JP6906085B2 - Sputtering target member and its manufacturing method - Google Patents

Description

The present invention relates to a Ga-Sn-O based sputtering target member and a method for manufacturing the same.

Conventionally, silicon-based materials such as polycrystalline silicon films and amorphous silicon films have been used as semiconductor layers used for channel layers of thin film transistors (TFTs). However, since the silicon-based material absorbs in the visible light region, there is a problem that the thin film transistor malfunctions due to the generation of carriers due to light incident. As a preventive measure, a light blocking layer made of metal or the like is provided, but there is a problem that the aperture ratio is reduced. Further, in order to maintain the screen brightness, it is necessary to increase the brightness of the backlight, which has a drawback such as an increase in power consumption.

Therefore, in recent years, thin film transistors using transparent oxide semiconductors instead of silicon-based materials have been developed. A typical example thereof is an In-Ga-Zn-O-based (IGZO) material (Patent Document 1). However, since IGZO is a multi-component system, it is difficult to optimize the properties and states of each raw material powder, the composition of the components, and the sintering conditions. For this reason, the properties of IGZO are liable to fluctuate, and there is a problem that nodules and abnormal discharge occur during sputtering. In addition, IGZO is a factor that raises the cost because it contains rare metals, and there is a risk that supply will be insufficient in the future.

Against this background, Ga—Sn—O-based (GTO) oxide targets with few constituent elements have been studied (Patent Documents 2 to 3).

International Publication No. 2005/088726 International Publication No. 2010/018707 Japanese Unexamined Patent Publication No. 2013-40394

However, in the oxide sintered body described in Patent Document 2, in order to increase the strength of the sintered body and reduce the bulk resistance, in addition to the gallium succinate compound phase and the tin oxide phase, zinc and aluminum are further added. , Silicon, indium, germanium, titanium, niobium, tantalum, tungsten, molybdenum and at least one element selected from antimony is required to be dispersed. Further, in Patent Document 2, it is shown that when only gallium oxide and tin oxide are used as raw materials, the bulk resistance becomes unmeasurable when the gallium oxide concentration is high (Comparative Examples 1, 4, and 3. 6 and 7).

Further, although Patent Document 3 describes an oxide sintered body target for sputtering composed of gallium (Ga), tin (Sn), oxygen (O) and unavoidable impurities, the concentration of _{Ga 2} O _{3 is high.} The requirement is that it is 20 mol% or less. Patent Document 3 shows that when _{the concentration of Ga 2} O ₃ is 30 mol%, the bulk resistivity becomes unmeasurable (Comparative Examples 4 and 5).

As described above, in the Ga—Sn—O-based sputtering target member containing a high concentration of Ga, a material having a low bulk resistivity suitable for DC sputtering has not been obtained. The present invention has been created in view of the above circumstances, and in one embodiment, the bulk resistivity (the same as "volume resistivity"" is used in a Ga-Sn-O-based sputtering target member containing a high concentration of Ga. ) Is one of the issues to be provided as an effective means for lowering.

When the crystal structure of the Ga—Sn—O based sputtering target member containing a high concentration of Ga was analyzed by powder XRD, the present inventor analyzed the crystal structure of the Ga—Sn—O based sputtering target member. It was found that the amount of tin produced was extremely small. As a result of diligent studies based on this finding, when the ratio of the composite oxide phase of Ga and Sn is lowered and the ratio of the tin oxide phase is increased in the Ga—Sn—O-based sputtering target member, the overall composition is increased. It was found that the volume resistivity was significantly reduced even when the values were the same.

