JPS59154062A - Amorphous silicon image sensor and manufacture thereof - Google Patents

Abstract

PURPOSE:To reduce leakage current and thus improve charge retention by a method wherein a substance having a high resistance close to that of an insulator, a large coefficient of the absorption of a visible light, and no photosensitivity is used for a light shielding layer. CONSTITUTION:The titled device is constructed by including a transparent and insulator substrate 20, a stripe clear electrode 20 provided on this substrate, a fluorinated amorphous Si film 22 of a specific resistance at 10<9>OMEGAcm or more having a stripe window on the clear electrode, a transparent insulation film 23 which is provided by covering this Si film and said window and serves as a hole blocking layer, a hydrogenated amorphous Si layer 24 of a specific resistance at 10<9>OMEGAcm or more provided on this insulation film, a P type hydrogenated amorphous Si layer 25 which is provided on this hydrogenated layer and serves an electron blocking layer, and a plurality of metallic electrodes 26 provided on this P type layer. A signal light 27 is received on the undersurface of the substrate 20.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image sensor using amorphous silicon and a method for manufacturing the same.

In recent years, miniaturization of facsimile IJ devices has been desired in order to spread the use of facsimile IJs in households. The biggest obstacle to miniaturizing such an apparatus is the size of the photoelectric conversion system 49' in both image reading sections. ′Traditional fax
) Photoelectric conversion device (hereinafter referred to as image sensor) is M
OS i;:t, , CCl) type ring semiconductor ICs have been used. However, this semiconductor IC image sensor has a small chip size of several tens of millimeters, for example, 20C.
In order to convert a m-wide A4 size original into an electrical signal, an optical system is required to reduce the original image to a width of several tens of mm, and the required optical path length (40 to 6 Qcm for A4 size width) is required. This has been seen as a bottleneck in equipment miniaturization.

An image sensor called a contact image sensor is attracting attention as a solution to this problem. This is a large image sensor that has a large number of tiny optical a conversion elements arranged one-dimensionally in the same dimension as the width of the original.Since it is used in close contact with the original, a lens system is used to reduce the original image. Since there is no need to do this, the device can be significantly miniaturized. The optical sensor material used in such a contact image sensor must have excellent photoelectric conversion characteristics and be able to be formed uniformly over a large area. Hydrogenated amorphous silicon, which has recently attracted attention, is an excellent light-guiding material that meets the above objectives, and its application to contact image sensors has also begun to be considered. This hydrogenated amorphous silicon is usually formed by glow discharge decomposition of monosilane or reactive sputtering of silicon, and it is easy to obtain a uniform thin film over a large area, and the material forming the trench is non-polluting silicon. It has advantages such as being hydrogen. When applying hydrogenated amorphous silicon to a contact image sensor, it is operated in an accumulation type by taking advantage of the relatively high dark resistivity of hydrogenated amorphous silicon of 109 to 1012 Ω-cm. is desirable. The operating principle of such an accumulation type sensor will be explained using the drawings.

FIG. 1 is an equivalent circuit diagram of an example of a conventional storage type image sensor.

A sensor element is isometrically represented by an interelectrode capacitance 3, a diode 4 representing the rectifying contact, a resistor 5 representing the leakage current, and a voltage source 6 representing the photocurrent. In the figure, 1 is the power supply and 2 is the common electrode resistance. It is assumed that such sensor elements are arranged in multiple dimensions.

First, the individual sensor switch 7 is closed to accumulate charge in the sensor capacitor 3, and then the switch 7 is opened, and the photocurrent 6 generated by the light from the document causes the charge to be accumulated in the sensor capacitor 3 for a certain period of time. Erase. Then, when the switch 7 is closed again, the magnitude of the current flowing through the read resistor 8 can be read from the read terminal 9. Image signals are read by repeating the above-mentioned operations using the sensor elements arranged one-dimensionally.

As is clear from the above operating principle, in the case of an accumulation type sensor, a very high resistivity is required in order to retain charge. This resistivity is practically 10~lo i 4Ω-cm
It is said that Therefore, 109~1012Ω-c
In order to use hydrogenated amorphous silicon with a resistivity of m as an image sensor, it is necessary to prevent charge injection from the electrode in order to further increase the apparent resistivity. The inventors previously devised the use of P-ring hydrogenated amorphous silicon as a blocking layer for electrons and a transparent dielectric film such as 5iaN4, 5iOz as a blocking layer for holes.

In addition, when reading image signals with the above sensor elements, in order to improve resolution and S/N, it is necessary to reduce the leakage current of each sensor element when it is irradiated with light, and to reduce the leakage current from adjacent sensor elements. It is necessary to.

