JP2012151392A - Heat radiation material and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat radiation material which overcomes disadvantages of inorganic based materials such as ceramic substrates and diamond substrates, which have high hardness and low processability, and a disadvantage of carbonaceous materials such as graphite films and carbon nano-tubes, which have low heat radiation.SOLUTION: Mask particles 201a are deposited on a surface of a graphite substrate. Further, alongside the deposition, the surface of the graphite substrate is processed to form a nano-meter order irregular structure (step 101).

Description

  The present invention relates to a heat dissipation material and a method for manufacturing the same.

  The problem of cooling power converters and inverters used in semiconductor devices, solar cells, electric vehicles and the like mounted on electronic and electrical equipment such as computers, for example, has attracted attention.

  One method for cooling the heat generating component described above is to attach a fan to the device casing on which the heat generating component is mounted, thereby cooling the device casing. In another cooling method, a heat conducting medium such as a heat pipe, a heat sink, a fin, a fan, or the like is attached to the heat generating component, and heat from the heat generating component is transmitted to the outside by the heat conducting medium. At this time, a good heat conductive material such as copper or aluminum is brought into contact with the heat generating component, and is transmitted to the outside through the heat conductive material.

  However, in recent years, the amount of heat generated by the heat-generating component tends to increase as the power of semiconductor elements and the like is increased and the mounting space is reduced. In particular, when the device casing is downsized, the space for mounting the above-described heat conducting medium is reduced. As a result, sufficient heat convection cannot be obtained, the heat generating component becomes high temperature, and the performance of the element is lowered.

  Various heat dissipating materials have been proposed in order to efficiently cool the above-described heat generating components.

  Conventional heat dissipation materials include ceramic substrates made of SiC, AlN, etc. (Reference: Patent Document 1), diamond substrates with high thermal conductivity of 1000-2000 W / m · K (Reference: Patent Document 2), flexible graphite film (Reference: Patent Document 3) and carbon nanotubes (Reference: Patent Document 4) such as good heat dissipation, heat resistance, chemical resistance, and low cost.

Japanese Patent Laid-Open No. 2-7445 JP 2008-222468 A JP 2009-107904 A JP 2004-10978 A Japanese Patent Application No. 2009-195354

  However, the ceramic substrate, which is the first conventional heat dissipation material, is basically a ceramic powder having a particle size of 10-100 μm sintered using an appropriate binder. There is a problem that voids are generated between the layers, resulting in poor adhesion, resulting in poor heat dissipation. In addition, the thermal expansion coefficient of the ceramic substrate is very small. Therefore, there is a problem that peeling frequently occurs due to the difference in thermal expansion coefficient between the heat-generating component and the ceramic substrate. Furthermore, since SiC or AlN of the ceramic substrate has a high hardness and is a difficult-to-process material, it takes time for cutting and polishing, resulting in a high manufacturing cost.

  In addition, the diamond substrate, which is the second conventional heat dissipation material, has a very small thermal expansion coefficient of the diamond substrate, similar to the ceramic substrate. Therefore, peeling frequently occurs due to the difference in the thermal expansion coefficient between the heat generating component and the diamond substrate. There is a problem that occurs. Further, since the diamond substrate has a high hardness and is a difficult-to-process material, it takes time for cutting and polishing, and as a result, there is a problem that the manufacturing cost is high. Furthermore, since the diamond substrate is a very expensive material unlike the ceramic substrate, the manufacturing cost is remarkably increased.

  Furthermore, since the graphite film which is the third conventional heat dissipation material is a carbon-based material, there is a problem that heat dissipation is inferior compared to ceramic substrates and diamond substrates which are inorganic materials.

  Furthermore, since CNT, which is the fourth conventional heat dissipation material, is also a carbon-based material, there is a problem that heat dissipation is inferior to ceramic substrates and diamond substrates, which are inorganic materials. Another problem is that the adhesion between the heat-generating component and the CNT is low due to the vulnerability and hydrophobicity of the CNT. In this case, it is common to coat CNTs on a metal substrate such as copper with a dispersion, etc., but the adhesion between the metal substrate and the CNTs is poor, and the CNTs peel off immediately or do not peel off. In both cases, since the metal substrate and the CNT are not bonded at the atomic level, there arises a problem that heat resistance inevitably occurs and heat conduction loss occurs. In addition, if the paste is inserted between the metal substrate and the CNT, the CNT can be prevented from peeling off, but the paste itself causes a thermal resistance, resulting in a loss of heat conduction. Furthermore, there is a problem that explosive combustion occurs when CNT is heated to 400 ° C. or higher in the air.