The present invention has been completed based on the above findings, and is exemplified below.
[1]
It contains Ga, Sn and O, the balance is composed of unavoidable impurities, the atomic ratio of Ga and Sn satisfies 0.33 ≦ Ga / (Ga + Sn) ≦ 0.75, and the total peak area in powder X-ray diffraction measurement. A _{sputtering target member having a SnO 2-} phase peak area I _Sn ratio (I _Sn / I) to I of 0.02 or more.
[2]
The sputtering target member according to [1], wherein the ratio (I _Sn / I) of the peak area I _{Sn of the SnO 2} phase to the total peak area I in the powder X-ray diffraction measurement is 0.1 or more.
[3]
The sputtering target member according to [1] or [2], _wherein the ratio (I _GaSn / I) of the peak area I _{GaSn of the Ga 4} SnO _8- phase to the total peak area I in the powder X-ray diffraction measurement is 0.3 or less.
[4]
The sputtering target member according to [3], _wherein the ratio (I _GaSn / I) of the peak area I _{GaSn of the Ga 4} SnO ₈ phase to the total peak area I in the powder X-ray diffraction measurement is 0.25 or less.
[5]
The sputtering target member according to any one of [1] to [4], which has a volume resistivity of 50,000 Ω · cm or less.
[6]
The sputtering target member according to any one of [1] to [5], which has a relative density of 94% or more.
[7]
Ga ₂ O ₃ powder the powder mixture such that a 20 mol% or more 60 mol% or less of the molar concentration, a step 1 of preparing a mixed powder by mixing and milling the Ga ₂ O ₃ powder and SnO ₂ powder,
Step 2 of sintering the mixed powder in an oxygen-containing atmosphere at a heating temperature of 1500 ° C. or higher for 10 hours or longer to obtain a sintered body containing a Ga—Sn—O composite oxide phase.
Sinter under a nitrogen-containing atmosphere, and annealed for 10 hours or more at a heating temperature of 1000 ° C. to 1400 ° C. to decompose the Ga-SnO composite oxide phase, step 3 to produce a SnO ₂ phase,
The method for manufacturing a sputtering target member according to any one of [1] to [6], which comprises.
[8]
The method for manufacturing a sputtering target member according to [7], wherein step 2 and step 3 are continuously performed by lowering the heating temperature in step 2 to the heating temperature in step 3.
[9]
The method for manufacturing a sputtering target member according to [7] or [8], wherein step 3 is annealed at a heating temperature of 1200 ° C. to 1400 ° C.
[10]
A film forming method comprising sputtering the sputtering target member according to any one of [1] to [6].

According to one embodiment of the present invention, it is possible to obtain a Ga—Sn—O-based sputtering target member having a low volume resistivity despite a high gallium concentration. Further, according to one embodiment of the present invention, it is possible to provide a Ga-Sn-O based sputtering target having a high gallium concentration suitable for DC sputtering.

(1. Composition)
In one embodiment, the sputtering target member according to the present invention contains Ga, Sn and O, and the balance is composed of unavoidable impurities. Inevitable impurities are those that are generally present in the raw materials of metal products or are inevitably mixed in the manufacturing process, and are originally unnecessary, but they are in trace amounts and affect the characteristics of metal products. It is an acceptable impurity because it does not reach. In the sputtering target member according to the present invention, the total amount of unavoidable impurities is generally 5000 mass ppm or less, typically 3000 mass ppm or less, and more typically 2000 mass ppm or less.

In one embodiment, the sputtering target member according to the present invention satisfies the atomic ratio of Ga and Sn of 0.33 ≦ Ga / (Ga + Sn) ≦ 0.75. The reason why 0.33 ≦ Ga / (Ga + Sn) is set is that, in one embodiment, it is an object of the present invention to provide a Ga—Sn—O-based sputtering target member containing a high concentration of Ga. It is possible to set 0.4 ≦ Ga / (Ga + Sn), and it is also possible to set 0.5 ≦ Ga / (Ga + Sn). Further, the reason why Ga / (Ga + Sn) ≦ 0.75 is set is that it is easy to obtain a sputtering target having a low volume resistivity. From the viewpoint of lowering the volume resistivity, Ga / (Ga + Sn) ≦ 0.7 is preferable, and Ga / (Ga + Sn) ≦ 0.5 is more preferable.

In one embodiment of the sputtering target member according to the present invention, Ga and Sn can exist in the form of oxides. Oxides include gallium oxide (Ga ₂ O ₃ ), tin oxide (SnO ₂ ), and composite oxides of Ga and Sn (eg, Ga ₄ SnO ₈ , Ga ₄ Sn ₅ O ₁₆ and Ga ₃ Sn ₄ O). ₁₂ ) is illustrated.

