WO2013008697A1 - AlN基板およびその製造方法 - Google Patents
AlN基板およびその製造方法 Download PDFInfo
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- WO2013008697A1 WO2013008697A1 PCT/JP2012/067100 JP2012067100W WO2013008697A1 WO 2013008697 A1 WO2013008697 A1 WO 2013008697A1 JP 2012067100 W JP2012067100 W JP 2012067100W WO 2013008697 A1 WO2013008697 A1 WO 2013008697A1
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Definitions
- the present invention relates to an AlN substrate and a manufacturing method thereof.
- a heat spreader made of a material having high thermal conductivity is used.
- the heat spreader include a base substrate that forms a bonded substrate by bonding to a semiconductor substrate (see Patent Document 1).
- a semiconductor element such as the semiconductor light-emitting element is formed by epitaxially growing a single layer or multiple layers on the exposed surface on the semiconductor substrate side.
- the base substrate is required to have a small difference in thermal expansion coefficient from that of the semiconductor substrate in order to prevent warpage or peeling of the bonded substrate.
- an AlN substrate that satisfies these requirements is preferably used as the base substrate.
- a conventional AlN substrate manufactured by sintering AlN has a large number of defects (pores), and a bonding surface with a semiconductor substrate is formed. If the surface is mirror-polished to improve the efficiency of heat transfer, the pores are opened and appear as voids that prevent heat transfer between the semiconductor substrate and the bonding surface, so that a desired heat transfer effect cannot be obtained. There is a case.
- An object of the present invention is to provide an AlN substrate that is superior in efficiency of heat transfer between other members such as a semiconductor substrate bonded to a bonding surface as compared with the prior art, and a manufacturing method for manufacturing the AlN substrate. It is to provide.
- the present invention is an AlN substrate having a joint surface with another member, which is made of an AlN sintered body containing a 2A group element and a 3A group element, and the surface roughness Ra of the joint surface is 15 nm or less,
- the voids exposed on the joint surface having a major axis of 0.25 ⁇ m or more have an average value of the major axis of 1.5 ⁇ m or less and a maximum value of 1.8 ⁇ m or less.
- the AlN substrate of the present invention is made of a sintered body of AlN containing a 2A group element and a 3A group element as described above, and has a smooth surface with few voids having a surface roughness Ra of 15 nm or less, Moreover, since the average value of the major axis of the void having a major axis of 0.25 ⁇ m or more existing on the junction surface is defined as 1.5 ⁇ m or less and the maximum value is 1.8 ⁇ m or less, the semiconductor substrate to be joined to the junction surface The efficiency of heat transfer with other members such as the above can be improved as compared with the past.
- an AlN substrate of the present invention is bonded to a semiconductor substrate as a base substrate, for example, to form a bonded substrate, heat from a semiconductor element such as a semiconductor light emitting element formed on the semiconductor substrate is transferred to the semiconductor substrate. It can be transmitted from the substrate to the AlN substrate more efficiently than before, and can be removed as quickly as possible via a heat dissipation member connected to the AlN substrate, and the malfunction and damage of the semiconductor element due to the heat can be reliably ensured. Can be prevented.
- the 2A group element is preferably at least one selected from the group consisting of Ca and Mg.
- the AlN substrate of the present invention preferably contains the 2A group element in a proportion of 0.009% by mass or more and 0.28% by mass or less in terms of oxide.
- the group 3A element is preferably at least one selected from the group consisting of Y and lanthanoids.
- the AlN substrate of the present invention preferably contains the group 3A element in a ratio of 0.02% by mass to 4.5% by mass in terms of oxide.
- This invention is a manufacturing method for manufacturing the said AlN board
- the method includes a step of performing an isostatic pressing process (HIP (Hot Isostatic Pressing) process).
- HIP Hot Isostatic Pressing
- a sintered body of AlN having a theoretical density within a certain range, formed by sintering at a relatively low temperature within the above temperature range, from a precursor formed by a sintered material containing each of the above components By subjecting the pre-sintered body) to HIP treatment under the above-described conditions, the pores inherent in the sintered body can be filled, the size of each pore can be reduced, and the number of pores can be reduced. That is, the 2A group element contained in the sintered material reacts with the oxide on the surface of the AlN particles by heating within the temperature range in the HIP treatment step, and is contained in the sintered material.
- the 3A group element works to moderately adjust the viscosity of the generated liquid phase.
- the sintering aid that has become a semi-molten state flows at the grain boundary portion of the sintered body, and
- the crystal grains constituting the sintered body can be rearranged to densify the sintered body, and as a result, as described above, the pores inherent in the sintered body are filled to reduce the number of the pores, The size of the remaining pores can be reduced.
- the average value of the major axis of voids having a major axis of 0.25 ⁇ m or more that appears on the joint surface by opening the pores by mirror polishing the joint surface with the other member in a polishing process is 1
- the surface roughness Ra of the bonding surface as a parameter for the number of voids can be made 15 nm or less.
- the method (b) since the method (b) has open pores, it is impossible to produce a densified AlN substrate equivalent to that produced by the production method of the present invention. Furthermore, since the sintering aid is not sufficiently transferred even in the two-stage sintering of (c), it is possible to manufacture a densified AlN substrate equivalent to that manufactured by the manufacturing method of the present invention. Can not.
- an AlN substrate excellent in heat transfer efficiency between other members such as a semiconductor substrate bonded to a bonding surface, and a manufacturing method for manufacturing the AlN substrate. can be provided.
- the present invention is an AlN substrate having a joint surface with another member, which is made of an AlN sintered body containing a 2A group element and a 3A group element, and the surface roughness Ra of the joint surface is 15 nm or less,
- the voids exposed on the joint surface having a major axis of 0.25 ⁇ m or more have an average value of the major axis of 1.5 ⁇ m or less and a maximum value of 1.8 ⁇ m or less.
- the present invention is composed of a sintered body of AlN containing a group 2A element and a group 3A element, and the surface roughness Ra of the joint surface is 15 nm or less and is a smooth surface with few voids, Since the average value of the major axis of the void having a major axis of 0.25 ⁇ m or more existing on the junction surface is defined as 1.5 ⁇ m or less and the maximum value is 1.8 ⁇ m or less, a semiconductor substrate or the like joined to the junction surface The efficiency of heat transfer between the other members can be improved more than before.
- an AlN substrate of the present invention is bonded to a semiconductor substrate as a base substrate, for example, to form a bonded substrate, heat from a semiconductor element such as a semiconductor light emitting element formed on the semiconductor substrate is transferred to the semiconductor substrate. It can be transmitted from the substrate to the AlN substrate more efficiently than before, and can be removed as quickly as possible via a heat radiating member connected to the AlN substrate, and it is possible to reliably prevent malfunction or damage of the semiconductor element due to heat. Can be prevented.
- the surface roughness Ra of the bonding surface is limited to 15 nm or less for the following reason. That is, when the surface roughness Ra exceeds 15 nm, a large number of voids exist on the joint surface even if the range of the major axis of the void and the average value of the major axis are within the range. And the effect which improves the efficiency of the heat transfer between the other members joined to the said joint surface is not acquired. Moreover, there exists a possibility that the joint strength of another member may fall and it may become easy to peel off.
- the surface roughness Ra of the joint surface is preferably as small as possible within the above range, and particularly 10 nm or less. Is preferred. However, considering the productivity and yield of the AlN substrate, the surface roughness Ra is preferably 0.1 nm or more even within the above range. It is substantially difficult to make the surface roughness Ra less than the above range.
- the surface roughness Ra of the joint surface is defined by the Japanese Industrial Standard JIS B0601: 2001 “Product Geometrical Specification (GPS) —Surface Property: Contour Curve Method—Terminology, Definition, and Surface Property Parameter”. It will be expressed by the arithmetic average height Ra of the curve. Further, in the present invention, the major axis of the void for obtaining the average value and the maximum value of the major axis exposed on the joint surface is limited to 0.25 ⁇ m or more for the following reason.
