JPH08209347A - Synthetic diamond and its synthesis method - Google Patents

Abstract

PURPOSE: To reduce the warpage of diamond obtd. by a vapor phase synthesis method and to enhance yield and to reduce cost without causing trouble to a subsequent working process such as polishing and a device process. CONSTITUTION: The peripheral part 1 of the surface of a substrate 5 is not scratched but the remaining part 2 of the surface is scratched and diamond is synthesized using the resultant substrate 5. In other way, the peripheral part of the surface of a substrate is coated with a heat resistant material and diamond is synthesized using the resultant substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for synthesizing a diamond having a small residual stress using a vapor phase synthesis method, and a synthetic diamond having a small warp obtained by the method.

[0002]

2. Description of the Related Art As a method for producing diamond by vapor phase synthesis, many methods such as a hot filament CVD method, a microwave plasma CVD method, a high frequency plasma CVD method and a DC plasma jet method are known. Each of these methods is a method of obtaining a diamond film by thermally decomposing a raw material gas containing carbon by thermal plasma, activating it, and depositing it on the surface of a heated substrate.

As a substrate on which diamond is deposited by the vapor phase synthesis method, Si, Mo, etc. are generally used. Before synthesizing diamond, a scratch treatment with diamond powder or the like is carried out to promote generation of diamond nuclei during synthesis. The method is generally used. Also, without scratching,
There is also a method of applying a bias voltage to the substrate to promote the generation of diamond nuclei.

[0004]

Among all materials, diamond has the lowest elastic modulus and the lowest coefficient of thermal expansion. In vapor phase synthesis of diamond, Si, Mo, etc. are generally used as a substrate, but the stress acting between the substrate and the synthetic diamond or the stress remaining in the synthetic diamond poses a serious problem.

Although the generation mechanism of the intrinsic stress in synthetic diamond is not clear, the sum of this intrinsic stress and the thermal stress due to the vapor phase synthesis temperature or the difference in thermal expansion coefficient between the diamond and the base material is the synthetic diamond. Is the residual stress of. When diamond is synthesized on the substrate, this residual stress appears as a warp between the substrate and synthetic diamond. Moreover, the diamond free-standing film obtained by removing the substrate from the synthetic diamond is
It is common to show greater warpage.

These synthetic diamonds or diamond free-standing films are supplied to a processing process, but this warpage becomes a very serious problem at the processing stage. For example, in the polishing process, this warpage causes a serious problem such that the entire surface of the diamond cannot be uniformly polished or the diamond is cracked during polishing. Alternatively, in the device process or the metallization process, problems such as the inability to form a pattern and the reduction in yield occur due to the warp.

[0007] In order to reduce or avoid these problems, it is necessary to cut a warped diamond into small pieces, but in that case, problems such as an increase in process cost become apparent.

As described above, reducing warpage of synthetic diamond is a very important subject, and the present invention provides a synthetic method for reducing warpage of synthetic diamond in the vapor phase synthesis method, and its vapor phase synthesis. An object of the present invention is to provide a synthetic diamond whose warpage is reduced by the method.

[0009]

Means for Solving the Problems As a result of detailed examination of the mechanism by which the diamond obtained by the vapor phase synthesis method warps, the intrinsic stress of the synthetic diamond and the action between the substrate surface and the synthetic diamond It was discovered that not only the stress but also the diamond deposited on the side surface of the substrate and the stress acting between the side surface of the substrate and the synthetic diamond have a great influence on the warpage.

Further, in the diamond obtained by the ordinary vapor phase synthesis method, the film thickness on the outer peripheral side of the substrate is thicker than the film thickness near the center of the substrate surface. It was found that the residual stress in the thick portion of diamond and this non-uniform stress distribution are the major causes of warpage.

The present invention has been made on the basis of such knowledge, and a diamond film is formed by a synthesizing method such that the diamond film is not synthesized on the outer peripheral side of the substrate surface, or the stress is small even if synthesized. It is possible to significantly reduce the warpage of the film.

The present invention will be described in detail below. (1) Using a substrate in which the outer peripheral side portion of the surface is not scratched, but the outer peripheral side portion is scratched. There are a method of synthesizing diamond, and (2) a method of synthesizing diamond using a substrate whose outer peripheral portion of the surface is covered with a heat resistant material.