(2. XRD measurement)
In order to effectively reduce the volume resistivity of the sputtering target member, the ratio (I _Sn / I) of the peak area I _{Sn of the SnO 2} phase to the total peak area I in the powder X-ray diffraction measurement is 0.02 or more. It is preferably 0.05 or more, more preferably 0.10 or more, even more preferably 0.15 or more, and even more preferably 0.20 or more. .. The upper limit of I _Sn / I is not particularly set, but is generally 0.40 or less, and typically 0.30 or less.

In order to effectively reduce the volume resistivity of the sputtering target member, the ratio (I _GaSn / I) of the peak area I _{GaSn of the Ga 4} SnO ₈ phase to the total peak area I in the powder X-ray diffraction measurement is 0.30 or less. It is preferably 0.25 or less, and even more preferably 0.20 or less. The lower limit of I _GaSn / I is not particularly set, but is generally 0.05 or more, and typically 0.10 or more.

The XRD measurement is performed according to the following procedure. The sputtering target member to be measured is crushed into powder, and the powder under the sieve sieved with a sieve having a mesh size of 100 μm is powdered to prepare a measurement sample. Using the powder X-ray diffraction method, tube voltage: 40 kV. An X-ray diffraction chart having a horizontal axis of 2θ and a vertical axis of X-ray intensity (cps) is obtained under the conditions of tube current: 30 mA, scan speed: 5 ° / min, and step: 0.02 °. Next, the obtained X-ray diffraction chart is subjected to data processing of Kα2 removal and background removal by the Sonneveld-Bizer method.

_{Then, I sn} , I _GaSn and I are obtained according to the following criteria _{, and I Sn} / I and I _GaSn / I are calculated.
The peak area I _sn of the SnO ₂ phase is the sum of the peak areas in each range of 2θ = 26.2 ° to 26.9 °, 33.5 ° to 44.2 °, 51.4 ° to 52.0 °. Point to.
The peak area I _GaSn of the Ga ₄ SnO ₈ phase is 2θ = 14.2 ° to 14.8 °, 25.1 ° to 25.8 °, 34.5 ° to 35.0 °, 52.9 ° to 53. Refers to the total peak area in each range of 5 °.
The total peak area I refers to the total peak area in the range of 2θ = 10 ° to 60 °.

Each peak area is the maximum peak intensity Imax (height from 0 cps after background removal to the maximum peak intensity (unit: cps)) of each peak in the above angle range, and the half width Wh (unit: cps) of the peak. It is calculated by multiplying the peak width (unit: 2θ) at the position where the intensity is I _{max / 2.}

(3. Volume resistivity)
In one embodiment, the sputtering target member according to the present invention has a volume resistivity of 50,000 Ω · cm or less. Lowering the resistance of the sputtering target member can contribute to the stability of sputtering. The volume resistivity is preferably 25,000 Ω · cm or less, more preferably 15,000 Ω · cm or less, and can be, for example, 5,000 to 50,000 Ω · cm.

The volume resistivity is an average value when the volume resistivity at any five points of the sputtering target member to be measured is measured so as not to be biased at the measurement points using the DC four-probe method.

(4. Relative density)
The relative density of the sputtering target member affects the volume resistivity, so it is desirable that the relative density is high. From the viewpoint of suppressing the occurrence of cracks and cracks in the sputtering target member, it is preferable that the sputtering target member has a high relative density. In one embodiment, the sputtering target member according to the present invention has a relative density of 94% or more. The relative density is preferably 95% or more, more preferably 98% or more, and can be, for example, 94 to 98%.

