JPWO2015068535A1 - Sputtering target and manufacturing method thereof - Google Patents

Abstract

The present invention provides a sputtering target containing zinc oxide produced using a zinc oxide raw material having a metallic zinc content of 100 ppm or less, and a step of reducing the metallic zinc content of the zinc oxide raw material, and It is a manufacturing method of a sputtering target including the process of manufacturing a sputtering target using the zinc oxide raw material whose metal zinc content obtained at the said process is 100 ppm or less. The sputtering target of the present invention is a sputtering target containing zinc oxide and generates less arcing and nodules during sputtering. The sputtering target production method of the present invention can efficiently produce a sputtering target containing zinc oxide and generating less arcing and nodules during sputtering.

Description

  The present invention relates to a sputtering target and a manufacturing method thereof, and more particularly to a sputtering target containing zinc oxide with improved sputtering characteristics and a manufacturing method thereof.

A transparent conductive film typified by an AZO (ZnO—Al ₂ O ₃ ) thin film has high conductivity and excellent translucency, and is used as a thin film for liquid crystal displays and solar cells. Further, semiconductor films typified by IGZO (In ₂ O ₃ —Ga ₂ O ₃ —ZnO) thin films are various displays such as a liquid crystal display (LCD), an electroluminescence display (EL), and a field emission display (FED). In a device, a thin film transistor (TFT) is used as a switching element for driving a display device by applying a driving voltage to the display element. Thus, thin films containing zinc as a constituent element are used in many fields.

  As a method for producing these thin films, there are a spray method, a dip method, a vacuum deposition method, a sputtering method, etc., but manufacturing cost, productivity, large area uniformity, film quality, film characteristics (conductivity, translucency, etc.) The sputtering method has become the mainstream of the current production technology because the sputtering method is relatively superior in terms of

  For the targets used in these sputtering methods, it is required to improve the sputtering characteristics such as suppressing the generation of arcing and nodules. From the viewpoint of suppressing the occurrence of arcing and nodules, it is known that the target has a high density and the number of target divisions is small, that is, the number of divided target materials constituting the target is small. However, it is not well understood about the influence of the metal element which is a constituent element of the target on the sputtering characteristics.

Patent Document 1 describes a method of adding metallic zinc to increase the strength of a target in an IZO (In ₂ O ₃ —ZnO) target.

  Patent Document 2 describes a method in which zinc metal is added to lower the resistance of a zinc oxide-based sputtering target.

JP 2009-144226 A JP 2008-115453 A

  An object of the present invention is to provide a sputtering target containing zinc oxide that generates less arcing and nodules during sputtering.

  The present inventors have found that in a sputtering target containing zinc oxide, by making the metallic zinc contained in zinc oxide used as a raw material a certain amount or less, an excellent target with less arcing and nodules can be obtained. The present invention has been completed.

  That is, the present invention is a sputtering target containing zinc oxide, produced using a zinc oxide raw material having a metallic zinc content of 100 ppm or less, preferably an oxidation having a metallic zinc content of 10 ppm or less. A sputtering target containing zinc oxide manufactured using a zinc raw material.

  Examples of the sputtering target include AZO made of an oxide of zinc and aluminum and IGZO made of an oxide of zinc, indium and gallium.

  Moreover, this invention manufactures a sputtering target using the process which reduces content of metallic zinc of a zinc oxide raw material, and the zinc oxide raw material whose content of metallic zinc obtained at the said process is 100 ppm or less. It is a manufacturing method of a sputtering target including a process.

  In the manufacturing method, it is preferable that the step of reducing the content of metallic zinc in the zinc oxide raw material is a step of heat-treating the zinc oxide raw material.

  The sputtering target of the present invention is a sputtering target containing zinc oxide and generates less arcing and nodules during sputtering. The sputtering target production method of the present invention can efficiently produce a sputtering target containing zinc oxide and generating less arcing and nodules during sputtering.

<Sputtering target>
The sputtering target of this invention is a sputtering target containing zinc oxide manufactured using the zinc oxide raw material whose content of metallic zinc is 100 ppm or less.

