JPH03250769A - Large-scale thin film transistor and manufacture thereof - Google Patents

Abstract

PURPOSE:To make it possible to obtain a homogeneous thin film transistor over a wide area by a method wherein a specified SiNxHy (x+y<=4) film is used as a gate insulating film. CONSTITUTION:A thin film transistor comprises a gate insulating film 12 formed under the condition of a low temperature and this film 12 is an SiNxHy (x+y<=4) film, whose ratio of an Si-H absorption integrated intensity (a) to an N-H absorption integrated intensity (b) in an infrared absorption spectrum is a/b=0.25 or lower. Accordingly, the film 12 has a sufficiently high Si-H bond density and an N-H bond density and does not contain many Si-H bonds, which are the main factor for the formation of a dangling bond having an electron trap level and have a comparatively weak bonding power. Thereby, the homogenerous thin film transistor 21 is obtained over a wide area.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thin film transistor and a method for manufacturing the same.

[Prior Art] In recent years, liquid crystal displays in which thin film transistors using amorphous silicon are arranged in a two-dimensional matrix have been developed and are being applied to various display devices such as liquid crystal televisions and personal computers.

FIG. 5 shows a cross-sectional view of a conventional thin film transistor described in Japanese Patent Application Laid-Open No. 58-114453.

As shown in the figure, a conventional thin film transistor generally has a drain electrode 16, a gate electrode 11 on a substrate 10,
, Goo1-$! Edge film 12, amorphous 29321 layer 13, gold y for key barrier formation, 14, source electrode 15,
A passivation film 17 and a light shielding film 18 are laminated.

Furthermore, in the conventional technology, the gate insulating film 12 and the amorphous silicon i/1513 are formed by plasma CVD (Chemical
This plasma CVD method is a technique for depositing a thin film such as an oxide film or a nitride film on a substrate by a chemical reaction at high temperature.

On the other hand, in contrast to the plasma CVD method described above, a method has been proposed in which an electron cyclotron resonance plasma CVD method is used to form a gate insulating film or an amorphous silicon layer.

This technology, for example, as described in JP-A-62-71276 or JP-A-63-115328, generates a magnetic field using an electromagnetic coil and introduces microwaves from a magnetron into a static magnetic field. Electromagnetic energy is resonantly absorbed by the electrons of the film, and plasma is generated in a plasma generation chamber provided separately from the film forming chamber. Then, a gate insulating film or an amorphous silicon film is formed on the surface to be processed through interaction between the raw material gas introduced into the film forming chamber and the plasma introduced from the plasma generation chamber into the film forming chamber.

[Problems to be Solved by the Invention] When using the plasma CVD method described above, since a chemical reaction at high temperature is used, the substrate is heated to a high temperature of 250°C to 350°C, so selection of the substrate and lower material is required. In addition, the high temperature causes problems such as diffusion of impurities into the thin film. Therefore, there are problems in that the manufacturing yield is lowered and it is difficult to form a homogeneous thin film over a wide area.

Next, −i plus electron cyclotron resonance plasma C
The method of manufacturing a thin film transistor using the VD method enables film formation at a relatively low temperature compared to the plasma CVD method and reduces restrictions on the selection of substrate and lower layer materials, but it has the following problems.

In other words, cavity resonator type microwave plasma CV
Method I) is a thin film transistor manufacturing method in which plasma generated in a plasma generation chamber provided separately from a film formation chamber is diffused through a small opening and used as divergent plasma.

Therefore, the area of the plasma in contact with the surface to be processed is small.
The area where a thin film transistor with performance equivalent to that of a thin film transistor formed by plasma CVD can be formed is φ1-
There is a problem in that it has to be limited to about OOIIIT1.

Therefore, it is inappropriate as a means for forming a uniform thin film transistor over a wide area.

The present invention aims to solve the above problems of the prior art and provides a thin film transistor that is uniform over a wide area.

Another object of the present invention is to provide a method for manufacturing the above thin film transistor.

Furthermore, another object of the present invention is to provide a liquid crystal display device including the above thin film transistor.

[Means for solving the problem] The above purpose is to improve the 5j-H absorption (2200
a++ ) integrated intensity a and N-H absorption (3340ca
n) The ratio of integrated intensity to a/b = 0.25
This can be achieved by a thin film transistor using the following SiNxHy (x+y≦4) as a gate insulating film.

