JPH0653470A - Image sensor and fabrication thereof - Google Patents

Abstract

PURPOSE:To provide an image sensor, and fabrication thereof, in which dark current is prevented from increasing due to formation of a leak path by preventing short circuit of an upper transparent electrode and a lower metallic electrode through the side wall of an optoelectric conversion layer and the metallic electrode is protected against electrolytic corrosion. CONSTITUTION:A photoelectric conversion layer 3 is sandwiched by a metallic electrode 2 and a transparent electrode 4 to produce a light receiving element as a pixel and a plurality of pixels are arranged in main scanning direction to constitute an image sensor. An a-Si:H layer is laminated covering the metallic stripe electrode 2 and etching is carried out such that the protective film 3' of a-Si:H in the region other than the pixel becomes thinner than the optoelectric conversion layer 3 at the pixel part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image sensor used as an optical sensor for a facsimile or the like, and particularly an image sensor for suppressing an increase in dark current and preventing corrosion of electrodes in a severe environment of high temperature and high humidity. The present invention relates to a method for manufacturing a sensor and an image sensor.

[0002]

2. Description of the Related Art A conventional image sensor will be described with reference to FIGS. FIG. 4 is a plan view of a light receiving element portion of a conventional image sensor, and FIG.
It is a section explanatory view of a -B 'portion. As shown in FIGS. 4 and 5, the light receiving element portion of the conventional image sensor includes an insulating glass substrate 1 and a metal electrode 2 such as chromium (Cr) which is an individual electrode formed on the glass substrate 1. And the metal electrode 2
A photoelectric conversion layer 3 of hydrogenated amorphous silicon (a-Si: H) or the like formed in a strip shape in the main scanning direction on the top, and indium tin oxide (ITO) similarly formed in a strip shape on the photoelectric conversion layer 3. And transparent electrodes 4 and the like.

That is, in a sandwich type light receiving element in which a metal electrode 2, a photoelectric conversion layer 3 and a transparent electrode 4 are sequentially laminated on an insulating glass substrate 1, the upper layer is affected by the step difference of the lower pattern. Therefore, a structure has been desired in which the individual electrodes that require highly accurate patterning are arranged on the lower layer side and the transparent electrodes on the upper layer side are used as the common electrode. However, an image having a light receiving element of this structure
In the di-sensor, a thin film transistor (TF
In the case of integrating elements such as T), there is a problem that there is no degree of freedom in circuit design. Therefore, various improvements have been made, and an image having a light receiving element having transparent electrodes as individual electrodes has been added.
Jisensers have also been proposed.

Next, an image sensor having a light receiving element using transparent electrodes as individual electrodes will be described with reference to FIGS. 6 and 7. FIG. 6 is a plan view of a light receiving element portion of an image sensor using transparent electrodes as individual electrodes, and FIG. 7 is a sectional view of a CC portion of FIG. As shown in FIGS. 6 and 7, the light-receiving element portion of this image sensor is an insulating glass substrate 1, a metal electrode 2 such as Cr formed on the glass substrate 1 and serving as a common electrode, and a metal electrode. 2. A photoelectric conversion layer 3 made of hydrogenated amorphous silicon or the like, which is formed separately on each of the light receiving elements (pixels), and a transparent electrode 4 made of ITO or the like, which is also formed separately on the photoelectric conversion layer 3 and serves as an individual electrode. And an interlayer insulating layer 5 made of polyimide or the like formed so as to cover the entire light receiving element, and a wiring 6 made of aluminum (Al) or the like connected to the transparent electrode 4 via a contact hole provided in the interlayer insulating layer 5. It consists of and.

Then, the transparent electrode 4 is on the charge reading side, and T is provided through the wiring 6 drawn out in the sub-scanning direction.
The charge is read by the operation of a switching element for charge transfer such as FT. Further, the metal electrode 2 of the common electrode is formed in a band shape in the main scanning direction, and a positive bias is applied thereto. By configuring the light receiving element as described above, the degree of freedom in circuit design can be secured when elements such as thin film transistors (TFT) are integrated on the same substrate, and the output characteristics of each bit (pixel) are uniform. It was possible to increase the contrast ratio (see JP-A-63-67772).

[0006]

However, in the above conventional image sensor, when the ITO layer and the a-Si: H layer are completely separated for each pixel by using the transparent electrode 4 of ITO as an individual electrode, photoelectric conversion is performed. A leak path is formed between the transparent electrode 4 and the upper and lower electrodes of the metal electrode 2 through the side wall portion of the a-Si: H layer of the layer 3, and when a current-carrying operation is performed particularly in an environment of high temperature and high humidity, There was a problem that the Cr layer of the metal electrode 2 was dissolved by the electrolytic corrosion action, and the reliability of the image sensor was impaired.

