JP6252903B2 - Thin film transistor and manufacturing method thereof - Google Patents

Description

  The present invention relates to a thin film transistor and a method for manufacturing the same.

  Thin film transistors (TFTs) are widely used as switching elements for liquid crystal displays and organic electroluminescence (EL) displays that employ an active matrix drive system.

  As the TFT, a semiconductor layer (channel layer) using amorphous silicon or polysilicon is known. In recent years, in order to improve various characteristics, an In (indium) -Zn (zinc) -O (IZO) system, an In-Ga (gallium) -Zn-O (IGZO) system, or Sn (tin) is used for a semiconductor layer. A TFT using a -Zn-O (SZO) -based metal oxide has been studied (for example, see Patent Document 1).

  Such a thin film transistor has n-type conductivity and exhibits higher channel mobility than amorphous silicon or polysilicon, and thus can be suitably used as a switching element for a high-definition display or a large-screen display. Although there are various theories about the mechanism of n-type conduction, it is said that oxygen vacancies are mainly introduced by desorption of oxygen to the indium oxide structure, and as a result, charge is generated to serve as a semiconductor layer. In addition, since a semiconductor layer made of a metal oxide does not exhibit p-type conduction in principle and has a very small off current, the use of a thin film transistor has an advantage that power consumption can be reduced.

  However, IZO, IGZO, and SZO metal oxides, which are metal oxides described in the above-mentioned patent documents, tend to react with the water in the Zn, Ga, and Sn contained therein. As a physical structure, unstable suboxide is formed, and the amount of oxygen vacancies cannot be adjusted, resulting in a problem of greatly degrading transistor characteristics.

  In order to solve these problems, Patent Document 2 discloses, as a metal oxide, a substance containing at least one element of zinc and tin, yttrium, niobium, tantalum, hafnium, lanthanum, scandium, vanadium, titanium, magnesium. It is disclosed that at least one of aluminum, gallium and silicon is used. In addition, in order to suppress fluctuations in threshold voltage caused by the destruction effect due to plasma damage and the increase in carriers due to radiation effects in the thin film transistor manufacturing stage, at least one of gallium, indium, tin, zirconium, hafnium, and vanadium is added to zinc oxide. It is disclosed to dope one ion (Patent Document 3). Furthermore, electrical characteristics of an oxide film transistor of an IZO metal oxide doped with tantalum have been reported (Non-Patent Document 1). However, in any of the above cases, since zinc is contained as a main element, there is a serious problem that a considerable limitation is imposed on the process in order to suppress the formation of suboxides in the thin film transistor manufacturing stage.

  Furthermore, there is a report that indium oxide doped with any one of tin, titanium, and tungsten is used instead of IZO or IGZO as a metal oxide (Patent Document 4). However, in the oxide film transistor using indium oxide doped with either titanium or tungsten described in the above document as the metal oxide, the amount of oxygen vacancies introduced into the main structure indium oxide is adjusted at the metal oxide production stage. There is a big problem that the manufacturing process is limited because it is very difficult to do.

  The inventors of the present invention have stated that the energy of separation of oxygen in the metal (Me) -O bond or non-metal-O bond to the first metal oxide such as indium oxide is 200 kJ / mol than the oxygen separation energy of the first metal oxide. A thin film transistor in which the amount of oxygen vacancies in the above problem was controlled by adding a large oxide as described above and a method for manufacturing the same were filed (Japanese Patent Application No. 2013-099284). However, in order to satisfy other various requirements while solving the above-mentioned problem, by finding a means for solving the above-mentioned problem other than the conditions described in the above-mentioned prior patent application, It remains desirable to have as much design freedom as possible.

  An object of the present invention is to provide a thin film transistor and a method for manufacturing the same that solve the above-mentioned problems under composition conditions other than those shown in the above-mentioned prior patent application.

