JP2017024970A - Gallium nitride-based sintered body and manufacturing method therefor - Google Patents

Abstract

A method for producing a sputtering target for a gallium nitride thin film having a low oxygen content, a high density, and a low resistance is provided. The sintered body has an oxygen content of 1 atm% or less, a resistivity of 1×10 2 Ω·cm, preferably a density of 3.0 to 5.4 g/cm 3 or less, and a weight of 10 g. A gallium nitride-based sintered body as described above. Gallium nitride powder with an oxygen content of 2 atm% or less is used as a raw material, and is heated and sintered at a temperature of 1060 ° C. or more and less than 1300 ° C. at an ultimate vacuum of 70 Pa or less in a hot press, and at least one of indium, tin, and zinc. A method of manufacturing a sputtering target comprising a component as a bonding layer, wherein no layer containing tungsten is present between the target member and the bonding layer. [Selection figure] None

Description

  Gallium nitride is attracting attention as a light emitting layer for blue light emitting diodes (LEDs) and a raw material for blue laser diodes (LDs), and has recently been used for various applications such as white LEDs and blue LDs in the form of thin films and substrates. In the future, it is also attracting attention as a material for applications such as power devices. At present, gallium nitride thin films are generally manufactured by metal organic chemical vapor deposition (MOCVD). The MOCVD method is a method in which a vapor of a raw material is contained in a carrier gas and transported to the substrate surface, and the raw material is decomposed by reaction with a heated substrate to grow crystals.

  As a method for forming a thin film other than the MOCVD method, a sputtering method can be given. In this sputtering method, positive ions such as Ar ions are physically collided with a target placed on the cathode, the material constituting the target is released by the collision energy, and the composition is almost the same as the target material on the substrate placed on the opposite side. There are two methods of depositing a film, such as a direct current sputtering method (DC sputtering method) and a high frequency sputtering method (RF sputtering method).

  Until now, a metal gallium target has been used as a method of forming a gallium nitride thin film by a sputtering method (see, for example, Patent Document 1). However, when a metal gallium target is used, since the melting point of metal gallium is about 29.8 ° C., the metal gallium target melts at the time of sputtering, so that a gallium nitride film having highly stabilized characteristics such as crystallinity and permeability is obtained. In order to prevent this, an expensive cooling device is attached, and a method of forming a film with low power has been proposed. However, productivity is reduced and oxygen is incorporated into the film. There was a problem that it was easy.

  A high-density gallium nitride sintered body has also been proposed (see, for example, Patent Document 2), but according to this example, it is densified under a very high pressure condition of 58 Kbar (5.8 GPa). A device that applies a large pressure is a very expensive device, and a large-sized sintered body cannot be produced. For this reason, the sputtering target itself used in the sputtering method is very expensive and it is difficult to increase the size of the sputtering target.

  As a method of reducing the oxygen content, a method of reducing the oxygen content by nitriding a gallium nitride sintered body containing oxygen has been proposed (see, for example, Patent Document 3). However, there has been a problem that cracking may occur in the sintered body when the oxygen amount above a certain level is reduced.

  Moreover, when using direct current | flow sputtering method, it is calculated | required that the resistivity of a sputtering target is low. As a method therefor, a method for reducing the resistivity of a sputtering target by infiltrating metal gallium into a gallium nitride molded product has been proposed (for example, see Patent Document 4). However, this technique has a problem that the resistance is reduced, but metal gallium is deposited during bonding or sputtering, so that it reacts with a solder material such as indium and peels off the gallium nitride molded product, and discharge cannot be stably performed. there were. As a countermeasure, a method of suppressing the deposition of metal gallium by lining a thin film of tungsten has been proposed (see, for example, Patent Document 5). There was a problem that it was necessary to use a special material called a tungsten material.

JP-A-11-172424 JP 2005-508822 A JP 2012-144424 A JP 2014-159368 A JP 2014-91851 A

  An object of the present invention is to provide a gallium nitride-based sintered body that has a low oxygen content, high density, and low resistance and is unlikely to precipitate metal gallium, and a method for manufacturing the same.

