JPH0319366A - Image sensor - Google Patents

Abstract

PURPOSE:To obtain an image sensor of an individual electrode which is excellent in blocking properties and productivity and free of defect by a method wherein the individual electrode has such a structure that its side opposed to a common transparent electrode is formed of a flat film of Ti and its part exposed through the dry etching of an amorphous silicon hydride film is made to contain an Al film. CONSTITUTION:An Al film 2, a Ti film 3, and an Al film 4 are continuously formed on the whole face of a glass board 1, which is successively formed into an individual electrode thorough photolithography and etching. In succession, an i-type a-Si:H film 5 and a P-type a-Si:H film 6 are formed on the whole face. Then, an indium tin oxide(ITO) film 7 and an Al film 8 are deposited, and an auxiliary common electrode 8 of Al and a common transparent electrode 7 of ITO film are formed through photoetching. In succession, the right side of an amorphous film is removed through plasma etching performed for the formation of the a-Si:H films 5 and 6 and then the P-type a-Si:H film is removed using the transparent electrode as a mask. At this point, as the Al film 2 is left un-etched by plasma, an individual electrode of this design retains electrical properties as an individual electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an image sensor that performs contact type image reading using a hydrogenated amorphous film.

<Prior Art> Conventionally, IC sensors such as CCD sensors and MOS sensors fabricated using semiconductor single crystals have been used in image reading devices used in image scanners, facsimiles, and the like. However, this IC sensor has the problem of increasing manufacturing costs due to its large size and the use of multiple arrays, so a method is used in which the original image is reduced using a reduction optical system and then projected onto the C sensor and read. It was done. However, since the optical path length of the reduction optical system increases in proportion to the width of the document to be read, it has been difficult to downsize an image reading apparatus having the reduction optical system.

In order to solve the above problems, a-Si, which can easily be made into a large area, is
A close-contact image sensor with the same width as the original document is being developed using a :H (hydrogenated amorphous silicon) thin film.

Although the a-Si:H thin film image sensor is inferior to the ■C sensor in high-speed reading and high-resolution characteristics, it is characterized by low cost and the ability to form a large-sized contact type image sensor. Although there are many materials for thin films for optical sensors, currently most of them are a-Si:H films whose conductivity type can be controlled to p-type or n-type by adding impurities. The configuration of the photodiode that becomes the optical sensor is p-type and n-type of a-Si:H film.
p+n and i type and intrin7 type layers, respectively.
When expressed as transparent electrode/pin/pin junction type of metal electrode and transparent electrode/pi/metal [pole or transparent electrode/i
/Metal Schottky junction type such as metal electrode.

Since the dark resistance of the i-layer is very high in the metal 7gt key junction type (specific resistance is approximately 10 Ω・cIn), there is no need to provide an electrical isolation structure between pixels, and when used for forming individual electrodes, the process It has the feature of making it easier.

<Problems to be Solved by the Invention> In the metal sitat-key junction photodiode described above, the dark current blocking characteristics vary depending on the metal used for the electrode, so selection of the electrode metal is important.

Figure 5 (a) and (b) show the magnitude of the photocurrent and dark current with respect to the reverse bias voltage value in a metal Schottky junction of five types of metals, and as can be seen from this,
There is little difference in photocurrent depending on the metal of the electrode material, and the valence is almost the same. However, in the case of dark current, if Cr, Ti, At, etc. are used as the electrode, the dark current increases little with respect to the increase in reverse bias voltage (Fig. 5(b), but if Ni, Cr-Au, etc. are used as the electrode) , the dark current increases rapidly as the reverse bias voltage increases (Figure 5 (a)).The fact that the dark current fluctuates greatly with the reverse bias voltage indicates poor stability against voltage fluctuations. Therefore, it is not preferable to use such metal materials for electrodes.

Even though Cr has good blocking properties, when individual electrodes on a large substrate such as a contact sensor are formed by 7-photoetching, there is a problem of pollution due to Cr dissolved in the etching waste liquid, and when mass-produced, it is difficult to dispose of a large amount of etching waste liquid. The use of Cr is inappropriate because it causes problems.

In addition, when individual electrodes are formed using only Ti, when the a-Si:H film formed on top is dry etched with CF4 gas, the exposed Ti electrodes are also considerably etched with CF4 gas, resulting in a decrease in the resistance of the Ti electrodes. Depending on the increase in thickness and etching conditions, the Ti electrode may disappear.

