JP2017150089A - Sputtering target and production method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve yield of a production process by reducing generation of arcing during the production process.SOLUTION: In a sputtering target including a plurality of target members bonded to a substrate, the plurality of target members have a circular surface facing to each adjacent target member at an interval of 0.1 mm or more and 1.0 mm or less, when being bonded to the substrate, and a surface roughness (Ra) of the circular surface is 2.0 μm or more and 8.0 μm or less. The plurality of target members may have a hollow cylindrical shape.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a sputtering target and a manufacturing method thereof. In particular, it relates to the surface roughness of the sintered body constituting the target member.

  In recent years, a sputtering apparatus using a cylindrical sputtering target has been developed as a sputtering apparatus for forming a metal thin film or a metal oxide thin film on a large glass substrate. The cylindrical sputtering target refers to a sputtering target obtained by processing a sintered body made of a target material into a hollow cylindrical shape and joining it to a substrate called a backing plate or a backing tube.

  Such a cylindrical sputtering target has advantages in that the use efficiency of the target is high, the generation of erosion is small, and the generation of particles due to the peeling of the deposit is small compared to the flat plate type sputtering target. In particular, the advantage of low generation of particles is very advantageous in reducing the occurrence of arcing due to redeposition of particles on the target.

  For example, when manufacturing a cylindrical sputtering target for depositing ITO (indium tin oxide), a sintered body (ceramics) obtained by mixing and sintering indium oxide powder and tin oxide powder is hollow. It is processed into a cylindrical shape and bonded to a cylindrical substrate (backing tube).

  However, it is difficult to manufacture a target member made of ceramics in a long shape. Therefore, in order to increase the length (enlarge the area) of the cylindrical sputtering target, a plurality of cylindrical sintered bodies are formed, and these are continuously aligned and bonded to the base material, thereby forming a long cylindrical shape. A technique for realizing a type sputtering target has been developed (Patent Document 1).

  When a plurality of target members are arranged with no gap with respect to the base material, the target members may expand and contract due to heat during sputtering, and the target members may collide with each other, which may cause cracking or chipping. Therefore, in general, when joining a plurality of target members to a base material, it is carried out with a certain interval between the target members.

JP 7-228967 A

  However, as a result of intensive studies by the present inventors, when a gap is provided between the target members, redeposition of a thin film by sputtering in the gap (the sputtered target component does not reach the substrate and is re-applied to the target member). It has been found that when a certain phenomenon occurs, it may enter a plasma in which discharge is performed in a stable state. As a result, it was found that the potential balance in the plasma was disrupted and local charge concentration occurred, leading to accidental arcing.

  The subject of this invention is providing the sputtering target which can suppress generation | occurrence | production of the arcing in sputtering mentioned above and can improve the yield of the device manufacturing process using a sputtering process.

  A sputtering target according to an embodiment of the present invention includes a plurality of target members bonded to a base material, and the plurality of target members have a predetermined distance from each adjacent target member when bonded to the base material. It has a circular surface which is placed opposite to each other, and the surface roughness (Ra) in the circular surface is 2.0 μm or more and 8.0 μm or less.

  A sputtering target manufacturing method according to an embodiment of the present invention includes a plurality of target members bonded to a base material, and the surface roughness (Ra) of the circular surfaces of the plurality of target members is 2.0 μm or more and 8.0 μm. The plurality of target members are bonded to the base material so that the circular surfaces face each other with a predetermined distance from the adjacent target members.

  The target member may be made of ITO (Indium-Tin-Oxide), IZO (Indium-Zinc-Oxide), or IGZO (Indium-Gallium-Zinc-Oxide).

  The surface roughness (Ra) is measured according to ANSI standards using a non-contact type surface roughness measuring machine. The surface roughness is measured at each of the end surfaces of the target member at six locations at 60 ° intervals (12 locations per target member), and the weighted average value of all measured values is defined as the surface roughness of the target member.

It is a perspective view which shows the structure of the sputtering target which concerns on one Embodiment of this invention. It is sectional drawing which shows the structure of the sputtering target which concerns on one Embodiment of this invention. It is sectional drawing which shows the gap vicinity between the target members in the sputtering target which concerns on one Embodiment of this invention. It is a process flow figure showing a manufacturing method of a sputtering target concerning one embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention can be implemented in various modes without departing from the gist thereof, and is not construed as being limited to the description of the embodiments exemplified below.

