JPS60235456A - Image sensor - Google Patents

Abstract

PURPOSE:To obtain an image sensor having a high S/N, high reliability, high resolution and excellent productivity by forming laminated structure in which a blocking diode is shaped on a photodiode through conductive amorphous silicon. CONSTITUTION:A discrete electrode 22 is evaporated on an insulating substrate 21, blocking diodes 31 using amorphous silicon as base bodies are shaped and conductive amorphous silicon 32 and photodiodes 33 employing amorphous silicon as base bodies are formed continuously. Protective layers 34 are shaped, transparent conductive films 24 and light-shielding layers 25 are formed, lastly a polymer is spin-coated on an image sensor for colors, red, green and blue dyes are diffused into the polymer in succession, and an insular color filter 26 in three rows is formed. According to such a color image sensor, resolution, a S/N and productivity are improved largely.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a high-resolution image sensor using amorphous silicon.

(Prior Art and its Problems) Recently, the development of contact image sensors has been actively promoted in order to miniaturize document reading devices such as facsimiles. This is a photoelectric conversion device that incorporates a large image sensor having a width that corresponds one-to-one with the original. A photoelectric conversion system having a conventional CCD or MOS type IC image sensor requires a reduction lens system to project an original onto the image sensor. Therefore, a large space is required within the device to ensure the optical path length, making it difficult to miniaturize the device. However, in the above-mentioned contact type image sensor, since this reduction lens system is not required, the image sensor and the document are in close contact with each other, and therefore, the device can be significantly miniaturized.

This contact image sensor already uses arsenic-selenium-tellurium amorphous semiconductor, cadmium sulfide, and hydrogenated amorphous silicon (hereinafter abbreviated as a-8i) as photoelectric conversion materials.
It has been reported that using All of these materials are thin film materials that can form a uniform thin film over a large area, which is necessary for forming a large image sensor, and have high sensitivity to visible light. Among these, a-8i is a non-polluting material because its constituents are Si and hydrogen, and the material is stable and has high photosensitivity over the entire visible light range, fast photoresponse speed, and high resistivity. Therefore, it is a material suitable for high-speed, high-resolution color image sensors (0) When applying this a-8+ to contact type image sensors)
A method in which an a-8i optical sensor is driven by an S-X%O8 FET switch is generally used. Figure 1 shows the equivalent circuit of the a-8i image sensor.0 In Figure 1, 11
id a -8i light -1 = 7 +, 12 is SjM)
It is a Si IC chip incorporating an SFET switch array 13 and a scanning circuit 14. This 51M08FE
The T-switch 13 and the individual electrode 15 are connected by means such as bonding. The a-8i optical sensor is a photodiode type with a high optical response speed, making it possible to realize a high-speed image sensor. The photocurrent generated by the optical signal in the a-8i photodiode erases the charge in the diode, and after a certain scanning time (storage time), the MO8FET is switched and the charging current flowing from the external terminal is detected. Detects optical signals. In this signal detection method, the signal amount is proportional to the scanning time and the light receiving area, and the noise of the image sensor is almost determined by the switching noise of the MOS FET, and is almost unrelated to the dark current of the photodiode. Therefore, as the image sensor is operated at higher speed and higher resolution, 87N decreases.

In addition, to colorize a long image sensor, red (R) and green (G) are used in the photosensor array.

This is achieved by sequentially arranging photosensors that are sensitive to each type of light such as blue (B).
(As shown in the cross-sectional view and plan view of BL, a-8i 23 is deposited on the individual electrode 22, a transparent conductive film 24 is provided on the surface thereof, which serves as a photodiode, and a color filter 26 is placed on the light incident surface of the photosensor. 25 is a light-shielding film that is provided to improve resolution, but it is not essential. The same applies to the sensor described later. I can say it.

However, in the above case, in order to realize a high-resolution color image sensor, optical sensors are required for each color that can be distinguished compared to a monochromatic image sensor, and in a full-color image sensor, one red and one green color sensor is required. ．． In the case of a photodiode array sensitive to blue light, three times as many photosensors are required, and the light-receiving area of p per element is reduced. As a result, the signal amount decreases, causing a drop in S and also making high-speed operation difficult.

In addition, as mentioned above, the 7-photo sensors, MOS, and FET switches are connected by means such as bonding, but colorization requires 2 to 3 times more photosensors, which means that the number of connection points such as bonding increases. IC
The number of chips will also increase. This will lead to lower reliability of contact image sensors and higher costs. The above applies not only to color image sensors but also to high-resolution image sensors.

