阅读说明：本技术 一种微波cvd法控制多晶金刚石晶粒尺寸的生长方法 (Growth method for controlling polycrystalline diamond grain size by microwave CVD method ) 是由 李庆利 甄西合 赵丽媛 徐悟生 刘畅 朱逢旭 刘得顺 杨春晖 于 2021-10-21 设计创作，主要内容包括：一种微波CVD法控制多晶金刚石晶粒尺寸的生长方法,在沉积过程中,设有N组时间段,并在第一组时间段之后的每一组时间段内连续地通入不同体积比的混合气体；随着时间段的增加,在第N组时间段后通入的所述混合气体中的每一个气体的体积比均高于在第N-1组时间段后通入的相应气体的体积比；且在第N组时间段后,基于所述混合气体中每一个气体的体积比持续通入所述混合气体,直至生长结束。本发明通过分时间段逐步提高碳源浓度和氧气浓度,以阶梯性地提高金刚石的形核率来控制金刚石晶粒尺寸的大小,从而提升金刚石膜的质量；同时,还可阶梯地提高金刚石膜的生长速率,降低外延层的晶格缺陷,从而可减小生长应力,获得完整无裂纹的金刚石膜。(A growth method for controlling the grain size of polycrystalline diamond by a microwave CVD method is characterized in that N groups of time periods are set in the deposition process, and mixed gas with different volume ratios is continuously introduced into each group of time periods after a first group of time periods; with the increase of the time period, the volume ratio of each gas in the mixed gas introduced after the Nth group of time periods is higher than the volume ratio of the corresponding gas introduced after the Nth-1 group of time periods; and after the Nth group of time periods, continuously introducing the mixed gas based on the volume ratio of each gas in the mixed gas until the growth is finished. According to the invention, the carbon source concentration and the oxygen concentration are gradually increased in different time periods, so that the nucleation rate of diamond is increased in a stepped manner to control the size of diamond grains, and the quality of a diamond film is improved; meanwhile, the growth rate of the diamond film can be improved in a stepped manner, and the lattice defect of the epitaxial layer is reduced, so that the growth stress can be reduced, and the complete crack-free diamond film can be obtained.)

1. A growth method for controlling the grain size of polycrystalline diamond by a microwave CVD method is characterized by comprising the following steps: in the deposition process, N groups of time periods are set, and mixed gas with different volume ratios is continuously introduced into each group of time periods after the first group of time periods; the mixed gas comprises gaseous alkane and oxygen;

with the increase of the time period, the volume ratio of each gas in the mixed gas introduced after the Nth group of time periods is higher than the volume ratio of the corresponding gas introduced after the Nth-1 group of time periods; and is

After the Nth group of time periods, continuously introducing the mixed gas based on the volume ratio of each gas in the mixed gas until the growth is finished;

wherein N is an integer greater than 1.

2. A method of controlling the grain size of polycrystalline diamond according to claim 1, wherein the first set of time periods is not longer than any subsequent set of time periods.

3. A method of growing polycrystalline diamond according to claim 1 or claim 2, in which the gas mixture comprises methane and oxygen.

4. A method according to claim 3, wherein the methane and oxygen are continuously introduced at a predetermined volume ratio for each set of time periods after the first set of time periods.

5. A method according to claim 4, wherein the volume ratio of methane fed in any one of the first set of time periods to oxygen fed in is greater than the volume ratio of methane fed in any one of the first set of time periods.

6. A growth method for controlling the grain size of polycrystalline diamond according to claim 4 or 5, characterized in that, during the first set of time periods, the substrate temperature is 800-1000 ℃; the introduced gas is the mixed gas of methane and nitrogen and hydrogen respectively; wherein the methane volume ratio is 2%; the volume ratio of the nitrogen-hydrogen mixed gas is 0-0.2%.

7. A method according to claim 6, wherein from the second set of time periods until the deposition process is complete, the methane is passed in a volume ratio of 2-4%.

8. A method according to claim 6, wherein the oxygen is introduced in a proportion of 0to 2% by volume from the second set of time periods until the deposition process is complete.

