JP6775771B2 - Microwave plasma CVD equipment and diamond synthesis method using it - Google Patents

Description

The present invention relates to the production of diamond by microwave plasma CVD, and in particular, uses a microwave plasma CVD apparatus capable of synthesizing diamond at a relatively large synthesis rate even under conditions where the plasma gas temperature is relatively low. Regarding the method of synthesizing the diamond and the synthesized diamond.

It is known that some of the physical property values of diamond are the highest levels among substances, and in particular, the figure of merit as a power semiconductor material is superior to that of Si, SiC and GaN. Since diamond has excellent optical properties, thermal properties, and mechanical properties, it is expected to be applied in various fields in addition to the electronics field including power semiconductors.

Regarding the production of diamond, after it was shown that diamond can be synthesized by the high temperature and high pressure method, diamond crystals are now produced all over the world by the high temperature and high pressure method. The high-temperature and high-pressure method has problems such as a small size that can be synthesized (general size is about 2 to 3 mm square) and a high manufacturing cost. In recent years, plasma CVD has been studied as a diamond manufacturing method. ..

For example, Patent Document 1 below discloses a method for producing diamond using pulsed microwave plasma. In this manufacturing method, a diamond substrate is placed in a decompressed cavity, and a diamond is laminated on the diamond substrate by supplying a pulsed microwave with a carbon source and a hydrogen source introduced. It is disclosed that the duty cycle (ratio of heating time in one cycle) of the microwave pulse is a value of 10 to 50%.

Patent Document 2 below discloses a method for producing a diamond film used as an electron emission source of a field emission display (FED) by chemical vapor deposition using pulsed microwaves. As the pulse oscillation conditions, a repetition frequency of 0.1 to 1 Hz and a pulse width of 1 to 10 seconds are disclosed. The diamond film thus obtained has a duty cycle of 17.5%, for example, as compared with the case of manufacturing using continuously oscillating microwaves, and has a current intensity of about 3 times higher at an electric field strength of 20 V / μm. Is recognized, and it is disclosed that high brightness can be generated when used as an electron emission source.

Patent Document 3 below discloses a method for producing diamond using pulsed microwave plasma. In order to solve the problem that the microwave becomes unstable due to the time when the microwave is not input when the microwave is controlled on and off in a pulse shape, this manufacturing method has a predetermined non-zero power and a maximum power. The microwave is repeatedly pulsed with and from, and the microwave is supplied without interruption. Specifically, it is disclosed that the maximum power is changed while keeping the average power constant by using a microwave of 2.45 GHz and changing the duty ratio at a modulation pulse frequency of 10 Hz. Since the average power correlates with the temperature of the base material heated by microwaves and the maximum power correlates with the degree of excitation of the raw material gas, it is possible to control the temperature of the base material and the degree of excitation of the raw material gas individually. It is disclosed. As an example, a 10-hour synthesis yielded diamond with a film thickness of 20 μm or 27 μm in the case of a silicon nitride ceramic substrate, and diamond with a film thickness of 18 μm or 24 μm in the case of a cemented carbide substrate. Is disclosed.

Further, when synthesizing diamond by microwave plasma, a flow of a raw material gas (activated gas) to a substrate (hereinafter, also referred to as forced convection) is formed in a reactor (chamber), thereby synthesizing diamond. Is known to be able to increase. For example, in Patent Document 4, a gas circulation path in the reactor is provided outside the reactor, and the gas is circulated by a blowing means (high-speed recirculation pump or blower), so that the gas directed to the substrate in the reactor It is disclosed to form a flow. Patent Documents 5 and 6 disclose that a plurality of nozzles having a small diameter are arranged in an upper part of a chamber, and gas is supplied through the nozzles to form a gas flow toward a substrate in the chamber. There is.

Special Table 2006-513123 Japanese Unexamined Patent Publication No. 2000-247784 Japanese Unexamined Patent Publication No. 6-256952 Japanese Unexamined Patent Publication No. 4-259378 Japanese Patent Application Laid-Open No. 2014-503835 U.S. Patent Application Publication No. 2010/018924

Problems in diamond synthesis by microwave plasma CVD include low synthesis rate and too high plasma gas temperature. In order to improve the synthesis rate, it is known that the pressure of the raw material gas is increased, a high electric power is supplied to raise the gas temperature of the plasma, and nitrogen gas is introduced.

