JPH0774358A - Forming method of perovskite oxide film, thin film transistor using perovskite oxide film, and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a method of forming a perovskite oxide film and a means which forms an insulating film of high permittivity protecting a ground electrode against oxidation and enlargs the picture elements of a liquid crystal display device in opening rate in a thin film transistor provided with the above perovskite oxide film as a gate insulating film. CONSTITUTION:A first insulating film 3 of perovskite oxide film used for protecting a gate electrode 2 against oxidation is formed on the ground gate electrode 2 over an insulating transparent substrate 1 through an RF sputtering method wherein Ar mixed gas small in oxygen partial pressure or Ar gas is used. A second insulating film 4 comprising a perovskite oxide film high in permittivity is formed on it through an RF sputtering method wherein Ar mixed gas large in partial pressure of oxygen or oxygen gas is used. An a-Si acting semiconductor layer 5 and a channel protecting layer 6 of SiN or the like are formed over the insulating film 3, ohmic contact layers 71 and 72 used for a source and a drain are formed thereon confronting each other, and a source electrode 81 and a drain electrode 82 are formed thereon respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor for driving a liquid crystal display panel having a high aperture ratio pixel,
The present invention also relates to a method of forming a perovskite oxide film, which is a high dielectric insulating material, without oxidizing the base electrode.

[0002]

2. Description of the Related Art In a thin film transistor, the electrical conductivity of a conductor between a source electrode and a drain electrode is controlled by a voltage applied to a third electrode (gate electrode) provided via an insulating layer in contact with the conductor. It is known as a so-called field effect transistor. And, conventionally, attention has been paid to the point that a thin film transistor can easily form a switching array over a large area, or the cost can be reduced because the material is inexpensive, and in particular, for the purpose of using it for a switching array for a display element. Research and development continues.

FIG. 3 is a diagram showing the structure of a conventional thin film transistor using an insulating film such as silicon nitride or alumina. In this figure, 21 is an insulating transparent substrate, 22 is a gate electrode, 23 is a gate insulating film, 24 is an operating semiconductor layer,
Reference numeral 25 is a channel protective layer, 26 ₁ is an ohmic contact layer for source, 26 ₂ is an ohmic contact layer for drain, 27 ₁ is a source electrode, and 27 ₂ is a drain electrode.

The structure and manufacturing method of a conventional thin film transistor using an insulating film of silicon nitride, alumina or the like will be described with reference to this structure explanatory diagram.

First step: Cr, Ti,
A gate electrode 22 is formed by forming a metal film of Al, Mo or the like by sputtering and patterning.

Second Step On the insulating transparent substrate 21 including the gate electrode 22, a single layer film of silicon nitride (SiN) or a composite film of silicon nitride and alumina (Al ₂ O ₃ ) having a film thickness of several thousand Å. A gate insulating film 23 made of, for example, is formed.

Third step: An operating semiconductor layer 24 made of amorphous silicon is formed on the gate insulating film 23 by CVD of monosilane gas.
To form.

Fourth Step On the channel region of the operating semiconductor layer 24, SiN, Si
A channel protection layer 25 such as O ₂ is formed.

Fifth Step: A source ohmic source made of amorphous silicon doped with phosphorus (P) is provided in the source region and the drain region of the operating semiconductor layer 24 with the channel protection layer 25 interposed therebetween, with an interval of several μm to several tens μm. A contact layer 26 ₁ and a drain ohmic contact layer 26 ₂ are formed, and A is formed on the contact layer 26 _1.
Source electrode 27 ₁ and drain electrode 2 made of ₁ , Cr, etc.
7 ₂ is formed.

In this conventional thin film transistor using a gate insulating film such as silicon nitride or alumina, the dielectric constant of an insulating material such as a single layer film of silicon nitride used for the gate insulating film 23 or a composite film of silicon nitride and alumina is used. Rate is 1
Since it is as small as 0 or less, it is necessary to secure a gate width of a certain size or more in order to secure a constant drain current. Therefore, the area of the thin film transistor itself becomes large, and the aperture ratio of the pixel decreases. have.

