Crystalline oxide semiconductor thin films, laminates, and sputtering targets

Abstract

The crystalline oxide semiconductor thin film disclosed herein contains In and B elements, wherein the ratio of the In content (atomic %) to the B content (atomic %) satisfies the following formula 1, and the average grain size on the surface observed by electron microscopy is 0.25 μm or more. B / (In+B)≤0.20 ····(1)

Description

Technical Field

[0001] This disclosure relates to a crystalline oxide semiconductor thin film, a multilayer, and a sputtering target. Prior Technology

[0002] Thin-film transistors (TFTs) are becoming increasingly popular as active components used in organic electroluminescent (OLED) displays and the like. Some TFTs utilize stacked oxide semiconductor thin films containing elements such as indium (In), gallium (Ga), and zinc (Zn). It is known that there are oxide thin films for TFTs containing specified amounts of In and Ga, and where In₂O₃ has a beryl structure (Japanese Patent Application Publication No. 2014-098211). [Existing technical documents] [Patent Literature]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2014-098211 Summary of the Invention

[0004] [The problem that the invention aims to solve] In Patent Document 1, by reducing the lattice constant of indium oxide with gallium oxide, and thus setting indium oxide to a beryl structure, the intermetallic distance can be reduced, thereby increasing the carrier mobility of the oxide thin film. Generally, in semiconductor thin films with amorphous structures, the carrier mobility can be relatively high, but the carrier density tends to increase. In semiconductor thin films with crystalline structures with relatively large grains, the carrier density can be relatively low, but it is difficult to increase the carrier mobility. Low carrier density and high carrier mobility in semiconductor thin films are important factors for the operational stability of TFTs, and a balance between these two is required.

[0005] In view of this situation, the purpose of this disclosure is to provide a crystalline oxide semiconductor thin film that can improve carrier mobility while reducing carrier density. [Methods for solving problems]

[0006] The crystalline oxide semiconductor thin film disclosed herein contains In and B elements, wherein the ratio of the In content (atomic %) to the B content (atomic %) satisfies the following formula 1, and the average grain size on the surface observed by an electron microscope is 0.25 μm or more. B / (In+B)≤0.20 ····(1) [The effects of the invention]

[0007] The crystalline oxide semiconductor thin film disclosed herein can improve carrier mobility while reducing carrier density. Simple Explanation of the Diagram

[0008] Figure 1 is a SEM image showing a portion of Test Example 1 in the embodiments disclosed herein. Figure 2 is a SEM image showing a portion of Experiment Example 2. Figure 3 is a SEM image showing a portion of Experiment Example 3. Figure 4 is a SEM image showing a portion of Experimental Example 5. Figure 5 is a SEM image showing a portion of Experiment 6. Figure 6 is a SEM image showing a portion of Experiment 7. Figure 7 is a SEM image showing a portion of Experimental Example 8. Figure 8 is a SEM image showing a portion of Experimental Example 9. Figure 9 is a SEM image showing a portion of Experiment 10. Figure 10 is a SEM image showing a portion of Experiment 11. Figure 11 is a SEM image showing a portion of Experiment 12. Figure 12 is a SEM image showing a portion of Experiment 13. Figure 13 is a SEM image showing a portion of test example 9, which underwent heat treatment at a different temperature than that shown in Figure 8. Figure 14 is a SEM image showing a portion of test example 10 that underwent heat treatment at a different temperature than that shown in Figure 9. Figure 15 is a SEM image showing a portion of test example 11, which underwent heat treatment at a different temperature than that shown in Figure 10. Figure 16 is a SEM image showing a portion of test example 12, which underwent heat treatment at a different temperature than that shown in Figure 11. Figure 17 is a SEM image showing a portion of test example 13 that underwent heat treatment at a different temperature than that shown in Figure 12. Figure 18 is a SEM image showing a portion of test example 18. Figure 19 is a SEM image showing a portion of test example 19. Figure 20 is a SEM image showing a portion of test example 20. Figure 21 is an IQ mapping representing a portion of Experiment 18. Figure 22 shows the IQ mapping for a portion of Experiment 19. Figure 23 shows the IQ mapping for a portion of Experiment 20. Figure 24 is a SEM image showing a portion of Experiment 25. Figure 25 is a SEM image showing a portion of Experiment 26. Figure 26 is a SEM image showing a portion of Experiment 27. Figure 27 is a SEM image showing a portion of Experiment 28. Figure 28 is a SEM image showing a portion of test example 29. Figure 29 is a SEM image showing a portion of test example 32. Figure 30 is a SEM image showing a portion of test example 33. Figure 31 is a SEM image showing a portion of test example 34. Figure 32 is a SEM image showing a portion of test example 36. Figure 33 is a SEM image showing a portion of test example 37. Figure 34 is a SEM image showing a portion of test example 38. Figure 35 is a SEM image showing a portion of test example 39. Figure 36 is a SEM image showing a portion of test example 40. Figure 37 is a SEM image showing a portion of test example 41. Figure 38 is a SEM image showing a portion of test example 42. Figure 39 is a SEM image showing a portion of test example 43. Figure 40 is a SEM image showing a portion of test example 44. Figure 41 is an IQ mapping representing a portion of test example 39. Figure 42 is an IQ mapping representing a portion of test example 40. Figure 43 is an IQ mapping representing a portion of test example 41. Figure 44 is an IQ mapping representing a portion of test example 42. Figure 45 shows the IQ mapping for a portion of test example 43. Figure 46 is an IQ mapping representing a portion of test example 44. Figure 47 is a graph showing the particle size distribution of the granulated powder that forms the sputtering target. Figure 48 shows the X-ray diffraction spectrum of the sputtering target shown in Figure 47. Figure 49 is a reflection electron microscope image of the sputtering target shown in Figure 47. Implementation

[0009] [Description of the implementation form disclosed herein] First, the embodiments disclosed herein will be described.

[0010] In semiconductor thin films, carrier mobility is increased by suppressing phonon scattering, electron scattering caused by impurities such as oxygen vacancies or dopants, and electron scattering at grain boundaries. Therefore, it is considered effective to suppress defect formation through solid-state crystallization. Furthermore, to reduce these defects, increased crystallinity is required. In this regard, it is also possible to promote solid-state growth of semiconductor thin films, i.e., increase crystallinity and increase grain size, by mixing a specified gas such as hydrogen into the gas used in the deposition of semiconductor thin films (film-forming gas). However, this increases manufacturing complexity and manufacturing costs. Therefore, it is preferable to promote solid-state growth by adding elements to the semiconductor thin film. Adding Ga (gallium) to semiconductor thin films is also meaningful, but since it is a rare metal, there are concerns about the difficulty of stable supply. The inventors of this invention have not only diligently studied Ga-containing thin films, but also diligently studied the additive elements and their amounts that can be supplied more stably and promote solid-state growth of semiconductor thin films, thus completing this invention.

[0011] (1) The crystalline oxide semiconductor thin film disclosed herein contains In and B elements, wherein the ratio of the In content [atomic %] to the B content [atomic %] satisfies the following formula 1, and the average grain size on the surface observed by an electron microscope is 0.25 μm or more. B / (In+B)≤0.20 ····(1)

[0012] This crystalline oxide semiconductor thin film (hereinafter also referred to as the first crystalline thin film) contains elements such as In (indium) and a specified amount of B (boron). Therefore, heat treatment during the manufacturing process promotes solid-phase growth, which can reduce carrier density and increase carrier mobility. In addition, by setting the average grain size of the first crystalline thin film to 0.25 μm or more, the carrier density can be further reduced and the carrier mobility increased.

[0013] (2) As described in (1), the first crystalline film may further contain Fe (iron) element. By containing Fe in the first crystalline film, crystallinity can be improved.

