High Etch Resistance Research Articles

Advances in Resist Materials for 193 nm Lithography.

The performance of a 193nm single layer resist based on a norbornene-malefic anhydride matrix resin has been optimized through a series of statistical design experiments. The SDE demonstrated the importance of setting the PEB temperature above the SB temperature with optimum performance being observed at a SB of 150°C and a PEB of 160°C. The lithographic performance of the resist was also strongly influenced by polymer composition, specifically acrylate loading and blocking level. Optimizing the composition of the polymer, gave resists with high etch resistance, square profiles and 0.130 micron dense line ultimate resolution in 0.5 micron thick films. The resist formulations are compatible with industry standard 0.262N TMAH. During exposure the resist does not suffer from the outgassing of volatile species (less than 1e12 molecules/cm2 x sec). A new thermally curable undercoat for bi-layer application has also been developed whose optical properties have been optimized to reduce reflectivity at the desired wavelength. The reflectivity has been reduced by a factor of eight over an earlier UV-cured version.

ETCHING PROPERTIES OF AMORPHOUS HYDROGENATED CARBON FILMS IN A MULTIPOLE ELECTRON CYCLOTRON RESONANCE OXYGEN PLASMA SYSTEM

The etching properties of amorphous hydrogenated carbon films deposited from benzene vapor in a multipole electron cyclotron resonance (ECR) plasma-enhanced chemical vapor deposition system have been investigated.Etch rates of these carbon films as a function of the process variables,includ-ing gas pressure and microwave power were measured,and compared with other resist materials.The results show that the film has high etching resistance against oxygen,and etch rate of the film not only closely correlated with etching process parameters,but also with the deposition conditions.This film could be used as a resist in dry etching process.

Thin film imaging with CARL photoresist at the optical resolution limit.

Future lithography with exposure at 157nm, 126nm and 13nm require thin film resist techniques, because at these high exposure energies sufficiently transparent resist polymers for conventional singel layer resists are not available. Besides top-surface imaging dry developable bilayer resist systems offer excellent imaging properties (high resolution capability and wide focus windows) in a thin imaging photoresist layer that is applied on top of a thick light-absorbing and planarizing bottom resist. The high etch resistance of the underlying bottom coat provides unique process latitudes for the overall substrat treatment. Since 1995, Siemens has used the in-house developed CARL bilayer resist process [1, 2] as a from Clariant commercially available i-line version [3] in its high-volume DRAM and logic IC production [4]. The dramatic increase in focus latitudes at k1≤0.4, even with standard illumination and COG masks, allows shrinking down to 120nm with 193nm exposure or extending the lifetime of existing i-line and 248nm exposure tools. A chemically amplified CARL resist version is now investigated at 248 nm. With this material process development and optimization for the 193nm technology is possible because it is sensitive at both wavelengths (multi-wavelength characteristic). First results at 157nm exposure indicate that this process offers outstanding possibilities even with the methacrylate based polymers.

PECVD silicon carbide as a chemically resistant material for micromachined transducers

Plasma enhanced chemical vapor deposited (PECVD) amorphous hydrogenated silicon carbide is a material with many potential applications for micromachined transducers. Specifically, its resistance to etching in a broad range of media such as sulfuric acid/peroxide, hydrofluoric acid and potassium hydroxide make it an excellent choice for use as an encapsulating material for media compatible transducers. This etch resistance also makes it useful as a masking material for intermediate processing steps. Despite this wet chemical resistance, it can be patterned easily in fluorine-based plasmas. A series of trials were undertaken in an attempt to correlate stress, resistivity and wet etch resistance with the following deposition parameters: pressure, CH 4 flow rate, low frequency power, low frequency cycle time, high frequency power, and high frequency cycle time. Work to date has demonstrated a CMOS compatible, insulating thin film with a low stress (< 50 MPa) and high etch resistance. Four examples of its application are presented: an electrochemical probe, a fully packaged, encapsulated pressure sensor, a sealed and coated microfluidic channel, and deep-etched channels in glass.

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.

