Method and apparatus for focusing a laser beam on an integrated circuit

Abstract

A laser beam (38) is focused on the surface of a semiconductor substrate (10) by translating an objective lens (70) along the path of the laser beam (38). The substrate (10) is fabricated to have a region (12) of an opposite conductivity type and to have a barrier layer (18) to the laser beam (38). An opening (16) is provided in the barrier layer (18) to permit the laser beam (38) to strike the substrate (10). A voltage source (24) and resistance (26) are connected in series between the substrate (10) and the region (12) to form a reverse biased diode junction. When the laser beam (38) strikes the substrate (10) charge carriers (42) are generated to produce a current through the resistor (26). The current flow through the circuit is measured by a control circuit (84) which drives a mechanism (72, 74, 76, 78, 80) to position the objective lens (70) such that the focus point of the laser beam (38) is positioned at the surface of the substrate (10). The maximum current flow through the PN junction is produced when the maximum intensity of laser energy is directed to the substrate (10). The primary application of the focusing apparatus disclosed herein is for burning out links to substitute redundant circuit elements for defective elements in an integrated circuit.

Dependencies are inferred from the claim text.