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Throughput Enhancement of Scanning E-Beam Systems through Variation in Deflection Velocity

IP.com Disclosure Number: IPCOM000048258D
Original Publication Date: 1982-Jan-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 3 page(s) / 32K

Publishing Venue

IBM

Related People

Kern, D: AUTHOR [+2]

Abstract

Higher throughput can be achieved in a scanning E-beam system having variations in deflection amplitudes by causing each deflection cycle to be made in the same amount of time even though deflection velocity thereby varies. Constant exposure dosage may still be maintained by using a pulsed E-beam and suitably varying the repetition rate or duty cycle.

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Throughput Enhancement of Scanning E-Beam Systems through Variation in Deflection Velocity

Higher throughput can be achieved in a scanning E-beam system having variations in deflection amplitudes by causing each deflection cycle to be made in the same amount of time even though deflection velocity thereby varies. Constant exposure dosage may still be maintained by using a pulsed E-beam and suitably varying the repetition rate or duty cycle.

In a scanning E-beam system having constant beam deflection velocity, throughput is limited by the speed of the digital-to-analog (D/A) converter, the bandwidth of the deflection amplifiers and the resonance of the deflection coil itself. Fig. 1 illustrates an exemplary pattern which may be scanned as shown by the arrows. Deflection amplitude thus varies. Fig. 2 shows the corresponding deflection current as a function of time for a constant deflection velocity system. Constant deflection velocity means that the rising and falling parts of each triangular waveform have the same slope, as shown. As a result of this constraint variation in deflection amplitude also becomes a variation in time duration of each deflection cycle. The large deflections 10, 16 thus correspond with triangular waveforms having a time duration 4T, while the small deflection 14 corresponds with a triangular waveform having a time duration T.

The bandwidth required for a deflection amplifier to drive a coil with a triangular waveform is inversely related to the time duration of the triangular waveform. A triangular waveform will be produced without too severe distortion if the fundamental, the third harmonic and the fifth harmonic are passed. Thus, a triangular waveform of period T Fig. 2, waveform 14) requires a bandwidth of about 5/T. A triangular waveform of period 4T (Fig. 2, waveforms 10,
16) requires a bandwidth of of about 5/4T. It can be readily seen that the shortest time duration triangular waveform makes the highest demands upon the deflection system performance. For any physical system, the bandwi...