Helium Ion Beam Lithography Research Articles

Induced Chemical Networking of Organometallic Tin in a Cyclic Framework for Sub-10 nm Patterning and Interconnect Application

Given the need for advanced resist materials in view of fast shrinkage of semiconductor node scaling, this work demonstrates the lithography application of an organotin-based cyclotrimeric species (Sn–CT) as a molecular resist for sub-10 nm patterning using electron beam lithography (EBL) and helium ion beam lithography (HIBL) techniques. While the resist has been successfully used for patterning ∼15 nm line/space features and ∼9 nm discrete line features at a dose of 2.5 mC/cm2 using EBL, ∼15 nm line/space features were printed on silicon at a dose of 16 μC/cm2 using HIBL. Moreover, Sn–CT has also been used for patterning complex features at a single nanometer regime such as real-scale device designs at ∼7 nm structure on silicon. A mechanistic study using X-ray photoelectron spectroscopy (XPS) revealed the formation of Sn–O–Sn and Sn–OH networks along with the loss of carbon-based group(s) upon radiation exposure, resulting in the generation of insoluble products in the exposed region, which becomes the basis of polarity switching and hence pattern development. The resist was found to have good etch resistance with respect to silicon. Moreover, Sn–CT has been explored as a good gap-filling material for silicon (Si) front-end devices and interconnects due to its low-κ dielectric (∼1.9) and high diffusion barrier properties.

Ultrasensitive metal-organic cluster resist for patterning of single exposure high numerical aperture extreme ultraviolet lithography applications

BackgroundAn incredible increase in the integration of electronic chips has pushed the semicon industries to endorse high numerical aperture (h-NA ∼ 0.5), extreme-ultraviolet (EUV) lithography (EUVL) (λ ∼ 13.5 nm) at the commercial scale. Induction of h-NA postulates EUV resists that could outperform the resolution, line pattern roughness, and sensitivity (RLS) trade-off for chip fabricators, which is currently extremely limited.AimThe development of EUV resist to balance RLS trade-off as well as overcome throughput limitations of h-NA EUV system to facilitate high volume semiconductor manufacturing.ApproachHere, we developed indium-methacrylic acid-based metal-organic clusters resist for h-NA, EUVL. To examine the h-NA single exposure patterning potential of the resist, prescreening by sub-10 nm next-generation lithography (NGL) tools such as electron beam lithography (EBL), and helium ion beam lithography (HIBL) were conducted as a prelude to EUV exposure.ResultsDense ∼13 nm, (l/s) patterns at ∼45 and ∼30 μC / cm2 were well resolved by EBL and HIBL, on the top this the line edge roughness (LER) was 2.48 ± 0.04 nm, and etch resistance ∼1.98 and ∼0.34 times lower than Si and SiO2 / Si systems. Also, In-MAA MOCs resist shows ultra-sensitivity of 2.3 mJ / cm2 towards h-NA EUVL for patterning up to 26 nm half-pitch line patterns with LER ∼2.36 ± 0.16 nm.

Macrocycle Network-Aided Nanopatterning of Inorganic Resists on Silicon

Inorganic resists have emerged as promising candidates in semiconductor industries to realize sub-10 nm node technology. However, controlling vertical shrinkage of resist films during the pattern development process, particularly for ultralow thin film applications, is among the highly pressing limitations of inorganic resists along with pattern roughness and poor resist shelf-life characteristics. Tin-based clusters and small molecules have been recently introduced as resist materials. They possess a high absorption coefficient and fast solubility transitions under irradiation exposure. As we investigated, n-butylstannoic acid (BTA) showed ∼38% vertical shrinkage when its film was exposed with deep ultraviolet photons (DUV, ∼254 nm) and could pattern features of ∼120 nm. We hypothesized and experimentally validated an approach that provided control on shrinkage issues, along with improving its patterning potential to sub-15 nm regime. In our approach, BTA was embedded into a polyhydroxy organic host matrix composed of noria (water-wheel-like macrocycle) derivatives. The rigid molecular cage structure and photo-inert nature of noria (N-Me) were utilized as the host matrix that apprehended the inorganic resist material within its intermolecular space. Ultrathin films (∼20 nm) were coated on silicon, and various nanofeatures including 10 nm lines, meshlike grids with 10 nm width, complex patterns, and so forth were patterned using electron beam and helium ion beam lithography. Most importantly, we were able to drastically reduce the vertical shrinkage to ∼13% with respect to initial thickness, which substantiates the potential of our hypothesis. We also noticed good shelf-life (6 months), good etch resistance, and low line edge roughness (LER)/line width roughness (LWR) for the developed resist composition.

