JPH04215475A - Image sensor and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve insulation of an image sensor by employing polyimide having excellent step flattening as a first insulating layer and employing a silicon inorganic film having excellent insulation, water resistance as a second insulating layer after the step is flattened, as an interlayer insulating layer. CONSTITUTION:Polyimide having excellent step flattening is used as a first insulating film 5, and an SiNx or a silicon inorganic film having excellent insulation, water resistance, is used as a second insulating film 6. Thus, an interlayer insulating layer is not reduced in thickness near the edge of a photodetector to prevent a leakage of a current between a lower electrode 2 and wiring 7 with sufficient insulation and to simultaneously obtain excellent water resistance. That is, since the inorganic film is disposed after the polyimide is sufficiently flattened, the inorganic film can be formed with substantially uniform thickness. As a result, sufficient insulation, water resistance are obtained to improve reliability of an image sensor.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an image sensor used in a document reading section of a facsimile machine or an image input terminal device, etc., and a method for manufacturing the same. -Relating to a sensor and a method for manufacturing the same.

0002

2. Description of the Related Art A conventional image sensor is a contact type image sensor which is an assembly of light receiving elements and has a light receiving element array having the same width as the width of an original, and is used in close contact with the original.

The structure of the light-receiving element in this contact-type image sensor is a sandwich structure in which hydrogenated amorphous silicon (a-Si:H) is used as a photoconductive layer, and this is sandwiched between a metal electrode and a transparent electrode. However, because it is difficult to manufacture, the common electrode is usually the transparent electrode, and the metal electrode is the individual electrode.

However, in the above-mentioned sandwich structure photodetector, since the photoconductive layer is not individualized, interference occurs between adjacent bits, making it impossible to achieve uniform output and obtaining good diode characteristics. Therefore, a light-receiving element has been considered in which the metal electrode is used as a common electrode, the transparent electrode is used as an individual electrode, and the photoconductive layer is also made individual in order to reduce the variation between each light-receiving element. was.

[0005] In this way, if the photoconductive layer is made individual in the same manner as the transparent electrode, leakage current due to the wraparound of light can be suppressed and the resolution of the image sensor can be improved.

[0006] Here, the structure of a light-receiving element having a metal electrode as a common electrode will be specifically explained using FIG. 5, which is a plan view, and FIG. 6, which is a cross-sectional view taken along line BB' in FIG.

[0007] A chromium (Cr) is integrally formed in a band shape as a lower electrode 2 on an insulating substrate 1 made of glass or the like.
) layer, and a layer formed separately for each element.
A photoconductive layer 3 made of a -Si:H layer and a transparent upper electrode 4 made of an indium tin oxide (ITO) layer formed in the same way are sequentially laminated, and a layer of polyimide or the like is formed so as to cover the entire light receiving element. An interlayer insulating layer 10 is formed, and a constant potential is applied to the metal electrode of the lower electrode 2. Aluminum (Al) is used from the transparent electrode of the upper electrode 4.
A lead wire 7a such as the one shown in FIG.

Next, a method for manufacturing the light receiving element of this image sensor will be explained.

A chromium layer with a thickness of approximately 1000 to 1500 angstroms is deposited on a substrate 1 made of glass or the like by a sputtering method, and this is patterned into a band shape to form a metal common electrode that will become the lower electrode 2. Form an electrode.

[0010] Then, a film thickness of about 1
Deposit an a-Si:H layer with a thickness of ~2 μm. The deposition conditions at this time were as follows: silane (SiH4) gas was used as the source gas;
Flow rate 200~500sccm, pressure 0.2~0.5
Torr, the substrate temperature is 150 to 250°C, the RF power is 80 to 150 mW/cm2, and the time is 30 to 60 minutes.

Next, after forming an ITO film with a thickness of about 800 angstroms by DC magnetron sputtering, a resist is applied and patterned by photolithography to form individual electrodes that will become the upper electrode 4. Form a transparent electrode.

Furthermore, the resist pattern is left as it is, and using this as a mask, the a-Si:H
The layers are etched to form individually segmented photoconductive layers 3. After peeling off the resist, it was
Annealing treatment is performed at ℃ for 30 minutes.