[0014] (3) As described in (1) or (2), wherein the peak value detected by the microwave photoconductivity decay (μPCD) method is more than four times the peak value before crystallization by heat treatment. By making the peak value detected by the μPCD method of the first crystalline film after heat treatment more than four times the value before crystallization, the carrier density can be further reduced and the carrier mobility can be further increased.

[0015] (4) The stack of the present invention is a stack for forming a thin film transistor, wherein the stack comprises an amorphous oxide semiconductor thin film and a crystalline oxide semiconductor thin film as described in (1) to (3).

[0016] The stack (hereinafter also referred to as the first stack) has an amorphous oxide semiconductor thin film (hereinafter also referred to as the first amorphous thin film) and the first crystalline thin film stacked together, which can improve the reliability of promoting solid-state growth.

[0017] (5) As described in (4), the amorphous oxide semiconductor thin film may also contain In and B elements. By including In and B elements in the first amorphous thin film, the crystallinity of the first crystalline thin film can be further improved.

[0018] (6) The sputtering target of the present invention forms a crystalline oxide semiconductor thin film as described in any one of (1) to (3).

[0019] The first crystalline film can be easily manufactured by using a sputtering target formed from the sputtering target material.

[0020] (7) The crystalline oxide semiconductor thin film of the present invention contains In element, the grain size of the grain in the electron backscattering diffraction method is 0.30 μm or more, the (111) face of the crystalline phase is aligned in the Z-axis direction, and the white area / black area of ​​the IQ mapping in the normal direction of the Z-axis is 0.5 or more.

[0021] This crystalline oxide semiconductor thin film (hereinafter also referred to as the second crystalline thin film) achieves a relatively large grain size by having a grain diameter of 0.3 μm or more and aligning the (111) planes of the crystalline phase along the Z-axis, thereby reducing oxygen defects and thus lowering carrier density and increasing carrier mobility. Furthermore, the white / black area ratio in the image quality (IQ) mapping along the Z-axis of the second crystalline thin film is 0.5 or more. The black areas in the IQ mapping represent areas with more defects; therefore, an increase in the proportion of white areas indicates a decrease in defects. The second crystalline thin film has a white / black area ratio of 0.5 or more, resulting in fewer defects and easily improving carrier mobility. Furthermore, the so-called "the (111) facets of the crystal plane are aligned in the Z-axis direction" means that when viewed from the Z-axis direction, the (111) facets in the crystal plane are abundant. Specifically, it means that the ratio of the regions containing (111) facets in the inverse pole diagram (IPF) mapping of the crystal plane is greater than 0.50 or greater than 0.55.

[0022] (8) As described in (7), the crystalline oxide semiconductor thin film may further contain element B. By including B, it is easier to increase carrier mobility while reducing carrier density.

[0023] (9) As described in (8), wherein the ratio of the In content [atomic %] to the B content [atomic %] satisfies Equation 2 below. By including B in the second crystalline film in a manner that satisfies Equation 2 below, the carrier mobility can be increased while reducing the carrier density. B / (In+B)≤0.10 ····(2)

[0024] (10) The stacked volume layer of the present invention includes an amorphous oxide semiconductor thin film containing In and Ga elements, and a crystalline oxide semiconductor thin film containing In and Al or Ga elements.

[0025] The stack (hereinafter also referred to as the third stack) is formed by stacking an amorphous oxide semiconductor thin film containing In and Ga elements (hereinafter also referred to as the third amorphous thin film) and a crystalline oxide semiconductor thin film containing In, Al or Ga elements (hereinafter also referred to as the third crystalline thin film). Therefore, solid-state growth is promoted in the third crystalline thin film, and the crystallinity is improved. In the third stack, the carrier density can be reduced while the carrier mobility is increased.

[0026] (11) As described in (10), the laminate may also have the amorphous oxide semiconductor film further deposited on the crystalline oxide semiconductor film. By further depositing the third amorphous film, the crystallinity of both surfaces of the third crystalline film can be improved.

[0027] (12) As described in (10) or (11), wherein the ratio of the In content [atomic %] to the Al or Ga content [atomic %] in the crystalline oxide semiconductor thin film satisfies Equation 3 or Equation 4 below. By ensuring that the Al or Ga content in the third crystalline thin film satisfies Equation 3 or Equation 4 below, the reliability of the carrier density reduction effect and the carrier mobility improvement effect of the third laminate can be improved. Al / (In+Al)≤0.10 ····(3) Ga / (In+Ga)≤0.15 ····(4)

[0028] (13) As described in any one of (10) to (12), wherein, alternatively, in the crystalline oxide semiconductor thin film, the grain size in the electron backscattering diffraction method is 0.3 μm or more, the (111) facets of the crystalline phase are aligned in the Z-axis direction, and the white region / black region ratio in the IQ mapping in the normal direction of the Z-axis is 0.5 or more. In this way, the reliability of the carrier density reduction effect and the carrier mobility improvement effect in the third stack can be further improved.

[0029] (14) The stacked volume layer of the present invention includes an amorphous oxide semiconductor thin film containing In and Ga elements, and a crystalline oxide semiconductor thin film containing In and B elements.

[0030] The stack (hereinafter also referred to as the fourth stack) is formed by stacking an amorphous oxide semiconductor thin film containing In and Ga elements (hereinafter also referred to as the fourth amorphous thin film) and a crystalline oxide semiconductor thin film containing In and B elements (hereinafter also referred to as the fourth crystalline thin film). Therefore, solid-state growth is promoted in the fourth crystalline thin film, thereby increasing crystallinity. In the fourth stack, the carrier density can be reduced while the carrier mobility can be increased.

[0031] (15) As described in (14), it is also possible to further deposit the amorphous oxide semiconductor film on the crystalline oxide semiconductor film. By further depositing the amorphous oxide semiconductor film, the crystallinity of both surfaces of the fourth crystalline film can be improved.

[0032] (16) As described in (14) or (15), wherein the amorphous oxide film may further contain Zn or B elements. By further containing Zn or B elements, the degradation of the amorphous oxide film can be suppressed.

[0033] (17) The sputtering target disclosed herein contains In and B elements, and is formed by an oxide sintered body whose ratio of the content of In [atomic %] to the content of B [atomic %] satisfies the formula 2.

[0034] By using this sputtering target, thin films with high carrier mobility can be easily obtained.

[0035] (18) The sputtering target disclosed herein contains In and Al or Ga elements, and is formed by an oxide sintered body whose ratio of the In content [atomic %] to the Al or Ga content [atomic %] satisfies the formula 3 or the formula 4.

[0036] By using this sputtering target, thin films with high carrier mobility can be easily obtained.

[0037] (19) The sputtering target disclosed herein contains In, B and Ga elements, and is formed from an oxide sintered body whose content of B [atomic %] satisfies the following formula 5. 0.1≤B≤40 ····(5)

[0038] By using this sputtering target, amorphous oxide semiconductor thin films with high carrier mobility for forming stacks can be easily obtained.

[0039] Furthermore, the so-called average grain size refers to the average grain size of an image obtained by electron microscopy and EBSD (Electron Backscattering Diffraction) where, for lines of 2.5 μm length drawn at three or more locations, the number of crystals with an azimuth difference of 2° or more that are considered to affect carrier mobility is counted. Specifically, regarding crystals, an azimuth difference of 2° or more is detected from the azimuth mapping (deriving and mapping the azimuth of each pixel) derived by EBSD, an image depicting the crystal is extracted, and its number is counted. In previous methods, crystals with an azimuth difference of approximately 10° or more were also considered, but in this disclosure, the conditions are tightened to focus on crystals with an azimuth difference of 2° or more, which are more likely to have a smaller average grain size. The term "crystalline" refers to the presence of crystal grains under a scanning electron microscope (SEM) at 10,000x magnification, while "amorphous" refers to the absence of crystal grains under a SEM at 10,000x magnification.

