WO2012029455A1 - 酸化物焼結体及び酸化物半導体薄膜 - Google Patents

酸化物焼結体及び酸化物半導体薄膜 Download PDF

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WO2012029455A1
WO2012029455A1 PCT/JP2011/067133 JP2011067133W WO2012029455A1 WO 2012029455 A1 WO2012029455 A1 WO 2012029455A1 JP 2011067133 W JP2011067133 W JP 2011067133W WO 2012029455 A1 WO2012029455 A1 WO 2012029455A1
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oxide
thin film
sintered body
oxide semiconductor
semiconductor thin
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PCT/JP2011/067133
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English (en)
French (fr)
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英生 高見
幸三 長田
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Jx日鉱日石金属株式会社
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Priority to KR1020137007631A priority Critical patent/KR101331293B1/ko
Publication of WO2012029455A1 publication Critical patent/WO2012029455A1/ja

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    • H01L29/772—Field effect transistors
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    • H01L29/7869—Thin film transistors, i.e. transistors with a channel being at least partly a thin film having a semiconductor body comprising an oxide semiconductor material, e.g. zinc oxide, copper aluminium oxide, cadmium stannate
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Definitions

  • the present invention relates to an oxide sintered body and a transparent oxide semiconductor thin film useful for the production of a thin film transistor and a transparent electrode in a display device.
  • Transparent oxide semiconductors are used as active electrodes of thin film transistors in display devices such as liquid crystal display devices, plasma display devices and organic EL display devices, as well as transparent electrodes such as solar cells and touch panels.
  • display devices such as liquid crystal display devices, plasma display devices and organic EL display devices, as well as transparent electrodes such as solar cells and touch panels.
  • IGZO-based an In—Ga—Zn—O-based
  • tin (Sn) is intended to improve characteristics.
  • gallium (Ga) which is an essential component of these systems, is a rare element and has a large limitation in terms of industrial use because of its high price.
  • Patent Document 3 As a transparent oxide semiconductor not using Ga, there is a report on an In—Zn—Sn—O system (see Patent Document 3).
  • the atomic ratio of [Sn] with respect to the sum of) exceeds 0.1 and less than 0.2, the following atomic ratio 1 is satisfied, and when it is 0.2 or more and less than 0.3, the following atomic ratio 2 is satisfied. Is described.
  • Atomic ratio 1 0.1 ⁇ [In] / ([In] + [Sn] + [Zn]) ⁇ 0.5 0.1 ⁇ [Sn] / ([In] + [Sn] + [Zn]) ⁇ 0.2 0.3 ⁇ [Zn] / ([In] + [Sn] + [Zn]) ⁇ 0.8 Atomic ratio 2 0.01 ⁇ [In] / ([In] + [Sn] + [Zn]) ⁇ 0.3 0.2 ⁇ [Sn] / ([In] + [Sn] + [Zn]) ⁇ 0.3 0.4 ⁇ [Zn] / ([In] + [Sn] + [Zn]) ⁇ 0.8
  • Patent Document 3 has a problem that abnormal discharge is likely to occur during sputtering because of high bulk resistance.
  • an object of the present invention is to provide an oxide sintered body that is a scarce resource and does not contain expensive gallium (Ga) and can reduce bulk resistance.
  • Another object of the present invention is to provide an oxide semiconductor thin film having the same composition as the oxide sintered body.
  • the present inventor is promising as an alternative element for gallium (Ga), which is a rare and expensive element, aluminum (Al), which is the same trivalent metal element as gallium, and titanium (Ti), which is the tetravalent metal element.
  • Ga gallium
  • Al aluminum
  • Ti titanium
  • indium (In), zinc (Zn), a metal element X (where X represents one or more elements selected from Al and Ti), oxygen (O),
  • An oxide sintered body comprising: in atomic ratios of indium (In), zinc (Zn), and metal element X are 0.2 ⁇ In / (In + Zn + X) ⁇ 0.8 and 0.1 ⁇ , respectively.
  • the oxide sintered body satisfies Zn / (In + Zn + X) ⁇ 0.5 and 0.1 ⁇ X / (In + Zn + X) ⁇ 0.5.
  • the oxide sintered body according to the present invention has a relative density of 98% or more.
  • the oxide sintered body according to the present invention has a bulk resistance of 3 m ⁇ cm or less.
  • indium (In), zinc (Zn), a metal element X (where X represents one or more elements selected from Al and Ti), oxygen (O
  • the atomic ratio of indium (In), zinc (Zn), and metal element X is 0.2 ⁇ In / (In + Zn + X) ⁇ 0.8, 0.1 ⁇ Zn. /(In+Zn+X) ⁇ 0.5 and 0.1 ⁇ X / (In + Zn + X) ⁇ 0.5.
  • the oxide semiconductor thin film according to the present invention is amorphous.
  • the oxide semiconductor thin film according to the present invention has a carrier concentration of 10 16 to 10 18 cm ⁇ 3 .
  • the oxide semiconductor thin film according to the present invention has a mobility of 1 cm 2 / Vs or more.
  • the present invention is a thin film transistor including the oxide semiconductor thin film as an active layer.
  • the present invention is an active matrix drive display panel including the thin film transistor.
  • an oxide sintered body that does not contain gallium (Ga) and can reduce bulk resistance can be provided.
  • This oxide sintered body is useful as a sputtering target.
  • a transparent oxide semiconductor film can be formed by sputtering using this target.
  • the oxide sintered body according to the present invention includes indium (In), zinc (Zn), metal element X (where X represents one or more elements selected from Al and Ti), and oxygen (O ) As a constituent element.
