JPH0793416B2 - Light receiving element and manufacturing method thereof - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light receiving element and a method of manufacturing the same, and more particularly, to a crosstalk occurrence in a one-dimensional image sensor in an image reading apparatus such as a facsimile. The present invention relates to a light-receiving element suitable for preventing and having a good resolution and improving the yield, and a manufacturing method thereof.

[Conventional technology]

Conventionally, a light receiving element made of hydrogenated amorphous silicon used for a one-dimensional image sensor is disclosed in, for example, NIKKEI ELECTRONICS, April 28, 1982, Issue 149.
As described on pages 161 to 161, metal / hydrogenated amorphous silicon (hereinafter referred to as a-Si: H) / Indium Tin Oxide (hereinafter referred to as ITO).
That is) is proposed.

That is, as shown in FIG. 2, a structure is proposed in which a metal electrode 2 made of Al or Cr, an a-Si: H film 3, and an ITO electrode 4 which is a transparent electrode are laminated in this order on a glass substrate 1. ing.

[Problems to be solved by the invention]

In putting the above-mentioned prior art into practical use, in order to protect the wiring as shown in FIG. 3, the metal electrode 2 is covered with Si ₃ N ₄ or S.
A structure covered with a transparent protective film 5 formed of iO ₂ or the like is used. However, covering with this protective film 5 involves a problem that the characteristics of the light receiving element are significantly deteriorated as described below.

That is, in the environment of the upper limit temperature of 70 ° C. in which the one-dimensional image sensor is used, the voltage in the dark place where the protective film 5 is formed and the reverse current (current flowing from the metal electrode 2 to the protective film 5 This type of light receiving element has been used in the past). The characteristic is that, as shown in FIG. 4, the reverse current 6 before the protective film 5 is formed against the reverse current 6 before the protective film 5 is formed. The current 7 has increased by about 3 orders of magnitude. Normally, the reverse current in a one-dimensional image sensor is 1 × 10 ^-7 A / at 70 ° C.
Since it is desirable that the thickness is cm ² or less, the characteristics of the light receiving element having the protective film 5 formed are deteriorated.

It is considered that the deterioration of the characteristics is caused by the deterioration of the bonding characteristics at the interface between the a-Si: H film 3 and the ITO electrode 4 due to the film formation of Si ₃ N ₄ or SiO _2. Is
A first layer of a-Si: H (hereinafter referred to as i layer) 3'obtained by glow discharge decomposition of only a SiH ₄ gas as shown in FIG. 5 on the a-Si: H film 3 shown in FIG. And a second layer of B-added a-Si: H obtained by glow discharge decomposition of a mixed gas of SiH ₄ gas and B ₂ H ₆ gas as a doping gas (hereinafter referred to as P layer)
It was found that this can be solved by using a two-layer structure composed of 8 and 8.

The two-layer structure will be described with reference to FIG. Figure 6 shows
3 is a diagram showing a relationship between a reverse current 9 before formation of the protective film 5 shown in FIG. 3 and a reverse current 10 after formation of the protective film 5 in the light receiving element having the structure shown in FIG. As shown, there is no difference between the two, and there is no deterioration in characteristics due to the formation of the protective film 5. The P layer 8 at this time is formed by glow discharge decomposition of a mixed gas of B ₂ H ₆ / SiH ₄ = 0.04% by volume,
The film thickness is 250Å.

However, when the a-Si: H is formed into an island-shaped independent shape as shown in the sectional view of FIG. 7, characteristic deterioration due to the formation of the translucent protective film 5 shown in FIG. The increase in the current is canceled in the same manner as in the case of FIG. 5, but the reverse current after the formation of the protective film 5 increases with time under a certain constant voltage, and as shown in FIG. to degrade.

That is, FIG. 8 shows the translucent protection shown in FIG. 3 at 70 ° C. when a constant voltage of 5 V is applied to a light receiving element formed in an island shape as shown in FIG. The time course of the reverse current after the formation of the film 5 is shown, but the change is so large that practical application is impossible with this characteristic. This deterioration of the characteristics is caused by the formation of a-Si: H in the shape of an island as shown in FIG. 7, so that the i-layer 3'is exposed at the side surface portion 15 of the a-Si: H. And the joining characteristics of the interface between ITO electrode 4 and
It is considered that the side surface portion 15 is deteriorated due to the formation of the translucent protective film 5 and the current leaks. This is fully conceivable from the following facts.

