Gallium nitride sintered body or gallium nitride molded article, and method for producing same

Abstract

The present invention provides a gallium nitride sintered body and a gallium nitride molded article which have high density and low oxygen content without using a special apparatus. According to the first embodiment, a gallium nitride sintered body, which is characterized by having density of 2.5 g/cm.sup.3 to less than 5.0 g/cm.sup.3 and an intensity ratio of the gallium oxide peak of the (002) plane to the gallium nitride peak of the (002) plane of less than 3%, which is determined by X-ray diffraction analysis, can be obtained. According to the second embodiment, a metal gallium-impregnated gallium nitride molded article, which is characterized by comprising a gallium nitride phase and a metal gallium phase that exist as separate phases and having a molar ratio, Ga/(Ga+N), of 55% to 80%, can be obtained.

Claims

1. A metal gallium-impregnated gallium nitride molded article, wherein the molded article comprises a gallium nitride phase having voids contained therein and a metal gallium phase which exist as separate phases, and the molded article has a molar ratio of Ga/(Ga+N) of 55% to 80%, wherein said gallium nitride phase has a density of 2.5 g/cm.sup.3 to less than 5.0 g/cm.sup.3 and a composition having an intensity ratio of a gallium oxide peak of the (002) plane to a gallium nitride peak of the (002) plane of less than 3%, as determined by X-ray diffraction analysis.

2. The metal gallium-impregnated gallium nitride molded article according to claim 1, wherein not less than 30% of a total volume of said voids contained therein is filled with said metal gallium.

3. The metal gallium-impregnated gallium nitride molded article according to claim 1, wherein the molded article has density of 3.20 g/cm.sup.3 to less than 6.05 g/cm.sup.3.

4. The metal gallium-impregnated gallium nitride molded article according to claim 1, wherein the molded article has resistance of not higher than 1 Ω.Math.cm.

5. The metal gallium-impregnated gallium nitride molded article according to claim 1, wherein the molded article contains oxygen in an amount of not more than 11 atm %.

6. The metal gallium-impregnated gallium nitride molded article according to claim 1, wherein said voids contained therein comprise open pores and closed pores, and the volume ratio of said open pores with respect to a total volume of said voids is not less than 70%.

7. A method of producing the metal gallium-impregnated gallium nitride molded article according to claim 1, wherein the method comprises impregnating a liquid metal gallium into a gallium nitride molded article having density of 2.0 g/cm.sup.3 to less than 5.0 g/cm.sup.3.

8. The method according to claim 7, wherein said impregnating the liquid metal gallium into a gallium nitride molded article includes subjecting said gallium nitride molded article and said metal gallium to a vacuum treatment in the same container and then isotropically applying a pressure to said container.

9. The method according to claim 7, wherein said gallium nitride molded article is obtained by a process comprising: obtaining a molded article by sintering a gallium nitride powder having a specific surface area (BET) of 0.4 m.sup.2/g to 15 m.sup.2/g, untamped bulk density of not less than 0.4 g/cm.sup.3, and a repose angle of not larger than 40°; and heat-treating the obtained molded article in an ammonia-containing atmosphere.

10. The method according to claim 9, wherein said gallium nitride powder is obtained by subjecting a gallium oxide powder to a nitridation treatment in an ammonia atmosphere at a temperature of 1000° C. to 1100° C.

11. A gallium nitride sputtering target, comprising the metal gallium-impregnated gallium nitride molded article according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows an X-ray diffraction spectrum of the gallium nitride sintered body prepared in Example 1 of the first embodiment.

(2) FIG. 2 shows an X-ray diffraction spectrum of the gallium nitride sintered body prepared in Comparative Example 1 of the first embodiment.

(3) FIG. 3 is a schematic diagram showing a cross-section of a metal gallium-impregnated gallium nitride molded article according to the second embodiment.

(4) FIG. 4 is a schematic diagram showing a cross-section of a gallium nitride molded article from which gas was removed, in the second embodiment.

(5) FIG. 5 is a schematic diagram showing a cross-section of a gallium nitride molded article and metal gallium that are packaged in a vacuum packaging container, in the second embodiment.

(6) FIG. 6 is a schematic diagram showing a cross-section of a gallium nitride molded article impregnated with metal gallium under a prescribed pressure.

(7) FIG. 7 shows a powder X-ray diffraction spectrum of the metal gallium-impregnated gallium nitride molded article obtained in Example 1 of the second embodiment.

EXAMPLES

(8) The first embodiment of the present invention will now be described by way of examples thereof; however, this embodiment is not limited thereto.

(9) (Density)

(10) The density of a sintered body was measured in accordance with the method of measuring the bulk density prescribed in JIS R1634.

(11) (Oxygen Content)

(12) The oxygen content of a sintered body was measured using an oxygen/nitrogen analyzer (manufactured by LECO Corporation).

(13) (Repose Angle)

(14) The repose angle, which is a parameter of powder fluidity, was measured using a powder tester (Model PT-N, manufactured by Hosokawa Micron Group).

(15) (Specific Surface Area)

(16) The specific surface area of a powder was measured using Micromeritics Tristar (manufactured by Shimadzu Corporation).

(17) (Untamped Bulk Density)

(18) The untamped bulk density of a powder was measured in accordance with JIS 22504.

First Embodiment—Example 1

(19) A gallium nitride powder (100 g, purity of 4 N; manufactured by Kojundo Chemical Lab. Co., Ltd.) having a specific surface area (BET) of 14 m.sup.2/g, untamped bulk density of 0.551 g/cm.sup.3, and a repose angle of 39° was loaded in a 102 mmϕ carbon-made die to perform hot-pressing. The hot-pressing treatment was performed by heating the gallium nitride powder at a rate of 200° C./h to a final temperature of 1000° C., increasing the pressing pressure to 40 MPa when the temperature reaches 1000° C., and maintaining the temperature and pressure for 2 hours. After the 2 hours of retention time, the resultant was cooled to about 50° C. over a period of 5 hours and the die was taken out to remove a gallium nitride sintered body. The thus obtained gallium nitride sintered body had density of 2.75 g/cm.sup.3, and the volume ratio of open pores with respect to the total volume of open pores and closed pores was 98%. The gallium nitride sintered body was then processed into a 76.2 mmϕ×2.0 mmt disk.

