JP5058469B2 - Sputtering target and method for forming a thin film using the target - Google Patents

Description

  The present invention relates to a sputtering target, particularly a sputtering target suitable for forming an amorphous oxide film, and a method for forming a thin film using the target.

  In recent years, TFTs using a transparent conductive oxide polycrystalline thin film containing ZnO as a main component not only for a transparent electrode but also for a channel layer have been actively developed. Since the thin film can be formed at a low temperature and is transparent to visible light, it is said that a flexible transparent TFT can be formed on a substrate such as a plastic plate or a film. As a forming means, a sputtering method capable of forming a uniform thin film over a large area is promising.

For example, Patent Document 1 discloses a TFT using a transparent conductive oxide polycrystalline thin film containing ZnO as a main component for a channel layer. Patent Document 2 describes that an amorphous oxide film of Zn _x M _y In _z O _{(x + 3y / 2 + 3z / 2)} is used for a transparent electrode (M is a combination of Al and Ga). And at least one element, the ratio x / y is in the range of 0.2 to 12, and the ratio z / y is in the range of 0.4 to 1.4).

As a means for forming these transparent conductive oxide films, a sputtering method capable of forming a uniform thin film over a large area is promising.
JP 2004-103957 A Japanese Patent Laid-Open No. 2000-044236

  In a conductive transparent oxide containing ZnO as a main component, oxygen defects are likely to occur, a large number of carrier electrons are generated, and it is difficult to reduce the electrical conductivity. Furthermore, abnormal discharge occurs during film formation by sputtering, and the stability of the film formation is impaired, and the uniformity and reproducibility of the resulting film are reduced. For this reason, for example, when used as an active layer (channel layer) of a TFT (thin film transistor), even when no gate voltage is applied, a large current flows between the source terminal and the drain terminal, realizing a normally-off operation of the TFT. Can not. It is also difficult to increase the on / off ratio of the transistor.

Further, when a mixed crystal sintered body or a homologous sintered body having a relative density of 40% or 70% or more described in Patent Document 2 is used in the sputtering method, unstable elements in the sputtering film formation become apparent. There is a case. In some cases, the reproducibility and yield of the manufactured TFT may be low. Therefore, it has been difficult to stably obtain a film having an electron carrier concentration less than 10 ¹⁸ / cm ³ suitable for a TFT channel layer.

  As a result of the analysis, the cause of the unstable factors is the occurrence of abnormal discharge called micro-arcing that is acceptable for film formation of a transparent conductive film such as ITO, acicular protrusions called nodules that occur with abnormal discharge, black This was caused by a change in the oxidation state of the target surface such as crystallization.

According to the knowledge of the present inventors, these changes also change the electron carrier concentration of the amorphous oxide thin film. Since the change in the electron carrier concentration directly affects the electrical characteristics of the TFT, it adversely affects the uniformity and yield of the TFT. Therefore, it is difficult to stably obtain a film having an electron carrier concentration less than 10 ¹⁸ / cm ³ suitable for a TFT channel layer.

  Therefore, an object of the present invention is to solve these problems and provide a sputtering target for obtaining high reproducibility and yield when an amorphous oxide film is formed by sputtering.

As a result of intensive research and development on the growth conditions of the InGaO ₃ (ZnO) _m film and related films, the present inventors adjust the composition, resistance value, and density of the sputtering target within a predetermined range. The knowledge that the said subject can be solved was obtained.

Specifically, in addition to the various conditions during sputtering film formation, the oxide sintered compact sputtering target is adjusted to have a relative density of 75% or more and a resistance value ρ of 50 Ωcm or less. By using such a specific target, it becomes possible to improve the controllability of the electron carrier concentration and stably produce an amorphous oxide thin film having an electron carrier concentration of less than 10 ¹⁸ / cm ³ .

  Here, the resistance value of the target in the present invention is also referred to as “bulk resistance value”. In a sample having a bulk shape (having a sufficiently large size that does not affect the resistance value when measuring the resistance value), the resistance value can be obtained by, for example, a four-terminal method.

The present invention provides a sputtering target suitable for forming the above InGaO ₃ (ZnO) _m film and a method for forming a thin film using the target.

