Thin film transistor and method for manufacturing the same

Abstract

To provide a thin film transistor with high transfer conductance capable of maintaining the transfer conductance at a high level for a long period of time, and manufacturing method thereof.SOLUTION: The thin film transistor has a gate electrode, a gate insulating layer, a channel layer, a source electrode, and a drain electrode arranged on a substrate. The gate insulating layer is a film containing LaZrO, the channel layer is a sputtered film containing InO, and the sputtered film is crystalline and the average diameter of crystal grains is 10 nm or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a thin film transistor and a method for manufacturing a thin film transistor. [Background technology]

[0002] Thin film transistors that use an IGZO film for the channel layer are used (Patent Document 1). Also known is a thin film transistor that uses a film containing LaZrO as the gate insulating layer and a film containing InO as the channel layer (Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-165529 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-60962 Summary of the Invention [Problem to be solved by the invention]

[0004] Thin film transistors that use a film containing LaZrO as the gate insulating layer and a film containing InO as the channel layer have high transconductance, but this high transconductance can decrease over time.

[0005] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a thin film transistor having a high transfer conductance and capable of maintaining the transfer conductance at a high level for a long period of time, and a method for manufacturing the same. [Means for solving the problem]

[0006] In order to achieve the above object, a thin film transistor of the present invention includes a gate electrode, a gate insulating layer, a channel layer, a source electrode, and a drain electrode, which are arranged on a substrate, wherein the gate insulating layer is a film containing LaZrO, and the channel layer is a sputtered film containing InO; The film containing LaZrO contains hydrogen in a range of 2 atom % to 20 atom %. The sputtered film containing InO is crystalline and has an average crystal grain diameter of 10 nm or more. 100nm or less The structure is as follows.

[0007] The thin-film transistor of the present invention thus configured has a high transconductance because the gate insulating layer is a film containing LaZrO and the channel layer is a sputtered film containing InO. Furthermore, the thin-film transistor of the present invention has a crystalline InO-containing sputtered film with a large average crystal grain diameter of 10 nm or more, which increases electron mobility and therefore transconductance. At the same time, the film formed by sputtering is dense and resistant to changes in structure and composition. The structure and composition of the crystals constituting the film and the interface with the gate insulating layer are stable, reducing changes in these properties with the application of high gate voltages and over time, allowing the high transconductance to be maintained for a long period of time.

[0008] In the thin film transistor of the present invention, the film containing LaZrO may be a sputtered film. In this case, forming the film using the sputtering method makes the film containing LaZrO dense and high-density, which reduces changes in the transistor characteristics due to the application of a high gate voltage or the passage of time.

[0011] A method for manufacturing a thin film transistor of the present invention is a method for manufacturing a thin film transistor having a gate electrode, a gate insulating layer, a channel layer, a source electrode, and a drain electrode disposed on a substrate, wherein the gate insulating layer is a film containing LaZrO and the channel layer is a sputtered film containing InO, the method comprising: a film formation step of forming the sputtered film containing InO by a sputtering method using an InO target containing carbon; and a heat treatment step of heating the sputtered film containing InO at a temperature of 200°C or higher and 500°C or lower.

[0012] According to the thin-film transistor manufacturing method of the present invention configured as described above, the sputtered film containing InO is formed by sputtering using an InO target containing carbon in the film formation process, which makes it difficult for InO crystals to grow. Therefore, a sputtered film with fine InO microcrystals uniformly scattered can be formed in the film formation process. Then, by heating the sputtered film in the heat treatment process, the InO microcrystals grow, resulting in a crystalline sputtered film containing InO with a large average crystal grain diameter of 10 nm or more.

[0013] In the method for manufacturing a thin film transistor of the present invention, the film forming step may be performed in the presence of water vapor or hydrogen gas. In this case, since the film formation process is performed in the presence of water vapor or hydrogen gas, it becomes more difficult for InO crystals to grow, and the sputtered film obtained in the film formation process has finer InO microcrystals uniformly scattered throughout. Therefore, by heating the sputtered film in the heat treatment process, it becomes easier to produce a sputtered film containing crystalline InO with an average crystal grain diameter of 10 nm or larger.

