JP2002033486A - Thin-film transistor and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin-film transistor which uses an interlayer insulating film of high flatness. SOLUTION: In the thin-film transistor, the interlayer insulating film 5 is formed in the upper part of a semiconductor film 101, a gate insulating film 102 and a gate electrode 103; and a metal interconnection 1 is electrically connected to the semiconductor film 101 via a contact hole in the film 5. The film contains a silicon oxide film formed by using liquid silica. Since the flatness of the film 5 which is coated with the liquid silica by a spin-on method so as to be formed is high, the flatness of the thin-film transistor as a whole can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image sensor applicable to a facsimile, an image scanner, a digital copying machine and the like. In addition, the present invention relates to a thin film transistor for forming them and a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, with the spread of facsimile,
There is a demand for smaller size, lighter weight, and lower price. Image sensors used in facsimile machines and the like are roughly classified into three types: non-contact type, contact type, and perfect contact type. At present, the non-contact type using a CCD projects an original onto a CCD through a reduction lens system, so it is disadvantageous in terms of miniaturization and weight reduction compared to the other two methods. This is advantageous in terms of price because it can be produced by the LSI process used and the CCD chip can be small.

The contact type and the complete contact type are more advantageous than the non-contact type in miniaturization and weight reduction, but the production cost is high due to the difficulty in the manufacturing process, mounting and assembly, and the selfoc lens array and thin plate The use of high-priced components such as glass is a major factor preventing the cost reduction of these two types of image sensors.

[0004] Contact image sensors for facsimile are mainly of a multi-chip type in which a number of MOS LSI chips are mounted, and a thin-film type in which an amorphous silicon thin film or the like is formed on a transparent substrate using an optical sensor portion. Each of these uses a selfoc lens array. The multi-chip type has a high yield and can be supplied stably. On the other hand, the production cost of the thin film type is high because the yield is low.

A perfect contact type image sensor using a thin film element is most advantageous particularly in terms of size reduction and weight reduction because it does not use a reduction lens system or a selfoc lens array.
It was desired to supply this at a low price. One of the major factors that hinder the cost reduction of the complete contact type image sensor is that the production yield of the thin film element portion is low. Further, as described above, the contact type image sensor has the same problem when the photoelectric conversion element portion is a thin film element.

[0006] As a photoelectric conversion element of an image sensor, a photoconductor type and a photodiode type are known.
In general, a photoconductor type is capable of flowing a relatively large current, and thus has a feature of being resistant to noise, but has a poor optical response and is disadvantageous for a demand for a high-speed facsimile. On the other hand, the photodiode type has a small current, but has a fast response to light, and is expected to become mainstream in the future.

[0007]

In the photodiode type, since a small amount of current flows, it is stored in a capacitor which is necessarily formed by a structure in which a positive electrode and a negative electrode are stacked via a photodiode. In general, an image reading method called a charge storage type in which a charged electric charge is discharged is adopted. However, it is necessary to increase the area of the capacitor portion in view of the requirement that the value of the capacitance of the capacitor be an optimum value of 10 pF.

Normally, since the sensor portion of the image sensor is arranged in the reading width direction, in order to increase the area of the capacitor portion, the length of the capacitor portion is increased to 0.5 to 2 mm. The number of image sensors that can be taken from dimensions has decreased, and it has been difficult to satisfy the two requirements of cost reduction and size reduction of the image sensor and finer dot spacing of the photoelectric conversion element.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems by reducing the production cost and realizing the miniaturization of a contact type and a complete contact type image sensor using a thin film. It is assumed that.

According to the present invention, a first thin-film electrode is provided on an insulating substrate;
An image sensor having a photoelectric conversion element composed of a thin film semiconductor and a second thin film electrode, wherein an image sensor is provided between the first thin film electrode and the second thin film electrode constituting the photoelectric conversion element. An image sensor characterized in that a capacitor is provided in parallel with the photoelectric conversion element by forming an insulating film.

Further, the insulating film between the extended portions of the first thin film electrode and the second thin film electrode at the same time is formed by the thin film semiconductor of the photoelectric conversion element portion and the first thin film electrode or the second thin film electrode. This is an image sensor that extends between the thin film electrodes.

FIG. 7 is a schematic sectional view of the image sensor of the present invention. A first thin-film electrode 2 is formed on a light-transmitting substrate 100, and this electrode has a window 9 through which reading light applied to a document 200 is transmitted. A thin film semiconductor 3 having a photoelectric conversion function is laminated on the electrode 2,
A translucent electrode 4 is formed in a portion where the reflected light from the document 200 enters.

