Method for reducing resistance for programmed antifuse

• US 5,095,362 A
• Filed: 10/23/1990
• Issued: 03/10/1992
• Est. Priority Date: 10/23/1990
• Status: Expired due to Fees

• Current Assignee: Instant Circuit Corporation
• Original Assignee: Instant Circuit Corporation
• Inventors: Roesner, Bruce B.
• Primary Examiner(s): WOJCIECHOWICZ, EDWARD JOSEPH
• Application Number:
  US07/604,133
• Time in Patent Office: 504 Days
• Field of Search: 357/23.4, 357/23.6, 357/51, 365/100
• US Class Current: 257/330
• CPC Class Codes: G11C 17/16 using electrically-fusible links
• CPC Class Codes: H01L 23/5252 comprising anti-fuses, i.e. connections having their state changed from non-conductive to conductive
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00

Abstract

A Read-Only Memory is comprised of a plurality of memory cells. An antifuse film is disposed between and in contact with an underlying heavily N-doped word line layer and an overlying metallic address line layer. The word line is disposed on an insulating semiconductor substrate and is in contact with a surrounding oxide layer. The programmable material is irreversibly configured between the two resistivity states by application of a threshold voltage. The threshold voltage alters the electrical state of the programmable material only in the proximity of that portion of the programmable material to which the threshold voltage has been applied. The resistivity of the low resistivity state is selectively decreased by implanting nonactivated conductive dopants into film. These dopants are characterized by having a nonactivated state where the conduction of carriers in the film is not enhanced, and an activated state where the conduction of carriers in the film is enhanced. The dopants are configured from the nonactivated state into the activated state by application of the same threshold voltage that is applied across the antifuse film to program the material.

Claims

1. An improved semiconductor device comprising:

antifuse film of the type composed of semiconductor material having a first electrical state which is characterized by high electrical resistivity and a second electrical state which is characterized by low electrical resistivity, said material being electrically and permanently configured to said second electrical state from said first electrical state upon application of a voltage exceeding a predetermined threshold voltage applied across at least a portion of said material, only that portion being subjected to said threshold voltage being configured from said first state to said second state, the remaining portion of said material, which is not exposed to said threshold voltage, remaining in said first state; and

means for selectively decreasing the resistivity of said second electrical state of said portion of said material without decreasing the resistivity of said first electrical state before selective activation of said portion of said material to said second electrical state,

wherein said means for selectively decreasing resistivity comprises deliberately added nonactivated conductive dopants dispersed within said material, said dopants characterized by having a nonactivated state wherein said dopants do not enhance the conduction of carriers in said film, said dopants further characterized by having an activated state wherein said dopants enhance the conduction of carriers in said film, said dopants being configured from said nonactivated state into said activated state upon application of a threshold voltage being applied across a predetermined and selected portion of said material in which said dopants are disposed.

2. The improved antifuse film of claim 1 wherein said dopants are ion implanted.

3. The improved antifuse film of claim 2 wherein said dopants are selected from the group consisting of boron, phosphorous, and arsenic.

16. The device of claim 1 wherein said means for means for balancing forward and reverse programming voltage across said antifuse film comprises ion implanted dopants dispersed within a shallow upper interface portion of said material, conductivity type and dosage of said dopants being selected so that forward and reverse programming voltages are substantially balanced.

4. An antifuse film comprising:

semiconductor material having a first electrical state which is characterized by high electrical resistivity and a second electrical state which is characterized by low electrical resistivity, said material being electrically and permanently configured to said second electrical state from said first electrical state upon application of a voltage exceeding a predetermined threshold voltage applied across at least a portion of said material, only that portion being subjected to said threshold voltage being configured from said first state to said second state, the remaining portion of said material, which is not exposed to said threshold voltage, remaining in said first state; and

deliverately added nonactivated conductive dopants dispersed within said semiconductor material, said dopants characterized by having a nonactivated state wherein said dopants do not enhance the conduction of carriers in said film, said dopants further characterized by having an activated state wherein said dopants do enhance the conduction of carriers in said film, said dopants being configured from said nonactivated state into said activated state upon application of said threshold voltage being applied across a predetermined and selected portion of said material in which said dopants are disposed.

5. A method of reducing the electrical resistivity of a second electrical state of semiconductor material, said material having a first electrical state which is characterized by high electrical resistivity and said second electrical state being characterized by low electrical resistivity, said material being electrically and permanently configured to said second electrical state from said first electrical state upon application of a voltage exceeding a predetermined threshold voltage applied across at least a portion of said material, only that portion being subject to said threshold voltage being configured from said first state to said second state, the remaining portion of said material, which is not exposed to said threshold voltage, remaining in said first state, said method comprising the steps of:

implanting nonactivated conductive dopants into said material, said dopants characterized by having a nonactivated state wherein said dopants do not enhance the conduction of carriers in said film, said dopants further characterized by having an activated state wherein said dopants do enhance the conduction of carriers in said film, said dopants being configured from said nonactivated state into said activated state upon application of said threshold voltage being applied across a predetermined and selected portion of said material in which said dopants are disposed; and

applying said threshold voltage across said predetermined and selected portion of said material to activate a corresponding selected portion of said dopants implanted into said material.