[0016] Still another method for manufacturing a thin film transistor of the present invention is a method for manufacturing a thin film transistor having a gate electrode, a gate insulating layer, a channel layer, a source electrode, and a drain electrode arranged on a substrate, wherein the gate insulating layer is a sputtered film containing LaZrO, and the channel layer is a sputtered film containing InO, the method comprising the steps of: a first film formation step of forming the sputtered film containing LaZrO by a sputtering method; The, The method includes a second film formation step of forming a film by a sputtering method using an InO target containing carbon, and a heat treatment step of heating the sputtered film containing LaZrO and the sputtered film containing InO at a temperature of 200°C or higher and 500°C or lower.

[0017] According to the thin-film transistor manufacturing method of the present invention configured as described above, a sputtered film containing LaZrO is formed in the first film-forming step, and therefore, when the sputtered film containing InO is heated in the heat-treatment step, crystal grains may be generated using the crystals of the sputtered film containing LaZrO as seeds. By using the crystals of the sputtered film containing LaZrO as seeds to generate InO crystal grains, a crystalline sputtered film containing InO with a large average crystal grain diameter of 10 nm or more can be obtained.

[0018] Here, in the above-described method for manufacturing a thin film transistor, both or either one of the first film-forming step and the second film-forming step may be performed in the presence of water vapor or hydrogen gas. When the first film formation step is performed in the presence of water vapor or hydrogen gas, hydrogen is added to the LaZrO-containing film, increasing the ionic conductivity of the film and improving the effective dielectric constant, thereby improving transistor characteristics. Furthermore, when the second film formation step is performed in the presence of water vapor or hydrogen gas, InO crystals are less likely to grow, resulting in a sputtered film obtained in the second film formation step with fine InO crystallites uniformly scattered throughout. Therefore, heating the sputtered film containing InO in the heat treatment step makes it easier to produce a crystalline sputtered film containing InO with a large crystal grain average diameter of 10 nm or more. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a thin film transistor having a high transconductance and capable of maintaining the high transconductance for a long period of time, and a method for manufacturing the same. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a cross-sectional view of an example of a thin film transistor according to an embodiment of the present invention. [Figure 2] 10 is a graph showing the transistor characteristics (Id-Vg characteristics) of the thin film transistor obtained in Example 2 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] FIG. 1 is a cross-sectional view of an example of a thin film transistor according to one embodiment of the present invention. 1, a thin film transistor 10 according to this embodiment includes a gate electrode 2, a gate insulating layer 3, a channel layer 4, a source electrode 5, and a drain electrode 6, which are arranged on a substrate 1. The source electrode 5 and the drain electrode 6 are arranged on the channel layer 4 and in positions facing each other.

[0022] The substrate 1 may be, for example, an insulating substrate or a semiconductor substrate. Examples of insulating substrates include heat-resistant glass, a silicon substrate (SiO2 / Si substrate) with a thermally oxidized film (silicon oxide film), an alumina (Al2O3) substrate, an STO (SrTiO) substrate, and a Si substrate with an STO (SrTiO) layer formed on the surface via an SiO2 layer and a Ti layer. Examples of semiconductor substrates include a Si substrate, a SiC substrate, and a Ge substrate. The thickness of the substrate 1 is, for example, in the range of 10 μm to 1 mm.

[0023] The gate electrode 2 may be a single-layer film consisting of one conductive film, or a laminated film consisting of two or more conductive film layers. Examples of materials that can be used for the conductive film include metals, alloys containing such metals, and metal oxides. Examples of metals include platinum, gold, silver, copper, aluminum, molybdenum, palladium, ruthenium, iridium, tungsten, and titanium. Examples of metal oxides include indium tin oxide (ITO) and ruthenium oxide (RuO2). The thickness of the gate electrode 2 is, for example, in the range of 10 nm to 500 nm. To improve adhesion between the gate electrode 2 and the substrate 1, an oxide film such as titanium oxide (TiO2) may be inserted between them.

[0024] The gate insulating layer 3 is a LaZrO-containing film containing an oxide (LaZrO) containing lanthanum and zirconium. The LaZrO-containing film may be a sputtered film formed by a sputtering method or a film formed by a coating and baking method. The lanthanum content of the LaZrO-containing film is preferably equal to or less than the zirconium content. The lanthanum to zirconium content of the LaZrO-containing film is, for example, in the range of 1:9 to 5:5 (atomic ratio). The LaZrO-containing film may contain hydrogen. The hydrogen content of the LaZrO-containing film is, for example, in the range of 2 atom % to 20 atom %. The thickness of the gate insulating layer 3 is, for example, in the range of 10 nm to 500 nm. The hydrogen (H) content can be measured, for example, using a Pelletron 3SDH manufactured by National Electrostatics Corporation, by Rutherford Backscattering Spectrometry (RBS analysis), Hydrogen Forward Scattering Spectrometry (HFS analysis), and Nuclear Reaction Analysis (NRA analysis).