Now, an insulating film 5, for example, a silicon oxide film is formed on the upper surface, and a second thin film electrode 1 is formed thereon, and these are connected to a capacitor 10 near the end of the thin film semiconductor 3. Make up. This part is a high-capacity capacitor with an insulating film having a high dielectric constant interposed. In the case of this figure, the insulating film 5 covers the upper surface of the thin film semiconductor 3, and therefore, the first thin film electrode 2 and the second thin film electrode 1 are formed by a pinhole or the like generated at the time of manufacturing the thin film semiconductor. It also has the function of preventing short circuit.

As described above, the high-capacity condenser can be incorporated in the sensor structure with a small area.
Was reduced by about 25%, the number of image sensors per substrate was increased by 25%, and the production yield was improved by the effect of the area reduction, so that the production cost was significantly reduced.

As the insulating film usable in the present invention, any material having a high dielectric constant can be used. Further, if the insulating film has excellent light-transmitting properties, it can be formed on the light-transmitting electrode 4 as well. In addition, it has the function of protecting the light-transmitting electrode 4 and, at the same time, cutting out the reflected light from the non-corresponding part of the reflected light from the original, thereby achieving high reading resolution.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIGS. 1 to 7 are longitudinal sectional views showing steps of manufacturing a photoelectric conversion element portion of a complete contact type image sensor used for a facsimile or the like on a transparent substrate 100 such as glass or quartz. It is.

FIG. 1 shows that a metal 2, such as chromium, having a sufficiently low etching rate with respect to a dry etching gas such as silicon or silicon oxide, is sputtered to a thickness of 100 to 20%.
This is a step of patterning the electrode 2 also serving as a light shielding layer by a photolithography process after forming a 0 nm film. This electrode is provided with a light introducing window corresponding to one sensor bit.

Next, a photodiode 3 was formed (FIG. 2). This is an N-layer amorphous silicon carbide doped with phosphorus, an I-layer amorphous silicon not doped with impurities,
The P-layer amorphous silicon carbide doped with boron is formed. The film thickness depends on the required electrical characteristics, for example, the first
The capacitance between the thin film electrode 2 and the second thin film electrode 1 and the characteristics of the diode of the photodiode may be optimized. The P and N layers are 10 to 60 nm each, and the I layer is 30 nm.
0 nm to 1.2 μm is appropriate.

Successively, a transparent conductive film of ITO4 was
A 200 nm film was formed, patterned, and the previously formed photodiode was dry etched (FIG. 3).

Next, as shown in FIG. 4, for example, a liquid silica such as SOG (spin-on glass) is applied by a spin-on method or the like, and annealed at a temperature that does not affect the characteristics of the photodiode 3, for example, about 200 to 300 ° C. By
An insulating film 5 is formed. The film thickness to be formed may be determined in consideration of the capacitance between the electrode 1 and the electrode 2. By setting conditions such as the dilution ratio of the liquid silica, the number of revolutions during spin coating, and the time, the film thickness is about 30 nm to 1.6 μm.
The film thickness can be changed arbitrarily to the extent.

The insulating film is not limited to the method of forming with liquid silica, but may be formed by sputtering, plasma CVD, photo CVD, normal pressure CVD or the like to form SiO ₂ , Si ₃ N ₄ , SiO 2.
An insulating material such as N or Ta ₂ O ₅ may be deposited.
Similar effects were obtained. In particular, Si ₃ N ₄ having a large dielectric constant
In the case of Ta ₂ O _5, a large capacitor capacity can be obtained, so that the effect of reducing the sensor area is great.

Next, FIG. 5 shows a step of forming a contact hole for making the ITO 4 and the second thin film electrode 1 contact with each other by photolithography in the insulating film formed as described above. Further, as shown in FIG. 6, aluminum is formed as the second thin-film electrode wiring 1 by a sputtering method and then patterned by photolithography, thereby completing the thin-film process.

Thereafter, a thin glass 8 having a thickness of 50 to 100 μm is attached with an adhesive 7 to complete the image sensor. As shown in FIG. 7, a protective film 6 made of polyimide or the like may be formed before the thin glass is attached.

For example, when the thickness of the silicon oxide film having a relative dielectric constant of 4 formed between the thin film electrodes according to the present invention is 10
When the capacitance portion at 0 nm is used, the dielectric constant is 9.4.
The area of the capacitance part can be reduced to about 1/3 compared to the case where the sensor photodiode of the above is used as the capacitance as it is. Therefore, the reduction in the area of the capacitor portion was suppressed to １1 mm (〜25%). However, in the case of the close contact type, the original and the platen roller do not directly contact the sensor, so that it can be made thinner.

