Reactive Ion Etching Pattern Transfer Research Articles

Assessing tolerances in direct write laser grayscale lithography and reactive ion etching pattern transfer for fabrication of 2.5D Si master molds

Assessing tolerances in direct write laser grayscale lithography and reactive ion etching pattern transfer for fabrication of 2.5D Si master molds

Roll-to-roll reactive ion etching of large-area nanostructure arrays in Si: Process development, characterization, and optimization

Roll-to-roll (R2R) nanofabrication processes are recognized as key enabling-technologies for many next-generation applications in flexible electronics, displays, energy generation, storage, as well as healthcare. However, R2R processing techniques reported in the literature currently lack a scalable method of performing high-throughput nanoscale pattern transfer of geometry requiring a high degree of fidelity in terms of critical dimension resolution, etch uniformity, and aspect ratio. Reactive ion etching (RIE) addresses the need for sub-10 nm pattern transfer with large-area uniformity in wafer-scale semiconductor manufacturing, but adapting plasma etch systems for use in R2R nanopatterning has proven to be nontrivial. Moreover, robust models for simulating R2R RIE do not exist, which is an obstacle to the creation of computational approaches to design, control, and scale-up of nanoscale R2R equipment and processes. To address these challenges, we demonstrate a process flow for fabricating Si nanopillar arrays utilizing a combination of nanoimprint lithography and RIE with all pattern transfer steps performed using a R2R plasma reactor system. Specifically discussed are process development details for etching imprint resist and Si including etch rates, cross-web etch uniformity, etch directionality, and etch selectivity at varying gas chemistries, powers, and pressures. 2k full-factorial Design of Experiments (DoEs) and ordinary least-squares regression analysis are also employed to study influence of process parameters on multiple outgoing etch quality characteristics and generate stochastic models of the R2R RIE pattern transfer process into Si. Utilizing these DOE-based models and desired targets for etch quality characteristics, we describe a bounded multivariate inverse-optimization scheme for automated etch process parameter tuning. The culmination of these efforts, to the best of the authors' knowledge, is the first reported RIE-based pattern transfer of 100 nm-scale features performed in continuous R2R fashion with control of feature geometry over large area. The methodology employed herein may be applied similarly to additional materials and geometries for future applications.

Influence of block copolymer feature size on reactive ion etching pattern transfer into silicon

A successful realisation of sub-20 nm features on silicon (Si) is becoming the focus of many technological studies, strongly influencing the future performance of modern integrated circuits. Although reactive ion etching (RIE), at both micrometric and nanometric scale has already been the target of many studies, a better understanding of the different mechanisms involved at sub-20 nm size etching is still required. In this work, we investigated the influence of the feature size on the etch rate of Si, performed by a cryogenic RIE process through cylinder-forming polystyrene-block-polymethylmethacrylate (PS-b-PMMA) diblock copolymer (DBC) masks with diameter ranging between 19–13 nm. A sensible decrease of the etch depth and etch rate was observed in the mask with the smallest feature size. For all the DBCs under investigation, we determined the process window useful for the correct transfer of the nanometric cylindrical pattern into a Si substrate. A structural and physicochemical investigation of the resulting nanostructured Si is reported in order to delineate the influence of various RIE pattern effects. Feature-size-dependent etch, or RIE-lag, is proved to significantly affect the obtained results.

Submicron-patterning of bulk titanium by nanoimprint lithography and reactive ion etching

Nanopatterns on titanium may enhance endosseous implant biofunctionality. To enable biological studies to prove this hypothesis, we developed a scalable method of fabricating nanogrooved titanium substrates. We defined nanogrooves by nanoimprint lithography (NIL) and a subsequent pattern transfer to the surface of ASTM grade 2 bulk titanium applying a soft-mask for chlorine-based reactive ion etching (RIE). With respect to direct write lithographic techniques the method introduced here is fast and capable of delivering uniformly patterned areas of at least 4 cm2. A dedicated silicon nanostamp process has been designed to generate the required thickness of the soft-mask for the NIL–RIE pattern transfer. Stamps with pitch sizes from 1000 nm down to 300 nm were fabricated using laser interference lithography (LIL) and deep cryogenic silicon RIE. Although silicon nanomachining was proven to produce smaller pitch sizes of 200 nm and 150 nm respectively, successful pattern transfer to titanium was only possible down to a pitch of 300 nm. Hence, the smallest nanogrooves have a width of 140 nm. An x-ray photoelectron spectroscopy study showed that only very few contaminations arise from the fabrication process and a cytotoxicity assay on the nanopatterned surfaces confirmed that the obtained nanogrooved titanium specimens are suitable for in vivo studies in implantology research.