In the above method (2), as a preferable method, diamond is synthesized using a substrate in which the outer peripheral side portion of the scratched surface is covered with a heat-resistant material, or the surface which is not scratched. There is a method of synthesizing diamond after applying a bias voltage using a substrate whose outer peripheral portion is covered with a heat resistant material.

According to such a method of the present invention, diamond having a substantially uniform film thickness is formed on a portion (central side portion) of the substrate surface excluding the outer peripheral side portion, and the outer peripheral side portion including the side surface portion includes diamond. Is not deposited, or even if deposited, the diamond film thickness is smaller than the diamond film thickness in the central portion.

Therefore, according to the present invention, it is possible to obtain a synthetic diamond having a uniform film thickness and a small residual stress in the central portion, and by removing the substrate, the self-standing film is warped in a length of 10 mm. Of 10 μm or less can be obtained.

[0016]

In the vapor phase synthesis of diamond on a substrate other than diamond such as Mo or Si, the synthesis is generally performed after the surface of the substrate is scratched with diamond powder or the like. This scratching treatment is an extremely important process for improving the diamond nucleation density on the substrate.

On the contrary, if this scratching treatment is not carried out, the nucleation density will be extremely low, and it will take a long time until diamond is not synthesized, or even if it is synthesized, it becomes a film. Using this scratching process, if diamond is synthesized on the substrate that has a region that is not partially scratched, diamond will not be synthesized in the region that is not scratched, or the diamond film thickness Is thin, and the stress in that portion can be reduced.

The method (1) of the present invention utilizes the characteristic of the scratching treatment to perform the diamond scratching treatment only on the central side of the surface and not on the peripheral side of the diamond. This is a method for synthesizing diamond, and by suppressing synthesis of diamond on the outer peripheral side portion of the substrate, stress is reduced, and a synthetic diamond with less warpage can be obtained.

Further, in general, even in the region where the scratching process is not performed, the diamond film is synthesized if it is synthesized for a long time. On the other hand, in the method in which a bias voltage is applied to the substrate in advance to promote the generation of diamond nuclei, diamond is synthesized on the entire surface of the substrate regardless of whether the substrate is scratched or not.

Therefore, as an effective method also in such a case, there is the method (2) of the present invention, in which diamond is synthesized with the outer peripheral portion of the substrate surface covered with another heat-resistant material. , By removing or removing the covered material after the synthesis, thereby removing the diamond synthesized on the covered material together with it from the substrate, thereby avoiding the diamond synthesis on the outer peripheral side portion of the substrate, It is possible to reduce the stress at.

In the case of the method of covering the outer peripheral portion of the surface, specifically, a substrate whose entire surface is scratched in advance is used, and the outer peripheral portion of the surface is covered with a heat resistant material to synthesize diamond. Alternatively, a substrate that has not been subjected to a scratching treatment may be used, the outer peripheral side portion of the surface thereof may be similarly covered, and then diamond nucleation treatment such as bias treatment may be performed to synthesize diamond.

The material for covering the outer peripheral portion of the substrate surface has a substrate temperature of 500 ° C. or higher during diamond synthesis.
It is necessary that the material has heat resistance. Further, it is advantageous in terms of post-treatment and reuse, to select a material to which diamond is relatively unlikely to adhere. Specifically, Fe,
Metals such as Mo and W, their alloys, or S
It may be a semiconductor such as i or Ge, a compound semiconductor, or an oxide such as SiO ₂ .

As a method of applying these heat-resistant materials to the surface of the substrate, the outer peripheral portion of the surface is coated by a method such as vapor deposition, or a frame-shaped plate material of these heat-resistant materials is fixed while maintaining thermal contact. Is preferred. Also, as the substrate material, it is advantageous to select a material that diamond can be easily synthesized from the viewpoint of synthesis cost, but it is a standard for the use of synthetic diamond and a material that can be easily dissolved into a substrate to obtain a diamond free-standing film. Therefore, it may be selected appropriately.

In the case of the above method (1), as shown in FIG. 1, the area of the outer peripheral side portion 1 of the surface of the substrate which is not damaged is S1, and the area 2 of which is damaged is processed. When the area of S2 is S2, S1 / S2 <0.000
In 1, there are too few areas that have not been scratched,
S1 / S2 with no effect of warping of synthetic diamond
> 1 is uneconomical because the synthetic area of diamond is less than half the surface area of the substrate.