[0025] The channel layer 4 is made of an InO-containing sputtered film containing indium oxide (InO). The InO-containing sputtered film is crystalline. The shape of the crystal grains in the InO-containing sputtered film is, for example, columnar, spherical, or oval-spherical. The average diameter of the crystal grains is 10 nm or more, and preferably in the range of 10 nm to 100 nm. The average diameter of the crystal grains is the average of the longest diameters of the crystal grains obtained by observing the cross section of the InO-containing sputtered film with a TEM (transmission electron microscope). The thickness of the channel layer 4 is, for example, in the range of 50 nm to 200 nm. The channel layer 4 may be patterned to be a rectangle with sides of several tens to several hundreds of μm.

[0026] The source electrode 5 and the drain electrode 6 may be a single layer film made of one conductive film, or a laminated film made of two or more conductive films. Examples of materials that can be used for the conductive film include metals, alloys containing such metals, and metal oxides. Examples of metals and metal oxides are the same as those for the gate electrode 2. The thickness of the source electrode 5 and the drain electrode 6 is, for example, in the range of 10 nm to 500 nm. The source electrode 5 and the drain electrode 6 are opposed to each other by a distance (inter-electrode distance L T ) is, for example, in the range of 1 μm or more and 100 μm or less. S , the electrode length L of the drain electrode 6 D ) is, for example, in the range of 1 μm or more and 1000 μm or less, and preferably in the range of 10 μm or more and 200 μm or less. In addition, the length of the source electrode 5 and the drain electrode 6 in the second direction (the y direction in FIG. 1 ) perpendicular to the length in the first direction (the electrode width W of the source electrode 5) is S , the electrode width W of the drain electrode 6 D ) are each, for example, in the range of 1 μm or more and 1000 μm or less, and preferably in the range of 10 μm or more and 100 μm or less.

[0027] The thin film transistor of this embodiment can be manufactured, for example, by stacking a gate electrode 2, a gate insulating layer 3, and a channel layer 4 in this order on a substrate 1, and then forming a source electrode 5 and a drain electrode 6 on the channel layer 4.

[0028] The conductive film that forms the gate electrode 2 can be formed by a method that is conventionally used to form gate electrodes of thin film transistors, such as a sputtering method, a vapor deposition method, or a coating and baking method. The coating and baking method is a method in which a conductive film is formed by applying a conductive film-forming coating liquid that generates a conductive film by heating to form a coating film, and then the coating film is heated to form a conductive film.

[0029] The LaZrO film forming the gate insulating layer 3 can be formed by, for example, sputtering or coating and baking. In the sputtering method, a sintered target made of, for example, a sintered body of La2O3 and ZrO can be used as the LaZrO target. The LaZrO target may contain carbon. The carbon content is preferably in the range of 0.1% by mass to 5.0% by mass. The plasma gas supplied to the sputtering device may be, for example, a mixed gas containing argon and oxygen. The content ratio of argon to oxygen is preferably in the range of 95:5 to 80:20 (partial pressure ratio). The plasma gas may contain hydrogen gas or water vapor. The content ratio of the argon and oxygen mixed gas to the hydrogen gas or water vapor is preferably in the range of 99:1 to 99:5 (partial pressure ratio).

[0030] The coating and baking method involves applying a coating solution for forming a LaZrO-containing film, which generates a LaZrO-containing film upon heating, to form a coating film, and then heating the coating film to form a LaZrO-containing film. The coating solution for forming a LaZrO-containing film can be, for example, a solution containing a lanthanum source, a zirconium source, and propionic acid. Lanthanum acetate can be used as the lanthanum source. Zirconium butoxide can be used as the zirconium source. The total content of lanthanum and zirconium in the coating solution for forming a LaZrO-containing film is preferably in the range of 0.05 mol / kg to 2.0 mol / kg in terms of molar concentration in terms of LaZrO. The coating solution for forming a LaZrO-containing film can be applied, for example, by spin coating. Alternatively, the thickness of the LaZrO-containing film may be adjusted by repeating the process of applying a coating solution for forming a LaZrO-containing film to form a coating film, calcining the coating film to form a calcined film, multiple times, and finally performing main firing when the calcined film laminate reaches the desired thickness. In this case, the calcination temperature is preferably in the range of 100°C to 300°C, and the main firing temperature is preferably in the range of 300°C to 500°C.

