JP2011089161A - Composite material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composite material which is suitable for the heat radiation member of a semiconductor element, to provide a method for producing the same, to provide a heat radiation member, and to provide a semiconductor device. <P>SOLUTION: The composite material is obtained by dispersing diamond into the metal matrix made of magnesium (Mg) or a magnesium alloy (Mg alloy). The composite material is produced by infiltrating melted Mg or melted Mg alloy (molten Mg) into a powder compact produced using diamond powder and Si powder. Before the infiltration, the powder compact is heated to a prescribed holding temperate of the melting point of Si or higher, the surface of the powder compact is converted into SiC, and is further oxidized so as to convert at least the surface side part of the SiC into silicon oxide. When the oxidized compact including the silicon oxide is brought into contact with the molten Mg, by reaction with the silicon oxide, Mg<SB>2</SB>Si is produced. The oxidized compact in which the silicon oxide is formed has excellent wettability with the molten Mg, and from which a composite material having excellent thermal conductivity can be obtained. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a composite material in which magnesium (so-called pure magnesium) or a magnesium alloy and diamond are combined, a heat radiating member composed of the composite material, a semiconductor device including the heat radiating member, and a method for manufacturing the composite material Is. In particular, the present invention relates to a composite material that has excellent thermal characteristics and is suitable as a constituent material of a heat dissipation member of a semiconductor element.

  In recent years, high functionality and high density mounting of various electronic devices are desired. For this reason, it is necessary to sufficiently dissipate the semiconductor element so that the semiconductor element incorporated in these electronic devices does not reach the operating upper limit temperature. Conventionally, a heat radiating member (heat spreader) for expanding a heat radiating area is used in addition to natural convection and forced air blowing for heat radiation of a semiconductor element.

  As a material for the heat dissipation member, a composite material of a metal and a non-metallic inorganic material (typically ceramics) such as Al-SiC is used in addition to a metal material such as copper, Cu-W, or Cu-Mn. Has been. In recent years, a composite material using magnesium (Mg), which is lighter than aluminum (Al) or an alloy thereof, as a metal matrix has been studied mainly for the purpose of reducing the weight of the heat dissipation member (see Patent Document 1).

JP 2006-299304 A

The heat dissipation member of the semiconductor element has excellent thermal conductivity, and the coefficient of thermal expansion of the semiconductor element and its peripheral parts (typically, 4 ppm / K (4 × 10 ⁻⁶ / K) to 8 ppm / K (8 × It is desirable to have excellent consistency with 10 ^-6 / K). Ideally, it is desirable that the heat radiating member, the semiconductor element, and its peripheral devices have the same thermal expansion coefficient.

  Since the above copper and copper alloys have a large coefficient of thermal expansion, when a semiconductor element is placed on a heat dissipation member made of copper or the like, thermal stress is generated at the interface between the two under a heat cycle, and the semiconductor element is distorted. In the worst case, the semiconductor element and the heat dissipation member may be peeled off. Moreover, the said copper and copper alloy are heavy, and when it is desired to be lightweight, such as a vehicle-mounted apparatus and a portable apparatus, it is not preferable.

  On the other hand, although Al-SiC and the magnesium-based composite material described in Patent Document 1 are lightweight, they have lower thermal conductivity than copper. Considering further higher performance and higher density mounting in the future, further improvement in thermal conductivity is desired.

  In order to improve the thermal conductivity, it is conceivable to use diamond having the highest thermal conductivity among the substances. However, since diamond has a very low thermal expansion coefficient and a large Young's modulus, when a semiconductor element is placed directly on diamond, a very large thermal stress is generated at the interface between the two. Therefore, it is inappropriate to use diamond as it is as a constituent material of the heat dissipation member.

  On the other hand, there is a sintered body obtained by sintering a formed body of diamond and copper at a temperature equal to or higher than a temperature at which a liquid phase is generated in copper. However, this sintered body is heavy as described above because it contains copper. Copper generally has poor wettability with diamond. Therefore, even when diamond and molten copper are combined, pores are easily formed, and only the composite material having a large thermal resistance at the interface between them can be obtained due to the presence of the pores, and the composite material has a high thermal conductivity as expected. Not.

