Dry Etch Resistance Research Articles

Surface property control for 193 nm immersion resist by addition of Si compound

In ArF immersion lithography, the presence of immersion liquid between the resist surface and the lens causes problems, such as the leaching of the photoacid generator into the liquid and the presence of residual liquid on the resist surface, which can result in watermarks and other defects. One method to address such issues is adding an F-based compound with low dry-etch resistance to the resist. In the present study, we developed a novel resist for ArF immersion exposure that replaces the F compound with an Si (dimethylpolysiloxane)-based additive to enhance dry-etch resistance. We experimentally evaluated contact angles with respect to water and developer solution, depth concentration of the additives (segregation), agent dissolution (leaching), dry-etch resistance, and spectral transmittance of the comparative resists. Simulation studies were performed to evaluate pattern profiles. The developed resist with the Si-based additive showed improved properties compared with that with the F-based additive.

Dust-acoustic Gardner solitons in cryogenic plasma with the effect of polarization in the presence of a quantizing magnetic field

Abstract A theoretical investigation is presented for dust-acoustic (DA), Gardner solitons (GSs), and double layers (DLs) in a magnetized cryogenic plasma system. The plasma consists of inertial negatively charged dust, Boltzmann distributed electrons, and ions, all existing in a quantizing magnetic field. The Korteweg–de Vries (KdV), a modified KdV (mKdV), and Gardner equations are derived by using the reductive perturbation method. It is found that the KdV solitons and DLs are either compressive or rarefactive depending on the plasma parameters, whereas only compressive mKdV and rarefactive GSs solitons exist. These GSs and DLs are significantly modified due to the introduction of the polarization force effect. The present results are considered to be beneficial in understanding the waves propagating at cryogenic temperatures in the experiments of the nano-electromechanical application such as cryogenic etching of silicon that leads to etched silicon and makes it highly anisotropic with a high etch rate, lower side etching, and increases the dry etch resistance of organic masks.

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.

Effect of ZnO and TiO2 doping on the sintering behavior of Y2O3 ceramics

Full densification of Y 2 O 3 is challenging and requires a very high sintering temperature (above 1700 °C). In this study, the effect of ZnO and TiO 2 dopants on its densification was investigated, showing that both dopants lowered the sintering temperature and improved the process. Moreover, ZnO promoted the grain growth, while TiO 2 inhibited it; hence, the ZnO TiO 2 co-doping and the change in the ZnO/TiO 2 ratio allowed the control of the sintered body microstructure while maintaining high densification. Since Y 2 O 3 has a higher plasma erosion resistance than conventional Si-based materials, the plasma dry etching resistance of the sintered Y 2 O 3 was also evaluated and found superior due to the improved densification and controlled grain size of the doped samples.

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.

Chemical fixation of SO2using norbornene with different side-chain groups and control of the physical properties of poly(olefin sulfone)

Photoresists involving polymer solubility and degradation play a crucial role in the manufacture of integrated circuits by photolithography. Conventional photoresists typically rely on a single switching mechanism based on a change in either polarity or molecular weight of the polymer. Here we report a new type of poly(olefin sulfone) as a photoresist which overcomes the drawback of poor dry etching resistance, solubility and thermal degradation. The effects of different side-chain groups (acetyl, acetoxy and carboxylic acid) of norbornene on the properties of poly(norbornene sulfone)s were analyzed with the aim of developing a new type of photoresist. Thermogravimetry and gel permeation chromatography results revealed that bond breaking occurred at different temperatures, because of the different side-chain groups, and the three side-chain groups affect the solubility and stability of the poly(norbornene sulfone)s. A novel photoresist material based on a poly(olefin sulfone) with different side-chain groups was synthesized and its physical properties examined. © 2017 Society of Chemical Industry

Enhancing the dry etch resistance of polymethyl methacrylate patterned with electron beam lithography

