Rodney A. Kendall

Projection reduction exposure with variable axis immersion lenses: Next generation lithography

Projection reduction exposure with variable axis immersion lenses (PREVAIL) represents the high throughput e-beam projection approach to NGL, which IBM is pursuing in cooperation with Nikon as alliance partner; another e-beam projection approach is SCALPEL pursued by Lucent Technologies. This article discusses the challenges and accomplishments of the PREVAIL project. It will focus on the results obtained with the proof of concept (POC) system. This system was developed to demonstrate key technical building blocks required for high throughput, high resolution e-beam step, and scan projection lithography. The supreme challenge facing all e-beam lithography approaches has been and still is throughput. Since the throughput of e-beam projection systems is severely limited by the available optical field size, the key to success is the ability to overcome this limitation. The PREVAIL technique overcomes field-limiting off-axis aberrations through the use of variable axis lenses, which electronically shift the o...

A servo guided X–Y–theta stage for electron beam lithography

This paper describes a high precision X–Y–theta stage for use inside the variable axis immersion lens of IBM’s EL3+ direct write e‐beam lithography systems. X–Y stages typically use some form of rail and bearing combination to provide guidance along the X and Y axes. The planar stage presented in this paper has no X or Y guide rails or bearings, instead both guidance and positioning are provided by the simultaneous operation of three mechanical drives controlled by closed‐loop velocity, position, and theta servos. The control requirements, architecture, and performance of the servo electronics is discussed. The design and materials constraints imposed by having to operate inside a magnetic lens are discussed and stage performance data is presented. Servo guided stages eliminate the need for precise alignment of guide rails and bearings, while the kinematic nature of the design results in low sensitivity to temperature variations and reduces the need for extreme mechanical tolerances.

High emittance source for the PREVAIL projection lithography system

In the PREVAIL proof of concept electron beam projection lithography system, 1 mm×1 mm sq reticle subfields are illuminated and imaged to a wafer with 4× demagnification. A relatively large beam semiangle (5–8 mr at the wafer) is required to optimize resolution at the beam currents (5–15 μA) needed for high-throughput lithography. A high emittance source and illumination system have been developed which can uniformly illuminate the reticle subfield with a beam semiangle up to 16.3 mr (1/e) at the wafer. The source utilizes a tantalum single crystal 10 mm in diameter. The crystal is heated by electron bombardment incident on the side opposite the emitting surface, which is a low work function crystal plane. A variation of the “critical Kohler” illumination scheme is utilized wherein the cathode surface is imaged approximately to a square shaping aperture, and the shaping aperture is conjugate to the reticle (and the wafer). The emission is temperature limited, so care must be taken to obtain a uniform temp...

EBM-9000: EB mask writer for product mask fabrication of 16nm half-pitch generation and beyond

EBM-9000 equipped with new features such as new electron optics, high current density (800A/cm2) and high speed deflection control has been developed for the 11nm technology node(tn) (half pitch (hp) 16nm). Also in parallel of aggressive introduction of new technologies, EBM-9000 inherits the 50kV variable shaped electron beam / vector scan architecture, continuous stage motion and VSB-12 data format handling from the preceding EBM series to maintain high reliability accepted by many customers. This paper will report our technical challenges and results obtained through the development.

EL5: One tool for advanced x-ray and chrome on glass mask making

The state-of-the-art for mask making continues to be driven by 1× x-ray masks. The IBM EL4+ e-beam mask writer at the Advanced Mask Facility in Burlington, Vermont, was originally designed for 0.35 μm ground rules (GRs) direct write at 50 kV, but delivered at 75 kV operation to achieve 0.25 μm GR performance for 1× mask making. Over the next 2 years, with optimization and improvements in each of the subsystems, its performance was enhanced beyond the 0.18 μm GR requirements. It is clear, however, that for 0.13 and 0.1 μm GR mask manufacturing, a new tool is required. It has also become apparent that because of the very high development and tool build costs, and small number of required x-ray mask makers, the same technology must be applicable for chrome on glass (COG) mask making. Based on the experience with EL4+, IBM is designing an EL5 tool which will provide the 0.13/0.1 μm GR performance for 1×, and easily convert to 4× COG exposure for 9 in. glass as well as 300 mm wafer direct write operation. As w...

