Active solid-state devices (e.g. – transistors – solid-state diode – Integrated circuit structure with electrically isolated... – Passive components in ics
Reexamination Certificate
1999-02-08
2002-04-16
Lee, Eddie (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Integrated circuit structure with electrically isolated...
Passive components in ics
C257S209000
Reexamination Certificate
active
06373120
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device and more particularly, to a semiconductor device for simultaneously achieving high reliability to laser light radiation and small occupation region and method of manufacturing it.
2. Description of the Related Art
This type of semiconductor device is provided in, for example, a power source wire to supply a power source to a circuit. The semiconductor device is used when the supply of the power source to the circuit is stopped as necessary. The function of the semiconductor device is executed by cutting off a wiring layer constituting a fuse connected to the power supply wire by a laser light. The conventional semiconductor device will be described below.
FIG. 1
shows a semiconductor device disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 5-41481) (hereafter, referred to as a conventional technique
1
). It is intended to easily adjust the strength of a laser light to be radiated. A field oxide film
42
is formed on a P-type semiconductor substrate
41
. Moreover, a first interlayer insulating film
43
and a second interlayer insulating film
44
are formed on the field oxide film
42
.
A polysilicon film
45
as a fuse element is formed on the first interlayer insulating film
43
. The polysilicon film
45
is connected through contacts
48
-
1
,
48
-
2
to wires
46
-
1
,
46
-
2
formed of aluminum. The whole element is covered with a cover film
47
. An opening
49
is formed in the cover film
47
and the second interlayer insulating film
44
. The laser light is radiated to the opening
49
to cut off the polysilicon film
45
.
At this time, the strength of the laser light must be finely adjusted. The reason is described below. If the radiated laser light penetrates not only the polysilicon film
45
but also the first interlayer insulating film
43
and the field oxide film
42
and further reaches the P-type semiconductor substrate
41
, there may be a possibility that the polysilicon film
45
and the P-type semiconductor substrate
41
are in contact with each other.
When they are in contact with each other, if it is assumed that the wire
46
-
1
or
46
-
2
is supplied with a bias voltage Vcc and the semiconductor substrate
41
is biased to a ground potential GND, a leakage current is generated.
Thus, in this semiconductor device, an N-type diffusion layer
40
having a conductive type opposite to that of the semiconductor substrate
41
is formed in the semiconductor substrate
41
below the opening
49
. According to such a configuration, even if the laser light is slightly strong, the insulation between the wires
46
-
1
and
46
-
2
and the semiconductor substrate
41
is kept unless the laser light penetrates the N-type diffusion layer
40
. That is, if the polysilicon film
45
becomes in contact with the N-type diffusion layer
40
, the portion between the N-type diffusion layer
40
and the semiconductor substrate
41
is in the state of PN converse junction. Hence, the leakage current does not flow.
The similar semiconductor device is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 7-211779) (hereafter, referred to as a conventional technique
2
). In this device, fuses
55
-
1
,
55
-
2
are provided above an N-well
56
formed in a P-type semiconductor substrate
51
, as shown in
FIGS. 2A and 2B
. Moreover, P-type wells
50
-
1
,
50
-
2
are formed to prevent these fuses
55
-
1
,
55
-
2
from becoming in contact with the N-type well
56
when the fuses
55
-
1
,
55
-
2
are cut off.
Incidentally, the reference number
52
denotes a field oxide film,
53
denotes an interlayer insulating film and
54
denotes a cover film. In the semiconductor device, it is not desirable that the N-type well
56
and the like are kept in floating states since the charges accumulated in the N-type well
56
may cause the potential of the P-type semiconductor substrate
51
to be changed. Hence, the N-type well
56
is biased through the contacts
57
to the bias potential Vcc.
In these conventional techniques
1
and
2
, it is difficult to simultaneously achieve the improvement of the reliability to the laser light radiation and the miniaturization of the semiconductor device. In this case, the improvement of the reliability to the laser light radiation is to reduce the possibility that the leakage current flows when the fuse is in contact with the semiconductor substrate (or the well).
In the conventional technique
1
, the N-type diffusion layer
40
must be deeply formed to attain the high reliability. However, when the thermomigration is performed for a long time to form deeply the diffusion layer, the diffusion layer is expanded even in a lateral direction.
The diffusion layer is usually biased to a certain potential as described in the explanation of the conventional technique
2
. Typically, the diffusion layer is biased to the bias potential Vcc in the case of the N-type diffusion layer formed in the P-type semiconductor substrate, and it is biased to the ground potential GND in the case of the P-type diffusion layer formed in the N-type semiconductor substrate.
Hence, the range to implant an impurity to form the diffusion layer is determined to overlap a position of the contact of the wire to supply the bias voltage to the diffusion layer. The position of the contact is set to a position apart from the opening
49
by considering the dispersion of fragment when the laser light is radiated and the like.
If the diffusion layer is deeply formed, the diffusion layer is further expanded in the periphery from the position of the contact formed in the position apart from the opening
49
. This causes the region occupied by the semiconductor device to be made larger.
In the conventional technique
2
, the P-type wells
50
-
1
,
50
-
2
are originally formed in the N-type well
56
. Thus, the P-type wells
50
-
1
,
50
-
2
can not be formed extremely deeply. To deeply form the P-type wells
50
-
1
,
50
-
2
, the N-type well
56
must be made deeper. If the N-type well
56
is formed deeply, the problem similar to that of the conventional technique
1
is brought about. Moreover, if the P-type wells
50
-
1
,
50
-
2
are biased, the problem similar to that of the conventional technique
1
is also brought about. Furthermore, if the laser light penetrates the N-type well
56
, the fuse
55
and the P-type semiconductor substrate
51
become in contact with each other and the leakage current flows.
A semiconductor device described below is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 8-204129). This semiconductor device is provided with a well
12
having a conductive type opposite to that of a silicon substrate
11
, an insulating layer
13
formed on the well
12
and a laser trimming wiring layer
14
formed on the insulating layer
13
.
However, the approach to solve the above-mentioned subjects in the present invention is not disclosed in the semiconductor device disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 8-204129).
Moreover, a semiconductor device described below is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 3-83361). This semiconductor device is provided with a semiconductor substrate having a first conductive type, a diffusion layer having a second conductive type that is opposite to the first conductive type formed in the semiconductor substrate, an insulating film formed above the diffusion layer and the semiconductor substrate, and a cutoff fuse formed on the insulating film on the diffusion layer.
However, the approach to solve the above-mentioned subjects in the present invention is not disclosed in the semiconductor device disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 3-83361).
SUMMARY OF THE INVENTION
The present invention is made to solve the above-described problems in the related arts as mentioned above.
The present invention is accomplished to solve the above-mentioned problem. Therefore, an object of the present invention i
Díaz José R
Hutchins, Wheeler & Dittmar
Lee Eddie
LandOfFree
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