  In view of such a background, the present inventors made extensive studies. As a result, gallium nitride powder with low oxygen content and high bulk density is used, and hot press treatment is performed at high temperature under high vacuum, thereby nitriding with low oxygen content and high density and low resistance. The inventors have found that a gallium-based sintered body can be produced, and that a conductive gallium nitride-based sputtering target can be produced without performing a backing treatment using a special material, and the present invention has been completed.

That is, the aspects of the present invention are as follows.
(1) A gallium nitride-based sintered body having an oxygen content of 1 atm% or less and a resistivity of 1 × 10 ² Ω · cm or less.
(2) The sintered body according to (1), wherein the density is 3.0 g / cm ³ or more and 5.4 g / cm ³ or less.
(3) The sintered body according to (1) or (2), wherein an average particle size of the sintered body is 0.5 μm or more and 3 μm or less.
(4) The sintered body according to any one of (1) to (3), wherein the weight of the sintered body is 10 g or more.
(5) The sintered body according to any one of (1) to (4), wherein the deposition of metal gallium cannot be visually confirmed from the target member even if heat treatment at 250 ° C. is performed for 1 hour in the air. .
(6) A method for producing a gallium nitride-based sintered body by a hot press method using a gallium nitride powder having an oxygen content of 2 atm% or less as a raw material, and an ultimate vacuum in the chamber during hot press being 70 Pa or less and 1060 ° C. or more A method for producing a gallium nitride based sintered body characterized by heating at less than 1300 ° C.
(7) A gallium nitride sputtering target using the sintered body according to any one of (1) to (5).
(8) The sputtering target according to (7), wherein there is no layer containing tungsten between the target member and the bonding layer.
(9) The sputtering target according to (7) or (8), wherein the bonding layer contains at least one component of indium, tin, and zinc.
(10) A method for producing a gallium nitride thin film characterized by using the sputtering target according to (6) to (9).

  Hereinafter, although the present invention is explained in detail, the present invention is not limited to the following embodiments.

  The sintered gallium nitride of the present invention is characterized in that the oxygen content is 1 atm% or less, and preferably 0.5 atm% or less. By reducing the oxygen content in the sintered body, when used as a sputtering target, it is possible to reduce the mixing of oxygen as an impurity during film formation and obtain a higher crystalline film.

Further, gallium nitride sintered body of the present invention, the resistivity, characterized in that at 1 × 10 ² Ωcm or less, more preferably ¹ × 10 1 Ωcm or less, more preferably 1 × 10 ⁰ Ωcm or less . The low-resistance sintered body can be used not only for RF sputtering but also for DC sputtering when used as a sputtering target.

The gallium nitride sintered body of the present invention preferably has a density of 3.0 g / cm ³ or more and 5.4 g / cm ³ or less, and the lower limit thereof is more preferably 3.5 g / cm ³ , and 4.0 g / cm ^{3. 3} is more preferable. The density of the gallium nitride sintered body described here indicates the density including open pores, and indicates the measurement result of bulk density in JIS R1634. Such a gallium nitride based sintered body can be used as a sputtering target.

  The gallium nitride sintered body of the present invention preferably has an average particle size of 0.5 μm or more and 3 μm or less. By setting it as such a particle diameter, it becomes possible to obtain the sintered compact with few open pores, a low oxygen content, and high intensity | strength.

  Next, a method for manufacturing a gallium nitride sintered body will be described.

  As a result of examining in detail the relationship between the specific surface area (BET) of the gallium nitride powder as a raw material, the light bulk density, and the particle size of the primary particles and the strength of the sintered body, the above physical property values of the gallium nitride powder are controlled. It has been found that a sintered body having a high strength can be obtained with reduced oxygen contamination of impurities.

  That is, the manufacturing method of the present invention is a manufacturing method of a gallium nitride sintered body by a hot press method, using gallium nitride powder having an oxygen content of 2 atm% or less as a raw material, and the ultimate vacuum in the chamber during hot pressing is Heating is performed at 70 Pa or less, 1060 ° C. or more and less than 1300 ° C. With such a manufacturing method, even a gallium nitride-based sintered body having a weight of 10 g or more can be manufactured with a high yield.

