JP2010212436A - Field effect transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a field effect transistor having metal oxide used for a channel, which has a structure having an excellent interface between a gate insulating layer and a channel layer. <P>SOLUTION: The field effect transistor includes a substrate 1, wherein the transistor further includes, on the substrate 1; a gate electrode 5; the gate insulating film 6; the channel layer 4; a source electrode 2; and a drain electrode 3. The gate insulating layer 6 and channel layer 4 are layers consisting of at least gallium (Ga) and oxygen (O). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a field effect transistor.

A field effect transistor (FET) is an element having a gate electrode, a source electrode, and a drain electrode. A switching function is achieved by controlling the current flowing in the channel layer between the source and drain electrodes by applying a voltage to the gate electrode. This is an electronic device to be developed. In particular, an FET manufactured on a substrate is called a thin film transistor (TFT). A metal-insulator-semiconductor field effect transistor (MIS-FET) using polycrystalline silicon or amorphous silicon as a channel layer is often used as this TFT.
In order to fabricate the above transistor on a substrate such as plastic, it is necessary to produce TFTs at a low temperature. For example, a method using an organic substance has been proposed.

On the other hand, metal oxides are currently attracting attention as materials used for the channel layer. Many of these materials are transparent to visible light, and those produced at low temperatures have been reported, and application to so-called flexible displays is expected.
Among them, for example, TFTs having SnO ₂ , ZnO or the like as a main component and used for the channel layer have been developed. These can be produced at a relatively low temperature and can be produced on a plastic substrate. Non-Patent Document 1 discloses a transistor in which tin-doped gallium oxide is used for a channel layer.
More recently, TFTs using InGaZnO ₄ as a channel layer have been reported (for example, Patent Documents 1 and 2, Non-Patent Document 2, etc.). This transistor can be manufactured at room temperature and is transparent to visible light.

JP 2007-288156 A JP 2006-165529 A

Appl. Phys. Lett. , 88,092106 (2006) Nature, 432, 488 (2004)

  An object of the present invention is to provide a field effect transistor in which the interface between the gate insulating layer and the channel layer is better than when the gate insulating layer and the channel layer do not contain gallium oxide.

The above problem is solved by the following means. That is,
The invention according to claim 1
A substrate,
A gate electrode, a gate insulating layer, a channel layer, a source electrode, and a drain electrode on the substrate;
The gate insulating layer and the channel layer are field effect transistors including gallium oxide.

The invention according to claim 2
In the gallium oxide contained in the gate insulating layer, when the number of gallium (Ga) atoms is I _Ga and the number of oxygen (O) atoms is _IO , the value of I _O / I _Ga is 1.3 or more and 1 The field effect transistor according to claim 1, which is 0.5 or less.

The invention according to claim 3
In the gallium oxide contained in the gate insulating layer, the number of gallium (Ga) atoms is I _Ga and the number of oxygen (O) atoms is I 2 _O, and the gallium oxide in the gallium oxide contained in the channel layer. The value of S _O / S _Ga is smaller than the value of I _O / I _Ga , where S _{Ga is} the number of atoms of S _Ga and the number of atoms of oxygen (O) is S 2 _O. 3. It is a field effect transistor.

The invention according to claim 4
The field effect transistor according to any one of claims 1 to 3, wherein the substrate has flexibility.

The invention according to claim 5
The gate insulating layer and the channel layer are formed through a step of reacting an organic gallium compound and activated oxygen at 100 ° C. or lower in an atmosphere containing at least one of oxygen and hydrogen. The field effect transistor according to any one of claims 4 to 5.

  According to the first aspect of the present invention, the interface between the gate insulating layer and the channel layer becomes better than when the gate insulating layer and the channel layer do not contain gallium oxide.

  According to the invention of claim 2, the insulating property of the gate insulating layer is good as compared with the case where the atomic ratio of gallium (Ga) and oxygen (O) in the gallium oxide contained in the gate insulating layer is not considered. Become.

  According to the invention of claim 3, the gate insulating layer and the channel layer are compared with the case where the atomic ratio of gallium (Ga) and oxygen (O) in the gallium oxide contained in the gate insulating layer and the channel layer is not considered. The function of is secured.

  According to the fourth aspect of the present invention, a field effect transistor is formed even if the substrate has flexibility.

  According to the fifth aspect of the present invention, a field effect transistor can be formed on any substrate as compared with the case where the layer is formed at a temperature exceeding 100 ° C.

It is the schematic block diagram which showed an example of the layer structure of the field effect transistor of this embodiment. It is the schematic block diagram which showed an example of the layer structure of the field effect transistor of this embodiment. It is the schematic block diagram which showed an example of the layer structure of the field effect transistor of this embodiment. FIG. 5A is a schematic cross-sectional view when an example of a film formation apparatus used for forming a gate insulating layer and a channel layer is viewed from the side, and FIG. 5B is a cross-sectional view taken along line A1-A2 in FIG. . It is a schematic block diagram which shows the other example of a plasma generator. In one example of a field effect transistor of the present embodiment, the source when changing the gate voltage V _G - is a graph showing the correlation between the drain voltage V _SD - drain current I _SD and source.

  Hereinafter, although an embodiment of the present invention is described with reference to drawings, it is not necessarily limited to this.

[Field effect transistor]
1 to 3 are schematic cross-sectional views showing an example of the configuration of a field effect transistor (hereinafter sometimes referred to as “FET”) according to the present embodiment. 1 to 3, members having the same functions are denoted by the same reference numerals, 1 being a substrate, 2 being a source electrode, 3 being a drain electrode, 4 being a channel layer, 5 being a gate electrode, and 6 being a gate. Represents an insulating layer.
Hereinafter, the structure of the field effect transistor shown in FIGS. 1 to 3 will be described in order.

  In the field effect transistor shown in FIG. 1, for example, a gate electrode 5, a gate insulating layer 6, and a channel layer 4 are provided in this order on a substrate 1, and a source electrode 2 and a drain electrode 3 are separated on the channel layer 4. Provided in position.

