WO2015107812A1

WO2015107812A1 - Aln substrate

Info

Publication number: WO2015107812A1
Application number: PCT/JP2014/082845
Authority: WO
Inventors: 広瀬　義幸; 由佳近藤; 伊藤　靖; 石津　定; 上西　昇; 山本　剛久
Original assignee: 株式会社アライドマテリアル
Priority date: 2014-01-14
Filing date: 2014-12-11
Publication date: 2015-07-23
Also published as: JPWO2015107812A1; JP6412886B2

Abstract

[Problem] To provide an AlN substrate in which voids do not tend to generate due to steps when bonding with a semiconductor substrate. [Solution] A semiconductor substrate which is composed of an AlN sintered body including 0.009 to 0.28 mass% of a Group 2A element as oxide and 0.02 to 4.5 mass% of a Group 3A element as oxide, and which has a PV value of 300 nm or less, the PV value being a profile irregularity of a bonding surface with another member. The semiconductor substrate can be produced through a step of mirror polishing the bonding surface of the sintered body using polishing grains having a Knoop hardness HK of 4000 kgf/mm² or more and an average particle size of 0.03 to 2 μm and under a condition of a polishing load of 50 to 300 g/cm².

Description

AlN substrate

The present invention relates to an AlN substrate.

For example, a heat spreader made of a material having high thermal conductivity is used to remove heat from a semiconductor element that generates heat during operation, such as a semiconductor light emitting element.

As the heat spreader, for example, a base substrate that forms a bonded substrate by bonding to a semiconductor substrate can be cited (see Patent Document 1).

In such a bonded substrate, a semiconductor element is formed by epitaxially growing a single layer or multiple layers of semiconductor layers on the exposed surface of the semiconductor substrate.

The base substrate is required not only to have high thermal conductivity as described above, but also to have a small difference in thermal expansion coefficient from the semiconductor substrate in order to prevent warpage or peeling of the bonded substrate. It is done.

For example, when a semiconductor substrate made of GaN or the like is used, an AlN substrate made of a sintered body of AlN (aluminum nitride) is preferably used as the base substrate in order to satisfy these requirements.

However, as described in Patent Document 2, a large number of defects (pores) are inherent in the sintered body of AlN.

Therefore, in order to improve the efficiency of heat transfer between the sintered body of the AlN substrate and the semiconductor substrate, when the bonding surface of the AlN substrate to the semiconductor substrate is mirror-polished, the inherent pores are heated. There is a case where a desired heat transfer efficiency cannot be obtained because the void is hindered from being opened at the joint surface.

Therefore, in a bonded substrate including a conventional AlN substrate as a base substrate, heat from a semiconductor element formed on the semiconductor substrate cannot be efficiently transferred to the AlN substrate and removed, and the semiconductor element malfunctions or is damaged by the heat. There is a problem that the reliability of the semiconductor element is lowered.

Therefore, in Patent Document 3, a hot isostatic pressing process (HIP (Hot Isostatic Pressing) process) is performed after sintering to reduce the size of pores existing in the AlN substrate and reduce the number of pores. It has been proposed to limit the size of the opening appearing on the joint surface after polishing to a predetermined value or less.

However, even if the size of the opening that appears on the joint surface after mirror polishing is limited to a predetermined value or less by the method described in Patent Document 3, a step may be formed on the joint surface in the mirror polishing process.

This is because a sintered body of AlN has a porous structure in which a large number of crystal grains are sintered with crystal orientations randomly oriented, and the plane orientation of individual crystal grains exposed on the substrate surface is also random. In this case, it is considered that the crystal grains that are easily cut by polishing and the crystal grains that are hard to be cut are adjacent to each other.

That is, a step is generated based on a difference in polishing amount between adjacent crystal grains.

If a step is formed on the bonding surface, a gap that prevents heat conduction is generated between the semiconductor substrate and the semiconductor substrate based on the step, and a portion where the desired heat transfer efficiency cannot be obtained occurs, thereby reducing the reliability of the semiconductor element. May invite.

JP 2008-300562 A JP 2002-293637 A Japanese Patent No. 5189712

An object of the present invention is to provide an AlN substrate that is unlikely to generate a gap due to a step when bonded to a semiconductor substrate.

The present invention includes a 2A group element of 0.009% by mass or more and 0.28% by mass or less in terms of oxide, and a 3A group element of 0.02% by mass or more and 4.5% by mass or less in terms of oxide. It is made of a sintered body of AlN and has a joint surface with another member, and the joint surface is an AlN substrate having a PV value indicating surface accuracy of 300 nm or less.