9. A microwave CVD method for controlling the grain size of polycrystalline diamond according to claim 7 or claim 8 wherein the methane, oxygen and nitrogen-hydrogen mixed gas each have a purity of greater than 5N; and the volume ratio of the hydrogen to the nitrogen in the nitrogen-hydrogen mixed gas is 99: 1.

10. a method of controlling the grain size of polycrystalline diamond according to any one of claims 1 to 2, 4 to 5, and 7 to 8 in which N is 3.

11. A method of microwave CVD method for controlling growth of the grain size of polycrystalline diamond according to claim 10, wherein the first set of time periods is between 10 and 50 hours;

the time length of the second group of time periods is 20-100 h;

the time length of the third group of time periods is 20-100 h.

12. A microwave CVD method of controlling the grain size of polycrystalline diamond according to any one of claims 1-2, 4-5, 7-8, 11, further comprising diamond nucleation on the pre-treated substrate surface prior to the deposition process; wherein the content of the first and second substances,

when the temperature of the pretreated substrate material is 750-900 ℃, nucleation is started, and the diamond nucleation time is 30-60 min; and the substrate material is any one of monocrystalline silicon, molybdenum or tungsten.

Technical Field

The method belongs to the technical field of diamond preparation by a chemical vapor deposition method, and particularly relates to a growth method for controlling the grain size of polycrystalline diamond by a microwave CVD method.

Background

The diamond has excellent performances such as high hardness, high thermal conductivity, high chemical inertness, high optical transparency, high forbidden bandwidth, high carrier concentration and the like, and has great application value in high-precision fields such as machining, high-power device radiating fins, high-power wave-transmitting windows, semiconductor devices, semiconductor chips and the like.

In the application, the requirements on the thickness and quality of the diamond film and the surface appearance and the smoothness of the diamond film are met, so that the prepared diamond film can meet the use requirements only after being subjected to post-processing treatment such as grinding, polishing and the like. In the post-processing treatment process, the problems of difficult grinding and polishing, low efficiency, serious heating, easy generation of microcracks and the like can be caused due to high purity, large crystal grains and high hardness of the diamond film, so that the diamond film can not efficiently meet the industrial requirement and can not be used due to generation of cracks, and the production cost of the diamond film is greatly improved. How to efficiently post-process the diamond film for the application on the premise of ensuring the thickness and the quality of the diamond film is urgent to solve.

Disclosure of Invention

The method provides a growth method for controlling the size of polycrystalline diamond grains by a microwave CVD method, and solves the technical problems that the diamond film grains obtained by the prior art are large, so that the post-processing is difficult, the lattice defect is easy to occur, and the grains are cracked.

In order to solve the technical problems, the method adopts the technical scheme that:

a growth method for controlling the grain size of polycrystalline diamond by a microwave CVD method comprises the following steps: in the deposition process, N groups of time periods are set, and mixed gas with different volume ratios is continuously introduced into each group of time periods after the first group of time periods; the mixed gas comprises gaseous alkane and oxygen;

with the increase of the time period, the volume ratio of each gas in the mixed gas introduced after the Nth group of time periods is higher than the volume ratio of the corresponding gas introduced after the Nth-1 group of time periods; after the Nth group of time periods, continuously introducing the mixed gas based on the volume ratio of each gas in the mixed gas until the growth is finished;

wherein N is an integer greater than 1.

Further, the time of the first group of time periods is not more than the time of any subsequent group of time periods.

Further, the mixed gas includes methane and oxygen.

Further, the methane and the oxygen are continuously introduced according to a set volume ratio in each set time period after the first set time period.

Further, the volume ratio of the methane introduced in any time period after the first time period is larger than the volume ratio of the oxygen introduced in any time period after the first time period.

Further, during the first group of time period deposition, the substrate temperature is 800-; the introduced gas is the mixed gas of methane and nitrogen and hydrogen respectively; wherein the methane volume ratio is 2%; the volume ratio of the nitrogen-hydrogen mixed gas is 0-0.2%.

Further, from the second set of time periods until the deposition process is complete, the methane is introduced in a volume ratio of 2-4%.

