JPH03116979A - Close contact type linear image sensor - Google Patents

Abstract

PURPOSE:To prevent an image sensor of this design from lessening in modulation transfer function by a method wherein the planar outer shape of an individual electrode on a photosensitive layer is formed only of a chrome layer smaller than the photosensitive layer, and a chrome silicide layer formed on the surface of the photosensitive layer between the individual electrodes at the formation of the chrome layer is removed. CONSTITUTION:A photosensitive layer 10 is composed of a P-type 11, an I-type 12, and an N-type 134 of a-Si semiconductor laminated in this sequence on a common electrode 4, an individual electrode 20 on the photosensitive layer 10 is formed only of a Cr layer 21 whose outer shape is smaller than the photosensitive layer 10, and a CrSi layer formed on the surface of the photosensitive layer 10 between the individual electrodes 20 is removed. Therefore, not only a leakage photocurrent flowing through an N-type a-Si semiconductor can be prevented but also an a-Si semiconductor can be prevented from deteriorating due to the thermal diffusion of Al when the part of the individual electrode 20 in contact with the photosensitive layer 10 is formed only of an Al layer 31. Furthermore, a leakage photocurrent flowing through a Cr Si layer of low resistance can be also prevented. By this setup, a linear image sensor of this design can be prevented from decreasing in modulation transfer function.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a contact type linear image sensor.

[Prior Art and Problems to be Solved by the Invention] Conventionally, linear image sensors have been used in image scanners, reading sections of facsimile machines, and the like. Among these, the contact type linear image sensor, in which the reading section and the pixel row are the same,
It is preferably used because of its compactness and the ease of mechanical design of equipment that incorporates it.

Among conventional contact type linear image sensors, a photoconductive type sensor in which a photosensitive layer is composed of only an n-type amorphous silicon (A-5I) semiconductor has a problem of slow response.

On the other hand, a photovoltaic sensor employing a three-layered photosensitive layer made of p-type, i-type, and n-type amorphous silicon semiconductors is capable of high-speed reading of pixel signals. In other words, the pixel output current remains almost constant without depending on the reverse bias voltage for reading, and the response speed is improved by two orders of magnitude.

Furthermore, there is almost no problem with afterimages.

However, in this pin structure, since the n-layer has a low resistance, photocurrent leakage occurs between adjacent pixels, and the MTF (modulation red transfer ψ function), which indicates the sensitivity when reading black and white patterns, becomes large. There was a problem with the decline.

The present invention has been made in view of the above points, and includes M.
It is an object of the present invention to realize a contact type linear image sensor including a photosensitive layer with a pln structure that does not cause a decrease in TF.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the contact type linear image sensor according to the present invention has a one-dimensional arrangement of photosensitive layers separated from each other on a transparent common electrode, and a layer on each photosensitive layer. Individual electrodes are formed on the photosensitive layer, and the photosensitive layer is p-type, p-type,
It is composed of n-type and n-type a-3j semiconductors, and the individual electrodes on the photosensitive layer are made of chromium (Cr) whose planar outline is smaller than that of the photosensitive layer.
It is characterized in that the chromium silicide (CrSi) layer formed on the surface of the photosensitive layer between the individual electrodes during the formation of the Cr layer is removed.

More specifically, a silicon oxide (S i O2) film is formed on at least one surface of a glass substrate, and this S io
Further above the transparent common electrode on the two films, photosensitive layers separated from each other are arranged one-dimensionally, and individual electrodes are formed on each photosensitive layer.