[0031] The InO-containing sputtered film that forms the channel layer 4 can be formed using the following methods (1) to (4). (1) A method comprising: a film formation step of forming an InO-containing sputtered film to a thickness of 80 nm or more by a sputtering method using an InO target; and a heat treatment step of heating the InO-containing sputtered film at a temperature of 200°C or more and 500°C or less. (2) A method comprising: a film-forming step of forming an InO-containing sputtered film by a sputtering method using an InO target containing carbon; and a heat-treating step of heating the InO-containing sputtered film at a temperature of 200°C or higher and 500°C or lower. (3) A method comprising: a film-forming step of forming an InO-containing sputtered film by a sputtering method using an InO target in the presence of water vapor or hydrogen gas; and a heat-treating step of heating the InO-containing sputtered film at a temperature of 200°C or higher and 500°C or lower. (4) A method comprising: a first film formation step of forming a LaZrO-containing sputtered film by a sputtering method; a second film formation step of forming an InO-containing sputtered film by a sputtering method using an InO target or an InO target containing carbon; and a heat treatment step of heating the InO-containing sputtered film at a temperature of 200°C or higher and 500°C or lower.

[0032] In the above method (1), the InO target used in the film formation step may be, for example, a sintered target made of In2O3 sintered body. The thickness of the InO-containing sputtered film formed in the film formation step is preferably 100 nm or more.

[0033] In the above method (2), the carbon-containing InO target used in the film formation step may be, for example, a sintered target made of a sintered body of In2O3 and carbon. The carbon content of the carbon-containing InO target is preferably in the range of 0.1 mass% to 5.0 mass%. The plasma gas supplied to the sputtering device may be, for example, a mixed gas containing argon and oxygen. The content ratio of argon to oxygen is preferably in the range of 95:5 to 80:20 (partial pressure ratio). The plasma gas may contain hydrogen gas or water vapor. The content ratio of the argon and oxygen mixed gas to the hydrogen gas or water vapor is preferably in the range of 99:1 to 99:5 (partial pressure ratio).

[0034] In the method (3) above, the InO target used in the film formation step may be, for example, a sintered target made of an In2O3 sintered body. A method for forming a film in the presence of water vapor or hydrogen gas can be used in which a gas containing hydrogen gas or water vapor is supplied to a sputtering apparatus as a sputtering gas. The sputtering gas can be a mixed gas containing hydrogen gas or water vapor, argon, and oxygen. The content ratio of the argon / oxygen mixed gas to the hydrogen gas or water vapor is preferably within a range of 99:1 to 99:5 (partial pressure ratio). The content ratio of argon to oxygen is preferably within a range of 95:5 to 80:20 (partial pressure ratio).

[0035] In the method (4) above, the method for forming the LaZrO-containing sputtered film by sputtering in the first film formation step is the same as the method for forming the LaZrO-containing sputtered film described above. The carbon-containing InO target used in the second step may be, for example, a sintered compact target made of In2O3 and carbon, as in the film formation step (2) above. The InO target may also be, for example, a sintered compact target made of In2O3, as in the film formation steps (1) and (3) above. The plasma gas supplied to the sputtering apparatus may be, for example, a mixed gas containing argon and oxygen. The content ratio of argon to oxygen is preferably within the range of 95:5 to 80:20 (partial pressure ratio). The plasma gas may contain hydrogen gas or water vapor. The content ratio of the argon-oxygen mixed gas to the hydrogen gas or water vapor is preferably within the range of 99:1 to 99:5 (partial pressure ratio). In addition, either or both of the first film-forming step and the second film-forming step may be performed in the presence of water vapor or hydrogen gas.

[0036] In the above methods (1) to (4), the heat treatment of the InO-containing sputtered film in the heat treatment step may be performed in the atmosphere. The heat treatment temperature is preferably in the range of 300°C to 400°C. The heat treatment time may be, for example, in the range of 0.5 hours to 1 hour. The heat treatment step may be performed after the source electrode 5 and the drain electrode 6 are formed on the channel layer 4.

[0037] The channel layer 4 can be formed into a desired shape by photolithography.

[0038] The conductive film forming the source electrode 5 and the drain electrode 6 can be formed by, for example, sputtering, vapor deposition, or coating and baking. The coating and baking method is a method in which a conductive film is formed by applying a coating liquid for forming a conductive film, which generates a conductive film by heating, and then heating the coating film to form a conductive film. Methods for forming the source electrode 5 and the drain electrode 6 into the desired shape include wet etching using photolithography, dry etching, lift-off, and mask film formation using a contact mask.