The present invention has been made in view of the above circumstances, and the transparent electrode 4 of the upper electrode and the metal electrode 2 of the lower electrode, which have caused the dissolution of the chromium layer constituting the metal electrode 2 of the light receiving element, Solves the problem of short-circuiting through the side wall of the photoelectric conversion layer 3, and thus suppresses an increase in dark current that occurs due to the formation of a leak path due to short-circuiting, and the metal electrode 2 due to electric contact. It is an object of the present invention to provide an image sensor capable of preventing corrosion of the metal and a method for manufacturing the image sensor.

[0008]

According to a first aspect of the present invention for solving the problems of the conventional example, a light receiving element having a semiconductor layer sandwiched between a metal electrode and a transparent electrode is defined as one pixel, and is arranged in the main scanning direction. In the image sensor in which the plurality of pixels are arranged, the metal electrode is formed in a strip shape in the main scanning direction, the transparent electrode is separately formed for each pixel, and the semiconductor layer is formed to cover the metal electrode. The thickness of the semiconductor layer in the portion other than the pixel portion is smaller than the thickness of the semiconductor layer in the pixel portion.

According to a second aspect of the present invention for solving the problems of the conventional example, in a method of manufacturing an image sensor, a step of laminating a metal electrode on an insulating substrate and a step of covering the metal electrode. A step of stacking semiconductor layers, a step of separately forming a transparent electrode for each pixel on the semiconductor layer, and a step of etching so that a thin semiconductor layer remains on the metal electrode in a portion other than the pixel portion Is characterized by.

According to a third aspect of the present invention for solving the above-mentioned problems of the conventional example, in a method for manufacturing an image sensor, a semiconductor layer of a semiconductor layer is formed after the manufacturing process according to the second method for manufacturing an image sensor. It is characterized by adding a process of oxidizing the surface portion.

[0011]

According to the invention described in claim 1, the semiconductor layer is formed so as to cover the metal electrode, and the thickness of the semiconductor layer in the portion other than the pixel portion is smaller than the thickness of the semiconductor layer in the pixel portion. Since the image sensor has the formed light receiving element, the semiconductor layer is inserted between the transparent electrode and the metal electrode, so that a leak path of the current leak is prevented from occurring and the dark current increases. Can be suppressed, and since the water-resistant semiconductor layer protects the metal electrode, corrosion of the metal electrode can be prevented.

According to the second aspect of the present invention, the semiconductor layer is formed so as to cover the metal electrode formed on the insulating substrate, and the transparent electrode is divided and formed so as to be an individual electrode for each pixel. Since it is a method of manufacturing an image sensor in which a thin semiconductor layer is left on the metal electrode at a portion other than the above, the semiconductor layer is inserted between the transparent electrode and the metal electrode by making the etching time shorter than before. An image sensor capable of preventing the occurrence of a leak path of a current leak and suppressing an increase in dark current, and having a water-resistant semiconductor layer protecting a metal electrode to prevent corrosion of the metal electrode. Easy to manufacture.

According to the third aspect of the invention, the image sensor is manufactured by the method for manufacturing the image sensor according to the second aspect, and then the surface portion of the semiconductor layer is subjected to oxidation treatment. Releasing between transparent electrodes of each pixel
Thus, it is possible to obtain an image sensor capable of preventing the generation of the black current.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional explanatory view in the main scanning direction of an image sensor according to an embodiment of the present invention, and FIG. 2 is a plan explanatory view of one pixel of the image sensor of the present embodiment.
FIG. 3 is a cross-sectional explanatory diagram of a portion AA ′ in FIG. 2. It should be noted that portions having the same configurations as those in FIGS. 6 and 7 are described with the same reference numerals.

As shown in FIG. 1, in the light receiving element portion of the image sensor of this embodiment, a metal electrode 2 of chromium (Cr) or the like serving as a common electrode is formed in a band shape in the main scanning direction on a glass substrate 1. , A hydrogenated amorphous silicon (a-Si: H) layer is formed in a strip shape on the metal electrode 2, and on the a-Si: H layer, such as indium tin oxide (ITO), which becomes an individual electrode of each light receiving element, is formed. The transparent electrode 4 is formed separately, an interlayer insulating layer 5 made of polyimide or the like is formed so as to cover the entire light receiving element, and molybdenum () is formed via a contact hole formed in the interlayer insulating layer 5 on the transparent electrode 4. The wiring 6 made of Mo) and aluminum (Al) is connected to the transparent electrode 4. Here, a portion where the photoelectric conversion layer 3 is sandwiched between the metal electrode 2 and the transparent electrode 4 becomes a light receiving element, and this light receiving element becomes one pixel and a plurality of pixels are arranged in the main scanning direction.
It constitutes a line image sensor.