  The zinc oxide raw material is usually zinc oxide powder. The sputtering target of the present invention is usually produced using zinc oxide powder. A specific method for producing the sputtering target of the present invention will be described later.

  The zinc oxide raw material has a metallic zinc content of 100 ppm or less, preferably 10 ppm or less, more preferably 2 ppm or less. Here, ppm means mass ppm (ppmw).

  Zinc oxide powder that can be used as a target raw material is produced by volatilizing high-purity metallic zinc at a high temperature and reacting the zinc vapor with oxygen in the air. At this time, unreacted metallic zinc remains in the zinc oxide powder depending on the reaction conditions. A target produced using a zinc oxide raw material containing a large amount of metallic zinc is dotted with portions having a high content of metallic zinc. In addition, these parts are considered to have less oxygen content than other parts. If there is a part with a low oxygen content in the target, the electrical resistance value is locally different from that part only, and uniform sputtering cannot be performed. As a result, arcing and nodules are likely to occur. On the other hand, in sputtering targets manufactured using a zinc oxide raw material with a low metallic zinc content, there are few parts with a high metallic zinc content and there are few parts with a low oxygen content. As a result, the occurrence of arcing and nodules during sputtering can be reduced, and uniform sputtering becomes possible. The present inventor has found the above knowledge uniquely and completed the present invention.

  The smaller the metallic zinc content of the zinc oxide raw material, the less arcing and nodules are generated. When the content of metallic zinc in the zinc oxide raw material is 100 ppm or less, the generation of arcing and nodules can be sufficiently reduced practically.

  The sputtering target of the present invention is preferably a ceramic sputtering target. If it contains zinc oxide, there is no restriction | limiting in particular in the kind of ceramics, a composition ratio, etc. For example, an aluminum oxide zinc oxide (AZO), an indium oxide gallium oxide zinc oxide (IGZO) etc. are mentioned.

  The ceramic sputtering target is manufactured from a zinc oxide raw material and other metal oxide raw materials necessary for producing the ceramic. For example, in the case of an AZO sputtering target, the target is usually manufactured from zinc oxide powder and aluminum oxide powder. In the case of an IGZO sputtering target, the target is usually manufactured from zinc oxide powder, indium oxide powder, and gallium oxide powder. Among these raw materials, only zinc oxide raw materials may contain metallic zinc, and other raw materials are substantially free of metallic zinc.

When the sputtering target of the present invention is an AZO sputtering target, the Al content is 0.1 to 10% by mass in terms of Al ₂ O ₃ and the Zn content is 90 to 99.9% by mass in terms of ZnO. The ones are common. There exists an advantage that a target becomes low resistance in content of Al and Zn in the said range.

When the sputtering target of the present invention is an IGZO sputtering target, for example, the In content is 43.7 to 44.7% by mass in terms of In ₂ O ₃ content, and the Ga content is in terms of Ga ₂ O ₃ content. 29.2 to 30.6% by mass, the balance being ZnO and inevitable impurities. When the contents of In, Ga and Zn are within the above ranges, there is an advantage that good TFT (Thin Film Transistor) characteristics can be obtained by sputtering.

  Examples of the shape of the sputtering target of the present invention include a plate shape and a cylindrical shape.

  The sputtering target of the present invention can be used for sputtering by bonding to a substrate using a low melting point solder by a conventional method.

As described above, the sputtering target of the present invention generates less arcing and nodules during sputtering. It should be noted that the occurrence of arcing during sputtering and the generation of nodules are in a parallel relationship, and it can be evaluated that the occurrence of arcing is small if the generation of nodules is small.
<Manufacturing method of sputtering target>
The sputtering target can be manufactured according to a conventionally known manufacturing method. That is, it can be produced by molding raw material powder and firing the obtained molded body. As the molding method, for example, the following casting method can be used. However, as a molding method, a method of obtaining a molded body by uniaxial pressing of a dried and granulated raw material, a method of molding by CIP molding (Cold Isostatic Pressing), or the like is also used. Can do. Here, as an example, a method of manufacturing a flat ceramic sputtering target using a casting method will be described. This manufacturing method can also be applied to a cylindrical target.