  • indium (In) zinc (Zn)
  • zinc (Zn) zinc (Zn)
  • metal element X where X represents one or more elements selected from Al and Ti
  • oxygen (O ) oxygen
  • elements that are inevitably included in the purification process of raw materials that are usually available, and impurity elements that are inevitably mixed in the oxide sintered body manufacturing process are inevitably contained at a concentration, for example, each element. What contains about 10 ppm is included in the sintered compact which concerns on this invention.
  • the ratio [In] / ([In] + [Zn] + [X]) of the number of indium atoms to the total number of atoms of indium, zinc and metal element X is preferably 0.2 to 0.8. If [In] / ([In] + [Zn] + [X]) is less than 0.2, the relative density during target fabrication becomes small, the bulk resistance becomes high, and abnormal discharge occurs during sputtering. It becomes easy to do. On the other hand, when [In] / ([In] + [Zn] + [X]) exceeds 0.8, the carrier concentration of the film obtained by sputtering the target having the composition becomes too high, and the transistor As a channel layer, the on / off ratio becomes small.
  • [In] / ([In] + [Zn] + [X]) is more preferably in the range of 0.25 to 0.6, and still more preferably in the range of 0.3 to 0.5.
  • [In] represents the number of atoms of indium
  • [Zn] represents the number of atoms of zinc
  • [X] represents the number of atoms of the metal element X.
  • the ratio of the number of zinc atoms to the total number of atoms of indium, zinc and metal element X [Zn] / ([In] + [Zn] + [X]) is preferably 0.1 to 0.5. If [Zn] / ([In] + [Zn] + [X]) is less than 0.1, the carrier concentration of the film becomes too high. On the other hand, when [Zn] / ([In] + [Zn] + [X]) 0.5 is exceeded, the carrier concentration of the film becomes too small. The relative density at the time of target preparation will become small. [Zn] / ([In] + [Zn] + [X]) is more preferably in the range of 0.15 to 0.4, and still more preferably in the range of 0.2 to 0.35.
  • the ratio [X] / ([In] + [Zn] + [X]) of the total number of atoms of the metal element X to the total number of atoms of indium, zinc and the metal element X is 0.1 to 0.5. Is desirable. When [X] / ([In] + [Zn] + [X]) is less than 0.1, the carrier concentration of the film obtained by sputtering the target having the composition becomes too high, and the channel of the transistor As a layer, the on / off ratio becomes small.
  • [X] / ([In] + [Zn] + [X]) exceeds 0.5, the carrier concentration of the film becomes too small, the relative density at the time of target fabrication becomes small, and the bulk Resistance becomes high, and abnormal discharge at the time of sputtering tends to occur.
  • [X] / ([In] + [Zn] + [X]) is more preferably in the range of 0.15 to 0.4, and still more preferably in the range of 0.2 to 0.35.
  • the relative density of the oxide sintered body correlates with the generation of joules on the surface during sputtering. If the oxide sintered body has a low density, the oxide sintered body is processed into a target to form a sputter film. At the same time, a high-resistance portion called a protruding nodule, which is a lower oxide of indium, is generated on the surface as the film formation of the sputter occurs, and it tends to be the starting point of abnormal discharge during subsequent sputtering.
  • the relative density of the oxide sintered body can be set to 98% or more. If the density is at this level, there is almost no adverse effect due to nodules during sputtering.
  • the relative density is preferably 99% or more, more preferably 99.5% or more.
  • the relative density of the oxide sintered body is obtained by dividing the density calculated from the weight and outer dimensions after processing the oxide sintered body into a predetermined shape by the theoretical density of the oxide sintered body. Can be sought.
  • the bulk resistance of the oxide sintered body has a correlation with the ease of occurrence of abnormal discharge during sputtering, and when the bulk resistance is high, abnormal discharge is likely to occur during sputtering.
  • the bulk resistance can be reduced to 3 m ⁇ cm or less by optimizing the appropriate range of the composition and the manufacturing conditions. With such a low bulk resistance, there is almost no adverse effect on the occurrence of abnormal discharge during sputtering.
  • the bulk resistance is preferably 2.7 m ⁇ cm or less, more preferably 2.5 m ⁇ cm or less. Bulk resistance can be measured using a resistivity meter by the four-probe method.
  • the oxide sintered body of various compositions according to the present invention includes, for example, the mixing ratio of each raw material powder such as indium oxide and zinc oxide as raw materials, the particle size of the raw material powder, the pulverization time, the sintering temperature, and the sintering. It can be obtained by adjusting conditions such as time and kind of sintering atmosphere gas.
  • the raw material powder preferably has an average particle size of 1 to 2 ⁇ m.
  • the average particle diameter exceeds 2 ⁇ m, the density of the sintered body is difficult to improve. Therefore, wet pulverization or the like is performed as the raw material powder alone or as a mixed powder, and the average particle diameter is preferably reduced to about 1 ⁇ m.
  • wet pulverization or the like is performed as the raw material powder alone or as a mixed powder, and the average particle diameter is preferably reduced to about 1 ⁇ m.
  • it is also effective to perform calcination.
  • raw materials having a particle size of less than 1 ⁇ m are difficult to obtain, and if the particle size is too small, agglomeration between particles tends to occur and handling becomes difficult.
  • the average particle diameter of the raw material powder refers to the median diameter in the volume distribution measured by a laser diffraction particle size distribution measuring device.
  • the molded product is sintered to obtain a sintered body.
  • Sintering is preferably performed at 1400 to 1600 ° C. for 2 to 20 hours. Thereby, a relative density can be 98% or more. If the sintering temperature is less than 1400 ° C., the density is difficult to improve. Conversely, if the sintering temperature exceeds 1600 ° C., the composition of the sintered body changes due to volatilization of constituent elements, or voids are generated due to volatilization. May cause a decrease in density. Air can be used as the atmosphere gas during sintering, and the amount of oxygen vacancies in the sintered body can be increased to reduce the bulk resistance. However, depending on the composition of the sintered body, a sufficiently high density sintered body can be obtained even if the atmospheric gas is oxygen.
