Frequency modulation matching microwave plasma generator

Abstract

The invention discloses a frequency modulation matching microwave plasma generator, which is characterized in that a circulator is connected between a microwave source and a plasma resonant cavity, microwaves are input from a port 1 of the circulator, and are output to the plasma resonant cavity from a port 2, so that the reflected microwaves are output from a port 3. Meanwhile, a matched load and a power meter are connected to a port 3 of the circulator, microwaves output by the port 3 of the circulator are absorbed by the matched load, most returned microwaves are absorbed by the matched load, a small part of the microwaves are reflected back to the port 3, the microwaves input by the port 3 are output at a port 1, the microwave power borne by the microwave source is reduced, and the stability and the service life of the microwave source are improved. The control system adjusts the output frequency of the microwave source according to the measured power, so that the output frequency of the microwave source is improved, and the output impedance of the microwave source is matched with the working impedance of the plasma resonant cavity again, so that the back-and-forth reflection loss of microwaves is avoided; and the impedance matching adjustment speed is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave plasma generation, and more specifically, relates to a frequency modulation matching microwave plasma generator. Background Art

[0002] Microwave plasma utilizes electromagnetic waves to excite different types of gases. After the gas molecules and trace initial electrons present in the gas are accelerated by the electric field generated by the microwave, elastic and inelastic collisions occur, resulting in gas ionization and the formation of plasma. With the continuous input of microwave energy, a stable plasma state is maintained, and various applications are generated using the plasma and active free radicals.

[0003] Microwave plasma chemical vapor deposition (MPCVD) is a more efficient method for preparing materials such as diamond and SiC that has rapidly developed in the past thirty years. The plasma generated by using microwave as the external energy excitation is a non-self-sustained discharge, with the highest plasma density. The materials and film layers prepared by its chemical vapor deposition have the advantages of high purity, good crystal morphology, large growth area, good uniformity, low energy consumption cost, simple operation of the equipment, no vulnerable parts in the equipment itself, and can operate stably for a long time. Compared with the previous DC, high-frequency, and hot filament emission methods, MPCVD is considered the most advanced method for semiconductor material preparation in the world today and is also the only method that can prepare high-quality diamond films for optics and electronics.

[0004] Microwave plasma etching is also a newly developed etching method. By using microwave to excite plasma, CF4, Cl2, etc. are ionized into F and Cl ions. The highly active ions combine with Si to form SiF4, which is discharged, thereby realizing deep high-aspect-ratio etching.

[0005] Currently, there are various types of microwave plasma generators. Starting from the earliest quartz tube type, it has developed to the current microwave resonant cavity type, gradually overcoming many disadvantages such as low power and many impurities in the early stage. From the perspective of the mode of generating the electric field in the microwave plasma resonant cavity, it can generally be divided into a single-mode resonant cavity device and a multi-mode resonant cavity device. Classified by the shape of the cavity, it can be divided into three categories: rectangular, ellipsoidal, and cylindrical resonant cavity devices. In addition, according to different microwave frequencies, the system can be divided into two categories: 2.45 GHz and 915 MHz.

[0006] Regardless of which type of microwave plasma generator, there is the same problem, that is, the impedance changes greatly before and after the plasma is lit. This leads to impedance matching between the resonant cavity and the feeding impedance before lighting, and microwave energy can enter the resonant cavity to heat the plasma. When lit, the plasma density increases and can be regarded as a medium with a certain conductivity. At this time, the impedance is not matched, and almost all the microwave power is reflected back.

[0007] The existing processing method is generally to add a three-pin adjustment structure to reflect the microwave power back into the resonant cavity. For example, the Chinese invention patent application with publication number CN116939939A published on October 24, 2023, published "A Microwave Plasma Device", including a resonant cavity, a vacuum cavity, and a microwave generator, a circulator, a three-pin microwave tuner, a microwave mode converter, and a short-circuit piston connected in sequence. The two ends of the resonant cavity are respectively connected to the microwave mode converter and the vacuum cavity. The microwave mode converter is provided with a microwave antenna extending into the resonant cavity. A quartz window is provided between the resonant cavity and the vacuum cavity. The quartz window is used to isolate the resonant cavity and the vacuum cavity; wherein, along the axial direction of the vacuum cavity, the dimensions of both ends of the vacuum cavity are greater than the dimensions of the middle of the vacuum cavity. The above method makes the electric field distribution in the middle of the vacuum cavity the strongest, so as to excite and generate a stable plasma at this position and avoid the generation of secondary plasma in other areas. In addition, the microwave plasma device of the present application does not need to be ignited, avoiding the problem of introducing impurities due to ignition. Among them, the three-pin microwave tuner adjusts the load impedance matching to reduce microwave reflection. However, the use of three pins to adjust impedance matching actually reflects the electromagnetic wave power back to the resonant cavity, so the electromagnetic wave undergoes multiple reflections and the loss increases; secondly, the adjustment speed is slow, and relative to the microsecond lighting speed of the plasma, the high-power reflection may cause damage to the microwave source; thirdly, the three-pin adjustment structure is large in size and slow in response. Summary of the invention

