JP2014125365A - Igzo raw material powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide raw material powder for an IGZO sputtering target with which cracking is scarcely generated in a sintering step and a high production yield is achieved, and to provide a sintered compact, and the sputtering target.SOLUTION: By increasing a ratio of zinc oxide particles with a particle size of 2 μm or less to 95% or more, cracking control in the sintering step is improved, and incidence of sintering crack is drastically reduced even in sintering of a large target.

Description

  The present invention relates to a raw material powder, a sintered body, and a sputtering target for a sputtering target used for forming an In—Ga—Zn—O (IGZO) semiconductor thin film made of indium, gallium, zinc and oxygen used for a thin film transistor (TFT). It is about.

  Oxide semiconductor films made of several metal composite oxides have high mobility and visible light transmission, and are used for switching elements and drive circuit elements such as liquid crystal display devices and thin-film electroluminescence display devices. Has been. In particular, an oxide containing indium oxide-gallium oxide-zinc oxide or an oxide semiconductor film containing these as a main component has an advantage that the mobility is higher than that of an amorphous silicon film, and for organic EL where high mobility is required. Application is progressing as a TFT element application.

  In order to form such an oxide semiconductor film, a sintered body obtained by mixing, forming, and firing each raw material oxide, for example, each raw material powder of indium oxide-gallium oxide-zinc oxide is usually desired. It is formed by a sputtering method using an IGZO sputtering target obtained by processing into a shape (Patent Document 1).

  The IGZO sintered body used here exhibits a homologous crystal structure having a layered structure, and the strength of the sintered body is low due to anisotropy due to the layered structure, and cracking is likely to occur during sintering. For this reason, it is extremely difficult to produce a large IGZO sintered body or a cylindrical IGZO sintered body whose shape is more complicated than a flat plate shape, and the yield in the firing process has been reduced. A decrease in yield leads to an increase in target manufacturing cost, which has been a major problem for future practical use and mass production.

In general, the reaction that occurs in the firing of the IGZO sintered body is that indium oxide, gallium oxide, and zinc oxide, which are raw material oxides, increase in sintering temperature, ZnGa ₂ O ₄ , InGaZn ₂ O ₅ , In ₂ Ga ₂ ZnO. ₇ and InGaZnO ₄ change to a plurality of crystal phases, so the reaction is complicated and its control is extremely difficult. In order to reduce cracks due to the formation or change of the crystal phase, Patent Document 2 discloses a method of calcining raw material powder at a temperature of 1000 ° C. in advance. According to this method, since the raw material powder is changed into a final crystal phase by calcination and then pulverized and then sintered again to produce an IGZO sintered body, the crystal phase changes during sintering. Since the stress is reduced, the sintered body is hardly cracked in the sintering process. However, since crystal grains grow by calcination, it is difficult to obtain a high-density, high-strength sintered body. Further, when trying to obtain a high-density sintered body, it is necessary to pulverize after calcining until the average particle size becomes 1 μm or less, which not only complicates the process and causes an increase in manufacturing cost but also contains impurities during pulverization. Therefore, there is a problem that a high-quality sintered body cannot be obtained.

  As a method for reducing the calcining process, in Patent Document 3, indium oxide, gallium oxide, and zinc oxide are mixed and pulverized to a median diameter of 0.6 to 1 μm, so that high-density IGZO firing is performed without performing the calcining process. The method by which a ligation is obtained is shown. However, there is no mention of cracks in the sintered body, and there is no report that a large target can be produced with good yield.

JP 2007-73312 A JP 2000-44236 A JP 2008-214697 A

  An object of the present invention is to provide a raw material powder for an IGZO sputtering target that has less cracking in the firing step and realizes a high production yield.

In order to solve the above-mentioned problems, the present inventors have conducted detailed analysis on the sintering behavior of the indium oxide-gallium oxide-zinc oxide composite oxide and the newly formed crystal phase in the middle of the temperature rise, and The cause of the occurrence was considered. As a result, it has been found that a part of the crystal phase newly formed by indium oxide-gallium oxide-zinc oxide is accompanied by severe volume expansion in the temperature rising process. As a result of intensive studies, it was found that this volume expansion depends on the abundance ratio of the coarse particles of zinc oxide, and by using the IGZO raw material powder in which the particle size of the zinc oxide powder is controlled, cracking of the sintered body can be prevented. It has been found that it can be greatly reduced. Furthermore, in a sintered body having only a homologous crystal structure represented by InGaZnO ₄ , the number of ZnGa ₂ O ₄ crystal phases is extremely reduced, and at the same time, pores (pores) of 10 μm or more are reduced, and cracks are generated in the firing process. Has been found to be significantly reduced, and the present invention has been completed.