In order to solve this problem, in recent years, as a gate insulating film of a thin film transistor, since it is a high dielectric constant insulating material, it is used as an insulating material for capacitance of DRAM of 1 G or more, and it is easy to increase the area. It is conceivable to use a perovskite-based oxide, which is attracting attention as an insulating material for low-voltage driving EL.

FIG. 4 is a diagram showing the structure of a conventional thin film transistor using a perovskite oxide film. In this figure, 31 is an insulating transparent substrate, 32 is a gate electrode,
33 is a perovskite oxide film, 34 is a silicon nitride film, 35 is an operating semiconductor layer, 36 is a channel protective layer, and 37
₁ is an ohmic contact layer for source, 37 ₂ is an ohmic contact layer for drain, 38 ₁ is a source electrode, 3
8 ₂ is a drain electrode.

The structure and manufacturing method of a conventional thin film transistor using a perovskite oxide film will be described with reference to this structure explanatory diagram.

First step: Cr, Ti,
A gate electrode 32 is formed by forming a metal film of Al, Mo or the like by sputtering and patterning.

Second Step On the insulating transparent substrate 31 including the gate electrode 32, an insulating film 3 made of a perovskite oxide having a film thickness of several thousand liters.
A gate insulating film which is a composite film of 3 and the silicon nitride (SiN) film 24 is formed.

Third Step: An operating semiconductor layer 35 made of amorphous silicon is formed on the silicon nitride film 34 constituting the gate insulating film by CVD of monosilane gas.

Fourth Step On the channel region of the operating semiconductor layer 35, SiN, Si
A channel protection layer 36 such as O ₂ is formed.

Fifth Step In the source and drain regions of the operating semiconductor layer 36 sandwiching the channel protection layer 36, a source ohmic layer made of amorphous silicon doped with phosphorus (P) is provided at a distance of several μm to several tens μm. A contact layer 37 ₁ and a drain ohmic contact layer 37 ₂ are formed, and A is formed on the contact layer 37 _1.
source electrode 38 ₁ and drain electrode 3 made of ₁ , Cr, etc.
8 ₂ is formed.

[0019]

The thin film transistor using the above-mentioned conventional perovskite oxide film is formed of Sr.
A perovskite-based oxide such as TiO ₃ or PbTiO _{3 is} mixed with an argon mixed gas having an extremely large oxygen partial pressure or 10
By reactive sputtering with 0% oxygen gas, it is possible to form a film having excellent insulation, high dielectric constant and high quality, and increasing the gate insulation capacitance to generate a large drive current by a constant bias voltage, thereby increasing the storage capacitance. While there is an advantage that the sustain voltage applied to the pixel electrode can be increased by increasing the amount, the perovskite-based oxide can be replaced with Mo or C.
When formed on a base electrode made of r, Ti or the like, there is a problem that even if the substrate temperature is relatively low, most of the base electrode is oxidized and the resistance becomes high.

An object of the present invention is to provide a thin film transistor for driving a liquid crystal display panel having pixels having a large aperture ratio, and a method for forming a perovskite oxide film having a high dielectric constant without oxidizing a base electrode. .

[0021]

In the method of forming a perovskite oxide film according to the present invention, a first perovskite oxide film for preventing oxidation of a base electrode is formed on a base electrode formed on an insulating substrate. Ar with extremely low oxygen partial pressure
It is formed by RF sputtering of mixed gas or 100% Ar gas, and then a second perovskite oxide film of high quality having a large insulation resistance is formed by reactive RF of Ar mixed gas or 100% oxygen gas having an extremely large oxygen partial pressure. A step of adopting a step of forming the first perovskite-based oxide film and the second perovskite-based oxide film together by sputtering to obtain a target film thickness was adopted.