  Further, in order to make the explanation clearer, the drawings may be schematically represented with respect to the width, thickness, shape, and the like of each part as compared with the actual embodiment, but are merely examples, and the interpretation of the present invention. It is not intended to limit. In addition, in the present specification and each drawing, elements having the same functions as those described with reference to the previous drawings may be denoted by the same reference numerals and redundant description may be omitted.

<Configuration of sputtering target>
FIG. 1 is a perspective view showing a configuration of a sputtering target according to an embodiment of the present invention. Moreover, FIG. 2 is sectional drawing which shows the structure of the sputtering target which concerns on one Embodiment of this invention.

  In this embodiment, a cylindrical sputtering target is illustrated. The cylindrical sputtering target 100 according to this embodiment includes a base material 101 and a plurality of target members 102a and 102b. The target members 102a and 102b are bonded to the base material 101 via the bonding material 103, respectively. At this time, the bonding material 103 is provided so as to fill a gap provided between the base material 101 and the target members 102a and 102b.

  The sputtering target 100 according to the present embodiment is characterized by a sintered body constituting the plurality of target members 102a and 102b. Specifically, each of the target members 102a and 102b has a circular surface 104 facing the adjacent target member at a predetermined interval, and the surface roughness Ra of the circular surface 104 is 2.0 μm or more. This point will be described later.

  The plurality of target members 102 a and 102 b are provided so as to surround the outer peripheral surface of the base material 101. The plurality of target members 102 a and 102 b are preferably provided coaxially or substantially coaxially with the central axis of the substrate 101. With such a configuration, when the cylindrical sputtering target 100 is mounted on the sputtering apparatus and rotated around the base material 101, the distance between each target member 102a, 102b and the film formation surface (sample substrate) is constant. Can be kept in.

  In the cylindrical sputtering target 100, when the plurality of cylindrical sputtering target members 102a and 102b are mounted on the substrate 101, the target members 102a and 102b are arranged at predetermined intervals. The gap may be 1 mm or less, for example, 0.1 to 0.5 mm. As described above, by disposing the plurality of target members 102a and 102b at a predetermined interval, it is possible to prevent damage due to collision between the target members.

  The cylindrical sputtering target 100 of this embodiment can be made into a long-sized sputtering target having a length of 100 mm or more by bonding a plurality of target members 102 to the base material 101 by the bonding material 103.

<Base material>
It is preferable that the base material 101 has an outer surface shape along the inner surface of the target members 102a and 102b having a hollow cylindrical shape. As described above, the outer diameter of the base material 101 is slightly smaller than the inner diameters of the target members 102a and 102b, and is adjusted so that a gap is formed when the two are stacked coaxially. A bonding material 103 is provided in the gap.

  Each target member 102a, 102b is heated by the ion irradiation at the time of film-forming by sputtering, and temperature rises. In order to suppress the temperature rise of each target member 102a, 102b at the time of film formation by sputtering, it is preferable to make the base material 101 function as a coolant (heat sink) for each target member 102a, 102b. For example, it is possible to configure the base material 101 to have a hollow structure so that the coolant flows through the base material 101. Therefore, it is preferable to use a material having good conductivity and thermal conductivity as the substrate 101.

  At the same time, the base material 101 is preferably a metal that has good wettability with the bonding material 103 and can provide high bonding strength. From the above, it is preferable to use, for example, copper (Cu) or titanium (Ti), or a copper alloy, titanium alloy, or stainless steel (SUS) as a material constituting the substrate 101. As the copper alloy, an alloy mainly composed of copper (Cu) such as chromium copper can be applied. Further, if titanium (Ti) is used as the base material 101, a light and rigid base material can be obtained.

  The substrate 101 is not only formed of a single metal or a metal alloy, but may be one in which a coating of another metal is provided on the surface of the metal substrate. For example, a metal film containing titanium (Ti), copper (Cu), silver (Ag), nickel (Ni), or the like may be formed.

  The cylindrical sputtering target 100 does not irradiate ions on the entire surface of the target members 102a and 102b at the time of sputtering, but rotates while irradiating ions only on a part of the surfaces. There will be a temperature difference between the irradiated surface and its back surface. However, since the base material 101 has a cooling function, an increase in the temperature of the target members 102a and 102b can be suppressed, and the influence of thermal distortion due to the above-described temperature difference can also be suppressed.