Acrylic resists are used for both electron beam lithography and for deep-ultraviolet (UV) lithography at 193 nm wavelength. Polymethyl methacrylate (PMMA) is the most widely used acrylic positive tone electron beam resist. While it offers superb resolution in this role, its dry etch resistance is quite poor. Here, the authors present a new technique for enhancing the dry etch resistance of PMMA. This involves adding Irgacure 651—a photo-cross-linking agent to PMMA. Irgacure-containing PMMA can be spin-coated onto substrates in exactly the same way as pure PMMA. Addition of Irgacure does not impair the chain scissioning properties of PMMA under electron beam irradiation. Electron beam lithography can be carried out with this resist in exactly the same manner as with pure PMMA, although at a higher dose. After electron beam exposure, the exposed sample can be developed in diluted methyl isobutyl ketone solvent, again just as with pure PMMA. A postlithography UV exposure step then cross-links the patterned resist; substantially enhancing its dry etch resistance. This technique enables the fabrication of deeper etched structures than is possible with PMMA alone.

Strain-controlled boron and nitrogen doping of amorphous carbon layers for hard mask applications

Nitrogen- and boron-doped amorphous carbon layers (ACLs) were grown by plasma- enhanced chemical vapor deposition (PECVD) on a Si substrate and characterized by Raman and X-ray photoelectron spectroscopy (XPS) techniques. Increasing doping levels resulted in a shift in the Raman G-peak of the doped ALCs, indicating a change in bond lengths upon doping. The XPS N1s and B1s spectra revealed the presence of different types of N-related (involving pyridinic, pyrrolinic, and graphitic N) and B-related (corresponding to BC2O and BC species) bonds in the N- and B-doped ACLs, with N and B doping levels ranging from 2.03 to 3.94at.% and from 1.44 to 10.4at.%, respectively. These results suggest that the dry etch resistance of the present ACLs was enhanced by B doping and negatively affected by N doping. Density functional theory calculations highlighted the strengthening of CC bonds induced by B doping and their corresponding weakening caused by N doping as possible explanations for the effects of doping on the dry etching characteristics of the ACLs.

Non-chemically amplified resists containing polyhedral oligomeric silsesquioxane for a bilayer resist system

Abstract Silicon-containing photoresists are gaining increasing interest for bilayer resist systems due to their high oxygen plasma resistance. Bilayer resist materials based on a nonchemically amplified resist system were prepared by copolymerization of polyhedral oligomeric silsesquioxane (POSS)-containing monomer, 2-(2-diazo-3-oxobutyryloxy)ethyl methacrylate (DOBEMA), 2-hydroxyethyl methacrylate (HEMA) and styrene. A series of POSS-containing resists with varying POSS contents were synthesized to optimize the dry etch resistance and selectivity. Upon UV irradiation, the resist film produced high resolution negative tone patterns. A bilayer pattern can be fabricated readily by pattern transfer of a thin silicon-containing top layer into a thick crosslinked organic bottom layer by anisotropic O 2 reactive ion etching. Finally, potential of the POSS-containing resist as an etch mask has been established by successful transfer of patterns into a silicon substrate through dry etching in CF 4 /O 2 plasma.

Correlation between dry etching resistance of Ta masks and the oxidation states of the surface oxide layers

Mechanisms of dry etching resistance of Ta masks, which are widely used for magnetic random access memory etching processes, have been investigated for a better understanding of their faceting characteristics. In magnetic-material etching processes by CO/NH3 or CH3OH plasmas, CO+ ion is considered as one of the most dominant ion species irradiating the substrate surface. An earlier study by Li et al. [J. Vac. Sci. Technol. A 33, 040602 (2015)] has shown that the Ta sputtering yield by CO+ ion irradiation depends strongly on the ion irradiation angle and the level of the surface oxidation. In this study, the primary focus is placed on the effects of surface oxidation and physical sputtering only (without possible chemical effects of carbon) on the etching rate of Ta, and the etching characteristics of Ta and Ta2O5 have been examined with Ar+ and/or oxygen ion beams. It has been found that there is a strong negative correlation between the etching rate of Ta and the oxidation states of the surface oxide layer formed during the etching process; the higher the oxidation states are, the lower the etching rate becomes. The results indicate that a strong propensity of a Ta mask to taper by irradiation of oxidizing ions (i.e., strong ion-irradiation-angle dependence of the Ta etching rate) arises from less efficient oxidation of a tapered surface by incident oxidizing ions, which enter the surface with an oblique angle.

