicon surfaces by dry laser cleaning (no water layer condensed on the surface) but SiO₂ particles could not be so removed. However, during steam laser cleaning, in which a thin film of water is deposited on the surface as both an energy transfer medium and an adhesion force reduction agent, these 0.1-0.2 μm SiO₂ particles were almost entirely removed. Calculations of the various forces contributing to adhesion indicate that hydrogen bonds are the major contributor to the adhesion of inorganic particles to substrate surfaces. Photoacoustic detection, using piezoelectric transducers, monitored the surface vibrations induced by the laser pulses.     

Excimer Laser Induced Removal of Particles from Hydrophilic Silicon Surfaces

A pulsed KrF excimer laser was used to remove several types of submicron-sized particles from silicon surfaces. Polystyrene latex particles, 0.1 μm and larger, were removed from silicon surfaces by dry laser cleaning (no water layer condensed on the surface) but SiO₂ particles could not be so removed. However, during steam laser cleaning, in which a thin film of water is deposited on the surface as both an energy transfer medium and an adhesion force reduction agent, these 0.1–0.2 μm SiO₂ particles were almost entirely removed. Calculations of the various forces contributing to adhesion indicate that hydrogen bonds are the major contributor to the adhesion of inorganic particles to substrate surfaces. Photoacoustic detection, using piezoelectric transducers, monitored the surface vibrations induced by the laser pulses.     

Evaluation of pressure-sensitive tape adhesion and backing directionality by excimer laser methods

The effects of 248 nm KrF excimer laser irradiation on a pressure-sensitive adhesive tape bonded to a glass substrate were investigated as a possible method to evaluate the quality of adhesion, as well as the directionality induced during manufacture. The model pressure-sensitive tape consisted of biaxially-oriented polypropylene (PP) tape coated with a hot-melt rubber resin. Analysis of the front-shot experiments, which were performed by irradiation through the PP backing, allowed correlation between the excimer laser irradiation-induced detachment and the peel adhesion strength. For this purpose, peel tests were performed before and after laser shots. The directionality induced during manufacture resulted in a more ablated area in the strength direction than in the transverse direction when the bonded tapes were irradiated with an elliptically-shaped laser beam above the ablation threshold. A correlation was found between the detachment bubbles created by irradiation below the ablation threshold and their respective peel adhesion values, which allows us to evaluate the quality of adhesion for pressure-sensitive tapes. Thus, a method to evaluate the quality of adhesion using an excimer laser is proposed based on the findings of this work.     

Clay dispersion effects on excimer laser ablation of polymer–clay nanocomposites

The ablation behavior of polystyrene‐organically modified montmorillonite (OMMT) nanocomposites was evaluated by measuring the weight loss induced by KrF excimer laser irradiation of the nanocomposite specimens under air atmosphere. The characteristic values of ablation, ablation threshold fluence, and effective absorption coefficient for polystyrene and its nanocomposites were calculated based on the weight loss data. The effects of morphology due to spatial variation in injection molded samples are also discussed in this article. Results demonstrate that both the dispersion state and the concentration of clay play important roles in excimer laser ablation. The sensitivity of threshold fluence and absorption coefficient to dispersion state of OMMT seem to depend on the clay concentration. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2336–2344, 2013     

Surface pretreatment of glass fiber-reinforced liquid crystalline polymer composites by excimer laser for adhesive bonding

This paper reports the results of using a new laser surface pretreatment technique to improve the strength of adhesive joints. A high power KrF excimer laser at 248 nm output was used to surface-treat a glass fiber-reinforced liquid crystalline polymer (LCP) composite. With optimum process parameters, the polymer matrix at the surface was etched away efficiently and the bare fibers anchored on the matrix were left dangling and undamaged. The surface morphology produced by this new technique resulted in high quality adhesive joints. Both lap-joint and butt-joint configurations were investigated. A 350% improvement in the butt-joint strength was achieved by this new pretreatment technique as compared with that of the untreated one.