The other object described above is to have a horn whose cross-sectional area gradually increases, and the opening area of the horn is larger than the area of the area where the film is to be formed. A gas blowing method in which the flow velocity distribution of the gas during blowing out is made almost uniform over an area larger than the area where a film is to be formed, and the direction of the flow velocity distribution is substantially perpendicular to the surface of the object to be processed. This can be achieved by a microwave plasma CVD apparatus comprising:

Furthermore, the other object mentioned above is to blow out the gas so as to have a substantially uniform flow velocity distribution to the surface of the object to be processed on which film formation is to be performed, and to make the irradiation density of the gas substantially uniform.
This can be achieved by a thin film manufacturing method in which plasma is generated in a film forming chamber by irradiating microwaves over an area larger than the area where the film is to be formed.

[Function] In the microwave plasma CVD apparatus using electron cyclotron resonance according to the present invention, microwaves of a specific wavelength (
For example, 2.45 GIIz) is irradiated into a space having a specific magnetic field strength (for example, 875 Gauss).

At this time, since the microwave radiating part is equipped with a microwave radiating part whose opening area is larger than the area of the separation area where the film is formed, the whole area of the plasma generation part in the film forming chamber is covered. , microwaves are introduced.

On the other hand, almost simultaneously with the introduction of the microwave, the gas to be introduced into the plasma generation section is passed through a gas introduction pipe near the inner wall of the film forming chamber by a gas supply means provided separately from the two apparatuses, and the gas is emitted by the microwave. The entire surface of the opening is guided. From here, the gas is introduced into the plasma generating section 5 with an approximately uniform flow velocity distribution via a gas blowing means. In this way, according to principle 110, which is introduced with almost the same flow velocity distribution, taking into account the pressure and flow rate of the film forming chamber, for example, the size of the hole is made larger in the peripheral part of the gas blowing plate, and the size of the hole is made larger in the central part. This is because the size is reduced.

Therefore, a uniform plasma is formed, and this plasma is
By transporting it toward the object to be treated along the magnetic field, a homogeneous thin film can be deposited over a wide area on the surface to be treated.

Furthermore, by combining the thin film transistor according to the present invention with a liquid crystal and using it as a liquid crystal driving transistor, a highly accurate liquid crystal display device can be manufactured.

The reason for this is that the above-mentioned thin film transistor includes an insulating film formed under low temperature conditions, and this insulating film has an integrated Si-H absorption intensity a in an infrared absorption spectrum and a N-H absorption The ratio of the integrated intensity to is a/
b =0.25 or less S jNxI-1y (x 1y
≦4), it has a sufficiently high S j -N system bond density and a relatively low bond that is a factor in the formation of dangling bonds that have an electron L-wrap level. This is because it does not contain many weak S j-II bonds.

(below margin) [Example] The present invention will be explained in detail with reference to the drawings.

FIG. 1 shows a first embodiment of the present invention.

FIG. 1 shows a cross-sectional view of a microwave plasma CVD apparatus capable of applying a magnetic field used to manufacture the thin film transistor of the present invention.

As shown in the figure, the device of this embodiment includes a microwave generation source 33, a microwave introduction tube 5, and an electromagnetic horn 2 which is a microwave radiator that magnifies and irradiates microwaves over a large area. The basic configuration includes a film forming chamber 7 connected to the electromagnetic horn 2 for forming plasma, and a magnetic field applying device 4 arranged around the outer periphery of the electromagnetic horn 2 and the film forming chamber 7. A partition plate 1 made of a material that transmits microwaves, such as fused silica, is disposed above the electromagnetic horn 2 to spatially partition the film forming chamber 7 and the electromagnetic horn 2.

Furthermore, a gas introduction pipe 6 is arranged in the film forming chamber 7 for introducing a gas containing nitrogen such as nitrogen gas or ammonia gas, and a metal compound containing hydrogen, such as silane gas. .

A ring-shaped gas introduction port 30 is connected to the gas introduction pipe 6, and a large number of holes for blowing out gas are provided inside the gas introduction port 30.

Further, inside the film forming chamber 7, a holder 9 that supports the object to be processed 8 is provided facing the partition plate 1.