In the manufacturing method, a slurry containing a ceramic raw material powder and an organic additive is poured into a mold, and then drained and molded to produce a molded body, Step 1 for drying the molded body, Step 2 for drying the molded body, and the dried It is a manufacturing method including the step 3 for obtaining a fired body by firing the molded body and the step 4 for obtaining a target by processing the fired body.
(Process 1)
In step 1, a slurry containing ceramic raw material powder and an organic additive is poured into a mold, and then drained and molded to produce a molded body.

  The ceramic raw material powder contains zinc oxide powder. The metallic zinc content of this zinc oxide powder is 100 ppm or less.

  Prior to step 1, a step of reducing the content of metallic zinc in the zinc oxide raw material can be performed. As described above, the smaller the content of metallic zinc in the zinc oxide raw material, the lower the generation of arcing and nodules. Therefore, before step 1, the metallic zinc content in the zinc oxide raw material is reduced. It is effective to carry out the process. By performing this step, step 1 can be performed after further reducing the metallic zinc content of the zinc oxide raw material having a metallic zinc content of 100 ppm or less. Further, when the content of metallic zinc in the zinc oxide raw material is more than 100 ppm, Step 1 can be performed after the content of metallic zinc in the zinc oxide raw material is reduced to 100 ppm or less.

  A method for reducing the content of metallic zinc in the zinc oxide raw material is not particularly limited, but a method of heat-treating the zinc oxide raw material, that is, a so-called calcination method is the most effective. The heat treatment is usually performed in the atmosphere, and the heat treatment temperature is usually 800 to 1200 ° C, preferably 800 to 1000 ° C. When the heat treatment temperature is lower than 800 ° C., the reduction of metallic zinc does not proceed efficiently. On the other hand, when the heat treatment temperature is higher than 1200 ° C., primary particles grow and the specific surface area decreases, resulting in insufficient sintering after molding. Thus, the density of the sintered body may decrease. The heat treatment time is usually 3 to 12 hours, preferably 5 to 8 hours. The degree to which the content of metallic zinc is reduced can be appropriately adjusted by the heat treatment temperature, the heat treatment time, and the like.

When the ceramic is AZO, a mixed powder of Al ₂ O ₃ powder and ZnO powder can be used as the ceramic raw material powder, and an AZO powder may be used in combination. The Al ₂ O ₃ powder, ZnO powder and AZO powder each have a specific surface area of usually 1 to ²⁰ m ² / g measured by the BET method. The mixing ratio of the Al ₂ O ₃ powder, the ZnO powder, and the AZO powder is appropriately determined so that the content of the constituent elements in the target is within the above range. In this production method, when a mixed powder of Al ₂ O ₃ powder and ZnO powder is used as the ceramic raw material powder, the content (mass%) of the Al ₂ O ₃ powder and ZnO powder in the ceramic raw material powder is finally It has been confirmed that the obtained target can be equated with the Al content (mass%) in the Al ₂ O ₃ substitution and the Zn content (mass%) in the ZnO substitution.

  The specific surface area is, for example, a fully automatic specific surface area measuring device (Macsorb (registered trademark) HM model-1210, manufactured by Mountec Co., Ltd.), a mixed gas containing 30% nitrogen and 70% helium as an adsorption gas, and BET It can be measured by the single point method.

When the ceramic is IGZO, a mixed powder of In ₂ O ₃ powder, Ga ₂ O ₃ powder and ZnO powder can be used as the ceramic raw material powder, and IGZO powder may be used in combination. In ₂ O ₃ powder, Ga ₂ O ₃ powder, ZnO powder and IGZO powder each have a specific surface area of usually 1 to ²⁰ m ² / g measured by the BET method. The mixing ratio of the In ₂ O ₃ powder, the Ga ₂ O ₃ powder, the ZnO powder, and the IGZO powder is appropriately determined so that the content of the constituent elements in the target is within the above-described range. In this production method, when a mixed powder of In ₂ O ₃ powder, Ga ₂ O ₃ powder and ZnO powder is used as the ceramic raw material powder, In ₂ O ₃ powder, Ga ₂ O ₃ powder and ZnO powder in the ceramic raw material powder are used. The content (mass%) of In is the In content (mass%) in the substitution of In ₂ O ₃ in the target finally obtained, the Ga content (mass%) in the substitution of Ga ₂ O ₃ and the amount of ZnO It has been confirmed that it can be equated with the Zn content (% by mass) in the substitution.

