JPH0426789B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a semiconductor device formed on a light-transmitting substrate, such as a self-scanning photoelectric conversion device for facsimile, a liquid crystal flat display device, etc. Regarding devices.

[Background of the Invention] With the full-scale development of large area or long image devices, there is a demand for large area or long active element arrays.

For example, recently, attempts have been made to lengthen the primary light receiving element array for image reading in the transmitting section of a facsimile machine. Conventionally, a MOS type or CCD type (charge transfer type) silicon sensor has been used as a one-dimensional light receiving element array. However, the sensor length is currently 30 mm, and the limit of the sensor length that can be produced technically is determined by the size of the single crystal silicon wafer that can be produced, and is 125 mm.
That's about it. In any case, the image is reduced using a lens optical system, and the document width (for example, A4 size, 210
There is no choice but to adopt a method of reading with a shorter sensor (mm). In this case, the optical path length is long, for example 200 mm,
This is a major cause that prevents miniaturization of devices. Recently, with the aim of downsizing devices, development of one-dimensional photodetector arrays using close-contact reading has gained momentum. This replaces silicon sensors.
This method uses a thin film photodiode array such as Se-As-Ts or CdS to realize a one-dimensional sensor with a length equal to the width of the original, and reads the image by bringing the original into close contact with the sensor. This method does not use a lens optical system, so the device can be made smaller, the optical system is easy to adjust, and there is no problem with blurring around the lens.
It has the advantage of being capable of high resolution. However, because there is no suitable long active element array, it is difficult to realize a long self-scanning sensor that integrates the sensor part and the scanning circuit part, and this makes the contact reading method long. This is a major obstacle to the practical application of shaku sensors. In order to realize a self-scanning long sensor, the development of a long active element array suitable for this purpose is awaited.

Further, as another example, liquid crystal display devices and electroluminescent display devices have been developed as thin image display devices to replace the conventional Brannun tube.
Prototypes of display devices combined with CdSe or other thin film transistor arrays and display devices combined with silicon scanning circuits have already been made.
In the former case, there are problems such as the inability to realize a defect-free thin film transistor array and the unstable operating characteristics of the thin film transistors. In the latter case, there is a limit to the size of single-crystal silicon wafers that can be manufactured, so currently the maximum element size limit is 75 mm x 79 mm, which is too small when considering application to flat TVs. There is a drawback. In order to apply liquid crystal display devices and electroluminescent display devices to flat panel televisions, the development of a suitably large-area active element array is awaited.

[Summary of the Invention] An object of the present invention is to provide an image device that has good and stable active characteristics and uses a large-area or long active element array. Furthermore, in terms of structure, the present invention aims to provide an image device that allows light to enter from either the element side or the substrate side.

The present invention provides an amorphous glass substrate, a light receiving element array provided on the amorphous glass substrate, a polycrystalline film mainly made of silicon provided on the amorphous glass substrate, and a polycrystalline film mainly made of silicon. In a photoelectric conversion device having an active element array formed on a polycrystalline film as a main body, the softening temperature of the amorphous glass substrate is 820°C or less, and the length of the amorphous glass substrate is less than 125 mm. The carrier mobility of the long, silicon-based polycrystalline film is 1.
cm ² /V・sec or higher, and the photoelectric conversion device has a softening temperature of the amorphous glass substrate of 780° C. or lower, and further has a softening temperature of the amorphous glass substrate of 780° C. or lower. is 630° C. or lower, and the amorphous glass substrate is translucent.

In the present invention, a glass substrate or Al ₂ O ₃
A polycrystalline silicon film is formed on a ceramic substrate, etc. at a substrate temperature within the operating temperature range of the substrate (for example, lower than the softening point temperature in the case of glass), and a semiconductor device is manufactured using this polycrystalline silicon film as a material. Adopt a method to form a Here, the term "substrate" refers to something that has physical strength by itself and can support itself. In the present invention, a transparent substrate such as glass is used.