  The base material 101 may be roughened on the surface side in contact with the bonding material 103. By roughening the surface of the base material 101, the surface area in contact with the bonding material 103 can be increased. For example, the surface of the substrate 101 may be roughened by sandblasting or the like, and the surface roughness (Ra) may have a value of 1.8 μm or more.

<Bonding material>
The bonding material 103 is provided between the base material 101 and the target members 102a and 102b. The bonding material 103 preferably bonds the base material 101 and the target members 102a and 102b and has good heat resistance and thermal conductivity. Further, since it is placed under vacuum during sputtering, it is preferable that it has a characteristic that gas emission is small in vacuum.

  Furthermore, from the viewpoint of manufacturing, it is preferable that the bonding material 103 has fluidity when the base material 101 and the target members 102a and 102b are bonded. In order to satisfy these characteristics, a low melting point metal material having a melting point of 300 ° C. or lower can be used as the bonding material 103. For example, as the bonding material 103, a metal such as indium or tin, or a metal alloy material containing any one of these elements may be used. Specifically, indium or tin alone, an alloy of indium and tin, a solder alloy containing tin as a main component, or the like may be used.

<Target member>
As shown in FIGS. 1 and 2, each target member 102a, 102b is formed into a hollow cylindrical shape. Each target member 102a, 102b has a thickness of at least several millimeters to several tens of millimeters, and the entire thickness portion can be used as a target member.

  When the target members 102 a and 102 b are attached to the base material 101, the base material 101 is inserted into the hollow portions of the target members 102 a and 102 b, and then both are joined by the joining material 103. That is, the outer diameter of the base material 101 is smaller than the inner diameter (the diameter of the hollow portion) of each of the target members 102a and 102b, both are arranged at a predetermined interval, and the bonding material 103 is filled so as to fill this gap. Is provided. In order to stably hold the target members 102a and 102b and the base material 101, the bonding material 103 is provided with no gap in the gap.

  Each of the target members 102 a and 102 b has a cylindrical outer surface as a target surface, and a cylindrical inner surface that faces the base material 101 and comes into contact with the bonding material 103. For this reason, at the time of manufacture, the outer surface of each target member 102a, 102b may be formed into a smooth surface, and the inner surface of the cylinder may be roughened to enhance the adhesion.

  Each target member 102a, 102b is formed using various materials that can be formed by sputtering. For example, the target members 102a and 102b may be ceramics. As the ceramic, a metal oxide, a metal nitride, a sintered body of metal oxynitride, or the like can be used. As the metal oxide, an oxide of a metal belonging to a typical element such as indium oxide, tin oxide, zinc oxide, or gallium oxide can be used.

  Specifically, a compound of tin oxide and indium oxide (Indium Tin Oxide: ITO), zinc oxide (Zinc Oxide: ZnO), a compound of indium oxide and zinc oxide (Indium Zinc Oxide: IZO), indium oxide, zinc oxide, and A sintered body of a compound selected from a compound of gallium oxide (Indium Gallium Zinc Oxide: IGZO) can be used as the target members 102a and 102b.

  In addition, said specific example is an example and the sputtering target which concerns on this embodiment can use various sputtering materials as a target member.

  Here, a gap of a predetermined interval (preferably 1 mm or less, for example, 0.1 to 0.5 mm) is provided between the target member 102a and the target member 102b. This gap is a safety measure for preventing the target members from colliding with each other, and as described above, the present inventors have found that the thin film re-deposited in this gap leads to the occurrence of arcing. .

  Accordingly, as a result of intensive studies, the present inventors have determined that the surface roughness of the surface where the target member 102a and the target member 102b face each other (that is, the circular surface 104 shown in FIGS. 1 and 2) is 2.0 μm or more. It was found that the occurrence of arcing can be suppressed by adjusting the thickness to 8.0 μm or less. That is, in the sputtering target 100 according to the present embodiment, the surface roughness of the surface where the target member 102a and the target member 102b face each other is set to 2.0 μm or more and 8.0 μm or less.