  • the oxide sintered body obtained as described above can be used as a sputtering target by performing processing such as grinding and polishing, and by using this film, the same composition as that of the target can be obtained. It is possible to form an oxide film having At the time of processing, it is desirable that the surface roughness (Ra) be 5 ⁇ m or less by grinding the surface by a method such as surface grinding. By reducing the surface roughness, the starting point of nodule generation that causes abnormal discharge can be reduced.
  • the sputtering target is affixed to a backing plate made of copper or the like, placed in a sputtering apparatus, and sputtered under appropriate conditions such as an appropriate degree of vacuum, atmospheric gas, and sputtering power, so that the film has almost the same composition as the target. Can be obtained.
  • the degree of vacuum reached in the chamber before film formation is 2 ⁇ 10 ⁇ 4 Pa or less. If the pressure is too high, the mobility of the obtained film may decrease due to the influence of impurities in the residual atmospheric gas.
  • a mixed gas of argon and oxygen can be used as the sputtering gas.
  • a gas cylinder with 100% argon and a gas cylinder with 2% oxygen in argon are used, and the supply flow rate from each gas cylinder to the chamber is appropriately set by mass flow.
  • the oxygen concentration in the mixed gas means oxygen partial pressure / (oxygen partial pressure + argon partial pressure), and is equal to the oxygen flow rate divided by the sum of oxygen and argon flow rates.
  • the oxygen concentration may be appropriately changed according to the desired carrier concentration, but it can typically be 1 to 3%, more typically 1 to 2%.
  • the total pressure of the sputtering gas is about 0.3 to 0.8 Pa. If the total pressure is lower than this, the plasma discharge is difficult to stand up, and even if it stands, the plasma becomes unstable. On the other hand, if the total pressure is higher than this, the film formation rate becomes slow, which causes inconveniences such as adversely affecting productivity.
  • the film is formed with a sputtering power of about 200 to 1200 W. If the sputtering power is too low, the film forming speed is low and the productivity is poor. Conversely, if the sputtering power is too high, problems such as cracking of the target occur. 200 ⁇ 1200 W when converted to a sputtering power density is 1.1W / cm 2 ⁇ 6.6W / cm 2, it is desirable that the 3.2 ⁇ 4.5W / cm 2.
  • the sputtering power density is a value obtained by dividing the sputtering power by the area of the sputtering target, and even with the same sputtering power, the power actually received by the sputtering target varies depending on the sputtering target size, and the film formation speed differs. It is an index for uniformly expressing the power applied to the sputtering target.
  • a vacuum deposition method As a method for obtaining a film from an oxide sintered body, a vacuum deposition method, an ion plating method, a PLD (pulse laser deposition) method, or the like can be used.
  • This is a DC magnetron sputtering method that satisfies requirements such as film formation and discharge stability.
  • the substrate there is no need to heat the substrate during sputter deposition. This is because a relatively high mobility can be obtained without heating the substrate, and it is not necessary to spend time and energy for raising the temperature.
  • the resulting film becomes amorphous.
  • the film since the same effect as annealing after film formation at room temperature can be expected by heating the substrate, the film may be formed by heating the substrate.
  • carrier concentration of oxide film correlates with various characteristics of the transistor when the film is used for the channel layer of the transistor. If the carrier concentration is too high, a minute leakage current is generated even when the transistor is turned off, and the on / off ratio is lowered. On the other hand, if the carrier concentration is too low, the current flowing through the transistor becomes small.
  • the carrier concentration of the oxide film can be set to 10 16 to 10 18 cm ⁇ 3 depending on an appropriate range of the composition and the like, and a transistor with favorable characteristics can be manufactured within this range.
  • the mobility is one of the most important characteristics of the transistor, and the oxide semiconductor has a mobility of 1 cm 2 / Vs or more which is the mobility of amorphous silicon which is a competitive material used as a channel layer of the transistor. Is desirable. Basically, the higher the mobility, the better.
  • the oxide film according to the present invention can have a mobility of 1 cm 2 / Vs or more, preferably a mobility of 3 cm 2 / Vs or more, more preferably 5 cm 2 depending on an appropriate range of the composition. It can have a mobility of / Vs or higher. Thereby, it becomes a characteristic superior to amorphous silicon, and industrial applicability is further increased.
  • the oxide semiconductor thin film according to the present invention can be used, for example, as an active layer of a thin film transistor.
  • the thin film transistor obtained by using the above manufacturing method can be used as an active element and used for an active matrix drive display panel.
  • the physical properties of the sintered bodies and films were measured by the following methods.
  • A Relative density of sintered body It was determined from the measurement results of weight and outer dimensions and the theoretical density from the constituent elements.
  • B Bulk resistance of sintered body The bulk resistance was determined by a four probe method (JIS K7194) using a model ⁇ -5 + apparatus manufactured by NPS.
  • C Composition of sintered body and film It was determined by an ICP (high frequency inductively coupled plasma) analysis method using a model SPS3000 manufactured by SII Nanotechnology.
  • D Film thickness It was determined using a step meter (Veeco, Model Dektak8 STYLUS PROFILER).
  • Example 1 Indium oxide powder (average particle size: 1.0 ⁇ m), zinc oxide powder (average particle size: 1.0 ⁇ m), and aluminum oxide powder (average particle size: 1.0 ⁇ m), the atomic ratio of metal elements (In: Zn: Al ) was 0.4: 0.3: 0.3, and wet mixed and pulverized.
  • the average particle size of the mixed powder after pulverization was 0.8 ⁇ m. This mixed powder was granulated with a spray dryer, filled into a mold, pressed, and then sintered at 1450 ° C. for 10 hours in an air atmosphere.
