JPH06183889A - Production of diamond thin film device having high bonding strength - Google Patents

Abstract

PURPOSE:To obtain a diamond thin film device having high bonding strength with a simple procedure by forming a diamond thin film on a substrate and heating the film together with the substrate under a reduced pressure, thereby forming an intermediate layer between the substrate and the diamond thin film. CONSTITUTION:A diamond thin film is formed on the surface of a substrate material by an arbitrary conventional method. The substrate having the diamond thin film is annealed by heating in a vessel containing oxygen or nitrogen atmosphere under a reduced pressure to form an intermediate layer between the substrate and the diamond thin film and improve the bonding strength of both components. The bonding strength of the diamond thin film can remarkably be improved by the above simple process compared with conventional method to form an intermediate layer consisting of a different kind of material. A practical diamond thin film device can be produced by thus process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a diamond thin film having good adhesion and excellent film quality on the surface of a semiconductor substrate material, a sintered material or a metal material.

[0002]

2. Description of the Related Art Research on the synthesis of artificial diamond materials has been conducted and developed for a long time. The synthetic method of artificial diamond can be divided into a high pressure synthesis method and an atmospheric pressure or low pressure vapor phase growth method. In the high-pressure synthesis method, various types of diamond materials such as fine crystal particles, polycrystalline sintered bodies, millimeter-sized single crystal particles, etc. can be formed by the impact method using temperature difference method, flux method, explosion, etc. I can. The vapor phase growth method is a method of forming a diamond thin film on the surface of various substrate materials, and includes diamond-like carbon (a carbon material that does not have a crystal structure and has a hardness close to that of diamond; hereinafter referred to as DLC). Has been widely researched.

Hardness peculiar to artificial diamond
Various applications have been proposed by utilizing transparency, thermal conductivity, and high insulation. For example, by utilizing hardness and thermal conductivity, for long-life cutting tool materials and heat sinks for electronic materials, by utilizing transparency in the visible to infrared range, for optical window materials such as infrared lasers, etc. With the material
Many proposals and studies have been made.

In the high-pressure synthesis method, it seems that the cutting tool materials and heat sinks are finally being put to practical use among the above-mentioned application examples, but only simple samples such as plates and rods can be obtained. Also, there are still restrictions such as the maximum size being 10 mm square. Therefore, it can be said that there is a great disadvantage in providing a tool having a complicated shape required in the field of machine tools.

The vapor phase epitaxy method is a method for forming a diamond thin film on various kinds of substrates. It can overcome the size and shape limitations of the above high pressure synthetic diamond and can be applied to various fields such as semiconductor materials. It is expected to expand the sex. Not only tools, but also attempts to develop semiconductor elements are being actively targeted.

[0006]

As described above, the range of application of artificial diamond has expanded greatly by the vapor phase epitaxy method. However, diamond thin films are problematic in various diamond products using the method. There is adhesion to the substrate. It is important not only for those exposed to mechanically harsh environments such as tool materials, but also for the purpose of ensuring a stable thin film structure on the substrate in the field of heat sinks and semiconductor materials. However, the adhesion is very poor regardless of the type of substrate material.

The reason why the adhesion of the diamond thin film is weak is considered to be as follows. 1. Difference in coefficient of thermal expansion between diamond thin film and substrate The diamond film-forming substrate needs to be heated to 500 to 800 ° C, and depending on the method, to around 1000 ° C. For example, the coefficient of thermal expansion of a Si substrate, which is a typical semiconductor substrate material, is 2.4, while that of diamond is 1.0 to
It is as small as 1.5. It has been clarified that the adhesiveness greatly changes depending on the film forming conditions other than the temperature, but it is known that the difference in the coefficient of thermal expansion also has a very large effect.

2. Internal stress accumulated in the diamond thin film From the observation of the cross section of the completed diamond thin film, the growth of the diamond thin film shows that crystals grow isotropically from the nuclei of the substrate surface, and during the growth, the crystal grains collide and the growth direction changes. It is considered that the structure is changed into tapered and / or columnar crystal grains due to the limitation, and an anisotropically grown thin film is formed substantially perpendicular to the substrate.
Therefore, a very strong compressive stress is accumulated inside the film.