At this time, the photosensitive layer is made of p-type doped carbon (C) having a film thickness of 50 Å or more and 3000 Å or less in order from the common electrode side.
a-8i semiconductor containing 3°5 layers with a film thickness of 0.5 μm or more 1
It is composed of three layers: an undoped l-type a-Si semiconductor with a thickness of m or less and an n-type doped a-8i semiconductor with a film thickness of 50 Å or more and 3000 Å or less. The circumference of the planar outline of the individual electrode on the photosensitive layer is 1 μm or more 2 μm or more from the photosensitive layer.
It consists of a pixel portion formed as small as 0 μm or less, a lead portion extending from the pixel portion to the outside of the photosensitive layer, and a wire bonding pad portion for external connection connected to the tip of the lead portion. At this time, the pixel part and the lead part are composed only of a Cr layer with a thickness of 50 Å or more and 10,000 Å or less, and the wire bonding pad part is composed of a Cr layer with a thickness of 50 Å or more.
Cr layer with a thickness of at least 10,000 Å and a film thickness of 0.5
It is composed of a composite layer with an aluminum (AII) layer having a thickness of .mu.m or more and 3 .mu.m or less, and when forming these Cr layers, the CrSi layer formed on the surface of the photosensitive layer between the individual electrodes is removed. Further, at least an A1 layer is formed on the common electrode at a position different from the photosensitive layer forming position to constitute an extraction electrode, and almost the entire area except the wire bonding pad part and a part of the extraction electrode is made of a protective resin with low moisture permeability. cover.

In order to suppress the occurrence of defects during wire bonding work, the length of the bonding pad section for external connection of the individual electrodes that derive the output of the pixel is set to 5 times the width of this pad section.
More than twice as much. In order to increase the width of the pad portions and suppress the occurrence of problems during wire bonding work, it is sufficient to arrange three rows of bonding pad portions.

To improve the output accuracy of the sensor, the area of the leads or their resistance values are made substantially the same between each individual electrode.

[Function] In the contact type linear image sensor according to the present invention, light is incident from the transparent common electrode side. The light transmitted through this electrode enters the photosensitive layer made of an a-8i semiconductor with a pin structure from the p-layer side, and a photocurrent is generated there. This current is read through separate photosensitive layers, ie, an individual electrode and a common electrode provided for each pixel.

At this time, since each pixel of the pin structure is formed separately from each other on the common electrode, photocurrent leakage between adjacent pixels is prevented even if the n-layer has a low resistance. In addition, since the individual electrodes on the photosensitive layer are composed only of a Cr layer whose planar outline is smaller than that of the photosensitive layer, it is possible to not only prevent short circuits with the common electrode, but also prevent photosensitive Deterioration of the a-Si semiconductor due to heat diffusion into the layer can be prevented. However, when forming this Cr layer, a low resistance CrSi layer is formed on the surface of the photosensitive layer between the individual electrodes. If this is left unattended, a small photocurrent leak will still occur, so in the sensor according to the present invention, this CrSi layer at the edge of the pixel is removed to thoroughly prevent current leakage.

More specifically, SlO□ is deposited on the light incident side surface of the glass substrate.
After forming a film to achieve complete insulation, a transparent common electrode is formed. The photosensitive layer arranged one-dimensionally on this common electrode is
In order from the common electrode side, p-type a-5iC semiconductor with a film thickness of 50 Å or more and 3000 Å or less, a film thickness of 0.5 m or more and 3.5 a
i-type a-8i semiconductor with a thickness of 50 Å or more and a thickness of 300 Å or less
It is composed of three layers of n-type a-Si semiconductor of 0A or less. p
The thinner the layer, the better from the viewpoint of light transparency, but the most appropriate thickness is 500 mm so that the film does not form an island shape. 50Å
A range of 3000 Å or less is practical. 1
Regarding the layer, this layer is in a reverse bias state when the sensor is used, and considering that the signal reading of the sensor is based on the charge accumulation method, even if the amount of charge generated by the pixel is constant, the pixel part and the lead part of the individual electrode The larger the capacitance including , the smaller the read output voltage will be. Conversely, if this capacitance is small, the output voltage will be large. That is, the output voltage increases as the thickness of one layer increases. On the other hand, as the thickness of one layer increases, the load on the manufacturing equipment increases.

From the above, the thickness of the i layer is 0.5 μm or more and 3.5 μm.
m or less is appropriate. The thickness of the n layer is 50 Å or more and 300 Å or more.
A suitable thickness is 0 Å or less.

The pixel part of the individual electrode is composed only of a Cr layer with a thickness of 50 Å or more and 10,000 Å or less, and the wire bonding pad part is composed of a Cr layer with a thickness of 50 Å or more and 10,000 λ or less, and a Cr layer with a thickness of 0.5 μm or more and 3 μm or less on top of this. Consists of a composite layer with A47 layer.

