Frederick Raymond

Feasibility study of new graybeam writing strategies for raster scan mask generation

The simplicity of the raster scan beam technology has made it the dominant choice for maskmaking production tools. Nevertheless, building patterns on a grid resolution determined by the address of the raster scan mask generator places limitations on the location of pattern edges. Furthermore, as pattern dimensions shrink to 0.5 μm, and eventually to 0.15 μm, the standard technique of decreasing the address unit size decreases write time throughput. One promising approach to avoid this throughput bottleneck is pixel‐level intensity and position modulation (graybeam plus pixel deflection to displace edge locations of patterns at a resolution smaller than the address grid size. In this article, methods for modulating the intensity and position of writing pixels are shown, along with simulation and experimental results using test patterns. Simulation results are presented that show the relationship between grid size and the discrete intensity levels needed to achieve a given edge placement requirement. Intens...

Evaluation of OPC mask printing with a raster scan pattern generator

MEBESR 50 kV mask pattern generators use Raster GraybeamTM writing, providing an effective grid that is 32X finer than the print grid. The electron beam size and print pixel size are variable between 60 nm and 120 nm, allowing a tradeoff between resolution and write time. Raster scan printing optimizes throughput by transferring precisely the amount of data to the mask that is consistent with the chosen resolution. As with other raster output devices, mask write times are not affected by pattern complexity. This paper examines the theoretical performance of Raster Graybeam for model-based optical proximity correction (OPC) patterns and provides examples of mask patterning performance. A simulation tool is used to model the MEBES eXaraTM system writing strategy, which uses four writing passes, interstitial print grids, offset scans, and eight dose levels per pass. It is found that Raster Graybeam produces aerial image quality equivalent to the convolution of the input pattern data with a Gaussian point spread function. Resolution of 90 nm is achieved for equal lines and spaces, supporting subresolution assist features. Angled features are a particular strength of raster scan patterning, with feature quality and write time that are independent of feature orientation.

Lithographic performance results for a new 50-kV electron-beam mask writer

Current pattern generation tool designs will be inadequate to meet the advanced requirements for next-generation masks, particularly at the 100 nm node. Etec Systems, Inc. has developed a complete raster-based patterning solution to provide improved resolution, critical dimension (CD) uniformity, positional accuracy, and throughput. This solution meets the challenges of the 130-nm device generation with extendibility to at least 100 nm devices. Our complete patterning solution includes an electron-beam (e-beam) pattern generation system and a new 50 kV process. The e-beam system includes a column with 50 kV accelerating voltage and a new graybeam writing technique. To accomplish this technique, a pulse-width modulated blanking system, per-pixel deflection, retrograde scanning, and multiphase and multipass writing are used. This combination of features results in markedly improved lithographic performance and enables the use of conventional high-contrast resists for faster process implementation. Additional significant innovations of this pattern generation system include a novel stage design, an integrated automated material handling system (AMHS), on-board diagnostics, and improved environmental/thermal management. We believe this comprehensive patterning solution offers the best combination of benefits to the user in terms of versatility and extendibility.

Dynamic corrections in MEBES 4500

Some systematic errors of the mebes raster scan lithography system are examined and how significant accuracy improvements can be achieved is demonstrated. The accuracy improvements result from error compensation hardware and software applying corrections that are either a function of time (write scan position) or of position on the substrate. Error analysis shows the following correctable errors to be among the largest error sources in the mebes iv: electronic noise, stage z runout, deflection alignment drift, mask flatness, and clamping distortion, and scan nonlinearity. These errors contribute to placement/overlay accuracy and to butting accuracy. The dynamic corrections implemented are automatic write scan correction, which reduces deflection alignment errors, scan linearity measurement and correction, grid correction, and height detection and correction, which reduce cassette height and mask flatness errors. With these corrections implemented, system performance improves dramatically.

Electron Beam Column Developments for Submicron- and Nanolithography

Recent advances in thermal field emission (TFE) electron beam optics column design for lithography are described. Innovations include source vibration mode mapping, accelerating electron gun lens, gun arc-suppression, automated cathode pyrometer, and experimental deflection control system. Several of these column optics and system enhancements, which improve the accuracy and reliability of MEBES°R IV-TFE systems, have enabled patterning of 64 Mbit dynamic random access memory (DRAM) 5×-reduction reticles. A 13000-hour cathode lifetime has been achieved in a production environment. Automated column setups over the entire operating range with 99% success and 5 min average times are possible. Blanking at 160 MHz with 30 nm (3σ) critical dimension control is achieved. Data obtained with a new experimental deflection control method can quickly compensate stripe butting drift to high accuracy. Challenges in mask patterning for advanced applications are then considered. Several accuracy and throughput issues for advanced 5× reticles for DRAM, 1× masks, and nanolithography are discussed. Examples are given of scaling recent system data as a means of estimating future error budget components.

