Inorganic Electron Beam Research Articles

Influence of Chemical Structures on E-Beam Lithography Performance of Polysilsesquioxanes.

Hydrogenated silsesquioxane (HSQ) is a key inorganic electron beam resist, celebrated for its sub-10 nm resolution and etching resistance, but it faces challenges with stability and sensitivity. Our innovative study has comprehensively assessed the lithographic performance of three functionalized polysilsesquioxane (PSQ) resist series─olefins, halogenated alkanes, and alkanes─under electron beam lithography (EBL). We discovered that the addition of olefin groups, such as in the HMP-30 formulation with 30% propyl acrylate, remarkably increased the sensitivity to 0.6 μC/cm2. The inclusion of halogenated aromatic and hydrogen-substituted methyl groups further enhanced sensitivity and contrast, with HClBN-50 achieving a 22.9 nm resolution pattern. At the same time, the storage of PSQ resists was significantly improved compared to commercial HSQ with increasing alkane group content. Crucially, our research has unveiled the lithography reaction mechanism, highlighting how group encapsulation and steric hindrance influence PSQ performance. This insight is groundbreaking, offering a deeper understanding of the molecular structure-performance relationship and laying the groundwork for developing next-generation electron beam resists with superior sensitivity, resolution, and contrast for microelectronics manufacturing.

Synergetic Degradation of Corn Cob with Inorganic Salt (or Hydrogen Peroxide) and Electron Beam Irradiation

This study focused on the influence of inorganic salt (MnCl2, FeCl3, NaHCO3) or H2O2 combined with electron beam irradiation (EBI) at 90, 180, and 270 kGy on the content and structure of the three major components (cellulose, hemicellulose, and lignin) of corn cob in the pretreatment process. Acemonium cellulase (10 FPU/g of corn cob) were used to hydrolyze the pretreated samples for 96 h. The results indicated that the combined methods showed an obvious synergetic effect on the removal of hemicellulose and lignin and the reduction of degree of polymerization (DP) of cellulose, while the cellulose recovery decreased slightly during the treatment. Particularly, at the optimum conditions (2% NaHCO3 with EBI at 180 kGy), the highest 70.5% hemicellulose and 34.7% lignin removal were achieved with the DP of cellulose decreasing from 1081 of raw to 82. The results of Fourier-transform infrared spectra (FTIR) and scanning electron microscopy (SEM) analysis showed that the IR crystallinity index of cellulose decr...

Fabrication of a seamless roll mold using inorganic electron beam resist with postexposure bake

The fabrication of next-generation devices via roll-to-roll (RTR) nanoimprinting has received considerable attention due to the high throughput and resolution associated with the process. In particular, RTR nanoimprinting with ultraviolet (UV)-curable resin is expected to be useful for the fabrication of large-area devices such as nonreflective films, transparent conductive sheets, and organic solar cells. In order to improve the resolution of such devices, the roll mold must be able to produce seamless fine patterns. Generally, a roll mold for nanoimprinting is made by attaching a planar mold replicated from the master mold via a nickel electroforming technique. However, this method produces seams, which reduces the product yield. In order to resolve these issues, the authors have developed a direct writing method using electron beam (EB) lithography on a rotating cylindrical substrate. In this study, the authors examined the potential for fabricating a seamless roll mold using high-resolution inorganic EB resist and the pattern shrink effect from postexposure bake (PEB). The authors used the dip-and-pull method to form the EB resist layer on the roll mold substrate (32 mm diameter, made of brass). The cleaned roll mold was dipped in the inorganic EB resist and then pulled out at a constant speed. The resulting sample was cured at 300 °C for 1 h. Next, the sample was mounted on rotating equipment and placed in a scanning electron microscope (SEM) equipped with an EB writing system, and the roll substrate was exposed to 10 kV EB while rotating at a constant speed. The revolution speed was set to ten turns per line pattern. Subsequently, PEB was carried out at 200 °C for 10 min in air. After the sample was cooled to room temperature, the EB-exposed area of the EB resist layer was developed using buffered HF. The obtained pattern on the roll mold was examined with the same SEM used for writing. Finally, RTR nanoimprinting using the obtained roll mold was carried out using UV-photocurable resin. At that time, the sample was coated with an antisticking layer of fluorinated silane coupling agent. As a result, a seamless line pattern 190 nm wide was obtained on a polyethylene terephthalate film over a length of 10 cm.

