JP6350466B2 - Oxide sintered body and method for manufacturing the same, sputter target, and method for manufacturing semiconductor device - Google Patents

Description

  The present invention provides an oxide sintered body that can be suitably used as a sputtering target for forming an oxide semiconductor film by a sputtering method, a method for producing the oxide sintered body, a sputtering target (sputtering target) including the oxide sintered body, The present invention also relates to a method for manufacturing a semiconductor device including an oxide semiconductor film formed by sputtering (sputtering) using the sputtering target.

  Conventionally, in a liquid crystal display device, a thin film EL (electroluminescence) display device, an organic EL display device, etc., an amorphous silicon (a-Si) film has been mainly used as a semiconductor film functioning as a channel layer of a TFT (thin film transistor) that is a semiconductor device. Has been used.

  In recent years, a composite oxide containing indium (In), gallium (Ga), and zinc (Zn) as a material to replace a-Si, that is, an In—Ga—Zn-based composite oxide (also referred to as “IGZO”). Is attracting attention. The IGZO-based oxide semiconductor can be expected to have higher carrier mobility than a-Si.

  For example, Japanese Patent Laid-Open No. 2008-199005 (Patent Document 1) discloses that an oxide semiconductor film containing IGZO as a main component is formed by a sputtering method using an oxide sintered body as a target.

  Japanese Patent Laying-Open No. 2008-192721 (Patent Document 2) discloses an oxide sintered body containing In and tungsten (W) as a material suitably used when an oxide semiconductor film is formed by a sputtering method or the like. .

  Japanese Unexamined Patent Publication No. 09-071860 (Patent Document 3) discloses an oxide sintered body containing In and Zn.

JP 2008-199005 A JP 2008-192721 A Japanese Patent Application Laid-Open No. 09-071860

A problem with the TFT including the IGZO-based oxide semiconductor film described in Patent Document 1 as a channel layer is that the field effect mobility is as low as about 10 cm ² / Vs.

  In Patent Document 2, a TFT including an oxide semiconductor film formed using an oxide sintered body containing In and W as a channel layer has been proposed, but the reliability of the TFT has not been studied. .

  A thin film formed using the oxide sintered body described in Patent Document 3 is a transparent conductive film, and has a lower electric resistance than a semiconductor film such as a thin film used for a channel layer of a TFT, for example. Further, when an oxide sintered body is used as a sputtering target, the oxide sintered body is desired to have a high density (apparent density). In the oxide sintered body described in Patent Document 3, this is used. The apparent density cannot be increased unless the sintering temperature during preparation is increased. However, if the sintering temperature is set to a high temperature, the temperature rise time and the temperature fall time become long, and the amount of electric power increases to maintain the sintering atmosphere at a high temperature, resulting in a decrease in productivity. Further, when the sintering temperature is increased, the raw material tungsten oxide is evaporated, and an oxide sintered body containing W cannot be obtained.

  When thin film formation is performed using an oxide sintered body as a sputtering target, a predetermined power is applied to the sputtering target. At this time, as the applied power is increased, the temperature of the sputter target increases, and thermal fatigue or the difference in thermal expansion between the oxide sintered body and the copper backing plate to which the oxide sintered body is attached to the oxide sintered body. Cracks may occur, making it impossible to use as a sputtering target. In order to increase the applied voltage without causing cracks as described above, in order to improve the efficiency of water cooling performed through the copper backing plate, the thermal conductivity of the oxide sintered body is increased. It is desirable to increase.

  Accordingly, the present invention provides an oxide sintered body capable of exhibiting a high apparent density even at a relatively low sintering temperature and exhibiting a high thermal conductivity, a method for producing the same, and a sputter including the oxide sintered body. It is an object of the present invention to provide a target and a method for manufacturing a semiconductor device including an oxide semiconductor film formed using the sputter target.

  An oxide sintered body according to one embodiment of the present invention is an oxide sintered body containing indium, tungsten, and zinc, is a main component of the oxide sintered body, and includes a bixbite type crystal phase. A first crystal phase and a second crystal phase having a first diffraction peak at a position larger than 34.74 deg of 2θ in X-ray diffraction and smaller than 34.97 deg.

A sputter target according to another aspect of the present invention includes the oxide sintered body according to the above aspect.
A method for manufacturing a semiconductor device according to still another aspect of the present invention is a method for manufacturing a semiconductor device including an oxide semiconductor film, the step of preparing the sputter target of the above aspect, and a sputtering method using the sputter target. Forming an oxide semiconductor film.

  The method for manufacturing an oxide sintered body according to still another aspect of the present invention is a method for manufacturing the oxide sintered body according to the above aspect, and prepares a primary mixture of indium oxide powder and tungsten oxide powder. Forming a calcined powder by heat-treating the primary mixture, preparing a secondary mixture of raw material powders containing the calcined powder, and molding the secondary mixture. A step of forming an oxide sintered body by sintering the formed body, and the step of forming the calcined powder includes 700 ° C. or higher and 1400 ° C. in an oxygen-containing atmosphere. Forming a double oxide powder containing indium and tungsten as the pre-fired powder by heat-treating the primary mixture at a temperature lower than

  The method for producing an oxide sintered body according to still another aspect of the present invention is a method for producing an oxide sintered body according to the above aspect, wherein a primary mixture of zinc oxide powder and tungsten oxide powder is prepared. Forming a calcined powder by heat-treating the primary mixture, preparing a secondary mixture of raw material powders containing the calcined powder, and molding the secondary mixture. A step of forming an oxide sintered body by sintering the compact, and the step of forming the calcined powder is performed at 550 ° C. or higher and 1200 ° C. in an oxygen-containing atmosphere. Forming a double oxide powder containing zinc and tungsten as the pre-fired powder by heat-treating the primary mixture at a temperature below.

  According to the above, it is possible to provide an oxide sintered body capable of exhibiting a high apparent density even at a relatively low sintering temperature and exhibiting a high thermal conductivity, and a method for producing the same. Moreover, according to the above, it is possible to provide a semiconductor device that can achieve both high field effect mobility and high reliability.

1A and 1B are schematic views illustrating an example of a semiconductor device according to one embodiment of the present invention, in which FIG. 1A is a schematic plan view and FIG. 1B is a schematic cross-sectional view taken along line IB-IB shown in FIG. It is a schematic sectional drawing which shows another example of the semiconductor device which concerns on 1 aspect of this invention. It is a schematic sectional drawing which shows another example of the semiconductor device which concerns on 1 aspect of this invention. It is a schematic sectional drawing which shows an example of the manufacturing method of the semiconductor device shown by FIG. It is a schematic sectional drawing which shows an example of the manufacturing method of the semiconductor device shown by FIG.

<Description of Embodiment of the Present Invention>
First, embodiments of the present invention will be listed and described.

  [1] An oxide sintered body according to one embodiment of the present invention is an oxide sintered body containing indium (In), tungsten (W), and zinc (Zn), and the oxide sintered body A first crystal phase that is a main component and includes a bixbite type crystal phase, and a second crystal phase having a first diffraction peak at a position greater than 34.74 deg of 2θ in X-ray diffraction and less than 34.97 deg. The second crystal phase is included in a part of the oxide sintered body. The oxide sintered body of the present embodiment can exhibit a high apparent density (meaning an apparent density after sintering, also referred to as a sintered density) even at a relatively low sintering temperature, and has a high heat Conductivity can be shown. The oxide sintered body of this embodiment can be suitably used as a sputtering target for forming an oxide semiconductor film (for example, an oxide semiconductor film functioning as a channel layer) included in a semiconductor device. According to the oxide sintered body, a semiconductor device having high field effect mobility and high reliability can be obtained.

  [2] The oxide sintered body of the present embodiment is a crystal phase different from the first crystal phase, and can include a third crystal phase containing zinc, and particles constituting the third crystal phase The average major axis diameter is preferably 3 μm or more and 50 μm or less, and the average aspect ratio is preferably 4 or more and 50 or less. This is advantageous in realizing an oxide sintered body having a high apparent density and a high thermal conductivity even at a relatively low sintering temperature, and also improves the field effect mobility and reliability of the semiconductor device. It is advantageous also in raising.

  [3] In the oxide sintered body of the present embodiment, the third crystal phase is preferably dispersed in the first crystal phase. This is advantageous when the oxide sintered body of the present embodiment is used as a sputtering target.

  [4] In the oxide sintered body of the present embodiment, the third crystal phase includes a fourth crystal phase having a second diffraction peak at a position larger than 31.77 deg of 2θ in X-ray diffraction and smaller than 32.00 deg. be able to. The fourth crystal phase is a phase that can be included in a part of the oxide sintered body. The inclusion of the fourth crystal phase is advantageous in realizing an oxide sintered body that has a high apparent density and a high thermal conductivity even at a relatively low sintering temperature, and also has a field effect transfer of the semiconductor device. It is also advantageous to increase the degree and reliability.

  [5] In the oxide sintered body of the present embodiment, the ratio Ia / Ib between the peak intensity Ia of the first diffraction peak and the peak intensity Ib of the second diffraction peak can be 0.05 or more and 3 or less. An Ia / Ib of 0.05 or more and 3 or less is advantageous for realizing an oxide sintered body having a high apparent density and a high thermal conductivity even at a relatively low sintering temperature. This is also advantageous in increasing the field effect mobility and reliability of the semiconductor device.

  [6] In the oxide sintered body of the present embodiment, the third crystal phase can include a fifth crystal phase that is a zinc tungstate compound crystal phase. This is advantageous in realizing an oxide sintered body having a high apparent density and a high thermal conductivity even at a relatively low sintering temperature, and also improves the field effect mobility and reliability of the semiconductor device. It is advantageous also in raising.

  [7] In the oxide sintered body of the present embodiment, the first crystal phase may further include an indium tungstate compound crystal phase. This is advantageous in realizing an oxide sintered body having a high apparent density and a high thermal conductivity even at a relatively low sintering temperature, and also improves the field effect mobility and reliability of the semiconductor device. It is advantageous also in raising.

[8] The oxide sintered body of the present embodiment has an apparent density of greater than 6.4 g / cm ³ and 7.5 g / cm ³ or less, based on the sum of indium, tungsten and zinc in the oxide sintered body. The content of tungsten (hereinafter also referred to as “W content” of the oxide sintered body) is larger than 0.5 atomic% and not larger than 5.0 atomic%, and indium, tungsten and The zinc content relative to the total zinc (hereinafter also referred to as “Zn content” of the oxide sintered body) is 1.2 atomic% or more and less than 40 atomic%, and zinc relative to tungsten in the oxide sintered body The atomic ratio (hereinafter also referred to as “Zn / W ratio” of the oxide sintered body) is preferably larger than 1.0 and smaller than 80. The apparent density within the above range is advantageous when the oxide sintered body of the present embodiment is used as a sputtering target. The W content, Zn content, and Zn / W ratio being in the above ranges are advantageous for realizing an oxide sintered body that has a high apparent density and a high thermal conductivity even at a relatively low sintering temperature. It is also advantageous for enhancing the field effect mobility and reliability of the semiconductor device.

  [9] A sputter target according to another embodiment of the present invention includes the oxide sintered body of the above embodiment. Since the sputter target of this embodiment includes the oxide sintered body of the above-described embodiment, it is preferably used for forming an oxide semiconductor film of a semiconductor device with high field effect mobility and high reliability by a sputtering method.

  [10] A method for manufacturing a semiconductor device according to still another embodiment of the present invention is a method for manufacturing a semiconductor device including an oxide semiconductor film, the step of preparing the sputter target of the above embodiment, and the sputter target And forming the oxide semiconductor film by sputtering using a sputtering method. Since the semiconductor device obtained by the manufacturing method of this embodiment includes an oxide semiconductor film formed by sputtering using the sputtering target of the above embodiment, high field-effect mobility and reliability can be exhibited. The semiconductor device described here is not particularly limited, but a TFT (thin film transistor) including an oxide semiconductor film formed by a sputtering method using the sputtering target of the above embodiment as a channel layer is a preferable example.

  [11] In the method for manufacturing a semiconductor device of this embodiment, the content of tungsten with respect to the sum of indium, tungsten and zinc in the obtained oxide semiconductor film (hereinafter also referred to as “W content” of the oxide semiconductor film). ) Is larger than 0.5 atomic% and not larger than 5.0 atomic%, and the zinc content relative to the total of indium, tungsten and zinc in the oxide semiconductor film (hereinafter referred to as “Zn content ratio” in the oxide semiconductor film) Is 1 atomic percent or more and less than 40 atomic percent, and the atomic ratio of zinc to tungsten in the oxide semiconductor film (hereinafter also referred to as “Zn / W ratio” of the oxide semiconductor film) is from 1.0. It is preferably larger and smaller than 80. Since the semiconductor device obtained by the manufacturing method of this embodiment includes an oxide semiconductor film formed using the sputtering target of the above embodiment, high field-effect mobility and reliability can be exhibited.

  [12] In the semiconductor device manufacturing method of the present embodiment, the obtained oxide semiconductor film can be composed of at least one of nanocrystalline oxide and amorphous oxide. This is advantageous in increasing the field effect mobility and reliability in a semiconductor device including an oxide semiconductor film as a channel layer, for example.

  [13] A method for manufacturing an oxide sintered body according to still another embodiment of the present invention is a method for manufacturing an oxide sintered body according to the above-described embodiment, and includes an indium oxide powder and a tungsten oxide powder. A step of preparing a primary mixture, a step of forming a calcined powder by heat-treating the primary mixture, a step of preparing a secondary mixture of raw material powders including the calcined powder, and forming the secondary mixture The step of forming a sintered body and the step of forming an oxide sintered body by sintering the molded body, and the step of forming the calcined powder is performed at 700 ° C. or higher and lower than 1400 ° C. in an oxygen-containing atmosphere. Forming a double oxide powder containing indium and tungsten as a pre-fired powder by heat-treating the primary mixture at a temperature of According to the method for producing an oxide sintered body of the present embodiment, an oxide sintered body having a high apparent density at a relatively low sintering temperature and suitable for use as a sputtering target, and having a high thermal conductivity. It can be obtained relatively easily.