  The present invention will be specifically described below.

A sputtering target suitable for forming an amorphous oxide film used for an active layer of a semiconductor element according to the present invention relates to a sintered body target used when sputtering an amorphous oxide film containing at least In, Zn, and Ga. (1) When the composition contains In, Zn, and Ga, and the target has a homologous phase single crystal structure and the density is 100%, the relative density is 75% or more and the resistance value ρ is It is characterized by being 50 Ωcm or less.

  In the present invention, (2) a sintered compact target used when sputtering an amorphous oxide film containing at least In, Zn, and Ga is a polycrystalline oxide sintered body having a homologous crystal structure. Preferably there is.

  In the present invention, (3) the sintered compact target used when sputtering the amorphous oxide film is a polycrystalline oxide sintered body, and the atomic ratio is In: Ga: Zn = 1: x ( 0.1 ≦ x ≦ 10): m (m <6) is preferable.

The thin film formation method using the sputtering target according to the present invention relates to a sintered compact target used when an amorphous oxide film is formed by sputtering. And the amorphous oxide film used for the active layer of the semiconductor element whose electron carrier concentration is less than 10 < ¹⁸ > / cm < ³ > using the sputtering target described in any one of said (1)-(3) is room temperature or more and 450 degreeC. The sputtering film formation is performed at the following film formation temperature.

  The present invention constitutes a sputtering target having a relative density of 75% or more and a resistance value ρ of 50 Ωcm or less. When such a high-density and low-resistance target is used, abnormal discharge called minute arcing that causes unstable elements is significantly suppressed during sputtering of an amorphous oxide film. And generation | occurrence | production of the acicular protrusion called nodule which generate | occur | produces with abnormal discharge, and the change of the oxidation state of the target surface, such as blackening, are also suppressed significantly.

These changes also change the electron carrier concentration of the amorphous oxide thin film obtained by sputtering film formation. For this reason, when an amorphous oxide thin film is used as a channel layer of a TFT, it directly affects the electrical characteristics of the TFT and is very effective in improving the uniformity and yield of the TFT. For this reason, when the amorphous oxide thin film is used as the active layer of the TFT, the normally-off operation of the TFT can be reliably realized. In addition, the on / off ratio of the transistor can be increased to 10 ⁶ or more.

According to the present invention, for example, the electron carrier concentration controllability of an amorphous oxide thin film suitably used for a TFT channel layer can be improved. Furthermore, it is possible to provide a sputtering target capable of realizing an amorphous oxide thin film having an electron carrier concentration of less than 10 ¹⁸ / cm ³ with high reproducibility and yield.

  As described above, according to the present invention, it is possible to provide a sputtering target for obtaining high reproducibility and yield when sputtering an amorphous oxide film.

  The best mode for carrying out a sputtering target suitable for forming an amorphous oxide film according to the present invention and a method for forming a thin film using the target will be specifically described below with reference to the drawings.

  A sputtering target (hereinafter referred to as an oxide sputtering target) suitable for forming an amorphous oxide film according to the present invention is a sintered body target used when an amorphous oxide film containing at least In, Zn, and Ga is formed by sputtering. . This target is characterized in that its composition contains In, Zn, and Ga, the relative density is 75% or more, and the resistance value ρ is 50 Ωcm or less. Preferably, the relative density is 90% or more and the resistance value ρ is 0.5 Ωcm or less. More preferably, the relative density is 95% or more and the resistance value ρ is 0.1 Ωcm or less.

  In this invention, since the said relative density is so good that it is large, there is no upper limit (ideally 100%). Similarly, the smaller the resistance value, the better. Therefore, there is no lower limit value (ideally 0 Ωcm).

In the present invention, the “relative density” is normalized by setting the density when a desired InGaO ₃ (ZnO) _m target has a homologous single crystal structure as 100%, for example. And, “the density of the actually produced InGaO ₃ (ZnO) _m sputtering target is divided by the ideal density obtained from the calculation when the desired InGaO ₃ (ZnO) _m target has a single crystal structure of the homologous phase, It is defined as “Standardized”.