Further, from the second set of time periods until the deposition process is completed, the oxygen is introduced in a volume ratio of 0-2%.

Further, the purity of the methane, the oxygen and the nitrogen-hydrogen mixed gas is more than 5N; and the volume ratio of the hydrogen to the nitrogen in the nitrogen-hydrogen mixed gas is 99: 1.

Further, N is 3.

Further, the duration of the first group of time periods is 10-50 h;

the time length of the second group of time periods is 20-100 h;

the time length of the third group of time periods is 20-100 h.

Further, before the deposition process, diamond nucleation is carried out on the surface of the pretreated substrate; wherein the content of the first and second substances,

when the temperature of the pretreated substrate material is 750-900 ℃, nucleation is started, and the diamond nucleation time is 30-60 min; and the substrate material is any one of monocrystalline silicon, molybdenum or tungsten.

The growth method for controlling the grain size of the polycrystalline diamond by adopting the microwave CVD method is designed, and the size of the grain size of the polycrystalline diamond is controlled by gradually increasing the concentration of a carbon source and the concentration of oxygen in different time periods so as to increase the nucleation rate of the diamond in a stepped manner, thereby improving the quality of a diamond film; meanwhile, the growth rate of the diamond film can be improved in a stepped manner, and the lattice defect of the epitaxial layer is reduced, so that the growth stress can be reduced, and the complete crack-free diamond film can be obtained.

Drawings

FIG. 1 is a flow chart of a method for controlling polycrystalline diamond grain size growth by microwave CVD in accordance with an embodiment of the present method;

FIG. 2 is a microscopic view of the grain size of polycrystalline diamond obtained by the present method;

fig. 3 is a microscopic view of the grain size of polycrystalline diamond obtained using a prior art method.

Detailed Description

The method is described in detail below with reference to the figures and specific examples.

The longer the crystal grain of the diamond film is, the larger the crystal grain becomes with the extension of the growth time, the more difficult the post-processing when the crystal grain is large to a certain extent, and the diamond film with a large number of lattice defects and cracks is easily grown. The conventional method for growing polycrystalline diamond grains is to continuously perform the growth according to the carbon source and the oxygen in the same gas ratio when the substrate temperature reaches a certain temperature. However, when the concentration of the carbon source is too high, non-diamond phases such as graphite and the like can be formed, and the quality of the diamond film is seriously influenced; when the proportion of other gases is unreasonable, the growth rate of the diamond film is reduced, the lattice defect of the epitaxial layer can be enlarged, the growth stress is increased, the multi-crack diamond film is easily grown, and the whole film rate is extremely poor.

In order to solve the above problem, the present embodiment proposes a growth method for controlling the grain size of polycrystalline diamond by a microwave CVD method, as shown in fig. 1, the method includes the steps of:

in the deposition process, N groups of time periods are set, and mixed gas with different volume ratios (vol%, the same follow-up volume ratio) is continuously introduced in each group of time periods after the first group of time periods;

with the increase of the time period, the volume ratio of each gas in the mixed gas introduced after the Nth group of time periods is higher than the volume ratio of the corresponding gas introduced after the Nth-1 group of time periods; and is

After the Nth group of time periods, continuously introducing the mixed gas based on the volume ratio of each gas in the mixed gas until the growth is finished;

wherein N is an integer and greater than 1, and the mixed gas comprises methane and oxygen. The mixed gas composed of methane and oxygen is progressively introduced into the substrate for chemical vapor deposition to obtain nucleation structures of different batches to control the size of the diamond grains, so that the diamond grains gradually grow in an expanding way and are uniformly and densely distributed on the substrate. Methane may also be replaced with other gaseous alkanes in certain embodiments of the invention.

The volume ratio of all introduced gases is the ratio of the volume of hydrogen in the reaction chamber, and because the main gas is hydrogen in the actual deposition process, the hydrogen can form plasma to form a deposition environment required by the growth of diamond grains; meanwhile, the hydrogen atoms of the plasma can etch the graphite phase generated in the growth process of the diamond grains, and the growth of the diamond is facilitated.