According to the present invention, it is possible to provide an AlN substrate that is unlikely to generate a gap due to a step when bonded to a semiconductor substrate.

<AlN substrate>
The AlN substrate of the present invention comprises a group 2A element of 0.009% by mass to 0.28% by mass in terms of oxide, and a group 3A of 0.02% by mass to 4.5% by mass in terms of oxide. It is made of a sintered body of AlN containing an element, and has a joint surface with another member, and the joint surface has a PV value indicating surface accuracy of 300 nm or less.

According to the present invention, by limiting the PV (Peak-to-Valley) value of the joint surface showing the surface accuracy to the above range, the step generated on the joint surface can be made as small as possible. Therefore, a desired heat transfer efficiency can be achieved by eliminating a gap due to a step at the time of bonding to the semiconductor substrate, and the reliability of the semiconductor element can be improved.

In addition, in order to further improve such an effect and allow the semiconductor element to be used for an application requiring high reliability such as in-vehicle use, the PV value of the bonding surface is 100 nm or less even in the above range. Preferably there is.

Also, the PV value of the joint surface is preferably 10 nm or more. It is substantially difficult to make the PV value of the joint surface smaller than this range also by the manufacturing method described later.

In the present invention, the PV value of the joint surface is the maximum value of the result of measurement in a field of view of 260 μm × 190 μm using a scanning interferometer using white light at any five locations on the joint surface. Let's represent.

The step of the joining surface has also occurred in the past in the sintered body of AlN, but there is no particular problem in applications other than the base substrate for bonded substrates, for example, and the smoothness of the surface is, for example, a roughness curve It was only prescribed by arithmetic mean roughness Ra (Japanese Industrial Standard JIS B0601: 2001).

Further, even in the base substrate for the bonded substrate, the step is not particularly taken into consideration, and the smoothness of the joint surface is defined by, for example, the arithmetic average roughness Ra of the roughness curve as described in Patent Document 3. It was only.

However, the surface properties obtained by so-called surface roughness tests such as arithmetic mean roughness Ra all represent the state of irregularities on a very short distance line such as a roughness curve, and crystals aligned on the joint surface. It was impossible to grasp the state of a step generated in an arbitrary direction at an arbitrary position of the grain.

On the other hand, in the present invention, the state of the step between adjacent crystal grains is more accurately grasped from the interference pattern in the planar visual field as described above, by the PV value obtained irrespective of the step direction or the like. Thus, since the level difference is small, it is possible to obtain an AlN substrate that does not generate a gap when bonded to the semiconductor substrate.

The AlN substrate of the present invention preferably has a thermal conductivity of 80 W / m · K or more in consideration of imparting high thermal conductivity for removing heat from the semiconductor element as quickly as possible.

The thermal conductivity is preferably 260 W / m · K or less even in the above 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.

Further, when the AlN substrate of the present invention is used as a base substrate as described above and bonded to a semiconductor substrate made of GaN or the like to form a bonded substrate, the thermal expansion coefficient of the AlN substrate and the semiconductor substrate is reduced. The difference is required to be small. Specifically, the thermal expansion coefficient of the AlN substrate is preferably 3.5 × 10 ⁻⁶ / K or more, and preferably 4.8 × 10 ⁻⁶ / K or less.

In addition, the AlN substrate of the present invention can be suitably used for constituting the bonded substrate, and can also be used as an insulating substrate for directly bonding a semiconductor element or the like to the bonding surface.

In any case, the AlN substrate of the present invention has high thermal conductivity and excellent heat transfer efficiency with other members on the joint surface, so that heat from the semiconductor element is efficiently transferred to the AlN substrate. Further, it can be removed as quickly as possible through 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 and improve its reliability.

In order to form a bonded substrate by bonding the AlN substrate of the present invention to a semiconductor substrate, various methods such as a direct bonding method and a surface activation method are employed.

For the bonding, at least one layer of a metal such as Ti, Pt, Pd, Au, Ag, Al, solder such as Au—Sn, or SiO ₂ is formed on the bonding surface of the AlN substrate of the present invention. It may be formed.

As a method for forming the film, for example, a known method such as a vapor deposition method, a sputtering method, or a CVD method can be used.