By supplying a few kW of electric power, the gas temperature of the plasma becomes 3000 ° C. or higher. Usually, the substrate on which diamond is grown is controlled to about 1000 ° C. or lower by a cooling function by a stage or the like on which the substrate is arranged. Since the distance from the substrate to the center of the plasma is at most several tens of mm, a temperature difference of several thousand degrees occurs at such a narrow interval, and it may be difficult to measure the substrate temperature itself. Temperature control is difficult. Further, when the temperature of the substrate is high, abnormal growth of crystals is likely to occur, so that the substrate temperature is preferably set low. Therefore, it is desired to realize a high synthesis rate when the gas temperature of the plasma is relatively low.

Further, in order to improve the synthesis speed, a synthesis method is also known in which the power density is improved by limiting the discharge region by increasing the gas pressure at the time of discharge and reducing the region where the supplied power is absorbed. ing. However, this method has a problem that the gas temperature of the plasma becomes extremely high. In addition, this method sacrifices the stability of the synthetic environment and the area that can be synthesized. That is, with this method, it is not possible to stably synthesize diamond having a large area with high efficiency.

These problems cannot be solved by the techniques disclosed in Patent Documents 1 to 6.

Therefore, the present invention is a microwave plasma CVD apparatus capable of synthesizing diamond at a relatively high synthesis rate even under relatively low plasma gas temperature conditions, and in particular, synthesizing high-quality single crystal diamond. It is an object of the present invention to provide a method for synthesizing diamond using it and a synthesized diamond.

The microwave plasma CVD apparatus according to the first aspect of the present invention is a microwave plasma CVD apparatus that supplies a microwave pulse to a raw material gas to generate plasma. This microwave plasma CVD apparatus includes a microwave supply unit that supplies a microwave pulse of a predetermined electric power to a raw material gas that is supplied at a predetermined flow rate and a predetermined pressure and contains hydrogen. In the microwave supply unit, the first emission intensity when a microwave pulse is supplied is higher than the second emission intensity when a continuous microwave having the same power as a predetermined power is supplied to the above-mentioned raw material gas. The microwave pulse can be supplied so as to be large, and the first emission intensity and the second emission intensity represent the intensity of the Hα ray emitted from the hydrogen atom in the plasma.

As a result, diamond can be synthesized at a relatively high synthesis rate even under conditions where the plasma gas temperature is relatively low, as compared with the case of using a continuous microwave wave.

Preferably, the on-time and off-time in one cycle of the microwave pulse output by the microwave supply unit are set so that the first emission intensity is larger than the second emission intensity.

Thereby, the diamond synthesis rate can be increased by adjusting the on time and the off time of the microwave pulse.

More preferably, the on-time and the off-time are 1 msec or less, respectively.

More preferably, the microwave plasma CVD apparatus further includes a gas supply unit that supplies a mixed gas of a carbon source and hydrogen as a raw material gas.

Preferably, the gas supply unit supplies nitrogen gas in addition to the mixed gas, and the microwave supply unit supplies microwave pulses to the mixed gas containing the nitrogen gas.

More preferably, the carbon source is a hydrocarbon gas.

More preferably, the microwave plasma CVD apparatus further includes a forced convection forming portion capable of forming a flow of the source gas in the region where the plasma is formed when the microwave pulse is supplied to the source gas.

As a result, the synthesis rate of diamond can be further increased.

Preferably, the microwave plasma CVD apparatus further includes a reaction vessel in which the plasma is formed, and the forced convection forming unit discharges the raw material gas from one end of the reaction vessel and then returns it to the reaction vessel from the other end of the reaction vessel. Includes circulation.

As a result, forced convection can be efficiently formed in the reaction vessel, and gas consumption can be saved.

The diamond according to the second aspect of the present invention is a diamond synthesized by using the above-mentioned microwave plasma CVD apparatus.

The diamond synthesized by this is a crystal with small thermal strain in which abnormal growth is suppressed.

The diamond synthesis method according to the third aspect of the present invention is a diamond synthesis method using a microwave plasma CVD apparatus. In this diamond synthesis method, a raw material gas containing hydrogen is supplied to a substrate at a predetermined flow rate and a predetermined pressure, and a microwave pulse of a predetermined electric power is supplied to the raw material gas to generate plasma, and the substrate is generated. Includes steps to grow diamonds on top. In the step of growing a diamond, the first emission intensity when a microwave pulse is supplied is higher than the second emission intensity when a continuous microwave of the same power as a predetermined power is supplied to the raw material gas. A microwave pulse is supplied so as to be large, and the first emission intensity and the second emission intensity represent the intensity of Hα rays emitted from hydrogen atoms in the plasma.

As a result, diamond can be synthesized at a relatively high synthesis rate even under conditions where the plasma gas temperature is relatively low, as compared with the case of using a continuous microwave wave.

