Direct-write Electron Beam Research Articles

The AZ 5214E Resist in EBDW Lithography and its Use as a RIE Etch–Mask in Etching Thin Ag Layers in N2 Plasma

Abstract In this article we describe the electron-beam direct-write (EBDW) lithography process for the AZ 5214E photoresist which is, besides its sensitivity to UV radiation, sensitive also to electrons. An adapted process flow is provided. At the same time we examine the resistance of this resist to RIE and its suitability as an etch-mask for etching thin Ag layers in N2 plasma. A comparison with several chosen resists (PMMA, ma-2405, ma-N 1402, SU-8 2000) is provided.

Pure Platinum Nanostructures Grown by Electron Beam Induced Deposition

Platinum has numerous applications in catalysis, nanoelectronics, and sensing devices. Here we report a method for localized, mask-free deposition of high-purity platinum that employs a combination of room-temperature, direct-write electron beam induced deposition (EBID) using the precursor Pt(PF3)4, and low temperature (≤400 °C) postgrowth annealing in H2O. The annealing treatment removes phosphorus contaminants through a thermally activated pathway involving dissociation of H2O and the subsequent formation of volatile phosphorus oxides and hydrides that desorb during annealing. The resulting Pt is indistinguishable from pure Pt films by wavelength dispersive X-ray spectroscopy (WDS).

High-Throughput Electron Beam Direct Writing of VIA Layers by Character Projection with One-Dimensional VIA Characters

High-Throughput Electron Beam Direct Writing of VIA Layers by Character Projection with One-Dimensional VIA Characters

Active-matrix nanocrystalline Si electron emitter array for massively parallel direct-write electron-beam system: first results of the performance evaluation

We present a prototype electron emitter array integrated with an active-matrix driving large-scale integrated circuit (LSI) for a high-speed massively parallel direct-write electron-beam (e-beam) system. In addition, we describe the results of a performance evaluation of it as an electron source for massively parallel operations. The electron source is a nanocrystalline Si (nc-Si) ballistic surface electron emitter in which a 1∶1 projection of the e-beam can resolve patterns 30 nm wide. The electron-emitting part of the device consists of an array of nc-Si dots fabricated on an SOI or Si substrate and through silicon via (TSV) plugs connected to the dots from the back of the substrate. The device consists of an aligned joint of TSV plugs with driving pads on the active-matrix LSI. Electron emissions are driven by the LSI and are boosted to an appropriate level using a built-in voltage level shifter in accordance with a bitmap image preliminarily stored in the embedded memory. Electron emissions from a test array work as intended, showing the possibility of switching on and off the beamlets by changing the CMOS-compatible voltage.

Evaluation of direct patternable inorganic spin-on hard mask materials using electron beam lithography

Two inorganic non-chemically amplified resists (XE15CB and XE15IB) were investigated. The resists are based on hafnium oxide sulfate and spin-cast from aqueous solution. They differ in sensitivity and resolution. In contrast to other studies, the materials were coated for the first time on 300 mm wafers and exposed on a 50 kV VISTEC SB3050DW variable shaped electron beam direct writer in a near-production environment at Fraunhofer CNT. In this paper, the evaluation of this resist family and its feasibility for production will be discussed. The resists were evaluated in terms of contrast, sensitivity and resolution. The process characteristics required for CMOS manufacturing such as delay stability were also examined. Furthermore, by exposing a large SRAM pattern (design CD of 22 nm), the exposure of a real application pattern was demonstrated.

Characterization of Fogging and Develop-Loading Effects in Electron-Beam Direct-Writing Technology

We investigated long-range critical dimension (CD) error factors, such as fogging and develop loading, to improve CD uniformity in electron-beam direct-writing (EBDW) technology. It was found that the impact of both effects reached 20 mm and the CD of the monitor pattern decreased by no less than 10%. Fogging and develop loading were separated by comparing the newly designed test patterns that were exposed using both EB and a krypton-fluoride excimer laser. We confirmed that the impact of fogging and develop loading by arranging dummy patterns with a density of 40% was estimated to be +8.9 and -18.9% in the CD, respectively. Based on success in separating each effect, fogging and develop loading were decreased by applying an antistatic agent and multipuddle development, respectively.

Characterization of Fogging and Develop-Loading Effects in Electron-Beam Direct-Writing Technology

Characterization of Fogging and Develop-Loading Effects in Electron-Beam Direct-Writing Technology

Electron beam lithography writing strategies for low loss, high confinement silicon optical waveguides

The authors present a robust process for fabricating passive silicon photonic components by direct-write electron beam lithography (EBL). Using waveguide transmission loss as a metric, we study the impact of EBL writing parameters on waveguide performance and writing time. As expected, write strategies that reduce sidewall roughness improve waveguide loss and yield. In particular, averaging techniques such as overlap or field shift writing reduce loss, however, the biggest improvement comes from writing using the smaller field-size option of our EBL system. The authors quantify the improvement for each variation and option, along with the tradeoff in writing time.