Similarly, in the case of the above method (2), FIG.
As shown in, when the area of the outer peripheral side portion 3 of the substrate surface covered with the heat resistant material is S3 and the area of the uncovered portion 4 is S4, the range of 0.0001 ≦ S3 / S4 ≦ 1 Is desirable.

According to the above method (1) or (2), the diamond film is not formed on the outer peripheral portion of the substrate surface, or even if it is formed, the diamond film is thinner than the average diamond film thickness. It is possible to avoid or reduce the stress on the outer peripheral side portion of the substrate surface including the side surface.

For example, when diamond is synthesized on the surface of the substrate 5 of FIG. 1 in which only the outer peripheral side portion is scratched, as shown in FIG. 2, the surface scratched portion (central portion) 2) the diamond film 7 is synthesized as usual, but the diamond film is not synthesized on the outer peripheral side portion 1 which is not scratched, and the diamond grains 8 are deposited or the diamond film 7 in the central portion is deposited. Only a thinner diamond film is deposited.

Further, when diamond is synthesized on the surface of the substrate whose outer peripheral side portion is covered with a heat resistant material, for example, the substrate 5 whose outer peripheral side portion is covered with the frame-shaped plate member 6 as shown in FIGS. By removing the heat-resistant material such as removing the frame-shaped plate material 6 after the synthesis, regardless of whether diamond is synthesized or deposited on the heat-resistant material,
As shown in FIG. 5, the diamond film 7 is synthesized only in the central portion which is not covered with the heat resistant material, and diamond is not synthesized in the outer peripheral side portion which is covered with the heat resistant material.

On the other hand, when the whole surface of the substrate is scratched and the diamond is synthesized without covering the outer peripheral side portion with the heat resistant material as in the conventional case, as shown in FIG.
The diamond film 7 is synthesized on the entire surface of the substrate 5. The diamond film 7 has a film thickness on the outer peripheral side and the side surface of the substrate 5 larger than the film thickness on the central part of the substrate 5, and a large stress is applied to this part.

As a result, the substrate 5 is largely warped, the diamond film 7 may be peeled off in some cases, and, for example, in the case of a Si substrate, the diamond film may be cracked together with the substrate. In addition, the diamond film 7 having such a large warp has a problem in that it can be partially polished due to the warp of the diamond film 7 in the polishing step, and it takes a long time to polish it because the outer peripheral portion has a large film thickness. is there.

As described above, in the synthetic diamond obtained by the method of the present invention, the diamond is not deposited at all on the outer peripheral side of the substrate, or even if it is deposited, the diamond film thickness is less than the average diamond film thickness. It is also characteristic that it is thin. Further, since diamond is not deposited on the side surface and the outer peripheral side portion of the substrate, the stress of the synthesized diamond film is greatly reduced.

As a result, defects due to delamination, cracks, substrate cracks, etc. of the diamond film during or after the synthesis can be reduced, and the synthetic diamond film synthesized on the substrate is less warped, resulting in defects in the subsequent processing processes. The generation can be remarkably reduced, and the cost can be reduced. Further, the synthetic diamond free-standing film obtained by removing the base material also has little warpage, and is effective in reducing the cost of subsequent processing and device processes.

Next, stress and warpage of synthetic diamond generally synthesized on a substrate will be considered. As shown in FIG. 7, the stress of the synthesized diamond film 7 is σ, and the substrate 5
, E is the elastic coefficient, v is the Poisson's ratio, D is the thickness of the substrate
When the radius of curvature is R and the film thickness of the diamond film 7 is d, and the film thickness d of the diamond film 7 is sufficiently smaller than the thickness D of the substrate 5, the following relationship is established.

[0034]

## EQU1 ## σ = [E / (1-v)] × [D ² / 6Rd]

Here, assuming a disk-shaped substrate 5,
When the diameter of the substrate 5 is a and the warp (Z displacement) is z, the radius of curvature R can be approximated by the following equation.

[0036]

[Formula 2] R = a ² / 8z

Therefore, from the above two relational expressions, the relation between the stress σ and the warp (Z displacement) z is expressed by the following equation.

[0038]

## EQU3 ## σ = [E / (1-v)] × [D ² / 6d] ×
[8z / a ² ]

As is clear from this equation, in order to reduce the warpage z of the synthetic diamond, the stress σ of the synthetic diamond is reduced, the substrate material having a large elastic coefficient E is selected, the thickness D of the substrate is increased, It is effective to reduce the synthetic diamond film thickness and the substrate diameter a.