<Sintered body>
The sintered body that is the basis of the AlN substrate of the present invention is, for example, a powder of AlN, a 2A group element oxide, a 3A group oxide oxide, and other sintering aid component powders after sintering. The proportion of the group element is 0.009% by mass or more and 0.28% by mass or less in terms of oxide, and the proportion of the 3A group element is 0.02% by mass or more and 4.5% by mass or less in terms of oxide. It is formed using a blended sintered material.

That is, after a precursor of the AlN substrate is formed with such a sintered material, the precursor is sintered to form a sintered body.

Further, after sintering, as described in Patent Document 3, HIP treatment may be performed to reduce the size of the pores contained therein and reduce the number of pores as a sintered body.

The group 2A element reacts with oxides on the surface of the AlN powder during sintering to promote the formation of a liquid phase together with other sintering aid components contained in the sintered material, and the group 3A element is It works to moderately adjust the viscosity of the generated liquid phase.

Therefore, since the bonding force between AlN crystal grains can be increased to make it difficult for degranulation or the like to occur, an AlN substrate in which the PV value of the bonding surface is adjusted to 300 nm or less by mirror polishing under the conditions described later can be obtained.

The Group 2A element is preferably at least one selected from the group consisting of Ca and Mg. The group 3A element is preferably at least one selected from the group consisting of Y and lanthanoids.

In the present invention, the ratio of the group 2A element in the sintered body is limited to 0.009 mass% or more and 0.28 mass% or less in terms of oxide for the following reason.

That is, the reason why the ratio of the group 2A element is less than this range is that the ratio of the group 2A element in the sintered material that is the starting material is small, and in that case, by mixing the group 2A element into the sintered material. The above effect cannot be obtained, and it becomes easy for degranulation to occur, and the PV value of the bonding surface of the AlN substrate may exceed 300 nm even after mirror polishing.

Further, the reason why the ratio of the group 2A element exceeds the above range is that the ratio of the group 2A element in the sintered material is large. In this case, segregation of the sintering aid in the sintered body is promoted, so The surface cannot be mirror-polished uniformly, and the PV value may partially exceed 300 nm.

Further, the reason why the ratio of the 3A group element in the sintered body is limited to 0.02% by mass or more and 4.5% by mass or less in terms of oxide is as follows.

That is, the reason why the ratio of the group 3A element is less than this range is that the ratio of the group 3A element in the sintered material that is the starting material is small, and in that case, the ratio of the group 3A element is added to the sintered material. The effects described above cannot be obtained, and it becomes easy for degranulation and the like to occur, and the PV value of the bonding surface of the AlN substrate may exceed 300 nm even after mirror polishing.

Further, the reason why the ratio of the group 3A element exceeds the above range is that the ratio of the group 3A element in the sintered material is large. In this case, the viscosity of the liquid phase at the time of sintering is increased to prevent the sintering. Thus, the thermal conductivity of the manufactured AlN substrate may be insufficient.

On the other hand, by setting the composition of the sintered material so that the ratio of the group 2A element and the group 3A element in the sintered body is in the above range, it has high thermal conductivity, and by mirror polishing. An AlN substrate having a joint surface with a PV value adjusted to 300 nm or less over the entire surface can be obtained.

The AlN substrate may contain Si in a proportion of 0.3% by mass or less in terms of oxide, in order to improve the bondability when bonded to the semiconductor substrate by the direct bonding method.

The Si ratio exceeds this range because the Si ratio in the sintered material is large. In this case, SiAlON composite oxide crystal grains are formed, and the crystal grains are shed during mirror polishing, resulting in a bonded surface. There is a risk that large defects will occur.

The lower limit of the Si ratio includes 0% by mass, that is, the case where Si is not included.

The balance of the sintered body is AlN.

The proportion of AlN in the sintered body is preferably 94.22% by mass or more, and preferably 99.971% by mass or less.

If the proportion of AlN is less than this range, the thermal conductivity of the AlN substrate may be insufficient.

On the other hand, the proportion of AlN exceeds this range because the proportion of sintering aid components such as 2A group elements and 3A group elements in the sintered material is small. In this case, the bonding strength between the crystal grains of AlN However, even when mirror polishing is performed, the PV value of the bonding surface of the AlN substrate may exceed 300 nm.

The ratio of each of the above components can be determined from the result of analyzing the mirror-polished bonded surface of the AlN substrate by glow discharge mass spectrometry (GDMS).

<< Method of manufacturing AlN substrate >>
In the AlN substrate of the present invention, for example, the bonding surface of the AlN substrate is polished using a Knoop hardness HK: 4000 kgf / mm ² or more and an average particle size: 0.03 μm or more and 2 μm or less. It is manufactured through a step of mirror polishing under conditions of 50 g / cm ² or more and 300 g / cm ² or less.

