Patent Grant
9058887
This application is related to co-pending U.S. patent application Ser. No. 10/908,245, filed on May 4, 2005, which is hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to fuses included within semiconductor structures. More particularly, the present invention provides an electrical fuse that can be reprogrammed using a reverse electro-migration effect, and associated design structure.
2. Related Art
As is known in the art, many modern semiconductor integrated circuits include fuses to protect sensitive parts during the manufacturing process, and for the activation of redundant circuits, such as redundant memory cells in the case of Dynamic Random Access Memories (DRAMs). There are typically two types of fuses, a laser-blowable fuse, and an electrically (e.g., current) blowable-fuse. Electrically blowable fuses provide an advantage over laser-blowable fuses in terms of size.
With laser blowable fuses, the fuses are typically formed at or near the surface of the integrated circuit. A laser beam striking the fuse material renders the fuse non-conductive, thereby inhibiting current from flowing through the fuse. Although laser blowable fuses are relatively simple to fabricate, there are disadvantages associated with them. For example, laser blowable fuses tend to be surface oriented, which places a limitation on the design of the integrated circuit. Further, laser blowable fuses tend to occupy a large amount of space on the surface of an integrated circuit, since adjacent fuses or devices must not be placed too close to the fuse or risk being inadvertently damaged by the laser beam during the fuse blowing operation.
Electrically blowable fuses, on the other hand, do not have to be placed at or near the surface of the an integrated circuit. Accordingly, they give designers greater latitude in fuse placement. In general, electrically blowable fuses tend to be smaller than laser blowable fuses, which render them highly suitable for use in modern high density integrated circuits. Further, electrically blowable fuses have a high programming speed compared to conventional laser blowable fuses.
Various means have been used in the past to blow electrically blowable fuses. One recently used technique for opening the connection at the fuse employs the electro-migration effect, which has long been identified as a major metal failure mechanism. Electro-migration is the process whereby the ions of a metal conductor move in response to the passage of a high density current flow though the conductor. Such motion can lead to the formation of “voids” in the conductor, which can grow to a size where the conductor is unable to pass current. One can take advantage of the electro-migration effect to selectively open up metal connections (e.g., fuses) at desired locations within an integrated circuit.
One limitation of such electrically blowable fuses is they can be programmed only once (e.g., from a state “1” (conducting) to a state “0” (non-conducting)). In other words, once an electrically blowable fuse has been opened using the electro-migration effect it can not be closed again. Therefore, to reprogram or reconfigure an integrated circuit, redundant electrically blowable fuses and complicated supporting circuitry would be necessary.
Studies have been made regarding the healing of electro-migration related damage using a current reversal method. Evidence of such healing has been reported by E. Castano, et al, in a paper entitled “In Situ Observation of DC and AC Electro-migration in Passivated Al Lines,” Applied Physics Letters, Volume 59, Issue 1, Jul. 1, 1991, pp. 129-131. In this paper, it was shown that void size could be decreased by applying current stress in a reverse direction. As depicted in
The present invention provides an electrical fuse that can be reprogrammed using a reverse electro-migration effect, and associated design structure. Electro-migration is used to open a connection in the electrical fuse, while reverse electro-migration is used to subsequently close the opened connection. A programming/reprogramming circuit is provided to enable the use of such a reprogrammable electrical fuse.
An aspect of the present invention is directed to a design structure embodied in a machine readable medium used in a design flow process, the design structure comprising a fuse system, the fuse system comprising: an electrically blowable fuse; circuitry for programming the electrically blowable fuse using an electro-migration effect; circuitry for reprogramming the electrically blowable fuse using a reverse electro-migration effect; a reference resistance provided by a portion of the electrically blowable fuse; and circuitry for determining a state of the electrically blowable fuse by comparing a resistance of the electrically blowable fuse to the reference resistance.
