Active solid-state devices (e.g. – transistors – solid-state diode – Integrated circuit structure with electrically isolated... – Passive components in ics
Reexamination Certificate
2002-03-22
2004-02-03
Loke, Steven (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Integrated circuit structure with electrically isolated...
Passive components in ics
C257S530000, C257S211000, C438S132000, C438S215000
Reexamination Certificate
active
06686644
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims priority of Japanese Patent Applications No. 2001-126046, filed in Apr. 24, 2001 and No. 2002-044950, filed in Feb. 21, 2002, the contents being incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device provided with a fuse to be disconnected by a laser and to a method of disconnecting a fuse provided on a semiconductor circuit.
2. Description of the Prior Art
As higher performance of semiconductor devices are required in recent years, downsizing and higher integration of elements are accelerated. However, more defects tend to occur as downsizing and higher integration of the elements progress, thus incurring a drop in fabrication yields. In order to avoid the foregoing, a redundant circuit is sometimes provided inside a semiconductor device. The semiconductor device provided with such a redundant circuit is generally designed to use a fuse in order to switch a defective circuit to the redundant circuit.
FIG. 1
is a view showing one example of a method of switching circuits with a fuse.
A redundant circuit
51
has a constitution identical to that of a basic circuit
52
. This redundant circuit
51
is connected with a contact point a of a switch circuit
53
and the basic circuit
52
is connected with a contact point b of the switch circuit
53
. A center tap c of the switch circuit
53
is connected with a buffer
54
. Moreover, a control terminal s of the switch circuit
53
is connected with a node N between a resistor R and a fuse F. The resistor R and the fuse F are serially connected between a power source line Vh and a ground line Vgnd.
When the fuse is not disconnected, the electric potential of the control terminal s of the switch circuit
53
is equal to the electric potential of the ground line Vgnd (which is referred to as a “L” level), and the center tap c of the switch circuit
53
is connected with the contact point b. Therefore, the buffer
54
is electrically connected with the basic circuit
52
and electrically separated from the redundant circuit
51
.
When the basic circuit
52
is defective, the fuse F is disconnected by a laser. Accordingly, the electric potential of the control terminal s of the switch circuit
53
is made equal to the electric potential of the power source line Vh (which is referred to as a “H” level), whereby the center tap c and the contact point a are connected. Therefore, the buffer
54
is electrically connected with the redundant circuit
51
and electrically separated from the basic circuit
52
.
In this way, the defective circuit can be switched into the redundant circuit by disconnecting the fuse F by a laser.
FIG. 2
is a cross-sectional view showing a conventional semiconductor device provided with a fuse. An insulating film
62
is formed on a semiconductor substrate
61
, and lower wiring including lines
63
a
and
63
b
is formed on this insulating film
62
. Another insulating film
64
is formed on both of the insulating film
62
and the lower wiring, and a fuse
65
is formed on the insulating film
64
. Both ends of this fuse
65
are electrically connected with the lower lines
63
a
and
63
b
severally through via contact portions
64
a
and
64
b
formed inside the insulating film
64
. Another insulating film
66
is formed on both of the insulating film
64
and the fuse
65
.
In the semiconductor device thus constituted, a laser is irradiated onto the center portion of the fuse
65
via the insulating film
66
when the fuse
65
is disconnected. In this way, the center portion of the fuse
65
irradiated by the laser is heated up above the melting point thereof and changed from a solid phase to a liquid phase or a gas phase, and a sudden rise of pressure causes a so-called thermal explosion. The fuse
65
is disconnected by this thermal explosion, and a part of the insulating film
66
(an upper part of the disconnected portion of the fuse) is exfoliated as shown in FIG.
3
.
The inventers of the present invention perceive that the above-described conventional semiconductor device and the method of disconnecting the fuse bear the following problem.
As described above, the thermal explosion occurs upon disconnecting the fuse
65
by the laser. In this event, large pressure is also applied to the insulating film
64
under the fuse
65
, whereby a part of the insulating films
64
and
62
may be exfoliated and a crack may also occur in the insulating film
64
and
62
. When damages such as exfoliation or cracks occur in the insulating films
64
and
62
, water may easily infiltrate into the semiconductor substrate
61
and a wiring layer, thus causing deterioration of characteristics.
Incidentally, Japanese Patent Laid-Open No. Hei 9 (1997)-36234 discloses a fuse, which is composed of first and second fuse elements disposed vertically via an insulating film, and a contact portion which connects tip portions of these first and second fuse elements electrically. Moreover, Japanese Patent Laid-Open No. Hei 9 (1997)-36234 also discloses a fuse, in which the first and the second fuse elements are formed in the same layer, whereby the fuse is composed by electrically connecting the first and the second fuse elements with the contact portion. These fuses are designed as surely disconnectable by irradiating a laser onto the contact portion.
Meanwhile, Japanese Patent Laid-Open No. Hei 4 (1992)-14245 discloses a fuse composed of a partially thinned aluminum line, in which a member easily heated by a laser (a heating member) such as a polysilicon film is disposed under the fuse. According to the publication, the fuse made of aluminum can be surely disconnected by means of heating the heating member by the laser to cause thermal explosion.
However, the fuses disclosed in those publications cannot yet avoid damages on insulating films under the fuses upon disconnection.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a semiconductor device and a method of disconnecting a fuse capable of reducing damages on an insulating film under a fuse upon disconnecting the fuse by a laser.
A semiconductor device according to the present invention includes a semiconductor substrate, an insulating film formed on the semiconductor substrate, a fuse formed on the insulating film, and a protective member formed stronger than the insulating film and disposed under a disconnecting point of the fuse.
In the semiconductor device of the present invention, the high-strength protective member is disposed under the disconnecting point of the fuse. When a laser is irradiated on the disconnecting point of the fuse, the temperature at the disconnecting point is suddenly increased and thermal explosion occurs. In this event, the protective member protects the lower insulating film, whereby occurrence of damages such as exfoliation and cracks can be prevented. Moreover, as the thermal explosion occurs on the high-strength protective member, destructive pressure is concentrated on an upper side of the protective member. In this way, the fuse can be efficiently disconnected. In addition, a form of destruction of the fuse is also stabilized.
Only one protective member may be disposed per fuse, or a plurality of protective members may be also disposed. Moreover, in the case of a semiconductor device provided with a plurality of fuses, it is preferable that the fuses are arrayed within a certain area in consideration of operating efficiency upon disconnection of the fuses.
A method of disconnecting a fuse according to the present invention is a method of disconnecting a fuse of a semiconductor device including a semiconductor substrate, a first insulating film formed on the semiconductor substrate, wiring formed on the first insulating film, a second insulating film formed on the first insulating film and the wiring, a fuse formed on the second insulating film, and a via contact portion formed inside the second insulating film to connect the fuse and the wirin
Arisaka Yoshikazu
Nakada Masayuki
Sawada Toyoji
Sukegawa Kazuo
Tatematsu Tsutomu
Fujitsu Limited
Kang Donghee
Loke Steven
Staas & Halsey
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