  In the field effect transistor shown in FIG. 2, for example, a gate electrode 5 and a gate insulating layer 6 are provided in this order on a substrate 1, and a source electrode 2 is provided on the gate insulating layer 6. The channel layer 4 is provided so that one end of the channel layer 4 covers the surface of the source electrode 2 opposite to the side in contact with the gate insulating layer 6. Furthermore, the drain electrode 3 is provided on the channel layer 4 at the end opposite to the one end covering the source electrode 2 of the channel layer 4.

  Further, in the field effect transistor shown in FIG. 3, for example, the source electrode 2 and the drain electrode 3 are provided on the substrate 1 at a separated position, and the channel layer 4 is provided so as to cover the source electrode 2 and the drain electrode 3. Is provided. A gate insulating layer 6 and a gate electrode 5 are provided in this order on the channel layer 4.

  In the field effect transistor as shown in FIGS. 1 to 3, the current flowing through the channel layer 4 between the source electrode 2 and the drain electrode 3 is controlled by the voltage applied to the gate electrode 5.

  In the case where an electronic device is manufactured using the field effect transistor of this embodiment, it is used as a configuration (semiconductor device) in which one or more field effect transistors of this embodiment are mounted on a substrate. Alternatively, an electronic device may be manufactured by further combining other elements, circuits, and the like with this semiconductor device.

  Next, each member constituting the field effect transistor of this embodiment will be described in detail. In the following description, the reference numerals are omitted.

<Gate insulation layer>
The gate insulating layer is a layer containing gallium oxide.

When the numbers of gallium (Ga) and oxygen (O) atoms in the gallium oxide contained in the gate insulating layer are I _Ga and I 2 _O , respectively, the value of I 2 _{O 3} / I _Ga is 1.3 or more and 1.5 or less. It is preferable that it is 1.4 or more and 1.5 or less, and 1.5 is the most preferable. When the value of I _O / I _Ga is in the above range, the gate insulating layer has high insulating properties (that is, high electrical resistance), excellent pressure resistance, transparency, water vapor barrier properties, and oxygen barrier properties, and Changes in physical properties over time are extremely small.

  The gallium oxide contained in the gate insulating layer is preferably a hydrogen-containing gallium oxide containing hydrogen (H) as a third element in addition to gallium (Ga) and oxygen (O). If gallium oxide contained in the gate insulating layer contains hydrogen (H), hydrogen compensates for dangling bonds and structural defects of gallium oxide, so that electrical stability, chemical stability, and mechanical stability can be obtained. It is improved, high hardness and high transparency are obtained, and high water repellency and low friction coefficient of the surface of the gate insulating layer are obtained.

In the case where gallium oxide contained in the gate insulating layer contains hydrogen (H), if the number of hydrogen (H) atoms in the gallium oxide contained in the gate insulating layer is I _H , I _H / (I _Ga + I _O ) The value is preferably from 0.01 to 0.30, and more preferably from 0.05 to 0.20. When the value of I _H / (I _Ga + I _O ) is 0.01 or more, the structural disturbance inside the film is reduced, the electrical stability is improved, and the mechanical characteristics are improved, and I _H / (I _Ga When the value of (+ I 2 _{O 3} ) is 0.30 or less, the hardness and chemical stability (particularly water resistance) of the gate insulating layer are improved.
In the case where the field-effect transistor is formed over a flexible substrate, I _H / (I _Ga + I _O ) can be used from the viewpoint that the gate insulating layer can withstand bending and distortion of the substrate. The value is more preferably 0.1 or more and 0.2 or less.

The gallium oxide contained in the gate insulating layer may contain carbon (C). In this case, the carbon (C) content in the gate insulating layer is preferably 15 atomic% or less. If the content of carbon (C) in the gate insulating layer is 15 atomic% or less, the presence of carbon as —CH ₂ or —CH ₃ in the gate insulating layer is suppressed. The hydrogen (H) content is kept low, and the chemical stability in the atmosphere in the gate insulating layer is further increased.

  Note that gallium oxide contained in the gate insulating layer is gallium oxide containing no metal atoms other than gallium (Ga). In particular, in this embodiment, since the gallium oxide included in the gate insulating layer does not include indium (In), which is a rare metal, a transistor is manufactured without using indium (In), thereby reducing the price of the transistor. It can be suppressed.

  The composition in the thickness direction of the gate insulating layer may be uniform. However, if the composition contains Ga and oxygen, the composition has a gradient structure in the thickness direction of the film, or has a multilayer structure. It may be a thing.

  The concentration distribution of oxygen in the thickness direction of the gate insulating layer may decrease toward the supporting base material side that supports the electrode or the like, or may increase toward the supporting base material side.

The content of elements such as gallium (Ga), oxygen (O), and carbon (C) contained in the gate insulating layer is determined by Rutherford backscattering (RBS).
Here, the Rutherford back scattering (RBS) will be described in detail. In RBS, 3S-R10 is used as an accelerator (3SDH Pelletron manufactured by NEC, end station, RBS-400 manufactured by CE & A) and a system, and HYPRA program manufactured by CE & A is used for analysis.
The RBS measurement conditions are as follows.
-He ⁺⁺ ion beam energy: 2.275 eV
Detection angle: Grazing angle 109 ° with respect to 160 ° incident beam
-RBS measurement In measurement, it is measured including the distribution in the thickness direction. Specifically, a He ⁺⁺ ion beam is incident on the sample perpendicularly, the detector is set at a position of 160 ° with respect to the direction of the ion beam, and the back scattered He signal is measured. The composition ratio and the film thickness are determined from the detected energy and intensity of He. In order to improve the accuracy of obtaining the composition ratio and the film thickness, the spectrum may be measured at two detection angles. Accuracy is improved by measuring and cross-checking at two detection angles with different depth resolution and backscattering dynamics.
The number of He atoms back-scattered by the target atom is determined only by three factors: 1) the atomic number of the target atom, 2) the energy of the He atom before scattering, and 3) the scattering angle. The density is assumed by calculation from the measured composition, and this is used to calculate the film thickness. The density error is within 20%.