The AlN substrate of the present invention in which the PV value of the joint surface is 300 nm or less can be manufactured by mirror polishing the joint surface under the above conditions.

That is, polishing is performed when the Knoop hardness HK (Japanese Industrial Standard JIS Z2251: 2009) of the abrasive grains is less than 4000 kgf / mm ² , the average particle diameter is less than 0.03 μm, or the polishing load is less than 50 g / cm ^2. The capacity becomes insufficient, and the steps of crystal grains cannot be removed sufficiently.

On the other hand, when the average grain size of the abrasive grains exceeds 2 μm or the polishing load exceeds 300 g / cm ² , the polishing ability is too strong and the surface roughness of the joint surface becomes rough.

Therefore, in any of these cases, the PV value of the joint surface cannot be made 300 nm or less by mirror polishing.

On the other hand, the PV value of the bonded surface is adjusted to 300 nm or less by mirror polishing the bonded surface with a polishing load in the above range using abrasives having Knoop hardness HK and average particle size in the above range. it can.

Examples of abrasive grains satisfying the Knoop hardness HK include cBN (cubic boron nitride, Knoop hardness HK: 4700 to 4800 kgf / mm ² ), diamond (Knoop hardness HK: 7000 to 8000 kgf / mm ² ), and the like. Can be mentioned.

In consideration of making the PV value of the bonding surface as small as possible even in the range of 300 nm or less, the Knoop hardness HK of the abrasive grains is preferably 6000 kgf / mm ² or more, and the average particle diameter is preferably 1 μm or less. . The polishing load is preferably 100 g / cm ² or more, more preferably 200 g / cm ² or less.

For the mirror polishing, a normal polishing method such as mechanical polishing (fixed abrasive grains, loose abrasive grains), chemical mechanical polishing, or the like can be employed. Regardless of which polishing method is employed, the PV value of the bonding surface of the AlN substrate can be reduced to 300 nm or less by mirror polishing with the above polishing load using the above abrasive grains.

<Preparation of sintered body>
Although the sintered compact used as the origin of the AlN board | substrate of this invention is not limited to this, For example, it can manufacture through the following process using the following sintered material.

(Sintered material)
The average particle diameter of the AlN powder that is the basis of the sintered body is preferably 0.1 μm or more, and preferably 3.0 μm or less. The average particle size of the 2A group element compound powder is preferably 0.2 μm or more, more preferably 5.0 μm or less. The average particle size of the 3A group element compound powder is preferably 0.2 μm or more, more preferably 4.0 μm or less. Further, the average particle size of the powder of the Si compound is preferably 0.5 μm or more, and preferably 6.0 μm or less.

If the average particle size of each component is less than the above range, the powder becomes bulky and it becomes difficult to mix uniformly, and the required sintered density may not be obtained. On the other hand, if the average particle size of each component exceeds the above range, each component is not sufficiently pulverized in the mixing step, resulting in a non-uniform composition, resulting in density variations after sintering, or a mirror polishing step There is a risk that graining or the like may occur due to, or the surface roughness after processing may increase.

Each component other than AlN can be blended in the state of a compound such as oxide, nitride, carbide, carbonate, composite oxide or the like. When a compound other than an oxide is used, the blending amount may be adjusted so that the ratio of the 2A group element and the like contained in the compound is in the range described above in terms of oxide.

(Preliminary molding process)
The above-mentioned AlN powder, group 2A element oxide, group 3A element oxide and other sintering aid component powder are further mixed with a binder and a dispersion medium to prepare a slurry, and the slurry is formed into a sheet. To form a green sheet.

As the binder, either one using an organic solvent as a dispersion medium or one using water as a dispersion medium can be used.

Among these, examples of the binder using an organic solvent as a dispersion medium include one or more binders such as acrylic, polyvinyl butyral, and cellulose. As an organic solvent, 1 type, or 2 or more types, such as various alcohol, is mentioned, for example.

Also, examples of the binder using water as a dispersion medium include one or more binders such as polyvinyl alcohol, acrylic, urethane, and vinyl acetate.

Further, for example, a dispersant or a plasticizer may be added to the slurry in order to improve the stability of the slurry, the dispersibility of the sintered material, or the flexibility of the green sheet.

For the mixing of the slurry, any of a dry mixing method and a wet mixing method using a general mixing device such as a ball mill, an attritor, and 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 μm, for example.

