JPH06172089A - Synthesis of diamond - Google Patents

Abstract

PURPOSE:To provide a process for producing a thick diamond single crystal layer having high uniformity and quality by keeping the epitaxial growth by vapor-phase synthesis over a long period. CONSTITUTION:Epitaxial growth of a diamond film is carried out by using a substrate having a main growth plane deviated from the {100} plane by <=10 deg. and alternately repeating a process to grow a diamond layer of 0.1-300mum thick under a condition of A>=1.5% wherein A (=[C]/[H]) is ratio of carbon element to hydrogen element in vapor phase and a process to grow a diamond layer of 0.1-300mum thick under a condition of A<1.5%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing diamond, and more particularly to a method for producing large diamond single crystals used for cutting tools, abrasion resistant tools, precision tools, semiconductor materials, electronic parts, optical parts and the like. .

[0002]

2. Description of the Related Art Conventionally, relatively large area diamonds have been artificially produced on various substrates by a vapor phase synthesis method, but these are polycrystalline films and large area single crystals have not been obtained. . However, among diamond applications, single crystal diamond is required when it is used for ultra-precision tools, optical parts, semiconductors, etc., which require a particularly smooth surface. Therefore, the conditions for epitaxial growth of a single crystal by the vapor phase synthesis method have been studied, and further, the method for producing a large area single crystal by the vapor phase synthesis method has been studied.

It has been known for a long time that a diamond single crystal layer can be relatively easily grown by homoepitaxial growth by using a diamond single crystal as a substrate in diamond vapor phase synthesis. However, in order to obtain a diamond layer having a sufficient thickness even by such homoepitaxial growth, it is necessary that the epitaxial growth be maintained during growth, that is, the grown crystal should have exactly the same crystal orientation as the underlying crystal. Is.

However, it has been a serious problem that as the growth progresses, the amount of components in which the epitaxial relationship between the original substrate crystal and the grown crystal is lost increases. That is, a part of which the orientation is deviated from that of the substrate is formed, and polycrystallization progresses from this part. Therefore, the problem is that defects increase in the crystal as the epitaxial layer becomes thicker. Such non-epitaxial components (hereinafter abbreviated as abnormal growth) are caused by small diamond particles generated during polishing of the substrate surface, secondary nucleation on the growth surface, and {11
1} Twin crystals are formed.

In order to suppress abnormal growth in epitaxial growth, it has hitherto been known that growth can be continued while maintaining a flat single crystal surface by growing a relatively high carbon concentration on the {100} plane. . (For example, JP-A-2-233591) However, when a thick epitaxial layer having a thickness of 20 μm or more is grown under such a high carbon concentration condition, there is a problem that diamond containing a large amount of non-diamond components easily grows in the diamond crystal. Furthermore, since a large diamond single crystal having a diameter of 1 cm or more is extremely expensive, it has been difficult to obtain a good quality large single crystal diamond even by homoepitaxy of diamond.

There are roughly two methods for growing a large area single crystal diamond by vapor phase synthesis. The first method is heteroepitaxial growth. That is, a large area single crystal is obtained by epitaxially growing diamond on a single crystal substrate of a material capable of preparing a large single crystal substrate by a vapor phase synthesis method. For example, as a substrate on which diamond is heteroepitaxially grown, cubic boron nitride (cB) has hitherto been used.
N), silicon carbide, silicon, nickel, cobalt and the like have been reported (JP-A-63-224225, JP-A-2-2).
33591, JP-A-4-132687).

However, for nickel and cobalt, although island-shaped diamond is epitaxially grown, it is difficult to obtain a continuous film of diamond single crystal, and the problem caused by homoepitaxy occurs more significantly on any substrate, and abnormal growth occurs. Is known to occur in large numbers.

Therefore, a second method that does not use heteroepitaxy has been considered. These are techniques based on the growth of diamond on a diamond substrate, ie homoepitaxial growth. For example, in the case of diamond, a method of arranging mm-order diamond single crystals by a high-pressure synthesis method with aligned orientations to obtain an integrated single crystal diamond (JP-A-3-075298), which is used as an abrasive grain, A method of arranging particles of about several tens to 100 μm on a selectively etched Si substrate and growing diamond on it (MWGeis HISmith A. Argoit
ia J. Angus GHMMa JTGlass J. Butler CJ Robinso
n R. Pryor, Appl. Phys. Lett., Vol.58, (1991), p2485).

