Shohei Suzuki

High accuracy aerial image measurement for electron beam projection lithography

A direct means of measuring an image blur of electron beam projection lithography (EPL) tools is described. An aerial image sensor used for the image blur measurement was fabricated and evaluated. The signal to noise ratio (SNR) was very high and the signal contrast was 97%. The measured image blur, defined as the distance between 12% and 88% of the beam edge profile, under the optimum condition was 13 nm and the measurement repeatability was 3 nm (e sigma). The measurement error due to the sensor was extremely small, and a quantitative measurement of the image blur can be realized using this technique. The application of this technique to a system calibration is demonstrated. Focus and astigmatism were measured and the optimum settings of focus coils and stigmators were determined with an excellent repeatability. The potential for this technique to provide an automated self-calibration system on the EPL tools is clearly shown.

Novel electron optics for large subfield electron-beam projection lithography (EPL)

In Electron-beam Projection Lithography (EPL), achieving the requirements for the ITRS 45 nm roadmap node will require decreasing simultaneously both the beam blur from the Coulomb interaction effects and the geometrical aberrations from their present values. Because next generation lithography tools are required to have both high resolution and throughput, the Coulomb effect becoems more of an issue. In this paper, we propose a novel concept to effectively decrease the Coulomb effect. Based on this new concept we develop an EPL electron optical system in which not only the Coulomb effect but also the geometrical aberrations are greatly reduced. We report on the properties of this new EPL optical system.