JPH0239117B2 - TASOMAKUKONETSUDENDOSEIZETSUENKIBAN - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a multilayer film high thermal conductivity insulating substrate used as a high thermal conductivity substrate for IC. [Prior art and problems to be solved by the invention] Diamond is an electrical insulator with high thermal conductivity and good insulation properties, so it is used in high-power semiconductor devices, microwave oscillation devices, and super LSIs. The use of diamond as a heat dissipation plate is progressing. However, when actually manufacturing a diamond thin film, generally when this thin film is formed by vapor phase synthesis, amorphous carbon and graphite other than diamond are also precipitated, which poses the problem of interfering with the subsequent formation of diamond. be. In addition, the thin film formed by this has a polycrystalline structure, and a graphite layer is formed at the grain boundaries, so the produced diamond thin film has a problem of extremely poor insulation properties, especially dielectric breakdown. There is. Problems with conventional diamond and/or diamond-like carbon thin films formed by various vapor phase growth methods will be described below. (1) The tungsten heater that heats the substrate on which film formation is performed using the hot filament CVD method is approximately
Since it is heated to about 2000°C, a large amount of tungsten evaporates, causing the tungsten heater to wear out in a short period of time, making it easier to cut.
In addition, temperature variations tend to occur due to changes in the tungsten heater over time, and graphite-like portions are present, making it difficult to form only diamond, especially when producing a large-area thin film. (2) Film formation by ion beam sputtering method or ion plating method In the thin film obtained by this method, amorphous carbon and gutefite other than the aforementioned diamond are precipitated in the thin film, and the electrical resistivity of the thin film becomes small, making it insulating. There are problems such as insufficient sexuality. (3) Film formation by microwave CVD method In this case, it is necessary to add hydrogen gas to generate hydrogen radicals to remove amorphous carbon and graphite generated in the thin film, as described below. Then, methane gas as a raw material gas is diluted with hydrogen gas to reduce the methane gas concentration to 1%.
There is a problem in that the film forming rate is limited due to the need to: Furthermore, when the film forming area is increased, there is a problem that the concentration of hydrogen radicals becomes non-uniform and graphite is formed, as will be described later. When producing a thin film of diamond and/or diamond-like carbon by the method described above, it is necessary to etch amorphous carbon or graphite formed in the thin film using hydrogen radicals or the like. However, in practice, for example, when forming a thin film of diamond and/or diamond-like carbon on a silicon substrate, the concentration of hydrogen radicals etc. tends to be unevenly distributed along the substrate surface. Sections of graphite are formed, thereby reducing the insulation properties. The film obtained by any of the above methods has a polycrystalline structure, and the formation of graphite portions at the grain boundaries in the film is unavoidable, and sufficient insulation cannot be obtained, making it impossible to use the film as a highly thermally conductive insulating substrate. If a film with a larger area is manufactured, it is currently impossible to use it as an insulating film. The present invention was made in view of the above-mentioned problems, and by forming a multi-layered layer of diamond and/or diamond-like carbon and a thin silicon carbide layer, it has excellent insulation properties and thermal conductivity even over a large area. The purpose of the present invention is to provide a multilayer film high thermal conductivity insulating substrate with a large thickness. [Means for Solving the Problems] The multilayer high thermal conductivity insulating substrate of the present invention is a multilayer film in which layers of diamond and/or diamond-like carbon and layers of silicon carbide are alternately laminated on a thermally conductive substrate. was formed. In the vapor phase growth method used for film formation in the present invention, the substrate on which the film is formed is one important factor. Of course, it is possible to form a film of diamond and/or diamond-like carbon on a diamond substrate, but it is also possible to form a film of diamond and/or diamond-like carbon on a substrate such as silicon carbide, tungsten, etc., on which such carbides are likely to be formed. In this case, as described above, if amorphous carbon or graphite precipitates, diamond and/or diamond-like carbon will not be formed thereon. Therefore, it is difficult to form a thick and uniform diamond and/or diamond-like carbon film. Therefore, in the present invention, a very thin layer of diamond and/or diamond-like carbon is formed, and a very thin layer of insulating silicon carbide is formed on top of that, and these layers are alternately formed in multiple layers. I did it like that. This layer of silicon carbide not only acts as an insulating layer, but also facilitates the formation of a layer of diamond and/or diamond-like carbon thereon. This is because the SP ³ bonds of silicon carbide are preserved, so that a graphite layer having SP ² bonds is no longer deposited on that layer. In the general diamond vapor phase growth method, there is a problem that once graphite is formed, graphite is formed on the layer, but with this multilayer film, a graphite layer is partially formed on the scale. However, since a silicon carbide layer exists above that layer, no graphite layer is formed on that layer.