Further, the time of the first group of time periods is not more than the time of any subsequent group of time periods. The overall nucleation growth rate is adjusted by controlling the time of different groups of sections, so that the crystal grains of the diamond film are gradually improved, the lattice defects of the epitaxial layer are reduced, and the growth stress is furthest reduced by enough time in the subsequent nucleation stabilization process, so that the complete crack-free diamond film is obtained. Meanwhile, because the time for initial deposition is short, the quality of the matrix can be influenced by prolonging the time; prolonging the subsequent deposition time can increase the growth rate of the crystal grains, and optimize the crystal grain size of the diamond film through multiple nucleation rates so as to obtain densified and homogenized crystal grains of the diamond film.

Further, the methane and the oxygen are continuously introduced according to the set volume ratio in each group of time periods after the first group of time periods. The aim is to ensure the stability and consistency in the nucleation and nucleation process.

Further, the volume ratio of methane introduced in any time period after the first time period is larger than the volume ratio of oxygen introduced in any time period after the first time period. In the nucleation process after nucleation, the diamond film particles have large requirements on the concentration of a carbon source and have deeper influence on the nucleation of the diamond crystal particles; the oxygen concentration has less influence on the diamond film crystal grains; meanwhile, the crystal grains of the diamond film can be promoted to be more uniform and compact by methane and oxygen under the condition of a certain proportion.

Specifically, in the deposition process, from the second group of time periods to the completion of the deposition process, the methane is introduced in a volume ratio of 2-4%; and the volume ratio of the introduced oxygen is 0-2%.

Further, during the first group of time period deposition, the substrate temperature is 800-; the introduced gas is respectively methane and nitrogen-hydrogen mixed gas; wherein the volume ratio of methane is 2%; the volume ratio of the nitrogen-hydrogen mixed gas is 0-0.2%. Because the deposition in the first group of time periods is used as a substrate for epitaxial growth in the next stage, only the mixed gas of methane and nitrogen and hydrogen is needed, and oxygen gas is not needed to be introduced; and continuously introducing the nitrogen-hydrogen mixed gas according to the set volume ratio from the time after the first group of time periods until the deposition process is finished. The purpose of the nitrogen-hydrogen mixed gas is to improve the growth rate of diamond grains and reduce defects of diamond lattices in the deposition process.

Further, in a second group of time periods after the first group of time periods, methane is introduced into the reactor in a volume ratio of 2.5-3%; the volume ratio of oxygen is 0-0.5%. Wherein the volume ratio of methane is greater than 2% of the volume ratio of methane introduced during the first set of time periods; and oxygen is introduced into the crystal at the stage to stabilize the growth quality of the crystal grains.

Preferably, after the Nth group of time periods, the methane volume ratio introduced into the furnace body is 3.5-4%; the volume ratio of oxygen is 1-2%. Namely, in the time period from the second time period to the Nth time period, the methane is introduced with the volume ratio of 3-3.5%; the volume ratio of oxygen is 0.5-1%. And after the last time period, introducing methane into the furnace body in a volume range of 3.5-4% and oxygen in a volume ratio of 1-2%. The distributed mixed gas can more fully deposit long nuclei to obtain more uniform and compact diamond film particles, so that the size of the diamond film particles reaches below 10um, and cracks can not occur.

Furthermore, in the whole deposition process, the purity of the mixed gas of methane, oxygen and nitrogen and hydrogen is more than 5N; and the volume ratio of the hydrogen to the nitrogen in the nitrogen-hydrogen mixed gas is 99: 1.

Preferably, N is 3. That is, in the embodiment, three time periods are set in total, and the duration of the first group of time periods is 10-50 h; the time length of the second group of time periods is 20-100 h; the time length of the third group of time periods is 20-100 h. Three groups of time periods are set, nucleation growth is carried out in batches in the deposition process, the first time period, the second time period and the third time period are primary, diamond film grains with fine, compact and uniform grain sizes can be obtained after secondary nucleation, and the nucleation rate is adjusted without adding more steps.