Further, in order to improve the adhesion, the following attempts have been made. 1. Forming an intermediate layer An intermediate layer is provided as a buffer zone at the interface between the substrate material and a diamond by a thin film of a material having a lattice constant and a coefficient of thermal expansion that are intermediate. For example, silicon nitride, silicon carbide (preferably β-type silicon carbide), boron nitride (preferably cubic boron nitride), titanium carbide, titanium nitride, etc. are used as the crystalline thin film,
If the film forming process is to be simplified, an amorphous thin film such as DLC or silicon nitride / silicon carbide / boron nitride / boron carbonitride / titanium carbide / titanium nitride may be used. As a result, the difference in the coefficient of thermal expansion and the difference in the lattice constant between the substrate and the thin film are eliminated, and the internal stress accumulation is relaxed. However just process for the intermediate layer deposition mechanism intervenes is complicated. In addition, for application as a semiconductor device, it is necessary to consider the influence of changes in electrical characteristics due to the formation of the intermediate layer.

2. Reduction of internal stress of diamond thin film By reducing the heating temperature during film formation, the strain generated during cooling is reduced and peeling of the film is prevented. However, in general, in the film formation below a temperature range suitable for the film formation method and film formation conditions, the quality of the film is deteriorated due to the formation of an amorphous carbon component,
Alternatively, the film formation rate may be extremely reduced. By introducing impurities such as nitrogen into the film, the crystal grain size is reduced,
Attempts have been made to alleviate the accumulation of internal stress due to the taper of the crystal grains described above, but it goes without saying that the film quality will deteriorate.

3. Utilization of anchor effect The surface of the substrate is subjected to mechanical or chemical etching or fine unevenness by laser or the like, and then a diamond film is formed through an ordinary pretreatment process. As a result, a structure in which a fine diamond anchor bites into the surface of the substrate is formed to form a diamond thin film having good adhesion. This is a method especially proposed in the field of tool materials, but as is clear from the fact that sufficient adhesion is not obtained in the WC sintered body used as the base, the size of the base and the anchor function It is difficult to clearly differentiate the unevenness of the, and it is not a practical method.

[0012]

Means for Solving the Problems As means for solving the above-mentioned problems, the inventors of the present invention have conducted a vacuum condition or reduced pressure nitrogen or reduced pressure on a substrate material having a diamond thin film formed on its surface by various commonly used methods. It was found that it is possible to solve the problem of weakness of adhesion by heating by heat, electromagnetic induction, or light and annealing in an oxygen state. The present invention will be described below.

In the present invention, any method may be used for forming the diamond film. The type of substrate or base material is 1000 ± 100 ° C, including the time of annealing treatment described later.
Any material can be used as long as it can be held to some extent. The lower limit of this temperature range can be changed to some extent depending on the type of the substrate material, but the upper limit of the temperature range is significantly deteriorated at higher temperatures. Further, if the annealing is performed in a reduced pressure oxygen atmosphere, the substrate is required to have high oxidation resistance. It is apparent that most of the materials described in the above-mentioned commonly used film forming methods have sufficient durability in this temperature range.

After subjecting a semiconductor material substrate such as a sintered / single crystal substrate based on Si, alumina, silicon nitride, silicon carbide, boron nitride or the like, a quartz glass substrate or the like to an appropriate pretreatment, if necessary, Film formation may be performed using a hot filament / plasma CVD method or plasma jet / arc discharge,
At this time, if a large area is required, a CVD method using a large-sized hot filament or magnetic field plasma may be suitable. In addition to the above method, the film can be formed by DC arc or combustion flame method.

The method of annealing the formed sample is such that the processing container used is a vacuum degree of about 0.005 to 10 Torr, preferably about 0.1 to 0.01 Torr, or a reduced pressure nitrogen atmosphere or a reduced pressure oxygen atmosphere. Then
700 samples in the vessel without mechanical degradation
Any method capable of heating to ˜1100 ° C. may be used. For example, a method in which a sample is held inside a furnace core tube in a vacuum state and externally heated using a tubular electric furnace, or if the film forming apparatus has a vacuum film forming chamber and a substrate heating function, the film forming is performed. It is also possible to hold the substrate for which film formation processing has been completed on the substrate / substrate holding stage / holder of the apparatus as it is, and perform annealing by heating from the stage / holder. Plasma discharge or induction heating similar to plasma CVD may be applied by electromagnetic waves.

