JPH04271178A - Optical converter - Google Patents

Abstract

PURPOSE:To allow a lower part electrode at an offset section of a substrate to comprise a lower layer made of a low melting point metal layer having a specific film thickness and an upper layer made of a high melting point metal layer having a specific film thickness and avoid the generation of discontinuity and prevent faulty picture elements even when a partial electrode in the lower part of a photo sensor is used as a wiring electrode on said substrate. CONSTITUTION:A lower part electrode film electrically connected with a switch by way of an opening section of an interlaminar insulation film 406 so as to constitute a photo sensor arrayed in one or two dimensional direction on a scanning integrated circuit 401 is deposited based on a sputtering process wherein a low melting point metal Cr layer 407 is deposited with a thickness of or smaller than 5000Angstrom while a high melting point Al layer 408 is deposited at a thickness which exceeds 5000Angstrom . Except for the Al layer which forms picture elements, two lower part electrode layers are formed in such a fashion that the Al layer may remain on an offset portion of a take out section from an MOS transistor. The application of the lower melting point metal for the upper layer makes it possible to cover the offset on the substrate and protect the wiring from discontinuity.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric conversion element, and more particularly to a scanning device configured to extract photoelectric charges from photosensors arranged in one or two dimensions using a scanning element via a switch. The present invention relates to a photoelectric conversion device in which the photosensor described above is deposited on an integrated circuit board using a laminating means.

0002

[Prior Art] In recent years, facsimiles, digital copying machines,
2. Description of the Related Art With the spread of image information processing devices such as image readers and video cameras, long line sensors in which photo sensors are arranged in one dimension and area sensors in which photosensors are arranged in two dimensions are frequently used. Various forms of photosensors are conceivable for use in these applications, but (1) functions can be separated according to the characteristics of the material. (2) Large area can be created all at once. (3) It is a low temperature process that is not limited by the substrate. (4) The production process is easy and costs can be reduced. In consideration of this functionality, applications of stacked photoelectric conversion devices in which thin film photosensors are stacked on a substrate on which switching elements and scanning circuits are formed are being actively applied.

[0003] When forming such a thin film type photosensor, electrodes are laminated above and below a photoconductive film, but the material for forming the electrodes placed below the photoconductive film is In order to avoid damage to the underlying substrate as much as possible, or to prevent the effects of heat from the layer formed on top,
A metal with a high melting point is usually used to suppress reaction with the layer formed on top.

0004

[Problems to be Solved by the Invention] However, the lower electrode also serves as wiring for connection to the switch element of the underlying scanning circuit section, and has to cross many steps caused by the formation of the element pattern. become. Therefore, for wiring electrodes, it is necessary to select a material that allows for a thick film to avoid disconnection, but normally the metal used for the lower electrode of a photosensor is a material with a high melting point and low reactivity. Because of this, the film is hard and brittle against bending, and it cannot be made sufficiently thick. Therefore, there is a problem in that disconnections often occur at the stepped portions, resulting in pixel defects.

[0005]

OBJECTS OF THE INVENTION The present invention has been made based on the above circumstances, and even when the lower electrode of a photosensor is also used as a wiring electrode on a substrate, it is possible to avoid the occurrence of disconnection and to avoid pixel defects.
The aim is to provide a highly reliable photoelectric conversion device.

[0006]

[Means for solving the problem] Therefore, in the present invention,
An interlayer insulating film is formed on a scanning integrated circuit board configured to extract photocharges from photosensors arranged in one or two dimensions using a scanning element via a switch. In a photoelectric conversion device in which a lower electrode film electrically connected to the switch through an opening, a photoconductive film that generates photocharges, and an upper electrode film are deposited in this order, the lower electrode is a pixel area determined by the overlapping portion of the upper electrode and the lower electrode, and is composed of a single metal or metal silicide electrode layer with a film thickness of 5000 Å or less and a low melting point,
Further, the step portion existing on the substrate is composed of two metal or metal silicide electrode layers, and one of the two metal or metal silicide layers has a
One is a low melting point metal or metal silicide layer with a thickness of 10,000 Å or more, and the other is a high melting point metal or metal silicide layer with a thickness of 10,000 Å or more.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically explained below with reference to illustrated embodiments.