[0039] In this manner, the thin film transistor of this embodiment can be manufactured.

[0040] The thin-film transistor 10 of this embodiment configured as described above has a high transconductance because the gate insulating layer 3 is a LaZrO-containing film and the channel layer 4 is an InO-containing film. Furthermore, the thin-film transistor 10 of this embodiment has a crystalline InO-containing sputtered film with a large average crystal grain diameter of 10 nm or more, which increases electron mobility and therefore transconductance. At the same time, the film formed by sputtering is dense and resistant to changes in structure and composition. The structure and composition of the crystals constituting the film and the interface with the gate insulating layer 3 are stable, reducing changes in these properties with the application of a high gate voltage and over time, allowing the high transconductance to be maintained for a long period of time.

[0041] In the thin-film transistor 10 of the present embodiment, when the LaZrO-containing film forming the gate insulating layer 3 is a sputtered film, the film becomes dense and high-density, and therefore changes due to application of a high gate voltage and the passage of time are reduced, resulting in small changes in the transistor characteristics.

[0042] In the method for manufacturing the thin film transistor 10 of this embodiment, when the InO-containing sputtered film that forms the channel layer 4 is formed by the above method (1), the thickness of the InO-containing sputtered film formed in the film formation step is as thick as 80 nm or more. This facilitates the growth of InO crystals in the InO-containing sputtered film in the subsequent heat treatment step, and a crystalline sputtered film containing InO with a large average crystal grain diameter of 10 nm or more can be obtained.

[0043] In the manufacturing method of the thin-film transistor 10 of this embodiment, when the InO-containing sputtered film that forms the channel layer 4 is formed by the above-described method (2), the InO-containing sputtered film is formed by a sputtering method using a carbon-containing InO target in the film formation process, which makes it difficult for InO crystals to grow. Therefore, in the film formation process, a sputtered film in which fine InO microcrystals are uniformly scattered can be formed. Then, by heating the InO-containing sputtered film in the heat treatment process, the microcrystals grow, resulting in a crystalline InO-containing sputtered film with a large crystal grain average diameter of 10 nm or more.

[0044] Furthermore, in the above-described method for manufacturing the thin-film transistor 10, by performing the film formation process in the presence of water vapor or hydrogen gas, InO crystals are less likely to grow, and the InO-containing sputtered film obtained in the film formation process has finer InO crystallites uniformly scattered therein. Therefore, by heating the InO-containing film in the heat treatment process, it becomes easier to produce a crystalline sputtered film containing InO with a large average crystal grain diameter of 10 nm or more.

[0045] In the manufacturing method of the thin-film transistor 10 of this embodiment, when the InO-containing sputtered film that forms the channel layer 4 is formed by the above method (3), the film formation process is performed in the presence of water vapor or hydrogen gas, making it difficult for InO crystals to grow. Therefore, a sputtered film with fine InO microcrystals uniformly scattered therein can be formed in the film formation process. Then, the InO-containing sputtered film is heated in the heat treatment process, so that the InO microcrystals grow, resulting in a crystalline InO-containing sputtered film with a large average crystal grain diameter of 10 nm or more.

[0046] In the method for manufacturing the thin-film transistor 10 of this embodiment, when the InO-containing sputtered film that forms the channel layer 4 is formed by the above method (4), the LaZrO-containing sputtered film is formed in the first film formation step, and therefore, when the InO-containing sputtered film is heated in the heat treatment step, crystal grains may be generated using the crystals of the LaZrO-containing sputtered film as seeds. By generating InO crystal grains using the crystals of the LaZrO-containing sputtered film as seeds, a crystalline InO-containing sputtered film can be obtained, with the average crystal grain diameter being as large as 10 nm or more.

[0047] Furthermore, in the above method, when the first film formation step is performed in the presence of water vapor or hydrogen gas, hydrogen is added to the LaZrO-containing film, increasing the ionic conductivity of the film and improving the effective dielectric constant, thereby improving transistor characteristics. Furthermore, when the second film formation step is performed in the presence of water vapor or hydrogen gas, InO crystals are less likely to grow, resulting in a sputtered film obtained in the second film formation step with fine InO crystallites uniformly scattered throughout. Therefore, heating the sputtered film containing InO in the heat treatment step makes it easier to produce a crystalline sputtered film containing InO with a large crystal grain average diameter of 10 nm or more.