The Cr layer of the individual electrode needs to have a thickness that can be formed uniformly without pinholes, and there is no problem if the thickness is 50 Å or more and 10,000 Å or less. The thickness of the A1 layer itself affects ultrasonic wire bonding properties, so the thickness is 0.5 μm or more and 3 μm.
Although the following film thickness is desirable, consideration should be given to the load on the manufacturing equipment.

Further, at least an Au layer is formed on the common electrode at a position different from the position where the photosensitive layer is formed to form an extraction electrode, and almost the entire area except the wire bonding pad part and a part of the extraction electrode is covered with a protective resin with low moisture permeability. Covering the pixel protects the pixel from moisture degradation without compromising external connectivity.

Furthermore, the length of the wire bonding pad part is 5 times the width of the wire bonding pad part.
If the thickness is more than double, wire bonding can be performed at a position that is sufficiently layered from the contact position of the probe needle for inspecting the presence or absence of sensor damage. Therefore, traces of the probe needle on this pad portion do not affect wire bonding. Further, by adopting a three-row arrangement of the bonding pad sections, the width of the pad section can be increased, and the positions of adjacent pad sections can be shifted.

Therefore, problems such as bonding errors and wire contact can be prevented.

In addition, for a charge storage type signal reading IC, the area of the lead part is made substantially the same between each individual electrode, and for a current reading type signal reading IC, the resistance value of the lead part is set between each individual electrode. are substantially the same. If the areas of the lead portions are made the same, the stray capacitance will be constant, so accurate output can be obtained from the charge storage type IC. If the resistance values of the lead parts are made the same, accurate output can be obtained through the current reading type IC.

[Example] FIGS. 1 and 2 are a plan view and a sectional view taken along the line 1--2 of a contact type linear image sensor according to an example of the present invention, respectively.

First, there are five S layers on at least one side for insulation.
A transparent common electrode (4) is formed on the glass substrate (2) on which the film is formed.

The transparent conductive film constituting the common electrode (4) is made of tin oxide (S
Thin films of ITO (a mixture of indium oxide and tin oxide) can be used. This transparent conductive film must be set to have low resistance, sufficient light transmittance, and non-reflection. When combining an ITO film with an a-8i semiconductor, the film thickness must be 800 Å or more and 1000 λ or less. It is appropriate to do so. This common electrode (4) is patterned into a predetermined shape using photofabrication and wet etching techniques.

Furthermore, a photosensitive layer (lO) made of an a-8L semiconductor is formed over the side edge of this common electrode (4) by a plasma CVD process. This photosensitive layer (10) is composed of p-type (11), n-type (12) and n-type in order from the common electrode (4) side.
It is composed of a-8i semiconductor of type (13). p layer (11
), silane (S i H4) gas, diborane (
82H8) gas and methane (CH,) gas, a-8IC semiconductor doped to p-type with 500
Let it be the thickness of a person's skin. Subsequently, a layer (12) of undoped intrinsic a-8t is formed to a thickness of 2 μm.

The n-layer (13) is 300 nm thick of n-type doped a-3i. This n-layer (13) is formed by plasma discharge using a mixed gas of silane gas and phosphine (PH3) gas as a raw material. However, p layer (ll)
is in the range of 50 Å to 3000 Å, the five layer (12) is in the range of 0.5 μm to 3.5 μm, and the n layer (13) is in the range of 0.5 μm to 3.5 μm.
The film thickness can be changed within the range of 50 Å or more and 3000 Å or less. As mentioned above, this photosensitive layer (10
) has the same structure as the a-3i solar cell, so a multi-chamber or single-chamber plasma device that is a solar cell film forming device can be used as is, which is advantageous in terms of mass production.

After this, the photosensitive layer (lO) is divided into each pixel. For this separation, not only the photofabrication and wet etching methods described above but also a plasma etching method can be employed.