[14] In the method for manufacturing an oxide sintered body according to the embodiment according to [13], the double oxide may include an In ₆ WO ₁₂ type crystal phase. This is advantageous in obtaining an oxide sintered body with high apparent density and high thermal conductivity.

  [15] A method for manufacturing an oxide sintered body according to still another embodiment of the present invention is a method for manufacturing an oxide sintered body according to the above-described embodiment, and includes a zinc oxide powder and a tungsten oxide powder. A step of preparing a primary mixture, a step of forming a calcined powder by heat-treating the primary mixture, a step of preparing a secondary mixture of raw material powders including the calcined powder, and forming the secondary mixture The step of forming a calcined powder including the step of forming a molded body by sintering and the step of forming an oxide sintered body by sintering the molded body is performed at 550 ° C. or more and less than 1200 ° C. in an oxygen-containing atmosphere. Forming a double oxide powder containing zinc and tungsten as a pre-fired powder by heat-treating the primary mixture at a temperature of According to the method for producing an oxide sintered body of the present embodiment, an oxide sintered body having a high apparent density at a relatively low sintering temperature and suitable for use as a sputtering target, and having a high thermal conductivity. It can be obtained relatively easily.

[16] In the method of manufacturing an oxide sintered body according to the embodiment according to [15], the double oxide may include a ZnWO ₄ type crystal phase. This is advantageous in obtaining an oxide sintered body with high apparent density and high thermal conductivity.

[17] In the method for manufacturing an oxide sintered body according to the embodiments of [13] to [16], the tungsten oxide powder is selected from the group consisting of a WO ₃ crystal phase, a WO ₂ crystal phase, and a WO _2.72 crystal phase. It may contain at least one selected crystal phase. This is advantageous in obtaining an oxide sintered body with high apparent density and high thermal conductivity.

  [18] In the method for producing an oxide sintered body according to the embodiments of [13] to [17], the tungsten oxide powder may have a median particle diameter d50 of 0.1 μm or more and 4 μm or less. This is advantageous in obtaining an oxide sintered body with high apparent density and high thermal conductivity.

<Details of Embodiment of the Present Invention>
[Embodiment 1: Oxide sintered body]
The oxide sintered body of the present embodiment is an oxide sintered body containing indium (In), tungsten (W), and zinc (Zn). The oxide sintered body of the present embodiment includes a first crystal phase that is a main component of the oxide sintered body and includes a bixbyite crystal phase, and 34.97 deg which is larger than 34.74 deg of 2θ in X-ray diffraction. And a second crystal phase having a first diffraction peak at a smaller position. The second crystal phase is included in a part of the oxide sintered body. The oxide sintered body of the present embodiment can exhibit a high apparent density and a high thermal conductivity even at a relatively low sintering temperature. The oxide sintered body of the present embodiment can be suitably used as a sputtering target for forming an oxide semiconductor film (for example, an oxide semiconductor film functioning as a channel layer) of a semiconductor device. According to the sintered body, it is possible to obtain a semiconductor device with high field effect mobility and high reliability.

(1) First Crystal Phase The first crystal phase is a main component of the oxide sintered body and is an indium high-content crystal phase described later including at least a bixbite type crystal phase. In this specification, the “bixbite type crystal phase” means a bixbite crystal phase, and a phase in which at least one of the metal elements other than In is included in at least a part of the bixbite crystal phase, A generic term for those having the same crystal structure. The bixbite crystal phase is one of the crystal phases of indium oxide (In ₂ O ₃ ), refers to the crystal structure defined in JCPDS card 6-0416, and is a rare earth oxide C-type phase (or C-rare). Also called soil structure phase.

  The inclusion of a bixbite type crystal phase can be identified by X-ray diffraction. That is, the existence of a bixbite type crystal phase is confirmed by X-ray diffraction, and the spacing between each plane can be measured. As the measurement conditions for X-ray diffraction, the conditions shown in the following “(2) Second crystal phase” are employed.

  “The first crystal phase including the bixbite type crystal phase is the main component of the oxide sintered body” means that in the oxide sintered body, the bixbite type crystal phase, the indium tungstate compound crystal phase, etc. This means that the ratio of the indium-rich crystal phase containing In in terms of content (the indium-rich crystal phase occupancy) is 50% or more.

The “indium-rich crystal phase occupancy” is measured as follows. First, a sample is taken from a part of the oxide sintered body, and the surface of the sample is polished and smoothed. Next, using SEM-EDX (scanning secondary electron microscope with an energy dispersive fluorescent X-ray analyzer), the surface of the sample is observed with SEM (scanning secondary electron microscope), and each crystal particle The metal elemental composition ratio is analyzed by EDX (energy dispersive fluorescence X-ray analyzer). Then, the crystal particles are grouped based on the tendency of the composition ratio of the metal elements of the crystal particles. Specifically, a group A of crystal grains containing Zn and more typically having a Zn content [Zn content (atomic%) with respect to the sum of In, W and Zn] higher than Group B described later. A group of crystal grains having a very low Zn content or no Zn content and a high In content (In content (atomic%) with respect to the sum of In, W and Zn) compared to Group A And B (indium-rich crystal phase). At this time, the crystal grains of group B are determined to be the first crystal phase (such as In ₂ O ₃ phase). The first crystal phase may include an indium tungstate compound crystal phase in addition to the bixbyite crystal phase. The “indium-rich crystal phase occupancy ratio” in the oxide sintered body is defined as the ratio (percentage) of the area of the indium-rich crystal phase (group B) to the measurement surface of the oxide sintered body. Is done. The oxide sintered body according to this embodiment including the first crystal phase (indium-rich crystal phase) as a main component has an indium-rich crystal phase occupancy of 50% or more according to this definition.

  In the first crystal phase, W and / or Zn may be dissolved in at least a part thereof. This is advantageous in realizing an oxide sintered body having a high apparent density and a high thermal conductivity even at a relatively low sintering temperature, and is formed using the oxide sintered body. This is also advantageous in increasing the field effect mobility and reliability of a semiconductor device including an oxide semiconductor film as a channel layer.

  “W and / or Zn is solid-dissolved in at least a part of the first crystal phase” means that W and / or Zn is a substitutional solid in at least a part of the crystal lattice of the first crystal phase. It means a dissolved form, an interstitial solid solution form between crystal lattices, or a solid solution form in both substitutional and interstitial forms.

  In the oxide sintered body according to the present embodiment, when W and / or Zn is dissolved in at least a part of the bixbite type crystal phase included in the first crystal phase, it is defined in JCPDS card 6-0416. It becomes wider or narrower than the surface spacing. In X-ray diffraction, the peak position shifts to the high angle side or shifts to the low angle side. While such peak shift is confirmed, SEM-EDX (scanning secondary electron microscope with an energy dispersive fluorescence X-ray analyzer) and TEM-EDX (transmission with an energy dispersive fluorescence X-ray analyzer) Surface analysis by a type secondary electron microscope), and when the presence of a region in which In and W and / or Zn are mixed is confirmed, the bixbite type crystal phase contained in the first crystal phase contains W and / or Zn. It can be determined that is dissolved.

  Alternatively, the presence element is identified using ICP (inductively coupled plasma) mass spectrometry, SEM-EDX, and other element identification methods, and the presence of W and / or Zn together with In is confirmed. It can also be determined that W and / or Zn is solid-solved in the bixbite type crystal phase contained in the first crystal phase when the oxide of W and / or Zn is not confirmed by diffraction.

  The first crystal phase may further include an indium tungstate compound crystal phase. Further inclusion of an indium tungstate compound crystal phase is advantageous for realizing an oxide sintered body having a high apparent density and a high thermal conductivity even at a relatively low sintering temperature. This is also advantageous in increasing the field-effect mobility and reliability of a semiconductor device including an oxide semiconductor film formed using a combined body as a channel layer.

In this specification, “indium tungstate compound crystal phase” is a crystal phase mainly composed of In, W and O. For example, In ₆ WO ₁₂ crystal phase, InW ₃ O ₉ phase and the like can be mentioned. The In ₆ WO ₁₂ crystal phase is a trigonal crystal structure and is an indium tungstate compound crystal phase having a crystal structure defined by JCPDS card 01-074-1410. As long as the crystal system is shown, oxygen may be deficient or metal may be dissolved, and the lattice constant may be changed. The InW ₃ O ₉ phase has a hexagonal crystal structure and is an indium tungstate compound crystal phase having a crystal structure defined by JCPDS card 33-627. As long as the crystal system is shown, oxygen may be deficient or metal may be dissolved, and the lattice constant may be changed.

The presence of the indium tungstate compound crystal phase can be confirmed by the presence of a peak attributed to the “indium tungstate compound crystal phase” in X-ray diffraction. For example, it can be confirmed by the presence of peaks attributed to the above-mentioned In ₆ WO ₁₂ crystal phase and InW ₃ O ₉ phase. As the measurement conditions for the X-ray diffraction, the conditions shown in the above “(2) Second crystal phase” are employed.

(2) Second Crystal Phase The second crystal phase is a crystal phase different from the first crystal phase, and has a first diffraction peak at a position larger than 34.74 deg of 2θ in X-ray diffraction and smaller than 34.97 deg. Crystalline phase. The oxide sintered body according to the present embodiment including the first crystal phase and a second crystal phase different from the first crystal phase can exhibit a high apparent density even at a relatively low sintering temperature, and also exhibits a high thermal conductivity. be able to. The position of the first diffraction peak is preferably smaller than 34.90 deg of 2θ from the viewpoint of apparent density and thermal conductivity. The second crystal phase is included in a part of the oxide sintered body.

  The presence of the second crystal phase can be confirmed by X-ray diffraction. X-ray diffraction is measured under the following conditions or equivalent conditions.

(Measurement conditions for X-ray diffraction)
θ-2θ method,
X-ray source: Cu Kα ray,
X-ray tube voltage: 45 kV,
X-ray tube current: 40 mA,
Step width: 0.03 deg.
Step time: 1 second / step,
Measurement range 2θ: 10 deg to 90 deg.

The fact that the first diffraction peak is observed at a position larger than 34.74 deg of 2θ in X-ray diffraction and smaller than 34.97 deg means that the surface interval is larger than 2.56 Å and smaller than 2.58 Å. It has been clarified that the first diffraction peak does not coincide with the diffraction peak position of an oxide or composite oxide composed of one or more of In, W and Zn and an oxygen atom. Examples of the oxide include In ₂ O ₃ phase, which is a bixbite type crystal phase, hexagonal wurtzite crystal ZnO, and monoclinic WO ₃ . Examples of the composite oxide include ZnWO ₄ , In ₆ WO ₁₂ , and In ₂ O ₃ (ZnO) _m (m is a natural number). A second crystal phase having a first diffraction peak that does not coincide with the diffraction peak position of the oxide or the composite oxide and is located in a range of 2θ greater than 34.74 deg and less than 34.97 deg in X-ray diffraction In addition, the oxide sintered body of the present embodiment that further includes can exhibit a high apparent density and a high thermal conductivity even at a relatively low sintering temperature. According to the oxide sintered body, field effect mobility and reliability of a semiconductor device including an oxide semiconductor film formed using the oxide sintered body as a channel layer can be improved.

(3) Third Crystal Phase The oxide sintered body of the present embodiment is preferably a crystal phase different from the first crystal phase and includes a third crystal phase containing zinc (Zn). The inclusion of the third crystal phase is advantageous in realizing an oxide sintered body having a high apparent density and a high thermal conductivity even at a relatively low sintering temperature. This is also advantageous in increasing the field-effect mobility and reliability of a semiconductor device including the oxide semiconductor film formed using the channel layer as a channel layer. The third crystal phase may be the same phase as the second crystal phase. The third crystal phase is a phase that can be included in part of the oxide sintered body.

  The third crystal phase is a crystal phase containing Zn, and more typically a phase in which the Zn content [the Zn content (atomic%) relative to the sum of In, W and Zn] is higher than that of the first crystal phase. is there. The presence of the third crystal phase can be confirmed by surface analysis using SEM-EDX performed when obtaining the indium-rich crystal phase occupancy ratio. The crystal phase constituting the crystal particles is the third crystal phase. The third crystal phase preferably has a Zn content of 50 atomic% or more. From the viewpoint of realizing an oxide sintered body having a high apparent density and a high thermal conductivity even at a relatively low sintering temperature, the Zn content of the third crystal phase is more preferably 60 atomic% or more, More preferably, it is 70 atomic% or more. The Zn content of the third crystal phase may be 100 atomic%.

  The third crystal phase may be at least one crystal phase selected from the group consisting of a fourth crystal phase described later, a fifth crystal phase that is a zinc tungstate compound crystal phase described later, and a hexagonal wurtzite crystal phase. The third crystal phase may consist of only one type of crystal phase or may contain two or more types of crystal phases.

  The crystal grains constituting the third crystal phase preferably have an average major axis diameter of 3 to 50 μm and an average aspect ratio of 4 to 50. This is advantageous in realizing an oxide sintered body having a high apparent density and high thermal conductivity even at a relatively low sintering temperature, and is formed using the oxide sintered body. This is also advantageous in increasing the field effect mobility and reliability of a semiconductor device including an oxide semiconductor film as a channel layer.

  The average major axis diameter and average aspect ratio are determined as follows. When a reflected electron image is used for SEM observation in the surface analysis using SEM-EDX, which is performed when obtaining the indium-rich crystal phase occupancy, group A, which is the third crystal phase, is classified as the first crystal phase. It is observed in a dark gray color compared to Group B. The major axis length and minor axis length of the crystal grains constituting the third crystal phase observed in dark gray in the backscattered electron image taken at 500 times are measured, and the ratio of the major axis length to the minor axis length (long The aspect ratio is calculated (axis length / short axis length). The minor axis length is measured at a position that is 1/2 the major axis length. Note that the third crystal phase to be measured does not have to be a single crystal, and may be a particle in which polycrystals are gathered together. One independent third crystal phase region surrounded by the first crystal phase may be used. Measure as one particle.

  In the SEM observation, 100 short axis lengths and 100 long axis lengths of the third crystal phase in the 170 μm × 250 μm field of the backscattered electron image taken at 500 times are measured randomly, and the long axis length is measured in order from the longest. The average value of 20 from the 3rd position to the 22nd position arranged in the above is defined as the average major axis diameter.