  Below, this manufacturing method is demonstrated in detail.

First, the raw material gallium nitride powder needs to have an oxygen content of 2 atm% or less. In order to reduce oxygen, since it is necessary to suppress surface oxidation, it is desirable that the specific surface area of the powder is small, preferably 1.5 m ² / g or less, more preferably 0.8 m ^2. / G. By using such a powder, it becomes possible to reduce the amount of oxygen mixed from the powder. The lower limit is preferably larger than 0.1 m ² / g. If the specific surface area is smaller than that, the crystal particles are too large, the adhesion between the particles is weak, it is difficult to retain the shape when finally fired, and further, if the specific surface area is small, In general, since sinterability is lowered, firing becomes difficult.

In order to obtain a sintered body having sufficient strength as a sputtering target, the light bulk density of gallium nitride as a raw material is preferably 0.8 g / cm ³ or more, more preferably 1.0 g / cm 3. ³ or more. The light bulk density is a value obtained by filling a container having a constant volume without applying a load such as vibration and dividing the capacity of the filled powder by the volume of the container. The light bulk density is preferably less than 2.5 g / cm ³ . If the light bulk density is increased more than that, the strength of the granules constituting the powder becomes too high, and the strength of the sintered body is remarkably lowered because the granules remain uncrushed during molding and firing.

  The average particle diameter of gallium nitride used as a raw material is preferably 0.5 μm or more and 3 μm or less. By using such a powder, it becomes possible to produce a sintered body having both sinterability and low oxygen. In particular, in gallium nitride, the sintering start temperature and the decomposition temperature are close, the sintering temperature range is narrow, and large grain growth does not occur during sintering, so the distribution of primary particles before sintering has a large effect on the sintered body. give. The particle diameter of primary particles refers to the diameter of the smallest unit particles observed by SEM, the average particle diameter is measured by the diameter method, and is measured for at least 100 particles, and then a numerical value at a 50% particle diameter. Point to. In the case of a molded product using a powder in this range, the particle diameter is larger and the adhesion force is smaller than before, so if there are open pores that can be immersed, the bonding force between the particles is relatively weak. When the immersion is performed, cracks are generated due to the stress generated during the immersion and the difference in thermal expansion coefficient caused by heating and sputtering.

  Note that it is desirable to use a gallium nitride powder that does not contain impurities as much as possible because the semiconductor characteristics change by obtaining high crystallinity of the sputtering film or by adding an element.

  As the firing method, a hot press method is used. Hot pressing is a method in which sintering is carried out by applying temperature while pressing the powder. By uniaxial pressing during heating, diffusion during firing is assisted, and a material that has a low diffusion coefficient and is difficult to sinter is used. It is a firing method that allows sintering.

  The firing temperature is 1060 ° C. or higher and lower than 1300 ° C. In order to advance the sintering of gallium nitride, 1060 ° C. or higher is necessary, and in order to suppress decomposition of gallium nitride into nitrogen and metal gallium to a certain amount, it must be lower than 1300 ° C. Moreover, in order to improve the density of a sintered compact, it is preferable that the pressure at the time of baking shall be 30 Mpa or more and 100 Mpa or less, More preferably, it is 50 Mpa or more and 90 Mpa or less.

The hot press atmosphere is performed under vacuum. The degree of vacuum at the start of heating is 70 Pa or less, preferably 10 Pa or less, more preferably 10 ⁻¹ Pa, and particularly preferably 10 ⁻² Pa or less. Accordingly, oxygen and oxygen elements such as water mixed from the atmosphere can be reduced, and oxidation during firing can be suppressed.

  In addition, when sintered under vacuum, the decomposition of the gallium nitride powder gradually proceeds from around 1060 ° C., but by sintering under vacuum, a part of the metal gallium that is decomposed and generated together with nitrogen as a decomposition gas. It is discharged from the sintered body to the outside. For this reason, in the hot press die, it is preferable that the clearance between the die and the upper punch is 0.2 mm or more. Alternatively, it is preferable to use a material having a low density such as carbon felt between the powder and the upper and lower punches.

