JP2011179056A - Sputtering target - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sputtering target that hardly causes arcing during sputtering. <P>SOLUTION: The sputtering target comprises a zinc oxide sintered body, wherein a crystalline orientation degree I<SB>002</SB>/(I<SB>002</SB>+I<SB>110</SB>) calculated by peak intensities in the X-ray diffraction measurement on the major face 11a to be exposed to a sputtering atmosphere, is 0.2 to <0.58. The zinc oxide sintered body is prepared by calcining a cast compact, and the cast compact is prepared by casting a slurry having a dispersion of the raw material powder into a casting die having a bottom formed of a water-absorbing material and a side wall formed of a material having no water absorptivity, and depositing the raw material powder while absorbing water by the water-absorbing material. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a sputtering target for forming a transparent conductive film used for transparent electrodes such as solar cells and touch panels by a sputtering method.

In recent years, a zinc oxide transparent conductive film having high transparency, conductivity and chemical stability at low cost has attracted attention. As a method for forming a zinc oxide-based transparent conductive film, a sputtering method is most suitable, in which a dense and good film quality can be easily obtained, and various zinc oxide sintered bodies used for sputtering target materials have been studied.

For example, Patent Document 1 discloses a molded body in which a (110) plane is preferentially oriented in a direction in which a magnetic field is applied by applying a high magnetic field in a specific direction to a slurry obtained by adding a solvent to zinc oxide powder. Disclosed is zinc oxide-based sintering that can be produced and has an oriented surface oriented in the (110) plane by firing the shaped body.

In Patent Document 1, casting molding using a slurry is used as a powder molding method. An example in which such casting is applied to a method for producing a sputtering target material is described in Patent Document 2. In Patent Document 2, as shown in FIG. 1, a non-liquid-absorbing lower mold 13 having a molding recess 12 provided on the upper surface and a liquid-absorbing upper mold 14 covering the upper surface of the lower mold 13 are formed. In addition, a solid mud casting mold is used in which one or more casting ports 16 communicating with the molding recess 12 are provided.

JP 2002-121067 A JP-A-11-19910

Here, when forming a film using a zinc oxide sintered body as a sputtering target, arcing occurs, the plasma discharge state becomes unstable, and stable film formation may not be performed. The conventional zinc oxide sintered body has been insufficient in measures against such arcing.

The present invention has been made in view of these problems, and provides a sputtering target in which arcing is unlikely to occur.

In order to solve these problems, the present invention is composed of a zinc oxide sintered body, and the degree of crystal orientation I ₀₀₂ / (I ₀₀₂ + I calculated by the peak intensity of the X-ray diffraction measurement of the main surface exposed to the sputtering atmosphere. ₁₁₀ ) is 0.25 or more and less than 0.58.

In particular, it has been found effective if there is a strong tendency that the c-axis of zinc oxide is parallel to the main surface exposed to the sputtering atmosphere. The reason for this is not clear, but arcing at the time of sputtering has a correlation with the conductivity of the generation site, and orientation prevents the oxygen atoms in the zinc oxide from being preferentially sputtered. This is presumably due to the fact that it is difficult to produce a portion with low electrical conductivity.

However, it is not preferable that the c-axis tends to be parallel, and the crystal orientation degree I ₀₀₂ / (I ₀₀₂ + I ₁₁₀ ) is preferably 0.25 or more.

Moreover, this invention provides the sputtering target in which the said zinc oxide sintered compact contains 1 or more types of elements chosen from Al, Ga, B, Si, and In. These are added to impart conductivity to the zinc oxide sintered body, and a material suitable for a sputtering target can be obtained by adjusting the amount of addition and the like.

Further, according to the present invention, the zinc oxide sintered body is obtained by firing a cast molded body, and the cast molded body disperses the raw material powder in a mold having a bottom portion of the water absorbent material and a side wall portion of the non-water absorbent material. A sputtering target is provided, in which the slurry is cast, and raw material powder is deposited together with water absorption of the water-absorbing material. When the main surface of the sputtering target is formed using such casting, the degree of crystal orientation calculated by the peak intensity of the X-ray diffraction measurement for the main surface is different from the case where other forming methods are used.