- small voids having a major axis of less than 0.25 ⁇ m are buried when other members such as a semiconductor substrate are bonded to the bonding surface by, for example, a direct bonding method or a surface activation method. Even when it remains as a void after pasting, heat transfer between the joined other members is not hindered. Therefore, in the present invention, small voids having a major axis of less than 0.25 ⁇ m are not counted as voids when obtaining the average value and the maximum value of the major axis of the voids exposed on the joint surface.
- the voids having a major axis of 0.25 ⁇ m or more exposed on the joining surface have an average value of the major axis limited to 1.5 ⁇ m or less and a maximum value of 1.8 ⁇ m or less.
- the average value or the maximum value of the major axis of the void exposed on the bonding surface exceeds the above range, even if the surface roughness Ra of the bonding surface is within the range of 15 nm or less.
- the effect of improving the efficiency of heat transfer with other members joined to the joining surface cannot be obtained.
- the average value of the major axis of the void is preferably 1.0 ⁇ m or less even within the above range.
- the maximum value of the major axis of the void is preferably 1.2 ⁇ m or less even within the above range.
- the average value of the major axis of the void is preferably 0.3 ⁇ m or more even within the above range, and the maximum value is 0.5 ⁇ m or more even within the above range. Preferably there is. It is substantially difficult to make the average value or the maximum value less than the above range.
- the major axis of the void exposed on the joint surface is represented by a value measured by the following method. That is, carbon is vapor-deposited on the joint surface of the AlN substrate that has been subjected to mirror polishing or the like, and any five fields of view are photographed at a magnification of 1000 times using a scanning electron microscope. Next, the photographed image is stretched three times, all the voids confirmed in the field of view are approximated to an ellipse, and the major axis is measured as the major axis.
- the average value and the maximum value of the major axis are obtained from the measured values of the major axis of all voids having a major axis of 0.25 ⁇ m or more excluding those having a major axis of less than 0.25 ⁇ m.
- the group 3A element is preferably at least one selected from the group consisting of Y and lanthanoids, for example.
- the AlN substrate manufactured by the manufacturing method of the present invention described later has a ratio of the 2A group element of 0.009% by mass or more in terms of oxide based on the composition of the sintered material as the starting material. Is preferably 0.28% by mass or less. Further, the proportion of the group 3A element is preferably 0.02% by mass or more, and preferably 4.5% by mass or less, in terms of oxide.
- the reason why the ratio of the 2A group element is less than the above range is that the ratio of the 2A group element in the sintered material used as the starting material in the production method of the present invention is smaller than the predetermined value described above. There are many. In that case, the effect obtained by adding the group 2A element to the sintered material is not obtained, and the voids exposed on the bonded surface of the AlN substrate after polishing become larger than the range defined in the present invention. There is a fear.
- the reason why the ratio of the 2A group element exceeds the above range is often because the ratio of the 2A group element in the sintered material is larger than the predetermined value described above.
- the voids exposed on the bonded surface of the AlN substrate after polishing may become larger than the range defined in the present invention due to the action of the excess group 2A element.
- the reason why the ratio of the group 3A element is less than the above range is that the ratio of the group 3A element in the sintered material is often less than the predetermined value described above.
- the effect obtained by blending the group 3A element with the binder is not obtained, and voids exposed on the bonded surface of the AlN substrate after polishing may be larger than the range defined in the present invention.
- the reason why the ratio of the group 3A element exceeds the above range is often because the ratio of the group 2A element in the sintered material is more than the predetermined value described above.
- the thermal conductivity of the manufactured AlN substrate cannot be maintained within a suitable range of thermal conductivity required for the AlN substrate, particularly a range of 80 W / m ⁇ K or more, which will be described later.
- the AlN substrate may contain Si in an amount of 0.3% by mass or less in terms of oxide.
- the lower limit of the Si content ratio includes 0% by mass, that is, the case where Si is not included.
- the balance of the AlN substrate is substantially AlN.
- substantially may include Al not constituting AlN, O, or other inevitable impurities in the complex oxide constituting the crystal grain boundaries in addition to AlN. Means that.
- the content ratio of each component in terms of oxide can be determined from the result of analyzing the mirror-polished bonding surface of the AlN substrate by glow discharge mass spectrometry (GDMS).
- GDMS glow discharge mass spectrometry
- the AlN substrate of the present invention has a thermal conductivity of 80 W / m ⁇ K or more in consideration of imparting high thermal conductivity for removing heat from a semiconductor element such as a conductor light emitting element as quickly as possible. Is preferred. Moreover, it is preferable that thermal conductivity is 260 W / m * K or less also in the said range.
- the thermal conductivity can be adjusted by appropriately changing the grain size of AlN crystal grains constituting the sintered body of AlN, the composition of the sintered material, etc., but 260 W / m ⁇ K for the sintered body of AlN. It is practically difficult to form an AlN substrate having a high thermal conductivity exceeding.
- the thermal expansion coefficient of the AlN substrate and the semiconductor substrate is reduced.
- the difference is required to be small.
- the thermal expansion coefficient of the AlN substrate is preferably about 3.5 ⁇ 10 ⁇ 6 / K or more and about 4.8 ⁇ 10 ⁇ 6 / K or less.
- the AlN substrate of the present invention is suitably used to form a bonded substrate by being bonded to a semiconductor substrate as a base substrate, as well as an insulating substrate for directly bonding a semiconductor element or the like to the bonding surface. It can also be used.
- the AlN substrate has high thermal conductivity and excellent heat transfer efficiency with other members as described above, for example, heat from a semiconductor element such as a semiconductor light emitting element is used as the AlN substrate. It can be transmitted to the substrate more efficiently than before, and can be removed as quickly as possible via a heat radiating member connected to the AlN substrate, thereby reliably preventing malfunction or damage of the semiconductor element due to the heat. be able to.
- AlN is 88.7% by mass or more and 98.5% by mass or less
- 2A group element is 0.01% by mass or more and 0.3% by mass or less in terms of oxide.
- a step of sintering to form a sintered body (sintering step), and a step of HIP processing the sintered body at a temperature of 1450 ° C. or higher and 2000 ° C. or lower and a pressure of 9.8 MPa or higher (HIP processing step) It can manufacture by the manufacturing method of this invention containing this.
- the AlN, the 2A group element, the 3A group element, etc. which are removed before the sintering process, excluding organic substances such as a binder and an organic solvent described later, or water, the sintering process, and the HIP
- Various materials that are raw materials constituting the AlN substrate through the processing steps are collectively referred to as sintered materials.
- the mass% of the AlN, 2A group element, 3A group element, etc. is the content ratio in the total amount of the sintered material.
- the total content rate (in oxide conversion) of the 2 or more types of elements used together needs to be in the above range.
- the content ratio of AlN in the total amount of the sintered material is limited to 88.7 mass% or more and 98.5 mass% or less for the following reason. That is, when the content ratio of AlN is less than the above range, the thermal conductivity of the AlN substrate manufactured through each of the above steps is the preferred range of the thermal conductivity required for the AlN substrate, particularly the 80 W / m ⁇ K described above. There is a possibility that it cannot be maintained within the above range.
- the content of the sintering aid is relatively reduced, so that the sintered grains are densified by rearranging the crystal grains constituting the sintered body during the HIP process.
- the effect of filling the pores contained in the sintered body or reducing the diameter cannot be obtained.
- the reason why the content ratio of the group 2A element in the total amount of the sintered material is limited to 0.01% by mass or more and 0.3% by mass or less in terms of oxide is as follows.
- the other grouping element reacts with the oxide on the surface of the AlN particles described above, and the other sintering aid contained in the sintered material.
- generation of a liquid phase with a component is not acquired. Therefore, low-temperature sintering does not proceed, the crystal grains constituting the sintered body are rearranged at the time of HIP processing to densify the sintered body, and pores contained in the sintered body are filled or reduced in diameter. Effect is not obtained.
