JP6966966B2 - Sputtering target material and its manufacturing method - Google Patents

Description

The present disclosure relates to a sputtering target material and a method for producing the same. More specifically, the present invention relates to a sputtering target containing In and Ag and a method for producing the same.

The CIGS-based solar cell is a compound semiconductor-based solar cell whose main raw material is four types of elements: copper (Cu), indium (In), gallium (Ga), and selenium (Se). Examples of the CIGS film forming method include a printing method, a simultaneous vapor deposition method, and a sputtering method.

Non-Patent Document 1 reports that high efficiency can be realized by adding Ag to the absorption layer of a CIGS solar cell. The document discloses a method of depositing an Ag precursor on an SLG / Mo substrate and then simultaneously vapor-depositing using each of Cu, In, Ga and Se as a method for forming a film.

Patent Document 1 discloses an InAg alloy material used for optical high-reflecting mirrors, brazing materials, manufacturing of silver ornaments, and ultrafine silver alloy wires for semiconductor packages. It is disclosed that the alloy material is obtained by mixing silver granules and indium granules, vacuum heating, cooling with a vacuum device, and annealing.

U.S. Patent Application Publication No. 2016/0376668

Solar Energy Materials & SolarCells 146 (2016) 114-120

As described above, examples of the film forming method include a simultaneous vapor deposition method and a sputtering method, but the vapor deposition method is excellent when the composition is changed in a small area. On the other hand, in the case of film formation over a large area, the sputtering method is superior from the viewpoint of good film thickness distribution. However, when a thin film of CIGS to which Ag is added is formed by a sputtering method, a sputtering target material containing Ag and In that can be used in the sputtering method has not yet been developed. For practical use, it is desirable to be able to sputter at a constant Ag concentration throughout the life of the target. For that purpose, a sputtering target material containing Ag and In in which Ag is uniformly distributed in the thickness direction is desired. Therefore, an object of the present disclosure is to provide a sputtering target material containing Ag and In, which can be used in a sputtering method and has a high uniformity of Ag distribution.

As a result of diligent research by the present inventor, it has been found that an InAg sputtering target material in which Ag is uniformly distributed can be obtained by performing alloying, casting, quenching and the like. Based on these findings, the invention according to the embodiment is specified as follows.

(Invention 1)
A sputtering target material containing Ag, the balance of which is In and unavoidable impurities.
Sputtering target material whose uniformity in the thickness direction of Ag is expressed by the following formula:
| BC | / A × 100 ≦ 30 (%)
here,
A: Ag content (atomic%) in the entire sputtering target material
B: Content (atomic%) of one Ag when the sputtering target material is divided into two in the thickness direction.
C: The content (atomic%) of the other Ag when the sputtering target material is divided into two in the thickness direction.
(Invention 2)
The sputtering target material of the invention 1 containing 1 to 10 atomic% of Ag.
(Invention 3)
The sputtering target material of the invention 1 or 2 having an oxygen concentration of 150 mass ppm or less.
(Invention 4)
The sputtering target material according to any one of Inventions 1 to 3, wherein the Fe concentration is 3% by mass or less.
(Invention 5)
The sputtering target material according to any one of Inventions 1 to 4, wherein AgIn _{2 is present.}
(Invention 6)
The sputtering target material according to any one of the inventions 1 to 5, further containing Cu and / or Ga.
(Invention 7)
The sputtering target material according to any one of the inventions 1 to 5.
Further provided with a backing plate or backing tube and a bonding layer,
The bonding layer is a sputtering target material containing one or more selected from In, InAg alloy, InSn alloy, InGa alloy, InBi alloy, and InZn alloy.
(Invention 8)
The method for producing a sputtering target material according to any one of the inventions 1 to 7.
The process of alloying Ag and In,
The process of casting alloyed materials and
Including
The casting step comprises cooling the mold with water.
The method.
(Invention 9)
The method according to the invention 8, further comprising a step of removing oxide slag.

In one aspect, the invention of the present disclosure is an InAg sputtering target material in which Ag is in a particular distributed state. This makes it possible to sputter a large area with a constant silver concentration from the start of sputtering to the life end.

