A system and method for plasma processing

Abstract

The application relates to a system and method for plasma processing. The system comprises a base, a gas delivery device and a full-wavelength spiral resonance device; wherein the full-wavelength spiral resonance device comprises n reaction cavities, n induction coils and a radio frequency power source for generating resonance and providing uniform plasma distribution; wherein the induction coils are located in the reaction cavities and are electrically connected with the radio frequency power source, the n reaction cavities are sequentially connected, the n induction coils are connected in series, the sum of the electrical lengths of the induction coils is an integral multiple of the wavelength of the radio frequency signal emitted by the radio frequency power source, and three induction loop zones are formed inside the reaction cavities. Compared with the prior art, the application has the advantages of realizing zero total magnetic moment design, improving processing efficiency, improving stability and simplifying structure.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and in particular to a system and method for plasma processing. Background Technology

[0002] This invention relates to a technical solution for plasma processing, particularly for processing applications achieved through inductive discharge. The invention is primarily applied to photoresist stripping processes in semiconductor device manufacturing. Furthermore, the technology of this invention can be widely applied to other plasma processing scenarios, such as material etching and the deposition of materials such as silicon, silicon nitride, silicon dioxide, and polycrystalline silicon.

[0003] Plasma technology plays a crucial role in modern semiconductor manufacturing, with typical applications including Chemical Dry Etching (CDE), Ion-Assisted Etching (IAE), and Plasma-Enhanced Chemical Vapor Deposition (PECVD). These processes typically introduce radio frequency power through induction coils, transferring energy to the working gas to excite plasma for tasks such as material removal, surface treatment, or thin film deposition.

[0004] In many processing scenarios, plasma-generated neutral reactive materials are used to achieve ion-free surface reactions, thereby reducing the risk of damage to the substrate. However, in some processing techniques, unavoidable ion bombardment can negatively impact material properties, such as causing interfacial mixing, oxide degradation, or changes in surface morphology. Traditional techniques to mitigate the effects of ion bombardment typically rely on increasing the distance between the plasma source and the processing chamber, or using shielding structures, baffles, or mesh structures to reduce charged particle migration. However, these methods often come with other problems, such as loss of neutral reactive materials, decreased process efficiency, increased device complexity, and potential metal ion contamination. Photoresist ashing or stripping refers to the process of completely removing the photoresist layer from the substrate. Photoresist stripping can also be achieved through chemical processes. However, wet chemical processes generate toxic waste. Oxygen plasma photoresist ashing processes utilize oxygen free radicals to oxidize organic photoresists, with byproducts typically being non-toxic COx and H2O gases.

[0005] In traditional plasma processing technologies, simply using baffles, shielding structures, or increasing the spatial separation between the plasma source and the processing chamber often fails to effectively prevent the generation of parasitic plasma currents. These parasitic currents typically occur between the wafer and the plasma source, or between the plasma source and the chamber wall. The main reason is that, in the presence of initially charged matter in the electric field, this charged matter accelerates and dissociates from neutral particles, causing a multiplication effect in charge concentration. If the initial charge level is sufficiently high, and the radio frequency electric field strength is large, the charge density of the parasitic plasma can significantly increase near the wafer surface, potentially even reaching or exceeding the plasma density within the plasma source region. This phenomenon leads to excessive ion flux acting directly on the substrate, resulting in serious adverse consequences. Higher charge densities can also generate significant voltage differences between the plasma source and the processing chamber or substrate support. This voltage difference further enhances the electric field, causing charged particles to be accelerated from the plasma source and transported to the substrate surface in an irregular manner, forming non-uniform ion-assisted etching characteristics. This not only reduces process selectivity but can also cause localized over-etching or damage to the substrate material layer.

[0006] Furthermore, in traditional induction discharge power supplies, the high voltage selection of the coil and the capacitive coupling between the plasma discharge easily lead to high potential fluctuations of the plasma relative to ground. These high potential fluctuations can trigger high-energy ion bombardment on the substrate, resulting in adverse consequences such as material mixing, surface amorphization, and contamination implantation. This effect is particularly pronounced in dynamic coupling caused by changes in radio frequency voltage, further exacerbating the wide range of variations in charged particle energy distribution and making it difficult to achieve uniform control of the ion flow.

[0007] To address these issues, previous studies have attempted to introduce internal conductive shielding or electrode elements into downstream processing equipment to regulate the voltage difference between the plasma source and the processing chamber. However, when the plasma potential increases significantly relative to the shielding electrodes, capacitive discharge can easily occur between the shield and the plasma source. This discharge not only leads to sputtering effects and becomes a source of contamination but also generates parasitic plasma currents, causing additional interference to the process environment. Furthermore, the small holes in the shielding design, typically used for gas flow, increase pressure loss and trigger recombination of neutral reactive materials. Additionally, discharge phenomena within the shielding holes can lead to a "hollow cathode effect," further reducing system stability.

[0008] Traditional spiral resonator designs incorporate a conductive shield between the external shield and the induction coil to suppress capacitive effects. However, this design often struggles to achieve reliable turn-on or stable discharge, especially under low-voltage conditions. Furthermore, unshielded sources (such as quarter-wavelength resonators) can introduce higher capacitive coupling, leading to greater parasitic currents and plasma potential instability, thus exacerbating the adverse effects of ion bombardment on the substrate. Therefore, in traditional induction source designs, the voltage difference between the plasma and ground can induce irregular ion flows due to capacitive coupling. These uncontrolled ion flows not only reduce process selectivity but also damage the substrate material layers and may even introduce particulate contamination. Simultaneously, the use of shielding and baffles can lead to RF power loss, increase system complexity, and necessitate more maintenance. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the prior art and provide a system and method for plasma processing.