Further, the hydrogen content in the gate insulating layer is determined by hydrogen forward scattering (HFS). As the HFS, an accelerator (3SDH Pelletron manufactured by NEC, end station, RBS-400 manufactured by CE & A) is used, and 3S-R10 is used as a system. For the analysis, the HYPRA program manufactured by CE & A is used.
The measurement conditions of HFS are as follows.
-He ⁺⁺ ion beam energy: 2.275 eV
Detection angle: Grazing Angle 30 ° with respect to 160 ° incident beam
-HFS measurement The measurement picks up the hydrogen signal scattered in front of the sample by setting the detector at 30 ° and the sample at 75 ° from the normal with respect to the direction of the He ⁺⁺ ion beam. . At this time, the detector is preferably covered with a thin aluminum foil to remove He atoms scattered together with hydrogen. The quantification is performed by comparing the hydrogen counts of the reference sample and the sample to be measured after normalization with the stopping power. As a reference sample, a sample in which H is ion-implanted in Si and muscovite are used. It is known that muscovite has a hydrogen concentration of 6.5 atomic%. Hydrogen (H) adsorbed on the outermost surface is obtained by subtracting the amount of H adsorbed on the clean Si surface.

As a method for measuring the content of each element in the entire gate insulating layer, in addition to the above method, a method of measuring by X-ray photoelectron spectroscopy (XPS) or secondary electron mass spectrometry may be used.
As a method for measuring the hydrogen content in the gate insulating layer, in addition to the above method, the hydrogen content is estimated from the intensity of the peak due to the gallium-hydrogen bond or the peak due to the N—H bond by infrared absorption spectrum measurement. The method of doing is also mentioned.

The crystallinity and non-crystallinity of the gate insulating layer are not particularly limited, and examples thereof include microcrystal, polycrystal, and amorphous, and any of them may be used.
Note that the gate insulating layer may be amorphous including microcrystals, microcrystal including amorphous, or polycrystalline including amorphous from the viewpoint of stability and hardness. However, it is preferably amorphous from the viewpoint of the smoothness and friction of the semiconductor film surface. Crystallinity and non-crystallinity are discriminated based on the presence or absence of a point or a line in a diffraction image obtained by RHEED (reflection high-energy electron diffraction) measurement. Amorphousness is also determined by the absence of a sharp peak specific to the diffraction angle in X-ray diffraction spectrum measurement.

  Regardless of whether the crystallinity and non-crystallinity of the gate insulating layer are microcrystalline, polycrystalline, or amorphous, the gate insulating layer is free from bonding defects, dislocation defects, and grain boundary defects contained in the internal structure. In order to activate, hydrogen or a halogen element may be contained in the gate insulating layer. Hydrogen or a halogen element in the gate insulating layer has a function of being taken into the above-described defect and the like so that the reaction active point disappears and electrical compensation is performed. Therefore, unnecessary carrier generation due to the defect level of the gate insulating layer is suppressed.

<Manufacturing method of gate insulating layer>
Next, a method for manufacturing the gate insulating layer will be described.
For the gate insulating layer, for example, plasma CVD (Chemical Vapor Deposition) method, metal organic vapor phase epitaxy method, molecular beam epitaxy method, vapor deposition, sputtering, and other known vapor deposition methods are used. It is preferable to use a metal organic chemical deposition method.

In this case, the substance containing oxygen is activated by activating means that activates the substance containing oxygen to an energy state or an excited state necessary for the reaction, and the active species and the non-activated gallium (Ga) are used. It is preferable to form a gate insulating layer on a base material by reacting with an organometallic compound containing.
Accordingly, when the base material includes an organic material, for example, when forming a flexible plastic substrate or electrode, the gate insulating layer having the above-described characteristics without causing thermal damage to the base material Is formed. Note that when forming the gate insulating layer, the surface of the base material may be previously cleaned by plasma.

  The gate insulating layer is usually a substance containing oxygen, an organometallic compound containing Ga atoms, or a gas obtained by vaporizing these, into a reaction chamber in a reaction chamber (film formation chamber) in which a substrate is arranged. While supplying each component or a gas containing these components, the reaction is completed while exhausting the gas after the reaction from the reaction chamber. From such a viewpoint, it is preferable to introduce an organometallic compound containing Ga into the downstream side of the activating means for activating the substance containing oxygen. As a result, the oxygen-containing substance activated on the upstream side of the position where the Ga-containing organometallic compound is introduced joins on the downstream side of the activating means, so that the non-activated Ga-containing organometallic compound And a step of reacting the activated oxygen-containing substance.

  In this step, when the base material contains an organic material, for example, when using a PET (polyethylene terephthalate) film substrate on which an ITO (tin-doped indium oxide) electrode is formed, PEDOT (polyethylene terephthalate) and PSS (polystyrene sulfonic acid) In the case of using a substrate on which an electrode including the electrode is formed, the maximum temperature of the surface of the base material (substrate etc.) when forming the gate insulating layer is preferably 100 ° C. or less, and preferably 50 ° C. or less. The closer to normal temperature (25 ° C.), the better. When the maximum temperature of the substrate surface is 100 ° C. or lower, the deformation of the substrate is suppressed, and the physical properties can be kept good by suppressing the decomposition of the organic material contained in the substrate.

Hereinafter, a method for manufacturing a gate insulating layer by a remote plasma organometallic chemical deposition method will be described in detail with reference to FIG. FIG. 4 is a schematic configuration diagram illustrating an example of a film formation apparatus used for forming an electrode, and FIG. 4A is a schematic cross-sectional view of the film formation apparatus viewed from the side, and FIG. These are the A1-A2 sectional view taken on the line in FIG. 4 (A).
In FIG. 4, 10 is a film forming chamber, 11 is an exhaust port, 12 is a substrate rotating unit, 13 is a substrate holder, 14 is a substrate, 15 is a gas introducing unit, 16 is a shower nozzle, 17 is a plasma diffusion unit, and 18 is A high-frequency power supply unit, 19 is a plate electrode, 20 is a gas introduction tube, and 21 is a high-frequency discharge tube unit.

  In the film forming apparatus shown in FIG. 4, an exhaust port 11 connected to a vacuum exhaust device (not shown) is provided at one end of the film forming chamber 10, and the side on which the exhaust port 11 of the film forming chamber 10 is provided. On the opposite side, a plasma generator comprising a high-frequency power supply unit 18, a plate electrode 19, and a high-frequency discharge tube unit 21 is provided.