Fabrication of Less than 20-nm-Diameter Nanodot Arrays Using Inorganic Electron Beam Resist and Post Exposure Bake

Next-generation NanoImprint Lithography (NIL) includes photolithography and high-voltage-acceleration (>50 kV) Electron-Beam Lithography (EBL) both of which are expensive, which is why Low-Acceleration-Voltage (LAV) EBL has attracted attention. We fabricated nanodot arrays with a diameter of 20 nm or less combining inorganic resist and LAV EBL. Using Post-Exposure Bake (PEB), we reduced dot-array pattern size and conducted Ultra-Violet (UV) NIL using these nanodot molds. The results we obtained using nanodot arrays 10 nm in diameter fabricated by EBL at an acceleration voltage of 4 kV with PEB yielded a checkerboard design 10 nm in diameter spaced at 20 nm intervals using 10 kV EB. This density corresponds to nanodot-arrays of 1 Tb/in2.

Effect of Post Exposure Bake in Inorganic Electron Beam Resist and Utilizing for Nanoimprint Mold

A high-aspect-ratio structural mold has been fabricated using a simple process that comprises of electron beam lithography (EBL) and post exposure bake (PEB) of inorganic resist. Using developed inorganic resist for mold, pattern transfer to a photo-curable polymer was carried out by ultraviolet nanoimprint lithography (UV-NIL). The developed inorganic resist has enough hardness to be used for mold because this resist structure is almost equivalent to that of quartz. The aspect ratio of the fabricated mold with PEB was 2.59; this value is twice the size of aspect ratio of fabricated mold without PEB (1.16). Thus, PEB is very effective in fabricating high-aspect ratio pattern in inorganic resist. The size of the fabricated mold with PEB was 1004 nm developed depth and 388 nm line and 252 nm space. Using the mold, UV-NIL was carried out. The size of replicated pattern was 942 nm height and 278 nm line and 241 nm space. The replicated height and line width were slightly smaller than mold depth and line width because of volume shrinkage of photo-curable polymer by UV irradiation. The aspect ratio of the replicated pattern using the mold with PEB was 3.39; thus, high-aspect-ratio transfer was also possible. This process is useful for rapid fabrication of quarter wavelength plates.

Fabrication of the nanoimprint mold using inorganic electron beam resist with post exposure bake

Nanoimprint lithography (NIL) is the preferred technique for next-generation nanometer-scale patterning because of its cost effectiveness and simplicity when compared to conventional technology. The replicated pattern depends on the mold pattern, hence efficient methods for fabricating the fine mold are critically required and have recently become intensive subjects of research. This study reports a new method for the fabrication of a fine mold: this method uses low-acceleration-voltage (4kV) electron beam lithography with spin on glass (SOG), which is used as a positive-tone inorganic resist. Although our SOG process does not contain chemically amplified material, postexposure bake (PEB) was characteristically used in the authors’ process. The PEB process caused the annealing effect for the SOG and also suppressed the proximity effect. Consequently, a line-and-space pattern nanoimprint mold with a sub-50nm spacing was fabricated at 4kV using their process, and ultraviolet NIL was successfully carried out using the fabricated mold.

Improving the sensitivity and line edge roughness in inorganic positive electron beam resist

Need for inorganic electron beam resist with higher sensitivity and resolution is indisputable. We have developed such a resist that also shows lower line edge roughness. It is pre-baked at 300 °C. By using 4 kV EB we have delineated 40 nm lines pattern and honeycomb structure Photonic crystal pattern.