In the present invention, "relative density" is represented by relative density = (measured density / theoretical density) x 100 (%). The theoretical density is a density value calculated from the theoretical density of oxides of the elements excluding oxygen in each constituent element of the sintered body. In the case of the Ga-Sn-O target of the present invention, among the constituent elements gallium, tin, and oxygen, gallium oxide (Ga ₂ O ₃ ) and tin oxide (Ga 2 O 3) and tin oxide (Gallium oxide (Ga 2 O 3)) and tin oxide ( SnO ₂ ) is used to calculate the theoretical density. Here, the elemental analysis value (at% or mass%) of gallium and tin in the sintered body is converted into the mass ratio of _{gallium oxide (Ga 2} O ₃ ) and tin oxide (SnO _2). For example, as a result of conversion, in the case of a GTO target in which gallium oxide is 25% by mass and tin oxide is 75% by mass, the theoretical density is (Ga ₂ O ₃ density (g / cm ³ ) × 25 + SnO ₂ density (g / g /). Calculated as cm ³ ) × 75) / 100 (g / cm ^3). Theoretical density of Ga ₂ O ₃ is the theoretical density of 6.44g / cm ^3, SnO ₂ is calculated as 6.95 g / cm ^3. On the other hand, the measured density is a value obtained by dividing the weight by the volume. In the case of a sintered body, the volume is calculated by the Archimedes method.

(5. Manufacturing method)
Hereinafter, a suitable manufacturing method of the sputtering target member according to the present invention will be described exemplarily. As raw material powder, gallium oxide (Ga ₂ O ₃ ) powder and tin oxide (SnO ₂ ) powder are prepared. In order to avoid adverse effects on electrical characteristics due to impurities, it is preferable to use a raw material powder having a purity of 3N (99.9% by mass) or more, and more preferably to use a raw material powder having a purity of 4N (99.99% by mass) or more. ..

Next, Ga ₂ O ₃ powder and _{Sn O 2} powder are mixed and pulverized at a predetermined molar ratio to prepare a mixed powder. _{The Ga 2} O ₃ powder and the _{Sn O 2} powder are mixed so that the atomic ratio of Ga and Sn in the mixed powder satisfies the above-mentioned 0.33 ≦ Ga / (Ga + Sn) ≦ 0.75. Specifically, the Ga ₂ O ₃ powder in the mixed powder is preferably 20 mol% or more. From the viewpoint of providing a Ga-Sn-O-based sputtering target member containing a high concentration of Ga, _{it is possible to increase the Ga 2} O ₃ powder in the mixed powder to 30 mol% or more, and Ga in the mixed powder. It is also possible to make the ₂ O _{3 powder 40 mol% or more.} Further, from the viewpoint of reducing the volume resistivity of the obtained sputtering target, _{it is possible to reduce the Ga 2} O ₃ powder in the mixed powder to 60 mol% or less, and the Ga ₂ O ₃ powder in the mixed powder is 55 mol%. It is also possible to do the following.

If mixing and pulverization are insufficient, each component segregates in the manufactured sputtering target member, and a high resistivity region and a low resistivity region exist. It is desirable to mix and pulverize sufficiently because it causes abnormal discharge such as arcing due to charging. As a suitable mixing and pulverizing method, for example, a method in which raw material powder is put into water, dispersed to form a slurry, and the slurry is finely pulverized using a wet medium stirring mill (bead mill or the like) can be mentioned.

The slurry after fine grinding is preferably dried. Drying can be performed, for example, in a hot air dryer under the conditions of 100 to 150 ° C. × 5 to 48 hr, although not limited. After drying, it is preferable to separate the coarse particles by sieving. Sieve separation is preferably performed with a sieve having a mesh size of 500 μm or less, and more preferably performed with a sieve having a mesh size of 250 μm or less. Here, the opening is measured according to JIS Z8801-1: 2006.

The mixed powder obtained by mixing and pulverizing preferably has a median diameter of 5 μm or less, more preferably 3 μm or less, and even more preferably 1 μm or less.

The median diameter of the mixed powder refers to the median diameter (D50) based on the volume when the cumulative distribution of the particle size is measured using a laser diffraction / scattering method particle size measuring device after ultrasonic dispersion for 1 minute using ethanol as a dispersion medium.

Next, a mold having a desired shape is filled with the mixed powder and pressed to prepare a molded product. The surface pressure during pressing can be, for example, 400 to 1000 kgf · cm ^2.