Fabrication of nanogaps for MEMS prototyping using focused ion beam as a lithographic tool and reactive ion etching pattern transfer

In this paper we present a different approach using a focused ion beam (FIB) as lithographic tool to define nanometric width gaps, which are then transferred to a silicon substrate by reactive ion etching (RIE). This process has been developed to fit the technological requirements for micro- and nano-electromechanicals systems (M-NEMS) applications.

CCl4-Based RIE Pattern Transfer into Facets of Mesas Formed by Wet Etching in InP(100)

We performed reactive ion etching (RIE) in plasma to transfer patterns into (100), (110), and (211)A wet-etch exposed in InP(100) wafers. At a power, pressure, self-bias, and substrate temperature of 100 W, 0.8 Pa, , and 25°C, respectively, etching rates were: ; ; , respectively. Original and dry-etched (100) surfaces exhibited root-mean-square roughness and 1.65 nm, respectively. suggests that the etching removed surface chlorides more efficiently from the slanted (211)A and (110) facets than from the normal-incidence (100) surface.

Optically matched trilevel resist process for nanostructure fabrication

A novel trilevel resist process has been developed which enables high-contrast imaging of periodic structures with spatial periods down to 200 nm in thick resist on highly reflective substrates, using λ=351.1 nm argon-ion laser exposure. The process utilizes a 200-nm-thick, high-contrast, imaging resist layer, a thin (∼15-nm) evaporated dielectric interlayer, and a 300–600-nm-thick bottom antireflection coating (ARC) which suppresses reflections from the substrate. Our trilevel resist scheme has been implemented in a manufacturing process which utilizes a high-contrast interferometric lithography system for the formation of large-area, 200–1000 nm period grating and dot array images. The choice of interlayer is the most critical feature of this process. This material must have good deposition and adhesion properties, must be optically matched to the resist and ARC, must etch quickly during the reactive-ion etching (RIE) pattern transfer from the resist into the interlayer, must display very high selectivity to the ARC during the RIE pattern transfer into the bottom layer, and must be easily stripped after the trilevel resist structure has served its purpose. We also report on computer modeling which elucidates the factors influencing standing wave formation and present results of tests with several interlayer materials which display good optical matching and selectivities of up to 240:1 during RIE of the ARC.

Simulation of reactive ion etching pattern transfer

This paper describes a model that simulates etching profiles and process latitudes in glow-discharge bombardment-induced reactive-etching processes. Numerical results are presented for the pattern-transfer step in trilayer lithography, but this analysis is applicable to many other pattern-transfer processes. The inputs to the interface-evolution model described here are a kinetic model for the yield per incident energetic particle and a statistical mechanical model that relates the incident-yield-weighted angular distribution to the pressure, sheath thickness, and sheath voltage drop. The kinetic model is based on experimental evidence and assumes that the yield per bombarding particle is proportional to its energy. The resulting interface-evolution equation is mathematically analogous to a free-surface evolution equation in hydrodynamics. This convective partial differential equation is reduced to a coupled set of ordinary differential equations via the method of characteristics and solved numerically. More general energy-dependent yields are easily incorporated in the present formulation, but angle-dependent yields are more difficult and are not treated here. This model describes how shadowing of the surface being etched results in proximity effects in line etching and aspect-ratio-dependent etching rates in trench etching. Simulated profiles are compared to experimental trilayer etching profiles and qualitatively describe their shape and the trends that are observed as pressure or other processing parameters are varied. Simulations showing the effect of angular distributions, line proximity, and trench aspect ratio on process latitudes in trilayer lithography are presented and discussed.