  Therefore, one of the objects of the present invention is to provide a composite material having thermal characteristics suitable for a heat dissipation member of a semiconductor element. Another object of the present invention is to provide a method for manufacturing a composite material suitable for manufacturing the composite material. Furthermore, the other object of this invention is to provide the heat radiating member which consists of the said composite material, and a semiconductor device provided with this heat radiating member.

  The inventors of the present invention are magnesium or a magnesium alloy (hereinafter referred to as Mg or Mg alloy) as a material that is lightweight but has a high thermal conductivity and a coefficient of thermal expansion that is close to that of a semiconductor element and its peripheral devices. ) And diamond are preferable, and a method for combining them was studied.

  For example, as a composite method, it is conceivable to produce a mixed powder molded body of diamond powder and Mg or Mg alloy powder, melt the Mg or Mg alloy by holding the molded body at a high temperature, and then solidify it. . However, Mg or Mg alloy powder is a difficult material to handle, and molten Mg or Mg alloy (hereinafter referred to as molten Mg) has poor wettability with diamond as it is. Accordingly, pores are easily formed, and the presence of the pores causes deterioration of thermal characteristics as described above.

  In view of this, the present inventors examined the use of an infiltration method in which molten Mg is infiltrated into a diamond compact in the same manner as in Patent Document 1. However, also in the infiltration method, it is necessary to improve the wettability between molten Mg and diamond as described above.

  Here, molten Mg has a property of being very easy to react with oxygen (easy to bond). Therefore, by forming a layer containing oxygen, for example, an oxide layer, on the surface of diamond, the wettability between molten Mg and diamond can be improved. However, providing an oxide layer directly on the surface of diamond is considered to be expensive, and this is not preferable in view of industrial productivity.

  On the other hand, diamond can be used as a carbon source. Therefore, when combining diamond and molten Mg, an oxide layer is not formed directly on the surface of the diamond, but a carbide is once formed on the surface of the diamond, and this carbide is reduced to form an oxide layer. Propose. In particular, the above carbide is made of SiC so that the thermal characteristics are hardly deteriorated even if it remains in the composite material.

The method for producing a composite material according to the present invention relates to a method for producing a composite material of diamond and Mg or an Mg alloy, and includes the following preparation step, oxidation step, and composite step.
Preparation step: A step of forming a SiC-coated molded body in which the surface of a powder molded body made of diamond is converted to SiC.
Oxidation step: a step of oxidizing the SiC-coated molded body to convert at least the surface side portion of the SiC into silicon oxide to form an oxidized molded body comprising silicon oxide.
Composite step: Infiltrating molten Mg or Mg alloy into the oxidized molded body, while producing Mg ₂ Si by reaction of the silicon oxide and the molten Mg or Mg alloy, the Mg or Mg alloy and the above The process of compounding with diamond.

  In the production method of the present invention, in forming the SiC coated molded body, the SiC carbon source is diamond itself. Therefore, it is not necessary to prepare a carbon source separately, and diamond particles and SiC are excellent in adhesion, and pores do not substantially exist at the interface between the two. In addition, by converting at least a part of the SiC thus adhered to an oxide, it is possible to easily form a diamond particle having an oxide on at least the outermost surface portion. Excellent adhesion. Then, by preparing an oxidized formed body having the oxide layer, the manufacturing method of the present invention is excellent in wettability between the oxidized formed body and molten Mg. Specifically, since the molten Mg has a high ability to take in oxygen of the silicon oxide present on the surface of the oxidized molded body, the molten Mg reduces the silicon oxide when combined with the diamond and molten Mg. , Wetting the diamond. Such wetting is the driving force, and molten Mg is spontaneously infiltrated into the oxide compact. Therefore, according to the production method of the present invention, pores are hardly generated at the time of compounding, diamond and Mg or Mg alloy can be sufficiently compounded, and a composite material having excellent thermal characteristics can be obtained because the pores are small and dense. .