Represents the sampling position when measuring the Ag content in the entire sputtering target material. Represents the range of sampling when measuring the Ag content in all or part of the sputtering target material. Represents the peak in XRD of each component in the sputtering target material. Each curve represents Ag10at%, Ag8at%, Ag6at%, Ag3at%, In, and AgIn ₂ in order from the top. Represents a method for manufacturing a cylindrical sputtering target material.

Hereinafter, specific embodiments for carrying out the invention of the present disclosure will be described. The following description is intended to facilitate understanding of the inventions of the present disclosure. That is, it is not intended to limit the scope of the invention of the present disclosure.

1. 1. Target material
1-1. Composition In one embodiment, the sputtering target material of the present disclosure may be a sputtering target material containing Ag and the balance being In and unavoidable impurities.

The lower limit of the Ag content may be 1 atomic% or more (more preferably 2 atomic% or more). On the other hand, the upper limit of the Ag content may be 10 atomic% or less (more preferably 8 atomic% or less). When it is 1 atomic% or more, the effect of adding Ag to the CIGS layer can be sufficiently obtained. On the other hand, even if Ag of more than 10 atomic% is blended, the effect of adding Ag to the CIGS layer does not greatly increase, and the cost of producing the target increases. Further, from the viewpoint of ensuring the uniformity of Ag distribution, it is preferably 10 atomic% or less.

In addition to Ag and In, Cu and / or Ga, which are constituents of CIGS, may be blended. Regarding the lower limit of the Cu content, for example, if it is mass ppm, it may be 30 mass ppm or more, more preferably 50 mass ppm or more. The upper limit of the Cu content may be 2000 mass ppm or less, more preferably 1000 mass ppm or less, as long as it is mass ppm. The lower limit of the Ga content may be 10 mass ppm or more, more preferably 20 mass ppm or more, as long as it is mass ppm. The upper limit of the Ga content may be 1000 mass ppm or less, more preferably 500 mass ppm or less, as long as it is mass ppm.

1-2. Impurities Generally, it is desirable that the sputtering target material has less impurities. As an example, the oxygen concentration may be 150 mass ppm or less (more preferably 120 mass ppm or less). When it is 150 mass ppm or less, the possibility of efficiency decrease due to impurities in the absorption layer can be suppressed. The lower limit of the oxygen concentration is not particularly limited, but is typically 0 mass ppm or more.
Further, as an impurity, it is preferable to suppress Fe to 5 mass ppm or less. More preferably, it is suppressed to 3% by mass or less. The lower limit is not particularly limited, but is typically 0 mass ppm or more. Fe is an element that reduces the efficiency of CIGS solar cells in particular.

1-3. Alloying In the sputtering target material according to the embodiment _{of the present disclosure, a compound of AgIn 2} may be formed. That is, at least an In phase and an AgIn ₂ phase may be formed. By _{forming the AgIn 2} phase, it is possible to realize uniform distribution of Ag in the sputtering target material. The presence of AgIn ₂ phase and the like can be confirmed by detecting the presence of a unique peak by XRD measurement.
The XRD measurement conditions may be as follows, for example.
-X-ray diffractometer: Fully automatic horizontal multipurpose X-ray diffractometer SmartLab (X-ray source: Cu line) manufactured by Rigaku Co., Ltd.
・ Goniometer: Ultima IV
・ Tube voltage: 40kV
・ Tube current: 30mA
・ Scan speed: 10 ° / min
・ Step: 0.02 °
For example, the peak peculiar to _{AgIn 2} shown in FIG. 3 can be detected by measuring with XRD.

1-4. Distribution of Ag In the sputtering target material according to the embodiment of the present disclosure, it is preferable that the uniformity of Ag in the thickness direction is high. More specifically, the uniformity can be expressed by the following equation.
| BC | / A × 100 ≦ 30 (%) (more preferably 16% or less)
here,
A: Ag content (atomic%) in the entire sputtering target material
B: Content (atomic%) of one Ag when the sputtering target material is divided into two in the thickness direction.
C: Content (atomic%) of the other Ag when the sputtering target material is divided into two in the thickness direction.

Here, the value of A is measured by taking samples from a plurality of points of the material. The location where the sample is collected is shown in FIG. 1 (hatched portion in FIG. 1). If the shape of the sputtering target material is a circular flat plate, take a sample from a place that divides the circumference into four equal parts. When the shape of the sputtering target material is a rectangular flat plate, samples are taken from four corners. When the shape of the sputtering target material is cylindrical, samples are taken from places where the circumferences of both ends are divided into four equal parts (a total of eight places). The same applies to the values of B and C.

