Frequency modulation matching radio frequency plasma generator

Abstract

The invention discloses a frequency modulation matching radio frequency plasma generator which is not provided with an independent impedance matcher any more, an output structure in a high-frequency radio frequency source is provided with a simple inverted L-shaped LC matching device, and the inverted L-shaped LC matching device adjusts impedance matching in advance according to different plasma generation cavities. When the high-frequency radio frequency source is turned on, a radio frequency signal (power) is input (fed into) into the plasma generation cavity, and the plasma is heated and ignited. After ignition, the plasma can be regarded as a medium to cause the impedance change of the plasma generation cavity, and the impedance changes along with the change of the plasma density. The output impedance of the high-frequency radio frequency source is not matched with the input impedance of the plasma generation cavity at the moment, the radio frequency power is reflected, the high-frequency radio frequency source measures the reflection power or standing-wave ratio of a reflection radio frequency signal, and the frequency of the radio frequency signal is increased according to the measured reflection power or standing-wave ratio until the measured reflection power is 0 and the measured standing-wave ratio is reduced to 1; impedance matching is obtained again, all the radio frequency power is input into the plasma generation cavity, and reflection is avoided. The high-frequency radio frequency source is free of mechanical adjustment and high in adjustment speed, reduces reflection power borne by the high-frequency radio frequency source and prevents the high-frequency radio frequency source from being damaged.

Description

Technical Field

[0001] The present invention belongs to the technical field of radio frequency plasma generation. More specifically, it relates to impedance matching technologies between high-frequency radio frequency power supplies and plasma chambers in semiconductor etching, thin-film deposition, and surface treatment equipment such as radio frequency plasma etchers, radio frequency plasma chemical vapor deposition, and molecular beam epitaxy. Background Art

[0002] Plasma, also called plasma, is a gaseous substance composed of atoms and atomic groups after some electrons are stripped, forming positive and negative ions, and is electrically neutral as a whole. It exists widely in the universe and is called the fourth state of matter. The development of plasma physics has provided new technologies and processes for the further development of sciences such as materials, energy, information, environmental space, space physics, and geophysics.

[0003] A radio frequency plasma generator refers to a device that generates plasma by heating with radio frequency power. Using radio frequency to generate specific plasma for semiconductor etching, thin-film deposition, and surface treatment is a newly developed high-precision process technology. Typical applications mainly include chip processing below 28 nm. At present, there are various types of radio frequency plasma devices, and the commonly used operating frequencies are 400 kHz, 13.56 MHz, 27.12 MHz, etc. The commonly used structures are capacitive coupled plasma, inductively coupled plasma, and inductively coupled plasma with a magnetic core.

[0004] Regardless of which radio frequency plasma device, there is the same problem, that is, the impedance changes drastically before and after the plasma is ignited. Because after the plasma is ignited, the plasma density increases and can be regarded as a medium with a certain conductivity, which results in impedance mismatch at this time, and almost all the radio frequency power is reflected back.

[0005] As Figure 1 shown, the traditional radio frequency plasma generator mainly generates radio frequency power from a high-frequency radio frequency source, which is transmitted to an impedance matcher. The impedance matcher outputs to a plasma generation chamber to generate plasma. Among them, the impedance matcher consists of two variable capacitors C1, C2 and one inductor L. When not heated, the variable capacitors are adjusted to achieve impedance matching between the output impedance of the high-frequency radio frequency source and the impedance of the plasma chamber, so as to feed the radio frequency power into the plasma chamber. After the plasma is ignited, the impedance of the plasma chamber changes, and all the radio frequency power is emitted. At this time, the two variable capacitors C1, C2 in the impedance matcher are adjusted again, so that the radio frequency power is reflected between the impedance matcher and the plasma chamber. For the high-frequency radio frequency source, the output impedance is matched. The two variable capacitors C1, C2 in the impedance matcher are adjusted to achieve matching through mechanical means, with slow matching speed, high reflected power, and easy damage to the high-frequency radio frequency source. Summary of the Invention

[0006] The object of the present invention is to overcome the deficiencies of the prior art and provide a frequency modulation matching radio frequency plasma generator to improve the adjustment speed of impedance matching, reduce the reflected power borne by the high-frequency radio frequency source, and prevent its damage.