Note that, in this figure, an exhaust system that evacuates the inside of the electromagnetic horn 2 and the film forming chamber 7 is omitted.

Next, the operation of this embodiment will be explained.

For example, a mixed gas of nitrogen gas and silane gas is introduced into the plasma generation unit 3 from the gas introduction port 30, and microwaves are further introduced from the microwave introduction pipe 5,
A magnetic field is generated by the magnetic field applying device 4 to generate plasma of the mixed gas.

Note that the microwave propagates through the electromagnetic horn 2 without disturbing its mode, passes through the partition plate 1, and is introduced into the plasma generation section 3 with a nearly uniform irradiation density.

Therefore, due to the interaction of microwaves and magnetic fields.

By causing electron cyclotron resonance to occur, it is possible to cause the plasma generation section 3 to generate high-density plasma over a wide range.

According to measurements by the inventors, plasma having an electron concentration of about 10" to 1012 square meters is uniformly formed over a wide range (φ500wn).

The active species of nitrogen and silane in the plasma are accelerated toward the object to be processed 8 provided inside the film forming chamber 7 by the magnetic field formed by the magnetic field applying device 4, and as a result,
It is possible to form a silicon nitride thin film with a uniform thickness and dense film quality on the surface of the object 8 having a large diameter.

Further, according to the present invention, since electron cyclotron resonance with high-density plasma is used, silicon nitride film that has excellent optical or electrical properties without having to heat the object to a particularly high temperature is used. It is possible to form a film.

The reason for this is that the above thin film deposited under low temperature conditions has a sufficiently high 5i-N bond density and N-
5i-, which has a H-based bond density and has a relatively weak bonding force, is a factor in the formation of dangling bonds that become electron trap levels.
This is because it does not contain many H thread bonds.

Therefore, if the silicon nitride thin film described above is used as a gate insulating film of a thin film transistor, it is possible to suppress changes over time in transistor characteristics, such as the threshold voltage h: value, caused by the movement of electrons.

Note that the elemental bonding state of the thin film can be easily detected by analysis using, for example, single-reflection infrared analysis.

Next, a second embodiment of the present invention will be described using FIG. 6.

FIG. 6 shows a cross-sectional view of an embodiment of a microwave plasma CVD apparatus capable of applying a magnetic field used to manufacture the thin film transistor of the present invention. As shown in the figure, the microwave plasma CVD apparatus of this embodiment has the same basic configuration as the microwave plasma CVD apparatus of the first embodiment.

The difference between the microwave plasma CVD apparatus of this embodiment and the microwave plasma CVD apparatus of the first embodiment lies in the means for introducing gas into the plasma generation section.

The configurations and functions of the microwave generation source 33, electromagnetic horn 2, etc., which are the constituent elements of the microwave plasma CVD apparatus of this embodiment, are the same as those of the first embodiment, so their explanation will be omitted.

The means for introducing gas into the plasma generation section, which is a feature of this embodiment, will be explained.

The means for introducing the gas into the plasma generation section 3 is the sixth
In the figure, it is composed of a gas introduction device 32 and a gas blowing plate 31.

The gas introduction device 32 is provided along the inner wall of the film forming chamber 7.
It consists of two approximately cylindrical pieces with different diameters. Note that the gas introduction device 32 may be formed by making the inner wall of the film forming chamber 7 double. Furthermore, the gas introduction device 32 can be formed by arranging a plurality of tubes at appropriate intervals.

Further, the gas blowing plate 31 is made of a material that transmits microwaves, and is provided on the partition plate 1 at a predetermined interval.

Its shape is a plate with a large number of holes, and the diameter of the holes may be, for example, about 0.3m+n, but preferably, the number and diameter of the holes should be adjusted in consideration of the supply gas pressure during film formation. teeth,
It is preferable to adjust the flow rate so that gas is blown out from each hole at a uniform flow rate from the outer periphery of the gas blowing plate 31 toward the center. For example, if the diameters of the holes are all the same, the number of holes is reduced in the portion near the outer periphery of the gas blowing plate 31, and the number of holes is increased in the portion far from the outer periphery. That is, depending on the pressure and gas flow rate of the film forming chamber 7 during film formation, the partition plate 1
Since the conductance for gas flow differs from the ends to the center, the number and size of the holes are adjusted taking these into consideration.

