Active solid-state devices (e.g. – transistors – solid-state diode – Contacts or leads including fusible link means or noise...
Reexamination Certificate
1999-01-28
2001-10-02
Smith, Matthew (Department: 2825)
Active solid-state devices (e.g., transistors, solid-state diode
Contacts or leads including fusible link means or noise...
C257S209000
Reexamination Certificate
active
06297541
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device including a fuse circuit which can be disconnected by laser ablation and a method for fabricating the semiconductor device, and a laser system suitable to disconnect a fuse of the semiconductor device.
Semiconductor devices, such as memory devices of DRAMs, SRAMs, etc., logic devices, etc., are constituted by a very large number of elements, and a part of the circuit or of the memory cells are often inoperative due to various cause in their fabrication processes. In this case, when semiconductor devices partially defective circuits or memory cells are generally regarded as defective devices, the semiconductor devices have low fabrication yields, which might lead to fabrication cost increase. In view of this, recently such defective semiconductor devices have defective circuits or defective memory cells replaced by redundant circuits or redundant memory cells which have been prepared in advance, to create properly functioning devices. In some semiconductor devices, a plurality of circuits having functions different from each other are formed integrated and later those of certain functions are replaced, and in other semiconductor devices prescribed circuits are formed, and later characteristics of the semiconductor devices are adjusted. In such reconstruction of semiconductor devices, usually a fuse circuit having a plurality of fuses is formed on the semiconductor devices, and after operation tests, etc., the fuses are disconnected by laser beam irradiation.
A conventional semiconductor device including a fuse circuit and a method for fabricating the same will be explained with reference to
FIGS. 11A-11C
.
FIG. 11A
is a diagrammatic sectional view of the conventional semiconductor device, which shows a structure thereof.
FIG. 11B
is a plan view of the conventional semiconductor device, which shows the structure thereof.
FIG. 11C
is a diagrammatic sectional view of the conventional semiconductor device with a fuse disconnected, which shows the structure thereof.
A fuse
202
is formed on a substrate
200
, connected to a prescribed circuit for replacing the circuit. An inter-layer insulation film
204
for covering the fuse
202
is formed thereon. An interconnection layer
206
is formed on the inter-layer insulation film
204
, connected to the fuse
202
therethrough. A passivation film
211
is formed on the interconnection layer
206
. A part of the passivation film
211
on the fuse
202
is removed. A plurality of the fuses
202
are formed on the substrate
22
at a prescribed pitch (FIGS.
11
A and
11
B).
To disconnect the fuse
202
in such fuse circuit, a laser beam
208
is irradiated to a region where the fuse is formed, whereby the fuse
202
is rapidly heated by its absorbed energy to a high temperature and undergoes laser explosion (FIG.
11
C).
Here to further micronize the semiconductor device, it is necessary to further decrease a pitch between the fuses
202
, but a pitch P of the fuses
202
is determined by a spot size
210
of the laser beam
208
and alignment accuracy of the laser beam
208
.
A spot size of the laser beam
208
has a lower limit which is determined by a wavelength of the laser beam
208
, and the spot size
208
can be decreased as the laser beam has a shorter wavelength. However, when a wavelength of the laser beam is too short, there is a risk that the laser beam may pass through a region where the fuse
202
is not formed, arrives at the base semiconductor substrate and is absorbed therein, and cause thermal laser explosion. In a case that the semiconductor substrate is silicon, the laser beam has an about 1 &mgr;m wavelength, at which silicon substrates absorb small amounts of laser beams. That is, a lower limit is about 1.5-2.0 &mgr;m in spot size.
On the other hand, alignment accuracy is required for the prevention of a disadvantage that the base silicon substrate is damaged if the laser explosion regions overlap each other in blowing both fuses
202
adjacent to each other and also for the prevention of a disadvantage that in disconnecting one of fuses
202
adjacent to each other, the other is damaged or blown. Usually a lower limit of the alignment accuracy is about 0.5 &mgr;m.
Thus, a lower limit of the fuse pitch of the above-described conventional fuse disconnecting method is about 2.0-2.5 &mgr;m.
As a method for narrowing a pitch P of the fuses, a party of the applicants of the present application has proposed a method using a photoresist.
In the method using a photoresist, a photoresist
212
is formed on a semiconductor device shown in
FIG. 11A
(FIG.
12
A), a laser beam
208
whose power is low enough not to cause laser explosion is irradiated to expose the photoresist
212
(FIG.
12
B), the exposed photoresist
212
is developed to remove the photoresist
212
in the exposed region
214
(
FIG. 12C
, and a fuse
202
is removed by the usual etching process with the photoresist
212
as a mask (FIG.
12
D).
According to this method, the laser beam
208
may have a power which is sufficient only to expose the photoresist
212
, and it is not necessary that the power is high enough to laser explode the fuse
202
or the semiconductor substrate. Accordingly, the laser beam
208
can easily have a shorter wavelength and can have a spot size
210
which is decreased in accordance with a wavelength of the laser beam
208
. Accordingly, a fuse pitch P, which is determined by a spot size
210
of the laser beam can be decreased.
However, the method using a photoresist must additionally include a photoresist application step and a photoresist development step, a fuse etching step and a photoresist releasing step. Conventionally, it has caused no trouble that the test process following completion of the wafer process has lower cleanliness in comparison with that in the wafer process clean room, but in a case that a process, such as etching or others, is performed after the test, it is necessary to perform the test process in a clean room of high cleanliness so that dust on wafers does not pollute the etching system, or an etching system which is exclusively used for the fuse disconnection is installed, which leads to higher fabrication costs rather than simple increase of fabrication steps.
As described above, in the conventional fuse disconnecting method, it is difficult to narrow a fuse pitch corresponding to increased integration of a semiconductor device while depressing increase of fabrication steps and fabrication costs.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a structure of a semiconductor device including a fuse circuit which is easily higher integrated and does not add to fabrication costs and a method for fabricating the semiconductor device, and a laser system suitable to disconnect the fuses.
The present invention provides a semiconductor device and a method for fabricating the same for disconnecting a fuse by laser ablation, and a laser system suitable to disconnect fuses of the semiconductor device. Laser ablation is a phenomena that a laser beam of high intensity is irradiated to an object-to-be-irradiated to disconnect bonds of substances by energy of the irradiated laser beam and instantaneously sublimate the object-to-be-irradiated.
The conventional fuse disconnecting method using laser explosion due to absorption of a laser beam converts optical energy to vibrations of stretches, etc. of bonds of substances, i.e., to thermal energy for laser explosion, while laser ablation dissociates bonds of substances directly by optical energy, and is based on the phenomena which is quite different from laser explosion.
Due to such mechanism difference, in the laser ablation, a part a laser beam irradiated to vanishes with a boundary with respect to a part the laser beam has not been irradiated to remain in a beautiful facet. On the other hand, in the conventional laser explosion, the laser explosion takes place up to the vicinity of a part a laser beam is irradiated to, generating a number of part
Ema Taiji
Richardson Thomas W.
Sun Yunlong
Swenson Edward J.
Armstrong Westerman Hattori McLeland & Naughton LLP
Fujitsu Limited
Lee Calvin
Smith Matthew
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