[0040] [Details of the implementation methods disclosed herein] The embodiments disclosed herein will now be described in detail with reference to the accompanying drawings. Furthermore, for the values ​​described in this specification, only one of the described upper and lower limits can be used, or any combination of the upper and lower limits can be used. In this specification, all possible ranges of values ​​from the upper to the lower limits are described as preferred ranges.

[0041] <First Implementation Form> The crystalline oxide semiconductor thin film contains In and B elements, and the ratio of the In content (atomic %) to the B content (atomic %) satisfies the following formula 1. The average grain size on the surface observed by an electron microscope is 0.25 μm or more. B / (In+B)≤0.20 ····(1)

[0042] The first crystalline film is preferably entirely crystalline, or at least partially (or partially) crystalline. That is, all or part of the oxide forming the first crystalline film is crystalline. By making the first crystalline film crystalline, the carrier mobility can be increased while reducing the carrier density.

[0043] The first crystalline film may also contain Fe. By including Fe, solid-state growth can be promoted by heat treatment at a lower temperature.

[0044] (In) In is an element that helps improve carrier mobility by increasing crystallinity. The higher the In content, the higher the carrier mobility and conductivity of the first crystalline film. In this first crystalline film, In exists in the form of In₂O₃. The upper limit of the In content relative to the total number of metal elements contained in the first crystalline film is less than 100 atomic%. There is no particular limitation on the lower limit of the content, for example, it can be 75 atomic% or 80 atomic%. By setting the In content within the above range, sufficient carrier mobility can be obtained.

[0045] (B) Botanicals (B) are elements that help reduce carrier density by increasing the crystal grain size during solid-state growth. In this first crystalline film, B exists in the forms of B₂O₃ and B(OH)₃ (boric acid: an oxyacid of boron). Since B₂O₃ is a difficult material to crystallize, it can be considered that the crystallization temperature of In₂O₃ shifts to a higher temperature side, thereby achieving a larger crystal grain size. B(OH)₃ is considered to have the effect of passivating the aforementioned defects. In addition, since B has a small ionic radius, it also helps to improve carrier mobility by entering the interstices between In₂O₃ particles. The content of B in this first crystalline film satisfies Equation 1. The lower limit of the content of B in this first crystalline film is more than 0 atoms.

[0046] (Fe) Fe is considered an element that helps improve crystallinity. The upper limit of the Fe content relative to the total number of metallic elements contained in the first crystalline film is preferably 2 atomic%, more preferably 1 atomic%. By containing Fe within this range in the first crystalline film, a complex of FeO and B2O3 is easily formed, and this complex acts as a nucleus for crystallization, effectively contributing to crystallization.

[0047] In this first crystalline thin film, the elements other than those mentioned above are O (oxygen) and unavoidable impurities. Unavoidable impurities may be present due to raw materials, resources, manufacturing equipment, etc. Examples of such unavoidable impurities include: Pb (lead), Si (silicon), Ni (nickel), Ti (titanium), Mg (magnesium), Cr (chromium), Zr (zinc), etc. The content of unavoidable impurities in the first crystalline thin film is preferably 0.02 atomic% or less for each element, more preferably 0.01 atomic% or less. Furthermore, the content of In, B, and Fe in the first crystalline thin film can also be referred to as the proportion of all elements except O.

[0048] The lower limit of the thickness of the first crystalline thin film is not particularly limited and can be 30 nm, 35 nm, or 40 nm. The upper limit of the thickness is also not particularly limited and can be 150 nm, 125 nm, or 100 nm. By setting the thickness within the aforementioned range, the productivity of the first crystalline thin film can be improved.

[0049] The average grain size on the surface of the first crystalline thin film, as observed by an electron microscope, is 0.25 μm or more. The lower limit of this average grain size can be 0.35 μm or 0.45 μm. The upper limit of this average grain size is not particularly limited and can be 1.00 μm. By setting the average grain size within the range of film thickness, grain boundary defects can be effectively suppressed, and carrier mobility can be improved.

[0050] The peak value detected by μPCD of the first crystalline thin film is preferably at least four times the peak value before crystallization. That is, the peak value of the first crystalline thin film crystallized by film formation and heat treatment is preferably at least four times the peak value before film formation and heat treatment (before crystallization). The lower limit of the ratio of the peak value after crystallization to the peak value before crystallization can be 5 or 6. The upper limit of the ratio is not particularly limited, for example, it can be 10. The peak value is obtained by measuring the attenuation waveform of the first crystalline thin film by μPCD and plotting the values. By ensuring that the ratio of the peak value after crystallization to the value before crystallization is within the specified range, a sufficient reduction in carrier density and a sufficient increase in carrier mobility can be obtained.

[0051] [Laminated body] The first crystalline thin film can be deposited on an amorphous oxide semiconductor thin film (first amorphous thin film) to form a stack (first stack) for forming a thin film transistor. The first stack is a stack for forming a thin film transistor, comprising a first amorphous thin film and the first crystalline thin film deposited on the first amorphous thin film.

[0052] The first amorphous thin film may contain In and B elements. The first amorphous thin film may also further contain Ga and Zn elements.

[0053] The ratio of the content (atomic %) of at least one of Ga and Zn in the first amorphous thin film to the content (atomic %) of In is preferably 0.5 or more and 1.5 or less. The ratio of the content (atomic %) of B in the first amorphous thin film to the content (atomic %) of In is preferably 0.5 or more and 2 or less.

[0054] By depositing and layering the first crystalline thin film on the first amorphous thin film, the average grain size tends to decrease, but crystallinity can be improved. This is believed to be because, by depositing the first crystalline thin film on the first amorphous thin film, the number of crystal nuclei formed at the interface between the In₂O₃ of the first crystalline thin film and the first amorphous thin film changes, thus creating differences in grain growth and altering the grain size. Specifically, it can be considered that the presence of numerous crystal nuclei at the interface facilitates collisions between grains, resulting in a smaller average grain size, while suppressing orientational unevenness.

[0055] [Sputtering target] The first crystalline thin film can be formed using a sputtering target. That is, the first crystalline thin film can be formed by sputtering using a sputtering target. After film formation, heat treatment is performed to improve the film quality.

[0056] The sputtering target used to manufacture the first crystalline thin film contains In and B as elements, and is formed by sputtering the target material with their contents satisfying Formula 1. The sputtering target material may also further contain Fe. Elements other than those mentioned above in the sputtering target material are unavoidable impurities. The sputtering target material is formed as an oxide sintered body.

[0057] There is no particular limitation on the method for forming the first crystalline thin film using the sputtering target, and the film can also be formed by known methods. For example, as the film-forming gas, a mixture of argon and oxygen can be used to form the film at an oxygen partial pressure of 24 / 1 sccm (4%) and room temperature. After film formation, the film is heated in an atmospheric environment at a temperature of 250°C or higher and 400°C or lower for 0.5 hours or more and 2 hours or less to obtain the first crystalline thin film.

[0058] <Second Implementation Form> As another embodiment of the present disclosure, the crystalline oxide semiconductor thin film (second crystalline thin film) contains In element, the grain size in the electron backscattering diffraction method is 0.30 μm or more, the (111) facets of the crystalline phase are aligned in the Z-axis direction, and the white area / black area in the IQ mapping in the normal direction of the Z-axis is 0.5 or more.

[0059] The second crystalline film may also contain more boron (B). Since B binds strongly to oxygen (O), O loss can be suppressed. Furthermore, due to its high hygroscopicity, B can reduce the variation in atmospheric environment or steam treatment during the heat treatment process of manufacturing the second crystalline film.