Next, the molded product is sintered in an oxygen-containing atmosphere at a heating temperature of 1500 ° C. or higher for 10 hours or longer to obtain a sintered body containing a Ga—Sn—O composite oxide phase. The reason for heating in an oxygen-containing atmosphere is _{to suppress the evaporation of SnO 2} and improve the density of the sintered body. Examples of the oxygen-containing atmosphere include an oxygen atmosphere and an air atmosphere. The heating temperature in the sintering step was set to 1500 ° C. or higher because the sintering reaction rate was sufficiently high. The heating temperature in the sintering step is preferably 1550 ° C. or higher, more preferably 1600 ° C. or higher. The heating time at a heating temperature of 1500 ° C. or higher is set to 10 hours or longer in order to allow the sintering to proceed sufficiently. The heating time is preferably 15 hours or more, more preferably 20 hours or more.

After the sintering step, when implementing the predetermined annealing step, the SnO ₂ phases generated by the decomposition of Ga-SnO composite oxide phase. As a result, _{the ratio of SnO 2} phase increases and the volume resistivity decreases significantly. Annealing is preferably performed on the sintered body in a nitrogen-containing atmosphere at a heating temperature of 1000 ° C. to 1400 ° C. for 10 hours or more. The reason for heating in a nitrogen-containing atmosphere is to reduce the bulk resistivity of the sintered body by reducing _{SnO 2.} Examples of the nitrogen-containing atmosphere include a nitrogen atmosphere and an air atmosphere. The heating temperature in the annealing step is preferably 1000 ° C. or higher, more preferably 1100 ° C. or higher, and even more preferably 1200 ° C. or higher, at which the reaction rate of decomposition is sufficiently fast. Further, the heating temperature in the annealing step is preferably 1400 ° C. or lower, which does not generate Ga—Sn—O composite oxide, and more preferably 1300 ° C. or lower. Annealing at a heating temperature of 1000 to 1400 ° C. for 10 hours or more is to allow the decomposition reaction to proceed sufficiently. The heating time is preferably 15 hours or more, more preferably 20 hours or more.

It is preferable in terms of production efficiency that the sintering step and the annealing step are continuously performed by lowering the heating temperature in the sintering step to the heating temperature in the annealing step. However, after the sintering step, the sintered body may be heated to the annealing temperature again after cooling to room temperature.

The oxide sintered body obtained by the above step can be finished into a sputtering target member by processing it into a desired shape with a processing machine such as a surface grinder, a cylindrical grinder, or a machining center, if necessary. The sputtering target member may be used alone or may be appropriately bonded to a backing plate. Examples of the method of joining with the backing plate include a method of bonding an indium alloy or the like as a bonding metal to a copper backing plate.

(6. Film formation method)
According to one embodiment of the present invention, there is provided a film forming method including sputtering a sputtering target member. The sputtering method is not limited, but an RF magnetron sputtering method, a DC magnetron sputtering method, an AC magnetron sputtering method, a pulse DC magnetron sputtering method and the like can be preferably used. In one embodiment of the sputtering target member according to the present invention, since it has a low volume resistivity, it is particularly suitable for the DC magnetron sputtering method and the pulse DC magnetron sputtering method.

Hereinafter, examples for facilitating the understanding of the present invention and its advantages will be shown, but the present invention should not be limited to the examples.

In the examples and comparative examples shown below, various measurements and evaluations are required, and the conditions are shown below.
(Median diameter)
The median diameter of various powders is based on the volume when the cumulative distribution of particle size is measured using a laser diffraction / scattering method particle size measuring device (Microtrac MT3000 manufactured by Nikkiso Co., Ltd.) after ultrasonic dispersion for 1 minute using ethanol as a dispersion medium. Refers to the median diameter (D50) according to.

(Volume resistivity)
Volume of sputtering target member by the method described above using a resistivity measuring device (manufactured by NPS Co., Ltd., model FELL-TC-100-SB-Σ5 +, measuring jig RG-5) using the DC four-probe method. Measure the resistivity.

(Relative density)
The measured density of the sputtering target member to be measured is obtained by the Archimedes method, and the relative density is obtained by relative density = measured density / theoretical density.