Preferably, the method of synthesizing diamond further comprises forming a flow of source gas towards the substrate while performing the step of growing diamond on the substrate.

As a result, the synthesis rate of diamond can be further increased.

According to the present invention, by supplying a microwave pulse so that the emission intensity from the plasma is increased, the power to be supplied is relatively low and the gas temperature of the plasma is relatively low, even under conditions of relatively low. Diamond can be synthesized at a high synthesis rate. If a single crystal diamond is used as a substrate for growing diamond, the single crystal diamond can be grown at a high synthesis rate.

Further, by introducing nitrogen gas, the synthesis rate of diamond can be further increased.

Further, by forming a flow of the raw material gas toward the substrate, the diamond synthesis rate can be further increased.

In addition, the occurrence of abnormal crystal growth can be suppressed, and high-quality diamond can be synthesized. Furthermore, diamond with low thermal strain can be synthesized.

Further, since it is not necessary to increase the gas pressure at the time of discharge in order to improve the synthesis rate, the discharge region is not limited and a large area of diamond can be synthesized.

It is a schematic diagram which shows the diamond manufacturing apparatus which concerns on 1st Embodiment of this invention. It is a waveform diagram which shows the microwave pulse used in the manufacturing apparatus of FIG. It is a map showing the emission intensity of plasma when plasma is generated by changing the on-time and the off-time of a microwave pulse at a constant gas pressure. It is a table which shows the result of synthesizing diamond under various synthesis conditions. 3 is a laser micrograph showing the diamond produced in Example 3. 6 is a laser micrograph showing the diamond produced in Example 5. It is a table which shows the result of synthesizing diamond.

In the following embodiments, the same parts are given the same reference numbers. Their names and functions are also the same. Therefore, detailed explanations about them will not be repeated.

(First Embodiment)
With reference to FIG. 1, the diamond manufacturing apparatus 100 according to the first embodiment of the present invention includes a microwave generating unit 102, a waveguide 104, an antenna 106, a first cavity 108, a quartz plate 110, and a second cavity. It includes 112, a susceptor 114, a substrate holder 116, a support 118, a gas introduction pipe 120, a pulse power supply 122, and a control unit 124.

The microwave generation unit 102 generates and outputs microwaves. The microwave generation unit 102 is, for example, a magnetron. The microwave generation unit 102 is supplied with electric power in a pulsed manner by the pulse power supply 122, and generates microwaves having a predetermined frequency as shown in FIG. In FIG. 2, the broken line indicates a part of the microwave, and the pulse waveform is the envelope of the microwave. The time T (sec) represents the period of the pulse that is repeatedly output, the time Ton is the time when the microwave is output, and the time Toff is the time when the microwave is not output. The frequency f (Hz) of the pulse is f = 1 / T, and the duty D is D = Ton / T.

The control unit 124 accepts the pulse conditions of the microwave pulse, that is, the setting of Ton, Toff, and the power to be supplied. The control unit 124 controls the pulse power supply 122 so that the set microwave pulse is output from the microwave generation unit 102. As will be described later, the emission intensity of the plasma (the intensity of the Hα ray emitted from the hydrogen atom of the plasma) when the microwave pulse is supplied supplies a continuous microwave having the same power as the power supplied as the microwave pulse. A high synthesis rate can be obtained by setting the microwave pulse so that it becomes larger than the emission intensity of the plasma at that time.

The microwave output from the microwave generation unit 102 is propagated by the waveguide 104 and introduced into the first cavity 108 and the second cavity 112 via the antenna 106 to form a standing wave. In the second cavity 112 isolated from the first cavity 108 across the quartz plate 110, a gas serving as a plasma source is supplied from a gas supply device (not shown) at a predetermined pressure through a gas introduction pipe 120. Will be supplied. Therefore, an electric discharge occurs in the vicinity above the substrate holder 116 on the susceptor 114, and plasma P is generated.

The susceptor 114 and the substrate holder 116 are made of, for example, molybdenum (Mo). Inside the support portion 118 that supports the susceptor 114, there is a mechanism for circulating cooling water (see the broken line arrow). Further, the outer wall of the second cavity 112 also has a mechanism (not shown) for circulating cooling water.

The gas introduced into the second cavity 112 is a raw material gas for diamond, and for example, methane (CH ₄ ) and hydrogen (H ₂ ) are introduced at predetermined flow rates, respectively. When a single crystal diamond substrate (not shown) is placed on the substrate holder 116, carbon as a carbon source of plasma is laminated on the substrate, and diamond grows.

