Radiant energy – With charged particle beam deflection or focussing – Magnetic lens
Patent
1985-06-28
1987-06-23
Anderson, Bruce C.
Radiant energy
With charged particle beam deflection or focussing
Magnetic lens
250307, 324 713, G01N 2700
Patent
active
046755284
ABSTRACT:
The technique of measuring the spotsize and edgewidth of an electron beam by incrementally scanning the beam through discrete scan locations across a sharp edge is improved by processing the resulting beam current signals directly rather than the differentiated beam current signal. A linear regression is performed on beam current data points expected to fall in the linear portion of the beam current versus beam position characteristic in order to provide a linear approximation of the overall characteristic. Extrapolation of the linear function to its intersections with the maximum (I.sub.1) and minimum (I.sub.0) beam current levels yields corresponding beam positions Z.sub.B and Z.sub.A, such that (Z.sub.B -Z.sub.A) is a measure of spotsize in the scan direction. Edgewidth between the twelve and eighty-eight percent amplitude levels is obtained by locating measured beam currents at incremental scan locations on both sides of beam positions Z.sub.A and Z.sub.B, and interpolating to find the actual beam currents I.sub.A and I.sub.B at these positions. Edgewidths D.sub.A and D.sub.B are computed as D.sub.A =4.sqroot..pi.(Z.sub.B -Z.sub.A)(I.sub.A -I.sub.0)(I.sub.1 -I.sub.0) and D.sub.B =4.sqroot..pi.(Z.sub.B -Z.sub.A)(I.sub.1 -I.sub.B)(I.sub.1 -I.sub.0). In the case of a square beam with rounded corners, spotsize (i.e., side of square) is measured by a diagonal incremental scan and determination, by interpolation, of the beam positions Z.sub.C and Z.sub.D at which the beam current is I.sub.C =I.sub.0 +19(I.sub.1 -I.sub.0)/64 and I.sub.D =I.sub.0 +45(I.sub.1 -I.sub.0)/64. The spotsize is then computed from the formula 3.01816 (Z.sub.C -Z.sub.D).
REFERENCES:
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patent: 4086491 (1978-04-01), Vaughan
patent: 4336597 (1982-06-01), Okubo et al.
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Groves et al., "Electron-Beam Broadening Effects Caused by Discreteness of Space Charge," J Vac Sci Tech, 10(6), Nov./Dec. 79.
Dalterio Michael J.
Fishbein Marvin
Harte Kenneth J.
Langner Guenther O.
Anderson Bruce C.
Control Data Corporation
Guss Paul A.
Helzer Charles W.
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