As a forming method for forming a green sheet by forming a slurry into a 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.

If the drying temperature is less than this 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.

On the other hand, when the drying temperature exceeds this range, 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 is wrinkled and warped. May be easier.

Further, the drying time is preferably 1 hour or more, more preferably 10 hours or more, and particularly preferably 20 hours or more.

If the drying time is less than this range, drying is not sufficient, and in the binder removal step that is the next step, cracks or the like due to volatilization of the dispersion medium remaining in the preform may easily occur.

In consideration of the productivity of the AlN substrate, the drying time is preferably 48 hours or less even in the above range.

(Binder removal process)
Next, the pre-formed 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 preparing a pre-sintering 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 promote thermal decomposition of the binder, or may be performed in an inert atmosphere such as a nitrogen atmosphere.

When the binder removal treatment is performed in the atmosphere, the temperature is preferably 400 ° C. or higher, and preferably 600 ° C. or lower.

If the temperature of the binder removal treatment is less than this range, the binder cannot be removed sufficiently, and in the next sintering step, sintering is hindered by the binder remaining in the precursor, or the binder is gasified. There is a risk of causing cracks in the sintered body.

On the other hand, if the temperature of the binder removal treatment exceeds the above range, the surface oxidation may inhibit the sintering.

When the binder removal treatment is performed in a nitrogen atmosphere, the temperature is preferably 500 ° C. or higher, and preferably 900 ° C. or lower.

On the other hand, even if the temperature of the binder removal processing exceeds the above range, not only the effect is not obtained, but also the energy required for heating becomes excessive, and the productivity of the AlN substrate may be lowered.

Also, the binder removal time is preferably 1 hour or more, and preferably 10 hours or less, when the binder removal treatment is performed in any atmosphere.

If the binder removal time is less than this range, the binder cannot be sufficiently removed, and in the subsequent sintering step, sintering is hindered by the binder remaining in the precursor, or the binder is gasified. There is a risk of causing cracks in the sintered body.

On the other hand, even if the binder removal time exceeds the above range, not only the effect can be obtained, but also the energy required for heating becomes excessive, which may reduce the productivity of the AlN substrate.

(Sintering process)
Next, the above precursor is sintered in an inert atmosphere such as a nitrogen atmosphere to form a sintered body.

The sintering temperature is preferably 1500 ° C. or higher, particularly preferably 1600 ° C. or higher, and is preferably 1900 ° C. or lower, particularly preferably 1750 ° C. or lower.

If the sintering temperature is less than this range, the sintering is insufficient, the bonding strength between the AlN crystal grains is reduced, and it is easy to cause degranulation, etc. The PV value of the bonding surface of the AlN substrate is 300 nm even after mirror polishing. May be exceeded.

On the other hand, if the sintering temperature exceeds the above range, sintering proceeds excessively, and segregation of the sintering aid in the sintered body is promoted, so that the joint surface cannot be uniformly mirror-polished, There is a possibility that the PV value partially exceeds 300 nm.

Also, the sintering time is preferably 1 hour or more, and preferably 10 hours or less.

If the sintering time is less than this range, the time required for the rearrangement and bonding of crystal grains in the sintering process is short, so the density variation in the sintered body increases, and the thermal conductivity of the AlN substrate increases. There is a risk that it may decrease or the overall strength may decrease.

On the other hand, if the sintering time exceeds the above range, sintering proceeds excessively, and segregation of the sintering aid in the sintered body is promoted, so that the joint surface cannot be uniformly polished. There is a possibility that the PV value partially exceeds 300 nm.

The pressure during sintering is preferably 1 atmosphere (= 1013.25 hPa) or more, and preferably 10 atmospheres (= 10132.5 hPa) or less.

If the sintering pressure is less than this range, AlN may be decomposed.

On the other hand, when the sintering pressure exceeds this range, segregation of the sintering aid in the sintered body is promoted, so that the joint surface cannot be uniformly mirror-polished, and the PV value partially exceeds 300 nm. There is a risk that.

<Example 1>
(Preparation of sintered material)
As a sintering material, powders of the following components were prepared.