According to one aspect of the present invention, a source electrode and a drain electrode, a semiconductor layer provided in contact with the source electrode and the drain electrode, and a channel between the source electrode and the drain electrode are provided. A gate electrode; and an insulator layer provided between the gate electrode and the semiconductor layer, wherein the semiconductor layer has tin oxide, an oxygen separation energy greater than that of tin oxide, and oxygen of the tin oxide. It is a composite metal oxide to which a metal oxide having a difference from the separation energy of less than 200 kJ / mol is added, and the semiconductor layer has an additional oxide whose oxygen dissociation energy is smaller than that of tin oxide than the metal oxide. A thin film transistor containing only a small amount is provided.
Also, the content of said additional oxide of the semiconductor layer may be 20 wt% or less.
The content of the additional oxide in the semiconductor layer may be 4% by weight or less.
The semiconductor layer may be amorphous.
The semiconductor layer may have a thickness of 5 nm to 20 nm.
The additional oxide may be at least one oxide selected from the group consisting of lead, palladium, platinum, sulfur, antimony, strontium, thallium, and ytterbium.
The metal oxide may be at least one oxide selected from the group consisting of samarium, tungsten, neodymium, and gadolinium .
Also, the content of the metal oxide of the semiconductor layer may be less than 50 wt% greater than 0.
Also, the content of the metal oxide before Symbol semiconductor layer may be 5% by weight or less.
According to another aspect of the present invention, there is provided a method for producing any one of the above thin film transistors, wherein the semiconductor layer is formed at 10 ° C. or more and 500 ° C. or less.
Here, you may form the said semiconductor layer at 10 degreeC or more and 300 degrees C or less.

According to the present invention, when a tin oxide having a large oxygen separation energy of 528 kJ / mol is used as a metal oxide capable of generating electron carriers by introducing oxygen defects, the metal oxide added thereto is A composite metal oxide in which the oxygen separation energy of the metal oxide to be added is larger than the oxygen separation energy of the tin oxide and the difference from the oxygen separation energy of the tin oxide is less than 200 kJ / mol. By using the semiconductor layer, a thin film transistor with excellent transistor characteristics can be provided.
Further, according to the present invention, in addition to the metal oxide to be added, a composite metal in which an oxide having an oxygen separation energy smaller than that of tin oxide is added in a smaller amount than the metal oxide to be added. By using an oxide semiconductor layer, a thin film transistor with excellent transistor characteristics can be provided.

1 is a schematic cross-sectional view of a thin film transistor according to a first embodiment of the present invention. FIG. 6 is a schematic cross-sectional view of another thin film transistor according to the second embodiment of the present invention. 1 is a schematic cross-sectional view of a thin film transistor according to an embodiment of the present invention. FIG. 5 is a graph showing Id-Vg characteristics of the thin film transistor of the first embodiment of the present invention. It shows the first of the two O _{2 /} the sputtering deposition of the semiconductor material (O 2 + _Ar) ratio and conductive relation embodiment of the present invention. The figure which shows the X-ray-diffraction pattern for confirming that the semiconductor film used by the 2nd Example of this invention is amorphous. The figure which shows the Id-Vd characteristic of the thin-film transistor of the 2nd Example of this invention.

  Hereinafter, a thin film transistor and a method of manufacturing the thin film transistor according to an embodiment of the present invention will be described with reference to the drawings. In all the drawings below, the dimensions and ratios of the constituent elements are appropriately changed in order to make the drawings easy to see.

  In the present invention, when tin oxide having a large oxygen release energy of 528 kJ / mol is used as an oxide for generating an electron carrier, the oxygen release energy of the metal oxide to be added is higher than the oxygen release energy of tin oxide. Based on the new knowledge of the present inventors that the amount of oxygen deficiency in the above problem can be controlled by making the difference between the oxygen separation energy of tin oxide large and less than 200 kJ / mol. A thin film transistor of one embodiment and a method for manufacturing the same are provided.

  In addition to the above metal oxides, the present inventors further add an additional oxide whose oxygen separation energy is smaller than that of tin oxide, and the addition amount is less than the addition amount of the above metal oxide. The present inventors have found that the amount of oxygen vacancies can be controlled and the amorphous stable formation temperature range can be expanded. The present invention also provides a thin film transistor and a manufacturing method thereof according to the second embodiment based on this finding.