  • the sputtering target prepared above was attached to a copper backing plate using indium as a brazing material, and was installed in a DC magnetron sputtering apparatus (APLVA SPL-500 sputtering apparatus).
  • the glass substrate uses Corning 1737, and the sputtering conditions are as follows: substrate temperature: 25 ° C., ultimate pressure: 1.2 ⁇ 10 ⁇ 4 Pa, atmospheric gas: Ar 99%, oxygen 1%, sputtering pressure (total pressure): 0.
  • a thin film having a thickness of about 100 nm was prepared at 5 Pa and input power of 500 W. No abnormal discharge was observed during the formation of the oxide semiconductor thin film.
  • Example 2 to Example 6 An oxide sintered body and an oxide semiconductor thin film were obtained in the same manner as in Example 1 except that the composition ratio of the raw material powder was set to the respective values shown in Table 1. The relative density, bulk resistance, carrier concentration, and mobility of each were as shown in Table 1. The composition of the sintered body and the film was the same as the composition ratio of the raw material powder.
  • the oxide sintered bodies according to the examples of the present invention have a high relative density and a low bulk resistance.
  • an oxide semiconductor thin film having an appropriate carrier concentration and high mobility can be obtained.

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Abstract

　高価なガリウム（Ｇａ）を含有せず、バルク抵抗が小さい酸化物焼結体を提供することを課題とする。また、当該酸化物焼結体と同一組成をもつ酸化物半導体薄膜を提供することを別の課題とする。インジウム（Ｉｎ）と、亜鉛（Ｚｎ）と、金属元素Ｘ（但し、ＸはＡｌ及びＴｉから選択される１種以上の元素を表す）と、酸素（Ｏ）とからなる酸化物焼結体であって、インジウム（Ｉｎ）、亜鉛（Ｚｎ）、及び金属元素Ｘの原子数比がそれぞれ、０．２≦Ｉｎ／（Ｉｎ＋Ｚｎ＋Ｘ）≦０．８、０．１≦Ｚｎ／（Ｉｎ＋Ｚｎ＋Ｘ）≦０．５、及び０．１≦Ｘ／（Ｉｎ＋Ｚｎ＋Ｘ）≦０．５を満たす酸化物焼結体及びこれと同一組成をもつ酸化物半導体膜。

Description

酸化物焼結体及び酸化物半導体薄膜
　本発明は表示装置中の薄膜トランジスタや透明電極の作製に有用な酸化物焼結体及び透明酸化物半導体薄膜に関する。
　透明酸化物半導体は液晶表示装置、プラズマ表示装置及び有機ＥＬ表示装置などの表示装置中の薄膜トランジスタの活性層のほか、太陽電池及びタッチパネル等の透明電極として利用されている。従来、透明酸化物半導体としてはＩｎ－Ｇａ－Ｚｎ－Ｏ系（以降、「ＩＧＺＯ系」と記載）が知られており（非特許文献１参照）、更に、特性改善を意図して錫（Ｓｎ）を添加した系についての報告もある（特許文献１及び２参照）。しかし、これらの系の必須構成要素であるガリウム（Ｇａ）は希少元素であり、価格も高い等の理由から、産業上、大量に使用するには大きな制約があった。
　Ｇａを使用しない透明酸化物半導体としては、Ｉｎ－Ｚｎ－Ｓｎ－Ｏ系（特許文献３参照）についての報告がある。特許文献３では、インジウム、錫、亜鉛及び酸素を含有し、インジウムの原子の数（＝［Ｉｎ］）と錫の原子の数（＝［Ｓｎ］）と亜鉛の原子の数（＝［Ｚｎ］）の合計に対する前記［Ｓｎ］の原子比が、０．１を超え０．２未満のときは下記原子比１を満たし、０．２以上０．３未満のときは下記原子比２を満たすことが記載されている。