AlN: Average particle size 0.9 μm
CaCO ₃ : average particle size 6 μm
Yb ₂ O ₃ : Average particle size 1.2 μm
Nd ₂ O ₃ : Average particle size 3.5 μm
Al ₂ O ₃ : Average particle size 0.3 μm
SiO ₂ : Average particle size 3.8 μm
(Preparation of slurry and preparation of preform)
The ratio of the powder of each component above after sintering is
AlN: 97.82% by mass
Ca as a 2A group element (as oxide): 0.09% by mass
Yb (as oxide) as Group 3A element: 0.99% by mass
Nd (as oxide) as group 3A element: 0.9% by mass
Si (oxide conversion): 0.2% by mass
And a slurry was prepared by blending a dispersion medium and a binder.

Next, this slurry was formed into a sheet having a length of 260 mm × width of 260 mm × thickness of 1.2 mm by an extrusion method to produce a green sheet. After punching the produced green sheet into a disk, the temperature was 24 ± 4 ° C., Time: A preform was produced by natural drying under conditions of 24 hours.

(Binder removal process)
The prepared 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. Was made.

(Sintering process)
The above precursor was sintered in a nitrogen atmosphere under conditions of temperature: 1650 ° C., time: 5 hours, pressure: 1 atm to produce a sintered body.
(Mirror polishing process)
The bonded surface, which is one side of the disk of the sintered body, was prepared using diamond abrasive grains having a Knoop hardness of HK: 7000 kgf / mm ² and an average particle size of 1 μm, and a polishing load of 150 g / cm ² . Then, it was mirror-polished by lapping with loose abrasive grains to produce a disc-shaped AlN substrate having a diameter of 200 × 0.7 mmt. The warpage of the AlN substrate was 0.8 μm / mm.

<Examples 2 to 5, Comparative Examples 1 and 2>
The polishing load in the mirror polishing step is 30 g / cm ² (Comparative Example 1), 50 g / cm ² (Example 2), 100 g / cm ² (Example 3), 200 g / cm ² (Example 4), 300 g / An AlN substrate was produced in the same manner as in Example 1 except that cm ² (Example 5) and 400 g / cm ² (Comparative Example 2) were used.

<Examples 6 to 10, Comparative Examples 3 and 4>
In the mirror polishing process, diamond abrasive grains having Knoop hardness HK: 7000 kgf / mm ² and average particle diameter: 0.03 μm were used, and the polishing load was 30 g / cm ² (Comparative Example 3), 50 g / cm ² (Example 6). ), 100 g / cm ² (Example 7), 150 g / cm ² (Example 8), 200 g / cm ² (Example 9), 300 g / cm ² (Example 10), and 400 g / cm ² (Comparative Example) An AlN substrate was produced in the same manner as in Example 1 except that 4).

<Examples 11 to 15, Comparative Examples 5 and 6>
In the mirror polishing process, diamond abrasive grains having Knoop hardness HK: 7000 kgf / mm ² and average particle diameter: 2 μm were used, and the polishing load was 30 g / cm ² (Comparative Example 5), 50 g / cm ² (Example 11), 100 g / cm ² (Example 12), 150 g / cm ² (Example 13), 200 g / cm ² (Example 14), 300 g / cm ² (Example 15), and 400 g / cm ² (Comparative Example 6) An AlN substrate was manufactured in the same manner as in Example 1 except that.

<Example 16>
An AlN substrate is manufactured in the same manner as in Example 1 except that cBN abrasive grains having a Knoop hardness of HK: 4800 kgf / mm ² and an average particle size of 1 μm are used in the mirror polishing step, and the polishing load is 150 g / cm ^2. did.

<Comparative Example 7>
An AlN substrate is manufactured in the same manner as in Example 1 except that SiC abrasive grains having a Knoop hardness of HK: 3200 kgf / mm ² and an average particle diameter of 1 μm are used in the mirror polishing process, and the polishing load is 150 g / cm ^2. did.

<Comparative Example 8>
An AlN substrate in the same manner as in Example 1 except that diamond polishing grains having a Knoop hardness of HK: 7000 kgf / mm ² and an average particle diameter of 0.01 μm were used in the mirror polishing step, and the polishing load was 150 g / cm ^2. Manufactured.

<Comparative Example 9>
An AlN substrate in the same manner as in Example 1 except that diamond polishing grains having Knoop hardness HK: 7000 kgf / mm ² and average particle diameter: 2.5 μm were used in the mirror polishing step, and the polishing load was 150 g / cm ^2. Manufactured.

<Measurement of PV value>
The PV values of the mirror-polished joint surfaces of the AlN substrates manufactured in each Example and Comparative Example were measured. The measurement was carried out in a field of 260 μm × 190 μm using a scanning interferometer (NewView (registered trademark) 7300 manufactured by ZYGO) using white light at any five locations on the joint surface. The PV value of the bonding surface of the AlN substrate of each example and comparative example was taken as the maximum value.