The diamond manufacturing apparatus 100 may include an apparatus for measuring the state of the plasma P and the temperature of the diamond substrate arranged in the substrate holder 116. The device for measuring the state of the plasma P includes, for example, a light receiving element that receives light emitted by the plasma P, a spectroscope, and an optical fiber that transmits an output signal of the light receiving element to the spectroscope. The output signal of the light receiving element is input to the spectroscope via an optical fiber, and for example, the intensity of the Hα ray (wavelength 656.28 nm), Hγ ray (wavelength 434.05 nm), etc. in the Palmer series of the hydrogen atom spectrum. Is measured. The device for measuring the temperature of the diamond substrate is, for example, an optical thermometer-type pyrometer.

A method for synthesizing diamond using the diamond manufacturing apparatus 100 of FIG. 1 will be described in more detail. A single crystal diamond substrate is placed on the substrate holder 116, the air in the second cavity 112 is exhausted to reduce the pressure in the second cavity 112, and methane is used as a raw material gas from the gas supply device via the gas introduction pipe 120. And hydrogen are supplied into the second cavity 112 at a predetermined flow rate, respectively, so that the pressure of the mixed gas becomes a predetermined pressure. A microwave pulse is supplied from the microwave generation unit 102 with a predetermined average power (electric power). The microwave pulse is set under conditions such that the emission intensity of the plasma is greater than the emission intensity of the plasma when continuously supplying microwaves having the same power as the average power of the microwave pulse under the same environment. ..

At this time, since the temperature of the plasma P becomes high (about 3000 ° C.), it is preferable to adjust the temperature to a predetermined temperature (for example, about 1000 ° C. or lower) so that the diamond substrate does not become too high.

As a result, single crystal diamond is synthesized on the substrate at a higher synthesis rate than when continuous microwaves are supplied as described later. At this time, the temperature of the plasma gas is lower than that in the case of supplying continuous microwaves, the substrate temperature can be relatively easily controlled to be low, and high-quality diamond is synthesized.

In the above, the case where the microwave generation unit 102 is operated by using the pulse power supply 122 to generate the microwave pulse has been described, but the present invention is not limited to this. For example, the microwave generator 102 is continuously operated by using a normal power source, the continuously output microwave is gated by a high-speed switch element or the like, and the microwave pulse shown in FIG. 2 is guided. The output may be made to the tube 104.

In the above, the case where the carbon source gas is methane has been described, but the present invention is not limited to this, and any hydrocarbon gas may be used.

In the above, the case where the single crystal diamond is synthesized on the single crystal diamond substrate has been described, but the present invention is not limited to this. Instead of the single crystal diamond substrate, a different material such as silicon may be used. In that case, polycrystalline diamond is synthesized.

The experimental results are shown below, and the effectiveness of the first embodiment of the present invention is shown. A microwave plasma CVD apparatus AX5200 manufactured by Cornes Technology Co., Ltd. was used for the experiment. In order to generate a microwave pulse, the magnetron of the microwave plasma CVD apparatus was driven by a pulse power source.

A substrate holder having a diameter of 2 inches (about 5 cm) was placed on a stage (susceptor) in the cavity, and a diamond single crystal substrate was placed in the center thereof. The pressure of the gas was 90 torr (about 12 kPa), and hydrogen was supplied into the cavity at a flow rate of 500 sccm. In that state, the ON time and the OFF time were set, and microwave pulses having an average power value in the range of 2.6 to 3 kW were continuously supplied, and plasma emission spectroscopy was performed.

FIG. 3 shows the results of mapping the measured values of the emission intensity during diamond synthesis under each condition on a log-log graph. In FIG. 3, the horizontal axis and the vertical axis are the ON time and the OFF time (both in milliseconds) of the microwave pulse, respectively. It represents a power of 10 e, e-3 and e + 3 means ^{10 -3} and ^{10 + 3,} respectively.

The mapped rectangle corresponds to each experiment, and its color (brightness) represents the emission intensity (arbitrary unit). The observed emission intensity between 940 and 2600 counts is divided into equal intervals (332 counts), and five kinds of colors (brightness) are assigned. In FIG. 3, for convenience, different brightnesses are represented by different patterns. The emission intensity can be used as a guide for the synthesis rate of diamond. That is, a large emission intensity (high brightness) indicates a high synthesis rate, and a low emission intensity (low brightness) indicates a low synthesis rate. The arrow with the symbol CW represents the emission intensity when continuous microwaves are used, and the value thereof is “1260”.

The shaded area in the upper left corner of the map of FIG. 3 is a region where the ON time is very short and the OFF time is very long, and it is difficult to generate stable plasma in this region. Further, the shaded area in the lower right corner of the map of FIG. 3 is a region where the ON time is very long and the OFF time is very short, and the pulse condition in this region is close to a continuous wave.