FIGS. 1 and 2 show cross sections of a photosensor proposed for understanding the present invention, and show cases in which the lower electrode of the pixel portion is formed of Cr and Al, respectively. It is a conceptual diagram. If a metal with a low melting point such as Al is used for the lower electrode of the photosensor, short circuits due to hillocks and characteristic deterioration due to reactions with the photoconductive film are likely to occur. Therefore, a high melting point metal such as Cr is usually used for this lower electrode. In this way, if Cr or the like is used, the above problem does not occur. Of course, as high melting point metals, Mo and T can be used instead of Cr.
A similar effect can be obtained by using i,W. However, if this lower electrode is formed to cross the step and also serves as a wiring electrode for the underlying scanning circuit section, there is a risk that it will break at the step and cause a disconnection. This is because the lower electrode is usually thinner than the stepped portion and is made of a harder material.

Therefore, in the present invention, as shown in FIG. 3, the lower electrode at the step portion of the substrate is formed into two layers, for example, the lower layer is made of Cr and the upper layer is made of Al. In this case, the thickness of the Cr film is usually smaller than the dimension of the step therein, and since it is hard, it is easy to break and may cause step breakage. This is not Cr but Mo, T
The same applies to i and W. However, substantial disconnection can be avoided by using Al as the upper layer of the lower electrode, for example. That is, since a low melting point metal such as Al has a soft film quality and can be deposited to a thickness greater than the step difference, it is possible to sufficiently cover the step difference and prevent wiring breakage. For the reasons described above, it is possible to suppress the occurrence of pixel defects and realize a highly reliable photoelectric conversion device.

In the present invention, the low melting point metal and the high melting point metal which are selectively used as materials for the lower electrode formed under the photoconductive film are shown below.

[Low melting point metal] Generally has a melting point of 1300°C
Among the metals belonging to Groups 1B to 3B and Group 2A below, those typically used are Al, Mg, Cu, Ag, and Au.
, Zn, and Cd. Moreover, these silicides also serve as low melting point electrode materials. As for the manufacturing method of this film, a normal vapor deposition method, a sputtering method, a CVD method, etc. are used for a single metal, and a sputtering method is used for a silicide.

The thickness of the deposited film should be greater than the largest single step among the steps existing on the substrate surface. Usually, the maximum height difference is 7,000 to 10,000 Å, so it may be 10,000 Å or more.

[High melting point metal] Generally has a melting point of 1200°C
Among the transition metals belonging to the above 3A to 7A and 8 groups, those typically used are Ti, Ta, Cr, Mo, W,
These are Ni, Pd, and Pt. Moreover, these silicides also serve as high melting point electrode materials. As for the manufacturing method of this film, a normal vapor deposition method, a sputtering method, a CVD method, etc. are used for a single metal, and a sputtering method is used for a silicide.

The thickness of the deposited film is determined by taking into consideration the magnitude of stress generated during heating and cooling due to the difference in thermal expansion coefficient between the films deposited above and below the metal and the substrate. Although this cannot be said with absolute certainty depending on the type of substrate or film, if the thickness is less than 5000 Å, there is a high probability that cracking, peeling, etc. will occur in the metal film. That is, the film thickness of the high melting point metal must be 5000 Å or less.

[0015]

[Embodiment 1] Next, a first embodiment of the present invention will be specifically explained based on FIG. 4. First, SiH4 was deposited on a quartz substrate 401 at a gas flow rate of 50 by the usual LP-CVD method.
The polysilicon layer 402 was deposited for 10 minutes using SCCM, a substrate temperature of 620° C., and an internal pressure of 0.3 Torr.
000 Å, and this polysilicon layer is etched into a desired shape by a normal photolithography process. After that, 9
By performing thermal oxidation for 2.5 hours in an O2 atmosphere at 00.degree. C., an oxide film 404 with a thickness of 500 .ANG. is formed on the surface of the polysilicon layer 402.