<Measurement of arithmetic average roughness Ra>
For comparison, each of the examples and comparative examples of the AlN substrate manufactured in the mirror polished surface at any five locations within a field of view of 0.6 mm × 0.5 mm using a non-contact type surface roughness meter Each arithmetic average roughness Ra was obtained from the roughness curve measured in step (b), and the average value was calculated as the arithmetic average roughness Ra of the bonding surfaces of the AlN substrates of the examples and comparative examples.

The above results are shown in Tables 1 to 5.

From the results of Examples 1 to 16 and Comparative Examples 1 to 9 in Table 1 to Table 5, in order to make the PV value of the bonded surface of the AlN substrate 300 nm or less, Knoop hardness HK: 4000 kgf / mm ² or more, average particle diameter: 0.03 .mu.m or more, using the following abrasive 2 [mu] m, polishing load: 50 g / cm ² or more, is necessary to mirror polishing was found that at 300 g / cm ² following conditions .

In addition, from the results of each example, in order to make the PV value of the joint surface as small as possible even within a range of 300 nm or less, the Knoop hardness HK of the abrasive grains is preferably 6000 kgf / mm ² or more, and the average particle diameter is 1 μm. It has been found that the following is preferable, the polishing load is preferably 100 g / cm ² or more, and preferably 200 g / cm ² or less.

<Examples 17 to 21>
The temperature in the sintering process was 1500 ° C. (Example 17), 1600 ° C. (Example 18), 1750 ° C. (Example 19), 1850 ° C. (Example 20), and 1900 ° C. (Example 21). An AlN substrate was manufactured in the same manner as in Example 1 except for the above.

<Examples 22 and 23>
An AlN substrate was manufactured in the same manner as in Example 1 except that the time in the sintering step was 1 hour (Example 22) and 10 hours (Example 23).

The PV value and arithmetic average roughness Ra of the AlN substrates manufactured in the above examples and comparative examples were measured by the method described above. The results are shown in Table 6 together with the results of Example 1.

From the results of Examples 1 and 17 to 23 in Table 6, the temperature of the sintering process is preferably 1500 ° C. or more, particularly preferably 1600 ° C. or more in order to make the PV value of the bonding surface of the AlN substrate 300 nm or less. It was found that the temperature is preferably 1900 ° C. or lower, particularly 1750 ° C. or lower, the time is preferably 1 hour or longer, and preferably 10 hours or shorter.

<Examples 24 and 25, Comparative Examples 10 and 11>
An AlN substrate was produced in the same manner as in Example 1 except that any sintered material in which each component was blended so that the ratio after sintering was a value shown in Table 7 below.

As the Y sintering material, Y ₂ O ₃ powder having an average particle size of 0.9 μm was used.

The PV value and arithmetic average roughness Ra of the AlN substrates manufactured in the above examples and comparative examples were measured by the method described above. The results are shown in Table 7 together with the results of Example 1.

From the results of Examples 1, 24 and 25 and Comparative Examples 10 and 11 in Table 7, in order to make the PV value of the bonding surface of the AlN substrate 300 nm or less, the ratio of the 2A group element is set to 0. It was found that the content must be 009% by mass or more and 0.28% by mass or less.

<Examples 26 to 28, Comparative Examples 12 and 13>
An AlN substrate was produced in the same manner as in Example 1 except that any sintered material in which each component was blended so that the ratio after sintering was a value shown in Table 8 below.

The PV value and arithmetic average roughness Ra of the AlN substrates manufactured in the above examples and comparative examples were measured by the method described above. The results are shown in Table 8 together with the results of Example 1.

From the results of Examples 1, 26 to 28 and Comparative Examples 12 and 13 in Table 8, in order to make the PV value of the bonding surface of the AlN substrate 300 nm or less, the ratio of the group 3A element is set to 0. It was found that it was necessary to be 02 mass% or more and 4.5 mass% or less.

<Examples 29 and 30, Comparative Example 14>
An AlN substrate was manufactured in the same manner as in Example 1 except that any sintered material in which each component was blended so that the ratio after sintering was a value shown in Table 9 below.

The PV value and arithmetic average roughness Ra of the AlN substrates manufactured in the above examples and comparative examples were measured by the method described above. The results are shown in Table 9 together with the results of Example 1.