  As described above, abnormal discharge called arcing occurs during sputtering, and acicular protrusions called nodules are likely to occur on the target surface. In order to suppress this, it is required to make the density of the target as high as possible and to reduce the resistance value uniformly and uniformly. In the sintered body target, the resistance value ρ varies depending on the composition, but the absolute value of the resistance value ρ is the most effective control factor for the stability during sputtering.

  A hot press method may be used for high density and low resistance of the target. However, it is desirable to take a manufacturing process generally called a cold press method from the viewpoint of cost as the target size for enabling large-area film formation increases. The cold press method is a method in which a mixture of oxide powders, which are raw materials for an oxide film, is pressed at room temperature, sintered in an oxygen-containing atmosphere at 1250 ° C to 1650 ° C, and further machined. is there. The sintering temperature at that time is preferably 1400 ° C. or higher.

  It is preferable that the sintered compact target used when sputtering the amorphous oxide film containing In, Zn, and Ga in the present invention has a homologous phase crystal structure. The “crystal structure of the homologous phase” in the present invention is a crystal having a “natural superlattice” structure having a long period in which several crystal layers of different substances are stacked. When the crystal cycle or thickness of each thin film layer is on the order of nanometers, depending on the combination of the chemical composition of these layers and the thickness of the layers, it differs from the properties of a single substance or a mixed crystal in which each layer is uniformly mixed. Unique characteristics can be obtained. The crystal structure of the homologous phase can be confirmed, for example, because the X-ray diffraction pattern of the powder obtained by pulverizing the target matches the crystal structure X-ray diffraction pattern of the homologous phase assumed from the composition ratio. Specifically, it can be confirmed from the coincidence with the crystal structure X-ray diffraction pattern of the homologous phase obtained from a JCPDS (Joint Committee of Powder Diffraction Standards) card.

  The sputtering target according to the present invention is a polycrystalline oxide sintered body containing In, Zn, and Ga. The atomic ratio is preferably adjusted to a range of In: Ga: Zn = 1: x: m (0.1 ≦ x ≦ 10, m <6).

For producing the sputtering target of the present invention, for example, In ₂ O ₃ , Ga ₂ O ₃ and ZnO (each 4N reagent) as starting materials are wet-mixed at a predetermined ratio, calcined, dry pulverized, and finally sintered (1400 ° C. ). An amorphous oxide thin film whose composition in the crystalline state is represented by InGaO ₃ (ZnO) _m (m is a natural number less than 6) is stable in an amorphous state up to a high temperature of 800 ° C. or higher when the value of m is less than 6. To be kept. However, as the value of m increases, that is, the ratio of ZnO to InGaO ₃ increases, and as it approaches the ZnO composition, it becomes easier to crystallize.

  Therefore, the value of m is preferably less than 6 for the channel layer of the amorphous oxide TFT. In addition, the electrons that are carriers of the amorphous oxide thin film are thought to originate from oxygen defects as in the case of a transparent conductive oxide film such as ITO. Therefore, by adjusting the oxygen gas partial pressure and the applied power density, which are sputtering film formation conditions, Can be controlled.

  Furthermore, the electron carrier concentration can also be controlled by the ratio of Ga to In. When the Ga composition ratio is 10 or more, the electron carrier concentration is low and the field effect mobility is small even when the oxygen gas partial pressure, which is the sputter film formation condition, is zero. That is, one control factor was lost as a TFT manufacturing condition, and the reproducibility was low. Further, when the Ga composition ratio is less than 0.1, crystallization is facilitated regardless of the value of m which is the Zn composition ratio.

The electron carrier concentration of the amorphous oxide thin film is controlled by the material, composition ratio, and sputtering film forming conditions of the amorphous oxide thin film. However, the reproducibility and uniformity over a large area largely depend on the target characteristics. Sputtering film formation using the target of the present invention is excellent in controllability of the electron carrier concentration, and can stably produce an amorphous oxide thin film having an electron carrier concentration of less than 10 ¹⁸ / cm ³ .