Moreover, free Si is produced | generated by the above reduction reactions. Here, Si hardly dissolves in molten Mg. Therefore, the generated free Si is combined with Mg to generate Mg ₂ Si. Therefore, Mg ₂ Si is present in the composite material obtained by the production method of the present invention. Although Mg ₂ Si does not have high thermal conductivity, it is difficult to greatly deteriorate the thermal conductivity of the composite material by being dispersed as fine particles.

The composite material of the present invention is obtained by the production method of the present invention. The composite material of the present invention is a composite material in which diamond and Mg or Mg alloy are combined, and diamond particles are dispersed in a metal matrix made of Mg or Mg alloy. The metal matrix contains Mg ₂ Si. In addition, at least some of the diamond particles include a SiC layer on the surface thereof.

  The composite material of the present invention is very lightweight because the metal matrix is made of Mg or Mg alloy, and has excellent thermal conductivity by containing diamond. In addition, a continuous heat dissipation path is constructed by the presence of Mg or Mg alloy mainly between diamond particles. Also from this fact, the composite material of the present invention is excellent in thermal conductivity.

  In addition, since the composite material of the present invention is a composite of metal and diamond, the thermal expansion coefficient does not become too small as compared to the case of a single diamond. Specifically, the composite material of the present invention can have, for example, a thermal expansion coefficient of about 1.5 W / m · K to 4 W / m · K.

  Since the composite material of the present invention has a high thermal conductivity as described above and is excellent in the consistency of the thermal expansion coefficient with the semiconductor element and its peripheral components, it can be suitably used as a constituent material of the heat radiating member. In addition, since the composite material of the present invention is a composite of metal and diamond, the Young's modulus does not become too high compared to the case of diamond alone, and chipping or the like is unlikely to occur during post-processing such as cutting.

Hereinafter, the present invention will be described in more detail.
[Composite material]
<Metal matrix>
The metal matrix is so-called pure magnesium composed of 99.8% by mass or more of Mg and impurities, or a magnesium alloy composed of additive elements and the balance Mg and impurities. When the metal matrix is pure magnesium, compared to the case of an alloy, the thermal conductivity of the composite material can be improved, and a uniform structure is less likely to cause defects such as non-uniform precipitation of crystallized materials during solidification. It has the advantage that it is easy to obtain a composite material having it. When the metal matrix is a magnesium alloy, the liquidus temperature is lowered, so that the temperature at the time of melting can be lowered, and the corrosion resistance and mechanical properties (strength, etc.) of the composite material can be improved. Examples of the additive element include at least one of Li, Ag, Ni, Ca, Al, Zn, Mn, Si, Cu, and Zr. Since these elements cause a decrease in thermal conductivity when the content increases, the total content is preferably 20% by mass or less (the metal matrix is 100% by mass; the same applies to the content of additive elements). In particular, Al is preferably 3% by mass or less, Zn is 5% by mass or less, and other elements are each preferably 10% by mass or less. Addition of Li has the effect of reducing the weight of the composite material and improving the workability. Known magnesium alloys such as AZ (AZ31, AZ61, AZ91, etc.), AS, AM, ZK, ZC, LA, etc. may be used. A metal raw material is prepared so as to have a desired composition.

<Diamond>
"component"
The diamond composited with the metal matrix can be used as a raw material as it is. The raw material diamond may be artificial or natural. In particular, the lower the impurities such as nitrogen and the higher the purity, the higher the thermal conductivity of diamond (for example, the thermal conductivity at room temperature is about 700 W / m ・ K), so a composite material with excellent thermal conductivity can be obtained. it can. The nitrogen content is 200 ppm or less, particularly 150 ppm or less in terms of mass ratio. However, since high-purity natural diamond is generally used for jewelry and is expensive, diamond having a high purity among industrial diamonds with a nitrogen content of 10 ppm or more, particularly 50 ppm or more can be suitably used. .

<SiC layer>
At least some of the diamond particles present in the composite material have a SiC layer on the surface thereof. In producing the composite material of the present invention as described above, the surface of the diamond particles is converted into SiC and then converted into a silicon oxide such as SiO ₂ . Here, since SiC has high oxidation resistance, the entire SiC is not converted into the above oxide, at least the surface side portion of SiC is converted into the above oxide, and the remainder is not converted as SiC as it is. Can exist. By using such an oxidized compact, at least some of the diamond particles present in the manufactured composite material can have a SiC layer on the surface thereof. Although SiC is inferior in thermal conductivity to diamond, it has the effect of suppressing the thermal expansion coefficient of the composite material from becoming too small because the thermal expansion coefficient is larger than diamond and smaller than Mg or Mg alloy. .