  Similarly, 100 short axis lengths and long axis lengths of the third crystal phase in the 170 μm × 250 μm field of the backscattered electron image taken at 500 times in SEM observation were measured at random, and the aspect ratio ( (Major axis length / minor axis length) is calculated, and an average value of 20 average values from the 3rd position to the 22nd position in which the obtained aspect ratios are arranged in order from the longest side is defined as the average aspect ratio.

  An average major axis diameter of 3 μm or more and 50 μm or less is advantageous in increasing the apparent density and thermal conductivity of the oxide sintered body. When the average major axis diameter is smaller than 3 μm, a sufficiently high thermal conductivity tends not to be obtained. When the average major axis diameter is larger than 50 μm, a sufficiently high apparent density tends not to be obtained. The average major axis diameter is more preferably 10 μm or more, and further preferably 15 μm or more. The average major axis diameter is more preferably 40 μm or less, and further preferably 30 μm or less.

  An average aspect ratio of 4 or more and 50 or less is advantageous in increasing the apparent density and thermal conductivity of the oxide sintered body. When the average aspect ratio is less than 4, a sufficiently high thermal conductivity tends not to be obtained. When the average aspect ratio is greater than 50, a sufficiently high apparent density tends not to be obtained. The average aspect ratio is more preferably 6 or more, and still more preferably 8 or more. The average aspect ratio is more preferably 40 or less, and still more preferably 30 or less.

  The third crystal phase is preferably dispersed in the first crystal phase. This is advantageous when the oxide sintered body of the present embodiment is used as a sputtering target.

  In the sputtering method, the voltage applied to the sputtering target may be a DC voltage. In this case, the sputtering target is desired to have conductivity. This is because when the electric resistance of the sputtering target is increased, a direct-current voltage cannot be applied and film formation by sputtering (formation of an oxide semiconductor film) cannot be performed.

  In the oxide sintered body used as a sputtering target, there is a region with a high electrical resistance in a part thereof, and when the region is wide, a direct current voltage is not applied to the region with a high electrical resistance, so that region is not sputtered. May cause problems. Alternatively, abnormal discharge called arcing may occur in a region with high electrical resistance, which may cause problems such as film formation not being performed normally.

  Since the third crystal phase has a higher electrical resistance than the first crystal phase, there is a possibility that the above-described problem occurs when the third crystal phase exists over a wide region. In view of this point, as described above, the third crystal phase is preferably dispersed in the first crystal phase. The term “dispersion” as used herein means that the crystal grains having an average major axis diameter of 3 μm or more and 50 μm or less and an average aspect ratio of 4 or more and 50 or less are preferably present in an aggregate of 1 or at most 5 or less. Means that Confirmation of the dispersion state can be confirmed by the reflected electron image obtained by SEM observation of 500 times as described above.

  The third crystal phase is a crystal phase different from the first crystal phase, and includes a fourth crystal phase having a second diffraction peak at a position larger than 31.77 deg of 2θ in X-ray diffraction and smaller than 32.00 deg. Is preferred. The inclusion of the fourth crystal phase is advantageous in realizing an oxide sintered body having a high apparent density and a high thermal conductivity even at a relatively low sintering temperature. This is also advantageous in increasing the field-effect mobility and reliability of a semiconductor device including the oxide semiconductor film formed using the channel layer as a channel layer. The fourth crystal phase may be the same phase as the second crystal phase. The fourth crystal phase is a phase that can be included in a part of the oxide sintered body.

  In order to realize an oxide sintered body having a high apparent density and a high thermal conductivity even at a relatively low sintering temperature, the position of the second diffraction peak is preferably larger than 31.8 deg, and preferably 31. .96 deg or less. The fact that the second diffraction peak is observed at a position larger than 31.77 deg of 2θ and smaller than 32.00 deg in X-ray diffraction means that it has an interplanar spacing larger than 2.795 mm and smaller than 2.814 mm.

The presence of the fourth crystal phase can be confirmed by X-ray diffraction. As the measurement conditions for the X-ray diffraction, the conditions shown in the above “(2) Second crystal phase” are employed. For example, In ₂ O ₃ (ZnO) ₅ can be considered as the fourth crystal phase, but the position of the second diffraction peak indicated by the fourth crystal phase is generally more than the diffraction peak position of In ₂ O ₃ (ZnO) _5. Since it is in the vicinity of 31.92 deg on the low angle side, it is not certain at present whether the fourth crystal phase is actually In ₂ O ₃ (ZnO) ₅ . Further, when the fourth crystal phase is actually In ₂ O ₃ (ZnO) ₅ , the fourth crystal phase is different from the second crystal phase.

  In the oxide sintered body of the present embodiment, the ratio Ia / Ib between the peak intensity Ia of the first diffraction peak and the peak intensity Ib of the second diffraction peak is preferably 0.05 or more and 3 or less. Ia / Ib of 0.05 or more and 3 or less is advantageous in realizing an oxide sintered body having a high apparent density and a high thermal conductivity even at a relatively low sintering temperature, This is also advantageous in increasing the field effect mobility and reliability of a semiconductor device including an oxide semiconductor film formed using an oxide sintered body as a channel layer.

  When Ia / Ib is less than 0.05, the thermal conductivity of the obtained oxide sintered body tends not to be sufficiently high. From this viewpoint, Ia / Ib is more preferably 0.1 or more, and further preferably 0.2 or more. It is not easy to prepare an oxide sintered body having Ia / Ib greater than 3. From the viewpoint of obtaining high thermal conductivity, Ia / Ib is more preferably 2 or less.

The peak intensities Ia and Ib in X-ray diffraction are obtained as follows. First, the average value Iave of the signal intensity I of X-ray diffraction in the range where 2θ is 32.15 deg or more and 32.90 deg or less is calculated. Next, the signal intensity Ia ′ of the first diffraction peak and the signal intensity Ib ′ of the second diffraction peak are measured, and the peak intensity Ia of the first diffraction peak is expressed by the following formula:
Ia = Ia′−Iave
Ask more. Similarly, the peak intensity Ib of the second diffraction peak is expressed by the following formula:
Ib = Ib′−Iave
Ask more. The purpose of this calculation is to remove the background in X-ray diffraction.

  Ia / Ib shows a value specific to the material when the sample is non-oriented, but in the oxide sintered body of the present embodiment, Ia / Ib may show a value different from the value specific to the material. . In this case, when the second crystal phase having the first diffraction peak and the fourth crystal phase having the second diffraction peak are the same compound, it is considered that the present compound has orientation. Further, when the second crystal phase having the first diffraction peak and the fourth crystal phase having the second diffraction peak are different compounds, the second crystal phase and / or the fourth crystal phase have orientation. Or a value reflecting the ratio of the second crystal phase and the fourth crystal phase. The thermal conductivity and mechanical strength of the oxide sintered body may vary depending on the crystal orientation, but in the oxide sintered body of this embodiment, Ia / Ib is high when it is 0.05 or more and 3 or less. This is advantageous in realizing thermal conductivity and high mechanical strength.

  The third crystal phase is a crystal phase different from the first crystal phase, and can include a fifth crystal phase that is a zinc tungstate compound crystal phase. Further including the fifth crystal phase is advantageous in realizing an oxide sintered body having a high apparent density and a high thermal conductivity even at a relatively low sintering temperature. This is also advantageous in increasing the field effect mobility and reliability of a semiconductor device including an oxide semiconductor film formed using a silicon oxide as a channel layer. The fifth crystal phase may be the same phase as the second crystal phase or the fourth crystal phase. The fifth crystal phase is a phase that can be included in part of the oxide sintered body.

In this specification, the “zinc tungstate compound crystal phase” is a crystal phase mainly composed of Zn, W and O. For example, a ZnWO ₄ type crystal phase can be mentioned. The "ZnWO ₄ type crystal phase", ZnWO ₄ crystalline phase, and at least a portion of ZnWO ₄ crystalline phase a phase that contains at least one element other than Zn and W, the same crystal structure as ZnWO ₄ crystalline phase This is a general term for those having The ZnWO ₄ crystal phase is a zinc tungstate compound crystal phase having a crystal structure represented by the space group P12 / c1 (13) and having a crystal structure defined by JCPDS card 01-088-0251. As long as the crystal system is shown, oxygen may be deficient or metal may be dissolved, and the lattice constant may be changed.

The presence of the fifth crystal phase can be confirmed by the presence of a peak attributed to the “zinc tungstate compound crystal phase” in X-ray diffraction. For example, it can be confirmed by the presence of a peak attributed to the above-described ZnWO ₄ type crystal phase. As the measurement conditions for the X-ray diffraction, the conditions shown in the above “(2) Second crystal phase” are employed.

  The third crystal phase can further include a hexagonal wurtzite crystal phase. Further inclusion of a hexagonal wurtzite crystal phase is advantageous for realizing an oxide sintered body having a high apparent density and a high thermal conductivity even at a relatively low sintering temperature. This is also advantageous in increasing the field-effect mobility and reliability of a semiconductor device including an oxide semiconductor film formed using a combined body as a channel layer. The hexagonal wurtzite crystal phase may be the same phase as the fourth crystal phase. When the hexagonal wurtzite crystal phase is the fourth crystal phase, the fourth crystal phase and the second crystal phase are different. The hexagonal wurtzite crystal phase is a phase that can be included in part of the oxide sintered body.

  As used herein, the term “hexagonal wurtzite crystal phase” refers to a hexagonal wurtz crystal phase and a phase in which at least a part of the hexagonal wurtz crystal phase contains at least one metal element other than Zn, A generic term for those having the same crystal structure as the Wurtz crystal phase. The hexagonal wurtz crystal phase is one of the crystal phases of zinc oxide (ZnO), and space group: P63mc, space group no. : A crystal structure represented by 186 and defined in JCPDS card 01-079-0207.

  The presence of the hexagonal wurtzite crystal phase can be confirmed by the presence of a peak attributed to the “hexagonal wurtzite crystal phase” in X-ray diffraction. For example, it can be confirmed by the presence of a peak attributed to the above zinc oxide. As the measurement conditions for the X-ray diffraction, the conditions shown in the above “(2) Second crystal phase” are employed.

  The hexagonal wurtzite crystal phase may contain ZnO as a main component, and W and / or In may be dissolved in substitutional or interstitial forms at least in part. In the confirmation of the solid solution, X-ray diffraction, SEM-, as well as the above-mentioned method for confirming that “W and / or Zn is dissolved in at least a part of the first crystal phase”. A technique using EDX or TEM-EDX can be applied.

(4) Apparent density, W content, Zn content, and Zn / W ratio of the oxide sintered body The oxide sintered body of the present embodiment has an apparent density greater than 6.4 g / cm ³ and 7.5 g / It is preferable that it is cm ³ or less. The oxide sintered body of the present embodiment preferably has a relative density (relative density / theoretical density) of 94% or more, which is the ratio of the apparent density to the theoretical density. Theoretical density of the oxide sintered body of the present embodiment, the In content, depending on the W content and Zn content, calculated ^{on, 6.8g / cm 3 ~7.5g / cm} 3 range of values Can be taken.

  The apparent density within the above range is advantageous when the oxide sintered body of the present embodiment is used as a sputtering target. When an oxide sintered body is used as a sputter target, the apparent density of the oxide sintered body is preferably as high as possible. The low apparent density of the oxide sintered body means that there are many voids in the oxide sintered body. The sputter target is used while its surface is etched with argon ions during use. Therefore, if there are vacancies in the oxide sintered body, they are exposed during film formation and the internal gas is released, so that the gas released from the target is mixed into the deposited oxide semiconductor thin film. As a result, the film characteristics deteriorate. In addition, it is known that if the apparent density of the oxide sintered body is low, an In insulator called nodule is generated on the target during film formation, and good sputter discharge is inhibited. It is desired to increase the apparent density of the oxide sintered body.

  The oxide sintered body of the present embodiment has a W content greater than 0.5 atomic% and 5.0 atomic% or less, a Zn content of 1.2 atomic% or more and less than 40 atomic%, Zn / The W ratio is preferably larger than 1.0 and smaller than 80. The W content, Zn content, and Zn / W ratio being in the above ranges are advantageous for realizing an oxide sintered body that has a high apparent density and a high thermal conductivity even at a relatively low sintering temperature. In addition, it is advantageous in increasing the field effect mobility and reliability of a semiconductor device including an oxide semiconductor film formed using an oxide sintered body as a channel layer.

  From the viewpoint of enhancing field effect mobility and reliability, the W content of the oxide sintered body is more preferably 0.6 atomic percent or more and 3 atomic percent or less, and further preferably 2 atomic percent or less. When the W content of the oxide sintered body is 0.5 atomic% or less, in a semiconductor device including an oxide semiconductor film formed using the oxide sintered body as a channel layer, the reliability becomes low. End up. When the W content of the oxide sintered body exceeds 5 atomic%, in a semiconductor device including an oxide semiconductor film formed using a sputtering target including the oxide sintered body as a channel layer, field effect mobility Will be lower.

  Thus, preferably, the range of the W content of the oxide sintered body is determined by the characteristics of the semiconductor device including the oxide semiconductor film formed using the oxide sintered body of the present embodiment as a channel layer. The W content of the oxide semiconductor film usually indicates a value corresponding to the W content of the oxide sintered body. However, the W content of the oxide semiconductor film does not necessarily match the W content of the oxide sintered body.

  An oxide sintered body obtained by mixing indium oxide and tungsten oxide generally has a small apparent density. Although the apparent density can be increased by containing Zn and increasing the contact points between W and Zn, the desired W content determined in consideration of the characteristics of the semiconductor device is greater than 0.5 atomic%. Since the amount is as small as 0 atomic% or less, it is preferable to increase the Zn content in order to realize an oxide sintered body having a higher apparent density. When the Zn content is less than 1.2 atomic%, it tends to be difficult to obtain a sufficiently high apparent density. When the Zn content is 40 atomic% or more, the electric resistance of the oxide sintered body increases, and it tends to be difficult to perform sputtering by applying a DC voltage. Further, when the Zn / W ratio is 1.0 or less, it tends to be difficult to obtain a sufficiently high apparent density. When the Zn / W ratio is 80 or more, the electric resistance of the oxide sintered body becomes high, and it tends to be difficult to perform sputtering by applying a DC voltage. The contents of In, Zn, and W in the oxide sintered body can be measured by ICP mass spectrometry.