  FIG. 3 is a cross-sectional view showing the vicinity of a gap between adjacent target members. Specifically, in FIG. 2, a schematic diagram in which the inside of the frame indicated by reference numeral 105 is enlarged is shown. As shown in FIG. 3, a gap of 0.2 to 0.5 mm is provided between the target member 102a and the target member 102b, and the surface 104 on which each target member faces is intentionally rough. It is processed to become. That is, each of the target members 102a and 102b has a circular surface 104 facing the adjacent target member at a predetermined interval when bonded to the base material 101, and the surface roughness (Ra ) Is 2.0 μm or more and 8.0 μm or less.

  According to the study by the present inventors, the occurrence of arcing was confirmed when the surface roughness (Ra) of the circular surface 104 of each target member 102a, 102b was less than 2.0 μm, but when it became 2.0 μm or more. It was not confirmed. Further, when the surface roughness (Ra) exceeded 8.0 μm, the occurrence of arcing was confirmed again, and cracks in the target member were also confirmed.

  The reason that the occurrence of arcing is suppressed when the surface roughness (Ra) is 2.0 μm or more is that the surface becomes rough, the surface area of the circular surface 104 increases, and the adhesion of the redeposited film increases. This is considered to be due to the reduction of abnormal plasma discharge caused by peeling of the deposited film.

  Conversely, when the surface roughness (Ra) exceeds 8.0 μm, the reason for the occurrence of arcing and cracking is that the damage that occurs during grinding to make the surface roughness 8.0 μm or more is affected. It is thought that there is. In other words, in order to achieve a surface roughness of 8.0 μm or more, it is necessary to intentionally roughen the surface by grinding with a coarse count stone or by applying abrasive blasting (bead blasting) with a strong pressure. As a result, it is considered that processing damage (fine cracks or the like) remains at the end of the target member, and that damage extends and leads to cracking.

  As described above, the sputtering target 100 according to this embodiment has an arcing during sputtering by setting the surface roughness (Ra) of the circular surface 104 of each target member 102a, 102b to 2.0 μm or more and 8.0 μm or less. Can be suppressed. As a result, it is possible to improve the yield of the device manufacturing process using the sputtering process.

<Manufacturing method of sputtering target>
Next, the manufacturing method of the sputtering target 100 according to the present embodiment will be described in detail. FIG. 4 is a process flow diagram showing a method for manufacturing the sputtering target 100 according to an embodiment of the present invention.

  In the present embodiment, an example in which indium tin oxide (ITO) sintered bodies are used as the target members 102a and 102b is shown, but the material of the sintered body is not limited to ITO, and IZO, IGZO or other metal oxide compounds are used. You can also.

  First, raw materials constituting the target members 102a and 102b are prepared. In this embodiment, an indium oxide powder and a tin oxide powder are prepared (S401, S402). The purity of these raw materials is usually 2N (99% by mass) or more, preferably 3N (99.9% by mass) or more, more preferably 4N (99.99% by mass) or more. If the purity is lower than 2N, the target members 102a and 102b contain a large amount of impurities, so that desired physical properties cannot be obtained (for example, the transmittance of the formed thin film is increased, the resistance value is increased, the particle size associated with arcing is reduced). Problem).

  Next, these raw material powders are pulverized and mixed (S403). The raw material powder is pulverized and mixed using a dry method using balls and beads (so-called media) of zirconia, alumina, nylon resin, etc., media agitating mills using the balls and beads, and medialess containers Wet methods such as a rotary mill, a mechanical stirring mill, and an airflow mill can be used. Here, since the wet method is generally superior in pulverization and mixing ability compared to the dry method, it is preferable to perform the mixing using the wet method.

  Although there is no restriction | limiting in particular about the composition of a raw material, It is desirable to adjust suitably according to the composition ratio of target target member 102a, 102b. When it is desired to reduce the crystal grain size of the raw material powder, the raw material powders may be pulverized before mixing, or may be simultaneously pulverized by the powder processing during mixing.

  In addition, when the powder of a fine particle diameter is used, the densification of the sintered compact used as the target members 102a and 102b can be achieved. Although it is possible to obtain a fine powder by strengthening the pulverization conditions, the amount of media (zirconia, etc.) used during pulverization also increases, and the impurity concentration in the target members 102a and 102b may increase. is there. Thus, it is necessary to optimize the pulverization conditions while observing the balance between the high density of the sintered body and the impurity concentration in the target members 102a and 102b.