Furthermore, by forming a multilayer film, there are no clear grain boundaries in the film, the dielectric breakdown voltage increases, and thermal conductivity does not decrease due to grain boundaries. Therefore, even if the film area is increased, a highly thermally conductive insulating film with excellent insulation properties can be obtained. In terms of thermal conductivity, silicon carbide has high thermal conductivity and is thin, so it has a thermal conductivity comparable to that of diamond. [Examples] Next, the present invention will be explained based on specific examples. The multilayer film high thermal conductivity insulating substrate according to the present invention is the first
It has a structure as shown in the figure. In FIG. 1, 1 is a substrate made of silicon, aluminum, silicon carbide, tungsten, aluminum alloy, copper alloy, etc.
There is no particular limitation as long as its thermal conductivity is 50 W/m·k or more, but silicon, aluminum, silicon carbide, and copper are suitable. A layer 2 of diamond and/or diamond-like carbon is formed on a substrate 1, and a layer 3 of silicon carbide is formed thereon. Further, on the silicon carbide layer 3, the layers 2 and 3 are sequentially and alternately laminated to form a multilayer film 4, and the substrate (1) and the multilayer film 4 form a multilayer film highly thermally conductive insulating substrate. 5 is formed. The thickness of the layer 2 of diamond and/or diamond-like carbon and the layer 3 of silicon carbide varies considerably depending on the film forming conditions, but the thickness of the layer 2 of diamond and/or diamond-like carbon is 10 Å to 2000 Å.
The thickness of silicon carbide layer 3 is 10 Å.
~1000 Å, preferably 10 Å to 300 Å.
Under film-forming conditions where graphite is easily precipitated, the diamond and/or diamond-like carbon layer 2 should be thinner, and under conditions where graphite is less likely to be precipitated, the diamond and/or diamond-like carbon layer 2 should be thicker. Good too. It is preferable that the thickness of the silicon carbide layer 3 be as thin as possible, but if it is less than 10 Å, it will lose its effectiveness as a silicon carbide layer, so it needs to be at least 10 Å. In the case of microcrystalline silicon carbide or amorphous silicon carbide, silicon carbide Si _1-x C _x can be used with X = 0 to 0.99, but the average of the layer is preferably X = 0.1 to 0.8. More preferably, X=0.4 to 0.6. The reason why silicon carbide, diamond, and diamond-like carbon are used as components of the multilayer film 4 is that each has a very high thermal conductivity. Further, the thickness of the multilayer film 4 varies depending on the insulation properties required depending on the application, but is generally 1000 Å to 20 μm. It is preferable that the thermal conductivity of the multilayer film 4 is higher than that of the substrate 1, but since the thickness of the multilayer film 4 is thin, even if the thermal conductivity of the multilayer film 4 is slightly smaller than the thermal conductivity of the substrate 1, the multilayer film 4 can be used. It is sufficient that the thermal conductivity of the film high thermal conductivity insulating substrate 5 is 45 W/m·k or more. Next, a method for forming the diamond and/or diamond-like carbon layer 2 and the silicon carbide layer 3, which are the constituent elements of the multilayer film 4, will be described. FIG. 2 shows an apparatus for manufacturing the multilayer film 4 by the plasma CVD method. This device is capable of mixed discharge of DC discharge and high-frequency discharge, and has a magnetic field in a direction perpendicular to the electric field. In FIG. 2, 21 is a reaction chamber, into which raw material gas is introduced. In the reaction chamber 21, an electrode 22 and an electrode 23 are provided in parallel and facing each other.
The substrate 1 is fixed by contacting with. A substrate heater 24 is provided around the reaction chamber 21 to heat the substrate 1 from the outside. A high frequency voltage is supplied by a high frequency power supply 25 via a matching circuit 26, and a DC voltage is further supplied by a DC power supply 27 via a chiyoke coil 28. Further, magnetic fields are provided in a direction perpendicular to the electric field (direction B shown in FIG. 2) and in a direction perpendicular to the electric field (direction perpendicular to the plane of the paper in FIG. 2). A multilayer film 4 is formed on the lower surface of the substrate 1 in FIG. 2 by performing a mixed discharge of DC discharge and high frequency discharge. The general conditions for forming a layer of diamond and/or diamond-like carbon are that the flow rate of H ₂ gas, which is a raw material gas, is 100 to 500 SCCM, and similarly, the flow rate of CH ₄ gas is 10 to 20 SCCM. Also, the high frequency power is 0.2
~2W/ ^cm2 , and the DC voltage is -200V to -1kV. The magnetic field strength is 200 Gauss to 800 Gauss. The general conditions for forming a silicon carbide layer are that the flow rate of _H2 gas, which is the raw material gas, is 100~
500SCCM, and the flow rate of _CH4 gas is 0.1~
20SCCM, and the flow rate of _SiH4 gas is 0.1 ~
It is 50SCCM. Here the flow rate of _SiH4 gas is _CH4
Slightly more than the gas flow rate. In addition, the high frequency power is 0.1 to 1W/cm ² and the DC voltage is -300V to 1.5kV.