When individual electrodes are made of At, they will not be etched by CF4 gas, but due to the characteristics of At metal, when a thin film is formed over a large area, the surface may become uneven or the a-Si:H film may During film formation, the unevenness on the At film surface becomes large, causing many defects due to short circuits between the common transparent electrode formed on the thin a-Si:H film and the At individual electrodes. There was a problem.

The present invention solves the problems associated with metal Schittky junction electrode materials that do not require a pixel separation structure, and provides an individual electrode image sensor with excellent blocking characteristics, high productivity, and no defects. The purpose is to

<Means for Solving the Problems> In the image sensor of the present invention, the individual electrodes forming the sitat-key junction have good characteristics and high productivity. That is, the individual electrodes include at least the At film and the T film.
It is formed of a metal film having a portion that becomes two layers of the i-film, and
The surface facing the common transparent electrode sandwiching the a-Si:H film is T.
The Ti film is made into an i film, with a thickness that covers the irregularities of the substrate on which the Ti film is formed, and the lead-out portions of the individual electrodes exposed when the a-Si:H film is dry-etched are configured to include at least an At film. ing.

Effects> The individual electrodes of the image sensor of the present invention have a bonding surface with the a-Si:H film that has good prosocating properties, and also forms a smooth surface to prevent short circuits between the transparent electrode and the transparent electrode due to unevenness. In addition to using a Ti film that does not generate defects, it also has an At film that is not affected by dry etching even if it is exposed during dry etching of the a-Si:H film, so image sensors with good characteristics can be manufactured with high yield. can do.

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

First Embodiment FIG. 1 is a sectional view showing the manufacturing process of an image sensor according to the present invention.

FIG. 1(a) shows an At film 2 with a thickness of about 50 OA, a Ti film 3 with a thickness of about 200 OA, and an At film with a thickness of about 1.6 μm on the entire upper surface of a glass substrate 1 having a length longer than the width of A4. 4 was continuously formed by sputtering, and then individual electrodes were formed by photolithography and etching (photoetch).
It was formed.

This individual electrode has 125
1,728 pieces separated at a μm pitch are arranged in a row. A portion of the At film 4 is a bonding point for wire bonding with an LSI that controls signal detection from the individual electrodes.

A mixed solution of phosphoric acid and nitric acid was used for enoching the At film, and a mixed solution of hydrogen peroxide, aqueous ammonia, and ethylenediaminetetraacetic acid (EDTA) was used for enoching the Ti film.

Next, an i-type a-Si:H film 5 and a p-type a-Si:H film are formed on the entire surface.
Figure 1 (b) shows the film 6 formed. This amorphous film is produced by plasma CV in which low pressure gas of SiH4 diluted with H2 is decomposed by high frequency discharge and deposited on the substrate 1.
By method D, the film 5 is about 1.5 μm thick, and the film 6 is about 200× deposited using a mixture of SiH4 gas and B2H6 gas at a volume ratio of 0.1 to 10%. During film formation by plasma CVD, the temperature of the substrate 1 reached approximately 250°C.

The above amorphous film had poor smoothness only on the surface of the At film 4.

Subsequently, an indium-tin oxide (ITO) film 7 of about 7
As shown in <c> in FIG. 1, an auxiliary common electrode 8 of At and a common transparent electrode 7 made of an ITO film were formed by photolithography after depositing 00X and an At film 8 by sputtering with a thickness of about 2000 λ. A mixed solution of hydrochloric acid and diiron chloride solution was used for etching ITO.

Next, in order to form the a-Si:H films 5 and 6, the right side of the amorphous film in the figure was removed by plasma etching with CF4 gas using a mask of a 7-year-old resist film (not shown), and then The first image shows the state in which the p-type a-Si:H film is removed using the common transparent electrode as a mask.
It is figure (d). Using the common transparent N-electrode 7 as a mask, the exposed p-type film 6 was etched away using a low-resistance p-type film.
This is to prevent current leakage between the common transparent electrode 7 and the individual electrodes 2 through the mold film.

FIG. 1(d) shows a state in which the plasma etching of the a-Si:H films 5 and 6 has been completed and a part of the Ti film 3 is exposed, but the area of the image sensor substrate l has become larger. Therefore, the thickness of a certain a-Si:H film becomes less uniform even on the same substrate 1, and when the partially remaining a-Si:H film is completely removed, other parts become less uniform. In some cases, plasma etching of the Ti film is performed for a long time, and almost all of the Ti film is removed. However, since the At film 2 that is not plasma etched remains, there is no problem with the electrical characteristics of the individual electrodes.

