Active solid-state devices (e.g. – transistors – solid-state diode – Integrated circuit structure with electrically isolated... – Passive components in ics
Reexamination Certificate
2000-10-26
2002-08-13
Meier, Stephen D. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Integrated circuit structure with electrically isolated...
Passive components in ics
C257S531000
Reexamination Certificate
active
06433406
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to semiconductor devices and manufacturing methods of the same, particularly to semiconductor devices provided with fuse elements.
2. Description of the Related Art
Recent semiconductor devices, in particular, memory devices such as dynamic random access memories (DRAMs) are provided with laser fuses (hereinafter, simply referred to as fuses) as switches for replacing defective memory cells with redundancy cells, or as change-over switches for controlling internal levels.
Fuses of various forms are known. But, mostly used is the form that part of usual metal wiring is formed as a fuse in the upper part of the structure on a semiconductor substrate, to be blown out with laser beams.
FIGS. 1A
to
1
D show a fuse structure mostly used hitherto.
FIG. 1A
is a plan view showing the disposition of fuse elements formed in the upper part of the structure on a semiconductor substrate
101
.
FIG. 1B
is a schematic sectional view taken along dot-dash line IV-IV′ in FIG.
1
A.
FIGS. 1C and 1D
are schematic sectional views taken along dot-dash line III-III′ in FIG.
1
A.
FIGS. 1C and 1D
show states before and after a fuse element is blown out with laser beams, respectively.
The conventional fuse structure will be described with reference to
FIGS. 1A
to
1
D. Referring to
FIGS. 1A and 1B
, fuse elements
102
are disposed in parallel with one another in the upper part of the structure on the semiconductor substrate
101
. Each of the fuse elements
102
electrically connects wiring layers
106
and
107
with each other via through-holes
108
. The side and upper surfaces of each fuse element
102
are covered with an insulating interlayer
109
. As the uppermost layer of the structure on the semiconductor substrate
101
, a silicon nitride film
110
is formed on the insulating interlayer
109
.
When a fuse element
102
is to be blown out, laser beams are applied to the fuse element
102
from above of the semiconductor substrate
101
, to raise the temperature of the fuse element
102
. The heated fuse element
102
changes in its state from solid phase to liquid phase and further to gas phase. When the rising pressure attendant upon the change in phase of the fuse element
102
exceeds the mechanical strength of the portion surrounding the fuse element
102
, an explosion occurs and the fuse element
102
is blown out. After the blowout, the part of the insulating interlayer
109
which has covered the side and upper surfaces of the fuse element
102
, and the corresponding part of the silicon nitride film
110
are blown away to form a recess (crater)
112
, as shown in FIG.
1
D.
The conventional fuse structure is provided with a moisture-proof ring structure
103
around the fuse elements
102
. The ring structure
103
is made up from ring-shaped wiring layers
104
formed at different levels in the structure on the semiconductor substrate
101
. All the wiring layers
104
are electrically connected via through-holes
105
, and the lowermost wiring layer
104
is electrically connected to the semiconductor substrate
101
. When a fuse element
102
is blown out by applying laser beams, a crack
111
may be generated in the insulating interlayer
109
near the blowout portion. The moisture-proof ring structure
103
is for preventing moisture coming through such a crack
111
from spreading beyond the moisture-proof ring structure
103
.
However, the conventional fuse structure as shown in
FIGS. 1A
to ID has the following problem. When a fuse element
102
is blown out, pieces of the fuse element
102
may adhere to the bottom or side wall of the recess
112
, as a result, part
102
′ of the fuse element
102
may remain. This may cause incomplete blowout of the fuse element
102
, and so reduces the reliability of blowout.
Besides, the minute structures of recent semiconductor devices demand to narrow the intervals between fuse elements. But, in case of narrow intervals, the above-described recess
112
may be formed near an adjacent fuse element
102
. In this case, when the adjacent fuse element
102
is next blown out, applied laser beams can not sufficiently raise the temperature of the fuse element
102
before explosion because a weak point is present in the portion surrounding the fuse element
102
. This also may cause incomplete blowout, and so reduces the reliability of blowout.
Further, the remaining part
102
′ of the blown-out fuse element
102
as described above may react with moisture, acid, alkali, or the like, to produce aqueous oxide. In this case, electric disconnection at the blowout portion is obtained in a certain time after the blowout occurs. But, when high voltages are repeatedly applied between the wiring layers
106
and
107
on both sides of the blowout portion, the aqueous oxide gradually spreads over the blowout portion finally to make an electric path. This is deterioration of cutoff resistance with age.
Further, high-pressure metal vapor of, e.g., aluminum as the material of fuse elements
102
, may enter the above-described crack
111
extending from the bottom of the recess
112
, to cause a short circuit with an adjacent fuse element
102
or another wiring layer. Such a crack
111
may cause not only leakage between neighboring fuse elements or undesirable cutoff of an adjacent fuse element, but also a damage to wiring around the fuse elements or corrosion due to entering moisture.
Japanese Patent Application Laid-open No. 7-307387 (1995) discloses a fuse structure in which grooves are provided on both sides of each fuse element.
FIGS. 2A
to
2
D show the fuse structure of this related art in the same fashion as
FIGS. 1A
to
1
D.
FIG. 2A
is a plan view showing the disposition of fuse elements formed in the upper part of the structure on a semiconductor substrate.
FIG. 2B
is a schematic sectional view taken along dot-dash line VI-VI′ in FIG.
2
A.
FIGS. 2C and 2D
are schematic sectional views taken along dot-dash line V-V′ in FIG.
2
A.
FIGS. 2C and 2D
show states before and after a fuse element is blown out with laser beams, respectively. In
FIGS. 2A
to
2
D, the corresponding components to those in
FIGS. 1A
to
1
D are respectively denoted by the same numerical references as those in
FIGS. 1A
to
1
D.
Referring to
FIGS. 2A
to
2
D, a groove
113
is provided on either side of each of parallel fuse elements
102
. The other construction is the same as in
FIGS. 1A
to
1
D.
According to the structure of this related art, when a fuse element
102
is blown out with laser beams, a large opening is formed at the blowout portion because of the grooves
113
on both sides of the fuse element
102
as shown in FIG.
2
D. This can prevent metal pieces of the blown-out fuse element
102
from adhering to the blowout portion. Besides, unlike the case of
FIGS. 1A
to
1
D, since no recess
112
is formed, such a crack
111
as shown in
FIG. 1D
is hardly generated.
The grooves
113
of this fuse structure can be formed as follows. A photoresist is formed on the silicon nitride film
110
, and processed with a mask into a pattern having openings at the positions respectively corresponding to the grooves
113
to be formed. Anisotropic etching is then performed to the silicon nitride film
110
and the insulating interlayer
109
to form the grooves
113
having their bottoms at a level lower than the bottom level of the fuse elements
102
.
In this case, however, unless severe positioning of the grooves
113
to the fuse elements
102
is done, the insulating interlayer
109
may differ in its lateral thickness on both sides of each fuse element
102
.
As described above, a fuse element
102
is blown out by the manner that the temperature of the metal material of the fuse element
102
is raised to gasify the material. Since the side and upper surfaces of the fuse element
102
are covered with the insulating interlayer
109
, the internal pressure gradually rises with the temperature rising. When the
Fujitsu Limited
Meier Stephen D.
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