[0060] As the amount of B added, the ratio of the In content (atomic %) to the B content (atomic %) satisfies Equation 2 below. By adding B in a manner that satisfies Equation 2 below, solid-state growth can be efficiently promoted. B / In+B≤0.10 ····(2)

[0061] The lower limit of the film thickness is not particularly limited and can be 5 nm or 10 nm. The upper limit of the film thickness is also not particularly limited and can be 120 nm, 100 nm, 80 nm, or 60 nm. By setting the film thickness within the aforementioned range, the increase in crystal grain size can be promoted.

[0062] When the film thickness is less than 25 nm or 20 nm, the upper limit of Formula 2 can be set to 5.

[0063] [Sputtering target] The second crystalline film can be formed using a sputtering target. That is, the second crystalline film can be formed by sputtering using a sputtering target.

[0064] The sputtering target material forming the sputtering target contains In and B as elements, and their contents satisfy Formula 2. The sputtering target material is formed as an oxide sintered body.

[0065] The upper limit of Formula 2 can also be set to 5, depending on the heat treatment temperature (e.g., above 350°C) after film formation using the sputtering target.

[0066] <Third Implementation Form> As another embodiment of the present disclosure, the stack (the third stack) has an amorphous oxide semiconductor thin film containing In and Ga elements, and a crystalline oxide semiconductor thin film containing In, Al or Ga elements.

[0067] (Ga) The element Ga enhances the oxygen barrier function of the thin films (amorphous oxide semiconductor thin films and crystalline oxide semiconductor thin films), thus suppressing degradation.

[0068] (Al) Al (aluminum) can inhibit the penetration of H2 and H2O into the third crystalline film, thereby improving the photostress resistance of the third crystalline film.

[0069] The third laminate can also be formed by further depositing the third amorphous film on the third crystalline film. That is, the third laminate can also be a three-layer laminate in which the third amorphous film is deposited on both surfaces of the third crystalline film. By depositing the third amorphous film on both surfaces of the third crystalline film, the crystallinity of the two surfaces can be improved, and the carrier mobility can be easily increased.

[0070] By depositing the third crystalline film onto the third amorphous film, the crystal size tends to decrease, but the carrier mobility can be increased due to the improved alignment in the (111) plane.

[0071] The ratio of the In content (atomic %) to the Al or Ga content (atomic %) in the third crystalline film can satisfy Equation 3 or Equation 4 below. If the Al or Ga content is increased without satisfying Equation 3 or Equation 4 below, heat treatment at high temperatures is required during the manufacturing process of the third crystalline film, which may reduce productivity. Al / (In+Al)≤0.10 ····(3) Ga / (In+Ga)≤0.15 ····(4)

[0072] The third crystalline thin film may have a grain size of 0.3 μm or more in the electron backscattering diffraction method, the (111) planes of the crystalline phase are aligned in the Z-axis direction, and the ratio of white area to black area in the IQ mapping in the normal direction of the Z-axis is 0.5 or more.

[0073] [Sputtering target] The third crystalline film can be formed using a sputtering target. That is, the third crystalline film can be formed by sputtering using a sputtering target.

[0074] The sputtering target material forming the sputtering target contains In and Al or Ga elements, and the ratio of the In content (atomic %) to the Al or Ga content (atomic %) satisfies Equation 3 or Equation 4. The sputtering target material is formed as an oxide sintered body.

[0075] <Fourth Implementation Form> As another embodiment of the present disclosure, the laminate (fourth laminate) is laminated with an amorphous oxide semiconductor thin film containing In and Ga elements (fourth amorphous thin film) and a crystalline oxide semiconductor thin film containing In and B elements (fourth crystalline thin film).

[0076] The fourth amorphous thin film may also be deposited on the fourth crystalline thin film. The fourth amorphous oxide thin film may further contain Zn or B elements.

[0077] (Zn) Zn inhibits the infiltration of H2 and H2O into the fourth amorphous film.

[0078] [Sputtering target] The fourth amorphous thin film can be formed using a sputtering target. That is, the fourth amorphous thin film can be formed by sputtering using a sputtering target.

[0079] The sputtering target material forming the sputtering target contains In, B and Ga elements, and is formed from an oxide sintered body whose B content [atomic %] satisfies the following formula 5. 0.1≤B≤40 ····(5)

[0080] The optimal content of In, B, and Ga in the sputtering target is approximately equal (In:B:Ga = 1:1:1).

[0081] [Other Implementation Forms] The embodiments described do not limit the structure of the present invention. Therefore, the constituent elements of the embodiments can be omitted, replaced, or added based on the description in this specification and common technical knowledge, and these should be interpreted as all falling within the scope of the present invention. [Example]

[0082] The present invention will now be described in detail based on embodiments, but the invention is not to be limited to the description of the embodiments.

[0083] <First Embodiment> In oxide semiconductor thin films, In and Ga oxide semiconductor thin films, and In and B oxide semiconductor thin films were formed on glass substrates. The film-forming conditions were: Ar / O2 = 24 / 1 sccm, oxygen partial pressure set to 4% or 60% by volume, and gas pressure set to 1 m / Torr. The stage temperature was set to room temperature, and film formation was performed by sputtering at 250 W direct current to a thickness of 40 nm or 100 nm. After film formation, carrier mobility and carrier density were measured (Hall measurement) and compared between films that underwent heat treatment in an atmospheric environment and those that did not. The results are shown in Table 1. Furthermore, in Table 1, "-" indicates no measurement, and "OR" indicates values ​​below the measurement limit (Over Range).

[0084] [Table 1] Test subject Contains elements (ratio) Film thickness [nm] oxygen partial pressure [vol%] Carrier density [cm⁻³] Carrier mobility [cm² / Vs] No heat treatment Heat treatment temperature [°C] No heat treatment Heat treatment temperature [°C] 250 300 350 400 500 250 300 350 400 500 Experimental Example 1 In 100 4 2.1E+19 2.4E+18 - 8.6E+17 - - 46.5 4.6 - 4.8 - - Experimental Example 2 In, Ga (90 / 10) 100 4 (OR) 9.7E+18 - 6.2E+17 - - (OR) 10.4 - 6.1 - - Experimental Example 3 In, B (95 / 5) 100 4 1.2E+20 1.6E+19 5.1E+17 3.0E+17 - - 37.4 10.1 13.9 12.7 - - Test Example 4 In, B (90 / 10) 100 4 1.0E+20 1.3E+19 2.0E+19 6.3E+18 - - 30.1 27.3 27.9 23.3 - - Experimental Example 5 In 40 4 2.8E+19 4.4E+18 - 1.9E+18 - - 44.9 11.8 - 10.4 - - Experimental Example 6 In, Ga (88.1 / 11.9) 40 4 1.2E+19 - 1.8E+17 3.3E+17 2.0E+17 1.3E+19 26.1 - 14.9 14.5 11.4 34.9 Experimental Example 7 In, Ga (84.9 / 15.1) 40 4 6.6E+18 - 1.3E+17 3.2E+17 2.2E+17 2.1E+19 19.6 - 16.3 16.9 15.4 40.3 Experimental Example 8 In, Ga (84.9 / 15.1) 40 60 - 1.9E+18 1.6E+18 4.7E+18 3.9E+18 3.8E+19 - 11.0 6.6 9.5 10.8 30.8 Experimental Example 9 In, Ga (80.7 / 19.3) 40 4 4.8E+18 - 1.8E+19 2.9E+19 1.1E+18 1.6E+19 16.3 - 25.7 33.0 8.7 34.1 Experimental Example 10 In, B (90 / 10) 40 4 7.0E+19 - 2.7E+19 4.6E+19 5.5E+18 5.9E+19 31.2 - 31.5 34.6 17.4 39.2 Experimental Example 11 In, B, Fe (90 / 9 / 1) 40 4 1.1E+19 - 3.4E+19 3.4E+18 2.3E+18 5.7E+19 23.5 - 33.5 18.6 16.8 41.1 Experimental Example 12 In, B (97.5 / 2.5) 40 4 1.1E+19 6.2E+18 - 1.4E+18 1.6E+18 - 23.2 27.0 - 14.8 18.4 - Experimental Example 13 In, B (95 / 5) 40 4 9.2E+18 4.8E+18 - 3.1E+18 2.6E+18 - 18.3 21.7 - 22.5 17.2 -

[0085] If we compare the carrier mobility in Table 1, at a film thickness of 100 nm and a heat treatment temperature of 350 °C, the carrier mobility is higher in Test Examples 3 and 4 (containing B) and lower in Test Examples 1 and 2 (not containing B). At a film thickness of 40 nm and a heat treatment temperature of 350 °C, the carrier mobility is highest in Test Example 10 (containing B) and lower in Test Examples 5 to 9 (not containing B).