Next, an interlayer insulating layer 10 made of polyimide or the like is applied to the entire light receiving element, baked, and a contact via hole 8 for leading out the lead wiring 7 from the upper electrode 4 is formed by photolithographic etching.

Furthermore, a film of aluminum (Al) is deposited and patterned by photolithography to form a pattern for the lead wiring 7. In this way, the light receiving element of the image sensor is formed (Japanese Patent Laid-Open No. 63-67
(See Publication No. 772).

[0015]

[Problems to be Solved by the Invention] However, in the above conventional image sensor and its manufacturing method, the interlayer insulating layer is usually formed by spin coating of polyimide, etc. It is excellent in smoothing out and flattening the steps caused by lamination, but if the film thickness of the polyimide part is up to about 1 μm,
The thickness of the polyimide film becomes thinner near the edges (steps) of the light-receiving element, and current leakage is likely to occur between the common electrode of the lower electrode and the lead wiring at the location indicated by the arrow in Figure 6. Furthermore, since polyimide itself has high water permeability, water easily penetrates through the thin portions of the polyimide membrane, resulting in a sensor with low water resistance.

[0016] In addition, in order to obtain sufficient insulation, it is necessary to
As shown in the cross-sectional diagram, the polyimide is made thicker by 2μ.
However, if the film thickness is large, it becomes difficult to microfabricate the contact hole, and this poses a problem in that it hinders miniaturization of the entire light-receiving element.

In order to further improve water resistance, it may be possible to use a silicon nitride film (SiNx) or a silicon oxide film (SiOx) as an interlayer insulating layer in place of the polyimide film, but these insulating layers cannot be formed by plasma CVD. When depositing these insulating layers, the upper electrode of the ITO film is damaged by the plasma, deteriorating the sensor characteristics.
Another problem was that the membrane was directly exposed to SiH4 and reduced.

As yet another method, polyimide is used as the interlayer insulating layer, and after forming the image sensor, a SiNx film or Si film is used as the passivation film to improve water resistance.
A method of depositing an Ox film is also considered, but it does not solve the leakage problem mentioned above, and the lead wiring from the upper electrode is formed before forming the passivation film, so it is not possible to solve the problem. In order to obtain a good passivation effect, S
The iNx film and SiOx film must be formed thickly, but the thicker the film, the greater the stress on the film, which tends to cause cracks and peeling of the SiNx film, SiOx film, and underlying electrode film. There was a problem with that.

The present invention has been made in view of the above circumstances, and improves the insulation in the light receiving element of an image sensor, reduces current leakage between the lower electrode and the lead wiring, and further improves water resistance. An object of the present invention is to provide an image sensor and a method for manufacturing the same, which can improve the reliability of a light-receiving element by improving the reliability of the light-receiving element, and can be manufactured with high yield without increasing the number of photolithography steps.

[0020]

[Means for Solving the Problems] The invention according to claim 1 for solving the problems of the above-mentioned conventional example has a lower electrode formed on a substrate as a common electrode, and a lower electrode formed on the lower electrode for each pixel. a photoconductive layer formed individually; an upper electrode formed on the photoconductive layer so as to correspond to each photoconductive layer;
an interlayer insulating layer formed to cover the lower electrode, the photoconductive layer, and the upper electrode; and an interlayer insulating layer formed on the interlayer insulating layer to be connected to the upper electrode through an opening provided in the interlayer insulating layer. In the image sensor having a light-receiving element having a lead-out wiring formed in It is characterized by

The invention according to claim 2 for solving the problems of the conventional example is a method for manufacturing an image sensor, in which a lower electrode serving as a common electrode is formed on a substrate, and a photoconductive layer is formed on the lower electrode. A layer and an upper electrode are individually formed for each pixel, and a first layer made of polyimide is formed to cover the upper electrode.
an insulating layer is laminated, a second insulating layer made of a silicon-based inorganic film is laminated on the first insulating layer to form an interlayer insulating layer, and an opening is formed in the interlayer insulating layer to form an opening from each of the upper electrodes. The invention is characterized in that a lead-out wiring is formed on the interlayer insulating layer.