The surface of a diamond thin film sample held in a decompression chamber having a window material showing good infrared transmittance is scanned with laser light oscillated at a wavelength at which diamond is transparent, so that the thin film and the substrate are exposed. It is also very effective to apply selective light heating to the interface.
As the laser light source used here, for example, an infrared laser typified by a CO ₂ gas laser can be widely selected, and a wide selection can be made. Some semiconductor lasers could be used.

Regardless of the annealing method, the sample must be in a vacuum state, a reduced pressure nitrogen state, or a reduced pressure oxygen state. Although the reason for this is not fully understood, the present inventors consider the following. When heating in a depressurized state, thermal energy is transferred to the sample by the inner wall of the furnace tube, the holder and the laser beam, but since the depressurized state above the diamond film surface, that is, the adiabatic state, heat concentration occurs inside the sample, As a result, the carbon in the thin film and the atoms of the base material cause mutual diffusion, and an intermediate layer composed of both of them is formed.

Therefore, by using this method, it becomes possible to form an intermediate layer having a strong bonding force without complicating the process and without worrying about the adverse effect on the electrical characteristics of the film. . The present inventors have found that in the case of Si,
It is considered that the gradation intermediate layer of SiC to β-SiC and diamond mixed phase to diamond thin film may be similar to that of other materials. In particular, forming a reduced pressure atmosphere with oxygen is very effective not only for improving the adhesiveness but also for improving the film quality as described in the examples.

[0019]

【Example】

[Embodiment 1] This embodiment relates to a vacuum annealing method using a tubular electric furnace having a structure in which a vacuum furnace core tube is externally heated. The sample is Si using a magnetic field microwave plasma CVD apparatus.
A polycrystalline diamond thin film formed on a (100) substrate was used. Alternatively, a diamond sample that is homoepitaxially or heteroepitaxially grown on a substrate such as single crystal diamond or single crystal cubic boron nitride may be used.

FIG. 1 shows a device diagram. This device is a general one as a magnetic field microwave plasma CVD device,
The sample is arranged to face the microwave waveguide (5) in the sample and sample holder (1) shown. Here, the sample and the sample holder (1) are transferred to the plasma reaction chamber (3) after the sample exchange in the preliminary chamber (2), and heated by the heater incorporated in the sample holder. At this time, in the spare chamber (2) and the plasma reaction chamber (3), a wide area type turbo molecular pump (hereinafter TMP), a roughing and TMP back pressure rotary pump (hereinafter RP), and an exhaust system (7) consisting of a pressure adjusting valve. Vacuum is pulled to around 10 ^-5 Torr.

After the sample reaches the set temperature, the reaction gas is introduced from the reaction gas supply pipe (6) into the plasma reaction chamber (3), and the microwave and magnet coil () fed from the microwave waveguide (5) are supplied. 4) A method in which high density plasma is generated by the effect of the magnetic field applied and the film is formed by this. Here, a bias voltage is applied to the sample and the sample holder (1) from the DC power supply device (8).

The film forming conditions are the general conditions used in this method. That is, the reaction pressure is 0.5 Torr, the input microwave power is 4 kW (reflection 0 kW), the magnetic field is 2.2 kW near the waveguide window, and 8 at a position about 200 mm from the waveguide window.
A voltage was applied so as to form an ECR condition of 75 G, and a sample holder (1) equipped with a φ4 in Si (100) substrate was placed in the vicinity thereof. The substrate heating preset temperature from the sample holder (1) was 800 ° C., and the bias voltage applied from the DC power supply (8) to the substrate holder was DC 50V. Vaporization C from the reaction gas supply pipe (6) to the plasma reaction chamber
H ₃ OH 50 ccm and H ₂ 100 ccm were introduced. 8
After the time-depositing step, the collected sample was confirmed by Raman spectroscopic analysis to be a diamond having a very good crystallinity with a sharp peak only at 1332 cm ^-1 . The center portion of the sample thus obtained was cut out with a width of 15 mm and a length of 30 mm to obtain an annealed sample.