[0008] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a frequency modulation matching microwave plasma generator to avoid round-trip reflection loss, improve the impedance matching adjustment speed, reduce the microwave power borne by the microwave source, and improve the stability and life of the microwave source.

[0009] To achieve the above-mentioned purpose, the frequency modulation matching microwave plasma generator of the present invention comprises:

[0010] A microwave source, used for generating microwaves;

[0011] Plasma resonant cavity, used to generate stable plasma under microwave excitation;

[0012] It is characterized by further comprising:

[0013] A circulator is connected between the microwave source and the plasma resonant cavity. The circulator has three ports. The microwave source inputs the microwave it generates into port 1 of the circulator. The circulator outputs the microwave input from port 1 to the plasma resonant cavity at port 2. The microwave reflected from the plasma resonant cavity is input from port 2 of the circulator and output from port 3.

[0014] The matching load and the power meter are both connected to the circulator port 3. The microwave output from the circulator port 3 is absorbed by the matching load. The power meter is used to measure the power of the microwave output from the circulator port 3.

[0015] A control system for receiving the power measured by a power meter and adjusting the output frequency of a microwave source according to the measured power:

[0016] Before the plasma is lit, i.e., generated, the microwave from the microwave source is fed into port 1 of the circulator and output to the plasma resonant cavity through port 2. At this time, the impedance is matched, and all microwave power is fed into the plasma resonant cavity without any microwave being reflected back from the plasma resonant cavity. The power measured by the power meter at port 3 of the circulator is 0.

[0017] After the plasma is lit, i.e., generated, the microwave source also feeds microwave into port 1 of the circulator. At this time, since a plasma is formed inside the plasma resonant cavity, its impedance changes, and the input impedance does not match the impedance of the plasma resonant cavity. Almost all the microwave is reflected. The reflected microwave enters through port 2 of the circulator and is output through port 3, and is absorbed by the matched load. At the same time, the power meter connected to port 3 of the circulator measures a power almost equal to the input microwave.

[0018] The control system receives the microwave power measured by the power meter and adjusts the output frequency of the microwave source. Since the plasma is regarded as a medium, after the plasma is lit, the frequency of the plasma resonant cavity will continuously increase. After the control system increases the output frequency of the microwave source, the output impedance of the microwave source and the operating impedance of the plasma resonant cavity are matched again, so as to continuously feed microwave energy into the plasma resonant cavity. At this time, the power measured by the power meter at port 3 of the circulator decreases until it becomes 0.

[0019] The object of the present invention is achieved in this way.

[0020] In the frequency modulation matching microwave plasma generator of the present invention, a circulator is connected between the microwave source and the plasma resonant cavity. Microwaves are input through port 1 of the circulator and output to the plasma resonant cavity through port 2, so that the reflected microwaves are output from port 3. At the same time, a matching load and a power meter are connected to port 3 of the circulator. The microwaves output from port 3 of the circulator are absorbed by the matching load, so that most of the returned microwaves are absorbed by the matching load, and a small part is reflected back to port 3. The microwaves input to port 3 are output from port 1, reducing the power of the microwaves borne by the microwave source, and improving the stability and service life of the microwave source. The power meter is used to measure the power of the microwaves output from port 3 of the circulator. The control system receives the power measured by the power meter and adjusts the output frequency of the microwave source according to the measured power, so that the output frequency of the microwave source is increased, and the output impedance of the microwave source and the working impedance of the plasma resonant cavity are matched again, so as to continuously feed microwave energy into the plasma resonant cavity. At this time, the power measured by the power meter at port 3 of the circulator decreases until it is 0, thus avoiding the loss of microwave back-and-forth reflection. At the same time, by adjusting the output frequency of the microwave source by the control system according to the reflected power to adjust the impedance matching, compared with the prior art of adjusting the impedance matching by using three large-sized pin structures, the impedance matching adjustment speed is greatly improved. Description of the Drawings