- the crystal grains constituting the sintered body are rearranged to densify the sintered body, and the effect of filling pores or reducing the diameter of the sintered body cannot be obtained. . Therefore, in any case, the void exposed on the bonded surface of the AlN substrate after polishing becomes larger than the range defined in the present invention.
- the 2A group element is preferably at least one selected from the group consisting of Ca and Mg in consideration of the promoting effect and the like, and particularly preferably Ca. Furthermore, the reason why the content of the group 3A element in the total amount of the sintered material is limited to 0.05% by mass or more and 5% by mass or less in terms of oxide is as follows. That is, when the content ratio of the group 3A element is less than the above range, the viscosity of the liquid phase is too low, and the liquid phase component is less likely to remain at the grain boundary. It is impossible to obtain an effect of rearranging crystal grains constituting the body to densify the sintered body and filling pores or reducing the diameter of the sintered body.
- the void exposed on the bonded surface of the AlN substrate after polishing becomes larger than the range defined in the present invention.
- the thermal conductivity of the AlN substrate manufactured through the above steps is calculated as the thermal conductivity required for the AlN substrate. There is a possibility that it cannot be maintained within the preferable range of 80 W / m ⁇ K or more, particularly as described above.
- the group 3A element is preferably at least one selected from the group consisting of Y and lanthanoids in consideration of the effect of adjusting the viscosity of the liquid phase, and in particular, among the lanthanoids, Yb and Nd are used in combination. Furthermore, it is preferable to use both of them together with Y.
- Al that does not constitute AlN is further contained in a range of 0.05% by mass or more and 5% by mass or less in terms of oxide in the total amount of the sintered material. Is preferred.
- the amount of liquid phase generated may be small and sintering may not proceed.
- the liquid phase formation temperature rises and the AlN crystal grains may become coarse.
- the grain boundary phase is likely to segregate at the triple points of the AlN crystal grains, and when such segregation occurs, the movement of the sintering aid is hindered during the HIP treatment, so that the grains constituting the sintered body are rearranged.
- the sintered body may be densified, and the effect of filling pores or reducing the diameter of the sintered body may not be obtained.
- the oxide of Al that does not constitute AlN includes an oxide that exists on the surface of AlN particles as a raw material.
- the amount of oxide contained in AlN as a raw material is obtained in advance, and when the amount of oxide is less than a predetermined value within the above range, an oxide of Al is added so that the total amount of oxide becomes the predetermined value. Further, the additional amount may be set.
- the oxide equivalent weight x of the group 2A element and the oxide equivalent weight y of Al not constituting AlN are represented by the formula (1): 0.05 ⁇ x / (x + y) ⁇ 0.35 (1) It is preferable to adjust to a range that satisfies the above.
- the oxide equivalent weight z of the group 3A element and the oxide equivalent weight y of Al not constituting AlN are expressed by the formula (2): 0.20 ⁇ y / (z + y) ⁇ 0.60 (2) It is preferable to adjust to a range that satisfies the above.
- the sintered material may contain Si in order to enhance bondability to the semiconductor substrate or the like by the direct bonding method or the like.
- Si when Si is contained in a large amount, a complex oxide SiAlON crystal is generated, and there is a possibility that grain separation occurs in the polishing step after the HIP treatment. Therefore, it is preferable not to contain Si, and even if it is contained, it is preferable to make it a ratio of 1% by mass or less in the total amount of the sintered material in terms of oxide.
- each component other than AlN can be blended with AlN in the state of compounds such as oxides, nitrides, carbides, carbonates, composite oxides, and the like.
- the compounding amount of the compound may be adjusted so that the content ratio of the 2A group element and the like contained in the compound is within the above range in terms of oxide.
- the average particle diameter of the AlN powder is preferably 0.1 ⁇ m or more and 3.0 ⁇ m or less.
- the average particle size of the 2A group element compound powder is preferably 0.2 ⁇ m or more and 5.0 ⁇ m or less.
- the average particle size of the 3A group element compound powder is preferably 0.2 ⁇ m or more and 4.0 ⁇ m or less.
- the average particle size of the Al compound powder not constituting AlN is preferably 0.1 ⁇ m or more and 3.0 ⁇ m or less.
- the average particle size of the Si compound powder is preferably 0.5 ⁇ m or more and 6.0 ⁇ m or less.
- each component is less than the above range, the powder becomes bulky and cannot be easily mixed uniformly, and the required sintered density may not be obtained.
- each component is not sufficiently pulverized in the mixing step, so that the composition becomes non-uniform, resulting in density variation after sintering, or polishing after HIP treatment. There is a possibility that degranulation occurs in the process or the like, or the surface roughness after processing increases.
- a binder and a dispersion medium are further blended into the sintered material to prepare a slurry, and the slurry is formed into a sheet shape to produce a green sheet.
- the binder either one using an organic solvent as a dispersion medium or one using water as a dispersion medium can be used.
- examples of the binder using an organic solvent as a dispersion medium include one or more binders such as acrylic, polyvinyl butyral, and cellulose.
- examples of the binder using water as a dispersion medium include one or more binders such as polyvinyl alcohol, acrylic, urethane, and vinyl acetate.
- the slurry may be mixed with, for example, a dispersant or a plasticizer.
- a dispersant or a plasticizer for example, a dry mixing method or a wet mixing method using a general mixing device such as a ball mill, an attritor, or a planetary mill can be employed.
- the slurry mixed by the wet mixing method may be used to screen coarse particles using a mesh having a hole diameter of about 1 ⁇ m, for example.
- a forming method for forming the slurry into a sheet to produce a green sheet for example, an extrusion method or the like is employed. Further, a green sheet may be produced by superposing a plurality of thin sheets produced by a doctor blade method or the like. Next, the green sheet is dried to obtain a preform.
- the drying temperature is preferably 0 ° C. or higher, particularly 15 ° C. or higher, and is preferably 80 ° C. or lower, particularly 50 ° C. or lower.
- the temperature is lower than the above range, the volatilization rate of the dispersion medium from the green sheet is too slow, and it takes a long time to dry, so the productivity of the AlN substrate may be reduced.
- the volatilization rate of the dispersion medium from the green sheet is too high, and the degree of drying tends to be uneven, and accordingly, the preform may be easily wrinkled or warped. There is.
- the drying time is preferably 1 hour or longer, more preferably 10 hours or longer, and particularly preferably 20 hours or longer. When the time is less than the above range, the drying is not sufficient, and in the binder removal step which is the next step, there is a possibility that cracking due to volatilization of the dispersion medium remaining in the preform is likely to occur. In consideration of the productivity of the AlN substrate, the drying time is preferably 48 hours or less even within the above range.
- Binder removal process Next, the pre-molded body is heated to a temperature equal to or higher than the thermal decomposition temperature of the binder to remove the binder and other organic substances, thereby producing a pre-sintered precursor made of only a sintered material.
- the binder removal treatment may be performed in an oxidizing atmosphere such as the air in order to accelerate the thermal decomposition of the binder, or may be performed in an inert atmosphere such as a nitrogen atmosphere.
- the temperature is preferably 400 ° C. or higher and 600 ° C. or lower. If the temperature is lower than the above range, the binder cannot be sufficiently removed, and in the subsequent sintering step, the sintering is inhibited by the binder remaining in the precursor, or the binder is gasified and sintered. There is a risk of causing cracks.
- the temperature is 500 degreeC or more and 900 degrees C or less. If the temperature is lower than the above range, the binder cannot be sufficiently removed, and in the subsequent sintering step, the sintering is inhibited by the binder remaining in the precursor, or the binder is gasified and sintered. There is a risk of causing cracks.
- the binder removal time is preferably 1 hour or more and 10 hours or less when the binder removal treatment is performed in any atmosphere. If the time is less than the above range, the binder cannot be sufficiently removed, and in the subsequent sintering step, the sintering is hindered by the binder remaining in the precursor, or the binder is gasified and sintered. There is a risk of causing cracks.