[0048] Although the embodiment of the present invention has been described above, the present invention is not limited to this and can be modified as appropriate within the scope of the technical idea of ​​the invention. [Example]

[0049] [Example 1 of the present invention] As a substrate, a boron-doped silicon substrate (a disk with a diameter of 4 inches and a thickness of 0.38 mm) having a thermal oxide film (film thickness: 100 nm) on its surface was prepared. A titanium film (5 nm thick) was formed on the thermal oxide film of the substrate, and then heat-treated using an infrared lamp high-speed annealing device to form a titanium oxide film. A platinum film (100 nm thick) was then formed on top of this to form a gate electrode with a two-layer laminate of titanium oxide film and platinum film. The platinum and titanium films were deposited using the sputtering method as follows: A platinum target (purity: 3N) was used for the platinum film; a titanium target (purity: 3N) was used for the titanium film. The sputtering device used was a load-lock magnetron sputtering device (ULVAC, Inc., CS-200). The sputtering conditions were: ultimate vacuum: 2.0 × 10-4 Pa or less, sputtering gas: Ar, sputtering gas pressure: 0.4 Pa, and sputtering power: DC 100 W.

[0050] Next, La 0.3 Zr 0.7 An O-containing film (100 nm) was formed by coating and baking to form a gate insulating layer. 0.3 Zr 0.7 The O-containing film was formed as follows: Lanthanum acetate, zirconium butoxide, and propionic acid were mixed in a molar ratio of lanthanum to zirconium of 3:7. 0.3 Zr 0.7 Mix them in a ratio that gives a molar concentration of 0.2 mol / kg in terms of La 0.3 Zr 0.7 A coating solution for forming an O-containing film was prepared. Next, La was applied to the center of the gate electrode. 0.3 Zr 0.7 0.5 mL of the O-containing film-forming coating solution was dropped and spin-coated at a rotation speed of 1500 rpm for 15 seconds to form a coating film. The resulting coating film was then calcined at 250°C for 5 minutes on a hot plate to form a calcined film. This process was repeated five times. The five-layer calcined film laminate was then calcined at 450°C for 20 minutes on a hot plate to form the La 0.3 Zr0.7 An inclusion film was formed.

[0051] Next, an InO-containing film (100 nm) was formed on the gate insulating layer by sputtering to form a channel layer. The InO-containing film was formed as follows. The target used was an In2O3 target obtained by sintering In2O3 alone. The sputtering device used was a load-lock magnetron sputtering device (CS-200, manufactured by ULVAC, Inc.). The sputtering conditions were: ultimate vacuum: 2.0 × 10 -4 The sputtering gas was a mixed gas of Ar and O2 (partial pressure ratio of Ar:O2 = 9:1), the sputtering gas pressure was 0.4 Pa, and the sputtering power was DC 100 W.

[0052] The resulting InO-containing film was heated at 300° C. for 30 minutes using a hot plate.

[0053] Next, the source electrode and the drain electrode were formed on the channel layer by the lift-off method. In the lift-off method, a resist pattern was formed in advance by photolithography, with no resist in the area where the desired pattern was to be formed. After the source electrode and the drain electrode were formed on top of that, the resist was peeled off to form the patterned electrodes. The source electrode and the drain electrode were each a two-layer laminate, with a platinum film (thickness: 100 nm) laminated on an ITO film (thickness: 20 nm). The distance between the source electrode and the drain electrode (L T ) is 50 μm, and the electrode length (L S , L D ) is set to 200 μm, and the electrode width (W S , W D) was patterned to 100 μm. The platinum film and ITO film were formed using a sputtering method. The platinum film was formed in the same manner as the platinum film of the gate electrode described above. The ITO film was formed as follows. The target used was a sintered target made of a sintered body containing In2O3 and SnO2 in a mass ratio of 9:1. The sputtering device used was a load-lock type magnetron sputtering device (CS-200, manufactured by ULVAC, Inc.). The sputtering conditions were: ultimate vacuum: 2.0 × 10 -4 The sputtering gas was a mixed gas of Ar and O2 (partial pressure ratio of Ar:O2 = 9:1), the sputtering gas pressure was 0.4 Pa, and the sputtering power was DC 100 W.

[0054] In this manner, a thin film transistor was fabricated in which a gate electrode, a gate insulating layer, and a channel layer were formed in this order on a substrate, and a source electrode and a drain electrode were formed on the channel layer.