  Next, the raw material powder slurry is dried and granulated (S404). At this time, the slurry may be rapidly dried using rapid drying granulation. The rapid drying granulation may be performed by using a spray dryer and adjusting the temperature and air volume of hot air. By using quick drying granulation, it is possible to suppress separation of the indium oxide powder and the tin oxide powder due to the difference in sedimentation speed due to the difference in specific gravity of the raw material powder. By granulating in this way, the ratio of the blending components is made uniform, and the handling property of the raw material powder is improved. Moreover, you may perform temporary baking before and after granulation.

  Next, the mixture obtained by mixing and granulating as described above (or pre-baked when pre-baked is provided) is pressure-formed to form a cylindrical shaped body (S405). Through this step, the target member 102a or 102b is formed into a suitable shape. Examples of the molding process include mold molding, cast molding, injection molding, and the like. In order to obtain a complicated shape such as a cylindrical mold, cold isostatic pressing (CIP) is used. It is preferable to form by, for example.

  In molding by CIP, first, a rubber mold is filled with raw materials weighed to a predetermined weight. At this time, by filling the rubber mold while swinging or tapping, filling irregularities and voids of the raw material in the rubber mold can be eliminated. What is necessary is just to set suitably the pressure of shaping | molding by CIP with the density required for target member 102a, 102b.

Next, the cylindrical molded body obtained in the molding process is sintered (S406). An electric furnace is used for sintering. The sintering conditions can be appropriately selected depending on the composition of the sintered body. For example, SnO ₂ is 10 wt. % ITO can be sintered by placing it in an oxygen gas atmosphere at a temperature of 1500 to 1600 ° C. for 10 to 26 hours. When the sintering temperature is less than 1500 ° C., the density of the target members 102a and 102b is reduced. On the other hand, when the temperature exceeds 1600 ° C., the electric furnace and the furnace material are greatly damaged and frequent maintenance is required, so that the work efficiency is remarkably lowered. Further, if the sintering time is less than 10 hours, the density of the target is lowered, and if it is longer than 26 hours, the tact time is increased and the production cost is increased. Further, the pressure during sintering may be atmospheric pressure, or a reduced pressure or pressurized atmosphere.

  Here, when sintering by an electric furnace, generation | occurrence | production of a crack can be suppressed by adjusting the temperature increase rate and temperature decrease rate of sintering. Specifically, the temperature rising rate of the electric furnace during sintering is preferably 300 ° C./hour or less, more preferably 180 ° C./hour or less. Moreover, the temperature lowering rate of the electric furnace during sintering is preferably 5 ° C./hour or less. Note that the rate of temperature increase or the rate of temperature decrease may be adjusted to change stepwise.

  Cylindrical compacts shrink due to sintering, but before entering the temperature range where heat shrinkage is common to all materials, the temperature inside the furnace is kept constant in order to keep the temperature inside the furnace uniform. . Thereby, the temperature unevenness in the furnace is eliminated, and all the sintered bodies installed in the furnace contract uniformly. In addition, it is possible to obtain a homogeneous sintered body by setting appropriate conditions for the ultimate temperature and holding time for each material.

  Next, the formed cylindrical sintered body is machined into a desired cylindrical shape using a machining machine such as a surface grinding machine, a cylindrical grinding machine, a lathe, a cutting machine, or a machining center (S407). . The machining performed here is a step of processing a cylindrical sintered body to have a desired shape and surface roughness, and finally, the target members 102a and 102b are formed through this step.

  Regarding the outer surfaces (surfaces to be sputtered) of the target members 102a and 102b, the surface roughness (Ra) is preferably 0.5 μm or less. Thereby, an electric field concentrates with respect to a projection part during sputtering, and the risk that abnormal discharge will occur can be reduced.

  Further, in the present embodiment, the circular surface 104 of the target members 102a and 102b is subjected to grinding using a grindstone or processing using bead blasting, so that the surface roughness (Ra ) Between 2.0 μm and 8.0 μm. For example, it is possible to keep the surface roughness within the range of 2.0 μm or more and 8.0 μm by grinding with a coarse grindstone such as # 40 or # 20 or by bead blasting. .