In such a method, if the epitaxial growth can be maintained for the crystal substrate grown by the vapor phase synthesis method, even if the grain boundaries exist at the boundaries between the diamond layers grown from the adjacent single crystals of the substrates, they become minute angular grain boundaries. It is possible to obtain a large-area crystal having characteristics electrically and optically comparable to a single crystal. However, even with these methods, the problems caused by homoepitaxy are naturally left in the same manner, and at the boundary between the single crystals of the substrate, it is more than that when homoepitaxial growth is performed on one single crystal. It is known that abnormal growth occurs at a density of.

The reason why it is difficult to maintain homoepitaxial growth of a diamond single crystal for a long time is considered as follows. For example, considering homoepitaxial growth on the diamond {100} plane, the growth direction is uniformly <100> when complete homoepitaxial growth is maintained. However, when an abnormal region (3 in FIG. 2) facing another direction is formed for some reason, the growth direction is no longer <100>.

If the growth rate of the abnormal region is <1
When the growth rate of 00> is exceeded, the region gradually grows as shown in FIG. 2, and this causes polycrystallization. Abnormal growth can be suppressed by growing under the condition that the growth rate of {100} is relatively fast (abbreviated as {100} orientation condition), but under this condition, the film quality is very good as evaluated by Raman spectroscopy and infrared absorption spectrum. I know it's not. That is, even if a single crystal is obtained, a high quality crystal cannot be expected.

In general, a single crystal grown by the CVD method,
It is known that the diamond quality is improved when the polycrystalline carbon concentration is low, or when oxygen, carbon dioxide, or water is added. However, this condition corresponds to the case where the growth rate of <100> described above is slower than in other directions, and once an abnormal region is formed, the epitaxial growth state is lost as the growth proceeds. That is, the {100} substrate is a preferable substrate for diamond epitaxial growth, but only an epitaxial film which maintains the crystal orientation but is inferior in crystallinity or a film which is good in crystallinity but includes abnormal growth has been known.

[0013]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, maintains the epitaxial growth of diamond by the vapor phase synthesis method for a long time, has little abnormal growth, has good crystallinity, and has a uniform and high-quality thickness. An object of the present invention is to provide a method for producing a film diamond single crystal layer.

[0014]

[Means for Solving the Problems] When epitaxially growing diamond from a vapor phase on a single crystal substrate, the {100} plane is used as a main growth surface, and the epitaxial growth is performed under the condition that {100} growth easily occurs, that is, carbon. And a hydrogen ratio A (A = [C] / [H]) of 1.5% or more to grow a diamond layer of 0.1 μm or more and 300 μm or less, and a low carbon concentration condition, that is, A is 1.
Diamond is grown by alternately repeating the process of growing a diamond layer of less than 5% and having a thickness of 0.1 μm or more and 300 μm or less.

Here, the ratio of carbon and hydrogen is an effective ratio. That is, when oxygen is added to the source gas at any stage of growth, B = ([C] − [O]) / [H] is calculated from the element amounts of carbon, hydrogen and oxygen in the vapor phase.
The ratio B determined by is the effective carbon concentration. Other than the method of growing while repeating the change of the carbon concentration, the same effect can be obtained by alternately repeating the conditions of the growth temperature of 1100 ° C. or higher and 1000 ° C. or lower.

In addition to single crystal diamond, the substrate is a single crystal of cubic boron nitride, silicon carbide, silicon, germanium or an alloy of silicon and germanium, or one or more selected from nickel, copper, cobalt and iron. A single crystal of a metal or an alloy containing two or more kinds as main components can be used.

[0017]

As a result of earnest studies, the inventors of the present invention have maintained high quality and abnormal growth by periodically performing growth under {100} orientation conditions that suppress abnormal growth and growth under conditions that give high quality diamond. It has been found that epitaxial growth with suppressed crystal growth can be obtained. The growth condition characterized by having the effect of suppressing abnormal growth is called the first condition, and the growth condition characterized by having good crystallinity is called the second condition.

If the thickness of the epitaxial layer grown under the first condition is less than 0.1 μm, there is no effect of suppressing abnormal growth, so 0.1 μm or more is necessary, and more preferably 3 μm or more. Even under the first condition, when the thickness is 20 μm, diamond can be grown while maintaining the quality of the underlying diamond layer. However, when it exceeds 20 μm, non-diamond carbon is mixed into the crystal, and when it exceeds 300 μm, deterioration in characteristics as a semiconductor or an optical material is observed. Therefore, it is necessary to be 300 μm or less.

Under the first condition, if the ratio of carbon (C) to hydrogen (H) ([C] / [H]) in the gas is less than 1.5%, there is no effect of suppressing abnormal growth. % Or more, and more preferably 4 to 8%. When the carbon concentration exceeds 8%, the amount of non-diamond carbon mixed in increases, and at most 15% or less is a preferable range.