As mentioned above, single crystal materials cannot be used to obtain large area or long semiconductor devices. Further, in order to obtain good operating characteristics, it is necessary to use a material with a mobility of about 1 cm ² /V·sec or more, so amorphous materials with low mobility are also inappropriate. Therefore, it is necessary to use a polycrystalline material as the material because it can be made into a large area and has a mobility of about 1 cm ² /V·sec or more. Among polycrystalline materials, polycrystalline silicon has the advantage that its physical and chemical properties are suitable for application to semiconductor devices, and that the highly developed technology of the silicon semiconductor industry can be used as is or with slight modification. Therefore, it is suitable as the semiconductor material of the present invention.

In particular, for application to image devices, it is desirable to have a structure in which a semiconductor device can be formed on a transparent substrate such as glass. However, conventionally, in order to obtain a polycrystalline silicon film with a mobility of 1 cm ² /V·sec or more, it was necessary to go through a process at a high temperature of 900° C. or more. For example, according to the low-temperature vapor phase growth method, the mobility of a polycrystalline silicon film formed at a growth temperature of 880° C. is less than 1 cm ² /V·sec. Therefore, in the conventional technology, the softening point temperature is 630
Of course, the softening point temperature is
On top of 820℃ super hard glass (JIS class 1 hard glass),
It has been difficult to form a polycrystalline silicon film with a mobility of 1 cm ² /V·sec or more.

In the present invention, the degree of vacuum during vapor deposition is 1× in pressure.
A polycrystalline silicon film with a mobility of 1 cm ² /V・sec or more can be obtained by vacuum deposition at a substrate temperature lower than the softening point temperature of the glass used, by deposition in a high vacuum of less than 10 ^-8 torr. provide a way to obtain In particular, _O2 in the residual gas during deposition has a negative effect on material properties, so in the present invention, the oxygen partial pressure is set to 1×
Keep it below 10 ^-9 torr.

The deposition rate is usually 1000 Å/hour or more.
Use 10000 Å/hour. Preferably 1000Å/
Hour to 4000 Å/hour is used.

The problem with the deposition rate is mainly related to the technology of the deposition source, that is, when attempting to increase the deposition rate, the degree of vacuum tends to decrease at the same time. If the degree of vacuum can be maintained at a specified value, for example, 50000Å/
Hour or more may also be used. Also, the substrate temperature during vapor deposition is 400°C or higher, preferably 500°C.
Use the above. A desired polycrystalline silicon film can be obtained by such a manufacturing method.

Although there are many details that are unclear as to why a desired high-quality polycrystalline silicon film can be formed by such a manufacturing method, it is speculated as follows. That is, it is thought that this is because residual gas molecules colliding with the substrate surface can be substantially ignored under the conditions of this manufacturing method.

In order to fabricate a semiconductor device by processing a polycrystalline silicon film, it is necessary to go through several steps, but in the present invention, the heat treatment temperature in these steps is set to 820°C, which is the softening point of ultra-hard glass. I held it lower. When a glass substrate with a low softening point is used, it is possible to keep the softening point even lower, for example, 550° C. or lower. In the following, a MOS field effect transistor will be described as an example of a semiconductor device.

Gate oxide films are generally obtained by thermal oxidation of silicon substrates, but thermal oxidation requires high temperatures of 1000°C or more, so it cannot be used for the current purpose. In the present invention, SiH ₄ and O ₂ are reacted at a temperature of 300°C to 500°C, or SiH ₄ and NO ₂ are reacted at a temperature of 400°C to 800°C,
A SiO ₂ film is grown in a vapor phase, and this vapor-grown SiO ₂
The film is used as a gate oxide film. SiO ₂ films obtained by vapor phase growth have traditionally been used to prevent deterioration, and have rarely been used as gate oxide films, but have been used in combination with transparent substrates such as glass. There are no examples.