[Structure of thin film transistor]
The thin film transistor of the first embodiment is provided corresponding to a source electrode and a drain electrode, a semiconductor layer provided in contact with the source electrode and the drain electrode, and a channel between the source electrode and the drain electrode. A gate electrode, and an insulator layer provided between the gate electrode and the semiconductor layer, wherein the semiconductor layer is tin oxide, and the oxygen separation energy of the tin oxide is greater than the oxygen separation energy of the tin oxide, It is a composite metal oxide to which a metal oxide having a difference in oxygen separation energy of tin oxide of less than 200 kJ / mol is added.

  Further, in the thin film transistor of the second embodiment, the semiconductor layer of the thin film transistor of the first embodiment further includes an additional oxidation in which the oxygen separation energy is smaller than that of tin oxide and the addition amount is smaller than that of the above metal oxide. It is a composite metal oxide to which a product is added.

  The thin film transistor manufacturing method of the present embodiment includes a step of forming the semiconductor layer at 10 ° C. or higher and 500 ° C. or lower when manufacturing the thin film transistor.

  FIG. 1 is a schematic cross-sectional view of a thin film transistor 1 according to the first embodiment. As the substrate 2, a substrate formed of a known forming material can be used, and any of those having optical transparency and those having no optical transparency can be used. For example, an inorganic substrate made of alkali silicate glass, quartz glass, silicon nitride, or the like; a silicon substrate; a metal substrate whose surface is insulated; acrylic resin, polycarbonate resin, PET (polyethylene terephthalate), or PBT (polybutylene) Various substrates such as a resin substrate made of a polyester resin such as terephthalate) or a paper substrate can be used. Further, the substrate may be a composite material formed by combining a plurality of these materials. The thickness of the substrate 2 can be appropriately set according to the design.

  The thin film transistor 1 is a so-called bottom gate type transistor. The thin film transistor 1 includes a gate electrode 3 provided on a substrate 2, an insulator layer 4 provided to cover the gate electrode 3, a semiconductor layer 5 provided on the upper surface of the insulator layer 4, It has a source electrode 8 and a drain electrode 9 provided in contact with the semiconductor layer 5 on the upper surface. The gate electrode 3 is provided corresponding to the channel region of the semiconductor layer 5 (at a position overlapping the channel region in a plan view). The semiconductor layer 5 is composed of a composite metal oxide obtained by adding a metal oxide 7 to tin oxide 6. As a matter of course, the semiconductor layer may contain components other than the metal oxide 7 and inevitable impurities as long as the adverse effects of the present invention are not adversely affected. The same applies to the case of adding an oxide of a non-metallic element described in other embodiments described below. In FIG. 1, for convenience of illustration, the semiconductor layer 5 (composite metal oxide) can be seen as if particles of the metal oxide 7 are scattered in the tin oxide 6. Although drawn, it should be noted that the metal oxide is actually uniformly added to the tin oxide, that is, doped, so that the composite metal oxide becomes a uniform material.

  As the gate electrode 3, the source electrode 8, and the drain electrode 9, those formed of a generally known material can be used. Examples of the material for forming these electrodes include aluminum (Al), gold (Au), silver (Ag), copper (Cu), nickel (Ni), molybdenum (Mo), tantalum (Ta), and tungsten (W). Examples thereof include metal materials such as these, alloys thereof, and conductive oxides such as indium tin oxide (ITO) and zinc oxide (ZnO). Moreover, these electrodes may form the laminated structure of two or more layers, for example by plating the surface with a metal material.

  The gate electrode 3, the source electrode 8, and the drain electrode 9 may be formed of the same forming material or may be formed of different forming materials. Since manufacture becomes easy, it is preferable that the source electrode 8 and the drain electrode 9 are the same formation material.

If the insulator layer 4 has insulating properties and can electrically insulate between the gate electrode 3 and the source electrode 8 and the drain electrode 9, either an inorganic material or an organic material is used. It may be formed. Examples of the inorganic material include normally known insulating oxides such as SiO ₂ , SiN _x , SiON, Al ₂ O ₃ , and HfO ₂ , nitrides, and oxynitrides. Examples of the organic material include acrylic resin, epoxy resin, silicon resin, and fluorine resin. The organic material is preferably a photocurable resin material because it is easy to manufacture and process.