In this case, the thickness of the first perovskite oxide film for preventing the oxidation of the base electrode is set to 500 Å or less, and it is formed thinner than the second perovskite oxide film having a large insulation resistance. The combined film characteristics of the first perovskite oxide film and the second perovskite oxide film can be brought close to the large insulation resistance and good film quality of the second perovskite oxide film.

Further, in the method of manufacturing a thin film transistor according to the present invention, a step of forming a gate electrode which is a base electrode on an insulating substrate and an Ar mixed gas having an extremely small oxygen partial pressure or 100 on the gate electrode. % Ar gas RF sputtering to form a first perovskite oxide film for preventing oxidation of the base electrode, and subsequently, a reactive RF of Ar mixed gas or 100% oxygen gas having an extremely large oxygen partial pressure. A step of forming a good quality second perovskite oxide film having a large insulation resistance and a high dielectric constant by sputtering, a step of forming an operating semiconductor layer on the second perovskite oxide film, and the operating semiconductor layer The step of forming the source electrode and the drain electrode was adopted.

In the thin film transistor according to the present invention, the gate electrode is formed on the insulating substrate, and the gate insulating film is formed on the insulating substrate including the gate electrode.
An operating semiconductor layer is formed on the gate insulating film, a source electrode and a drain electrode are formed on the operating semiconductor layer so as to face each other, and the gate insulating layer has two or more insulating layers having different dielectric constants. The insulating film that is in contact with the operating semiconductor layer is a silicon nitride film, and the insulating film that is not in contact with the operating semiconductor layer is a perovskite oxide film having a large dielectric constant.

In this case, the thickness of the silicon nitride film of the insulating film which is in contact with the operating semiconductor layer can be 500 Å or more.

[0026]

As in the present invention, the gate insulating film is made of a perovskite oxide film such as SrTiO ₃ having a high relative dielectric constant and Si.
When a stacked film including an N layer is used, the capacitance between the electrodes sandwiching the gate insulating film can be increased, so that the area of the pixel electrode and the storage capacitor electrode can be reduced and the driving L
The aperture ratio of the pixels of the CD panel can be increased.

Further, as in the present invention, an Ar oxygen mixed gas having an extremely small oxygen partial pressure or 100 on the surface of the base electrode is used.
% Perovskite oxide film is formed extremely thin by sputtering Ar gas to suppress the oxidation of the base electrode, and high-quality insulation with excellent insulation by reactive sputtering with Ar gas or 100% oxygen gas, which has an extremely large oxygen partial pressure. When the film is formed to a large part of the target thickness and made composite, the underlying electrode is not oxidized to the inside of the electrode, so the resistance of the electrode itself does not increase and the dielectric constant of the entire insulating film is increased. You can

[0028]

EXAMPLES Examples of the present invention will be described below. (First Embodiment) FIG. 1 is a diagram for explaining the structure of the thin film transistor of the first embodiment. In this figure, 1 is an insulating transparent substrate, 2 is a gate electrode, 3 is a first insulating film, 4 is a second insulating film, 5 is an operating semiconductor layer, 6 is a channel protective layer, and 7 ₁
Is an ohmic contact layer for source, 7 ₂ is an ohmic contact layer for drain, 8 ₁ is a source electrode, and 8 ₂ is a drain electrode.

The configuration and manufacturing method of the thin film transistor of the first embodiment will be described with reference to the configuration explanatory diagram of this thin film transistor.

First Step Mo, Cr, T is formed on an insulating transparent substrate 1 such as a glass substrate.
The gate electrode 2 is formed by forming a metal film such as i by sputtering and patterning the metal film.