Aspects of the present invention are as follows.
(1) An IGZO raw material powder comprising indium oxide, gallium oxide and zinc oxide powder, wherein 95% or more of the zinc oxide powder is zinc oxide particles having a particle size of 2 μm or less.
(2) The IGZO raw material powder according to (1), wherein indium oxide, gallium oxide and zinc oxide are blended so that the atomic ratio is In: Ga: Zn = 1: 1: 1.

In the present invention, the IGZO sintered body refers to a sintered body containing indium, gallium, zinc and oxygen and having a homologous crystal structure represented by InGaZnO ₄ . A "sintered body having only homologous crystal structure represented by InGaZnO _4" is referred to in the present invention, X-ray diffraction pattern is consistent with the diffraction pattern of InGaZnO _4, it does not include a peak that is not attributable to the diffraction pattern of InGaZnO ₄ Means that.

  Hereinafter, the present invention will be described in detail.

  The present invention is an IGZO raw material powder comprising indium oxide, gallium oxide and zinc oxide powder, wherein 95% or more of the zinc oxide powder is zinc oxide particles having a particle size of 2 μm or less. is there. The zinc oxide particles having a particle size of 2 μm or less in the zinc oxide powder are preferably 98% or more, and more preferably 99% or more.

The present inventors analyzed the phase state in the middle of the firing temperature of the compact | molding | casting after powder shaping | molding using the mixed powder of an indium oxide, a gallium oxide, and a zinc oxide powder. As a result, indium oxide, gallium oxide and zinc oxide change into a crystalline phase such as ZnGa ₂ O ₄ , InGaZn ₂ O ₅ , In ₂ Ga ₂ ZnO ₇ and InGaZnO ₄ with a sintering temperature, and some of them It was found that ZnGa ₂ O ₄ formed at a low temperature reacts with indium oxide at a high temperature of 1000 ° C. or more with volume expansion, and that intense volume expansion occurs when InGaZnO ₄ is formed.

When the number of zinc oxide particles larger than 2 μm is more than 5%, a coarse crystal of ZnGa ₂ O ₄ is formed, and when the phase changes to InGaZnO ₄ at 1000 ° C. or higher, the expansion of the region centering on the particles is And the local stress is generated in the sintered body, so that cracking is likely to occur. In addition, when coarse zinc oxide particles are present, a local composition distribution occurs, and pores of 10 μm or more are likely to be generated in the sintered body, which causes cracks in the sintered body and decreases the strength of the sintered body. Cause.

The present invention is particularly effective in cracking when an IGZO sintered body having only a homologous crystal structure represented by InGaZnO ₄ is produced. When manufacturing an IGZO sintered body having only a homologous crystal structure represented by InGaZnO ₄ , the atomic ratio of indium oxide, gallium oxide, and zinc oxide is In: Ga: Zn = 1: 1: 1. What is necessary is just to mix | blend with.

Even if the IGZO sintered body is a sintered body having only a homologous crystal structure represented by InGaZnO ₄ in X-ray diffraction, when observed by EPMA, ZnGa ₂ O _{4 of 2} μm or more may locally exist. However, when an IGZO raw material powder characterized in that 95% or more of the zinc oxide powder is zinc oxide particles having a particle size of 2 μm or less, the ZnGa ₂ O ₄ crystal phase of ₂ μm or more is in 236 μm × 178 μm. An average of 0.3 or less IGZO sintered bodies can be obtained. In such a sintered body, pores of 10 μm or more have an average of 0.3 or less in 172 μm × 125 μm, and cracking hardly occurs. The ZnGa ₂ O ₄ phase can be confirmed as a phase free of In by measuring element mapping using energy dispersive X-ray analysis (EDS). It can also be confirmed by electron beam microanalyzer analysis (EPMA). The pores can be observed with an electron microscope (SEM). First, after searching for a relatively large ZnGa ₂ O ₄ phase or pore in a low magnification field of view, the size is confirmed at a high magnification. The number of ZnGa ₂ O ₄ phases and pores is measured multiple times at different locations, and the average value is obtained. The more measurement points, the better. However, it is preferable to measure at least 5 points and calculate the average value.

  Next, the manufacturing method of the sintered compact of this invention is demonstrated for every process.