It is. The magnetic field strength is 200 Gauss to 800 Gauss. In this example, a diamond and/diamond-like carbon layer 2 of 60 Å was formed by discharging for 60 seconds under the following conditions. Conditions for forming the layer _{2 of} diamond and/ ^or diamond-like carbon After the formation, the discharge was stopped once, and the discharge was continued for 15 seconds under the following conditions to form a silicon carbide layer 3 with a thickness of 20 Å. Conditions for forming silicon carbide layer 3 H ₂ gas flow rate 200 SCCM CH ₄ gas flow rate 1 SCCM SiH ₄ gas flow rate 2 SCCM High frequency power 0.3 W/cm ² DC voltage -400 V Magnetic field strength 700 Gauss Then, the above two discharge operations were repeated sequentially to form the first A multilayer film of sample No. 3 in the table was produced.
The other samples in Table 1 are multilayer films prepared under the same conditions as above except for the discharge time, with only the discharge time being changed, and Table 1 shows the configurations of these samples.

[Table] Furthermore, Table 2 shows the results of various characteristics investigated for the multilayer film sample according to the present example shown in Table 1.

[Table] Figure 3 shows samples No. 1, No. 2, and No. of Table 1.
15 layers, 77 layers, and 125 layers of diamond and/or diamond-like carbon, respectively, under the same conditions as in 3.
15 layers each and 77 layers of silicon carbide
The results of examining the dielectric breakdown voltages of multilayer films A, B, and C each formed with 125 layers are shown. Here, the thickness of the multilayer films A, B, and C is approximately 1 μm. In addition, the film forming equipment is not only the one-chamber plasma CVD equipment shown in Fig. 2, but also an equipment that forms films of diamond and/or diamond carbon and silicon carbide in separate chambers, which means that the substrate can be moved. Good too. The dielectric breakdown voltage was measured by depositing an Al electrode with a diameter of 4 cm (area: 13 cm ² ) on each sample and applying a voltage thereto. As is clear from FIG. 3, each of the multilayer films A, B, and C has sufficient insulating properties even with an area of 13 cm ² . Also shown in FIG. 3 is the dielectric breakdown voltage measured for a diamond and/or diamond-like carbon film D having a film thickness of 1 μm produced by a conventional method. Multilayering the film in this way increases the dielectric breakdown voltage. This is because the dielectric breakdown voltage is determined by the part of the film with the lowest dielectric strength, and in films made using conventional methods, there is a graphitized part, albeit a very small one, which lowers the dielectric strength of the film. . [Effects of the Invention] The multilayer film high thermal conductivity insulating substrate according to the present invention is obtained by forming a multilayer film by alternately laminating layers of diamond and/or diamond-like carbon and layers of silicon carbide on a thermally conductive substrate. Even if the film area is increased, the film can have high insulating properties and high thermal conductivity, making it particularly suitable as an IC substrate.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the structure of a multilayer film highly thermally conductive insulating substrate according to the present invention, FIG. Figure 3 shows the dielectric breakdown voltage between multilayer film samples A, B, and C made corresponding to samples No. 1, No. 2, and No. 3 in Table 1, and a film made by the conventional method. It is a figure showing the measured result. (Main symbols in the drawings) 1: Substrate, 2: Layer of diamond and/or diamond-like carbon,
3: Silicon carbide layer, 4: Multilayer film, 5:
Multilayer film high thermal conductivity insulating substrate.

Claims (1)

[Claims] 1. A multilayer highly thermally conductive insulating substrate in which a multilayer film is formed by alternately laminating diamond and/or diamond-like carbon layers and silicon carbide layers on a thermally conductive substrate. 2. The multilayer highly thermally conductive insulating substrate according to claim 1, wherein the diamond and/or diamond-like carbon layer has a thickness of 10 Å to 2000 Å. 3 The thickness of the silicon carbide layer is 10 Å ~
1000 Å, and the silicon carbide layer is 3
A multilayer film high thermal conductivity insulating substrate according to claim 1, which is formed of more than one layer. 4 The thermal conductivity of the thermally conductive substrate is 50W/m・
The multilayer high thermal conductivity insulating substrate according to claim 1, wherein the multilayer high thermal conductivity insulating substrate has a thermal conductivity of 45 W/m·k or more. 5. The multilayer high thermal conductivity insulating substrate according to claim 1, wherein the multilayer high thermal conductivity insulating substrate has a surface Vickers hardness of 1500 or more. 6. The multilayer film high thermal conductivity insulating substrate according to claim 1, wherein the multilayer film has an electrical resistivity of 10 ¹² Ωcm or more and a dielectric breakdown voltage of 100 V/μm or more. 7. The multilayer film high thermal conductivity insulating substrate according to claim 1, wherein the silicon carbide is single crystal, polycrystal, microcrystal, or amorphous. 8 Plasma caused by a mixed discharge of direct current and high frequency in which the multilayer film has a magnetic field perpendicular to the electric field.
A multilayer film high thermal conductivity insulating substrate according to claim 1 obtained by a CVD method.