[0021] Figure 1 is a schematic structural diagram of a specific embodiment of the frequency modulation matching microwave plasma generator of the present invention;

[0022] Figure 2 is a simulation diagram of the plasma density distribution generated by the cylindrical microwave plasma cavity of the frequency modulation matching microwave plasma generator of the present invention;

[0023] Figure 3 is a reflection characteristic curve diagram of the plasma resonant cavity simulated after the plasma of the frequency modulation matching microwave plasma generator of the present invention is lit. Specific Embodiment

[0024] The following describes the specific embodiments of the present invention with reference to the drawings, so that those skilled in the art can better understand the present invention. It should be particularly noted that in the following description, when the detailed description of known functions and designs may dilute the main content of the present invention, these descriptions will be omitted here.

[0025] Figure 1 is a schematic structural diagram of a specific embodiment of the frequency modulation matching microwave plasma generator of the present invention.

[0026] In this embodiment, as Figure 1 shown, the frequency modulation matching microwave plasma generator of the present invention includes a microwave source 1, a plasma resonant cavity 2, a circulator 3, a matching load 4, a power meter 5, and a control system 6.

[0027] The microwave source 1 is used to generate microwaves, and the plasma resonant cavity 2 is used to generate a stable plasma under microwave excitation. A circulator 3 is connected between the microwave source 1 and the plasma resonant cavity 2. The circulator has three ports. The microwave source 1 inputs the microwaves it generates into port 1 of the circulator 3. The circulator 3 outputs the microwaves input from port 1 to the plasma resonant cavity 2 at port 2. The microwaves reflected back from the plasma resonant cavity 2 are input from port 2 of the circulator 3 and output at port 3.

[0028] The matching load 4 and the power meter 5 are both connected to port 3 of the circulator 3. The microwaves output from port 3 of the circulator 3 are absorbed by the matching load 4. The power meter 5 is used to measure the power of the microwaves output from port 3 of the circulator 3.

[0029] The control system 6 is used to receive the power measured by the power meter 5 and adjust the output frequency of the microwave source according to the measured power:

[0030] Before the plasma is lit, that is, before it is generated, the microwave power of the microwave source 1 is fed into port 1 of the circulator 3 and output to the plasma resonant cavity 2 through port 2. At this time, the impedance is matched, and all the microwave power is fed into the resonant cavity, and no microwaves are reflected back from the plasma resonant cavity 2. The power meter at port 3 of the circulator 3 measures a power of 0.

[0031] After the plasma is lit, that is, after it is generated, the microwave source 1 also feeds microwaves into port 1 of the circulator 3. At this time, since a plasma is formed inside the plasma resonant cavity 2, its impedance changes, and the input impedance and the impedance of the plasma resonant cavity 2 are not matched. Almost all the microwaves are reflected. The reflected microwaves enter through port 2 of the circulator 3 and are output from port 3, and are absorbed by the matching load 4. At the same time, the power meter 5 connected to port 3 of the circulator 3 measures a power that is nearly equal to the input microwave power.

[0032] The control system 6 receives the microwave power measured by the power meter and adjusts the output frequency of the microwave source 1. Since the plasma is regarded as a medium, after the plasma is lit, the frequency of the plasma resonant cavity 2 will continuously increase. After the control system 6 increases the output frequency of the microwave source, the output impedance of the microwave source 1 and the operating impedance of the plasma resonant cavity 2 are matched again, so as to continuously feed microwave energy into the plasma resonant cavity 2. At this time, the power measured by the power meter at port 3 of the circulator 3 decreases until it is 0.

[0033] The frequency modulation matching microwave plasma generator proposed by the present invention has the following advantages: 1) small size and simple structure, and the matching can be adjusted by only monitoring the power meter of the circulator port 3; 2) a circulator is used, and the 3 ports are connected to the matching load, so that most of the returned microwaves are absorbed by the matching load, and a small part is reflected back to the 3 ports, and the microwaves input at the 3 ports are output at the 1 port, thereby reducing the microwave power borne by the microwave source and improving the stability and life of the microwave source; 3) after matching, all microwave energy is fed into the plasma resonant cavity, and there will be no back and forth reflection loss; 4) the adjustment speed is fast.