Another aspect of the present invention is directed to a design structure embodied in a machine readable medium used in a design flow process, the design structure comprising a fuse system, the a fuse system comprising: means for programming an electrically blowable fuse using an electro-migration effect; means for reprogramming the electrically blowable fuse using a reverse electro-migration effect; means for providing a reference resistance using a portion of the electrically blowable fuse; and means for determining a state of the electrically blowable fuse by comparing a resistance of the electrically blowable fuse to the reference resistance.
Another aspect of the present invention is directed to a design structure embodied in a machine readable medium used in a design flow process, the design structure comprising an integrated circuit, the integrated circuit comprising a fuse system, the fuse system comprising: an electrically blowable fuse; circuitry for programming the electrically blowable fuse using an electro-migration effect; circuitry for reprogramming the electrically blowable fuse using a reverse electro-migration effect; a reference resistance provided by a portion of the electrically blowable fuse; and circuitry for determining a state of the electrically blowable fuse by comparing a resistance of the electrically blowable fuse to the reference resistance.
These and other features of this invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings in which:
The drawings are merely schematic representations, not intended to portray specific parameters of the invention. The drawings are intended to depict only typical embodiments of the invention, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numbering represents like elements.
The general operation of a reprogrammable electrical fuse 10, hereafter referred to as an “e-fuse 10” in accordance with an embodiment of the present invention is depicted in
During reprogramming, as shown in
Different voltages and currents may be applied to the e-fuse 10 to perform programming and reprogramming. During programming, the resistance of the e-fuse 10 will rise higher than the reference resistance Rref, while during reprogramming the resistance of the e-fuse 10 will drop lower than the reference resistance Rref.
The present invention provides a sensor circuit (described in greater detail below) to sense the change of resistance of the e-fuse 10 and latch the results into a corresponding register. One reference resistance can be shared by a bank of e-fuses 10 to save power and area overhead. In this case, sensing can be done in sequential manner, for example, during a power-on sequence to read the bank of e-fuses 10, and the results stored in one or more registers. The stored results can be used to provide information regarding programming state. The registers can comprise a small cache memory like that of DRAMs, or local registers.
As shown in
Cross-sectional views of the e-fuse 10 taken along line 4B-4B and 4C-4C are illustrated in
A metal material 22, such as aluminum (Al), copper (Cu), aluminum-copper (Al/Cu) alloy, or other suitable metal material susceptible to electro-migration, is then deposited and planarized (e.g., using chemical-mechanical-polishing (CMP)). A depletion region d1 is formed at the surface of the body regions 12, 14. A dielectric material (not shown) is deposited to cap the top surface of the e-fuse 10.
The sidewall 24 of the e-fuse 10 comprises a barrier liner formed of a material such as Ti, Ta, W, TiN, or a combination thereof. Other conductive materials such as doped poly-silicon or a silicided diffusion region can also be used. The barrier liner can be used to provide the reference resistance Rref described above with regard to the programming/reprogramming of the e-fuse 10. The material of the barrier liner is not sensitive to the electro-migration effect and has a resistance value higher than that of the e-fuse 10 prior to programming (and after reprogramming) and a resistance value much lower than that of the e-fuse 10 after programming. The material of the barrier liner is preferably compatible with back end of line (BEOL) metallization processes to limit processing costs.
After programming, as shown in
As shown in
During the programming of the e-fuse 10, high-voltage and high-current are applied to the e-fuse 10 at room or high temperature (e.g., 100 to 250° C.) to “open” the e-fuse 10 in a relatively short period of time. Care must be taken, however, to ensure that at least some of the metal material 22 remains within the neck region 16 to allow a reverse current to be applied during a subsequent reprogramming of the e-fuse 10.