(20) Then, 25.0 g of the thus processed gallium nitride sintered body was loaded in a tube furnace. The sintered body was heated to 1000° C. at a rate of 300° C./h and maintained at 1000° C. for 2 hours in an ammonia atmosphere in which ammonia gas was flowed through at 200 ml/min, to perform a nitridation treatment of the sintered body. The gallium nitride sintered body was analyzed by a powder X-ray diffraction (XRD; RINT Ultima III, manufactured by Rigaku Corporation) after the nitridation treatment to obtain the X-ray diffraction spectrum shown in FIG. 1. There was observed no peak corresponding to gallium oxide in the X-ray diffraction spectrum shown in FIG. 1; therefore, it was found that the thus obtained gallium nitride sintered body contained either no gallium oxide or only a trace amount of gallium oxide below the lower detection limit. The density, open porosity, oxygen content, and presence/absence of cracking of the obtained gallium nitride sintered body are shown in Table 2.

(21) The obtained gallium nitride sintered body was bonded onto a backing plate made of Cu by using an indium solder as a bonding material to obtain a gallium nitride sputtering target.

First Embodiment—Example 2

(22) The same gallium nitride powder as used in Example 1 (3 g, purity: 4 N) was loaded in a 20-mmϕ carbon-made die to perform hot-pressing. The hot-pressing treatment was performed by heating the gallium nitride powder at a rate of 200° C./h to a final temperature of 1000° C., increasing the pressing pressure to 100 MPa when the temperature reaches 1000° C., and maintaining the temperature and pressure for 2 hours. After the 2 hours of retention time, the resultant was cooled to about 50° C. over a period of 5 hours and the die was taken out to remove a gallium nitride sintered body. The gallium nitride sintered body was then processed into a 20.0 mmϕ×2.0 mmt disk.

(23) Then, 2.5 g of the thus processed gallium nitride sintered body was loaded in a tube furnace. The sintered body was heated to 900° C. at a rate of 300° C./h and maintained at 900° C. for 2 hours in an ammonia atmosphere in which ammonia gas was flowed through at 100 ml/min, to perform a nitridation treatment of the sintered body. The gallium nitride sintered body was analyzed by the XRD after the nitridation treatment, and there was observed no peak corresponding to gallium oxide in the X-ray diffraction spectrum; therefore, it was found that the thus obtained gallium nitride sintered body contained either no gallium oxide or only a trace amount of gallium oxide below the lower detection limit. The density, open porosity, X-ray peak intensity ratio, oxygen content, and presence/absence of cracking of the obtained gallium nitride sintered body are shown in Table 2.

First Embodiment—Example 3

(24) A gallium oxide powder (200 g, purity: 4 N, manufactured by Nippon Rare Metal, Inc.) was loaded in a tube furnace. The gallium oxide powder was heated to 1050° C. at a rate of 600° C./h and maintained at 1050° C. for 5 hours to be nitrided in an ammonia atmosphere in which ammonia gas was flowed through at 400 ml/min, to obtain a gallium nitride powder. A portion of this gallium nitride powder was collected, and its specific surface area (BET), untamped bulk density, and repose angle were measured. The physical property values of the obtained gallium nitride powder are shown in Table 1.

(25) Then, 100 g of the thus obtained gallium nitride powder was loaded in a 102 mmϕ carbon-made die to perform a hot press. A hot-pressing treatment was performed by heating the gallium nitride powder at a rate of 200° C./h to a final temperature of 1050° C., increasing the pressing pressure to 50 MPa when the temperature reaches 1050° C., and maintaining the temperature and pressure for 2 hours. After the 2 hours of retention time, the resultant was cooled to about 50° C. over a period of 5 hours and the die was taken out to remove a gallium nitride sintered body. The obtained sintered body was then processed into a 76.2 mmϕ×2 mmt disk.

(26) Then, 28.0 g of the thus processed gallium nitride sintered body was loaded in a tube furnace. The sintered body was heated to 1050° C. at a rate of 300° C./h and maintained at 1050° C. for 2 hours in an ammonia atmosphere in which ammonia gas was flowed through at 200 ml/min, to perform a nitridation treatment of the sintered body.

(27) The gallium nitride sintered body was analyzed by the XRD after the nitridation treatment, and there was observed no peak corresponding to gallium oxide in the X-ray diffraction spectrum; therefore, it was found that the thus obtained gallium nitride sintered body contained either no gallium oxide or only a trace amount of gallium oxide below the lower detection limit. The density, open porosity, X-ray peak intensity ratio, oxygen content, and presence/absence of cracking of the obtained gallium nitride sintered body are shown in Table 2.

(28) The gallium nitride sintered body was bonded onto a backing plate made of Cu by using an indium solder as a bonding material to obtain a gallium nitride sputtering target having no breakage or cracking.

First Embodiment—Example 4

(29) The same gallium oxide powder as used in Example 3 (200 g, purity: 4 N) was loaded in a tube furnace. The gallium oxide powder was heated to 1000° C. at a rate of 600° C./h and maintained at 1000° C. for 5 hours to be nitrided in an ammonia atmosphere in which ammonia gas was flowed through at 400 ml/min, to obtain a gallium nitride powder. A portion of this gallium nitride powder was collected, and its specific surface area (BET), untamped bulk density, and repose angle were measured.

(30) The physical property values of the obtained gallium nitride powder are shown in Table 1.

(31) After subjecting the thus obtained gallium nitride powder to a hot-pressing treatment under the same conditions as in Example 3, a nitridation treatment of the resulting gallium nitride sintered body was performed under the same conditions as in Example 3. The density, open porosity, X-ray peak intensity ratio, oxygen content, and presence/absence of cracking of the obtained gallium nitride sintered body are shown in Table 2.

First Embodiment—Example 5

(32) The same gallium oxide powder as used in Example 3 (200 g, purity: 4 N) was loaded in a tube furnace. The gallium oxide powder was heated to 1,100° C. at a rate of 600° C./h and maintained at 1,100° C. for 5 hours to be nitrided in an ammonia atmosphere in which ammonia gas was flowed through at 400 ml/min, to obtain a gallium nitride powder. A portion of this gallium nitride powder was collected, and its specific surface area (BET), untamped bulk density, and repose angle were measured. The physical property values of the gallium nitride powder are shown in Table 1.

(33) After subjecting the thus obtained gallium nitride powder to a hot-pressing treatment under the same conditions as in Example 3, a nitridation treatment of the resulting gallium nitride sintered body was performed under the same conditions as in Example 3. The density, open porosity, X-ray peak intensity ratio, oxygen content, and presence/absence of cracking of the obtained gallium nitride sintered body are shown in Table 2.

First Embodiment—Example 6

(34) A gallium nitride powder in an amount of 100 g, which was obtained in the same manner as in Example 3, was loaded in a 102 mmϕ carbon-made die to perform hot-pressing. The hot-pressing treatment was performed by heating the gallium nitride powder at a rate of 200° C./h to a final temperature of 1050° C., increasing the pressing pressure to 100 MPa when the temperature reaches 1050° C., and maintaining the temperature and pressure for 2 hours. After the 2 hours of retention time, the resultant was cooled to about 50° C. over a period of 5 hours and the die was taken out to remove a gallium nitride sintered body. The obtained sintered body was then processed into a 76.2 mmϕ×2 mmt disk.