From FIG. 3, it can be seen that when both the ON time (Ton) and the OFF time (Toff) of the microwave pulse are set to less than 1 msec, high emission intensity can be obtained. It can also be seen that if the pulse width is made too short, the emission intensity will decrease.

When both Ton and Toff were smaller than 0.1 msec, a larger emission intensity than that of CW was obtained in all cases. It can be seen that when both Ton and Toff are smaller than 0.01 msec, the emission intensity is higher than that in the case of CW, but higher emission intensity can be obtained with a longer pulse width.

With the same configuration as in Example 1, methane was supplied into the cavity in addition to hydrogen to perform diamond synthesis. The gas pressure was 90 torr (about 12 kPa) and the flow rates of methane and hydrogen were 25 sccm and 500 sccm, respectively. In that state, the ON time and the OFF time are 0.008 msec and 0.01 msec, respectively, and a microwave pulse having an average value of 2.7 kW is continuously supplied for 4.5 hours to synthesize diamond on a single crystal substrate. Was done.

The thermal contact state between the substrate and the substrate holder was adjusted so that the substrate temperature during diamond synthesis did not become too high and became a desired temperature. The substrate temperature during diamond synthesis was measured non-contact using a pyrometer-type pyrometer. The substrate temperature during diamond synthesis was 930 ° C.

The difference in the film thickness of the diamond crystals before and after the synthesis was 32 μm, and the synthesis rate per hour was about 7 μm / Hr. The conditions and results of the synthesis are shown in FIG.

Diamonds were synthesized with the same configuration as in Example 2 under different conditions. The ON time and OFF time of the microwave pulse were 0.058 msec and 0.025 msec, respectively, and the average value of the microwave power was 2.5 kW. In addition to methane and hydrogen, nitrogen was fed at 0.02 sccm and microwave pulses were fed continuously for 5.1 hours. Other conditions were the same as in Example 2.

Similar to Example 2, the thermal contact state between the substrate and the substrate holder was adjusted. The substrate temperature during diamond synthesis, measured non-contact with a pyrometer, was 1050 ° C. The difference in the film thickness of the diamond crystals before and after the synthesis was 65 μm, and the synthesis rate was about 13 μm / Hr. The conditions and results of the synthesis are shown in FIG.

A laser micrograph of the produced diamond crystal is shown in FIG. What appears like black grains in FIG. 5 is an abnormally grown portion of the crystal. Abnormal growth indicates particles having an orientation other than {100} (for example, {111}) in the crystal grown on the {100} plane. When a device or the like is manufactured using a diamond crystal having abnormal growth, it causes deterioration of electrical characteristics, so it is preferable that the abnormal growth is small.

The substrate used in Example 3 was produced from a seed crystal having a predetermined off-angle by a known method (see Patent No. 5382742). That is, after ion implantation is performed on one surface of the seed crystal to form an ion implantation layer near the surface, a single crystal diamond is grown on the ion-implanted layer by a vapor phase synthesis method (microwave plasma CVD), and the grown diamond is grown. It was separated at the ion-implanted layer to form a diamond-synthesized substrate.

Diamond was synthesized under the same conditions as in Example 3 except that nitrogen was not supplied with the same configuration as in Example 2. That is, the ON time and the OFF time of the microwave pulse were 0.058 msec and 0.025 msec, respectively, the average value of the microwave power was 2.5 kW, and the microwave pulse was continuously supplied for 6 hours. The substrate used was prepared from the same seed crystal as the seed crystal used for producing the substrate used in Example 3 by the same method as described above.

Similar to Example 2, the thermal contact state between the substrate and the substrate holder was adjusted. The substrate temperature during diamond synthesis, measured non-contact with a pyrometer, was 985 ° C. The synthesis rate calculated from the difference in the film thickness of the diamond crystals before and after the synthesis was about 13 μm / Hr, which was the same as in Example 3. The conditions and results of the synthesis are shown in FIG.

Diamonds were synthesized with the same configuration as in Example 2 under different conditions. The ON time and OFF time of the microwave pulse were both 0.1 msec, and the average value of the microwave power was 3 kW. In addition to methane and hydrogen, nitrogen was supplied at 0.02 sccm. The gas pressure was 120 torr (about 16 kPa), and microwave pulses were continuously supplied for 4 hours. Other conditions are the same as in Example 2.

Similar to Example 2, the thermal contact state between the substrate and the substrate holder was adjusted. The substrate temperature during diamond synthesis, measured non-contact with a pyrometer, was 1030 ° C. The difference in the film thickness of the diamond crystals before and after the synthesis was 33 μm, and the synthesis rate was about 8 μm / Hr. The conditions and results of the synthesis are shown in FIG.

