Active solid-state devices (e.g. – transistors – solid-state diode – Integrated circuit structure with electrically isolated... – Passive components in ics
Reexamination Certificate
2003-01-22
2003-12-23
Prenty, Mark V. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Integrated circuit structure with electrically isolated...
Passive components in ics
C257S758000
Reexamination Certificate
active
06667535
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fuse structure used in an integrated circuit device, and more particularly, to a novel fuse structure having a backup conductive layer.
2. Description of the Related Art
Fuses are routinely used in the design of monolithic integrated circuits (IC), and in particular in memory devices as elements for altering the configuration of the circuitry contained therein. As such, memories are commonly built with programmed capabilities wherein fuses are selectively “blown” by, e.g., a laser beam.
It is well known that random access memories (RAM) are designed with redundancies which include spare columns, rows, or even fully functional arrays, wherein when any of these spare elements fails, the defective row, column and the like are replaced by a corresponding element. Disabling and enabling of spare elements is accomplished by fuses which are blown (i.e., melted away) when required, preferably, by a laser beam.
Additionally, the technique of laser fuse deleting (trimming) has been widely used both in the memory and logic IC fabrication industries, as an effective way to improve functional yields and to reduce development cycle time. Yet, fuse blow yield and fuse reliability have been problematic in most conventional fuse designs.
FIG. 1
is a sectional view of a traditional fuse structure.
FIG. 2
is a top view of a traditional fuse structure. And
FIG. 1
shows the cross section C-C′ of FIG.
2
.
Referring to
FIG. 1
, symbol
100
shows an insulated layer substrate. A metal layer M
0
is formed on part of the substrate
100
. An oxide layer
120
is formed on the metal layer M
0
and part of the substrate
100
. A metal layer M
1
having an optimal position of laser spot
110
is formed on part of the oxide layer
120
. At least one conductive plug
130
is defined through the oxide layer
120
, for electrically connecting the M
0
layer and the M
1
layer. A fuse window
140
is formed above part of the M
1
layer comprising the position
110
and part of the oxide layer
120
. Symbol
150
shows a passivation layer.
In
FIG. 2
, there are plural fuse structures
210
,
220
,
230
in the fuse window
140
. Each fuse structure
210
,
220
,
230
comprises the M
0
layer, the plug
130
and the M
1
layer. The solid line area shows the M
1
layer, the dash line area shows the M
0
layer, and each structure
210
,
220
,
230
comprises its own optimal position of laser spot
110
. To give an example, a laser beam
290
blows the position
110
of the fuse structure
220
. Because of misalignment of the laser beam
290
or thermal scattering of the laser beam
290
, thermal shock from the laser blow process can damage the M
0
layer of the fuse structures
210
,
230
, located near the fuse structure
220
. This can cause the fuse structures
210
,
230
to crack, seriously affecting device reliability and yield.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a novel fuse structure. An optimal position of laser spot is defined above a substrate. A first conductive layer is formed on part of the substrate. A first dielectric layer is formed on the substrate and the first conductive layer. A second conductive layer is formed on the first dielectric layer. A second dielectric layer is formed on the first dielectric layer and the second conductive layer. A third conductive layer comprising the position of laser spot is formed on part of the second dielectric layer. A plurality of first conductive plugs penetrate the first dielectric layer, to electrically connect the first conductive layer and the second conductive layer. At least one second conductive plug penetrates the second dielectric layer, to electrically connect the second conductive layer and the third conductive layer.
The present invention improves on the prior art in that the first conductive layer, serving as a backup conductive layer, is placed under the second conductive layer. Thus, the invention can prevent the fuse structure from failing when both misalignment of the laser beam and thermal scattering of the laser beam damage the second layer of the fuse structure in the laser blow process, raises reliability and yield, and ameliorates the disadvantages of the prior art.
REFERENCES:
patent: 6522021 (2003-02-01), Sakihama et al.
patent: 2002/0063305 (2002-05-01), Koike
patent: 2002/0100956 (2002-08-01), Brintzinger et al.
Ladas & Parry
Nanya Technology Corporation
Prenty Mark V.
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