An ordinary transparent conductive oxide film such as ITO has an electron carrier concentration of 10 ²¹ / cm ³ . On the other hand, in the amorphous oxide thin film applied to the channel layer of the TFT, the electron carrier concentration is preferably less than 10 ¹⁸ / cm ³ , more preferably 10 ¹⁴ / cm ³ or more and 10 ¹⁶ / cm ³ or less.

The present inventors have found that the amorphous oxide thin film has a unique characteristic that the electron mobility increases as the number of conduction electrons increases. Then, a TFT was formed using the film, and it was found that transistor characteristics such as an on / off ratio, a saturation current in a pinch-off state, and a switch speed were further improved. Then, by using the amorphous oxide film as a channel layer of the thin film transistor, the electron mobility can be set to 1 cm ² / (V · sec) or more, preferably 5 cm ² / (V · sec) or more.

In addition to the above conditions, the electron carrier concentration can be set to less than 10 ¹⁸ / cm ³ . Preferably, when it is 10 ¹⁴ / cm ³ or more and 10 ¹⁶ / cm ³ or less, the current between the drain and source terminals at the time of off (when no gate voltage is applied) is less than 10 microamperes, preferably 0.1 micron Can be less than amperes.

When the thin film is used, when the electron mobility is 1 cm ² / (V · sec) or more, preferably 5 cm ² / (V · sec) or more, the saturation current after pinch-off can be 10 microamperes or more and -Off ratio can be 10 ³ or more.

  In the TFT, in a pinch-off state, a high voltage is applied to the gate terminal, and high-density electrons exist in the channel. Therefore, according to the present invention, the saturation current value can be further increased by the amount of increase in electron mobility. As a result, almost all transistor characteristics such as an increase in on / off ratio, an increase in saturation current, and an increase in switching speed are improved. In a normal compound, when the number of electrons increases, electron mobility decreases due to collisions between electrons.

  In the present invention, the amorphous oxide film only needs to have a substantially amorphous structure, and not only the whole film has an amorphous structure but also the film may contain microcrystals or polycrystals. .

  According to the knowledge of the present inventors, when a mixed crystal sintered body or a homologous sintered body having a relative density of 40% or 70% or more described in Patent Document 2 is used in the sputtering method, an amorphous material is obtained. In some cases, the electron carrier concentration of the oxide thin film gradually shifts.

Electrical conductivity can be controlled by forming an amorphous oxide thin film whose composition in the crystalline state is represented by InGaO ₃ (ZnO) _m (m is a natural number less than 6) in an atmosphere having a specific oxygen partial pressure. . Specifically, the electrical conductivity can be lowered to less than 10 S / cm by forming a film in an atmosphere having an oxygen partial pressure of 1 × 10 ⁻³ Pa or higher, preferably 1 × 10 ⁻² Pa or higher. . In this case, the temperature of the substrate is maintained at substantially room temperature without intentionally heating. When using a glass substrate, it is desirable to control the substrate temperature to a low temperature of 450 ° C. or lower. In order to use a low heat-resistant material such as a plastic film as the substrate, the substrate temperature is preferably controlled to 200 ° C. or lower. More preferably, it is preferably kept below 100 ° C. By further increasing the oxygen partial pressure, the number of electron carriers can be reduced.

A transistor having a normally-off and an on / off ratio of 10 ⁶ or more can be formed using the amorphous oxide film of the present invention. Further, the uniformity and reproducibility of the TFT characteristics are improved, and a high yield can be realized.

In the thin film transistor using the amorphous oxide film, a gate insulating film is preferably formed using a mixed crystal compound containing at least two of Al ₂ O ₃ , Y ₂ O ₃ , HfO ₂ , or a compound thereof. If there is a defect at the interface between the gate insulating thin film and the channel layer thin film, the electron mobility is lowered and the transistor characteristics are hysteresis. Further, the leakage current varies greatly depending on the type of the gate insulating film. For this purpose, it is necessary to select a gate insulating film suitable for the channel layer. If an Al ₂ O ₃ film is used, leakage current can be reduced. In addition, the hysteresis can be reduced by using a Y ₂ O ₃ film. Further, if a high dielectric constant HfO ₂ film is used, the electron mobility can be increased. Further, by using mixed crystals of these films, a TFT with small leakage current and hysteresis and high electron mobility can be formed. In addition, since the gate insulating film formation process and the channel layer formation process can be performed at room temperature, both a staggered structure and an inverted staggered structure can be formed as the TFT structure.