  The applicant of the present application has already proposed a heat dissipation material made of a carbon-based substrate having a nanometer-order fine concavo-convex structure formed on the surface by a plasma etching method or the like (see Patent Document 5). However, it is not possible to form a fine concavo-convex structure with a high aspect ratio only by a plasma etching method or the like. Therefore, the reflectance in the visible region and the far infrared region cannot be sufficiently reduced, and as a result, the heat dissipation efficiency cannot be increased. .

  Further, a photolithography / etching method is conceivable as a method for forming a fine concavo-convex structure with a high aspect ratio on the order of nanometers on the surface of a carbon-based substrate. That is, a photoresist layer coating process on a carbon substrate, a pattern exposure process of the photoresist layer through a mask using light, electron beam, etc., a removal process of unnecessary portions of the photoresist layer by washing, and a surface of the carbon substrate. A step of forming a fine concavo-convex structure with a high aspect ratio and a step of removing the remaining photoresist layer are performed by dry etching or wet etching. However, the number of processes is complicated and the manufacturing cost is high because precise control is required in each process. Further, the manufacturing cost is high because a mask is required in the pattern exposure process, and the surface area of the fine concavo-convex structure is high. Therefore, the reflectance in the visible region and the far infrared region cannot be sufficiently reduced, and as a result, the heat dissipation efficiency cannot be increased.

  Accordingly, an object of the present invention is to provide a heat dissipating material comprising a carbon-based substrate in which a fine concavo-convex structure with a high aspect ratio of nanometer order is randomly and widely formed on a surface without using a photolithography / etching method and a method for manufacturing the same. Is to provide.

  In order to solve the above-described problems, a heat dissipation material according to the present invention includes a carbon-based substrate in which a concavo-convex structure having a nanometer order is formed on a surface on which mask particles are deposited. Thereby, the concavo-convex structure has a high aspect ratio, and the surface area is increased. As a result, the reflectance of light having a wavelength in the region including visible light is lowered, and the reflectance of light having a wavelength in the far infrared region is also lowered.

  The method for manufacturing a heat dissipation material according to the present invention includes a mask particle deposition step of depositing mask particles on the surface of the carbon-based substrate, and processes the surface of the carbon-based substrate on which the mask particles are deposited into an uneven structure on the order of nanometers. It has a concavo-convex structure processing step. The concavo-convex structure processing step is performed in parallel with or after the mask particle deposition step.

  According to the present invention, the surface area is increased by the concavo-convex structure having a high aspect ratio. Therefore, the reflectivity in the region including the visible light and the far infrared region is decreased, and the heat dissipation by radiation can be increased.

It is a flowchart for demonstrating 1st Embodiment of the manufacturing method of the uneven structure of the nanometer order of the graphite board | substrate of the heat dissipation material which concerns on this invention. It is a figure which shows the sputtering / plasma etching apparatus used for the flowchart of FIG. FIG. 2 is a cross-sectional view for supplementarily explaining the flowchart of FIG. 1. It is a scanning electron microscope (SEM) photograph of the surface of the graphite substrate after the sputtering / plasma etching of FIG. It is a graph which shows the reflectance of the surface of the graphite substrate after the sputtering / plasma etching of FIG. It is a scanning electron microscope (SEM) photograph of the surface of the graphite substrate after the plasma etching when not performing the sputtering of FIG. 1 as a comparative example (without mask particles). It is a flowchart which shows the example of a change of the flowchart of FIG. It is a flowchart for demonstrating 2nd Embodiment of the manufacturing method of the uneven structure of the nanometer order of the graphite board | substrate of the heat dissipation material which concerns on this invention. It is a figure which shows the sputtering device used for the flowchart of FIG. It is a figure which shows the plasma etching apparatus used for the flowchart of FIG. FIG. 9 is a cross-sectional view for supplementarily explaining the flowchart of FIG. 8. It is a flowchart which shows the example of a change of the flowchart of FIG.

  In general, in a heat dissipation material, when the reflectance R decreases, the emissivity I increases, and conversely, when the reflectance R increases, the emissivity I decreases. In this case, the emissivity is used as an index indicating the light radiation, that is, the light emission capability. When the light transmittance is almost zero, the emissivity is expressed by emissivity I≈1-R (reflectance). Therefore, ideally, it is understood that the heat dissipation efficiency is increased when the heat dissipation material has a reflectance R as close to 0 as possible in the region including visible light and the far-infrared region, for example.

