Static information storage and retrieval – Read/write circuit – Having fuse element
Reexamination Certificate
1998-12-18
2001-06-19
Hoang, Huan (Department: 2818)
Static information storage and retrieval
Read/write circuit
Having fuse element
C365S200000, C257S530000
Reexamination Certificate
active
06249472
ABSTRACT:
FIELD OF THE INVENTION
The invention pertains to an antifuse used for a semiconductor. In particular, this invention pertains to an antifuse used for a semiconductor memory device.
BACKGROUND OF THE INVENTION
The current semiconductor device usually has a very high integrity. Consequently, in order to prevent the entire semiconductor device from becoming a defective product because of a partial defective circuit, a redundant circuit is formed in advance so that the defective circuit detected by examination can be switched to the redundant circuit.
In general, fuses are prearranged in the semiconductor device. When it is necessary to switch a defective circuit to the redundant circuit, the fuse corresponding to the defective circuit is cut off by a laser beam, followed by programming according to the state of the fuses. In this way, the defective circuit can, in practice, be switched to the redundant circuit.
However, the wiring width becomes narrower to accompany the improvement in the integrity of the semiconductor device. On the other hand, the spot size of the laser beam cannot be reduced. As a result, the fuses cannot be arranged close to each other.
Consequently, the technology using antifuses in a semiconductor device has attracted much attention in recent years. According to this technology, programming is performed after the antifuse corresponding to a defective circuit is shorted by applying a prescribed voltage.
FIG. 18
shows an example of the conventional antifuse. As shown in the figure, lower wiring
211
and upper wiring
212
on an insulating film formed on the surface of the lower wiring are connected to circuit modules
221
and
222
, respectively. Each crossing part of lower wiring
211
and upper wiring
212
is used as an antifuse
205
. When a prescribed breakdown voltage (5-20 V) is applied to an antifuse
205
corresponding to a defective circuit, the insulating film sandwiched between lower wiring
211
and upper wiring
212
in the portion of said antifuse
205
is punctured. As a result, a short circuit is formed between lower wiring
211
and upper wiring
212
, and the desired circuit blocks in circuit modules
221
and
222
are connected to lower wiring
211
and upper wiring
212
, respectively. In this way, the problem caused by the defective circuit can be solved.
Symbol
251
in
FIG. 19
represents a diffused layer formed in silicon substrate
250
. The two ends of the diffused layer are connected to film wiring
241
. An ONO film (oxide
itride/oxide film)
253
is formed as an insulating film on diffused layer
251
, and a polysilicon film
252
with its two ends connected to film wiring
242
is formed on said ONO film
253
. An antifuse
245
is formed at the intersection of diffused layer
251
and polysilicon film
252
.
FIG. 20
shows a cross-sectional view along line A—A of said antifuse
245
. When antifuse
245
is shorted, a prescribed voltage is applied between two wirings
251
and
252
to puncture ONO film
253
between diffused layer
251
and polysilicon film
252
. As a result, a short circuit is formed between wirings
251
and
252
.
There is no need to use a laser beam if electrically shorted antifuses are used as described above. Consequently, the antifuses can be arranged close to each other so that the area occupied by the chip can be reduced.
Unlike the fuse cut off by the laser beam, the punctured surface of the antifuse is not exposed to the surface of the semiconductor device. Therefore, a highly-reliable semiconductor device can be obtained because moisture and impurities cannot enter the punctured surface.
However, when said antifuses
205
and
245
are used in the semiconductor memory device, it is necessary to use a special-purpose film for forming antifuses
205
and
245
in a process separate from the process for forming the memory cell and the peripheral circuit. Consequently, the manufacturing cost is increased, while the yield drops as a result of using more films.
An object of this invention is to solve the aforementioned problems of the conventional technology by providing a semiconductor memory device having antifuses without adding a film manufacturing process.
SUMMARY OF THE INVENTION
This and other objects are attained, in accordance with one aspect this invention discloses a semiconductor memory device characterized by the following facts: data is stored when a capacitor comprising a first electrode formed on a semiconductor substrate, a dielectric film formed on the surface of the aforementioned first electrode, and a second electrode formed on the surface of the aforementioned dielectric film is charged or discharged; the semiconductor memory device has an antifuse formed by the aforementioned first and second electrodes as well as the dielectric film; the semiconductor memory device also has a MOS transistor which is connected in series with the aforementioned antifuse; when a breakdown voltage higher than the voltage applied to the aforementioned capacitor is applied to the circuit formed by the aforementioned antifuse and MOS transistor which are connected in series with each other, the aforementioned MOS transistor is turned on; at that time, the aforementioned dielectric film of the antifuse is punctured to form a short circuit between the aforementioned first and second electrodes.
When the semiconductor memory device of this invention has a first polysilicon film formed on the aforementioned semiconductor substrate and a second polysilicon film formed on the aforementioned first polysilicon film, the first electrode of the aforementioned capacitor and antifuse can be formed by the aforementioned first polysilicon film and the second polysilicon film deposited on the first polysilicon film.
On the other hand, when the first electrode of the aforementioned capacitor is formed by the aforementioned first polysilicon film and the second polysilicon film deposited on the first polysilicon film, the first electrode of the aforementioned antifuse can be formed by the aforementioned first polysilicon film and the aforementioned second polysilicon film formed on the surface of the first polysilicon film. The second electrode can be formed by a metal film.
In a further aspect of the invention, one end of another MOS transistor is connected to the mode between the aforementioned antifuse and MOS transistor, and a power supply voltage lower than the aforementioned breakdown voltage can be applied to the other end of said another MOS transistor.
As described in claim
6
of this invention, in the semiconductor memory device described in any of claims
1
-
5
, plural circuits, each of which is formed by connecting the aforementioned antifuse and MOS transistor in series, are connected in parallel to form an antifuse array which is configured appropriately so that one antifuse of the aforementioned plural antifuses can be punctured at the desired position.
In the semiconductor memory device another aspect of this invention, a capacitor is formed by the first electrode formed on the semiconductor substrate, the dielectric film formed on the surface of the first electrode, and the second electrode formed on the surface of the dielectric film. The capacitor is charged or discharged to store the data.
The semiconductor memory device of a still further aspect of this invention also has an antifuse, which is formed by the first and second electrodes as well as the dielectric film, and a MOS transistor which is connected in series with the antifuse. When the data is stored, if the MOS transistor is turned on by applying a breakdown voltage higher than the voltage applied to the MOS transistor to the circuit formed by connecting the antifuse and the MOS transistor in series, the dielectric film in the antifuse will be punctured. As a result, a short circuit will be formed between the aforementioned first and second circuits. The programming can be carried out appropriately in electrical fashion to save the semiconductor memory device with a redundant circuit by shorting the antifuse corresponding to the defe
Fukuhara Hideyuki
Nasu Takumi
Numaga Shigeki
Tamura Yoshimitsu
Hoang Huan
Kempler William B.
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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