- the precursor is sintered at a temperature of 1500 ° C. or higher and 1900 ° C. or lower in an inert atmosphere such as a nitrogen atmosphere to form a sintered body.
- the reason why the sintering temperature is limited to 1500 ° C. or higher and 1900 ° C. or lower is as follows. That is, if the temperature is less than the above range, the sintering is insufficient, and the pores contained in the sintered body are too large. Therefore, in the HIP processing step which is the next step, the crystal grains constituting the sintered body are rearranged. While densifying the sintered body, it is not possible to obtain the effect of filling pores or reducing the diameter of the sintered body.
- the sintering temperature Is preferably 1600 ° C. or more, and preferably 1750 ° C. or less even within the above range.
- the sintering time is preferably 1 hour or more and 10 hours or less. If the time is less than the above range, the time required for the rearrangement and bonding of crystal grains in the sintering process is short, so the variation in density in the sintered body becomes large, and even if the HIP process is performed in the next process, There is a risk that the pores can only be partially filled or reduced in diameter.
- HIP treatment process Next, the sintered body is subjected to HIP treatment in an inert atmosphere such as a nitrogen atmosphere or an argon atmosphere at a temperature of 1450 ° C. or higher and 2000 ° C. or lower and a pressure of 9.8 MPa or higher.
- an inert atmosphere such as a nitrogen atmosphere or an argon atmosphere
- the reason why the temperature of the HIP process is limited to 1450 ° C. or more and 2000 ° C. or less is as follows.
- the liquid phase described above due to the reaction between the sintering aid and the oxide on the surface of the AlN particles does not proceed.
- the effect of filling the pores contained in the sintered body or reducing the diameter thereof may not be obtained while rearranging the constituting crystal grains to densify the sintered body. For this reason, the surface roughness Ra may exceed 15 nm.
- the temperature is 1600 ° C. or higher in consideration of further densifying the sintered body and filling pores or reducing the diameter in the sintered body. Is preferable, and it is preferable that it is 1900 degrees C or less.
- the reason why the pressure of the HIP process is limited to 9.8 MPa or more is as follows. In other words, if the pressure is less than the above range, the crystal grains constituting the sintered body are rearranged to densify the sintered body, and the effect of filling pores or reducing the diameter in the sintered body is obtained. I can't get it.
- the pressure is preferably 196 MPa or less even within the above range.
- the HIP treatment time is preferably 1 hour or more and 10 hours or less. If the time is less than the above range, the sintering aid is not sufficiently moved even if a liquid phase is generated. Therefore, the sintered body is densified by rearrangement of crystal grains, and is inherent in the sintered body. There is a possibility that the effect of filling the pores or reducing the diameter is not sufficiently obtained.
- the bonded surface of the AlN substrate after the HIP process is mirror-polished to have a surface roughness Ra of 3 nm or less and a void having a major axis of 0.25 ⁇ m or more exposed on the bonded surface.
- any of various polishing methods such as mechanical polishing such as lapping with loose abrasive grains and fixed abrasive grains, or chemical mechanical polishing can be employed.
- HIP treatment process After the HIP treatment, the AlN substrate before the polishing step may be heat-treated while being pressed in the surface direction in an inert atmosphere such as a nitrogen atmosphere or an argon atmosphere as necessary. By performing such heat treatment, warping of the AlN substrate can be corrected.
- the temperature of the heat treatment is preferably 1500 ° C. or higher, and preferably 1900 ° C. or lower.
- the time for the heat treatment is preferably 0.5 hours or more, and preferably 5 hours or less. If the heat treatment time is less than the above range, the warp correction effect may not be sufficiently obtained. Moreover, even if it exceeds the said range, the effect beyond it is not acquired and it is not rational.
- the pressurizing pressure in the surface direction is preferably 150 Pa or more, more preferably 1000 Pa or less in terms of surface pressure. If the pressure is less than the above range, the warping correction effect may not be sufficiently obtained. Moreover, even if it exceeds the said range, the effect beyond it is not acquired and it is not rational.
- the warpage of the AlN substrate is within ⁇ 0.7 ⁇ m / 1 mm, especially within ⁇ 0.3 ⁇ m / 1 mm in terms of the maximum displacement in the orthogonal direction of the bonding surface per 1 mm length on the bonding surface of the AlN substrate. Is preferred.
- Example 1> (Preparation of sintered material) As a sintering material, powders of the following components were prepared. AlN: Average particle size 0.9 ⁇ m, oxygen content 0.8 mass% CaCO 3 : average particle size 6 ⁇ m Yb 2 O 3 : Average particle diameter 1.2 ⁇ m Nd 2 O 3 : Average particle size 3.5 ⁇ m Al 2 O 3 : Average particle size 0.3 ⁇ m SiO 2 : Average particle size 3.8 ⁇ m (Preparation of slurry and preparation of preform) The content ratio of the powder of each component in the total amount of the sintered material is: AlN: 96.8% by mass Ca (as oxide) as Group 2A element: 0.1% by mass Yb (as oxide) as Group 3A element: 1.1% by mass Nd (as oxide) as group 3A element: 1.0% by mass Al not constituting AlN (as oxide): 0.8% by mass Si (oxide conversion): 0.2% by mass (The composition is referred to as “Composition A
- the slurry was formed into a sheet having a length of 260 mm, a width of 260 mm, and a thickness of 1.2 mm by extrusion to produce a green sheet.
- the green sheet was subjected to conditions of temperature: 24 ⁇ 4 ° C. and time: 24 hours.
- the mixture was naturally dried to prepare a preform. (Binder removal process)
- the preform is placed on a boron nitride jig, and is subjected to binder removal treatment in the atmosphere under conditions of temperature: 500 ° C. and time: 5 hours, and is a precursor before sintering consisting only of a sintered material.
- the body was made.
- the precursor was sintered in a nitrogen atmosphere at a temperature of 1650 ° C., a time of 5 hours, and a pressure of 1 atm to prepare a sintered body.
- HIP treatment process-polishing process The sintered body was subjected to HIP treatment in a nitrogen atmosphere at a temperature of 1790 ° C., a time of 1 hour, and a pressure of 98 MPa, and then the outer shape was shaped by lapping with free abrasive grains and the joint surface was mirror-polished.
- a disc-shaped AlN substrate having a diameter of ⁇ 200 ⁇ 0.7 mmt was manufactured. The warpage of the AlN substrate was 0.8 ⁇ m / mm.
- Examples 2 to 6 Comparative Examples 1 and 2>
- the sintering temperature in the sintering step is 1480 ° C. (Comparative Example 1), 1500 ° C. (Example 2), 1600 ° C. (Example 3), 1750 ° C. (Example 4), 1850 ° C. (Example 5),
- An AlN substrate was manufactured in the same manner as in Example 1 except that the temperature was 1900 ° C. (Example 6) and 1920 ° C. (Comparative Example 2).
- the arithmetic average height Ra was obtained from the contour curve of the surface roughness measured in the visual field, and the average value was calculated as the surface roughness Ra of the bonding surface of the AlN substrates of the examples and comparative examples.
- ⁇ Measurement of the major axis of the void> carbon is vapor-deposited on the joint surface, which is one side of the disk, of the AlN substrate manufactured in each of the above examples and comparative examples, and an arbitrary five fields of view are magnified 1000 times using a scanning electron microscope. Taken with Next, the photographed image was stretched 3 times, all the voids confirmed in the field of view were approximated to an ellipse, the major axis was measured as the major axis, and those with a major axis of less than 0.25 ⁇ m were excluded. The average value and the maximum value of the major axis were determined from the measured values of the major axis of all voids of 25 ⁇ m or more.
- ⁇ Measurement of thermal conductivity> The thermal conductivity in the thickness direction of the AlN substrate manufactured in each of the examples and comparative examples was measured by a laser flash method.
- ⁇ Measurement of thermal expansion coefficient The coefficient of thermal expansion in the surface direction of the AlN substrate produced in each of the examples and comparative examples was measured using a differential thermal dilatometer.
