阅读说明：本技术 基于射频电源施加偏压以增强cvd金刚石异质外延形核的方法 (Method for enhancing CVD diamond heteroepitaxial nucleation based on radio frequency power supply applied bias voltage ) 是由 朱嘉琦 代兵 王伟华 王杨 舒国阳 于 2020-07-27 设计创作，主要内容包括：基于射频电源施加偏压以增强CVD金刚石异质外延形核的方法,本发明属于化学气相沉积法异质外延单晶金刚石生长领域,它为了解决绝缘异质衬底难以有效施加负偏压的问题。外延形核的方法：一、将底部开有凹槽腔的样品托放置于CVD腔体内的水冷台上,射频电源的一电极通过导线连接到CVD腔体外壳上并接地,射频电源的另一电极通过导线经水冷台连接到样品托上；二、将异质衬底放置在样品托中心位置,CVD腔体抽真空；三、升温过程,通入氢气；四、控制甲烷气体浓度,进行偏压增强形核；五、生长过程及结束。本发明通过射频电源,避免了直流偏压施加过程中绝缘异质衬底电势升高导致无法正常施加偏压,实现了绝缘异质衬底上高密度外延形核。(The invention discloses a method for enhancing CVD diamond heteroepitaxy nucleation based on radio frequency power supply bias voltage application, belongs to the field of chemical vapor deposition heteroepitaxy single crystal diamond growth, and aims to solve the problem that an insulating heterogeneous substrate is difficult to effectively apply negative bias voltage. The method of epitaxial nucleation: placing a sample holder with a groove cavity at the bottom on a water cooling table in a CVD cavity, connecting one electrode of a radio frequency power supply to a CVD cavity shell through a lead and grounding, and connecting the other electrode of the radio frequency power supply to the sample holder through the water cooling table through the lead; secondly, placing the heterogeneous substrate in the center of the sample holder, and vacuumizing the CVD cavity; thirdly, in the temperature rising process, introducing hydrogen; fourthly, controlling the concentration of methane gas, and carrying out bias enhanced nucleation; fifthly, finishing the growth process. The invention avoids the situation that the bias voltage cannot be normally applied due to the potential rise of the insulating heterogeneous substrate in the direct current bias voltage application process by the radio frequency power supply, and realizes high-density epitaxial nucleation on the insulating heterogeneous substrate.)

1. A method for enhancing CVD diamond heteroepitaxial nucleation based on applying bias voltage by a radio frequency power supply is characterized in that the heteroepitaxial nucleation method is realized according to the following steps:

firstly, connecting a radio frequency power supply:

placing a sample holder with a groove cavity at the bottom on a water cooling table in a CVD cavity, connecting one electrode of a radio frequency power supply to a CVD cavity shell through a lead and connecting the other electrode of the radio frequency power supply to the sample holder through the water cooling table through the lead, and completing the connection of the radio frequency power supply;

secondly, air extraction of equipment:

placing a heterogeneous substrate at the center of a sample holder, enabling one end of an air exhaust path to penetrate through a water cooling table to be communicated with a groove cavity of the sample holder, enabling the other end of the air exhaust path to be connected with a vacuum pump, vacuumizing the cavity after closing the CVD cavity, starting the vacuum pump, opening an air path valve to enable the vacuum degree in the CVD cavity to reach 5.0 multiplied by 10^-7～5.0×10^-6Torr, the gas pressure of a gas path of the sample holder is 1-10 Torr, and the equipment is pumped;

thirdly, heating process:

a. controlling the hydrogen flow to be 200-400 sccm and the gas pressure in the CVD cavity to be 5-10 torr, starting a microwave generator, and activating plasma;

b. gradually increasing the air pressure in the CVD cavity, the power of the microwave generator and the temperature of the heterogeneous substrate;

c. continuously measuring the surface temperature of the heterogeneous substrate by a temperature measuring meter along with the fact that the air pressure in the CVD cavity reaches 30-500 Torr;

d. adjusting the internal air pressure of the sample holder to ensure that the air pressure of the sample holder is lower than the air pressure in the CVD cavity, and the temperature of the heterogeneous substrate reaches 600-1500 ℃;