(XRD measurement)
XRD measurements, fully automatic multi-purpose X-ray diffractometer manufactured by Rigaku Corporation (model: Ultima) performed according to the measurement conditions described above is used to calculate the I _sn / I and I _GaSn / I from the resulting XRD chart.

(Comparative Example 1)
As raw material powders, Ga ₂ O ₃ powder (median diameter 2.60 μm) and SnO ₂ powder (median diameter 1.25 μm) were prepared. _{Ga 2 O 3: SnO 2 =} 1: was slurried charged with Ga ₂ O ₃ powder and SnO ₂ powder in water in a molar ratio. The slurry was pulverized and mixed using a bead mill. The slurry after pulverization and mixing was dried in a hot air dryer at 120 ° C. for 20 hours, sieved with a sieve having a mesh size of 250 μm, and the mixed powder under the sieve was recovered. The median diameter of the mixed powder was 0.84 μm. Next, 1000 g of the obtained mixed powder was filled in a mold having a diameter of 210 mm ^{and pressed at a surface pressure of 400 to 1000 kgf / cm 2} to obtain a disk-shaped molded product. This molded product was heated to a temperature of 1600 ° C. in an oxygen atmosphere and held for 10 hours to obtain a sintered body (sputtering target member).

(Comparative Example 2)
A molded product prepared under the same conditions as in Comparative Example 1 was heated to a temperature of 1550 ° C. in an oxygen atmosphere and held for 10 hours to obtain a sintered body (sputtering target member).

(Comparative Example 3)
A molded product produced under the same conditions as in Comparative Example 1 was heated to a temperature of 1600 ° C. in an air atmosphere and held for 10 hours to obtain a sintered body (sputtering target member).

(Example 1)
The molded product prepared under the same conditions as in Comparative Example 1 was heated to a temperature of 1600 ° C. in an oxygen atmosphere and held for 10 hours. Then, the temperature was lowered to 1000 ° C. and kept in an air atmosphere for 20 hours to obtain a sintered body (sputtering target member).

(Example 2)
The molded product prepared under the same conditions as in Comparative Example 1 was heated to a temperature of 1600 ° C. in an oxygen atmosphere and held for 10 hours. Then, the temperature was lowered to 1200 ° C. and kept in an air atmosphere for 20 hours to obtain a sintered body (sputtering target member).

(Example 3)
Ga ₂ O ₃ powder and SnO ₂ powder of _{Ga 2 O 3: SnO 2 =} 20: except that were mixed to obtain 80 molar ratio, under the same conditions as in Example 1 to prepare a mixed powder. The median diameter of the mixed powder was 0.92 μm. Next, a molded product was produced and sintered under the same heating conditions as in Example 1 to obtain a sintered body (sputtering target member).

<Discussion>
It was understood that in Comparative Examples 1 to 2 and Examples 1 and 2, although the raw material compositions were the same, the volume resistivity was significantly reduced in Examples 1 and 2 due to the large In _{Sn / I.} can. Further, from the results of Example 3, it can be understood that the volume resistivity is further greatly reduced by lowering the molar ratio of Ga.

Claims (3)

Ga ₂ O ₃ powder the powder mixture such that a 20 mol% or more 60 mol% or less of the molar concentration, a step 1 of preparing a mixed powder by mixing and milling the Ga ₂ O ₃ powder and SnO ₂ powder,
Step 2 of sintering the mixed powder in an oxygen atmosphere or an air atmosphere at a heating temperature of 1500 ° C. or higher for 10 hours or longer to obtain a sintered body containing a Ga—Sn—O composite oxide phase.
Sinter under a nitrogen-containing atmosphere, and annealed for 10 hours or more at a heating temperature of 1000 ° C. to 1400 ° C. to decompose the Ga-SnO composite oxide phase, step 3 to produce a SnO ₂ phase,
Method for producing a free steaming sputtering target member. By lowering the heating temperature in the heating temperature in the step 3 in the step 2, the manufacturing method of the sputtering target member according to claim 1 for step 2 and step 3 continuously. The method for manufacturing a sputtering target member according to claim 1 or 2 , wherein step 3 is annealed at a heating temperature of 1200 ° C. to 1400 ° C.