- ⁇ Composition analysis> A mirror-polished joint surface, which is one side of a disk, of the AlN substrate manufactured in each of the examples and comparative examples was analyzed by glow discharge mass spectrometry (GDMS). From the analysis results, 2A contained in the AlN substrate was analyzed. The ratio (mass%) of the group element and the group 3A element was determined in terms of oxide.
- the surface roughness Ra of the joint surface and the average value or maximum value of the major axis of the void are set to be as small as possible even within the above range. It has been found that it is preferable to set the temperature to 1600 ° C. or higher and 1750 ° C. or lower even within the range. Further, from the results of Examples 1, 7, and 8, it was found that the sintering time in the sintering step is preferably set to 1 to 10 hours.
- Example 14 An AlN substrate was manufactured in the same manner as in Example 1 except that the pressure of the HIP treatment was 8.5 MPa (Comparative Example 5), 9.8 MPa (Example 14), and 196 MPa (Example 15).
- Example 1 except that the HIP treatment step was omitted and the sintering temperature in the sintering step was 1500 ° C. (Comparative Example 6), 1650 ° C. (Comparative Example 7), and 1900 ° C. (Comparative Example 8).
- an AlN substrate was manufactured.
- the temperature of the HIP treatment is set to be as low as possible. Even within the above range, it was found that it is preferable to set the temperature to 1600 ° C. or higher and 1900 ° C. or lower.
- the surface roughness Ra of the joint surface of the manufactured AlN substrate, and the average value and maximum value of the major axis of the voids were determined according to the present invention.
- the content ratio of the group 2A element must be set to 0.01% by mass or more and 0.3% by mass or less of the total amount of the sintered material in terms of oxide. I understood.
- composition J (Example 20)
- composition K (Example 21)
- composition L (Example 22)
- composition M (Comparative Example 13)
- composition shown in Table 11 below An AlN substrate was manufactured in the same manner as in Example 1 except that the sintered material of N (Comparative Example 14) was used.
- the surface roughness Ra of the manufactured AlN substrate and the average value and maximum value of the major axis of the voids are calculated according to the present invention.
- the total content ratio of the group 3A elements it is necessary to set the total content ratio of the group 3A elements to 0.05% by mass or more and 5% by mass or less of the total amount of the sintered material in terms of oxide. I understood.
- the sintering conditions in the sintering step are a nitrogen atmosphere, temperature: 1500 ° C., time: 5 hours, pressure: 1 atm, and HIP treatment conditions in nitrogen atmosphere: temperature: 1450 ° C., time: 1 hour,
- An AlN substrate was manufactured in the same manner as in Example 1 except that the pressure was 19.6 MPa.
- Example 15 The temperature of the HIP treatment was 1440 ° C. (Comparative Example 15), 1650 ° C. (Example 24), 1790 ° C. (Example 25), 2000 ° C. (Example 26), and 2015 ° C. (Comparative Example 16).
- An AlN substrate was manufactured in the same manner as in Example 23. About the AlN board
- the HIP in order to make the average value and maximum value of the surface roughness Ra of the joint surface and the major axis of the void as small as possible within the above range, the HIP It has been found that the treatment temperature is preferably set to 1600 ° C. or higher and 1900 ° C. or lower even within the above range.
- Example 27 An AlN substrate was prepared in the same manner as in Example 1 except that heat treatment was performed at 1700 ° C (Example 28), 1800 ° C (Example 29), and 1900 ° C (Example 30) for 2 hours. It manufactured and measured the curvature (micrometer / 1mm). The results are shown in Table 16 together with the results of Example 1.
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Abstract
Description
