JPS61251158A - Radiating substrate - Google Patents

Abstract

PURPOSE:To enable a diamond substrate with an excellent heat conductivity and a low cost to be obtained by forming a diamond thin film on a substrate by way of a vapor growth method and mixing an impurity for improving an electric conductivity in the thin film. CONSTITUTION:A diamond thin film mixed with an impurity B for improving an electric conductivity is formed on an Si substrate or the like by flowing CH4, B2H6 and H2 thereover at flow rates 1, 0.2 and 100cm<3>/min, respectively, and processing the substrate for 300hr in a vacuum 30Torr by way of a plasma CVD method. Then, the Si substrate is dipped in a solution HF:HNO3 (1:3) to be dissolved.

Description

[Detailed description of the invention] 11↓9μ months! The present invention relates to a heat dissipation board. More specifically, the present invention relates to a diamond heat dissipating substrate that has excellent thermal conductivity and is inexpensive.

Conventional technology Semiconductor devices and devices and equipment that use them have the problem of heat generation in active elements such as semiconductor elements, or passive elements such as resistors and coils.Therefore, it is necessary to operate these elements stably and reliably. In order to achieve this, it is necessary to perform the best thermal design during packaging, which is extremely important in the design and manufacture of semiconductor devices.

Furthermore, in recent years, there has been a trend toward faster operation and higher density of semiconductor devices, and with this, an increase in the amount of heat generated by semiconductor elements has become a major problem. Therefore, it has become necessary to further improve the heat dissipation of substrates for mounting semiconductor devices, that is, to further improve the thermal conductivity of the entire substrate in the thickness direction.

In particular, when mounting various semiconductor devices such as semiconductor lasers that generate a large amount of heat, they generate heat due to their own power consumption, so it is necessary to carefully consider how to dispose of this heat. It featured innovations such as fins and water cooling.

On the other hand, there are cases in which heat radiation is required not only from the entire element, but also from a specific portion of the element.

For example, in semiconductors for lasers, heat generation is significant at the end face where the laser beam is emitted, so much so that the laser output of the device is determined by the heat removal ability in the vicinity.

Al2O3 has traditionally been a common substrate material for ICs and semiconductors, but it cannot be said to be an excellent material from the standpoint of thermal conductivity.Therefore, there is a need to develop materials with higher thermal conductivity, and recently Al2O3 has been used as a substrate material for ICs and semiconductors. , SiC, etc. are attracting attention as suitable for such purposes. Further, substrates using metals such as Cu alloys have also been proposed.

Among the substances known so far, diamond has the best thermal conductivity, and heat dissipation substrates for semiconductor devices using diamond have already been put into practical use in some fields.

However, as is well known, diamond is extremely expensive and difficult to process, so it has not been widely used.

That is, for example, a diamond heat sink normally requires a plate thickness of about 0.2+t+m in order to achieve three-dimensional heat diffusion, but diamond is extremely expensive and cannot be processed into this shape. This is extremely difficult. It is also possible to use artificially synthesized diamonds, but as only fine crystals have been obtained so far, there is a limit to the size of the heat sink.
It can only be used for very limited devices.

Problems to be Solved by the Invention As described above, thermal design is an important problem that must be solved when mounting semiconductor elements and devices. This problem is an important issue that must be solved in parallel with improving the performance of semiconductor devices and devices themselves.In particular, for devices that generate a high amount of heat, such as high-power laser devices, mounting parts such as substrates must be It has such a significant influence that it determines the performance of the device.

However, Al, which has been commonly used as a substrate material,
2O, had insufficient heat dissipation properties (thermal conductivity) as a material for a substrate of an element having a high calorific value. Furthermore,
Diamond, which is known to have the best thermal conductivity of any known material, is not only expensive;
Because it is difficult to process, it has only been put into practical use in some areas, and is far from being made into a film.

Therefore, it is strongly desired to develop a new substrate that can be expected to have high heat dissipation properties in place of Al2O3, and this will make it possible to fully demonstrate the original characteristics of semiconductor elements and devices. Therefore, this is extremely significant in terms of the implementation of these elements and devices, especially in terms of their thermal design.

The purpose of the present invention is also in this point, and has excellent thermal conductivity.
Moreover, the object is to provide an inexpensive diamond heat dissipation substrate.

