JP5545448B2 - Sputtering target - Google Patents

Description

  Conventionally, the present invention relates to a sputtering target for forming a ZnO-based thin film used as a transparent conductive film in flat panel displays (liquid crystal displays, plasma displays, organic EL displays, etc.) and solar cells.

As a transparent conductive film for a flat panel display, ITO (In ₂ O ₃ + SnO ₂ ) having a low resistivity is usually used. However, recently, the rapid spread of large-sized liquid crystal televisions and the like has caused problems such as depletion of In resources and price increases, and studies are underway on ZnO-based transparent conductive films that are less expensive and have more resources instead of ITO. . In addition, thin film solar cells using CIGS thin films made of copper, indium, gallium, selenium, etc., use ZnO-based transparent conductive films for electrode layers and window layers. Expected to be used.
Of the thin film forming methods, the sputtering method can form a film on a large-area substrate stably and stably. In particular, a ZnO-based target having a low resistance and capable of direct current (DC) sputtering is suitable for mass production. As typical ZnO-based targets for sputtering, targets as shown in the following documents have been disclosed so far.

For example, Patent Documents 1 and 2 relate to high-density AZO (ZnO + Al ₂ O ₃ ) and GZO (ZnO + Ga ₂ O ₃ ) targets obtained by doping ZnO with Al and Ga, respectively. Since these have low bulk resistance of the target itself and conductivity, DC sputtering is possible, and a relatively low resistance transparent conductive film can be stably formed.
However, the conventional ZnO-based transparent conductive film formed using these targets has a problem that the resistivity is higher than that of ITO, particularly when the film thickness is thin.
The problem that the resistivity becomes high in the ZnO-based thin film occurs because in the film-forming process of the ZnO-based thin film, oxidation of Al and Ga in the thin film easily proceeds, and carrier electrons decrease. This is considered to be caused by poor crystallinity at the initial stage of film growth and low mobility. In order to suppress the progress of oxidation of Al and Ga in the thin film as much as possible, there is a method using a reduced ZnO-based target as shown in Patent Document 3, for example.

However, even the method using the reduced ZnO-based target does not sufficiently suppress the progress of oxidation, and the ZnO-based thin film produced by the method has a thickness of about 4 × 10 ⁻⁴ Ω · cm when the thickness is about 300 nm. However, when the resistivity is still higher than that of ITO and the film thickness is thinner, the effect of reduction is hardly seen and the film has a high resistivity.
Therefore, in order to further suppress the oxidation of Al and Ga in the ZnO-based thin film, for example, as shown in Patent Documents 4 and 5, a target in which metal powder such as Zn is dispersed in a ZnO sintered body is also made. It has been.
However, what is described in Patent Document 4 has a high resistivity of 1 × 10 ⁻³ Ω · cm or more because the resistivity of the film formed using the target is not sufficiently low.

In addition, as shown in Patent Document 5, a target in which AlTi alloy powder is dispersed in a ZnO sintered body has also been made.
This target is a target in which an AlTi alloy (Ti: about 10% by mass or less) is sintered in a state where the alloy phase remains without being completely oxidized in the ZnO matrix, and sputtering is performed using this target. A ZnO-based thin film having a relatively low resistance can be obtained. However, since the sintering temperature is about 1000 ° C., from the Al—Ti alloy phase diagram, when Ti is 10% by mass or less, when the temperature is increased to 1000 ° C., the liquid phase of the Al—Ti alloy and the solid phase of Al ₃ Ti are increased. Since the phases coexist, the Al—Ti alloy melts on the surface of the sintered body during the sintering, and the surface of the sintered body becomes uneven and voids are formed inside. Moreover, the oxidation of the Al—Ti alloy melted during sintering proceeds, and the resistance of the target may not be sufficiently lowered. Therefore, when sputtering is performed using the target, abnormal discharge is likely to occur, and cracks may occur when a large amount of power is applied.

  As described above, with a sputtering method using a conventional ZnO-based target, it is difficult to stably obtain a film with low resistivity, particularly when the film thickness is thin (200 nm or less) by DC sputtering. There is a need for a ZnO-based target capable of obtaining a low resistivity ZnO-based transparent conductive film by stable DC sputtering even when the film thickness is as thin as 200 nm or less.