Note that the oxide sintered body of the present embodiment may further contain zirconium (Zr). The content is, for example, 1 × 10 ¹⁷ atms / cm ³ or more and 1 × 10 ²⁰ atms / cm ³ or less. Zr is an element that can be mixed in the manufacturing process of the oxide sintered body, but does not hinder achieving a high apparent density. The presence of Zr and its content can be confirmed with a secondary ion mass spectrometer.

(5) Application of oxide sintered body to sputter target The oxide sintered body of the present embodiment can be suitably used as a sputter target. The sputter target is a raw material for the sputtering method. In the sputtering method, a sputtering target and a substrate are placed facing each other in a film forming chamber, a voltage is applied to the sputtering target, and the surface of the target is sputtered with rare gas ions, thereby forming atoms constituting the target from the target. This is a method of forming a film composed of atoms constituting the target by releasing and depositing on the substrate.

  The sputtering target is heated because a current flows according to the applied voltage. For this reason, the oxide sintered body is generally attached to a copper backing plate with indium metal and water-cooled from the copper side. The higher the power applied to the sputtering target, the higher the heating temperature of the sputtering target.

  In order to further improve the reliability of a semiconductor device including an oxide semiconductor film formed by sputtering using an oxide sintered body as a sputtering target, it is preferable to increase the power applied to the sputtering target during sputtering. However, since the heating temperature of the sputter target increases as the applied power is increased, the oxide sintered body is subject to tensile stress and cracks due to the difference in thermal expansion between the copper backing plate and the oxide sintered body during film formation. There is. In order to suppress this cracking, it is desired to increase the cooling efficiency by water cooling by increasing the thermal conductivity of the oxide sintered body, and to suppress the heating temperature of the oxide sintered body even when the same power is applied. . The oxide sintered body of the present embodiment is an oxide sintered body with high thermal conductivity that meets such requirements, and a third crystal phase (a crystal phase composed of columnar particles) having a large average aspect ratio. In an oxide sintered body containing (preferably containing many), particularly high thermal conductivity can be exhibited.

[Embodiment 2: Method for producing oxide sintered body]
One method for producing an oxide sintered body according to this embodiment is a method for producing an oxide sintered body according to Embodiment 1, in which a primary mixture of zinc oxide powder and tungsten oxide powder is used. A step of preparing, a step of forming a calcined powder by heat-treating the primary mixture, a step of preparing a secondary mixture of raw material powders including the calcined powder, and a molded body by molding the secondary mixture A step of forming, and a step of forming an oxide sintered body by sintering the formed body. In the step of forming the calcined powder, the primary mixture is heat-treated at a temperature of 550 ° C. or higher and lower than 1200 ° C. in an oxygen-containing atmosphere, thereby forming a double oxide powder containing Zn and W as the calcined powder. Including that.

  According to the above manufacturing method, in the step of forming the calcined powder, the primary mixture of the zinc oxide powder and the tungsten oxide powder is heat-treated at a temperature of 550 ° C. or more and less than 1200 ° C. in an oxygen-containing atmosphere. Thus, it includes forming a double oxide powder containing Zn and W as the calcined powder, so that the apparent density is high even at a relatively low sintering temperature, and it is suitably used as a sputtering target having a high thermal conductivity. An oxide sintered body that can be obtained can be obtained. The double oxide may be deficient in oxygen or substituted with metal.

  If the temperature of the heat treatment is less than 550 ° C., a double oxide powder containing Zn and W cannot be obtained, and if it is 1200 ° C. or higher, the double oxide powder containing Zn and W is decomposed or scattered. The particle size of the double oxide powder tends to be too large for use.

  In addition, by forming a double oxide powder containing Zn and W as a calcined powder by the heat treatment, an oxide semiconductor film formed using a sputter target containing an oxide sintered body obtained is formed into a channel layer. In the semiconductor device including the field effect mobility and reliability can be increased more effectively.

The double oxide containing Zn and W preferably contains a ZnWO ₄ type crystal phase. Thereby, the apparent density of oxide sintered compact can be raised more effectively. The ZnWO ₄ type crystal phase is a zinc tungstate compound crystal phase having a crystal structure represented by the space group P12 / c1 (13) and having a crystal structure defined by JCPDS card 01-088-0251. . As long as the crystal system is shown, oxygen may be deficient or metal may be dissolved, and the lattice constant may be changed. The ZnWO ₄ type crystal phase is identified by X-ray diffraction measurement.

  Moreover, another one of the manufacturing methods of the oxide sintered compact which concerns on this embodiment is a manufacturing method of the oxide sintered compact which concerns on Embodiment 1, Comprising: Indium oxide powder and tungsten oxide powder A step of preparing a primary mixture, a step of forming a calcined powder by heat-treating the primary mixture, a step of preparing a secondary mixture of raw material powders including the calcined powder, and forming the secondary mixture The step of forming a molded body by the above and the step of forming an oxide sintered body by sintering the molded body are included. In the step of forming the calcined powder, the primary mixture is heat-treated at a temperature of 700 ° C. or higher and lower than 1400 ° C. in an oxygen-containing atmosphere, thereby forming a double oxide powder containing In and W as the calcined powder. Including that.

  According to the above manufacturing method, in the step of forming the calcined powder, the primary mixture of the indium oxide powder and the tungsten oxide powder is heat-treated at a temperature of 700 ° C. or higher and lower than 1400 ° C. in an oxygen-containing atmosphere. Therefore, it is suitable for use as a sputtering target having a high apparent density and a high thermal conductivity even at a relatively low sintering temperature. An oxide sintered body that can be obtained can be obtained. The double oxide may be deficient in oxygen or substituted with metal.

  If the temperature of the heat treatment is less than 700 ° C., a double oxide powder containing In and W cannot be obtained. The particle size of the double oxide powder tends to be too large for use.

  In addition, by forming a double oxide powder containing In and W as the calcined powder by the heat treatment, an oxide semiconductor film formed using a sputter target containing an oxide sintered body obtained is formed into a channel layer. In the semiconductor device including the field effect mobility and reliability can be increased more effectively.

The double oxide containing In and W preferably contains an In ₆ WO ₁₂ type crystal phase. Thereby, the apparent density of oxide sintered compact can be raised more effectively. The In ₆ WO ₁₂ crystal phase is a trigonal crystal structure and is an indium tungstate compound crystal phase having a crystal structure defined by JCPDS card 01-074-1410. As long as the crystal system is shown, oxygen may be deficient or metal may be dissolved, and the lattice constant may be changed. Note that the indium tungstate compound crystal phase disclosed in Japanese Patent Application Laid-Open No. 2004-091265 is an InW ₃ O ₉ crystal phase, has a hexagonal crystal structure, and is defined in JCPDS Card 33-627. The crystal structure is different from the In ₆ WO ₁₂ crystal phase. In ₆ WO ₁₂ type crystal phase is identified by X-ray diffraction measurement.

  It is known that W inhibits the sintering of indium oxide, and consequently inhibits the achievement of a high apparent density of the oxide sintered body. However, according to the manufacturing method of the present invention, a powder of a double oxide containing In and W and / or a powder of a double oxide containing Zn and W and / or a double oxide containing In and Zn By using this powder, it is possible to obtain an oxide sintered body having a high apparent density at a low sintering temperature. Moreover, the obtained oxide sintered body has a high thermal conductivity.

  In order to increase the apparent density of an oxide sintered body containing In, W and Zn, it is effective to have a double oxide containing Zn and W having a low melting point present during sintering. For this purpose, it is preferable to increase the contact points of tungsten oxide and zinc oxide during sintering to form a double oxide containing Zn and W. Therefore, from the viewpoint of obtaining a high apparent density even at a low sintering temperature, a method of using a pre-synthesized composite oxide powder containing Zn and W in a manufacturing process, a pre-synthesized composite oxide containing In and W, It is preferable to use a method of increasing the contact point with Zn by using powder. These methods may be used alone or in combination. For example, a method of using a composite oxide powder containing Zn and W synthesized in advance in a manufacturing process and a method using a composite oxide powder containing indium and tungsten synthesized beforehand may be used in combination. From the viewpoint of realizing a high apparent density and high thermal conductivity at a low sintering temperature, it is more preferable to use at least a method of using a powder of a complex oxide containing Zn and W synthesized in advance in the manufacturing process.

It is preferable that the tungsten oxide powder used for manufacturing the oxide sintered body includes at least one crystal phase selected from the group consisting of a WO ₃ crystal phase, a WO ₂ crystal phase, and a WO _2.72 crystal phase. Thereby, the apparent density of the oxide sintered body can be increased more effectively, and it is advantageous for increasing the field-effect mobility and reliability.

  The tungsten oxide powder preferably has a median particle diameter d50 of 0.1 μm to 4 μm, more preferably 0.2 μm to 2 μm, and further preferably 0.3 μm to 1.5 μm. preferable. Thereby, the apparent density of oxide sintered compact can be raised more effectively. The median particle size d50 is determined by BET specific surface area measurement. When the median particle size d50 is smaller than 0.1 μm, it is difficult to handle the powder, and it tends to be difficult to uniformly mix the zinc oxide powder and the tungsten oxide powder or the indium oxide powder and the tungsten oxide powder. .

  When the median particle size d50 is larger than 4 μm, the mixed oxide powder containing Zn and W obtained by heat treatment at a temperature of 550 ° C. or more and less than 1200 ° C. in an oxygen-containing atmosphere after mixing with the zinc oxide powder. The particle size also increases, and it tends to be difficult to increase the apparent density of the oxide sintered body. Similarly, the particle size of the double oxide powder containing In and W obtained by heat treatment at a temperature of 700 ° C. or higher and lower than 1400 ° C. in an oxygen-containing atmosphere after being mixed with the indium oxide powder is also increased. Therefore, it tends to be difficult to increase the apparent density of the oxide sintered body.

  Although the manufacturing method of the oxide sintered compact which concerns on this embodiment does not have a restriction | limiting in particular, From a viewpoint of forming the oxide sintered compact of Embodiment 1 efficiently, the following processes are included, for example.

(1) Step of preparing raw material powder Indium oxide powder (for example, In ₂ O ₃ powder), tungsten oxide powder (for example, WO ₃ powder, WO _2.72 powder, WO ₂ powder) as the raw material powder of the oxide sintered body A metal element oxide powder constituting the oxide sintered body, such as zinc oxide powder (for example, ZnO powder), is prepared. As the tungsten oxide powder, it is possible to use not only WO ₃ powder but also powder having a chemical composition deficient in oxygen as compared with WO ₃ powder such as WO _2.72 powder and WO ₂ powder as a raw material. It is preferable from the viewpoint of improving mobility and reliability. From this viewpoint, it is more preferable to use at least one of WO _2.72 powder and WO ₂ powder as at least a part of the tungsten oxide powder. The purity of the raw material powder is preferably a high purity of 99.9% by mass or more from the viewpoint of preventing unintentional mixing of metal elements and Si into the oxide sintered body and obtaining stable physical properties.

  As described above, the median particle diameter d50 of the tungsten oxide powder is preferably 0.1 μm or more and 4 μm or less from the viewpoint of increasing the apparent density of the oxide sintered body.

(2) Step of preparing primary mixture (2-1) Step of preparing primary mixture of zinc oxide powder and tungsten oxide powder Among the above raw material powders, zinc oxide powder and tungsten oxide powder. Mix (or pulverize and mix). At this time, when it is desired to obtain a ZnWO ₄ type crystal phase as the crystal phase of the oxide sintered body, the tungsten oxide powder and the zinc oxide powder are mixed at a molar ratio of 1: 1 to Zn ₂ W ₃ O _8. In order to obtain a type crystal phase, the tungsten oxide powder and the zinc oxide powder are mixed at a molar ratio of 3: 2. As described above, from the viewpoint of more effectively increasing the apparent density of the oxide sintered body, and from the viewpoint of increasing the field effect mobility and reliability of the semiconductor device, the oxide sintered body has a ZnWO ₄ type phase. It is preferable to include. There is no particular limitation on the method of mixing the tungsten oxide powder and the zinc oxide powder, and any of dry and wet methods may be used, and specifically, pulverized and mixed using a ball mill, a planetary ball mill, a bead mill or the like. Is done. In this way, a primary mixture of raw material powders is obtained. A drying method such as natural drying or a spray dryer can be used to dry the mixture obtained using the wet pulverization and mixing method.

(2-2) Step of preparing a primary mixture of indium oxide powder and tungsten oxide powder Among the raw material powders, indium oxide powder and tungsten oxide powder are mixed (or ground and mixed). At this time, when it is desired to obtain an In ₆ WO ₁₂ type crystal phase as the crystal phase of the oxide sintered body, the tungsten oxide powder and the indium oxide powder are mixed at a molar ratio of 1: 3. There is no particular limitation on the method of mixing the tungsten oxide powder and the indium oxide powder, and any of dry and wet methods may be used. Specifically, pulverized and mixed using a ball mill, a planetary ball mill, a bead mill or the like. Is done. In this way, a primary mixture of raw material powders is obtained. A drying method such as natural drying or a spray dryer can be used to dry the mixture obtained using the wet pulverization and mixing method.

(3) Step of forming calcined powder (3-1) Step of forming calcined powder of zinc tungstate oxide The obtained primary mixture is heat-treated (calcined) to obtain calcined powder (Zn and W). A double oxide powder). The calcining temperature of the primary mixture is preferably less than 1200 ° C. so that the particle size of the calcined product becomes too large and the apparent density of the sintered body does not decrease. Zn and W are used as calcined products. In order to obtain a double oxide powder containing, and in order to obtain a ZnWO ₄ type crystal phase, the temperature is preferably 550 ° C. or higher. More preferably, it is 550 degreeC or more and less than 1000 degreeC, More preferably, it is 550 degreeC or more and 900 degrees C or less. As long as the calcination temperature is a temperature at which a crystal phase is formed, a lower calcination temperature is preferable from the viewpoint that the particle size of the calcination powder can be made as small as possible. In this way, a calcined powder containing a ZnWO ₄ type crystal phase can be obtained. The calcining atmosphere may be an atmosphere containing oxygen, but an air atmosphere having a higher pressure than atmospheric pressure or air, or an oxygen-nitrogen mixed atmosphere containing 25% by volume or more of oxygen having a pressure higher than atmospheric pressure or air. preferable. Since the productivity is high, an air atmosphere at atmospheric pressure or in the vicinity thereof is more preferable.