  There is no restriction | limiting in particular in the mixing method of powder, For example, each powder and a zirconia ball | bowl can be put into a pot, and ball mill mixing can be carried out.

  The organic additive is a substance added in order to suitably adjust the properties of the slurry and the molded body. Examples of the organic additive include a binder and a dispersant. As the binder, an emulsion-based binder is generally used, and as the dispersant, ammonium polycarboxylate or the like is generally used.

  There is no restriction | limiting in particular in the dispersion medium used when preparing the slurry containing ceramic raw material powder and an organic additive, According to the objective, it can select from water, alcohol, etc. suitably and can be used.

  The method for preparing the slurry containing the ceramic raw material powder and the organic additive is not particularly limited, and for example, a method in which the ceramic raw material powder, the organic additive and the dispersion medium are placed in a pot and ball mill mixed can be used.

The obtained slurry is poured into a mold and then drained to perform molding. As the mold, a gypsum mold or a resin mold that discharges water under pressure is common.
(Process 2)
In step 2, the molded body formed in step 1 is dried.

Drying is performed by leaving the compact in a constant environment. A drying temperature is 25-100 degreeC normally, Preferably it is 25-50 degreeC. The drying time is usually 10 to 72 hours, preferably 24 to 48 hours.
(Process 3)
In step 3, the dried molded body obtained in step 2 is fired. There is no restriction | limiting in particular in a baking furnace, The baking furnace conventionally used for manufacture of the ceramic targets can be used.

When the ceramic is AZO, the firing temperature is usually 1250 to 1500 ° C, preferably 1300 ° C to 1450 ° C, more preferably 1350 ° C to 1450 ° C. When ceramics are IGZO, they are 1300-1500 degreeC normally, Preferably it is 1400-1450 degreeC. The higher the firing temperature, the higher the density of the target is obtained. However, when the firing temperature is too high, the sintered structure of the target is enlarged and easily cracked.
(Process 4)
In step 4, the fired body obtained in step 3 is cut. Processing is performed using a surface grinder or the like. The surface roughness Ra after processing can be controlled by selecting the size of the abrasive grains of the grindstone. The value of the surface roughness Ra is preferably 1.5 μm or less, more preferably 1.0 μm or less, and most preferably 0.8 μm or less from the viewpoint of further suppressing the generation of arcing and nodules.

  The evaluation method about the relative density of the sputtering target obtained in the Example and the comparative example, and the presence or absence of a nodule is as follows. The evaluation results for the AZO sputtering target (Examples 1 to 6, Comparative Examples 1 and 2) are shown in Table 1, and the evaluation results for the IGZO sputtering target (Examples 7 to 9 and Comparative Examples 3 and 4) are shown in Table 2.

Tables 1 and 2 show the content of the metal oxide powder contained in the ceramic raw material powders prepared in the examples and comparative examples, and the metallic zinc content of the ZnO powder used in the examples and comparative examples. . The measuring method of metallic zinc content of ZnO powder is as mentioned later.
1. Relative density The relative density of the sputtering target was measured based on the Archimedes method. Specifically, the air weight of the sputtering target is divided by the volume (the weight of the sputtering target in water / the specific gravity of water at the measurement temperature), and the percentage value with respect to the theoretical density ρ (g / cm ³ ) based on the following formula (X) is obtained. Relative density (unit:%) was used.
_{ρ = ((C 1/100} ) / ρ 1 + (C 2/100) / ρ 2 + ··· + (C i / 100) / ρ i) -1 ··· (X)
(In the formula, C _{1 to} C _i indicate the content (% by weight) of the constituent material of the sputtering target, respectively, and ρ _{1 to} ρ _i are the density of each constituent material corresponding to C _{1 to} C _i (g / cm ³ ). Is shown.)
2. Presence or absence of nodules A sputtering target was bonded to a Cu substrate using indium as a low melting point solder, and sputtering was performed under the following conditions.