Furthermore, Si (100) having a diameter a of 50 mm
The case of synthesizing diamond on the substrate will be specifically examined. Now, [E / (1-v)] si = 166Gp
8 shows the relationship between the warp z and the stress σ when the thickness a of the Si substrate is D = 1 mm, and FIG. 9 shows the relationship between the warp z and the thickness D of the Si substrate when the stress is 0.1 GPa. In both cases, the film thickness d of the diamond film is used as a parameter, and the vertical axis and the horizontal axis are shown on a logarithmic scale.

As can be seen from FIGS. 8 and 9, the warpage of the diamond film to be synthesized depends largely on the film thickness, but in order to reduce the warpage z, synthesis is performed under the condition that the stress of diamond is reduced. It is effective to increase the thickness of the substrate.

However, in reality, the stress of synthetic diamond is not evenly distributed over the entire synthetic region, so that the warpage does not always follow the calculated value. As shown in FIG. 6, the diamond film thickly synthesized on the outer peripheral side portion and the side surface portion of the substrate is subjected to particularly strong stress, and the warp of this portion is larger than the warp of the central portion.
Therefore, if the synthesis of the diamond on the outer peripheral side portion and the side surface portion of the substrate is avoided, the relationship between the radius of curvature and the warp according to the equations (1) and (3) is established.

Next, optimization of the warp of the diamond film on the substrate obtained by the method for synthesizing diamond according to the present invention will be considered. When the stress of the diamond film is zero, the warpage becomes zero, which is clear from the above equation (3), but in reality it is almost impossible to control the stress to zero. However, considering the subsequent processing process and device process, it is extremely important to minimize the warpage of the synthetic diamond.

Generally, the warp of the synthetic diamond film is preferably 10 μm or less in the width range of 10 mm and 10 μm in the width range of 50 mm in the device process, although it depends largely on the required accuracy of the subsequent processes.
In some cases, the following may be required.

Therefore, it is desirable that a = 10 mm and z ≦ 1.
Since it is 0 μm, the radius of curvature R is

## EQU4 ## It is necessary that the synthetic diamond film satisfy R ≧ a ² /8z=1.25 m.

Therefore, from the above equations (1) and (4),

Equation 5] R = [E / (1- v)] × [ stress synthetic diamond that satisfies D ² /6σd]≧1.25m σ, the elastic modulus of the substrate E, Poisson's ratio v, the thickness of the substrate D, It suffices to synthesize diamond under the condition of the combination of the synthetic diamond film thickness d.

The free-standing diamond film from which the substrate of synthetic diamond is removed has a different warp state due to the release of stress. As described above, the free-standing diamond film has a warp of 10 μm or less at least within a width of 10 mm. Is desirable.

[0048]

Example 1 A disk-shaped substrate made of single crystal (100) Si, having a diameter of 50 mm and a thickness of 1 mm was used, and the surface thereof was partially scratched as described below, and then a hot filament was used. CV
Diamond was synthesized by the D method.

That is, as shown in FIG. 1, in the process of scratching the substrate 5, a region of 3 mm from the outer periphery is covered with a jig made of Mo in advance so that the scratching process is not performed, and the exposed surface is removed. It was treated with # 2000 diamond powder by brush for about 5 minutes. The ratio S1 / S2 of the area S1 of the outer peripheral side portion 1 which is not scratched and the area S2 of the portion (center side portion) 2 which is scratched is 0.29.
Met.

This substrate was placed on a cooled substrate support just below the filament, and the pressure in the synthesis container was 13.3 kPa.
(100 Torr), the distance between the filament and the substrate surface is 8 mm, the filament temperature is 2100 ° C., the hydrogen flow rate is 1000 cc / min, and the methane flow rate is 20 cc / m.
In, diamond was synthesized for 30 hours under the condition that the substrate temperature was 800 ° C.

After synthesizing the diamond, as shown in FIG. 2, a diamond film 7 having a film thickness of 22 μm was synthesized on the portion (center side portion) 2 of the substrate 5 on which the scratching treatment was performed. In the outer peripheral side portion (unprocessed portion) 1 which has not been performed, the film thickness is 10 μm at maximum, and there are portions where the diamond grains 8 do not become film-like or are not deposited at all, and are formed on the side surface of the substrate 5. Almost no diamond was deposited.