Next, regarding the value of A, the value of B, and the value of C, how to take a sample in the thickness direction will be described with reference to FIG. The thickness of the target material is T (mm). The thickness shall be the length excluding 1 mm on the backing plate (or back tube) side. The reason for exclusion is that a bonding layer exists at the interface between the sputtering target material and the backing plate, and the components of the bonding layer (eg, In, InAg alloy, InSn alloy, InZn alloy, InBi alloy, InGa alloy, etc.) are the sputtering target. This is because it can diffuse into the wood (ie, to exclude contaminants from the brazing wood).

The value of A is measured by acquiring a sample so that the thickness of the sample is T (mm). On the other hand, the values of B and C are measured by acquiring a sample so that the thickness of the sample is T / 2 (mm).

The dimensions of the other samples are not particularly limited as long as they are collected so as to have the above-mentioned thickness. It is preferable to have an analyzable weight (for example, 1 g or more for ICP analysis, typically 10 g or less).

The lower limit of uniformity is not particularly limited, but may be typically 0% or more.

1-5. Shape, size, etc. The sputtering target material in one embodiment of the present disclosure may be, for example, a flat plate (for example, a circle, a rectangle, etc.) or a cylinder. In the case of a flat plate, the thickness may be, for example, 4 to 25 mm. The thickness referred to here is the length including the contamination portion (1 mm, FIG. 2) of the brazing material. In the case of a circular flat plate, the diameter may be φ101.6 to 460 mm. In the case of a rectangular flat plate, the long side may be 300 to 3500 mm, and the short side may be 100 to 500 mm. In the case of a cylindrical shape, the length may be L300 to 3500 mm, and the inner diameter may be I. D100 to 140 mm may be used, and the outer diameter is O.D. It may be D106 to 190 mm.

2. 2. Manufacturing Method The manufacturing method of the above-mentioned sputtering target material will be described below. The method can include at least the following steps.
-A process of alloying Ag and In.
-The process of casting alloyed materials.

In a preferred embodiment (eg, when the target material is a flat plate), the manufacturing method can further include the step of rolling the material after casting. In another preferred embodiment, a step of removing oxide slag can be further included.

Each of these steps will be described in detail below.

2-1. Alloying First, a silver shot or ingot is mixed with an indium shot or ingot. The shape of the raw material is not particularly specified, but in the case of a ribbon shape, the surface area is large, so there are many oxidized parts and a large amount of slag is generated. Therefore, it is preferable to carefully remove the slag in the casting process. .. The mixing ratio of the two may be adjusted so as to have the above-mentioned composition. The resulting mixture can be heated under an inert atmosphere or under vacuum. This forms a compound of silver and indium (eg, AgIn _{2 and the} like). As the heating conditions, 400 ° C. or higher is preferable, and 500 ° C. or higher is more preferable. On the other hand, even if the heating temperature is raised too high, the effect does not change and energy loss increases. Therefore, the temperature is preferably 700 ° C. or lower, and preferably 600 ° C. or lower. Further, the holding time is preferably 1 hour or more, more preferably 2 hours or more, and since the effect does not change even if it is made too long, it is preferably 10 hours or less, preferably 9 hours or less. Is more preferable. For example, it can be 500 ° C. for 2 hours. After alloying, the AgIn alloy ingot can be obtained by allowing it to cool under an inert atmosphere or under vacuum. By going through this step, the alloying of indium and silver can be promoted more reliably, and the composition variation due to the presence of the elemental silver phase can be prevented.

2-2. The above-mentioned ingot obtained by casting can be redissolved in the atmosphere. The temperature condition for redissolving may be + 20 ° C. to 50 ° C. (preferably + 20 ° C. to 30 ° C., for example, + 25 ° C.) rather than the melting point depending on the composition of indium and silver.

Next, the mold can be heated so that the temperature of the molten metal is within the range of ± 20 ° C. and higher than the melting point of the above composition, for example, + 5 ° C. Then, the ingot can be poured into the mold.

