GB1361804A - Alignment of members to electron beams - Google Patents

Abstract

1361804 Positioning electron beams WESTINGHOUSE ELECTRIC CORP 16 Sept 1971 [6 Oct 1970] 43302/71 Heading H4D A plurality of areas on the surface of a silicon semi-conductor wafer 32, Fig. 1, are to be electron beam worked by respective electron beams. Apparatus is provided for exactly and repeatedly aligning the electron beams on the areas to be worked. Two alignment electron beams, produced by the photocathode 40 producing the working beams are roughly aligned with respective conductive areas 72, 74, Fig. 2, having the same cross-sections as the beams and positioned in diametrically opposed hollows 64, 68 on the peripheral surface of the wafer 32. X and Y deflection circuits in coils 56 and 58 move the beams until maximum current is detected for the areas 72, 74 whence exact alignment is achieved. The photo-cathode and wafer and their mounting means are enclosed in a vacuum chamber. Ultra-violet light from source 50 is used to illuminate the photocathode comprising a quartz base 40, ultraviolet opaque areas 42 and electron emitting areas 44 of palladium or gold exposed to the ultra-violet. The electron beam emitted by areas 44 are focused on the wafer by coils 54 and - 10,000 V. bias 46. The alignment beam may be two selected ones of these beams, or source 50 may be covered apart from two areas, or a light guide may convey the ultra-violet from a source to an area 44. Wafer 52 is roughly positioned by stops 61, 62, 63, 65. The alignment beam 92, Fig. 4, for area 72 is first used for X direction beam deflection wherein the D.C. component in the output 87, Fig. 8, varies as shown at Fig. 4B, the maximum at O indicating when alignment in the X-direction has been achieved. A more exact measurement is enabled by imposing a small component of circular oscillation on the beam deflection by means of orthogonal sinusoids from oscillator 108 fed to the amplitude modulators 126, 130 in the deflection feed paths. Such oscillations give rise to an A.C. component in the output 87, having a phase reversal at the alignment point. This is detected by phase detector 106. The procedure is repeated for deflection in the Y-direction. The deflection correction signals are produced by integrating the outputs of the detector and are then modulated. The beam for area 74 is now used and the same method used to swing the beam in an arc about beam 92 until a maximum output of area 74 is detected and the alignment beams are angularly aligned. Detection of alignment causes detector 156 to stop oscillator 108 and, via delay 166, causes the main or working electron beams to be included. Various shapes of areas 72, 74 and corresponding crosssection of beams are shown, Figs. 5, 6, 7 (all not shown) together with the variation of their output.