[0086] When comparing the carrier densities in Table 1, compared to those without heat treatment, the carrier densities decreased in Test Examples 1, 3 to 7, and 10 to 12 after heat treatment at 350°C, and increased in Test Example 9. In Test Example 10, which contained B, the carrier density was further reduced by heat treatment at 400°C. In Test Example 11, which contained both B and Fe, the carrier density was lower than that of Test Example 10, which contained only B.

[0087] [SEM Observation] The surfaces of each thin film were observed using an electron microscope based on reflected electron images. Figure 1 shows the surface image of Test Example 1 after heat treatment at 350°C, Figure 2 shows the surface image of Test Example 2 after heat treatment at 350°C, and Figure 3 shows the surface image of Test Example 3 after heat treatment at 350°C. In Test Example 1 without B, the average grain size was 0.025 μm, while in Test Example 3 including B, the average grain size was 0.63 μm.

[0088] Figures 4 to 12 show surface images of the thin film after heat treatment at 350°C. Figure 4 is an image of Test Example 5, Figure 5 is an image of Test Example 6, Figure 6 is an image of Test Example 7, Figure 7 is an image of Test Example 8, Figure 8 is an image of Test Example 9, Figure 9 is an image of Test Example 10, Figure 10 is an image of Test Example 11, Figure 11 is an image of Test Example 12, and Figure 12 is an image of Test Example 13.

[0089] Excluding example B, grains were confirmed in Examples 5 to 8. The average grain size was 0.037 μm in Example 5 and 0.16 μm in Example 7. The average grain size in Example 6 was 0.23 μm, but crystallization began at temperatures below 350°C, as described later. In Example 8, the grain size was 0.03 μm, but unchanged from before heat treatment (crystallization before heat treatment). Grains could not be confirmed in Example 9, but they were confirmed by heat treatment at 400°C. In Example 9, which underwent heat treatment at 400°C, the average grain size was relatively large at 0.56 μm, but it was a mixture of crystalline and amorphous materials (micrograins were mixed within the larger grains). Figure 13 shows Example 9, which underwent heat treatment at 400°C.

[0090] Regarding the test examples containing B, in Test Example 10, no grains could be identified during heat treatment at 350°C, but grains of 0.91 μm could be identified during heat treatment at 400°C. In Test Example 11, which contained both B and Fe, the average grain size was 0.36 μm during heat treatment at 350°C and 0.44 μm during heat treatment at 400°C. In Test Example 12, the average grain size was 0.53 μm during heat treatment at 350°C and 0.71 μm during heat treatment at 400°C. In Test Example 13, no grains could be identified during heat treatment at 350°C, but grains with an average grain size of 0.71 μm could be identified during heat treatment at 400°C. Figures 14, 15, 16, and 17 show Test Examples 10, 11, 12, and 13, respectively, after heat treatment at 400°C.

[0091] [μPCD determination] In Examples 5 to 11, the average grain size after heat treatment at 350°C and the peak value obtained by μPCD were measured, or the average grain size after heat treatment at 400°C in cases where the film was amorphous after heat treatment at 350°C and the peak value obtained by μPCD were measured. The results, the assumed crystallization temperature, and the state (shape) of the crystals on the film surface are shown in Table 2. Furthermore, in Table 2, "facet" in "crystallization state" refers to a surface covered with relatively fine (small) granular crystals, and "dendritic" refers to a surface covered with relatively coarse (large) dendritic crystals. In Table 2, "-" indicates no measurement was performed.

[0092] [Table 2] Experimental Example 5 Experimental Example 6 Experimental Example 7 Experimental Example 8 Experimental Example 9 Experimental Example 10 Experimental Example 11 Peak value [mV] No heat treatment 118.7 307.0 405.0 1144.0 786.0 0.6 215.2 250℃ 2021.5 2504.0 79.0 1243.0 158.0 - - 300℃ - 1746.0 819.0 944.0 173.0 76.9 28.4 350℃ 2118.2 1159.0 1331.0 1113.0 64.0 7.5 966.6 400℃ - 2169.0 1645.0 1084.0 1509.0 825.2 1184.3 500℃ - 667.0 202.0 125.0 264.0 - - Ideal crystallization temperature <250℃ 250℃ 350℃ After film formation 400℃ 400℃ 350℃ Average grain size [µm] after heat treatment at 350℃ or 400℃ 0.04 (350℃) 0.23 (350℃) 0.16 (350℃) 0.03 (350℃) Amorphous regions exist (400℃) 0.91 (400℃) 0.36 (350℃) Crystalline state small facet small facet dendrites +small plane small facet dendrites dendrites +small plane dendrites +small plane

[0093] It can be concluded that Experiment 5 generates a large number of crystal nuclei at low temperatures, promotes crystallization at temperatures below 250°C, but also causes a large number of collisions between adjacent crystals, resulting in smaller grain sizes. However, the grains treated at 250°C exhibit high crystallinity and a large peak value (over 2000 mV).

[0094] In Example 6, with a low Ga content, the crystallization behavior was similar to that of Example 5, but the crystallization temperature was higher, around 250°C, and the average grain size increased. In Example 7, with a higher Ga content, the crystallization temperature became even higher, around 350°C, the average grain size increased slightly, and the crystals exhibited a streamlined shape resembling fireworks. On the other hand, the peak value of Example 7 was lower than that of Example 6. In Example 8, with the same Ga content as Example 7 and an oxygen partial pressure of 60% by volume, no change in grain size caused by heat treatment was observed. In Example 9, with a higher Ga content than Example 7, the crystallization temperature further increased, and streamlined crystals dominated. However, the crystallization temperature became too high, and even after heat treatment at 400°C, some amorphous regions were identified.

[0095] It can be assumed that Experiment 8 generates a large number of crystal nuclei by including a large amount of oxygen in the film-forming gas, and performs microcrystallization at low temperature. This is also indicated by the small grain size in the SEM image at 350°C (see Figure 7) and the high peak value in the non-thermal treatment.

[0096] In Experiment 10, which contains B, the grains are dendritic and planar, similar to those in Experiment 7. Simultaneously, the crystallization temperature becomes higher, thereby increasing the average grain size. On the other hand, the amorphous regions observed in Experiment 7 are not observed in Experiment 10. In the thin film 11 containing B and Fe, the same crystallinity as in Experiment 10 can be obtained through lower-temperature heat treatment.

[0097] [Laminated body] A laminate was formed on a glass substrate, and Hall effect measurements were performed and compared. The laminate consisted of a 10 nm thick amorphous oxide semiconductor thin film (first amorphous thin film) formed on the glass substrate, and a crystalline oxide semiconductor thin film (thin film) was deposited on the first amorphous thin film. The element content ratios of the first amorphous thin film listed in Table 3 were all set to 1:1:1. For the thin film and the first amorphous thin film, the film-forming conditions were Ar / O2 = 24 / 1 sccm, oxygen partial pressure was set to 4% by volume, and gas pressure was set to 1 m / Torr. The stage temperature was set to room temperature, and the first amorphous thin film was formed with a thickness of 10 nm by sputtering at DC 250 W, and the thin film was formed with a thickness of 40 nm. The heat treatment after film formation was performed at 350°C or 400°C for 1 hour in an atmospheric environment. The element content of the thin film, the element content of the first amorphous thin film, the heat treatment temperature, the Hall effect measurement results, and the crystallinity results of the thin film for each test example are shown in Table 3.