  This plasma generator is disposed in a high-frequency discharge tube portion 21, a high-frequency discharge tube portion 21, a flat plate electrode 19 provided with a discharge surface on the exhaust port 11 side, and disposed outside the high-frequency discharge tube portion 21. The high-frequency power supply unit 18 is connected to the surface of the electrode 19 opposite to the discharge surface. Note that one end of a gas introduction tube 20 for supplying gas into the high frequency discharge tube portion 21 is connected to the high frequency discharge tube portion 21, and the other end of the gas introduction tube 20 is a first not shown. Connected to the gas supply.

In this embodiment, the plasma generator shown in FIG. 5 may be used instead of the plasma generator provided in the film forming apparatus shown in FIG. FIG. 5 is a schematic configuration diagram showing another example of the plasma generator used in the film forming apparatus shown in FIG. 4, and is a side view of the plasma generator.
In FIG. 5, 22 represents a high frequency coil, 23 represents a quartz tube, and 20 is the same as the gas introduction tube shown in FIG. This plasma generator comprises a quartz tube 23 and a high frequency coil 22 provided along the outer peripheral surface of the quartz tube 23, and one end of the quartz tube 23 is connected to a film forming chamber 10 (not shown in FIG. 5). ing. The other end of the quartz tube 23 is connected to a gas introduction tube 20 for introducing gas into the quartz tube 23.

  As shown in FIG. 4, a rod-shaped shower nozzle 16 parallel to the discharge surface is connected to the discharge surface side of the plate electrode 19, and one end of the shower nozzle 16 is connected to a gas introduction pipe 15. The introduction pipe 15 is connected to a second gas supply source (not shown) provided outside the film forming chamber 10.

  In addition, a substrate rotating unit 12 is provided in the film forming chamber 10, and the substrate holder 13 is placed so that the cylindrical substrate 14 faces the longitudinal direction of the shower nozzle and the axial direction of the substrate 14 in parallel. It is adapted to be attached to the base rotating part 12 via During film formation (formation of the gate insulating layer), the substrate rotating unit 12 rotates, whereby the substrate 14 rotates in the circumferential direction. Examples of the substrate 14 include a substrate on which a gate electrode is formed in advance, or a substrate on which a source electrode, a drain electrode, and a channel layer are formed in advance. Since the base 14 shown in FIG. 4 is a flexible base, the base 14 is installed on the outer peripheral surface of the base holder 13 in a cylindrical shape. However, the base 14 is not limited to this and is, for example, rigid. When the gate insulating layer is formed on the substrate, a substrate holder that fixes the substrate on a flat plate may be used instead of the substrate holder 13. At the time of film formation, the substrate rotating unit 12 rotates, whereby the substrate 14 rotates in the circumferential direction, and a gate insulating layer is formed. Note that in the case where the gate insulating layer has a specific shape, the gate insulating layer may be covered with a mask having an opening having the shape, or may be patterned by etching or the like after the entire surface is formed.

The formation of the gate insulating layer is performed, for example, as follows using the above film forming apparatus.
First, H ₂ gas, He gas, and oxygen gas are introduced into the high-frequency discharge tube 21 from the gas introduction tube 20, and a 13.56 MHz radio wave is supplied from the high-frequency power supply unit 18 to the plate electrode 19. At this time, the plasma diffusion portion 17 is formed so as to spread radially from the discharge surface side of the flat plate electrode 19 to the exhaust port 11 side. Here, the three types of gases introduced from the gas introduction pipe 20 flow from the plate electrode 19 side to the exhaust port 11 side through the film forming chamber 10. The plate electrode 19 may be one in which the electrode is surrounded by a ground shield.

Next, trimethylgallium gas diluted with hydrogen as a carrier gas is introduced into the film forming chamber 10 through the gas inlet tube 15 and the shower nozzle 16 located downstream of the flat plate electrode 19 serving as the activating means. A non-single-crystal film containing gallium (Ga) and oxygen is formed on the surface of the substrate 14.

  When a substrate using an organic material is used as the substrate 14, the surface temperature of the substrate 14 during film formation is preferably 100 ° C. or less, more preferably 80 ° C. or less, and particularly preferably 50 ° C. or less. Even if the temperature of the surface of the substrate 14 is 100 ° C. or less at the beginning of film formation, if the temperature becomes higher than 150 ° C. due to the influence of plasma, the substrate and the organic thin film may be damaged by heat. It is preferable to control the surface temperature of the substrate 14 in consideration of the above.

The surface temperature of the substrate 14 may be controlled by heating and / or cooling means (not shown), or may be left to a natural temperature rise during discharge. When heating the substrate 14, a heater may be installed outside or inside the substrate 14. When cooling the substrate 14, a cooling gas or liquid may be circulated inside the substrate 14.
Further, in order to avoid an increase in the surface temperature of the substrate 14 due to discharge, it is effective to adjust a high-energy gas flow that strikes the surface of the substrate 14. In this case, conditions such as the gas flow rate, discharge output, and pressure are adjusted so as to achieve the required temperature.

  As the gas containing Ga, for example, a gas containing trimethyl gallium, triethyl gallium, or the like is used. Moreover, you may mix 2 or more types of these gas.

  In the case where an organometallic compound containing an oxygen atom is used as a Ga supply material and a GaO film mainly containing Ga and oxygen is formed, it is preferable that active hydrogen exists in the deposition chamber 10. The active hydrogen may be supplied from hydrogen atoms used as a carrier gas or hydrogen atoms contained in an organometallic compound. Further, when a rare gas such as helium or hydrogen is used in combination as a carrier gas, high temperature growth is possible even at a low temperature of 100 ° C. or lower due to the etching effect of the film grown on the surface of the substrate 14 by the rare gas such as helium and hydrogen. An amorphous Ga and oxygen compound with less hydrogen equivalent to the time is formed.

  By the above-described method, activated hydrogen, oxygen, rare gas, and Ga are present in the vicinity of the surface of the substrate 14, and the activated rare gas or hydrogen is a methyl group or ethyl group that constitutes the organometallic compound. It has an effect of desorbing hydrogen of a hydrocarbon group such as a molecule as a molecule. Therefore, the surface of the substrate 14 is a hard film having a low hydrogen content and oxygen and Ga constituting a three-dimensional bond, and a surface layer is formed at a low temperature.