The image sensor manufactured in this way has few defects such as short circuit and leak, and has a large number of sensors per substrate and a high production yield.
This is very advantageous for cost reduction. Further, since the silicon oxide film was provided also on the light introduction window of the photoelectric conversion element, the silicon oxide film had an effect of removing the wraparound light from the periphery, and high reading resolution with little noise could be realized at the same time.

[Embodiment 2] FIGS. 8 to 18 show the fabrication process of the complementary thin film transistor mounted on the image sensor substrate similar to that of the "embodiment 1" and the fabrication process of the photoelectric conversion element portion subsequently fabricated. FIG.

FIG. 8 shows a state in which amorphous silicon 101 is formed to a thickness of 30 to 300 nm on a transparent substrate, and the recrystallized film is patterned into an island shape by photolithography.

Further, the gate silicon oxide film 102 is
After forming a film having a thickness of 200 to 200 nm and subsequently forming amorphous silicon 103 having a thickness of 100 to 300 nm doped with phosphorus at a high concentration, patterning was performed as shown in FIG.

FIG. 10 shows that boron is applied to the entire surface at 5 × 10 ^{14 to} 3 × 1.
This is a step of implanting ions at a dose of about 0 ¹⁵ atoms / cm ² . FIG. 11 shows a process in which a portion to be formed into a PMOS is covered with a mask for ion implantation such as a resist 104 and phosphorus is ion-implanted into a portion to be formed into an NMOS at a dose of 2 to 10 times that of boron. Thereafter, the impurities implanted as described above were activated at a temperature of 600 ° C. or higher, and a hydrogenation treatment was performed to further improve the characteristics of the thin film transistor. In the hydrogenation treatment, it was confirmed that the method of producing hydrogen atoms by plasma in a vacuum chamber and exposing the thin film transistor therein, or the method of diffusing hydrogen by heat were effective.

FIG. 12 shows a process of forming a silicon oxide film having a thickness of 500 nm to 1.5 μm as the interlayer insulating film 105. As the interlayer insulating film 105, silicon oxide, PSG film, BP
An SG film or the like is suitable, and these are formed using, for example, a normal pressure CVD method, a low pressure CVD method, a sputtering method, or the like. Alternatively, a silicon oxide film having a thickness of 50 to 200 nm may be formed by a sputtering method or a photo-CVD method, and an insulating film may be formed thereon by using liquid silica by a method as in the first embodiment.

Next, FIGS. 13 to 15 show steps of fabricating the photodiode 3 in the same manner as in "Example 1", and the processing in this step is the same as in Example 1.

FIG. 16 shows a step of forming a contact hole for bringing the thin film transistor into contact with the second thin film electrode. At this time, since the mask is designed so that the ITO 4 and the second thin film electrode and the contact hole for contacting the second thin film electrode and the impurity region of the transistor are formed at the same time, the insulating film of the present invention is formed. There is no increase in the number of photomasks due to the formation.

FIG. 17 shows a process of forming and patterning a wiring metal, and FIG. 18 is a view showing a completed image sensor by forming a protective film 6 and pasting a thin glass 8 thereon. The image sensor manufactured in this manner was manufactured at a very low cost because the production yield was high and the driving circuit was already configured on the substrate.

[0034]

According to the present invention, by forming a capacitor having a structure in which an insulating film is interposed between a first thin film electrode and a second thin film electrode constituting a photoelectric conversion element, the length of the sensor can be reduced to about 25.
%, And the number of image sensors that can be obtained from one substrate increases by 25%. As a result, the manufacturing cost of the image sensor can be made easier, and at the same time, the area of the element portion can be reduced, so that the manufacturing yield has been significantly improved. .

Further, since the area per sensor is reduced, the rate of occurrence of pinholes due to dust and particles is reduced, and the yield is increased. Furthermore, a secondary effect was observed in that the formation of the insulator between the thin film wiring and the photoelectric conversion layer dramatically reduced pinholes generated in the photoelectric conversion layer.

[Brief description of the drawings]

1A and 1B are a plan view and a longitudinal sectional view showing a manufacturing process and a structure of an image sensor having a structure according to an embodiment of the present invention.

2A and 2B are a plan view and a longitudinal sectional view showing a manufacturing process and a structure of an image sensor having a structure according to an embodiment of the present invention.

3A and 3B are a plan view and a longitudinal sectional view showing a manufacturing process and a structure of an image sensor having a structure according to an embodiment of the present invention.

4A and 4B are a plan view and a longitudinal sectional view showing a manufacturing process and a structure of an image sensor having a structure according to an embodiment of the present invention.