100-nm OPC mask patterning using raster-scan 50-kV pattern generation technology

ABSTRACT The complexity of photomasks is rapidly increasing as semiconductor devices are scaled down and optical proximitycorrection (OPC) becomes commonplace. Raster scan architectures are well suited to the challenge of maintaining maskthroughput despite these trends. Electron-beam techniques have the resolution to support OPC requirements into theforeseeable future. The MEBES ® eXara mask pattern generator combines the resolution of a finely focused electronprobe with the productivity and accuracy of Raster Graybeam patterning. Features below 100nm can be created, andOPC designs are produced with consistent fidelity. Write time is independent of resist sensitivity, allowing high-doseprocesses to be extended, and relaxing sensitivity constraints on advanced chemically amplified resists. The system isdesigned for the production of 100nm photomasks, and w ill support the development of 70nm masks.Keywords: MEBES, electron beam, lithography, photomask, graybeam, CAR, OPC 1. INTRODUCTION

Multipass gray printing for the new MEBES 4500S mask lithography system

Etec Systems, Inc. has developed a new e-beam mask lithography system, the MEBES 4500S, featuring a higher productivity writing strategy called multipass gray and a number of mechanical and electrical improvements. This new system, based on the proven technologies introduced in the MEBES 4500 system, provides improved throughput and accuracy. The MEBES 4500S system with multipass gray supports smaller mask design addresses needed for high resolution masks, while providing higher dose for high contrast processes with low sensitivity and improved CD linearity. Improved print performance is achieved by the introduction of several system design changes that work in conjunction with the multipass gray writing mode. These changes include improved column deflection system temperature control, enhanced TFE current control, improved work chamber thermal management, and improved stage drive vibration damping. Details of these features are presented along with first performance data for the new system.

Address data reduction and lithography performance of graybeam writing strategies for raster scan mask generation

Graybeam (GB) writing methods [Muray, Abboud, and Raymond, J. Vac. Sci. Technol. B 11, 2390 (1993)], including the new combination of graybeam plus per pixel deflection (GBPPD), were first investigated last year as a method for improving throughput on an e‐beam raster scan machine. These techniques were shown to produce pattern edge placement resolution equivalent to writing at a smaller address unit, thereby improving throughput. The GB and GBPPD writing techniques are further investigated to address data reduction and lithographic performance. Accurate simulations and lithography on two‐dimensional test patterns for GBPPD writing are presented.

Electrodynamics of fast beam blankers

Performance characteristics of an advanced electron beam blanker for lithography are presented. Various electrodynamic effects are discussed, which must be eliminated to achieve high beam placement accuracy during and after blanking. These electric and magnetic field effects have been measured over six orders of magnitude in time. The fast beam jitter characteristic of transit time effects in a double‐deflection blanker is captured with nanosecond time resolution. Eddy current effects measured in the micro‐ to millisecond time domain are shown to be an inherent problem in earlier double‐deflection blanker designs. A consequence is beam misplacement after the unblank transition, which can be 0.05 μm even after 500 μs. Several examples of pattern artifacts in purposely underdeveloped resist are given to illustrate graphically the lithographic consequences of the eddy current effect. All of these electrodynamic effects have been addressed with a new ‘‘virtual ground’’ blanker design. The MEBES IV‐TFE maskmak...

Design considerations for an electron-beam pattern generator for the 130-nm generation of masks

The critical dimension (CD) requirements of the SIA roadmap require continued improvements in pattern generation (PG) tool technology. This includes electron-beam (e-beam) delivery, resist and process, writing strategy, and overall system throughput. In this paper, we discuss these interrelated topics and evaluate their impacts on the CD control, linearity, and uniformity performance of PG tools. By means of Monte Carlo simulations and experimental comparisons, we evaluate various parameters of e-beam delivery systems, including beam energy, spot size, writing strategy, and throughput. We also perform a thorough evaluation of mask heating effects due to e-beam exposure. Finally, we perform comparative studies of various resist and process combinations. The totality of our investigations allows us to conclude that a 50 kV raster scan e-beam system, using a high- contrast, high-sensitivity resist, such as SPR 700, with GHOST proximity effect correction (PEC), can meet the CD control, linearity, and uniformity requirements of the 130 nm technology node.