  A thin film transistor (TFT) is a three-terminal element including a gate terminal, a source terminal, and a drain terminal. A semiconductor thin film formed over an insulating substrate such as ceramic, glass, or plastic is used as a channel layer through which electrons or holes move. The active element has a function of switching the current between the source terminal and the drain terminal by controlling the current flowing through the channel layer by the voltage applied to the gate terminal.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited at all by these Examples.

(Example 1: Production of oxide sputtering target)
First, In ₂ O ₃ , Ga ₂ O ₃ , and ZnO (each 4N reagent) as a starting material are wet-mixed at a ratio of 1: 1: 1, and calcined, dry pulverized, and main-sintered to perform InGaO ₃ An oxide sputtering target having a (ZnO) ₄ composition was prepared. (This process is generally called a cold press.) There are three types of oxide sputtering targets prepared in this example: Invention product A, Invention product B, and Comparison product C. With respect to this product A, product B and comparative product C, the relative density (%) and the resistance value ρ (Ωcm) were measured. The relationship is shown in FIG. 1 (horizontal axis: target relative density (%), vertical axis: target resistance value (Ωcm)).

According to this, the product A of the present invention has a relative density of 96.9% and a resistance value ρ of 1.3 × 10 ⁻² Ωcm, and the product B of the present invention has a relative density of 75.0% and a resistance value ρ of 5 0.0 × 10 Ωcm. On the other hand, the comparative product C had a relative density of 66.0% and a resistance value ρ of 2.9 × 10 ⁶ Ωcm (see Table 1 described later).

(Example 2: Formation of an In-Zn-Ga-O-based amorphous oxide film by sputtering)
An In—Zn—Ga—O-based amorphous oxide film was deposited over a glass substrate (Corning Corp., 1737) by a high-frequency sputtering method using a mixed gas of oxygen and argon as an atmosphere. At that time, three types of polycrystalline sintered bodies of the invention product A, the invention product B, and the comparison product C having the above-described InGaO ₃ (ZnO) ₄ composition were used as targets. The substrate temperature is 25 ° C.

  The obtained film was subjected to X-ray diffraction by making X-rays incident on the film surface at an incident angle of 0.5 degree. As a result, a clear diffraction peak was not detected, and it was confirmed that all the produced In—Zn—Ga—O-based films were amorphous films.

  Next, for the product B of the present invention, the oxygen partial pressure (Pa) of the atmosphere during film formation was changed, and the electrical conductivity (S / cm) of the obtained amorphous oxide film was measured. The results are shown in FIG. 2 (horizontal axis: oxygen partial pressure (Pa), vertical axis: electrical conductivity (S / cm)).

According to this, it was possible to make the electric conductivity about 10 ⁻⁵ S / cm by forming a film in a mixed gas atmosphere of oxygen and argon having an oxygen partial pressure of 1.8 × 10 ⁻² Pa or more. (Refer to the second measured value from the right side of the graph of FIG. 2). The electron mobility was about 5 cm ² / V · sec, and the electron carrier concentration was less than 10 ¹⁸ / cm ³ . In this case, the temperature of the substrate is maintained at substantially room temperature without intentionally heating. The surface of the obtained amorphous oxide film was flat.

Furthermore, when the oxygen partial pressure was increased to 1 × 10 ⁻¹ Pa, the electrical conductivity could be reduced to less than 10 ⁻¹⁰ S / cm (this measured value is outside the range of the graph shown in FIG. 2). Not shown). In this case, although the electron mobility could not be measured, the electron mobility was estimated to be about 1 cm ² / V · second by extrapolating from the value in the film having a high electron carrier concentration.

Even when a polyethylene terephthalate (PET) film having a thickness of 200 μm was used instead of the glass substrate, the obtained InGaO ₃ (ZnO) ₄ amorphous oxide film exhibited the same characteristics as described above.