[0022]

According to the invention as set forth in claim 1, the first insulating layer is made of polyimide, which is excellent in flattening steps, and after flattening the steps caused by stacking each layer of the light receiving element, the second insulating layer is formed as an interlayer insulating layer. Since the image sensor layer is made of a silicon-based inorganic film with excellent insulation and water resistance, it is possible to prevent the interlayer insulation layer from becoming thinner near the edge of the photodetector, improving the insulation properties of the image sensor. Therefore, current leakage between the lower electrode and the lead wiring can be reduced, and water resistance can be improved by the silicon-based inorganic film of the second insulating layer.

According to the second aspect of the invention, the first insulating layer is formed on the upper electrode of the light-receiving element using polyimide, which is excellent in flattening steps, and after flattening the steps caused by stacking each layer of the light-receiving element. Since this method of manufacturing an image sensor laminates a second insulating layer made of a silicon-based inorganic film with excellent insulation and water resistance, thinning of the interlayer insulating layer near the edge of the photodetector can be prevented. It is possible to improve the insulation properties of the image sensor, reduce current leakage between the lower electrode and the lead wire, and further improve water resistance by using a silicon-based inorganic film as the second insulating layer. I can do it.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is an explanatory plan view of a light receiving element of an image sensor according to an embodiment of the present invention, and FIG.
FIG. Note that parts having the same structure as in FIGS. 5 and 6 will be described using the same reference numerals.

The image sensor of this embodiment includes a long light-receiving element array consisting of a plurality of sandwich-type light-receiving elements (photodiodes) arranged on an insulating substrate 1 made of glass or the like; It is composed of a drive circuit connected to each light receiving element, and the electric charge generated in each light receiving element is output as an image signal by the drive circuit in a time-series manner.

As shown in the plan view of FIG. 1 and the cross-sectional view of FIG. A photoconductive layer 3 made of amorphous silicon (a-Si:H) and an upper electrode 4 made of indium tin oxide (ITO) are successively laminated to form a sandwich type.

Note that here, the lower electrode 2 of the metal electrode is formed in a strip shape in the main scanning direction, and a photoconductive layer 3 is formed on the lower electrode 2.
are formed by being discretely divided in the main scanning direction, and similarly, the transparent electrode of the upper electrode 4 is also formed by being divided into discrete parts in the main scanning direction.
The portion sandwiched between the upper electrode 4 of the transparent electrode constitutes each light-receiving element, and a collection thereof forms a light-receiving element array.

Further, a first insulating layer 5 made of polyimide is formed so as to cover the entire light-receiving element, and a silicon-based inorganic film (Si
A second insulating layer 6 made of Nx, SiOx, etc.) is formed, and in order to connect the upper electrode 4 and the lead wire 7, a contact via is formed through the first insulating layer 5 and the second insulating layer 6.
An a-hole 8 is provided.

[0030] Furthermore, the upper electrode 4 is formed by discretely dividing.
A wiring 7 made of aluminum or the like is pulled out from one end of the
Connected to the thin film transistor of the charge transfer section. In the light receiving element, it is also possible to use CdSe (cadmium selenium) or the like as the photoconductive layer instead of hydrogenated amorphous silicon.

Next, a method for manufacturing the light receiving element of the image sensor of this embodiment will be explained as shown in FIGS. 3(a) to 3(c) and 4(d) to
This will be explained using the manufacturing process cross-sectional explanatory diagram f).

First, in order to form a metal electrode that will become the lower electrode 2 on a substrate 1 made of glass or the like, a Cr film with a thickness of about 700 angstroms is deposited by DC magnetron sputtering and patterned into a band shape. do. In addition to Cr, this metal may be nickel chromium (NiCr), tungsten (W), tantalum (Ta), or the like.