(3-2) Step of forming a calcined powder of indium tungstate oxide The obtained primary mixture is heat-treated (calcined) to form a calcined powder (a double oxide powder containing In and W). To do. The calcining temperature of the primary mixture is preferably less than 1400 ° C. so that the particle size of the calcined product becomes too large and the apparent density of the sintered body does not decrease. In order to obtain a double oxide powder containing, and in order to obtain an In ₆ WO ₁₂ type crystal phase, the temperature is preferably 700 ° C. or higher. More preferably, it is 800 degreeC or more and less than 1300 degreeC. As long as the calcination temperature is a temperature at which a crystal phase is formed, a lower calcination temperature is preferable from the viewpoint that the particle size of the calcination powder can be made as small as possible. In this way, a calcined powder containing an In ₆ WO ₁₂ type crystal phase can be obtained. The calcining atmosphere may be an atmosphere containing oxygen, but an air atmosphere having a higher pressure than atmospheric pressure or air, or an oxygen-nitrogen mixed atmosphere containing 25% by volume or more of oxygen having a pressure higher than atmospheric pressure or air. preferable. Since the productivity is high, an air atmosphere at atmospheric pressure or in the vicinity thereof is more preferable.

(4) Step of preparing a secondary mixture of raw material powder including calcined powder Next, the obtained calcined powder and the remaining powder of the raw material powder [indium oxide powder (for example, In ₂ O ₃ powder) ) Or zinc oxide powder (for example, ZnO powder)] is mixed (or ground and mixed) in the same manner as the preparation of the primary mixture. In this way, a secondary mixture of raw material powders is obtained. The tungsten oxide is preferably present as a double oxide by the calcination step.

(5) The process of forming a molded object by shape | molding a secondary mixture Next, the obtained secondary mixture is shape | molded. Although there is no restriction | limiting in particular in the method of shape | molding a secondary mixture, From the point which makes the apparent density of oxide sintered compact high, a uniaxial press method, a CIP (cold isostatic pressure processing) method, a casting method, etc. are preferable.

(6) Step of forming oxide sintered body by sintering molded body Next, the obtained molded body is sintered to form an oxide sintered body. At this time, it is preferable not to use the hot press sintering method in terms of productivity. Although there is no restriction | limiting in particular in the sintering temperature of a molded object, In order to make the apparent density of the oxide sintered compact formed larger than 6.4 g / cm < ³ >, it is preferable that it is 900 degreeC or more and lower than 1200 degreeC. There is no particular limitation on the sintering atmosphere, but from the viewpoint of preventing the generation of cracks by preventing the grain size of the constituent crystals of the oxide sintered body from increasing, an air atmosphere at or near atmospheric pressure is preferable. .

[Embodiment 3: Sputtering target]
The sputter target according to the present embodiment includes the oxide sintered body according to the first embodiment. Therefore, the sputter target according to this embodiment can be suitably used for forming an oxide semiconductor film of a semiconductor device having high field effect mobility and high reliability by a sputtering method.

  The sputter target according to this embodiment is preferably used for forming an oxide semiconductor film of a semiconductor device with high field effect mobility and high reliability by a sputtering method. It is preferable that a bonded body is included, and it is more preferable that the oxide sintered body of Embodiment 1 is included.

[Embodiment 4: Semiconductor Device and Manufacturing Method Thereof]
Referring to FIG. 1, a semiconductor device 10 according to the present embodiment is formed using the oxide sintered body of the first embodiment, or formed by sputtering using the sputter target of the third embodiment. A membrane 14 is included. Since the oxide semiconductor film 14 is included, the semiconductor device according to this embodiment can have characteristics of high field-effect mobility and high reliability.

  The semiconductor device 10 according to the present embodiment is not particularly limited, but is preferably a TFT (thin film transistor) because it has, for example, high field effect mobility and high reliability. The oxide semiconductor film 14 included in the TFT is preferably a channel layer because it has high field-effect mobility and high reliability.

  In the semiconductor device 10 according to the present embodiment, the W content of the oxide semiconductor film 14 is preferably greater than 0.5 atomic% and equal to or less than 5.0 atomic%, and the Zn content of the oxide semiconductor film 14 is The Zn / W ratio of the oxide semiconductor film 14 is preferably greater than 1.0 and less than 80. Thereby, the field effect mobility and reliability of the semiconductor device 10 can be improved.

  From the viewpoint of increasing the field effect mobility and reliability, the W content of the oxide semiconductor film 14 is more preferably not less than 0.6 atom% and not more than 3 atom%, and still more preferably not more than 2 atom%. When the W content of the oxide semiconductor film 14 is 0.5 atomic% or less, the reliability of the semiconductor device including the oxide semiconductor film 14 as a channel layer is lowered. When the W content of the oxide semiconductor film 14 exceeds 5 atomic%, field effect mobility is lowered in a semiconductor device including the oxide semiconductor film as a channel layer.

  When the oxide semiconductor film 14 has a Zn content of 1 atomic% or more and less than 40 atomic% and the oxide semiconductor film 14 has a Zn / W ratio of greater than 1.0 and less than 80, the oxide semiconductor film 14 is In a semiconductor device including a channel layer, field effect mobility can be increased and reliability can be increased.

  From the viewpoint of enhancing field effect mobility and reliability, the Zn content of the oxide semiconductor film 14 is more preferably greater than 3 atomic percent and less than 40 atomic percent, and even more preferably greater than 5 atomic percent and greater than 20 atomic percent. small.

  When the Zn content of the oxide semiconductor film 14 is smaller than 1 atomic%, the reliability of the semiconductor device including the oxide semiconductor film 14 as a channel layer is lowered. When the Zn content of the oxide semiconductor film 14 is 40 atomic% or more, field effect mobility is lowered in a semiconductor device including the oxide semiconductor film 14 as a channel layer.

  When the Zn / W ratio in the oxide semiconductor film 14 is 1.0 or less, the reliability of the semiconductor device including the oxide semiconductor film 14 as a channel layer is lowered. The Zn / W ratio is more preferably 3.0 or more, and further preferably 5.0 or more. When the Zn / W ratio in the oxide semiconductor film 14 is 80 or more, field effect mobility is low in a semiconductor device including the oxide semiconductor film 14 as a channel layer. The Zn / W ratio is more preferably less than 20.

  The chemical composition of the oxide semiconductor film 14, that is, the content of various elements is measured by RBS (Rutherford backscattering analysis). Based on this measurement result, W content rate, Zn content rate, and Zn / W ratio are calculated. When the analysis by RBS cannot be performed, it is measured by TEM-EDX (transmission electron microscope with an energy dispersive fluorescent X-ray analyzer). RBS measurement is desirable because of the accuracy of chemical composition measurement. When using TEM-EDX, first of all, it is composed of In, W, Zn, and O as a sample for preparing a calibration curve, has a composition close to the oxide semiconductor film to be measured, and can be analyzed by RBS At least three or more oxide semiconductor films are prepared. Next, for these samples, the contents of In, W and Zn are measured by RBS, and the contents of In, W and Zn are measured by TEM-EDX. From these measured values, a calibration curve showing the relationship between the measured values of In, W and Zn contents by TEM-EDX and the measured values of In, W and Zn contents by RBS is created. Then, after measuring the contents of In, W, and Zn by TEM-EDX for the oxide semiconductor film to be measured, the measured values are measured for the contents of In, W, and Zn by RBS based on the calibration curve. Convert to value. This converted value is the content of In, W, and Zn in the oxide semiconductor film to be measured.

The oxide semiconductor 14 may further contain zirconium (Zr). The content is, for example, 1 × 10 ¹⁷ atms / cm ³ or more and 1 × 10 ²⁰ atms / cm ³ or less. Zr is an element that can be mixed in the manufacturing process of the oxide sintered body, and can also be mixed in the oxide semiconductor film 14 formed using this oxide sintered body as a raw material. It does not hinder high field effect mobility and high reliability. The presence and content of zirconium can be confirmed with a secondary ion mass spectrometer.

  Here, the reliability of the semiconductor device will be described. In general, the reliability of a semiconductor device including an oxide semiconductor can change depending on the temperature of heat treatment during the manufacture of the semiconductor device. Reliability can be improved by increasing the temperature of the heat treatment. However, generally, when the heat treatment temperature is increased, the field effect mobility is lowered. For this reason, it has been desired that the field effect mobility does not decrease even at a high heat treatment temperature. In this specification, “the field effect mobility is high and the reliability is high” means that the field effect mobility does not decrease even at a high heat treatment temperature, and high reliability is obtained at a high heat treatment temperature. I mean.

  The oxide semiconductor film 14 is composed of at least one of a nanocrystalline oxide and an amorphous oxide, and has a high field effect mobility in a semiconductor device (for example, TFT) including this as a channel layer, and This is preferable because the reliability can be increased.

  In the present specification, the “nanocrystalline oxide” means that only a broad peak appearing on a low angle side called a halo is observed without observing a peak due to a crystal even by X-ray diffraction measurement according to the following conditions. And when the transmission electron beam diffraction measurement of a micro area | region is implemented according to the following conditions using a transmission electron microscope, the ring-shaped pattern is observed. The ring-shaped pattern includes a case where spots are gathered to form a ring-shaped pattern.

  Also, in this specification, “amorphous oxide” means that only a broad peak appearing on the low angle side called a halo is observed without a peak due to a crystal being observed even by X-ray diffraction measurement under the following conditions. In addition, an oxide in which an unclear pattern called a halo is observed even when transmission electron beam diffraction measurement of a fine region is performed according to the following conditions using a transmission electron microscope.

(X-ray diffraction measurement conditions)
Measuring method: In-plane method (slit collimation method),
X-ray generation part: counter cathode Cu, output 50 kV 300 mA,
Detector: Scintillation counter,
Incident part: slit collimation,
Solar slit: Incident side Longitudinal divergence angle 0.48 °
Light receiving side Longitudinal divergence angle 0.41 °,
Slit: incident side S1 = 1mm * 10mm
Light-receiving side S2 = 0.2mm * 10mm,
Scanning condition: scanning axis 2θχ / φ,
Scanning mode: step measurement, scanning range 10-80 °, step width 0.1 °,
Step time 8 sec. .

(Transmission electron diffraction measurement conditions)
Measuring method: Micro electron diffraction method,
Acceleration voltage: 200 kV,
Beam diameter: Same or equivalent to the thickness of the oxide semiconductor film to be measured.

  When the oxide semiconductor film 14 is composed of a nanocrystalline oxide, a ring-shaped pattern is observed as described above and a spot-shaped pattern is observed when transmission electron diffraction measurement of a fine region is performed according to the above conditions. Not. On the other hand, an oxide semiconductor film as disclosed in, for example, Japanese Patent No. 5172918 includes c-axis-oriented crystals along a direction perpendicular to the surface of the film. When the nanocrystals in the region are oriented in a certain direction, a spot-like pattern is observed. In the case where the oxide semiconductor film 14 is formed using a nanocrystalline oxide, the nanocrystal has a crystal with respect to the surface of the film when at least a plane (film cross section) perpendicular to the film plane is observed. It is non-oriented and has random orientation. That is, the crystal axis is not oriented with respect to the film thickness direction.

  Since the oxide semiconductor film 14 is composed of nanocrystalline oxide or amorphous oxide, high field-effect mobility can be achieved in a semiconductor device including the oxide semiconductor film 14 as a channel layer. In order to increase the field effect mobility, the oxide semiconductor film 14 is preferably made of an amorphous oxide. The film thickness of the oxide semiconductor film 14 is, for example, not less than 2 nm and not more than 60 nm.

In the semiconductor device of this embodiment, the oxide semiconductor film 14 preferably has an electrical resistivity of 10 ⁻¹ Ωcm or more. Many transparent conductive films using indium oxide have been studied so far, but the electrical resistivity is required to be smaller than 10 ⁻¹ Ωcm in applications of these transparent conductive films. On the other hand, the oxide semiconductor film included in the semiconductor device of this embodiment preferably has an electric resistivity of 10 ⁻¹ Ωcm or more, and thus can be suitably used as a channel layer of the semiconductor device. When the electrical resistivity is less than 10 ⁻¹ Ωcm, it is difficult to use as a channel layer of a semiconductor device.

  The oxide semiconductor film 14 can be obtained by a manufacturing method including a step of forming a film by a sputtering method. The meaning of the sputtering method is as described above. As a method for forming the oxide semiconductor film, a pulse laser deposition (PLD) method, a heating deposition method, and the like have been proposed in addition to the sputtering method. The sputtering method is preferable from the viewpoint of productivity.

  As the sputtering method, a magnetron sputtering method, a counter target type magnetron sputtering method, or the like can be used. Ar gas, Kr gas, and Xe gas can be used as the atmosphere gas at the time of sputtering, and oxygen gas can be mixed and used with these gases.

  The oxide semiconductor film 14 can also be obtained by heat treatment after film formation by sputtering, or heat treatment while film formation by sputtering. Accordingly, an oxide semiconductor film composed of nanocrystalline oxide or amorphous oxide can be easily obtained. In addition, an oxide semiconductor film obtained by this method is advantageous in increasing field effect mobility and reliability in a semiconductor device (for example, TFT) including the oxide semiconductor film as a channel layer.

  The heat treatment performed while performing film formation by sputtering can be performed by heating the substrate during the film formation. The substrate temperature is preferably 100 ° C. or higher and 250 ° C. or lower. The heat treatment time corresponds to the film formation time, and the film formation time depends on the thickness of the oxide semiconductor film 14 to be formed, but can be, for example, about 10 seconds to 10 minutes.

