JPH04170392A - Production of high thermal conductivity diamond film - Google Patents

Abstract

PURPOSE:To produce the diamond thin film by depositing diamond single crystal grains on many nucleus generating origins regularly formed on a substrate at regular intervals and growing the grains into film. CONSTITUTION:An Si single crystal substrate 1 having (100) face orientation, for example, is inserted into alcohol in which diamond abrasive grains having 20mum average diameter are dispersed, and ultrasonic vibration is imparted to form minute ruggednesses on the nucleus generating origins on the substrate 1 surface. A resist pattern 2 as a mask having 1mum diameter is then formed on the substrate 1 with 5mum spacing by photolithography, and the substrate is etched by an Ar ion beam of 1000Angstrom . The pattern 2 is removed with acetone, and a diamond single crystal grain 3 is formed on the nucleus generating origin by filament CVD method. Consequently, the diamond single crystal or twin crystal grain is deposited from the part on which the pattern 2 was formed, and the grains are grown and associated to obtain a diamond film.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method for manufacturing a diamond film used as a heat sink for semiconductor devices such as semiconductor laser devices, microwave oscillation devices, and VLSIs.

[Conventional technology]

Diamond has traditionally been known to have the highest thermal conductivity among existing materials, and therefore has high utility value as a highly efficient heat sink. Specifically, thin slices of natural or synthetic diamond are attached to, for example, semiconductor lasers or high-frequency oscillation elements to dissipate the heat generated by the elements themselves. Incidentally, in recent years, an example has been reported in which diamond ffM was produced by vapor phase synthesis and the diamond thin film was applied to a heat sink (Electronic Materials, September 1989 issue, 7).
(pages 4 to 79). In this case, the thermal conductivity of the diamond thin film produced by the vapor phase synthesis is largely dependent on the production conditions and is at most 1.
000 W/m-. Note that the thermal conductivity of diamond is that of natural diamond H.
200 OW/m- or more for type a (type with few impurities) and 100 OW/m for type Ia (type containing nitrogen as an impurity)
It is about OW/m-.

[X that the invention is trying to solve! Title: However,
Although diamond does not contain impurities such as nitrogen, II.
Its thermal conductivity is only about half that of A-type diamond. This is thought to be because the diamond thin film obtained by vapor phase synthesis is a polycrystalline thin film and contains many disordered grain boundaries. FIG. 3 shows the process of producing such a conventional diamond film. Since the nucleation base points 4a are disordered as shown in FIG. 3(a), as shown in FIG. 3(b), The film obtained by growing the single crystal grains 5 precipitated on the nucleation base point 4a has non-uniform grain sizes and varying grain boundary areas (FIG. 3(c)). Note that the presence of grain boundaries generally causes a decrease in thermal conductivity, so single crystals are more desirable as heat sinks than polycrystals, but with current technology, Si, GaAs, etc. used in semiconductor fabrication It is difficult to obtain a large area single-crystal diamond film on a substrate. In view of the above-mentioned circumstances, the present inventors and others have developed an applied
Physics Letters (53rd JJ, 1815 page,
In 1988), we reported a method for selectively forming diamond single-crystal particles in predetermined locations, and as a result of subsequent intensive studies, the present inventor found that it was possible to create a diamond thin film with high thermal conductivity. did.

[Means to try to solve the problem]

In the present invention, a large number of regions as nucleation points are regularly formed on a substrate at appropriate intervals, diamond single crystal particles are precipitated on the regions, and each of the precipitated It is characterized by growing single crystal grains to form a film. That is, in the diamond film produced by the production method of the present invention, since the position and amount of grain boundaries are controlled, it is possible to significantly improve thermal conductivity compared to the conventional example. Specifically, diamond nucleation base points are formed in a matrix at appropriate intervals, and diamond single crystal grains are grown and coalesced at the multi-nucleation base points, so that the grain size is almost uniform and grain boundaries are formed between the base points. A diamond film similar to that described above is formed.