A laser micrograph of the produced diamond crystal is shown in FIG. What appears like bubbles in FIG. 6 is an abnormally grown portion of the crystal. The magnification and the photographing area of FIG. 6 are the same as those of FIG. Comparing FIG. 6 and FIG. 5, it can be seen that the diamond produced in Example 3 (FIG. 5) has a lower density of abnormal crystal growth than the diamond produced in Example 5 (FIG. 6). .. That is, the diamond produced in Example 3 is of higher quality than the diamond produced in Example 5.

The substrate used in Example 5 was prepared from the same seed crystal as the seed crystal used for producing the substrate used in Example 3 by the same method as described above. Therefore, since the diamonds synthesized in Examples 3 and 5 are less affected by the quality of the substrate used, it can be said that the difference in abnormal crystal growth is mainly due to the difference in the ON time and OFF time of the microwave pulse. That is, by shortening the ON time and OFF time of the microwave pulse, abnormal growth of crystals can be suppressed, and high-quality single crystal diamond can be synthesized.

Comparative Example 1

As a comparative experiment, diamond synthesis was performed using continuous microwaves with the same configuration as in Example 2.

The gas pressure was 120 torr, and continuous microwaves having an average microwave power of 3.6 kW were continuously supplied for 4 hours. Other conditions are the same as in Example 2.

Similar to Example 2, the thermal contact state between the substrate and the substrate holder was adjusted. The substrate temperature during diamond synthesis, measured non-contact with a pyrometer, was 970 ° C. The difference in the film thickness of the diamond crystals before and after the synthesis was 5 μm, and the synthesis rate was about 1 μm / Hr. The conditions and results of the synthesis are shown in FIG.

Comparative Example 2

As a comparative experiment, diamond synthesis was performed using continuous microwaves with the same configuration as in Example 2.

Nitrogen was supplied at 0.02 sccm in addition to methane and hydrogen using continuous microwaves with an average microwave power of 2.5 kW. Microwaves were supplied continuously for 5.5 hours. Other conditions are the same as in Example 2.

Similar to Example 2, the thermal contact state between the substrate and the substrate holder was adjusted. The substrate temperature during diamond synthesis, measured non-contact with a pyrometer, was 1040 ° C. The difference in the film thickness of the diamond crystals before and after the synthesis was 13 μm, and the synthesis rate was about 2 μm / Hr. The conditions and results of the synthesis are shown in FIG.

The following can be seen from FIG. 4, which summarizes the experimental conditions and experimental results of Examples 2 to 5 and Comparative Examples 1 and 2. In diamond synthesis by the plasma CVD method, generally, when the pressure of the gas is increased, the plasma is concentrated and the synthesis rate is increased. Also, in general, when microwaves are supplied with a higher power, the gas temperature of the plasma becomes higher and the diamond synthesis rate becomes higher. From these viewpoints, when Example 2 and Comparative Example 1 are compared, in Example 2, the gas pressure is lower and the microwave power is smaller (the gas temperature is lower), but the comparative example is compared. The synthesis speed is higher than 1 (about 7 times). Therefore, as shown in FIG. 3, it can be seen that supplying microwaves in a pulse shape during the ON time and the OFF time in the region where the emission intensity is high is effective in improving the diamond synthesis rate.

Comparing Example 3 and Example 5 using the microwave pulse, Example 3 was carried out even though the gas pressure was lower and the microwave power was lower (the gas temperature was lower). The synthesis speed is higher than in Example 5. Therefore, as shown in FIG. 3, the ON time and OFF time of the microwave pulse in the region where the emission intensity is high are preferable because a larger synthesis rate can be obtained in diamond synthesis, and FIGS. 5 and 6 are shown on top of this. From the viewpoint of abnormal growth of the crystals shown above with reference to the above, it can be said that it is preferable for the synthesis of high-quality single crystal diamond.

In general, it is known that in the synthesis of diamond by the plasma CVD method, the synthesis rate is increased by introducing a small amount of nitrogen. Comparing Comparative Example 1 and Comparative Example 2 using continuous microwaves, Comparative Example 2 has a lower gas pressure and a smaller microwave power, but by introducing nitrogen, The synthesis speed is higher than that of Comparative Example 1 (about twice).

Comparing Example 2 and Comparative Example 2, the gas pressure, the flow rate of the gas, and the microwave power are almost the same, and Example 2 using the microwave pulse is compared with Comparative Example 2 in which nitrogen is introduced. The synthesis speed is faster than that (about 3.5 times). That is, the effect of improving the synthesis rate is greater when using a microwave pulse than when introducing nitrogen.