Electron beam lithography patterning of sub-10nm line using hydrogen silsesquioxane for nanoscale device applications

We investigated novel patterning techniques to produce ultrafine patterns for nanoscale devices. Hydrogen silsesquioxane (HSQ) was employed as a high-resolution negative tone inorganic electron beam resist. The nanoscale patterns with sub-10nm linewidth were successfully formed. A trimming process of HSQ by the reactive ion etcher (RIE) played an important role for the formation of 5nm nanowire patterns. Additionally, hybrid lithography was used to produce various device patterns as well as to minimize proximity effects of electron beam lithography (EBL). Finally, we successfully fabricated triple-gate metal oxide semiconductor field effect transistor (MOSFET) with a gate length of 6nm by using the proposed patterning process.

Nanoimprinted Focusing Grating Coupler for an Ultra Slim Optical Pickup Head

Nanoimprinted focusing grating couplers (FGCs) for ultra slim optical pickup head application have been investigated. Inorganic electron beam resist hydrogen silsesquinoxane (HSQ) was used as a master for FGC replication, and polymethylmethacrylate (PMMA) as a transparent stamper for ultra violet (UV) exposure embossing. UV embossing was employed to replicate the fine featured grating patterns in FGC. The focused spot size measured from the replicated coupler showed almost the same quality as theoretically predicted one.

Spin-polarized Tunneling in Ultrasmall Vertical Ferromagnetic Tunnel Junctions

We have developed nanometer-scale vertical ferromagnetic tunnel junctions using a Si-based inorganic electron beam resist process, including barrier layer fabrication using metal evaporation in ozone atmosphere. The current–voltage (I–V) characteristics of Ni/NiO/Co multiple junctions with diameters of 20 nm have been measured in a magnetic field to investigate spin-polarized tunneling in the Coulomb blockade regime. The temperature dependence of the I–V curve indicates that Coulomb blockade phenomena occur at temperatures below 40 K, agreeing with the estimation of the single-electron charging energy from the device geometries. The magnetoresistance is strongly enhanced by magnetization reversal of Ni and Co, and the obtained MR ratio is greater than 100% in the Coulomb blockade regime at 15 K.

3D Mold Fabrication Techniques Using an Inorganic Resist

We developed nanometer-order fabrication for 3-dimensional (3D) imprint molds, using acceleration-voltage-modulation electron beam (EB) direct writing. The inorganic EB resist was spin-on-glass (SOG), whose depth was controlled by changing the EB acceleration voltage. After EB exposure, the sample was developed using buffered hydrofluoric acid. The fabricated pattern depths on SOG were well gradated, and the depth resolution was 20 nm per 100V. The width resolution was 40 nm on SOG using an electron beam with a diameter of a few nanometers. Patterns were transferred by pressing the fabricated 3D SOG mold to a photo-curable resin under a pressure of 0.5 MPa and curing it with a 1 J/cm2 ultraviolet dose. Replicated patterns showed faithful, defect-free multigradation. Using SOG as the material for an ion beam etching mask, 3D molds were fabricated from diamond, engineering plastic, and quartz.

Fabrication technology of a Si nanowire memory transistor using an inorganic electron beam resist process

We report on a novel fabrication technology of a Si nanowire memory transistor using an inorganic SiO2 electron beam (EB) resist process. The inorganic EB resist process technique was put to practical use in Si nanodevice fabrication for the first time. We have successfully demonstrated the 15-nm-wide and 20-nm-thick Si nanowire memory transistor with a Si nanodot less than 10 nm in diameter. In the fabricated Si nanowire nanodot memory transistor, we have observed a large electron memory effect, i.e., a threshold voltage shift ΔVth of 2.2 V at room temperature. It is experimentally shown that the inorganic EB resist process is promising for fabricating various Si nanodevices.