For this reason, we first devised the use of a metal light-shielding film with striped windows to prevent light from hitting anything other than the light-receiving area of each sensor element, and the removal of the P-type amorphous silicon layer between each sensor element. did.

FIG. 2 is a cross-sectional view of an example of a conventional image sensor element.

This image sensor confectionery was previously devised by the present inventors. In FIG. 2, 10 is a transparent insulating substrate such as glass, 11 is a transparent electrode, 12 is a metal liner that serves as a light-shielding layer, 13 is a transparent insulating layer, 14 is high-resistance hydrogenated amorphous silicon, and 15 is a P ring. Hydrogenated amorphous silicon, 16 is the upper individual hole, pole ″:C.

The signal light enters from the transparent insulating substrate 10 side, and the sensor light receiving section is the transparent electrode 13. The photocurrent flows in the high-resistance amorphous silicon 14 along a path indicated by a solid arrow, and the dark current flows through a portion of the solid arrow and the dotted arrow. Therefore, there is a drawback that leakage current from sources other than lj required for light reception is large and charge retention is not sufficient.

An object of the present invention is to provide an amorphous silicon image sensor that eliminates the above-mentioned drawbacks, reduces frost leakage and improves charge retention, and a method for manufacturing the same.

The present inventors have discovered that the cause of large leakage current is light shielding.
He discovered that the use of metals.

We have found that it is best to use a material for the light-shielding layer that has high resistance similar to that of an insulator, has a large absorption coefficient for visible light, and is insensitive to light. Fluorinated amorphous silicon is a material that meets these requirements. Fluorinated amorphous silicon has a high resistivity with a specific resistance of 101 OΩ-α or more, a visible light absorption coefficient of 105, and a photosensitivity of almost zero. Therefore, the present invention is as follows.

It was composed of sea urchins.

The amorphous silicon image sensor of the present invention includes a transparent insulating substrate, a striped transparent electrode provided on the substrate, a side surface and a top surface of the transparent electrode exposed, and a striped transparent electrode provided on the substrate. Specific resistance 109Ω-α with striped windows
The above fluorinated amorphous silicon film, a transparent insulating film that is provided by rubbing the fluorinated amorphous silicon film and the window and serves as a hole blocking layer, and a transparent insulating film that is provided on the transparent insulating film. a hydrogenated amorphous silicon layer having a specific resistance of 109 Ω-α or more; a P-sugar hydrogenated amorphous silicon layer provided on the hydrogenated amorphous silicon layer and serving as an electron blocking layer; and a plurality of full area electrodes provided on the hydrogenated amorphous silicon layer. □The method for manufacturing an amorphous silicon image sensor of the present invention includes a step of forming a transparent layer with striped edges on a transparent insulating substrate, and a step of forming a transparent layer on the transparent electrode using a metal mask and a glow discharge decomposition method. a step of providing a striped window in the window and covering the rest with a high resistance fluorinated amorphous silicon film; a step of depositing a transparent insulating film on the fluorinated amorphous silicon film; and a step of depositing a transparent insulating film on the fluorinated amorphous silicon film; depositing a high resistance hydrogenated amorphous silicon layer over the membrane; and depositing a P-sugar hydrogenated amorphous silicon layer over the high resistance hydrogenated amorphous silicon layer. , forming a plurality of metal electrodes on the P-sugar hydrogenated amorphous silicon layer.

Next, examples of the present invention will be described.

First, an example of an amorphous silicon image sensor of the present invention will be described.

FIG. 3 is a partially cutaway perspective view of an embodiment flj of the amorphous silicon image sensor of the present invention.

This embodiment includes a transparent insulating substrate 20, a striped transparent electrode 21 provided on the substrate, and a striped window covering the side and top surfaces of the transparent electrode and on the top surface of the transparent electrode. a fluorinated amorphous silicon film 22 having a specific resistance of 109Ω-α or more; a transparent barrier film 23 that is provided to cover the fluorinated amorphous silicon film and the window and serves as a hole blocking layer; A hydrogenated amorphous silicon layer 24 with a specific resistance of 109Ω-α or more is provided on the transparent insulating film, and a P-type hydrogenated amorphous silicon layer 24 is provided on the hydrogenated amorphous silicon layer and serves as an electron blocking layer. It is composed of a crystalline silicon layer 25 and a plurality of metal electrodes 126 provided on the P sugar hydrogenated amorphous silicon layer. The signal light 27 is received on the lower surface of the substrate 20.