Further, before the deposition process, diamond nucleation is carried out on the surface of the pretreated substrate; wherein, when the temperature of the pretreated substrate material is 750-900 ℃, nucleation is started, and the diamond nucleation time is 30-60 min; and the substrate material is any one of monocrystalline silicon, molybdenum or tungsten.

In the pretreatment process, grinding the surface of the substrate for diamond growth by using diamond micropowder for 20min to generate uniform scratches; then the substrate is respectively placed in alcohol, acetone and alcohol for ultrasonic cleaning for 10min, and finally a dryer is adopted to dry the substrate.

Opening the cavity door of the equipment, placing the processed substrate on a molybdenum support and on a water-cooling deposition table in the reaction chamber, closing the cavity door, vacuumizing the reaction chamber, and vacuumizing the background to 1 × 10^-2Below torr.

And then, introducing hydrogen into the reaction chamber, adjusting the reaction pressure to 5-10torr, starting a microwave power supply, adjusting the microwave input power to 600-1000W, and exciting the plasma. Once this is done, the diamond nucleation process for the substrate surface can begin.

In order to make the method of the present invention more comprehensible to those skilled in the art, the technical solutions of the present invention will be explained in detail with reference to specific embodiments, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments.

Example 1:

a growth method for controlling the grain size of polycrystalline diamond by a microwave CVD method comprises the following steps:

pretreatment: grinding the surface of the monocrystalline silicon substrate by using diamond micro powder for 20min to generate uniform scratches; then the substrate is respectively placed in alcohol, acetone and alcohol for ultrasonic cleaning for 10min, and finally a dryer is adopted to dry the substrate.

Opening the cavity door of the device, placing the processed substrate on a molybdenum support and on a water-cooling deposition table in the reaction chamber, closing the cavity door, vacuumizing the reaction chamber, and vacuumizing the background to 1 × 10^-2Below torr.

Introducing hydrogen into the reaction chamber, adjusting the reaction pressure to 5-10torr, starting the microwave power supply, adjusting the microwave input power to 600-.

Regulating the microwave power and the reaction pressure to make the substrate temperature within the range of 750-900 ℃, and introducing 4% methane to perform the diamond nucleation process on the surface of the substrate.

After the nucleation process is finished, closing methane, adjusting the microwave power and the reaction pressure to ensure that the substrate temperature is within the range of 800-.

After 20 hours, the methane ratio was raised to 2.5% and 0.3% oxygen was introduced to continue the diamond deposition.

After 20 hours, the methane proportion is continuously increased to 3 percent, the oxygen proportion is increased to 0.5 percent, and the diamond deposition is continuously carried out.

After 20 hours, the methane proportion is increased to 3.5 percent, the oxygen proportion is increased to 1 percent, and the diamond deposition is continued until the deposition process is finished.

Example 2:

a growth method for controlling the grain size of polycrystalline diamond by a microwave CVD method comprises the following steps:

pretreatment: grinding the surface of the molybdenum substrate by using diamond micro powder for 20min to generate uniform scratches; then the substrate is respectively placed in alcohol, acetone and alcohol for ultrasonic cleaning for 10min, and finally a dryer is adopted to dry the substrate.

Opening the cavity door of the device, placing the processed substrate on a molybdenum support and on a water-cooling deposition table in the reaction chamber, closing the cavity door, vacuumizing the reaction chamber, and vacuumizing the background to 1 × 10^-2Below torr.

Introducing hydrogen into the reaction chamber, adjusting the reaction pressure to 5-10torr, starting the microwave power supply, adjusting the microwave input power to 600-.

Regulating the microwave power and the reaction pressure to make the substrate temperature within the range of 750-900 ℃, and introducing 4% methane to perform the diamond nucleation process on the surface of the substrate.

After the nucleation process is finished, closing methane, adjusting the microwave power and the reaction pressure to ensure that the substrate temperature is within the range of 800-.

After 20 hours, the methane ratio was raised to 2.5% and 0.3% oxygen was introduced to continue the diamond deposition.