(35) Then, 37.8 g of the thus processed gallium nitride sintered body was loaded in a tube furnace. The sintered body was heated to 1,050° C. at a rate of 300° C./h and maintained at 1,050° C. for 2 hours in an ammonia atmosphere in which ammonia gas was flowed through at 200 ml/min, to perform a nitridation treatment of the sintered body. The gallium nitride sintered body was analyzed by the XRD after the nitridation treatment, and a peak corresponding to gallium oxide was not observed in the X-ray diffraction spectrum; therefore, it was found that the thus obtained gallium nitride sintered body contained either no gallium oxide or only a trace amount of gallium oxide below the lower detection limit. The density, open porosity, X-ray peak intensity ratio, oxygen content, and presence/absence of cracking of the obtained gallium nitride sintered body are shown in Table 2.

(36) The gallium nitride sintered body was bonded onto a backing plate made of Cu by using an indium solder as a bonding material to obtain a gallium nitride sputtering target having no breakage or cracking.

First Embodiment—Example 7

(37) A gallium nitride powder in an amount of 100 g, which was obtained in the same manner as in Example 3, was loaded in a 102 mmϕ die made of SUS to perform a hot isostatic pressing. The hot isostatic pressing treatment was performed by heating the gallium nitride powder at a rate of 100° C./h to a final temperature of 1050° C., increasing the pressing pressure to 260 MPa when the temperature reaches 1050° C., and maintaining the temperature and pressure for 1 hour. After the 2 hours of retention time, the resultant was cooled to about 50° C. over a period of 8 hours and the die was taken out to remove a sintered body. The obtained sintered body was then processed into a 76.2 mmϕ×2 mmt disk.

(38) Then, 43.8 g of the thus processed gallium nitride sintered body was loaded in a tube furnace. The sintered body was heated to 1050° C. at a rate of 300° C./h and maintained at 1050° C. for 2 hours in an ammonia atmosphere in which ammonia gas was flowed through at 200 ml/min, to perform a nitridation treatment of the sintered body. The gallium nitride sintered body was analyzed by XRD after the nitridation treatment, and the intensity ratio of the gallium oxide peak to the gallium nitride peak in the (002) was determined to be 2.5% from the X-ray diffraction spectrum; therefore, it was found that the thus obtained gallium nitride sintered body contained only a minor amount of gallium oxide. The density, open porosity, X-ray peak intensity ratio, oxygen content, and presence/absence of cracking of the obtained sintered body are shown in Table 2.

(39) The gallium nitride sintered body was bonded onto a backing plate made of Cu by using an indium solder as a bonding material to obtain a gallium nitride sputtering target having no breakage or cracking.

First Embodiment—Comparative Example 1

(40) A gallium nitride sintered body was produced in the same manner as in Example 1 up to the point before the nitridation treatment. The obtained sintered body was analyzed by the XRD without performing a nitridation treatment, and the X-ray diffraction spectrum shown in FIG. 2 was obtained and the intensity ratio of the gallium oxide peak to the gallium nitride peak in the (002) plane was determined to be 5.9%; therefore, it was found that the obtained gallium nitride sintered body contained a large amount of gallium oxide.

First Embodiment—Comparative Example 2

(41) A gallium nitride powder was obtained by subjecting a gallium oxide powder to a nitridation treatment in the same manner as in Example 3, except that the nitridation temperature was changed to 960° C. A portion of this gallium nitride powder was collected, and its specific surface area (BET) was measured. In addition, the untamped bulk density was measured in accordance with JIS Z2504, and the repose angle was also measured using a powder tester (Model PT-N, manufactured by Hosokawa Micron Group). The physical property values of the obtained gallium nitride powder are shown in Table 1.

(42) The thus obtained gallium nitride powder was subjected to a hot-pressing, nitridation, and bonding in the same manner as in Example 3 to prepare a gallium nitride sintered body and a gallium nitride sputtering target. The resulting gallium nitride sintered body had a low strength, and cracking occurred when the sintered body was taken out of the carbon-made die used in the hot-pressing. The density, open porosity, X-ray peak intensity ratio, oxygen content, and presence/absence of cracking of the obtained sintered body are shown in Table 2.

First Embodiment—Comparative Example 3

(43) A gallium nitride powder was obtained by subjecting a gallium oxide powder to a nitridation treatment in the same manner as in Example 3, except that the nitridation temperature was changed to 1120° C. A portion of the thus obtained gallium nitride powder was collected, and its specific surface area (BET) was measured. In addition, the untamped bulk density was measured in accordance with JIS Z2504, and the repose angle was also measured using a powder tester (Model PT-N, manufactured by Hosokawa Micron Group). The physical property values of the obtained gallium nitride powder are shown in Table 1.

(44) The thus obtained gallium nitride powder was subjected to a hot-pressing, nitridation, and bonding in the same manner as in Example 3 to prepare a gallium nitride sintered body and a gallium nitride sputtering target. The thus obtained gallium nitride sintered body had a low strength, and cracking occurred when the sintered body was taken out of the carbon-made die used in the hot-pressing. The density, open porosity, X-ray peak intensity ratio, oxygen content, and presence/absence of cracking of the sintered body are shown in Table 2.

(45) TABLE-US-00001 TABLE 1 Nitridation temperature of gallium Surface Untamped oxide area bulk Repose powder (BET) density angle (° C.) (m.sup.2/g) (g/cm.sup.3) (°) First Example 1 — 14 0.551 39 embodiment Example 2 — 14 0.551 39 Example 3 1050 6 0.438 37 Example 4 1000 8 0.410 38 Example 5 1100 0.8 0.800 28 Example 6 1050 6 0.438 37 Example 7 1050 6 0.438 37 Comparative — 14 0.551 39 Example 1 Comparative 960 12 0.380 41 Example 2 Comparative 1120 0.3 1.000 25 Example 3

(46) TABLE-US-00002 TABLE 2 Nitridation X-ray Presence/ Sintering Sintered Open temperature of intensity Oxygen absence of Sintering temperature Pressure density porosity sintered body ratio content breakage/ method (° C.) (MPa) (g/cm.sup.3) (%) (° C.) (%) (atm %) cracking First Example 1 HP 1000 40 2.75 98 1000 0.0 4.5 absent Embodiment Example 2 HP 1000 100 4.05 88  900 0.0 4.9 absent Example 3 HP 1050 50 3.04 76 1050 0.0 3.3 absent Example 4 HP 1050 50 2.80 80 1050 0.0 3.8 absent Example 5 HP 1050 50 3.35 72 1050 0.0 1.3 absent Example 6 HP 1050 100 4.14 80 1050 0.0 5.1 absent Example 7 HIP 1050 260 4.80 70 1050 2.5 9.6 absent Comparative HP 1000 40 2.70 98 — 5.9 15.2 absent Example 1 Comparative HP 1050 50 2.43 90 1050 4.7 13.2 present Example 2 Comparative HP 1050 50 4.26 60 1050 0.0 0.9 present Example 3

(47) The second embodiment of the present invention will now be described by way of examples thereof; however, this embodiment is not limited thereto.

