JPH0245344B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a long thin film original reading element which has a laminated structure in which a lower electrode, a photoconductor, and an upper transparent electrode are deposited, and which has a heat treatment process added during the manufacturing process in order to improve the reading performance of the long thin film original reading element. Regarding the manufacturing method. In recent years, in order to downsize or simplify the mechanism of reading devices such as facsimile machines, long thin film document reading elements having a laminated structure in which a lower electrode, a photoconductor, and a transparent electrode are deposited have come into use. FIG. 1 is a schematic diagram showing the cross-sectional structure of a conventional long thin film original reading element in which a hydroxylated amorphous silicon layer is applied as a photoconductor. In FIG. 1, 1 is an insulating substrate, 2 is a lower electrode, and 3
4 is an amorphous silicon layer, and 4 is an upper transparent electrode. A conventional method for manufacturing the elongated thin film document reading element 5 having such a laminated structure will be described below. First, as the insulating substrate 1, ceramic, glass, plastic, etc. are generally used, but materials with strong mechanical strength, heat resistance to heat treatment performed during the manufacturing process, and sufficient insulation properties are used. If so, it can be used without being limited to these. Moreover, as the lower electrode 2,
Metal materials such as Cr, Ni, Pt, Pd, Ti, Mo, and Ta, or semiconductors such as highly doped amorphous silicon can be used. Next is the method of depositing the lower electrode 2 on the insulating substrate 1.
When a metal material is used as the lower electrode 2, an electron beam evaporation method is suitable, and when a semiconductor such as a polysilicon layer is used, a plasma CVD method or a CVD method is suitable. In any of the above cases, it is desirable that the deposited thickness of the lower electrode 2 be maintained at about 1000 Å to 5000 Å. Furthermore, the lower electrode 2 is patterned into a predetermined shape (generally a comb shape) by photolithography. Next, as the hydrogenated amorphous silicon layer 3, a non-doped one or a P-type layer doped with boron B or other elements of the periodic table group can be used. The plasma CVD method was used to deposit the amorphous silicon hydroxide layer on the insulating substrate 1 on which the lower electrode 2 was formed, and the film thickness was 1 μm.
The degree is appropriate. Further, as the upper transparent electrode 4, an ITO film (In ₂ O ₃ +SnO ₂ ) can be used. At this time, a reactive sputtering method is used as a deposition method on the insulating substrate 1 on which the lower electrode 2 and the amorphous silicon hydroxide layer 3 are formed.
Appropriate deposition thickness is about 500 Å to 2000 Å. The above is a general method for manufacturing the long thin film document reading element 5. Next, the principle of photoelectric conversion in this reading element 5 will be briefly described. First, when such a reading element 5 is normally operated, a bias voltage is applied between the lower electrode 2 and the upper transparent electrode 4. At this time, the lower electrode 2 is grounded and the upper transparent electrode 4 is
It is common to apply a negative bias voltage of . When the reading element 5 is irradiated with a predetermined light in this state, the light passes through the upper transparent electrode 4 and is irradiated onto the amorphous silicon layer 3. Inside the amorphous silicon layer 3, pairs of electrons and holes are generated by the energy of the irradiated light. As described above, since a reverse bias voltage is applied between the lower electrode 2 and the upper transparent electrode 4, the electrons flow toward the lower electrode 2, and the holes flow toward the transparent electrode 4.
A predetermined current flows through the amorphous silicon layer 3. Therefore, by extracting this current to the outside, a photoelectric conversion current for the irradiated light can be obtained. On the other hand, when the reading element 5 is not irradiated with light, the above-mentioned photoexcitation does not occur, but a weak current, that is, a dark current, flows in the amorphous silicon layer 3 due to the bias voltage applied between the two electrodes. It flows. FIG. 2 is a schematic diagram showing how the current generated by the reading element 5 described above is measured when it is irradiated with light and when it is not irradiated with light. In FIG. 2, a predetermined bias voltage is applied from a bias power supply 6 to the transparent electrode 4 side with the lower electrode 2 being on the ground side. In this state, the light emission of the lamp 7 is controlled, and the lamp 7 irradiates the reading element 5 with light or stops the irradiation. Then, the indication of the ammeter 8 during the light irradiation is measured as a photocurrent, and the indication of the ammeter 8 during the non-irradiation is measured as a dark current. This measurement is performed at each point by changing the bias voltage. Further, the illumination intensity (light amount) when the lamp 7 emits light at this time is 100x. FIG. 3 shows the general DCI-V characteristics of the above measurement results, in which a indicates the photocurrent and b indicates the dark current, respectively. The reason why the current density [A/cm ³ ] of the photocurrent shown in FIG. This shows that they work in blocking contact with each other. Note that all electron-hole pairs excited here are taken out to the outside. On the other hand, the dark current shown in FIG. 3b is suppressed to a lower value than the photocurrent. The cause of this is that the lower electrode 2 when not irradiated with light.
