JPH0612832B2 - 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, a contact type line sensor having the same size as a document width has been developed aiming at downsizing of an image input section of a facsimile machine or various OA devices and improvement of image distortion, and an image reading apparatus using this is widely used. Nowadays, there is a strong demand for improvements in performance, namely speeding up and improvement in image quality.

An optical sensor mainly composed of CdS, CdSe or solid solution CdS-CdSe is characterized by a large photocurrent. 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 light irradiation is slow, and the proportionality to the irradiation light intensity (that is, τ light intensity from the original) L is poor. That is, in the former, the rise time τ _r and the fall time τ _d of Lp are as long as 2 to 3 msec when the sensor surface strength is 100 lux during normal use, and in the latter, the γ value when Jp L is 50 to 100 lux is 0.6 to It is as small as 0.75.

As described above, if the rise time and fall time of the photocurrent of the sensor are long, the reading scanning speed of the line sensor using this sensor is limited to 4 to 5 ms / line. Further, 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 not proportional to this. Therefore, extra circuit processing is required to reproduce the halftone.

In the case of a photoconductive sensor obtained by subjecting a semiconductor thin film mainly composed of CdS, CdSe or a solid solution CdS-CdSe to activation heat treatment in CdCl ₂ vapor, increasing the γ value means increasing the Cu concentration which is a sensitizing impurity. It is realized by a method such as. However, at the same time, the fall time τ _d of the photocurrent is shortened, but the rise time τ _r is increased, which slows down the overall photoresponse speed and also reduces the photoelectric Jp.

In order to eliminate this defect, the inventors of the prior application have conducted heat treatment for activation of a semiconductor thin film, and then used Cu or Ag as a sensitizing impurity.
Was attached to the surface and was heated and diffused at a high temperature to some extent to form a rear electrode, and a high-speed and high-γ optical sensor was realized. The diffusion of the adhesion of the sensitizing impurities may be performed after the electrodes are formed. However, even with the sensor obtained in this way, τ _{r is} still τ _d
It was bigger and dissatisfied with its speed.

The present invention provides a method for increasing the γ value by increasing the photoresponse speed without decreasing the photocurrent Jp.

Means for Solving the Problems A semiconductor thin film containing no sensitizing impurities such as Cu or Ag, that is, undoped CdS, CdSe or a solid solution CdS-CdSe is formed on an insulating substrate, After exposing the thin film to a vapor of CdCl ₂ at a high temperature and subjecting it to a heat treatment under photoelectrical activation, a small amount of Cu or Ag is attached to the semiconductor thin film, heat treated at a high temperature and diffused into the thin film to provide a rear counter electrode, Further, in the method of manufacturing an optical sensor for forming a protective film, the insulating substrate which does not contain Cu or Ag is used. After providing the counter electrode, a small amount of Cu or Ag may be attached to the semiconductor thin film, heat-treated at high temperature, and diffused through the thin film.

Operation According to the method of the present invention, it is possible to significantly increase the photoresponse speed and further increase the γ value, without impairing the feature that the CdS optical sensor has a large photocurrent value. When a CdS-based semiconductor thin film is formed on a substrate containing Cu or Ag and activated by heat treatment in CdCl ₂ vapor, Cu or Ag in the substrate migrates into the sensor film and induces many electron traps in the film. However, as a result, the rise time τ _r upon light irradiation becomes long, and the speeding up of the sensor is impaired. Activated Cd on a substrate that does not contain Cu or Ag
A sensor in which an S-based thin film is formed and Cu or Ag is attached and diffused on the S-based thin film has a significantly reduced number of such electron traps, and τ _r is much higher than that of a sensor formed on a substrate containing Cu or Ag. It is small and therefore much faster.

Examples Hereinafter, examples of the present invention will be described.

A semiconductor thin film mainly composed of CdS, CdSe or CdS-CdSe is formed on an insulating substrate such as glass containing no Cu or Ag by a method such as vacuum deposition. This semiconductor thin film is also an undoped film to which sensitizing impurities such as Cu or Ag are not added. This thin film is exposed to a vapor of CdCl ₂ at a high temperature of about 500 ° C. and subjected to activation heat treatment. Then, a small amount of Cu or Ag is attached to the semiconductor thin film, and it is heated at 250 to 550 ° C. in an atmosphere containing neutral or a small amount of oxygen.
Heat treatment for 15 min or more to diffuse into the film. After that, NiC
The counter electrode is formed of a vapor-deposited film of r / Au, and a protective film of silicon resin or polyimide is formed to complete the optical sensor. The diffusion of Cu or Ag may be performed after forming the counter electrode and before forming the protective film.

Cu or Ag is attached by a vacuum vapor deposition method or a chemical attachment method. The chemical adhesion method is, for example, a method in which a semiconductor thin film is immersed in an aqueous solution containing Cu ion ions to deposit Cu on the surface of the semiconductor thin film.