Note that the distance between the partition plate 1 and the gas blowing plate 31 is approximately 0.
．． 5 strokes or less is desirable. The reason for this is that when the distance between the partition plate 1 and the gas blowing plate 31 is approximately 0.5 mm or more, plasma is generated between the partition plate 1 and the gas blowing plate 31, and a thin film forms in the holes of the partition plate 1. As it is deposited and the pore diameter changes,
This is because the gas blows out unevenly. Also, by making the pressure in the space relatively lower than the pressure in the film forming chamber 7, plasma can be prevented from being generated in the space.

Note that instead of the gas blowing plate 31, a pipe-shaped thing having an inner diameter similar to that of the gas blowing plate 31 is used.
It is also possible to cut them into lengths that are approximately the same as the thickness of the board and tighten them to replace the holes. The above-mentioned gas blowing plate 31, a pipe-like east combination, etc. correspond to the gas blowing means described in the claims.

Further, the gas introduction device 32 and the gas blowing plate 31 are connected so that all the gas introduced from the gas introduction device 32 is guided to the plasma generation section 3.

Further, the distance between the gas blowing plate 31 and the object to be treated 8 is 100
It is preferable to set it to 150 mm.

Next, the supply of gas to the plasma generation section 3 according to this embodiment will be explained.

A gas introduction device 3 connected to the outer peripheral part of the gas blowing plate 31
2, the gas supplied at a constant pressure passes through the gas blowing plate 3.
As a result, if the plasma generating section 3 is assumed to have a surface parallel to the gas blowing plate 31, a constant flow rate of gas will be generated on that surface. Supplied. That is, the object to be processed 8 arranged parallel to the gas blowing plate 31 is supplied with a substantially constant flow rate of gas. Note that the process of turning gas into plasma in the plasma generating section 3, etc. is the same as in the first embodiment, and will therefore be omitted.

Next, FIG. 3 shows the effect of film formation using the microwave plasma apparatus of the above embodiment.

FIG. 3 shows experimental results showing typical characteristics of a silicon nitride thin film formed using the microwave plasma CVD apparatus of this example.

As experimental conditions, each flow rate of nitrogen and silane was set to 10=1.
, pressure 1-3 mmTorr, microwave output 1-3
It was set to 2kw.

Figures (a) to (d) show, respectively, (a) the film thickness distribution characteristics when a transparent glass substrate is used as the object to be processed 8;
(b) shows its resistivity distribution characteristics, (C) its dielectric constant distribution characteristics, and (d) its infrared absorption spectrum film characteristics.

The vertical axes in (a) to (d) of the same figure are r
P: 3 thickness, (b) is the refractive index, (C) is the resistivity, and (d) is the absorption coefficient.

Further, on the horizontal axis, (a) to (C) indicate the distance from the center of the substrate, and (d) indicates the absorption intensity.

From this result, it is clear that the thin film realizes a uniform property distribution over a very wide range in the radial direction from the center of the transparent glass substrate.

Also, inferring from the infrared absorption spectrum characteristics, iJ
In II'J, there is a sufficiently high 5i that indicates a chemical refutational composition.
-N system bond density and N-)-I yarn bond density, and it can be seen that the structure has extremely excellent compactness.

The reason for this is the formation of silicon dangling bonds (without bonding, forming electron trap levels and adversely affecting film properties or transistor properties) that are generated during film formation in conventional technology. This is because it does not have S i -)I type bonds, which have a relatively weak bonding force, and therefore can maintain a dense atomic structure.

In this example, from the experimental results, 5i-H bond and N
The ratio of integrated absorption intensity to -11 bond is 0.1 or less.

If the value of this ratio is 0.25 or less, for the above reason,
When forming the thin film 1 to the transistor, it is possible to suppress temporal fluctuations in transistor characteristics that occur due to movement of electrons.

According to this embodiment, even if the workpiece is not heated to a high temperature,
A thin film containing silicon nitride as a main component can be formed over a large area. By using this thin film as the insulating film, it is possible to realize a thin film transistor that can maintain excellent electrical characteristics for a long period of time.

Next, a third embodiment of the present invention will be described using FIG. 2.

FIG. 2 shows a cross-sectional view of the thin film transistor of this example.

In the figure, 19 is an amorphous silicon n'' layer, and the other symbols are the same as those in the conventional example of FIG.