"size"
The diamond particles in the composite material of the present invention are typically dispersed and dispersed in the metal matrix. The average particle diameter of the diamond particles is preferably 10 μm or more and 100 μm or less. If it is less than 10 μm, the area of the interface between diamond particles and Mg or Mg alloy increases, so that the thermal resistance increases and the thermal conductivity of the composite material decreases. Larger diamond particles tend to have better thermal conductivity, but if the particle size exceeds 100 μm, the diamond particles in the composite material are too large, and chipping is likely to occur during processing such as cutting and polishing after the composite material is manufactured. These processes are difficult to perform. A more preferable average particle diameter is 20 μm or more and 70 μm or less. Diamond particles used as a raw material do not substantially grow during production of the composite material. Moreover, the SiC layer and oxide layer formed at the time of manufacture are also very thin. Therefore, the size of the diamond particles in the composite material substantially matches the size of the diamond particles used as the raw material.

"Content"
If there is too little diamond in the composite material, the thermal conductivity of the composite material will be low, and it will be difficult to form a powder molded body, or the strength of the powder molded body will be weak and may collapse. On the other hand, as the amount of diamond increases, the thermal expansion coefficient of the composite material having excellent thermal conductivity becomes too small, and it becomes difficult to form a powder compact having sufficient open pores for infiltrating molten Mg. Therefore, the content of diamond in the composite material is preferably 35% by volume or more and 85% by volume or less, and more preferably 50% by volume or more and 80% by volume or less with respect to the entire composite material.

《Mg ₂ Si》
The composite material of the present invention is characterized in that fine Mg ₂ Si is dispersed in the metal matrix. As described above, Mg ₂ Si is generated by wet reaction while molten Mg and silicon oxide present on the surface of the powder compact are reacted. As described above, Mg ₂ Si is a fine particle and dispersed in the composite material, so that the deterioration of the thermal conductivity of the composite material due to the presence of Mg ₂ Si is not substantially problematic. It is thought that.

Note that silicon oxide such as SiO ₂ formed in the manufacturing stage reacts with molten Mg during infiltration to form Mg ₂ Si and does not substantially remain in the composite material. Further, the total content of Si of Mg ₂ Si and SiC of SiC in the composite material is substantially equal to the amount of Si used as a raw material. If the Si in the composite material is large, a large amount of SiC or Mg ₂ Si will be present, leading to a decrease in thermal conductivity. Therefore, the Si content in the composite material is preferably 10% by volume or less.

<Thermal characteristics>
"Thermal conductivity"
The composite material containing diamond in the above range has a high thermal conductivity κ, for example, the thermal conductivity κ at room temperature satisfies 250 W / m · K or more. Depending on the diamond content, particle size, metal matrix composition, etc., a composite material having a thermal conductivity κ at room temperature of 300 W / m · K or more, particularly 400 W / m · K or more can be obtained. .

《Coefficient of thermal expansion》
A composite material containing diamond in the above range has a relatively small thermal expansion coefficient α, for example, a semiconductor element having a thermal expansion coefficient α of about 4 ppm / K and its peripheral devices, satisfying about 1.5 ppm / K to 4 ppm / K. Excellent thermal expansion coefficient consistency.

<Application>
As described above, the composite material of the present invention is excellent in the consistency of the thermal expansion coefficient with the semiconductor element and its peripheral devices and has high thermal conductivity, and therefore can be suitably used as a heat dissipation member for the semiconductor element. A semiconductor device including the heat radiating member and a semiconductor element mounted on the heat radiating member can be suitably used for parts of various electronic devices.

[Production method]
The composite material of the present invention can be produced by combining a diamond compact and molten Mg as described above (infiltration → solidification). In particular, as the molded body, a SiC layer is formed on the surface of diamond particles, and the SiC layer is converted into silicon oxide.