When a gas containing oxygen (O) is used, the difference between carbon and oxygen and the ratio of hydrogen ([C]-[O]) /
It suffices that the effective carbon concentration represented by [H] is 1.5% or more.

Further, if the thickness of the epitaxial layer grown under the second condition is less than 0.1 μm, there is no effect of maintaining high quality, so more is required, more preferably 15 μm.
That is all. However, if it exceeds 50 μm, abnormal growth is observed, and if it exceeds 300 μm, deterioration of characteristics as a semiconductor or an optical material is observed. Therefore, it is necessary to be 300 μm or less. Under the second condition, the ratio of carbon (C) hydrogen (H) ([C] / [H]) in the gas is 1.5%.
Since the crystallinity is deteriorated by the above, it is desirable to set it to less than 1.5%, more preferably 0.5 to 1.5%.

When a gas containing oxygen (O) is used, the difference between carbon and oxygen and the ratio of hydrogen ([C]-[O]) /
It is sufficient that the effective carbon concentration represented by [H] is less than 1.5%.

Further, instead of changing the carbon concentration ratio, the same effect can be obtained by changing the substrate temperature during growth to 1100 ° C. or higher under the first condition and to 1000 ° C. or lower under the second condition. It is also possible to combine the method of changing the effective carbon concentration and the method of changing the substrate temperature, and a more remarkable effect can be obtained.

The substrate used is most preferably diamond single crystal or cubic boron nitride, but may be silicon having a diamond structure, germanium or its alloy,
As the silicon carbide, both cubic and hexagonal crystal types can be used, and cubic single crystals of nickel, copper, cobalt, iron and alloys thereof are preferably used.

Whether the substrate used is a diamond single crystal or a semiconductor or metal single crystal other than diamond, it is polished close to the cubic {100}, {111}, and {110} crystal faces. It is desirable to grow the raised surface as the main surface of the single crystal substrate. However, the {100} plane is most preferable as the crystal plane, and the deviation from {100} is preferably within 10 degrees, more preferably within 2 degrees. Abnormal growth increases as the angle of deviation increases, and if it exceeds 10 degrees, polycrystalline components increase, which is not preferable.

In the vapor phase synthesis method of diamond, it is possible to control the characteristics of diamond by supplying elements other than carbon, hydrogen and oxygen to mix a small amount of impurities into diamond. In particular, boron, nitrogen, phosphorus, etc. are important as impurities for controlling the electrical and optical properties of diamond. However, since nitrogen also causes deterioration of crystallinity of diamond, it is preferable to mix nitrogen in the process of etching and growth at a [N] / [C] ratio of 500 ppm or less.

The single crystal substrate is preferably etched before the diamond is grown in the vapor phase. In the case of diamond, boron nitride, silicon carbide, silicon, or germanium, it can be carried out in an atmosphere containing active hydrogen or oxygen used when growing diamond. When a single crystal of a metal such as nickel is used, etching is not performed with oxygen or hydrogen, and therefore etching can be performed in an atmosphere containing halogen such as fluorine or chlorine. If the thickness of the substrate to be removed by etching is less than 1 nm, there is no effect, and in order to completely remove scratches and dust on the substrate surface,
It is more preferable to perform etching of 0 nm or more.

Since the method of the present invention can suppress the abnormal growth and the occurrence of defects even in the heteroepitaxial growth using a substrate other than diamond and the method using a plurality of single crystals as a base material, it is very effective and large. It is possible to manufacture a diamond that can be put to practical use as a diamond equivalent to a single crystal diamond having an area.

The present invention uses a thermal CVD method, a plasma CVD method, a laser CVD method, which is a known vapor phase synthesis process.
Any method such as the ion beam method is effective.

[0030]

【Example】

(Example 1) In this example, an Ib type diamond single crystal artificially synthesized by an ultrahigh pressure method was sliced and polished, and used as a substrate. Five substrates having a substrate plane orientation of {100} were prepared. The substrate size is 2 mm × 3 mm, and the thickness is 0.3 mm. It was confirmed by backscattered electron diffraction that the plane orientation deviation of all substrates was 1 degree or less.