原子比１
０．１＜［Ｉｎ］／（［Ｉｎ］＋［Ｓｎ］＋［Ｚｎ］）＜０．５
０．１＜［Ｓｎ］／（［Ｉｎ］＋［Ｓｎ］＋［Ｚｎ］）＜０．２
０．３＜［Ｚｎ］／（［Ｉｎ］＋［Ｓｎ］＋［Ｚｎ］）＜０．８
原子比２
０．０１＜［Ｉｎ］／（［Ｉｎ］＋［Ｓｎ］＋［Ｚｎ］）＜０．３
０．２≦［Ｓｎ］／（［Ｉｎ］＋［Ｓｎ］＋［Ｚｎ］）＜０．３
０．４＜［Ｚｎ］／（［Ｉｎ］＋［Ｓｎ］＋［Ｚｎ］）＜０．８
特開２００８－２８０２１６号公報 特開２０１０－１１８４０７号公報 特開２００８－２４３９２８号公報
Nature 432、p488-492、October 2004
　しかしながら、特許文献３に記載のＩｎ－Ｚｎ－Ｓｎ－Ｏ系では、バルク抵抗が高いためにスパッタ時に異常放電を発生し易いという問題が残されている。
　そこで、本発明は、希少資源であり、高価なガリウム（Ｇａ）を含有せず、バルク抵抗を小さくすることの出来る酸化物焼結体を提供することを課題とする。また、本発明は当該酸化物焼結体と同一組成をもつ酸化物半導体薄膜を提供することを別の課題とする。
　本発明者は、希少かつ高価な元素であるガリウム（Ｇａ）の代替元素として、ガリウムと同じ３価の金属元素であるアルミニウム（Ａｌ）、４価の金属元素であるチタン（Ｔｉ）が有望であることを見出し、これらの元素の原子比や焼結体や膜の製造条件等について、鋭意検討をして本発明を完成させた。
　本発明は一側面において、インジウム（Ｉｎ）と、亜鉛（Ｚｎ）と、金属元素Ｘ（但し、ＸはＡｌ及びＴｉから選択される１種以上の元素を表す。）と、酸素（Ｏ）とからなる酸化物焼結体であって、インジウム（Ｉｎ）、亜鉛（Ｚｎ）、及び金属元素Ｘの原子数比がそれぞれ、０．２≦Ｉｎ／（Ｉｎ＋Ｚｎ＋Ｘ）≦０．８、０．１≦Ｚｎ／（Ｉｎ＋Ｚｎ＋Ｘ）≦０．５、及び０．１≦Ｘ／（Ｉｎ＋Ｚｎ＋Ｘ）≦０．５を満たす酸化物焼結体である。
　本発明に係る酸化物焼結体は一実施形態において、相対密度が９８％以上である。
　本発明に係る酸化物焼結体は別の一実施形態において、バルク抵抗が３ｍΩｃｍ以下である。
　本発明は別の一側面において、インジウム（Ｉｎ）と、亜鉛（Ｚｎ）と、金属元素Ｘ（但し、ＸはＡｌ及びＴｉから選択される１種以上の元素を表す。）と、酸素（Ｏ）とからなる酸化物半導体薄膜であって、インジウム（Ｉｎ）、亜鉛（Ｚｎ）、金属元素Ｘの原子数比が、０．２≦Ｉｎ／（Ｉｎ＋Ｚｎ＋Ｘ）≦０．８、０．１≦Ｚｎ／（Ｉｎ＋Ｚｎ＋Ｘ）≦０．５、０．１≦Ｘ／（Ｉｎ＋Ｚｎ＋Ｘ）≦０．５を満たす酸化物半導体薄膜である。
　本発明に係る酸化物半導体薄膜は一実施形態において、非晶質である。
　本発明に係る酸化物半導体薄膜は別の一実施形態において、キャリア濃度が１０16～１０18ｃｍ-3である。
　本発明に係る酸化物半導体薄膜は更に別の一実施形態において、移動度が１ｃｍ2／Ｖｓ以上である。
　本発明は更に別の一側面において、上記酸化物半導体薄膜を活性層として備えた薄膜トランジスタである。
　本発明は更に別の一側面において、上記薄膜トランジスタを備えたアクティブマトリックス駆動表示パネルである。
　本発明によればガリウム（Ｇａ）を含有せず、バルク抵抗を小さくすることの出来る酸化物焼結体を提供することができる。本酸化物焼結体はスパッタリングターゲットとして有用である。本ターゲットを用いてスパッタ成膜することにより、透明酸化物半導体膜を作製することができる。
（酸化物焼結体の組成）
　本発明に係る酸化物焼結体は、インジウム（Ｉｎ）、亜鉛（Ｚｎ）、金属元素Ｘ（但し、ＸはＡｌ及びＴｉから選択される１種以上の元素を表す。）、並びに酸素（Ｏ）を構成元素とする。但し、通常入手可能な原料の精製工程上、不可避的に含まれてくる元素や、酸化物焼結体製造プロセス上不可避的に混入する不純物元素を、不可避的に含まれる濃度程度、例えば各元素１０ｐｐｍ程度まで含むものは本発明に係る焼結体に包含される。
　インジウム、亜鉛及び金属元素Ｘの合計原子数に対するインジウムの原子数の比［Ｉｎ］／（［Ｉｎ］＋［Ｚｎ］＋［Ｘ］）は０．２～０．８であることが望ましい。［Ｉｎ］／（［Ｉｎ］＋［Ｚｎ］＋［Ｘ］）が０．２未満であると、ターゲット作製時の相対密度が小さくなり、バルク抵抗が高くなって、スパッタ時の異常放電が発生し易くなってしまう。逆に、［Ｉｎ］／（［Ｉｎ］＋［Ｚｎ］＋［Ｘ］）が０．８を超えると、その組成のターゲットをスパッタして得られる膜のキャリア濃度が高くなりすぎてしまい、トランジスタのチャネル層としてはオンオフ比が小さくなってしまう。［Ｉｎ］／（［Ｉｎ］＋［Ｚｎ］＋［Ｘ］）は、より望ましくは０．２５～０．６の範囲であり、更に望ましくは０．３～０．５の範囲である。ここで、［Ｉｎ］はインジウムの原子数、［Ｚｎ］は亜鉛の原子数、［Ｘ］は金属元素Ｘの原子数をそれぞれ表す。