  The semiconductor layer 5 is obtained by adding, to tin oxide, a metal oxide in which the dissociation energy of oxygen is larger than the separation energy of oxygen in tin oxide and the difference in separation energy between the two is smaller than 200 kJ / mol.

In the present invention, tin oxide (SnO ₂ ) is used as the first metal oxide in the above-mentioned prior application of the present inventors. However, since the oxygen separation energy of tin oxide is as small as 528 kJ / mol, oxygen is easily generated from tin oxide. It is easy to generate oxygen deficiency. However, if the amount of oxygen vacancies becomes too large, it changes from semiconducting properties to metallic properties, making it unsuitable as a semiconductor layer. As a result of repeated studies to solve this problem, the inventors of the present application added a metal oxide having an oxygen separation energy larger than that of tin oxide in order to control the oxygen deficiency of tin oxide. I found out that I should do it. Specific examples of the metal oxide that can be added include samarium oxide having an oxygen separation energy of 573 kJ / mol, tungsten oxide of 720 kJ / mol, neodymium oxide of 703 kJ / mol, and gadolinium oxide of 715 KJ / mol.

  In addition, the content of the metal oxide added to make tin oxide a semiconductor layer having an appropriate amount of oxygen vacancies is preferably in the range of greater than 0 to 50% by weight. In particular, when the content of the metal oxide added to the tin oxide is in the range of more than 0 to 5% by weight or less, the semiconductor layer can be manufactured at a low temperature of 300 ° C. or less.

  In-Zn-O-based and In-Ga-Zn-O-based metal oxides tend to be polycrystalline when a semiconductor layer is formed. Therefore, in a generally known thin film transistor, the surface of the semiconductor layer does not become flat due to crystal grains contained in the semiconductor layer. In addition, the normally known semiconductor layer of an oxide film transistor has a reduced electrical conductivity in the plane direction due to such crystal grains. Therefore, in order to obtain planarization of the surface of the semiconductor layer and high electrical conductivity, the semiconductor layer preferably has an amorphous structure.

  The thickness of the semiconductor layer 5 is more preferably in the range of 5 nm or more and 20 nm or less. In the present embodiment, the thickness of the semiconductor layer 5 is measured by using a crystal oscillation type film thickness meter disposed mainly for film thickness calibration in the sputtering chamber in which the semiconductor layer 5 is formed.

  In the second embodiment of the present invention, the composite metal oxide constituting the semiconductor layer 5 is added to the above-described metal oxide added to tin oxide, and further has an oxygen separation energy smaller than that of tin oxide. It is the addition of an additional oxide that is less in amount than the metal oxide. The inventors of the present application have found that the semiconductor layer becomes amorphous even in a high temperature range of 500 ° C. by controlling the amount of oxygen vacancies by adding a metal oxide and adding an additional oxide. As the additional oxide, specifically, lead oxide having an oxygen release energy of 382.4 ± 3.3 kJ / mol, palladium oxide having 238.1 ± 12.6 kJ / mol, 418.6 ± 11.6 kJ / mol mol platinum oxide, 517.90 ± 0.05 kJ / mol sulfur oxide, 434 ± 42 kJ / mol antimony oxide, 426.3 ± 6.3 kJ / mol strontium oxide, 213 ± 84 kJ / mol thallium oxide, 387 7 ± 10 kJ / mol ytterbium oxide and the like.

  The thin film transistor 1 ′ of the second embodiment of the present invention shown in FIG. 2 has basically the same structure as the thin film transistor 1 of FIG. 1, but the semiconductor layer 5 ′ corresponding to the semiconductor layer 5 of FIG. Further, the metal oxide 7 is added to the metal oxide 7 in that the oxide separation energy is smaller than that of tin oxide, and the additional oxide 10 is added in an amount less than that of the metal oxide. 2 that are denoted by the same reference numerals as those in FIG. 1 are the same as the corresponding elements in FIG. 1, and thus the description thereof is omitted.

