JPH0462467B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a photoelectric conversion element. [Prior Art] It is generally well known that photo sensors are used as photoelectric conversion elements in photoelectric conversion devices conventionally used as optical input units of image information processing devices such as facsimile machines, digital copying machines, and character reading devices. . In particular, in recent years, photo sensors have been arranged one-dimensionally to form long line sensors.
This has also been used to construct a highly sensitive image reading device. As an example of a photo sensor constituting such a long line sensor, amorphous silicon (hereinafter referred to as a-Si) is used as a photoconductive material.
For example, a planar type photoconductive photosensor is provided with a pair of electrodes made of metal or the like that are arranged facing each other so as to form a gap that serves as a light receiving section on a photoconductive layer containing a photoconductive layer. Methods for producing a-Si constituting such a photo sensor include plasma CVD, reactive sputtering, and ion plating, all of which promote reactions by glow discharge. However, in any case, in order to obtain a high-quality a-Si film with high photoconductivity, it is necessary to form the film with a relatively low discharge power. However, the photoconductive layer obtained by film formation using such a low discharge power does not have sufficient adhesion to the substrate made of glass or ceramic, and may be difficult to adhere to during the subsequent photolithography process during electrode formation. There was a problem that the film was easily peeled off. Therefore, conventionally, in order to prevent film peeling, a method has been adopted in which a-Si is deposited after roughening the surface of the substrate. That is, the surface of the substrate is chemically etched with, for example, hydrofluoric acid, or physically rubbed with, for example, a brush. However, such a method has the following drawbacks. (1) When using chemicals such as hydrofluoric acid, the equipment in the cleaning line becomes complicated and expensive. (2) It is difficult to control the degree of unevenness on the substrate surface. (3) Microscopic defects are likely to occur when the substrate surface is roughened, and because the characteristics of the a-Si film deposited on the microscopic defects are different, variations in characteristics are likely to occur. [Objective] The first object of the present invention is to provide an a-Si photoelectric conversion element that can be manufactured at low cost and has uniform and good performance with a photoconductive layer that does not easily peel off. be. A second object of the present invention is to manufacture the above photoelectric conversion element at low cost and with good uniformity. [Means for Solving the Problems] According to the present invention, the above object is achieved by forming a photoelectric conversion layer containing amorphous silicon as a main component and a pair of electrodes electrically connected to the photoelectric conversion layer. In the photoelectric conversion element provided on the substrate, the photoelectric conversion layer has a region in which the refractive index changes continuously in the layer thickness direction, and the refractive index of the region located closest to the substrate of the photoelectric conversion layer is 6328 Å. This is achieved by a photoelectric conversion element characterized in that it is 3.2 or less in light of . [Example] As the substrate in the photo sensor of the present invention, glass such as #7059 manufactured by Corning, #7740 manufactured by Corning, SCG manufactured by Tokyo Ohka Co., Ltd., quartz glass, ceramic such as partially glazed ceramic, etc. can be used. In the photo sensor of the present invention, the photoconductive layer has a refractive index that changes continuously in at least a portion thereof in the thickness direction, and the refractive index near the substrate surface of the photoconductive layer is 6328 Å. 3.2 or less, but such a photoconductive layer can be used under conditions such as discharge power, substrate temperature, raw material gas composition, and raw material when performing glow discharge in methods such as plasma CVD, reactive sputtering, and ion plating. It can be formed by appropriately setting gas pressure and the like. In this specification, a layer of the photoconductive layer that is close to the substrate surface is sometimes referred to as an a-Si subbing layer, and one or more layers thereon are sometimes