Second Step On the insulating transparent substrate 1 including the gate electrode 2, SrTi
A first insulating film 3 of high dielectric constant made of O ₃ , PbTiO ₃ or the like is formed, and a second insulating film 4 of silicon nitride (SiN) is formed thereon. The first insulating film 3 made of SrTiO ₃ , PbTiO ₃ or the like is formed of, for example, 10 mTorr of 1% O ₂
The second insulating film 4 of silicon nitride can be easily formed by RF sputtering in a mixed gas of Ar / Ar, and the second insulating film 4 of silicon nitride is P-CV using ammonia gas and monosilane.
It can be formed by D.

Third Step On the second insulating film 4 made of silicon nitride, the operating semiconductor layer 5 made of amorphous silicon is formed by CVD of monosilane gas.

Fourth Step On the channel region of the operating semiconductor layer 5, SiN, SiO
₂And the channel protection layer 6 are formed. Of the operating semiconductor layer 5
The source and drain regions are doped with phosphorus (P).
Source ohmic contact made of morphus silicon
Layer 7₁And drain ohmic contact layer 7₂To
A source electrode 8 formed of Al, Cr or the like ₁
And drain electrode 8₂To form.

As in this embodiment, the first insulating film 3 is
SrTiO ₃ having a relative permittivity of 200 and a thickness of 8000Å was used, and the second insulating film 4 had a relative permittivity of 6.4 and a thickness of 55.
Compared with the case of using 0Å SiN and the case of using the SiN layer having a thickness of 4000Å as the gate insulating film, the capacity of the insulating layer can be increased five times in this embodiment, and therefore the same value can be obtained. When a thin film transistor having a constant gate width and a constant gate width is used for comparison, the magnitude of the drain current driving the liquid crystal display device increases as the gate insulating film capacitance increases. The aperture ratio of the pixels of the LCD panel can be increased to about ⅕. Further, the storage capacitor C _sg can be increased to increase the sustain voltage applied to the pixel electrode.

In the above embodiments, the insulating film in contact with the operating semiconductor layer is a silicon nitride film, and the insulating film not in contact with the operating semiconductor layer is a perovskite oxide film. This is because it easily occurs. Further, in this case, if the thickness of the silicon nitride film of the insulating film which is in contact with the operating semiconductor layer is 500 Å or more, the above characteristics are particularly likely to occur. Further, the perovskite-based oxide film forming the gate insulating film may be formed in two or more layers to compensate for pinholes and adjust the dielectric constant.

(Second Embodiment) FIG. 2 is an explanatory view of the structure of a thin film transistor of the second embodiment. In this figure, 1
1 is an insulating transparent substrate, 12 is a gate electrode, 13 is an oxidation preventing SrTiO ₃ layer, 14 is a high dielectric constant SrTiO ₃ layer,
Reference numeral 15 is a silicon nitride layer, 16 is an operating semiconductor layer, 17 is a channel protection layer, 18 ₁ is a source ohmic contact layer, 18 ₂ is a drain ohmic contact layer, 19
Reference numeral ₁ is a source electrode and 19 ₂ is a drain electrode.

The structure and manufacturing method of the thin film transistor of the second embodiment will be described with reference to the structure explanatory diagram of this thin film transistor.

Step 1 On the insulating transparent substrate 11 such as a glass substrate, Mo, Cr,
A gate electrode 12 is formed by forming a metal film of Ti or the like by sputtering and patterning it.

Second step: On the insulating transparent substrate 11 including the gate electrode 12, 20
₂ W / cm ² in 1% O ₂ / Ar mixed gas of mTorr
The RF power is used to bring the substrate temperature to 450 ° C. to form an oxidation preventing SrTiO ₃ layer (first insulating layer) 13 of 500 Å which is a perovskite oxide. Since the antioxidant SrTiO ₃ layer 13 lacks oxygen, it does not have excellent electric characteristics as a dielectric constant material, but since the oxygen content is small, it is necessary to oxidize the gate electrode 12 to the inside to increase the resistance. There is no.