"material"
The main raw material of the powder molded body is diamond powder. As described above, the average particle diameter of the diamond particles constituting the powder is preferably 10 μm to 100 μm. When producing a powder compact containing Si, Si powder is used in addition to the diamond powder.

<< Preparation process >>
[Formation of powder compact]
The powder compact can be formed, for example, by adding an appropriate binder to the raw material powder and press-molding it. The press molding may be a dry press or a wet press using a liquid such as water in addition to the raw material powder. The formed powder molded body is a porous body, and when it is converted into SiC or into an oxide, the binder disappears due to the heat generated when it is combined with molten Mg, so that the porous body has sufficient open pores. Become a body. A composite material is obtained by infiltrating molten Mg into these open pores.

  Examples of the powder compact include those substantially consisting of diamond powder or those consisting essentially of diamond powder and Si powder. The Si powder may be added as much as necessary for forming the SiC layer, and about 5% to 10% is appropriate for the total volume of the raw material powder forming the compact. Note that these powder compacts may be sintered to form a sintered body. By using a sintered body, it becomes easy to handle and can be easily placed on a mold or the like.

[Conversion to SiC]
Diamond forming the powder compact is used as a carbon source and reacted with liquid or vapor phase Si to form a SiC-coated compact in which the surface of the powder compact is converted to SiC.

  When a powder compact is formed using diamond powder and Si powder, Si powder becomes the Si source. For example, by heating the powder compact to a predetermined holding temperature equal to or higher than the melting point of Si, the surface of the diamond particles constituting the powder compact can be converted to SiC. Since the melting point of Si is about 1400 ° C., it is preferable to select at least a temperature at which Si is in a liquid phase state as the holding temperature. For example, about 1450 degreeC is mentioned in a vacuum. However, since the diamond is easily graphitized when the temperature exceeds 1000 ° C., the holding temperature is preferably not less than the melting point of Si and as low as possible. Since graphite is inferior in thermal conductivity and weaker than diamond, it is desired to suppress graphitization.

Alternatively, when a powder compact is formed using substantially only diamond powder without using Si powder, a Si source is prepared separately. For example, a gas containing Si, specifically, SiH ₄ , SiCl ₄ or the like can be used. In this case, the surface of the diamond particles constituting the powder compact can be converted to SiC by heating the powder compact to a predetermined holding temperature in a gas containing Si. The holding temperature may be appropriately selected as a temperature at which diamond and Si can react. When a gas containing Si is used, it can be lowered because it reacts more easily than the case of the Si powder, for example, about 800 ° C. can do. The holding temperature may be a temperature equal to or higher than the melting point of Si as in the case where Si powder is used, but is preferably 1000 ° C. or lower because graphitization can be suppressed.

  In the conversion to SiC, it is important to control the heating rate up to a predetermined holding temperature. Diamond has a tendency for the structural phase to transition from about 1000 ° C. to graphite even in a vacuum. Therefore, in particular, when the holding temperature is higher than 1000 ° C., if the heating rate is low, diamond is changed to graphite. However, since the structural phase transition to graphitization takes a certain amount of time, graphitization can be suppressed by increasing the rate of temperature increase. In order to increase the rate of temperature increase, for example, in the case of a powder compact using the Si powder, heating is performed in a furnace capable of rapid temperature increase, such as a discharge plasma sintering furnace or a millimeter wave heating furnace.

  In particular, when industrial diamond is used as the diamond powder and the holding temperature is higher than 1000 ° C., the heating time to a predetermined holding temperature (for example, 1450 ° C.) is preferably 10 minutes or less. More preferably, it is 5 minutes to 10 minutes (the heating rate is 145 ° C./min to 290 ° C./min). Note that high-purity diamond such as jewelry diamond is difficult to be graphitized, so the heating time to the predetermined holding temperature may be more than 10 minutes, but a shorter one is preferable.

  The heating time at the holding temperature may be about several tens of seconds. Even in such a short time, the surface of the diamond particles can be easily converted to SiC.

