Patent GB-1273082-A (GB)
Title: Apparatus and method utilizable in forming metal grids
Inventor: GARVIN HUGH LESLIE
IPC: H01J9/14
Filed: 1970-04-30
Abstract: 1,273,082. Making storage tube grids. HUGHES AIRCRAFT CO. April 30, 1970 [May 1, 1969], No.20917/70. Headings G2A and G2C. A metal grid for use in an electronic storage tube is made by a method generally comprising scribing a single slit in an aluminium coating on a transparent sheet, and moving the slit to form a series of consecutive exposures on a photosensitive sheet, such movement being controlled by an interferometer. Fig. 1 shows an apparatus for carrying out the process. The photo-mask 10 is a glass bar coated with aluminium, in which coating a slit 5 microns wide and several inches long has been very precisely scribed. This is secured, slit downwards, to the underside of an opaque shield 40 having a slit 8a aligned with the photo-mask slit. Shield 40 is fixed to a carriage 20, 22 which can slide between guide blocks 24, the whole apparatus being mounted on a table. The carriage is driven from a motor 44. Adjustably mounted above the slit 8a is a high intensity xenon arc lamp 30. This produces pulsed flashes of light which are controlled by an interferometer arrangement sensing the movement of the carriage. Light from a laser source 52 is reflected by mirrors 54, 56 into a housing 16 containing a beam-splitter. Part of the beam impinges on a stationary mirror in housing 16, and part impinges on a mirror 60 on the moving carriage. These two beams are reflected back to the housing 16, where they are recombined and directed to a photo-sensitive element forming part of an interference fringe detector 62, which fringes depend on the varying length of the reflected beam from mirror 60 as the carriage moves. The detector converts this variation in length into a sinusoidally varying current. This passes through a counter 64 to a circuit 66 for triggering a discharge pulse in the lamp 30, as for example 1000 flashes per inch of carriage travel. The photographic plate 34 having an emulsion film 36 on its upper surface is positioned on a stationary platform 14 supported on housing 16. Photo-mask 10 is caused to traverse across the film 36 with a layer of microscopic immersion oil 41 between them, so that a succession of sharp images of slit 8, uniformly spaced to a high degree of accuracy, is produced on the film. After development, these images show up as a series of opaque emulsion lines 68. This is inverted in contact with a submaster blank comprising a glass substrate carrying a metal layer covered with a photo-resist film, Fig. 4a (not shown). This is exposed to ultraviolet light through the transparent areas between the lines 68. The exposed areas are polymerized and hardened, and the non-hardened parts removed by a solvent. Thus a series of slits corresponding to the lines 68 are formed in the photo-resist. These slits are extended through the metal layer down to the glass substrate itself by ion beam micro-machining. The submaster blank 70a is now placed in contact with a target blank 90 having a metal layer 94 covered by a film of photo-resist material 96. This is exposed to ultraviolet light through the slits 82 of the submaster 70a, which is then rotated through 90 degrees and a further exposure made. After the unexposed parts have been removed by a solvent, an array of two sets of orthogonally intersecting hardened strips 98 remain. Removal of the exposed metal squares leaves a metal grid underlying the photo-resist grid. Removal of the resist leaves the grid itself, Fig. 5(d).