For example, in the case where a-Si: H3 is composed of the i layer 3'only, the increase in the reverse current after the formation of the protective film is represented by the reference numeral 7 in FIG.
As shown by, the voltage is about 2 × 10 ⁻⁵ A / cm ² when 5 V is applied. On the other hand, the pixel size of the island-shaped a-Si: H having the characteristics shown in FIG. 8 is 100 μm × 150 μm, and the film thickness is 1 μm. Therefore, the area of the exposed portion of the i layer 3 ′ on the side surface portion 15 is a
-Corresponds to about 3% of the surface area of Si: H. Since the increase in the reverse current is about 2 × 10 ^-5 A / cm ² , the reverse current increases at the side surface portion 15 by about 6 × 10 ^-7 A / cm ² , which is shown in FIG. It almost agrees with the value of the directional current increased with time. However, this deterioration of the characteristics does not form a-Si: H in an island shape, and
This does not occur as long as it has a two-layer structure of the layer 3'and the P layer 8.

However, when a-Si: H is not formed in an island shape, a-S
Each pixel is electrically connected by i: H, and the photocharge flows from the pixel that receives light to the pixel that does not receive light, and the pixel that does not receive light is as if it received light, that is, crossing. This causes a talk, and there is a problem in that the resolution of the one-dimensional image sensor using the above light receiving element deteriorates, particularly the resolution.

In the case where the a-Si: H film 3 is sandwiched between the metal electrode 2 and the ITO electrode 4 as described above, when a pinhole is generated in the a-Si: H film 3, the a-Si: H film 3 passes through the pinhole. As a result, the metal electrode 2 and the ITO electrode 4 are connected to each other and leak, which causes a problem that the yield is remarkably reduced.

In view of the above-mentioned problems of the prior art, the present invention can be used for a one-dimensional image sensor in an image reading apparatus such as a facsimile machine to prevent occurrence of crosstalk, have a good resolution, and improve the yield. An object of the present invention is to provide a light receiving element that can be manufactured and a manufacturing method thereof.

[Means for solving problems]

In order to achieve the above-mentioned object, the light receiving element of the present invention comprises: a plurality of metal electrodes which are independent island-shaped lower electrodes formed on an insulating substrate; and a hydrogen having a two-layer structure so as to cover each metal electrode. In a light receiving element formed by laminating a hydrogenated amorphous silicon film, the light-receiving element is formed by an interfacial reaction between a metal film directly formed on the entire surface of the hydrogenated amorphous silicon film and the hydrogenated amorphous silicon film. Among the translucent conductor layers, a translucent conductor layer for light incidence as a transparent electrode formed by removing the metal film in a predetermined region on each metal electrode formed in the island shape, An upper electrode serving as an extraction electrode of the transparent conductive layer formed by patterning the metal film in a strip-shaped region adjacent to the transparent conductive layer for light incidence, the upper electrode and the incident light Except for the region of the translucent conductor layer for By removing the formed translucent conductor layer and the hydrogenated amorphous silicon film having the two-layer structure by etching, the hydrogenated amorphous silicon film having the two-layer structure is independently formed for each metal electrode. The structure is characterized by being formed in an island shape.

In addition, the method for manufacturing the light receiving element of the present invention, on the insulating substrate,
In a method of manufacturing a light-receiving element, which comprises a plurality of metal electrodes each of which is an independent lower electrode and serves as a lower electrode, and a hydrogenated amorphous silicon film having a two-layer structure so as to cover the metal electrodes, (I) A metal film is directly formed on the entire surface of the hydrogenated amorphous silicon film, and (ii) a translucent conductor layer is formed by an interfacial reaction between the formed metal film and the hydrogenated amorphous silicon film. (Iii) of the translucent conductor layer, the metal film in a predetermined region on each of the island-shaped metal electrodes is removed to form a transparent electrode for transmitting light. Forming a conductor layer, and (iv) forming an upper electrode serving as a lead electrode of the light-transmitting conductor layer by patterning the metal film in a band-shaped region adjacent to the light-transmitting light-transmitting conductor layer. (V) Excluding the region of the upper electrode and the light-transmissive conductor layer for light incidence. The translucent conductor layer formed by the interface reaction and the hydrogenated amorphous silicon film having the two-layer structure are removed by etching, and the hydrogenated amorphous silicon film having the two-layer structure is formed for each metal electrode. The structure is such that it is formed in the shape of an independent island.

