Beams of electrons and ions are now fairly routinely focused to dimensions in the nanometer range. Since the beams can be used to locally alter material at the point where they are incident on a surface, they represent direct nanofabrication tools. The authors will focus here on direct fabrication rather than lithography, which is indirect in that it uses the intermediary of resist. In the case of both ions and electrons, material addition or removal can be achieved using precursor gases. In addition ions can also alter material by sputtering (milling), by damage, or by implantation. Many material removal and deposition processes employing precursor gases have been developed for numerous practical applications, such as mask repair, circuit restructuring and repair, and sample sectioning. The authors will also discuss structures that are made for research purposes or for demonstration of the processing capabilities. In many cases the minimum dimensions at which these processes can be realized are considerably larger than the beam diameters. The atomic level mechanisms responsible for the precursor gas activation have not been studied in detail in many cases. The authors will review the state of the art and level of understanding of direct ion and electron beam fabrication and point out some of the unsolved problems.

/pdf/gas-assisted-focused-electron-beam-and-ion-beam-processing-2wl9i66zrn.pdf

Gas-assisted focused electron beam and ion beam processing and fabrication

An extensive review is given of the results from literature on electron beam induced deposition. Electron beam induced deposition is a complex process, where many and often mutually dependent factors are involved. The process has been studied by many over many years in many different experimental setups, so it is not surprising that there is a great variety of experimental results. To come to a better understanding of the process, it is important to see to which extent the experimental results are consistent with each other and with the existing model. All results from literature were categorized by sorting the data according to the specific parameter that was varied (current density, acceleration voltage, scan patterns, etc.). Each of these parameters can have an effect on the final deposit properties, such as the physical dimensions, the composition, the morphology, or the conductivity. For each parameter-property combination, the available data are discussed and (as far as possible) interpreted. By combining models for electron scattering in a solid, two different growth regimes, and electron beam induced heating, the majority of the experimental results were explained qualitatively. This indicates that the physical processes are well understood, although quantitatively speaking the models can still be improved. The review makes clear that several major issues remain. One issue encountered when interpreting results from literature is the lack of data. Often, important parameters (such as the local precursor pressure) are not reported, which can complicate interpretation of the results. Another issue is the fact that the cross section for electron induced dissociation is unknown. In a number of cases, a correlation between the vertical growth rate and the secondary electron yield was found, which suggests that the secondary electrons dominate the dissociation rather than the primary electrons. Conclusive evidence for this hypothesis has not been found. Finally, there is a limited understanding of the mechanism of electron induced precursor dissociation. In many cases, the deposit composition is not directly dependent on the stoichiometric composition of the precursor and the electron induced decomposition paths can be very different from those expected from calculations or thermal decomposition. The dissociation mechanism is one of the key factors determining the purity of the deposits and a better understanding of this process will help develop electron beam induced deposition into a viable nanofabrication technique.

/pdf/a-critical-literature-review-of-focused-electron-beam-21cjric9ud.pdf

A critical literature review of focused electron beam induced deposition

Hybrid nanoscale patterning strategies combine the registration and addressability of conventional lithographic techniques with the chemical and physical functionality enabled by intermolecular, electrostatic and/or biological interactions. This review aims to highlight and to provide a comprehensive description of recent developments in hybrid nanoscale patterning strategies that enhance existing lithographic techniques or can be used to fabricate functional chemical patterns that interact with their environment. These functional structures create new capabilities, such as the fabrication of physicochemical surfaces that can recognize and capture analytes from complex liquid or gaseous mixtures. The nanolithographic techniques we describe can be classified into three general areas: traditional lithography, soft lithography and scanning-probe lithography. The strengths and limitations of each hybrid patterning technique will be discussed, along with the current and potential applications of the resulting patterned, functional surfaces.

http://iopscience.iop.org/article/10.1088/0034-4885/73/3/036501/pdf

Hybrid strategies in nanolithography

During the past decade, significant progress has been made in the field of resonant optics ranging from fundamental aspects to concrete applications. While several techniques have been introduced for the fabrication of highly defined metallic nanostructures, the synthesis of complex, free-standing three-dimensional (3D) structures is still an intriguing, but so far intractable, challenge. In this study, we demonstrate a 3D direct-write synthesis approach that addresses this challenge. Specifically, we succeeded in the direct-write fabrication of 3D nanoarchitectures via electron-stimulated reactions, which are applicable on virtually any material and surface morphology. By that, complex 3D nanostructures composed of highly compact, pure gold can be fabricated, which reveal strong plasmonic activity and pave the way for a new generation of 3D nanoplasmonic architectures that can be printed on-demand.

