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.

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

Lithography is a field in which advances proceed at a swift pace. This book was written to address several needs, and the revisions for the second edition were made with those original objectives in mind. Many new topics have been included in this text commensurate with the progress that has taken place during the past few years, and several subjects are discussed in more detail. This book is intended to serve as an introduction to the science of microlithography for people who are unfamiliar with the subject. Topics directly related to the tools used to manufacture integrated circuits are addressed in depth, including such topics as overlay, the stages of exposure, tools, and light sources. This text also contains numerous references for students who want to investigate particular topics in more detail, and they provide the experienced lithographer with lists of references by topic as well. It is expected that the reader of this book will have a foundation in basic physics and chemistry. No topics will require knowledge of mathematics beyond elementary calculus.

Principles of Lithography

Focused electron-beam-induced (FEB-induced) deposition and etching are versatile, direct-write nanofabrication schemes that allow for selective deposition or removal of a variety of materials. Fundamentally, these processes are governed by an electron-induced reaction with a precursor vapor, which may either result in decomposition to a solid deposit or formation of a volatile etch by-product. The ability to induce such localized reactions by placement of a nanometer-sized focused electron probe has recently drawn considerable attention. In response, we have reviewed much of the relevant literature pertaining to both focused electron-beam-induced etching and deposition. Because these nanoscale processing techniques are still in their relative infancy, a significant amount of scientific research is being conducted to understand, and hence improve, the processes. This article summarizes the associated physics of electron-solid-vapor interactions, discusses related physical processes, and provides an introdu...

Focused, Nanoscale Electron-Beam-Induced Deposition and Etching

Extreme ultraviolet lithography (EUVL) was thoroughly reviewed over a broad range of topics, including history, tools, source, metrology, condenser and projection optics, resists, and masks. Since 1988, many studies on EUVL have been conducted in North America, Europe, and Japan, through state sponsored programs and industrial consortiums. To date, no “show stopper” has been identified, but challenges are present in almost all aspects of EUVL technology. Commercial alpha lithography step-and-scan tools are installed with full-field capability; however, EUVL power at intermediate focus (IF) has not yet met volume manufacturing requirements. Compared with the target of 180W IF power, current tools can supply only approximately 55–62W. EUV IF power has been improved gradually from xenon- to tin-discharge-produced plasma or laser-produced plasma. EUVL resist has improved significantly in the last few years, with 25nm 1:1 line/space resolution being produced with approximately 2.7nm (3σ) line edge roughness. A...

Extreme ultraviolet lithography: A review

A method and apparatus for electron beam processing using an electron beam (101) activated gas to etch or deposit material. The invention is particularly suitable for repairing defects in lithography masks. By using an electron beam (101) in place of an ion beam, the many problems associated with ion beam mask repair, such as staining and riverbedding, are eliminated. Endpoint detection is not critical because the electron beam and gas will not etch the substrate. In one embodiment, xenon ditluoride gas is activated by the electron beam (101) to etch a tungsten, tantalum nitride, or molybdenum silicide film on a transmission or reflection mask. To prevent spontaneous etching by the etchant gas in processed sites at which the passivation layer was removed, processed sites can be re-passivated before processing additional sites.

Electron beam processing

The key challenge in extreme ultraviolet (EUV) mask defect repair is to avoid or limit the damage to the sensitive reflective multilayer (ML) stacks on the mask substrate and repair <55 nm mask defects. Our EUV mask design employs an oxide buffer layer between the ML and the absorber to protect the ML during repair. We have developed both opaque and clear EUV mask defect repair processes using focus ion beam (FIB) based gas-assisted etching (GAE) and ion-induced deposition. The process has been successfully demonstrated on our TiN baseline mask by 10× EUV print tests of 100 nm resist lines/spaces. More importantly we have assessed the current FIB tool performance capability and compared it with the general requirements for repairing the EUV mask for the 70 nm lithography node. The characterization includes minimum “effective” beam size, etch selectivity, and edge placement precision. We discussed the required improvements and future directions in repair tool research and development in order for the mask ...

Progress in extreme ultraviolet mask repair using a focused ion beam

In this paper, we will present our research work in EUVL mask absorber characterization and selection. The EUV mask patterning process development depends on the choice of EUVL mask absorber material, which has direct impact on the mask quality such as critical dimension (CD) control, and registration. EUVL mask absorber material selection consideration involves many aspects of material properties and processes. These include film absorption at EUV wavelength, film emissivity, film stress, mask CD and defect control, defect inspection contrast, absorber repair selectivity to the buffer layer, etc. The selection of the best candidate is non-trivial since no material is found to be superior in all aspects. In an effort of searching the best absorber materials and processes, we evaluated Al-Cu, Ti, TiN, Ta, TaN, and Cr absorbers. The comparison of material intrinsic properties and process properties allowed us to focus on the most promising absorbers and to further develop the corresponding processes to meet EUVL requirement.

EUV mask absorber characterization and selection

The introduction of extreme ultraviolet (EUV) lithography into high volume manufacturing requires the development of a new mask technology. In support of this, Intel Corporation has established a pilot line devoted to encountering and eliminating barriers to manufacturability of EUV masks. It concentrates on EUV-specific process modules and makes use of the captive standard photomask fabrication capability of Intel Corporation. The goal of the pilot line is to accelerate EUV mask development to intersect the 32nm technology node. This requires EUV mask technology to be comparable to standard photomask technology by the beginning of the silicon wafer process development phase for that technology node. The pilot line embodies Intel's strategy to lead EUV mask development in the areas of the mask patterning process, mask fabrication tools, the starting material (blanks) and the understanding of process interdependencies. The patterning process includes all steps from blank defect inspection through final pattern inspection and repair. We have specified and ordered the EUV-specific tools and most will be installed in 2004. We have worked with International Sematech and others to provide for the next generation of EUV-specific mask tools. Our process of record is run repeatedly to ensure its robustness. This primes the supply chain and collects information needed for blank improvement.

Fu-Chang Lo

Papers

Progress in extreme ultraviolet mask repair using a focused ion beam

EUV mask absorber characterization and selection

EUV mask pilot line at Intel Corporation