Laser coding of bipolar read-only memories

The application of a pulsed YAG laser beam to coding high-speed bipolar silicon integrated circuit read-only memories is discussed. Coding is accomplished by the selective vaporization of Ti-Pt links connecting the contact pads of each memory cell to Ti-Pt-Au bit lines. Vaporized link resistances of >10 9 ohms can be consistently obtained, with no melting of the adjacent gold patterns. Parameters that have been found to be relevant to the link vaporization process are described including the number of laser pulses per link, beam spot size, thickness of the gold metallization, and pulse energy.