High Dry Etch Resistance Research Articles

Polymer designs for dense metal infiltration for higher dry-etch resistance

Metal induced polymer enables high dry-etch resistance in nano-scale fabrication of electronic devices. Dense infiltration of metals into the polymer is critical to realize such functionality. In this article, mechanism of trimethylaluminum (TMA), a popular aluminum precursor, infiltration into the polymer is discussed with density functional theory calculations and experiments. New designs of polymers are proposed that could potentially increase the infiltration of TMA by increasing the number of carbonyls in the polymer chain. Such polymers were synthesized, followed by TMA infiltration where it was oxidized to yield robust hybrid materials. The number of carbonyls in the polymer unit plays an important role in the intake of TMA.

Plasma-Etched Pattern Transfer of Sub-10 nm Structures Using a Metal-Organic Resist and Helium Ion Beam Lithography.

Field-emission devices are promising candidates to replace silicon fin field-effect transistors as next-generation nanoelectronic components. For these devices to be adopted, nanoscale field emitters with nanoscale gaps between them need to be fabricated, requiring the transfer of, for example, sub-10 nm patterns with a sub-20 nm pitch to substrates like silicon and tungsten. New resist materials must therefore be developed that exhibit the properties of sub-10 nm resolution and high dry etch resistance. A negative tone, metal-organic resist is presented here. It can be patterned to produce sub-10 nm features when exposed to helium ion beam lithography at line doses on the order of tens of picocoulombs per centimeter. The resist was used to create 5 nm wide, continuous, discrete lines spaced on a 16 nm pitch in silicon and 6 nm wide lines on an 18 nm pitch in tungsten, with line edge roughness of 3 nm. After the lithographic exposure, the resist demonstrates high resistance to silicon and tungsten dry etch conditions (SF6 and C4F8 plasma), allowing the pattern to be transferred to the underlying substrates. The resist's etch selectivity for silicon and tungsten was measured to be 6.2:1 and 5.6:1, respectively; this allowed 3 to 4 nm thick resist films to yield structures that were 21 and 19 nm tall, respectively, while both maintained a sub-10 nm width on a sub-20 nm pitch.

Gold microelectrodes fabricated by a print-and-imprint method using laser-drilled polyimide through-hole masks

Multiple sets of gold (Au) four-terminal microelectrodes comprising 100 μm-scale pad electrodes and 20 μm-wide lead lines were fabricated on a silicon substrate by a print-and-imprint method involving laser drilling and screen printing. Laser drilling of 12.5 μm-thick polyimide (PI) sheets with a picosecond-pulse laser enabled the fabrication of PI membranes with designed patterns of through holes. The through holes had a frustum shape, and the average hole diameters on both the laser entry and exit sides of the PI films enlarged with an increase in the applied repetition rate. The hole patterns designed with submicrometer position accuracy were prepared using a linear motor stage. Liquid ultraviolet (UV)-curable resin, exhibiting a high viscosity (11.0 Pa s) and a high dry-etching resistance to argon (Ar) ion beam milling after UV curing, was placed onto a substrate surface as droplets by screen printing, corresponding to the hole patterns of the PI through-hole masks. The average volume of the liquid droplets could be tuned in the range of 0.02–0.54 pl, which depended on the volumes of the laser-drilled frustum holes. The volumes of liquid resin necessary to fill the mold recesses were adjusted site-selectively by the number of resin droplets printed on a metal-deposited substrate surface. Fluorescence microscopy with a fluorescent dye-doped resin indicated that the imprinted resist patterns had a residual layer thickness in the range of 15–28 nm. The Au electrodes with a 30 nm-thickness could be fabricated by subsequent Ar ion beam milling and removal of a sacrificial metal layer.

Low-Loss GaInAsP Wire Waveguide on Si Substrate with Benzocyclobutene Adhesive Wafer Bonding for Membrane Photonic Circuits

Low-power and compact optical interconnects can be realized using III–V membrane photonic integrated circuits fabricated from thin InP-based films bonded to a Si wafer using benzocyclobutene (BCB) adhesive wafer bonding method. However, the conditions of the bonding and fabrication process strongly affect the propagation loss of waveguides. This study investigated the process conditions during bonding and waveguide fabrication with a view to reducing the propagation loss. It was found that clean, large GaInAsP thin films without air voids or fractures could be obtained by using an appropriate solvent volatilization time of 20–30 min at 200 °C for BCB. Furthermore, by using a resist with high dry etching resistance and an SiO2 mask for the etching process, the sidewall roughness of the waveguide was significantly reduced, which finally afforded a waveguide propagation loss as low as 4 dB/cm.