In addition, the present invention provides a sputtering target in which a main surface exposed to a sputtering atmosphere is a surface that has been ground or polished so as to be perpendicular to the inking direction during casting. The degree of crystal orientation of the main surface can be controlled to a predetermined value by specifying the relationship between the inking direction and the main surface during molding.

It is possible to provide a sputtering target in which arcing during sputtering hardly occurs.

It is the schematic which shows the conventional casting molding. It is a schematic sectional drawing of the sputtering target of this invention. It is the schematic which shows the casting molding of this invention. Production No. 4 is an X-ray diffraction chart of Table 1 (Table 1).

Hereinafter, the sputtering target of the present invention will be described in more detail.

FIG. 2 shows a schematic cross section of the sputtering target. The sputtering target 21 is made of a zinc oxide sintered body and has a main surface 21a exposed to the sputtering atmosphere. The back surface 21 b of the sputtering target is bonded to the backing plate 22.

The zinc oxide sintered body can be added with one or more of Al, Ga, Si, B, and In to impart conductivity.

As what added Al, what made the content of Al in a sintered compact into the range of 0.5-3.5 mass% in conversion of aluminum oxide is preferable. By adding aluminum oxide in this range, a good conductive film can be obtained. When Al is present in the grain boundaries and grains of ZnO, it is generated by the reaction of ZnO and Al ₂ O ₃ , and constitutes ZnAl ₂ O ₄ present in the grain boundaries and grains of ZnO. By controlling the reaction of the added Al (aluminum oxide) and adjusting the generated spinel (ZnAl ₂ O ₄ ), it is possible to reduce cracking and arcing during use due to insufficient strength, and it is suitable as a target material A zinc sintered body is obtained.

As what added Ga, what was made into content of Ga of 0.03-5 mass% in conversion of gallium oxide is preferable. Usually, when a zinc oxide sintered body is produced by adding Ga, a composite oxide of zinc and Ga is generated. However, when the composite oxide is generated, pores are formed and arcing is likely to occur. Further, it is not preferable because unevenness in brightness is likely to occur. By setting the amount of Ga to be in the above range, generation of complex oxide and uneven brightness can be suppressed, so that arcing can be prevented and film formation uniformity can be improved. Furthermore, since an appropriate amount of Ga is dissolved in zinc oxide, the volume resistivity of the sputtering target can be easily controlled.

As for what added B, the content ratio of B (boron) in the ZnO sintered body is preferably 0.5 to 4% by mass in terms of B ₂ O ₃ . When the content of B is small, the amount of B of the dopant that is substituted and dissolved in the Zn site is too small, and it is difficult to obtain a low-resistance film even if the film is formed. The resistance can be lowered by setting the B content to a predetermined amount. On the other hand, if the content of B is too large, the resistance of the film does not change, but excessive B exceeding the solid solution limit remains in the grain boundary of the ZnO sintered body, causing sintering inhibition. It is not preferable because the sintered body is not sufficiently densified or causes arcing during sputtering.

The in-plane brightness difference ΔL * of the main surface exposed to the sputtering atmosphere is preferably 5 or less. In a sputtering target using a zinc oxide sintered body, the surface roughness is large if there is no processing after firing, and arcing frequently occurs during sputtering if it is used as it is as a sputtering target. In order to prevent this, the surface of the sintered body is ground after sintering. However, when stress is applied to the zinc oxide by grinding, the brightness of the surface of the sintered body changes as a result, and unevenness of brightness occurs in the same plane. When this is used as a sputtering target, arcing frequently occurs especially in the initial stage of sputtering, and the film quality also becomes uneven.

The reason for this is not clear, but it is presumed that the stress is accumulated at the crystal grain boundary due to the processing, so that the crystal is distorted, and that the directivity difference between the crystals is clearly revealed at the time of sputtering. Therefore, the in-plane brightness difference ΔL * is desirably 5 or less on the main surface exposed to the sputtering atmosphere.

