| 摘要 |
<p>The present invention relates to bi-directional raster scanning ('serpentine scanning') for an electron beam lithography system. Improved circuit components are described for generating the true triangular waveform required in bi-directional scanning. The circuitry of the present invention provides control of signal amplitude, frequency and phase to better than 1 ppm by making use of signal generation circuitry described pursuant to the present invention. A series of coarse and fine tuning delay adjustments pursuant to the present invention accommodate a variety of operating conditions. Another embodiment of the present invention relates to an optimization of the data path hardware for bi-directional scanning, including isolating a section of the data path hardware specifically to provide calibration scans. The delay circuit built into the data preparation hardware helps compensate for delays caused by finite bandwidth in the analogue drivers. A two-level beam deflection is described in which fast, low-voltage electrostatic deflectors are employed (preferably one for each scan direction) in conjunction with a slower magnetic beam deflector. The two level deflection system pursuant to the present invention allows for controlling the retroscan signal to match the polarity of the main magnetic deflection signal.</p> |