As a result, in the photosensitive layer (10), rectangular pixel portions (14) separated from each other are one-dimensionally arranged on the common electrode (4) along the side edges thereof, and a tongue-shaped pixel portion is formed from each pixel portion (14). A lead portion (16) protrudes above the glass substrate (2). This photosensitive layer lead part (16) is formed on the individual electrode (
20) and the common electrode (4). When the reading density of this contact type linear image sensor is 8 pixels/mm, the pixel pitch is 125 μm. At this time, the size of each pixel portion (14) is 110 μm.
degree is suitable.

Furthermore, individual electrodes (
20), and at the same time, an extraction electrode (30) is formed at the remaining position on the common electrode (4). Individual electrode (20)
The rectangular pixel portion (20) on the photosensitive layer pixel portion (14) and the lead portion (26) on the photosensitive layer lead portion (16) following this
and a wire bonding pad section (28) on the glass substrate (2) following this lead section (26). However, the pixel portion (24) of this individual electrode (20)
) and the lead part (2B) are made of one layer of Cr layer (21), and the pad part (28) is made of the Cr layer (21) and the A on top of this.
It has a composite layer structure with the g layer (22). Extracting electrode (30)
is strip-shaped and consists of a Cr layer (31) and an A1 layer (3
2) has a composite layer structure.

In order to form these individual electrodes (20) and extraction electrodes (30), C
After forming a film with a thickness of about 500 mm using electron beam (EB) deposition or sputtering, this C film is etched to form the individual electrodes (20) having the shape described above.
The layer (21) and the Cr layer (31) of the extraction electrode (30) are formed simultaneously. Next, patterned individual electrodes (20
) and around the Cr layer (31) of the extraction electrode (30).
A deposited film is formed to a thickness of about 1.5 μm, and patterned into the shape of a wire bonding pad portion (28) and an extraction electrode (30).

As a result, Alp layers (22, 31) are formed on each Cr layer (21, 31) of the individual electrode (20) and the extraction electrode (30).
32) can be formed simultaneously. The Ag film can be formed by either EB evaporation or sputtering. However, the Cr layer (2) of the patterned individual electrode (20)
1) An Al1 layer (22) may be formed on the entire upper surface. In the above explanation, the four processes of C"evaporation, Cr patterning, AII deposition, and L patterning were explained, but C"evaporation and 1
The vapor deposition may be performed continuously using one vapor deposition apparatus, and then one patterning and C "patterning may be sequentially performed.

Although the Cr layer (31) of the extraction electrode (30) is not necessarily required, it is desirable from the viewpoint of adhesion to the layer (32) formed thereon. Cr layer (31) is 50 Å
In the range of 10,000 Å or more, the Ag layer (32) has a thickness of 0.
The film thickness can be changed within the range of 5 μm or more and 3 μm or less.

Now, the pixel portion (24) of the individual electrode (20) is made smaller in circumference than the photosensitive layer pixel portion (14) by a size of 1 μm or more and 20 μm or less. The same holds true for the relationship between the individual electrode lead portion (26) and the photosensitive layer lead portion (1B). This is to prevent electrical contact between the common electrode (4) and the individual electrodes (20) due to misalignment.

In the non-overlapping portion between the photosensitive layer pixel portion (14) and the individual electrode pixel portion (24) and the non-overlapping portion between the photosensitive layer lead portion (1B) and the individual electrode lead portion (2B), C “C” is formed during film formation. The low-resistance CrSi is removed by a method such as plasma etching.This makes it possible to prevent minute leaks through the CrSi at the edges of each pixel.

After the above patterning is completed, almost the entire area except for the wire bonding pad portion (28) and a part of the extraction electrode (30) is covered with a resin having low moisture permeability to form a protective resin (40).

Next, modified examples of the individual electrodes (20) are shown in FIGS. 3 to 6.

In the individual electrodes (20) in FIG.
8) has a width narrower than the width a of the pixel portion (24), but the length C is more than five times the width. By adopting this shape of the bonding pad portion (28), the contact position of the probe needle during inspection and the wire bonding position can be sufficiently spaced apart. Therefore, traces of the probe needle do not affect wire bonding.