Furthermore, conventionally, in order to form a source region and a drain region, a method of forming a p ⁺ layer or an n ⁺ layer by thermal diffusion has been generally performed. However, this method requires heat treatment at about 1150°C, so it cannot be used for the current purpose.
In the present invention, instead of thermal diffusion, a method of forming a p ⁺ layer or an n ⁺ layer by ion implantation is used. After ion implantation, heat treatment is performed to electrically activate the material, but at this time, the heat treatment temperature must be kept below the softening point of the substrate used.
Therefore ^, in the present invention, for example, ₅₅₀
By implanting ions that can be highly activated by heat treatment at a low temperature of about 50°C, or by implanting B ⁺ ions, for example, at a temperature of about 500°C to 600°C, just before the reverse annealing effect occurs. A method such as heat treatment is adopted.
In the case of P ⁺ ions, As ⁺ ions, etc., the reverse annealing effect is not as pronounced as in the case of B ⁺ ions, but it can be sufficiently activated by heat treatment at about 500°C to 600°C. Therefore, in a low temperature process of about 500℃ to 600℃
Either a p ⁺ layer or an n ⁺ layer can be formed.
Of course, when using a substrate having a softening point higher than 800°C, such as ultra-hard glass, heat treatment may be performed at a temperature of 800°C.

[Examples of the Invention] The present invention will be described in detail below with reference to Examples.

Example The first example describes a case where a polycrystalline silicon film is formed on a glass substrate and a p-channel MOS field effect transistor is created in this polycrystalline silicon.
This will be explained using the cross-sectional diagram for explaining the process in the figure.

First, the substrate is placed in a vacuum evaporation device capable of achieving an ultra-high vacuum. General equipment may be used. On a normal hard glass (JIS class 2 hard glass) substrate 1, the substrate temperature is 550°C, the degree of vacuum during evaporation is 9 × 10 ^-9 torr, the partial pressure of oxygen during evaporation is 1 × 10 ^-10 torr, and the deposition rate is 3000 Å/
A silicon film 2 is deposited to a thickness of 6000 Å by vacuum evaporation under conditions of 1 hour (FIG. 1a).
The formed silicon film 2 is n-type polycrystalline silicon and has a mobility greater than 1 cm ² /V·sec.
Next, a SiO ₂ film 3 is deposited to a thickness of 5000 Å by vapor phase growth at a substrate temperature of 415° C. (FIG. 1b). Next, as shown in FIG. 1c, windows for the source and drain regions are formed in this SiO ₂ film. Then 150keV
A p ⁺ layer 4 ^was formed in ^the source and drain regions by implanting BF ⁺ ₂ ions with an energy of
form. Next, as shown in FIG. 1e, the SiO ₂ is removed leaving the field oxide film 5. A SiO ₂ film 6 is again grown for the gate oxide film using the vapor phase growth method.
A thickness of 2000 Å is deposited (FIG. 1f). Furthermore, holes for electrode contact are made by a photoetching process as shown in Figure 1g, and after Al is deposited on the entire surface, the Al is processed by a photoetching process to form a source electrode 7, a drain electrode 8, and a gate electrode 9. do. After this, heat treatment is performed at 400° C. for 30 minutes in an H ₂ atmosphere. Through the above steps, a MOS field effect transistor was fabricated in polycrystalline silicon.
This semiconductor device exhibits good and stable characteristics as a transistor.

Figure 2 shows an example of the characteristics of a prototype MOSFET. This is the drain current I _D versus drain voltage V _DS characteristic with the gate voltage V _G as a parameter. In this characteristic example
By increasing the SiO ₂ film thickness to 7000Å,
The threshold voltage is increased to 80V.