157-nm Single-Layer Resists Based on Main-Chain-Fluorinated Polymers

Fluoropolymers are key materials for the single-layer resists used in 157-nm lithography. We have been studying fluoropolymers to determine their potential for use as the base resins of 157-nm photoresists, and have developed a monocyclic fluorinated polymer with a protecting group of bicyclohexylyloxymethyl (BCHYOM) that has high transmittance (an absorption coefficient of 0.64 µm-1) at a 157-nm exposure wavelength and high dry-etching resistance (a dry-etching rate ratio to that of the KrF resist of 1.75) under organic bottom anti-reflective coating (BARC) / hard mask (HM) dry-etching conditions. Moreover, this polymer has a higher dissolution rate contrast than the polymers with other protecting groups that we evaluated. After exposure using a 157-nm laser microstepper (numerical aperture = 0.85) and our monocyclic-fluoropolymer-based resist with a protecting group of BCHYOM, a 65-nm line-and-space pattern was obtained when using a 150 nm film thickness. We found that this polymer simultaneously enables high transparency, high dry-etching resistance, and good imaging performance.

Characterization of Fluoropolymer Resist for 157-nm Lithography

Fluoropolymers are key materials for the single-layer resists used in 157-nm lithography. We have been studying fluoropolymers to determine their potential for use as the base resin. We developed a polymer that has high transmittance and high dry-etching resistance by attaching the cyclohexylcyclohexyloxymethyl (CCOM) blocking group to a monocyclic fluorinated polymer. The dry-etching rate of the 32 % blocked polymer was 1.5 times that of a KrF resist and its absorption coefficient at a 157-nm exposure wavelength was 1.1 /μm. The polymer with various photoacid generators (PAGs) was compared with the patterning profile and we found that the shape of the resist pattern depended on the ΔH, which was the change in enthalpy before and after the PAG generated acid. ΔH is related to acidity and triphenylsulfonium nonaflate has one of the highest acidity in the PAGs. The polymer with triphenylsulfonium nonaflate resolved a 55-nm line and space pattern. We also investigated the relation between the dissolution characteristics, transmittance and molecular weight of the PAG. We found that as the PAG’s molecular weight was low, maximum dissolution rate (Rmax) tended to become high and transmittance tended to become high. For onium salts, in particular, as the anion’s molecular weight of the PAG was low, transmittance tended to become high, and as the cation’s molecular weight of the PAG was low, Rmax tended to become high. These are guidelines in choosing a PAG.

Application of VEMA type ArF Resist to Sub-100nm Lithography.

It is expected that ArF lithography will be introduced for device manufacturing for sub-100nm nodes, as high NA ArF step and scan systems (NA=O.75) become available. We previously reported on a platform, based on a vinyl ether-maleic anhydride (VEMA) alternating polymer system. This platform demonstrated both good resolution and high dry etch resistance in comparison to other platforms based on acrylate and cyclic-olefin-maleic anhydride (COMA) polymer systems. The VEMA platform has been continuously improved to meet the increasing requirements, such as resolution, depth of focus (DOF), iso-dense bias, and post-etch roughness for real device manufacturing. This VEMA system is being implemented for sub-100nm device with high NA (NAO.75)=ArF exposure systems. In this paper, recent experimental results are reviewed.

New ArF Photoresist Based on Modified Maleic Anhydride Cycloolefin Polymers.

We have designed and synthesized peculiar copolymers of norbornene-alt-malefic anhydride derivatives for 193nm lithography.1, 2 These polymers were synthesized by copolymerization of norbornene-malefic anhydride and substitution reaction with bulky alicyclic acid-labile protecting groups. They showed a good physical properties such as high thermal stability and high transmittance for 193nm UV light. Also, photoresists made of our polymers showed a good pattern profile, high resolution, high dry-etching resistance. In this study, we have investigated several polymers and photoresists for line-and-space lithography and contact-hole one.

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

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.

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.

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.

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.

Submicron pattern transfer with newly designed siloxane e-beam resist and Bias-ECR etcher

Submicron pattern transfer was achieved using a newly designed siloxane resist and Bias-ECR plasma stream etcher. The newly developed micro-resinoid siloxane resist for use in electron beam lithography exhibits high resolution, excellent thermal stability, and high dry etch resistance against O 2 RIE. Resist patterns of under 0.1 um for point-beams and 0.2 um for variable-shaped beams were obtained by optimizing the resist structure and its molecular weight. A Bias-ECR plasma stream etcher was applied to realize high speed and high aspect etching, and 0.3 um bilayer resist patterns were obtained.

Study on a positive photoresist with high dry etching resistance.

Study on a positive photoresist with high dry etching resistance.