Third Step Subsequently, in the same reaction chamber, 20 mTorr
Of 100% O ₂ gas using RF power of ² W / cm ² , substrate temperature of 300 ° C., high dielectric constant S which is a perovskite oxide film having large insulation resistance and high dielectric constant.
The rTiO ₃ layer (second insulating layer) 14 is formed at 7500Å, and the oxidation preventing SrTiO ₃ layer 13 and the high dielectric constant SrTi are formed.
The sum of the thicknesses of the O ₃ layers 14 is set to a target film thickness of 8000Å.

Fourth Step On the high dielectric constant SrTiO ₃ layer 14, a silicon nitride (SiN) layer (third insulating layer) 15 of 500 Å is formed by P-CVD using ammonia gas and monosilane gas.

Fifth Step On the silicon nitride layer 15, an operating semiconductor layer 1 made of amorphous silicon is formed by CVD of monosilane gas.
6 is formed.

Sixth Step On the channel region of the operating semiconductor layer 16, SiN, Si
A channel protection layer 17 such as O ₂ is formed. A source ohmic contact layer 18 ₁ and a drain ohmic contact layer 18 ₂ made of amorphous silicon doped with phosphorus (P) are formed in the source region and the drain region of the operating semiconductor layer 16, and Al, Cr or the like is formed thereon. Then, the source electrode 19 ₁ and the drain electrode 19 ₂ are formed.

According to this embodiment, an Ar mixed gas having an extremely small oxygen partial pressure or 100% Ar is formed on the base electrode.
Since the perovskite-based oxide film for oxidation prevention is formed by RF sputtering of gas, oxygen in the perovskite-based oxide film does not oxidize the base electrode to the inside to increase the electric resistance, and the Ar partial pressure is extremely large.
Since a thick perovskite oxide film having a large insulation resistance and a high dielectric constant is formed by reactive RF sputtering of a mixed gas or 100% oxygen gas, a perovskite oxide film for oxidation prevention and a perovskite having a large insulation resistance and a high dielectric constant are provided. It is possible to prevent oxidation of the base electrode by providing the gate insulating film including the system oxide film with high insulation resistance and high dielectric constant. In this case, antioxidant SrTi
When the thickness of the O ₃ layer 13 is set to about 500 Å, the effect of sufficiently preventing the oxidation of the base electrode is produced.

In each of the above-mentioned embodiments, the case where the perovskite oxide film is applied to the gate insulating layer of the thin film transistor is described. However, when it is applied to the dielectric of the thin film capacitor forming the storage capacity of DRAM, it is generally used. Even when a perovskite oxide film is formed on the base electrode, the same effect as described above is produced. In this embodiment, the case where two layers of perovskite oxide film are formed by changing the pressure of oxygen gas has been described, but a plurality of layers of perovskite oxide films of different materials are laminated to compensate for the generated pinhole. It is also possible to adjust the characteristics as a dielectric by combining and stacking a perovskite oxide film and an insulating film made of another insulating material.

[0046]

As described above, according to the present invention,
Since the thin first perovskite oxide film formed by RF sputtering of Ar mixed gas or 100% Ar gas having an extremely small oxygen partial pressure is formed on the base electrode, oxygen in the first perovskite oxide film is formed. In order to form a thick second perovskite oxide film by reactive RF sputtering of Ar mixed gas or 100% oxygen gas having an extremely large oxygen partial pressure without oxidizing the base electrode to the inside to increase electric resistance. , The insulation resistance and the dielectric constant of the second perovskite oxide film can be remarkably increased, and these laminated bodies have a base electrode having a low electric resistance, and the insulation resistance and the dielectric constant are remarkably high, and the aperture ratio of the pixel can be increased. High LCD display device,
Alternatively, it is possible to realize a DRAM storage capacitor or the like having a small area and a large capacity.

[Brief description of drawings]

FIG. 1 is a structural explanatory view of a thin film transistor of a first embodiment.

FIG. 2 is a structural explanatory view of a thin film transistor according to a second embodiment.

