Lee H. Veneklasen

An electron‐beam inspection system for x‐ray mask production

SEMSpec is a scanning electron‐beam inspection system designed for high‐resolution die‐to‐die inspections of conductive x‐ray masks, wafer prints, or stencil masks in a production environment. The inspection sensitivity can be varied from 97% detection of 50‐nm defects, at a rate of 27 min cm−2, to 97% detection of 250‐nm defects at 1 min cm−2. A thermal‐field‐emission source produces a Gaussian profile electron beam that is moved by electrostatic deflectors over the continuously moving substrate that is being inspected. Secondary electrons from the substrate are collected in a high‐speed detector and the resulting digitized image data is stored in a specialized memory system. Pairs of images to be compared are continuously transferred from the memory to a high‐speed defect processor for analysis. Defect reports from the defect processor are analyzed during inspection and stored for subsequent review. We describe the overall system including the electron‐beam column with its six‐emitter field‐emission gun...

Demonstration of multiblanker electron-beam technology

A set of multiple electron-beam (e-beam) aperture/blanker chips have been fabricated using silicon microelectro-mechanical systems (MEMS) techniques. The aperture sizes range from 8 to 4 μm (nominal) squares, and the chip configurations feature either eight individually controlled monopolar blanker electrodes or four bipolar electrode pairs. The chips replace the shapers of a 20 kV AEBLE™ shaped e-beam lithography column. The apertures in the chips convert an incident 150 μm diameter e-beam into multiple beamlets. Each beamlet can be independently blanked off of a 100 μm aperture placed at the following beam crossover. Data are presented that demonstrates the ability to independently blank each beamlet by applying 10 V. Magnified images of the beamlets show square or rectangular shapes with sharp corners, indicating that the apertures were properly fabricated. The degree of electrostatic blanker crosstalk was measured and found to be up to 15% at the crossover plane for different pairs of beamlets, but no...

Raster shaped beam pattern generation

We propose a new approach to electron-beam (e-beam) pattern generation, in which the best attributes of raster scan writing are combined with beam shaping. The maximum dimension of the variable shaped flash is equal to the minimum feature size required in the pattern. The limited shaping range allows the use of very high speed, limited-resolution, digital-to-analog conversion circuits and amplifiers to form the shapes, and also allows thermal field emission cathode and optics to be used effectively, providing a very high current density. The system should support a sustained flash rate of at least 100 MHz, which is much higher than that found in conventional variable shaped beam architectures. The throughput is pattern independent and attractive for photomask fabrication at the 130 and 100 nm wafer technology nodes.

Implementation of real-time proximity effect correction in a raster shaped beam tool

A method for real-time backscatter correction has been implemented in a 50 keV raster-scan electron-beam mask exposure system. The real-time nature of the correction makes it an attractive, user transparent feature with flexibility to choose the correction algorithm and scattering parameters. This article describes the correction algorithms and the hardware added to the data path. We compare simulated critical dimension (CD) linearity with results from mask exposures in our new raster shaped beam proof-of-concept tool. Performance meets both throughput and CD linearity requirements for the 130 and 100 nm device generations.

Dynamic performance of a scanning X–Y stage for automated electron‐beam inspection

The design and performance of an X–Y stage for fast electron‐beam inspection of wafers and x‐ray masks is described. The inspection technique involves the comparison of images that are acquired by the raster scan acquisition of long swath images recorded while the stage moves at constant velocity. Pairs of images acquired serially must remain registered to about 0.05 μm net accuracy, requiring interferometer controlled motion with very low vibration. The system design requires high‐vacuum compatible, nonmagnetic construction, with provision for electron and light optical elements above the stage, and additional electron optics and substrate loading elements below it. Accordingly, an open frame stage with internal linear motors and bearings was selected. High stiffness and particular attention to smooth motion results in very low vibration with a relatively large moving mass. The stage is driven by brushless linear motors inside a 20 Hz bandwidth servo loop closed around high‐resolution λ/256=2.5 nm interf...

0.25-μm lithography using a 50-kV shaped electron-beam vector scan system

Performance data from a prototype 50 kV shaped electron-beam (e-beam) pattern generator is presented. This technology development is targeted towards 180-130 nm device design rules. It will be able to handle 1X NIST X-ray membranes, glass reduction reticles, and 4- to 8-inch wafers. The prototype system uses a planar stage adapted from the IBM EL-4 design. The electron optics is an 50 kV extension of the AEBLE%+TM) design. Lines and spaces of 0.12 micrometers with < 40 nm corner radius are resolved in 0.4 micrometers thick resist at 50 kV. This evolutionary platform will evolve further to include a new 100 kV column with telecentric deflection and a 21-bit (0.5 mm) major field for improved placement accuracy. A unique immersion shaper, faster data path electronics, and 15-bit (32 micrometers ) minor field deflection electronics will substantially increase the flash rate. To match its much finer address structure, the pattern generator figure word size will increase from 80 to 96 bits. The data path electronics uses field programmable gate array (FPGA) logic allowing writing strategy optimization via software reconfiguration. An advanced stage position control (ASPC) includes three-axis, (lambda) /1024 interferometry and a high bandwidth dynamic corrections processor (DCP). Along with its normal role of coordinate transformation and dynamic correction of deflection distortion, astigmatism, and defocus; the DCP improves accuracy by modifying deflection conditions and focus according to measured substrate height variations. It also enables yaw calibration and correction for Write-on-the FlyTM motion. The electronics incorporates JTAG components for built-in self- test (BIST), as well as syndrome checking to ensure data integrity. The design includes diagnostic capabilities from offsite as well as from the operator console. A combination of third-party software and an internal job preparation software system is used to fracture patterns. It handles tone reversal, overlap removal, sizing, and proximity correction. Processing of large files in a commercial mask shop environment is made more efficient by retaining hierarchy and using parallel processing and data compression techniques. Large GDSIITM and MEBES data files can be processed. Data includes timing benchmarks for a 1 Gbit DRAM on both proximity and reduction reticles. The paper presents 50 kV results on silicon and quartz substrates along with examples of overlay to an external grid, field butting, and critical dimension (CD) control data. Selective experiments testing system stability, calibration accuracy, and local correction software implementation on a VAX control computer are also given.

Electron-optical optimization for Gaussian, high-current, high-dose columns

This article demonstrates the electron-optical optimization of a high-current, high-dose column operating at 10 keV. The goal is to increase the available dose to the resist, which requires increasing the current density to more than 800 A/cm2. Our calculations use the MEBS Ltd. BOERSCH program. We model the complete column as a set of thin lenses, separated by field-free drift spaces. Monte Carlo simulation propagates discrete bunches of electrons through the column, taking into account the mutual repulsion between pairs of electrons. Gaussian spot size and current density in the column were calculated for three beam currents: 314, 75, and 35 nA. The results show that to achieve a higher current density, it is necessary to change the electron gun and the column. Specifically, a low aberration gun and a significantly shorter column are required. At 10 keV, the column performance at high beam currents (∼300 nA) is almost entirely dominated by electron–electron interactions. Major improvements in gun perfor...