(Objective of the Invention) An object of the present invention is to solve these problems and provide an image sensor with high S/N, high reliability, high resolution, and good productivity.

(Structure of the Invention) A photodiode based on amorphous silicon is formed on an insulating substrate, and a blocking diode based on amorphous silicon is disposed on the photodiode via conductive amorphous silicon. A closed image sensor is obtained, characterized in that it includes one or more sensors each having a laminated structure.

Toki contact, heterojunction, 1-kura-1-n junction, Y.

It is constructed using amorphous silicon as a base including one or more junctions selected from among the junctions.

Furthermore, in the present invention, since the photodiode, the blocking diode, and the conductive amorphous silicon are basically made of substantially the same material, they can be formed continuously in the same forming apparatus, resulting in excellent productivity.

of (Example) Next, a detailed explanation will be given using the drawings. Figure 3(a).

fbl schematically shows a cross-sectional view and a plan view of a first embodiment of an image sensor using the present invention. 70% of chromium is applied as individual electrodes 22 on an insulating substrate 21 such as a glass substrate.
The film is deposited with a thickness of 0 angstroms and etched to a width of about 100 .mu.m for the required linear density, for example, an image sensor with 8 elements/device. Next, a blocking diode 31 is formed using amorphous silicon as a base, and then a conductive amorphous silicon 32 having a total thickness of 2000 angstroms and a photodiode 33 with amorphous silicon as a base are successively formed. Furthermore, by a dry etching process, these blocking diodes, conductive amorphous silicon layers, and photodiodes are etched into islands.The area of this island is, for example, 100 μm x 14 Q μm in an 8 element -3'/- image sensor. After that, as the protective layer 34 of the blocking diode and photodiode, 1 μm of Sin was formed, and a contact hole was formed by etching, and then 700 angstrom of indium tin oxide was formed as the transparent conductive film 24, and 1500 angstrom of chromium was formed as the light shielding layer 25. Angstrom vapor deposition system,
The etching process creates an island shape as a common electrode. Finally, in the case of a color image sensor, after spin-coding the polymer, red, green, and blue dyes are successively diffused into the polymer to form three rows of island-shaped color filters 26. The dyes used in the dyeing process include, for example, Eastman Polyester Blue 4RL dye for blue;
Eastman Polyester Red 90-1 dye was used for red, and Eastman Yellow R-GFDQ-3 Eastman Blue BGN dye was used for line. The shape of these color filter islands is, for example, approximately 180 μm×220 μm in an A4 size image sensor.

In this way, the photodiode-blocking diode array with color filters is completed. Thereafter, as shown in FIG. 4, a Si IC chip 12 including a scanning circuit 14 and a switching element 13 is installed and connected on the substrate to complete an image sensor.

The color filter used here uses three primary colors: red, green, and blue, but other colors include white, yellow, cyan, white-green-cyan,
There are also combinations such as white-green-yellow, green-zoan-yellow, etc.

FIG. 5+a>, fbl schematically shows a sectional view and a plan view of a second embodiment of the present invention. In this figure, the same components as in FIG. 3 are indicated by the same symbols. In this embodiment, the second photodiode blocking diode array 52 in the sub-scanning direction is located between the first photodiode and the blocking diode 51 in the main scanning direction. By temporally adjusting and combining the signal output from the diode and the signal output from the second photodiode, an output signal having twice the resolution as the linear density of the individual electrodes 220 can be obtained.

In the above embodiments, the photodiode-conductive amorphous silicon-blocking diode will be described in more detail.

Figure 6 shows a photodiode using a ρ-4-n junction.
1 is a cross-sectional view showing an embodiment of the present invention of a blocking diode; FIG. 500 layers of n-type amorphous silicon 61 are placed on an insulating substrate 21 with a metal electrode 22 patterned into an island shape.
5 Angstrom, high resistance amorphous silicon layer 62
A p-type amorphous silicon layer 63 having a thickness of 600 angstroms is formed to form a blocking diode portion. After that, the n-type amorphous silicon layer 64 is
000 angstroms to form a conductive amorphous silicon layer. Further, a p-type amorphous silicon layer 63 with a thickness of 500
Angstrom, high resistance amorphous film IJ = + 7 layers 6
A photodiode portion is formed by forming an amorphous silicon layer 61 with a thickness of 200 angstroms and a thickness of 2 to 5000 angstroms. Finally, dry etching is performed to form islands to complete the n-1-p amorphous silicon photodiode, n-type amorphous silicon conductive layer, and p-J-n amorphous silicon blocking diode structure. let

In addition, in FIG. 6, for the sake of clarity, the protective layer and the light-shielding common electrode are omitted, and only the transparent conductive film 24 is shown.

