Patent GB-1480561-A (GB)
Title: Controlling the movement of a beam of charged particles
IPC: H01J37/304
Filed: 1975-01-08
Abstract: 1480561 Automatic control of particle beams INTERNATIONAL BUSINESS MACHINES CORP 8 Jan 1975 [28 Jan 1974] 817/75 Heading G3N In the use of a beam of charged particles {electrons}applied to a target, the latter being provided with reference markings 42 delineating four sided fields 40, the deviation of the markings for one field from their assumed positions as determined by control 17-19 is determined, and, on the basis of disclosed algebraic analysis, a set of parameters, determining the displacement and distortion of the actual field with respect to the assumed field, are evaluated and used so that, for each beam position in the assumed field, a correction is applied to define a corresponding position in the actual field, the correction of the assumed marking positions being their actual positions. The target may be a semi-conductor wafer, the beam being used to write a pattern on an electroresist, or on a silicon dioxide layer to enhance its etch rating, such that a single pattern may encompass a plurality of fields, or patterns on several levels may be written on one field, the correction ensuring correct registration. The pattern data from computer 19 is used to cause the electron beam 11 to be scanned, in accordance with the assumed field, (50), Fig. 3 (not shown) by magnetic deflection coils 23-26, voltages proportional to the instantaneous deflection currents being passed on lines 55, 56 to the correction circuit, Fig. 2 receiving also the determined values of the parameters for the field being scanned, the circuit calculating corresponding instantaneous deflection voltages which are applied to plates 31- 34 correcting the beam deflection for each point of the field from the assumed to the actual field (51, Fig. 3). The parameters A-H, Fig. 2 are received by the correction circuit in digital form, to be processed in multiplying, and normal d/a converters 58, 59, 62-67, Fig. 2. The correction allows for translation, magnification, rotation and/ or trapezoidal error in the field. A further electrostatic circuit, Fig. 7 (not shown) may be used in conjunction with the scan; which may be a raster, or with alternate X scans being in opposed senses; to provide corrections to ensure linearity, or a steady beam offset fed in via d/a converter (125). Magnetic deflection circuit, Fig. 6 (not shown). In accordance with digital input from control(18), or selected combination of the positive, and negative constant current sources (70-75) may be coupled to integrator (77, 84) providing a scanning waveform corrected for linearity by circuitry (85), and an auxiliary circuit receiving data from the control (18). Upon beam reversal at the end of a line, circuit (98, 95, 96) is active to ensure that the beam attains an end point determined by the input to d/a converter (96), an error signal from amplifier (95) controlling integrator (77, 84) at this time. Each marking, Fig. 5 (not shown), comprises orthogonal rows (43, 44) of depressions or raised portions, detected by the electron beam. The beam may be used to prepare engineering drawings on a CRT, or for electron beam welding or cutting, or for forming a mask.