PREVAIL-EPL alpha tool: Early results

The IBM/Nikon alliance is developing an EPL stepper alpha tool based on the PREVAIL technology. This article provides a status report on the alliance activity with particular focus on the electron optical subsystem developed at IBM. We have previously described design features of the PREVAIL Alpha system. The state-of-the-art e-beam lithography concepts have since been reduced to practice and turned into functional building blocks of a production level lithography tool. The electron optical subsystem has been designed, built, assembled, and tested at IBM’s Semiconductor Research and Development Center (SRDC) in East Fishkill, NY. After demonstrating subsystem functionality, the column, an interim mechanical system and all associated control electronics hardware and software have been shipped during January 2001 to Nikon’s facility in Kumagaya, Japan, for integration into the Nikon commercial e-beam stepper Alpha tool. Postshipment activity has been directed primarily toward demonstrating subfield stitchin...

Electron-beam mask writer EBM-6000 for 45 nm HP node

In order to comply with the demanding technology requirements for 45 nm half pitch (HP) node (32 nm technology node), Nuflare Technology Inc. (NFT) has developed Electron-beam mask writing equipment, EBM-6000, with increased current density (70A/cm2), while its other primary features basically remain unchanged, namely 50 kV acceleration voltage, Variable Shaped Beam (VSB)/vector scan, like its predecessors [1-5]. In addition, new functionalities and capabilities such as astigmatism correction in subfield, optimized variable stage speed control, electron gun with multiple cathodes (Turret electron gun), and optimized data handling system have been employed to improve writing accuracy, throughput, and up-time. VSB-12 is the standard input data format for EBM-6000, and as optional features to be selected by users, direct input function for VSB-11 and CREF-flatpoly are offered as well. In this paper, the new features and capabilities of EBM-6000 together with supporting technologies are reported to solidly prove the viability of EBM-6000 for 45 nm HP node.

New electron optics for mask writer EBM-7000 to challenge hp 32nm generation

Semiconductor scaling is expected to continue to hp32nm and beyond, accompanied by explosive data volume expansion. Required minimum feature size at hp 32nm will be less than 50nm on the mask, according to ITRS2007(1). EBM 7000 is a newly designed mask writer for the hp32 nm node with an improved electron optical column providing the beam resolution (10 nm measured in situ) and beam current density (200 A/cm2) necessary for cost effective mask production at hp32nm node. In this paper we report on column improvements, the in situ beam blur measurement method and writing results from EBM 7000. Written patterns show dose margin (CD change [nm] / 1 % dose change) of .94 nm /1 % dose for line/space arrays using chemically amplified resist PRL009 and our standard processing. Using a simple model to relate the measured beam intensity distribution to the measured dose margin, we infer an effective total blur of 30 nm, dominated by a contribution of 28 nm from the resist exposure and development process. Further evidence of the dominance of the process contribution is the measured improvement in dose margin to .64 nm/% dose obtained by modifying our standard process. Even larger process improvements will be needed for successful fabrication of hp22nm masks.

PREVAIL - Latest electron optics results

The PREVAIL electron optics subsystem developed by IBM has been installed at Nikons facility in Kumagaya, Japan, for integration into the Nikon commercial EPL stepper. The cornerstone of the electron optics design is the Curvilinear Variable Axis Lens (CVAL) technique originally demonstrated with a proof of concept system. This paper presents the latest experimental results obtained with the electron optical subsystem at Nikons facility. The results include micrographs illustrating proper CVAL operation through the spatial resolution achieved over the entire optical field of view. They also include data on the most critical issue of the EPL exposure approach: subfield stitching. The methodology of distortion correction will be described and both micrographs and metrology data of stitched subfields will be presented. This paper represents a progress report of the IBM/Nikon alliance activity on EPL.

PREVAIL e-beam stepper alpha tool

PREVAIL is the high throughput e-beam projection approach to NGL, which IBM is pursuing in cooperation with Nikon as alliance partner. Key lithographic building blocks of the technology have been demonstrated experimentally with a proof-of-concept (POC) system and results have been reported earlier at MNE 99 and elsewhere. This paper reports on the implementation of the PREVAIL technology in a production-level e-beam stepper. The architecture and writing strategy of the tool together with design features of the various tool subsystems are described.