JP-A-7-258836 JP-A-6-25838 JP-A-10-297963 JP 2007-31786 A JP 2009-263709 A

  Therefore, a technical problem to be solved by the present invention, that is, an object of the present invention is to provide a ZnO-based target obtained by stable DC sputtering with a thin film thickness (200 nm or less) and a low resistivity, and its A manufacturing method and a ZnO-based transparent conductive film having a low resistivity formed by using the manufacturing method.

First, the invention according to the claims 1, and oxide phase containing Zn, consists intermetallic compound phase consisting of Al and Ti, said intermetallic compound phase in the oxide phase is dispersed The above-described problems are solved by the sputtering target.

  The invention according to claim 2 is the sputtering target according to claim 1, wherein the intermetallic compound phase is dispersed in the oxide phase as fine crystal grains having an average particle size of 50 μm or less. The feature further solves the above problem.

  The invention according to claim 3 is characterized in that, in the sputtering target according to claim 1 or claim 2, the intermetallic compound phase is uniformly dispersed in the oxide phase. The above-described problems are further solved.

  The invention according to claim 4 is the sputtering target according to any one of claims 1 to 3, wherein the content of the intermetallic compound phase in the sputtering target is 0.1 mass% or more and 6 mass% or less. The above-described problem is further solved by being characterized.

According to the claim 5 the invention is a method of manufacturing a sputtering target according to any one of claims 1 to 4, the oxide powder and the intermetallic compound powder comprising Al ₃ Ti mixed containing ZnO The problem is solved by comprising a mixing step of obtaining a mixed powder and a sintering step of obtaining a sputtering target by sintering the mixed powder obtained in the mixing step. .

The invention according to claim 6 is a ZnO-based transparent conductive film formed by a sputtering method using the sputtering target according to any one of claims 1 to 4, wherein the film thickness is 200 nm or less and the resistance is The problem is solved by having a rate of 6 × 10 ⁻⁴ Ω · cm or less.

According to the manufacturing method of the sputtering target of the present invention, and an oxide powder containing ZnO, a high melting point (1300 ° C. or higher) and intermetallic compound powder comprising Al ₃ Ti as a raw material. This makes it possible to sinter for a long time at a high temperature (about 1300 ° C.), which could not be carried out in order to avoid melting of the Al—Ti alloy, and has a smooth surface, no voids, and a high density sputtering target. Is obtained. Such a sputter target is unlikely to cause abnormal discharge or cracking.

  Moreover, since the sputtering target of the present invention contains Al in the state of an intermetallic compound, Al is hardly oxidized during film formation. Thereby, in the ZnO-based thin film formed using the sputtering target of the present invention, more carrier electrons are generated from Al, and a sufficiently low resistivity is obtained.

  From the above results, according to the sputtering target of the present invention, abnormal discharge during sputtering is reduced, and it is difficult to break even when a large power is applied. Furthermore, a ZnO-based thin film formed by sputtering using the sputtering target of the present invention has a low resistivity.

It is a graph which shows the result of having pulverized a part of target of this invention into powder, and having performed the XRD measurement. It is a photograph which shows the result of having measured the cross-sectional structure | tissue of the sputtering target of this invention with the EPMA electron beam microprobe analyzer.

  Hereinafter, the sputtering target of this invention, the manufacturing method of a sputtering target, and the ZnO type transparent conductive film manufactured using this are given and demonstrated concretely. However, the present invention is not limited to this embodiment.

Sputtering target of the present embodiment, the oxide phase containing Zn, consists intermetallic compound phase consisting of Al and Ti, the intermetallic compound phase in the oxide phase, characterized in that the dispersed.
Since such a sputtering target contains Al in the state of an intermetallic compound, Al is hardly oxidized during film formation. Thereby, in the ZnO-based thin film formed using the sputtering target of this embodiment, more carrier electrons are generated from Al, and a sufficiently low resistivity is obtained.

In the sputtering target of this embodiment, the intermetallic compound phase is preferably dispersed in the oxide phase as fine crystal grains having an average particle size of 50 μm or less.
Here, when the average particle size of the intermetallic compound phase exceeds 50 μm, abnormal discharge is likely to occur, which is not preferable. The average particle size of the intermetallic compound phase is more preferably 1 μm or less.