(Second Embodiment)
In the second embodiment, in order to further increase the synthesis rate of diamond, a flow of raw material gas (forced convection) toward the diamond substrate is formed in the space where the plasma is formed.

Specifically, in the diamond manufacturing apparatus 100 shown in FIG. 1, a single crystal diamond substrate is arranged on the substrate holder 116 and microwave pulses are supplied from the microwave generating unit 102, as in the first embodiment. In the state where the plasma P is formed, a forced convection toward the substrate is formed in the second cavity 112. As described in Patent Document 4, in order to form forced convection in the second cavity 112, for example, in the configuration of FIG. 1, an exhaust pipe is provided between the lower portion of the second cavity 112 and the gas introduction pipe 120. , Provide a circulation path consisting of a pump and a return pipe. By the circulation path, the gas in the second cavity 112 is once discharged, and then introduced again from the gas introduction pipe 120 into the second cavity 112. As a result, forced convection of the raw material gas toward the substrate is formed, and the speed of diamond synthesis on the substrate can be further increased.

Gas propagation includes diffusion and convection (advection), and the rate of diamond synthesis can be increased if obvious convection is formed in the cavity 132. The speed of convection is preferably 1,000 to 20,000 cm / min.

The method of forming forced convection in the cavity is not limited to the method of providing a circulation path. The inner diameter of the connection portion of the gas introduction pipe 120 to the cavity may be reduced, or a nozzle may be provided as in Patent Documents 5 and 6 to supply the raw material gas into the cavity at a higher flow velocity. Even in that case, forced convection can be formed in the cavity.

Further, as shown in FIG. 1, the case is not limited to the case where the microwave pulse is supplied from the front surface (upper side) of the susceptor. For example, as disclosed in Patent Document 6, forced convection may be formed in the cavity in a configuration in which microwave pulses are supplied from the back surface of the susceptor.

The experimental results are shown below, and the effectiveness of the second embodiment of the present invention is shown. In the experiment, a microwave plasma CVD apparatus AX6500 manufactured by Cornes Technology Co., Ltd. was used. In order to generate a microwave pulse, the magnetron of the microwave plasma CVD apparatus was driven by a pulse power source.

Forced convection was formed in the cavity by forcibly flushing the raw material gas with a pump connected to the introduction pipe of the raw material gas into the cavity. The capacity (flow rate) of the pump used was 11 liters / minute at 100 torr (about 13.3 kPa). The flow velocity estimated from the diameter of the introduction hole of the gas introduction pipe into the cavity was 7,800 cm / min.

Similar to Examples 1 to 5 described above, a substrate holder having a diameter of 2 inches (about 5 cm) is placed on a stage (susceptor) in the cavity, and a diamond single crystal substrate is placed in the center thereof to perform diamond synthesis. It was.

Specifically, the pressure of the gas was 120 torr (about 16 kPa), and hydrogen, methane, nitrogen, and oxygen were supplied into the cavity at flow rates of 1000 sccm, 50 sccm, 0.06 sccm, and 6 sccm, respectively. Oxygen was supplied in order to synthesize highly crystalline diamond.

The pump was driven to form forced convection in the cavity while the ON time and the OFF time were 0.050 msec and a microwave pulse having an average power of 3 kW was supplied. This state was maintained continuously for 1.2 hours.

The thermal contact state between the substrate and the substrate holder was adjusted so that the substrate temperature during diamond synthesis did not become too high and became a desired temperature. The substrate temperature during diamond synthesis was measured non-contact using a pyrometer-type pyrometer. The substrate temperature during diamond synthesis was 1070 ° C.

The difference in the film thickness of the diamond crystals before and after the synthesis was 50 μm, and the synthesis rate per hour was about 42 μm / Hr. The conditions and results of the synthesis are shown in FIG.

The obtained synthesis rate cannot be directly compared with the synthesis rate of each experimental result shown in FIG. 4 because the flow rate of the raw material gas is different, but in addition to using the microwave pulse, in the cavity. It can be seen that the conventional synthesis rate (Comparative Examples 1 and 2) can be significantly improved by forming forced convection.

An experiment was conducted to confirm the effect of forming forced convection in the cavity in the present invention. That is, diamond synthesis on the single crystal substrate was continuously carried out for 50 hours under the same conditions as in Example 6 except that there was no forced convection.

The substrate temperature during diamond synthesis was measured non-contact using a pyrometer-type pyrometer. The substrate temperature during diamond synthesis was 1099 ° C.