referred to as an a-Si layer. In the photoconductive layer of the present invention, it is preferable that a portion where the refractive index changes continuously in the film thickness direction is formed between the a-Si subbing layer and the layer immediately above it. Further, it is preferable that the a-Si layer includes a layer with high photoconductivity. Hereinafter, the present invention will be explained in detail with reference to Examples. Example 1: A double-sided polished glass substrate (#7059 manufactured by Corning Incorporated) was subjected to ordinary cleaning using a neutral detergent or an organic alkaline detergent. Next, the glass substrate 1 was set in a capacitively coupled glow discharge decomposition apparatus as shown in FIG. 1, and maintained at 230° C. under an exhaust vacuum of 1×10 ⁻⁶ Torr. Next, epitaxial grade pure SiH ₄ gas (manufactured by Komatsu Electronics Co., Ltd.) was flowed into the apparatus at a flow rate of 10 SCCM, and the gas pressure was set at 0.07 Torr. After that, using a 13.56MHz high frequency power supply, the input voltage is 2.0kV, RF (Radio
Glow discharge was performed for 2 minutes at a discharge power of 120 W to form an a-Si subbing layer with a thickness of about 400 Å. Next, gradually lower the input voltage and after 5 minutes
It was set to 0.3kV. After that, glow discharge was performed for 4.5 hours at an input voltage of 0.3 kV and a discharge power of 8 W, and the thickness of the
A 0.85μ a-Si layer was formed. followed by _SiH4 diluted to 10% with _H2 and _H2
Using a gas mixed with PH ₃ diluted to 100ppm at a mixing ratio of 1:10 as a raw material, the n ⁺ layer (approximately 0.15μ thick), which is an ohmic contact layer, is formed at a discharge power of 30W.
was deposited. Next, A1 was manufactured using electron beam evaporation method.
was deposited to a thickness of 0.3μ to form a conductive layer. Next, a positive photoresist (manufactured by Shipley) was applied.
After forming a photoresist pattern in the desired shape using AZ-1370), phosphoric acid (85% by volume aqueous solution), nitric acid (60% by volume aqueous solution), glacial acetic acid, and water were added.
A liquid mixed at a volume ratio of 16:1:2:1 (hereinafter referred to as
The exposed portions of the conductive layer were removed using etching solution 1 (referred to as "etching solution 1"). Next, dry etching was performed using CF ₄ gas at an RF discharge power of 120 W and a gas pressure of 0.07 Torr using a plasma etching method using a parallel plate type device to remove the exposed portion of the n ⁺ layer. The photoresist was then peeled off. FIG. 2 shows a partial plan view of the planar photo sensor thus obtained, and FIG. 3 is an X-Y sectional view thereof. In the figure, 1 is the substrate, 2 is the a-Si subbing layer, 3 is the a-Si layer, and 4 is the a-Si subbing layer.
is an n ⁺ layer, and 5 is a conductive layer or electrode. still,
In Fig. 3, the boundary between the a-Si subbing layer 2 and the a-Si layer 3 is clearly illustrated, but in reality, the refractive index of this boundary changes continuously and there is a gap between the two layers. It is a layer with properties. On the other hand, for comparison, the surface of the same glass substrate as above was treated with hydrofluoric acid (49 volume% aqueous solution), nitric acid (60 volume%
Aqueous solution) and acetic acid were mixed in a volume ratio of 1:5:40 for 30 seconds to form a planar photosensor (hereinafter referred to as "substrate") in the same manner as the above process, except that an a-Si subbing layer was not formed. A photo sensor with acid treatment and without subbing layer was manufactured. When the photocurrent values obtained for the above two types of photosensors were compared under the same conditions when light of λ _nsx =565 nm was incident from the glass substrate 1 side, almost the same values were obtained for both. This shows that the presence of the a-Si subbing layer 2 in the photo sensor of the present invention does not deteriorate the photocurrent characteristics. Next, when the above two types of photo sensors were subjected to a durability test using a heat cycle under the same conditions, it was found that the films did not peel off and had sufficient adhesion. Example 2: In the photo sensor manufacturing process of Example 1, a
- When forming the Si subbing layer 2, perform glow discharge using the following combinations of the initially set discharge power (hereinafter abbreviated as "discharge power 1") and the discharge time at the discharge power 1. The same steps as in Example 1 were carried out except for the following.

