JPH0286170A - Image sensor - Google Patents

Abstract

PURPOSE:To obtain superior light-dark current ratio by interposing an oxide layer between a photo conducting layer and a light transmitting electrode, which oxide layer is formed by oxidizing a photo conducting layer surface, and prevents material constituting a wiring part from diffusing into the photo conducting layer. CONSTITUTION:After an Si3N4 insulative coating film 31, and a-Si semiconductor coating film 32 and an n<+> amorphous silicon semiconductor coating film 33 are formed one after another on a glass substrate 1, a Cr metal film (b') is formed, and an a-Si photo conducting film (c') is formed thereon. The glass substrate 1 is dipped in oxidizing agent solution; an SiOx layer 2s is formed on the surface by oxidizing the a-Si photo conducting film (c'); an indium oxide tin transparent metal film (d') is formed on the surface; then the transparent metal film (d'), the photo conducting film (c') and the Cr metal film (b') are individualized by photolithography etching. After polyimide resin is spread and thermoset, an aperture 2f is formed by photolithography etching using TMA as etching agent, and a photo transmitting insulating film 2e is formed. After a wiring part 2g is formed by using an Al metal film (g'), a passivation film is formed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a contact image sensor that includes a plurality of photoconductive elements on a substrate and is used in the input section of facsimile machines and various OA devices. This invention relates to the improvement of an image sensor that can obtain a good bright-to-dark current ratio.

[Prior Art] As shown in FIGS. 6 to 8, this type of image sensor includes a plurality of photoconductive elements (b) to (b) groups provided on a substrate (a) made of glass or the like. , each photoconductive element (b) to (
b) Driving thin film transistors (C) to (
The main part is composed of group C), and each photoconductive element (b)
A device is known in which image information is read based on the signals from (b) to (b).

The photoconductive element (b) constituting the image sensor (d) is formed of a metal such as chromium (Cr) through an appropriate intervening member (e) as shown in FIGS. 9 and 10. A common 1f[1(f) and a photoconductive layer (g) formed on this common electrode (f) and made of amorphous silicon etc.
(IIJ) group, and indium-tin oxide (Indium-Tin Oxid) formed on each light guide N layer (g) to (g).
e: Light-transmissive electrodes (h) to (h
) group, a light-transparent insulating film (j) that covers the light-transparent electrodes (h) to (h) group and insulates them from each other, and an opening provided in this light-transparent insulating film (j). The main part thereof is composed of signal readout wiring parts (k) to (k) connected to the light-transmitting electrodes (h) to (h) through (i) to (i), and the above-mentioned One end side of the wiring portions (k) to (k) is the source/drain electrode (C) of the thin film transistors (C) to (C).
1) to (C1) and each photoconductive element (b) to (b
) to the film transistors (C) to (C)
It is designed to output to the side. That is, a constant voltage is applied between the common electrode (f) and each of the light-transmitting electrodes (h) to (h), so that the reflected light from the document (not shown) is applied to each of the light-transmitting electrodes (h). ) to photoconductive layer (q) through (h)
(g), the resistance value of the photoconductive layers (g) to (g) changes depending on the difference in brightness of the incident light, and a current corresponding to the amount of incident light flows through each thin film transistor (C) to (C). The image information is read by being output to the side.

[Problems to be Solved by the Invention] Incidentally, in this type of image sensor, the wiring portion (k) connected to the light-transmitting electrode (h) is usually made of aluminum (Aj) or gold, which has excellent conductivity. (AU),
Metals such as nickel (N i ) are used.

However, these metals have large diffusion coefficients, so during the film deposition process and heating process of the metals during image sensor manufacturing, these metals diffuse into the photoconductive layer (g) through the light-transmitting electrode (h). There were cases where I ended up doing it.

For this reason, there is a drawback that the resistance value of the photoconductive layer (g) decreases, making it impossible to achieve a sufficient Schottky junction between the light-transmitting electrode (h) and the photoconductive layer (g), as shown in FIG. In some cases, the dark current increases when the photoconductive layer (g) is not irradiated with light, making it impossible to obtain a good light-to-dark current ratio.
There is a problem in that when reading a continuous tone original, it is not possible to produce tone differences corresponding to the tone.

[Means for Solving the Problems] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an image sensor that can obtain a good bright-to-dark current ratio.