After 50 hours, the methane proportion is continuously increased to 3.5 percent, the oxygen proportion is increased to 1 percent, and the diamond deposition is continuously carried out.

After 50 hours, the methane proportion is increased to 4 percent, the oxygen proportion is increased to 1.5 percent, and the diamond deposition is continued until the deposition process is finished.

Example 3:

a growth method for controlling the grain size of polycrystalline diamond by a microwave CVD method comprises the following steps:

pretreatment: grinding the surface of the monocrystalline silicon substrate by using diamond micro powder for 20min to generate uniform scratches; then the substrate is respectively placed in alcohol, acetone and alcohol for ultrasonic cleaning for 10min, and finally a dryer is adopted to dry the substrate.

Opening the cavity door of the device, placing the processed substrate on a molybdenum support and on a water-cooling deposition table in the reaction chamber, closing the cavity door, vacuumizing the reaction chamber, and vacuumizing the background to 1 × 10^-2Below torr.

Introducing hydrogen into the reaction chamber, adjusting the reaction pressure to 5-10torr, starting the microwave power supply, adjusting the microwave input power to 600-.

Regulating the microwave power and the reaction pressure to make the substrate temperature within the range of 750-900 ℃, and introducing 4% methane to perform the diamond nucleation process on the surface of the substrate.

After the nucleation process is finished, closing methane, adjusting the microwave power and the reaction pressure to ensure that the substrate temperature is within the range of 800-.

After 10 hours, the methane ratio was raised to 2.5% and 0.2% oxygen was introduced to continue the diamond deposition.

After 100 hours, the methane proportion is continuously increased to 3 percent, the oxygen proportion is increased to 0.8 percent, and the diamond deposition is continuously carried out.

After 100 hours, the methane proportion is increased to 4 percent, the oxygen proportion is increased to 1 percent, and the diamond deposition is continued until the deposition process is finished.

Example 4:

a growth method for controlling the grain size of polycrystalline diamond by a microwave CVD method comprises the following steps:

pretreatment: grinding the surface of the monocrystalline silicon substrate by using diamond micro powder for 20min to generate uniform scratches; then the substrate is respectively placed in alcohol, acetone and alcohol for ultrasonic cleaning for 10min, and finally a dryer is adopted to dry the substrate.

Opening the cavity door of the device, placing the processed substrate on a molybdenum support and on a water-cooling deposition table in the reaction chamber, closing the cavity door, vacuumizing the reaction chamber, and vacuumizing the background to 1 × 10^-2Below torr.

Introducing hydrogen into the reaction chamber, adjusting the reaction pressure to 5-10torr, starting the microwave power supply, adjusting the microwave input power to 600-.

Regulating the microwave power and the reaction pressure to make the substrate temperature within the range of 750-900 ℃, and introducing 4% methane to perform the diamond nucleation process on the surface of the substrate.

After the nucleation process is finished, closing methane, adjusting the microwave power and the reaction pressure to ensure that the substrate temperature is within the range of 800-.

After 15 hours, the methane ratio was raised to 2.7% and 0.2% oxygen was introduced to continue the diamond deposition.

After 50 hours, the methane proportion is continuously increased to 3.2 percent, the oxygen proportion is increased to 0.7 percent, and the diamond deposition is continuously carried out.

After 70 hours, the methane proportion is increased to 3.7 percent, the oxygen proportion is increased to 1.2 percent, and the diamond deposition is continued until the deposition process is finished.

Example 5:

a growth method for controlling the grain size of polycrystalline diamond by a microwave CVD method comprises the following steps:

pretreatment: grinding the surface of the molybdenum substrate by using diamond micro powder for 20min to generate uniform scratches; then the substrate is respectively placed in alcohol, acetone and alcohol for ultrasonic cleaning for 10min, and finally a dryer is adopted to dry the substrate.

Opening the cavity door of the device, placing the processed substrate on a molybdenum support and on a water-cooling deposition table in the reaction chamber, closing the cavity door, vacuumizing the reaction chamber, and vacuumizing the background to 1 × 10^-2Below torr.

Introducing hydrogen into the reaction chamber, adjusting the reaction pressure to 5-10torr, starting the microwave power supply, adjusting the microwave input power to 600-.

