Quicklogic Corporation

Quicklasic Corporation

Rajiv Jain

Mehul D Shroff

Andre N Stolmeijer

Kathryn E Gordon

Richard J Wong

An antifuse, which has a programmable material disposed between two conductive elements, is programmed using multiple current pulses of opposite polarity. The first pulse has a current that is insufficient to fully program the antifuse, i.e., produce a desired level of resistance. In one embodiment the first pulse is current limited. The first pulse advantageously drives a conductive filament from one conductive element through the antifuse material, which may be, e.g., amorphous silicon. The conductive filament from the first pulse, however, has a limited cross sectional area. A programming pulse having the same voltage with opposite polarity and a current with increased magnitude is used to drive material from the other conductive element into the antifuse material, which increases the cross sectional area of the conductive filament thereby reducing resistance. Additional programming pulses, as well as current limited pulses, may be used if desired. Programming an antifuse in accordance with the present invention results in an antifuse structure with a conductive filament that is in good contact with both conductive elements, which reduces resistance in the antifuse and increases yield. A programming circuitry is provided that includes a current source and a voltage clamp to program antifuses according the described method.

Method of programming an antifuse

A metal-to-metal conductive plug-type antifuse has a conductive plug disposed in an opening in an insulating layer. A programmable material feature (for example, amorphous silicon) overlies the conductive plug. A conductor involving a metal (for example, aluminum or copper) that migrates in the programmable material overlies the programmable material. To prevent migration of metal from the conductor into the programmable material when the antifuse is not programmed, the conductor has a layer of barrier metal between the metal that migrates and the programmable material. In some embodiments, there are two layers of barrier metal. An airbreak after formation of the first barrier metal layer improves the ability of the barrier metal to prevent diffusion between the programmable material and the overlying conductor. The airbreak may stuff grain boundaries in the upper surface of the first barrier metal and/or may cause the first barrier metal layer to have different grains and/or a different grain orientation than the overlaying second barrier metal layer. In some embodiments, a capping layer over the top surface of the programmable material protects the underlying programmable material during an ashing step when a mask used to etch the programmable material is removed. The capping layer and the programmable material form a capping layer/programmable material layer stack within the antifuse underneath the two barrier metal layers. The capping layer may also be made of a barrier metal and constitute an additional barrier.

Metal-to-metal antifuse having improved barrier layer

An antifuse is disposed between a first and second conductor. An insulating diffusion barrier (for example, silicon nitride) covers the sidewalls of the antifuse to inhibit contaminants (for example, copper, chlorine, fluorine, sodium, potassium, and moisture) from diffusing laterally into the antifuse from the interlayer dielectric, where a damascene copper conductor and/or a low-k dielectric is used. In a damascene antifuse structure, the insulating diffusion barrier layer covers an upper surface of the damascene conductor that is not covered by the antifuse. This insulating diffusion barrier layer inhibits copper from diffusing up into an interlayer dielectric and then diffusing laterally into the antifuse.

Metal-to-metal antifuse with non-conductive diffusion barrier

Method of forming a metal-to-metal antifuse with non-conductive diffusion barrier

A field programmable gate array has antifuses disposed over logic modules. Each of these antifuses includes a conductive plug and an overlaying region of programmable material (for example, amorphous silicon). To program one of these antifuses, an electric connection is formed through the programmable material to couple the conductive plug to a metal conductor that overlays the region of programmable material. The metal conductor includes a layer of a barrier metal to separate another metal of the conductor (for example, aluminum from an aluminum layer) from migrating into the programmable material when the antifuse is unprogrammed. In some embodiments, less than three percent of all antifuses of the field programmable gate array has a corner (from the top-down perspective) of the region of programmable material that is disposed (within lateral distance DIS of the conductive plug) underneath the metal conductor of that antifuse. In some embodiments, less than seventy-five percent of all antifuses of the field programmable gate array have an edge of the region of programmable material disposed (within lateral distance DIS of the conductive plug) underneath the metal conductor of that antifuse. Other antifuse structures and methods are also disclosed for preventing programmable material corners and/or edges from compromising yield and/or reliability of programmable devices.

Programmable device having antifuses without programmable material edges

A metal-to-metal conductive plug-type antifuise has a conductive plug disposed in an opening in an insulating layer. A programmable material feature (for example, amorphous silicon) overlies the conductive plug. A conductor involving a metal (for example, aluminum or copper) that migrates in the programmable material overlies the programmable material. To prevent migration of metal from the conductor into the programmable material when the antifuse is not programmed, the conductor has a layer of barrier metal between the metal that migrates and the programmable material. In some embodiments, there are two layers of barrier metal. An airbreak after formation of the first barrier metal layer improves the ability of the barrier metal to prevent diffusion between the programmable material and the overlying conductor. The airbreak may stuff grain boundaries in the upper surface of the first barrier metal and/or may cause the first barrier metal layer to have different grains and/or a different grain orientation than the overlaying second barrier metal layer. In some embodiments, a capping layer over the top surface of the programmable material protects the underlying programmable material during an ashing step when a mask used to etch the programmable material is removed. The capping layer and the programmable material form a capping layer/programmable material layer stack within the antifuse underneath the two barrier metal layers. The capping layer may also be made of a barrier metal and constitute an additional barrier.

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Palo Alto, CA, United States of America

Rajiv Jain