Susumu Ozasa

Variably shaped electron beam lithography system, EB55: II Electron optics

A variably shaped electron beam exposure system (EB55) with a high exposure rate is developed for direct beam lithography of 0.5 μm patterns. The electron beam column consists of seven magnetic lenses. The projection lens is specially designed to minimize deflection aberations and beam landing angle deviation on the wafer. The column design facilitates a shortened distance between the object and its image plane. Accelerating voltage is 30 kV due to decreased Coulomb interaction and proximity effect. In a shaped beam system, the electron gun should have a wide emission angle, high brightness, and large crossover size. A square rod type LaB6 cathode is developed for this purpose. The shaped beam is vector scanned by electrostatic deflection plates and electromagnetic coils. The scanning area is 2.6 mm square and the maximum beam size is 5.10 μm square. The size change unit is 0.02 μm. A beam current density higher than 10 A/cm2 is obtained with a small beam covergence angle. A shape edge slope smaller than ...

Yaw corrected precision X‐Y stage for high‐throughput electron‐beam lithography systems

Overhead time associated with a work stage is an important factor determining the throughput of step‐and‐repeat‐type electron‐beam lithography systems. In addition to increasing stage speed, utilization of large field electron optics contributes to reduction of such overhead time. However, when using large field optics, the stage is required to have minimal yaw to prevent field stitching error. Accordingly, a high‐speed, high‐precision work stage with a piezodrive yaw correction function has been developed for construction of high‐throughput e‐beam systems. To avoid leakage, magnetic field variation, and vacuum contamination, only the work table is located in the vacuum chamber. The table is driven by X,Y‐drive mechanisms located outside the chamber. To achieve high speed positioning, a unique, light‐weight X‐Y table structure using a PTFE slide bearing has been incorporated. To correct yaw error at the stage, the work table can be rotated ±8 arcsec with a piezoactuator. Positioning and yaw correction for...

Analysis of pattern dimension accuracy in electron‐beam lithography

The etched pattern dimension accuracy for an e‐beam lithography system is determined by machine‐, resist process‐, and proximity effect‐related errors. This paper reports mainly on analysis of such machine‐related errors, though process‐related and proximity effect‐related errors are also discussed. In a variably shaped vector writing system, machine‐related errors occur from four sources: (i) beam dimension and shape errors, (ii) dose change, (iii) beam edge resolution, and (iv) deflection distortion. Each error includes several inherent causes. The Hitachi e‐beam lithography system, the HL‐600, makes use of such variably shaped vector writing techniques. In the context of this system, then, the authors have made separate determination of each error through experiments. Beam dimension and shape error was found to be 0.045 μm, dose change dependent error was 0.02 μm, beam resolution dependent error was 0.03 μm, and deflection distortion dependent error was 0.05 μm. The major causes for each error have als...

A simplified focusing and deflection system with vertical beam landing

A focusing and deflection system with vertical beam landing and reduced aberrations was developed for direct electron beam lithography. The system consists of two magnetic lenses and a magnetic deflector. The excitations between the lenses are inverse to each other. The deflector, which has saddle‐type coils, is set inside the first lens. The pivot point introduced by the deflector and the first lens coincides with the focal point of the second lens to achieve a vertical beam landing. These arrangements and the operating conditions also enable minimized aberrations, especially elimination of transverse chromatic aberration. In computer simulation, the system gives a 2 mrad/mm landing angle coefficient and a 0.1 μm aberration disk after refocusing at each deflective point, when a converging semiangle of 2.5 mrad is used in a 3.2×3.2 mm2 deflection area at a 30 kV beam energy. The converging angle gives a current density of 10 A/cm2 using the LaB6 electron gun with 5×105A/cm2sr brightness. In the simulation...