This is presumed to be because the injection of holes from the upper transparent electrode 4 into the amorphous silicon layer 3 or the injection of electrons from the upper transparent electrode 4 into the amorphous silicon layer 3 is suppressed. Although the details of this have not yet been clarified, the present inventors believe that the latter is more likely based on various experimental results. In any case, the amorphous silicon layer 3 is
A charge barrier layer of some kind is formed at the interface between the two electrodes and the amorphous silicon layer 3 to suppress the injection of charge into the amorphous silicon layer 3, and the increase or decrease of the dark current changes depending on the height of this charge barrier layer. It is thought that then. As is well known, when a document reading element is mounted on a facsimile or the like, it illuminates the document with an illumination light source and reads information on the document based on the presence or absence of reflected light from the document, that is, bright and dark signals. Therefore, in order to improve the reading performance, it is desirable that the ratio between the photocurrent obtained during light irradiation and the dark current obtained during non-irradiation be as large as possible. However, in the reading element obtained by the above-mentioned conventional manufacturing method, although the dark current itself is low, when considering the reliability of identification, the ratio of the photocurrent to the dark current is by no means desirable. It was hard to say. The present invention has been made in view of this situation, and it is possible to suppress the dark current to a value as small as possible while keeping the photocurrent at a sufficiently large value, thereby increasing the ratio between the two currents. It is an object of the present invention to provide a method for manufacturing a long thin film document reading element that can reliably distinguish between bright signals and dark signals. Therefore, in the present invention, when manufacturing a long thin film reading element, after forming an upper transparent electrode by a sputtering method on a photoconductor layer made of an amorphous silicon hydroxide layer, the electrode is placed in air or an inert gas atmosphere containing oxygen gas. The above objective is achieved by applying heat treatment at 200 to 300°C. Embodiments of the present invention will be described in detail below in accordance with actual manufacturing processes with reference to the accompanying drawings. In the present invention, the substrate 1 is made of glass, and the lower electrode 2 is made of glass.
Cr, hydrogenated amorphous silicon for the photoconductor 3, ITO film (In ₂ O ₃ +
SnO ₂ ) was used in each case. First, 3000 Å of Cr is deposited on a glass substrate by electron beam evaporation, and then the deposited Cr is patterned into a comb shape by ordinary photolithography. Next, amorphous silicon, which is hydrogenated by decomposing silane gas (SiH ₄ ) by glow discharge, is deposited to a thickness of about 1 μm on the glass substrate and Cr electrode. Each deposition condition at this time is the substrate temperature
200~300℃, discharge pressure 0.2~1.0Torr, distance between plates
40mm, RF power 10~100W, silane gas flow rate 10~
The deposition time was 50Sccm and 1 hour. Furthermore, ITO was added on top of this in a reactive gas atmosphere containing a mixture of Ar and _O2 .
An ITO film of about 1500 Å is deposited using the DC magnetron sputtering method using (In ₂ O ₃ + SnO ₂ ) as a target. At this time, the substrate is not heated, but the substrate temperature is maintained at 50° C. or lower. Next, the bright current and dark current of the reading element obtained by the above method were measured by the same method as shown in FIG. At this time, -5V was applied as the bias voltage 6, and a green fluorescent lamp was used as the lamp 7. In addition, the illumination intensity during irradiation of this fluorescent lamp was set to 100x. As a result, photocurrent 9.2×10 ^-10 [A], dark current 6.8×
10 ^-13 Got [A]. Next, after measuring this current, the reading element 5 was subjected to heat treatment. FIG. 4 is a schematic diagram conceptually showing this situation, and the reading element 5 was placed in a heating furnace 10 kept at 200° C. by heating with a heater 9 in the atmosphere and left for about 30 minutes. Thereafter, the photocurrent and dark current of this reading element 5 were measured under the same conditions as described above.
A dark current of 9.8×10 ^-10 [A] and a dark current of 7.6×10 ^-14 [A] were obtained, respectively. Table 1 shows the measurement results of each photocurrent and dark current of the above-mentioned reading element 5 before and after heat treatment.

