Electrical fuse for semiconductor integrated circuits

Details Electrical fuse for semiconductor integrated circuits Electrical fuse for semiconductor integrated circuits

2002-07-23

2003-12-09

Vortman, Anatoly (Department: 2835)

Electricity: electrothermally or thermally actuated switches

Electrothermally actuated switches

Fusible element actuated

C337S296000, C337S290000, C365S225700, C257S529000, C438S467000

Reexamination Certificate

active

06661330

ABSTRACT:

TECHNICAL FIELD OF INVENTION
The present invention relates generally to fuses, and, more particularly, uses formed over a semiconductor substrate having controlled and predictable areas of degradation.
BACKGROUND OF THE INVENTION
In the semiconductor industry, fuse elements are a widely used feature in integrated circuits for a variety of purposes, such as improving manufacturing yield or customizing a generic integrated circuit. For example, by replacing defective circuits on a chip with duplicate or redundant circuits on the same chip, manufacturing yields can be significantly increased. Typically, in order to replace a defective circuit or memory cell, conductive connections, or fuses, are cut or “blown”, thereby allowing a redundant circuit to be used in place of the defective circuit. It is also common practice in the manufacture of integrated circuits to provide for customization of chips or modules to adapt chips to specific applications. By selectively blowing fuses within an integrated circuit which has multiple potential uses, a generic integrated circuit design may be economically manufactured and adapted to a variety of custom uses.
Typically, fuses or fusible links are incorporated in the design of the integrated circuit, wherein the fuses are selectively blown, for example, by passing an electrical current of a sufficient magnitude to cause the fusible link to change its structure, for example, by melting or otherwise become altered, thereby creating a more resistive path or an open circuit. Alternatively, a current that is weaker than the current required to entirely blow the fuse can be applied to the fuse in order to degrade the fuse, thus increasing a resistance through the fuse. The process of selectively blowing or degrading fuses is often referred to as “programming”. An alternative to blowing fusible links with an electrical current is to open a window above each fuse to be blown, use a laser to blow each of the fuses, and then fill the windows with a passivation layer. Blowing the fuses with a laser, however, can potentially increase manufacturing costs, since additional components such as the laser and other associated equipment for alignment of the laser is generally required.
One exemplary conventional fuse which can be blown using a programming current is illustrated in
FIGS. 1A-1C
.
FIGS. 1A and 1B
illustrate a top plan view and a cross-section, respectively, of a portion
10
of an integrated circuit (not shown) comprising a conventional fuse
15
prior to programming.
FIG. 1A
illustrates the fuse
15
which has been formed over an insulation layer
20
, wherein the fuse comprises two contacts
30
which are in electrical contact with an electrically conducting silicide layer
40
. As illustrated in cross-section in
FIG. 1B
, the silicide layer
40
is disposed over a polysilicon layer
50
, wherein the silicide layer
40
and the polysilicon layer
50
are generally arranged in a stack
55
residing over the insulation layer
20
. Typically, the insulation layer
20
is an oxide layer which has been deposited or grown on a semiconductor substrate
60
, such as monocrystalline silicon. Furthermore, the fuse
15
is generally covered with an insulative passivation layer
70
to electrically isolate the fuse from other devices (not shown).
During programming and operation, electrical current flowing through the fuse
15
will generally proceed from one contact
30
A, through the silicide layer
40
, to the other contact
30
B. If the current is increased to a level that exceeds a predetermined threshold current of the fuse
15
, the silicide layer
40
will change its state, for example, by melting, thereby altering a resistance of the structure. Note that depending on the sensitivity of the sensing circuitry (e.g., a sense amp), a fuse may be considered “blown” if a change in resistance is only modest. Therefore the term “blowing” a fuse may be considered to broadly cover a modest alteration of the resistance or alternatively may comprise a complete open circuit.
FIG. 1C
illustrates the cross section of the fuse
15
shown in
FIG. 1B
after the fuse has been programmed (e.g., a “blown” fuse), wherein the programming current has effectively melted or otherwise altered a state of the silicide layer
40
in a region
75
, thereby forming a discontinuity
85
in the silicide layer, wherein agglomerations
80
of silicide are formed on either side of the discontinuity.
The fuse
15
of the prior art, however, does not allow for reliable localization of the discontinuity
85
and agglomerations
80
in the silicide layer
40
. In other words, the region
75
of the fuse
15
that is melted can potentially occur at any location in the silicide layer
40
between the contacts
30
during programming. Since conventional processes involved in melting the silicide layer
40
typically generate a significant amount of potentially damaging heat, it is desirable to predict the region
75
in which the discontinuity
85
is potentially formed, and to further reduce an area (not shown) of the discontinuity in order to reduce an amount of energy required to program the fuse
15
.
Predicting the region
75
and reducing the area (not shown) of the potential discontinuity
85
may also reduce a potential for damage to adjacent components (not shown) when the fuse
15
is programmed. As illustrated in
FIG. 1D
, conventional attempts to localize the discontinuity (not shown) to a predefined region
90
of the silicide layer
40
have included narrowing regions
92
of the silicide layer
40
between generally equally-sized contacts
30
to form a narrowed region
95
(e.g., forming a “neck”). Other conventional attempts to minimize damage to a predefined region of the silicide layer have included extra process steps to form a weakness in the silicide layer, wherein the silicide melts under programming current.
Conventional fuse designs, however, have typically not eliminated the unwanted damage caused by blowing a fuse, or have added extra process steps, cost, or undesirable design qualities to the final product. Furthermore, commonly used fuses in the prior art have a relatively high parasitic resistance, making programming of the fuse more difficult, and raising concerns over stability and reliability of the fuse over time. Therefore, what is needed in the art is a reliable fuse that is fabricated such that programming of the fuse will result in reproducible degrading and melting of a silicide layer which uses less energy than conventional techniques, and wherein additional process steps are not required in the manufacture of the fuse.
SUMMARY OF THE INVENTION
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Its purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
The present invention relates generally to a fuse formed over a semiconductor substrate. According to one exemplary aspect of the present invention, the fuse resides over a patterned polysilicon layer, wherein a first region and a second region are defined. A silicide layer resides over the polysilicon layer, and a first contact member and a second contact member electrically contact the silicide layer in the first region and second region, respectively, thereby defining a first interface having a first contact area between the first contact member and the silicide layer, and a second interface having a second contact area between the second contact member and the silicide layer.
According to one exemplary aspect of the present invention, the second contact area is smaller than the first contact area, wherein the second interface defines a fusible link. During programming of the fuse, a current density in the second region is greater than a curr

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