[0007] To achieve the above object of the invention, the frequency modulation matching radio frequency plasma generator of the present invention includes:

[0008] A high-frequency radio frequency source for generating radio frequency signals and outputting them to the plasma generation chamber through a radio frequency cable;

[0009] A plasma generation chamber for receiving radio frequency signals from the high-frequency radio frequency source and heating to generate plasma;

[0010] It is characterized in that:

[0011] The output structure inside the high-frequency radio frequency source has a Γ-type LC matching device. For different plasma generation chambers, the Γ-type LC matching device pre-adjusts the impedance matching;

[0012] Inside the high-frequency radio frequency source, there is a power or standing wave ratio test probe. When the high-frequency radio frequency source is turned on, the radio frequency signal is input into the plasma generation chamber through the radio frequency cable. After heating and igniting the plasma, the reflected power or standing wave ratio of the radio frequency signal reflected back from the plasma generation chamber through the radio frequency cable is measured. The high-frequency radio frequency source increases the frequency of the radio frequency signal according to the measured reflected power or standing wave ratio until the measured reflected power is 0 or the standing wave ratio is reduced to 1, and impedance matching is obtained again. All the radio frequency power is input into the plasma generation chamber and there is no longer any reflection.

[0013] The object of the present invention is achieved in this way.

[0014] The frequency modulation matching radio frequency plasma generator of the present invention no longer has an independent impedance matcher. The output structure inside the high-frequency radio frequency source has a simple Γ-type LC matching device. For different plasma generation chambers, the Γ-type LC matching device pre-adjusts the impedance matching. When the high-frequency radio frequency source is turned on, at this time, the radio frequency signal (power) is input (fed) into the plasma generation chamber, heating and igniting the plasma. After ignition, the plasma can be regarded as a medium, resulting in a change in the impedance of the plasma generation chamber, and the impedance changes with the change in plasma density. Since the output impedance of the high-frequency radio frequency source does not match the input impedance of the plasma generation chamber at this time, reflected radio frequency power occurs. The high-frequency radio frequency source measures the reflected power or standing wave ratio of the reflected radio frequency signal, and according to the measured reflected power or standing wave ratio, increases the frequency of the radio frequency signal until the measured reflected power is 0 and the standing wave ratio is reduced to 1, and impedance matching is obtained again. All the radio frequency power is input into the plasma generation chamber and there is no longer any reflection. The present invention has no mechanical adjustment, has a fast adjustment speed, reduces the reflected power borne by the high-frequency radio frequency source, and prevents its damage.

[0015] In addition, the present invention also has the following advantages: 1) small volume and simple structure, no separate matcher is required anymore, and the frequency matching can be adjusted only by monitoring the reflected power or standing wave ratio of the reflected radio frequency signal; 2) all radio frequency energy is fed into the plasma generation cavity, while the traditional impedance matcher will cause energy loss and heat loss of the impedance matcher due to back and forth reflection; 3) fast adjustment speed, improving the stability and service life of the frequency modulation matching radio frequency plasma generator; 4) existing high-frequency radio frequency sources can adjust the frequency within an appropriate range by themselves, and the present invention does not require an additional adjustment structure and has good matching effect. Brief Description of the Drawings

[0016] Figure 1 is a schematic diagram of the composition structure and circuit of a traditional radio frequency plasma generator;

[0017] Figure 2 is a schematic diagram of the composition structure and circuit of a specific embodiment of the frequency modulation matching radio frequency plasma generator set of the present invention;

[0018] Figure 3 is a structural cross-section and magnetic induction distribution diagram of an inductively coupled plasma generation cavity (ICP);

[0019] Figure 4 is a standing wave ratio curve graph before plasma ignition;

[0020] Figure 5 is a schematic diagram of the electron density distribution after plasma ignition;

[0021] Figure 6 is a graph of the standing wave ratio varying with frequency after plasma ignition with 200W radio frequency power;

[0022] Figure 7 is a graph of the standing wave ratio varying with frequency at 400w radio frequency power. Detailed Embodiment

[0023] 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.

[0024] Figure 2 is a schematic diagram of the composition structure and circuit of a specific embodiment of the frequency modulation matching radio frequency plasma generator set of the present invention.

[0025] In this embodiment, as Figure 2 shown, the frequency modulation matching radio frequency plasma generator of the present invention includes a high-frequency radio frequency source 1 and a plasma generation cavity 2.

[0026] The high-frequency radio frequency source 1 is used to generate radio frequency signals and output them to the plasma generation chamber 2 through a radio frequency cable. In this embodiment, the radio frequency cable uses a coaxial cable for radio frequency power transmission. The plasma generation chamber 2 is used to receive the radio frequency signals from the high-frequency radio frequency source 1 and heat to generate plasma.

[0027] In the frequency modulation matching radio frequency plasma generator of the present invention, there is no longer an independent impedance matcher, but a Γ-type LC matching device is constructed in the output structure of the high-frequency radio frequency source 1 ( Figure 2 composed of the capacitor C and the inductor L in it). For different plasma generation chambers 2, the Γ-type LC matching device pre-adjusts the impedance matching. In addition, a power or standing wave ratio test probe is also constructed in the high-frequency radio frequency source 1. When the high-frequency radio frequency source is turned on, the radio frequency signal is input into the plasma generation chamber 2 through the radio frequency cable. After heating and igniting the plasma, the reflected power or standing wave ratio of the radio frequency signal reflected back by the plasma generation chamber 2 through the radio frequency cable is measured. The high-frequency radio frequency source 1 increases the frequency of the radio frequency signal according to the measured reflected power or standing wave ratio until the measured reflected power is 0 or the standing wave ratio is reduced to 1, and impedance matching is obtained again, and all the radio frequency power is input into the plasma generation chamber without reflection.