Fast characterization of line end shortening and application of novel correction algorithms in e-beam direct write

For the manufacturing of semiconductor technologies following the ITRS roadmap, we will face nodes well below a 32-nm half pitch in the next 2 to 3 years. Despite being able to achieve the required resolution, which is now possible with electron beam direct-write variable-shaped beam equipment and resists, it becomes critical to precisely reproduce dense line space patterns onto a wafer. This exposed pattern must meet the targets from the layout in both dimensions (horizontally and vertically). For instance, the end of a line must be printed in its entire length to allow a contact to be placed later. Up to now, the control of printed patterns such as line ends was achieved by a proximity effect correction mostly based on a dose modulation. This investigation of line end shortening (LES) includes multiple novel approaches, and contains an additional geometrical correction to push the limits of the available data preparation algorithms and the measurement. The designed LES test patterns, which aim to characterize the status of LES in a quick and easy way, were exposed and measured at Fraunhofer Center Nanoelectronic Technologies using its state-of-the-art electron beam direct writer and CD-SEM. Simulation and exposure results with the novel LES correction algorithms applied to the test pattern and a large production-like pattern in the range of our targeted critical structure dimensions in dense line space features smaller than 40 nm will be shown.

Emission characteristics of photonic crystal light-emitting diodes

Experimentally measured optical properties of photonic crystal LEDs are reported here. Photonic crystal and photonic quasi-crystal structures were fabricated on GaN epilayer LED wafer material using both direct-write electron beam lithography and nanoimprint lithography. Some of these structures were processed to make finished LEDs. Both electroluminescence and photoluminescence measurements were performed on these structures. Devices were characterized for their current-voltage characteristics, emission spectra, far-field emission pattern, and angular emission pattern. These results are useful for fabricating photonic crystal LEDs and assessing their operational properties.

A Highly Sensitive Inorganic Resist for Directly Fabricating Thermally Stable Oxide Pattern on Si Substrate by Low-Energy Electron-Beam Direct Writing

A simple process of 1-keV-range low-energy electron-beam direct writing (LE-EBDW) is proposed for a direct pattern of a thermally stable oxide layer on a Si substrate. An ultrathin multilayered structure is used as a highly sensitive inorganic negative resist for LE-EBDW, and it consists of an amorphous GaAs layer of 3 nm thick and its surface oxide. The EB-irradiated area is transformed into a thermally stable oxide pattern by heating the substrate to 750 °C in a vacuum after LE-EBDW. The heating process induces removal of the multilayered structure, while the oxide pattern can remain on the substrate. The remaining pattern can directly act as an ultrathin template for successive selective area growth on the Si substrate. It is assumed that the pattern is composed of thermally stable oxides such as SiO2 and Ga2O3 formed below the amorphous layer, not the surface oxide, of the multilayered structure.

A Highly Sensitive Inorganic Resist for Directly Fabricating Thermally Stable Oxide Pattern on Si Substrate by Low-Energy Electron-Beam Direct Writing

A simple process of 1-keV-range low-energy electron-beam direct writing (LE-EBDW) is proposed for a direct pattern of a thermally stable oxide layer on a Si substrate. An ultrathin multilayered structure is used as a highly sensitive inorganic negative resist for LE-EBDW, and it consists of an amorphous GaAs layer of 3 nm thick and its surface oxide. The EB-irradiated area is transformed into a thermally stable oxide pattern by heating the substrate to 750 °C in a vacuum after LE-EBDW. The heating process induces removal of the multilayered structure, while the oxide pattern can remain on the substrate. The remaining pattern can directly act as an ultrathin template for successive selective area growth on the Si substrate. It is assumed that the pattern is composed of thermally stable oxides such as SiO2 and Ga2O3 formed below the amorphous layer, not the surface oxide, of the multilayered structure.

Variable-shaped e-beam lithography enabling process development for future copper damascene technology

To realize fast and efficient integrated circuits the interconnect system gains an increasing importance. In particular, this is the case for logic and processor circuits with up to 12 metallization layers. In order to optimize this technology and the according processes it is desirable to generate flexible test structures in small lot production. In opposition to standard optical lithography using masks, Electron Beam Direct Write (EBDW) lithography can rapidly deliver special test structures at low cost. Furthermore, critical dimensions of future technology nodes which are not yet manufacturable by standard optical lithography tools can be produced. In this paper we demonstrate the potential of the 50kV variable shaped EBDW cluster for patterning of future back-end-of-line (BEOL) structures on full 200mm wafers. The patterned wafers have been used to develop next generation copper damascene interconnect processes for critical dimensions down to 50nm.

Patterning Nanomaterials on Fragile Micromachined Structures using Electron Beam Lithography

ABSTRACTIntegration of nanomaterials (in the form of quantum dots, nanotubes, nanowires, nanocrystalline thin films, and nanocomposite films) with micromachined structures and devices has the potential to enable the development of microelectromechanical systems (MEMS) with enhanced functionality and improved performance. Here, we present a fabrication approach that combines spray-coating of electron beam resist with direct-write electron beam lithography to pattern nanomaterials on fragile micromachined components. Polymers and metallic structures in the form of arrays of holes, concentric circles, and arrays of lines, with critical dimensions ranging from 135 nm to 500 nm, were patterned directly on various micromachined structures including commercial metal-coated silicon microcantilevers used for atomic force microscopy, and commercial plate-mode SiC/AlN microresonators used for sensing.