[Effect]

In the steps of the manufacturing method according to the present invention, first, a substrate on which diamond crystals can be grown by a vapor phase method is prepared. Such substrates include, for example, Si, G
Semiconductor substrates such as e, oxide substrates such as quartz and alumina, S
Examples include an iC substrate, a GaAs substrate, and a high melting point metal substrate such as W or Mo. Next, portions that serve as nucleation points for diamond crystals are regularly formed on the substrate. As a method for regularly forming such nucleation base points, for example, Japanese Patent Application Laid-Open No. 62-2
No. 97298, Japanese Patent Application Laid-Open No. 63-315598,
and an article in Applied Physics Letters (vol. 5FIS, 3 pages, 1815, 1988). An example is shown below. First, fine irregularities are formed on the surface of the substrate to serve as starting points for nucleation. This formation method involves treating scratches on the substrate surface using abrasive grains of diamond, cubic boron nitride, alumina, or silicon carbide, or inserting the substrate into a liquid such as alcohol or water in which the abrasive grains are dispersed. There are methods such as applying ultrasonic vibration. Next, masks are formed on the substrate at regular intervals. The material of the mask is not particularly limited, and may be, for example, a resist formed using a photolithography method (optical writing method) or an EB lithography method (a consonant beam writing method). Note that the size of the formed mask is preferably 10 μm 2 or less in order to precipitate diamond single crystal particles. If it is 10 μm2 or more, a plurality of nucleation base points will be formed, making it easy to form polycrystalline particles. Next, by etching the surface of the substrate through the mask, regions having fine irregularities are regularly formed. The etching may be either dry etching or wet etching. When performing wet etching, for example, etching with a mixed solution of fluorine and nitric acid can be used. Further, when performing dry etching, for example, plasma etching, ion beam etching, etc. can be used. Etching gases for plasma etching include CF4 gas, and etching gases for ion beam etching include rare gases such as argon, helium, and neon, and gases containing oxygen, fluorine, hydrogen, and carbon. . A sufficient pattern can be formed by etching to a depth of preferably 100 to 10,000, more preferably 500 to 1,000. Next, when the mask is removed and diamond single crystal particles are formed on the nucleation base points on the substrate, diamond nuclei are generated only in the areas where the unevenness remains due to the mask formation, and the diamond nuclei grow and coalesce. A diamond film is formed. The diamond film in the present invention may be formed by any known method such as hot filament CVD (chemical vapor deposition), microwave plasma CVD, direct current plasma CVD, or high frequency plasma CVD. CV
As the raw material gas D, hydrocarbon gases such as methane, ethane, and ethylene, oxygen-containing organic compounds such as methanol, ethanol, and acetone, and carbon oxide can be used. These gases are generally used mixed with hydrogen gas (carbon raw material gas concentration 0.01 to 50% by volume), but argon,
Inert gas such as helium, 02. There is no problem in adding an oxygen-containing gas such as H2O or CO2. Gas pressure varies depending on the manufacturing method, but is 0.01 to 1000 Torr.
That's about it. The gas flow rate varies depending on the capacity of the film forming equipment, but the total raw material gas flow rate is from 10mJ2/min to 50f! ,/
It is about min. The temperature of the substrate during film formation is generally about $250 to 1200°C. Further, the distance between the nucleation base points is preferably several μm or more, preferably 5 μm or more, in order to reduce the amount of grain boundaries. Diamond particles growing from the nucleation base tend to grow as single crystals from a single nucleus when the nucleation base area is narrow, such as 10 μm 2 or less. However, in diamond synthesized in a vapor phase, multiple twin grains (particles consisting of several crystals in a mirroring relationship) are likely to precipitate depending on the precipitation conditions. According to the findings of the present inventors, the precipitation of multiple twin grains does not cause a decrease in thermal conductivity. Therefore, the precipitation of single crystal grains in the present invention includes the precipitation of multiple twin crystal grains.