FIG. 1 is a flowchart for explaining a first embodiment of a method for producing a concavo-convex structure of a graphite substrate as a heat dissipation material according to the present invention. In step 101, the graphite substrate is put into the sputtering / plasma etching apparatus shown in FIG. 2, and the graphite substrate is subjected to sputtering / plasma etching by a sputtering / plasma etching method using Ar / O ₂ gas.

Referring to the sputtering / plasma etching apparatus of FIG. 2, in the vacuum chamber 200, the graphite substrate 201 is in close contact with a silicon substrate 202 as a mask material target larger than the graphite substrate 201, and the silicon substrate 202 is in close contact with the substrate holder 203. ing. The substrate holder 203 is connected to the high frequency power source 204 and functions as a cathode electrode. Further, the vacuum chamber 200 is provided with a gas inlet 205 for introducing Ar / O ₂ gas, and the reaction gas density can be set to an appropriate value by introducing a necessary flow rate of the reaction gas into the vacuum chamber 200. it can. Further, the vacuum chamber 200 is provided with a gas exhaust port 206 connected to a vacuum pump (not shown), so that the inside of the vacuum chamber 200 can be maintained at an appropriate degree of vacuum. The wall of the vacuum chamber 200 and the gas inlet 205 are grounded and function as an anode electrode.

In FIG. 2, Ar / O ₂ gas from the gas inlet 205 flows through the entire silicon substrate 202 including the graphite substrate 201 as indicated by arrows.

The conditions of the sputtering / plasma etching apparatus of FIG. 2 are as follows, for example.
RF power: 500W
Pressure: 6.65Pa (50mTorr)
Ar flow rate: 50sccm
O ₂ flow rate: 100sccm
Etching time: 30 minutes.

In the sputtering / plasma etching apparatus of FIG. 2, the silicon substrate 202 is sputtered by Ar ions of Ar / O ₂ gas, and silicon mask particles are deposited on the graphite substrate 201 as indicated by arrows. In parallel with this, the graphite substrate 201 is plasma-etched by Ar / O ₂ gas. Specifically, as shown in FIG. 3A, the mask particles 202a are randomly and widely deposited on the graphite substrate 201. In parallel with this, the graphite substrate 201 is plasma-etched by Ar / O ₂ gas. Finally, as shown in FIG. 3B, the surface of the graphite substrate 201 becomes a high-aspect-ratio nanometer-order uneven structure 201a by the action of the mask particles 202a as an etching stopper. FIG. 4 shows an SEM photograph of the fine concavo-convex structure having a high aspect ratio shown in FIG. In FIG. 4, for example, it is recognized that the aspect ratio is as large as about 5 μm / 0.25 μm = 20.

  The graphite substrate 201 described above can be a metal-impregnated dense graphite substrate. Thereby, since the toughness of the dense graphite substrate is further increased, the workability as a heat dissipation material and the adhesion with the heat-generating component are improved, and the gap between the heat-generating component and the heat-dissipating material is eliminated.

  Although the graphite substrate is used, a carbon-based substrate other than the graphite substrate, for example, a diamond substrate or a glassy carbon substrate may be used.

Further, the silicon substrate 202 as a mask material target may be a substrate made of SiO ₂ , Al, Al ₂ O ₃ , Cr or Ni. Furthermore, the mask material target also acts as a cover material for preventing corrosion of the substrate holder (cathode electrode) 203, and the substrate as the mask material may also serve as the substrate holder 203.

The plasma etching method in step 101 of FIG. 1 may be any of electron cyclotron resonance (ECR) etching method, reactive ion etching (RIE) method, atmospheric pressure plasma etching method, etc. The processing gas is Ar / O ₂ CO ₂ gas other than the gas, CF ₄ gas, may be any of such SF ₄ gas.

  As shown by the solid line in FIG. 5, the average reflectance over the entire wavelength range of 0.4 to 2.4 μm in the region including visible light is as low as 0.5% or less. Therefore, the absorption of the region including visible light is the highest. In addition, the average reflectance in the far-infrared region is as low as about the same. In this case, the measurement was performed using a radiation thermometer (KEYENCE FT-H20, trade name). When the surface temperature was 150 ° C, the emissivity of the graphite substrate was as high as 0.99. As a result, the plasma-etched graphite substrate can be used as a heat dissipation material as it is.

