JPH07109900B2 - Optical sensor manufacturing method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical sensor used in an image input section of an OA device such as a facsimile machine or an optical disk.

2. Description of the Related Art In recent years, an adhesive line sensor having the same size as the document width has been developed with the aim of downsizing the image input section of facsimile machines and various OA equipment and improving image distortion, and image reading devices using this have been widely used. Further, at present, there is a strong demand for improvement in performance, that is, speedup and improvement in image quality.

An optical sensor mainly composed of CdS, CdSe or solid solution CdS-CdSe has a feature that the photocurrent is large. Therefore, a contact type line sensor using this sensor can easily design a peripheral circuit. On the other hand, this photosensor has two drawbacks: the response speed of the photocurrent Jp to the light irradiation is slow, and the proportionality to the irradiation light intensity (that is, the reflected light intensity from the original) L is poor. That is, in the former case, the rise time τ _r and the fall time τ _{d of} Jp are the sensor surface strength during normal use.
It is as long as 2-3 msec at 100 lux, and in the latter case, the γ value when Jp is proportional to L ^γ is as small as 0.6-0.75 at 50-100 lux.

As described above, if the rise time and fall time of the photocurrent of the optical sensor are long, the reading scanning speed of the line sensor using the optical sensor is limited to 4 to 5 ms / line. . Also, if the γ value is small, the photocurrent generated according to the light intensity on the sensor surface, that is, the output signal value is proportional when γ = 1.0, but the proportionality is bad when γ = 0.6. Occurs. Therefore, extra circuit processing is required to reproduce the halftone.

In the case of a photoconductive sensor in which a semiconductor thin film mainly composed of CdS, CdSe or a solid solution CdS-CdSe is heat-treated for activation in CdCl ₂ vapor, increasing the γ value increases the Cu concentration, which is a sensitizing impurity, for example. It is realized by the method such as. However, at the same time, the fall time τ _d of the photocurrent becomes small, but the rise time τ _r becomes large, and the overall photoresponse speed becomes slow, and the photocurrent Jp also becomes small, which is a major drawback. In order to eliminate this drawback, in the prior invention (Japanese Patent Application No. 62-256553), after the semiconductor thin film is activated and heat-treated, Cu as a sensitizing impurity is attached to the surface and heat-diffused at 250 ° C. or lower. An electrode was formed and a high-speed and high-γ optical sensor was manufactured. However, a significant decrease in Jp was observed when heated above 250 ° C.

The present invention has been made in view of such problems of the conventional technology, and thus, the photocurrent Jp
It is an object of the present invention to provide a method for manufacturing an optical sensor which can increase the optical response speed and increase the γ value without decreasing the value.

Means for Solving the Problems The present invention provides CdS, CdSe or solid solution CdS on an insulating substrate.
-CdSe semiconductor thin film is formed, and the thin film is CdSe
In the method of manufacturing an optical sensor in which a counter electrode is provided after being exposed to Cl ₂ vapor, heat-treated and photoelectrically activated to form a protective film, a small amount of Cu is added before the electrode formation after the activation heat treatment. It is attached to a semiconductor thin film at 250 to 550 ° C in an atmosphere containing no CdCl ₂ vapor or containing a small amount of oxygen.
By heat-treating for 30 min or more and diffusing it in the film, the photocurrent is not reduced and the photoresponse speed is remarkably increased, and the γ value is increased.

Effect According to the method of the present invention, the photoresponse value of the CdS-based photoconductive sensor is not impaired, the photoresponse speed thereof can be significantly increased, and the γ value can be increased. The sensor in which Cu is heat-treated and diffused at 250 to 550 ° C for 30 minutes or more is much more excellent in stability than the sensor in which heat-treated and diffused at 250 ° C or less (the invention of the prior application). The photocurrent is almost proportional to the fall time τ _d , but the photocurrent does not decrease even if the fall time is short because the photocarrier (electron) in the semiconductor thin film is reduced by the method of the present invention. This is because the mobility of is increased.

Examples Examples of the present invention will be described below.

CdS, CdSe or CdS-Cd on an insulating substrate such as glass
A semiconductor thin film mainly composed of Se is formed by a method such as a vacuum deposition method. This thin film is subjected to CdC at a high temperature of about 500 ° C.
It is exposed to l ₂ vapor and subjected to activation heat treatment. Then a small amount
Cu is attached to the semiconductor thin film and heat-treated at 250 to 550 ° C. for 30 minutes or more in an atmosphere containing neutral or a small amount of oxygen to diffuse into the film. Then, a counter electrode is formed by a NiCr / Au deposition film or the like, and a protective film such as a silicon resin or polyimide is further formed to complete the optical sensor.

Cu is attached by a vacuum deposition method or a chemical attachment method. The chemical adhesion method is, for example, a method of immersing a semiconductor thin film in an aqueous solution containing Cu ions to adhere Cu to the surface of the semiconductor thin film.

Further, a small amount of sensitizing impurities Cu or Ag may be added to the semiconductor thin film before the activation heat treatment. Any sensitizing impurity may be used as long as it can increase the sensitizing effect, that is, increase the photocurrent and increase the ratio of the photocurrent to the dark current, that is, the so-called light-dark ratio. The amount of Cu and Ag at this time is 0.015 mol% with respect to the host semiconductor.
The following is required. Such addition of sensitizing impurities is not always preferable in terms of characteristics, that is, high-speed photoresponsiveness, but in the case of a sensor including a large number of elements, it is excellent in terms of uniformity of characteristics. If this amount exceeds 0.015 mol%, it becomes difficult to improve the characteristics such as high speed and high γ value.