Evaluation of second generation DUV resists for advanced microprocessors

DUV lithography is being implemented in factories as fast as equipment makers can produce tools. The obstacles to implementation of DUV resists have been well characterized and their solutions are readily available for all to use. The most widely used resist to date has been APEX-E, developed by IBM nearly a decade ago. It is reaching its useful limit in state-of-the art processing, as are the other resists based on this technology. The second generation resists promise greater environmental stability, better exposure latitude, higher etch resistance and less substrate interaction. These advances are necessary to enhance the process windows and manufacturability as we move to smaller geometries. In addition they will allow the updating of older DUV processes to potentially reduce variation and increase yield. In this paper we will discuss the results of our work with several second generation resists, and their ability to meet process requirements for both imaging and pattern transfer, for the critical DUV lithography levels. We will also discuss the importance of shifting exposure wavelength to enhance yield and process latitude.

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.

Polymerization ofN-(tert-butyldimethylsilyloxy)maleimide and applications of the polymers as resist materials

A new silicon-containing maleimide monomer, N-(tert-butyldimethylsilyloxy)-maleimide (SiOMI) has been synthesized. SiOMI was radically copolymerized with styrene derivatives (XSt) to obtain alternating copolymers, P(SiOMI/XSt), in high conversions. The copolymers have high glass transition temperatures above 190°C, and the tert-butyldimethylsilyloxy groups are thermally stable up to 300°C. The SiOMI units in the copolymers were converted into N-hydroxymaleimide (HOMI) units by acidolytic deprotection of the tert-butyldimethylsilyloxy protecting groups. The facile deprotection of the side-chain tert-butyldimethylsilyloxy groups from the protected copolymers provided a significant change in solubility of the polymers due to the large polarity change. Submicron positive-tone images were obtained from the copolymers containing an onium salt as a photoacid generator by irradiation with electron beam and development with alkaline solutions. The polymer films also showed very high oxygen plasma etch resistance compared with novolac resins. The silicon-containing maleimide polymers were found to have required properties, such as good alkaline solubility after deprotection, superior adhesion, low optical density, high thermal stability with high Tg, and high plasma etch resistance for applications as deep ultraviolet and electron beam resist materials. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2507–2516, 1997

Reactive ion etching of ion-plated carbon films

Accurate pattern transfer by dry etching methods requires resistant masks. Carbon is a good candidate due to its low sputtering rate, and it is widely used for high temperature superconductor patterning. This paper reports on radio frequency reactive ion etching of carbon films with diamond-like properties, deposited by ion plating at various bias voltages. Gold, polyimide and chalcogenide glass have been used as masks for deep carbon etching in oxygen, but failed to assure good selectivity. Best pattern transfer has been observed using a two-layer resist system based on photoresist and Mo or Ta. The etching is carried out on two stages: (1) metal etching in CF 4; (2) deep etching of carbon in oxygen plasma using the metal mask. A correlation has been found between film characteristics (etch rate, surface morphology, optical band gap) and the deposition bias voltage. The proposed technique is suitable for fine patterning of carbon films and production of masks with high ion etching resistance combined with good mechanical and thermal properties.

Diamond growth on hard carbon films

A three-step process for enhancing the nucleation density of diamond on unscratched silicon substrates using microwave-plasma-enhanced chemical vapor deposition is described. Hard diamond-like carbon (dlc) films with thickness in the range 5–100 nm were first formed on smooth (100) silicon surfaces using a vacuum-arc plasma deposition technique at room temperature. The dlc-coated silicon substrates were subsequently subjected to a low-temperature pretreatment with a methane-rich plasma for an hour before switching to the diamond nucleation conditions. To investigate the effect of the dlc film structure on diamond nucleation, experiments with silicon substrates coated with evaporated carbon films approximately 50–100 nm thick were also performed under similar pretreatment and diamond nucleation conditions. Diamond films with nucleation density about 2 × 10 8 cm −2 were obtained with pretreated dlc films, depending on the film thickness and the pretreatment time, whereas in the absence of the pretreatment and/or with evaporated carbon films the diamond nucleation density was less than 10 4 cm −2. The significant enhancement in diamond nucleation density obtained with pretreated dlc films is attributed to the inherently high etching resistance of the films resulting from the high fraction of sp 3 bonds. The actual nucleation sites might be very fine carbon or, possibly, SiC particles produced by etching back the dlc film.