The plasma generating means of the film forming apparatus shown in FIG. 4 uses a high-frequency oscillation device, but is not limited to this. For example, a microwave oscillation device, an electrocyclotron resonance method, or a helicon plasma is used. A type of apparatus may be used. Further, in the case of a high-frequency oscillation device, it may be inductive or capacitive.
Furthermore, two or more of these devices may be used in combination, or two or more of the same types of devices may be used. A high frequency oscillation device is preferable so that the temperature of the surface of the substrate 14 does not increase due to plasma irradiation, but a device for preventing heat irradiation may be provided.

When two or more different plasma generators (plasma generators) are used, it is preferable that discharges occur simultaneously at the same pressure. In addition, a pressure difference may be provided between the discharge area and the film formation area (the portion where the base is installed). These apparatuses may be arranged in series with respect to the gas flow formed in the film forming apparatus from the part where the gas is introduced to the part where the gas is discharged. You may arrange | position so that it may oppose.
For example, when two kinds of plasma generating means are installed in series with respect to the gas flow, the film forming apparatus shown in FIG. 2 is used as a plasma generator. In this case, a high frequency voltage is applied to the shower nozzle 16 through the gas introduction tube 15 to cause discharge in the film forming chamber 10 using the shower nozzle 16 as an electrode. Alternatively, instead of using the shower nozzle 16 as an electrode, a cylindrical electrode is provided at a position sandwiched between the substrate 14 in the film forming chamber 10 and the flat plate electrode 19 that is a plasma generation region. The discharge may be caused to occur in the film forming chamber 10 by using it.

  Also, when two different types of plasma generators are used under the same pressure, for example, when using a microwave oscillator and a high-frequency oscillator, the excitation energy of the excited species changes greatly, which is effective in controlling the film quality. . Moreover, you may perform discharge at atmospheric pressure. When discharging at atmospheric pressure, it is desirable to use He as a carrier gas.

<Channel layer>
The channel layer is a layer containing gallium oxide.

When the number of gallium (Ga) and oxygen (O) atoms in the gallium oxide contained in the channel layer is S _Ga and S _O , the value of S _O / S _{Ga is} the value of the I _O / I _Ga . It is preferable to be smaller than (gallium oxide composition ratio in the gate insulating layer). Thereby, the functions of the gate insulating layer and the channel layer are ensured.

The specific value of S 2 _{O 3} / S _Ga is preferably 1.1 or more and 1.5 or less, more preferably 1.1 or more and 1.4 or less, and further preferably 1.1 or more and 1.3 or less. By the value of S O _/ S _Ga is 1.1 or more, excellent in oxidation resistance in an oxygen and oxidizing atmosphere in the air over time property changes (changes in physical properties in electrical properties and mechanical properties) Becomes smaller. Moreover, compared with the case where the value of S 2 _{O 3} / S _Ga is less than 1.1, the properties of metallic gallium are imparted and softening is suppressed.

  The content of oxygen (O) contained in the gallium oxide in the channel layer is preferably 30 atomic% or less. When the content of oxygen (O) is 30 atomic% or less, deterioration of transistor characteristics due to excessively high resistance of the channel layer is suppressed, and the device operates normally.

The gallium oxide contained in the channel layer is preferably a hydrogen-containing gallium oxide containing hydrogen (H) as the third element in addition to gallium (Ga) and oxygen (O). When gallium oxide contained in the channel layer contains hydrogen (H), hydrogen compensates for dangling bonds and structural defects of gallium oxide, thereby improving electrical stability, chemical stability, and mechanical stability. In addition, high hardness and high transparency can be obtained, and high water repellency and a low friction coefficient on the surface of the gate insulating layer can be obtained. A preferable amount of hydrogen (H) contained in the gallium oxide in the channel layer is the same as that in the gallium oxide in the gate insulating layer.
Further, gallium oxide contained in the channel layer may contain carbon (C). The preferable amount of carbon (C) contained in the gallium oxide in the channel layer is the same as that in the gallium oxide in the gate insulating layer.

  The gallium oxide contained in the channel layer is gallium oxide containing no metal other than gallium (Ga), as in the case of the gate insulating layer. In particular, in this embodiment, since the gallium oxide contained in the channel layer does not contain indium (In) which is a rare metal, the transistor price is reduced by manufacturing the transistor without using indium (In). It is done.

  Since other matters such as the composition of the channel layer, the element content measurement method, and the crystallinity are the same as those in the case of the gate insulating layer, description thereof is omitted.

<Manufacturing method of channel layer>
The method for manufacturing the channel layer is the same as the method for manufacturing the gate insulating layer, and a description thereof will be omitted.
Note that when a channel layer is formed by a remote plasma organometallic chemical deposition method using the film formation apparatus illustrated in FIG. 4, the substrate 14 includes a substrate on which a gate electrode and a gate insulating layer are formed in advance, a gate electrode, Examples include a substrate on which a gate insulating layer and a source electrode are formed, and a substrate on which a source electrode and a drain electrode are formed in advance.

<Electrode>
The electrode material used for the source electrode, the drain electrode, and the gate electrode is not particularly limited, and specifically, for example, a metal, a metal oxide, a conductive polymer, or the like is used.
Examples of the metal include magnesium, aluminum, gold, silver, copper, chromium, tantalum, indium, palladium, lithium, calcium, and alloys thereof.
Examples of the metal oxide include metal oxide films such as lithium oxide, magnesium oxide, aluminum oxide, indium tin oxide (ITO), tin oxide (NESA), indium oxide, zinc oxide, and indium zinc oxide.
Examples of the conductive polymer include polyaniline, polythiophene, polythiophene derivatives, polypyrrole, polypyridine, and a complex of polyethylenedioxythiophene and polystyrene sulfonic acid.