FIG. 3 is a structural explanatory view of a conventional thin film transistor using an insulating film such as silicon nitride or alumina.

FIG. 4 is a structural explanatory view of a conventional thin film transistor using a perovskite oxide film.

[Explanation of symbols]

1 Insulating Transparent Substrate 2 Gate Electrode 3 First Insulating Film 4 Second Insulating Film 5 Operating Semiconductor Layer 6 Channel Protection Layer 7 ₁ Source Ohmic Contact Layer 7 ₂ Drain Ohmic Contact Layer 8 ₁ Source Electrode 8 ₂ Drain Electrode 11 Insulating Transparent Substrate 12 Gate Electrode 13 Antioxidation SrTiO ₃ Layer 14 High Dielectric Constant SrTiO ₃ Layer 15 Silicon Nitride Layer 16 Operating Semiconductor Layer 17 Channel Protection Layer 18 ₁ Source Ohmic Contact Layer 18 ₂ Drain Ohmic Contact Layer 19 ₁ Source electrode 19 ₂ Drain electrode 21 Insulating transparent substrate 22 Gate electrode 23 Gate insulating film 24 Operating semiconductor layer 25 Channel protective layer 26 ₁ Source ohmic contact layer 26 ₂ Drain ohmic contact layer 27 ₁ Source electrode 27 ₂ Drain electrode 31 Insulation Transparent substrate 3 The gate electrode 33 perovskite oxide film 34 a silicon film 35 operates ohmic semiconductor layer 36 a channel protective layer 37 for ₁ source nitride contact layer 37 Ohmic for ₂ drain contact layer 38 ₁ source electrode 38 _second drain electrode

Claims (5)

[Claims] 1. A first perovskite-based oxide film for preventing oxidation of a base electrode is formed on a base electrode formed on an insulating substrate by using Ar mixed gas having an extremely small oxygen partial pressure or 100.
% Ar gas by RF sputtering, and subsequently, a good quality second perovskite oxide film having a large insulation resistance is formed by reactive RF sputtering of an Ar mixed gas having an extremely high oxygen partial pressure or 100% oxygen gas. A method of forming a perovskite oxide film, wherein a total thickness of the first perovskite oxide film and the second perovskite oxide film is set to a target film thickness. 2. The first perovskite oxide film for preventing oxidation of the base electrode is formed to have a thickness of 500 Å or less, and is formed thinner than the second perovskite oxide film having a large insulation resistance. The film characteristics of the perovskite-based oxide film and the second perovskite-based oxide film are brought close to the large insulation resistance and good quality of the second perovskite-based oxide film. Of forming a perovskite oxide film. 3. A step of forming a gate electrode which is a base electrode on an insulating substrate, and an RF of Ar mixed gas or 100% Ar gas having an extremely small oxygen partial pressure on the gate electrode.
A step of forming a first perovskite oxide film for preventing the oxidation of the base electrode by sputtering, and then, a step of forming a first perovskite oxide film, followed by Ar mixed gas or 1
A step of forming a good quality second perovskite oxide film having a large insulation resistance and a high dielectric constant by reactive RF sputtering of 00% oxygen gas, and forming an operating semiconductor layer on the second perovskite oxide film. And a step of forming a source electrode and a drain electrode on the operating semiconductor layer. 4. A gate electrode is formed on an insulating substrate, a gate insulating film is formed on an insulating substrate including the gate electrode, an operating semiconductor layer is formed on the gate insulating film, and the operating semiconductor layer is formed. A source electrode and a drain electrode facing each other, the gate insulating layer is composed of two or more insulating films having different dielectric constants, and the insulating film in contact with the operating semiconductor layer is a silicon nitride film. A thin film transistor characterized in that the insulating film not in contact with the operating semiconductor layer is a perovskite oxide film having a large dielectric constant. 5. The thin film transistor according to claim 4, wherein the thickness of the silicon nitride film of the insulating film in contact with the operating semiconductor layer is 500 Å or more.