Sayaka Tanimoto

Optical properties of a multibeam column with a single-electron source

A novel single-column multi-electron-beam system, called a beam-split array, has been developed for a high-resolution, high-throughput lithography tool. In this system, a single electron beam is divided into 1024 beams by a multisource module (MSM) composed of an aperture array (a beam-dividing aperture), a static lens array (Einzel lenses for each divided beam), and a blanker array (BLA, blanking electrode pairs for each focused beam). The MSM is used to form multiple intermediate images of the electron source at the BLA. These images are demagnified to form final images through a projection optics consisting of a double lens doublet with a blanking aperture and deflector. To align the multiple beam paths in the MSM, aligners between these arrays are used, and the aligner conditions are determined by monitoring the blanking-aperture image. Moreover, because each beam current is about 0.1% of the total beam current on the specimen, a high-contrast transmission detection method is used to detect the electr...

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.

Optical system for a multiple-beam scanning electron microscope

A novel optical system for a multiple-beam scanning electron microscope (SEM) is proposed. In the case of multiple-beam SEM, multiple secondary-electron beams passing through the column are inherently blurred because of the large energy spread and broad angular distribution of secondary electrons. To avoid cross-talk between the multiple secondary-electron beams, the optical system is designed such that it is divided into two independent parts: one for primary-beam illumination and one for secondary-electron detection. As the key components for the secondary-electron detection, a scan-cancelling deflector, and accelerating electric field were applied. To demonstrate the proposed optical system, a prototype column with four beams was developed. This column enables four SEM images to be separately but simultaneously acquired with more than 99% of the generated secondary electrons. This result demonstrates that high-speed imaging with the proposed multiple-beam SEM is possible in the near future.

Monolithic multichannel secondary electron detector for distributed axis electron beam lithography and inspection

The attractiveness of electron beam systems would be greatly enhanced if the throughput could be improved. One approach, described previously by the authors employs a uniform axial magnetic field to focus thousands of electron beams simultaneously [D. S. Pickard et al., J. Vac. Sci. Technol. B 21, 2709 (2003); T. R. Groves and R. A. Kendall, ibid., 16, 3168 (1998)]. The beamlets never combine to form a common crossover, thereby avoiding the throughput limitations due to space charge blurring. With this approach, one challenge was to fashion a detection scheme that maintains a tight beamlet packing density (250μm pitch) while minimizing cross-talk between adjacent secondary electron signals, either by crossing trajectories or within the detector. A pin-diode-based detector was investigated as a potential component of the multielement detection scheme for the authors’ system. The detector features a two-dimensional array of elements on high resistivity float-zone silicon. The detector attributes that were a...

Inspection of all beams in multielectron beam system

A testing apparatus for inspecting the beams formed by a multisource module (MSM) was built for the feasibility study of a beam splitting array (BSA), a multielectron beam system the authors are developing. In this BSA, the MSM plays the following three key roles: splitting the beam from a single cathode into 32×32 beams, converging the 32×32 beams, and blanking them individually. Accordingly, the inspection of all beams formed by the MSM is essential for the feasibility study of the system. The testing apparatus was therefore designed for measuring all the beams formed by the MSM without demagnifying them. To maintain the accuracy during the inspection of all 32×32 beams, the measurement process was automated. This testing apparatus was used to measure the diameters and misalignments of all beams formed by a prototype MSM. As a result, the mean values of the transverse and the longitudinal diameters were found to be 0.88 and 0.92μm, respectively. A single stigmator can cancel the difference between these...

Simulation of Limited-Area Cathode as Mask-Irradiation Source

The possibility of using a limited-area thermionic electron cathode as a mask-irradiation electron source was demonstrated by simulation. A mask-irradiation source requires high brightness and good current density uniformity. It was found that both requirements were satisfied at a lower cathode temperature compared to a conventional triode electron gun. Moreover, in order to evaluate the cathode properties in practical use, the emission current uniformity was simulated by taking into account the diameter of a point defect and the shield materials potential at the surface of the electron cathode. The simulation showed that the effect of the point defect of the source crystal is reduced by thermal velocity of the emitted electrons. In addition, it was found that the shield materials potential deteriorates the uniformity when the source material evaporates. However, the lower cathode temperature can reduce the evaporation. It is concluded that the limited-area thermionic cathode is suitable for a mask-irradiation electron source.