[0098] [Table 3] Test Example 14 Experimental Example 15 Experimental Example 16 Experimental Example 17 The thin film contains elements (in proportions). In, B (95 / 5) In, B (90 / 10) In, B (95 / 5) In, B (95 / 5) The substrate thin film contains elements In, Ga, Zn In, Ga, Zn In, Ga, B In, B, Zn Heat treatment temperature 350℃ 400℃ 350℃ 400℃ 400℃ 400℃ Carrier density [cm⁻³] 8.90E+17 3.06E+18 6.80E+17 7.21E+18 1.86E+18 1.72E+18 Carrier mobility (cm² / Vs) 19.3 19.7 11.3 13.3 16.2 16.7 Crystallinity amorphous amorphous amorphous amorphous small facet small facet

[0099] Crystallization could not be confirmed in the films of Examples 14 and 15. Increasing the heat treatment temperature decreased the carrier density in Example 14, but increased it in Example 15. Conversely, increasing the heat treatment temperature increased the carrier mobility in both Examples 14 and 15. In Examples 16 and 17, where the first amorphous film contained B, crystallization was confirmed, with relatively low carrier densities and better carrier mobility. This is believed to be because including In and B as the first amorphous film modulates the interface between the film and the first amorphous film, allowing control over interface defects that could nucleate crystallization.

[0100] <Second Embodiment> An oxide semiconductor thin film containing In and an oxide semiconductor thin film containing In and 1 atom% B were formed on a glass substrate. The film formation conditions were set as follows: the film formation gas ratio was Ar / O2 = 24 / 1 sccm, and the gas pressure was 1 m / Torr. The stage temperature was set to room temperature, and films were formed at DC 250 W using sputtering to thicknesses of 15 nm, 23 nm, or 40 nm. After film formation, heat treatment was performed at 350°C in either an atmospheric or water vapor environment. The carrier mobility and carrier density of the formed films were measured (Hall measurement) and compared. Films with a carrier mobility of 14 cm² / Vs or higher were considered good. The results are shown in Table 4. Furthermore, in Table 4, "-" indicates films not measured.

[0101] [Table 4] No. oxide thin films Heat treatment Hall effect measurement Crystalline phase contain element Film thickness [nm] temperature [℃] environment Carrier mobility [cm2 / Vs] Carrier density [cm-3] Crystallinity Particle size [μm] (111) The direction the face is facing White / Black Areas in IQ Mapping The ratio of (111) surfaces in the inverse pole diagram IPF mapping Experimental Example 18 In 15 350 atmosphere 13.8 9.2E+17 dendrites 0.32 random 0.5 or more 0.36 Experimental Example 19 In 15 350 water vapor 21.7 2.2E+18 small facet 0.42 Z-axis 0.8 or more 0.59 Test Example 20 In, B twenty three 350 atmosphere 20.0 1.5E+18 small facet 0.37 Z-axis 0.8 or more 0.61 Experimental Example 21 In, B 15 350 atmosphere 19.1 3.1E+18 small facet - - - - Test Example 22 In twenty three 350 atmosphere 6.4 3.7E+17 small facet - - - - Experimental Example 23 In 40 350 atmosphere 8.7 1.8E+18 small facet Less than 0.3 - - - Test Example 24 In, B 40 350 atmosphere 22.7 8.5E+17 small facet More than 0.3 - - -

[0102] In Example 18, with a film thickness of 15 nm, the carrier mobility did not reach 14 cm² / Vs. In Examples 22 and 23, where the film thickness was increased to 23 nm and 40 nm respectively, the carrier mobility further decreased. On the other hand, in Example 19, it can be seen that the carrier mobility was sufficiently increased when the film formation was heated in a water vapor environment. In addition, in Examples 20, 21, and 24, where 1 atomic% of B was added, the carrier mobility was sufficiently increased even with a film thickness of 15 nm. The crystal grain size in Table 4 was calculated by the number method. If the grain size is large, the tendency for the carrier mobility to increase is visible. If IPF mapping is performed on the crystal plane, for the sample with high carrier mobility, the (111) plane shows a tendency for the IPF(Z) mapping to dominate compared to the IPF(X) mapping or the IPF(Y) mapping. SEM images of the oxide semiconductor thin films of Test Examples 18 to 20 are shown in Figures 18 to 20. IQ mappings of the oxide semiconductor thin films of Test Examples 18 to 20 are shown in Figures 21 to 23.

[0103] In oxide semiconductor thin films and In and B oxide semiconductor thin films were formed on a glass substrate. The B content varied from 1 atomic% to 10 atomic%. The film formation conditions were set as follows: Ar / O2 = 24 / 1 sccm, and gas pressure = 1 m / Torr. The stage temperature was set to room temperature, and films were formed at DC 250 W using sputtering to a thickness of 15 nm or 40 nm. After film formation, heat treatment was performed at 350 °C in an atmospheric environment. The results of the crystallization layers of each film are shown in Table 5.

[0104] [Table 5] oxide thin films Crystalline phase Contains elements (Amount of B added [atm%]) Film thickness nm Experimental Example 21 In、B(1) 15 Crystallinity Experimental Example 23 In 40 Crystallinity Test Example 25 In、B(1) 40 Crystallinity Experimental Example 26 In、B(2) 40 Crystallinity Test Example 27 In、B(4) 40 Crystallinity Experimental Example 28 In、B(10) 40 amorphous Test Example 29 In、B(10) 40 Crystallinity

[0105] SEM images of Experimental Examples 25 to 29 are shown in Figures 24 to 28. It can be seen that increasing the amount of B increases the crystal size.

[0106] <Third Embodiment> Oxide semiconductor thin films containing In and 8.5 atomic% Al, oxide semiconductor thin films containing In and 10.0 atomic% Ga, and laminates formed by depositing these thin films onto a substrate thin film containing In, Ga, and Zn in a 1:1:1 ratio were compared. Each of the thin films and the laminates were formed on a glass substrate. The film-forming conditions for each thin film and the substrate thin film were: Ar / O2 = 24 / 1 sccm, and gas pressure = 1 m / Torr. The stage temperature was set to room temperature, and films were formed at DC 250 W using sputtering to a thickness of 15 nm or 40 nm. After film formation, heat treatment was performed at 350°C in an atmospheric environment. The carrier mobility and carrier density of each of the formed thin films and laminates were measured (Hall measurement) and compared. A carrier mobility of 14 cm² / Vs or higher was considered good. The results are shown in Table 6. Furthermore, in Table 6, "-" indicates those not measured.