Now, when a glass substrate containing Cu (# 7059, Corning Co., 0.0005 wt% Cu content) is used as the insulating substrate, if a semiconductor thin film is formed on this glass, it is especially preferable to use CdCl ₂ in vapor during the formation. At the time of activation heat treatment, the phenomenon that Cu in the substrate migrates to the semiconductor thin film occurs. This is a kind of extraction effect, and even if the Cu content in the glass substrate is only 0.0005% by weight, 0.005 mol% is also contained in the semiconductor thin film after the activation heat treatment. After this activation heat treatment, Cu or Ag is attached and diffused on the semiconductor thin film to form an electrode, and a protective film is further formed. Alternatively, after activation heat treatment, an electrode is formed and Cu or Ag is attached and diffused on the semiconductor thin film. Further, a protective film is formed to complete the sensor. However, when Cu is not contained in the glass substrate, the rise time τ _{r of} Jp is very small and is close to the fall time τ _d . When Cu is contained in the glass substrate, τ _r becomes much larger than τ _d . Even if the glass substrate contains Ag, the same phenomenon is observed. Therefore, by using a substrate not containing Ag, the same effect as described above can be obtained. The sensor of the present invention formed on a substrate that does not contain Cu or Ag has much smaller τ _r than the sensor of the prior invention, and is further excellent in high speed.

Next, a specific example will be described.

Glass substrate (SiO ₂ 48.5% by weight, BaO 25.3% by weight, B ₂ O ₃
15.2% by weight, Al ₂ O ₃ 11.0% by weight, Cu or Ag is not contained, 230 × 25 × 1.2 mm ³ ), and CdS _0.6 Se with a thickness of 4000 A.
A vapor deposition film of _0.4 is formed, and 1728 bits are arranged at a rate of 8 bits / mm in an island shape (90 × 350 μm ² ) in the main scanning direction by photoetching. The island-shaped CdS _0.6 Se _0.4 film was
After heat treatment in saturated steam of CdCl ₂ to photoelectrically activate it to form a photoconductor film, 0.005 to 0.1 mol% of Cu or Ag is vapor-deposited with respect to the CdS _0.6 Se _0.4 film as a base material. . If the amount of Cu or Ag is less than 0.005 mol%, the effect is small, and if it is 0.1 mol% or more, the start-up characteristics deteriorate. After Cu or Ag deposition, heat treatment is further performed at 250 to 550 ° C. for 30 minutes in an atmosphere containing neutral or a small amount of oxygen. When the heating temperature exceeds 550 ° C, the sensor has low resistance and does not show photosensitivity. Then, 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 among these line sensors are examined, and the results when the substrate temperature during Cu or Ag vapor deposition is 150 ° C. and a polyimide protective film is used.
It is summarized in Table (Cu) and Table 2 (Ag). For comparison, a normal glass substrate (Corning, # 7059, the main component of the glass is the same as the previous glass, Cu content 0.0005% by weight)
A sensor formed in the same manner as above was also examined. The characteristics are applied voltage DC10V, light irradiation is green LED light (57
It was measured by blinking at 0 Hz, 100 lux) at 1 Hz (0.5 sec each). The response time is defined as the rise time τ _r when the photocurrent Jp rises from 0 to 50% of the saturation value, and the fall time τ _d when the photocurrent Jp drops from the saturation value to 50% of the saturation value. The γ value is an average value between 50 and 100 lux.

In this way, the fall time τ _d can be reduced to about 0.5 msec while the photocurrent is kept large at several μA or more, and the γ value can be increased to 0.70 or more, most of which is 0.80 or more. On the other hand, the rise time τ _{r of the} photocurrent can be made much smaller than in the case of a sensor usually formed on a substrate. When actually used as a line sensor, the reflected light (even at least 3%) that is present even in the black of the original becomes bias light, and this is constantly radiated to the sensor, so the effective rise time τ
_r ^* becomes even smaller. The effect is shown in Table 3.
Other characteristics (Jp, ι _d ,
There is almost no change in γ).

As described above, excellent characteristics can be obtained by using a substrate containing no Cu or Ag when Cu or Ag is attached and diffused after the activation heat treatment of the undoped 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.

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 photoreaction rate, and a large γ value. As a result, a constrained image reading device excellent in halftone reproduction can be obtained.

Claims (3)

[Claims] 1. A semiconductor thin film mainly composed of undoped CdS, CdSe or a solid solution CdS-CdSe is formed on an insulating substrate, and the thin film is exposed to CdCl ₂ vapor at a high temperature and subjected to photoelectric activation heat treatment. Then, a small amount of Cu or Ag is attached to the semiconductor thin film, heat-treated at a high temperature to diffuse into the thin film, a counter electrode is provided, and a protective film is further formed. Alternatively, a method of manufacturing an optical sensor, characterized in that a material not containing Ag is used. 2. A semiconductor thin film mainly composed of undoped CdS, CdSe or solid solution CdS-CdSe is formed on an insulating substrate, and the thin film is exposed to a vapor of CdSl _{2 at} a high temperature and subjected to photoelectrically activated heat treatment. In the method of manufacturing an optical sensor, a small amount of Cu or Ag is adhered to the semiconductor thin film after providing a counter electrode, heat treated at high temperature to diffuse into the thin film, and then a protective film is further formed. A method of manufacturing an optical sensor, characterized in that a material containing no Cu or Ag is used as the material. 3. The method of manufacturing an optical sensor according to claim 1, wherein the amount of attached Cu or Ag is 0.005 to 0.1 mol% with respect to the host semiconductor.