[0016] Next, by the usual LP-CVD method, S
Deposition is performed for 30 minutes under the conditions of an iH4 gas flow rate of 50 SCCM, a substrate temperature of 620° C., and an internal pressure of 0.3 Torr to form a polysilicon layer 405 with a thickness of 3000 Å. By normal ion implantation into this polysilicon layer, B-
Ions are implanted into the entire surface, and then annealing is performed using N2
By performing the process in an atmosphere of 800° C., B- ions are diffused and the polysilicon layer 405 is made P type. After this, the polysilicon layer 40 is formed by a normal photolithography process.
5 is etched into a desired shape and used as a gate electrode of a MOS transistor.

After this, P+ ions are implanted into the entire surface by normal ion implantation at a dose of 5 x 1015 cm-2 and 160 keV, and then annealing is performed with N.
2. By performing the process in an atmosphere of 800° C., P+ ions are diffused to form the source and drain electrodes 403 and 403' of the MOS transistor.

[0018] Subsequently, by the usual plasma CVD method,
SiH4 gas flow rate 0.5SCCM, NH3 14.4
SCCM, H2 4.5SCCM, substrate temperature 200℃,
Deposition was performed for 160 minutes under the conditions of RF power of 3.5 W and internal pressure of 0.15 Torr, and the SiN layer 406 was deposited to a thickness of 8000 Å.
The SiN layer and the oxide film 404 are etched into a desired shape by a normal photolithography process, and holes are formed to take out the source and drain electrodes.

On top of this, a Cr layer 407 is formed by sputtering.
A layer 408 is deposited to a thickness of 2000 Å and an Al layer 408 is deposited to a thickness of 10000 Å, and then etched into a desired shape by a normal photolithography process to form an A
A two-layer metal or metal silicide lower electrode is formed by removing the L layer and leaving the Al layer at the step of the lead-out portion from the MOS transistor.

[0020] Next, by the usual plasma CVD method,
SiH4 gas flow rate 0.5SCCM, NH3 14.4
SCCM, H2 4.5SCCM, substrate temperature 200℃,
Deposition is performed for 60 minutes under the conditions of RF power of 3.5 W and internal pressure of 0.15 Torr to form a SiN layer 408 with a thickness of 8000 Å, which serves as a passivation film for underlying circuits such as MOS transistors. This SiN layer is etched into a desired shape by a normal photolithography process, and the Cr electrode 4 is etched into a desired shape.
Part of the surface of 07 is exposed.

Next, by the usual plasma CVD method, S
i2 H6 Gas flow rate 1.0SCCM, PH3 1.0
SCCM, H248.0SCCM, substrate temperature 300℃,
1 under the conditions of RF power 1.5W and internal pressure 1.2Torr.
Deposition was performed for 0 minutes, and n+ type amorphous silicon (n+
-a-Si:H) layer 410 with a thickness of 1000 Å, followed by Si2 H6 gas flow rate 1 without breaking the vacuum.
．． 0SCCM, H2 48.0SCCM, substrate temperature 30
Deposition was performed for 140 minutes at 0° C., RF power 1.0 W, and internal pressure 1.15 Torr to form an undoped amorphous silicon (ia-a-Si:H) layer 411 with a thickness of 8000 Å. Continuously, without breaking the vacuum, SiH4 gas flow rate 0.1SCCM, B2 H6 0.2SCCM, H
2 74.5SCCM, substrate temperature 200℃, RF power 33.0W, and internal pressure 2.0Torr for 20 minutes to deposit p+ type microcrystalline silicon (p+ -μc
-Si:H) layer 412 is formed with a thickness of 1000 Å.

Thereafter, ITO 413 with a thickness of 700 Å is deposited by sputtering, and etched into a desired shape by a normal photolithography process to separate the upper electrode 413 of the photodiode into each pixel.

[0023] Next, p + -μc-Si:H layer 412
, ia-Si:H layer 411, and n+-a-Si:H layer 410 are etched into a desired shape using a normal photolithography process to perform pixel separation.

[0024] Thereafter, by ordinary plasma CVD method,
SiH4 gas flow rate 0.5SCCM, NH3 14.4
SCCM, H2 4.5SCCM, substrate temperature 200℃,
Deposition was performed for 160 minutes under the conditions of RF power of 3.5 W and internal pressure of 0.15 Torr, and the SiN layer 414 was deposited to a thickness of 8000 Å.
It was formed with a thickness of . This SiN layer 414 is etched into a desired shape by a normal photolithography process, and a hole is opened for the upper wiring electrode to be taken out.