The relative density of the zinc oxide sintered body is desirably 99% or less. This is because if the density is too high, stress accumulation during grinding becomes significant, and the brightness difference ΔL * tends to increase. However, if the density of the sintered body is too low, film quality unevenness is caused, so the relative density is preferably 75% or more.

In addition, the temperature of the sputtering target rises during sputtering. In particular, the temperature of the main surface near the magnet disposed on the back side of the sputtering target is highest. For this reason, a temperature gradient is generated in the sputtering target and may break. This is because, as the density of the sputtering target is higher, the stress generated by the difference in partial thermal expansion due to the temperature gradient cannot be relaxed.

As the density of the sintered body increases, both the Young's modulus and the bending strength are improved to some extent, but the Young's modulus follows it, whereas the bending strength stops increasing at a certain point and then decreases. This is because the Young's modulus has a large density dependence, whereas the bending strength depends on the structure of the sintered body. As a result, when the Young's modulus increases, the generated thermal stress also increases, but the bending strength does not improve as much as the Young's modulus, so the strength sufficient to withstand that stress is not exhibited and the risk of thermal stress cracking increases. . From this point of view, the relative density of the zinc oxide sintered body is desirably 99% or less.

The average particle size of the zinc oxide sintered body is desirably 15 μm or less. This is because as the average particle size increases, the stress generated during grinding increases and the brightness difference ΔL * increases.

Moreover, it is preferable that the maximum height Rz (JISB0601: 2001) of the zinc oxide sintered compact which comprises the main surface of a sputtering target is 1/2 or less of an average particle diameter. By reducing the arithmetic average surface Ra often used in the evaluation of the surface roughness, the arcing is not necessarily reduced, and the arc height can be more reliably reduced by controlling the maximum height Rz.

Furthermore, it is preferable that the zinc oxide sintered compact which comprises the sputtering target 21 contains the pore of the pore diameter below 1/2 of an average particle diameter. As described above, the relative density is desirably 99% or less, but it is not preferable that the pores contained in the sintered body are large. If the pores are larger than 1/2 of the average particle size, degaking can easily cause arcing during film formation, or the thermal conductivity can be lowered at the pores, resulting in a local temperature rise. Because.

The volume resistivity of the zinc oxide sintered body constituting the sputtering target 21 is preferably 1 × 10 ⁻² Ωcm or less. When a sputtering target having such a volume resistivity is used, the sputtering efficiency is improved.

In the sputtering target 21 of the present invention, the temperature of the main surface 21a becomes 100 ° C. or higher during sputtering, and the backing plate 12 bonded to the back surface 21b is cooled at 30 ° C. or lower. Therefore, the temperature difference between the main surface temperature of the sputtering target 11 and the backing plate 22, that is, the temperature difference between the main surface 21a and the back surface 21b of the target is 70 ° C. or more. It is suitable for use under conditions where such a temperature gradient can occur.

The backing plate 22 is preferably 100 W / m · K or more. Moreover, the thickness of the sputtering target 21 can be 8-20 mm. In recent years, in order to reduce the replacement frequency of a sputtering target, it tends to be thicker than before. Therefore, cooling of the sputtering target has become increasingly important, and it is preferable to use a backing plate having a thermal conductivity of 100 W / m · K or more, particularly when the thickness of the sputtering target 21 is 8 to 20 mm. .

Next, the manufacturing method of the sputtering target of this invention is demonstrated.

It is preferable to use a high-purity zinc oxide powder. It is desirable to use a raw material powder having a purity of preferably 99% or more, more preferably 99.8% or more.

The raw material powder of zinc oxide is preferably plate-like particles rather than spherical. By using such raw material powder, arcing can be further reduced. Specifically, a plate-like zinc oxide powder having an average equivalent circular diameter of 0.1 to 2.0 μm and an average thickness of 0.01 to 0.2 μm can be used. In addition, the magnitude | size of raw material powder can be calculated | required using a SEM observation photograph. The equivalent circle diameter refers to the diameter of a circle having the same area as the area of the plate-like plane portion.