For the vacuum annealing, a tubular electric furnace (11) having a uniform heating range of 200 mm and an inner diameter of the core tube phase entry portion of about 40 mm as shown in FIG. 2 was used. The core tube (10) is made of SUS as a material that can withstand heating under a reduced pressure and around 1000 ° C.
310 was selected to be a pipe having an outer diameter of 32 mm and an inner diameter of 21 mm. Annealing by electromagnetic induction heating such as high frequency induction heating is also possible if the material of the furnace tube is changed to, for example, quartz glass. The temperature inside the core tube was observed by a thermocouple inside the thin tube inserted inside. Preliminary experiments were conducted before actual annealing, and it was confirmed that the difference between this temperature measuring method and the actual temperature of the surface of the sample (1) was about 7 to 9 ° C. The temperatures described as annealing conditions in the present invention and the examples are all the temperatures of the sample surface corrected based on this.

A diamond thin film sample was placed on a uniform temperature portion in the core tube (10) through an alumina boat,
The inside pressure was reduced to 0.01 Torr by an RP equipped with an exhaust system. After that, it takes about 1 hour to set the temperature to 900 ° C.
The temperature was raised to and held for 5 hours.

After the end of the holding time, an adhesive tape (those available as office supplies, for example, vinyl tape or cellophane tape can be used enough) was attached to the surface of each diamond thin film before and after annealing, and peeled off to compare the adhesion. did. As a result of the 10-point peeling experiment, all the samples which were not annealed were completely peeled off by the adhesive tape, but the samples which were annealed were 10
It was confirmed that partial peeling was observed at the edge of the sample substrate at 3 of the points, and it was confirmed that the film adhesion was significantly improved by annealing.

Further, according to the experiments conducted by the present inventors, it has been found that the adhesion of the diamond thin film changes depending on the holding time, and the film quality of the residual diamond also changes depending on the holding time. For example, a sample having a holding time of 1 hour gave a significantly better adhesive force and adhesion in the preceding adhesive tape test than the sample having a holding time of 5 hours. However, when the surface of the diamond thin film after annealing was evaluated by Raman spectroscopic analysis, the film quality tended to deteriorate as the annealing time was lengthened, and the 5-hour annealing performed in this example can be said to be a moderate value.

[Embodiment 2] In this embodiment, a sample immediately after film formation is heated in the reaction chamber of a CVD apparatus as it is. As described above, the film forming method to be used may be any method such as hot filament / microwave plasma / magnetic field microwave plasma / DC plasma / arc plasma. However, it is necessary that the sample holder alone be capable of heating, and a method of performing induction heating by heat of plasma generated like some microwave plasma CVD cannot be used. In this example, the magnetic field microwave plasma CVD apparatus of FIG. 1 was used as in Example 1, and film formation was performed under the same conditions. Although the substrate is cooled after the film formation in the usual process, in this embodiment, the valve of the reaction gas supply pipe (6) is closed while the heating state of 800 ° C. is maintained, and the preliminary chamber (2) and the plasma reaction chamber (3) are closed. Is evacuated to about 0.001To
Hold at rr. The effect of gas on the heated substrate was not particularly observed in this example. This state was maintained for about 5 hours and then cooled to room temperature over about 2 hours.

In order to compare the adhesion between the annealed sample and the unannealed sample, the same adhesive tape test as in Example 1 was conducted. In the annealed case, although peeling occurred at the edge of 2 of the 10 samples,
All of the 10 samples that were not annealed peeled off, and it was found that adding vacuum annealing after the diamond film formation was very effective in improving the adhesion.

[Embodiment 3] In this embodiment, vacuum annealing is partially carried out in a single sample using laser light. As a method, laser heating annealing is performed inside the vacuum chamber. The advantages of introducing this laser annealing are, as already mentioned, that it is easy to control the change in adhesion and film quality due to annealing, and that the dotted or linear regions are different in the areas where the film quality and adhesion are different. Can be formed. Further, for example, by connecting the film forming chamber and the annealing chamber to form a multi-chamber as shown in FIG. 3, the annealing process can be performed cleanly in the as-deposited state, and the processing time can be shortened.