That is, the present invention includes a photoconductive layer made of an amorphous semiconductor material, a light-transparent electrode laminated on one surface of the photoconductive layer, and a signal readout wiring section connected to the light-transparent electrode. The premise is that the image sensor is equipped with a plurality of photoconductive elements, and reads image information based on signals from each photoconductive element. It is characterized in that an oxide layer is interposed to prevent the material constituting the formed wiring portion from diffusing into the photoconductive layer.

In such technical means, materials such as amorphous silicon, p-1-n type amorphous silicon, amorphous silicon/n-amorphous silicon, etc. can be used as the amorphous semiconductor material constituting the photoconductive layer. Indium tin oxide (ITO
), tin oxide (5nO2), indium oxide (In203
), zinc oxide (ZnO), and other conductive materials having optical transparency can be used.

On the other hand, the electrodes placed opposite the light-transmissive electrodes with the photoconductive layer in between are usually common electrodes that serve as electrodes for each photoconductive element group, such as chromium (
Cr), aluminum (Aj), molybdenum (MO),
Tungsten (W), nickel (N + ), gold (A
u), platinum (Pt), lead (Pd), Cr/A
Metal materials with good conductivity such as u can be used, and materials for forming the wiring part include aluminum (AI), gold (AU
), nickel (N i ), copper (CLI), chromium (
Metal materials with good conductivity such as Cr), tungsten (W), titanium (Ti>), molybdenum (MO), titanium nitride (TiN), titanium tungsten (TiW), and tantalum (Ta) can be used.

Suitable materials for the light-transparent insulating film that covers the light-transparent electrodes include polyimide resin, silicon nitride (SiN), which is widely used in this type of image sensor.
), silicon oxide (SiO2)X, etc. can be used.

In the present invention, an oxide layer formed by oxidizing the surface of the photoconductive layer during the manufacturing of the image sensor is interposed between the photoconductive layer and the light-transmitting electrode to form the wiring section. This prevents material from diffusing into the photoconductive layer.

Here, as the oxidizing agent for oxidizing the surface of the photoconductive layer, commonly used oxidizing agents that are widely used can be used, for example,
Mixture of sulfuric acid (H504) and hydrogen peroxide (H2O2)
Mixed aqueous solution of aqueous ammonia (NHOH) and hydrogen peroxide (1-1,202), nitric acid (HNO), perchloric acid (HCj)
? O), hydrogen peroxide (H2O2), chromic acid (HCrO
2) etc.

Note that if the oxide layer formed by this oxidation treatment is too thick, the conductivity of the photoconductive layer will drop and the photocurrent will decrease, so care must be taken to adjust the oxidation conditions appropriately to avoid making it too thick. It takes.

In addition, an oxide film with uneven thickness may be formed on the surface of the photoconductive layer due to natural oxidation during the process before oxidation treatment, and if oxidation treatment is performed in this state,
This is not preferable because the thickness of the formed oxide layer becomes uneven, resulting in variations in sensor characteristics.

In such cases, instead of performing oxidation treatment, the natural oxide film formed on the surface of the photoconductive layer is removed using an etching solution such as hydrogen fluoride (HF) to make the surface of the photoconductive layer uniform. It is recommended to perform oxidation treatment from the beginning.

[Function] According to the above-mentioned technical means, since the oxide layer is interposed between the light-transmitting electrode and the photoconductive layer, this oxide layer causes the photoconductive layer of the material constituting the wiring portion to How can we prevent its spread?

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

That is, as shown in FIG. 1, the image sensor according to this embodiment includes a glass substrate (1) and a plurality of photoconductive elements (2) to (2) groups provided on this substrate (1). , and a group of driving thin film transistors (3) to (3) connected to each photoconductive element (2) to (2).

The photoconductive element (2) includes a common electrode (2b) made of chromium (Cr) formed through an appropriate intervening member (2a), and this common electrode as shown in FIGS. (2b
) formed on amorphous silicon (a-8+)
The photoconductive M (2c) to (2c) group made of
A group of light-transmitting electrodes (2d) to (2d) made of indium tin oxide (ITO) formed on each of the photoconductors 1! (2d)
A light-transmissive insulating film (2e) made of polyimide resin that covers the groups (2d), openings (2f)-(2f) provided in this light-transmissive insulating film (2e), 2f)
~ (2f) through the above-mentioned light-transmissive electrode (2d) ~ (2d)
Aluminum (AI') for signal readout connected to
) wiring portions (2g) to (2g) constitute the main part, and one end side of the wiring portions (2g) to (2g) is connected to the source/drain electrodes (3) to (3) of the above thin film transistors 30) to (30).

