Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Charge transfer device
Reexamination Certificate
2000-11-08
2003-01-07
Zarabian, Amir (Department: 2824)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Charge transfer device
C257S225000, C257S294000, C257S432000, C257S435000, C257S443000
Reexamination Certificate
active
06504188
ABSTRACT:
RELATED APPLICATION DATA
The present application claims priority to Japanese Application No. P11-317109 filed Nov. 8, 1999, which application is incorporated herein by reference to the extent permitted by law.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a solid image pickup device comprising a transfer electrode having a shunt wiring layer formed thereon, and a process for producing the same.
2. Description of the Related Art
Polycrystalline silicon is generally used as a transfer electrode of a solid image pickup device.
Because polycrystalline silicon of the transfer electrode has high resistance, propagation delay is caused, and therefore it is difficult to realize high-speed operation of the image pickup device and an image pickup device having a large area.
In order to solve the problems, such a constitution has been proposed that a wiring layer formed with a metal having low resistance, i.e., a so-called shunt wiring layer, is formed on the transfer electrode through a dielectric film, and the shunt wiring layer is connected to the transfer electrode via a contact part. Because the propagation occurs through the shunt wiring layer of low resistance by using the constitution, high-speed operation can be realized.
A cross sectional view of the vicinity of a photo sensor unit of a CCD solid image pickup device is shown in
FIG. 6
as an example of a solid image pickup device using a shunt wiring layer.
The CCD solid image pickup device
50
comprises a semiconductor substrate
51
having formed thereon a photo sensor unit containing a photodiode, a vertical charge transfer unit transferring a charge, a readout unit conducting readout a signal charge between the photo sensor unit and the vertical charge transfer unit and a channel stop region separating from the adjacent pixels, and a transfer electrode
53
is formed on the region other than the photo sensor unit through a dielectric film
54
.
FIG. 6
shows a cross section of a part where two of the transfer electrodes
53
overlap each other through the dielectric film
54
.
A shunt wiring layer
56
formed with a metal, such as aluminum and a high melting point metal, is arranged on the transfer electrode
53
through the dielectric film
54
.
A buffer layer (buffer wiring)
55
is provided between the shunt wiring layer
56
and the transfer electrode
53
, and the buffer layer
55
is connected to the transfer electrode
53
and the shunt wiring layer
56
, respectively, via contact parts not shown in the figure.
A light shielding layer
57
covering the entirety is formed on the shunt wiring layer
56
through the dielectric film
54
. The light shielding layer
57
has an opening
52
formed on the photo sensor unit and is formed to cover the image pickup region other than the opening
52
.
Furthermore, an on-chip lens
59
is formed on the light shielding layer
57
through a dielectric layer
58
having a smoothened surface, so as to condense incident light, which is directed to the opening
52
.
In the CCD solid image pickup device
50
, the shunt wiring layer
56
is connected to the transfer electrode
53
via the buffer layer
55
to lower the resistance of the transfer electrode
53
, whereby the propagation velocity is improved.
However, when a high melting point metal, such as tungsten, is used in the shunt wiring layer
56
, such a problem is caused by a heat treatment conducted after the formation of the dielectric film on the light shielding layer
57
that the contact resistance between the shunt wiring layer
56
and the transfer electrode (accumulation electrode)
53
is increased in the constitution where the shunt wiring layer
56
and the transfer electrode
53
is directly connected without the buffer layer
55
, and the contact resistance between the shunt wiring layer
56
and the buffer layer
55
is increased in the constitution shown in FIG.
6
.
The increase in contact resistance is mainly caused by the following factor. The polycrystalline silicon of the buffer layer or the transfer electrode and the high melting point metal are reacted by the heat treatment to form a silicide layer at the contact part, and the volume is increased in forming the silicide layer to lift the shunt wiring layer
56
, so as to form a gap at the contact part with the buffer layer or the transfer electrode.
On the other hand, when Al is used in the shunt wiring layer
56
, the heat treatment cannot be conducted at a high temperature because the Al is melted when a heat treatment at a high temperature is conducted after the formation of the dielectric film on the light shielding layer
57
.
Therefore, defects caused by damages of the silicon substrate
51
received in pattering the light shielding layer
57
cannot be sufficiently recovered, so as to increase the dark current.
The dielectric layer on the shunt wiring layer
56
is necessarily a dielectric film that can be formed at a low temperature, and in order to sufficiently ensure the coverage and the withstand voltage of the dielectric film, it is necessary to form the dielectric film with a large thickness. Therefore, such a problem is caused that the film thickness from the surface of the silicon substrate
51
to the upper end of the light shielding layer
57
is increased to lower the utilization efficiency of light, whereby the sensitivity is deteriorated.
SUMMARY OF THE INVENTION
In order to solve the problems associated with the conventional techniques, an object of the invention is to provide a solid image pickup device that can be operated at high speed and can suppress the dark current with high sensitivity, and a process for producing the same.
The invention relates to a solid image pickup device comprising plural sensor units formed on a substrate, a transfer electrode provided among the sensor units on the substrate, and a shunt wiring electrically connected to the transfer electrode, the shunt wiring comprising a high melting point metal layer and a layer comprising a nitride or an oxide of a high melting point metal.
The invention also relates to a process for producing a solid image pickup device comprising a step of forming a transfer electrode on a substrate having sensor units formed thereon, a step of forming, on the transfer electrode, a shunt wiring layer comprising a layer comprising a nitride or an oxide of a high melting point metal and formed thereon a high melting point metal layer, and a step of conducting, after forming a dielectric film to have concave parts on the sensor units, a heat treatment at a temperature of from 800 to 900° C. or a heat treatment to subject the dielectric film to reflow.
According to the constitution of the invention, because the shunt wiring of the transfer electrode is formed with an accumulated film of a high melting point metal and a nitride or an oxide of a high melting point metal, the resistance of the transfer electrode is lowered by the shunt wiring, and a heat treatment at a high temperature can be conducted owing to the use of the high melting point metal.
According to the production process of the invention, because the heat treatment is conducted at a temperature of from 800 to 900° C., defects on the surface of the substrate can be recovered.
Furthermore, because the shunt wiring layer is formed with the accumulated film comprising a nitride layer or an oxide layer of a high melting point metal having a high melting point metal layer formed thereon, the reaction between the transfer electrode and the shunt wiring layer on conducing the heat treatment can be suppressed, and the increase of the contact resistance to the transfer electrode is suppressed to decrease the resistance of the transfer electrode.
REFERENCES:
patent: 5796154 (1998-08-01), Sano et al.
patent: 6030852 (2000-02-01), Sano et al.
patent: 6252216 (2001-06-01), Ohashi
patent: 6255640 (2001-07-01), Endo et al.
Maruyama Yasushi
Sugimoto Dai
Menz Douglas
Sonnenschein Nath & Rosenthal
Zarabian Amir
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