[0025] On top of this, 100% Al was applied by sputtering.
The upper wiring electrode 415 is deposited to a thickness of 0.00 Å and etched into a desired shape using a normal photolithography process. In this way, a line sensor, which is one of the photoelectric conversion devices of the present invention, was created. When the photoelectric conversion device formed by the above process was checked for operation, no pixel defects due to broken wiring were detected.

[0026]

Effects of the Invention As explained above, the present invention provides that the lower electrode is formed of a single layer of low melting point metal or metal having a film thickness of 5000 Å or less in a pixel area determined by the overlapping portion of the upper electrode and the lower electrode. The step portion existing on the substrate is composed of two metal or metal silicide electrode layers, and one of the two metal or metal silicide layers has a thickness of 50%.
One layer is a low melting point metal or metal silicide layer with a thickness of 00 Å or less, and the other is a high melting point metal or metal silicide layer with a thickness of 10000 Å or more, so that the lower electrode of the photosensor can be connected to the wiring electrode on the substrate. Even in the case of dual use, it is possible to avoid occurrence of disconnection and provide a highly reliable photoelectric conversion device without pixel defects.

[Brief explanation of the drawing]

FIG. 1 shows an example of the configuration of a solid-state image sensor formed by a conventional method.

FIG. 2 is a conceptual diagram for explaining the effects of the present invention.

FIG. 3 is a conceptual diagram for explaining the effects of the present invention.

FIG. 4 is a longitudinal sectional side view showing one embodiment of the present invention.

[Explanation of symbols]

101, 201 Substrate 102 Cr film 202
Al film 103, 203 Highly doped semiconductor layer 104, 204 showing one semiconductor type Undoped semiconductor layer 105, 2
05 Highly doped semiconductor layer 106, 206 showing the other semiconductor type Transparent electrode 21 Hillock 22
Al/Si reaction section 401
Substrate 402 Polycrystalline silicon film 40
3,403' source, drain 404
Gate insulating film 405
Gate electrode 406 Interlayer insulating film 407 Cr film 408
Al film 409
Passivation film 410
Highly doped semiconductor layer 411 showing one semiconductor type Undoped semiconductor layer 4
12 Highly doped semiconductor layer showing the other semiconductor type

Claims (4)

[Claims] 1. On a scanning integrated circuit board configured to extract photocharges from photosensors arranged in a one-dimensional or two-dimensional direction by a scanning element via a switch,
In order to configure the photosensor, a lower electrode film electrically connected to the switch through an opening in an interlayer insulating film, a photoconductive film that generates photocharges, and an upper electrode film are arranged in this order. In the photoelectric conversion device in which the lower electrode is deposited with
It is composed of one layer of metal or metal silicide electrode layer with a low melting point of 0 Å or less, and it is composed of two layers of metal or metal silicide electrode layer at the step part existing on the substrate. The metal or metal silicide layer is characterized in that one of them is a low melting point metal or metal silicide layer with a thickness of 5000 Å or less, and the other is a high melting point metal or metal silicide layer with a thickness of 10000 Å or more. Photoelectric conversion device. 2. At the stepped portion on the scanning integrated circuit board, a low melting point one having a thickness of 5000 Å or less among the two metal or metal silicide layers forming the lower electrode is formed as a lower layer. 2. The photoelectric conversion device according to claim 1, further comprising a high melting point material having a thickness of 10,000 Å or more as an upper layer. 3. Among the two metal or metal silicide layers forming the lower electrode in the step portion on the scanning integrated circuit board, a low melting point film having a thickness of 5000 Å or less and a temperature of 1300° C. or less is used. as the lower layer, the film thickness is 10
2. The photoelectric conversion device according to claim 1, further comprising a material having a high melting point of 000 Å or more and 1200° C. or more disposed in the upper layer. 4. The photoelectric conversion device according to claim 1, wherein the photoconductive film is made of hydrogenated amorphous silicon.