Laser activated polysilicon connections for redundancy

US4561906A · kind A · utility

Assignee

• Nortel Networks Limited · CA

Inventors

• Iain D. Calder · Gatineau, CA
• Hussein M. Naguib · Ottawa, CA

Key dates

• Filing date: Oct 24, 1983
• Grant date: Dec 31, 1985
• Expiry date: Oct 24, 2003

Classification

• Technology area (CPC Y): Emerging Cross-Sectional Technologies
• CPC primary: Y10S148/093
• WIPO field: Semiconductors
• WIPO sector: Electrical engineering

Abstract

An integrated circuit is fabricated with some redundant capacity by forming potential electrically conducting links which can subsequently be made electrically when extra circuit capacity is required. Field oxide is grown on a silicon substrate and then a layer of polysilicon deposited over the oxide. At the redundancy sites where electrical connections may subsequently be made, an anti-reflective silicon nitride coating is deposited and photodefined. The areas of this coating are used as masks in order to diffuse dopant into the polysilicon at parts of the polysilicon laterally adjacent the redundancy sites. When later it is necessary to bring spare capacity into the circuit the complete circuit is scanned with a continuous wave laser. The laser melts the polysilicon under the nitride mask permitting the dopant to diffuse from the adjacent parts of the polysilicon and so form a conducting link. However under parts of the polysilicon not covered by an anti-reflective coating the polysilicon is not melted by the laser beam and so its conductivity remains unchanged. The fabrication process is self-aligned since the intrinsic or undoped region of the polysilicon is the same as the reg…