Frank E. Abboud

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...

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.

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...

Evaluation of the MEBES 4500 reticle writer to commercial requirements of 250-nm design rule IC devices

The design rule requirements and error budget allocation for maskmaking have made the mask a critical component in the fabrication of 250 nm design rule IC devices. The MEBES 4500 raster-scan reticle writer was designed to meet the mask requirements for pilot production of this generation of devices. In this paper, we will review the IC device and user requirements that drove the design criteria of the MEBES 4500 system. The architecture of the MEBES 4500 system is described and compared to these design criteria. MEBES 4500 perfonnance results during development, manufacture, and installation are also compared to the commercial requirements of 250 nm design rule ICs.

MEBES 4000 optimization and characterization of MEBES 4500

Performance of a MEBES tool depends in part on how well it is optimized for a particular user application. This paper examines the efforts made to optimize a MEBES 4000 at Intel to meet performance goals of 350 nm design rules. The areas of particular concern are critical dimension, resolution, and composite positional accuracy. PBS resist processes and cassette- specific corrections (CAZOC) for six cassettes are examined to meet these goals. As part of a SEMATECH development program, a MEBES 4000 system at Etec is being upgraded to a MEBES 4500. The performance of the tool is characterized at each incremental phase of the upgrade. Results show that significant advances have been made in accuracy, system calibration and control, and data path.

MEBES reticle writers for 350-nm and 250-nm design rules

New MEBES reticle writers are described that meet the production requirements of the 350- nm and 250-nm design rules required for 64 Mb and first generation 256 Mb DRAM techniques. These raster scan e-beam systems are based on the MEBES IV thermal field emission (TFE) exposure system, in production use since early 1992. The MEBES IV-TFE system exceeds its 500-nm design rule requirement and is routinely used to product reticles of first-generation 64 Mb DRAMs, prototype 256 Mb DRAMs, and phase shift masks. The success of MEBES IV-TFE is based on a close working relationship with system users, who provided input to establish the requirements of the new reticle writers. The new reticle writers are the result of a two-phase development program. The initial phase, completed in 1993, focused on productivity improvements to the base system, which proved to have excellent accuracy. These improvements ease the handling of the large pattern files, improve the use of the 160 MHz writing rate with a faster data path and more efficient writing strategy, and improve overall system utilization with in situ (maskless) beam-calibration techniques. The second phase of development, completed early in 1994, focused on the production reticle requirements of second-generation 64 Mb DRAM, including optical proximity correction features, and first-generation 256 Mb DRAM. The second development phase improves data path speed, system accuracy, and system productivity. System and subsystem performance is shown for the first and second development phases. Lithographic and write-time performance on the product is presented and discussed in the context of system requirements.

Electron beam lithography using MEBES IV

The lithographic performance of the MEBESR IV maskmaker is described. This raster‐scan electron beam lithography system automates the thermal field emission (TFE) column and makes a number of advances in the electronics and software control subsystems to achieve the stability and accuracy sufficient for 64‐Mbit production and 256‐Mbit development. Key module developments are highlighted, including TFE column vibration reduction, column setup automation, 160 MHz blanking at a high slew rate, low noise, and increased linearity of the deflection control electronics, and multipoint system temperature control. Data on lithographic quality is presented, as well as ghostTM proximity correction results for 1× maskmaking applications with 0.2 μm minimum feature sizes.