Investigation on helium ion beam lithography with proximity effect correction

Our work presents and investigates the effectiveness of a model-based proximity effect correction method for helium ion beam lithography (HIBL). This method iteratively modulates the shape of a pattern by a feedback compensation mechanism until the simulated patterning fidelity satisfies specific constraints. A point spread function (PSF) is utilized to account for all phenomena involved during the scattering events of incident ion beam particles in the resist. Patterning prediction for subsequent correction process is derived from the energy intensity distribution due to convolution between the PSF and the pattern, with an adequate cut-off threshold. The performance of this method for HIBL is examined through several designed layouts from 15- to 5-nm in half pitches, under specific process parameters, including acceleration voltage, resist thickness, and resist sensitivity. Preliminary results show its effectiveness in improving the patterning fidelity of HIBL.

Direct visualization of beam-resist interaction volume for sub-nanometer helium ion beam-lithography

Interaction volume of beam-resist is a basis unit of beam-lithography, directly determines the critical parameters of beam-lithography. We have visualized the interaction volume at the state-of-the-art sub-10 nm scale by a spot irradiation of sub-nanometer helium ion beam into an approximately free-standing resist. The visualized interaction volume suggests helium ion beam has an excellent capability in nanofabrication. Specifically, helium ion beam-lithography is 1000 times more efficient than electron beam-lithography (EBL), owns a sub-4 nm resolution, can achieve a large pattern aspect ratio (greater than 8), and does not suffer from backscattering effect at a normal exposure dose. Furthermore, the interaction volume has been theoretically studied by considering the spatial distribution of energy deposited in the resist, and eventually lead to a model for pattern prediction and proximity effect corrections. We expect that, our approach to visualize the interaction volume may be applied to study other high resolution lithographic techniques such as x-ray lithography and EBL, and it may open new possibilities in other applications, like beam-imaging, beam-milling, and beam-modification.

Helium ion beam lithography and liftoff

We introduce a helium ion beam lithography and liftoff process to fabricate arbitrary nanostructures. Exploiting existing high-resolution positive tone resists such as poly (methyl methacrylate) (PMMA), the process offers three significant advantages over electron beam lithography: (a) the exposing helium ion beam produces a high secondary electron yield leading to fast patterning, (b) proximity effects are negligible due to the low count of backscattered helium ions from the substrate, and (c) the process is transferrable with minimal alteration among different types of substrates (e.g. silicon, fused silica). The process can be used to pattern any material compatible with liftoff such as evaporated metals or dielectrics, and allows overlay of nanostructures precision-aligned to microstructures realised beforehand on the same substrate. The process is demonstrated for several PMMA thicknesses to liftoff different thicknesses of deposited material. Resolution trials are conducted to determine the limits of the process for each PMMA thickness. Isolated lines as narrow as 14 nm, and line-space gratings of 40 nm pitch (50% duty cycle), are produced as resolution tests by lifting off a 20 nm thick Au film. Nanostructures of aspect ratio up to ∼3:1 have been realised. Plasmonic nanoantenna arrays overlaid to microscale contacts are produced as device demonstrators, for which optical measurements are in excellent agreement with theory.

Organoiodine Functionality Bearing Resists for Electron-Beam and Helium Ion Beam Lithography: Complex and Sub-16 nm Patterning

Given the current need for resist materials for patterning transistors with ultralow nodes, there has been a quest for developing resists with improved performance for nanoscale patterning with goo...

Large-Scale Focused Helium Ion Beam Lithography

Focused ion beam sources have recently been commercialized and are increasingly utilized for applications in nanotechnology. There is a desire to pattern large designs, millimeter in scale, while still achieving sub-nanometer resolution in the smallest features. However, focused helium ion beams are restricted to fields of view of roughly 100 micrometers. Recently, we have developed an automated process for layout designs with feature sizes from sub-nanometer to millimeter scales, using Raith lithography software in a Zeiss Orion Plus helium ion microscope. The technique relies on stitching writefields together and incorporating automated focusing algorithms in the Raith software. This procedure was demonstrated by scaling and automating the process of producing ion-damaged Josephson junctions in arrays in the high-temperature superconducting material YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-δ</sub> . We demonstrate that the automated process reduces operator input while maintaining consistency at the smallest resolutions.

Suppression of short channel effects in ferroelectric Si junctionless transistors with a sub-10 nm gate length defined by helium ion beam lithography

Short channel effects in Si junctionless transistors with a gate length below 10 nm are reduced by the ferroelectric Hf0.5Zr0.5O2gate oxide.

Resists for Helium Ion Beam Lithography: Recent Advances

Since the fabrication of micro-/nanoelectronic devices are marching toward ultralow node technology with dense patterns to meet the current industry demands, continuous advancement is needed in ter...