前記ヒートスプレッダとしては、例えば半導体基板と貼り合わせて貼り合わせ基板を構成する下地基板等が挙げられる(特許文献1等参照)。
前記貼り合わせ基板においては、半導体基板側の露出した表面に、単層または複層の半導体層をエピタキシャル成長させることにより、前記半導体発光素子等の半導体素子が形成される。
例えば半導体基板としてGaN等からなるものを用いる場合、前記下地基板としては、これらの要求を満足するAlN基板が好適に用いられる。
しかし特許文献2に記載されているように、AlN(窒化アルミニウム)を焼結して製造される従来のAlN基板には多数の欠陥(気孔)が内在されており、半導体基板との接合面を、熱伝達の効率を向上するために鏡面研磨等すると前記気孔が開口されて、前記接合面に半導体基板との間での熱伝達を妨げるボイドとして現れるため、所望の熱伝達効果が得られない場合がある。
本発明のAlN基板は、前記のように2A族元素、および3A族元素を含むAlNの焼結体からなり、接合面の表面粗さRaが15nm以下の、ボイドの少ない平滑面であって、しかも前記接合面に存在する、長径0.25μm以上のボイドの、前記長径の平均値が1.5μm以下、最大値が1.8μm以下に規定されるため、前記接合面に接合される半導体基板等の他部材との間の熱伝達の効率を、これまでよりも向上することができる。
また3A族元素としては、Y、およびランタノイドからなる群より選ばれた少なくとも1種が好ましい。本発明のAlN基板は、前記3A族元素を、酸化物換算で0.02質量%以上、4.5質量%以下の割合で含んでいるのが好ましい。
すなわちHIP処理の工程での前記温度範囲内での加熱により、前記焼結材料中に含まれる2A族元素は、AlN粒子の表面の酸化物と反応して、前記焼結材料中に含まれる他の焼結助剤成分とともに液相の生成を促進する働きをし、3A族元素は、生成した前記液相の粘性を適度に調整する働きをする。
したがってHIP処理後に、他部材との接合面を研磨工程で鏡面研磨等することにより、前記気孔が開口されて前記接合面に現れる、長径0.25μm以上のボイドの、前記長径の平均値を1.5μm以下、最大値を1.8μm以下とするとともに、ボイドの数のパラメータとしての、前記接合面の表面粗さRaを前記15nm以下とすることができる。
しかし(a)のホットプレス法では焼結助剤の移動が十分に行われないため、本発明の製造方法によって製造したものと同等の、緻密化されたAlN基板を製造することはできない。
さらに(c)の2段階の焼結でも、焼結助剤の移動が十分に行われないため、本発明の製造方法によって製造したものと同等の、緻密化されたAlN基板を製造することはできない。
本発明は、他部材との接合面を備えたAlN基板であって、2A族元素、および3A族元素を含むAlNの焼結体からなり、前記接合面の表面粗さRaが15nm以下、前記接合面に露出した、長径0.25μm以上のボイドの、前記長径の平均値が1.5μm以下で、かつ最大値が1.8μm以下であることを特徴とするものである。
そのため本発明のAlN基板を、例えば下地基板として半導体基板と貼り合わせて貼り合わせ基板を構成した場合には、前記半導体基板上に形成される半導体発光素子等の半導体素子からの熱を、前記半導体基板からAlN基板へこれまでよりも効率よく伝達して、さらに前記AlN基板に接続される放熱部材等を介してできるだけ速やかに除去することができ、前記半導体素子の熱による誤動作や破損等を確実に防止することができる。
すなわち表面粗さRaが15nmを超える場合には、たとえボイドの長径の範囲、および前記長径の平均値が前記範囲内であったとしても、前記接合面には多数のボイドが存在することになり、当該接合面に接合される他部材との間の熱伝達の効率を向上する効果が得られない。また、他部材の接合強度が低下して剥がれやすくなるおそれもある。
また本発明において、前記接合面に露出した、長径の平均値および最大値を求めるボイドの長径が0.25μm以上に限定されるのは、下記の理由による。
そのため本発明では、長径0.25μm未満の小さいボイドは、前記接合面に露出したボイドの長径の平均値および最大値を求める際には、ボイドとして計数しないこととする。
すなわち接合面に露出した前記ボイドの長径の平均値、あるいは最大値が、いずれか一方でも前記範囲を超える場合には、たとえ接合面の表面粗さRaが15nm以下の範囲内であったとしても、前記接合面に接合される他部材との間の熱伝達の効率を向上する効果が得られない。また、他部材の接合強度が低下して剥がれやすくなるおそれもある。
ただし、AlN基板の生産性や歩留まり等を考慮すると、前記ボイドの長径の平均値は、前記範囲内でも0.3μm以上であるのが好ましく、最大値は、前記範囲内でも0.5μm以上であるのが好ましい。平均値や最大値を前記範囲未満とすることは、実質的に困難である。
すなわちAlN基板の、鏡面研磨等した接合面にカーボンを蒸着し、走査型電子顕微鏡を用いて任意の5視野を倍率1000倍で撮影する。次いで撮影した画像を3倍に引き伸ばし、視野内で確認される全てのボイドを楕円近似して、その長軸を長径として測定する。そして長径0.25μm未満のものを除外した、長径0.25μm以上の全てのボイドの長径の測定値から、前記長径の平均値、および最大値を求める。
後述する本発明の製造方法によって製造されるAlN基板は、その出発原料としての焼結材料の組成に基づいて、前記2A族元素の割合が、酸化物換算で0.009質量%以上であるのが好ましく、0.28質量%以下であるのが好ましい。また3A族元素の割合は、酸化物換算で0.02質量%以上であるのが好ましく、4.5質量%以下であるのが好ましい。
また3A族元素の割合が前記範囲未満となるのは、前記焼結材料における前記3A族元素の割合が、先に説明した所定値よりも少ないためであることが多く、その場合には、焼結材料に3A族元素を配合することによる効果が得られず、研磨後のAlN基板の接合面に露出したボイドが、本願発明で規定した範囲を上回って大きくなってしまうおそれがある。
また前記AlN基板は、Siを、酸化物換算で0.3質量%以下の割合で含んでいても良い。Siの含有割合の下限値は0質量%、すなわちSiを含んでいない場合をも含む。
前記各成分の酸化物換算の含有割合は、AlN基板の、鏡面研磨した接合面を、グロー放電質量分析(GDMS)によって分析した結果から求めることができる。
また熱伝導率は、前記範囲内でも260W/m・K以下であるのが好ましい。熱伝導率は、AlNの焼結体を構成するAlNの結晶粒の粒径、焼結材料の組成等を適宜変更することで調整可能であるが、AlNの焼結体で260W/m・Kを超える高い熱伝導率を有するAlN基板を形成するのは実質的に困難である。
本発明のAlN基板は、前記のように下地基板として、半導体基板と貼り合わせて貼り合わせ基板を構成するために好適に用いられる他、前記接合面に直接に半導体素子等を接合する絶縁基板として用いることもできる。
前記本発明のAlN基板は、AlNを88.7質量%以上、98.5質量%以下、2A族元素を、酸化物換算で0.01質量%以上、0.3質量%以下、3A族元素を、酸化物換算で0.05質量%以上、5質量%以下の範囲で含む焼結材料によって前記AlN基板の前駆体を形成する工程、前記前駆体を1500℃以上、1900℃以下の温度で焼結して焼結体を形成する工程(焼結工程)、および前記焼結体を1450℃以上、2000℃以下の温度、および9.8MPa以上の圧力でHIP処理する工程(HIP処理工程)を含む本発明の製造方法によって製造することができる。
前記AlN、2A族元素、3A族元素等の質量%は、前記焼結材料の総量中の含有割合である。2A族元素、3A族元素として、それぞれ2種以上を併用する場合は、併用した2種以上の元素の合計の含有割合(酸化物換算)が前記範囲内である必要がある。
すなわちAlNの含有割合が前記範囲未満では、前記各工程を経て製造されるAlN基板の熱伝導率を、当該AlN基板に求められる熱伝導率の好適範囲、特に先に説明した80W/m・K以上の範囲に維持できないおそれがある。
また焼結材料の総量中の、2A族元素の含有割合が、酸化物換算で0.01質量%以上、0.3質量%以下に限定されるのは、下記の理由による。
そのためいずれの場合にも、研磨後のAlN基板の接合面に露出したボイドが、本願発明で規定した範囲を上回って大きくなってしまう。
さらに焼結材料の総量中の、3A族元素の含有割合が、酸化物換算で0.05質量%以上、5質量%以下に限定されるのは、下記の理由による。
すなわち3A族元素の含有割合が前記範囲未満では液相の粘性が低すぎて、前記液相成分が粒界に残りにくくなり、HIP処理時に焼結助剤の移動が阻害されるため、焼結体を構成する結晶粒を再配列させて当該焼結体を緻密化させるとともに、前記焼結体中に内在される気孔を埋めたり小径化したりする効果が得られない。
一方、前記範囲を超える場合には、液相の粘性が上がりすぎて焼結が妨げられるため、前記各工程を経て製造されるAlN基板の熱伝導率を、当該AlN基板に求められる熱伝導率の好適範囲、特に先に説明した80W/m・K以上の範囲に維持できないおそれがある。
前記焼結材料には、前記各成分に加えて、さらにAlNを構成しないAlを、酸化物換算で、焼結材料の総量中の0.05質量%以上、5質量%以下の範囲で含有させるのが好ましい。