  When plasma etching is performed without mask particles in step 101 of FIG. 1 (comparative example), as shown in FIG. 6, the aspect ratio of the concavo-convex structure on the surface of the graphite substrate is reduced, the surface area is reduced, and the reflectance is increased. Remains as a high part. As a result, as shown by the dotted line in FIG. 5, the reflectance is as high as 1.0 to 2.0%. In FIG. 6, for example, it is recognized that the aspect ratio is as small as about 1 μm / 0.25 μm = 4.

FIG. 7 shows a modification of the flow of FIG. 1, and prior to the sputtering / plasma etching step 101 of FIG. 1, mechanical surface polishing such as sandblasting and / or a high power laser such as a CO ₂ laser, YAG laser, excimer laser, etc. Pretreatment by surface polishing by irradiation is performed. As a result, a concavo-convex structure having an irregular period such as a micrometer order or a submicrometer order is formed. Accordingly, the surface area of the graphite substrate is increased and the heat dissipation efficiency is increased.

In addition, in the irregular period micron (submicron) unevenness processing step 701 in FIG. 7, a large number of irregular micrometer order or submicrometer order dents are formed on the surface of the graphite substrate to increase the surface area. May be. For example, a resist layer is applied, and then a pattern of the resist layer is formed by photolithography using a photomask having an irregular periodic pattern, and the graphite substrate is formed with H ₂ gas and O ₂ using the resist layer pattern. Plasma etching using gas, for example, RIE is performed, and then the resist layer pattern is removed. Further, the surface area can be increased by forming an irregular periodic micrometer order or submicrometer order sword mountain type concavo-convex structure by a cutting method using a mechanical ruling engine or the like. This sword mountain-type uneven structure can also be formed by forming a reverse sword mountain mold by etching and pouring a liquid graphite material, such as carbon black, into it.

  Here, the irregular structure of micrometer order or submicrometer order with a regular period causes a two-dimensional photonic crystal effect and increases the reflectivity in the far infrared region. Absent.

  FIG. 8 is a flowchart for explaining a second embodiment of the method for manufacturing the concavo-convex structure of the graphite substrate of the heat dissipation material according to the present invention.

  First, in step 801, the graphite substrate is put into the sputtering apparatus of FIG. 9, and sputtering using Ar gas is performed on the graphite substrate.

  Referring to the sputtering apparatus of FIG. 9, the graphite substrate 901 is in close contact with the substrate rotation holder 902 in the vacuum chamber 900. A silicon target 903 is provided opposite to the substrate rotation holder 902, and this target 903 is connected to a high-frequency power source 904 and functions as an anode electrode. A gas inlet 905 for introducing Ar gas is provided above the vacuum chamber 900, and a gas outlet 906 connected to a vacuum pump (not shown) is provided below the vacuum chamber 900. Yes. The wall of the vacuum chamber 900 and the gas inlet 905 are grounded and function as a cathode electrode.

  In the sputtering apparatus of FIG. 9, a silicon target 903 is sputtered by Ar gas, and silicon mask particles 902a are deposited on the graphite substrate 901 as indicated by arrows. Specifically, as shown in FIG. 11A, the mask particles 902a are randomly and extensively deposited on the graphite substrate 901.

Next, in step 802, the graphite substrate 901 on which the mask particles 902a are deposited is put into the plasma etching apparatus of FIG. 10, and the graphite substrate 901 is subjected to plasma etching using Ar / O ₂ gas.

The plasma etching apparatus of FIG. 10 will be described. In the vacuum chamber 1000, the graphite substrate 901 on which the mask particles 902 a are deposited is in close contact with the substrate holder 1003. The substrate holder 1003 is connected to the high frequency power supply 1004 and functions as a cathode electrode. A gas inlet 1005 for introducing Ar / O ₂ gas is provided on the upper side of the vacuum chamber 1000, and a gas outlet 1006 connected to a vacuum pump (not shown) is provided on the lower side of the vacuum chamber 1000. Is provided. The wall of the vacuum chamber 1000 and the gas inlet 1005 are grounded and function as an anode electrode.

The conditions of the plasma etching apparatus in FIG. 10 are, for example, as follows.
RF power: 500W
Pressure: 6.65Pa (50mTorr)
Ar flow rate: 50sccm
O ₂ flow rate: 100sccm
Etching time: 30 minutes.