<Oxidation process>
The SiC-coated molded body obtained as described above is oxidized to convert at least a part of SiC into silicon oxide. A typical example of the silicon oxide is SiO ₂ . The easiest way to carry out this oxidation step is to heat in the atmosphere. The holding temperature when heating is preferably 800 ° C. or higher, more preferably 850 ° C. or higher, and particularly preferably 875 ° C. or higher. The higher the holding temperature, the easier it can be converted to silicon oxide and it can be oxidized in a short time. However, as described above, when it exceeds 1000 ° C, it tends to be graphitized, and an oxide layer is excessively formed or non-uniform. There is a risk that it will be formed in a thickness. Therefore, considering the suppression of graphitization, the holding temperature is preferably 1000 ° C. or lower. When the holding temperature is higher than 1000 ° C., it is preferable that the heating time to a predetermined holding temperature is 10 minutes or less and the heating time is shortened, as in the case of forming SiC.

  Since SiC is excellent in oxidation resistance as described above, all of SiC does not become silicon oxide by this oxidation step, and SiC remains. That is, the particles constituting the oxidized molded body have a multilayer structure in which diamond, a SiC layer, and a silicon oxide layer are sequentially laminated.

[Manufacturing method of other oxidized compacts]
In addition, after preparing diamond powder and heating in a gas containing Si as described above to convert the surface of each particle to SiC, further heating in a gas containing oxygen as described above. An oxide powder is produced by converting at least the outermost surface of each particle into silicon oxide. A powder aggregate obtained by tapping this oxidized powder on a mold having a predetermined shape can be used as an oxidized molded body. This method is suitable for forming a composite material having a relatively low diamond content. Alternatively, the oxidized powder can be press-molded to form an oxidized molded body. Alternatively, these oxidized molded bodies may be sintered to form a sintered body. These methods of forming and using the oxidized powder can be suitably used when the composite material has a complicated shape. Further, for example, it can be suitably used when a member made of various materials having a melting point of 900 ° C. or higher and 1500 ° C. or lower (for example, a SUS pipe) is embedded in a composite material. A method for forming a molded body may be selected in accordance with the shape and application of the composite material.

《Composite process》
The oxidized molded body obtained as described above is stored in a mold having a predetermined shape, infiltrated with molten Mg, and then solidified with molten Mg, whereby a composite material is obtained. If this combined process is performed in an atmosphere at atmospheric pressure (generally 0.1 MPa (1 atm)) or less, it is difficult to take in the gas in the atmosphere, and it is difficult to generate pores that accompany the gas. However, since Mg has a high vapor pressure, it becomes difficult to handle molten Mg in a high vacuum state. Therefore, 0.1 × 10 ⁻⁵ MPa or more is preferable when the atmospheric pressure in the composite process is less than atmospheric pressure. Further, when the composite process is performed in an inert atmosphere such as Ar, the reaction between the Mg component and the atmospheric gas can be prevented, and the deterioration of the thermal characteristics due to the presence of the reaction product can be suppressed. The infiltration temperature is preferably 650 ° C. or higher, and the higher the infiltration temperature, the higher the wettability between molten Mg and silicon oxide. Therefore, 700 ° C. or higher, particularly 800 ° C. or higher, and more preferably 850 ° C. or higher is preferable. However, if the temperature exceeds 1000 ° C., defects such as shrinkage cavities and gas holes may occur or Mg may boil, so the infiltration temperature is preferably 1000 ° C. or less, particularly 900 ° C. or less.

  The composite material of the present invention and the heat dissipating member of the present invention composed of the composite material are excellent in thermal expansion coefficient matching with a semiconductor element and the like, and also in thermal conductivity. The manufacturing method of the composite material of the present invention can manufacture the composite material of the present invention with high productivity. The semiconductor device of the present invention has excellent thermal characteristics by including the heat dissipation member.

[Test example]
A composite material composed of pure magnesium and diamond was fabricated and the thermal characteristics were investigated.

The following were prepared as raw materials.
(1) Diamond: A commercially available diamond having the average particle size shown in Table 1.
Industrial: Yellowish diamond powder.
For jewelry: Transparent diamond powder for jewelry (high purity).
(2) Si powder: Powder having a purity of 99.9% and an average particle diameter of 1 μm.
(3) Pure magnesium: An ingot (commercially available product) comprising 99.8% by mass or more of Mg and impurities.