[Table] In Table 1, if the rate of change of each current from before heat treatment to after heat treatment is expressed as rate of change = (characteristic value after heat treatment) / (characteristic value before heat treatment), in the case of photocurrent, it is 1.07, which is too much. It can be seen that while there is no change, the dark current is 0.11, which is a significant decrease. Furthermore, when calculating the ratio of photocurrent to dark current, that is, the brightness ratio, before and after the heat treatment, before the heat treatment, it is 9.2×10 ^-10 /6.8×10 ^-13 ≒1400, while after the heat treatment, it is 9.8× 10 ^-10 /7.6×
10 ^-14 ≒ 13000, which shows that the ratio has increased significantly. The rate of change in photocurrent/dark current, ie, brightness/darkness ratio, from before to after heat treatment was 9.3. The above results are examples in which the upper transparent electrode 4 was deposited on the amorphous silicon 3 and the substrate 1 and then subjected to heat treatment in the atmosphere. Further, in the present invention, after depositing the transparent electrode 4, heat treatment was performed at 200 to 300° C. for 30 to 120 minutes in an atmosphere consisting of an inert gas (N ₂ or Ar) containing oxygen gas O ₂ .
As shown in Table 1, this result also confirmed a significant increase in the ratio of photocurrent to dark current before and after heat treatment. This is because when ITO is deposited as the upper transparent electrode on the hydrogenated amorphous silicon layer by sputtering method, dangling bonds are generated on the surface of the hydrogenated amorphous silicon layer, and the upper transparent electrode and the hydrogenated amorphous silicon layer This is thought to be because the interfacial properties between the upper transparent electrode and the hydrogenated amorphous silicon layer decreased and the dark current increased due to heat treatment, while the dangling bonds decreased and the interfacial properties between the upper transparent electrode and the hydrogenated amorphous silicon layer improved. . Furthermore, by performing heat treatment in an oxygen atmosphere, oxygen diffuses through the ITO and forms an oxide layer at the interface with the hydrogenated amorphous silicon layer, forming a shot barrier, thereby further reducing dark current. It is also possible that it was possible. Furthermore, after performing any of the heat treatments described above, vacuum heat treatment was further performed at 300°C for 120 minutes, and then the DCI-V characteristics were measured using the method shown in Figure 3.
Almost no change was observed in the characteristic values.
This means that there is a passivation film (an oxide film for isolating the element from electrical and chemical requirements from the outer periphery and providing electrical stability) on the reading element 5.
This shows that it can stably withstand the heat treatment process when depositing. As explained above, according to the method for manufacturing a long thin film original reading element of the present invention, damage to the surface of the hydrogenated amorphous silicon layer caused by sputtering is recovered by heat treatment at a predetermined temperature after transparent electrode deposition. However, the interfacial properties between the transparent electrode and the hydrogenated amorphous silicon layer are improved, and oxygen diffuses into the surface of the transparent electrode to form an oxide layer at the interface with the hydrogenated amorphous silicon layer, forming a shot barrier. It is possible to obtain a reading element 5 in which the dark current is maintained at a high value and the dark current is extremely low. Therefore, the ratio between the bright current and the dark current can be made sufficiently large, and the document reading performance can be significantly improved. In addition, since the heat treatment can be performed in the atmosphere or in an inert gas containing oxygen gas, special equipment such as a pressurizing device is not required, and it has various excellent effects such as contributing to the simplification of the mechanism and control of the manufacturing equipment. play. Furthermore, even if a heat treatment is applied to the element in which dangling bonds are reduced and the interfacial characteristics are stabilized by the heat treatment, the characteristics are maintained stably even if heat treatment is applied in the step of forming the passivation film.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram conceptually showing the cross-sectional structure of a general long thin film document reading element, and FIG. 2 is a schematic diagram showing a method for measuring photocurrent and dark current in the reading element shown in FIG. 1. FIG. 3 is a diagram showing typical DCI-V characteristics obtained by carrying out the above measurements, and FIG. 4 is a schematic diagram showing an example of a manufacturing apparatus according to the present invention. DESCRIPTION OF SYMBOLS 1... Insulating substrate, 2... Lower electrode, 3... Photoconductor, 4... Upper transparent electrode, 5... Long thin film original reading element, 6... Bias power supply, 7... Lamp, 8... ... Ammeter, 9... Heater, 10...
heating furnace.

Claims (1)

[Claims] 1. A lower electrode forming step of forming a lower electrode on an insulating substrate, and a photoconductor layer forming step of laminating a photoconductor layer made of a hydrogenated amorphous silicon layer on the lower electrode. and an upper transparent electrode forming step of laminating an upper transparent electrode on the photoconductor layer by a sputtering method, in a method for manufacturing a long thin film document reading element in which a plurality of photoelectric conversion elements are arranged on a substrate. After forming the upper transparent electrode, the photoelectric conversion element is subjected to a heat treatment step in which the photoelectric conversion element is heated at 200 to 300°C in the atmosphere or an inert gas atmosphere containing oxygen gas. A method for manufacturing a thin film document reading element.