Patent GB-1322034-A (GB)
Title: Production of precisely located altered surface areas on substrates by electron irradiation
IPC: F15C5/00
Filed: 1970-10-19
Abstract: 1322034 Electron beam irradiation apparatus; semi-conductor devices WESTINGHOUSE ELECTRIC CORP 19 Oct 1970 [24 Oct 1969] 49546/70 Headings H1D and H1K [Also in Division G3] In the manufacture of integrated circuits by exposure of a resist-coated silicon wafer to an electron beam, a photo-emissive cathode is prepared with emissive areas arranged in the desired exposure pattern, and the wafer is exposed to photo-electrons emitted from the cathode. In Fig. 6 the cathode 62 and wafer 70 are disposed at opposite ends of a spacer tube 66. The support 90 for the wafer is rotatable and translatable in two directions by means of motors to position it within 1 mil. or even 1 micron of a required position relative to the cathode, and deflection coils 46 and 48 allow the electron pattern to be aligned more precisely. The wafer should be provided with an alignment mark to facilitate these adjustments. The cathode may be provided with similar adjusting means and is disposed adjacent an ultra-violet lamp 10 which causes it to emit photo-electrons which are focused by means of a coil 44; the spiral path of the electrons preferably describes one complete rotation in passing from the cathode to the wafer. Vacuum locks may be provided for passing cathodes and wafers into the irradiation apparatus (Fig. 5, not shown) and a juke-box arrangement may be provided whereby selected ones of a number of cathodes and wafers may be placed in operative positions. After exposure and processing, a wafer may be returned for further exposure to a different pattern from a different cathode, and so on as often as required. The electron-resist may be negative acting, such as polyacrylamide with a molecular weight of 4À7 x 10<SP>7</SP>, or positive acting, such as polymethylmethacrylate with a molecular weight of over 10<SP>5</SP>. Inorganic materials such as silicon dioxide or silicon nitride (Si 3 N 4 ) are also suitable as exposure to an electron beam renders them more soluble to an etchant such as buffered hydrofluoric acid.  Cathode processing.-A substrate disc of quartz, sapphire or lithium fluoride is coated with a 600  layer of titanium which is slightly oxidized and coated with an electron resist. The disc is inserted in an electron beam apparatus which is controlled, either directly by a computer or by a magnetic tape produced from a computer, so that an area 80 mils square is exposed in a desired pattern corresponding to the integrated circuit to be produced. The disc is then moved 100 mils. in one direction and the process repeated, and so on until the whole disc has been exposed. After developing, the exposed titanium areas are etched away, the remaining electron resist is removed, and the titanium is fully oxidized in air at 400 C. to produce a patterned layer 1000  thick which is opaque to ultra-violet. If desired a protective layer of silica or ultra-violet transmissive glass may be sputtered over the titanium dioxide layer, and a 10 to 40  layer of palladium or gold is sputtered on to provide the photoemissive layer. Since the cathode deteriorates with use a master cathode may be used to prepare duplicates which are used to process the integrated circuits.