5A and 5B are a plan view and a longitudinal sectional view showing a manufacturing process and a structure of an image sensor having a structure according to an embodiment of the present invention.

6A and 6B are a plan view and a longitudinal sectional view showing a manufacturing process and a structure of an image sensor having a structure according to an embodiment of the present invention.

7A and 7B are a plan view and a longitudinal sectional view showing a manufacturing process and a structure of an image sensor having a structure according to an embodiment of the present invention.

FIG. 8 is a longitudinal sectional view showing a manufacturing process and a structure according to another embodiment of the present invention.

FIG. 9 is a longitudinal sectional view showing a manufacturing process and a structure of another embodiment of the present invention.

FIG. 10 is a longitudinal sectional view showing a manufacturing process and a structure of another embodiment of the present invention.

FIG. 11 is a longitudinal sectional view showing a manufacturing process and a structure of another embodiment of the present invention.

FIG. 12 is a longitudinal sectional view illustrating a manufacturing process and a structure according to another embodiment of the present invention.

FIG. 13 is a longitudinal sectional view showing a manufacturing process and a structure of another embodiment of the present invention.

FIG. 14 is a longitudinal sectional view showing a manufacturing process and a structure according to another embodiment of the present invention.

FIG. 15 is a longitudinal sectional view showing a manufacturing process and a structure according to another embodiment of the present invention.

FIG. 16 is a longitudinal sectional view showing a manufacturing process and a structure according to another embodiment of the present invention.

FIG. 17 is a longitudinal sectional view showing a manufacturing process and a structure of another embodiment of the present invention.

FIG. 18 is a longitudinal sectional view showing a manufacturing process and a structure according to another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... 2nd thin film electrode 2 ... 1st thin film electrode 3 ... Thin film semiconductor layer 4 ... Translucent conductive film 5 ... Insulating film 6 ... Protective film 7 ... Adhesive 8 ... Thin glass 100 ... Transparent substrate 101 ... Amorphous silicon 102 ... Gate silicon oxide 103 ... Gate silicon 104 ... Resist 105 ... Interlayer insulating film

Continued on front page F-term (reference) 4M118 AA10 BA04 BA05 CA05 CA09 CA32 CB05 CB06 FB13 FB16 GB15 5F058 BC08 BC11 BD01 BD04 BD05 BD07 BF02 BF12 BF46 BH01 5F110 AA18 BB04 BB10 CC02 DD02 DD03 EE08 FF02 GG02 GG02 GG02 GG02 NN22 NN23 NN24 NN25 NN33 NN34 NN35 NN36 NN72 QQ24 QQ25

Claims (8)

[Claims] An interlayer insulating film is provided above a semiconductor film, a gate insulating film, and a gate electrode, and a metal wiring is electrically connected to the semiconductor film via a contact hole provided in the interlayer insulating film. In the thin film transistor, the interlayer insulating film includes a silicon oxide film formed using liquid silica. 2. An interlayer insulating film is provided above a semiconductor film, a gate insulating film, and a gate electrode, and a metal wiring is electrically connected to the semiconductor film via a contact hole provided in the interlayer insulating film. In the thin film transistor, the interlayer insulating film has a silicon oxide film formed using liquid silica on a silicon oxide film formed by a sputtering method or a CVD method. 3. A silicon oxide film, a silicon nitride film, or a silicon nitride oxide film formed by a sputtering method or a CVD method on the silicon oxide film formed by using the liquid silica according to claim 1 or 2. A thin film transistor having a film or a tantalum oxide film. 4. An image sensor using the thin film transistor according to claim 1. 5. A facsimile using the image sensor according to claim 4. 6. An interlayer insulating film is formed above the semiconductor film, the gate insulating film and the gate electrode, a contact hole is formed in the interlayer insulating film, and a metal wiring electrically connected to the semiconductor film is formed. In a method for manufacturing a thin film transistor including a manufacturing method, at least one of the interlayer insulating films is formed using liquid silica. 7. An interlayer insulating film is formed above the semiconductor film, the gate insulating film and the gate electrode, a contact hole is formed in the interlayer insulating film, and a metal wiring electrically connected to the semiconductor film is formed. In the method for manufacturing a thin film transistor including a manufacturing method, the interlayer insulating film is formed by forming a silicon oxide film by a sputtering method or a CVD method, and then forming a silicon oxide film on the silicon oxide film by using liquid silica. A method for manufacturing a thin film transistor. 8. A silicon oxide film, a silicon nitride film, a silicon nitride oxide film or an oxide film formed on a silicon oxide film formed by using said liquid silica by a sputtering method or a CVD method. A method for manufacturing a thin film transistor, comprising forming a tantalum film.