Next, the semiconductor layer a-Si:H of the photoconductive layer 3
The film thickness is approximately 1.3 μm using plasma CVD (P-CVD) method.
Deposit a film. The formation conditions were SiH4 gas at a flow rate of approximately 200 to 500 sccm and a pressure of 0.2 to 0.5 To.
rr, substrate temperature 150~250℃, RF power -80~1
50 mW/cm2 Film deposition time is 30 to 60 minutes.

Next, in order to form a transparent electrode of the upper electrode 4 on the photoconductive layer 3, ITO is deposited to a thickness of about 700 angstroms by DC magnetron sputtering (FIG. 3(a)). reference). Thereafter, a resist is applied, exposed and developed using a photolithographic etching method, and the ITO is patterned into the shape shown in FIG. 1, thereby forming the upper electrode 4 of the transparent electrode as an individual electrode.

Furthermore, the a-Si:H layer is dry etched using a mixed gas of tetrafluoromethane (CF4) and oxygen (O2), leaving the resist pattern as it is and using this pattern as a photolithography mask. Then, individually divided photoconductive layers 3 are formed. Then, the resist is removed (see FIG. 3(b)).

Next, polyimide was applied to a film thickness of about 1 μm by spin coating, and the film was heated at 200 to 25 μm in the atmosphere.
Baking is performed at 0° C. for 1 to 2 hours to harden and form the first insulating layer 5. A second insulating layer 6 is formed by depositing SiNx on this layer to a thickness of about 6000 angstroms by P-CVD. An example of the formation conditions is SiH4
and NH3, the flow rate of SiH4 was set to 2.
50 sccm, the flow rate of NH3 was 40 sccm, the pressure was 0.2 Torr, the substrate temperature was 250°C, and the RF power was 2.
0 mW/cm2 (see Figure 3(c)).

In this example, a silicon nitride film (S
Although the second insulating layer 6 is formed using silicon oxide (SiOx), the second insulating layer 6 may be formed using a silicon oxide film (SiOx), and the second insulating layer 6 may be formed using a silicon-based inorganic film. shall be.

In order to form a contact via hole 8 so that the wiring 7 can be drawn out from the upper electrode 4, a photoresist 9 is applied, exposed and developed using a photolithographic etching method using a predetermined mask, and a resist pattern is formed. form a formation. And hydrofluoric acid (HF): ammonium fluoride (
SiNx using a mixed solution of NH4F) = 1:10
The film is etched (see FIG. 4(d)).

After peeling off the resist, oxygen (O2) and tetrafluoromethane (C) are exposed using the SiNx film as a mask.
The polyimide is etched by RIE using a mixed gas of F4) to form contact via holes 8 (see FIG. 4(e)).

Furthermore, a film of aluminum, which will become the wiring 7, is deposited to a thickness of about 15,000 angstroms by DC magnetron sputtering, and patterned into a desired pattern by photolithographic etching (FIG. 4(f)). reference). In this way, the light receiving element portion of the image sensor is manufactured.

According to the image sensor of this embodiment, the first insulating layer 5 is made of polyimide, which is excellent in flattening steps.
SiNx film or SiOx with excellent insulation and water resistance
Since the second insulating layer 6 is made of a silicon-based inorganic film such as a film, the interlayer insulating layer does not become thin near the edge of the light receiving element, and sufficient insulation is maintained between the lower electrode 2 and the wiring 7. This has the effect of preventing current leakage and at the same time obtaining good water resistance.

That is, since the silicon-based inorganic film as the second insulating layer is deposited after the polyimide as the first insulating layer has sufficiently flattened the steps, the silicon-based inorganic film as the second insulating layer is almost uniform. As a result, a silicon-based inorganic film is not eroded by water, so it has good water resistance and an image quality.
This has the effect of improving the reliability of the sensor.

According to the method of manufacturing the image sensor of this embodiment, since the polyimide as the first insulating layer 5 covers the light receiving element portion, the SiNx film or the SiOx film as the second insulating layer 6 is deposited. Sometimes ITO as the upper electrode 4
is not directly exposed to plasma or SiH4 gas and reduced, which has the effect of preventing deterioration of sensor characteristics. Similarly, when etching a SiNx film or a SiOx film, ITO is not exposed to the etching solution and is not damaged.