The reprogramming of the e-fuse 10 is illustrated in
Another embodiment of the present invention is depicted in
During programming of the e-fuse 30, as shown in
A first embodiment of programming and reprogramming circuitry 40 for a reprogrammable e-fuse 10 in accordance with the present invention is depicted in
Another embodiment of programming and reprogramming circuitry 40′ for a reprogrammable e-fuse 10 in accordance with the present invention is depicted in
An illustrative sensing circuit 50 for a reprogrammable e-fuse 10 in accordance with an embodiment of the present invention is depicted in
The sensing circuit 50 does not allow the reference element Rref to be shared among a plurality of e-fuses 10. If the size of the reference element Rref is relative small this approach is acceptable—a separate reference element Rref can be provided for each e-fuse 10. Otherwise, a sensing circuit 60 such as that shown in
Each e-fuse unit 66 includes an e-fuse 70. An identical amount of current I is mirrored via nMOS device N62. The output voltage at node B is Vdd−I*Rf, where Rf is the resistance of the e-fuse 70. A comparator 72 is formed by two PMOS devices P53 and P54, two nMOS devices N52 and N54, and a tail device N63.
The output from the reference unit 64 (node C) is tied to the gate of the nMOS device N53 and the output of the e-fuse path (node B) is tied to the gate of the nMOS device N54. After programming, Rf>Rref, and the voltage at node B is lower than at node C, so that output of the comparator 72 will go high and the high state will be latched by latch 74. Otherwise, after reprogramming, a low state will be latched by latch 74.
An illustrative physical layout of a reprogrammable e-fuse system 80 in accordance with the present invention is depicted in
As mentioned above, the use of a tapered neck region 16 facilitates the programming/reprogramming of the e-fuse 10. An analytical model illustrating the predicted electro-migration behavior in a tapered structure is presented below.
The tapered structure 100 used in this analysis is illustrated in
Based on these modeling assumptions, for a tapered neck region 106 with a length of 1.0 μm, the predicted void growth during forward current stressing (J0=70 mA/μm2 through 0.5 μm wide line) is illustrated in
From the above graphs, it can be seen that:
A machine readable computer program may be created by one of skill in the art and stored in computer system 900 or a data and/or any one or more of machine readable medium 975 to simplify the practicing of this invention. In operation, information for the computer program created to run the present invention is loaded on the appropriate removable data and/or program storage device 955, fed through data port 945, or entered using keyboard 965. A user controls the program by manipulating functions performed by the computer program and providing other data inputs via any of the above mentioned data input means. The display device 970 provides a way for the user to accurately control the computer program and perform the desired tasks described herein.
The design process 1010 includes using a variety of inputs; for example, inputs from library elements 1030 which may house a set of commonly used elements, circuits, and devices, including models, layouts, and symbolic representations, for a given manufacturing technology (e.g., different technology nodes, 32 nm, 45 nm, 90 nm, etc.), design specifications 1040, characterization data 1050, verification data 1060, design rules 1070, and test data files 1085, which may include test patterns and other testing information. The design process 1010 further includes, for example, standard circuit design processes such as timing analysis, verification tools, design rule checkers, place and route tools, etc. One of ordinary skill in the art of integrated circuit design can appreciate the extent of possible electronic design automation tools and applications used in design process 1010 without deviating from the scope and spirit of the invention.
Ultimately, the design process 1010 translates the circuit 100, along with the rest of the integrated circuit design (if applicable), into a final design structure 1090 (e.g., information stored in a GDS storage medium). The final design structure 1090 may comprise information such as, for example, test data files, design content files, manufacturing data, layout parameters, wires, levels of metal, vias, shapes, test data, data for routing through the manufacturing line, and any other data required by a semiconductor manufacturer to produce circuit 100. The final design structure 1090 may then proceed to an output stage 1095 of design flow 1000; where output stage 1095 is, for example, where final design structure 1090: proceeds to tape-out, is released to manufacturing, is sent to another design house, or is sent back to the customer.
The foregoing description of the preferred embodiments of this invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously, many modifications and variations are possible. Such modifications and variations that may be apparent to a person skilled in the art are intended to be included within the scope of this invention as defined by the accompanying claims.
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