Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having insulated gate
Reexamination Certificate
2003-02-14
2004-08-31
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having insulated gate
C438S209000, C438S208000
Reexamination Certificate
active
06784043
ABSTRACT:
TECHNICAL FIELD
The invention relates generally to integrated circuits (ICs), and more particularly to an IC that includes a fuse bank having aligned fuses, such as laser fuses, and methods for forming and programming the fuses. By including aligned fuses, the fuse bank occupies significantly less area of the IC than if it included fuses laid out side by side.
BACKGROUND OF THE INVENTION
Makers of today's electronic equipment consistently pressure IC manufacturers to: (1) reduce the sizes of ICs, and (2) maintain or increase the number and complexity of the functions the ICs perform. Therefore, IC designers continue to explore and develop new techniques for reducing the areas of IC dies without reducing the ICs' capabilities.
FIG. 1
is a block diagram of an IC
10
, which includes an array
12
of memory cells and redundancy circuitry for replacing defective ones of the cells. The array
12
includes a matrix array
14
of matrix memory cells that store data and that are arranged in rows and columns. An address generator
18
receives an external address on the ADDRESS bus and generates therefrom an internal row address on a bus
20
. This internal address identifies a respective row of matrix cells in the array
14
. A matrix circuit
21
includes matrix row decoders
22
0
-
22
n
—one for each row in the matrix array
14
—for firing the respective matrix rows.
In operation of the IC
10
, the decoders
22
0
-
22
n
receive a conventional address PRECHARGE signal before the generator
18
generates the row address. Next, the row decoders
22
0
-
22
n
receive and decode the row address on the bus
20
. Then, the row decoder
22
corresponding to the addressed row fires the word line WL of the addressed row. For example, if the address generator
18
addresses row
0
in the matrix array
14
, then the row
0
decoder
22
0
fires the word line WL
0
via a firing terminal
25
0
.
Unfortunately, one or more matrix cells in a row of the matrix array
14
may be defective and thus unable to reliably store data. For example, the respective word line WL or a part of the defective matrix cell or cells may be short-circuited to other nodes in the IC
10
.
To prevent a defective matrix cell from rendering the entire IC
10
unusable, the array
12
includes an array
23
of redundant memory cells, and the IC
10
includes a redundant circuit
24
for mapping a redundant cell to the address of a defective matrix cell. In one embodiment, the redundant cells are arranged in rows and columns, and the circuit
24
maps a redundant row to the address of a matrix row containing one or more defective matrix cells. The circuit
24
includes a programmable portion
26
and redundant row decoders
28
0
-
28
x
—one decoder for each row in the redundant array
23
—for firing the respective redundant rows. The programmable portion
26
includes a programmable redundancy address circuit
30
and a programmable redundancy control circuit
32
. Often, the circuits
30
and
32
contain laser-programmable fuses that are laid out side by side in a lower layer of the IC
10
.
If one finds a defective row in the matrix array
14
, then he programs the circuit
24
to map a redundant row in the array
23
to the address of the defective matrix row. For example, suppose that matrix row
1
is defective and one wishes to replace it with the redundant row
0
. To do this, he programs the redundancy address circuit
30
to address the redundant row
0
—and thus to activate the redundant row decoder
28
0
—whenever the address generator
18
generates the address of the matrix row
1
. He also programs the redundancy control circuit
32
to enable the redundant row decoder
28
0
. Therefore, in response to the redundant-row-
0
address from the circuit
30
and an enabling control signal from the circuit
32
, the redundant row decoder
28
0
fires the redundant word line RWL
0
via a firing terminal
29
0
.
A problem with the matrix circuit
21
, however, is that it continues to fire the word line WL of a defective matrix row even after one has programmed the redundant circuit
24
to replace the defective row with a redundant row. This firing may cause a malfunction that is not fixed by the mapping of the redundant row to the address of the defective row. For example, if the word line WL of the defective row is shorted to another word line or to a cell plate, then firing WL may cause data errors or other malfunctions.
FIG. 2
is a block diagram of an IC
40
, which is similar to the IC
10
of
FIG. 1
except that the matrix circuit
21
does not fire a defective matrix row. The matrix circuit
21
includes a programmable matrix control circuit
42
. If one finds a defective matrix row in the array
14
, then in addition to programming the redundant circuit
24
as discussed above in conjunction with
FIG. 1
, he programs the circuit
42
to disable the corresponding row decoder
22
from firing the word line WL of the defective row. For example, if the matrix row
0
is defective, then one programs the control circuit
42
to disable the row decoder
22
0
. Thus, even if the address generator
18
generates the address of the matrix row
0
, the disabled row decoder
22
0
does not fire the word line WL
0
.
Often, the matrix control circuit
42
includes laser fuses that are disposed in the same layer of the IC
40
as the fuses of the redundant circuit
24
. Therefore, the circuit
42
tends to increase the die area, and thus the overall size, of the IC
40
.
FIG. 3
is a cutaway cross-sectional view of a semiconductor structure
50
, which includes a stacked fuse
51
. The structure
50
includes an upper fuse element
52
disposed on an insulator layer
54
, and includes a lower fuse element
56
disposed beneath the insulator layer
54
and in alignment with the upper fuse element
52
. The fuse elements
52
and
56
are electrically connected in parallel by conductive vias
58
and
59
to form the stacked fuse
51
. Compared to a single fuse element, the stacked fuse
51
has approximately the same width, and thus occupies approximately the same die area, but has approximately twice the current-carrying capacity. During programming of the stacked fuse
51
, one uses a laser beam to cut both fuse elements
52
and
56
.
Unfortunately, including stacked fuses in the IC
40
would not reduce the number of fuses in the circuits
30
,
32
, and
42
, and thus would not reduce the die area of the IC
40
. In fact, including stacked fuses in the IC
40
would increase the manufacturing complexity of and could add a conductive layer to the IC
40
.
SUMMARY OF THE INVENTION
In one aspect of the invention, an IC includes a first conductive layer, an insulator layer disposed on the first conductive layer, and a second conductive layer disposed on the insulator layer. A first fuse is disposed in the first conductive layer and provides a first signal, and a second fuse is disposed in the second conductive layer in alignment with the first fuse and provides a second signal.
Such an IC includes fuses that are disposed one on top of the other. A fuse bank including such fuses occupies significantly less die area than a fuse bank including only side-by-side fuses. Therefore, an IC having such a fuse bank can be significantly smaller than an otherwise equivalent IC having a side-by-side fuse bank.
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patent: 4233643 (1980-11-01), Iverson et al.
patent: 4494103 (1985-01-01), Jarosz et al.
patent: 4714839 (1987-12-01), Chung
patent: 5420455 (1995-05-01), Gilmour et al.
patent: 5532966 (1996-07-01), Poteet et al.
patent: 5914524 (1999-06-01), Komenaka
patent: 5966339 (1999-10-01), Hsu et al.
patent: 5986321 (1999-11-01), Froehner
patent: 6008716 (1999-12-01), Kokubun
patent: 6372554 (2002-04-01), Kawakita et al.
Bissey Lucien J.
Carson Bryan C.
Hadzor Mark L.
Graybeal Jackson Haley LLP
Micro)n Technology, Inc.
Nelms David
Nguyen Thinh T
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