With this structure, both the photocurrent and the dark current are
Since the current flows only in the solid arrow portion shown in the figure, the charge retention characteristics are greatly improved.

Next, a method for manufacturing an amorphous silicon image sensor according to the present invention will be explained.

A glass plate is selected as the transparent insulator substrate 20, and tin oxide is applied thereon to a thickness of 500 mm as the transparent electrode 21, and patterned into a strike shape.

Next, a fluorinated amorphous silicon layer 22 is formed as a light shielding layer.
Formed to a thickness of 0.00 OA. This fluorinated amorphous silicon layer 22 is formed, for example, by glow discharge decomposition of a mixed gas of SiF4 and SiH4. At this time,
Using a metal mask, considering the resolution of facsimile,
A striped window of 00 μm is opened.

Next, Si is used as a transparent insulating film 23 which becomes a hole blocking layer.
s Na or SiO2 is formed to a thickness of 200A.

A high resistance hydrogenated amorphous silicon layer 24 doped with 20 ppm boron using diborane (B2H6) gas is then deposited to a thickness of 2.5 .mu.m. Subsequently, a P-type hydrogenated amorphous silicon layer 25 doped with 250 ppm of boron is deposited to a thickness of 0.3 μm.

Then, in order to isolate the elements, unnecessary P-type hydrogenated amorphous silicon is removed by mesa etching.

Finally, AA was deposited to a thickness of 0.5 μm, and 100 μm thick.
The entire electrode 26 is formed by etching to a width of . When the bit density is 8 bits/tomo, the 'electrode spacing is 25 μm.

' SigNt film or 5i as the above transparent insulating film 23
02 film, high resistance and P-type hydrogenated amorphous silicon element 24
, 25, the fluorinated amorphous silicon layer 22 can be formed using the same thin film forming apparatus by simply switching the raw material gas, and the manufacturing process is significantly shortened compared to the conventional method using a metal film.

The image sensor of the present invention manufactured by the above method includes:
At an applied voltage of 10μ, the leakage current per negative element is 2x
lO”A. This is the leakage current value 2 of the conventional product.
It is 1/10 compared to X 10-”A. Also, 550
The S/N value at 100Lx is 400 nm for the conventional product.
However, it has been significantly improved to 1200. Furthermore,
The reading characteristics at an accumulation time of 10 E were also good.

As described in detail above, according to the present invention, it is possible to manufacture an amorphous silicon image sensor that reduces leakage current, improves charge retention, and is easy to manufacture, so the effects are significant.

[Brief explanation of the drawing]

FIG. 1 is an equivalent circuit diagram of an example of a conventional storage type image sensor, FIG. 2 is a cross-sectional view of an example of the elements of a conventional image sensor, and FIG. 3 is a partially cutaway perspective view of an embodiment of the present invention. It is. 1...Power supply, 2...Common electrode resistance, 3
... Capacitance between element electrodes, 4 ... Diode representing rectifying contact', 5 ... Dark resistance, 6.
...A current source that represents photocurrent.

Claims (2)

[Claims] (1) A specific resistance comprising a transparent insulating substrate, a striped transparent electrode provided on the substrate, and a striped window covering the side and top surfaces of the transparent electrode and on the top surface of the transparent electrode. a 109Ω-crn Sakadono fluorinated amorphous silicon film, a transparent insulating film provided to cover the fluorinated amorphous silicon film and the window and serve as a hole blocking layer, and a transparent insulating film provided on the transparent insulating film. a hydrogenated amorphous silicon layer having a specific resistance of 109 Ω-cm or more; a P-type hydrogenated amorphous silicon layer provided on the hydrogenated amorphous silicon layer and serving as an electron blocking layer; An amorphous silicon image sensor comprising a plurality of metal electrodes provided on a P-type hydrogenated amorphous silicon layer. (2) A process of forming transparent electrodes in stripes on a transparent insulating substrate, forming striped windows on the transparent electrodes using a metal mask and glow discharge decomposition method, and forming windows in the form of high resistance on the other transparent electrodes. a step of covering with a fluorinated amorphous silicon film;
A transparent insulating film is placed on the fluorinated amorphous silicon film.
a step of depositing a high resistance hydrogenated amorphous silicon layer on the transparent insulating film; and a step of depositing a p-type hydrogenated amorphous silicon layer on the high resistance water-strengthened amorphous silicon layer. 1. A method for manufacturing an amorphous silicon image sensor, comprising the steps of: (1) covering the P-type hydrogenated amorphous silicon layer with a layer of pure silicon; and forming a plurality of metal electrodes on the P-type hydrogenated amorphous silicon layer.