The mold preferably has good cooling efficiency, and for example, it is preferable to provide a cooling water channel. After pouring the ingot into the mold, it is preferable to circulate the cooling water to quench the ingot.

By quenching, the particle size of the alloy such as _{AgIn 2 can be made finer.} Further, in the case of the two-phase state of _{In and AgIn 2 , AgIn 2} may be deposited first and settled, or may be deposited on the wall surface of the mold. As a result, the concentration of Ag may be biased. However, by quenching, it is possible to prevent the precipitated _{AgIn 2 from settling.} This makes it possible to improve the uniformity of Ag in the thickness direction.

2-3. Rolling The cast AgIn material can preferably be rolled (eg, cold rolled). The rolling conditions are not particularly limited, but for example, the degree of processing may be 10 to 90% (preferably 30 to 70%).

2-4. Oxide slag removal It is preferable to remove the oxide slag after placing the molten AgIn ingot in a mold. This makes it possible to reduce the oxygen concentration in the material. When the molten metal is poured into the mold, the oxide slag floats on the molten metal because of its low density. This surfaced slag can be scooped out with a jig.

2-5. Other Impurity Control As described above, Fe is mentioned as one of the impurities. In order to reduce the amount of Fe in the sputtering target material, it is preferable to reduce the surface roughness of the mold surface and remove slag. At low temperatures (~ 300 ° C) such as in this casting process, Fe does not dissolve in In, so it is thought that the source of contamination of Fe is mainly due to the mixing of fine pieces from the surface of the casting mold. .. Therefore, it is preferable to set the surface roughness of the mold surface to, for example, Ra <4 μm. Further, as a result of the research by the present inventors, it has been found that Fe is largely distributed to the oxide slag side. By removing slag well, it is possible to suppress contamination of Fe.

2-6. Processing (grinding, cutting, etc.)
The AgIn material can be processed into a desired shape. For example, in the case of a cylindrical sputtering target material, grinding or the like may be performed on the longitudinal end portion and the outer surface portion in order to achieve the desired concentricity and thickness uniformity. For example, if it is a sputtering target material of a rectangular flat plate or a circular flat plate, the end portion may be cut so as to have a desired rectangular or circular shape. Both sides may also be ground to achieve thickness uniformity. Since AgIn is soft, it is preferable to bond it to a backing plate or a backing tube in advance and then grind it to the final size. In the case of a cylindrical target, as shown in the cross-sectional view of the mold in FIG. 4, a backing tube having an In layer or an InAg layer provided in the bonding region by plating or the like can be used as a part of the mold, and casting and bonding can be performed at the same time. Is. In this case, from the viewpoint of suppressing shrinkage cavities, it is desirable to utilize the inside of the tube as a cooling water channel and design so that solidification proceeds from the inside to the outside of the cylinder. Further, instead of providing the InAg layer as the bonding layer in advance, the In layer may be provided and the InAg layer as the bonding layer may be formed by the Ag diffused from the InAg molten metal.

3. 3. Sputtering The sputtering target material obtained by the above method enables stable sputtering. Although not limited, sputtering can be performed under the following conditions to form a thin film.
・ Spatter gas: Ar
-Sputter gas pressure: 0.4 to 0.7 Pa (example: 0.5 Pa)
-Sputter gas flow rate: 5 to 20 SCCM (example: 10 SCCM)
-Sputtering temperature: R. T. (No heating)
・ Input spatter power density: 1.0 to 3.0 W / cm ² (example: 1.5 W / cm ² )
-Substrate: Corning Eagle 2000, φ4 inch x 0.7 mmt

Ag shots and In ingots were mixed so as to have the charged Ag concentration shown in Table 1 (in some examples, Cu shots and Ga shots were further mixed). These were alloyed by heating at a temperature of 500 ° C. for 2 hours in an Ar atmosphere. Then, it was left to cool and an AgIn ingot was obtained.

Then, the ingot was redissolved at the temperature shown in Table 1 and poured into a mold heated to the temperature shown in Table 1. After that, the oxide slag was removed. Further, the cooling water was circulated in the cooling water channel provided in the mold for rapid cooling (however, in some cases, the cooling water was left to cool).

After cooling, processing such as cutting and grinding was performed so as to have the shape shown in Table 1. In some cases, rolling was carried out (cold rolling, work rate 60%).