Regulating the microwave power and the reaction pressure to make the substrate temperature within the range of 750-900 ℃, and introducing 4% methane to perform the diamond nucleation process on the surface of the substrate.

After the nucleation process is finished, closing methane, adjusting the microwave power and the reaction pressure to ensure that the substrate temperature is within the range of 800-.

After 30 hours, the methane ratio was raised to 2.6% and 0.25% oxygen was introduced to continue the diamond deposition.

After 60 hours, the methane ratio is continuously increased to 3.3, the oxygen ratio is increased to 0.65%, and diamond deposition is continuously carried out.

After 80 hours, the methane proportion is increased to 3.7 percent, the oxygen proportion is increased to 1.1 percent, and the diamond deposition is continued until the deposition process is finished.

Example 6:

a growth method for controlling the grain size of polycrystalline diamond by a microwave CVD method comprises the following steps:

pretreatment: grinding the surface of the monocrystalline silicon substrate by using diamond micro powder for 20min to generate uniform scratches; then the substrate is respectively placed in alcohol, acetone and alcohol for ultrasonic cleaning for 10min, and finally a dryer is adopted to dry the substrate.

Opening the cavity door of the device, placing the processed substrate on a molybdenum support and on a water-cooling deposition table in the reaction chamber, closing the cavity door, vacuumizing the reaction chamber, and vacuumizing the background to 1 × 10^-2Below torr.

Introducing hydrogen into the reaction chamber, adjusting the reaction pressure to 5-10torr, starting the microwave power supply, adjusting the microwave input power to 600-.

Regulating the microwave power and the reaction pressure to make the substrate temperature within the range of 750-900 ℃, and introducing 4% methane to perform the diamond nucleation process on the surface of the substrate.

After the nucleation process is finished, closing methane, adjusting the microwave power and the reaction pressure to ensure that the substrate temperature is within the range of 800-.

After 40 hours, the methane ratio was raised to 2.2% and 0.3% oxygen was introduced to continue the diamond deposition.

After 70 hours, the methane proportion is continuously increased to 3.1 percent, the oxygen proportion is increased to 0.7 percent, and the diamond deposition is continuously carried out.

After 90 hours, the methane proportion is increased to 3.6 percent, the oxygen proportion is increased to 1.1 percent, and the diamond deposition is continued until the deposition process is finished.

The grain size and the film integrity of the diamond film obtained in the above examples and the grain size and the film integrity of the diamond film obtained by the prior art are shown in table 1, and it can be seen from table 1 that the grain size of the diamond film obtained by the growth method is between 5 and 10um, the film integrity is between 72 and 85 percent and is greater than 70 percent, while the grain size obtained by the prior art is between 20 and 30um, and the film integrity is only 60 percent; and any cracks were not found to occur in all the examples, whereas cracks occurred more in the diamond film obtained in the prior art. Further, a microscopic photograph of the diamond grains obtained by the present method is shown in fig. 2; a microscopic photograph of diamond grains obtained by the prior art method is shown in fig. 3; as can be seen from the two pictures, the diamond film obtained by the growing method has the advantages of finer grain size, uniform and compact distribution, high film finishing rate and no crack.

TABLE 1 comparison of diamond film grains obtained by the present method with existing methods

The growth method for controlling the grain size of the polycrystalline diamond by adopting the microwave CVD method is designed, and the size of the grain size of the polycrystalline diamond is controlled by gradually increasing the concentration of a carbon source and the concentration of oxygen in different time periods so as to increase the nucleation rate of the diamond in a stepped manner, thereby improving the quality of a diamond film; meanwhile, the growth rate of the diamond film can be improved in a stepped manner, and the lattice defect of the epitaxial layer is reduced, so that the growth stress can be reduced, and the complete crack-free diamond film can be obtained.

The above detailed description of the embodiments of the present method is only a preferred embodiment of the present method, and should not be taken as limiting the scope of the present method. All equivalent changes and modifications made within the scope of the application of the method shall fall within the scope of the patent of the method.