[Action]

As described above, the deterioration of the characteristics due to the formation of the protective film 5 shown in FIG. 3 is eliminated by making the a-Si: H structure into a two-layer structure of the i layer and the P layer. On the other hand, a-S
The characteristic deterioration of the side surface portion of a-Si: H that is exposed by forming i: H in the form of islands does not occur unless the side surface portion and ITO, which is a transparent electrode, are joined. As long as ITO is used as the transparent electrode, it is unavoidable to join the side surface of a-Si: H and ITO as shown in FIG. However, the present invention
The transparent electrode is changed to the ITO to form a light-transmissive conductor layer formed by an interfacial reaction between a-Si: H and a metal film directly formed on the a-Si: H, and the light-transmissive conductor layer and the island are formed. Processed into a
-Since the bonding with the side surface of Si: H is prevented,
It is possible to prevent leakage from occurring between the transparent electrode and the metal electrode, which is the lower electrode formed on the substrate, through the pinhole generated when the a-Si: H is formed. .

In addition, the extraction of the translucent conductor layer for light incidence to the outside is
Crosstalk can be prevented because the upper electrode also functions as a light shielding film formed by patterning the metal film and leaving it in a strip-shaped region adjacent to the light-transmitting conductive layer. it can.

〔Example〕

Hereinafter, a light receiving element according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 (a) is a plan view and FIG. 1 (b) is a sectional view.

As shown in FIG. 1, a plurality of metal electrodes 2'which are independent island-shaped lower electrodes are provided on an insulating substrate 1 '. In this embodiment, the metal electrode 2'is
Cr is formed by a 1000Å sputtering method, and is formed in an island shape by a photoetching process.

'Heating under vacuum were added to a reaction chamber of a plasma CVD device (not shown), by introducing SiH ₄ gas glow discharge decomposition method by a-Si: H i layer 3 of the membrane' the insulating substrate 1 of about 1μm to
After a thickness of about by introducing B ₂ H ₆ gas diluted with hydrogen
A P-layer 8'of a 250-Å-thick a-Si: H film is formed.

Next, the insulating substrate 1'is taken out from the plasma CVD apparatus and light etching is performed with an aqueous solution of hydrofluoric nitric acid in order to remove an oxide film of the i layer 3'and the P layer 8'by natural oxidation. Cr film is about 0.
It is directly formed on the entire surface of the a-Si: H P layer 8'of the insulating substrate 1'in a thickness of 1 .mu.m. In this case, the temperature of the insulating substrate 1'is preferably in the range of 100 ° C to 250 ° C.

The i layer 3'and the P layer 8'and the metal film (Cr in the present embodiment) formed directly on the entire upper surface by the above process.
The translucent conductor layer is formed by the interfacial reaction with the film).

Then, the Cr film is removed from above the region 13 shown by hatching in FIG. 1 by a photoetching method to form a light-transmitting conductive layer 12 for light incidence, and at the same time, it is shown in FIG. 1 in a band shape adjacent to the region 13. The Cr film is patterned in the region to form the upper electrode 11. The upper electrode 11 is a region to be a lead electrode of the translucent conductor layer 12. Next, a photoresist is laminated on the upper electrode 11 and the transparent conductive layer 12 shown by the region 13, and etching is performed. This etching is performed by using a transparent nitric acid aqueous solution for the transparent conductor layer 12 and a hydrazine aqueous solution for the i-layer 3'and the P layer 8'of a-Si: H. As a result, the i layer 3'and the P layer 8'are formed into independent islands.

Therefore, the side surfaces 15 of the i-layer 3'and the P-layer 8'are not bonded to the transparent electrodes as in the conventional case, and the pin holes generated when the i-layer 3'and the P-layer 8'are formed. The conventional transparent electrode (ITO electrode) and the metal electrode 2 can be prevented from leaking, and the yield can be significantly improved.

Further, since the upper electrode 11 also serves as the light shielding film, crosstalk can be prevented.

Using the light receiving element of this embodiment for a one-dimensional image sensor,
A protective film made of Si ₃ N ₄ having a thickness of 2 μm was formed on a predetermined portion of the light receiving element, and an experiment was conducted to examine the change with time of the reverse current after the protective film was formed at 70 ° C. when a constant voltage of 5 V was applied. As a result, no change with time was observed and it was confirmed that the characteristics were not deteriorated.