[Table] As a result, when the discharge power was 80W and 50W, it was possible to obtain a photo sensor without film peeling, but when the discharge power was 30W, 8W and 4W, it was possible to obtain a photo sensor using photoresist AZ-1370. Film peeling occurred during the lithography process (including cleaning with an ultrasonic cleaner), making it impossible to obtain the intended good photo sensor. Example 3: After forming the a-Si subbing layer 2 in the same manner as in Examples 1 and 2, the substrate 1 was taken out and the substrate 1
The refractive index of the a-Si subbing layer 2 formed thereon was measured. Discharge power of glow discharge and a-Si subbing layer 2
The relationship between the refractive index and the refractive index is shown in FIG. The adhesion between the substrate and the photoconductive layer is related to the discharge power of the glow discharge during film formation, and film peeling is caused by the difference in the coefficient of thermal expansion between the intrinsic stress induced depending on the internal structure of the thin film and the substrate. It is thought that this is due to the total stress due to the combination with the internal stress depending on . Therefore, the total stress of the a-Si subbing layer 2 formed on the substrate 1 was measured. The relationship between the discharge power 1 of glow discharge and the total stress of the a-Si subbing layer 2 is shown in FIG. Stress appears as compressive stress and reaches its maximum value when discharge power 1 is around 10W;
The stress decreases as the value increases. The reason why the stress decreases as the discharge power 1 increases is considered to be mainly because the increasing number of voids in the film generates tensile stress, which offsets the compressive stress. As mentioned above, the photoconductivity of the photoconductive layer is related to the discharge power during film formation, and in order to obtain the desired photoconductive properties it is necessary to perform the deposition at a relatively low discharge power, and therefore The a-Si layer 3 in Examples 1 and 2 was deposited at relatively low discharge power. From the above, it can be seen that the a-Si subbing layer 2 of the photo sensor of the present invention functions as a stress relaxation layer and exhibits the effect of improving the adhesion between the substrate and the photoconductive layer. In addition, in the photo sensor of the present invention, in order to obtain good photoconductive properties when using the photo sensor by irradiating light from the base 1 side, the a-Si subbing layer 2 is used.
It is preferable that the thickness of is not too thick, for example
The thickness is preferably 1000 Å or less. Note that when light is incident from the side opposite to the substrate 1 side, there is no need to consider the influence of light absorption in the a-Si subbing layer 2 on the photoconductive properties.
The Si sublayer 2 may be quite thick. Example 4: In the photo sensor manufacturing process of Example 1, a
−After the formation of Si layer 3, the discharge power was increased to 80W and 25
The same steps as in Example 1 were carried out, except that glow discharge was performed for a minute and an a-Si layer was further formed. FIG. 6 is a partial sectional view of the planar type photo sensor thus obtained, showing the same portion as FIG. 3. In FIG. 6, members similar to those in FIG. 3 are given the same reference numerals, and 3' is an a-Si layer.
The thickness of the a-Si layer 3' is 0.3μ, and the formation rate per unit thickness of this layer is increased by increasing the discharge power.
- significantly higher than the formation rate per unit thickness of the Si layer 3; In the photo sensor obtained in this example, a photoconductive layer is constituted by the a-Si subbing layer 2, the a-Si layer 3, and the a-Si layer 3'. According to the photo sensor of this embodiment, the obtained photocurrent is larger than that of the first embodiment due to the increased thickness of the a-Si layer. Example 5: In the photo sensor manufacturing process of Example 1, a
The same process as in Example 1 was carried out, except that during the formation of the -Si subbing layer 2, the substrate temperature was maintained at 70° C., the discharge power 1 was set to 8 W, and glow discharge was performed for 15 minutes. When the a-Si subbing layer 2 was formed under the same conditions, the substrate 1 was taken out and the refractive index of the a-Si subbing layer 2 was measured and found to be 3.10. The photo sensor obtained in this example was as good as the photo sensor obtained in Example 1. Example 6: In the photo sensor manufacturing process of Example 1, a
- H ₂ is used as a raw material gas when forming the Si subbing layer 2.