The laser light needs to be transparent to diamond as described above. Here, a YAG laser is generally used for diamond processing such as cutting, and a diamond having a thickness of about 1 mm can be cut depending on conditions. However, in the present invention, it is a thermal modification of the interface state between the substrate and the diamond thin film, and it is preferable to use a laser source that transmits the diamond thin film without affecting the diamond thin film and allows energy to reach the interface with the substrate. The light source is selected based on this condition.

In the present invention, CO, which is a kind of infrared laser,
_Two lasers were used. Since diamond with good crystallinity is transparent in the infrared region, it is possible to supply energy to the required interface by forming a diamond thin film with good film quality and performing laser processing during film formation. In addition to this, as a laser having a wavelength that does not cause absorption in diamond, some semiconductor lasers can be used.

In this example, the diamond thin film sample formed on the Si substrate was annealed using the independent laser annealing chamber in the same manner as in Examples 1 and 2. The annealing chamber used was an apparatus modified for laser annealing of a semiconductor device based on an optical CVD apparatus. The configuration will be described based on FIG. The laser oscillator (15) is an infrared CO ₂ laser. The laser output was 100 W. Further, the laser was applied as a continuous wave (CW), but by applying a pulse, it becomes easy to control the above-mentioned amorphous formation.

The φ4 inch sample substrate was mounted on the sample holder (1) as it was and placed inside the annealing chamber (12).
In this state, the pressure was reduced to 10 ^-2 Torr by the exhaust system (7). Laser light (14) is introduced into the annealing chamber (12) through the quartz glass laser window (13) and is irradiated to the sample substrate (1). At this time, the laser beam (14) was scanned, and an annealing region with a width of 1 μm was formed at the center of the sample (1).
20 pieces were provided at mm intervals.

Instead of the adhesive tape test as in Examples 1 and 2, hydrofluoric acid / nitric acid / acetic acid (5: 3:
When the sample was immersed in the mixed diluted etching solution of 3) for 1.5 hours, the diamond was peeled off leaving the annealed region. From the SEM observation of the sample, it was confirmed that diamond remained in the annealed region. Further, when the residual diamond region was evaluated by microscopic Raman, it was confirmed that the film quality was improved as compared with the Raman spectroscopic result immediately after film formation.

Example 4 In this example, the annealing shown in Example 1 was performed in a reduced pressure nitrogen environment. The experimental apparatus method is almost the same as that of the first embodiment. Of course, reduced pressure nitrogen may be introduced into the annealing environment of the second and third embodiments. A diamond thin film sample prepared on a Si substrate by a magnetic field microwave CVD apparatus under the same conditions as in Examples 1 to 3 was inserted into a furnace core tube, N ₂ 50 sccm was flown into the reaction vessel, and an automatic pressure adjuster was used to adjust the pressure. After setting the pressure to 1 Torr and stabilizing the temperature, the external tubular electric furnace takes about 1 hour for 9 hours.
The mixture was heated to 00 ° C and kept as it was for 5 hours.

After the annealing was completed, the sample was taken out, and Example 1 was used.
Adhesion comparison with the same adhesive tape was performed for 10 points, and it was confirmed that the adhesion was improved more than before annealing.

Example 5 In this example, the reduced pressure nitrogen environment annealing shown in Example 4 was performed in a reduced pressure oxygen environment. The annealing device and method are almost the same as those in the first and fourth embodiments. Further, the heating method may be the method of Examples 2 and 3. However, regarding the core tube, SUS310
Therefore, it was changed to a high-purity alumina sintered body of the same size.
A diamond thin film formed on a Si substrate by a magnetic field microwave CVD apparatus under the same conditions as in Examples 1 to 4 was inserted into a furnace core tube, 100 sccm of O ₂ was flown into the reaction vessel, and 0.1 Torr was adjusted by an automatic pressure regulator. After setting the pressure to 9 seconds, after stabilization, it takes about 1 hour for 9 hours with an external tubular electric furnace.
The mixture was heated to 00 ° C and kept as it was for 5 hours. After the annealing was completed, the sample was taken out, and the adhesiveness comparison with the adhesive tape was performed for 10 points in the same manner as in Examples 1 and 4, and it was confirmed that the adhesiveness was improved more than before the annealing.