  The method for forming the electrode is not particularly limited. For example, vacuum deposition, sputtering, CVD, casting, spin coating, dip coating, LB, ink jet, bar coating, nanoimprinting Law. More specifically, for example, a method of forming a thin film produced from the above electrode material using a known thin film forming method such as vapor deposition or sputtering, using a known photolithography method or lift-off method, ink jet For example, a method of etching into a desired pattern (electrode shape) using a resist, a method of directly transferring an electrode material such as aluminum, and the like. Moreover, when using a conductive polymer as an electrode material, the method of dissolving this in a solvent and patterning with an inkjet etc. is mentioned, for example.

<Board>
As the substrate, silicon single crystal or glass doped with a high concentration of phosphorus, etc., polycarbonate resin, polyester resin, methacrylic resin, acrylic resin, polyvinyl chloride resin, cellulose resin, urethane resin, epoxy resin, police styrene resin, polyvinyl acetate Examples thereof include, but are not limited to, resins, styrene butadiene copolymers, vinyl chloride-acrylonitrile copolymers, vinyl chloride-vinyl acetate-maleic anhydride copolymers, plastic substrates such as silicone resins, and the like.

In particular, when the field effect transistor of this embodiment is used in an electronic circuit used in an electronic device such as electronic paper, digital paper, or portable electronic device that requires flexibility, a flexible substrate should be used as the substrate. Is desirable. Specifically, by using a substrate having a flexural modulus of 1000 MPa or more, more preferably 5000 MPa or more as the substrate, it can be applied to a flexible display element drive circuit or electronic circuit.
An organic material can be used as a material for the flexible substrate. As described above, by forming the gate insulating layer and the channel layer at 100 ° C. or lower, the field effect type can be achieved without damaging the substrate. A transistor is fabricated.

As described above, in the field effect transistor of this embodiment, since the gate insulating layer and the channel layer are both gallium oxide, the interface between the gate insulating layer and the channel layer is good. / Off ratio is improved.
The reason is not clear, but is considered as follows.

For example, when the gate insulating layer is formed using Y ₂ O ₃ or HfO ₂ having a higher dielectric constant than SiO ₂ , SiN _x or the like conventionally used as a material for the gate insulating layer, the gate insulating layer is crystallized. May be grainy. The phenomenon that the gate insulating layer becomes granular occurs not only when the gate insulating layer is formed at a high temperature (for example, a temperature higher than 100 ° C.) but also when the gate insulating layer is formed at a low temperature (for example, 100 ° C. or lower). sell. Therefore, when such a material is used, it is very difficult to form a good interface between the gate insulating layer and the channel layer.

  On the other hand, in the present embodiment, since the gate insulating layer is gallium oxide as described above, the phenomenon that the gate insulating layer becomes granular is unlikely to occur. In this embodiment, as described above, gallium oxide is also used for the channel layer, the constituent elements of the gate insulating layer and the constituent elements of the channel layer are the same, and only the composition ratio is different. In comparison, it is considered that a good interface is formed.

  In particular, in this embodiment, it is considered that by forming the gate insulating layer and the channel layer continuously, mixing of impurities and the like at the interface between the gate insulating layer and the channel layer is suppressed, and a better interface can be obtained. Specifically, for example, using the film forming apparatus shown in FIG. 4, a substrate on which a gate electrode is formed in advance is used as the base 14, a gate insulating layer is formed, and then the base 14 is moved out of the film forming chamber 10. A method of forming a channel layer without taking it out is mentioned.

  In the present embodiment, the channel layer is gallium oxide as described above and does not use indium (In), which is feared for resource depletion.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, these examples do not limit the present invention.

Example 1
<Fabrication of field effect transistor>
A PET film in which an ITO film having a thickness of 0.2 μm was formed on one side of a 50 μm-thick PET film (manufactured by Toray Industries Inc., Lumirror) was used as the substrate. The gate insulating layer was formed on the substrate using a film forming apparatus having the configuration shown in FIG.

First, the substrate was placed and fixed on the substrate holder 13 in the film forming chamber 10 of the film forming apparatus.
Next, the inside of the film forming chamber 10 was evacuated through the exhaust port 11 until the pressure became 0.1 Pa. Next, 450 sccm (hydrogen gas 200 sccm, He gas 150 sccm, He gas 150 sccm, He gas, hydrogen gas, and oxygen gas mixed from the gas introduction tube 20 into the high-frequency discharge tube portion 21 provided with the electrode 19 having a diameter of 50 mm. 5% He diluted oxygen gas (100 sccm) is introduced, and a radio wave of 13.56 MHz is set to an output of 80 W by the high frequency power supply unit 18 and a matching circuit (not shown in FIG. 4), matching is performed by the tuner, and discharge from the electrode 19 went. The reflected wave at this time was 0 W.

  Next, a mixed gas containing trimethylgallium gas using hydrogen gas as a carrier gas is supplied from the shower nozzle 16 to the plasma diffusion portion 17 in the film forming chamber 10 through the gas introduction pipe 15 at a flow rate of 4 sccm. Introduced to be. Further, oxygen gas using He gas as a carrier gas was introduced at 1.5 sccm. At this time, the reaction pressure in the film forming chamber 10 measured with a Baratron vacuum gauge was 40 Pa. A GaO film containing hydrogen having a thickness of 0.13 μm was formed by forming a film for 35 minutes under these conditions.

Subsequently, a channel layer (semiconductor film) was formed on the gate insulating layer. As in the case of the gate insulating layer, it was fabricated by changing only the flow rate of the raw material as follows.
Specifically, 450 sccm (hydrogen gas 200 sccm, He gas 150 sccm, 5% He diluted oxygen gas 100 sccm) is introduced into the high-frequency discharge tube portion 21, and the high-frequency power supply unit 18 and a matching circuit (not shown in FIG. 4) A 13.56 MHz radio wave was set to an output of 80 W, matching was performed with a tuner, and discharge was performed from the electrode 19. The reflected wave at this time was 0 W.

  Next, a mixed gas containing trimethylgallium gas using hydrogen gas as a carrier gas is supplied from the shower nozzle 16 to the plasma diffusion portion 17 in the film forming chamber 10 through the gas introduction pipe 15 at a flow rate of 4 sccm. Introduced to be. Further, oxygen gas using He gas as a carrier gas was introduced at 0.5 sccm. At this time, the reaction pressure in the film forming chamber 10 measured with a Baratron vacuum gauge was 40 Pa. By depositing for 20 minutes, a GaO film containing 0.05 μm of hydrogen was formed on the gate insulating layer.