High resolution spin-on electron beam lithography resist with exceptional dry etching resistance

Presently, no resist material has suitable properties to satisfy simultaneously all requirements on lateral resolution and plasma etching resistance for pattern transfer of high aspect ratio nano-structures.Herein, a recent innovative alumina spin-on material for use as both positive and negative high resolution resist for electron beam lithography (EBL) is presented. This system turns into an almost completely inorganic alumina system when exposed to the electron beam, showing exceptional selectivity (100:1), compared to even the most robust polymeric resist, when used as mask for dry etching of silicon in fluorinated plasmas, obviating the need for a hardmask layer deposition. A full characterization of the resist selective removal under different processing conditions, such as electrons acceleration voltage and post-exposure bake temperature and time, is presented. Owing to the high selectivity and high resolution, silicon nano-structures of size down to 11nm and high aspect ratio (up to 20) have been obtained for the first time in a one-step process.

Water soluble and metal-containing electron beam resist poly(sodium 4-styrenesulfonate)

Popular electron beam resists such as PMMA, ZEP and HSQ all use solvent or base solutions for processing, which may attack the sub-layers or substrate that are made out of organic semiconducting materials. In this study we show that water soluble poly(sodium 4-styrenesulfonate), or sodium PSS, can be used as a negative electron beam resist developed in water. Moreover, since PSS contains metal sodium, its dry etching resistance is much higher than PMMA. It is notable that sodium PSS’s sensitivity and contrast is still far inferior to organic resists such as PMMA, thus it is not suitable for patterning dense and high-resolution structures. Nevertheless, feature size down to 40 nm was achieved for sparse patterns. Lastly, using very low energy (here 2 keV) electron beam lithography and liftoff process using water only, patterning of metal layer on an organic conductive material P3HT was achieved. The metallization of an organic conducting material may find applications in organic semiconductor devices such as OLED.

Design considerations for ultraviolet-nanoimprint lithography resists

Design considerations for ultraviolet-nanoimprint lithography resists were investigated focusing on the major issues of ink-jetting performance, pattern formability, release property, and dry etching resistance. Regarding ink-jetting performance, small droplet ink-jetting of 0.7 pl was successfully demonstrated by adjusting the resist fluid property to the ink-jet coater and controlling the resist volatilization. Regarding pattern formability, a resist pattern was imprinted from a mold pattern of 28 nm in width and 60 nm in depth without pattern dimension change. It was thought that modulus control of the resist was more important than resist shrinkage in achieving excellent pattern formability. As for release property, resist with fluorine monomer and with nonreactive fluorine antisticking agent were compared. The results indicated that resist design has the capability to both reduce separation force and maintain a clear mold surface. The mold release agent decomposed with an increasing number of imprint shots, but the low release-force resist with nonreactive antisticking agent was able to control degradation of the mold release agent and thus improve release property endurance. Regarding etching resistance, it was found that increasing the ring parameter of resist is essential for high etching resistance, and resulted in improved etched pattern features of the substrate.

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.

Functional Resist Materials for Negative Tone Development in Advanced Lithography

Challenges of lithography performance, dry etch resistance, and substrate dependency in resist materials dedicated to negative tone development (NTD) process were studied. The gamma-parameter in contrast curve was increased to achieve improvement in lithography performances, and CD-uniformity (CDU), DOF, and circularity of dense C/H pattern were studied for the resist material. Ohnishi-parameter of de-protected polymer was decreased to improve dry etch resistance, and dissolution property and lithography performance were studied to look at maturity of materials. Formulation dependency on pattern collapse property on spin-on-type Si-hard mask (Si-HM) were studied, and material property to suppress pattern collapse was discussed.