The growth was performed by a microwave plasma CVD method. Hydrogen (H ₂ ) 100 sccm, methane (CH ₄ )
A process of growing at 10 sccm and a substrate temperature of 850 ° C. for 10 hours (ratio A = 4.2%) and a process of growing at 100 sccm of hydrogen, 2 sccm of methane and a substrate temperature of 1000 ° C. for 30 hours (ratio A = 1.0%). 10 times, 40 in total
It was grown for 0 hours. As a result, abnormal growth was not seen on the growth surface, the spectrum by Raman spectroscopy signals of the diamond are sharp in 1332 cm ^-1 (half width <2 cm ^-1) and strong (S / B <signal / background >ratio> 1000) I was seen.

Further, no signal of amorphous carbon which should appear near 1580 cm ^-1 was observed. When the cross section of the growth layer was observed with a scanning electron microscope, it was found that methane of 10 sc
The layer grown for 10 hours in cm has a thickness of 12 μm per time,
It was found that the layer grown at 2 sccm of methane under the second condition for 30 hours had a thickness of 25 μm per time.

(Comparative Example 1) The same substrates as in Example 1, that is, five Ib {100} substrates artificially synthesized by the ultrahigh pressure method were used. Substrate size is 2mm x 3mm,
The thickness is 0.3 mm. It was confirmed by backscattered electron diffraction that the plane orientation deviation of all substrates was 1 degree or less. 100 sccm hydrogen by microwave plasma CVD method,
It was grown for 400 hours at 10 sccm of methane and a substrate temperature of 850 ° C. As a result, no abnormal growth was observed on the growth surface, but in the spectrum by Raman spectroscopy, the diamond signal was broad (half-width = 6 cm ^-1 ) and a strong background was observed, and the S / B ratio was 2 It was .5.

(Comparative Example 2) The same substrates as in Example 1, that is, five Ib {100} substrates artificially synthesized by the ultrahigh pressure method were used. Substrate size is 2mm x 3mm,
The thickness is 0.3 mm. It was confirmed by backscattered electron diffraction that the plane orientation deviation of all substrates was 1 degree or less. 100 sccm hydrogen by microwave plasma CVD method,
It was grown at a methane of 2 sccm and a substrate temperature of 1000 ° C. for 400 hours. As a result, abnormal growth was observed on the growth surface, and it was found that polycrystallization was advanced by X-ray diffraction.

Example 2 In this example, substrates obtained by slicing and polishing an Ib type diamond single crystal artificially synthesized by the ultra-high pressure method and slicing and polishing a natural type IIa diamond were used as substrates. Using. Three substrates each having a substrate plane orientation of {100} were prepared. The substrate size is 2 mm × 3 mm, and the thickness is 0.3 mm. It was confirmed by backscattered electron diffraction that the plane orientation deviation of each of the substrates was 0.5 degrees or less.

The growth was performed by the microwave plasma CVD method. Hydrogen (H ₂ ) 100 sccm, methane (CH ₄ )
A process of growing for 20 hours at a substrate temperature of 950 ° C. with the same gas component as the process of growing for 20 hours at 3 sccm and a substrate temperature of 1200 ° C. was grown 10 times, for a total of 400 hours. As a result, no abnormal growth was observed on the growth surface, and the Raman spectrum showed a sharp diamond signal (half-value width <
2.5 cm ⁻¹ ) and strongly (S / B ratio> 1000). Also, no signal of amorphous carbon was observed. It was found that the layer under the first condition had a thickness of 30 μm per time, and the layer under the second condition had a thickness of 24 μm per time.

Example 3 An Ib type diamond single crystal artificially synthesized by an ultrahigh pressure method was sliced and polished, and used as a substrate. Three substrates having a substrate plane orientation of {100} were prepared. Substrate size is 2mm x 4m
m and the thickness is 0.3 mm. It was confirmed by backscattered electron diffraction that the plane orientation deviation of all substrates was 2 degrees or less.

The growth was performed by the microwave plasma CVD method. Hydrogen (H ₂ ) 100 sccm, methane (CH ₄ )
12 sccm, carbon dioxide (CO ₂ ) ₂ sccm, substrate temperature of 950 ° C. for 5 hours for growth (ratio B = 4.
0), hydrogen (H ₂ ) 100 sccm, methane (CH ₄ )
8 sccm, carbon dioxide (CO ₂ ) 5 sccm, substrate temperature of 950 ° C. for 35 hours for growth (ratio B = 1.
3) was grown 10 times for a total of 400 hours.

As a result, no abnormal growth was observed on the growth surface, and the Raman spectrum showed that the diamond signal was sharp (half-width <2.0 cm ^-1 ) and strong (S / B ratio>).
1000) was seen. Also, no signal of amorphous carbon was observed. The first condition layer is 9μ thick
It was found that the layer under the second condition had a thickness of 28 μm per time.