In the a-Si: H layer, the portion sandwiched by the metal electrode 2 and the transparent electrode 4 becomes the photoelectric conversion layer 3 for each light receiving element (each pixel), and the gap between adjacent light receiving elements. The thin film portion of the a-Si: H layer that covers is the protective film 3 '. The film thickness of the protective film 3 ′ is set to be sufficiently thinner than the photoelectric conversion layer 3 by about 1/10. That is, since the photoelectric conversion layer 3 and the protective film 3 ′ have different film thicknesses, a step is formed, and the side wall 7 is formed on the photoelectric conversion layer 3.

Specifically, the film thickness of the photoelectric conversion layer 3 is 10
The thickness of the protective film 3'is about 1000 to 2000 angstroms. The metal electrode 2 has a film thickness of about 1000 Å, and the transparent electrode 4 has a film thickness of about 600 Å.

For one pixel of the image sensor of this embodiment, as shown in FIGS. 2 and 3, the wiring 6 is drawn out in the sub-scanning direction, and a thin film of 1000 to 2000 angstroms is protected. The film 3'covers the metal electrode 2 also in the sub-scanning direction. Since the protective film 3 ′ protects the metal electrode 2 from moisture and the like, it is preferable to completely cover the metal electrode 2 except for a necessary portion where a bias voltage is applied.

Next, a method of manufacturing the light receiving element portion of the image sensor of this embodiment will be described with reference to FIG. As the glass substrate 1, a non-alkali glass substrate is used, and after the substrate is cleaned, Cr to be the metal electrode 2 is deposited by DC sputtering to about 1000 angstroms. Subsequently, a-Si: H to be the photoelectric conversion layer 3 is deposited by plasma CVD method to about 10,000 angstroms, and then ITO to be the transparent electrode 4 is deposited to about 600 angstrom by DC sputtering method.

Subsequently, after forming a resist pattern on the ITO so that the transparent electrode 4 is used as an individual electrode, etching is performed with a chlorine-based etching solution. Next, using the same resist mask, a-Si: H is etched by a dry etching method using a CF ₄ -based gas. At that time, just etching time calculated from the etching rate by dry etching of the a-Si: H layer so that the a-Si: H protective film 3'is left on the metal electrode 2 in the region other than the pixel portion. The etching is stopped in 10 to 20% shorter time. That is, the film thickness of the photoelectric conversion layer 3 in the pixel portion sandwiched between the metal electrode 2 and the transparent electrode 4 is about 1
Approximately 0000 angstroms, other regions on the metal electrode 2 (including a gap between adjacent light receiving elements)
Has an aS of about 1000 to 2000 angstroms.
The i: H protective film 3'is left.

Then, during this etching, the ITO protruding in the shape of a canopy is removed again with a chlorine-based etching solution. Then, after forming a resist pattern of the metal electrode 2,
After the protective film 3'of a-Si: H is etched by the dry etching method, C is removed by a cerium nitrate-based etching solution.
The metal electrode 2 is formed by etching r.

Next, polyimide is used as the interlayer insulating layer 5 by a spin coater to form a film having a thickness of about 1.2 μm, and then a contact hole is formed on the transparent electrode 4 by photolithography, and the wiring 6 is DC. Mo by sputtering method
Of about 500 Å, and then about 1.5 of Al
Deposit a film with a thickness of μm. Next, the wiring 6 is patterned into a predetermined shape.
The light-receiving element portion of the image sensor of this embodiment is completed by performing the patterning.

According to the image sensor of the present embodiment having the above-mentioned light receiving element, the metal electrode 2 has the moisture resistance aS.
Since the i: H protective film 3'is covered, the leak path between the metal electrode 2 and the transparent electrode 4 is not formed, and therefore, the effect of suppressing the increase of dark current can be suppressed, and the high current can be suppressed. The metal electrode 2 can be protected from humidity even in an environment of high temperature and high humidity. Therefore, the metal electrode 2 has moisture resistance and side wall leak does not occur, so that the metal electrode 2 by electroplating is used.
Corrosion does not occur and there is an effect that the environmental resistance can be improved.

Further, according to the method of manufacturing the image sensor of the present embodiment having the above light receiving element, the etching time for dry etching of the a-SiH layer is simply shortened by about 10 to 20% with respect to the just etching time. Therefore, there is an effect that the dark current can be suppressed and the image sensor having environment resistance can be easily manufactured.

Further, when the density of the pixels of the image sensor is increased, the photocurrent generated in one pixel is very small, so that the influence of the dark current due to the side wall leak is large. If the configuration of the light receiving element portion of the image sensor in the example is adopted, it is possible to prevent the side wall leak from occurring, which is effective for increasing the resolution of the image sensor.

Here, the protective film 3'has a thickness of 1000 to 1,000 as compared with the photoelectric conversion layer 3 having a thickness of about 10,000 angstroms.
Since the thickness is as thin as 2000 angstroms, the protective film 3'has a high resistance, and it is effective in preventing the leak of the photocurrent between the adjacent light receiving elements.