[0107] [Table 6] No. Oxide semiconductor thin films substrate thin film Hall effect measurement Crystalline phase Contains elements Film thickness [nm] Film thickness [nm] Carrier mobility [cm2 / Vs] Carrier density [cm-3] Crystallinity Particle size [μm] (111) The direction the face is facing White / Black Areas in IQ Mapping The ratio of (111) surfaces in the inverse pole diagram IPF mapping Experimental Example 30 In、Al 15 none 11.0 3.22E+17 dendrites - - - - Experimental Example 31 In、Al 15 15 14.4 5.03E+17 dendrites - - - - Experimental Example 32 In、Al 40 none 12.3 6.39E+16 small facet 1.31 random 0.8 or more 0.16 Test Example 33 In、Al 40 15 14.4 1.47E+17 small facet 0.32 Z-axis direction 0.8 or more 0.66 Test Example 34 In、Al 100 none 10.6 9.78E+16 small facet 0.14 Z-axis direction Less than 0.5 0.67 Experimental Example 35 In、Al 100 15 7.0 1.96E+17 small facet - - - - Experimental Example 36 In、Al 100 40 3.3 5.80E+17 small facet - - - - Experimental Example 37 In, Ga 40 none 9.0 5.5E+16 small facet 0.54 random Less than 0.5 0.17 Experimental Example 38 In, Ga 40 15 17.1 1.4E+17 small facet More than 0.6 random 0.8 or more 0.14

[0108] In a thin film containing In and Al with a thickness of 15 nm (Example 30), the carrier mobility did not reach 14 cm² / Vs or more, but by fabricating a laminate (Example 31), the carrier mobility reached 14 cm² / Vs or more. However, if the film thickness was increased to 100 nm (Example 35), the carrier mobility decreased. Even for thin films containing In and Ga, by fabricating a laminate, the carrier mobility reached 14 cm² / Vs or more (Examples 37 and 38). In Example 36, due to the small particle size, the particle size and orientation of the (111) plane could not be determined.

[0109] SEM images of Test Examples 32, 33, and 34 are shown in Figures 29, 30, and 31, and SEM images of Test Examples 36, 37, and 38 are shown in Figures 32, 33, and 34. In the thin films containing In and Al with a thickness of 40 nm (Test Examples 32 and 33), the particle size was larger when forming a monolayer compared to when forming a laminate (Figures 29 and 30). This tendency was also observed in the thin films containing In and Ga with a thickness of 40 nm (Test Examples 37 and 38) (Figures 33 and 34). In the monolayers of thin films containing In and Al (Test Examples 32 and 34), the particle size decreased as the film thickness increased (Figures 29 and 31).

[0110] Comparing Example 34 and Example 35, where the oxide semiconductor thin film thickness is set to 100 nm, the carrier mobility of the laminate (Example 35) is lower. This is believed to be because increasing the film thickness reduces the grain size, and further reducing the grain size through the laminate construction. Evaluation using EBSD in Examples 32 and 33 confirmed that the orientation of the (111) plane of the oxide semiconductor thin film in Example 33 (laminated body) is aligned along the Z-axis. Therefore, the thickness of the oxide semiconductor thin film in the laminate can be set to 100 nm or less, preferably 80 nm or less, and more preferably 60 nm or less.

[0111] <Fourth Embodiment> Oxide semiconductor thin films containing In, oxide semiconductor thin films containing In and B, oxide semiconductor thin films containing In and 8.5 atomic% Al, and laminates formed by depositing these thin films onto a substrate thin film were compared. Regarding the substrate thin film, three types were prepared: one containing In, Ga, and Zn in a 1:1:1 ratio; one containing In, Ga, and B in a 1:1:1 ratio; and one containing In, B, and Zn in a 1:1:1 ratio. Each thin film and laminate was formed on a glass substrate. The film formation conditions for the thin films and the substrate thin film were: Ar / O2 = 24 / 1 sccm, and gas pressure = 1 m / Torr. The stage temperature was set to room temperature, and films were formed at DC 250 W using sputtering to a thickness of 15 nm or 40 nm. After film formation, heat treatment was performed at 350°C in an atmospheric environment. The carrier mobility and carrier density of the formed thin films and laminates were measured (Hall measurement) and compared. A carrier mobility of 14 cm² / Vs or higher was defined as good. The results are shown in Table 7. Furthermore, in Table 7, "-" indicates those not measured.

[0112] [Table 7] No. Oxide semiconductor thin films substrate thin film Hall effect measurement Crystalline phase Contains elements (Amount of B added [atm%]) Film thickness [nm] Contains elements Film thickness [nm] Carrier mobility [cm2 / Vs] Carrier density [cm-3] Crystallinity Particle size μm (111) The direction the face is facing In IQ mapping White area / Black area Inverse Pole Mapping (IPF) The ratio of the (111) face in the middle Experimental Example 18 In 15 - - 13.8 9.2E+17 dendrites 0.32 random Less than 0.5 0.36 Experimental Example 39 In 15 In, Ga, Zn 10 17.4 1.5E+18 small facet 0.28 Z-axis direction 0.8 or more 0.68 Test Example 40 In 15 In, Ga, B 10 13.4 1.5E+18 dendrites 0.36 random 0.8 or more 0.26 Test Example 41 In、B(1) 15 In, Ga, Zn 10 19.7 9.8E+17 dendrites 0.31 random Less than 0.5 0.32 Test Example 42 In、B(1) 15 In, Ga, B 10 18.0 3.3E+18 small facet 0.24 Z-axis direction 0.8 or more 0.70 Test Example 43 In、B(1) 15 In, B, Zn 10 10.2 1.3E+18 dendrites 0.31 random Less than 0.5 0.40 Test Example 44 In、B(1) 15 In, Ga, B 5 14.7 5.1E+18 small facet 0.23 Z-axis direction 0.8 or more 0.71 Test Case 45 In、B(2) 15 In, Ga, Zn 5 15.1 4.7E+18 middle - - - - Experimental Example 21 In、B(1) 15 - - 10.0 1.1E+18 dendrites 0.30 random - 0.26 Test Example 34 In、Al 100 - - 10.6 9.8E+16 small facet 0.14 Z-axis direction Less than 0.5 0.67 Experimental Example 36 In、Al 100 In, Ga, Zn 40 3.3 5.8E+17 small facet - - - -

[0113] In a 100 nm thick film containing In and Al, the crystallinity is small-faceted in a monolayer (Example 34), but the carrier mobility does not reach 14 cm² / Vs. By deposition on a 40 nm thick substrate film containing In, Ga, and Zn (Example 36), the grain size becomes smaller (below the measurement limit), and the mobility decreases.

[0114] In a thin film containing In with a thickness of 15 nm, compared to a single layer (Example 18), the carrier mobility was increased by deposition on a substrate thin film containing In, Ga, and Zn (Example 39). On the other hand, if the film was deposited on a substrate thin film containing In, Ga, and B (Example 40), the carrier mobility was not increased.

[0115] In a 15 nm thick film containing In and 1 atom% B, compared to a monolayer (Example 21), the carrier mobility was increased by deposition on a substrate film containing In, Ga, and Zn, and on a substrate film containing In, Ga, and B (Examples 41 and 42). On the other hand, the carrier mobility was not increased when deposited on a substrate film containing In, B, and Zn (Example 43).

[0116] SEM images of the surfaces of the laminates from Examples 39 to 44 are shown in Figures 35 to 40, and IQ mappings are shown in Figures 41 to 46. No SEM images are available for films containing In and Al, but compared to monolayers, the grain size of the crystals decreases by lamination onto a substrate film. The crystallinity of the In-containing film is dendritic in monolayers (Example 18), but becomes planar (Figure 35) by lamination onto a substrate film containing In, Ga, and Zn (Example 39). On the other hand, if laminated onto a substrate film containing In, Ga, and B (Example 40), it becomes dendritic (Figure 36).

[0117] The crystallinity of films containing In and B is dendritic in monolayer (Example 21). When the B content is 1 atomic%, it is also dendritic when deposited on a substrate film containing In, Ga, and Zn (Example 41) (Fig. 37). When the B content is 2 atomic%, it forms an intermediate shape between dendrites and facets when deposited on a substrate film containing In, Ga, and Zn (Example 45). Even when the B content is 1 atomic%, it forms facets when deposited on a substrate film containing In, Ga, and B (Example 42). On the other hand, it is also dendritic when deposited on a substrate film containing In, B, and Zn (Example 43).