[Preparation of powder compact]
Diamond powder and Si powder were prepared so as to have a predetermined volume ratio shown in Table 1, and mixed by a ball mill to obtain a mixed powder. This mixed powder and a binder (camphor) were press-molded to produce a disk-shaped powder compact having a diameter of 10 mm and a thickness of 2 mm. The density of the obtained powder compact was determined from the volume and mass, and the relative density (density of the compact / theoretical density) was determined. The results are also shown in Table 1.

[Conversion to SiC]
The produced powder compact was loaded into a split graphite mold of a discharge plasma sintering furnace, heated in vacuum to the holding temperature shown in Table 1, and this holding temperature was held for the holding time shown in Table 1. In this test, heating was performed by adjusting the rate of temperature rise so that the heating time to the holding temperature was the time shown in Table 1. After the heating, the graphite mold was removed from the sample (SiC coated molded body) and allowed to cool naturally.

[Conversion to silicon oxide]
The manufactured SiC coated molded body was charged into a horizontal electric furnace (atmospheric furnace) that was previously held at the holding temperature shown in Table 1, held for the holding time shown in Table 1, and then removed from the electric furnace. It was. When the surface composition was examined with an EDX apparatus in the cross section of the obtained sample (oxidized compact), it was confirmed that there were particles in which a SiC layer and an SiO ₂ layer were formed in this order on the diamond surface. Further, the relative density of the obtained oxidized molded body was determined in the same manner as the above powder molded body. The results are also shown in Table 1.

[composite]
The prepared ingot was put into an iron crucible of SF ₆ gas atmosphere and melted in an electric furnace to prepare a molten metal, and the molten metal was kept at 750 ° C. On the other hand, the produced oxidized molded body is placed in a carbon mold, and the molten metal is contacted to infiltrate the oxidized molded body (infiltration temperature: 750 ° C., Ar atmosphere, atmospheric pressure: atmospheric pressure), 1-2. After holding for about an hour, a composite material was formed by solidifying pure magnesium. In addition, the holding time at the time of infiltration can be appropriately changed according to the size of the composite material. In addition, when a commercially available release agent is applied to a portion of the mold where the oxidized molded body comes into contact, the mold release property is excellent. In addition, as the casting mold, a mold having an ingot placement location and a composite material formation location was prepared, and the produced oxidized molded body was placed at the formation location, and the mold was heated and placed at the placement location. The ingot may be melted and the molten metal may be infiltrated into the oxidized molded body.

[Evaluation of composite materials]
About the obtained composite material, thermal conductivity, a thermal expansion coefficient, and the production | generation phase were identified. The results are shown in Table 1. Moreover, the relative density of each obtained composite material was calculated | required similarly to the said powder molded object. The results are also shown in Table 1.

  For thermal conductivity, the thermal conductivity (W / m · K) at room temperature was measured with a laser flash type thermal conductivity measuring device.

  As for the thermal expansion coefficient, an average thermal expansion coefficient (ppm / K) from room temperature to 500 ° C. was measured with a differential transformer type thermal expansion coefficient measuring apparatus.

  For identification of the generated phase, each sample was observed with an electron microscope, and the vicinity of the interface between the metal matrix and the diamond particles was observed. And the production | generation phase which exists in the said interface vicinity was identified by X-ray diffraction. The observation magnification can be selected as appropriate.

Further, the cross-sectional composition of each sample in which the Mg ₂ Si phase was generated was examined by an EDX apparatus. As a result, Mg and diamond, the balance: Mg ₂ Si and unavoidable impurities, particles having a SiC layer on the surface of the diamond particles Was confirmed. Further, when the average particle diameter of the diamond particles was examined by observing the cross section of each sample under a microscope, the diamond particles generally coincided with the size of the diamond particles used as the raw material.