From the results of Examples 1, 29, 30 and Comparative Example 14 in Table 9, in order to make the PV value of the bonding surface of the AlN substrate 300 nm or less, the proportion of the 2A group element is oxide as described above. The ratio of the group 3A element is 0.009% by mass or more and 0.28% by mass or less in terms of oxide, and 0.02% by mass or more and 4.5% by mass or less in terms of oxide, and the ratio of AlN is 99.99%. It was found that the content was preferably 971% by mass or less.

Further, when the PV values of Examples 1 to 30 and Comparative Examples 1 to 14 in the above tables were compared with the arithmetic average roughness Ra, the magnitude of the PV value and the arithmetic average roughness Ra were not necessarily proportional. There were also cases where the magnitude relationship was reversed.

From this, it was found that the level of the step can be grasped more accurately according to the PV value defined in the present invention.

<Example 31>
A Ti film having a thickness of 0.1 μm, a Pt film having a thickness of 0.2 μm, and an Au film having a thickness of 1.0 μm are sequentially laminated on the bonding surface of the AlN substrate manufactured in Example 1 by a sputtering method, and further a thickness of 5 μm is formed thereon. An Au—Sn solder film (composition ratio Au: Sn = 70: 30) was formed.

Further, a disc-shaped sapphire substrate having a diameter of 200 × 0.7 mmt is prepared, and a Ti film having a thickness of 0.1 μm, a Pt film having a thickness of 0.2 μm, and a thickness of 1. A 0 μm Au film was laminated in order.

Next, the AlN substrate is placed with the Au—Sn solder film on top, and the sapphire substrate is overlaid so that the Au film is in close contact with the Au—Sn solder film, and heated to 320 ° C. in a nitrogen atmosphere. Both substrates were soldered together.

Then, the solder-bonded AlN substrate and sapphire substrate were cut along the stacking direction at almost the center of the disk, and the entire cut surface was observed with a scanning electron microscope (SEM) at a magnification of 1000 times. There were no voids.

<Example 32>
After a SiO ₂ film having a thickness of 0.1 μm was formed on the bonding surface of the AlN substrate manufactured in Example 1 by CVD, the AlN substrate was placed in the chamber and 100 W of 100 W was introduced while introducing 60 sccm of N ₂ gas. The surface of the SiO ₂ film was cleaned with RF plasma.

Also, a disc-shaped sapphire substrate having a diameter of 200 × 0.7 mmt was prepared, and the surface to be bonded was cleaned with 100 W RF plasma while introducing 60 sccm of N ₂ gas in the same manner as described above.

Next, the AlN substrate is placed with the SiO ₂ film on top, and the sapphire substrate is heated to 300 ° C. with the cleaned surface to be bonded so as to be in close contact with the SiO ₂ film. The substrates were joined.

Then, when the entire bonded AlN substrate and sapphire substrate were observed from the sapphire substrate side with a metal microscope at a magnification of 1000 times, no void was found on the bonded surface.

<Example 33>
The AlN substrate and the sapphire substrate were bonded in the same manner as in Example 32 except that the AlN substrate manufactured in Example 6 was used.

And when the whole of the bonded AlN substrate and the sapphire substrate was observed with a metal microscope from the sapphire substrate side at a magnification of 1000 times, 10 voids were found on the bonding surface, but the other areas were used as bonded substrates Judged that it was possible.

<Comparative Example 15>
The AlN substrate and the sapphire substrate were bonded in the same manner as in Example 32 except that the AlN substrate manufactured in Comparative Example 3 was used.

When the entire bonded AlN substrate and sapphire substrate were observed from the sapphire substrate side with a metal microscope at a magnification of 1000 times, 1000 or more voids were observed on the entire bonding surface, and an area that could be used as a bonded substrate was found. I couldn't.

Claims

Sintering of AlN containing 0.009% by mass or more and 0.28% by mass or less of 2A group element in terms of oxide, and 0.02% by mass or more and 4.5% by mass or less of 3A group element in terms of oxide An AlN substrate comprising a body and having a joint surface with another member, and the joint surface has a PV value indicating surface accuracy of 300 nm or less.
The AlN substrate according to claim 1, wherein the 2A group element is at least one selected from the group consisting of Ca and Mg.
3. The AlN substrate according to claim 1, wherein the 3A group element is at least one selected from the group consisting of Y and a lanthanoid.
At least one layer made of at least one metal selected from the group consisting of Ti, Pt, Pd, Au, Ag, and Al, Au—Sn, or SiO 2 is formed on the bonding surface. The AlN substrate according to any one of claims 1 to 3.