SiO2/poly-Si electron beam resist process for nanofabrication

An inorganic electron beam resist process for nanofabrication is described. Si-based bilayer inorganic electron beam resists, SixOy/Si3N4, Si3N4/SiO2, and SiO2/poly-Si were investigated. The SiO2/poly-Si system was found to be the most suitable for attaining deep undercut structures with fine patterns for metal–insulator–metal ultrasmall tunnel junction fabrication. Utilizing the multiple-angle deposition–oxidation deposition method, we have fabricated Al/Al2O3/Al tunnel junctions for which a clear Coulomb staircase was observed in the I–V characteristics at 12 K.

Self-Developing Properties of an Inorganic Electron Beam Resist and Nanometer-Scale Patterning Using a Scanning Electron Beam

The self-developing properties of an AlF3-doped LiF inorganic resist are studied. Electron-stimulated desorption (ESD) from the resist film is characterized by Auger electron spectroscopy and X-ray photoelectron spectroscopy. A conventional scanning electron microscope is employed for nanometer-scale direct writing and for in situ surface observation. Results show that a metal-rich layer which is formed by rapid and preferential fluorine desorption due to ESD suppresses subsequent fluorine desorption. This indicates that the surface diffusion of this residual metal plays an important role in the self-developing reaction. Nanometer-scale lithography onto the LiF(AlF3) film is achieved using a scanning electron beam.

Electron beam writing and direct processing system for nanolithography

This article describes the electron beam direct processing system developed for patterning beyond the resolution limit of conventional resists by using inorganic resists or electron beam induced surface reactions. A probe beam with a probe current of 120 pA was focused into 3 nm with the newly developed optical column. An ultrahigh vacuum sample chamber, which can coexist with a precise stage driving mechanism and a laser measuring system, was constructed by adapting a double chamber stage system. The base pressure of the sample chamber after baking was 1.5 × 10 −6Pa and differential evacuation of the sample chamber and the mechanism chamber was demonstrated. The stability of the stage was evaluated with a laser measuring system. The standard deviations of stitching and overlay accuracy measured by an exposure of PMMA were 20 nm and 40 nm, respectively. An exposure of PMMA resists revealed that this EB system can delineate the lines with the ultimate resolution of PMMA resists.

The influence of the substrate on proximity effect and exposure dose for the inorganic resist LiF(AlF 3)

The critical exposure does of the inorganic electron beam resist LiF(AlF 3) is an increasing function of resist thickness. The thickness of the substrate also has an influence, even when backscattering is negligible. A simple model is presented in order to predict the critical dose for given resist and substrate thickness. This model is based on stress relaxation during exposure within the highly tensile-strained resist film. Finally, an unusual proximity effect, which occurs predominantly in dense line gratings, is discussed in the context of the same model.

The resolution of the inorganic electron beam resist LiF(AlF3)

Abstract The resolution limit of the inorganic electron beam resist LiF(AlF3) was investigated. This lithium-fluoride-based resist is self-developing, because the exposure mechanism runs via desorption of the irradiated material (radiolysis). An important magnitude for the determination of the resolution limit seems to be the threshold energy. This is the energy, which is required for the initiation of an exposure event. Since the threshold energy for LiF(AlF3) is relatively high, an improved resolution is expected, compared to e.g. PMMA. Experimentally, 3nm lines & spaces were verified, in excellent agreement with a theoretical prediction.

Fabrication of Metallic Structures in the 10 nm Region Using an Inorganic Electron Beam Resist

In order to make the sub-10 nm region accessible to lithography, an ultrahigh-resolution electron beam resist has been developed. This inorganic and self-developing resist is based on AlF3-doped LiF films. The resolution limit is ≈3 nm lines & spaces. This result is in excellent agreement with a rule which gives a correlation between resolution and threshold energy of a resist. The sensitivity is sufficient for the fabrication of complex mesoscopic devices. The problems concerning pattern transfer are discussed. As a first result, metallic structures with lateral dimensions down to 10 nm have been obtained using a lift-off technique.