(1) Raw material mixing step As the raw material powder, indium oxide, gallium oxide, and zinc oxide powder can be used. The purity of each raw material powder is preferably 99.8% or more, more preferably 99.99% or more. This is because if the purity is low, the contained impurities may adversely affect the thin film TFT formed by the sputtering target using the IGZO sintered body of the present invention.

The powder of indium oxide and gallium oxide is not particularly limited, but a generally available powder having a BET value of 6 to 15 m ² / g may be used. These powders may be pulverized or calcined.

  As the zinc oxide powder, a powder in which 95% or more of the zinc oxide powder is zinc oxide particles having a particle diameter of 2 μm or less is used. However, since zinc oxide is a material that is difficult to grind and powder having a small particle size is expensive, JIS one or two kinds of zinc oxide that are generally available and relatively high in purity may be ground and used. Zinc oxide may be mixed with indium oxide and gallium oxide after weighing a predetermined weight and then mixed simultaneously with pulverization by a pulverizing and mixing device. It is more preferable to mix and disperse with indium and gallium oxide. When mixing and pulverizing each raw material powder at the same time, the ratio of particles of 2 μm or less to the mixed powder containing zinc oxide may be controlled to be 95% or more. By doing so, the particle diameter of zinc oxide can be managed also in the mixed powder. The particle size can be measured by a laser diffraction / scattering method.

  The powder pulverization and mixing device is not particularly limited, but dry type using a ball or bead such as alumina or nylon resin, wet type media stirring type mill, medialess container rotating type mixing, mechanical stirring type mixing, etc. The mixing method is exemplified. Specific examples include a ball mill, a bead mill, an attritor, a vibration mill, a planetary mill, a jet mill, a V-type mixer, a paddle mixer, and a twin-shaft planetary agitation mixer.

The composition of these raw materials may be any composition that produces a homologous crystal structure represented by InGaZnO ₄ , but the composition of In: Ga: Zn = 1: 1: 1 in terms of the atomic ratio of the metal element has particularly high strength. Since it is low, the effect of the present invention is great.

  When a wet ball mill, bead mill, attritor, vibration mill, planetary mill, jet mill or the like is used, it is necessary to dry the pulverized slurry. This drying method is not particularly limited, and examples thereof include filtration drying, fluidized bed drying, and spray drying.

  In the molding process, molding aids such as polyvinyl alcohol, acrylic polymer, methylcellulose, waxes, and oleic acid may be added to the raw material powder.

(2) Molding process The molding method is not particularly limited, and a molding method capable of molding the mixed powder of the raw material powders into a desired shape can be appropriately selected. Examples thereof include a press molding method, a casting molding method, and an injection molding method.

The molding pressure is not particularly limited as long as it does not cause cracks in the molded body and can be handled, but it is preferable to increase the molding density as much as possible. Therefore, it is also possible to use a method such as cold isostatic pressing (CIP) molding. CIP pressure is preferably for 1 ton / cm ² or more to obtain a sufficient consolidation effect, more preferably 2 ton / cm ² or more, especially preferably 2~3ton / cm ^2.

  Here, when the first molding is performed by a casting method and then CIP is performed, the binder may be removed for the purpose of removing moisture and organic substances such as binder remaining in the molded body after CIP. Good. Further, even when the first molding is performed by the press method, the same debinding treatment can be performed when a binder or the like is added in the raw material mixing step.

(3) Firing step The firing method is not particularly limited, and a firing method suitable for the sintering behavior of the raw material powder can be appropriately selected. Examples thereof include an electric furnace, a gas furnace, HIP (isotropic hot press), HP (hot press), and a microwave furnace.

  The firing temperature of the material to be fired is not particularly limited, but is preferably 1300 ° C. or higher and 1500 ° C. or lower in order to obtain a sintered body having high density and high strength. When the temperature is higher than 1500 ° C., the particles of the sintered body grow and the strength of the sintered body decreases. On the other hand, when the temperature is lower than 1300 ° C., the density of the sintered body decreases.

  The holding time of the object to be fired is not particularly limited, but is preferably 30 minutes or longer and 5 hours or shorter when firing with an electric furnace. More preferably, it is 1 hour or more and 2 hours or less. If it is shorter than 30 minutes, the sintering does not proceed sufficiently and a high-density sintered body cannot be obtained. If it is longer than 5 hours, crystal grains grow and a high-strength sintered body cannot be obtained.