(48) (Measurement of Repose Angle and Untamped Bulk Density of Gallium Nitride Powder)

(49) The repose angle of a gallium nitride powder, which is a parameter of the fluidity, was measured using a powder tester (Model PT-N, manufactured by Hosokawa Micron Group). The untamped bulk density of a gallium nitride powder was measured in accordance with JIS Z2504.

(50) The repose angle and untamped bulk density of the gallium nitride powders used in the respective examples are as shown below.

(51) TABLE-US-00003 TABLE 3 Bulk Repose density angle (g/cm.sup.3) (°) Second Example 1 0.3 46 embodiment Example 2 1.2 34 Example 3 1.2 34 Example 4 1.2 34 Example 5 0.3 46 Example 6 0.3 46 Comparative Example 1 0.3 46 Comparative Example 2 0.3 46 Comparative Example 3 0.3 46
(Measurement of Density of Gallium Nitride Molded Article)

(52) The density of a gallium nitride molded article obtained from the respective gallium nitride powders was calculated, based on its weight and the volume which is estimated from the apparent shape of the molded article.

(53) (Measurement of Resistivity of Molded Article)

(54) The resistivity of a molded article having low resistance was measured in accordance with a 4-probe method by use of Loresta HPMCP-T410 and that of a molded article having high resistance was measured by use of Hiresta MCP-T450.

(55) The obtained metal gallium-impregnated gallium nitride molded article was bonded onto a backing plate made of Cu by using an In solder as a bonding material to obtain a gallium nitride-based sputtering target.

(56) A film was formed by sputtering under the following film formation conditions by use of the obtained target, and the thus obtained film was evaluated:

(57) Electric discharge method: RF sputtering or DC sputtering Film formation apparatus: Magnetron sputtering apparatus (manufactured by Tokuda Seisakusho Co., Ltd.; CFS-4ES for 76.2 mmϕ or CFS-8EP for 127 mmϕ)

(58) Target size: 76.2 mmϕ or 127 mmϕ

(59) Film formation pressure: 0.8 Pa

(60) Added gas: Nitrogen

(61) Electric discharge power: 100 W.

Second Embodiment—Example 1

(62) A gallium nitride powder in an amount of 100 g (purity: 4 N, manufactured by Kojundo Chemical Lab. Co., Ltd.) was loaded in a 102 mmϕ carbon-made die to perform hot-pressing. The hot-pressing treatment was performed by heating the gallium nitride powder at a rate of 200° C./h to a final temperature of 1000° C., increasing the pressing pressure to 40 MPa when the temperature reaches 1000° C., and maintaining the temperature and pressure for 2 hours. After the 2 hours of retention time, the resultant was cooled to about 50° C. over a period of 5 hours and the die was taken out to remove a gallium nitride sintered body. The thus obtained sintered body had a size of about 100 mmϕ and density of 2.69 g/cm.sup.3. The sintered body was then processed into a 76.2 mmϕ×2 mmt disk.

(63) Then, 24.5 g of the thus processed gallium nitride sintered body and 33.0 g of metal gallium (purity: 6 N, oxygen content: 0.0174 atm %; manufactured by Dowa Electronics Materials CO., Ltd.) were placed in a vacuum packaging bag such that the metal gallium was arranged in the periphery of the gallium nitride sintered body. The vacuum packaging bag in which the gallium nitride sintered body and the metal gallium were placed was then vacuumed under reduced pressure of 1000 Pa to vacuum-package the gallium nitride sintered body along with the metal gallium. The thus packaged container was then heated to about 50° C. to completely melt the metal gallium and the resultant was then subjected to a cold isostatic pressing (CIP) at 100 MPa for 60 seconds to obtain a molded article. After removing the molded article from the CIP, the molded article was heated at about 50° C. to remove the metal gallium remaining in the periphery to obtain a metal gallium-impregnated gallium nitride molded article. The thus obtained metal gallium-impregnated gallium nitride molded article had density of 5.26 g/cm.sup.3 and resistance of 4.30×10.sup.−3 Ω.Math.cm.

(64) The obtained molded article was mirror-polished to expose a cross-section and the distribution of gallium and nitrogen in the cross-section was examined using an electron probe microanalyzer (EPMA; EPMA1610, manufactured by Shimadzu Corporation), and there were confirmed spots where nitrogen and gallium were in coexistence and spots where nitrogen was not detected excluding the background and gallium was predominantly present. In addition, a scanning electron microscope (SEM; JSM-7600F, manufactured by JEOL Ltd.) observation was performed for the same cross-section of the molded article to verify the positions of voids in the cross-section, and it was confirmed that the value of Ga/(Ga+N) in the cross-section of the molded article was 69% in terms of molar ratio and that the volume ratio of metal gallium with respect to the volume of the voids in the gallium nitride sintered body was 78%. Moreover, the same cross-section of the molded article was analyzed by a powder X-ray diffraction (XRD; RINT Ultima III, manufactured by Rigaku Corporation), and it was confirmed that gallium nitride and metal gallium coexisted as shown in the X-ray diffraction spectrum shown in FIG. 7.

(65) The thus obtained metal gallium-impregnated gallium nitride molded article was bonded onto a backing plate made of Cu by using an indium solder as a bonding material to obtain a gallium nitride-based sputtering target. Sputtering was then performed under the above-described film formation conditions by use of the obtained target, and a film having no cracking or the like was obtained by both RF sputtering and DC sputtering; therefore, it was confirmed that a film can be formed by both RF sputtering and DC sputtering by using the gallium nitride-based sputtering target of this Example. Further, the rate of film formation by DC sputtering was found to be 35 nm/min; therefore, it was confirmed that a film can be formed at a high rate.

