Kenichi Kawashima

Electron Beam Block Exposure

A new exposure technique called block exposure was examined in order to increase the throughput of direct writing of memory LSI devices using an electron beam. With this technique, an electron beam is projected to a block of aperture patterns in the stencil mask to change the beam shape. Frequently used LSI pattern components are defined as blocks to be reused during the exposure. Patterns that are rarely used are exposed by using a variable-shape beam. With the demagnification ratio of one percent, masks are easy to fabricate and very reliable. The patterns with a 0.13-µm minimum feature size are well projected on a single-layer resist. With block exposure, any shape can be accurately transferred irrespective of the pattern shape or size. The throughput of about ten 8-in wafers per hour is estimated for several pattern layers of a 64-Mbit dynamic random-access memory (DRAM).

`NOWEL-2' Variable-Shaped Electron Beam Lithography System for 0.1 µm Patterns with Refocusing and Eddy Current Compensation

We have developed a variable-shaped electron beam (EB) lithography system which we call NOWEL-2. The system has the following features: (1) a short objective lens and a four-stage major deflection system; the landing angle at the corner of the 1.6 mm square major field is less than 2 mrad, and patterns from 0.1 to 3.0 µm are well resolved over the whole deflection field, (2) 20-bit digital-to-analog converter and high-precision current output amplifier, in which the least significant bit (LSB) corresponds to 0.0025 µm; linearity error is less than 1/4 LSB at 23±5°C, (3) refocusing and refocus-flyback; the edge sharpness of a 3 µm square beam was improved from 0.5 µm to 0.25 µm, (4) eddy current compensation; for a 100 µm electromagnetic jump, the waiting time is less than 50 µs, (5) continuously moving stage mode exposure; beam position accuracy is about 0.05 µm (3σ).

Accuracy of exposure during continuous stage movement in a variable shaped vector scanning EB lithography system

Abstract We have developed a variable shaped electron beam lithography system “NOWEL-2” [1,2]. Continuously moving stage exposure mode, which we call CM exposure mode, is used in the system. To achieve high butting and overlay accuracy in CM exposure mode, we measured the beam positioning error using the continuously moving mark detection method. Up to a stage velocity of 10 mm/sec, beam positioning error caused by eddy current and system vibration was less than 0.04 μm. Total beam positioning drift during exposure was decreased to about 0.08 μm by keeping the temperature of the electromagnetic deflectors and lenses constant.