  Similarly, heat treatment performed after film formation by sputtering can be performed by heating the substrate. In order to obtain high reliability, heat treatment is preferably performed after film formation by sputtering. In this case, heat treatment may be performed immediately after the oxide semiconductor film 14 is formed, or heat treatment may be performed after the source electrode, the drain electrode, the etch stopper layer (ES layer), the passivation layer, and the like are formed. . In order to obtain high reliability, it is more preferable to perform heat treatment after forming the etch stopper layer.

  In the case where heat treatment is performed after the oxide semiconductor film 14 is formed, the substrate temperature is preferably 100 ° C. or higher and 500 ° C. or lower. The atmosphere for the heat treatment may be various atmospheres such as air, nitrogen gas, nitrogen gas-oxygen gas, Ar gas, Ar-oxygen gas, water vapor-containing air, water vapor-containing nitrogen. The atmospheric pressure can be atmospheric pressure, reduced pressure conditions (for example, less than 0.1 Pa), and pressurized conditions (for example, 0.1 Pa to 9 MPa), but is preferably atmospheric pressure. The heat treatment time can be, for example, about 3 minutes to 2 hours, and preferably about 10 minutes to 90 minutes.

  1 to 3 are schematic views showing some examples of a semiconductor device (TFT) according to this embodiment. A semiconductor device 10 shown in FIG. 1 includes a substrate 11, a gate electrode 12 disposed on the substrate 11, a gate insulating film 13 disposed as an insulating layer on the gate electrode 12, and a channel on the gate insulating film 13. An oxide semiconductor film 14 disposed as a layer, and a source electrode 15 and a drain electrode 16 disposed on the oxide semiconductor film 14 so as not to contact each other are included.

  The semiconductor device 20 shown in FIG. 2 is disposed on the gate insulating film 13 and the oxide semiconductor film 14, and is disposed on the etch stopper layer 17, the etch stopper layer 17, the source electrode 15 and the drain electrode 16 having contact holes. The semiconductor device 10 has the same configuration as that of the semiconductor device 10 shown in FIG. 1 except that the passivation film 18 is further included. In the semiconductor device 20 shown in FIG. 2, the passivation film 18 can be omitted as in the semiconductor device 10 shown in FIG. The semiconductor device 30 shown in FIG. 3 has the same configuration as the semiconductor device 10 shown in FIG. 1 except that it further includes a passivation film 18 disposed on the gate insulating film 13, the source electrode 15 and the drain electrode 16. Have.

  A semiconductor device according to this embodiment includes the oxide semiconductor film 14 and is a layer disposed in contact with at least a part of the oxide semiconductor film 14 and is an amorphous layer (hereinafter, referred to as “amorphous layer”). This layer is also referred to as “amorphous adjacent layer”). According to the semiconductor device including the amorphous adjacent layer, even when the temperature of the heat treatment described above is high, the oxide semiconductor film 14 can maintain a state in which the oxide semiconductor film 14 is formed of an amorphous oxide. High reliability can be realized. Examples of the amorphous adjacent layer include a gate insulating film 13, a passivation layer 18, and an etch stopper layer 17.

  The amorphous adjacent layer may be a layer formed in contact with the oxide semiconductor film 14 as a base (lower layer) of the oxide semiconductor film 14 or may be an upper layer formed in contact with the oxide semiconductor film 14. There may be. In addition, the semiconductor device according to the present embodiment can include two or more adjacent layers. In this case, these adjacent layers can be a lower layer and an upper layer of the oxide semiconductor film 14.

  For example, in the semiconductor device 10 shown in FIG. 1, the gate insulating film 13 may be an amorphous adjacent layer. In the semiconductor device 20 shown in FIG. 2, the gate insulating film 13 and / or the etch stopper layer 17 may be an amorphous adjacent layer. In the semiconductor device 30 shown in FIG. 3, the gate insulating film 13 and / or the passivation film 18 may be an amorphous adjacent layer.

The amorphous adjacent layer is preferably an oxide layer containing at least one of silicon and aluminum. The fact that the amorphous adjacent layer is an oxide layer containing at least one of silicon and aluminum is advantageous in increasing the field effect mobility and reliability of the semiconductor device. This is advantageous in providing a semiconductor device that can maintain a high field-effect mobility even when it is high. In addition, the amorphous adjacent layer being an oxide layer containing at least one of silicon and aluminum can be advantageous in reducing the OFF current. The oxide containing at least one of silicon and aluminum is not particularly limited, and examples thereof include silicon oxide (SiO _x ) and aluminum oxide (Al _m O _n ).

  Next, a method for manufacturing a semiconductor device according to this embodiment will be described. A method for manufacturing a semiconductor device includes a step of preparing the sputter target of the above embodiment and a step of forming the oxide semiconductor film by a sputtering method using the sputter target. First, the manufacturing method of the semiconductor device 10 shown in FIG. 1 will be described. Although this manufacturing method is not particularly limited, the substrate 11 is referred to with reference to FIG. A step of forming a gate electrode 12 thereon (FIG. 4A), a step of forming a gate insulating film 13 as an insulating layer on the gate electrode 12 and the substrate 11 (FIG. 4B), and a gate insulating film 13 A step of forming the oxide semiconductor film 14 as a channel layer thereon (FIG. 4C) and a step of forming the source electrode 15 and the drain electrode 16 over the oxide semiconductor film 14 so as not to contact each other (FIG. 4C). D)).

(1) Step of Forming Gate Electrode Referring to FIG. 4A, gate electrode 12 is formed on substrate 11. The substrate 11 is not particularly limited, but is preferably a quartz glass substrate, an alkali-free glass substrate, an alkali glass substrate, or the like from the viewpoint of increasing transparency, price stability, and surface smoothness. The gate electrode 12 is not particularly limited, but is preferably a Mo electrode, a Ti electrode, a W electrode, an Al electrode, a Cu electrode, or the like because it has high oxidation resistance and low electrical resistance. The method for forming the gate electrode 12 is not particularly limited, but is preferably a vacuum deposition method, a sputtering method, or the like because it can be uniformly formed on the main surface of the substrate 11 with a large area. As shown in FIG. 4A, when the gate electrode 12 is partially formed on the surface of the substrate 11, an etching method using a photoresist can be used.

(2) Step of Forming Gate Insulating Film Referring to FIG. 4B, a gate insulating film 13 is formed as an insulating layer on the gate electrode 12 and the substrate 11. The method for forming the gate insulating film 13 is not particularly limited, but is preferably a plasma CVD (chemical vapor deposition) method or the like from the viewpoint of being able to be uniformly formed in a large area and ensuring insulation.

The material of the gate insulating film 13 is not particularly limited, but is preferably silicon oxide (SiO _x ), silicon nitride (SiN _y ) or the like from the viewpoint of insulation. In the case where the gate insulating film 13 is the above-described amorphous adjacent layer, the gate insulating film 13 may be an oxide containing at least one of silicon and aluminum such as silicon oxide (SiO _x ) and aluminum oxide (Al _m O _n ). preferable.

(3) Step of Forming Oxide Semiconductor Film Referring to FIG. 4C, an oxide semiconductor film 14 is formed as a channel layer over the gate insulating film 13. As described above, the oxide semiconductor film 14 is preferably formed including a step of forming a film by sputtering. For example, heat treatment is performed after film formation by sputtering, or while film formation is performed by sputtering. It is preferably formed by heat treatment. As the raw material target (sputter target) of the sputtering method, the oxide sintered body of the first embodiment is used.

  In order to obtain high reliability, heat treatment is preferably performed after film formation by sputtering. In this case, heat treatment may be performed immediately after the oxide semiconductor film 14 is formed, or heat treatment may be performed after the source electrode 15, the drain electrode 16, the etch stopper layer 17, the passivation layer 18, and the like are formed. . In order to obtain high reliability, it is more preferable to perform heat treatment after the etch stopper layer 17 is formed. When the heat treatment is performed after the etch stopper layer 17 is formed, this heat treatment may be before or after the formation of the source electrode 15 and the drain electrode 16, but before the formation of the passivation layer 18. Is preferred.

(4) Step of Forming Source and Drain Electrodes Referring to FIG. 4D, source electrode 15 and drain electrode 16 are formed on oxide semiconductor film 14 so as not to contact each other. The source electrode 15 and the drain electrode 16 are not particularly limited, but have a high oxidation resistance, a low electric resistance, and a low contact electric resistance with the oxide semiconductor film 14, so that the Mo electrode, the Ti electrode, and the W electrode Al electrode, Cu electrode and the like are preferable. A method for forming the source electrode 15 and the drain electrode 16 is not particularly limited, but it can be uniformly formed in a large area on the main surface of the substrate 11 on which the oxide semiconductor film 14 is formed. It is preferable that it is a law etc. A method for forming the source electrode 15 and the drain electrode 16 so as not to contact each other is not particularly limited, but etching using a photoresist is possible because a pattern of the source electrode 15 and the drain electrode 16 having a large area can be formed uniformly. Formation by a method is preferred.

  Next, a manufacturing method of the semiconductor device 20 shown in FIG. 2 will be described. This manufacturing method further includes a step of forming an etch stopper layer 17 having a contact hole 17a and a step of forming a passivation film 18. 1 can be the same as the method of manufacturing the semiconductor device 10 shown in FIG. 1, and specifically, referring to FIGS. 4 and 5, a step of forming the gate electrode 12 on the substrate 11 (FIG. 4A). )), A step of forming a gate insulating film 13 as an insulating layer over the gate electrode 12 and the substrate 11 (FIG. 4B), and a step of forming an oxide semiconductor film 14 as a channel layer over the gate insulating film 13. (FIG. 4C), a step of forming an etch stopper layer 17 over the oxide semiconductor film 14 and the gate insulating film 13 (FIG. 5A), and an etch stopper layer 17 A step of forming the contact hole 17a (FIG. 5B) and a step of forming the source electrode 15 and the drain electrode 16 on the oxide semiconductor film 14 and the etch stopper layer 17 so as not to contact each other (FIG. 5C). And a step of forming a passivation film 18 on the etch stopper layer 17, the source electrode 15 and the drain electrode 16 (FIG. 5D).

The material of the etch stopper layer 17 is not particularly limited, but is preferably silicon oxide (SiO _x ), silicon nitride (SiN _y ), aluminum oxide (Al _m O _n ) or the like from the viewpoint of insulation. Further, when the etch stopper layer 17 is the above-described amorphous adjacent layer, it may be an oxide containing at least one of silicon and aluminum such as silicon oxide (SiO _x ) and aluminum oxide (Al _m O _n ). preferable. The etch stopper layer 17 may be a combination of films made of different materials. The method for forming the etch stopper layer 17 is not particularly limited, but from the viewpoint of being able to be uniformly formed in a large area and ensuring insulation, it is possible to use a plasma CVD (chemical vapor deposition) method, a sputtering method, a vacuum evaporation method, or the like. Preferably there is.

  Since the source electrode 15 and the drain electrode 16 need to be in contact with the oxide semiconductor film 14, the contact hole 17 a is formed in the etch stopper layer 17 after the etch stopper layer 17 is formed on the oxide semiconductor film 14. (FIG. 5B). Examples of the method for forming the contact hole 17a include dry etching or wet etching. By etching the etch stopper layer 17 by this method to form the contact hole 17a, the surface of the oxide semiconductor film 14 is exposed in the etched portion.

  In the manufacturing method of the semiconductor device 20 shown in FIG. 2, the source electrode 15 and the drain electrode 16 are formed on the oxide semiconductor film 14 and the etch stopper layer 17 in the same manner as the manufacturing method of the semiconductor device 10 shown in FIG. After forming so as not to contact each other (FIG. 5C), a passivation film 18 is formed on the etch stopper layer 17, the source electrode 15 and the drain electrode 16 (FIG. 5D).

The material of the passivation film 18 is not particularly limited, but is preferably silicon oxide (SiO _x ), silicon nitride (SiN _y ), aluminum oxide (Al _m O _n ) or the like from the viewpoint of insulation. Further, when the passivation film 18 is the above-described amorphous adjacent layer, it is preferably an oxide containing at least one of silicon and aluminum such as silicon oxide (SiO _x ) and aluminum oxide (Al _m O _n ). . The passivation film 18 may be a combination of films made of different materials. The formation method of the passivation film 18 is not particularly limited, but is a plasma CVD (chemical vapor deposition) method, a sputtering method, a vacuum evaporation method, etc. from the viewpoint that it can be uniformly formed in a large area and to ensure insulation. It is preferable.

  Further, as in the semiconductor device 30 shown in FIG. 3, the back channel etch (BCE) structure is adopted without forming the etch stopper layer 17, and the gate insulating film 13, the oxide semiconductor film 14, the source electrode 15 and the drain are formed. A passivation film 18 may be formed directly on the electrode 16. With respect to the passivation film 18 in this case, the above description of the passivation film 18 included in the semiconductor device 20 shown in FIG. 2 is cited.

(5) Other steps Finally, heat treatment is usually performed. The heat treatment can be performed by heating the substrate. The substrate temperature is preferably 100 ° C. or higher and 250 ° C. or lower. The atmosphere for the heat treatment may be various atmospheres such as air, nitrogen gas, nitrogen gas-oxygen gas, Ar gas, Ar-oxygen gas, water vapor-containing air, water vapor-containing nitrogen. An inert atmosphere such as nitrogen or Ar gas is preferable. The atmospheric pressure can be atmospheric pressure, reduced pressure conditions (for example, less than 0.1 Pa), and pressurized conditions (for example, 0.1 Pa to 9 MPa), but is preferably atmospheric pressure. The heat treatment time can be, for example, about 3 minutes to 2 hours, and preferably about 10 minutes to 90 minutes.

<Example 1 to Example 16>
(1) Production of oxide sintered body (1-1) Preparation of powder raw material It has the composition shown in Table 1 and the median particle size d50 (indicated as “W particle size” in Table 1), and the purity is 99. .99 mass% tungsten oxide powder (indicated as “W” in Table 1) and ZnO powder having a median particle diameter d50 of 1.0 μm and a purity of 99.99 mass% (referred to as “Z” in Table 1). And an In ₂ O ₃ powder (shown as “I” in Table 1) having a median particle diameter d50 of 1.0 μm and a purity of 99.99% by mass were prepared.