When hot pressing is performed under the above-described conditions, metal gallium does not become an inhibitor during sintering, and an appropriate amount is contained, so that the sintering progressed, resulting in high density and suppressed oxidation. A gallium nitride sintered body can be obtained. In particular, metal gallium is partially decomposed in the region of 1060 ° C. or higher and 1300 ° C. or lower. However, since sintering of gallium nitride also proceeds, it is inhibited by metal gallium by applying high pressure vacuum sintering. As the gallium nitride sintering progresses, the density is improved. When gallium nitride is used as a sputtering target, the sintered body is preferably conductive, and for that purpose, metallic gallium is preferably present. Whether or not metallic gallium is included in gallium nitride is clear by confirming the resistivity of the sintered body, and the substrate has a high resistivity as represented by gallium nitride single crystal. Such a sintered body has a resistivity as low as 10 ² Ω · cm or less. Molded products and sintered bodies in which decomposition of gallium nitride does not proceed even when the same raw material is used have high resistivity. Various methods for containing metal gallium in the gallium nitride sintered body are conceivable, but in order to make it uniformly present in a small amount, gallium nitride is dispersed in the gallium nitride raw material powder, or gallium nitride is decomposed during sintering. Thus, a method of generating gallium nitride is preferable. By doing so, a small amount of metal gallium can be uniformly dispersed in the sintered body. The content is preferably less than 30 wt%, more preferably less than 10 wt%.

  The obtained sintered body may be processed into a predetermined dimension according to the use of a sputtering target or the like. The processing method is not particularly limited, and a surface grinding method, a rotary grinding method, a cylindrical grinding method, or the like can be used.

  If necessary, the gallium nitride sintered body may be fixed (bonded) to a flat or cylindrical support with an adhesive such as a solder material to form a sputtering target. It is preferable that the sputtering target does not have a layer containing tungsten between the target member and the bonding layer. By not using an expensive metal tungsten target, the cost is reduced and a tungsten film formation step is not required, so that productivity is improved.

  The sputtering target of the present invention preferably uses a tin-based solder material, an indium-based solder material, or a zinc-based solder material as a bonding layer. Among them, indium solder having high conductivity and thermal conductivity and being soft and easily deformable is preferable.

  In addition, the sputtering target of the present invention is preferably made of a metal such as Cu, SUS, or Ti because of its high thermal conductivity and high strength as a support. As for the shape of the support, it is preferable to use a flat plate-shaped support for a flat plate-shaped molded product and to use a cylindrical support for a cylindrical molded product.

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

  The gallium nitride sintered body is bonded to the support through the bonding layer. Tin-based solder material, indium-based solder material, zinc-based solder material, etc. can be used for the bonding layer, but when using an indium-based solder material, indium wettability to the gallium nitride sintered body is improved. In order to improve, a layer for improving wettability may be formed between the sintered body and the solder material. The material of the layer is preferably inexpensive and has high wettability to indium. For example, it is preferable to use nickel or chromium. This layer is preferably formed uniformly over the entire interface with the solder material. A method for forming such a barrier layer is not particularly limited, and sputtering, vapor deposition, coating, or the like can be used.

  The gallium nitride sintered body of the present invention is suitable for use as a sputtering target because it has a low oxygen content, high density, and low resistance, and metal gallium does not easily precipitate.

