Hirotsugu Wada

Triangular Shaped Beam Technique in EB Exposure System EX-7 for ULSI Pattern Formation

The generation of a triangular and rectangular shaped beam is very useful in increasing throughput for writing ULSI patterns which often include many oblique lines. To make use of these shaped beams in ULSI pattern formation, a new rectangular and triangular shaped beam calibration method has been developed on the EB exposure system EX-7. The shaped beam calibration method is established by analyzing the beam current of shaped beams and the backscattered electron signal from a fine gold particle on the target. Resultant accuracies were 0.013 µm for a beam size of 1.6 µm and 0.025 %micro;m for the relative beam position on the target. Using this method, 0.2 µm ULSI patterns including oblique lines have been accurately formed.

Contamination Charging up Effect in a Variably Shaped Electron Beam Writer

We investigated the beam drift on the second shaping aperture caused by the charging up of contamination layers on shaping deflector surfaces in an EX-8D variably shaped beam (VSB) writer. A surface charging model which is based on the movement of the secondary electron (SE) charge-up area in a deflector in response to the direction and strength of the field was adapted to explain the beam drift phenomenon. It was found that SE charge-up causes the beam drift and its amount depends on the amount of SEs moving between the electrodes. It was also found that by removing the contamination layers using a downflow cleaning process the beam drift is significantly reduced even if SEs move between the electrodes.

Evaluation of Shaping Gain Adjustment Accuracy Using Atomic Force Microscope in Variably Shaped Electron-Beam Writing Systems

A method for the fine evaluation of shaping gain adjustment, in which resist patterns are measured using an atomic force microscope (AFM), has been explained for the variably shaped electron-beam (EB) writing systems. The shaping gain coefficient was adjusted so that the length between two beams deflected by a shaping deflector is equal to a parameter given to the writing system. For the evaluation of the absolute values of the adjustment, the authors drew line and space patterns on a poly-methyl methacrylate (PMMA) resist. The authors measured the resist height at the shot boundary with an AFM. When the beam size is equal to the shot pitch, the resist height at the shot boundary becomes zero. From the beam size and the shaping-gain shift at which the resist height at the shot boundary becomes zero, beam-size error was calculated. From the beam-size error for various beam sizes, the shaping gain adjustment error of 0.3 nm for the 1 µ m beam size and the shaping-offset error of 6.0 nm have been obtained.

Stage tracking of a mask-scan EB mask writer test stand

A stage tracking function has been developed for a mask-scan EB mask writer. Position error of EB mask on an EB-mask-stage induces position error of projection beam on the EB-mask and the position of a writing pattern. The position of the EB-mask is measured by a laser interferometer. The shift from the aimed position is fed back to a mask selection deflection and a main deflection. The velocity of EB-mask stage and specimen-stage is also fed back to the deflection. The deflection control unit for the stage tracking has been made and the tracking function confirmed from the test memory of the unit. Using the unit, scanning writing patterns have been obtained with step and repeat stage mode.

Patterning Accuracy Estimation of Electron Beam Direct-Writing System EX-8D.

Self-diagnosis functions related to patterning accuracy are important techniques for developing, improving and maintaining electron beam exposure systems. An evaluation method of beam position deviation has been developed to reduce fluctuation of patterning accuracy. High-frequency beam position deviation was detected by scanning the beam on a W mark with subsequent fast fourier transform analysis. A magnetic field compensator has been developed to reduce low-frequency beam position deviations induced by ambient magnetic field changes. The beam position deviations of high- and low-frequency have been restricted to about 17 nm (3σ). A mark stand, which carries a height-changeable mechanism, was developed to calibrate the beam deflection accuracy depending on the Z direction. By applying the above diagnostic function, a main frame stitching accuracy of 32 nm has been achieved with short turnaround time.