Effect of pretreatment process parameters on diamond nucleation on unscratched silicon substrates coated with amorphous carbon films

Diamond nucleation on unscratched silicon substrates was investigated using a conventional microwave plasma-enhanced chemical vapor deposition system. Silicon substrates were coated with thin films of amorphous carbon using a vacuum arc technique. The carbon-coated silicon substrates were pretreated with a methane-rich plasma at relatively low temperatures and were subsequently exposed to the diamond nucleation conditions. The significance of the pretreatment on the diamond nucleation density was examined by varying the methane concentration, chamber pressure, and exposure time. Scanning electron microscopy demonstrated that densely packed spherical nanoparticles on the pretreated surfaces played the role of diamond nucleation seeds. Raman spectroscopy analysis showed that the nucleation seeds consisted of nonhydrogenated carbon and that their structure was influenced by the pretreatment conditions. Transmission electron microscopy revealed that the nucleation seeds comprised disordered graphitic carbon and ultrafine diamond crystallites. Submicrometer films of good quality diamond possessing significantly higher nucleation densities (∼5×1010 cm−2) were grown from nanoparticles produced under optimum pretreatment conditions. The enhancement of the diamond nucleation density is mainly attributed to the formation of a large number of nanoparticles, which provided sufficient high-surface free-energy sites for diamond nucleation, in conjunction with their high etching resistance to atomic hydrogen stemming from the significant percentage of sp3 atomic carbon configurations, as evidenced by the presence of nanocrystalline diamond in the nanoparticle structure.

Ion beam deposition of alumina for recording head applications

In this work, aluminum oxide films were prepared by Ion Beam Deposition (IBD) in a dual-gun system. Films prepared from alumina target at high deposition beam parameters and low assist parameters resulted in lower compressive stress and better etch resistance than sputtered alumina films. Excellent thickness uniformity and topological step coverage were also achieved. Nano-crystalline alumina films with superior etch resistance were grown by reactive sputtering from an aluminum target at low deposition rate. Appropriate balance between the deposition beam and assist beam was important in order to get such high etch resistance. Discussions of both IBD and sputtering methods, the effect of beam parameters on the alumina properties, and structural analysis were presented in this paper.

Diamond nucleation on unscratched silicon substrates coated with various non-diamond carbon films by microwave plasma-enhanced chemical vapor deposition

The efficacy of various non-diamond carbon films as precursors for diamond nucleation on unscratched silicon substrates was investigated with a conventional microwave plasma-enhanced chemical vapor deposition system. Silicon substrates were partially coated with various carbonaceous substances such as clusters consisting of a mixture of C60 and C70, evaporated films of carbon and pure C70, and hard carbon produced by a vacuum are deposition technique. For comparison, diamond nucleation on silicon substrates coated with submicrometer-sized diamond particles and uncoated smooth silicon surfaces was also examined under similar conditions. Except for evaporated carbon films, significantly higher diamond nucleation densities were obtained by subjecting the carbon-coated substrates to a low-temperature high-methane concentration hydrogen plasma treatment prior to diamond nucleation. The highest nucleation density (∼3 × 108 cm−2) was obtained with hard carbon films. Scanning electron microscopy and Raman spectroscopy demonstrated that the diamond nucleation density increased with the film thickness and etching resistance. The higher diamond nucleation density obtained with the vacuum are-deposited carbon films may be attributed to the inherent high etching resistance, presumably resulting from the high content of sp3 atomic bonds. Microscopy observations suggested that diamond nucleation in the presence of non-diamond carbon deposits resulted from carbon layers generated under the pretreatment conditions.

A pretreatment process for enhanced diamond nucleation on smooth silicon substrates coated with hard carbon films

Diamond nucleation on unscratched silicon substrates coated with thin films of hard carbon was investigated experimentally with a microwave plasma-assisted chemical vapor deposition system. A new pretreatment process was used to enhance the nucleation of diamond. Relatively high diamond nucleation densities of ∼108 cm−2 were achieved by pretreating the carbon-coated silicon substrates with a methane-rich hydrogen plasma at a relatively low temperature for an hour. Scanning electron microscopy and laser Raman spectroscopy studies revealed that diamond nucleation occurred from nanometer-sized spherical particles of amorphous carbon produced during the pretreatment. The nanoparticles possessed a structure different from that of the original hard carbon film, with a broad non-diamond Raman peak centered at ∼1500 cm−1, and a high etching resistance in pure hydrogen plasma. The high diamond nucleation density is attributed to the significant percentage of tetrahedrally bonded (sp3) atomic carbon configurations in the nanoparticles and the presence of sufficient high-surface free-energy sites on the pretreated surfaces.