<Sputtering conditions>
Equipment: DC magnetron sputtering equipment, exhaust system cryopump, rotary pump Ultimate vacuum: 3 × 10 ⁻⁴ Pa
Sputtering pressure: 0.4 Pa
Oxygen partial pressure: 4 × 10 ^-2 Pa
The surface of the target after sputtering was photographed, and the ratio (%) of the nodule area on the target surface to the target surface area was evaluated as an amount of nodule by image analysis. When AZO has a nodule amount of 10.0% or less and IGZO has a nodule amount of 6.0% or less, it is evaluated that practically suitable sputtering can be carried out.
3. Metallic zinc content of ZnO powder 10 g of ZnO powder was weighed into a beaker, 100 ml of 10% ammonium chloride solution and 20 ml of aqueous ammonia were added and dissolved by heating. After allowing to stand, the liquid was discarded, and 100 ml of 10% ammonium chloride solution and 20 ml of aqueous ammonia were added to the residue and dissolved by heating. The above process was repeated 5 times or more until ZnO was completely dissolved. The final residue was washed with pure water, filtered, dissolved in hydrochloric acid, made up to a volume of 10 ml, and quantitatively analyzed by ICP-AES. This quantitative value corresponds to the metallic zinc content in the ZnO powder.
<AZO sputtering target>
[Example 1]
The content of metallic zinc is less than 2ppm, Al ₂ O ₃ powder is a ZnO powder specific surface area measured by the BET method is 4m ² / g, the measured specific surface area by the BET method 5 m ² / g Were mixed by ball milling with zirconia balls in a pot to prepare a ceramic raw material powder. The content of Al ₂ O ₃ powder in the ceramic raw material powder was 5% by mass, and the content of ZnO powder was 95% by mass.

  In this pot, 0.2% by mass of an acrylic emulsion binder with respect to the ceramic raw material powder as a binder, 0.5% by mass of ammonium polycarboxylate with respect to the ceramic raw material powder as a dispersing agent, and a ceramic raw material powder as a dispersion medium On the other hand, 20% by mass of water was added, and ball mill mixing was performed to prepare a slurry. This slurry was poured into a gypsum mold and then drained to obtain a molded body.

  The obtained molded body was dried at 25 ° C. for 48 hours and then fired to produce a fired body. Firing was performed at a firing temperature of 1400 ° C., a firing time of 10 hours, a heating rate of 300 ° C./h, and a cooling rate of 50 ° C./h.

The obtained fired body was cut to obtain an AZO sputtering target having a surface roughness Ra of 0.8 μm, a diameter of 152.4 mm, and a thickness of 6 mm. A # 170 grindstone was used for processing.
[Examples 2 to 4]
Examples 2 to 4 were all the same as Example 1 except that the content of Al ₂ O ₃ powder in the ceramic raw material powder was changed as shown in Table 1 and the remainder was changed to ZnO powder. An AZO sputtering target having the same dimensions as 1 was produced.
[Example 5]
Instead of the ZnO powder in Example 1, the same procedure as in Example 1 was used except that a ZnO powder having a metallic zinc content of 97 ppm and a specific surface area measured by the BET method of 3 m ² / g was used. An AZO sputtering target having the same dimensions as in Example 1 was manufactured.
[Example 6]
A ZnO powder having a metallic zinc content of 200 ppm and a specific surface area measured by the BET method of 3 m ² / g was calcined at 800 ° C. for 5 hours in the air. The content of metallic zinc in the ZnO powder after calcination was 32 ppm. An AZO sputtering target having the same dimensions as in Example 1 was produced in the same manner as in Example 1 except that the calcined ZnO powder was used instead of the ZnO powder in Example 1.
[Comparative Example 1]
Instead of the ZnO powder in Example 1, the same procedure as in Example 1 was used except that a ZnO powder having a metallic zinc content of 200 ppm and a specific surface area measured by the BET method of 4 m ² / g was used. An AZO sputtering target having the same dimensions as in Example 1 was manufactured.
[Comparative Example 2]
Instead of the ZnO powder in Example 1, the same procedure as in Example 1 was used except that a ZnO powder having a metallic zinc content of 1200 ppm and a specific surface area measured by the BET method of 4 m ² / g was used. An AZO sputtering target having the same dimensions as in Example 1 was manufactured.
<IGZO sputtering target>
[Example 7]
The content of metallic zinc is less than 2ppm, In ₂ O ₃ powder is a ZnO powder specific surface area measured by the BET method is 4m ² / g, the measured specific surface area by the BET method 7m ² / g Then, Ga ₂ O ₃ powder having a specific surface area measured by the BET method of 10 m ² / g was ball mill mixed with zirconia balls in a pot to prepare a ceramic raw material powder. The content of In ₂ O ₃ powder in the ceramic raw material powder was 44.2% by mass, the content of ZnO powder was 25.9% by mass, and the content of Ga ₂ O ₃ powder was 29.9% by mass.