　インジウム、亜鉛及び金属元素Ｘの合計原子数に対する亜鉛の原子数の比［Ｚｎ］／（［Ｉｎ］＋［Ｚｎ］＋［Ｘ］）は０．１～０．５であることが望ましい。［Ｚｎ］／（［Ｉｎ］＋［Ｚｎ］＋［Ｘ］）が０．１未満であると、膜のキャリア濃度が大きくなりすぎてしまう。逆に、［Ｚｎ］／（［Ｉｎ］＋［Ｚｎ］＋［Ｘ］）０．５を超えると、膜のキャリア濃度が小さくなりすぎてしまう。ターゲット作製時の相対密度が小さくなってしまう。［Ｚｎ］／（［Ｉｎ］＋［Ｚｎ］＋［Ｘ］）は、より望ましくは０．１５～０．４の範囲であり、更に望ましくは０．２～０．３５の範囲である。
　インジウム、亜鉛及び金属元素Ｘの合計原子数に対する金属元素Ｘの合計の原子数の比［Ｘ］／（［Ｉｎ］＋［Ｚｎ］＋［Ｘ］）は０．１～０．５であることが望ましい。［Ｘ］／（［Ｉｎ］＋［Ｚｎ］＋［Ｘ］）が０．１未満であると、その組成のターゲットをスパッタして得られる膜のキャリア濃度が高くなりすぎてしまい、トランジスタのチャネル層としてはオンオフ比が小さくなってしまう。逆に、［Ｘ］／（［Ｉｎ］＋［Ｚｎ］＋［Ｘ］）が０．５を超えると、膜のキャリア濃度が小さくなりすぎてしまい、ターゲット作製時の相対密度が小さくなり、バルク抵抗が高くなって、スパッタ時の異常放電が発生し易くなってしまう。［Ｘ］／（［Ｉｎ］＋［Ｚｎ］＋［Ｘ］）は、より望ましくは０．１５～０．４の範囲であり、更に望ましくは０．２～０．３５の範囲である。
（酸化物焼結体の相対密度）
　酸化物焼結体の相対密度は、スパッタ時の表面のジュール発生と相関があり、酸化物焼結体が低密度であると、その酸化物焼結体をターゲットに加工してスパッタ成膜する際に、スパッタの成膜の経過に従って、表面にインジウムの低級酸化物である、突起状のノジュールと呼ばれる高抵抗部分が発生してきて、その後のスパッタ時に異常放電の起点となり易い。本発明では、酸化物焼結体の相対密度を９８％以上とすることができ、この程度の高密度であれば、スパッタ時のノジュールによる悪影響は殆どない。相対密度は好ましくは９９％以上であり、より好ましくは９９．５％以上である。
　なお、酸化物焼結体の相対密度は、酸化物焼結体を所定の形状に加工した後の重量と外形寸法より算出した密度を、その酸化物焼結体の理論密度で除することで求めることができる。
（酸化物焼結体のバルク抵抗）
　酸化物焼結体のバルク抵抗は、スパッタ時の異常放電の発生のし易さと相関があり、バルク抵抗が高いとスパッタ時に異常放電が発生し易い。本発明では、組成の適正範囲や製造条件の適正化によってバルク抵抗を３ｍΩｃｍ以下とすることができ、この程度の低バルク抵抗であれば、スパッタ時の異常放電発生への悪影響は殆どない。バルク抵抗は好ましくは２．７ｍΩｃｍ以下であり、より好ましくは２．５ｍΩｃｍ以下である。
　なお、バルク抵抗は四探針法により抵抗率計を使用して測定することができる。
（酸化物焼結体の製造方法）
　本発明に係る各種組成の酸化物焼結体は、例えば、原料である酸化インジウム、酸化亜鉛等の各原料粉体の配合比や原料粉体の粒径、粉砕時間、焼結温度、焼結時間、焼結雰囲気ガス種類等の条件を調整することにより得ることができる。
　原料粉は平均粒径１～２μｍであることが望ましい。平均粒径が２μｍを超えると、焼結体の密度が向上し難くなるため、その原料粉単独又は混合粉として湿式微粉砕等を行って、平均粒径を約１μｍ程度に小さくすると良い。湿式混合粉砕前に焼結性の向上を目的として、仮焼することも有効である。一方、１μｍ未満の原料は入手し難く、また、あまり小さいと粒子間の凝集が起き易くなって扱い難くなるので、焼結前の混合粉の平均粒径は１～２μｍが好ましい。ここで、原料粉の平均粒径はレーザ回折式粒度分布測定装置によって測定した体積分布におけるメディアン径を指す。なお、本発明の均等と解釈できる範囲で、所定の原料粉の外に焼結体特性に悪影響を及ぼさず、焼結性を向上させる等の効果を有する他の成分を添加しても良い。粉砕後の原料混合粉をスプレードライヤー等で造粒して流動性や成形性を高めた後に成型するのが好ましい。成型は通常の加圧成形や冷間静水圧加圧等の方法を採用することができる。
　その後、成形物を焼結して焼結体を得る。焼結は、１４００～１６００℃で２～２０時間焼結することが好ましい。これにより、相対密度を９８％以上とすることができる。焼結温度が１４００℃未満では、密度が向上し難く、逆に、焼結温度が１６００℃を超えると、構成成分元素の揮発等により、焼結体の組成が変化したり、揮発による空隙発生による密度低下の原因となったりする。焼結時の雰囲気ガスには、大気を用いることができ、焼結体への酸素欠損量を増加させて、バルク抵抗を小さくすることができる。但し、焼結体の組成によっては、雰囲気ガスを酸素としても充分高密度の焼結体を得ることもできる。
（スパッタ成膜）
　上記の様にして得られた酸化物焼結体は、研削や研磨等の加工を施すことによりスパッタリング用ターゲットとすることができ、これを使用して成膜することにより、当該ターゲットと同一組成をもつ酸化物膜を形成することができる。加工の際は、平面研削等の方法で表面を研削することによって、表面粗さ（Ｒａ）を５μｍ以下とすることが望ましい。表面粗さを小さくすることによって、異常放電の原因となるノジュール発生の起点を減少させることができる。
　スパッタリング用ターゲットは、銅製等のバッキングプレートに貼り付けて、スパッタ装置内に設置して、適切な真空度、雰囲気ガス、スパッタパワー等の適切条件でスパッタすることで、ターゲットとほぼ同組成の膜を得ることができる。