Note that heating was not performed when the gate insulating layer and the channel layer were formed. Moreover, when the color of the thermotape stuck on Al pipe was confirmed after film-forming, it was 40 degreeC. That is, it means that the maximum temperature of the substrate during film formation is 40 ° C.
Thereafter, the source and drain electrodes were made of gold on the semiconductor film by EB vapor deposition (Showa Vacuum EB vapor deposition apparatus) using a metal mask. The electrode thickness at that time is 0.1 μm. The channel length and channel width were 50 μm and 500 μm, respectively.

<Analysis and evaluation of gate insulating layer and channel layer>
When the gate insulating layer and the channel layer were formed on the PET film, they were simultaneously formed on the Si substrate to form a gate insulating layer sample film and a channel layer sample film. When infrared absorption spectrum measurement was performed on the gate insulating layer sample film and the channel layer sample film, peaks caused by minute Ga—H bonds and Ga—O bonds were confirmed. From these facts, it was found that the gate insulating layer and the channel layer contain gallium, oxygen, and hydrogen.
In the diffraction images obtained by the RHEED (reflection high-energy electron diffraction) measurement of the gate insulating layer sample film and the channel layer sample film, only the halo pattern was seen, indicating that the film was an amorphous film.

The composition of the gate insulating layer sample film formed on the Si substrate was measured using Rutherford back scattering and hydrogen forward scattering. As a result, it was found that gallium, oxygen, and hydrogen were 33.3, 50.0, and 16.7 atomic%, respectively. The atomic ratio between gallium and oxygen is 1: 1.5. That is, the value of I _O / I _Ga is 1.5. Moreover, oxygen was distributed throughout the film, and carbon was not detected. As a result, it was found that the film formed on the PET film was an amorphous film containing hydrogen.
The channel layer sample film fabricated on the Si substrate was the same, and the ratio of each element (gallium, oxygen, and hydrogen) was found to be 36.3, 43.6, and 17.6 atomic%. The remaining 2.5 atomic% was carbon. The atomic ratio between gallium and oxygen is 1: 1.2. That is, the value of S _O / S _Ga is 1.2.

<Evaluation of transistor characteristics>
Using the semiconductor parameter analyzer (manufactured by Agilent, HP4156B) and a prober, the output and transfer characteristics of the transistor produced above were measured.
FIG. 6 shows the results of I _SD -V _SD characteristics obtained by measuring the correlation between the source-drain electrode current I _SD and the source-drain electrode voltage V _SD when the gate voltage V _G is changed. In Figure 6, ●, ■, ◆, ▲, and ▼, respectively the gate voltage _{V G} is _I SD _{-V SD} characteristics observed when the 0V, 5V, 10V, 15V and 20V,.
6, according to V _G is changed, because it is greatly changed even I _SD, it can be seen that work well as a field-effect transistor.

Further, the On / Off ratio and the FET mobility were obtained from the graph shown in FIG. 6 as follows. Specifically, the On / Off ratio indicates that when a voltage of 10 V is applied between the source and the drain, the source-drain current I _off when the gate voltage is 0 V, and the source when the gate voltage is 20 V. a drain current _{I on,} was determined from the ratio _I on _{/ I off} of.

The FET mobility μ was obtained from the following equation (1).
_{μ = 2L · I SD-sat} / {W · C · (V G -V th) 2} Equation (1)
Here, L is the channel length, W is the channel width, I _SD-sat is the saturation current value, C is the capacitance, V _G is the gate voltage, and V _th is the threshold voltage. The threshold voltage V _th, the transfer characteristic (constant source of transistor - measuring the current I _SD drain electrodes - source when while applying a voltage V _SD between the drain electrode, changing the gate voltage V _G in to _I SD -V _G characteristics _obtained), a threshold voltage at the gate voltage when _{I SD} is 0 (a), in the present embodiment is _V th = 0 _(V).

Incidentally, the saturation current value _{I SD-sat} is a current value when saturated, specifically, in FIG. 6, for example, the _{I SD-sat} when _{V G} is 5V 1.2μA, V The I _SD-sat when _G is 20 V is 5.7 μA.

Capacitance C is the capacitance of the gate insulating film, and was obtained from the following equation (2) using channel length L, channel width W, gate insulating film thickness d, and relative dielectric constant ε (ε = 10).
C = L · W · ε · ε ₀ / d Equation (2)
Wherein (2), ε ₀ is the permittivity of vacuum.

  In all Examples and Comparative Examples, the ON-OFF ratio and the FET mobility were obtained as described above. The results are shown in Table 1. Since the On / Off ratio is high and the FET mobility is high, it is presumed that a good interface is formed between the gate insulating layer and the channel layer.

(Example 2)
<Fabrication of field effect transistor>
When the gate insulating layer was formed, hydrogen gas was introduced as a carrier gas and a mixed gas containing trimethylgallium gas was introduced at a flow rate of 4 sccm, and oxygen gas using He gas as a carrier gas was introduced at 0.8 sccm. A field effect transistor was fabricated in the same manner as in Example 1 except for the above.

<Analysis and evaluation of gate insulating layer and channel layer>
As a result of evaluating the gate insulating layer in the same manner as in Example 1, it was found that gallium, oxygen, and hydrogen were 36.2, 47.0, and 16.8 atomic%, respectively. The atomic ratio between gallium and oxygen is 1: 1.3. That is, the value of I _O / I _Ga is 1.3. Moreover, oxygen was distributed throughout the film, and carbon was not detected. As a result, it was found that the film formed on the PET film was an amorphous film containing hydrogen.
The channel layer is the same as in Example 1, and the ratio of gallium to oxygen is 1: 1.2. That is, the value of S _O / S _Ga is 1.2.

<Evaluation of transistor characteristics>
As in Example 1, output and transfer characteristics were measured. The On / Off ratio and FET mobility are summarized in Table 1. Although the characteristics were inferior to those of Example 1, it was shown that they were operating as transistors.

