JPH01220478A - Manufacture of photosensor - Google Patents

Abstract

PURPOSE:To make a light response speed high with a photocurrent value kept large and to increase a gamma value, by activating and heat-treating a semiconductor thin film, attaching a small amount of Cu or Ag on the surface, and diffusing the Cu or Ag into the semiconductor thin film. CONSTITUTION:A semiconductor thin film of CdS, CdSe or CdS-CdSe incorporating a small amount of Cu or Ag is formed on an insulating substrate. After the thin film is activated and heat-treated, a small amount of Cu or Ag are attached and diffused into the semiconductor thin film. Thus, the mobility of photoelectrons in the semiconductor thin film becomes large. A photocurrent does not become small even if the fall-down time of the photocurrent becomes short. A light response speed becomes high with the photocurrent value kept large, and the gamma value can be made large.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to a method of manufacturing an optical sensor used in an image input section of an electronic device such as a facsimile machine or an optical disk.

Background of the Invention In recent years, a close-contact line sensor with the same dimensions as the document width has been developed in order to miniaturize the image information input section of facsimile machines and various OM devices and improve image distortion, and image reading devices using this have been developed. has begun to be used, and there is currently a strong desire for improvements in performance, that is, higher speeds and improved image quality.

Now, Cds, CdSe or solid solution 06B-CdS
An optical sensor mainly composed of e is characterized by a large photocurrent, and for this reason, it is easy to design peripheral circuits in a contact type line sensor using this sensor. On the other hand, this optical sensor has two drawbacks: its photocurrent and IP response speed to light irradiation are slow, and its proportionality to the irradiated light intensity, that is, the intensity of reflected light from the document, is poor. That is, in the former case, the rise time τr and fall time τd of Jp are 2 to 311 when the sensor surface strength is 100JuX during normal use! lee
In the latter case, γ when J p oe L is
The value is small at 60-1oo6ux and 0.6-0.76.

Problems to be Solved by the Invention As described above, if the rise time and fall time of the photocurrent of the sensor are long, the reading scanning speed of a line sensor using this sensor is limited to 4 to 71 in.

In addition, when the γ value is small, the photocurrent generated in response to the light intensity on the sensor surface, that is, the output signal value, is γ = 1, as shown in the figure.
．． It can be seen that although it is proportional when γ=0, the proportionality is extremely poor when γ=0.6. Therefore, extra circuit processing is required to reproduce halftones.

CdS, CdSe or solid solution CdS-CdSe
In the case of a photoconductive sensor subjected to activation heat treatment in aCl2 vapor, increasing the γ value is due to the presence of impurities such as Cu.
This is achieved by methods such as increasing the concentration. However, at the same time, the fall time τd of the photocurrent becomes small, but the rise time τr becomes large, and there is a big drawback that the overall photoresponse speed becomes slow and the photocurrent Jp becomes small.

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

A solution to the problem: CdS5G (1815 or solid solution 0) on an insulating substrate.
After forming a semiconductor thin film mainly composed of 65-CdSe and adding a small amount of Cu or Ag, and exposing the thin film to CdC712 vapor at high temperature and performing activation heat treatment,
The method for manufacturing an optical sensor in which a counter electrode is provided and a protective film is further formed is characterized in that, after the activation heat treatment, a small amount of Cu or Ag is further attached to the surface and diffused into the semiconductor thin film.

Effect: According to the method of the present invention, the photoresponse speed of the CdS-based photoconductive sensor can be significantly increased, and the γ value can be increased, without impairing the feature of the large photocurrent value of the CdS-based photoconductive sensor. Moreover, the variation in characteristics is small and the stability is excellent. The photocurrent is approximately proportional to its fall time τd, but the reason why the photocurrent does not become smaller even if the fall time becomes shorter is because the method of the present invention reduces photocarriers ( This is because the mobility of electrons increases.

Example The present invention will be explained in detail below.

A semiconductor thin film of CjaSlCdSe or 0d8-CdSe containing a small amount of Cu or Ag is formed on an insulating substrate such as glass by vacuum evaporation or the like.

This thin film is exposed to CdCl2 vapor at high temperature, typically 4
Activation heat treatment is performed at 60-eoo°C. After that, NiC
A counter electrode is formed using a vapor-deposited film of r/muU. Before or after this electrode formation, a small amount of Cu or Ag is further deposited and diffused on the activated semiconductor thin film. Cu, Ag, and the like added to the C (is-based optical sensor) are called sensitizing impurities.

Any sensitizing impurity may be used as long as it increases the sensitizing effect, that is, increases the photocurrent and increases the ratio of photocurrent to dark current, so-called brightness ratio, but Cu and Ag are particularly effective. The attachment of such sensitizing impurities may be carried out after the activation specific heat treatment and before the formation of the electrode, or after the formation of the electrode and before the formation of the protective film. Diffusion of the sensitizing impurity into the film is caused by heating, and this is achieved by heating the substrate during deposition or by heating after deposition. Heating after deposition may be performed before or after the electrode is formed, but depending on the case, heating during the formation of the protective film may be used. The sensitizing impurity is attached by a vacuum deposition method or a chemical deposition method. Chemical adhesion means, for example, when attaching Cu, C on the substrate is added to a solution of cuc12 dissolved in water.
This is a method in which an aS-based film is immersed and Cu is attached to the surface.

During this chemical attachment, the substrate temperature (ie, liquid temperature) is set at room temperature to 80°C. When the temperature exceeds 80°C, variations tend to occur. Further, the substrate temperature during vacuum deposition is from room temperature to 400'C. If it exceeds 400'C, it will cause variations and is not preferable.