Nanoaperture fabrication in ultra-smooth single-grain gold films with helium ion beam lithography

We demonstrate a simple three-step gold thin-film sample preparation process to enhance the morphology and lithographic precision using helium ion based direct-writing. The procedure includes metal deposition, heat treatment and template stripping, which produce smooth monocrystalline gold grains with sizes up to 500 nm and an average surface roughness of 0.267 nm. By using a helium ion microscope, we can fabricate structures with feature sizes less than 20 nm in a 100 nm thick gold film with high-quality sidewalls. We demonstrate the efficacy of this technique by producing high-quality double nanohole (DNH) nanoapertures for single nanoparticle trapping in a single grain of 100 nm thick gold. This procedure can be applied to a wide range of antenna geometries and features that need to be fabricated producing optical and or electronic devices.

Atomistic Positioning of Defects in Helium Ion Treated Single-Layer MoS2.

Structuring materials with atomic precision is the ultimate goal of nanotechnology and is becoming increasingly relevant as an enabling technology for quantum electronics/spintronics and quantum photonics. Here, we create atomic defects in monolayer MoS2 by helium ion (He-ion) beam lithography with a spatial fidelity approaching the single-atom limit in all three dimensions. Using low-temperature scanning tunneling microscopy (STM), we confirm the formation of individual point defects in MoS2 upon He-ion bombardment and show that defects are generated within 9 nm of the incident helium ions. Atom-specific sputtering yields are determined by analyzing the type and occurrence of defects observed in high-resolution STM images and compared with Monte Carlo simulations. Both theory and experiment indicate that the He-ion bombardment predominantly generates sulfur vacancies.

Development of Nickel-Based Negative Tone Metal Oxide Cluster Resists for Sub-10 nm Electron Beam and Helium Ion Beam Lithography.

Hybrid metal-organic cluster resist materials, also termed as organo-inorganics, demonstrate their potential for use in next-generation lithography owing to their ability for patterning down to ∼10 nm or below. High-resolution resist patterning is integrally associated with the compatibility of the resist and irradiation of the exposure source. Helium ion beam lithography (HIBL) is an emerging approach for the realization of sub-10 nm patterns at considerably lower line edge/width roughness (LER/LWR) and higher sensitivity as compared to electron beam lithography (EBL). Here, for the first time, a negative tone resist incorporating nickel (Ni)-based metal-organic clusters (Ni-MOCs) was synthesized and patterned using HIBL and EBL at 30 keV. This resist comprises a nickel-based metal building unit covalently linked with the organic ligand: m-toluic acid (C8H8O2). Dynamic light scattering confirmed a narrow size distribution of ∼2 nm for metal-organic cluster (MOC) formulations. High-resolution ∼9 nm HIBL line patterns were well developed at a sensitivity of 22 μC/cm2 and at a significantly low LER and LWR of 1.81 ± 0.06 and 2.90 ± 0.06 nm, respectively. Analogous high-resolution patterns were also observed in EBL with a sensitivity of 473 μC/cm2. Hence, the Ni-MOC-based resist investigated using HIBL and EBL elucidates the ability of its potential for the sub-10 nm technology node, under standard processing conditions.

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.

Charged particle single nanometre manufacturing.

Following a brief historical summary of the way in which electron beam lithography developed out of the scanning electron microscope, three state-of-the-art charged-particle beam nanopatterning technologies are considered. All three have been the subject of a recently completed European Union Project entitled “Single Nanometre Manufacturing: Beyond CMOS”. Scanning helium ion beam lithography has the advantages of virtually zero proximity effect, nanoscale patterning capability and high sensitivity in combination with a novel fullerene resist based on the sub-nanometre C60 molecule. The shot noise-limited minimum linewidth achieved to date is 6 nm. The second technology, focused electron induced processing (FEBIP), uses a nozzle-dispensed precursor gas either to etch or to deposit patterns on the nanometre scale without the need for resist. The process has potential for high throughput enhancement using multiple electron beams and a system employing up to 196 beams is under development based on a commercial SEM platform. Among its potential applications is the manufacture of templates for nanoimprint lithography, NIL. This is also a target application for the third and final charged particle technology, viz. field emission electron scanning probe lithography, FE-eSPL. This has been developed out of scanning tunneling microscopy using lower-energy electrons (tens of electronvolts rather than the tens of kiloelectronvolts of the other techniques). It has the considerable advantage of being employed without the need for a vacuum system, in ambient air and is capable of sub-10 nm patterning using either developable resists or a self-developing mode applicable for many polymeric resists, which is preferred. Like FEBIP it is potentially capable of massive parallelization for applications requiring high throughput.