In addition, regarding the above-mentioned intervening member (2a), the photoconductive element (2
) Amorphous silicon nitride ($13N4) insulating film (31) for the gate insulating film formed during the manufacturing process of the thin film transistor (3) connected to ) and amorphous silicon (a-3i) for the amorphous semiconductor layer. It is composed of a semiconductor film (32) and an n+ amorphous silicon semiconductor film (33) for ohmic contact.

In the image sensor configured in this way, a voltage is applied between the common electrodes (2b) to (2b) and each of the light-transmitting electrodes (2d) to (2d), as in conventional image sensors. The reflected light of each light-transmitting electrode (2d) ~
When the light enters the photoconductive layers (2c) to (2C) through the photoconductor (2d), a current having a value corresponding to the difference in brightness of the incident light is output to the thin film transistors (3) to (3) to provide image information. This is what is read.

In this case, in this image sensor, an oxide layer (
2S), it is possible to prevent the diffusion of aluminum (Aj) for the wiring part (2g) into the photoconductive layer (2C) during the manufacturing of the image sensor. Since a sufficient Schottky junction can be achieved between the light guide 1f (2C) and the light guide 1f (2C), a good bright/dark current ratio can be obtained, which has the advantage of improving reading accuracy.

Here, FIG. 4 shows the I of the image sensor according to this embodiment.
This graph shows the bright current (■ in the figure).
) is at the saturation level at an illuminance of 100 Ix (lux), confirming that there is no reduction in photocurrent due to the provision of the SiOx oxide layer (2S).On the other hand, the dark current (indicated by ) is a light-transmissive electrode (denoted by 2d
) and the good Schottky barrier of the photoconductive layer (2C), it was confirmed that the value was suppressed to a low value of approximately 1 pA when 5 ■ was applied, and a high contrast ratio of approximately 9000 to 110 Q0 was obtained. .

In addition, ■ in Fig. 4 indicates the dark current when aluminum (AI) for forming the wiring part (2g) is not deposited, that is, the dark current when there is no diffusion of aluminum into the photoconductive layer (2C). It was confirmed that the dark current (indicated by ■) does not occur in this image sensor even when aluminum (Aj) for forming the wiring portion (2Q) is deposited. In addition, ■ indicates the dark current of the conventional image sensor, which is an extremely high value (approximately 100 pA) compared to the image sensor according to this embodiment.
It was confirmed that it shows.

"Manufacturing Example of Image Sensor" First, as shown in FIG. 5(a), an amorphous silicon nitride (Si3N4) insulating film (31) and an amorphous silicon (a-8i) M semiconductor film are formed on a glass substrate (1). (32) and an n+ amorphous silicon semiconductor film (33), a chromium (Cr) metal film (bo) for forming a common electrode is deposited on this surface to a thickness of about 1500 angstroms by DC magnetron sputtering. amorphous silicon (a-8i) for forming a photoconductive layer on this surface.
) made light guide? ! ! A film (Co) having a thickness of about 1□3 μm is deposited by p-CVD (chemical vapor deposition).

Next, the glass substrate (1) was immersed for 10 minutes in an oxidizing agent solution (a solution in which NH40H, H2O2, and H2° were mixed in a weight ratio of 1:1:5, respectively) heated to 70°C, The amorphous silicon (a-8i) photoconductive film (Co) is oxidized to form S + Ox on the amorphous silicon (a-8i) photoconductive film (Co) as shown in FIG. 5(b). A transparent gold oxide layer (2S) made of indium tin oxide (ITO) is formed on this surface, as shown in FIG.
After depositing a film of approximately 750 angstroms by DC magnetron sputtering method, the transparent metal film (d') is coated with a photoconductive layer as shown in FIGS. 5(d) to 5(e). (C
') and the chromium metal film <bo) are individually separated by photolithography. In this case, a transparent metal film (d
Indium tin oxide (o) is etched by wet etching using dilute hydrochloric acid, and amorphous silicon (c') is etched by plasma etching using CF4+02.
Regarding (b'), the etching process was performed by a wet etching method using a mixed solution of ceric ammonium nitrate, perchloric acid, and pure water.