　スパッタ法の場合、成膜前のチャンバー内到達真空度を、２×１０-4Ｐａ以下とするのが望ましい。圧力が高すぎると、残留雰囲気ガス中の不純物の影響によって、得られた膜の移動度が低下する可能性がある。
　スパッタガスとして、アルゴン及び酸素の混合ガスを使用することができる。混合ガス中の酸素濃度を調整する方法としては、例えば、アルゴン１００％のガスボンベと、アルゴン中の酸素が２％のガスボンベを用いて、それぞれのガスボンベからチャンバーへの供給流量をマスフローで適宜設定することで行うことができる。ここで、混合ガス中の酸素濃度とは、酸素分圧／（酸素分圧＋アルゴン分圧）を意味するものであり、酸素の流量を酸素とアルゴンの流量の合計で除したものとも等しい。酸素濃度は所望のキャリア濃度に応じて適宜変更すればよいが、典型的には１～３％とすることができ、より典型的には１～２％とすることができる。
　スパッタガスの全圧は０．３～０．８Ｐａ程度とする。全圧がこれより低いと、プラズマ放電が立ち難くなり、立ったとしてもプラズマが不安定となってしまう。また、全圧がこれより高いと、成膜速度が遅くなり、生産性に悪影響を及ぼす等の不都合が生じる。
　スパッタパワーは、ターゲットサイズが６インチの場合、２００～１２００Ｗ程度で成膜する。スパッタパワーが小さすぎると、成膜速度が小さく、生産性に劣るし、逆に、大き過ぎると、ターゲットの割れ等の問題が生ずる。２００～１２００Ｗは、スパッタパワー密度に換算すると、１．１Ｗ／ｃｍ2～６．６Ｗ／ｃｍ2であり、３．２～４．５Ｗ／ｃｍ2とすることが望ましい。ここで、スパッタパワー密度とは、スパッタパワーをスパッタリングターゲットの面積で除したものであり、同じスパッタパワーでもスパッタリングターゲットサイズによって、スパッタリングターゲットが実際に受けるパワーが異なり、成膜速度が異なることから、スパッタリングターゲットに印加するパワーを統一的に表現するための指標である。
　酸化物焼結体から膜を得る方法としては、真空蒸着法、イオンプレーティング法、ＰＬＤ（パルスレーザーディポジション）法等も用いることもできるが、産業上利用し易いのは、大面積、高速成膜、放電安定性等の要件を満たすＤＣマグネトロンスパッタ法である。
　スパッタ成膜時には、基板を加熱する必要がない。基板を加熱せずとも、比較的高移動度を得ることができるためであり、また、昇温のための時間やエネルギーを掛ける必要がない。基板を加熱することなくスパッタ成膜すると、得られる膜は非晶質となる。但し、基板を加熱することで、室温成膜後のアニールと同様の効果を得ることも期待できるので、基板加熱で成膜しても良い。
（酸化物膜のキャリア濃度）
　酸化物膜のキャリア濃度は、その膜をトランジスタのチャネル層に使用した際に、トランジスタの各種特性と相関がある。キャリア濃度が高すぎると、トランジスタのオフ時にも、微少漏れ電流が発生してしまい、オンオフ比が低下してしまう。一方、キャリア濃度が低すぎると、トランジスタを流れる電流が小さくなってしまう。本発明では、組成の適正範囲等によって、酸化物膜のキャリア濃度を１０16～１０18ｃｍ-3とすることができ、この範囲であれば、特性が良好なトランジスタを作製することができる。
（酸化物膜の移動度）
　移動度はトランジスタの特性の中でも、最も重要な特性の一つであり、酸化物半導体がトランジスタのチャネル層として使用される競合材料であるアモルファスシリコンの移動度である１ｃｍ2／Ｖｓ以上であることが望ましい。移動度は基本的には、高ければ高いほど良い。本発明に係る酸化物膜は組成の適正範囲等によって、１ｃｍ2／Ｖｓ以上の移動度を有することができ、好ましくは３ｃｍ2／Ｖｓ以上の移動度を有することができ、より好ましくは５ｃｍ2／Ｖｓ以上の移動度を有することができる。これによって、アモルファスシリコンより優れた特性となって、産業上の応用可能性がより高まる。
　本発明に係る酸化物半導体薄膜は例えば薄膜トランジスタの活性層として使用することができる。また、上記製造方法を使用して得られた薄膜トランジスタをアクティブ素子として使用し、アクティブマトリックス駆動表示パネルに利用することができる。
　以下に本発明の実施例を比較例と共に示すが、これらの実施例は本発明及びその利点をよりよく理解するために提供するものであり、発明が限定されることを意図するものではない。従って、本発明は、本発明の技術思想の範囲内で、実施例以外の態様あるいは変形を全て包含するものである。
　下記の実施例及び比較例において、焼結体及び膜の物性は以下の方法によって測定した。
（ア）焼結体の相対密度
　重量及び外形寸法の測定結果と、構成元素からの理論密度とにより求めた。
（イ）焼結体のバルク抵抗
　四探針法（ＪＩＳ　Ｋ７１９４）により、ＮＰＳ（エヌピイエス）社製型式Σ－５＋装置を用いて求めた。
（ウ）焼結体及び膜の組成
　ＳＩＩナノテクノロジー社製型式ＳＰＳ３０００を用いてＩＣＰ（高周波誘導結合プラズマ）分析法によって求めた。
（エ）膜厚
　段差計（Ｖｅｅｃｏ社製、型式Ｄｅｋｔａｋ８　ＳＴＹＬＵＳ　ＰＲＯＦＩＬＥＲ）を用いて求めた。