The second insulating layer 6 is a pattern of the photoresist 9, and the first insulating layer 5 is a pattern of the second insulating layer 6.
Since each layer is etched in a separate etching process, the thickness of the film to be etched in one etching process does not become extremely thick, and the contact via hole 8 can be sufficiently microfabricated.

Furthermore, since the pattern of the SiNx film or SiOx film, which is the second insulating layer 6, is used as a mask for etching polyimide, which is the first insulating layer 5, there is no increase in the number of photolithography steps, and therefore, the yield can be improved. This has the effect of making it possible to manufacture a highly reliable image sensor.

[0045]

According to the invention as set forth in claim 1, the first insulating layer is made of polyimide which is excellent in flattening steps, and after flattening the steps caused by stacking each layer of the light receiving element, Since the image sensor uses a silicon-based inorganic film with excellent insulation and water resistance as the second insulating layer,
It is possible to prevent thinning of the interlayer insulating layer near the edge of the photodetector, improve the insulation of the image sensor, and reduce current leakage between the lower electrode and the lead wiring. The two insulating layers of the silicon-based inorganic film can improve water resistance and have the effect of improving the reliability of the image sensor.

According to the second aspect of the invention, the first insulating layer is formed on the upper electrode of the light-receiving element using polyimide, which is excellent in flattening steps, and after flattening the steps caused by laminating each layer of the light-receiving element. Since this method of manufacturing an image sensor laminates a second insulating layer made of a silicon-based inorganic film with excellent insulation and water resistance, thinning of the interlayer insulating layer near the edge of the photodetector can be prevented. It is possible to improve the insulation properties of the image sensor, reduce current leakage between the lower electrode and the lead wire, and further improve water resistance by using a silicon-based inorganic film as the second insulating layer. This has the effect of improving the reliability of the image sensor.

[Brief explanation of the drawing]

FIG. 1 is an explanatory plan view of an image sensor according to an embodiment of the present invention.

FIG. 2 is an explanatory cross-sectional view taken along line AA' in FIG. 1;

FIGS. 3A to 3C are cross-sectional explanatory views of the manufacturing process of this embodiment.

FIGS. 4(d) to 4(f) are cross-sectional explanatory views of the manufacturing process of this embodiment.

FIG. 5 is an explanatory plan view of a light receiving element of a conventional image sensor.

6 is an explanatory cross-sectional view taken along line BB' in FIG. 5; FIG.

FIG. 7 is a cross-sectional explanatory diagram of a conventional alternative.

[Explanation of symbols]

1 Board 2 Lower electrode 3 Photoconductive layer 4 Upper electrode 5 First insulating layer 6 Second insulating layer 7 Wiring 8 Via hole for contact 9 Photoresist 10 Interlayer insulation layer

Claims (2)

[Claims] 1. A lower electrode serving as a common electrode formed on a substrate, a photoconductive layer formed individually for each pixel on the lower electrode, and a photoconductive layer formed on each photoconductive layer on the photoconductive layer. An upper electrode formed in a corresponding manner, an interlayer insulating layer formed to cover the lower electrode, the photoconductive layer and the upper electrode, and an opening provided in the interlayer insulating layer to form the upper electrode. An image having a light receiving element comprising a lead wiring formed on the interlayer insulating layer so as to be connected to an electrode.
An image sensor characterized in that the interlayer insulating layer is formed by sequentially laminating a first insulating layer made of polyimide and a second insulating layer made of a silicon-based inorganic film. 2. A lower electrode serving as a common electrode is formed on a substrate, a photoconductive layer and an upper electrode are individually formed for each pixel on the lower electrode, and a layer made of polyimide is formed to cover the upper electrode. a second insulating layer made of a silicon-based inorganic film is laminated on the first insulating layer to form an interlayer insulating layer, and an opening is formed in the interlayer insulating layer to form an opening in each of the upper electrodes. 1. A method of manufacturing an image sensor, comprising forming lead wiring from the interlayer insulating layer on the interlayer insulating layer.