Exploring proximity effects and large depth of field in helium ion beam lithography: large-area dense patterns and tilted surface exposure

Helium ion beam lithography (HIL) is an emerging nanofabrication technique. It benefits from a reduced interaction volume compared to that of an electron beam of similar energy, and hence reduced long-range scattering (proximity effect), higher resist sensitivity and potentially higher resolution. Furthermore, the small angular spread of the helium ion beam gives rise to a large depth of field. This should enable patterning on tilted and curved surfaces without the need of any additional adjustments, such as laser-auto focus. So far, most work on HIL has been focused on exploiting the reduced proximity effect to reach single-digit nanometer resolution, and has thus been concentrated on single-pixel exposures over small areas. Here we explore two new areas of application. Firstly, we investigate the proximity effect in large-area exposures and demonstrate HIL’s capabilities in fabricating precise high-density gratings on large planar surfaces (100 μm × 100 μm, with pitch down to 35 nm) using an area dose for exposure. Secondly, we exploit the large depth of field by making the first HIL patterns on tilted surfaces (sample stage tilted 45°). We demonstrate a depth of field greater than 100 μm for a resolution of about 20 nm.

3D Volumetric Energy Deposition of Focused Helium Ion Beam Lithography: Visualization, Modeling, and Applications in Nanofabrication

AbstractIn this paper, 3D volumetric energy deposition and local crosslinking of hydrogen silsesquioxane (HSQ) are experimentally and numerically explored in focused helium ion beam lithography (HIBL). In particular, a through‐membrane exposure method is developed to make visible and subsequently to measure the 3D interaction volume and energy deposition of helium ions in HSQ. By comparing the actual dimensions of the crosslinked HSQ structures with Monte Carlo modeling of the spatial distribution of the energy deposition, the critical energy density for crosslinking HSQ is obtained. Finally, 3D nanofabrication of complex crosslinked HSQ nanostructures such as embedded nanochannels and suspended grids is demonstrated using two different exposure configurations. The proposed method expands the 2D point spread function of HIBL into three dimensions, thus opening a new avenue for nanoscale 3D fabrication.

Sub-10 nm electron and helium ion beam lithography using a recently developed alumina resist

Electron Beam Lithography (EBL) at sub-10nm resolution is mainly limited by resist contrast and proximity effects. In this work, we investigate the use of a recently developed alumina-based resist as a negative-tone resist for EBL at 100keV and focused helium ion beam lithography (FHIBL). The resist is synthesized using a sol-gel method and turns into a near completely inorganic alumina system when exposed to the electron/ion beam. We first investigate the effect on the resist contrast curve on i) development temperature; ii) stability of the resist after exposure and before post-baking and development; and iii) aging of the resist solution. We demonstrate the patterning of isolated features as small as 6.5nm using an EBL and 5nm using FHIBL and a resolution down to 10nm for FHIB exposed films. Finally, we demonstrate the pattern transfer of 10nm lines with an aspect ratio of 10 in silicon, using an optimized reactive ion etching process.

Nanoimprint lithography for nanodevice fabrication.

Nanoimprint lithography (NIL) is a compelling technique for low cost nanoscale device fabrication. The precise and repeatable replication of nanoscale patterns from a single high resolution patterning step makes the NIL technique much more versatile than other expensive techniques such as e-beam or even helium ion beam lithography. Furthermore, the use of mechanical deformation during the NIL process enables grayscale lithography with only a single patterning step, not achievable with any other conventional lithography techniques. These strengths enable the fabrication of unique nanoscale devices by NIL for a variety of applications including optics, plasmonics and even biotechnology. Recent advances in throughput and yield in NIL processes demonstrate the potential of being adopted for mainstream semiconductor device fabrication as well.

Helium ion beam lithography on fullerene molecular resists for sub-10 nm patterning

Helium ion beam lithography (HIBL) is an emerging technique that uses a sub-nanometre focused beam of helium ions generated in the helium ion microscope to expose resist. It benefits from high resolution, high sensitivity and a low proximity effect. Here we present an investigation into HIBL on a novel, negative tone fullerene-derivative molecular resist. Analysis of large area exposures reveals a sensitivity of ~40μC/cm2 with a 30keV helium beam which is almost three orders of magnitude higher than the sensitivity of this resist to a 30keV electron beam. Sparse line features with line widths of 7.3nm are achieved on the ~10nm thick resist. The fabrication of 8.5 half-pitched lines with good feature separation and 6nm half-pitched lines with inferior but still resolvable separation is also shown in this study. Thus, sub-10nm patterning with small proximity effect is demonstrated using HIBL using standard processing conditions, establishing its potential as an alternative to EBL for rapid prototyping of beyond CMOS devices.