Here, the softening point temperature of the substrate glass is
Normally hard glass heated to 780°C was used, but throughout the process no heat treatment is performed at temperatures higher than 550°C, so the glass substrate does not soften. Also,
The substrate will not soften even if inexpensive ordinary glass (soda glass) with a softening point of 630°C, ultra-hard glass with a softening point of 820°C, or quartz glass with a softening point of 1500°C is used as the substrate. So it is possible as well. From the viewpoint of practicality, it is also important that the manufacturing cost of semiconductor devices be low. In this respect, it is most advantageous to use inexpensive ordinary glass or the like as the substrate, second advantageous to use ordinary hard glass or ultrahard glass, and disadvantageous to use expensive quartz glass or the like. According to the present invention, it is also possible to manufacture a semiconductor device using an inexpensive glass substrate with a low softening point.

Furthermore, since the linear expansion coefficients of ordinary glass and ultra-hard glass are close to that of silicon, they are advantageous in that there are fewer problems such as peeling after deposition. Since the linear expansion coefficient of quartz glass is about one order of magnitude smaller than that of silicon, the difference can become a problem, especially when the substrate becomes long.

Moreover, ordinary glass and ultra-hard glass have lower hardness than quartz glass, that is, they are not brittle, so they have the advantage of being easier to handle when the substrate becomes long. This is particularly advantageous for long photoelectric conversion devices.

Regarding the light transmittance of the substrate glass, either ordinary transparent glass or filter glass that transmits only light having a wavelength in a certain range can be used.

In each process, including the process of forming a polycrystalline silicon film, due to the manufacturing method, it is necessary to increase the area of semiconductor devices,
There are no technical problems that would prevent lengthening. Furthermore, by using a light-transmitting substrate, light can also be incident from the substrate side.

As described above, according to the present invention, it is possible to easily and inexpensively form a large area or long semiconductor device having good and stable operating characteristics on a glass substrate. In addition, if necessary,
It is also possible to create a structure in which light enters from the substrate side.

Although the case where a glass substrate is used has been described above, it is also possible to use a ceramic substrate of Al ₂ O ₃ or the like.

In addition, in the above example, impurities were not intentionally added to the polycrystalline silicon film used as the raw material, but at the same time, a very small amount of impurities was added during silicon vapor deposition.
It is possible to intentionally add p-type impurities and n-type impurities by vapor depositing Ga, Sb, or the like. Furthermore, it is of course possible to control the impurity concentration.

For example, a depletion type MOS field effect transistor as shown below was manufactured. Silicon and a small amount of Ga were simultaneously deposited on a glass substrate at a substrate temperature of 500°C to form a p-type polycrystalline Si film. An n-channel MOS field effect transistor is manufactured using this polycrystalline film as a material. The basic manufacturing process is as described above. The source and drain regions are as before. For the source and drain regions, P ⁺ ions with an energy of 100 keV were applied 1× to the polycrystalline Si described above.
An n ⁺ layer was formed by implanting at a dose of 10 ¹⁶ /cm ² and annealing at 600°C. Also,
The gate oxide film was 2000 Å thick. The characteristics obtained are of a depletion type with a threshold voltage value of -25V, and low voltage drive of approximately VG = 10V is possible.

Next, as an application example, a one-dimensional self-scanning light receiving element in which a photodiode and a scanning integrated circuit are integrated will be described.

FIG. 3 is a plan view thereof, and FIG. 4 is a sectional view AA′ of the plan view.

21 is a transparent glass substrate on which Example 1 is printed.
The scanning IC section 22 and the photo sensor section 23 are constructed of MOSFETs according to the method described above.
is formed. FIG. 5 shows an example of the circuit configuration. The area within the broken line in FIG. 6 is an example of a scanning IC section, and 30 is a photo sensor array. In the figure, reference numeral 24 denotes a lower electrode of the photo sensor, which is made of metal such as Cr. 25 uses a transparent electrode, for example _SnO2 .
Reference numeral 26 denotes a photoconductive film, for example, an amorphous semiconductor film of Se-As-Te system may be used. This photoconductive film can be easily formed by vapor deposition.