The difference in the film thickness of the diamond crystals before and after the synthesis was 1082 μm, and the synthesis rate per hour was about 22 μm / Hr. The conditions and results of the synthesis are shown in FIG.

Since the conditions other than the presence or absence of forced convection are almost the same in Examples 6 and 7, the effect of forced convection in the present invention can be understood by comparing the synthesis rates resulting from them. The synthesis rate of diamond was about 22 μm / Hr in Example 7, whereas it was about 42 μm / Hr in Example 6 in which convection was forcibly formed in the cavity, which is about twice the value. .. Therefore, in the present invention, forming forced convection in the cavity is very effective in terms of diamond synthesis rate.

In Example 7, although the convection was not forcibly formed in the cavity, the synthesis rate was about 2 to 3 times higher than that of the first to fifth examples. This is mainly due to the large gas flow rate or the large ratio of the nitrogen flow rate to the total gas or methane gas flow rate.

Although the present invention has been described above by explaining the embodiments, the above-described embodiments are examples, and the present invention is not limited to the above-described embodiments, and various modifications are made. be able to.

100 Diamond manufacturing equipment 102 Microwave generator 104 Waveguide 106 Antenna 108 First cavity 110 Quartz plate 112 Second cavity 114 Suceptor 116 Substrate holder 118 Support 120 Gas introduction tube 122 Pulse power supply 124 Control unit

Claims (11)

A microwave plasma CVD device that generates plasma by supplying microwave pulses to the raw material gas.
A microwave supply means for supplying the microwave pulse of a predetermined electric power to the raw material gas supplied at a predetermined flow rate and a predetermined pressure and containing hydrogen is included.
The microwave supply means has a second emission intensity when the first emission intensity when the microwave pulse is supplied supplies the raw material gas with continuous microwaves having the same electric power as the predetermined electric power. The microwave pulse can be supplied so as to be greater than the intensity.
The first emission intensity and the second emission intensity represent the intensity of Hα rays emitted from hydrogen atoms in plasma.
A microwave plasma CVD apparatus in which each of the on-time and the off-time in one cycle of the microwave pulse output by the microwave supply means is less than 0.1 msec. The microwave plasma CVD apparatus according to claim 1, wherein the on-time and the off-time are set so that the first emission intensity is larger than the second emission intensity. The on-time is 0. 1msec less der is, and the off time is less than or 0.01Msec 0.1 msec, or,
The microwave plasma CVD apparatus according to claim 2, wherein the on-time is 0.01 msec or more and less than 0.1 msec, and the off-time is less than 0.1 msec . The microwave plasma CVD apparatus according to any one of claims 1 to 3, further comprising a gas supply means for supplying a mixed gas of a carbon source and hydrogen as the raw material gas. The gas supply means supplies nitrogen gas in addition to the mixed gas,
The microwave plasma CVD apparatus according to claim 4, wherein the microwave supply means supplies the microwave pulse to the mixed gas containing the nitrogen gas. The microwave plasma CVD apparatus according to claim 4 or 5, wherein the carbon source is a hydrocarbon gas. The method according to any one of claims 1 to 6, further comprising a forced convection forming means capable of forming a flow of the raw material gas in a region where the plasma is formed when the microwave pulse is supplied to the raw material gas. Microwave plasma CVD equipment. Further comprising a reaction vessel on which the plasma is formed
The microwave plasma CVD apparatus according to claim 7, wherein the forced convection forming means includes a circulation means for discharging the raw material gas from one end of the reaction vessel and then returning the raw material gas to the reaction vessel from the other end of the reaction vessel. .. The microwave plasma CVD apparatus according to any one of claims 1 to 8, wherein the single crystal diamond substrate is exposed to the plasma and diamond is synthesized on the single crystal diamond substrate. A diamond synthesis method using a microwave plasma CVD apparatus.
A step of supplying a raw material gas containing hydrogen to a substrate at a predetermined flow rate and a predetermined pressure.
A step of supplying a microwave pulse of a predetermined electric power to the raw material gas to generate plasma and growing diamond on the substrate is included.
In the step of growing the diamond, the first emission intensity when the microwave pulse is supplied is the second when the raw material gas is supplied with continuous microwaves having the same power as the predetermined power. The microwave pulse is supplied so as to be larger than the emission intensity of
The first emission intensity and the second emission intensity represent the intensity of Hα rays emitted from hydrogen atoms in plasma.
Each of the on-time and off-time in one cycle before Symbol microwave pulse is less than 0.1 msec, a method for synthesizing diamond. The diamond synthesis method according to claim 10, further comprising the step of forming a flow of the raw material gas toward the substrate while performing the step of growing the diamond.