When the warp of the back surface of the substrate 5 with the diamond film 7 was measured, the back surface was convex (the surface of the synthetic diamond was concave), and the warp was 1 in the range of 40 mm.
It was 0 μm.

Example 2 A substrate made of single crystal (100) Si, having a diameter of 50 mm and a thickness of 0.5 mm, was used, and 5 mm from the outer periphery of its surface.
The region was partially damaged in the same manner as in Example 1, and then diamond was synthesized by the hot filament CVD method. The ratio S1 / S2 of the area S1 of the outer peripheral side portion which was not scratched and the area S2 of the portion (center side portion) which was scratched was 0.56.

This substrate was placed on the cooled substrate support immediately below the filament, and the pressure in the synthesis container was 13.3 kpa.
(100 Torr), the distance between the filament and the substrate surface is 8 mm, the filament temperature is 2100 ° C., the hydrogen flow rate is 1000 cc / min, and the methane flow rate is 10 cc / m.
Diamond was synthesized for 50 hours under the conditions of substrate temperature of 750 ° C.

After synthesizing the diamond, a diamond film having a film thickness of 18 μm was synthesized on the portion (center side portion) where the substrate was scratched, but the outer peripheral portion (untreated portion) where the scratch treatment was not performed. In (1), most of the diamond film was not deposited, and almost no diamond was deposited on the side surface of the substrate. When the warp of the back surface of the substrate with the diamond film attached was measured,
The back surface was convex and the warp was 35 μm in the range of 40 mm.

Example 3 Two substrates each made of single crystal (100) Si and having a diameter of 25 mm and a thickness of 5 mm were used.
The region was partially damaged in the same manner as in Example 1, and then diamond was synthesized by the hot filament CVD method. The ratio S1 / S2 of the area S1 of the outer peripheral side portion not subjected to the scratching treatment and the area S2 of the portion (center side portion) subjected to the scratching treatment was 0.73.

The two substrates were placed on a cooled substrate support immediately below the filament, and the pressure in the synthesis container was set to 13.3.
kpa (100 Torr), the distance between the filament and the substrate surface is 8 mm, the filament temperature is 2100 ° C., the hydrogen flow rate is 1000 cc / min, and the methane flow rate is 20 c.
Diamond was synthesized for 200 hours under the conditions of c / min and substrate temperature of 700 ° C.

After the diamond is synthesized, the film thickness of the diamond film synthesized on the scratched portion (center side portion) of the two substrates is 140 μm and 120 μm, and the outer circumference is not scratched. The thickness of the diamond film in the side portion (untreated portion) was less than the average of the thickness of the central portion, and almost no diamond was deposited on the side surface of the substrate.

When the warp of the back surface of the substrate with the diamond film was measured, the back surface was convex (the surface of the synthetic diamond was concave), and the warp was 15 μm in the range of 20 mm.
m and 11 μm. After that, the Si substrate was dissolved and removed to obtain a diamond freestanding film, and the warps of the two diamond freestanding films were 23 μm and 13 μm in the range of 20 mm, respectively.

Comparative Example 1 A disk-shaped substrate made of single crystal (100) Si, having a diameter of 50 mm and a thickness of 1 mm, was used as in Example 1, and the entire surface thereof was subjected to the same scratch treatment as in Example 1. After doing
Diamond was synthesized by the hot filament CVD method under the same conditions as in Example 1.

The obtained diamond film had a thickness of 25 μm in the central portion of the substrate, but was thick in the outer peripheral side portion, and particularly 32 μm at the outermost peripheral edge portion of the substrate. Further, when the warp of the back surface of the substrate was measured, the back surface was convex (the surface of the diamond film was concave), and the warp was 120 μm in the range of 40 mm.

The film quality of the obtained diamond was poor,
Raman spectroscopic analysis showed many non-diamond carbon components. This is because the substrate warps greatly during diamond synthesis,
This is because the thermal contact on the back surface of the substrate deteriorates and the substrate temperature rises as a result.

Comparative Example 2 A substrate made of single crystal (100) Si and having a diameter of 50 mm and a thickness of 0.5 mm was used. The entire surface of the substrate was subjected to a scratch treatment in the same manner as in Example 1 and then, as Example 2. Diamond was synthesized by the thermal filament CVD method under the same conditions.

The obtained diamond film was greatly warped, and the diamond film was partially peeled off. This is because the substrate was greatly warped due to the large stress and the thin substrate thickness, the thermal contact was further deteriorated, and the substrate temperature rose, and the stress more than the adhesion strength between the substrate surface and the synthetic diamond worked. is there.