fourthly, a bias enhanced nucleation process:

e. etching and cleaning the heterogeneous substrate by using H plasma;

f. introducing methane gas, and controlling the concentration of the methane gas;

g. starting a radio frequency power supply to perform bias enhancement nucleation;

h. turning off the radio frequency power supply and stopping the bias enhanced nucleation process;

fifthly, growth process and end:

i. changing the concentration of methane, starting diamond vapor phase epitaxial growth, measuring the temperature of the heterogeneous substrate in real time, and adjusting the air pressure of a sample gas supporting path when the temperature of the heterogeneous substrate changes so as to keep the temperature of the sample stable until the deposition growth is finished;

j. reducing pressure and power, and vacuumizing the CVD chamber to make the vacuum degree in the CVD chamber reach 5.0 × 10^-7～5.0×10^{- 6}Torr；

k. And (3) deflating to enable the air pressure in the CVD cavity to reach 1atm, and then opening the cavity to finish the method for applying bias voltage based on the radio frequency power supply to enhance the heteroepitaxial nucleation of the CVD diamond.

2. The method of claim 1 wherein the foreign substrate in step two is Ir/MgO, Ir/SrTiO₃、Ir/SrTiO₃Si or Ir/YSZ/Si, Si, SiC.

3. The method of claim 1 wherein step a is performed by setting the flow rate of hydrogen to 200-250 sccm and the pressure in the CVD chamber to 10 Torr.

4. A method for enhancing CVD diamond heteroepitaxial nucleation based on radio frequency power bias as claimed in claim 1 wherein in step b in step three, the pressure is raised at a rate of 0.5to 5Torr/s and the microwave power is raised at a rate of 100to 1000W/min.

5. The method of claim 1 in which step d is a step in which the internal pressure of the sample holder is evacuated to 10to 100 Torr.

6. A method for enhanced heteroepitaxial nucleation of CVD diamond based on the application of a bias voltage from a radio frequency power supply according to claim 1, wherein the temperature of the foreign substrate in step d in step three is between 650 ℃ and 800 ℃.

7. The method for enhancing heteroepitaxial nucleation of CVD diamond based on RF bias applied from the RF power supply as claimed in claim 1, wherein the etching time in step four is 10-30 min.

8. The method for enhancing heteroepitaxial nucleation of CVD diamond based on RF power supply as claimed in claim 1, wherein the flow rate of the methane gas introduced in step f is 10-50 sccm, the volume fraction of the methane gas is 5% -8%, and the maintaining time is 1-5 min.

9. The method for enhancing heteroepitaxial nucleation of CVD diamond based on RF bias applied by claim 1, wherein in step four step g the power of the RF source is controlled to be 200-1000W and the frequency of the RF source is 13.56 MHz.

10. A method for enhancing CVD diamond heteroepitaxial nucleation based on radio frequency power supply bias voltage according to claim 1 wherein in step five the flow rate of methane is controlled to be 2-4 sccm in step i and diamond vapor phase epitaxy growth is started.

Technical Field

The invention belongs to the field of chemical vapor deposition heteroepitaxial single crystal diamond growth, and particularly relates to a method for enhancing heteroepitaxial nucleation of diamond based on bias voltage applied by a radio frequency power supply.

Background

Diamond has excellent properties such as force acoustoelectric light and the like, and is a typical ultra-wide bandgap semiconductor. Diamond can be further classified into polycrystalline diamond and single crystal diamond according to the presence or absence of grain boundaries. Generally, the polycrystalline diamond can meet application requirements in the aspects of heat sinks, infrared and microwave windows, wear-resistant coatings and the like, but the polycrystalline diamond cannot be comparable to the single-crystal diamond if the polycrystalline diamond is built in the key fields of detectors (such as ultraviolet detectors and radiation detectors), power devices (such as field effect transistors and diodes) and the like by really playing the excellent electrical properties of the diamond. This is mainly because the existence of the grain boundary in the polycrystal greatly reduces the carrier mobility and the charge collection efficiency, so that the performance of the electronic device prepared by the grain boundary is seriously inhibited.