Al, Ga, and B are preferably added as oxide powders, but are not limited thereto, and may be various forms such as carbides and nitrides that generate oxides after sintering in the atmosphere. good. It is desirable to use a raw material powder having a purity of preferably 99% or more, more preferably 99.9% or more. The shape of these powders is not particularly defined, but spherical particles are preferable to plate shapes, and the average particle size of the primary particles is preferably smaller than the average equivalent circular diameter of zinc oxide. These powders preferably have an average particle size of 2.0 μm or less. A more preferable range is 0.01 to 2.0 μm.

A slurry of raw material powder is prepared and used for casting. As the solvent for the slurry, known materials such as water and alcohol can be used. The binder used for molding is not particularly limited, and known materials such as polyvinyl alcohol and acrylic emulsion can be used, and a polycarboxylic acid-based general material can be applied as the dispersant. The raw material powder can be mixed by a method using slurry such as stirring and ball mixing.

Casting is performed by casting a slurry 35 in which raw material powder is dispersed in a molding die 30 having a bottom portion 31 made of a water-absorbing material and a side wall portion 32 made of a non-water-absorbing material. It is preferable to use a method of setting the thickness (FIG. 3). According to this method, the thickness direction can be made constant, so that it is possible to prevent the occurrence of a density difference due to the difference in the thickness direction. The “bottom part” does not necessarily mean that it is at a low position, but means that it is a deep bottom part in the direction of fleshing. Further, the positional relationship between the bottom and the side wall may be a configuration that can be set in a certain direction as shown in FIG.

When the X-ray diffraction measurement is performed on the main surface of the sputtering target using the above casting molding, a diffraction result different from the case of using another molding method is shown. Specifically, the degree of orientation I ₀₀₂ / (I ₀₀₂ + I ₁₁₀ ) indicating the relationship between the plane perpendicular to the c-axis and the parallel plane is 0.25 or more and less than 0.58. On the other hand, a sintered body having almost no orientation using CIP molding shows the degree of orientation of 0.58, but the main surface formed by the above method shows a degree of orientation smaller than this. That the peak intensity of the (002) plane perpendicular to the c-axis is relatively small means that there are few crystal planes having the c-axis in the direction perpendicular to the main surface. If the degree of orientation is within a predetermined range, the occurrence of arcing can be further reduced.

FIG. 4 shows an example of a chart obtained by XRD measurement of the zinc oxide sintered body constituting the sputtering target of the present invention. After _{obtaining the} peak intensities I ₀₀₂ and I ₁₁₀ for each surface, the degree of crystal orientation I ₀₀₂ / (I ₀₀₂ + I ₁₁₀ ) can be calculated.

Here, the main surface is a surface that is exposed to the sputtering atmosphere, and is a surface that has been ground or polished so as to be perpendicular to the inking direction during casting. In order to adjust the degree of orientation, it is preferable to control the exhaust speed of the vacuum pump at the time of vacuum suction from the groove 33 for vacuum suction. The higher the pumping speed of the vacuum pump, the easier the zinc oxide particles are oriented.

Further, in the casting molding of the present invention, when the slurry 35 is poured into the mold 30, a walled layer is formed on the bottom 31. However, it is preferable that the walled layer is always covered with an excess slurry. By being always covered with an excess slurry, uniforming of the flesh can be achieved. Therefore, after the thickness of the inking layer reaches the thickness required for the molded body, it is preferable to discharge the surplus slurry or to process and remove the portion that has been inked due to the surplus.

A sintering temperature of 1250 to 1600 ° C., particularly 1350 to 1550 ° C., is preferable because zinc oxide is less evaporated during sintering and can be easily densified. On the other hand, when the sintering temperature exceeds 1600 ° C., the evaporation of zinc oxide becomes intense and it becomes difficult to make it dense. When the sintering temperature is less than 1250 ° C., the sintering itself does not proceed so much and it is difficult to obtain a dense sintered body. The sintering time is preferably several hours to several tens of hours.

The sintering atmosphere is not particularly limited, and examples thereof include air, oxygen, and an inert gas atmosphere. In particular, sintering in an oxidizing atmosphere such as the air is preferable in order to reduce weight due to evaporation of oxides and reduce composition deviation during sintering. Of these, the atmosphere or the air stream is preferable. The pressure of the sintering atmosphere is not limited, and any pressure can be applied from reduced pressure, normal pressure to several atmospheric pressure. Normal pressure is preferable from the viewpoint of cost. In the case of hot press sintering, an inert gas atmosphere is preferable.