  As noted in the description of the first embodiment with reference to FIG. 1, the semiconductor layer 5 ′ (composite metal oxide) is made of tin oxide 6 for convenience of illustration also in FIG. 2. It is drawn in a form that can be seen as interspersed with additional oxide 10, but in this case as well, these oxides are actually uniformly added or doped in the tin oxide. Therefore, it should be noted that the composite metal oxide is a uniform material.

The addition of the metal oxide tungsten oxide (WO ₃ ) and the additional oxide ytterbium oxide (Yb ₂ O ₃ ) to the tin oxide (SnO ₂ ) is performed, for example, at the target preparation stage of the sputtering method.

Moreover, the amount of addition can be controlled by changing the ratio of the sputtering power by a co-sputtering method using a Sn—W—O target and a Yb ₂ O ₃ target, and the content is greater than 0 and 10% by weight. The following is more preferable.

[Thin Film Transistor Manufacturing Method]
Next, a method for manufacturing the thin film transistor 1 of the first embodiment will be described. The semiconductor layer of the thin film transistor of this embodiment can also be formed by using physical vapor deposition (or physical vapor deposition).

  Here, examples of physical vapor deposition include vapor deposition and sputtering. Examples of the vapor deposition method include vacuum vapor deposition, molecular beam vapor deposition (MBE), ion plating, and ion beam vapor deposition. Examples of the sputtering method include conventional sputtering, magnetron sputtering, ion beam sputtering, ECR (electron cyclotron resonance) sputtering, and reactive sputtering. When plasma is used in the sputtering method, a film forming method such as a reactive sputtering method, a DC (direct current) sputtering method, or a radio frequency (RF) sputtering method can be used.

Furthermore, what was manufactured using the following manufacturing method is preferable. When the following manufacturing method is used, a higher quality thin film transistor can be manufactured.

  In the method for manufacturing the thin film transistor 1 of this embodiment, the gate electrode 3 and the insulator layer 4 are formed on the substrate 2 by a generally known method, and then the semiconductor layer 5 is formed. In the manufacturing method of the present embodiment, the semiconductor layer 5 is made of a tin oxide powder and a metal oxide whose oxygen separation energy is larger than the oxygen separation energy of tin oxide, and the oxygen of the tin oxide and the metal oxide. It is manufactured by a physical vapor deposition method using a target which is a sintered body containing a powder having a difference in separation energy of less than 200 kJ / mol and a mixed gas of a rare gas and oxygen. Here, it demonstrates as using sputtering method as a physical vapor deposition method.

  For example, when a Sn—W—O-based metal oxide is employed as the semiconductor layer 5, a sintered body of a tin oxide powder and a tungsten oxide powder may be employed as the target. Further, the target may be mixed with impurities such as an additive (metal oxide or the like) at a mass% or less of tungsten oxide. For example, a metal oxide (such as zinc oxide) other than tin oxide and tungsten oxide may be mixed into the target at a ratio (weight ratio) equal to or lower than the tungsten oxide content in the target as an unintended impurity. .

  In that case, the content of tungsten oxide contained in the sintered body is preferably greater than 0% by mass and equal to or less than 50% by mass. Further, the content of tungsten oxide is more preferably 0% by mass to 5% by mass.

  In In-Zn-O-based and In-Ga-Zn-O-based metal oxides, which are generally known oxide semiconductors, when indium oxide is a "host material" and zinc oxide or gallium oxide is a "guest material" The guest material (zinc oxide or gallium oxide) is mixed with 20-30% of the host material (indium oxide).

  On the other hand, the semiconductor layer 5 of the thin film transistor 1 of the present embodiment is formed into a thin film using the above sintered body as a target. In the thin film transistor 1 manufactured by the manufacturing method of the present embodiment, the content of tungsten oxide is more preferably more than 0% by mass and 5% by mass or less as described above. Therefore, the semiconductor layer 5 in the case of this preferable composition. This oxide semiconductor has an extremely small content of the guest material (tungsten oxide) with respect to the host material (tin oxide) as compared with a conventionally known oxide semiconductor.