Using SiH ₄ diluted to 5% with
The same process as in Example 1 was carried out except that glow discharge was performed at 30 W for 10 minutes. When the a-Si subbing layer 2 was formed under the same conditions, the substrate 1 was taken out and the refractive index of the a-Si subbing layer 2 was measured and found to be 3.02. The photo sensor obtained in this example was as good as the photo sensor obtained in Example 1. Example 7: In the photo sensor manufacturing process of Example 1, a
The same steps as in Example 1 were carried out, except that when forming the -Si subbing layer 2, the gas pressure was 0.30 Torr, the discharge power 1 was 50 W, and glow discharge was performed for 5 minutes. When the a-Si subbing layer 2 was formed under the same conditions, the substrate 1 was taken out and the refractive index of the a-Si subbing layer 2 was measured and found to be 3.12. The photo sensor obtained in this example was as good as the photo sensor obtained in Example 1. Example 8: By the same method as Example 1, on the same substrate
It was manufactured by arranging 864 photo sensors in an array. This can be easily done by appropriately setting a mask during the photolithography process. A schematic partial plan view of the long photo sensor array thus obtained is shown in FIG. In FIG. 7, 11 is an individual electrode, and 12 is a common electrode. The density of this long photo sensor array is 8 bits/mm, and the length is the width of an A6 sheet. The uniformity of photocurrent and dark current between bits of the photo sensor array obtained in this example was measured. The results are shown in FIG. On the other hand, for comparison, the same substrate was coated with the method described in Example 1 with and without the subbing layer.
The uniformity of photocurrent and dark current between bits of a long photo sensor array manufactured by arranging 864 photo sensors in an array was measured. The results are shown in FIG. A comparison between FIG. 8 and FIG. 9 shows that the photo sensor of the present invention has no microscopic defects on the substrate.
Furthermore, it can be seen that since the a-Si subbing layer acts as a stress relaxation layer, the uniformity of the photoconductive properties is extremely good. Furthermore, 864 photo sensors were placed in an array on the same substrate in the same manner as in Example 1, except that the acid-treated substrate was used in the same manner as in the above method with acid-treated substrate and no subbing layer. Manufactured side by side. When we measured the uniformity of photocurrent and dark current between bits of the thus obtained long photo sensor array, we found that it was significantly improved compared to that obtained using the method with acid treatment of the substrate and no subbing layer. It was done. Therefore, it can be seen that even if there are microscopic defects on the substrate, the uniformity of properties is improved due to the presence of the subbing layer 2. Example 9: An attempt was made to drive an 864-bit long photo sensor array as obtained in Example 8 by dividing it into 27 blocks of 32 bits each in a matrix. That is, after manufacturing a long photo sensor array using the same process as in Example 8, a polyimide resin (PIQ manufactured by Hitachi Chemical Co., Ltd.) was coated on the entire surface and baked, and then a negative type photoresist (manufactured by Tokyo Ohka Co., Ltd.) was applied.
After forming a pattern in the desired shape using OMR-83), remove unnecessary portions of PIQ with polyimide resin etching solution (PIQ etchant manufactured by Hitachi Chemical Co., Ltd.), peel off OMR-83, and heat at 300℃. It was cured for 1 hour in a nitrogen atmosphere to form an insulating layer and through holes for matrix wiring.