A zinc oxide sintered body having an average particle size of 15 μm or less is obtained by adjusting the atmosphere at the above-mentioned sintering temperature.

The zinc oxide sintered body is ground or polished before being joined to the backing plate as a target material. The processing is performed so that the main surface exposed to the sputtering atmosphere is perpendicular to the direction of wall formation during casting. The degree of crystal orientation of the main surface can be controlled to a predetermined value by specifying the relationship between the inking direction and the main surface during molding. It should be noted that “perpendicular to the inking direction” does not need to be exactly matched, and allows a certain amount of deviation within a range in which the effect of the present invention can be obtained. However, it is preferable to suppress it to ± 5 ° or less.

Since processing distortion occurs when the main surface is processed, it is preferable to perform heat treatment after grinding or polishing in order to remove the distortion. The heat treatment can be performed at 600 to 800 ° C. Although the temperature pattern is not particularly defined, a temperature increase / decrease rate of 300 ° C./h or less is desirable in order to prevent cracking due to thermal shock. The atmosphere is not particularly limited, such as air or inert gas. Such heat treatment conditions are preferable because distortion can be sufficiently removed and grain growth of the sintered body does not occur. At this time, if the average particle diameter of the zinc oxide sintered body is 15 μm or less, the stress generated during the grinding process can be reduced, so that the brightness difference ΔL * of the sintered body can be reduced.

As a backing plate to which a target material made of a zinc oxide sintered body is bonded, a copper plate is preferable because it is excellent in heat conduction. In addition to the copper plate, a metal-ceramic composite material using aluminum alloy or copper as a matrix metal and ceramic as a reinforcing material is also suitable.

Indium bonding is suitable for the bonding between the backing plate and the target material made of the zinc oxide sintered body. However, the bonding layer formed of indium preferably has a contact area of at least 90% with respect to the bonding surface of the backing plate and the target material. If the target material of the present invention and a copper plate are joined with indium and the contact area is 90% or more, cracks due to thermal stress during production or use can be eliminated.

EXAMPLES Hereinafter, the Example of this invention is specifically given with a comparative example, and this invention is demonstrated in detail.

[Raw material powder]
As raw material powders, zinc oxide powder (purity 99.8%, average equivalent circular diameter 1.0 μm, average thickness 0.2 μm), aluminum oxide powder (purity 99.99%, average particle diameter 0.5 μm), gallium oxide Powder (purity 99.99%, average particle size 1.0 μm) and boron oxide powder (purity 99.7%, average particle size 0.5 μm) were prepared.

[Casting (Production Nos. 1 to 8)]
The slurry used for casting was prepared by adjusting the binder, dispersant and ion exchange water to the raw material powder.

Using a box-shaped mold 30 as shown in FIG. 3, the mold was placed in a horizontal place so that the wall surface of the bottom portion 31 was horizontal. The mold is composed of a water absorbing material bottom 31 made of gypsum, a side wall 32 made of hard plastic and a non-water absorbing material made of hard plastic, and a bottom plate 34 that supports the bottom surface of the bottom. Bonded to prevent leakage. Grooves 33 for vacuum suction are formed in the bottom 31 and each of the grooves 33 is connected to a vacuum source (not shown).

The slurry was poured into a mold, and vacuum suction was performed on each mold using a pump having an effective exhaust speed of 10 to 1400 L / min. Excess slurry on the inking layer was discharged when the inking thickness sufficient to extract the shaped body was reached, and a shaped body 36 was obtained. The molded body 36 was fired at 1350 to 1550 ° C. for 15 hours in the air to obtain a sintered body.

[CIP (Production Nos. 9 to 11)]
A binder was added to the raw material powder, and wet mixing was performed for 20 hours using Φ15 and Φ25 resin balls as a mixing medium and a resin pot as a container. The mixed slurry was taken out, and granulated powder was produced by spray drying. CIP molding was performed using the obtained mixed powder to produce a molded body. Thereafter, the molded body was fired at 1500 ° C. for 15 hours to obtain a sintered body.