  In the method for manufacturing the thin film transistor 1, a mixed gas of a rare gas and oxygen is used as a process gas. Examples of the rare gas include helium, neon, argon, krypton, and xenon. Further, the process gas does not include a compound having a hydrogen atom.

  In the thin film transistor manufacturing method of this embodiment, when the semiconductor layer is formed using a target containing tin oxide and tungsten oxide, the metal oxide constituting the semiconductor layer is changed to an amorphous film. It has been found that it does not require high temperatures to do. Therefore, in a method for manufacturing a thin film transistor, an amorphous semiconductor layer can be formed by performing a step of forming a semiconductor layer at 10 ° C. to 300 ° C. In addition, a suitable crystallized semiconductor layer can be formed by performing the process at a temperature higher than 300 ° C. and lower than or equal to 500 ° C. Further, the step of forming the semiconductor layer is preferably performed at room temperature. Here, “implemented at room temperature” means that the semiconductor layer is not heated for the step of forming the semiconductor layer, and the temperature adjustment of the working environment is unnecessary.

  As a sputtering method employed in the method for manufacturing the thin film transistor of the present embodiment, known methods such as RF sputtering and DC sputtering can be used.

  Further, the target may be a sintered body of a mixture of these powders or a sintered body of each powder as long as tin oxide powder and tungsten oxide powder are used. When a sintered body is formed for each metal oxide powder, the semiconductor layer can be formed by co-sputtering using a plurality of sintered bodies.

  Although silicon oxide has been described as the metal oxide, samarium oxide (Sm—O), tungsten oxide (W—O), neodymium oxide (Nd—O), and gadolinium oxide (Gd—O) were used instead. Even in this case, the semiconductor layer can be formed in a process range corresponding to the magnitude of the separation energy of oxygen.

  In the method for manufacturing the thin film transistor 1 of the second embodiment, the gate electrode 3 and the insulator layer 4 are formed on the substrate 2 by a generally known method, and then the semiconductor layer 5 is formed. In the manufacturing method of the present embodiment, the semiconductor layer 5 has a difference between the tin oxide powder and the oxygen separation energy of the tin oxide larger than that of the tin oxide, and the difference between the oxygen separation energy of the tin oxide is 200 kJ. A metal oxide powder having an oxygen separation energy of less than / mol, and an additional oxide in an amount where the oxygen separation energy is less than the oxygen separation energy for tin oxide and less than the addition amount of the metal oxide Is produced by a physical vapor deposition method using a target that is a sintered body containing a noble gas and a mixed gas of oxygen and oxygen. Here, it demonstrates as using sputtering method as a physical vapor deposition method.

  For example, when a Sn—W—Yb—O-based metal oxide is used as the semiconductor layer 5, a sintered body of a tin oxide powder, a tungsten oxide, and a ytterbium oxide powder may be used as the target. Further, the amount of ytterbium oxide added to the target is always smaller than the amount of tungsten oxide added.

  In that case, when the content of tungsten oxide contained in the sintered body is more than 0% by mass and 50% by mass or less, the content of ytterbium oxide is more than 0% by mass and less than 20% by mass. The content of ytterbium oxide is more preferably 0% by mass to 4% by mass.

  In the method for manufacturing the thin film transistor 1, a mixed gas of a rare gas and oxygen is used as a process gas. Examples of the rare gas include helium, neon, argon, krypton, and xenon. Further, the process gas does not include a compound having a hydrogen atom.

  In the method for manufacturing a thin film transistor of this embodiment, when the semiconductor layer is formed using a target containing tin oxide, tungsten oxide, and ytterbium oxide, the process of forming the semiconductor layer is 10 ° C. or higher, as studied by the inventors. It was found that an amorphous semiconductor layer can be formed by carrying out at 500 ° C. or lower. Further, the step of forming the semiconductor layer is preferably performed at room temperature. Here, “implemented at room temperature” means that the semiconductor layer is not heated for the step of forming the semiconductor layer, and the temperature adjustment of the working environment is unnecessary.