（オ）膜のキャリア濃度及び移動度
　成膜したガラス基板を約１０ｍｍ角に切り出し、四隅にインジウム電極をつけて、ホール測定装置（東陽テクニカ社製、型式Ｒｅｓｉｔｅｓｔ８２００）にセットして測定した。
（カ）膜の結晶又は非晶質構造
　リガク社製ＲＩＮＴ－１１００Ｘ線回折装置を用いて結晶性を判定した。バックグランドレベル以上の有意なピークが認められない場合、非晶質と判断した。
（キ）粉体の平均粒径
　島津製作所製ＳＡＬＤ－３１００で平均粒径を測定した。
＜実施例１＞
　酸化インジウム粉（平均粒径１．０μｍ）、酸化亜鉛粉（平均粒径１．０μｍ）、及び酸化アルミニウム粉（平均粒径１．０μｍ）、を金属元素の原子数比（Ｉｎ：Ｚｎ：Ａｌ）が０．４：０．３：０．３となる様に秤量し、湿式混合粉砕した。粉砕後の混合粉の平均粒径０．８μｍであった。この混合粉を、スプレードライヤーで造粒後、金型に充填し、加圧成形した後、大気雰囲気中１４５０℃の高温で１０時間焼結した。得られた焼結体を直径６インチ、厚さ６ｍｍの円盤状に加工し、平面研削してスパッタリングターゲットとした。当該ターゲットについて、重量と外形寸法との測定結果と理論密度から相対密度を算出したところ９９．８％であった。また、四探針法により測定した焼結体のバルク抵抗は２．１ｍΩｃｍだった。ＩＣＰ（高周波誘導結合プラズマ）分析法による焼結体組成分析の結果、Ｉｎ：Ｚｎ：Ａｌ＝０．４：０．３：０．３（原子比）であった。
　上記で作製したスパッタリングターゲットを銅製のバッキングプレートにインジウムをロウ材として使用して貼り付けて、ＤＣマグネトロンスパッタ装置（ＡＮＥＬＶＡ製ＳＰＬ－５００スパッタ装置）に設置した。ガラス基板はコーニング１７３７を用いて、スパッタ条件を、基板温度：２５℃、到達圧力：１．２×１０-4Ｐａ、雰囲気ガス：Ａｒ９９％、酸素１％、スパッタ圧力（全圧）：０．５Ｐａ、投入電力５００Ｗとして、膜厚が約１００ｎｍの薄膜を作製した。酸化物半導体薄膜の成膜時には、異常放電は認められなかった。
　得られた膜のホール測定を行ったところ、キャリア濃度５．０×１０17ｃｍ-3、移動度５．１ｃｍ2／Ｖｓを得た。ＩＣＰ（高周波誘導結合プラズマ）分析法による膜組成分析の結果、Ｉｎ：Ｚｎ：Ａｌ＝０．４：０．３：０．３（原子比）であった。Ｘ線回折による測定の結果、当該膜は非晶質であった。
＜実施例２～実施例６＞
　原料粉の組成比を表１に記載のそれぞれの値となる様にした以外は、実施例１と同様にして、酸化物焼結体及び酸化物半導体薄膜を得た。それぞれの相対密度、バルク抵抗、キャリア濃度、移動度は、表１に記載の通りであった。また、焼結体及び膜の組成はそれぞれ原料粉の組成比と同一であった。
＜比較例１～比較例１３＞
　原料粉の組成比を表１に記載のそれぞれの値となる様にした以外は、実施例１と同様にして、酸化物焼結体及び酸化物半導体薄膜を得た。それぞれの相対密度、バルク抵抗、キャリア濃度、移動度は、表１に記載の通りであった。また、焼結体及び膜の組成はそれぞれ原料粉の組成比と同一であった。
　表１に記載の結果から分かるように、本発明の実施例に係る酸化物焼結体は相対密度が高く、バルク抵抗が小さい。また、本発明に係る酸化物焼結体をスパッタリングターゲットとして成膜した場合、適切なキャリア濃度及び高い移動度をもつ酸化物半導体薄膜が得られる。
Figure JPOXMLDOC01-appb-T000001

Claims (9)

  1. 　インジウム（Ｉｎ）と、亜鉛（Ｚｎ）と、金属元素Ｘ（但し、ＸはＡｌ及びＴｉから選択される１種以上の元素を表す）と、酸素（Ｏ）とからなる酸化物焼結体であって、インジウム（Ｉｎ）、亜鉛（Ｚｎ）、及び金属元素Ｘの原子数比がそれぞれ、０．２≦Ｉｎ／（Ｉｎ＋Ｚｎ＋Ｘ）≦０．８、０．１≦Ｚｎ／（Ｉｎ＋Ｚｎ＋Ｘ）≦０．５、及び０．１≦Ｘ／（Ｉｎ＋Ｚｎ＋Ｘ）≦０．５を満たす酸化物焼結体。
  2. 　相対密度が９８％以上である請求項１に記載の酸化物焼結体。
  3. 　バルク抵抗が３ｍΩｃｍ以下である請求項１又は２に記載の酸化物焼結体。
  4. 　インジウム（Ｉｎ）と、亜鉛（Ｚｎ）と、金属元素Ｘ（但し、ＸはＡｌ及びＴｉから選択される１種以上の元素を表す）と、酸素（Ｏ）とからなる酸化物半導体薄膜であって、インジウム（Ｉｎ）、亜鉛（Ｚｎ）、金属元素Ｘの原子数比が、０．２≦Ｉｎ／（Ｉｎ＋Ｚｎ＋Ｘ）≦０．８、０．１≦Ｚｎ／（Ｉｎ＋Ｚｎ＋Ｘ）≦０．５、０．１≦Ｘ／（Ｉｎ＋Ｚｎ＋Ｘ）≦０．５を満たす酸化物半導体薄膜。
  5. 　非晶質である請求項４に記載の酸化物半導体薄膜。
  6. 　キャリア濃度が１０16～１０18ｃｍ-3である請求項４又は５に記載の酸化物半導体薄膜。
  7. 　移動度が１ｃｍ2／Ｖｓ以上である請求項４～６の何れか一項に記載の酸化物半導体薄膜。
  8. 　請求項４～７の何れか一項に記載の酸化物半導体薄膜を活性層として備えた薄膜トランジスタ。
  9. 　請求項８記載の薄膜トランジスタを備えたアクティブマトリックス駆動表示パネル。
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