前記各成分のうち、2A族元素の酸化物換算重量xと、AlNを構成しないAlの酸化物換算重量yとは、式(1):
0.05≦x/(x+y)≦0.35 (1)
を満足する範囲に調整するのが好ましい。また3A族元素の酸化物換算重量zと、AlNを構成しないAlの酸化物換算重量yとは、式(2):
0.20≦y/(z+y)≦0.60 (2)
を満足する範囲に調整するのが好ましい。
前記焼結材料には、半導体基板等に対する、前記直接接合法等による接合性を高めるためにSiを含有させてもよい。ただしSiを多量に含有させた場合には、複合酸化物SiAlON結晶が生成して、HIP処理後の研磨工程等で脱粒を生じるおそれがある。そのためSiは含有させないのが好ましく、もしも含有させる場合でも、酸化物換算で、焼結材料の総量中の1質量%以下の割合とするのが好ましい。
前記各成分のうちAlNの粉末の平均粒径は0.1μm以上、3.0μm以下であるのが好ましい。また2A族元素の化合物の粉末の平均粒径は0.2μm以上、5.0μm以下であるのが好ましい。3A族元素の化合物の粉末の平均粒径は0.2μm以上、4.0μm以下であるのが好ましい。AlNを構成しないAlの化合物の粉末の平均粒径は0.1μm以上、3.0μm以下であるのが好ましい。さらにSiの化合物の粉末の平均粒径は0.5μm以上、6.0μm以下であるのが好ましい。
前記焼結材料に、さらにバインダと分散媒とを配合してスラリーを調製し、前記スラリーをシート状に成形してグリーンシートを作製する。
前記バインダとしては、有機溶媒を分散媒として用いるものと、水を分散媒として用いるもののいずれも使用可能である。
また水を分散媒として用いるバインダとしては、例えばポリビニルアルコール系、アクリル系、ウレタン系、酢酸ビニル系等のバインダの1種または2種以上が挙げられる。
スラリーの混合には、例えばボールミル、アトライタ、遊星ミル等の一般的な混合装置を用いた乾式混合法、湿式混合法がいずれも採用できる。湿式混合法で混合したスラリーは、例えば穴径1μm程度のメッシュを用いて粗粒をふるい分けてもよい。
次いで、前記グリーンシートを乾燥させて予備成形体を得る。
乾燥の温度は0℃以上、特に15℃以上であるのが好ましく、80℃以下、特に50℃以下であるのが好ましい。
一方、前記範囲を超える場合には、グリーンシート中からの分散媒の揮発速度が速すぎて乾燥の度合いに不均一を生じやすくなり、それに伴って予備成形体にシワや反りを生じやすくなるおそれがある。
時間が前記範囲未満では乾燥が十分でなく、次工程である脱バインダ工程において、予備成形体中に残存する分散媒の揮発による割れ等を生じやすくなるおそれがある。
なおAlN基板の生産性等を考慮すると、乾燥の時間は、前記範囲内でも48時間以下であるのが好ましい。
次に前記予備成形体を、バインダの熱分解温度以上に加熱してバインダその他の有機物を除去することで、焼結材料のみからなる焼結前の前駆体を作製する。
脱バインダ処理は、バインダの熱分解を促進するために大気中等の酸化性雰囲気中で行ってもよいし、窒素雰囲気中等の不活性雰囲気中で行ってもよい。
温度が前記範囲未満ではバインダを十分に除去することができず、次工程である焼結工程において、前駆体中に残存したバインダによって焼結が阻害されたり、前記バインダがガス化して焼結体に亀裂を生じさせたりするおそれがある。
また脱バインダ処理を窒素雰囲気中で行う場合、その温度は500℃以上、900℃以下であるのが好ましい。
温度が前記範囲未満ではバインダを十分に除去することができず、次工程である焼結工程において、前駆体中に残存したバインダによって焼結が阻害されたり、前記バインダがガス化して焼結体に亀裂を生じさせたりするおそれがある。
また脱バインダ処理の時間は、いずれの雰囲気中で脱バインダ処理を実施する場合も1時間以上、10時間以下であるのが好ましい。
時間が前記範囲未満ではバインダを十分に除去することができず、次工程である焼結工程において、前駆体中に残存したバインダによって焼結が阻害されたり、前記バインダがガス化して焼結体に亀裂を生じさせたりするおそれがある。
(焼結工程)
次に前記前駆体を、窒素雰囲気等の不活性雰囲気中で1500℃以上、1900℃以下の温度で焼結して焼結体を形成する。
すなわち温度が前記範囲未満では焼結が不十分で、焼結体中に内在される気孔が大きすぎるため、次工程であるHIP処理工程において、焼結体を構成する結晶粒を再配列させて当該焼結体を緻密化させるとともに、前記焼結体中に内在される気孔を埋めたり小径化したりする効果が得られない。
なお、次工程であるHIP処理工程において、焼結体をより一層良好に緻密化させるとともに、前記焼結体中に内在される気孔を埋めたり小径化したりすることを考慮すると、焼結の温度は、前記範囲内でも1600℃以上であるのが好ましく、1750℃以下であるのが好ましい。
時間が前記範囲未満では、当該焼結工程において結晶粒の再配列や結合に要する時間が短いため、焼結体中での密度のばらつきが大きくなって、次工程でHIP処理をしても、部分的にしか気孔を埋めたり小径化したりできないおそれがある。
一方、前記範囲を超える場合には焼結が過度に進行して焼結助剤が表面に偏析しやすくなり、かかる偏析が発生すると、HIP処理時に焼結助剤の移動が阻害されるため、焼結体を構成する結晶粒を再配列させて当該焼結体を緻密化させるとともに、前記焼結体中に内在される気孔を埋めたり小径化したりする効果が得られないおそれがある。
圧力が前記範囲未満では、AlNが分解するおそれがあり、前記範囲を超える場合には、焼結助剤が焼結体内で偏析しやすくなり、かかる偏析が発生すると、HIP処理時に焼結助剤の移動が阻害されるため、焼結体を構成する結晶粒を再配列させて当該焼結体を緻密化させるとともに、前記焼結体中に内在される気孔を埋めたり小径化したりする効果が得られないおそれがある。
次いで前記焼結体を、例えば窒素雰囲気、アルゴン雰囲気等の不活性雰囲気中で、1450℃以上、2000℃以下の温度、および9.8MPa以上の圧力でHIP処理する。
HIP処理の温度が1450℃以上、2000℃以下に限定されるのは、下記の理由による。
なおHIP処理工程において、焼結体をより一層良好に緻密化させるとともに、前記焼結体中に内在される気孔を埋めたり小径化したりすることを考慮すると、前記温度は1600℃以上であるのが好ましく、1900℃以下であるのが好ましい。
すなわち圧力が前記範囲未満では、焼結体を構成する結晶粒を再配列させて当該焼結体を緻密化させるとともに、前記焼結体中に内在される気孔を埋めたり小径化したりする効果が得られない。
なお前記圧力は、前記範囲内でも196MPa以下であるのが好ましい。
さらにHIP処理の時間は、1時間以上、10時間以下であるのが好ましい。
時間が前記範囲未満では、液相が生成されても焼結助剤の移動が十分に行われないため、結晶粒の再配列により焼結体を緻密化させるとともに、前記焼結体中に内在される気孔を埋めたり小径化したりする効果が十分に得られないおそれがある。
(研磨工程)
HIP処理後のAlN基板の、他部材との接合面を、先に説明したように鏡面研磨等して、表面粗さRaが3nm以下、前記接合面に露出した、長径0.25μm以上のボイドの、前記長径の平均値が1.5μm以下で、かつ最大値が1.8μm以下の面に仕上げることにより、貼り合わせ基板の下地基板等として用いることができる。
(加熱処理工程)
HIP処理後、研磨工程前のAlN基板を、必要に応じて、例えば窒素雰囲気、アルゴン雰囲気等の不活性雰囲気中で、面方向に加圧しながら加熱処理しても良い。かかる加熱処理を実施することで、AlN基板の反りを矯正することができる。
また加熱処理の時間は0.5時間以上であるのが好ましく、5時間以下であるのが好ましい。加熱処理の時間が前記範囲未満では、反りの矯正効果が十分に得られないおそれがある。また前記範囲を超えてもそれ以上の効果が得られず、合理的でない。
なおAlN基板の反りは、当該AlN基板の接合面上の長さ1mmあたりの、前記接合面の直交方向の最大変位量で表して±0.7μm/1mm以内、特に±0.3μm/1mm以内であるのが好ましい。
(焼結材料の準備)
焼結材料としては、下記の各成分の粉末を準備した。
AlN:平均粒径0.9μm、酸素含量0.8質量%
CaCO3:平均粒径6μm
Yb2O3:平均粒径1.2μm
Nd2O3:平均粒径3.5μm
Al2O3:平均粒径0.3μm
SiO2:平均粒径3.8μm
(スラリーの調製および予備成形体の作製)
前記各成分の粉末を、焼結材料の総量中の含有割合が、
AlN:96.8質量%
2A族元素としてのCa(酸化物換算):0.1質量%
3A族元素としてのYb(酸化物換算):1.1質量%
3A族元素としてのNd(酸化物換算):1.0質量%
AlNを構成しないAl(酸化物換算):0.8質量%
Si(酸化物換算):0.2質量%
となるように配合するとともに(前記配合を「組成A」とする)、分散媒とバインダとを配合してスラリーを調製した。
(脱バインダ工程)
前記予備成形体を、窒化ホウ素製の治具上に配置し、大気中で、温度:500℃、時間:5時間の条件で脱バインダ処理して、焼結材料のみからなる焼結前の前駆体を作製した。
前記前駆体を、窒素雰囲気中で、温度:1650℃、時間:5時間、圧力:1気圧の条件で焼結させて焼結体を作製した。
(HIP処理工程~研磨工程)
