Junichi Kai

Multielectron beam blanking aperture array system SYNAPSE‐2000

A blanking aperture array (BAA) has 1024, 25‐μm‐square apertures and blanking electrodes on a 20‐μm‐thick Si membrane with a total aperture ratio of 1/6. These apertures are irradiated with an electron beam, and the electrons passing through the apertures are projected onto a wafer surface in a reduction ratio of about 1 to 200. A signal applied to each blanking electrode turns each beam on and off individually while raster‐scanning the electron flux with a deflector; thereby the desired pattern on the wafer can be drawn. The SYNAPSE‐2000 system uses 512 beams in the center of a BAA and exposes 18 8 in. wafers per hour using a single BAA column. Large convergence semiangle, refocusing, and multicolumns are effective measures to reduce Coulomb interaction and to accomplish higher throughput. This system provides a volume‐production microelectronic device manufacturing method.

Fast electron beam lithography system with 1024 beams individually controlled by blanking aperture array

A new electron beam lithography system with a two-dimensional blanking aperture array (BAA) is proposed. The BAA produces 1024 individually controlled beams. The demagnification ratio of BAA on the wafer is 0.3%. An actual BAA device was fabricated and a preliminary experiment was carried out with a block exposure system and Si stencil mask. Very high resolution of 0.08µm holes was confirmed. The system parameters are designed by setting the system throughput at more than twenty 8-inch wafers per hour. Below a 0.2 µm minimum feature size, BAA exposure is suitable for random patterning of wiring layers in dynamic random access memories (DRAMs), application specified integrated circuit (ASICs) and microcode processing units (MPUs), and will be a useful lithographic tool.

`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.

High‐precision reticle making by electron‐beam lithography

We have developed an electron‐beam (e‐beam) lithography system named ‘‘NOWEL’’ which utilizes very accurate pattern writing method and high‐speed data processing. Accordingly NOWEL makes it possible to manufacture reticles for 16‐Mbit dynamic random access memories (DRAM’s) or more densely integrated very large scale integrated circuits (VLSI’s). The NOWEL system has three key features: (1) Vertical landing deflection system. This consists of three yokes in series and one short‐working‐distance lens (M=0.86). The landing angle at the corner of the 5‐mm2 main field is <0.0025 rad. Therefore the butting error arising from a 10‐μ height variation of the substrate is <0.05 μ. Deflection aberration is about 0.2 μ. (2) Double exposure method called ‘‘A/B mode.’’ We adopted a variable shaped beam. The first exposure is made by serial writing with constant‐size rectangular spots, and the second one is made on the previously exposed area by shifting the beam position and reshaping the beam spots. One‐half dosage i...