Comparative Example 3 Two substrates made of single crystal (100) Si and having a diameter of 25 mm and a thickness of 5 mm were used, and the entire surface thereof was subjected to a scratching treatment in the same manner as in Example 1 and then as Example 3. Diamond was synthesized by the hot filament CVD method under the same conditions.

Of the two diamond films obtained, 1
The diamond film and the substrate were peeled off from each other, and the diamond film was a poor diamond film having a large amount of non-diamond components. The other one had no peeling of the diamond film, but the film thickness at the central part was 165 μm, whereas the film thickness at the outer peripheral side, especially at the substrate edge, was 200 μm or more, and the warp on the back surface of the substrate was It was extremely large at 55 μm.

Attempts were made to polish the surface of this synthetic diamond, but only the outer peripheral portion was polished, and even after polishing for 200 hours, it was only partially polished, and the entire surface was abandoned. After that, the Si substrate was dissolved and removed to obtain a diamond free-standing film, but a hexagonal crack was formed on the substrate surface side of the free-standing film, resulting in a defective product.

Example 4 A disk-shaped substrate made of single crystal (100) Si, having a diameter of 50 mm and a thickness of 3 mm was used, and the surface thereof was partially covered with a frame-shaped plate material as described below, and then a hot filament was used. CVD
Diamond was synthesized by the method.

That is, as shown in FIGS. 3 and 4, the substrate 5
After the entire surface of the substrate was scratched in the same manner as in Example 1, a 2 mm region from the outer periphery of the substrate 5 was covered with a frame-shaped plate member 6 made of Mo. The ratio S3 / S4 of the area S3 of the outer peripheral side portion 3 covered by the Mo frame-shaped plate member 6 of the substrate 5 and the area S4 of the uncovered portion (center side portion) 4 is 0.18.
Met.

This substrate was placed on the cooled substrate support just below the filament, and the pressure in the synthesis container was 13.3 kPa.
(100 Torr), the distance between the filament and the substrate surface is 7 mm, the filament temperature is 2150 ° C., the hydrogen flow rate is 1000 cc / min, and the methane flow rate is 30 cc / m.
In, diamond was synthesized for 100 hours under the condition that the substrate temperature was 800 ° C.

Frame-shaped plate material 6 made of Mo after synthesis of diamond
5, the diamond film 7 does not exist on the outer peripheral side portion 3 and the side surface portion of the substrate 5 which are covered with the Mo frame-shaped plate member 6, and the substrate 5 is covered with the frame-shaped plate member 6, as shown in FIG. The maximum film thickness is 1 in the non-exposed part (exposed center part) 4.
A 25 μm diamond film 7 was synthesized. In addition, almost no diamond was deposited on the frame-shaped plate member 6 made of Mo.

When the warp of the back surface of the substrate 5 with the diamond film 7 was measured, it was found that the warp of the back surface of the substrate was convex even though the stress was considerably large.
It was 23 μm in the range of 0 mm. Further, since the substrate was less warped, the obtained synthetic diamond film 7 was of high quality in which almost no non-diamond carbon component was observed. Thereafter, the substrate 5 was dissolved and removed to obtain a freestanding diamond film, and the warp of the freestanding film was 36 μm in the range of 40 mm.

Example 5 A disk-shaped substrate made of single crystal (100) Si and having a diameter of 50 mm and a thickness of 5 mm was used. After the entire surface was scratched as in Example 4, the substrate was removed from the outer periphery. A 2 mm area was covered with a frame plate made of Mo. The ratio S3 / S4 of the area S3 of the outer peripheral side portion of the substrate covered with the Mo frame-shaped plate material to the area S4 of the uncovered portion (center side portion) is 0.1.
It was 8.

This substrate is placed on a cooled substrate support of a DC plasma jet CVD apparatus having a structure of one cathode and two anodes, and the frame-shaped plate material is fixed to the substrate support by screws, so that the heat generated by the warp is generated. I tried to prevent the deterioration of contact. After that, the pressure in the synthesis container is 1.33 kPa (10 Torr).
And argon flow rate 5000 cc / min, hydrogen flow rate 2
Diamond was synthesized for 80 hours under the conditions of 000 cc / min, methane flow rate of 20 cc / min, and substrate temperature of 750 ° C.