In the sputtering target of this embodiment, it is preferable that the intermetallic compound phase is uniformly dispersed in the oxide phase.
Even if the intermetallic compound phase is uniformly dispersed in the oxide phase, there is no uneven composition due to the location of the sputtered film, and the composition of the film even if the target is gradually dug and the sputtered part moves inside The excellent effect of not shifting is obtained. As an example of the structure in which the intermetallic compound phase is uniformly dispersed in the oxide phase, FIG. 2 shows a cross-sectional structure of the sputtering target of this embodiment measured with an EPMA electron beam microprobe analyzer.
The target structure is observed by polishing the observation surface (surface parallel to the surface to be sputtered) to a mirror surface, and then using a high-resolution FE-EPMA (field emission electron probe microanalyzer, JEOL JXA-8500F). , Hereinafter referred to as EPMA), using a secondary electron image, a reflected electron image (COMPO image), and an element distribution image showing the composition distribution of each element. The secondary electron image, the COMPO image, and the element distribution image are shown in FIG.
The element distribution image by EPMA is originally a color image, but is described after being converted into a black and white image, and thus a light and dark portion (relatively white portion) is a portion where the concentration of the predetermined element is high. .
From these images, it can be seen that the intermetallic compound phase is uniformly dispersed in the oxide phase.

In the sputtering target of this embodiment, the content of the intermetallic compound phase is preferably 0.1% by mass or more and 6% by mass or less.
Here, the lower limit value of the Al ₃ Ti intermetallic compound is 0.1% by mass, and if it is less than that, the effect of impurity doping is lost, the carrier concentration decreases, and the sputtering target and its This is because any resistance value of the film formed using the sputtering target is increased. Further, the upper limit value is 6% by mass. If the upper limit is exceeded, the doping amount of impurities increases, the crystallinity of the film formed using the sputtering target deteriorates, and the mobility decreases. This is because the resistance value increases.

  In addition, although the sputtering target of this invention uses the sintered compact which consists of zinc, aluminum, titanium, and oxygen as a target material, in the range which does not impair the effect of this invention, the inevitable impurity contained in a raw material, a target It may contain inevitable impurities mixed in during the manufacturing process.

Method for producing the sputtering target of the present embodiment, an oxide powder containing ZnO, a mixing step of obtaining a mixed powder by mixing the intermetallic compound powder containing Al 3 _Ti, the mixed powder obtained in the mixing step Sintering to obtain a sputtering target.
As the oxide powder, for example, a zinc oxide powder having an average particle diameter of 5 μm or less and a purity of 99% or more is preferable. Further, as the intermetallic compound powder, for example, an Al ₃ Ti powder having an average particle diameter of 50 μm or less and a purity of 95% or more is preferable. The average particle diameter of each powder is more preferably 1 μm or less.

In the mixing step, it is preferable to prepare a mixed powder by mixing the raw material powders so that the content of the intermetallic compound powder is 0.1% by mass or more and 6% by mass or less.
Here, the lower limit value of the Al ₃ Ti intermetallic compound is 0.1% by mass, and if it is less than that, the effect of impurity doping is lost, the carrier concentration decreases, and the sputtering target and its This is because any resistance value of the film formed using the sputtering target is increased. Further, the upper limit value is 6% by mass. If the upper limit is exceeded, the doping amount of impurities increases, the crystallinity of the film formed using the sputtering target deteriorates, and the mobility decreases. This is because the resistance value increases.

In the sintering step, for example, the mixed powder is sintered using a normal pressure sintering method, a hot press method, an energized plasma sintering method, and the like, and a sputtering target is produced.
If produced by the normal pressure sintering method, the mixed powder is formed into a predetermined shape by cold isostatic pressing or uniaxial pressing. Next, the obtained molded body is fired at a temperature of 800 to 1300 ° C. in an atmosphere such as air or nitrogen gas to obtain a sintered body. The sintered body is shaped and polished as necessary, and then bonded to a backing plate to obtain a sputtering target.