A sub‐0.5 μm bilevel lithographic process using the deep‐UV electron‐beam resist p(si‐cms)

AbstractOptimization of the deep‐UV and electron‐beam lithographic properties of a copolymer of trimethylsilylmethyl methacrylate (SI) and chloromethylstyrene (CMS), P(SI‐CMS), within a weight average molecular weight range of 1.4 to 4.1 × 105 and 90 to 93 mole percent SI composition has been achieved. The solubility behavior of P(SI‐CMS) resist was examined using the Hansen 3‐dimensional solubility parameter model and dissolution rate measurements. Swelling of the resist has been minimized through the identification of a single component developer (2‐propanol) and rinse (water) system. For the material containing 90 mole percent SI (14.9 weight percent Si) and M̄ω = 1.4 × 105, the sensitivity to 248 nm radiation is 65 mJ/cm2 and to electron‐beam exposure is 3.4 μC/cm2 at 20 kV. This material Is applicable to bilevel lithographic processes, and the O2 reactive ion etching (RIE) rate is 16 times slower than standard hard‐baked photoresist. Using a He/O2(60/40) RIE pattern transfer process, 0.4 μm line/space patterns have been resolved in a 1.3 μm bilayer structure for deep‐UV exposures, and 0.25 μm imaging has been demonstrated in a 0.7 μm thick planarizing layer using electron beam irradiation. The loss in linewidth associated with the 0.25 μm process is ∼0.04 μm.

Factors controlling the etching rate and etching profile in the O2 reactive ion etching pattern transfer step in multilevel lithography

AbstractPhysical bombardment plays a dominant role in the O2 reactive ion etching (RIE) pattern transfer step in multilevel lithography. Etching rates are determined by the flux and energy distribution of the bombarding ions and energetic neutrals (charge transfer products), while anisotropy is determined by their directionality. Measurements of the sheath thickness and voltage drop may be used to estimate flux, energy distribution, average energy, and angular distribution of ions and the energetic neutral products of charge transfer collisions. The estimated flux of bombarding particles allows measured etching rates to be converted into yields. The trends for the etching rate as a function of pressure, bias voltage, and other system variables reflect a single fundamental trend for the yield as a function of bombardment energy. Etching rates of an organic novolac polymer are proportional to the energy flux from bombarding particles while the yield per bombarding particle is proportional to its energy. These kinetics are combined with angular distribution and interface evolution models to predict etching profiles in multilevel lithography.

Thin titanium dioxide films as interlayers in trilayer-resist structures

The use of thin titanium dioxide (TiO2 ) films as interlayers in trilayer-resist structures was investigated in this paper. TiO2 layers, 30–200 Å thick, were formed on the surface of thick positive photoresist films by the reaction of titanium tetrachloride (TiCl4 ) with water adsorbed on the surface of the films. The TiCl4 -treated films served as the bottom two layers in trilayer-resist structures. Using a thin TiO2 interlayer that acted as the mask in the final reactive ion etching pattern transfer step, 0.5-μm features were transferred from a top imaging layer to a 1.2-μm-thick bottom layer with ∼0.05-μm linewidth loss. Processing variables that affect the thickness of the TiO2 films were investigated. We discuss these variables, etching techniques for transfer of the resist pattern from the top imaging layer to the TiO2 interlayer and pinhole defects in the TiO2 films.

Highly sensitive thermally developable positive resist systems

Acid-catalyzed thermal depolymerization of polyphthalaldehyde derivatives has been utilized in the design of highly sensitive, thermally developable, positive resist systems incorporating two stages of chemical amplification. Poly(4-chlorophthalaldehyde) mixed with triphenylsulfonium hexafluoroantimonate can be thermally developed to the substrate simply by heating the resist after exposure to <1 mJ/cm2 of 254-nm radiation or 1 μC/cm2 of 18-keV electron beam radiation. The images obtained by postbaking at 160 °C do not exhibit any thermal flow. Poly(4-trimethylsilylphthalaldehyde) (PSPA) sensitized with triphenylsulfonium triflate exhibits a high deep UV sensitivity of <2 mJ/cm2 and a high electron beam sensitivity of 1 to 2 μC/cm2 (20 keV) when the thermal development is performed at 100–130 °C. The high contrast (γ=4.3) of the PSPA resist allows thermal imaging of submicrometer features, which can then be transferred to the bottom planarizing layer by oxygen reactive ion etching (RIE). The combination of the thermal development and oxygen RIE pattern transfer provides a new mode of all dry bilayer processes.