The manufacturing method of the thin film transistor of this example will be explained.

The gate insulating film 12 is formed using, for example, a silicon nitride film using the technique using the electron cyclotron resonance plasma CVD apparatus shown in the second embodiment.

In FIG. 2, the object to be treated 8 has a refractive index of 1, for example.
．． It is fixed to the holder 9 using a transparent glass 10 of No. 52.

First, a goo 1 made of metal such as Cr is placed on a transparent glass 10.
4 poles]-1 are formed using a known sputtering method or the like.

Next, nitrogen gas and silane gas are introduced from the gas introduction device 32, and the silane is separated in the nitrogen plasma to form the gate electrode 11'' and the insulating films 1 to 12 with a thickness of 300 mm.
0 to 4000 silicon nitride thin films are formed.

Next, the supply of nitrogen gas from the gas introducing device 32 is stopped, and the amorphous silicon layer 13 and the amorphous silicon n'' layer 19 are deposited in predetermined areas by 3,000 to 4,000 layers and 300 to 4,000 layers, respectively.
Form 00 people continuously.

In addition, as a dopant for amorphous silicon n''l19,
For example, phosphine (PH3) is supplied from the gas introduction device 32.

Next, a transparent electrode is formed in a predetermined area using a known anodic oxidation method for making two IT○ films.

Thereafter, a part of the amorphous silicon r1'' layer 19 is removed by an etching method, and a drain electrode 15 and a source electrode 16 are formed using a metal such as AM using a vacuum evaporation method, thereby forming a thin film transistor. is completed.

The gate insulating film 12 is formed using the technique using the electron cycloresonant plasma CVI) apparatus shown in the second embodiment as described above. In other words, plasma whose activity has become extremely high due to electron cyclotron resonance is extracted with appropriately adjusted energy using a magnetic field and is formed by colliding with the surface of the object to be processed 8. .

Therefore, due to the combined effect of the high activity of the plasma and the limited intensity of collisions of ions and electrons with the workpiece,
Surface treatment reactions such as thin film formation occur efficiently. Since this reaction occurs without external heating, it can be processed at room temperature.

As a result, as described with reference to FIG. 3, it is possible to suppress temporal fluctuations in transistor characteristics that occur due to movement of electrons when a thin film transistor is formed.

Therefore, by the thin film manufacturing method using the plasma CVD apparatus of the second embodiment, it is possible to realize a thin film transistor that can maintain excellent electrical characteristics for a long period of time.

Next, a fourth embodiment will be described using FIG. 4.

FIG. 4 is a partially cutaway perspective view of a liquid crystal display device, showing a large screen display device in which a thin film transistor including a gate insulating film and a liquid crystal according to the third embodiment are combined.

The large screen display device of this embodiment has a structure in which it is sandwiched between two polarizing plates 26°26.

In FIG. 4, transparent glass 10. Thin film 1 - transistor 21, electrode 22, liquid crystal 23,
Color filter 24, surface protection glass 25, polarizing plate 2
6 were sequentially laminated using a known method.

The large screen display device 27 is configured.

In the large screen display device 27, the screen size is determined by the area in which the thin film transistor 21 can be formed, as described in the above embodiment.

Since the film is formed by a microwave plasma CVD apparatus using an electromagnetic horn, the thin film 1-transistor 21 can be formed in an area of approximately φ500I. That is, it is possible to form a display device with a screen of about 20 inches.

[Effects of the Invention] As described above, according to the present invention, when forming the gate insulating film of a thin film transistor using an amorphous silicon thin film using a microwave plasma CVD apparatus, An electromagnetic horn with a built-in plate magnifies the microwave and irradiates it over a large area, making use of the highly active plasma that exists in the space between the partition plate and the object to be processed (glass substrate), so it can be applied to an area of approximately φ5001TI11. , it is possible to form an extremely dense thin film having a stoichiometric composition and excellent electrical and optical properties.

Since the thin film that constitutes the thin film transistor is formed using highly active plasma due to electron cyclotron resonance, there is no need for special high-temperature heat treatment to reduce the temperature of the object during formation, and dangling A dense film can be formed that does not contain many relatively weak S i -H bonds that cause bond defects.

Therefore, a thin film transistor formed using the above thin film can maintain stable electrical and optical characteristics over time.