Contrast and sensitivity enhancement of resists for high-resolution lithography

Novolac based resists have received much attention in the submicron device fabrication area because of their high dry etch resistance. In high‐resolution device fabrication requirements novolac resists suffer from a lack in sensitivity and resolution capability. In order to make use of these high‐quality resists, approaches to improve the resolution capability and sensitivity of conventional positive resists have been a major interest of research. Development techniques such as two‐step and spray development techniques to improve resist contrast have been reported, but neither is well characterized and well understood. In this paper, we report an interrupted development technique which enhances the contrast of an electron beam (e‐beam) exposed diazonapthoquinone novolac, AZ‐type resist. As a result of this enhancement, submicron features varying in density can be controlled properly in size and in image profile. The resolution capability of this resist as a single‐layer system is extended to the one‐quarter micron regime with good linewidth control. In the optically exposed AZ resist, a smaller enhancement in contrast was observed and the resolution improvement is minimal. However, vertical sidewalls are readily obtained by employing appropriate interrupted development schemes on optically as well as e‐beam exposed AZ resists. This difference in response to interrupted development is related to the difference in the energy deposited in the resist film due to electron scattering. In the e‐beam exposed AZ film, the energy deposited in the resist gradually increases through the bulk of the film. On the other hand, because of the UV absorption characteristics of the novolac resist in optical lithography, the energy deposited is attenuated as it penetrates the resist. Sensitivity enhancement by this technique is on the order of 30% to 50%. A sulfone novolac resist with an inductive effect was examined to try to understand the mechanism of contrast enhancement of AZ resist by interrupted development. No response to interrupted development was observed. Possible mechanisms for the delayed lateral erosion of the AZ resist images are proposed, based on the studies of these resists anddeveloper interactions. Using this interrupted development technique on a single‐layer e‐beam exposed resist system, various profiles can be tailored to fit different applications in device processing requirements, namely an undercut profile for metal lift‐off, straight sidewalls for etch masks or ion implantation masks.

Plasma developable photoresist containing electronic excitation energy quenching system

AbstractA dry developable negative working resist composition comprised of poly(methyl isopropenyl ketone) (PMIPK) and 4‐methyl‐2,6‐di(4′‐azido‐benzylidene) cyclohexanone‐1 was examined. The main photochemical product formed in the resist pattern was found to be a secondary amine which crosslinks PMIPK. Post‐annealing forms a hydrogen‐bonded product which shows a powerful electronic excitation energy quenching effect. The quencher is more powerful than the aromatic compound arising from the azide by post‐annealing only. The residual resist thickness of the negative pattern is about 80 percent of the initial thickness of the coating in spite of all the azide compound remaining in the resist coating. The obtained dry developed resist pattern has a high dry etch resistance. Etchings of Si and SiO2 were performed by plasma and reactive ion etching, respectively.

Application of chlorinated polymethylstyrene, CPMS, to electron beam lithography

Swelling behavior and resist performance of a series of chlorinated polymethylstyrenes, CPMS, were investigated. Measurements of swelling ratio and resolution of the CPMS resist coating in a wide variety of organic solvents disclosed that resolution depends on the swelling ratio. In addition, it was found that Cellosolve acetate or methyl isobutyl ketone was the most suitable developer, and that the critical swelling ratio might be 3.2 (=1.473) for screening of a developer. Functional testings on CPMS showed the resist had considerably high sensitivity as well as high contrast and dry etch resistance. The selectivity ratio of the resist to aluminum, when the resist was used in a dry etching process, was 1.5 times as high as that of the conventional Novolak-type positive-working photoresist.

Molecular parameters and lithographic performance of poly(chloromethylstyrene)—a high-performance negative electron resist

Poly(chloromethylstyrene) (PCMS) is shown to have a desirable combination of properties, including high sensitivity, high dry-etch resistance, and high resolution. As a consequence, it is a very attractive candidate for high performance (throughput, resolution, process compatibility) electron beam lithography. PCMS lithographic performance is higher than that of any other previously reported, high-sensitivity negative electron resist. Performance results are compared specifically with COP, PGMA, and CMPS, and are correlated with molecular and chemical properties. PCMS synthesis and evaluation results are reported for polymers with molecular weights (?w) between 20 000 and 450 000 and polydispersivities between 1.3 and 2.3. A typical high molecular weight (?w = 381 000) material with polydispersivity of about 1.6 has sensitivity (Dg0.5)<0.5 μC/cm2, contrast ≳1.5, and resolution <1.0 μm (equal lines and spaces). Respective values for a typical low molecular weight (?w = 22 000) material with polydispersivity of about 1.3 are sensitivity <7 μC/cm2, contrast ≳2.0, and resolution <0.5 μm.