  Next, the machined cylindrical sintered body (that is, the target members 102a and 102b) is bonded to the substrate 101 (S408). In particular, in the case of the cylindrical sputtering target 100, the target members 102a and 102b are bonded to a cylindrical base material 101 called a backing tube using the bonding material 103 as an adhesive, as shown in FIGS. The cylindrical sputtering target 100 according to this embodiment can be obtained through the above steps.

[Example]
The inventors prepared target members using three different materials (ITO, IZO, and IGZO), and investigated the relationship between the surface roughness and the occurrence of arcing and cracking for each. The results are shown in Tables 1-3. Each experimental condition was as follows: target thickness: 9 mm, sputtering pressure: 0.6 Pa, Ar (argon) flow rate: 300 sccm, input power: 4 kW / m, sputtering time: 24 hours. Moreover, since it was target durability evaluation at the time of performing continuous discharge, discharge was performed without setting the substrate or the like. The surface roughness (Ra) was measured according to ANSI standards using a small surface roughness measuring machine (Surf Test SJ-301: manufactured by Mitutoyo Corporation). The surface roughness was measured at six locations on the end surface of the target member at 60 ° intervals (12 locations per target member), and the weighted average value of all measured values was the surface roughness of the target member.

  As described above, according to the experiment by the present invention, the surface roughness (Ra) of the circular surface of each target member in the plurality of target members constituting the cylindrical sputtering target is 2.0 μm or more and 8.0 μm or less. By doing this, it was found that cracking of the target can be suppressed while reducing the occurrence of arcing during sputtering.

  The embodiments described above as the embodiments of the present invention can be implemented in appropriate combination as long as they do not contradict each other. Also, those in which those skilled in the art appropriately added, deleted, or changed the design based on the display device of each embodiment, or those in which the process was added, omitted, or changed in conditions are also included in the present invention. As long as the gist is provided, it is included in the scope of the present invention.

  In addition, even for other operational effects different from the operational effects brought about by the aspects of the above-described embodiments, those that are apparent from the description of the present specification, or that can be easily predicted by those skilled in the art, Of course, it is understood that the present invention provides.

DESCRIPTION OF SYMBOLS 100: Cylindrical type sputtering target 101: Base material 102a, 102b: Target member 103: Joining material 104: Circular surface 105: Frame line S401: The process of preparing an indium oxide powder S402: The process of preparing a tin oxide powder S403: Raw material Step of crushing and mixing powder S404: Step of drying and granulating raw material powder slurry S405: Step of forming cylindrical shaped body S406: Step of sintering cylindrical shaped body S407: Desired cylindrical shape Step S408: Step of bonding cylindrical sintered body to base material

Claims (10)

Including a plurality of target members bonded to a substrate;
The plurality of target members have circular surfaces that face each other with an interval of 0.1 mm or more and 1.0 mm or less when adjacent to the target member when bonded to the base material,
The sputtering target, wherein the surface roughness (Ra) on the circular surface is 2.0 μm or more and 8.0 μm or less.   The sputtering target according to claim 1, wherein the plurality of target members have a hollow cylindrical shape.   The sputtering target according to claim 1, wherein the plurality of target members are made of ITO (Indium-Tin-Oxide).   The sputtering target according to claim 1, wherein the plurality of target members are made of IZO (Indium-Zinc-Oxide).   The sputtering target according to claim 1, wherein the plurality of target members are made of IGZO (Indium-Gallium-Zinc-Oxide). Polishing the circular surfaces of the plurality of target members so that the surface roughness (Ra) is 2.0 μm or more and 8.0 μm or less,
A method of manufacturing a sputtering target, comprising bonding the plurality of target members to the base material so that the circular surfaces face each other with a distance of 0.1 mm to 1.0 mm between adjacent target members. .   The method of manufacturing a sputtering target according to claim 6, wherein the plurality of target members have a hollow cylindrical shape.   The method for manufacturing a sputtering target according to claim 6, wherein the plurality of target members are made of ITO (Indium-Tin-Oxide).   The method of manufacturing a sputtering target according to claim 6, wherein the plurality of target members are made of IZO (Indium-Zinc-Oxide).   The method of manufacturing a sputtering target according to claim 6, wherein the plurality of target members are made of IGZO (Indium-Gallium-Zinc-Oxide).

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