(Example 3: Production of TFT panel using In-Zn-Ga-O-based amorphous oxide film (glass substrate))
1) Fabrication of TFT Panel A top gate TFT device shown in FIG. 3 was fabricated as a TFT device using the amorphous oxide of this example as a channel layer.

First, an In—Ga—Zn—O-based amorphous oxide film is formed on the glass substrate 1 having a size of 12 cm × 12 cm under the condition of an oxygen partial pressure of 1.8 × 10 ⁻² Pa by an RF sputtering method. 2 to a thickness of 120 nm. At that time, three types of polycrystalline sintered bodies of the invention product A, the invention product B, and the comparison product C having the above-described InGaO ₃ (ZnO) ₄ composition were used as targets.

Further thereon, a gold film having a thickness of 30 nm was laminated, and a drain terminal 5 and a source terminal 6 were formed by a photolithography method and a lift-off method. Finally, a Y ₂ O ₃ film used as the gate insulating film 3 is formed by electron beam evaporation (thickness: 90 nm, relative dielectric constant: about 15, leakage current density: 10 ⁻³ A / cm when 0.5 MV / cm is applied) ² ).

  A gold film was formed thereon, and a gate terminal 4 was formed by a photolithography method and a lift-off method. The channel length was 10 μm and the channel width was 150 μm. In the substrate, 10 × 10 = 100 TFTs were arranged at equal intervals.

2) Characteristic Evaluation of TFT Panel FIG. 4 shows current-voltage characteristics of a TFT element measured at room temperature (horizontal axis: drain voltage V _DS (V), vertical axis: drain current I _DS (A)).

According to this, it can be understood that the channel is of n-type conduction because the drain current I _DS increases with the increase of the drain voltage V _DS . I _DS shows the behavior of a typical semiconductor transistor that saturates (pinch off) at about V _DS = 6V. When the gain characteristic was examined, the threshold value of the gate voltage V _GS when V _DS = 6 V was applied was about 1.4V. Further, when V _G = 6 V, a current of I _DS = 2.3 × 10 ⁻⁴ A flowed. This corresponds to the fact that carriers can be induced in the insulator In—Ga—Zn—O-based amorphous oxide film by the gate bias. The on / off ratio of the transistor was about 10 ⁸ . Further, when the field effect mobility was calculated from the output characteristics, a field effect mobility of about 11.5 cm ² (Vs) ⁻¹ was obtained in the saturation region.

Moreover, all the characteristics of 100 elements in the TFT panel were evaluated. The field effect mobility is in the range of 8 to 11.5 cm ² / (V · sec), and the threshold value of V _GS is in the range of 0.5 to 2.0 V, except for two gate short circuits. It was. In particular, there was almost no difference in characteristics between adjacent TFT elements.

  Regarding the change in the characteristics of the TFT panel thus obtained, TFTs were prepared for 5 continuous batches using each of the three types of targets of the present product A, the present product B, and the comparative product C. As an object, the uniformity and reproducibility of TFT characteristics were evaluated.

  Here, for the evaluation of the uniformity of TFT characteristics, the ratio (maximum value / minimum value) of the maximum value and the minimum value of the on-current at Vg = 6 V in the same panel was measured. As a result, the TFT characteristics were evaluated in four stages in order from the better uniformity of TFT characteristics: within 1.05: ◎, within 1.10: ◯, within 1.20: Δ, greater than 1.20: x.

  Moreover, about evaluation of the reproducibility of TFT characteristics, ratio (1st batch / 5th batch) of the average field effect mobility of the 1st batch and 5th batch in continuous 5 batches was measured. As a result, the TFT characteristics were evaluated in four stages in order from those with good reproducibility of TFT characteristics: 1.10 or less: 、, 1.20 or less: ○, 1.50 or less: Δ, greater than 1.50: x.

  Table 1 shows the relative density, resistance value ρ, uniformity of TFTs produced using the target, and reproducibility of TFTs produced using the target for the inventive product A, the inventive product B, and the comparative product C. Indicates.