Second Embodiment—Example 2

(66) 50 g of the same gallium nitride powder as used in Example 1 and 1000 g of iron-cored resin balls of 15 mm in diameter were loaded in a 1-L nylon pot. The loaded materials were dry-mixed for 20 hours using a rotary ball mill, and the resin balls and coarse particles were then removed using a 500-μm sieve. Thereafter, the thus sieved powder was subjected to rolling granulation for 2 hours and the resultant was collected to obtain a gallium nitride granulated powder in an amount of about 50 g. A gallium nitride granulated powder was prepared twice by this method to obtain a total of 100 g of a gallium nitride granulated powder.

(67) The entire amount of the obtained gallium nitride granulated powder was loaded in a 102 mmϕ carbon-made die to perform hot-pressing. The hot-pressing treatment was performed by heating the gallium nitride granulated powder at a rate of 200° C./h to a final temperature of 1000° C., increasing the pressing pressure to 40 MPa when the temperature reaches 1000° C., and maintaining the temperature and pressure for 2 hours. After the 2 hours of retention time, the resultant was cooled to about 50° C. over a period of 5 hours and the die was taken out to remove a gallium nitride sintered body. The thus obtained sintered body had a size of about 100 mmϕ and density of 3.16 g/cm.sup.3. The sintered body was then processed into a 76.2 mmϕ×2 mmt disk.

(68) Then, 28.8 g of the thus processed gallium nitride sintered body and 30 g of the same metal gallium as used in Example 1 were placed in a vacuum packaging bag such that the metal gallium was arranged in the periphery of the gallium nitride sintered body. The vacuum packaging bag in which the gallium nitride sintered body and the metal gallium were placed was then vacuumed under reduced pressure of 1000 Pa to vacuum-package the gallium nitride sintered body along with the metal gallium. The thus packaged container was then heated to about 50° C. to completely melt the metal gallium and the resultant was then subjected to a cold isostatic pressing (CIP) at 100 MPa for 60 seconds to obtain a molded article. After removing the molded article from CIP, the molded article was heated at about 50° C. to remove the metal gallium remaining in the periphery to obtain a metal gallium-impregnated gallium nitride molded article. The thus obtained metal gallium-impregnated gallium nitride molded article had density of 5.30 g/cm.sup.3 and resistance of 8.60×10.sup.−2 Ω.Math.cm.

(69) The obtained molded article was mirror-polished to expose a cross-section and the distribution of gallium and nitrogen in the cross-section was examined using an EPMA, and, there were confirmed spots where nitrogen and gallium were in coexistence and spots where nitrogen was not detected excluding the background and gallium was predominantly present. In addition, a scanning electron microscopic image (SEM image) was examined for the same cross-section of the molded article to verify the positions of voids in the cross-section, and it was confirmed that the value of Ga/(Ga+N) in the cross-section of the molded article was 65% in terms of molar ratio and that the volume ratio of metal gallium with respect to the volume of the voids in the gallium nitride sintered body was 75%.

(70) The thus obtained metal gallium-impregnated gallium nitride molded article was bonded onto a backing plate made of Cu by using an indium solder as a bonding material to obtain a gallium nitride-based sputtering target. Sputtering was then performed under the above-described film formation conditions by use of the obtained target, and a film having no particular cracking or the like was obtained by both RF sputtering and DC sputtering; therefore, it was confirmed that a film can be formed by both RF sputtering and DC sputtering by using the gallium nitride-based sputtering target of this Example. Further, the rate of film formation by DC sputtering was found to be 35 nm/min; therefore, it was confirmed that a film can be formed at a high rate.

Second Embodiment—Example 3

(71) A total of 350 g of a gallium nitride granulated powder was prepared in the same manner as in Example 2 and the entire amount thereof was loaded in a 170-mmϕ carbon-made die to perform hot-pressing. The hot-pressing treatment was performed by heating the gallium nitride granulated powder at a rate of 200° C./h to a final temperature of 1000° C., increasing the pressing pressure to 40 MPa when the temperature reaches 1000° C., and maintaining the temperature and pressure for 2 hours. After the 2 hours of retention time, the resultant was cooled to about 50° C. over a period of 5 hours and the die was taken out to remove a gallium nitride sintered body. The thus obtained sintered body had a size of about 170 mmϕ and density of 3.09 g/cm.sup.3. The sintered body was then processed into a 127 mmϕ×3 mmt disk.

(72) Then, 117.5 g of the thus processed gallium nitride sintered body and 120 g of the same metal gallium as used in Example 1 were placed in a vacuum packaging bag such that the metal gallium was arranged in the periphery of the gallium nitride sintered body. The vacuum packaging bag in which the gallium nitride sintered body and the metal gallium were placed was then vacuumed under reduced pressure of 10 Pa to vacuum-package the gallium nitride sintered body along with the metal gallium. The thus packaged container was then heated to about 50° C. to completely melt the metal gallium and the resultant was then subjected to a cold isostatic pressing (CIP) at 100 MPa for 60 seconds to obtain a molded article. After removing the molded article from CIP, the molded article was heated at about 50° C. to remove the metal gallium remaining in the periphery to obtain a metal gallium-impregnated gallium nitride molded article. The thus obtained metal gallium-impregnated gallium nitride molded article had density of 5.23 g/cm.sup.3 and resistance of 6.20×10.sup.−3 Ω.Math.cm.

(73) The obtained molded article was mirror-polished to expose a cross-section and the distribution of gallium and nitrogen in the cross-section was examined using an EPMA, and there were confirmed spots where nitrogen and gallium were in coexistence and spots where nitrogen was not detected excluding the background and gallium was predominantly present. In addition, a SEM observation was performed for the same cross-section of the molded article to verify the positions of voids in the cross-section, and it was confirmed that the value of Ga/(Ga+N) in the cross-section of the molded article was 65% in terms of molar ratio and that the volume ratio of metal gallium with respect to the volume of the voids in the gallium nitride sintered body was 73%.

(74) The thus obtained metal gallium-impregnated gallium nitride molded article was bonded onto a backing plate made of Cu by using an indium solder as a bonding material to obtain a gallium nitride-based sputtering target. Sputtering was then performed under the above-described film formation conditions by use of the obtained target, and a film having no particular cracking or the like was obtained by both RF sputtering and DC sputtering; therefore, it was confirmed that a film can be formed by both RF sputtering and DC sputtering by using the gallium nitride-based sputtering target of this Example, and that a large-sized sputtering target can be produced.

Second Embodiment—Example 4

(75) A gallium nitride sintered body was prepared and processed in the same manner as in Example 2 to obtain a sintered body in the form of a 76.2 mmϕ×2 mmt disk. The obtained sintered body had density of 3.10 g/cm.sup.3.