Non-conjugated cyclic dienes and maleic anhydride co-polymers, and derivatives for base resin of deep UV resist.

Non-conjugated cyclic dienes and maleic anhydride co-polymers were synthesized via co-polymerization which involves an addition cyclization process, and they were investigated an application to a photo resist base resin. Every these polymers, which have an alicyclic hydrocarbon main-chain, showed excellent transparency in the wavelength regions of deep UV rays, and some of these polymers have high reactive ion etch resistance as similar as phenolic base resin; i.e. polyvinyl-phenol. One of these polymers (EBH-MAH) was modified to a photo resist, which has diazo photo sensitive functional groups. This polymer appeared high sensitivity for exposure of the deep UV ray. Solubility rate of the polymer in an aqueous alkaline solution, which could be dissolved difficulty for the solution, increased excellently after deep UV exposure. Namely this polymer showed a function as a deep UV positive resist that could be developed in alkaline.

Precise pattern delineation by refractive index matching in a trilayer resist system

In order to obtain precise pattern dimension control, optical indexes of the middle layer (ML) in a trilayer resist system are investigated. Photoabsorption in ML and bottom layer (BL) is important. However, optimization of photoabsorption in these layers is not sufficiently to suppress linewidth variations. From calculations of the reflection at each interface of the trilayer resist system, the matching of the refractive index between each layer [top layer (TL), ML, and BL] is found to be also important. The optimal refractive index of the ML for the novolac-type of TL and BL materials is estimated to be 1.7 at i line, which is the same value as that of novolac resin. To confirm this matching effect, an admixture material of Ti–alkoxide and silanol is used as the ML material. The mixing ratio is 50 wt %. The refractive index of this material with curing at 230 °C is 1.7. Using this material, the linewidth variation caused by the interference effect can be reduced as 0.04 μm, which is half that using spin-on glass as the ML. The material also shows a high O2 reactive ion etching resistance (1.7 nm/min) and good adhesion to the TL and BL. In the trilayer resist system, it is possible to fabricate a fine, precise pattern even on a large topography.

Metallized photoresists: A new approach to surface imaging

G-line photoresists are exposed at 248 nm and subjected to aqueous development and electroless plating to produce submicron, metallized photoresist patterns. The high plasma etch resistance of the photoresist/metal structure allows for efficient pattern transfer into silicon dioxide. A key feature is that optical exposure of only the near-surface of the photoresist is required to achieve selective metallization. This process represents a new approach to surface imaging, reducing complications from substrate reflectivity and topography. 0.4 μm line/space pairs have been transferred into 5000 Å of SiO2 on Si.

Aqueous phase silylation a new route to plasma developable high resolution resists

Abstract A novel O 2 /RIE developable photoresist system with aqueous phase silylation of the exposed areas is presented. The silylation includes a spontaneous crosslinking reaction between the anhydride groups of the base resin and the aminosiloxane silylating reagent. The silylation leads to a considerable growth of the film thickness which is promoted by higher exposure dose, acidity of the exposed resist, normality of the aminosiloxane solution, silylation time and temperature. The system demonstrates several benefits such as fast silylation with existing equipment (puddle development track) at room temperature, high etch resistance of the silylated layer against O 2 /RIE (same as polyphenylmethylsilane), possibility of water inspection after silylation and applicability of the same resist formulation for 366 nm and 248 nm . First i-line stepper experiments gave 0.5μm lines and spaces with an aspect ratio of 4.5.

Metal Surface Treatment and Reduction in Pitting Corrosion of 304L Stainless Steel by Excimer Laser

Abstract The use of excimer lasers to produce thin rapidly quenched melts on metal surfaces is discussed. Results obtained using a XeCl laser on a variety of metal samples are given. The surface refinement and smoothing induced by laser treatment, giving improved resistance to pitting corrosion and higher etch resistance suggest significant potential for this method as a means of ‘micro-engineering’ surfaces.