  As shown in Table 1, it can be seen that by combining diamond and pure magnesium, a composite material having a high thermal conductivity and a low thermal expansion coefficient can be obtained. In particular, it can be seen that the composite material can be obtained by converting the surface of a powder compact using diamond powder into SiC and then converting it into silicon oxide. Also, during the conversion of SiC or conversion to silicon oxide, the heating rate is increased (the heating time to the holding temperature is shortened), diamond powder with a large average particle diameter is used, or high-purity diamond is used. It can be seen that a composite material having high thermal conductivity can be obtained. When the temperature increase rate was small, the thermal conductivity was small. The reason for this is considered to be that a part of the diamond was graphitized. In addition, when jewelry diamond is used, a composite material having a very high thermal conductivity of about 700 W / m · K can be obtained. It is expected that such a composite material with high thermal conductivity and excellent thermal compatibility with a semiconductor element having a thermal expansion coefficient of about 4 ppm / K and its peripheral components can be suitably used as a constituent material of a heat dissipation member of the semiconductor element. Is done.

  On the other hand, when it was not converted to silicon oxide after conversion to SiC, molten Mg was not sufficiently infiltrated, and infiltration did not progress in the middle. Moreover, when the content of diamond was small, the powder compact collapsed. Note that the content (volume%) of diamond in the composite material generally corresponds to the relative density of the powder compact × the volume ratio of the diamond.

  The present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the gist of the present invention. For example, the content of diamond in the composite material, the composition of the metal component (e.g., magnesium alloy), conditions for conversion to SiC (e.g., temperature and heating rate), conditions for conversion to silicon oxide (e.g., temperature and The rate of temperature increase, etc.) and the conditions during combination (temperature, atmosphere, pressure, etc.) can be changed as appropriate.

  The composite material of the present invention is suitably used for a heat spreader (a heat dissipating member of the present invention) of a semiconductor element used for a CPU, GPU (Graphics Processing Unit), chip set, memory chip provided in a personal computer or a mobile electronic device. be able to. The method for producing a composite material of the present invention can be suitably used for producing the composite material. The semiconductor device of the present invention can be suitably used for the components of various electronic devices such as the personal computer and mobile electronic devices.

Claims (12)

Diamond particles are dispersed in a metal matrix made of magnesium or a magnesium alloy,
Mg ₂ Si is contained in the metal matrix,
A composite material characterized in that at least some of the diamond particles have a SiC layer on the surface thereof.   2. The composite material according to claim 1, wherein a content of the diamond is 35% by volume or more and 85% by volume or less with respect to the entire composite material.   3. The composite material according to claim 1, wherein a content of the diamond is 50% by volume or more and 80% by volume or less with respect to the entire composite material.   4. The composite material according to claim 1, wherein an average particle diameter of the diamond particles is 10 μm or more and 100 μm or less.   5. The composite material according to claim 1, wherein a thermal conductivity of the composite material at room temperature is 250 W / m · K or more.   A heat radiating member comprising the composite material according to any one of claims 1 to 5.   7. A semiconductor device comprising: the heat dissipating member according to claim 6; and a semiconductor element mounted on the heat dissipating member. A preparation step of preparing a SiC-coated molded body in which the surface of a powder molded body made of diamond is converted to SiC;
Oxidizing the SiC coated molded body, converting at least the surface side portion of the SiC into silicon oxide, and forming an oxidized molded body comprising silicon oxide; and
Infiltrating molten magnesium or a magnesium alloy into the oxidized molded body, and producing Mg ₂ Si by reaction of the silicon oxide and the molten magnesium or magnesium alloy, the magnesium or magnesium alloy and the diamond A composite material manufacturing method comprising: a composite step of combining. In the preparation step,
After forming a powder compact using diamond powder and Si powder, the powder compact is heated to a predetermined holding temperature above the melting point of Si to convert the surface of the powder compact to SiC. 9. The method for producing a composite material according to claim 8, wherein In the preparation step,
After forming a powder compact using diamond powder, the powder compact is heated to a predetermined holding temperature in a gas containing Si to convert the surface of the powder compact to SiC. 9. A method for producing a composite material according to claim 8. The diamond powder is industrial diamond,
11. The method for producing a composite material according to claim 9, wherein a time for heating to the predetermined holding temperature is 10 minutes or less. In the oxidation step,
12. The method for producing a composite material according to claim 8, wherein the oxidized molded body is formed by heating the SiC-coated molded body to a predetermined holding temperature in the atmosphere.