前記焼結体を、窒素雰囲気中で、温度:1790℃、時間:1時間、圧力98MPaの条件でHIP処理した後、遊離砥粒によるラップ加工によって外形を整形するとともに接合面を鏡面研磨して、φ200×0.7mmtの円板状のAlN基板を製造した。前記AlN基板の反りは0.8μm/mmであった。
焼結工程での焼結の温度を1480℃(比較例1)、1500℃(実施例2)、1600℃(実施例3)、1750℃(実施例4)、1850℃(実施例5)、1900℃(実施例6)、および1920℃(比較例2)としたこと以外は実施例1と同様にしてAlN基板を製造した。
焼結工程での焼結の時間を1時間(実施例7)、および10時間(実施例8)としたこと以外は実施例1と同様にしてAlN基板を製造した。
〈表面粗さRaの測定〉
前記各実施例、比較例で製造したAlN基板の、円板の片面である接合面上の任意の5箇所で、非接触型の表面粗さ計を用いて、0.6mm×0.5mmの視野で測定した表面粗さの輪郭曲線から算術平均高さRaを求め、その平均値を算出して各実施例、比較例のAlN基板の、接合面の表面粗さRaとした。
先に説明したように、前記各実施例、比較例で製造したAlN基板の、円板の片面である接合面にカーボンを蒸着し、走査型電子顕微鏡を用いて任意の5視野を倍率1000倍で撮影した。
次いで、撮影した画像を3倍に引き伸ばし、視野内で確認される全てのボイドを楕円近似して、その長軸を長径として測定して、長径0.25μm未満のものを除外した、長径0.25μm以上の全てのボイドの長径の測定値から、前記長径の平均値、および最大値を求めた。
〈熱伝導率測定〉
前記各実施例、比較例で製造したAlN基板の厚み方向の熱伝導率を、レーザーフラッシュ法によって測定した。
前記各実施例、比較例で製造したAlN基板の面方向の熱膨張係数を、示差熱膨張計を用いて測定した。
〈組成分析〉
前記各実施例、比較例で製造したAlN基板の、円板の片面である鏡面研磨した接合面を、グロー放電質量分析(GDMS)によって分析し、分析結果から、前記AlN基板中に含まれる2A族元素、および3A族元素の割合(質量%)を、酸化物換算で求めた。
さらに実施例1、7、8の結果より、前記焼結工程での焼結の時間は1~10時間に設定するのが好ましいことが判った。
HIP処理の温度を1430℃(比較例3)、1450℃(実施例9)、1600℃(実施例10)、1700℃(実施例11)、1900℃(実施例12)、2000℃(実施例13)、および2030℃(比較例4)としたこと以外は実施例1と同様にしてAlN基板を製造した。
HIP処理の圧力を8.5MPa(比較例5)、9.8MPa(実施例14)、および196MPa(実施例15)としたこと以外は実施例1と同様にしてAlN基板を製造した。
〈比較例6~8〉
HIP処理工程を省略するとともに、焼結工程での焼結の温度を1500℃(比較例6)、1650℃(比較例7)、および1900℃(比較例8)としたこと以外は実施例1と同様にしてAlN基板を製造した。
HIP処理工程を省略するとともに、焼結工程を、下記(A)(B)の2段階で実施したこと以外は実施例1と同様にしてAlN基板を製造した。
(A) 温度:1650℃、時間:5時間、圧力:1気圧
(B) 温度:1790℃、時間:1時間、圧力:1気圧
前記各実施例、比較例で製造したAlN基板について、先の評価試験を行なって、その特性を評価した。結果を、実施例1の結果と併せて表3、表4に示す。
また実施例1、9~13の結果より、前記接合面の表面粗さRa、およびボイドの長径の平均値や最大値を、前記範囲内でもできるだけ小さくするためには、前記HIP処理の温度を、前記範囲内でも1600℃以上、1900℃以下に設定するのが好ましいことが判った。
〈実施例16、17、比較例10〉
前記組成Aの焼結材料に代えて、下記表5に示す組成B(実施例16)、組成C(実施例17)、および組成D(比較例10)の焼結材料を用いたこと以外は実施例1と同様にしてAlN基板を製造した。
〈実施例18、19、比較例11、12〉
前記組成Aの焼結材料に代えて、下記表8に示す組成E(実施例18)、組成F(実施例19)、組成G(比較例11)、および組成H(比較例12)の焼結材料を用いたこと以外は実施例1と同様にしてAlN基板を製造した。
〈実施例20~22、比較例13、14〉
前記組成Aの焼結材料に代えて、下記表11に示す組成J(実施例20)、組成K(実施例21)、組成L(実施例22)、組成M(比較例13)、および組成N(比較例14)の焼結材料を用いたこと以外は実施例1と同様にしてAlN基板を製造した。
〈実施例23〉
焼結工程での焼結の条件を窒素雰囲気中、温度:1500℃、時間:5時間、圧力:1気圧とし、かつHIP処理の条件を窒素雰囲気中、温度:1450℃、時間:1時間、圧力19.6MPaとしたこと以外は実施例1と同様にしてAlN基板を製造した。
HIP処理の温度を1440℃(比較例15)、1650℃(実施例24)、1790℃(実施例25)、2000℃(実施例26)、および2015℃(比較例16)としたこと以外は実施例23と同様にしてAlN基板を製造した。
前記各実施例、比較例で製造したAlN基板について、先の評価試験を行なって、その特性を評価した。結果を表14、表15に示す。
〈実施例27~30〉
実施例1と同条件で作製した、HIP処理後、研磨工程前のAlN基板の両面を窒化ホウ素板で挟み、面圧が490Paとなるように、モリブデン板を錘として載せた状態で、1500℃(実施例27)、1700℃(実施例28)、1800℃(実施例29)、1900℃(実施例30)で、それぞれ2時間加熱処理したこと以外は実施例1と同様にしてAlN基板を製造し、その反り(μm/1mm)を測定した。結果を、実施例1の結果と併せて表16に示す。
Claims (8)
- 他部材との接合面を備えたAlN基板であって、2A族元素、および3A族元素を含むAlNの焼結体からなり、前記接合面の表面粗さRaが15nm以下、前記接合面に露出した、長径0.25μm以上のボイドの、前記長径の平均値が1.5μm以下で、かつ最大値が1.8μm以下であることを特徴とするAlN基板。
- 前記2A族元素はCa、およびMgからなる群より選ばれた少なくとも1種である請求項1に記載のAlN基板。
- 前記2A族元素を、酸化物換算で0.009質量%以上、0.28質量%以下の割合で含んでいる請求項1または2に記載のAlN基板。
- 前記3A族元素はY、およびランタノイドからなる群より選ばれた少なくとも1種である請求項1ないし3のいずれか1項に記載のAlN基板。
- 前記3A族元素を、酸化物換算で0.02質量%以上、4.5質量%以下の割合で含んでいる請求項1ないし4のいずれか1項に記載のAlN基板。
- 前記請求項1ないし5のいずれか1項に記載のAlN基板を製造するための製造方法であって、AlNを88.7質量%以上、98.5質量%以下、2A族元素を、酸化物換算で0.01質量%以上、0.3質量%以下、3A族元素を、酸化物換算で0.05質量%以上、5質量%以下の範囲で含む焼結材料によって前記AlN基板の前駆体を形成する工程、前記前駆体を1500℃以上、1900℃以下の温度で焼結して焼結体を形成する工程、および前記焼結体を1450℃以上、2000℃以下の温度、および9.8MPa以上の圧力で熱間静水圧加圧処理する工程を含むことを特徴とするAlN基板の製造方法。
- 前記焼結材料は、さらにAlNを構成しないAlを、酸化物換算で0.05質量%以上、5質量%以下の範囲で含んでいる請求項6に記載のAlN基板の製造方法。
- 前記焼結材料は、Siを含まないか、また酸化物換算で1質量%以下の範囲で含んでいる請求項6または7に記載のAlN基板の製造方法。
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WO2015174186A1 (ja) * | 2014-05-12 | 2015-11-19 | 住友電気工業株式会社 | AlN焼結体、AlN基板およびAlN基板の製造方法 |
JP2019029600A (ja) * | 2017-08-03 | 2019-02-21 | 日本特殊陶業株式会社 | セラミックス部材の製造方法 |
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JP6208646B2 (ja) * | 2014-09-30 | 2017-10-04 | 信越化学工業株式会社 | 貼り合わせ基板とその製造方法、および貼り合わせ用支持基板 |
CN105948759A (zh) * | 2016-06-08 | 2016-09-21 | 山东鹏程陶瓷新材料科技有限公司 | 真空热压烧结法制备的氮化铝陶瓷基片及其制备方法 |
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US20140124700A1 (en) | 2014-05-08 |
KR101705024B1 (ko) | 2017-02-09 |
EP2733132A4 (en) | 2015-01-07 |
CN103608313B (zh) | 2016-03-02 |
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