[0028] The present invention measures the reflected power or standing wave ratio on the radio frequency cable and combines frequency modulation to achieve impedance matching. Therefore, regardless of the structure of the plasma generation chamber, including structures such as capacitive coupling, inductive coupling, planar inductor, and iron-core inductor coupling, as long as radio frequency excitation is used to generate plasma and frequency modulation impedance matching is adopted, it belongs to the protection scope of the present invention.

[0029] In the actual application process, according to different designs, the reflected power or the measured standing wave ratio can be measured by a three-probe test, a directional coupler, etc. The radio frequency signal transmission can use a conventional coaxial cable or a high-power all-metal coaxial cable (made of conductive metals such as stainless steel, oxygen-free copper, and aluminum), and all belong to the protection scope of the present invention.

[0030] Difference from other inventions: Shanghai Huahong Integrated Circuit Manufacturing Co., Ltd. once submitted a patent application for an invention "Structure and Method for Improving Plasma Stability" (publication number CN119400678A, publication date February 7, 2025), which uses a discharge voltage consistent with the discharge current to improve plasma stability. The present invention adjusts the operating frequency to achieve plasma impedance matching.

[0031] Example

[0032] In this example, the plasma generation chamber uses an inductively coupled plasma generation chamber (ICP), and its structural section and magnetic induction distribution are as Figure 3As shown in the figure, the radius of the plasma cavity is 30 mm and the height is 23 mm. There is a quartz dielectric sheet on the plasma cavity to isolate the vacuum. Four coils are placed on the quartz dielectric sheet as inductive coupling windings. The magnetic induction lines of the coil windings are shown in Figure 3.

[0033] The impedance of the coil winding of the above ICP structure is measured to be 0.6614 + 156.65i during cold testing. The high-frequency RF source operates at 13.56 MHz and has an in-built Γ-type matching structure, where the capacitance is 2e-9 F and the inductance is 1.77e-6 H. At this time, the standing wave ratio is as Figure 4 shown. The impedance matching is pre-adjusted to achieve matching at 13.56 MHz with the minimum standing wave ratio.

[0034] When RF power is applied, when the RF power is 200 W, the plasma can be ignited, and its electron density distribution is as Figure 5 shown.

[0035] Figure 6 After the plasma is ignited with 200 W, the impedance becomes 1.05 + 155.5i and the power reflection is relatively large. At this time, the frequency is adjusted to 13.67 MHz, which can reduce the standing wave ratio and meet the application requirements.

[0036] Figure 7 In the case of 400 W RF power, as the plasma density increases, the frequency also needs to be increased to 13.82 MHz to meet the application requirements.

[0037] It can be seen from the above examples that the standing wave ratio can be reduced by increasing the frequency of the RF signal to achieve impedance matching. Moreover, the greater the power, the greater the amplitude of the increase in the frequency of the RF signal, thus achieving the purpose of the present invention.

[0038] Although the above describes the illustrative specific embodiments of the present invention for the convenience of those skilled in the art to understand the present invention, 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, 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 radio frequency plasma generator, comprising: A high frequency radio frequency source is used to generate a radio frequency signal and output it to the plasma generating chamber through a radio frequency cable; The plasma generating chamber is used to receive a radio frequency signal from a high frequency radio frequency source and to heat and generate plasma; Features: The output structure of the high-frequency radio frequency source has a Γ-type LC matching device, and the Γ-type LC matching device pre-adjusts the impedance matching for different plasma generating cavities; The high-frequency radio frequency source has a power or standing wave ratio test probe, which is used to turn on the high-frequency radio frequency source, input the radio frequency signal into the plasma generating chamber through the radio frequency cable, heat and ignite the plasma, and measure the reflected power or standing wave ratio of the radio frequency signal reflected back from the plasma generating chamber through the radio frequency cable. The high-frequency radio frequency source increases the frequency of the radio frequency signal according to the measured reflected power or standing wave ratio until the measured reflected power is 0 or the standing wave ratio is reduced to 1, and impedance matching is obtained again, and the radio frequency power is fully input into the plasma generating chamber without any reflection.

2. The frequency modulation matching radio frequency plasma generator according to claim 1, characterized in that: The plasma generating chamber adopts a capacitive coupling, inductive coupling, planar inductance or iron core inductive coupling structure.

3. The frequency modulation matching radio frequency plasma generator according to claim 1, characterized in that: The radio frequency cable is a coaxial cable or a high-power all-metal coaxial cable.

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