The individual electrode (20) in FIG. 4 has wire bonding pad portions (28) arranged in three rows. That is, n
When is a natural number, the (3n - 2)th pad part (
28-1) forms the first column that is parallel to the column of pixel sections (24) and is the most distant from this column, and the (3n-1)th pad section (H-2) The 3nth pad part (28-3) forms the second row near the row of part (24).
) forms the third column closest to the column of the pixel section (24). Therefore, although the arrangement pitch of the bonding pad section (28) is narrower than the arrangement pitch of the pixel section (24), the width B of each pad section (28) is wider than Ijl a of the pixel section (24). .

Moreover, the positions of the adjacent pad portions (28) are shifted.

However, in the lead portion (2B), l] is the same for all individual electrodes. If this three-row arrangement of the pounding pad portions (28) is adopted, the width B of the pad portions (28) is large;
Moreover, since the position of the adjacent pad part (28) is shifted,
It is possible to prevent problems such as bonding errors and wire contact from occurring.

However, since the lengths of adjacent lead portions (26) of these individual electrodes differ greatly, the stray capacitance and resistance value differ between the individual electrodes, causing the problem that accurate output cannot be obtained from the signal reading IC. be.

In other words, when using a charge accumulation type signal reading IC that uses the lead part (26) etc. as an electrical capacitor and sequentially reads the charge accumulated in each pixel while switching, the stray capacitance including the lead part (2B) is Nonuniformity greatly affects output accuracy. On the other hand, individual Ifis (20)
When using a current reading type signal reading IC that reads the current value of each pixel through This greatly affects accuracy.

Solutions to this problem are shown in FIGS. 5 and 6, respectively.

In the individual electrode (20) whose plan view is shown in FIG. 5, the width of the long lead portion (2B-1) is narrowed, while the width of the short lead portion (
By widening the width of 2B-3), the area of all lead portions (2B) is made constant and the stray capacitance is made uniform. Therefore, accurate output can be obtained from the charge accumulation type signal reading IC.

On the other hand, in the individual electrode (20) shown in FIG. The L/D (L: length, D=width) of the portion (26) is kept constant. As a result, the resistance value of the lead portion (2B) becomes almost the same between each individual electrode.

Therefore, accurate output can be obtained through the current/read type signal reading IC.

[Effects of the Invention] As explained above, the contact type linear image sensor according to the present invention has photosensitive layers separated from each other arranged one-dimensionally on a transparent common electrode, and individual electrodes formed on each photosensitive layer. The photosensitive layer is composed of p-type, n-type, and n-type a-St semiconductors in order from the common electrode side, and the individual electrodes on the photosensitive layer are composed only of a Cr layer whose planar outline is smaller than that of the photosensitive layer. ,
Since the CrSi layer formed on the surface of the photosensitive layer between the individual electrodes is removed during the formation of this Cr layer, the separation of pixels can only prevent photocurrent leakage through the n-type A-3I semiconductor. AI!, which becomes a problem when the individual electrode portion in contact with the photosensitive layer is composed of only the A11 layer! While preventing the a-Si semiconductor from deteriorating due to thermal diffusion, it is also possible to prevent photocurrent leakage through the low-resistance CrSi layer.

Therefore, according to the present invention, it is possible to realize a contact type linear image sensor including a photosensitive layer with a pin structure that does not cause a decrease in MTF.

Moreover, since the a-8i semiconductor layer has a pin structure, it can be formed using the same process and equipment as a normal a-8L solar cell, improving productivity.

Now, in an element structure in which opaque individual electrodes are formed on a glass substrate, and a photosensitive layer and a transparent common electrode are sequentially formed thereon, it is necessary to use a transparent protective resin. However, it is difficult to form a protective resin without bubbles or scratches and with a constant thickness by screen printing. On the other hand, when adopting an element structure in which a transparent common electrode is formed on a glass substrate and a photosensitive layer and individual electrodes are sequentially formed thereon as claimed in claim 2, an opaque protective resin is used. This increases the flexibility in printing conditions for this resin. Further, in the contact type linear image sensor according to the second aspect of the present invention, by using a-SiC for the p-type semiconductor layer, the output current increases, while the dark current decreases, and the bright/dark sensitivity ratio increases.