[0034] The present invention uses the measurement of the reflected power of the circulator's three ports combined with frequency modulation to achieve impedance matching. Therefore, no matter the plasma resonant cavity adopts a cylindrical resonant cavity, a rectangular resonant cavity, or an elliptical resonant cavity, the reflected power is measured using various power meters or directional couplers, which all fall within the protection scope of the present invention.

[0035] In actual application, depending on the design, the resonant cavity material can be made of metal materials or alloy materials such as oxygen-free copper, stainless steel, tungsten, etc. The microwave channel can be a waveguide or a coaxial line, and the circulator can also be a waveguide circulator or a coaxial line circulator, all of which belong to the protection scope of the present invention.

[0036] Figure 2 This is a simulation diagram of plasma density distribution generated by the frequency modulation matching microwave plasma generator of the present invention using a cylindrical microwave plasma cavity, wherein the cavity radius is 180 mm, the height is 150 mm, the plasma resonance cavity frequency is calculated to be 2.466 GHz, and 500 W, 2.466 GHz microwaves are fed to generate plasma. The plasma density distribution is shown in FIG. Figure 2 shown.

[0037] Figure 3 This is a reflection characteristic curve diagram of the plasma resonance cavity after the plasma of the frequency modulation matching microwave plasma generator of the present invention is lit. Figure 3 As shown, we can see that the S11 of the original working frequency of 2.466GHz is about -0.5dB, that is, almost all the fed power is reflected, and the S11 of 2.71GHz is about -10dB, that is, about 10% of the power is reflected. Obviously, the frequency modulation to 2.71GHz meets the engineering requirements. Therefore, after the control system of the present invention increases the output frequency of the microwave source, the output impedance of the microwave source and the working impedance of the plasma resonant cavity are matched again, so that the microwave energy is continuously fed into the plasma resonant cavity.

[0038] Although the above description of the illustrative embodiments of the present invention has been provided for the understanding of those skilled in the art of the present technology, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art of the present technology, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions made using the concept of the present invention are within the scope of protection.

Claims

1. A frequency modulation matching microwave plasma generator, comprising: A microwave source, used for generating microwaves; Plasma resonant cavity, used to generate stable plasma under microwave excitation; It is characterized by further comprising: A circulator is connected between the microwave source and the plasma resonant cavity. The circulator has three ports. The microwave source inputs the microwave it generates into port 1 of the circulator. The circulator outputs the microwave input from port 1 to the plasma resonant cavity at port 2. The microwave reflected from the plasma resonant cavity is input from port 2 of the circulator and output from port 3. The matching load and the power meter are both connected to the circulator port 3. The microwave output from the circulator port 3 is absorbed by the matching load. The power meter is used to measure the power of the microwave output from the circulator port 3. The control system is used to receive the power measured by the power meter and adjust the output frequency of the microwave source according to the measured power: Before the plasma is lit, microwaves from the microwave source are fed into the plasma resonant cavity from port 1 of the circulator and output to the plasma resonant cavity through port 2. At this time, the impedance is matched, all microwave power is fed into the plasma resonant cavity, and no microwave is reflected back from the plasma resonant cavity. The power measured by the power meter at port 3 of the circulator is 0. When the plasma is lit, the microwave source also feeds microwaves from port 1 of the circulator. At this time, due to the formation of plasma inside the plasma resonant cavity, its impedance changes, and the input impedance does not match the impedance of the plasma resonant cavity. Almost all microwaves are reflected. The reflected microwaves enter from port 2 of the circulator, are output from port 3, and are absorbed by the matching load. At the same time, the power meter connected to port 3 of the circulator measures a power that is almost equal to the input microwave. The control system receives the microwave power measured by the power meter and adjusts the output frequency of the microwave source. Since the plasma is regarded as a medium, the frequency of the plasma resonant cavity will continue to increase after the plasma is lit. After the control system increases the output frequency of the microwave source, the output impedance of the microwave source and the working impedance of the plasma resonant cavity are matched again, thereby continuously feeding microwave energy into the plasma resonant cavity. At this time, the power measured by the circulator 3-port power meter decreases until it reaches 0.

2. The frequency modulation matching microwave plasma generator according to claim 1, characterized in that: The plasma resonant cavity is a cylindrical resonant cavity, a rectangular resonant cavity or an elliptical resonant cavity.

3. The frequency modulation matching microwave plasma generator according to claim 1, characterized in that: The channel for transmitting microwaves adopts a waveguide or a coaxial line, and the circulator adopts a waveguide circulator or a coaxial line circulator.

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