Example 4 A substrate was prepared by slicing and polishing an Ib type diamond single crystal artificially synthesized by an ultrahigh pressure method. Two substrates having a substrate plane orientation of {100} were prepared. Substrate size is 2mm x 3m
m and the thickness is 0.3 mm. It was confirmed by backscattered electron diffraction that the plane orientation deviation of all substrates was 2 degrees or less.

The growth was performed by the microwave plasma CVD method. Hydrogen (H ₂ ) 100 sccm, methane (CH ₄ )
6 sccm, process of growing at a substrate temperature of 1150 ° C. for 15 hours (ratio A = 2.7%), and hydrogen (H ₂ ) 100 sc
cm, methane (CH ₄ ) 3 sccm, substrate temperature 830 ° C.
10 hours during the process of growing for 25 hours (ratio A = 1.4%)
Once, it was grown for a total of 400 hours.

As a result, no abnormal growth was observed on the growth surface, and the Raman spectrum showed that the diamond signal was sharp (half width <2.5 cm ^-1 ) and strong (S / B ratio>).
1000) was seen. Also, no signal of amorphous carbon was observed. The thickness of the layer under the first condition is 25μ per time.
It was found that the layer under the second condition had a thickness of 21 μm per time.

[0043]

According to the present invention, it is possible to easily obtain a thick film diamond single crystal which is homogeneous and has little abnormal growth. Since the growth is performed by the vapor phase synthesis method, it is possible to dope various kinds of diamond such as boron and nitrogen. Therefore, the diamond obtained by the manufacturing method of the present invention is a precision tool cutting edge, a wear resistant tool, a heat resistant tool,
Semiconductor substrate, heat dissipation substrate, high voltage phase semiconductor material, optical material,
It can be widely used as an acoustic diaphragm.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a single crystal grown by the method of the present invention without abnormal growth.

FIG. 2 is a growth example in which abnormal growth occurs according to a conventional method.

[Explanation of symbols]

 1: single crystal substrate 2: grown diamond single crystal layer 3: abnormally grown portion

Claims (6)

[Claims] 1. A {100} plane or {10} of a single crystal substrate.
A method of epitaxially growing diamond from a vapor phase containing at least carbon and hydrogen on a plane having a deviation from the 0} plane of 10 degrees or less, wherein the ratio of the element amounts of carbon and hydrogen in the vapor phase A (A = [C] /
A process of growing a diamond layer of 0.1 μm or more and 300 μm or less under the condition that [H]) is 1.5% or more, and a process of growing a diamond layer of 0.1 μm or more and 300 μm or less when A is less than 1.5%. A method for synthesizing diamond, which comprises repeating two or more different processes consisting of, at least alternately two or more times. 2. A {100} plane or a {10} plane of a single crystal substrate.
A method for epitaxially growing diamond from a vapor phase containing at least carbon and hydrogen on a plane having a deviation from the 0} plane of 10 degrees or less, wherein a raw material containing oxygen is added to the vapor phase at any stage of the growth. When supplied, the value B obtained from the elemental amounts of carbon, hydrogen, and oxygen in the gas phase
= ([C]-[O]) / [H]) is 1.5% or more, a process of growing a diamond layer of 0.1 μm or more and 300 μm or less and B is less than 1.5% and at least 0.1 μm. A method for synthesizing diamond, which comprises repeating a process of growing a diamond layer having a thickness of 300 μm or less and two or more different processes consisting of at least alternately two or more times. 3. A {100} plane or a {10} plane of a single crystal substrate.
A method for epitaxially growing diamond from a vapor phase containing at least carbon and hydrogen on a plane having a deviation from the 0} plane of 10 degrees or less, wherein a raw material containing oxygen is added to the vapor phase at any stage of the growth. When supplying, set the substrate temperature to 1100 ° C or higher and 0.1 μm or higher to 300
a step of growing a diamond layer of less than μm, a step of growing a diamond layer of 0.1 μm or more and 300 μm or less at a substrate temperature of 1000 ° C. or less, and repeating two or more different types of steps at least twice. A method for synthesizing diamond, which is characterized in that 4. The method for synthesizing diamond according to claim 1, 2 or 3, wherein the single crystal substrate is diamond. 5. The diamond according to claim 1, 2 or 3, wherein the single crystal substrate is a single crystal of an alloy whose main component is one or more selected from nickel, copper, cobalt and iron. Method of synthesis. 6. The single crystal substrate is a single crystal of cubic boron nitride, silicon carbide, silicon, germanium, or an alloy of silicon and germanium.
Alternatively, the method for synthesizing diamond according to 3 above.