Direct-write electron beam lithography in silicon dioxide at low energy

Electron beam lithography in silicon dioxide has been investigated with energies ranging from 0.5 up to 6 keV. The etch ratio of SiO2 has been studied and interpreted with regard to the limited penetration of electrons at such low energies. Monte Carlo simulations have been carried out to investigate the depth of penetration and the density of energy absorbed by SiO2. The etch ratio is also shown to depend on the dilution of the developer (a buffered hydrofluoric acid diluted in water). Finally, a possible application of low energy direct writing in silicon dioxide is described for the control of damascene processes, enabling the fabrication of nanodevices embedded in an insulator.

Nanofabrication of gallium nitride photonic crystal light-emitting diodes

We describe a comparison of nanofabrication technologies for the fabrication of 2D photonic crystal structures on GaN/InGaN blue LEDs. Such devices exhibit enhanced brightness and the possibility of controlling the angular emission profile of emitted light. This paper describes three nano lithography techniques for patterning photonic crystal structures on the emitting faces of LEDs: direct-write electron beam lithography, hard stamp nanoimprint lithography and soft-stamp nanoimprint lithography with disposable embossing masters. In each case we describe variations on the technique as well as its advantages and disadvantages. Complete process details have been given for all three techniques. In addition, we show how high performance GaN dry etch techniques, coupled with optical process monitoring can transfer resist patterns into underlying GaN material with high fidelity.

Batch fabrication of cantilever array aperture probes for scanning near-field optical microscopy

We have developed a novel batch fabrication process for cantilever array aperture probes used in scanning near-field optical microscopy (SNOM). The array probes, consisting of 16 parallel cantilevers with each tip having an identical aperture, are proposed to dramatically reduce the scanning time for imaging or increase the throughput of near-field optical microscopy and lithography. In this study, apertures are defined by direct-write electron beam lithography and subsequent pattern transfer by reactive ion etch. Better quality and reproducibility of apertures are demonstrated through optical throughput measurement of the probes. The fabrication of apertures having complex shapes is also demonstrated. The process includes such novel elements as the use of local oxidation of silicon and the use of an aluminium – compatible release etch. The process has demonstrated very high yield with a measured reproducibility of aperture diameter of 5 nm. Thermal oxide cantilevers allow the use of the probes at wavelengths as short as 250 nm.

Electron Beam Direct Writing technology for LSI prototyping business

When manufacturing prototype devices or small volume production custom logic LSIs, the products are being less profitable because of the skyrocketing mask and design costs recent technology node. For 65 nm technology node and beyond, the reduction of mask cost becomes critical issue for logic devices especially. We have applied to Electron Beam Direct Writing (EBDW) technology mainly to critical interconnect layers which are more cost sensitive than other layers. We required a breakthrough to apply EBDW technology to a production environment, and we overcame some difficult issues. We have already started EBDW technology for 65 nm node business with sufficient yield and process margin of production level. In this paper, our technical outputs to achieve practical use of EBDW for 65 nm node and beyond, and our future prospects for EBDW evolution to play a principal part in next generation lithography will be discussed.

Development of Multibeam Electron Beam Direct Writing System Using Third-Order Imaging Technique

We report the development of a new electron beam direct writing (EBDW) system embodying a concept that can realize both high throughput and fine resolution. The equipment has a multicolumn system with the third-order imaging technology, which obtains steep edge acuity with high current density as compared with conventional shaped beam methods. We attempt to apply this to via/contact layers, for which it is difficult to obtain resist patterns using any optical lithography systems. We also showed proof of concept of third-order imaging serving as a technique for simultaneously satisfying improvement in current density without beam blur and forming a beam to a desired shape. The advantage of the third-order imaging technique is a potential solution that may break through the technological impasse of high current density versus high resolution. We are currently engaged in enhancing the high-acceleration-energy and multicolumn system and in its development for mass production.

Direct write electron beam patterning of DNA complex thin films

The authors report on the first use of direct write electron beam lithography (DW-EBL) patterning of DNA-based materials. Water insoluble and organic solvent soluble DNA:CTMA complexes were formed by reaction of DNA polymers with cationic surfactants and other molecular species. Thin films with thicknesses ranging from 85 to 300 nm were prepared by spin coating. DW-EBL was conducted using a Raith 150 system. The resulting exposed areas demonstrated either positive or negative resist properties depending on development solution. The characteristics of the DNA:CTMA material as a patternable electron sensitive resist medium are presented for different exposure conditions (10–30 kV), development conditions, structure sizes (100 nm to 20 μm), and structure complexities. Contrast values of ∼2 have been obtained in both positive and negative resist modes. Both simple (20 μm diameter circle and square) and complex (Fresnel lens) patterns with nanometer scale features (<100 nm) in DNA films are possible using this method.