Boehmite filled hybrid sol–gel system as directly writable hard etching mask for pattern transfer

We discuss some preliminary results on the development of a new kind of positive tone resist whose peculiarity is an extreme dry etch resistance. This profitable property is obtained by loading and compatibilizing with ceramic nano particles a radiation sensitive sol–gel silica based hybrid organic/inorganic system. With an appropriate choice of the nano particles, the investigated approach is suitable to be adapted and optimized for achieving high selectivity in plasma etching processes of different materials. Here, we specifically demonstrate how the filling with boehmite nano particles (aluminum hydroxide, y-AlO(OH)) confers a much higher selectivity (>60) to the radiation sensitive silica based system when used for the etching of silicon, that show a selectivity <2 if unloaded. The patterning of the new resist was carried out by X-ray lithography while the dry etching tests were made with a fluorine-based chemistry.

High-Resolution Functional Epoxysilsesquioxane-Based Patterning Layers for Large-Area Nanoimprinting

Epoxysilsesquioxane (SSQ)-based materials have been developed as patterning layers for large-area and high-resolution nanoimprinting. The SSQ polymers, poly(methyl-co-3-glycidoxypropyl) silsesquioxanes (T(Me)T(Ep)), poly(phenyl-co-3-glycidoxypropyl) silsesquioxanes (T(Ph)T(Ep)), and poly(phenyl-co-3-glycidoxypropyl-co-perfluorooctyl) silsesquioxanes (T(Ph)T(Ep)T(Fluo)), were precisely designed and synthesized by incorporating the necessary functional groups onto the SSQ backbone. The materials possess a variety of characteristics desirable for NIL, such as great coatability, high modulus, good mold release, and excellent dry etch resistance. In particular, the presence of epoxy functional groups allows the resists to be solidified within seconds under UV exposure at room temperature, and the presence of the fluoroalkyl groups in the SSQ resins greatly facilitate mold release after the imprint process. In addition, the absence of metal in the resins makes the materials highly compatible with applications involving Si CMOS integrated circuits fabrication.

High aspect ratio contact hole etching using relatively transparent amorphous carbon hard mask deposited from propylene

In this study, a high aspect ratio contact pattern, beyond 70 nm technology, in a very-large-scale integrated circuit, was achieved using hydrogenated amorphous carbon (a-C:H) film as the dry etching hard mask. The effect of temperature on the a-C:H deposits prepared by plasma enhanced chemical vapor deposition was studied. The a-C:H films resulting from propylene (C 3H 6) decomposition exhibited high transparency incorporated rich hydrogen concentration with a decreasing deposition temperature. A matrix of dispersed cross-linked sp 3 clusters in a-C:H films, which has an increasing optical band gap and higher hydrogen content, is attributed to reduce the defect density of status and obtain high transmittance rate. Moreover, the higher transparency of a-C:H films could afford lithographic aligned capability as well as compressive stress and dry etching resistance. These explorations provided insights into the role of hydrogen in a-C film and also into the practicality of its future nano-scale device applications.

Synthesis of silicon-containing materials for UV-curable imprint etch barrier solutions

Silicon-containing acrylate and vinyl-ether derivatives, i.e., bis-(acryloxyethyloxy)-dimethylsilane, bis-(acryloxyethyloxy)-bis-(trimethylsilylmethyl)-silane, and bis-(vinyloxyethyloxy)- dimethylsilane, were synthesized. These materials, together with Irgacure 184 as a radical photoinitiator, were used as components for UV-curable imprint etch barrier (IEB) solutions. The effects of each material on the imprint properties of the IEB solution, such as viscosity and dry-etching resistance, were evaluated. The etch resistance of cured IEB films against oxygen plasma increased with the amount of silicon in the synthesized material. The vinyl-ether derivative had a much lower viscosity than the acrylate derivative. Formulations based on the three synthesized materials were made to find the optimum composition among them in terms of the required properties for the nanoimprinting and the following processes. The optimized formulation was applied to the nanoimprinting and subsequent lift-off process to define nanoscale features of eight chrome (Cr) metal lines with 65 nm linewidth at 250 nm pitch.