27 is an upper metal electrode.

When using a NESA film for a transparent electrode, a NESA transparent conductive film is first formed on a substrate. Next, wiring for connection to the scanning IC is formed, and aligned with this to form the scanning IC section. The manufacturing method is as described above. After completing the scanning IC, the photoconductor film 26
Then, an upper metal electrode 27 is formed by vapor deposition to complete a self-scanning light receiving element.

This device is useful as a photoelectric conversion device such as a facsimile transmitter or OCR to convert image information on a flat image recording medium into a time-series electrical signal.

Example 2 An example in which the present invention is applied to a pn junction diode will be described. FIG. 6 is a sectional view of the element.

A transparent glass substrate 11 is prepared, and on its upper surface
A Cr film is deposited to a thickness of approximately 2000 Å. The substrate temperature is 200°C and vacuum evaporation is used. The electrode 12 is processed into a desired shape using a normal photo-etching method. This substrate is placed in a vacuum evaporation device, and the degree of vacuum is 8×.
Ga and Si were simultaneously deposited in an atmosphere of 10 ^-9 Torr,
A polycrystalline silicon film containing Ga (p
Mold) 13 is formed. The substrate temperature is 550℃.
Next, Sb and Si are simultaneously deposited in the same atmosphere as described above to form a polycrystalline silicon film (n-type) containing Sb with a thickness of 1 μm. The board temperature is 550
℃ and eggplant. Note that Ga and Sb are introduced to make the silicon p-type or n-type, and are usually only introduced to form an n-p junction. Furthermore, Al is vapor-deposited on these laminated layers. The substrate temperature at this time was 200°C. Process the electrode into a desired shape using the well-known photocotting method.

In this way, a pn junction diode is completed.

All of the above steps are low-temperature processes below 550℃. As described in the first embodiment, according to the present invention, a large area or long pn junction diode array can be formed easily and at low cost.

The examples so far have simply shown diode arrays with p-n junctions, but of course it is also possible to form pnp bipolar transistors and npn bipolar transistors on glass substrates, etc. using the method of the present invention. be. In addition, by low-temperature vapor phase growth method,
It is also possible to form an integrated circuit by combining two or more semiconductor elements by separating the elements using a SiO ₂ film.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a device for explaining a process for explaining an embodiment of the present invention, FIG. 2 is a diagram showing drain current versus drain voltage characteristics of a field effect transistor of the present invention, and FIGS. The figures are a plan view and a sectional view showing an example in which the present invention is applied to a photoelectric conversion element, Figure 5 is a diagram showing an example of a circuit used in the example of a photoelectric conversion element, and Figure 6 is a diagram showing another embodiment of the present invention. FIG. 1... Amorphous or polycrystalline substrate, 2... Polycrystalline silicon film, 3... SiO ₂ film, 4... Impurity region, 5... Oxide film, 6... Gate oxide film.

Claims (1)

[Scope of Claims] 1. an amorphous glass substrate, a light receiving element array provided on the amorphous glass substrate, a polycrystalline film mainly made of silicon provided on the amorphous glass substrate, In the photoelectric conversion device having the active element array formed on the polycrystalline film mainly composed of silicon, the softening temperature of the amorphous glass substrate is 820°C.
The length of the above amorphous glass substrate is 125
A photoelectric conversion device characterized in that the carrier mobility of the polycrystalline film mainly composed of silicon is longer than 1 cm ² /V·sec and is longer than 1 mm 2 /V·sec. 2 The temperature at which the amorphous glass substrate softens is 780°C.
The photoelectric conversion device according to claim 1, characterized in that the temperature is below .degree. 3 The softening temperature of the above amorphous glass substrate is 630°C.
The photoelectric conversion device according to claim 1, characterized in that the temperature is below .degree. 4. The photoelectric conversion device according to any one of claims 1 to 3, wherein the amorphous glass substrate is translucent.