The substrate 1 holder 12 on which the image detection section was fabricated as described above
The LSIIO and the At film 4 of each individual electrode were then connected by bonding using wires 11, as shown in FIG. 1(e).

As described above, a light guide section for an image to be read, a protective cover, an illumination light source, etc. are added to an image sensor with a reading section, and the image sensor is used as an image sensor.

Second Embodiment The second embodiment shows a cross-sectional view of the image sensor of the second embodiment.
It is a diagram. The second embodiment differs from the first embodiment only in the configuration of the individual electrodes. That is, the At film 2 of the first embodiment was omitted and the T1 film 13 was formed on the substrate 1 to improve the adhesion to the substrate 1 and the smoothness of the surface of the Ti film 13. The At film 14 used for the first bonding panel is a-Si:H.
It extends so as to partially overlap the membrane 5. Although the a-Si:H film 5 overlapping the At film 14 may have an abnormally uneven shape, there was no adverse effect unless it was configured to be extremely close to the common transparent electrode 7 of the detection operation section.

This second embodiment can be manufactured through almost the same steps as the first embodiment, and the effects of the present invention are also the same, so a description thereof will be omitted.

Third Example The structure or breakdown of the image sensor manufactured in the third example is shown in the third example.
Shown in the figure.

In this example, the detection section of the photodiode has the same structure as in the first example, but the switching process for selecting signals from the individual electrodes is a thin film MOS field effect transistor (TFMOSFET) formed on the same substrate. They are different in some respects. FIG. 3 shows polycrystalline Si deposited on substrate 1 using the reduced ICVD method.
A film (15, 16, 17) is formed, and its surface is thermally oxidized to form a gate film to form a gate electrode 18, and then phosphorus (P) is ion-implanted into the polycrystalline Si film to form a drain 16 and a drain 17. was formed. This is the l5 channel section. Next, a Si02 insulating film 19 is formed on the entire surface by CVD,
Contact holes are formed above the drain 16 and source 17 of the TFMOSFET by etching.

Next, an At film 20 of 5ooX as in the first embodiment and z
The Ti film 21 of oooX was formed into a continuous layered structure, and was then photoetched to form an electric wire connecting the individual electrodes to the drain layer 6 and connecting the source 17. The following steps are the first
Since it is the same as the example, the explanation is omitted, but a-
During the plasma etching of the Si:H film, the exposed Ti film 21 was also etched and the film thickness became thinner or disappeared in some places, but due to the presence of the underlying At film 20, there was no problem with the function of the electrode.

Fourth Example @ FIG. 4 is a cross-sectional view showing the structure of the image sensor manufactured in the fourth example.

As can be seen from the figure, the detection section of the photodiode of this example has the same configuration as the second example, and the TFM is formed in the same way as the third example by extending the individual electrodes.
The terminal L/-716K of the OSFET is connected, and the terminal terminal 17 is also formed. Because of the above structure, in this embodiment as well, the electrode facing the common transparent electrode 7 is a flat smooth electrode, which is suitable for the plasma etching process of the a-Si:H film. Since the exposed surface of the individual electrode is the KT film 23, the performance of the T-pole is not damaged by plasma etching.

The above is a description of the embodiments, and the present invention is not limited to the shapes of the embodiments, and may be hydrogenated amorphous.

Further, in the examples, sputtering was used to form the At film and the Ti film, but other methods such as vacuum evaporation method using electron beam heating, MB method, or ICB method may be used. may be pure aluminum, or may be an alloy in which sit or Cu is added to At.

Effects of the Invention The present invention provides individual electrodes of an image sensor using a photodiode with an extremely thin hydrogenated amorphous film by dry etching the hydrogenated amorphous film using 11 smooth films on the surface facing a common transparent electrode. By configuring the exposed portion to include at least an At film, an image sensor with good characteristics can be manufactured with a high yield.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the manufacturing process of the first embodiment of the present invention,
FIG. 2 is a sectional view showing the configuration of the second embodiment of the present invention, and FIG.
The figure is a cross-sectional view showing the structure of a third embodiment of the present invention, FIG. 4 is a cross-sectional view showing the structure of a fourth embodiment of the present invention, and FIG. It is a diagram.

Claims (1)

[Claims] 1 Consisting of an insulating substrate on which a plurality of individual electrodes are arranged closely, a hydrogenated amorphous film formed on the individual electrode and forming a Schottky junction with the individual electrode, and a common transparent electrode formed on the amorphous film. In the image sensor, the surface of the individual electrode forming the Schottky junction is a titanium (Ti) film, and the lead-out portion connected to the outside includes at least an aluminum (Al) film. .