Moreover, if it produces by a hot press method, it is 1-60 MPa with respect to the said molded object, More preferably, it is a sintered compact by hold | maintaining at the temperature of 800-1300 degreeC for 1 hour or more under the pressurization of 5-50 MPa. Is made. The obtained sintered body is shaped and polished as necessary, and then bonded to a backing plate to obtain a sputtering target.
On the other hand, if produced by an energized plasma sintering method, for example, a DC pulse current of about 2,000 to 10,000 A is applied to the molded body under a pressure of 10 to 60 MPa, and the temperature rise is started. A high-density ZnO-based oxide sintered body can be produced in a short time of about 100 minutes or less until the completion of sintering. The temperature at the time of sintering may be selected in consideration of the composition of the raw material, the particle size and particle size distribution of the raw material powder, the size of the sintered body, the applied pressure, the amount of applied current, etc., but about 500 to 1500 ° C. Preferably, it is about 800-1300 degreeC. The obtained sintered body is subjected to machining such as grinding as necessary, and then bonded to a backing plate to obtain a sputtering target.

The ZnO-based transparent conductive film of this embodiment is formed by a sputtering method using the above-described sputtering target, and has a film thickness of 200 nm or less and a resistivity of 6 × 10 ⁻⁴ Ω · cm or less.
Here, if the film thickness of the ZnO-based transparent conductive film exceeds 200 nm, it is not preferable because the transmittance decreases and the time required for forming the film becomes long. Further, if the resistivity of the ZnO-based transparent conductive film exceeds 6 × 10 ⁻⁴ Ω · cm, it is not preferable because it is necessary to increase the film thickness in order to obtain a low resistance film.

The ZnO-based transparent conductive film is produced as follows, for example. The ZnO-based sputtering target is placed in a sputtering apparatus and evacuated. In order to obtain a transparent conductive film composed of good crystals, the substrate temperature is preferably 100 ° C. or higher. As the sputtering gas, an inert gas such as Ar is used. If necessary, an oxidizing gas or a reducing gas may be introduced.
As the sputtering method, a DC sputtering method, an RF sputtering method, a pulsed DC sputtering method, or a combination thereof can be used, but the DC sputtering method is most preferable.

(Examples 1-8)
As raw material powders, zinc oxide powder having an average particle size of 0.5 μm or less and a purity of 99.9% or more, and Al _{3 having an} average particle size (derived by the microtrack method) of 1 μm or less and a purity of 99% or more Ti intermetallic compound powder was prepared. The Al ₃ Ti metal compound powder was prepared by melting an Al ₃ Ti alloy lump by non-contaminating plasma skull melting and shaving it, and then performing ultra-cooled centrifugal spraying.
These raw material powders were blended so as to have the blending composition shown in Table 1, and sintered bodies were produced by a hot press method and an energized plasma sintering method.

In the hot press method, it was produced as follows. A predetermined amount of the raw material powder was put in a pot and mixed for 24 hours by a dry ball mill to prepare a mixed powder. This mixed powder was put into a graphite mold for a hot press machine and heated at a press pressure of 30 MPa and 1000 ° C. for 3 hours to obtain a sintered body. The obtained sintered body was ground to produce a target having a diameter of 101.4 mm and a thickness of 6 mm. The sintered density of the target was determined from volume and weight measurements. Moreover, about the resistivity, the volume resistivity of five places or more was measured with the four-probe method using the resistivity measuring machine, and the average value was computed. The results are shown in Table 1 (Claim 5).
Moreover, as a result of pulverizing a part of the target into powder and performing XRD measurement, as shown in FIG. 1, diffraction peaks derived from ZnO and Al ₃ Ti can be confirmed, respectively, and Al and Ti are dissolved in ZnO. I confirmed that I did not.