Furthermore, when the substrate temperature is low when the sensitizing impurity is attached, or in order to obtain the required characteristics, it is recommended to perform heat treatment at 150 to 400°C in a neutral or a small amount of oxygen atmosphere after the sensitizing impurity is attached. good. A protective film made of silicone resin or polyimide is then formed to complete the optical sensor. The above heat treatment may be replaced by drying, heating, or other treatments for the protective film. Diffusion is achieved by these heating processes during or after the sensitizing impurity deposition.

Example 1 Glass substrate (Corning, ≠7059.230X26
X1,27) 4000 thick Cd8o on top, 6860
, 4: A vapor-deposited film of Cu (0,005 molti) was formed, and an island-like (90X
350μ1a2), 1728 pits are arranged at a rate of 8 bits/mm. The amount of Cu is parent caso6Seo,
0.005 to 0.015 mol % based on 4 is preferable.

If it is less than 0.005 molar ratio, the properties may be excellent but the uniformity may be poor, and if it is more than 0.015 molar ratio, the rise time τr of Jp becomes large. This island-like CdSo, 6 seo
, 4: CdCj! of Cu film at 500'C! After photoelectrically activation by heat treatment in saturated steam of step 2 to form a photoconductor film, a counter electrode (NiCr/mu U) was placed on each of the island-like films.
evaporated film), that is, form a common electrode and individual electrodes. The gap between the opposing electrodes is 60 μm. After that, the parent CdS (0.005 to 0.6 g for 60.4 membranes)
1 molten Cu is vapor-deposited and diffused. Cu amount is 0.005
If the mulch is less than 0.1 molt, the effect of improving the falling property will be small, and if the mulch is more than 0.1 molt, the rising property will deteriorate. 160-4 in a neutral or a small amount of oxygen-containing atmosphere after Cu deposition
Heat treatment is performed at 00°C. Thereafter, a silicone resin retainer MM is formed to complete a sill line sensor. We investigated the characteristics of one bit of these line sensors and found that the substrate temperature during CU deposition was 1.
The results for the case of 50°C are summarized in Table 1. For comparison,
Normal C (i5o, 6 S・Q, 4: Cu (QO
A sensor in which a vapor-deposited film (1 to 0.1 mol %) was subjected to the activation specific heat treatment and then formed into an electrode was also investigated. The characteristics are that the applied voltage is 1oV DC, and the light irradiation is green LID light (570 nm).
, 1001ux) was measured by blinking at 1Hz (0.5sea each). The response time is the rise time τr%, which is the time it takes for the photocurrent Jp to rise from 0 to 50% of the saturation value.
The time required for Jp to drop from the saturation value to 60 degrees was defined as the fall time τd. Moreover, γ is an average value between 60 and 10071 ux.

(Margins below) In this way, the fall time τd can be reduced to about 0, s mgec while keeping the photocurrent large at several microns or more, and the γ can also be increased to 0.70 or more, often 0.80 or more. You can make it bigger. On the other hand, unlike in the case of a normal sensor, the rise time τr of the photocurrent does not increase even if τd becomes small, and when actually used as a line sensor, the reflected light that exists even on the black background of the original (at least 3%) becomes bias light, which is constantly irradiated onto the sensor, so the effective light becomes significantly smaller. The effects are shown in Table 2. There is almost no change in other characteristics (, yp, τd, γ) due to the bias light irradiation.

(The following is a blank space) Example 2 An optical sensor was produced using the same manufacturing method as in Example 1, using Ag instead of CuO. CdS, ), 63eO,4: The amount of Ag in the Ag deposited film is 0 with respect to the parent CdSo6S004.
．． The amount of Ag deposited and diffused after polarization formation is 0.005 to 0.1 mol based on the base material.

Among the optical sensors obtained in this way, Ag in the first vapor-deposited film
Table 3 shows the characteristics of one bit of each of the line sensors in which the amount of λg is 0.005 molar, the amount of λg to be vaporized and diffused is o, and the amount of 01 to 0.1 molar is shown in Table 3. Table 4 shows the characteristics when irradiating with 3 beams of bias light.

(Left below) It can be seen that excellent properties can be obtained by additional adhesion and diffusion of Cu or Ag. CdS(1,6seO,4:
Even if Ag is attached and diffused on Cu, on the contrary “5o6s8
o4: Cu may be attached and diffused on Ag. However, the amount of Cu or Ag initially contained is very small (0,006
~0.015 molar ratio).

In the above example, Cd5o6S e O4 was taken as an example, but CdS, CdSe, and solid solution CdS with other composition ratios may also be used.
Similar effects can be obtained with -CdSe.

Effects of the Invention According to the present invention, it is possible to realize an optical sensor that has a significantly high photoresponse speed and a large γ value while maintaining a large photocurrent value. This allows for a high-speed image reading device with excellent halftone reproduction.

[Brief explanation of the drawing]

The figure is a diagram showing the relationship between photocurrent and light intensity in an optical sensor. Name of agent: Patent attorney Toshio Nakao and one other person

Claims (1)

[Claims] (1) A semiconductor thin film mainly composed of CdS, CdSe or solid solution CdS-CdSe with a small amount of Cu or Ag added is formed on an insulating substrate, and the thin film is exposed to CdGl_2 vapor at high temperature to activate it. A method for manufacturing an optical sensor in which a counter electrode is provided after activation heat treatment and a protective film is further formed, characterized in that, after the activation heat treatment, a small amount of Cu or Ag is further attached to the surface and diffused into the semiconductor thin film. A method for manufacturing an optical sensor.