  In this pot, 0.2 mass% acrylic emulsion binder as a binder with respect to the ceramic raw material powder, 0.6 mass% ammonium polycarboxylate with respect to the ceramic raw material powder as a dispersing agent, and ceramic raw material powder as a dispersion medium. On the other hand, 20% by mass of water was added, and ball mill mixing was performed to prepare a slurry. This slurry was poured into a gypsum mold and then drained to obtain a molded body.

  The obtained molded body was dried at 25 ° C. for 48 hours and then fired to produce a fired body. Firing was performed at a firing temperature of 1400 ° C., a firing time of 10 hours, a heating rate of 300 ° C./h, and a cooling rate of 50 ° C./h.

The obtained fired body was cut to obtain an IGZO sputtering target having a surface roughness Ra of 0.7 μm, a diameter of 152.4 mm, and a thickness of 6 mm. For processing, a # 170 grindstone was used.
[Example 8]
Instead of the ZnO powder in Example 7, the same procedure as in Example 7 was used except that a ZnO powder having a metallic zinc content of 97 ppm and a specific surface area measured by the BET method of 3 m ² / g was used. An IGZO sputtering target having the same dimensions as in Example 7 was produced.
[Example 9]
A ZnO powder having a metallic zinc content of 200 ppm and a specific surface area measured by the BET method of 4 m ² / g was calcined at 800 ° C. for 5 hours in the air. The content of metallic zinc in the ZnO powder after calcination was 32 ppm. An IGZO sputtering target having the same dimensions as in Example 7 was produced in the same manner as in Example 7 except that the calcined ZnO powder was used instead of the ZnO powder in Example 7.
[Comparative Example 3]
Instead of the ZnO powder in Example 7, the same procedure as in Example 7 was used except that a ZnO powder having a metallic zinc content of 200 ppm and a specific surface area measured by the BET method of 4 m ² / g was used. An IGZO sputtering target having the same dimensions as in Example 7 was produced.
[Comparative Example 4]
Instead of the ZnO powder in Example 7, the same procedure as in Example 7 was used except that a ZnO powder having a metallic zinc content of 1200 ppm and a specific surface area measured by the BET method of 3 m ² / g was used. An IGZO sputtering target having the same dimensions as in Example 7 was produced.

Claims (6)

  The sputtering target containing zinc oxide manufactured using the zinc oxide raw material whose content of metallic zinc is 100 ppm or less.   The sputtering target containing zinc oxide manufactured using the zinc oxide raw material whose content of metallic zinc is 10 ppm or less.   The sputtering target according to claim 1 or 2, wherein the sputtering target is made of AZO.   The sputtering target according to claim 1 or 2, wherein the sputtering target is made of IGZO.   A step of reducing the content of metallic zinc in a zinc oxide raw material, and a step of producing a sputtering target using a zinc oxide raw material in which the content of metallic zinc obtained in the step is 100 ppm or less Production method.   The method for producing a sputtering target according to claim 5, wherein the step of reducing the content of metallic zinc in the zinc oxide raw material is a step of heat-treating the zinc oxide raw material.