  The temperature increase rate of the object to be fired is not particularly limited, but is preferably 50 ° C./hour or more in order to shorten the firing time as much as possible to suppress the growth of crystal grains in the sintered body and obtain a high-strength sintered body. More preferably, it is 100 ° C./hour or more. However, in the case of a molded body containing moisture and a binder, particularly in a large molded body, when the moisture and the binder component are volatilized, the molded body may be cracked when accompanied by rapid volume expansion. For this reason, it is preferable to make a temperature increase rate into 20-100 degreeC / hour in the temperature range in which the water | moisture content and the binder component are volatilizing, for example, the temperature range of 100-400 degreeC. Preferably, it is preferably 20 to 100 ° C./hour in the temperature range of 100 to 600 ° C.

  The temperature lowering rate is 150 ° C./hour or more, preferably 200 ° C./hour or more, from the firing temperature to 1100 ° C. By lowering the temperature range at 150 ° C./hour or more, oxygen taken into the surface of the sintered body can be reduced, and color unevenness on the surface of the sintered body can be suppressed. In a temperature range other than this, the temperature drop rate is not particularly limited, and can be appropriately determined in consideration of the capacity of the sintering furnace, the size and shape of the sintered body, ease of cracking, and the like.

  The atmosphere at the time of firing is not particularly limited, but is preferably an air or oxygen atmosphere in order to suppress zinc sublimation. Further, for the purpose of suppressing uneven color on the surface of the sintered body and lowering the specific resistance of the sintered body, it is possible to create a non-oxidizing atmosphere such as nitrogen when the temperature is lowered from the firing temperature.

(4) Targeting process The obtained sintered body is formed into a desired shape such as a plate shape, a circular shape, or a cylindrical shape by using a machining machine such as a surface grinder, a cylindrical grinder, a lathe, a cutting machine, or a machining center. To grind. Furthermore, the sputtering target which used the sintered compact of this invention as the target material can be obtained by joining to the backing plate and backing tube which consist of oxygen-free copper, titanium, etc. as needed using indium solder.

  The size of the sintered body is not particularly limited, but since the sintered body according to the present invention has few cracks in the sintering process, a large target can be produced.

  The thickness of the target is not particularly limited, but is preferably 4 mm or more and 15 mm or less. If it is thinner than 4 mm, the target utilization is low and not economical. On the other hand, if it is thicker than 15 mm, uneven sintering is likely to occur, and it is difficult to obtain a target having uniform quality up to the central portion.

  The surface roughness of the target is not particularly limited, but it takes a long time to reduce the surface roughness and is not economical. Therefore, the surface roughness (Ra) is preferably 1 μm or more.

  As described above, by optimizing the firing conditions, cracks in the sintered body are improved, and the firing crack generation rate can be dramatically reduced even when firing a large target.

  By using the IGZO raw material powder of the present invention, cracks can be reduced in the sintering process of the IGZO sintered body, and a large cost improvement effect due to yield improvement can be expected.

It is an element mapping figure by EDS of the sintered compact of the comparative example 1 (e). It is a SEM photograph of the sintered compact of comparative example 1 (e).

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto. In addition, each measurement in a present Example was performed as follows.

(1) Particle size of powder It measured using the Shimadzu laser diffraction and the laser scattering method particle size distribution measuring apparatus (SALD-7100).

  The raw material powder was measured after being placed in a sodium hexametaphosphate (0.2%) solution and pulverized for 1 minute by a 500 W bombinizer.

(2) X-ray diffraction measurement An X-ray diffraction pattern in a range of 2θ = 20 to 70 ° was measured, and a diffraction pattern of InGaZnO ₄ (database No. 01 of X-ray diffraction analysis software JADE 7.0 of Rigaku Corporation) -070-3626).
(Measurement conditions for X-ray diffraction test)
Scanning method: Step scan method (FT method)
X-ray source: CuKα
Power: 40kV, 40mA
Step width: 0.02 °
(3) Observation of sintered particles Microscopic observation using JEOL field emission scanning electron microscope (FE-SEM) JSM-7600F and Thermo Fisher Scientific energy dispersive X-ray analyzer (EDS) NSS312E + UltraDry30mm ² Elemental mapping measurement was performed.

  The pores were observed using an electron microscope (SEM) VE-9800 manufactured by KEYENCE.

  The sample used was that whose surface was mirror-polished and then subjected to electrolytic etching.