Next, A1 was deposited to a thickness of 2 μm by electron beam evaporation, and the upper electrode of the matrix wiring was formed using a positive photoresist AZ-1370 and etching solution 1. A schematic partial plan view of the matrix wiring portion of the long photo sensor array thus obtained is shown in FIG. 10, and an X-Y sectional view thereof is shown in FIG. 1st
In FIG. 0 and FIG. 11, 21 is a base body,
22 is an a-Si subbing layer, 23 is an a-Si layer, 24 is an n ⁺ layer, 25 is a common electrode, 26 is an individual electrode, 27 is an insulating layer, 28 2 is a through hole, and 29 is an upper electrode of the matrix wiring. FIG. 12 shows a driving circuit diagram for matrix driving the long photo sensor array of 8 bits/mm and A6 width obtained in this manner. In FIG. 12, 31 indicates the photoconductive layer of the photo sensor;
2 is a block selection switch, 33 is a common switch, and 34 is an amplifier. When the long array was driven in a matrix manner as described above, the uniformity of the output photocurrent between bits was measured after 100 μsec of voltage application. The results are shown in FIG. As can be seen from FIG. 13, the output photocurrent of each bit shows extremely good uniformity, indicating that signal readout is sufficiently possible with matrix driving. In the above embodiment, an a-Si subbing layer 2 having a constant refractive index and an a-Si subbing layer 2 having a constant refractive index are used.
Although the example in which a layer with a refractive index that continuously changes in the film thickness direction is formed between the Si layer 3 and the Si layer 3 is shown, in the photo sensor of the present invention, Without forming the a-Si subbing layer 2 having a refractive index, a layer having a refractive index that gradually and continuously changes in the film thickness direction may be formed from the surface of the substrate 1. [Effects of the Invention] According to the present invention as described above, an a-Si photoelectric conversion element having excellent adhesion and uniformity can be obtained at low cost without subjecting the surface of the substrate to any surface treatment in advance.
In addition, in the photoelectric conversion element of the present invention, since the refractive index of the photoelectric conversion layer changes continuously in the film thickness direction, stress relaxation at the layer interface is achieved, resulting in good adhesion. In this case, reflection at the layer interface becomes extremely small, and loss of light amount can be prevented.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an apparatus used in the manufacturing method of the present invention. FIG. 2 is a partial plan view of the photo sensor of the present invention, and FIG. 3 is an X-Y sectional view thereof. FIGS. 4 and 5 are graphs showing the characteristics of the subbing layer. FIG. 6 is a partial sectional view of the photo sensor of the present invention. FIG. 7 is a partial plan view of the photo sensor array, and FIGS. 8 and 9 are graphs showing the characteristics of the photocurrent and dark current. FIG. 10 is a partial plan view of the matrix wiring section.
Figure 1 is its X-Y sectional view. FIG. 12 is a diagram of the matrix drive circuit, and FIG. 13 is a graph of its output photocurrent. 1...Substrate, 2...a-Si subbing layer, 3, 3'
... a-Si layer, 4 ... n ⁺ layer, 5 ... conductive layer, 11
... Individual electrode, 12 ... Common electrode, 21 ... Base, 22 ... a-Si subbing layer, 23 ... a-Si
Layer, 24...n ⁺ layer, 25... Common electrode, 26...
... Individual electrode, 27 ... Insulating layer, 28 ... Through hole, 29 ... Upper electrode.

Claims (1)

[Scope of Claims] 1. A photoelectric conversion element comprising, on a substrate, a photoelectric conversion layer mainly composed of amorphous silicon and a pair of electrodes electrically connected to the photoelectric conversion layer, comprising: The photoelectric conversion layer has a region in which the refractive index changes continuously in the layer thickness direction, and the refractive index of the region located closest to the substrate of the photoelectric conversion layer is 3.2 or less for light with a wavelength of 6328 Å. element. 2 Thickness of the photoelectric conversion layer located closest to the substrate
The photoelectric conversion element according to claim 1, wherein the refractive index in a region of 1000 Å or less is 3.2 or less for light with a wavelength of 6328 Å.