(1-2) Preparation of Primary Mixture of Raw Material Powder First, in the prepared raw material powder, tungsten oxide powder and ZnO powder or tungsten oxide powder and indium oxide powder are put into a ball mill for 18 hours. A primary mixture of raw material powders was prepared by pulverization and mixing. The molar mixing ratio of the tungsten oxide powder and the ZnO powder was approximately tungsten oxide powder: ZnO powder = 1: 1. The molar mixing ratio of the tungsten oxide powder and the indium oxide powder was approximately tungsten oxide powder: In ₂ O ₃ powder = 1: 3. During the pulverization and mixing, ethanol was used as a dispersion medium. The obtained primary mixture of raw material powders was dried in the air.

(1-3) Formation of calcination powder by heat treatment of primary mixture Next, the obtained primary mixture of raw material powders was put into an alumina crucible and heated in an air atmosphere at the calcination temperature shown in Table 1 for 8 hours. Calcination was performed to obtain a calcined powder composed of a ZnWO ₄ type crystal phase or a calcined powder composed of an In ₆ WO ₁₂ type crystal phase. Table 1 shows the composition (type) of the crystal phase constituting the calcined powder obtained.

(1-4) Preparation of secondary mixture of raw material powder containing calcined powder Next, the obtained calcined powder is put into a pot together with the remaining raw material powder, In ₂ O ₃ powder or ZnO powder. Further, the mixture was pulverized and mixed for 12 hours in a pulverizing and mixing ball mill to prepare a secondary mixture of raw material powders. The mixing ratio of these powders was such that the molar ratio of W, Zn and In in the mixture was as shown in Table 1. During the pulverization and mixing, ethanol was used as a dispersion medium. The obtained mixed powder was dried by spray drying.

(1-5) Formation of molded product by molding of secondary mixture Next, the obtained secondary mixture was molded by pressing, and further applied with CIP at a pressure of 190 MPa in still water at room temperature (5 ° C to 30 ° C). By pressure forming, a disk-shaped molded body having a diameter of 100 mm and a thickness of about 9 mm was obtained.

(1-6) Formation of Oxide Sintered Body by Sintering of Molded Body Next, the obtained molded body was sintered at a sintering temperature shown in Table 1 for 8 hours under atmospheric pressure in an air atmosphere. In addition, an oxide sintered body including a first crystal phase including a bixbite type crystal phase (In ₂ O ₃ type phase) in which tungsten and zinc were dissolved was obtained. The determination that tungsten and zinc are in solid solution is based on confirmation that the peak position is deviated from the peak position defined in JCPDS card 6-0416 in the measurement of X-ray diffraction.

(1-7) Physical property evaluation of oxide sintered body [A] Identification of first crystal phase, second crystal phase, and fourth crystal phase A sample was taken from a part of the oxide sintered body, and powder X-rays were obtained. A crystal analysis is performed by a diffraction method, and a bixbite type crystal phase, a second crystal phase having a first diffraction peak at a position smaller than 34.74 deg of 2θ and smaller than 34.97 deg, and 32 larger than 31.77 deg of 2θ. The presence or absence of the fourth crystal phase having the second diffraction peak at a position smaller than 0.000 deg was confirmed. The measurement conditions for X-ray diffraction were as follows.

(Measurement conditions for X-ray diffraction)
θ-2θ method,
X-ray source: Cu Kα ray,
X-ray tube voltage: 45 kV,
X-ray tube current: 40 mA,
Step width: 0.03 deg.
Step time: 1 second / step,
Measurement range 2θ: 10 deg to 90 deg.

  The oxide sintered bodies of the examples all had a bixbite type crystal phase, a second crystal phase, and a fourth crystal phase. Table 2 shows the angle of the first diffraction peak of the second crystal phase and the angle of the second diffraction peak of the fourth crystal phase. Further, the peak intensity IIn of the diffraction peak having the highest intensity among the diffraction peaks attributed to the bixbyite crystal phase of X-ray diffraction and the highest intensity among the diffraction peaks not attributed to the bixbite crystal phase. Since the ratio IIn / Im of the peak intensity Im of the diffraction peak was 3.0 or more, it can be said that the oxide sintered bodies of the examples are mainly composed of the bixbite type crystal phase.

[B] Confirmation that first crystal phase is main component and measurement of indium high content type crystal phase occupancy Sample was taken from a part of oxide sintered body, and the surface of the sample was polished and smoothed did. Next, using SEM-EDX (scanning secondary electron microscope with an energy dispersive fluorescent X-ray analyzer), the surface of the sample is observed with SEM (scanning secondary electron microscope), and each crystal particle The metal elemental composition ratio was analyzed by EDX (energy dispersive fluorescence X-ray analyzer). And based on the tendency of the composition ratio of the metal elements of those crystal grains, the crystal grains were grouped. Specifically, a group A of crystal grains containing Zn and more typically having a Zn content [Zn content (atomic%) with respect to the sum of In, W and Zn] higher than Group B described later. A group of crystal grains having a very low Zn content or no Zn content and a high In content (In content (atomic%) with respect to the sum of In, W and Zn) compared to Group A B (indium-rich crystal phase). The crystal grains of group B were judged to be the first crystal phase.

  The “indium-rich crystal phase occupancy” in the oxide sintered body is defined as the ratio (percentage) of the area of the indium-rich crystal phase (group B) to the measurement surface of the oxide sintered body. . In each of the oxide sintered bodies of Examples, the indium-rich crystal phase occupation ratio was 50% or more, and the first crystal phase was the main component.

[C] Measurement of ratio Ia / Ib between peak intensity Ia of first diffraction peak and peak intensity Ib of second diffraction peak [A] Identification of first crystal phase, second crystal phase, and fourth crystal phase Based on the X-ray diffraction measurement results, Ia and Ib were measured according to the above formula, and Ia / Ib was calculated. The results are shown in Table 2.

[D] Confirmation of existence of third crystal phase and measurement of average major axis diameter and average aspect ratio of crystal grains constituting the same [B] Confirmation that first crystal phase is main component and high content of indium In the measurement of the type crystal phase occupancy, the crystal phase divided into group A was judged as the third crystal phase. In addition, in the SEM observation in this surface analysis, a 500-fold backscattered electron image is measured, and the crystal particles constituting the third crystal phase observed in dark gray compared to the group B classified as the first crystal phase, The average major axis diameter and average aspect ratio were measured according to the method described above. The results are shown in Table 2.

[E] Confirmation of presence of fifth crystal phase, indium tungstate compound crystal phase, hexagonal wurtzite crystal phase and In ₂ O ₃ (ZnO) _{5 In} the measurement of [A] X-ray diffraction described above, The presence or absence of a crystal phase, an indium tungstate compound crystal phase, a hexagonal wurtzite crystal phase, and In ₂ O ₃ (ZnO) ₅ was confirmed. In any of the examples and comparative examples, the presence of an indium tungstate compound crystal phase was not observed.

  In the column of “Crystal Phase” in Table 2, the crystal phases present in the oxide sintered body are summarized. Regarding crystal phases, the abbreviations in the table mean the following crystal phases. In the column of “Crystal Phase” in Table 2, those that can be identified by the above X-ray diffraction measurement are shown, and the oxide sintered body is described in the “Crystal Phase” column. It does not mean that it is composed only of what is present.

I: Bixbite type crystal phase (first crystal phase),
Z: hexagonal wurtzite crystal phase (third crystal phase),
ZW: zinc tungstate compound crystal phase (third crystal phase and fifth crystal phase),
IZ: In ₂ O ₃ (ZnO) ₅ (third crystal phase).

[F] Measurement of In, Zn and W contents in oxide sintered body The contents of In, Zn and W in the obtained oxide sintered body were measured by ICP mass spectrometry. Based on these contents, the W content (atomic%), the Zn content (atomic%), and the Zn / W ratio (atomic ratio) of the oxide sintered body were determined. The results are shown in Table 2.

[G] Measurement of apparent density of oxide sintered body The apparent density of the obtained oxide sintered body was determined by the Archimedes method.

[H] Measurement of Thermal Conductivity of Oxide Sintered Body The thermal diffusivity, specific heat capacity, and thermal conductivity were measured according to the method defined in JIS R 1611: 2010. Table 2 shows the thermal conductivity ratios of the examples and the comparative example when the thermal conductivity of the comparative example 1 is 1.

<Comparative Examples 1 to 2>
The mixing ratio of the tungsten oxide powder, the ZnO powder and the In ₂ O ₃ powder as the raw material powder was as shown in Table 1, and these raw material powders were formed without forming a calcined powder. Except that they were mixed at one time and sintered at the temperature shown in Table 1, oxide sintered bodies were produced in the same manner as in Examples, and physical properties were evaluated. The oxide sintered bodies of the comparative examples all had the first crystal phase, but had the second crystal phase, the third crystal having a predetermined average major axis diameter and average aspect ratio, and the fourth crystal phase. I did not. In the oxide sintered body of Comparative Example 2, the third crystal phase is not dispersed in the indium-rich crystal phase but is in contact with each other, and the particle shape of the third crystal phase can be specified. As a result, the average major axis diameter and average aspect ratio could not be measured. In any of the comparative examples, in order to increase the apparent density, it was necessary to increase the sintering temperature as compared with the examples. Oxide sintered bodies were produced in the same manner as in Comparative Example 1 and Comparative Example 2 except that the sintering temperature was 1160 ° C. The apparent density of these oxide sintered bodies was 6.3 g / cm. It was ³ .

(1-8) Production of Sputter Target The obtained oxide sintered body was processed into a diameter of 3 inches (76.2 mm) × thickness of 6 mm, and then attached to a copper backing plate using indium metal.

(2) Manufacture and evaluation of semiconductor device (TFT) provided with oxide semiconductor film (2-1) Measurement of maximum limit value (cracking power) of sputtering power Film formation of sputtering apparatus (not shown) for prepared sputtering target Installed indoors. The sputter target is water cooled via a copper backing plate. The target was sputtered as follows with the vacuum in the film formation chamber being about 6 × 10 ⁻⁵ Pa.

A mixed gas of Ar (argon) gas and O ₂ (oxygen) gas was introduced into the deposition chamber up to a pressure of 0.5 Pa. The O ₂ gas content in the mixed gas was 20% by volume. Sputtering discharge was caused by applying DC power of 300 W to the target and held for 60 minutes. After 60 minutes, after cooling for 10 minutes, the film forming chamber was opened to the atmosphere, and it was confirmed whether or not cracks occurred in the oxide sintered body of the sputter target. It was increased from 300 W by 50 W, and sputtering was performed for 60 minutes for each stage, and it was confirmed whether or not cracks occurred in the oxide sintered body of the sputter target. When cracking occurred in the oxide sintered body, the experiment was stopped and the sputtering power was set as cracking power (W). Table 2 shows the cracking power of the example and the comparative example. All of the sputter targets of the examples did not crack up to a high sputtering power. This is probably because the oxide sintered body includes a predetermined second crystal phase, and thus the thermal conductivity is increased. In addition, including a crystal phase other than the first crystal phase and the second crystal phase (in particular, a third crystal phase composed of crystal particles having a high aspect ratio) contributes to high thermal conductivity. Conceivable.

  The sputter target of Comparative Example 2 was severely cracked and could not be formed by sputtering using DC power.

(2-2) Production of Semiconductor Device (TFT) Having Oxide Semiconductor Film A TFT having a configuration similar to that of the semiconductor device 30 shown in FIG. 3 was produced by the following procedure. Referring to FIG. 4A, first, a synthetic quartz glass substrate having a size of 50 mm × 50 mm × thickness 0.6 mm is prepared as a substrate 11, and a Mo electrode having a thickness of 100 nm is formed on the substrate 11 as a gate electrode 12 by sputtering. Formed. Next, as shown in FIG. 4A, the gate electrode 12 was formed into a predetermined shape by etching using a photoresist.

Referring to FIG. 4 (B), then, as a gate insulating film 13 by a plasma CVD method on the gate electrode 12 and the substrate 11, thereby forming a SiO _x film having a thickness of 200nm which is an amorphous oxide layer.

  4C, next, an oxide semiconductor film 14 having a thickness of 35 nm was formed over the gate insulating film 13 by a DC (direct current) magnetron sputtering method. A plane having a target diameter of 3 inches (76.2 mm) was a sputter surface. As the target used, the oxide sintered body obtained in the above (1) was used.

The formation of the oxide semiconductor film 14 will be described more specifically. A substrate in which the gate electrode 12 and the gate insulating film 13 are formed on a water-cooled substrate holder in a film formation chamber of a sputtering apparatus (not shown). 11 is arranged so that the gate insulating film 13 is exposed. The target was disposed at a distance of 60 mm so as to face the gate insulating film 13. The target was sputtered as follows with the vacuum in the film formation chamber being about 6 × 10 ⁻⁵ Pa.

First, a mixed gas of Ar (argon) gas and O ₂ (oxygen) gas was introduced to a pressure of 0.4 Pa into the film forming chamber with a shutter between the gate insulating film 13 and the target. The O ₂ gas content in the mixed gas was 20% by volume. In the case of the Example, DC electric power 50W lower than the cracking electric power calculated | required by said (2-1) was applied to the target, the sputtering discharge was started, and thereby the target surface cleaning (pre-sputtering) was performed for 5 minutes. In Comparative Example 1, sputtering discharge was caused with DC power of 500 W, and pre-sputtering was performed for 5 minutes.

  Next, the same value of DC power was applied to the same target, and the oxide semiconductor film 14 was formed over the gate insulating film 13 by removing the shutter while maintaining the atmosphere in the film formation chamber. Note that no bias voltage was applied to the substrate holder. In addition, the substrate holder was water-cooled or heated to adjust the temperature of the substrate 11 during and after film formation. Among the examples and comparative examples, in the example described as “Yes / 120 ° C.” in the column of “Heat treatment during film formation” in Table 3 below, the substrate temperature is set by heating the substrate holder during film formation. By adjusting the temperature to 120 ° C. or the like, heat treatment was performed simultaneously with film formation. In this case, the heat treatment time corresponds to the film formation time. Even when heat treatment is performed at the same time as film formation, the substrate is heated after film formation (after formation of a passivation layer, as will be described later), and heat treatment is performed at 250 ° C. for 10 minutes or 350 ° C. for 10 minutes. The semiconductor device characteristics to be measured were measured. On the other hand, in the examples and comparative examples, when “None” is described in the column of “Heat treatment during film formation” in Table 3 below, the substrate temperature is set to 20 by cooling the substrate holder with water during film formation. The substrate was heated after film formation (after formation of a passivation layer, as will be described later), and heat treatment was performed at 250 ° C. for 10 minutes or 350 ° C. for 10 minutes, and semiconductor device characteristics described later were measured.

