Masahide Okumura

Preparatory Study for the Matrix-Pattern Imaging, EB System

A new method for electron-beam lithography –called matrix-pattern imaging (MPI)– for use as a high-throughput exposure system has been proposed. In MPI, the electron sources are arranged in a matrix so that they produce an electron beam in the shape of a circuit-pattern element; the beam is focused on the target. An evaluation system for measuring the properties of the MIM cathode, a promising candidate for the electron source of an MPI-based system, was constructed. The measured current density (at the cathode) is 2.5 mA/cm2, and the brightness is 1×102 A/cm2/sr (at an accelerating voltage of 50 kV). An image of the cathode was successfully projected onto the target, and delineated on a wafer. Moreover, the composition of the exposure system was optimized so as to increase throughput with an MIM cathode, and the throughput of the resulting MPI system was estimated as one six-inch reticle per hour.

Electron optical column for high speed nanometric lithography

Abstract An electron beam lithography system has been developed for the fabrication of nanometric level devices. The system has the ability of 0.1um resolution, ±0.04um overlay accuracy and 1 wafer/hr throughput. Key technologies used in the system are a newly developed field emission cathode, a variable gaussian optics and a three stage deflection system.

Active Vibration Correction in Electron Beam Lithography System

In an electron beam (EB) lithography system, beam positional vibration is one of the most influential factors of positioning accuracy degradation. We propose a new correction method for improving this accuracy and investigate its effectiveness by applying it to a nanometer EB system. In our method, first, the correction signal is generated by detecting the beam positional vibration as the variation of the backscattered or the transmitted electron signal and then extracting one period of this signal. Then, the correction signal is added to that of the beam deflection control. The effectiveness of this correction is evaluated by measuring beam positional vibration and stitching accuracy of the delineated pattern between subfields with size of 8 µ m×8 µ m. As a result, both an amplitude of the beam vibration of less than 10 nm and a stitching accuracy of less than 8 nm (3σ) are achieved, which confirms that the beam vibration has been actively corrected, and the positioning accuracy has been improved. The above results indicate that this correction method is very valuable for the EB lithography system.

High Speed Data Control Circuit For Nanometric Electron Beam Lithography

A nanometric electron beam lithography system was developed with 0.1 um resolution using 0.03 μm electron beam. To get practical writing speed of 1 wafer/ hr with 0.1 μm resolution, many new technologies were developed in the system. Here, the high speed data control circuit is precisely described. It consists of a pattern generator (a buffer memory, a framing processor, decomposition processor and correction processor ) and a beam deflection controller.

Digital Processing Of Beam Signals In A Variably Shaped Electron Beam Lithography System

This paper discusses signal processing procedures which have been developed for three important beam adjustments required by variably shaped electron beam lithography systems: dynamic focussing adjustment, deflection distortion correction and beam size adjustment. Precise and speedy measurement of edge slope, beam position and beam size are all necessary in this context. To execute these measurements, backscattered electron signals are stored in a buffer memory following digital scanning of a shaped beam across a fiducial mark. These signals are then digitally processed in a control computer. These procedures have been applied to an EB lithography system (HL-600). Pattern accuracy of 0.2 μm over a 6.5x6.5 mm field and overlay accuracy of 0.1 μm were obtained.

High-resolution and high-stability electromagnetic-deflection control system for EB lithography system

A stable high-resolution electromagnetic deflection control circuit for an electron-beam lithography (EBL) system has been developed. This deflection control circuit has enabled an EBL system to deal with a wide deflection area of 2.5-mm square having fine address units for a pattern placement of 1.25 nm. The deflection-control circuit consists of a new digital to analog converter (DAC) circuit, whose resolution is 21 bits, and a low-drift current-amplifier circuit. To achieve such high-stability and high-resolution, we had to develop a low noise-current cell structure for the new DAC circuit, because the output-signal noise of the DAC circuit is a major source of interference at the desired resolution. A local temperature control technique has been incorporated into the circuit to reduce fluctuations of the deflection control signal caused by ambient thermal variations. The low noise-current cell structure, which consists of multiple current buffers and low-pass filters, is placed between a constant current source circuit and a differential-switch circuit for each bit of the DAC circuit. The simulation results of the DAC circuit showed that the output-signal noise of the DAC circuit could be reduced to less than 0.4 nm rms, which is small enough to achieve the desired resolution. As the results of the experimentally evaluation of the deflection control circuit show, the total noise of the deflection-control signal obtained was less than 0.6 nm rms and the signal stability obtained was better than 0.3 nm rms. An evaluation of the performance of the new EBL system to which the new deflection control circuit was applied, showed that the critical-dimension accuracy obtained was better than 5 nm (3sigma) and the positioning accuracy obtained was better than 10 nm (3sigma) for the area controlled by electromagnetic deflector.

Active noise cancellation technique for highly accurate EB lithography systems

We propose a compensation method, which we call the active noise cancelation technique, to improve the pattern positioning accuracy in electron-beam (EB) lithography. This compensation method corrects pattern positioning error by eliminating EB vibration at the power-supply (PS) frequency (50 or 60 Hz), which is one of the main causes of the error. In this compensation method, a compensatory signal is generated by extracting one period from the EB vibration, which is measured before exposure. During exposure, this signal is added to the deflection-control signal. Because the EB is constantly deflected in the direction opposite to the EB vibration, the pattern positioning error due to EB vibration can be corrected. To evaluate the improvement of the accuracy of an EB lithography system with this compensation method, we applied it to our EB lithography system (HL-800 series). We found that the EB vibration at the PS frequency, whose amplitude was about 0.03 micrometer without the use of this compensation method could be reduced to less than 0.01 micrometer with the compensation. We also evaluated the stitching accuracy between stripes of continues stage moving. Without compensation, the accuracy (mean plus 3 sigma) was improved from 0.064 micrometer in the X direction and 0.044 micrometer in the Y direction to 0.027 and 0.014 micrometer respectively by using this compensation. Therefore, we confirmed that this compensation method was effective to improve the accuracy of EB lithography systems.

A High Speed Nanometric Electron Beam Lithography System

An electron beam lithography system has been developed for research and development of fine structure advanced devices. The system is capable of 0.1 um resolution, 0.04 um stitching accuracy, 0.04 um overlay accuracy and 1 wafer/hr throughput. One of key technologies used in this system is a variable gaussian optics and a pattern edging-process. This makes it possible to realize ten times higher throughput than the conventional fixed gaussian beam method and provide a simple means of proximity correction.