Furthermore, by combining the thin film transistor having a large area with a liquid crystal or the like, it is possible to realize a display device with a large screen (approximately 20 inches).

[Brief explanation of drawings]

FIG. 1 is a sectional view of an embodiment of a microwave plasma CVD apparatus for forming a thin film L-transistor, which is an embodiment of the present invention, and FIG. 2 is a sectional view of a thin film transistor, which is an embodiment of the present invention. Figure 3 is a characteristic diagram explaining the characteristics of the gate insulating film (silicon nitride film) that constitutes the thin film transistor.
FIG. 4 is a partially cutaway perspective view of a liquid crystal display device, FIG. 5 is a sectional view of a thin film transistor showing the prior art, and FIG. 6 is a microwave to which a magnetic field can be applied used to manufacture the thin film transistor of the present invention 1 is a sectional view of an embodiment of a plasma CVD apparatus. DESCRIPTION OF SYMBOLS 1... Partition plate, 2... Electromagnetic horn, 3... Plasma generation part, 4... Magnetic field application device, 5... Microwave introduction tube, 6... Gas introduction tube, 7... Structure Film chamber, 8... Processing object, 9... Holder, 10... Substrate, 11...
Gate electrode, 12... Gate insulating film, 13... Amorphous 99325 layer, 14... Schottky barrier forming metal, 15... Source electrode, 16... Drain electrode,
17... Passivation film, 18... Light shielding film, 19
...Amorphous silicon n'' layer, 20...ITO film, 21
...Thin film 1 helangister, 22.. Electrode, 23.. Liquid crystal, 24.. Color filter, 25.. Surface protection glass, 26.. Polarizing plate, 27.. Large screen display device, 31..
...Gas blow-off plate, 32...Gas introduction device, 33...
Microwave source.

Claims (1)

[Claims] 1. Si-H absorption in infrared absorption spectrum (220
SiN_x where the ratio between the integrated intensity a (0 cm) and the integrated intensity b of N-H absorption (3340 cm) is a/b = 0.25 or less
A thin film transistor characterized in that H_y (x+y≦4) is used as a gate insulating film. 2. A microwave plasma CVD apparatus, comprising a microwave radiating section having a horn whose cross-sectional area gradually increases, and the opening area of the radiating section is larger than the area of the region where the film is to be formed. Microwave plasma C
VD device. 3. A microwave plasma CVD apparatus, comprising a film forming chamber that generates plasma therein to form a thin film on the surface to be processed, and a microwave introducing means that introduces microwaves into the plasma generating section, A partition plate for spatially partitioning the microwave introducing means and the film forming chamber is provided, and a gas blowout having a plurality of holes is provided on the surface facing the surface to be processed on the microwave introducing side of the film forming chamber. Microwave plasma C characterized by being provided with means
VD device. 4. In a microwave plasma CVD apparatus, the flow velocity distribution of the gas when blown into the plasma generation section is made almost uniform over an area larger than the area where the film is to be formed, and the direction of the flow velocity distribution is set so that the direction A microwave plasma CVD apparatus comprising a gas blowing means for blowing out gas substantially perpendicular to a processing surface. 5. It has a horn whose cross-sectional area gradually increases, and the opening area of the horn is larger than the area of the area where the film is to be formed. A microwave emitting part, and a gas flow rate when being blown out to the plasma generation part. A gas blowing means for blowing out the gas so that the distribution is substantially uniform over an area larger than the area of the region where the film is to be formed, and the direction of the flow velocity distribution is substantially perpendicular to the surface to be processed of the object to be processed; Microwave plasma CVD equipment configured. 6. Blow out the gas so that it has a substantially uniform flow velocity distribution on the surface of the object to be treated, and make the irradiation density of the gas almost uniform, so that the area is larger than the area on which the film is to be formed. A thin film manufacturing method characterized by irradiating an area with microwaves to generate plasma in a film forming chamber and forming a film. 7. A thin film transistor comprising a gate insulating film formed by the film forming method according to claim 6. 8. A liquid crystal display device using the thin film transistor according to claim 1 or 7 as a liquid crystal driving transistor. 9. A microwave plasma CVD apparatus in which a film forming chamber is provided with means for blowing out gas in accordance with the direction of propagation of microwaves.