[0055] [Example 2] A thin film transistor was fabricated in the same manner as in Example 1 of the present invention, except that in forming the InO-containing film of the channel layer, a sintered target containing In2O3 and carbon in a mass ratio of 9:1 was used instead of a sintered target containing only In2O3.

[0056] [Example 3] The gate electrode, source electrode, and drain electrode are made of molybdenum film (thickness: 100 nm), and the gate insulating layer is made of La 0.3 Zr 0.7 A thin film transistor was fabricated in the same manner as in Invention Example 2, except that the O-containing film was a sputtered film (film thickness: 100 nm). Molybdenum was deposited by sputtering as follows. A molybdenum target (purity: 3N) was used as the target. A load-lock magnetron sputtering device (CS-200, manufactured by ULVAC, Inc.) was used as the sputtering device. The sputtering conditions were: ultimate vacuum: 2.0 × 10 -4The sputtering gas pressure was 0.4 Pa or less, sputtering gas: Ar, sputtering gas pressure: 0.4 Pa, and sputtering power: DC 100 W. La 0.3 Zr 0.7 The O-containing film was formed as follows. The target used was a sintered target containing La2O3, ZrO, and carbon in a molar ratio of 16:76:8. The sputtering device used was a load-lock magnetron sputtering device (CS-200, manufactured by ULVAC, Inc.). The sputtering conditions were: ultimate vacuum: 2.0 × 10 -4 The sputtering gas was a mixed gas of Ar and O2 (partial pressure ratio Ar:O2 = 9:1), the sputtering gas pressure was 0.4 Pa, and the sputtering power was RF 100 W.

[0057] [Example 4] La in the gate insulating layer 0.3 Zr 0.7 A thin-film transistor was fabricated in the same manner as in Example 3 of the present invention, except that the sputtering gas used in forming the O-containing film was a mixed gas of Ar, O2, and H2O (partial pressure ratio of Ar, O2, and H2O = 90:8:2).

[0058] [Comparative Example 1] A thin-film transistor was fabricated in the same manner as in Example 1 of the present invention, except that the channel layer was formed by coating and baking an InO-containing film. The InO-containing film was formed as follows. Indium acetate and ammonium acetate were mixed in a ratio such that the molar concentration in terms of In2O3 was 0.2 mol / kg to prepare a coating solution for forming an InO-containing film. Next, 1.0 mL of the coating solution for forming an InO-containing film was dropped onto the center of the gate insulating layer and spin-coated at a rotation speed of 1500 rpm for a rotation time of 15 seconds to form a coating film. The resulting coating film was calcined on a hot plate at 250°C for 5 minutes to form a calcined film. This process was repeated five times. The five-layer calcined film stack was then baked on a hot plate at 250°C for 30 minutes to form an InO-containing film.

[0059] Comparative Example 2 An IGZO-containing film (thickness: 100 nm) was formed on the thermal oxide film of the substrate 1 by sputtering. The target used was an InGaZnO4 target containing In, Ga, Zn, and O in an atomic ratio of 1:1:1:4. The sputtering device used was a load-lock magnetron sputtering device (CS-200, manufactured by ULVAC, Inc.). The sputtering conditions were: ultimate vacuum: 2.0 × 10 -4 The sputtering gas was a mixed gas of Ar and O2 (partial pressure ratio of Ar:O2 = 9:1), the sputtering gas pressure was 0.4 Pa, and the sputtering power was DC 100 W.

[0060] Next, a pair of titanium electrodes (thickness: 100 nm) was formed on the IGZO-containing film. The titanium electrodes were formed in the same manner as the titanium film of the gate electrode in Example 1 of the present invention, and a thin film transistor was fabricated. The titanium electrodes were separated by a distance (L T ) is 50 μm, and the electrode length (L S , L D ) is 200 μm, and the electrode width (W S , W D ) was patterned to 100 μm by using the lift-off method in the same manner as in Example 1 of the present invention. In this thin-film transistor, the silicon part of the substrate serves as the gate electrode, the thermal oxide film on the substrate serves as the gate insulating layer, the IGZO film serves as the channel layer, and the pair of titanium electrodes serves as the source and drain electrodes, respectively.

[0061] [evaluation] The average particle diameter of the InO-containing film (channel layer) of the thin film transistors obtained in Examples 1 to 4 of the present invention and Comparative Example 1 was measured by the following method. In addition, the transistor characteristics (I d -V g The electrical properties and transconductance were measured by the following methods.