  As described above, the oxide semiconductor film 14 was formed by the DC (direct current) magnetron sputtering method using the target processed from the oxide sintered body obtained in the above (1). The oxide semiconductor film 14 functions as a channel layer in the TFT. The thickness of the oxide semiconductor film 14 formed in each example and comparative example was set to 35 nm.

Next, by etching a part of the formed oxide semiconductor film 14, a source electrode forming portion 14s, a drain electrode forming portion 14d, and a channel portion 14c were formed. The main surfaces of the source electrode forming portion 14s and the drain electrode forming portion 14d have a size of 50 μm × 50 μm and a channel length C _L (refer to FIGS. 1A and 1B, the channel length C _L refers to the distance of the channel portion 14c between the source electrode 15 and the drain electrode 16.) is 30 μm, and the channel width C _W (refer to FIGS. 1A and 1B) C _W is the width of the channel portion 14c.) Was 40 μm. The channel portion 14c has 25 × 25 × 25 mm in the main surface of 75 mm × 75 mm and 25 × 25 in the main surface of the 75 mm × 75 mm so that the TFTs are arranged in the length of 25 × 25 in the main surface of 75 mm × 75 mm. Arranged.

  For the etching of part of the oxide semiconductor film 14, an etching aqueous solution having a volume ratio of oxalic acid: water = 5: 95 is prepared, and the gate electrode 12, the gate insulating film 13, and the oxide semiconductor film 14 are formed in this order. The substrate 11 was immersed in the etching aqueous solution at 40 ° C.

  Referring to FIG. 4D, next, the source electrode 15 and the drain electrode 16 were formed on the oxide semiconductor film 14 separately from each other.

  Specifically, first, a resist (not shown) is applied on the oxide semiconductor film 14 so that only the main surfaces of the source electrode forming portion 14s and the drain electrode forming portion 14d of the oxide semiconductor film 14 are exposed. , Exposed and developed. Next, a Mo electrode having a thickness of 100 nm, which is the source electrode 15 and the drain electrode 16, respectively, was formed on the main surfaces of the source electrode forming portion 14s and the drain electrode forming portion 14d of the oxide semiconductor film 14 by sputtering. Thereafter, the resist on the oxide semiconductor film 14 was peeled off. Each of the Mo electrode as the source electrode 15 and the Mo electrode as the drain electrode 16 has one channel portion 14c so that the TFTs are arranged 25 × 25 × 3 mm apart at an interval of 3 mm in the main surface of the substrate of 75 mm × 75 mm. One for each.

Next, with reference to FIG. 3, a passivation film 18 was formed on the gate insulating film 13, the oxide semiconductor film 14, the source electrode 15 and the drain electrode 16. The passivation film 18 is an amorphous oxide layer formed by forming a 200 nm thick SiO _x film by a plasma CVD method and then forming a 200 nm thick SiN _y film thereon by a plasma CVD method, or an amorphous oxide layer. An Al _m O _n film having a thickness of 120 nm was formed by a sputtering method, and then a SiN _y film having a thickness of 200 nm was formed thereon by a plasma CVD method. When the amorphous oxide layer is an SiO _x film, “SiO _x ” is described in the “PV layer” column in Table 3 below, and when the amorphous oxide layer is an Al _m O _n film, the “PV layer” "" Describes "Al _m O _n ". The atomic composition ratio of the SiO _x film is an oxygen content closer to Si: O = 1: 2, and the atomic composition ratio of the Al _m O _n film is an oxygen content closer to Al: O = 2: 3. This is desirable from the viewpoint of improving reliability.

  Next, the passivation film 18 on the source electrode 15 and the drain electrode 16 was etched by reactive ion etching to form a contact hole, thereby exposing a part of the surface of the source electrode 15 and the drain electrode 16.

  Finally, heat treatment was performed in an atmospheric pressure nitrogen atmosphere. This heat treatment was performed for all the examples and comparative examples. Specifically, the heat treatment was performed at 250 ° C. for 10 minutes in a nitrogen atmosphere or at 350 ° C. for 10 minutes in a nitrogen atmosphere. Through the above steps, a TFT including the oxide semiconductor film 14 as a channel layer was obtained.

(2-3) Crystallinity of oxide semiconductor film, W content, Zn content, and Zn / W ratio The crystallinity of the oxide semiconductor film 14 included in the manufactured TFT was evaluated according to the above-described measurement method and definition. In the column of “Crystallinity” in Table 3, “nanocrystal” is described when it is a nanocrystal, and “amorphous” when it is amorphous. In addition, the contents of In, W, and Zn in the oxide semiconductor film 14 were measured by RBS (Rutherford backscattering analysis). Based on these contents, the W content (atomic%), the Zn content (atomic%), and the Zn / W ratio (atomic ratio) of the oxide semiconductor film 14 were determined. The results are shown in Table 3.

(2-4) Characteristic Evaluation of Semiconductor Device The characteristics of the TFT which is the semiconductor device 10 were evaluated as follows. First, a measuring needle was brought into contact with the gate electrode 12, the source electrode 15, and the drain electrode 16. A source-drain voltage V _ds of 0.2 V is applied between the source electrode 15 and the drain electrode 16, and a source-gate voltage V _gs applied between the source electrode 15 and the gate electrode 12 is changed from −10 V. The voltage was changed to 15 V, and the source-drain current I _ds at that time was measured. Then, the relationship between the source-gate voltage V _gs and the square root [(I _ds ) ^1/2 ] of the source-drain current I _ds was graphed (hereinafter this graph is _expressed as “V _gs − (I _ds ) ^1”. Also called " ^{/ 2} curve".) A tangent is drawn on the V _gs- (I _ds ) ^1/2 curve, and the point (x intercept) where the tangent with the point where the slope of the tangent is the maximum intersects the x axis (V _gs ) is defined as the threshold voltage V _th . did. The threshold voltage V _th is obtained after performing a heat treatment at 250 ° C. for 10 minutes in an atmospheric pressure nitrogen atmosphere (V _th (250 ° C.)) and after performing a heat treatment in an atmospheric pressure nitrogen atmosphere at 350 ° C. for 10 minutes (V _Th (350 ° C.) TFT was measured. V _th is desirably 0 V or more. Further, when a TFT is used in a display device, it is desirable that V _th is closer to 1.0 V because of the same driving voltage as a-Si.

The following formula [a]:
g _m = dI _ds / dV _gs [a]
Thus, g _m was derived by differentiating the source-drain current I _ds with respect to the source-gate voltage V _gs . Then, using the value of g _m at V _gs = 10.0V, the following formula [b]:
μ _fe = g _m · C _L / (C _W · C _i · V _ds ) [b]
Based on the above, the field effect mobility μ _fe was calculated. The channel length C _L in the above formula [b] is 30 μm, and the channel width C _W is 40 μm. The capacitance C _i of the gate insulating film 13 was 3.4 × 10 ⁻⁸ F / cm ² and the source-drain voltage V _ds was 0.5V.

The field effect mobility μ _fe after the heat treatment at 250 ° C. for 10 minutes in the atmospheric pressure nitrogen atmosphere is shown in the column of “mobility (250 ° C.)” in Table 3. Further, the field effect mobility μ _fe after the heat treatment at 350 ° C. for 10 minutes in the atmospheric pressure nitrogen atmosphere is shown in the column of “mobility (350 ° C.)” in Table 3. As shown in Table 3, the larger the Zn / W ratio, the smaller the difference between mobility (250 ° C.) and mobility (350 ° C.).

Further, the following reliability evaluation test was performed. The source-gate voltage V _gs applied between the source electrode 15 and the gate electrode 12 was fixed at +35 V, and this was continuously applied for 1 hour. 1s from application start, 10s, 100s, 300s, determine the threshold voltage V _th to the above-described method after 3600s, it was determined the difference [Delta] V _th between the maximum threshold voltage V _th and the minimum threshold voltage V _th. It is determined that the smaller ΔV _th is, the higher the reliability is. ΔV _th after the heat treatment at 250 ° C. for 10 minutes in the atmospheric pressure nitrogen atmosphere is shown in the column of “ΔV _th (250 ° C.)” in Table 3. Further, ΔV _th after the heat treatment at 350 ° C. for 10 minutes in the atmospheric pressure nitrogen atmosphere is shown in the column of “ΔV _th (350 ° C.)” in Table 3.

  The embodiment disclosed this time is to be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above-described embodiment but by the scope of claims, and is intended to include meanings equivalent to the scope of claims and all modifications within the scope.

10, 20, 30 Semiconductor device (TFT)
11 Substrate 12 Gate electrode 13 Gate insulating film 14 Oxide semiconductor film 14c Channel portion 14d Drain electrode forming portion 14s Source electrode forming portion 15 Source electrode 16 Drain electrode 17 Etch stopper layer 17a Contact hole 18 Passivation film

Claims (18)

An oxide sintered body containing indium, tungsten and zinc,
A first crystal phase that is a main component of the oxide sintered body and includes a bixbite type crystal phase;
A second crystal phase having a first diffraction peak at a position larger than 34.74 deg of 2θ in X-ray diffraction and smaller than 34.97 deg;
An oxide sintered body containing A crystal phase different from the first crystal phase, comprising a third crystal phase containing zinc;
2. The oxide sintered body according to claim 1, wherein the particles constituting the third crystal phase have an average major axis diameter of 3 μm or more and 50 μm or less and an average aspect ratio of 4 or more and 50 or less.   The oxide sintered body according to claim 2, wherein the third crystal phase is dispersed in the first crystal phase.   4. The oxide according to claim 2, wherein the third crystal phase includes a fourth crystal phase having a second diffraction peak at a position larger than 31.77 deg of 2θ in X-ray diffraction and smaller than 32.00 deg. Sintered body.   5. The oxide sintered body according to claim 4, wherein a ratio Ia / Ib between a peak intensity Ia of the first diffraction peak and a peak intensity Ib of the second diffraction peak is 0.05 or more and 3 or less.   The oxide sintered body according to any one of claims 2 to 5, wherein the third crystal phase includes a fifth crystal phase which is a zinc tungstate compound crystal phase.   The oxide sintered body according to any one of claims 1 to 6, wherein the first crystal phase further includes an indium tungstate compound crystal phase. The apparent density of the oxide sintered body is greater than 6.4 g / cm ^{3 and not} more than 7.5 g / cm ³ ;
The content of tungsten with respect to the total of indium, tungsten and zinc in the oxide sintered body is greater than 0.5 atomic% and not greater than 5.0 atomic%;
The zinc content relative to the total of indium, tungsten and zinc in the oxide sintered body is 1.2 atomic percent or more and less than 40 atomic percent,
The oxide sintered body according to any one of claims 1 to 7, wherein an atomic ratio of zinc to tungsten in the oxide sintered body is larger than 1.0 and smaller than 80.   A sputter target comprising the oxide sintered body according to any one of claims 1 to 8. A method of manufacturing a semiconductor device including an oxide semiconductor film,
Preparing a sputter target according to claim 9;
Forming the oxide semiconductor film by a sputtering method using the sputter target;
A method for manufacturing a semiconductor device, comprising: The content of tungsten with respect to the total of indium, tungsten and zinc in the oxide semiconductor film is greater than 0.5 atomic% and not greater than 5.0 atomic%;
The zinc content relative to the total of indium, tungsten and zinc in the oxide semiconductor film is 1 atomic% or more and less than 40 atomic%,
The method for manufacturing a semiconductor device according to claim 10, wherein an atomic ratio of zinc to tungsten in the oxide semiconductor film is larger than 1.0 and smaller than 80.   The method for manufacturing a semiconductor device according to claim 10, wherein the oxide semiconductor film is composed of at least one of a nanocrystalline oxide and an amorphous oxide. A method for producing an oxide sintered body according to any one of claims 1 to 8,
Preparing a primary mixture of indium oxide powder and tungsten oxide powder;
Forming a calcined powder by heat-treating the primary mixture;
Preparing a secondary mixture of raw material powders containing the calcined powder;
Forming a molded body by molding the secondary mixture;
Forming an oxide sintered body by sintering the molded body;
Including
The step of forming the calcined powder is performed by heat-treating the primary mixture at a temperature of 700 ° C. or higher and lower than 1400 ° C. in an oxygen-containing atmosphere, whereby a powder of a complex oxide containing indium and tungsten as the calcined powder. The manufacturing method of oxide sinter including forming. The method for producing an oxide sintered body according to claim 13, wherein the double oxide includes an In ₆ WO ₁₂ type crystal phase. A method for producing an oxide sintered body according to any one of claims 1 to 8,
Preparing a primary mixture of zinc oxide powder and tungsten oxide powder;
Forming a calcined powder by heat-treating the primary mixture;
Preparing a secondary mixture of raw material powders containing the calcined powder;
Forming a molded body by molding the secondary mixture;
Forming an oxide sintered body by sintering the molded body;
Including
The step of forming the calcined powder is a powder of a double oxide containing zinc and tungsten as the calcined powder by heat-treating the primary mixture at a temperature of 550 ° C. or higher and lower than 1200 ° C. in an oxygen-containing atmosphere. The manufacturing method of oxide sinter including forming. The method for producing an oxide sintered body according to claim 15, wherein the double oxide includes a ZnWO ₄ type crystal phase. The tungsten oxide powder according to any one of claims 13 to 16, wherein the tungsten oxide powder includes at least one crystal phase selected from the group consisting of a WO ₃ crystal phase, a WO ₂ crystal phase, and a WO _2.72 crystal phase. The manufacturing method of the oxide sintered compact of description.   The method for producing an oxide sintered body according to any one of claims 13 to 17, wherein the tungsten oxide powder has a median particle diameter d50 of 0.1 µm or more and 4 µm or less.

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