In the plasma etching apparatus of FIG. 10, the silicon substrate 902 is plasma-etched by Ar / O ₂ etching gas. Specifically, as shown in FIG. 11B, the surface of the graphite substrate 901 becomes a high-aspect-ratio nanometer-order concavo-convex structure 901a by the action of the mask particles 902a as an etching stopper.

Note that, as in the first embodiment, the above-described graphite substrate 901 can be a metal-impregnated dense graphite substrate. Thereby, since the toughness of the dense graphite substrate is further increased, the workability as a heat dissipation material and the adhesion with the heat-generating component are improved, and the gap between the heat-generating component and the heat-dissipating material is eliminated. Although the graphite substrate is used, a carbon-based substrate other than the graphite substrate, for example, a diamond substrate or a glassy carbon substrate may be used. Further, the silicon target 903 as the mask material may be a substrate made of SiO ₂ , Al, Al ₂ O ₃ , Cr or Ni.

Note that the plasma etching method in step 802 of FIG. 8 may be any of an electron cyclotron resonance (ECR) etching method, a reactive ion etching (RIE) method, an atmospheric pressure plasma etching method, or the like, and the processing gas is Ar. / O ₂ CO ₂ gas other than the gas, CF ₄ gas, may be any of such SF ₄ gas.

FIG. 12 shows a modified example of the flow of FIG. 8, and similarly to the first embodiment, before the sputtering step 801 of FIG. 8, mechanical surface polishing such as sandblasting and / or CO ₂ laser, YAG laser, Pretreatment is performed by surface polishing by irradiation with high power laser such as excimer laser. As a result, a concavo-convex structure having an irregular period such as a micrometer order or a submicrometer order is formed. Accordingly, the surface area of the graphite substrate is increased and the heat dissipation efficiency is increased.

  The nanometer order in the above-described embodiment indicates a range of about 10 to 500 nm, the submicrometer order indicates a range of about 0.2 to 10 μm, and the micrometer order indicates a range of about 10 to 500 μm. .

101: Sputtering / plasma etching step 200, 900: Vacuum chamber 201, 901: Graphite substrate 202: Silicon substrate 202a, 902a: Mask particle 203: Substrate holder 204, 904: High frequency power source 205, 905: Gas inlet 206, 906: Gas outlet 701: Irregular periodic micron (submicron) unevenness processing step 801: Sputtering step 802: Plasma etching step 903: Silicon target 1000: Vacuum chamber 1003: Substrate holder 1004: High frequency power supply 1005: Gas inlet 1006: Gas outlet

Claims (12)

  A heat dissipating material comprising a carbon-based substrate having a nanometer-order first concavo-convex structure formed on a surface on which mask particles are deposited.   The heat dissipation material according to claim 1, wherein a second uneven structure having an irregular period larger than the size of the first uneven structure is formed on the carbon-based substrate.   The heat dissipating material according to claim 2, wherein the size of the second concavo-convex structure is not less than a submicrometer order.   The heat dissipation material according to claim 1, wherein the carbon-based substrate is a metal-impregnated graphite substrate. A mask particle deposition step of depositing mask particles on the surface of the carbon-based substrate;
And a first concavo-convex structure processing step of processing the surface of the carbon-based substrate on which the mask particles are deposited into a first concavo-convex structure having a nanometer order.   The method for manufacturing a heat dissipation material according to claim 5, wherein the mask particle deposition step and the first concavo-convex structure processing step are performed in parallel.   The method for manufacturing a heat dissipation material according to claim 5, wherein the first uneven structure processing step is performed after the mask particle deposition step.   The method for manufacturing a heat dissipation material according to claim 5, wherein the mask particle deposition step is a sputtering step.   The method for manufacturing a heat dissipation material according to claim 5, wherein the first uneven structure processing step is a plasma etching step.   Furthermore, before the mask particle deposition step and the first uneven structure processing step, a second uneven structure having an irregular period larger than the size of the first uneven structure is processed on the surface of the carbon-based substrate. The manufacturing method of the thermal radiation material of Claim 6 which comprises a process.   The method for manufacturing a heat dissipation material according to claim 10, wherein the size of the second concavo-convex structure is not less than a submicrometer order. The method for manufacturing a heat dissipation material according to claim 5, wherein the carbon-based substrate is a metal-impregnated graphite substrate.