Electronic digital logic circuitry – Multifunctional or programmable – Array
Reexamination Certificate
2002-03-20
2003-12-30
Le, Don (Department: 2819)
Electronic digital logic circuitry
Multifunctional or programmable
Array
C326S044000, C327S525000
Reexamination Certificate
active
06670824
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to integrated circuits, and more particularly to fuses and diodes.
BACKGROUND OF THE INVENTION
Some CMOS integrated circuit processes have tried to form a one-time programmable element called a “poly fuse.” A poly fuse may comprise a Co, Ti or other metal layer formed on a polysilicon layer, such as a LPCVD poly film. The LPCVD poly film may be doped/implanted with a contaminant to lower the bulk resistivity. The metal layer is silicided with some of the poly layer, and the result is a silicided polysilicon layer (also called a “polysilicide”) over an unsilicided polysilicon layer.
Some processes “program” a poly fuse by passing a sufficiently high current through the silicided polysilicon (fuse material). The current heats the silicide such that the temperature rises above a certain critical temperature where the silicide changes phase and increases in resistance. The change of phase may increase the density and be accompanied by a clustering or agglomeration of the silicided doped polysilicon molecules, which can form voids in the silicide layer, and thus increase the resistance substantially. The phase change may reduce one or more geometric dimensions of the silicided polysilicon. In some cases, the reduced dimensions may cause the silicided polysilicon film to separate at or physically move away from a junction of highest heat dissipation, which can be ascertained by post-processing physical analysis. The amount of silicide agglomeration may vary from fuse to fuse. The process of applying current to change the silicided polysilicon from a relatively low resistance state to a relatively high resistance state may be referred to as “programming” the fuse.
SUMMARY OF THE INVENTION
The invention recognizes that a standard CMOS integrated circuit process does not have the capability of creating diodes that are sufficiently isolated from the substrate, unless additional mask and implant steps are added. The invention also recognizes that one-time programmable elements, such as silicided poly fuses, may be used as programmable elements in a wide range of integrated circuit applications.
An integrated polysilicon fuse and diode circuit and methods of making the same are provided in accordance with the present invention. The integrated polysilicon fuse and diode combination described herein may be implemented in a programmable cross point fuse array. The integrated poly fuse and diode may advantageously be used in a nonvolatile, random access memory (RAM) cell/element. The poly fuse and diode described herein are less expensive to manufacture than other types of nonvolatile memory elements, such as FERAM and MRAM, which may require adding process steps to a standard CMOS process. As an example, the poly fuse and diode may be used to store a serial or part number of a device, such as a computer mouse.
Compared to other types of diodes that may be used in a memory array with fuses as the memory element, the polysilicon diode described herein may be isolated from a substrate and from other devices, use less area on a substrate, and cost less to manufacture.
REFERENCES:
patent: 5536968 (1996-07-01), Crafts et al.
patent: 5780918 (1998-07-01), Aoki
patent: 6410367 (2002-06-01), Marr et al.
patent: 6452248 (2002-09-01), Le
Alexander Kalnitsky, Irfan Saadat, Albert Bergemont and Pascale Francis, “CoSi2 Integrated fuses on poly silicon for low voltage 0.18 &mgr;m CMOS Application”, National Semiconductor, Santa Clara, CA 95052, 0-7803-5413-399, (1999), 4 pages.
Mohsen Alavi, Mark Bohr, Jeff Hicks, Martin Denham, Allen Cassens, Dave Douglas, Min-Chun Tsai, “A PROM Element Based on Salicide Agglomeration of Poly Fuses in a CMOS Logic Process”, IEEE International Electron Devices Meeting (Dec. '97), 4 pages.
Jerome B. Lasky, James S. Nakos, Orison J. Cain, and Peter J. Geiss, “Comparison of Transformation to Low-Resistivity Phase and Agglomeration of TiSi2 and CoSi2”, IEEE Transactions on Electron Devices, vol. 38, No. 2, Feb. 1991, pp. 262-269.
Feng Chris
Goodbread Jon
Johnson Molly
Stanback John
Agilent Technologie,s Inc.
Le Don
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