(76) Then, 29 g of the thus processed gallium nitride sintered body and 30 g of the same metal gallium as used in Example 1 were placed in a vacuum packaging bag such that the metal gallium was arranged in the periphery of the gallium nitride sintered body. The vacuum packaging bag in which the gallium nitride sintered body and the metal gallium were placed was then vacuumed under reduced pressure of 1000 Pa to vacuum-package the gallium nitride sintered body along with the metal gallium. The thus packaged container was then heated to about 50° C. to completely melt the metal gallium and the resultant was then subjected to the CIP at 100 MPa for 60 seconds to obtain a molded article. After removing the molded article from the CIP, the molded article was heated at about 50° C. to remove the metal gallium remaining in the periphery to obtain a metal gallium-impregnated gallium nitride molded article. The thus obtained metal gallium-impregnated gallium nitride molded article was heat-treated in vacuum at 200° C. for 2 hours and then cooled to room temperature. The resulting metal gallium-impregnated gallium nitride molded article had density of 4.60 g/cm.sup.3 and resistance of 5.1×10.sup.−3 Ω.Math.cm.

(77) The obtained molded article was mirror-polished to expose a cross-section and the distribution of gallium and nitrogen in the cross-section was examined using an EPMA, and there were confirmed spots where nitrogen and gallium were in coexistence and spots where nitrogen was not detected excluding the background and gallium was predominantly present. In addition, a SEM observation was performed for the same cross-section of the molded article to verify the positions of voids in the cross-section, and it was confirmed that the value of Ga/(Ga+N) in the cross-section of the molded article was 62% in terms of molar ratio and that the volume ratio of metal gallium with respect to the volume of the voids in the gallium nitride sintered body was 51%.

(78) The thus obtained metal gallium-impregnated gallium nitride sintered body was bonded onto a backing plate made of Cu by using an indium solder as a bonding material to obtain a gallium nitride-based sputtering target. Sputtering was then performed under the above-described film formation conditions by use of the obtained target, and a film having no particular cracking or the like was obtained by both RF sputtering and DC sputtering; therefore, it was confirmed that a film can be formed by both RF sputtering and DC sputtering by using the gallium nitride-based sputtering target of this Example.

Second Embodiment—Example 5

(79) The same gallium nitride powder as used in Example 1 (100 g) was loaded in a 102-mmϕ carbon-made die to be press-molded at room temperature with a pressure of 30 MPa. Thereafter, the resultant was subjected to a CIP treatment at 300 MPa to obtain a gallium nitride molded article having density of 2.19 g/cm.sup.3. The obtained molded article was then processed into a 76.2 mmϕ×2 mmt disk.

(80) Then, 20.0 g of the thus processed gallium nitride molded article and 38 g of the same metal gallium as used in Example 1 were placed in a vacuum packaging bag such that the metal gallium was arranged in the periphery of the gallium nitride molded article. The vacuum packaging bag in which the gallium nitride molded article and the metal gallium were placed was then vacuumed under reduced pressure of 300 Pa to vacuum-package the gallium nitride molded article along with the metal gallium. The thus packaged container was then heated to about 50° C. to completely melt the metal gallium and the resultant was then subjected to a CIP treatment at 100 MPa for 60 seconds to obtain a molded article. After removing the molded article from the CIP, the molded article was heated at about 50° C. to remove the metal gallium remaining in the periphery to obtain a metal gallium-impregnated gallium nitride molded article. The thus obtained metal gallium-impregnated gallium nitride molded article had density of 5.48 g/cm.sup.3 and resistance of 2.40×10.sup.−3 Ω.Math.cm.

(81) The obtained molded article was mirror-polished to expose a cross-section and the distribution of gallium and nitrogen in the cross-section was examined using an EPMA, and there were confirmed spots where nitrogen and gallium were in coexistence and spots where nitrogen was not detected excluding the background and gallium was predominantly present. In addition, a SEM observation was performed for the same cross-section of the molded article to verify the positions of voids in the cross-section, and it was confirmed that the value of Ga/(Ga+N) in the cross-section of the molded article was 74% in terms of molar ratio and that the volume ratio of metal gallium with respect to the volume of the voids in the gallium nitride sintered body was 87%.

(82) The thus obtained metal gallium-impregnated gallium nitride molded article was bonded onto a backing plate made of Cu by using an indium solder as a bonding material to obtain a gallium nitride-based sputtering target. Sputtering was then performed under the above-described film formation conditions by use of the obtained target, and a film having no particular cracking or the like was obtained by both RF sputtering and DC sputtering; therefore, it was confirmed that a film can be formed by both RF sputtering and DC sputtering by using the gallium nitride-based sputtering target of this Example.

Second Embodiment—Example 6

(83) The same gallium nitride powder as used in Example 1 (100 g) was loaded in a 102 mmϕ carbon-made die to perform hot-pressing. The hot-pressing treatment was performed by heating the gallium nitride powder at a rate of 200° C./h to a final temperature of 1050° C., increasing the pressing pressure to 50 MPa when the temperature reaches 1050° C., and maintaining the temperature and pressure for 2 hours. After the 2 hours of retention time, the resultant was cooled to about 50° C. over a period of 5 hours and the die was taken out to remove a gallium nitride sintered body. The thus obtained sintered body had density of 3.04 g/cm.sup.3. The sintered body was then processed into a 76.2 mmϕ×2 mmt disk.

(84) Then, 27.7 g of the thus processed gallium nitride sintered body and 38 g of the same metal gallium as used in Example 1 were placed in a vacuum packaging bag such that the metal gallium was arranged in the periphery of the gallium nitride sintered body. The vacuum packaging bag in which the gallium nitride sintered body and the metal gallium were placed was then vacuumed under reduced pressure of 300 Pa to vacuum-package the gallium nitride sintered body along with the metal gallium. The thus packaged container was then heated to about 50° C. to completely melt the metal gallium and the resultant was then subjected to a CIP treatment at 100 MPa for 60 seconds to obtain a molded article. After removing the molded article from the CIP, the molded article was heated at about 50° C. to remove the metal gallium remaining in the periphery to obtain a metal gallium-impregnated gallium nitride molded article. The thus obtained metal gallium-impregnated gallium nitride molded article had density of 5.32 g/cm.sup.3 and resistance of 1.80×10.sup.−3 Ω.Math.cm.

(85) The obtained molded article was mirror-polished to expose a cross-section and the distribution of gallium and nitrogen in the cross-section was examined using an EPMA, and there were confirmed spots where nitrogen and gallium were in coexistence and spots where nitrogen was not detected excluding the background and gallium was predominantly present. In addition, a SEM observation was performed for the same cross-section of the molded article to verify the positions of voids in the cross-section, and it was confirmed that the value of Ga/(Ga+N) in the cross-section of the molded article was 72% in terms of molar ratio and that the volume ratio of metal gallium with respect to the volume of the voids in the gallium nitride sintered body was 81%.