Example 3
<Fabrication of field effect transistor>
In addition to introducing a mixed gas containing trimethylgallium gas using hydrogen gas as a carrier gas when producing a channel layer to a flow rate of 4 sccm, and further introducing oxygen gas using He gas as a carrier gas at 0.3 sccm Produced a field effect transistor in the same manner as in Example 1.

<Analysis and evaluation of gate insulating layer and channel layer>
As a result of evaluating the gate insulating layer in the same manner as in Example 1, the atomic ratio of gallium to oxygen was 1: 1.5. That is, the value of I _O / I _Ga is 1.5.
On the other hand, the channel layer was found to contain 36.8, 40.5, and 22.7 atomic% of gallium, oxygen, and hydrogen, respectively. The atomic ratio between gallium and oxygen is 1: 1.1. That is, the value of S _O / S _Ga is 1.1. Oxygen was distributed throughout the film, and no carbon was detected. As a result, it was found that the film formed on the PET film was an amorphous film containing hydrogen.

<Evaluation of transistor characteristics>
As in Example 1, output and transfer characteristics were measured. The On / Off ratio and FET mobility are summarized in Table 1. Although the characteristics were inferior to those of Example 1, it was shown that they were operating as transistors.

Example 4
<Fabrication of field effect transistor>
Introduced so that the flow rate of a mixed gas containing trimethylgallium gas using hydrogen gas as a carrier gas when forming the channel layer is 4 sccm, and oxygen gas using He gas as a carrier gas is introduced at 1.0 sccm Produced a field effect transistor in the same manner as in Example 1.

<Analysis and evaluation of gate insulating layer and channel layer>
As a result of evaluating the gate insulating layer in the same manner as in Example 1, the atomic ratio of gallium to oxygen was 1: 1.5. That is, the value of I _O / I _Ga is 1.5.
On the other hand, the channel layer was found to contain 35.0, 47.0, and 18.0 atomic% of gallium, oxygen, and hydrogen, respectively. The atomic ratio between gallium and oxygen is 1: 1.3. That is, the value of S _O / S _Ga is 1.3. Oxygen was distributed throughout the film, and no carbon was detected. As a result, it was found that the film formed on the PET film was an amorphous film containing hydrogen.

<Evaluation of transistor characteristics>
As in Example 1, output and transfer characteristics were measured. The On / Off ratio and FET mobility are summarized in Table 1. Since the resistance of the channel layer is very high, it is difficult for current to flow, and although the characteristics are inferior to those of Example 1, it is shown that the transistor operates as a transistor.

(Example 5)
<Fabrication of field effect transistor>
Introduced so that the flow rate of the mixed gas containing trimethylgallium gas using hydrogen gas as a carrier gas when producing the channel layer is 4 sccm, and further introducing oxygen gas using He gas as a carrier gas at 0.2 sccm Produced a field effect transistor in the same manner as in Example 1.

<Analysis and evaluation of gate insulating layer and channel layer>
As a result of evaluating the gate insulating layer in the same manner as in Example 1, the atomic ratio of gallium to oxygen was 1: 1.5. That is, the value of I _O / I _Ga is 1.5.
On the other hand, the channel layer was found to contain 39.7, 40.2, and 20.1 atomic% of gallium, oxygen, and hydrogen, respectively. The atomic ratio between gallium and oxygen is 1: 1.0. That is, the value of S _O / S _Ga is 1.0. Oxygen was distributed throughout the film, and no carbon was detected. As a result, it was found that the film formed on the PET film was an amorphous film containing hydrogen.

<Evaluation of transistor characteristics>
As in Example 1, output and transfer characteristics were measured. The On / Off ratio and FET mobility are summarized in Table 1. Although the characteristics were inferior to those of Example 1 (that is, the value of the On / Off ratio was small because the resistance of the semiconductor film of the channel layer was very small), it was shown that it was operating as a transistor.

(Comparative Example 1)
<Fabrication of field effect transistor>
As a gate electrode, 0.01 μm of Ti and 0.1 μm of Au were deposited on a 3-inch silicon wafer by EB deposition (EB deposition apparatus manufactured by Showa Vacuum). Furthermore, hafnium oxide was vapor-deposited as a gate insulating film by EB vapor deposition in the same manner. Zinc oxide was also deposited on the substrate by 0.1 μm by EB vapor deposition. Thereafter, as in Example 1, the source and drain electrodes were made of gold on the semiconductor film using a metal mask. The electrode thickness at that time is 0.1 μm. The channel length and channel width were 50 μm and 500 μm, respectively.

<Evaluation of transistor characteristics>
As in Example 1, output and transfer characteristics were measured. The On / Off ratio and FET mobility are summarized in Table 1. It can be seen that both the On / Off ratio and the FET mobility are low as compared with Example 1 to Example 5. This is probably because the interface between hafnium oxide and zinc oxide is not good.

1: Substrate 2: Source electrode 3: Drain electrode 4: Channel layer 5: Gate electrode 6: Gate insulating layer

Claims (5)

A substrate,
A gate electrode, a gate insulating layer, a channel layer, a source electrode, and a drain electrode on the substrate;
A field effect transistor in which the gate insulating layer and the channel layer contain gallium oxide. When the in the gallium oxide contained in the gate insulating layer, the atomic number _{I Ga} gallium (Ga), the number of atoms of oxygen (O) was _{I O,} the value of I O _{/ I Ga} is 1.3 or more 1 The field effect transistor according to claim 1, which is 0.5 or less. In the gallium oxide contained in the gate insulating layer, the number of gallium (Ga) atoms is I _Ga and the number of oxygen (O) atoms is I 2 _O, and the gallium oxide in the gallium oxide contained in the channel layer. The value of S _O / S _Ga is smaller than the value of I _O / I _Ga , where S _{Ga is} the number of atoms of S _Ga and the number of atoms of oxygen (O) is S 2 _O. 3. Field effect transistor.   The field effect transistor according to claim 1, wherein the substrate has flexibility.   The gate insulating layer and the channel layer are formed through a step of reacting an organic gallium compound and activated oxygen at 100 ° C. or lower in an atmosphere containing at least one of oxygen and hydrogen. The field effect transistor according to claim 1.

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