In view of the current state of the prior art described above, the inventors of the present invention have conducted various studies to develop a board for mounting semiconductor devices, etc. that has high heat dissipation characteristics that have not been seen before. We continued our research with the idea that it would be effective to develop a technology to inexpensively manufacture diamond substrates, which are said to have conductivity.
The invention has been completed.

That is, the heat dissipation substrate of the present invention is obtained by vapor phase synthesis and is characterized in that it is made of diamond containing impurities to improve electrical conductivity.

In the heat dissipation substrate of the present invention, the substrate is mainly composed of diamond, and has a 1100 ppm content to improve electrical conductivity.
Contains impurities in the range of m to 5%. The impurity may include at least one element selected from the group consisting of B5Si, P, As, Sb, etc., with B being the most preferred.

Such a heat dissipation substrate of the present invention can be obtained according to the following method. That is, for example, it is manufactured by forming a diamond thin film on a substrate such as Si using a vapor phase method, mixing impurities, and removing the resulting laminate, such as the Si substrate, using an etching technique.

Here, the well-known CVD method is used as a diamond vapor phase synthesis method.
method, plasma CVD method, ion beam evaporation method, etc. can be used. Furthermore, as a method of mixing impurities, the diamond film is formed by CVD method or plasma CVD method.
When carrying out method D, B 2 H is used together with the raw material gas.
This can be performed simultaneously with film formation by introducing a gaseous impurity source such as - and decomposing it. Further, in the ion beam evaporation method, it is also possible to add an impurity source such as B using an ion beam. Furthermore, it can also be carried out by repeating the steps of forming about 1,000 to 5,000 diamond thin films and then performing ion implantation.

Various etching methods can be used to remove the substrate for forming a film such as Si, and the optimum method can be selected from wet etching and dry etching depending on the type and properties of the substrate material. For example, when using a Si substrate as the substrate, HF:HNO3 (1:
3) It can be removed by wet etching using a mixed solution or the like.

In the heat dissipation board of the present invention, the thickness is 50 μm to 1
l1 [within the range of 11. The lower limit for this thickness is −
This is particularly important; if it is too thin, a three-dimensional path for heat dissipation cannot be secured. On the other hand, although the upper limit is not particularly important, it is uneconomical if it is too thick, and in this sense, a reasonable value is about 1 inch.

Further, according to the vapor phase deposition method as described above, by using a substrate having a considerably large area and depositing diamond thereon, it is possible to obtain a film-like diamond substrate material having a large area. In actual use, such a large-area membrane is cut into a predetermined size and shape.

An important point for a substrate for mounting semiconductor devices, devices, etc. is that it has high heat dissipation properties. This heat dissipation problem is solved by using diamond, which is known to have the best thermal conductivity, as the main component of the heat dissipation substrate according to the present invention.

However, since diamond usually has a high electrical resistance, its workability is insufficient as it is, and it is difficult to obtain a heat dissipation substrate that can be mass-produced at a low cost. Therefore,
This problem was solved by adding impurities that could improve the electrical resistance of diamond. The most suitable impurity is B, and its amount is generally <1100p as described above.
pm to 5% (by weight). Naturally produced diamonds are also known to contain B (II
t, type), its thermal conductivity is similar to that of ordinary diamond (I
It is said to be about 4 times that of Type A). According to studies conducted by the present inventors, it has been found that even in vapor phase synthesized diamond films, films to which B is added have significantly superior thermal conductivity.

The amount of impurities to be added is selected depending on the physical properties of the resulting film, particularly the electrical resistance and thermal conductivity, and needs to be within the above range. If it is less than iooppm, it is not sufficient to lower the electrical resistance of the diamond film, and if it is used in excess of 5%, a different phase will occur in the diamond film, making it difficult to obtain a heat dissipating substrate with the physical properties intended by the present invention. Both are undesirable because they cannot be obtained.

In addition, there is no problem if the amount of graphite mixed in is small, but if it is in a large amount (3% or more), it is inappropriate because the inherent thermal conductivity of diamond will be greatly affected. Further, other impurities pose no problem as long as they do not affect the crystalline form of diamond; for example, Si, P, As, Sb, etc. are preferable examples since they reduce electrical resistance.