(86) A portion of the thus obtained metal gallium-impregnated gallium nitride molded article was collected and its oxygen content was measured using an oxygen-nitrogen analyzer (manufactured by LECO Corporation), and it was found that the metal gallium-impregnated gallium nitride molded article had an oxygen content of 6.03 atm %. In addition, the same cross-section of the molded article was analyzed by a powder X-ray diffraction (XRD; RINT Ultima III, manufactured by Rigaku Corporation), and the X-ray diffraction spectrum comparable to the one observed in Example 1 was obtained; therefore, it was confirmed that the gallium nitride and the metal gallium coexisted. Moreover, it was found that the obtained metal gallium-impregnated gallium nitride molded article contained either no gallium oxide or only a trace amount of gallium oxide below the lower detection limit, since there was no (002) peak of gallium oxide in the analyzed X-ray diffraction spectrum.

(87) Furthermore, the metal gallium-impregnated gallium nitride molded article had thermal conductivity of 14.3 W/mK; therefore, it was confirmed that the thermal conductivity was improved as compared to the gallium nitride sintered body prior to being impregnated with metal gallium.

(88) Then, RF sputtering was performed on a surface to be bonded (a surface to form an interface with a solder material) of the obtained metal gallium-impregnated gallium nitride molded article by using a tungsten target to form a barrier layer of tungsten. This film formation was carried out by a magnetron sputtering apparatus using the tungsten target of 76.2 mmϕ in size, an added gas of argon, and an electrical discharge powder of 100 W. The thus obtained tungsten barrier layer had a thickness of 2 μm.

(89) The thus obtained gallium-impregnated gallium nitride molded article having a barrier layer of tungsten formed thereon was bonded onto a backing plate made of Cu by using an indium solder as a bonding material to obtain a gallium nitride-based sputtering target. Sputtering was then performed under the above-described film formation conditions by use of the obtained target, and a film having no particular cracking or the like was obtained by both RF sputtering and DC sputtering; therefore, it was confirmed that a film can be formed by both RF sputtering and DC sputtering by using the gallium nitride-based sputtering target of this Example.

(90) A portion of each of the metal gallium-impregnated gallium nitride molded articles obtained in Examples 1 to 5 was collected to measure the oxygen content and the thermal conductivity in the same procedures. The measurement results are shown in Table 7.

Second Embodiment—Comparative Example 1

(91) The same gallium nitride powder as used in Example 1 (100 g) was loaded in a 102 mmϕ carbon-made die to be press-molded at room temperature with a pressure of 30 MPa. Thereafter, the resultant was subjected to a CIP treatment at 300 MPa to obtain a gallium nitride molded article having density of 2.30 g/cm.sup.3. The obtained molded article was then processed into a 76.2 mmϕ×2 mmt disk. The molded article had resistance of 2.6×10.sup.7 Ω.Math.cm.

(92) The obtained molded article was mirror-polished to expose a cross-section and the distribution of gallium and nitrogen in the cross-section was examined using an EPMA, and there were confirmed spots where nitrogen and gallium were in coexistence; however, a spot where nitrogen was not detected excluding the background and gallium was predominantly present was not observed. In addition, a SEM observation was performed for the same cross-section of the molded article to verify the positions of voids in the cross-section, and it was confirmed that the value of Ga/(Ga+N) in the cross-section of the molded article was 50% in terms of molar ratio and that the volume ratio of metal gallium with respect to the volume of the voids in the gallium nitride sintered body was 0%.

(93) The thus obtained molded article was bonded onto a backing plate made of Cu by using an indium solder as a bonding material to obtain a gallium nitride-based sputtering target. When sputtering was performed using the obtained target under the same film formation conditions as in Example 1, cracking occurred in the target, and a film could not properly formed.

Second Embodiment—Comparative Example 2

(94) A gallium nitride molded article was produced in the same manner as in Example 5. The obtained gallium nitride molded article had density of 2.20 g/cm.sup.3.

(95) Then, 20 g of the thus processed gallium nitride molded article and 4 g of the same metal gallium as used in Example 1 were placed in a vacuum packaging bag such that the metal gallium was arranged in the periphery of the gallium nitride molded article. The vacuum packaging bag in which the gallium nitride molded article and the metal gallium were placed was then vacuumed under reduced pressure of 1000 Pa to vacuum-package the gallium nitride molded article along with the metal gallium. The thus packaged container was then heated to about 50° C. to completely melt the metal gallium, and the resultant was then subjected to a CIP treatment at 100 MPa for 60 seconds to obtain a molded article. The thus obtained metal gallium-impregnated gallium nitride molded article had density of 2.58 g/cm.sup.3 and resistance of 2.00×10.sup.2 Ω.Math.cm.

(96) The obtained molded article was mirror-polished to expose a cross-section and the distribution of gallium and nitrogen in the cross-section was examined using an EPMA, and there were confirmed spots where nitrogen and gallium were in coexistence and spots where nitrogen was not detected excluding the background and gallium was predominantly present; however, the number of the spots where gallium was predominantly present was smaller as compared to Example 5. In addition, spots where metal gallium did not impregnate were also confirmed by visual observation of the molded article. Moreover, a SEM observation was performed for the same cross-section of the molded article to verify the positions of voids in the cross-section, and it was confirmed that the value of Ga/(Ga+N) in the cross-section of the molded article was 54% in terms of molar ratio and that the volume ratio of metal gallium with respect to the volume of the voids in the gallium nitride sintered body was 10%.

(97) The thus obtained metal gallium-impregnated gallium nitride molded article was bonded onto a backing plate made of Cu by using an indium solder as a bonding material to obtain a gallium nitride-based sputtering target. Sputtering was then performed under the above-described film formation conditions by use of the obtained target. RF sputtering was able to be performed; however, DC sputtering could not be performed.

Second Embodiment—Comparative Example 3

(98) The same gallium nitride powder as used in Example 1 (100 g) was sintered by a hot isostatic pressing method using a 102 mmϕ die. The hot isostatic pressing treatment was performed by heating the gallium nitride powder at a rate of 100° C./h to a final temperature of 1050° C., increasing the pressing pressure to 280 MPa when the temperature reaches 1050° C., and maintaining the temperature and pressure for 2 hours. After the 2 hours of retention time, the resultant was cooled to about 50° C. over a period of 10 hours and the die was taken out to remove a gallium nitride sintered body. The thus obtained sintered body had density of 5.07 g/cm.sup.3 and resistance of 1.2×10.sup.7 Ω.Math.cm. The sintered body was then processed into a 76.2 mmϕ2 mmt disk.