Example 1
Zirconium oxide powder having a median diameter of 0.55 μm and a ratio of particles of 2 μm or less of 91% was slurried in pure water, and the slurry concentration was 50 wt%, using 0.3 mmφ zirconia beads. Grinding was performed in a wet bead mill. At this time, a dispersant was appropriately added so that the slurry viscosity was 1000 ps or less. Four types of raw material powders (a) to (d) were produced by adjusting the pulverization time and having different abundance ratios of particles of 2 μm or less. Next, an indium oxide powder having a median diameter of 1.00 μm and a particle ratio of 2 μm or less being 86%, and a gallium oxide powder having a median diameter of 2.11 μm and a particle ratio of 2 μm or less being 50.2% Were weighed so that In: Ga: Zn = 1: 1: 1 in terms of the atomic ratio of the metal elements, and charged into each slurry. In order to disperse these mixed powders, a dispersion treatment was performed in a short-time wet bead mill with a slurry concentration of 50 wt% with pure water and a suitable dispersant added so that the slurry viscosity was 1000 ps or less.

Next, these pulverized / dispersed slurries are granulated and dried with a spray dryer, and after using these powders to form a molded body with a die press at a pressure of 300 kg / cm ² , ² ton / cm CIP treatment was performed at a pressure of ² to produce a flat molded body. Also, this mixed powder is filled while tapping into a cylindrical mold composed of a urethane rubber frame and lid, and a metal core (mandrel), and after the mold is sealed, 2 ton / cm. CIP treatment was performed at a pressure of ² to obtain a cylindrical molded body.

  Next, this compact was fired in an electric furnace. The rate of temperature increase was from 600 ° C. to 1400 ° C. at 100 ° C./hour. The firing temperature was 1400 ° C. and the holding time was 1 hour. The temperature decreasing rate was 200 ° C./hour from 1400 ° C. to 1100 ° C. After firing, a 300 mm × 300 mm × 8 mmt flat plate sintered body and a cylindrical sintered body having an inner diameter of 75 mm, an outer diameter of 96 mm, and a length of 280 mm were obtained.

Moreover, the sintered body for a composition analysis and a physical-property measurement was produced by the same method, respectively. Table 1 shows the relative density of the obtained sintered body and the measurement results of the identified species by X-ray diffraction (XRD). In addition, the sintered body was searched for a relatively large ZnGa ₂ O ₄ phase in a low magnification field of view by EDS observation, then the size was measured at a high magnification, and the number of ZnGa ₂ O ₄ phases of ₂ μm or more in 236 μm × 178 μm I counted. Further, the number of pores having a size of 10 μm or more in 172 μm × 125 μm was counted by dark field observation with SEM in the same manner. Table 5 shows the average value of the number of pores and the number of ZnGa ₂ O ₄ phases of ₂ μm or more calculated at 5 locations by changing the location.

Example 2
Using the powder (d) produced in Example 1, a plate-shaped molded body was produced. Next, this compact was fired in a microwave firing furnace. The heating rate was 600 ° C. to 1400 ° C. at 300 ° C./hour. The firing temperature was 1400 ° C. and the holding time was 1 hour. The temperature decreasing rate was 200 ° C./hour from 1400 ° C. to 1100 ° C. After firing, a plate-like sintered body of 300 mm × 300 mm × 8 mmt was obtained.

Table 1 shows the physical properties of the sintered body, the number of ZnGa ₂ O ₄ phases of ₂ μm or more, and the number of pores measured in the same manner as in Example 1.

Comparative Example 1
Three types of raw material powders (e) to (g) are prepared by using the same zinc oxide powder as in Example 1, pulverizing in the same wet bead mill, adjusting the pulverization time, and having different abundance ratios of particles of 2 μm or less. Produced. Next, using the same indium oxide and gallium oxide as in Example 1, a raw material powder was produced by the same method, and molding and firing were performed. Cracks were observed in all the sintered bodies.

Table 1 shows the physical properties of the sintered body, the number of ZnGa ₂ O ₄ phases of ₂ μm or more, and the number of pores measured in the same manner as in Example 1. As an example, FIG. 1 shows the result of observing the ZnGa ₂ O ₄ phase of the sintered body obtained from the powder (e) by EDS, and FIG. 2 shows the result of observing the pores by SEM.

Claims (2)

  An IGZO raw material powder comprising indium oxide, gallium oxide and zinc oxide powder, wherein 95% or more of the zinc oxide powder is zinc oxide particles having a particle size of 2 µm or less.   The IGZO raw material powder according to claim 1, wherein indium oxide, gallium oxide, and zinc oxide are blended so that an atomic ratio of In: Ga: Zn = 1: 1: 1.

Images