The amorphous silicon used here is generally (-l 8iH
.

0- or n-type amorphous silicon formed by glow discharge decomposition of gas, Si, H, and gas is mixed with PH3 and As8. The p-type amorphous silicon is formed by B2”
Since it is formed by a glow discharge decomposition method using a mixture of six gases, it is easy to continuously form n-type, p-type, and high-resistance amorphous silicon by simply changing the gas used. Can be formed.

Further, in this embodiment, an n-i-p amorphous silicon photodiode, an n-type amorphous silicon conductive layer, a p-i
-n amorphous silicon blocking diode structure is used, but p -i -n amorphous silicon -p type amorphous -
A combination of ta silicon conductive layer n-1-p amorphous silicon blocking diode may also be used.

FIG. 7 is a sectional view showing an embodiment using a Peter junction. In this figure, the same components as in FIG. 6 are indicated by the same symbols. In this example: p-type amorphous silicon carbon
-1-n amorphous silicon photodiode, p-type amorphous silicon conductive layer 71n-i-p amorphous silicon blocking diode stacked structure is shown. The amorphous silicon vertical elements 72 used here are SiH, SI, )J
Amorphous silicon can be obtained using the same equipment as amorphous silicon by mixing a mixed gas such as CH4 or CtHa with 6 gases and performing a glow discharge decomposition method. By using this amorphous silicon carbon, an image sensor with good sensitivity in the visible light region of 400 nm to 500 nm was obtained.

In this example as well, n-amorphous silicon carbon-1-
The present invention is also effective even when a Peter junction is used for a blocking diode that is realized by a p-amorphous silicon photodiode, an n-type amorphous silicon layer, and a p-i-n amorphous silicon blocking diode stacked structure. be. FIG. 8 shows a cross-sectional view of an embodiment using Schottky contact. In this figure, the same components as in FIG. 6 are indicated by the same symbols.

In this example, a transparent conductive layer-1-p-amorphous silicon photodiode, an n-type amorphous silicon conductive layer,
It has a p-1-n amorphous silicon blocking third-layer structure, and a junction is formed by Schottky contact between the transparent conductive layer 24 and the high-resistance amorphous silicon layer 62. Therefore, even in this case, the laminated structure can be formed continuously within the same apparatus.

(Effects of the Invention) The present invention has been described in detail through examples, but in order to make the effects of the present invention clearer, the characteristics of the 8-element/diameter color image setter will be compared with the conventional structure as follows. become that way.

Furthermore, when eight color image sensors with the same resolution are prototyped, the results are as follows: As described above, according to the present invention, the resolution is 87N.

A significant improvement in productivity (yield) has been achieved, and the effects of the present invention are remarkable.

[Brief explanation of drawings]

FIG. 1 shows an equivalent circuit of a conventional color image sensor. In the figure, 11 is an amorphous silicon photodiode, 12 is a 5i IC chip, and 13 is a MOS FET.
A switch, 14 scanning circuits, and 15 individual electrodes are shown. Figure 2 1a+, (bl is an explanatory diagram of a cross-sectional view and a plan view showing a conventional color image sensor. In the figure, 21 is an insulating substrate such as glass ceramic, 22 is an individual electrode, and 23 is amorphous silicon. , 24 is a transparent electrode, 25 is a light-shielding film, and 26 is a color filter. FIGS. A blocking diode, 32 is conductive amorphous silicon, and 33 is a photodiode. Components that are the same as those shown in FIG. A cross-sectional view showing another embodiment of the invention is schematically shown. In the figure, 61 is n
62 is a high resistance amorphous silicon layer, 63 is a p-type amorphous silicon layer, 64 is an n-type amorphous silicon conductive layer, and 71 is a p-type amorphous silicon conductive layer. layer, 7
2 indicates a p-type amorphous carbon layer. Figure l Figure 2 Figure 1 (b) Half 3 Figure (a) Half 6 Figure 7 Figure 8

Claims (1)

[Claims] 1. A photodiode based on amorphous silicon is formed on an insulating substrate, and blocking based on amorphous silicon is provided on the photodiode via conductive non-silicon. An image sensor comprising one or more sensors each having a laminated structure provided with a diode. 2. A claim in which the photodiode and the blocking diode each include one or more junctions selected from MIS junction/Schottky contact, heterojunction, p-4-n junction, and P-n junction. The image sensor according to item 1. 3. The image sensor according to claim 1, wherein the sensors having the laminated structure are arranged one-dimensionally or two-dimensionally.