ENCODING OF READ ONLY MEMORY BY LASER VAPORIZATION

• US 3,740,523 A
• Filed: 12/30/1971
• Issued: 06/19/1973
• Est. Priority Date: 12/30/1971
• Status: Expired due to Term

• Current Assignee: Alan William Fulton, Melvin Irwin Cohen
• Original Assignee: Alan William Fulton, Melvin Irwin Cohen
• Inventors: Cohen, Melvin Irwin, Fulton, Alan William
• Primary Examiner(s): Truhe, J. V.
• Assistant Examiner(s): Montanye, George A.
• Application Number:
  US05/214,343
• Time in Patent Office: 537 Days
• Field of Search: 219/121L,121FB 156/2,17 331/94SA
• US Class Current: 219/121.69
• CPC Class Codes: G11C 17/08 using semiconductor devices, e.g. bipolar elements G11C17/06, G11C17/14 take precedence
• CPC Class Codes: H01L 21/00 Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
• CPC Class Codes: H01L 23/4822 Beam leads
• CPC Class Codes: H01L 23/5258 the change of state resulting from the use of an external beam, e.g. laser beam or ion beam
• CPC Class Codes: H01L 24/01 Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/10253 Silicon [Si]
• CPC Class Codes: H01L 2924/12042 LASER
• CPC Class Codes: H01L 2924/14 Integrated circuits

Abstract

A beam-lead silicon integrated circuit read-only memory is made in a conventional manner by forming an array of transistors on a silicon substrate, except that the gold portion of one conductive lead to each memory cell is severed, as by gold etching. Conductive connection to each memory cell is, however, maintained by the platinum-titanium intermediate layer that underlays the gold conductor. The array is permanently encoded by selectively vaporizing, with a laser beam, the exposed platinum layer of certain memory cells. This technique permits laser encoding of a beam-lead silicon integrated circuit with a sufficiently low power beam as not to endanger the silicon substrate.

Claims

2. A method for producing a read-only memory by beam-lead technology comprising the steps of:

forming a plurality of memory cells in a silicon substrate;

forming metal conductors extending to each memory cell comprising the steps of first, forming an insulative layer of silicon dioxide of a major part of the substrate, second, forming a thin layer of titanium on the insulative layer, third, forming a thin layer of platinum on the titanium layer, and fourth, forming over the platinum layer a layer of gold that is relatively thick with respeCt to the platinum and titanium layers, thereby to provide structural support in accordance with the principles of beam-lead technology;

forming a window in the gold portion of each conductor, thereby to expose a platinum-titanium bridge conductor in each conductor; and

coding the read-only memory comprising the step of vaporizing selected platinum-titanium bridge conductors by directing a focused laser beam upon said selected conductors, the intensity of said focused beam being sufficiently high to vaporize the platinum-titanium bridge conductor, but being insufficiently high to vaporize the gold portion or to damage the silicon substrate.

3. The method of claim 2 wherein:

the intensity of said focused beam is less than 0.37 X 108 watts per square centimeter.

4. The method of claim 3 wherein:

the wavelength of the focused laser beam is on the order of 1.06 micrometers.