The conditions for XRD measurement are as follows.
Preparation of sample: The sample was wet-polished with SiC-Paper (grit 180) and dried, and then used as a measurement sample.
Equipment: Rigaku Electric (RINT-Ultima / PC)
Tube: Cu
Tube voltage: 40 kV
Tube current: 40 mA
Scanning range (2θ): 10 ° to 90 °
Slit size: Divergence (DS) 0.5 degree, Scattering (SS) 0.5 degree, Received light (RS) 0.15mm
Measurement step width: 002 degrees at 2θ Scan speed: 2 degrees per minute

Next, the molecular weight composition ratio of these two phases was calculated from the calibration curve for the diffraction line intensity ratio. That is, XRD measurement was performed on mixed powders of several ZnO powders and Al ₃ Ti powders having different weight composition ratios, and the intensity ratio between the Al ₃ Ti112 peak and the ZnO (101) peak was compared with the weight composition ratio of Al ₃ Ti. creating a calibration curve by plotting Te, calculated on the weight composition ratio of _Al 3 Ti and ZnO from the obtained diffraction line intensity ratio by XRD measurement of the target powder, ZnO as a whole 1, the _Al 3 Ti composition ratio by weight of Calculated. The molecular weight composition ratio is shown together in Table 1. As a result, it was confirmed that the content of the intermetallic compound phase in the target of the present invention was 0.1% by mass or more and 6.0% by mass or less (claim 4).

Further, a part of each target was cut out, and atomic composition surface analysis by EPMA, structure observation by SEM, and calculation of average particle diameter were performed. The average grain size is within a range of magnifications of 50 to 1000 times that the crystal grain boundary can be discriminated after the cut sample surface is polished to a mirror surface and etched with an etching solution consisting of hydrogen peroxide and ammonia water. A micrograph was taken with an optical microscope, and binarized using image analysis software (Winroof) and counted by equivalent circle diameter. The average particle size is shown in Table 1. From these results, it was confirmed that the Al ₃ Ti intermetallic compound was uniformly dispersed in the base ZnO polycrystalline matrix as fine crystal grains having an average particle size of 50 μm or less. That is, the sputtering target of the present invention, the oxide phase containing Zn, consists intermetallic compound phase consisting of Al and Ti, the intermetallic compound phase the oxide phase as the following fine crystal grains with an average grain diameter of 50μm It is uniformly dispersed therein (claims 1 to 3).

In the energization plasma sintering method, production was performed as follows. As the apparatus, an energized plasma sintering apparatus was used. The mold was made of graphite and had a cylindrical shape with an inner diameter of 101.4 mm. The starting raw material powder obtained above was put uniformly in this mold, Al ₂ O ₃ powder was spread on the top and bottom, a pressure of 35 MPa was applied, and the inside of the sintering chamber was deaerated to 10 Pa. Next, by applying a DC pulse current of about 1000 to 6000 A to the mold, the periphery of the raw material was heated to a predetermined temperature of 1000 ° C. at a rate of temperature increase of about 40 ° C./min. After maintaining this state for 15 minutes, the application of current and pressure was stopped, the formed sintered body was cooled to room temperature, the inside of the sintering chamber was returned to atmospheric pressure, and the sintered product was taken out. All of the obtained sintered products had a disk shape with a diameter of about 101.4 mm and a thickness of 6.5 mm. Next, the Al ₂ O ₃ layers present on the upper and lower surfaces of each sintered product were removed by polishing to obtain a target disk-shaped sintered body. The sintered density of the sintered body was determined from the measurement of volume and weight. Further, the volume resistivity was measured at five or more locations by a four-probe method using a resistivity measuring machine, and an average value was calculated. The results are shown in Table 1 (Claim 5).

Further, a part of the target was pulverized into a powder, and the molecular weight composition ratio of ZnO and Al ₃ Ti was determined by the XRD calibration curve method in the same manner as the target prepared by the hot press method. The results are shown in Table 1. As shown in Table 1, it can be seen that the content of the intermetallic compound phase in the target of the present invention is 0.1 mass% or more and 6.0 mass% or less (claim 4).
Similarly to the targets prepared by the above hot press method, a part of each target was cut out and subjected to atomic composition surface analysis by EPMA, structure observation by SEM, and calculation of average particle diameter (described in Table 1). It was. As a result, it was confirmed that the Al ₃ Ti intermetallic compound was uniformly dispersed in the base ZnO polycrystalline matrix as fine crystal grains having an average particle diameter of 50 μm or less (claims 1 to 3).

  Next, the sintered body obtained by the above two sintering methods is bonded to a backing plate made of oxygen-free copper using indium solder, and the target is used to form a thin film under the conditions shown below by the DC magnetron sputtering method. Formed.