[0118] Evaluation using EBSD revealed that in films containing In and Al, within a 100 nm thick monolayer, the (111) plane oriented towards the Z-axis, but the white / black region ratio, as indicated by IQ mapping (not shown), was low, suggesting poor crystallinity. In contrast, if a laminated structure was fabricated, the crystal grain size decreased, reaching the limit of EBSD measurement. Therefore, in Experiment 36, the grain size, the orientation of the (111) plane, and the white / black region ratio could not be determined.

[0119] In films containing In, by depositing on a substrate film containing In, Ga, and Zn (Example 39), with the (111) plane facing the Z-axis, the crystallinity is improved according to the IQ mapping (Fig. 35, Fig. 41). If deposited on a substrate film containing In, Ga, and B (Example 40), the crystallinity is not limited to the (111) plane but is randomly aligned, but the crystallinity is still improved (Fig. 36, Fig. 42).

[0120] In thin films containing In and 1 atomic% B, the crystallinity is poor when the film is deposited on a substrate of In, Ga, and Zn (Example 41), with the (111) plane not being limited to, but rather randomly aligned (Fig. 37, Fig. 43). However, in thin films containing In and 2 atomic% B (Example 45), the crystallinity is improved by forming a shape between dendrites and facets. In thin films deposited on a substrate of In, Ga, and B (Examples 42, 44), the (111) plane is oriented towards the Z-axis, and the crystallinity is also improved according to the IQ mapping (Fig. 38, Fig. 44, Fig. 40, Fig. 46). If the film is deposited on a substrate of In, B, and Zn (Example 43), the crystallinity is poor when the film is randomly aligned (without being limited to the (111) plane (Fig. 39, Fig. 45).

[0121] For Test Examples 39 to 42 and Test Example 44, the characteristics of TFT (Thin Film Transistor) were evaluated. The results are shown in Table 8.

[0122] [Table 8] TFT characteristics Movement rate [cm2 / Vs] critical voltage [V] S [V / dec.] Experimental Example 39 21.3 4.0 1.12 Test Example 40 22.8 5.5 0.69 Test Example 41 33.5 3.5 1.14 Test Example 42 37.7 2.5 0.49 Test Example 44 50.7 2.0 0.31

[0123] If a film containing In is deposited on a substrate containing In, Ga, and Zn, or on a substrate containing In, Ga, and B (Examples 39 and 40), the carrier mobility exceeds 20 cm² / Vs. If a film containing In and B is deposited on a substrate containing In, Ga, and Zn (Example 41), the carrier mobility exceeds 30 cm² / Vs, but the S-value, which indicates the steepness of the drain current rise, is relatively large. If a film containing In and B is deposited on a substrate containing In, Ga, and B (Examples 42 and 44), the carrier mobility is further improved, and the S-value is relatively low.

[0124] <Fifth Embodiment> A sputtering target is formed, wherein an amorphous oxide semiconductor thin film containing In and B elements is formed.

[0125] First, In₂O₃ (indium oxide) and B₂O₃ (boron oxide) are prepared as raw material powders. The raw material powders are weighed with an atomic percentage ratio of In:B = 99:1 (excluding O) according to the target value. The weighed raw material powders, water, and an organic dispersant are added to a nylon crucible using zirconia balls as a medium, and the mixture is mixed in a ball mill for 3 hours to obtain a slurry.

[0126] Next, the slurry was granulated using a spray dryer. The composition of the granulated powder was investigated by inductively coupled plasma (ICP) luminescence spectrophotometry, and the results confirmed In:B = 99.2 [atm%]:0.8 [atm%], which is close to the target value. The particle size distribution of the granulated powder is shown in Figure 47. The particle size was determined using an electromagnetic vibrating screen. The granulated powder showed the largest particle size distribution between 38 μm and 63 μm, with most particles below 75 μm.

[0127] Subsequently, the granulated powder is degreased in air at 200°C for 12 hours to obtain degreased granulated powder. The degreased granulated powder is then sintered by hot pressing to obtain a sputtering target containing InB oxide. Sintering is not limited to hot pressing; it can also be performed using atmospheric pressure sintering or hot isostatic pressing (HIP). The hot pressing sintering is carried out at a sintering temperature of 950°C, a sintering pressure of 40 MPa, a sintering time of 8 hours, and in a nitrogen environment. Since there is a positive correlation between the sintering pressure and the relative density of the obtained sintered body (sputtering target), sintering at a pressure higher than the sintering pressure can increase the relative density of the sintered body.

[0128] The composition of the sputtering target (excluding O) was investigated by ICP-N PLC, and the results confirmed that In:B = 99.2 [atm%]:0.8 [atm%], with no change in composition ratio caused by sintering under high temperature and pressure. To investigate the crystallinity of the sputtering target, X-ray diffraction (manufactured by Rigaku Corporation: Cu target, Kβ filter) and scanning electron microscopy were performed. The X-ray diffraction spectrum is shown in Figure 48, and the reflection electron microscope image is shown in Figure 49.

[0129] The X-ray diffraction spectrum (Figure 48) shows that, in addition to In₂O₃ as the main diffraction peak, trace amounts of InBO₃ diffraction peaks were also observed. This indicates that InBO₃ crystals are also formed by adding B. The ratio of In₂O₃, InBO₃, and In calculated from the semi-quantitative X-ray diffraction analysis is 98.9:0.7:0.4. It can be assumed that the trace amounts of In detected in the sputtering target are due to the reduction of the graphite mold after hot pressing.

[0130] From the electron microscope image (Figure 49), three different contrasts can be observed. Based on the semi-quantitative results of the crystalline phases shown in Figure 48, region A, which occupies most of the area, can be considered to be In₂O₃; region B, with a deeper contrast than region A, can be considered to be InBO₃; and region C, which is scattered white in region A, can be considered to be In. If the trace amount of In generated during the reduction of the graphite mold at 950°C is removed, the oxides of In and B can be considered to contain the crystalline phases of In₂O₃ and InBO₃.

[0131] A sputtering target is manufactured by machining and bonding the sputtering target material. The machining is performed in the order of roughing, peripheral machining, and finishing to produce a 4-inch diameter sputtering target (ϕ101.5 mm × t5.2 mm). After cleaning and drying, the target is inspected for size, weight, etc. The relative density of the target, calculated based on its size and weight, is 80.5%. The resistivity of the target, measured using a four-probe measuring instrument, is 1.6 × 10⁻² Ωcm, sufficient for use in a DC discharge sputtering apparatus.

[0132] As a final step, bonding to the water-cooling backing plate is performed. The target is bonded to the Cu backing plate using indium to complete the InB oxide sputtering target, and a post-bonding inspection is conducted. The post-bonding positional offset is 0.19 mm, and the warpage is -0.04 mm (warpage on the backing plate side). Furthermore, the adhesion rate, measured by a UT (Universal Testing Machine), is 100%. [Industry availability]

[0133] As explained above, the crystalline oxide semiconductor thin film of this invention exhibits high operational stability and can be used in thin-film transistors suitable for applications such as organic EL displays.

[0134] none

Claims

1. A crystalline oxide semiconductor thin film comprising In, B and Fe elements, wherein the ratio of the content of In (atomic %) to the content of B (atomic %) satisfies the following formula 1, the average grain size on the surface observed by an electron microscope is 0.25 μm or more, and B / (In+B) ≤ 0.20 ···· (1).

2. The crystalline oxide semiconductor thin film as claimed in claim 1, wherein, The peak value detected by microwave photoconductivity attenuation method is more than 4 times the peak value before crystallization after heat treatment.

3. A stack for forming a thin-film transistor, the stack comprising an amorphous oxide semiconductor thin film and a crystalline oxide semiconductor thin film as described in claim 1.

4. The laminate as described in claim 3, wherein, The amorphous oxide semiconductor thin film contains In and B elements.

5. A sputtering target for forming a crystalline oxide semiconductor thin film as described in claim 1 or 2.

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