  As a sputtering method employed in the method for manufacturing the thin film transistor of the present embodiment, known methods such as RF sputtering and DC sputtering can be used.

  In the above, the manufacturing method of the thin-film transistor of this invention was demonstrated.

  According to the thin film transistor of the present invention as illustrated in FIGS. 1 and 2 as described above, the characteristic change is suppressed by using the novel composite metal oxide for the semiconductor layer.

  In addition, according to the semiconductor device having the above-described configuration, the thin film transistor in which the change in characteristics is suppressed has high reliability.

Further, according to the method for manufacturing a thin film transistor as described above, a thin film transistor in which a change in characteristics is suppressed can be easily manufactured by using a novel composite metal oxide for a semiconductor layer.

Note that although a so-called bottom-gate thin film transistor has been described in this embodiment, the present invention can also be applied to a so-called top-gate thin film transistor.

  In the present embodiment, a so-called top contact type thin film transistor has been described. However, the present invention can also be applied to a so-called bottom contact type thin film transistor.

  The preferred embodiments according to the present invention have been described above with reference to the accompanying drawings, but it is needless to say that the present invention is not limited to such examples. Various shapes, combinations, and the like of the constituent members shown in the above-described examples are examples, and various modifications can be made based on design requirements and the like without departing from the gist of the present invention.

  EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[First embodiment]
In this example corresponding to the first embodiment, the thin film transistor shown in FIG. 3 was manufactured and the operation was confirmed. The thin film transistor shown in the figure has the same configuration as the thin film transistor 1 shown in FIG. 1, and uses a Si layer 11 doped with a large amount of p-type impurities in place of the gate electrode 3 of the thin film transistor 1 shown in FIG. It has become.

  The thin film transistor of the example uses a Si substrate doped with a p-type impurity, forms the insulator layer 4 by oxidizing the surface, and then forms the semiconductor layer 5 on the surface of the insulator layer 4 using a method described later. It was manufactured by doing. The source electrode 8 and the drain electrode 9 were formed by mask vapor deposition on the surface of the semiconductor layer 5.

  The source electrode 8 and the drain electrode 9 are made of gold (Au) and have a thickness of 50 nm. Further, the separation distance (gate length) between the source electrode 8 and the drain electrode 9 was 350 μm, and the length of the facing portion was 940 μm.

  The semiconductor layer 5 was formed by sputtering (DC sputtering) using a sputtering apparatus and using a Sn—W—O target as a target material under the following sputtering conditions. As the Sn—W—O target, a 20% W-added Sn-based sample product was used. The thickness of the deposited semiconductor layer 5 was 20 nm.

(Sputtering conditions)
DC power: 200W
Degree of vacuum: 0.2 Pa
Process gas flow rate: Ar 20 sccm / O _{2 2} sccm
(Sccm: Standard Cubic Centimeter per Minute)
Substrate temperature: 25 ° C. Without heating

  The characteristics of the thin film transistor thus fabricated were measured under the evaluation environment of 25 ° C., dark place, and vacuum. FIG. 4 shows the measurement results of the transfer characteristics of this thin film transistor.

In addition, FIG. 5 shows the electric conduction characteristics of Sn—O and Sn—W—O thin film transistors when the ratio of O ₂ / (Ar + O ₂ ) is changed in the range of 5 to 25% under the above sputtering conditions. . Sn—W—O exhibits superior electrical conductivity compared to Sn—O at all oxygen ratios in FIG. This is suitable from tin oxide (Sn—O) with high accuracy because the oxygen separation energy of W—O bond (720 ± 71 kJ / mol) is larger than that of Sn—O (528 kJ / mol). This is the effect of controlling the amount of oxygen deficiency by desorbing oxygen. In addition, Sn—W—O indicates that the change in the electric conduction characteristic is smaller than the change in the ratio of O ₂ / (Ar + O ₂ ). From this result, it can be seen that Sn-W-O has a larger process margin.