The large-size natural single crystal diamond is extremely rare and expensive, and the application is basically impossible, so that the preparation of the large-size high-quality single crystal diamond is a technical problem which needs to be solved in order to really apply the excellent electrical properties of the single crystal diamond to the relevant military and civil fields. There are two types of single crystal diamond production, HPHT method and CVD method, respectively. The single crystal diamond prepared by the HPHT method generally contains nitrogen impurities, which affects the quality of the diamond; small in size (typically a few millimeters in size); the cost is high, the technical requirement is strict, and the defects directly determine that the HPHT diamond can only be applied to the low-end field and cannot meet the requirements in the high and new technical field. CVD methods can be further divided into homoepitaxy processes and heteroepitaxy processes. The heteroepitaxy process is a method for obtaining a large-size epitaxial monocrystalline diamond film by performing high-density epitaxial nucleation on a non-diamond substrate and controlling the growth process to realize grain merging and texture growth. Compared with homoepitaxy, the method for realizing large size usually needs a mosaic splicing method, a repeated growth method, a three-dimensional growth method and other methods, but has more advantages compared with the method that crystal boundaries cannot be completely annihilated.

The most important problem to be solved by the heteroepitaxy process is high-density epitaxy nucleation, and the most typical method at present is a bias enhanced nucleation process, namely, a certain direct current negative bias is applied on a heterogeneous substrate, and high-energy C in plasma in a CVD resonant cavity is under the action of an electric field_xH_y ⁺The ions rapidly bombard the surface of the substrate and interact with the substrate, then an amorphous carbon, graphite or other transition layer is formed on the surface of the substrate based on the dissolution-precipitation process of C in the substrate, diamond is limited by the boundary condition of the template effect of the substrate due to the fluctuation of concentration on the surface of the transition layer or the interface with the substrate, finally, the self-assembly epitaxial nucleation process occurs, and a large number of secondary crystal nuclei are generated around the crystal nuclei after the formation of the primary crystal nuclei, namely, the high-density epitaxial nucleation is completed.

The currently reported bias applying mode is realized by an external direct current bias power supply, namely, a positive electrode of a control power supply is externally connected with a CVD equipment cavity and then grounded, a sample holder for placing the heterogeneous substrate is connected with a negative electrode, or the positive electrode is connected with a ring electrode extending into the plasma, the negative electrode is connected with the sample holder for placing the heterogeneous substrate and then grounded, and then negative bias of a certain size is obtained on the heterogeneous substrate. However, the DC bias cannot be applied to the insulating foreign substrate due to the high energy C_xH_y ⁺When ions bombard the insulating substrate, positive charges are gathered on the substrate, so that the potential of the surface of the substrate is raised, the potential difference between the heterogeneous substrate and the anode is gradually reduced to 0, and further, a bias power supply cannot be directly applied to the insulating substrate but completely avoids the substrate to be applied to the conductive sample holder. The prior heterogeneous substrate mainly has a multilayer composite structure, such as Ir/MgO, Ir/SrTiO₃,Ir/SrTiO₃Si, Ir/YSZ/Si, Si, SiC, etc. These heterogeneous substrates all present an insulating oxide ceramic as a transitionThe layer, when biased, inevitably suffers from the above-mentioned problems.

Disclosure of Invention

The invention aims to solve the problems that an insulating heterogeneous substrate is difficult to effectively apply negative bias and nucleation density is low, and provides a method for applying bias by a radio frequency power supply to enhance CVD diamond epitaxial nucleation.

The method for enhancing CVD diamond heteroepitaxial nucleation based on applying bias voltage by a radio frequency power supply is realized according to the following steps:

firstly, connecting a radio frequency power supply:

placing a sample holder with a groove cavity at the bottom on a water cooling table in a CVD cavity, connecting one electrode of a radio frequency power supply to a CVD cavity shell through a lead and connecting the other electrode of the radio frequency power supply to the sample holder through the water cooling table through the lead, and completing the connection of the radio frequency power supply;

secondly, air extraction of equipment:

placing a heterogeneous substrate at the center of a sample holder, enabling one end of an air exhaust path to penetrate through a water cooling table to be communicated with a groove cavity of the sample holder, enabling the other end of the air exhaust path to be connected with a vacuum pump, vacuumizing the cavity after closing the CVD cavity, starting the vacuum pump, opening an air path valve to enable the vacuum degree in the CVD cavity to reach 5.0 multiplied by 10^-7～5.0×10^-6Torr, the gas pressure of a gas path of the sample holder is 1-10 Torr, and the equipment is pumped;

thirdly, heating process:

a. controlling the hydrogen flow to be 200-400 sccm and the gas pressure in the CVD cavity to be 5-10 torr, starting a microwave generator, and activating plasma;

b. gradually increasing the air pressure in the CVD cavity, the power of the microwave generator and the temperature of the heterogeneous substrate;

c. continuously measuring the surface temperature of the heterogeneous substrate by a temperature measuring meter along with the fact that the air pressure in the CVD cavity reaches 30-500 Torr;

d. adjusting the internal air pressure of the sample holder to ensure that the air pressure of the sample holder is lower than the air pressure in the CVD cavity, and the temperature of the heterogeneous substrate reaches 600-1500 ℃;

fourthly, a bias enhanced nucleation process:

e. etching and cleaning the heterogeneous substrate by using H plasma;

f. introducing methane gas, and controlling the concentration of the methane gas;

g. starting a radio frequency power supply to perform bias enhancement nucleation;

h. turning off the radio frequency power supply and stopping the bias enhanced nucleation process;

fifthly, growth process and end:

i. changing the concentration of methane, starting diamond vapor phase epitaxial growth, measuring the temperature of the heterogeneous substrate in real time, and adjusting the air pressure of a sample gas supporting path when the temperature of the heterogeneous substrate changes so as to keep the temperature of the sample stable until the deposition growth is finished;

j. reducing pressure and power, and vacuumizing the CVD chamber to make the vacuum degree in the CVD chamber reach 5.0 × 10^-7～5.0×10^-6Torr；

k. And (3) deflating to enable the air pressure in the CVD cavity to reach 1atm, and then opening the cavity to finish the method for applying bias voltage based on the radio frequency power supply to enhance the heteroepitaxial nucleation of the CVD diamond.

In the bias enhanced nucleation process of the fourth step of the invention, when the equipment cavity is grounded, the electric potential on the sample holder is periodically changed in positive and negative directions due to the radio frequency power supply, when the sample holder is in positive electric potential, electrons in the plasma migrate to the sample holder and the heterogeneous substrate under the action of the electric field, and C_xH_y ⁺The ions migrate to the cavity, and the electrons are gathered on the insulating heterogeneous substrate; c in the plasma when the sample holder is at a negative potential_xH_y ⁺The ions migrate to the sample support and the heterogeneous substrate under the action of the electric field, and then are neutralized with the electrons collected before, and the electrons migrate to the cavity. But electrons and C_xH_y ⁺The ions have different masses, so that the rate of electron migration is greater than C under the same electric field intensity_xH_y ⁺The rate of ion migration results in the sample holder and the insulating foreign substrate overall assuming a negative potential during one cycle of potential change. By the radio frequency power supply, the invention avoids insulation in the process of applying direct current bias voltageThe heterogeneous substrate potential rises to cause a situation where the bias voltage cannot be normally applied.

The method for enhancing CVD diamond heteroepitaxy nucleation by applying bias voltage based on the radio frequency power supply solves the problems that the potential difference between an insulating heterogeneous substrate and a cavity is greatly reduced, the electric field intensity is seriously weakened, and C is generated due to the fact that the surface potential of the insulating heterogeneous substrate is increased due to charge accumulation_xH_y ⁺The ions can not normally bombard the surface of the substrate, thereby realizing high-density epitaxial nucleation.

Drawings

FIG. 1 is a schematic view of a CVD apparatus to which a radio frequency power source is connected according to the present invention; the device comprises a CVD cavity, a 2-heterogeneous substrate, a 3-sample holder, a 4-water cooling table, a 5-vacuum gauge, a 6-pumping pipeline, a 7-vacuum pump and an 8-radio frequency power supply.

Detailed Description