The advantage of performing in an oxygen environment can be confirmed by performing Raman spectroscopic analysis before and after annealing and comparing them. When the sample before annealing, the sample of Examples 1 and 4, that is, the sample annealed in the reduced pressure environment and the reduced pressure nitrogen environment, and the sample obtained in this example were compared by Raman spectroscopy, respectively, Examples 1 and 4 were obtained. In the sample obtained in ¹⁾ , the peak at 1332 cm ⁻¹ was lower than that before annealing, and a broad increase was observed at 1580 cm ^{−1 although} it was weak, whereas in the sample obtained in this example, it was rather 1332 cm ^−. The peak of ¹ was sharper and no broadening was observed at 1580 cm ^-1 . It is well known that the sharpness of the peak at 1332 cm ^-1 , that is, the full width at half maximum is a measure of the crystallinity of a diamond thin film. According to the method of the present invention, the effect of removing amorphous carbon by oxygen can be obtained, and it is possible to improve the adhesion and film quality of the film at the same time.

[0039]

According to the present invention, the adhesion of the diamond film-forming sample can be markedly improved and the adhesion and the film quality can be improved at the same time by a simpler process than in the case of providing the intermediate layer made of different materials. It is expected that the present invention will further accelerate the practical application of the diamond device.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a magnetic field microwave plasma CVD apparatus used for film formation in Examples 1, 3 to 5 and film formation and annealing in Example 2.

FIG. 2 is a schematic view of an annealing apparatus used in Examples 1, 4, and 5.

FIG. 3 is a schematic diagram of a multi-chamber laser annealing apparatus introduced in a third embodiment.

[Explanation of symbols]

1 Sample Substrate and Sample Holder 3 Plasma Reaction Chamber 4 Magnet / Coil 5 Microwave Waveguide 6 Reaction Gas Supply Pipe 7 Exhaust System 10 Core Tube 11 Tubular Electric Furnace 12 Annealing Chamber 13 Laser Window 14 Laser Light 15 CO ₂ Laser Oscillator 16 Transfer valve

Claims (6)

[Claims] 1. A diamond thin film formed on a substrate having a surface to be formed is heated together with the substrate in a container under a reduced pressure containing an oxygen or nitrogen atmosphere to form an intermediate layer between the substrate and the diamond thin film. A method for manufacturing a high-adhesion diamond thin film device, characterized by improving the adhesion between the two by squeezing. 2. A method for producing a high adhesion diamond thin film, characterized in that the reduced pressure state in claim 1 is a pressure state in the range of 0.005 to 1 Torr by exhausting the inside of a closed container. 3. The depressurized state of the oxygen or nitrogen atmosphere according to claim 1 is 0.01 to 10 T by exhausting the whole of the container while supplying oxygen or nitrogen gas to the closed container.
A method for manufacturing a high-adhesion diamond thin film device, which is characterized in that it is formed in a range of orr. 4. A method for producing a diamond film having high adhesion, wherein the intermediate layer according to claim 1 is composed of a mixed phase of the base material and carbon. 5. A diamond thin film formed on a substrate made of a semiconductor material such as Si or a sintered body material made of alumina, silicon carbide, silicon nitride, boron nitride or the like as a raw material is exposed to an oxygen or nitrogen atmosphere together with the substrate. Enclosed in a decompression container containing, and selectively heating the interface between the diamond thin film and the substrate by irradiating the diamond thin film with laser light oscillating at a transparent wavelength, and between the substrate and the diamond thin film. A method for producing a high-adhesion diamond thin film, which comprises selectively generating an intermediate layer to improve the adhesion between them. 6. A method of manufacturing a diamond thin film having high adhesion, wherein the laser light in claim 5 is a CO ₂ laser.