[Second Embodiment]
Also in this example corresponding to the second embodiment, the thin film transistor shown in FIG. 3 was manufactured and the operation was confirmed. The semiconductor layer 5 was formed by a sputtering method (DC sputtering) using a sputtering apparatus and using a Sn—W—Yb—O target as a target material under the following sputtering conditions. As the Sn—W—O target, 20% W and 2% Yb-added Sn-based sample products were used. The thickness of the deposited semiconductor layer 5 was 20 nm.

(Sputtering conditions)
DC power: 150W
Degree of vacuum: 0.2 Pa
Process gas flow rate: Ar 20 sccm / O _{2 2} sccm
(Sccm: Standard Cubic Centimeter per Minute)
Substrate temperature: 25 ° C. Without heating

  In order to examine the crystal structure of the Sn—W—Yb—O film by post-heat treatment, an X-ray film was formed by forming a 20 nm-thick Sn—W—O film on a glass substrate and heat-treating at 450 ° C. for 15 minutes in the air. The diffraction pattern is shown in FIG. Only a glass substrate is also shown for comparison. Even when heat-treated at 450 ° C. for 15 minutes, no peak was observed, indicating that the film was amorphous.

  The characteristics of the thin film transistor manufactured using this amorphous Sn—W—Yb—O film were measured in an evaluation environment of 25 ° C. in a dark place and in a vacuum. FIG. 7 shows the results of measuring the characteristics of the thin film transistor of the present invention.

  From the above results, the operation of the thin film transistor of the present invention was confirmed, and the usefulness of the present invention was confirmed.

  As described above, according to the present invention, a composite metal oxide semiconductor layer in which the amount of oxygen vacancies is controlled can be realized, which can greatly contribute to improvement in performance of a thin film transistor.

1, 1 '--- thin film transistor 2 --- substrate 3--gate electrode 4 --- insulating film layer 5, 5'-semiconductor layer 6 --- tin oxide 7 --- metal oxide 8-- --Source electrode 9--Drain electrode 10 --- Oxide 11--Si substrate doped with p-type impurities.

JP 2011-4425 A JP 2013-70052 A JP 2010-21520 A JP 2008-192721 A

APPLIED PHYSICS LETTERS 102, 102102 (2013).

Claims (11)

A source electrode and a drain electrode;
A semiconductor layer provided in contact with the source electrode and the drain electrode;
A gate electrode provided corresponding to a channel between the source electrode and the drain electrode;
Providing an insulator layer provided between the gate electrode and the semiconductor layer;
The semiconductor layer is a composite metal oxide in which tin oxide is added with a metal oxide having an oxygen separation energy larger than that of tin oxide and a difference from the oxygen separation energy of tin oxide being less than 200 kJ / mol ,
The semiconductor layer, the dissociation energy of oxygen includes additional oxides smaller than tin oxide by an amount less than the metal oxide, the thin film transistor. The thin film transistor according to claim 1, wherein a content of the additional oxide in the semiconductor layer is 20% by weight or less. The thin film transistor according to claim 2, wherein a content of the additional oxide in the semiconductor layer is 4% by weight or less. Wherein the semiconductor layer is an amorphous thin film transistor according to claim 1 or et 3. The thickness of the semiconductor layer is 5nm or more and 20nm or less, a thin film transistor according to claim 1 or al 4. 6. The thin film transistor according to claim 1 , wherein the additional oxide is at least one oxide selected from the group consisting of lead, palladium, platinum, sulfur, antimony, strontium, thallium, and ytterbium. The metal oxide is samarium, tungsten, neodymium, at least one oxide selected from the group consisting of gadolinium, a thin film transistor according to claim 1 or al 6. The content of the metal oxide semiconductor layer is not more than 50 wt% greater than 0, the thin film transistor according to claim 1 or et 7. The content of the metal oxide before Symbol semiconductor layer is not more than 5% by weight, a thin film transistor according to claim 8. The semiconductor layer is formed at 10 ° C. or higher 500 ° C. A method for fabricating a thin film transistor according to any one of claims 1 through 9. The method for manufacturing a thin film transistor according to claim 10, wherein the semiconductor layer is formed at 10 ° C. or more and 300 ° C. or less.