Hereinafter, although demonstrated with an Example, it is not limited to this.
(Specific surface area)
The specific surface area of the powder was measured using a Micrometrics Tristar.
(Light bulk density)
Measurement was performed using a powder tester PT-N type (manufactured by Hosokawa Micron Corporation).
(Bulk density of sintered body)
The bulk density of the sintered body was measured in accordance with the bulk density measurement method in JIS R1634.
(Oxygen content)
The oxygen content of the sintered body was measured with an oxygen / nitrogen analyzer (manufactured by LECO).
(Heating test)
The sintered body was subjected to a heat treatment at 250 ° C. for 1 hour in the air using a hot plate, and the presence or absence of deposition of metal gallium from the sintered body was visually confirmed.
(Measurement of particle diameter)
The particle diameters of the powder and the sintered body were measured for at least two fields of view by the diameter method from an image observed with an SEM, and after measuring 100 or more particles, the 50% particle diameter was defined as the average particle diameter.
(Crystal plane confirmation, half width, strength ratio measurement method)
A normal powder X-ray diffractometer (device name: Ultimate III, manufactured by Rigaku Corporation) was used for normal measurement. The conditions for XRD measurement are as follows.
Radiation source: CuKα ray (λ = 0.15418 nm)
Measurement mode: 2θ / θ scan
Measurement interval: 0.01 °
Divergence slit: 0.5 deg
Scattering slit: 0.5 deg
Receiving slit: 0.3mm
Measurement time: 1.0 seconds
Measurement range: 2θ = 20 ° -80 °
XRD analysis software (trade name: JADE7, manufactured by MID) was used for identification analysis of the XRD pattern. Hexagonal crystals are JCPDSNo. The gallium nitride crystal plane is confirmed with reference to 00-050-0792, the half width of the (002) plane is measured, and the intensity ratio is calculated using the following formula for I (002) and I (101). .
Intensity ratio = I (002) / I (101)
When a peak that seems to be the (101) plane is not detected, the background peak intensity of 36 to 37 ° is regarded as I (101) and the calculation is performed.

High-accuracy measurement was performed using the following configuration of the XRD device (Bruker D8 DISCOVER), using a HIGH RESOLUTION mode, Ge (220) monochromator under conditions of 40 kV and 40 mA, removing CuKα2 and performing an ω scan. .
Radiation source: CuKα ray (λ = 0.15418 nm)
Monochromator: Ge (220)
Pathfinder: Crystal3B
Measurement mode: ω scan
Measurement interval: 0.01 °
(If the half width is 0.1 ° or less, 0.0005 °)
Measurement time: 0.5 seconds
Measurement range: ω = 0 ° -35 °
(Measurement of oxygen content in membrane)
The oxygen content in the film was measured using SIMS (secondary ion mass spectrometer). The oxygen content was measured in the depth direction of the film, and the minimum content between 5 nm and 30 nm from the interface was calculated for the place assumed to be the substrate.

(Examples 1-4)
Using 30 g of the gallium nitride powder shown in Table 1, it was put into a 51 mmφ carbon mold and put into a hot press. The ultimate vacuum before starting the temperature rise starts firing under the conditions shown in Table 1, the temperature is raised at 200 ° C./h, and finally increased to the temperature shown in Table 1. The pressure condition was increased to the pressure shown in Table 1 when the maximum temperature was maintained, and the hot press treatment was performed at a temperature and pressure holding time of 1 hour. The temperature was lowered to about 50 ° C. in 5 hours, the mold was taken out, and the sintered body was recovered. All were sintered bodies of 10 g or more. Table 2 shows the weight, density, oxygen content, resistivity, average particle diameter, and heating test results of the obtained polycrystalline gallium nitride sintered body.

  Furthermore, after processing the sintered body and bonding it to the backing plate, it was confirmed whether it was possible to form a film with DC or RF as a sputtering target. It was confirmed that film formation was possible.

(Example 5)
Using 250 g of the gallium nitride powder shown in Table 1, it was put into a 130 mmφ carbon mold and put into a hot press. The ultimate vacuum before starting the temperature rise starts firing under the conditions shown in Table 1, the temperature is raised at 200 ° C./h, and finally increased to the temperature shown in Table 1. The pressure condition was raised to the pressure shown in Table 1 when the maximum temperature was maintained, and the hot press treatment was performed at a temperature and pressure retention time of 2 hours. After the temperature was lowered, the mold was taken out and the sintered body was recovered. Table 2 shows the weight, density, oxygen content, resistivity, average particle diameter, and heating test results of the obtained polycrystalline gallium nitride sintered body.