When the Mo frame-shaped plate material was removed after the diamond was synthesized, the diamond film was not present on the outer peripheral side portion and the side surface portion of the substrate covered with the Mo frame plate material,
The maximum film thickness is 4 in the center side that was exposed without being covered.
A 10 μm diamond film was synthesized.

When the warp of the back surface of the substrate with the diamond film was measured, it was found that the warp was convex on the back surface and was 15 μm in the range of 40 mm in spite of the synthesis condition in which the stress was considerably large. Further, although the DC plasma jet CVD method has a film thickness distribution peculiar to it, thermal contact with the back surface of the substrate was good, and thus the obtained synthetic diamond film was of high quality in which almost no non-diamond carbon components were observed.
Then, the substrate was dissolved and removed to obtain a freestanding diamond film, and the freestanding film had a warp of 25 μm in a range of 40 mm.

Example 6 A disk-shaped substrate made of single crystal (100) Si and having a diameter of 50 mm and a thickness of 1 mm was used, and after the entire surface thereof was scratched in the same manner as in Example 4, from the outer periphery of the substrate. By masking the 1 mm area and depositing SiO ₂ ,
Covered with SiO ₂ coating. The ratio S3 / S4 of the area S3 of the outer peripheral side portion of the substrate covered with the SiO ₂ coating and the area S4 of the uncovered portion (center side portion) is 0.0.
It was 85.

This substrate was placed on a cooled substrate support table just below the filament of a hot filament CVD apparatus, the pressure of the synthesis container was 13.3 kPa (100 Torr), the distance between the filament and the substrate surface was 7 mm, and the filament temperature was 2100 ℃, hydrogen flow rate 1000cc / m
in, methane flow rate 20 cc / min, substrate temperature 750 ° C.
Diamond was synthesized under the conditions of 30 hours.

When the SiO ₂ coating was removed after the synthesis of diamond, the diamond film did not exist on the outer peripheral side portion and side surface portion of the substrate covered with the SiO ₂ coating, and the central side portion which was exposed without being covered. A diamond film having a maximum film thickness of 25 μm was synthesized.

When the warp of the back surface of the substrate with the diamond film was measured, it was found that the back surface was convex and
It was extremely small at 8 μm in the range of 0 mm. After that, the substrate was dissolved and removed to obtain a self-supporting diamond film. The warp of the self-supporting film was as small as 12 μm in the range of 40 mm, and it was found that the free-standing diamond film was good.

Example 7 A disk-shaped substrate made of single crystal (100) Si and having a diameter of 25 mm and a thickness of 3 mm was used. An area of 1 mm from the outer circumference was covered with a SiO ₂ coating. Area S3 of the outer peripheral side portion of the substrate covered with the SiO ₂ coating
And the ratio S of the area S4 of the uncovered part (center side part)
3 / S4 was 0.18.

This substrate was placed on the substrate support of the microwave CVD apparatus, and a pressure of −150 V (40 Torr) was applied to the synthesis container while a bias voltage of −150 V was applied to the substrate.
r), microwave output 800 W, hydrogen flow rate 200 cc /
min, methane flow rate 6 cc / min, substrate temperature 900 ° C
Bias processing was performed for 15 minutes under the conditions.

Next, the pressure in the synthesis container was set to 6.7 kPa (5
0 Torr) and hydrogen flow rate 1000 cc / mi
Diamond was synthesized by microwave CVD for 100 hours under the conditions of n, methane flow rate of 4 cc / min, and substrate temperature of 900 ° C.

When the SiO ₂ coating was removed after the diamond was synthesized, the outer peripheral side portion and the side surface portion of the substrate covered with the SiO ₂ coating did not have a diamond film, and the central side portion which was exposed without being covered. A diamond film having a maximum film thickness of 145 μm was synthesized.

When the warp of the back surface of the substrate with the diamond film was measured, the warp was concave on the back surface (convex on the diamond surface) and was 20 m even though the film thickness was thick.
It was 12 μm in the range of m. When this diamond film was polished, the entire surface could be polished in 10 hours.
After that, the substrate was dissolved and removed to obtain a free-standing diamond film, but the free-standing film had a small warp of 17 μm in the range of 20 mm, and it was found that the free-standing diamond film was good.

[0086]

According to the present invention, it is possible to reduce the warp of the synthetic diamond synthesized on the substrate by the vapor phase synthesis method, and further to reduce the warp of the diamond free-standing film from which the substrate has been removed.