  According to this, the TFT produced using the product A of the present invention having a relative density of 95% or more and a resistance value ρ of 0.1 Ωcm or less had both excellent evaluation results of TFT characteristic uniformity and reproducibility. . In addition, the TFT produced using the product B of the present invention having a relative density of 75% and a resistance value ρ of 50 Ωcm had a good evaluation result of uniformity and reproducibility of TFT characteristics. On the other hand, the TFT produced using the comparative product C having a relative density of less than 75% and a resistance value ρ exceeding 50 Ωcm had Δ and x evaluation results of uniformity and reproducibility of TFT characteristics. From this, it was confirmed that it is effective to use an oxide sputtering target having a relative density of 75% or more and a resistance value ρ of 50 Ωcm or less in terms of uniformity and reproducibility of TFT characteristics.

  FIG. 5 shows an X-ray diffraction pattern obtained from powder obtained by pulverizing the targets of the present invention product A and the present product product B, and a homologous phase crystal structure X-ray diffraction pattern obtained from a JCPDS card. (Horizontal axis: 2θ (degrees: degree), vertical axis: intensity (arbitrary units: arbitrary unit)) As is clear from FIG. 5, both of the products A and B of the present invention have a crystal structure X of a homologous phase. It was confirmed that a line diffraction pattern was shown.

  In the above-described embodiments, the amorphous oxide thin film has been mainly described when the TFT channel layer is used. However, the present invention is applied when the amorphous oxide thin film is used for the TFT channel layer. It is not limited. As an application other than the channel layer of the TFT, for example, an optical sensor element can be cited.

  The sputtering target according to the present invention can be used for the formation of an amorphous oxide thin film suitably used for a channel layer of a TFT. Furthermore, it can be used as a switching element for LCDs and organic EL displays. In addition, it can be widely applied to IC cards and ID tags, as well as flexible displays in which semiconductor thin films are formed on flexible materials such as plastic films.

It is a graph which shows the relationship between the relative density and resistance value (rho) of the sputtering target (this invention product A, this invention product B, comparative product C) produced in Example 1 of this invention. Using the sputtering target of the present invention (Product B of the present invention) produced in Example 1, the electrical conductivity of the In—Ga—Zn—O-based amorphous film formed by sputtering and the oxygen partial pressure during film formation It is a graph which shows a relationship. It is a schematic diagram which shows the top gate type MISFET element structure produced in Example 3 of this invention. It is a graph which shows the current-voltage characteristic of the top gate type MISFET element produced in Example 3 of this invention. An X-ray diffraction pattern obtained from a powder obtained by pulverizing the sputtering target of the present invention (Invention product A and Invention product B) produced in Example 1, and a homologous phase crystal structure X-ray diffraction pattern obtained from a JCPDS card It is a graph which shows.

Explanation of symbols

1 Substrate 2 Channel layer 3 Gate insulating film 4 Gate electrode (gate terminal)
5 Drain electrode (drain terminal)
6 Source electrode (source terminal)

Claims (7)

A sintered compact target containing at least In, Zn, and Ga in its composition, where the density is 100% when the target has a single crystal structure of a homologous phase and the relative density is 75% or more and resistance A sputtering target for forming an amorphous oxide film used for an active layer of a semiconductor element, wherein the value ρ is 50 Ωcm or less. The sputtering target according to claim 1, wherein the relative density is 95% or more and the resistance value ρ is 0.1 Ωcm or less.   The sputtering target according to claim 1, wherein the target is a polycrystalline oxide sintered body having a homologous phase crystal structure. The target is a polycrystalline oxide sintered body, and the atomic ratio is In: Ga: Zn = 1: x: m (0.1 ≦ x ≦ 10, m <6). The sputtering target according to any one of 1 to 3 . The amorphous oxide thin film has an electron carrier concentration of 10 ¹⁸ / Cm ³ The sputtering target according to claim 1, wherein the sputtering target is less than 5. Using the sputtering target according to claim 1, any one of 5, electron carrier concentration 10 18 ^/ cm ³ less than the semiconductor forming an amorphous oxide film used for the active layer of 450 ° C. or less than room temperature element A method for forming a thin film, wherein the thin film is formed by sputtering at a temperature. The thin film forming method according to claim 6, wherein the amorphous oxide film is formed as a channel layer of a thin film transistor.