In this embodiment, after the a-Si: H layer is dry-etched, the side wall 7 of the photoelectric conversion layer 3 and the protective film 3'are formed.
It is more effective to prevent the current from leaking through the a-Si: H layer between the ITO elements separated from each other by oxidizing the surface of the element with O ₂ plasma.

Further, in the light receiving element portion of the image sensor of this embodiment, an example using ITO as the transparent electrode 4, an a-Si: H layer as the photoelectric conversion layer 3 and the protective film 3 ', and Cr as the metal electrode 2 is used. In addition, Sn is also used as the transparent electrode 4.
O ₂ (tin oxide) or ZnO (zinc oxide), Ti (titanium), Ta (tantalum), W (tungsten) as the metal electrode 2, a-Si: H layer 3 as NI type a-Si: H (NI type from the metal electrode side)
Alternatively, NIP type a-Si: H (from the metal electrode 2 side to NI
Similar effects can be expected in the image sensor using either of the P type.

Further, the light receiving element portion of the image sensor of this embodiment is connected to a thin film transistor (TFT), and, for example, as shown in Japanese Patent Laid-Open No. 62-67864, a TFT is used.
If it is used as a drive-type image sensor, a highly reliable image sensor can be realized.

[0030]

According to the invention described in claim 1, the semiconductor layer is formed so as to cover the metal electrode, and the film thickness of the semiconductor layer in the portion other than the pixel portion is larger than the film thickness of the semiconductor layer in the pixel portion. Since it is an image sensor having a thin light receiving element, a semiconductor layer is inserted between the transparent electrode and the metal electrode, so that a leak path for the current leak is prevented and a dark current is prevented. The effect of preventing corrosion of the metal electrode can be suppressed, and since the water-resistant semiconductor layer protects the metal electrode.

According to the second aspect of the present invention, the semiconductor layer is formed so as to cover the metal electrode formed on the insulating substrate, and the transparent electrode is divided and formed so as to be an individual electrode for each pixel. Since it is a method of manufacturing an image sensor in which a thin semiconductor layer is left on the metal electrode at a portion other than the above, the semiconductor layer is inserted between the transparent electrode and the metal electrode by making the etching time shorter than before. An image sensor capable of preventing the occurrence of a leak path of a current leak and suppressing an increase in dark current, and having a water-resistant semiconductor layer protecting a metal electrode to prevent corrosion of the metal electrode. There is an effect that it can be easily manufactured.

According to the third aspect of the invention, since the image sensor is manufactured by the method for manufacturing the image sensor according to the second aspect, and thereafter the surface portion of the semiconductor layer is subjected to the oxidation treatment, the method for manufacturing the image sensor is provided. Releasing between transparent electrodes of each pixel
There is an effect that it is possible to obtain an image sensor capable of preventing the generation of the black current.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view in a main scanning direction of an image sensor according to an embodiment of the present invention.

FIG. 2 is an explanatory plan view of one pixel of the image sensor of this embodiment.

3 is a cross-sectional explanatory view of a portion AA ′ in FIG.

FIG. 4 is an explanatory plan view of a light receiving element portion of a conventional image sensor.

5 is a cross-sectional explanatory view of a BB ′ portion of FIG.

FIG. 6 is a plan view of a light receiving element portion of a conventional image sensor.

7 is a cross-sectional explanatory view of a CC ′ portion of FIG.

[Explanation of symbols]

1 ... Glass substrate, 2 ... Metal electrode, 3 ... Photoelectric conversion layer,
3 '... protective film, 4 ... transparent electrode, 5 ... interlayer insulating layer,
6 ... Wiring, 7 ... Side wall of photoelectric conversion layer 3, P ... Light receiving element

Claims (3)

[Claims] 1. An image sensor in which a light receiving element having a semiconductor layer sandwiched between a metal electrode and a transparent electrode is one pixel, and the plurality of pixels are arranged in the main scanning direction. In the image sensor, the metal electrode is striped in the main scanning direction. The transparent electrode is formed separately for each pixel, the semiconductor layer is formed so as to cover the metal electrode, and the semiconductor in a portion other than the pixel portion is thicker than the film thickness of the semiconductor layer in the pixel portion. An image sensor having a thin layer. 2. A step of laminating a metal electrode on an insulating substrate, a step of laminating a semiconductor layer so as to cover the metal electrode, and a step of separately forming a transparent electrode for each pixel on the semiconductor layer. And a step of etching so that a thin semiconductor layer remains on the metal electrode in a portion other than the pixel portion. 3. The method of manufacturing an image sensor according to claim 2, further comprising a step of subjecting the surface portion of the semiconductor layer to an oxidation treatment after the manufacturing step of the image sensor manufacturing method according to claim 2.