As can be seen from the data shown in Table 1 of the prior invention, the photocurrent Jp is extremely small when the heat treatment temperature at which Cu is diffused after deposition is 250 ° C. or higher. This is because the heat treatment time was as short as 15 min, although not particularly described. CdS
The characteristics of the system semiconductor thin film change by heat treatment, but the change usually saturates in 10 minutes.

However, the sensor of the present invention requires 30 minutes for this saturation. A high resistance layer was formed on the sensor surface when the heat treatment was carried out for 15 minutes, and the photocurrent was remarkably reduced when the electrodes were formed after that. Therefore, this heat treatment time requires 30 minutes or more. And up to about 1H is practically sufficient. The sensor subjected to the diffusion heat treatment at 250 to 550 ° C is more excellent in stability such as shelf life than the sensor of the invention of the prior application.

Next, a specific example will be further described.

Glass substrate (Corning, # 7059, 230 × 25 × 1.2m
A 4000A thick CdS _0.6 Se _0.4 evaporated film is formed on m ³ ), and is photo-etched to form islands (90 × 350μ) in the main scanning direction.
1728 bits are allocated to m ² ) at a rate of 8 bits / mm. After the photoconductor film is photoelectrically activate this island CdS _0.6 Se _0.4 film by heat treatment in saturated steam of CdCl ₂ at 500 ° C., relative CdS _0.6 Se _0.4 film is maternal 0.005-0.1 mol% C
u is vapor-deposited and diffused. If the Cu content is less than 0.005 mol%, the effect is small, and if it is 0.1 mol% or more, the start-up characteristics are deteriorated. The substrate temperature during Cu deposition is room temperature to 400 ° C. If the substrate temperature exceeds 400 ° C, variations in characteristics will occur, which is not preferable. After Cu deposition, this time, in a neutral atmosphere containing no CdCl ₂ vapor or in an atmosphere containing a small amount of oxygen, at 250 to 550 ° C for 30 min.
Heat treatment. When the heating temperature exceeds 550 ° C, the sensor has low resistance and no photosensitivity. afterwards,
A counter electrode (NiCr / Au vapor deposition film), that is, a common electrode and an individual electrode are formed on each of the island-shaped films. The gap between the counter electrodes is 60 μm. After that, a protective film of silicon resin or polyimide is formed to complete the line sensor. The characteristics of 1 bit of these line sensors are investigated, and the results when the substrate temperature during Cu deposition is 150 ° C and the polyimide protective film is summarized in Table 1. For comparison, normal CdS _0.6 Se _0.4 : Cu (0.03
A sensor was also investigated in which electrodes were formed after heat treatment for activation of the vapor-deposited film in the same manner as above. The characteristics are applied voltage DC10
V, light irradiation is green LED light (570nm, 100lux) 1Hz (0.5sec)
Each) to blink and measure. The photocurrent Jp is 0 for the response time.
Rise time τ from the time to rise to 50% of the saturation value
_{The time taken for r} and Jp to fall from the saturation value to 50% thereof was defined as the fall time τ _d . The γ value is an average value between 50 and 100 lux.

In this way, the fall time τ _d is reduced to about 0.5 msec while the photocurrent is kept large at several μA or more, and the γ value is 0.70.
As mentioned above, many can be as large as 0.80 or more. On the other hand, the rise time τ _{r of the} photocurrent does not increase even if τ _d becomes small unlike the case of a normal sensor, and when actually used as a line sensor, there is reflected light (even at least 3% exists) even in a black document. ) Becomes bias light, which is constantly irradiated on the sensor, so that the effective rise time τ _r ^* is significantly reduced. The effect is shown in Table 2. There is almost no change in other characteristics (Jp, τ _d , γ) due to bias light irradiation to this extent.

In this way, excellent properties can be obtained by depositing and diffusing Cu after the activation heat treatment of CdS _0.6 Se _0.4 vapor deposition film in CdCl ₂ vapor.

In this embodiment, CdS _0.6 Se _0.4 is taken as an example, but similar effects can be obtained with CdS, CdSe, and other solid solution CdS-CdSe having other composition ratios. The sensor of the present invention is also superior in stability as compared with the sensor of the invention of the prior application. That is, for example, the sensor of the embodiment of the invention of the prior application (Table 1 of the specification, 5 from the top left side)
2) and the sensor of the embodiment of the present invention (Table 1, 4th from the top) were stored at 60 ° C. for 2000 hours in the dark, the photocurrent Jp had an initial value of 24 μA. The sensor of the invention of the present application reduced the amount by 10%, but the sensor of the present invention reduced the amount by 3%.

EFFECTS OF THE INVENTION According to the present invention, it is possible to realize an optical sensor having a large photocurrent value, a significantly high photoresponse speed, a large γ value, and excellent stability. As a result, it is possible to manufacture a high-speed image reading device that is excellent in halftone reproduction.

Claims (3)

[Claims] 1. CdS, CdSe or solid solution CdS on an insulating substrate.
-Patterning a semiconductor thin film mainly composed of CdSe,
The semiconductor thin film is exposed to CdCl ₂ vapor at a high temperature and subjected to photoelectrically activating heat treatment, and then a counter electrode is provided, and in the method for manufacturing an optical sensor in which a protective film is further formed, after the activation heat treatment, the counter electrode is formed. An optical sensor characterized in that a small amount of Cu is previously attached to the semiconductor thin film, and heat-treated at 250 to 550 ° C. for 30 minutes or more in an atmosphere containing no CdCl ₂ vapor or containing a small amount of oxygen to diffuse into the thin film. Manufacturing method. 2. 0.015 in a semiconductor thin film before activation heat treatment
The method for manufacturing an optical sensor according to claim 1, wherein Cu is added in an amount of not more than mol%. 3. The method for producing an optical sensor according to claim 1, wherein the amount of Cu deposited after the activation heat treatment is 0.005 to 0.1 mol% with respect to the base semiconductor.