The obtained target material was partially cut by the method described above, and a sample for measuring the Ag concentration of the entire material was taken (Sample A). Further, the cut piece was divided into two at the position of 1/2 in the thickness direction, and the samples divided into two in the thickness direction were collected (samples B and C). Then, the compositions of Ag, Cu, Ga, and Fe were analyzed for these materials by using ICP analysis. Specifically, the collected material was dissolved with an acid or the like and analyzed using an ICP emission spectroscopic analyzer (SPS3100HV manufactured by Hitachi High-Tech Science Co., Ltd.). O was measured using an infrared absorption method (TC600 manufactured by LECO) after heating and gasifying the cut pieces of the target.

Next, the obtained sputtering target member was bonded to a copper backing plate or backing tube, and sputtering was performed under the following conditions.

・ Spatter gas: Ar
・ Spatter gas pressure: 0.5Pa
・ Spatter gas flow rate: 25SCCM
-Sputtering temperature: R. T. (No heating)
・ Input spatter power density: 1.5 W / cm ²
-Substrate: Corning Eagle 2000, φ4 inch x 0.7 mmt

In both cases, DC sputtering was possible.

The results are shown in Table 1. The surface to be sputtering was set to the upper side, and the surface on the opposite side (the surface in contact with the backing plate or backing tube) was set to the lower side.

In Examples 1 to 10, Ag was uniformly distributed in the thickness direction. On the other hand, in Comparative Examples 1 and 2, since the cooling was performed by leaving it to stand, the deviation of the Ag concentration in the thickness direction became large. Further, in Comparative Examples 3 to 4, since the Ag concentration was too large, the bias of the Ag distribution became large.

In the present specification, the description of "or" or "or" includes the case where only one of the options is satisfied, the case where some options are satisfied, or the case where all the options are satisfied. For example, in the case of the description of "A, B or C" and "A, B or C", there are cases where only A is satisfied, only B is satisfied, only C is satisfied, and only A and B are satisfied. , B and C only, A and C only, A to C all satisfied, and the like are intended to be included.

The specific embodiments of the present disclosure have been described above. The embodiment is merely a specific example, and the invention of the present disclosure is not limited to the embodiment. For example, the technical features disclosed in one of the above embodiments can be provided in another embodiment. Further, for a specific method, it is possible to replace some steps with the order of other steps, and an additional step may be added between the two specific steps. The scope of the invention of the present disclosure is defined by the claims.

Claims (7)

A sputtering target material containing 1 to 10 atomic% of Ag, the balance of which is In and unavoidable impurities.
Oxygen concentration is 150 mass ppm or less,
Sputtering target material whose uniformity in the thickness direction of Ag is expressed by the following formula:
| BC | / A × 100 ≦ 30 (%)
here,
A: Ag content (atomic%) in the entire sputtering target material
B: Content (atomic%) of one Ag when the sputtering target material is divided into two in the thickness direction.
C: The content (atomic%) of the other Ag when the sputtering target material is divided into two in the thickness direction. A sputtering target material containing 1 to 10 atomic% of Ag, further containing Cu and / or Ga, and the balance consisting of In and unavoidable impurities.
Oxygen concentration is 150 mass ppm or less,
Sputtering target material whose uniformity in the thickness direction of Ag is expressed by the following formula:
| BC | / A × 100 ≦ 30 (%)
here,
A: Ag content (atomic%) in the entire sputtering target material
B: Content (atomic%) of one Ag when the sputtering target material is divided into two in the thickness direction.
C: The content (atomic%) of the other Ag when the sputtering target material is divided into two in the thickness direction. The sputtering target material according to claim 1 or 2 , wherein the Fe concentration is 3% by mass or less. The sputtering target material according to any one of claims 1 to 3 , wherein AgIn _{2 is present.} The sputtering target material according to any one of claims 1 to 4.
Further provided with a backing plate or backing tube and a bonding layer,
The bonding layer is a sputtering target material containing one or more selected from In, InAg alloy, InSn alloy, InGa alloy, InBi alloy, and InZn alloy. The method for manufacturing a sputtering target material according to any one of claims 1 to 5.
The process of alloying Ag and In,
The process of casting alloyed materials and
Including
The casting step comprises cooling the mold with water.
The method. The method according to claim 6 , further comprising a step of removing oxide slag.

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