[0062] (Method for measuring the average particle size of InO-containing films) The thin film transistor was cut in the thickness direction, and the cross section of the InO-containing film was observed using a TEM (transmission electron microscope) to measure the particle diameter (longest diameter) of the crystal grains in the InO-containing film. The average diameter was measured for 10 crystal grains at each of three locations on the cross section of the InO-containing film. The average diameter of the 30 measured crystal grains was taken as the average diameter of the crystal grains. The measurement results are shown in Table 1.

[0063] (Method of measuring transistor characteristics and transconductance) Transistor characteristics (I d -V g characteristics) is the drain voltage V d is set to 2V, and the gate voltage V g The drain current I when the voltage is changed from -2V to +5V d The transistor characteristics (I d -V g The characteristics are shown in Figure 2.

[0064] Transfer conductance G m was calculated from the following formula: I d = μC i W / L×{(V g -V th )V d -V d 2 / 2} G m =∂I d / ∂V g = μC i W / L×V d where I d is the drain current, and V g is the gate voltage, μ is the field-effect mobility, and C i is the capacitance per unit area, W is the channel width, L is the channel length, and V g is the gate voltage, V d is the drain voltage, V th and represent the threshold voltage, respectively. The results are shown in Table 1. The transconductance was measured after the first measurement (i.e., with a gate voltage of V gA second measurement was immediately performed after applying a voltage of 5 V to the thin-film transistor. The transconductance was also measured one month after the first measurement. During the one month period following the first measurement, the thin-film transistor was stored in a desiccator with a humidity of 20% or less.

[0065] [Table 1]

[0066] The results in Table 1 show that the thin-film transistors fabricated in Examples 1 to 4 of the present invention, in which the InO-containing film was an InO-containing sputtered film and the average crystal grain diameter was 10 nm or more, showed small variations in transconductance between the first and second times, and after one month. In contrast, the thin-film transistor of Comparative Example 1, in which the InO-containing film was not a sputtered film and the average crystal grain diameter was 5.2 nm, showed a 60% decrease in transconductance after one month compared to the initial transconductance. Furthermore, the thin-film transistor fabricated in Comparative Example 2 showed small variations in transconductance between the first and second times, and after one month, but its transconductance value was lower than that of the thin-film transistors fabricated in Examples 1 to 4 of the present invention. [Explanation of symbols]

[0067] 1 board 2 gate electrode 3 Gate insulating layer 4 Channel Layer 5. Source electrode 6 Drain electrode 10 Thin-film transistor

Claims

1. a gate electrode disposed on a substrate, a gate insulating layer, a channel layer, a source electrode, and a drain electrode; the gate insulating layer is a film containing LaZrO, the channel layer is a sputtered film containing InO, The film containing LaZrO contains hydrogen in a range of 2 atom % to 20 atom %. The thin film transistor is characterized in that the sputtered film containing InO is crystalline and the average diameter of the crystal grains is 10 nm or more and 100 nm or less.

2. 2. The thin film transistor according to claim 1, wherein the film containing LaZrO is a sputtered film.

3. A method for manufacturing a thin film transistor having a gate electrode, a gate insulating layer, a channel layer, a source electrode, and a drain electrode disposed on a substrate, wherein the gate insulating layer is a film containing LaZrO, and the channel layer is a sputtered film containing InO, a film formation step of forming the sputtered film containing InO by a sputtering method using an InO target containing carbon; and a heat treatment step of heating the sputtered film containing InO at a temperature of 200° C. or higher and 500° C. or lower.

4. 4. The method for producing a thin film transistor according to claim 3, wherein the film forming step is carried out in the presence of water vapor or hydrogen gas.

5. A method for manufacturing a thin film transistor having a gate electrode, a gate insulating layer, a channel layer, a source electrode, and a drain electrode disposed on a substrate, wherein the gate insulating layer is a sputtered film containing LaZrO, and the channel layer is a sputtered film containing InO, a first film formation step of forming a sputtered film containing the LaZrO by a sputtering method; a second film formation step of forming the sputtered film containing InO by a sputtering method using an InO target containing carbon; and a heat treatment step of heating the sputtered film containing LaZrO and the sputtered film containing InO at a temperature of 200° C. or higher and 500° C. or lower.

6. 6. The method for manufacturing a thin film transistor according to claim 5, wherein both or either one of the first film-forming step and the second film-forming step is performed in the presence of water vapor or hydrogen gas.

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