In addition, if the length of the wire bonding pad section for external connection of the individual electrodes is made at least five times the width of this pad section, or if the width of this pad section is made wider by arranging three rows of wire bonding pad sections, It is possible to suppress the occurrence of defects during wire bonding work such as various bonding mistakes and contact between connecting wires. Furthermore, regarding the individual electrodes, for a charge accumulation type signal reading IC, the area of the lead part is made substantially the same between each individual electrode, and for a current reading type signal reading IC, the resistance value of the lead part is made to be the same for each individual electrode. If the individual electrodes are made substantially the same, the output accuracy can be improved for any reading method.

[Brief explanation of drawings]

Fig. 1 is a plan view of a contact type linear image sensor according to an embodiment of the present invention, and Fig. 2 is a plan view of the previous contact type linear image sensor.
A sectional view, FIG. 3 is a plan view showing a modified example of the individual electrode, and FIG. 4 is a
FIG. 5 is a plan view showing still another modification of the individual electrode. FIG. 6 is a plan view showing still another modification of the individual electrode. Explanation of symbols 2...Glass substrate, 4...Common electrode, 10...Photosensitive layer, 11...P layer, 12...1 layer, 13...n
Layer, 14... Photosensitive layer pixel portion, 16... Photosensitive layer lead portion, 20... Individual electrode, 21-Cr layer, 22 ・A
N layer, 24... Individual electrode pixel portion, 26... Individual electrode lead portion, 28... Wire bonding pad portion, 3
0... Extraction electrode, 31... Cr layer, 32... A1
Layer, 40...protective resin. Patent Applicant Kanebuchi Chemical Industry Co., Ltd. f:3-1 (Mr cqcn Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. A contact type linear image sensor in which photosensitive layers separated from each other are arranged one-dimensionally on a transparent common electrode, and individual electrodes are formed on each photosensitive layer, the photosensitive layer being on the side of the common electrode. The individual electrodes on the photosensitive layer are composed of only a chromium layer whose planar outline is smaller than the photosensitive layer. A contact type linear image sensor characterized in that a chromium silicide layer formed on the surface of a photosensitive layer has been removed. 2. A silicon oxide film is formed on at least one surface of the glass substrate, photosensitive layers separated from each other are arranged one-dimensionally above a transparent common electrode on the silicon oxide film, and individual electrodes are provided on each photosensitive layer. In the formed contact type linear image sensor, the photosensitive layer has a film thickness of 50 Å or more and 300 Å in order from the common electrode side.
Amorphous silicon semiconductor containing p-type doped carbon with a thickness of 0 Å or less, undoped i-type amorphous silicon semiconductor with a film thickness of 0.5 μm or more and 3.5 μm or less, and n-type doped amorphous silicon with a film thickness of 50 Å or more and 3000 Å or less Consisting of three semiconductor layers, the individual electrodes include a pixel portion whose planar outline is smaller than the photosensitive layer by 1 μm or more and 20 μm or less on the photosensitive layer, and a pixel portion that extends outside the photosensitive layer from this pixel portion. The pixel part is made up of only a chromium layer with a thickness of 50 Å or more and 10,000 Å or less, and the wire bonding pad part is made of A chromium layer with a thickness of 50 Å or more and 10,000 Å or less and a film thickness of 0.5 μ on this
It is composed of a composite layer with an aluminum layer with a thickness of 3 μm or more, and the chromium silicide layer formed on the surface of the photosensitive layer between the individual electrodes is removed when forming these chromium layers, and the photosensitive layer on the common electrode is further removed. A claim characterized in that the extraction electrode is formed by forming at least an aluminum layer at a position different from the position, and almost the entire area except for the wire bonding pad portion and a part of the extraction electrode is covered with a protective resin with low moisture permeability. The contact type linear image sensor according to item 1. 3. The contact type linear image sensor according to claim 2, wherein the length of the wire bonding pad portion of the individual electrode is five times or more the width thereof. 4. The contact type linear image sensor according to claim 2, wherein the wire bonding pad portions of the individual electrodes are arranged in three rows. 5. The contact type linear image sensor according to any one of claims 2 to 4, wherein the areas of the lead portions of the individual electrodes are substantially the same between the individual electrodes. 6. The contact type linear image sensor according to claim 2, wherein the resistance values of the lead portions of the individual electrodes are substantially the same between the individual electrodes.