GB1174727A - A Method of Fabricating a Memory Device - Google Patents

Abstract

1,174,727. Read-only stores. INTERNATIONAL BUSINESS MACHINES CORP. 17 July, 1968 [17 Aug., 1967], No. 34106/68. Heading G4A. [Also in Division H1] A method of making a memory device comprises the steps of depositing a first plurality of substantially parallel metallic lines on a substrate, applying an insulating coating over the lines, removing portions of the coating at selected points over selected ones of the lines so as to define a pattern of stored information, and applying a second plurality of substantially parallel metallic lines over the coating, the second plurality of lines crossing the first and being connected to them at the points where the coating was removed. A matrix read-only data store having conductive connections between selected row and column lines is made by the following steps: (1) a one-micron metal layer (e.g. aluminium) is evaporated on to a quartz, silicon or ceramic substrate, then covered with a half-micron layer of (positive or negative) photoresist (insulator) using spinning to distribute the photoresist, (2) the photoresist is exposed photographically through a mask or using an electron beam instead of light, then developed, (3) etching using NaOH solution leaves parallel metallic column lines on the substrate, (4) a layer of positive photoresist is coated over the side of the substrate bearing the column lines including over the column lines, exposed at selected points over the column lines using light or an electron beam, developed and etched to have holes at the exposed points, (5) another metal layer is evaporated all over the last layer of photoresist, inter alia filling the holes left by the etching of that layer, (6) another coating of photoresist is applied, exposed through a mask, and etched to leave parallel metallic row lines perpendicular to the column lines and connected to them by metal at selected rowcolumn cross-overs. The connections between row and column lines may be of a different higher-resistivity metal (e.g. chromium) than the lines themselves. In this case, step (5) uses the higherresistivity metal and is followed by etching to remove all this metal except that in the holes, then another layer of the first metal is deposited, followed by step (6).