EXAMPLES Next, the present invention will be described more specifically and in detail with reference to the drawings.゛ (Example 1) Diamond forming substrate 1 as shown in iS1 figure (a)
As a silicon single crystal substrate, that is, the plane orientation is (10
0) with a diameter of 25 mm and a thickness of 0.5 mm. First, a Si substrate is inserted into alcohol in which diamond abrasive grains having an average particle size of 20 μm are dispersed, and ultrasonic vibration is applied using an ultrasonic cleaner to remove the substrate 1.
Fine irregularities are formed on the surface of the substrate to serve as nucleation base points 4 (FIG. 1(b), FIG. 2(a)). Next, a resist pattern 2 serving as a mask with a diameter of 1 μm is formed on the substrate 1 using a photolithography method to form a resist pattern 2 with a thickness of 5 μm.
Etching of 1,000 people was performed using Ar ion beam etching equipment (Fig. 1(d)). At this time, the acceleration voltage of the Ar ion beam was 0.6 kV, and the etching time was 6 minutes. Next, remove the resist pattern 2 with acetone,
Diamond single-crystal particles 3 were formed at the nucleation base point by a known hot filament CVD method (see Fig. 1).
e)). In addition, the gas flow rate at that time was 200 mJ2 of hydrogen.
The temperature of the tungsten filament as a heat source was 2000° C., the temperature of the substrate 1 was 800° C., the pressure was 100 Torr, and the film forming time was 6 hours. Through the above diamond formation, diamond single crystal grains or twin crystal grains were selectively precipitated from the portion where resist pattern 2 had been formed, and these grew and coalesced to obtain a diamond film (Fig. 1 (f) )). As shown in Fig. 2 (a), (b), and (C), the nucleation base points 1a are formed in a matrix shape at appropriate intervals, and diamond single crystal particles 3 are formed on the multi-nucleation base points 1a. was precipitated, and due to the growth of each single crystal grain 3, a diamond film was formed in which the grain size was approximately uniform and the grain boundaries existed between the base points. In addition, when the thermal conductivity of the diamond film was measured using the AC calorimetry method, the measured value was 1500 W/m.
-I got K. (1i, Stream side 2) A diamond film was formed under the same conditions as in Example 1 above, except that the resist pattern 2 was formed at intervals of 10 μm and the film formation time was 10 hours. When the conductivity was measured, a measured value of 1720 W/mK was obtained. (Comparative Example 1) A diamond film was formed under the same conditions as in Example 1 above, except that a silicon substrate with minute irregularities formed by ultrasonic vibration was used as it was, and a polycrystalline film containing particles with a grain size of 1 μm or less was formed. was gotten. The measured thermal conductivity of the membrane in this case was 700 W/m-.

【Effect of the invention】

As described above, according to the present invention, a large number of regions as nucleation points are regularly formed on a substrate at appropriate intervals, and diamond single crystal particles are precipitated on the regions,
Furthermore, since each of the precipitated single crystal grains is grown individually to form a film, the position and amount of grain boundaries, which were formed randomly in conventional techniques, can be controlled as desired. This made it possible to obtain a diamond film with high thermal conductivity. The highly thermally conductive diamond film obtained in this way is
It is extremely useful as a heat sink for semiconductor devices such as semiconductor lasers, microwave oscillation devices, and VLSI devices.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the diamond manufacturing process for heat sinks of the present invention, FIG. 2 is a schematic diagram of diamond crystal growth of the present invention, and FIG. 3 is a schematic diagram of conventional diamond crystal growth. (Explanation of symbols) 1... Substrate, 1a... Nucleation base point, 2... Resist pattern, 3... Diamond single crystal particle. Fig. 1 Fig. 2 0 0 (m” o O. 3rd y!J,.°. -40 (a)',”

Claims (1)

[Claims] A large number of regions as nucleation points are formed regularly on the substrate at appropriate intervals, diamond single crystal particles are precipitated on the regions, and each of the precipitated single crystal particles is grown individually. A method for producing a highly thermally conductive diamond film, which is characterized in that it is formed into a film shape.