The critical-dimension scanning electron microscope (CD-SEM) is an essential tool for semiconductor fabrication process control because of its high resolution and high precision. However, in ArF lithography, the CD of resist changes during CD-SEM measurement due to shrinkage caused by the electron beam irradiation. This shrinkage can be reduced by measurement parameters; however, there is a trade-off relationship between shrinkage and precision. Thus, measuring the CD of an ArF resist pattern precisely with small shrinkage is difficult. The authors propose an optimization method using the Taguchi method. Four measurement parameters were chosen as control factors for an L18 orthogonal array: probe current, acceleration voltage, horizontal length of field-of-view, and number of image acquisitions. As a result, high prediction accuracy was obtained that is smaller than 0.2 nm for shrinkage and 0.1 nm for precision. Moreover, an optimum measurement condition that achieves 0.28 nm shrinkage and 0.37 nm precision was also obtained. Thus, the proposed method was demonstrated as a promising method to optimize CD measurement parameters.

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Fundamental characteristics of beam extraction from a Hall-type accelerator working with permanent magnets were investigated. Ions were extracted by an axial electric field E(z) in a small annular plasma channel with a radial magnetic field B(r). Effects of discharge current and voltage, length of discharge channel, and gas flow rate were examined. It can deliver a large beam current density of more than 100 mA/cm(2) with low beam energy of 50 eV. By biasing an additional plasma chamber attached at the extraction area, the beam energy was controlled independently of the beam current.

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