As described above, in the present invention, since ITO is not used as the transparent electrode, there are problems when ITO is used, damage to a-Si: H during ITO formation, and difficulty in obtaining high quality ITO. It is possible to solve various problems such as dissolution of ITO due to weak chemical resistance.

Furthermore, in the present invention, after forming the a-Si: H film, a metal film is laminated, and a translucent conductor layer is formed by an interfacial reaction between the metal film and the a-Si: H film. Since it is possible to form the light-transmitting conductive layer for light incidence only by removing the metal film in the predetermined region, the official manufacturing limit is reduced as compared with the case where ITO is used as the transparent electrode as in the conventional case. be able to.

〔The invention's effect〕

As described above, the present invention can be applied to a one-dimensional image sensor in an image reading apparatus such as a facsimile machine to prevent crosstalk from occurring, have a good resolution, and improve the yield. Play.

[Brief description of drawings]

FIG. 1 is a configuration explanatory view of a light receiving element according to an embodiment of the present invention. FIG. 2 is a sectional view of a conventional light receiving element before forming a protective film, and FIG.
FIG. 4 is a sectional view of a conventional light receiving element after forming a protective film, FIG. 4 is a reverse current curve diagram of the conventional light receiving element, and FIG.
A cross-sectional view showing a two-layer photodetector made of -Si: H, 6th
5 is a reverse current curve diagram before and after formation of a protective film of the conventional light receiving element shown in FIG. 5, FIG. 7 is a sectional view of a conventional island-shaped light receiving element, and FIG. 8 is shown in FIG. It is a reverse current curve figure of the conventional light receiving element. 1, 1 '... Insulating substrate 2, 2' ... Metal electrode (lower electrode), 3 ... a-Si: H, 3 '... a-Si: H i layer, 4
...... ITO electrode, 5 ...... Transparent protective film, 8, 8 '... a
-Si: H P layer, 11 ... upper electrode, 12 ... translucent conductor layer,
13 ... Area for light incidence, 15 ... Side surface.

Claims (2)

[Claims] 1. A plurality of metal electrodes to be lower electrodes, which are formed in the form of independent islands, and a hydrogenated amorphous silicon film having a two-layer structure so as to cover each metal electrode are laminated on an insulating substrate. In the light receiving element formed by, among the translucent conductor layers formed by the interfacial reaction between the metal film formed directly on the entire surface of the hydrogenated amorphous silicon film and the hydrogenated amorphous silicon film, A light-transmitting conductor layer as a transparent electrode formed by removing the metal film in a predetermined region on each of the island-shaped metal electrodes, and a light-transmitting conductor. A strip-shaped region adjacent to the layer, the upper electrode serving as an extraction electrode of the transparent conductive layer formed by patterning the metal film, and the upper electrode and the transparent conductive layer for light incidence. Except for the area, the translucent conductor layer and the The hydrogenated amorphous silicon film having the two-layer structure is removed by etching, so that the hydrogenated amorphous silicon film having the two-layer structure is formed in an island shape for each metal electrode. And a light receiving element. 2. A plurality of metal electrodes serving as lower electrodes, which are formed in the shape of independent islands, and a hydrogenated amorphous silicon film having a two-layer structure are laminated on an insulating substrate so as to cover the metal electrodes. (I) a metal film is directly formed on the entire surface of the hydrogenated amorphous silicon film, and (ii) an interface between the formed metal film and the hydrogen amorphous silicon film. A transparent conductive layer is formed by a reaction, and (iii) the transparent electrode is formed by removing the metal film in a predetermined region on each of the island-shaped metal electrodes of the transparent conductive layer. A light-transmissive conductor layer as a light-incident layer is formed, and (iv) the light-transmissive conductor layer is patterned by patterning the metal film in a band-shaped region adjacent to the light-transmissive conductor layer. Forming an upper electrode to be a lead-out electrode of (v) the upper electrode and the light incident transparent electrode. Except the region of the conductive conductor layer, the translucent conductor layer formed by the interfacial reaction and the hydrogenated amorphous silicon film having the two-layer structure are removed by etching to obtain the hydrogenated amorphous film having the two-layer structure. A method for manufacturing a light-receiving element, characterized in that a silicon film is formed in an island shape independently for each metal electrode.