Direct-Write 3D Nanoprinting of Plasmonic Structures

Focused electron beam induced deposition meets materials science

High-resolution electron-beam-assisted deposition and etching is an enabling technology for current and future generation photomask repair. NaWoTec in collaboration with Carl Zeiss NTS (formerly LEO Electron Microscopy) has developed a mask repair tool capable of processing a wide variety of mask types, such as quartz binary masks, phase shift masks, extreme ultraviolet masks, and e-beam projection stencil masks. Specifications currently meet the 65nm device node requirements, and tool performance is extendible to 45nm and below. The tool combines LEO’s ultra-high-resolution Supra scanning electron microscope platform with NaWoTec’s proprietary e-beam deposition and etching technology, gas delivery system, and mask repair software. In this article, we focus on tool performance results; that is, the reproducibility and accuracy of repair of clear and opaque programmed defects on Cr binary and MoSi phase shift masks. These masks have in the past been difficult to repair due to beam position instability caus...

Electron-beam-based photomask repair

In this follow-up paper for our contribution at BACUS 2010, first evidence is shown that also the more advanced
Lasertec M7360 has missed a few printing reticle defects caused by an imperfection of its EUV mirror, a so-called multilayer
defect (ML-defect). This work continued to use a combination of blank inspection (BI), patterned mask inspection
(PMI) and wafer inspection (WI) to find as many as possible printing defects on EUV reticles. The application of more
advanced wafer inspection, combined with a separate repeater analysis for each of the multiple focus conditions used for
exposure on the ASML Alpha Demo Tool (ADT) at IMEC, has allowed to increase the detectability of printing MLdefects.
The latter uses the previous finding that ML-defects may have a through-focus printing behavior, i.e., they cause
a different grade of CD impact on the pattern in their neighborhood, depending on the focus condition. Subsequent
reticle review is used on the corresponding locations with both SEM (Secondary Electron Microscope) and AFM
(Atomic Force Microscope). This review methodology has allowed achieving clear evidence of printing ML defects
missed by this BI tool, despite of an unacceptable nuisance rate reported before. This is a next step in the investigation if
it is possible to avoid actinic blank inspection (ABI) at all, the only presently known technique that is expected to be
independent from the presence of a (residual) topography of the ML-defect at the top of the EUV mirror, in detecting
those defects. This is considered an important asset of blank inspection, because the printability of a ML-defect on the
EUV scanner and its detectability by ABI is determined by the distortion throughout the multilayer, not that at the
surface.

Evidence of printing blank-related defects on EUV masks missed by blank inspection

An apparatus for investigating and / or modifying a sample with charged particles, in particular a scanning electron microscope, is provided. The apparatus comprises a beam (1, 2) of charged particles, a shielding element (10) having an opening (30) for the beam of charged particles to pass through, wherein the opening (30) is sufficiently small and the shielding element (10) sufficiently closely positioned to the surface (20) of the sample to reduce the influence of charge accumulation effects at the surface on the beam of charged particles.

Apparatus and method for investigating or modifying a surface with a beam of charged particles

The invention relates to a method for processing a substrate with a focussed particle beam which incidents on the substrate, the method comprising the steps of: (a) generating at least one reference mark on the substrate using the focused particle beam and at least one processing gas, (b) determining a reference position of the at least one reference mark, (c) processing the substrate using the reference position of the reference mark, and (d) removing the at least one reference mark from the substrate.

Method and apparatus for processing a substrate with a focused particle beam

After a short overview of the historical developments of the technique of gas-assisted focused electron beam-induced processing (mostly deposition and etching), this paper deals with the applications of this technology to photolithographic mask repair. A commented list of results is shown on different mask types, for different types of defects, and at different node generations. The scope of this article is double: summarize the state of the art in a fast-paced highly specific industrial environment driven by “Moore’s law” and feedback to academic researchers some technologically relevant directions for further investigations.

Thorsten Hofmann

Papers

Electron-beam-based photomask repair

Evidence of printing blank-related defects on EUV masks missed by blank inspection

Apparatus and method for investigating or modifying a surface with a beam of charged particles

Method and apparatus for processing a substrate with a focused particle beam

Industrial perspective on focused electron beam-induced processes