6. The method of claim 5 wherein said step of implanting dopants comprises the step of ion implantation.

7. The method of claim 6 wherein said dopants are selected from the group consisting of boron, phosphorous and arsenic.

8. A method of creating an antifuse film composed of semiconductor material having a first electrical state which is characterized by high electrical resistivity and a second electrical state which is characterized by low electrical resistivity, said material being electrically and permanently configured to said second electrical state from said first electrical state upon application of a voltage exceeding a predetermined threshold voltage applied across at least a portion of said material, only that portion being subjected to said threshold voltage being configured from said first state to said second state, the remaining portion of said material, which is not exposed to said threshold voltage, remaining in said first state, comprising the steps of:

providing said material from essentially a single element semiconductor selected from a group of silicon, germanium, carbon and alpha-tin; and

implanting nonactivated conductive dopants into said material, said dopants characterized by having a nonactivated state wherein said dopants do not enhance the conduction of carriers in said film, said dopants further characterized by having an activated state wherein said dopants do enhance the conduction of carriers in said film, said dopants being configured from said nonactivated state into said activated state upon application of said threshold voltage being applied across a predetermined and selected portion of said material in which said dopants are disposed.

9. The method of claim 8 further comprising the step of

applying said threshold voltage across said predetermined and selected portion of said material to ohmically heat said portion to a predetermined degree to activate said dopants.

10. The method of claim 8 wherein said step of implanting dopants comprises the step of ion implantation.

11. The method of claim 10 wherein said dopants are selected from the group consisting of boron, phosphorous and arsenic.

12. An improved electrical programmable read-only memory of the type having:

a semiconductor substrate;

a plurality of conductive word lines disposed on said substrate;

an oxide layer of material disposed between said plurality of word lines and on said substrate;

a plurality of antifuse films each disposed on one of said plurality of word lines in electrical contact with said word line, said antifuse film composed of semiconductor material having a first electrical state which is characterized by high electrical resistivity and a second electrical state which is characterized by low electrical resistivity, said material being electrically and permanently configured to said second electrical state from said first electrical state upon application of a voltage exceeding a predetermined threshold voltage applied across at least a portion of said material, only that portion being subjected to said threshold voltage being configured from said first state to said second state, the remaining portion of said material, which is not exposed to said threshold voltage, remaining in said first state;

a plurality of conductive bit lines each disposed on one of said antifuse films and aligned at least with one of said word lines, wherein the improvement comprises;

nonactivated conductive dopants deliberately implanted and dispersed within said antifuse film, said dopants characterized by having a nonactivated state wherein said dopants do not enhance the conduction of carriers in said film, said dopants further characterized by having an activated state wherein said dopants do enhance the conduction of carriers in said film, said dopants being configured from said nonactivated state into said activated state upon application of said threshold voltage being applied across a predetermined and selected portion of said material in which said dopants are disposed.

13. The improved read-only memory of claim 12 wherein said dopants are selected from the group consisting of boron, phosphorous and arsenic.

14. An improved semiconductor device comprising:

antifuse film of the type composed of semiconductor material having a first electrical state which is characterized by high electrical resistivity and a second electrical state which is characterized by low electrical resistivity, said material being electrically and permanently configured to said second electrical state from said first electrical state upon application of a voltage exceeding a predetermined threshold voltage applied across at least a portion of said material, only that portion being subjected to said threshold voltage being configured from said first state to said second state, the remaining portion of said material, which is not exposed to said threshold voltage, remaining in said first state; and

means for balancing forward and reverse programming voltage across said antifuse film comprising ion implanted dopants dispersed within a shallow upper interface portion of said material, conductivity type and dosage of said dopants being selected so that forward and reverse programming voltages are substantially balanced.

15. The device of claim 14 further comprising:

means for selectively decreasing the resistivity of said second electrical state of said portion of said material.

17. An improvement in a method of balancing forward and reverse programming voltages across a semiconductor material, said material having a first electrical state which is characterized by high electrical resistivity and said second electrical state being characterized by low electrical resistivity, said material being electrically and permanently configured to said second electrical state from said first electrical state upon application of a voltage exceeding a predetermined threshold voltage applied across at least a portion of said material, only that portion being subject to said threshold voltage being configured from said first state to said second state, the remaining portion of said material, which is not exposed to said threshold voltage, remaining in said first state, said improvement comprising the step of:

shallowly ion implanting dopants into an upper interface portion of said material to form a high dopant gradient to produce an electric field in said interface portion, said dopants characterized by a conductivity type and dopant gradient so that of forward and reverse programming threshold voltages of said semiconductor material are alterable, including being set substantially equal absolute magnitudes, regardless of direction of voltage across said material.

18. The improvement of claim 17 further comprising the steps of:

implanting nonactivated conductive dopants into said material, said dopants characterized by having a nonactivated state wherein said dopants do not enhance the conduction of carriers in said film, said dopants further characterized by having an activated state wherein said dopants do enhance the conduction of carriers in said film, said dopants being configured from said nonactivated state into said activated state upon application of said threshold voltage being applied across a predetermined and selected portion of said material in which said dopants are disposed; and

applying said threshold voltage across said predetermined and selected portion of said material to activate a corresponding selected portion of said dopants implanted into said material.