[Production and evaluation of sputtering target]
The obtained zinc oxide sintered body was ground to a diameter of 100 × 12 mm, then heat treated at 700 ° C. to form a sputtering target, and a copper plate backing plate was indium bonded to the back surface.

The X-ray diffraction measurement was performed using a mirror-polished sintered body surface, a Rigaku X-ray diffractometer MultiFlex, and a CuKα ray source, an acceleration voltage of 40 kV, and 40 mA. The density of the zinc oxide sintered body was measured by the Archimedes method. The average particle size of the sintered body was obtained from the intercept method by mirror-polishing the surface of the sintered body, thermally corroding the polished surface to precipitate crystal grain boundaries, and performing SEM observation. The maximum height Rz was measured with a contact-type surface roughness measuring instrument. The obtained zinc oxide sintered body had a relative density of 95 to 99%, an average particle size of 5 to 15 μm, and a maximum height Rz of 2 to 4 μm. The arithmetic average surface roughness Ra of the main surface was all 0.5 μm or less.

The obtained sputtering target was mounted on a DC magnetron sputtering apparatus and used to examine whether cracking or arcing occurred. Sputtering was performed in a pure argon atmosphere, a pressure of 0.5 Pa, and an input power of 200 W. During sputtering, the backing plate was extracted with cooling water so that the backing plate was kept at 30 ° C. or lower. At this time, the main surface of the sputtering target was 100 ° C. or higher. For arcing, arcing generated during film formation was counted and evaluated by the number of times per unit time. In the column for evaluation in Table 1, the number of times per unit time was expressed as “◯”, “20” to “20” as Δ, and “40” as “×”.

Production No. 1 to 8 had a degree of crystal orientation of 0.25 to 0.57 and little arcing. In particular, no. 3 to 8 had very little arcing. On the other hand, Production No. 9 to 11 had a crystal orientation of 0.58, and arcing occurred frequently. Note that FIG. 4 is an XRD chart of FIG.

Next, using a manufacturing oxide No. using aluminum oxide as an additive. No. 4 was evaluated in the same manner as in Example 4 and fired at 1350 to 1600 ° C. for 15 hours in the air. Table 2 shows the results. In addition, preparation No. No. 22 was adjusted by changing the abrasive grains so that the surface roughness Rz was increased during grinding.

Production No. All of 21 to 25 had the same degree of crystal orientation. Among them, production No. In Nos. 23 to 25, the maximum height Rz was 1/2 or less of the average particle diameter, and the arcing was very small and the performance was extremely excellent. Production No. No. 21 has an average particle size exceeding 15 μm. In No. 22, the maximum height Rz exceeded 1/2 of the average particle diameter. These are the production numbers. There was a little arcing compared with 23-25. Therefore, in addition to setting the degree of crystal orientation within a predetermined range, it is preferable to reduce the maximum height Rz of the zinc oxide sintered body surface to ½ or less of the average particle diameter in order to reduce arcing. It can be said.

Claims (4)

It consists of a zinc oxide sintered body,
Sputtering characterized in that the degree of crystal orientation I ₀₀₂ / (I ₀₀₂ + I ₁₁₀ ) calculated by the peak intensity of X-ray diffraction measurement of the main surface exposed to the sputtering atmosphere is 0.2 or more and less than 0.58 target. The sputtering target according to claim 1, wherein the zinc oxide sintered body includes one or more elements selected from Al, Ga, Si, B, and In. The zinc oxide sintered body is obtained by firing a cast molded body,
The cast molding is formed by casting a slurry in which raw material powder is dispersed in a mold having a bottom part of a water-absorbing material and a side wall part of a non-water-absorbing material, and depositing the raw material powder together with water absorption of the water-absorbing material. The sputtering target according to claim 1 or 2. The sputtering target according to claim 3, wherein the main surface exposed to the sputtering atmosphere is a surface that has been ground or polished so as to be perpendicular to the direction of casting during casting.

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