Next, 1 μm of polyimide resin for forming a light-transmissive insulating film is applied onto the above surface by spin coating, and
After heating and thermosetting in a clean oven, an opening (2f) is opened by photolithography using tetramethylammonium hydroxide (TMA) as an etching agent to transmit light as shown in Figure 5(f). A conductive insulating film (2e) is formed.

Furthermore, as shown in FIG. 5(g), an aluminum metal film (g) for forming wiring portions was deposited to a thickness of 1 μm on the above surface by sputtering, and then a film was deposited on this surface as shown in FIG. 5(h). Photoresist pattern (5) for forming wiring part as shown
form.

Then, after etching the aluminum metal film (g'') for forming the wiring part using an etching agent made of hot phosphoric acid to form the wiring part (2g), the wiring part (2g) is formed.
As shown in i), the seven photoresist patterns (5) are peeled off and a passivation film (not shown) is formed on this surface to obtain an image sensor.

In addition, the above amorphous silicon light guide 'Rm (c')
When forming an oxide layer (2S) made of SiOx through oxidation treatment, an oxide film with uneven thickness may have already been formed on the surface of the photoconductive film (Co) due to natural oxidation before this oxidation treatment. . In such cases, glass substrate (1)
An oxide film dissolving agent (HF and H2C: 1:2 by weight)
A photoconductive film (Co) is formed by immersing it in a solution mixed with Co.
It becomes possible to form an oxide layer (2S) of -like SiOx[ on top of the substrate (1), which has the advantage of suppressing variations in sensor characteristics within the substrate (1) or between substrates (1).

Furthermore, when manufacturing this image sensor, it goes without saying that the manufacturing process of the driving thin film transistor is also progressing at the same time.

[Effects of the Invention] As described above, in the present invention, since the oxide layer is interposed between the light-transmitting electrode and the photoconductive layer, the photoconductivity of the material constituting the wiring portion is reduced by the action of the oxide layer. It becomes possible to prevent diffusion into the layer.

Therefore, a sufficient Schottky junction can be created between the light-transmitting electrode and the photoconductive layer, and an increase in dark current can be suppressed.
This has the effect of obtaining a good bright-to-dark current ratio and improving reading accuracy.

[Brief explanation of the drawing]

1 to 5 show embodiments of the present invention, FIG. 1 is a partial perspective view of an image sensor according to the embodiment, FIG. 2 is a partial plan view thereof, and FIG. 3 is a partial perspective view of an image sensor according to the embodiment. ■-■ cross-sectional view Figure 4 is a graph showing the iV characteristics of the image sensor according to the example, and Figures 5 (a) to (i) are process explanatory diagrams for manufacturing examples of the image sensor according to the example. 6 to 11 show a conventional image sensor, FIG. 6 is a partial perspective view thereof, and FIG. 7 is a Vt shown in FIG. 6.
-■ plane sectional view, Fig. 8 is its plan view, Fig. 9 is its partial plan view, Fig. 10 is the XX plane sectional view of Fig. 9, and Fig. 11 shows the IV characteristics of this image sensor. It is a graph diagram. [Code explanation <1)...Substrate (2)...Photoconductive element (3)...Thin film transistor (5)...Photoresist pattern (2b)...Common electrode (2c)... Photoconductive layer (2d)...Light-transparent electrode (2e)...Light-transparent insulating film (2f)...Opening (2g)...Wiring portion (2S)...Oxide layer Patent Applicant Fuji Xerox Co., Ltd. Representative Patent Attorney Tomohiro Nakamura (3 others) Figure 10 Figure 11 Figure 1゜Applied voltage (volts)

Claims (1)

[Claims] A photoconductive layer made of an amorphous semiconductor material;
A plurality of photoconductive elements each having a light-transmitting electrode laminated on one surface of the photoconductive layer and a wiring section for signal readout connected to the light-transmitting electrode are provided, and based on signals from each photoconductive element, In an image sensor that reads image information by using An image sensor characterized by having a protective oxidation layer interposed therein.