(Comparative Examples 1-3)
Using the gallium nitride powder shown in Table 1, hot press treatment was performed under the same temperature rise rate, holding time, and temperature lowering conditions as in Example 1 except that the vacuum degree, firing temperature, and load shown in Table 1 were used. Table 2 shows the weight, density, oxygen content, resistivity, average particle diameter, and results of the heating test of the obtained polycrystalline gallium nitride sintered body. In Comparative Example 2, the shape could not be retained, and a sintered body could not be obtained.

(Comparative Example 4)
Compared to 24.5 g of the processed gallium nitride sintered body, the gallium nitride sintered body manufactured under the same conditions as in Comparative Example 1 was used, whereas metal gallium (purity 6N, oxygen content 0.0174 atm%, DOWA Electronics Co., Ltd.) Company) was prepared in an amount 1.35 times the amount of the sintered body, and both were put into a vacuum packaging bag and vacuum packaged at 1000 Pa. The packaging container was heated to about 50 ° C. to completely dissolve the metal gallium, and then charged into CIP and pressurized at 100 MPa for 60 seconds. After taking out, the metal gallium remaining in the periphery after heating at about 50 ° C. was removed to obtain a metal gallium permeated gallium nitride sintered body. On the other hand, when a heating test was performed at 250 ° C., precipitation of Ga metal was observed. In addition, the value of the average particle diameter described in Table 2 relates to the average particle diameter of the sintered body before infiltrating the metal gallium, and the results of weight, density, oxygen content, resistivity, and heating test are as follows. The present invention relates to a metal gallium permeable gallium nitride sintered body.

(Reference example)
For the sintered body produced by the same method as in Example 1, an attempt was made to produce a metal gallium infiltrate by the same method as in Comparative Example 4, but cracking occurred during the infiltration.

実施例５と比較例１について下記の条件にて成膜を実施したところ、本発明により膜中の酸素量、膜の結晶性、配向性が大きく改善することを確認した。
（スパッタ成膜条件）
ターゲットサイズ：１２０ｍｍφ
放電電力 ：１２５Ｗ
スパッタガス圧 ：０．０７Ｐａ
スパッタガス ：窒素のみ
成膜温度 ：６００℃
膜厚 ：約３００ｎｍ

When film formation was performed for Example 5 and Comparative Example 1 under the following conditions, it was confirmed that the amount of oxygen in the film, crystallinity and orientation of the film were greatly improved according to the present invention.
(Sputter deposition conditions)
Target size: 120mmφ
Discharge power: 125W
Sputtering gas pressure: 0.07 Pa
Sputtering gas: Nitrogen only Film forming temperature: 600 ° C
Film thickness: about 300nm

Claims (10)

A gallium nitride-based sintered body having an oxygen content of 1 atm% or less and a resistivity of 1 × 10 ² Ω · cm or less. The sintered body according to claim 1, wherein the density is 3.0 g / cm ³ or more and 5.4 g / cm ³ or less. The sintered body according to claim 1 or 2, wherein the sintered body has an average particle size of 0.5 µm or more and 3 µm or less. The sintered body according to any one of claims 1 to 3, wherein the weight of the sintered body is 10 g or more. The sintered body according to any one of claims 1 to 4, wherein the metal gallium cannot be visually confirmed from the target member even if heat treatment at 250 ° C is performed for 1 hour in the atmosphere. A method for producing a gallium nitride-based sintered body by a hot press method, using a gallium nitride powder having an oxygen content of 2 atm% or less as a raw material, and an ultimate vacuum in a chamber at the time of hot press being 70 Pa or less, 1060 ° C. or higher and lower than 1300 ° C. A method for producing a gallium nitride-based sintered body, characterized by heating at a temperature. A gallium nitride sputtering target using the sintered body according to claim 1. The sputtering target according to claim 7, wherein no layer containing tungsten exists between the target member and the bonding layer. The sputtering target according to claim 7 or 8, wherein the bonding layer contains at least one component of indium, tin, and zinc. A method for producing a gallium nitride-based thin film using the sputtering target according to claim 7.