(Sputtering film formation conditions)
Equipment: DC magnetron sputtering equipment Magnetic field strength: 1000 Gauss (directly above the target, vertical component)
Substrate temperature: 200 ° C
Ultimate vacuum: 5 × 10 ⁻⁵ Pa
Sputtering gas: Ar
Sputtering gas pressure: 0.5 Pa
DC power: 200W
Film thickness: 200nm
Substrate used: alkali-free glass (Corning # 1737 glass)

  The number of abnormal discharges that occurred during sputtering was measured with an arcing counter equipped with a DC power source. Further, the surface of the target was observed after the sputtering, and it was confirmed whether there was any crack. The resistivity of the obtained thin film was measured by a 4-probe method. The results are shown in Table 2.

(Comparative Examples 1-4)
As comparative examples, zinc oxide powder, aluminum oxide powder, aluminum metal powder, aluminum titanium alloy powder (96 mass% Al-4 mass% Ti) having an average particle diameter of 0.5 μm or less and a purity of 99.9% or more are used. Were prepared and blended so as to have the ratio shown in Table 1, and a ZnO-based target was produced in the same manner as in Examples 1 to 4 by a hot press method. In Comparative Example 4, a ZnO target was produced using only zinc oxide powder. Their component composition, density, resistivity, and average particle diameter were determined in the same manner as in the examples. The results are shown in Table 1. When the additive was a sintered body of aluminum metal and aluminum titanium alloy, all or part of Al was oxidized and the XRD peak of aluminum oxide (Al ₂ O ₃ ) was detected. The weight composition ratio was determined using two calibration curves for the product and ZnO and _two calibration curves for Al ₂ O ₃ and ZnO. Others in the table indicate Al ₂ O ₃ . Further, a thin film was formed by the sputtering method in the same manner as in the Examples, and the number of abnormal discharges, target cracks, and resistivity were determined. The results are shown in Table 2.

From the results shown in Tables 1 and 2, all of the targets of the present invention have a resistivity of 1.0 × 10 ⁻³ Ω · cm or less and can be subjected to DC sputtering. Further, when sputtering is performed using the target of the present invention, abnormal discharge is reduced as compared with the case of using the target of the comparative example, cracks are not generated, and sputtering can be performed stably. Furthermore, Al 3 weight composition ratio of _Ti is less than 6 wt% 0.1 wt% target (Examples 1-8) a transparent conductive film formed using a fourth aspect of the present invention, compared It turns out that a resistivity is low compared with the transparent conductive film formed using the target of an example. It can be seen that the resistivity is as low as 6.0 × 10 ⁻⁴ Ω · cm or less even when the film thickness is as thin as 200 nm (Claim 6).
As described above, it has been found that when an AZO thin film is formed by a sputtering method using the ZnO-based sputtering target of the present invention, abnormal discharge is reduced and a low-resistance transparent conductive film can be formed without cracking of the target.

  The transparent conductive film formed using the sputtering target of the present invention has a thin film thickness (200 nm or less) and a low resistivity, and can be suitably used for flat panel displays, solar cells, etc. Very big.

Claims (6)

And oxide phase containing Zn, it consists intermetallic compound phase consisting of Al and Ti,
The sputtering target, wherein the intermetallic compound phase is dispersed in the oxide phase.   The sputtering target according to claim 1, wherein the intermetallic compound phase is dispersed in the oxide phase as fine crystal grains having an average particle diameter of 50 μm or less.   The sputtering target according to claim 1, wherein the intermetallic compound phase is uniformly dispersed in the oxide phase.   4. The sputtering target according to claim 1, wherein the content of the intermetallic compound phase in the sputtering target is 0.1% by mass or more and 6% by mass or less. A mixing step of mixing an oxide powder containing ZnO and an intermetallic compound powder made of Al ₃ Ti to obtain a mixed powder;
A sintering step of obtaining a sputtering target by sintering the mixed powder obtained in the mixing step;
The method of manufacturing a sputtering target according to any one of claims 1 to 4, further comprising: A ZnO formed by a sputtering method using the sputtering target according to any one of claims 1 to 4, having a film thickness of 200 nm or less and a resistivity of 6 × 10 ^-4 Ω · cm or less. Based transparent conductive film.

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