Since the synthetic diamond having a small amount of warp has good thermal contact with the substrate support or the like during the synthesis, defective synthesis such as peeling of the film or generation of cracks is reduced, and high-quality synthetic diamond is efficiently synthesized. can do.

Further, the synthetic diamond and the self-supporting diamond film having less warpage can be expected to improve the yield in the subsequent processing process such as polishing or device process such as pattern baking, and thus can reduce the total cost of the synthetic diamond application product. It is extremely effective.

[Brief description of drawings]

FIG. 1 is a front view of a substrate that is partially scratched except for an outer peripheral side portion.

FIG. 2 is a cross-sectional view showing a state in which diamond is synthesized on the substrate of FIG.

FIG. 3 is a front view of a substrate in which an outer peripheral side portion is covered with a frame-shaped plate material.

FIG. 4 is a cross-sectional view of the substrate of FIG. 3 in which an outer portion is covered with a frame-shaped plate material.

5 is a cross-sectional view showing a state where the frame-shaped plate material is removed after synthesizing diamond on the substrate of FIG.

FIG. 6 is a cross-sectional view showing a state in which diamond is synthesized on a substrate whose entire surface is scratched.

FIG. 7 is a cross-sectional view for explaining warpage of diamond synthesized on a substrate.

FIG. 8 is a graph showing the relationship between stress and warpage of diamond.

FIG. 9 is a graph showing the relationship between substrate thickness and warpage.

[Explanation of symbols]

 1 Peripheral side part that is not scratched 2 Part that is scratched 3 Peripheral side part that is covered by frame-shaped plate material 4 Part that is not covered by frame-shaped plate material 5 Substrate 6 Frame-shaped plate material 7 Diamond film 8 diamond grains

Claims (9)

[Claims] 1. A method for vapor phase synthesis of diamond in which a source gas containing carbon is activated to deposit diamond on the surface of a heated substrate, wherein the outer peripheral portion of the surface is not scratched, and the portion other than the outer peripheral portion is not treated. A method for synthesizing diamond, which comprises synthesizing diamond using a substrate that has been subjected to a scratch treatment. 2. The area S1 of the outer peripheral side portion where the substrate is not scratched and the area S2 of the portion where the substrate is scratched have a relationship of 0.0001 ≦ S1 / S2 ≦ 1. The method for synthesizing diamond according to claim 1, wherein 3. A method for vapor phase synthesis of diamond in which a source gas containing carbon is activated to deposit diamond on the surface of a heated substrate, the diamond is synthesized using a substrate whose outer peripheral portion is covered with a heat resistant material. A method for synthesizing diamond, which comprises: 4. A diamond is synthesized by using a substrate having a heat-resistant material covering the outer peripheral side portion of the substrate surface whose entire surface is scratched, or the outer peripheral side portion of the surface not being scratched is treated. The method for synthesizing diamond according to claim 3, wherein the substrate is covered with a heat resistant material, and the diamond is synthesized after applying a bias voltage. 5. The heat-resistant material is coated on the outer peripheral side portion of the substrate surface, or the outer peripheral side portion is held in thermal contact with a frame-shaped plate material of the heat resistant material.
The method for synthesizing diamond according to claim 3 or 4. 6. The area S3 of the outer peripheral side portion of the substrate surface covered with the heat resistant material and the area S4 of the uncovered portion are
The method of synthesizing diamond according to claim 3, wherein the relationship of 0.0001 ≦ S3 / S4 ≦ 1 is satisfied. 7. The stress σ of the synthetic diamond, the elastic modulus E of the substrate, the Poisson's ratio v, the thickness D of the substrate and the synthetic diamond film thickness d are [E / (1-v)] × [D ² / 6σd] ≧ The diamond synthesizing method according to claim 1 or 3, wherein the diamond is synthesized under a condition satisfying a relationship of 1.25 m 2. 8. A synthetic diamond formed on a portion of a substrate surface excluding an outer peripheral side portion, wherein diamond is not deposited on the outer peripheral side portion, or the deposited diamond has a film thickness of the synthetic diamond. Synthetic diamond characterized by being thinner than. 9. A synthetic diamond as a self-supporting film obtained by removing the substrate from the synthetic diamond according to claim 8, which has a warp of 10 mm in length.
Synthetic diamond characterized by having a size of less than μm.