Since the heat dissipation substrate of the present invention has improved electrical conductivity by adding impurities such as B, electrical discharge machining can be advantageously used during processing. For this electrical discharge machining, the electrical resistance needs to be 10'Ω·cm or less, and from this point of view, the lower limit of the amount of impurities added needs to be 100 ppm.

In the present invention, a diamond film can be formed on a Si substrate or the like having a fairly large surface area and an arbitrary shape by the method described above, and this is then cut into required dimensions and used as a heat dissipation substrate. In this case, the cutting and polishing of the diamond film can be performed using various conventionally known methods in addition to the above-mentioned electric discharge machining, and it is significantly easier than cutting from a normal diamond crystal. It can be processed at a lower cost.

Thus, the heat dissipation substrate of the present invention can be used for mounting various semiconductor elements and devices, and is particularly useful as a substrate for semiconductor lasers with high heat generation, highly integrated ICs, LSIs, etc.

The heat dissipating substrate of the present invention will be explained in more detail below using examples. However, the scope of the present invention is not limited in any way by the following examples.

Example 1 CH,, B 2 Hs, H
were flowed at a flow rate of L0.2 and 100 cj/min, respectively, and 3
A 250 μm film was formed on the Si substrate by processing under a vacuum degree of 0 Torr for 300 hours, and then HF:HNO3 (
The Si substrate was dissolved by immersing it in a mixed solution of 1:3).

When the crystal structure of the thus obtained B-doped diamond plate was examined by X-ray diffraction, it was found that it has a diamond structure with a lattice constant of 3.572 (the lattice constant of natural diamond is 3.568). It was confirmed that it was close.

The thermal conductivity of this diamond plate was 12 W/cm-, and the electrical resistance was 2 Xl0-2Ω·cffl, making it possible to perform electrical discharge machining.

Example 2 A diamond film having a B concentration as shown in Table 1 below was formed to a thickness of 100 μm using the same method as in Example 1 while varying the concentration of B2H. The thermal conductivity and electrical resistance of the obtained diamond film were measured and the results are shown in Table 1.

Table 1 As is clear from the results in Table 1, the content of B is 1100
It can be seen that within the range of ppm to 51%, a substrate with satisfactory electrical resistance and thermal conductivity was obtained, and the crystal form was also in the diamond state.

Example 3 Known plasma CVD method (plasma is 13.5 MHz
(generated by high frequency), C2Hs, H2
and B 2 Hs gas at a flow rate of 0.5 cc/min, 1
Flow at 00cc/min and 0.003cc/min, 30
Processed for 80 hours under Torr vacuum, 5.000p
A diamond plate with a thickness of 200 μm and containing pm of B was produced. This was cut into a size of 3 mm x 3 mm by electric discharge machining and used as a substrate for a semiconductor laser device.

The semiconductor laser fabricated using the thus obtained substrate of the present invention exhibited a service life of more than 150 hours at an output of 15 mW, but the laser produced as a comparative example using Al2O3 as the substrate had a service life of 5+y! ! The maximum output was 50 hours of use.

Effects of the Invention As described in detail above, according to the present invention, the diamond film is formed by a vapor phase synthesis method and contains impurities such as B for improving electrical conductivity, so that it has excellent thermal conductivity. A heat dissipation board for mounting semiconductor elements and devices can be realized at extremely low cost.

Furthermore, since the diamond substrate of the present invention has low electrical resistance due to the inclusion of impurities, it can be subjected to electric discharge machining, which is extremely advantageous in terms of mass production.

Claims (6)

[Claims] (1) A heat dissipation substrate characterized by being made of diamond obtained by vapor phase synthesis and containing impurities for improving electrical conductivity. (2) The heat dissipation substrate according to claim 1, wherein the impurity is at least one selected from the group consisting of B, Si, P, As, and Sb. (3) The heat dissipation substrate according to claim 2, wherein the content of the impurity is within a range of 100 ppm to 5%. (4) The heat dissipation substrate according to claim 3, wherein the impurity is B. (5) The heat dissipation substrate according to claim 4, wherein the thickness of the diamond film is within the range of 50 μm to 1 mm. (6) The heat dissipation substrate according to any one of claims 1 to 5, wherein the vapor phase synthesis method is CVD, plasma CVD, or ion beam evaporation.