(99) Then, 46.2 g of the thus processed gallium nitride sintered body and 9 g of the same metal gallium as used in Example 1 were placed in a vacuum packaging bag such that the metal gallium was arranged in the periphery of the gallium nitride sintered body. The vacuum packaging bag in which the gallium nitride sintered body and the metal gallium were placed was then vacuumed under reduced pressure of 1000 Pa to vacuum-package the gallium nitride sintered body along with the metal gallium. The thus packaged container was heated to about 50° C. to completely melt the metal gallium and the resultant was then subjected to cold isostatic pressing (CIP) at 100 MPa for 60 seconds to obtain a molded article, in the same manner as in Example 1. The thus obtained metal gallium-impregnated gallium nitride molded article had density of 5.34 g/cm.sup.3 and resistance of 2.13×10.sup.2 Ω.Math.cm. It is noted here that, although the amount of the metal gallium used was smaller than the weight of the processed gallium nitride sintered body, the amount of the metal gallium was sufficient for the volume of the voids calculated from the volume and density of the gallium nitride sintered body prior to being impregnated with the metal gallium, as in the metal gallium impregnation treatment performed in Examples 1 to 6.

(100) The obtained molded article was mirror-polished to expose a cross-section and the distribution of gallium and nitrogen in the cross-section was examined using an EPMA, and there were confirmed spots where nitrogen and gallium were in coexistence and spots where nitrogen was not detected excluding the background and gallium was predominantly present; however, the number of the spots where gallium was predominantly present was smaller as compared to Example 1. In addition, spots where metal gallium did not impregnate were also confirmed by visual observation of the molded article. Moreover, it was confirmed that the value of Ga/(Ga+N) in the cross-section was 53% in terms of molar ratio and that the volume ratio of metal gallium with respect to the volume of the voids in the gallium nitride sintered body was 16%, by performing a SEM observation of the same cross-section of the molded article.

(101) The thus obtained metal gallium-impregnated gallium nitride molded article was bonded onto a backing plate made of Cu by using an indium solder as a bonding material to obtain a gallium nitride-based sputtering target. Sputtering was then performed under the above-described film formation conditions by use of the obtained target. RF sputtering was able to be performed; however, DC sputtering could not be performed.

(102) The processing conditions used in the respective Examples and Comparative Examples of the second embodiment are shown in Table 4.

(103) TABLE-US-00004 TABLE 4 Metal gallium impregnation step Gallium nitride molding step Amount of Molding gallium nitride Amount of Vacuum CIP Molding temperature Pressure sintered body metal gallium pressure Pressure method (° C.) (MPa) (g) (g) (Pa) (MPa) Second Example 1 HP 1000 40 24.5 33 1000 100 Embodiment Example 2 HP 1000 40 28.8 30 1000 100 Example 3 HP 1000 40 117.5 120 10 100 Example 4 HP 1000 40 29 30 1000 100 Example 5 Uniaxial pressing 25 30 20 38 300 100 Example 6 HP 1050 50 27.7 38 300 100 Comparative Uniaxial pressing 25 30 — — — — Example 1 Comparative Uniaxial pressing 25 30 20 4 1000 100 Example 2 Comparative HIP 1050 280 46.2 9 1000 100 Example 3

(104) Table 5 shows the density of the respective gallium nitride molded articles as well as the density, Ga/(Ga+N) in terms of molar ratio (%), the volume ratio of metal gallium contained in the voids, and the resistivity of the respective metal gallium-impregnated gallium nitride molded articles obtained in Examples and Comparative Examples of the second embodiment.

(105) TABLE-US-00005 TABLE 5 Density of metal Resistivity of metal Density of gallium-impregnated Ratio of gallium-impregnated gallium nitride gallium nitride metal gallium gallium nitride molded article molded article Ga/(Ga + N) contained in voids molded article (g/cm.sup.3) (g/cm.sup.3) (%) (%) (Ω .Math. cm) Second Example 1 2.69 5.26 69 78 4.30 × 10.sup.−3 Embodiment Example 2 3.16 5.30 65 75 8.60 × 10.sup.−2 Example 3 3.09 5.23 65 73 6.20 × 10.sup.−3 Example 4 3.10 4.60 62 51 5.10 × 10.sup.−3 Example 5 2.19 5.48 74 87 2.40 × 10.sup.−3 Example 6 3.04 5.32 72 81 1.80 × 10.sup.−3 Comparative 2.30 2.30 50 0 2.60 × 10.sup.7  Example 1 Comparative 2.20 2.58 54 10 2.00 × 10.sup.2  Example 2 Comparative 5.07 5.34 53 16 2.13 × 10.sup.2  Example 3

(106) Table 6 shows whether or not RF sputtering and DC sputtering could be carried out using the respective gallium nitride-based sputtering targets that were obtained in Examples and Comparative Examples of the second embodiment.

(107) TABLE-US-00006 TABLE 6 RF DC sputtering sputtering Second Example 1 Good Good embodiment Example 2 Good Good Example 3 Good Good Example 4 Good Good Example 5 Good Good Example 6 Good Good Comparative No Good No Good Example 1 Comparative Good No Good Example 2 Comparative Good No Good Example 3

(108) Table 7 shows the density of the respective gallium nitride molded articles as well as the density, the oxygen content, X-ray intensity ratio, and the thermal conductivity of the respective metal gallium-impregnated gallium nitride molded articles obtained in Examples and Comparative Examples of the second embodiment.

(109) TABLE-US-00007 TABLE 7 Density of metal Physical property values Density of gallium-impregnated X-ray gallium nitride gallium nitride Oxygen intensity Thermal molded article molded article content ratio conductivity (g/cm.sup.3) (g/cm.sup.3) (atm %) (%) (W/mK) Second Example 1 2.69 5.26 8.39 0.0 13.9 embodiment Example 2 3.16 5.30 10.5 2.5 13.5 Example 3 3.09 5.23 8.74 0.0 12.2 Example 4 3.10 4.60 9.22 0.7 11.5 Example 5 2.19 5.48 7.81 0.0 14.7 Example 6 3.04 5.48 6.03 0.0 14.3 Comparative 2.30 — 16.1 8.5 2.6 Example 1 Comparative 2.20 2.58 12.5 3.4 2.8 Example 2 Comparative 5.07 5.34 13.3 4.1 2.7 Example 3

DESCRIPTION OF SYMBOLS

(110) 1: Peak of the (002) plane of gallium nitride 2: Peak of the (002) plane of gallium oxide 11: Metal gallium-impregnated gallium nitride molded article 12: Gallium nitride phase 13: Metal gallium phase 14: Void 15: Metal gallium 16: Vacuum packaging bag