[0010] The objective of this invention can be achieved through the following technical solutions:

[0011] According to one aspect of the present invention, a system for plasma processing is provided, comprising: a base, a gas delivery device, and a full-wavelength helical resonator;

[0012] The base is used to support the substrate to be processed and employs a rarefied heat transfer mechanism to provide a stable temperature control environment;

[0013] The gas delivery device includes multiple airflow guiding components for supplying process gas into the reaction chamber;

[0014] The full-wavelength spiral resonant device includes n reaction cavities, n induction coils, and a radio frequency power source, which are used to generate resonance and provide a uniform plasma distribution. The induction coils are located in the reaction cavities and are electrically connected to the radio frequency power source. The n reaction cavities are connected in sequence, and the n induction coils are connected in series. The sum of the electrical lengths of the induction coils is an integer multiple of the wavelength of the radio frequency signal emitted by the radio frequency power source. Three induction ring regions are formed inside the reaction cavities, where n > 0 and is an integer.

[0015] As a preferred technical solution, the three sensing ring regions include a central sensing region and two reverse sensing regions at both ends; the power density of the central sensing region is twice that of the two reverse sensing regions at both ends.

[0016] As a preferred technical solution, the reaction chamber includes an internal conductive shielding layer and an external metal shielding layer. The internal conductive shielding layer is made of quartz material to suppress parasitic discharge and reduce the impact of ion bombardment on the substrate. The external metal shielding layer is made of conductive material. The external metal shielding layer is used to isolate radio frequency interference and prevent stray electromagnetic fields in the external environment from affecting plasma excitation.

[0017] As a preferred technical solution, an insulating gap is provided between the internal conductive shielding layer and the induction coil to prevent the radio frequency current of the induction coil from causing electric shock or parasitic discharge through the reaction cavity.

[0018] As a preferred technical solution, the base surface is coated with an anti-fouling coating to avoid particulate contamination.

[0019] As a preferred technical solution, the system is also equipped with a cooling device to maintain a stable operating temperature for the radio frequency coil and the reaction chamber.

[0020] As a preferred technical solution, the geometric parameters and shielding distance of the induction coil meet the preset characteristic impedance requirements of the full-wavelength spiral resonant device, thereby achieving intrinsic impedance optimization. The preset characteristic impedance requirement is that the characteristic impedance matches the output impedance of the RF power source, and its specific formula is:

[0021]

[0022] Among them, Z in It is the input impedance of the induction coil; Z c β is the characteristic impedance of the induction coil; L is the propagation constant; j is the electrical length of the induction coil; and j is the imaginary unit used to represent the imaginary part of the impedance.

[0023] As a preferred technical solution, the radio frequency power source is also connected to a radio frequency slider, which is slidably fixed on the induction coil. By changing the different positions of the radio frequency slider on the induction coil, the plasma distribution in the reaction cavity can be changed.

[0024] According to another aspect of the present invention, a method for plasma treatment is provided, which is applied to a plasma treatment system as described above. In the method, the substrate to be treated is first fixedly placed on a base in a reaction chamber. A radio frequency power source in a full-wavelength spiral resonant device provides a radio frequency to the induction coil, causing the induction coil to generate a resonant frequency and generate three induction ring regions inside the reaction chamber. Gas is supplied to the reaction chamber by a gas delivery device to complete the plasma treatment.

[0025] As a preferred technical solution, the resonant frequency generated by the induction coil is determined by the geometric parameters of the induction coil, satisfying the following conditions:

[0026]

[0027] Where β is the wave number; H is the total length of the induction coil; n is an integer; is an integer multiple of the resonant mode; v is the propagation speed of the electromagnetic wave; and f is the resonant frequency.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. This invention includes a full-wavelength spiral resonator; the full-wavelength spiral resonator comprises n reaction chambers, n induction coils, and a radio frequency power source, used to generate resonance and provide a uniform plasma distribution; wherein, the induction coils are located in the reaction chambers and electrically connected to the radio frequency power source, the n reaction chambers are connected sequentially, and the n induction coils are connected in series, the sum of the electrical lengths of the induction coils is an integer multiple of the wavelength of the radio frequency signal emitted by the radio frequency power source, where n > 0 and is an integer. The optimized design of the full-wavelength spiral resonator significantly improves the plasma excitation efficiency, enabling the device to maintain stable operation over a wide process window (e.g., pressure from 20 mTorr to 1 Torr). Furthermore, the uniform plasma distribution combined with the current-free damage characteristic further improves the adhesive removal rate and process yield.

[0030] 2. In this invention, the full-wavelength spiral resonator generates three induction ring regions inside the reaction cavity through induction coils, achieving a zero total magnetic moment design. The three induction ring regions include a central induction region and two opposing induction regions at both ends. The power density of the central induction region is twice that of the opposing induction regions at both ends. This eliminates the magnetic field bias problem present in traditional resonators. With a quality factor as high as 2360, most of the radio frequency energy is absorbed by the plasma, improving processing efficiency. A uniform plasma density distribution can be obtained without additional plasma distribution optimization devices, thereby improving the rate consistency and long-term stability of the adhesive removal process. The uniformity of the plasma is improved through magnetic field complementarity.

[0031] 3. In this invention, the induction ring region includes a central induction region and two opposing induction regions at both ends. The power density of the central induction region is twice that of the opposing induction regions at both ends. Based on this full-wavelength resonant discharge mechanism, the central induction region inside the resonant device has approximately twice the energy density of the side regions, forming a high-conductivity path. The current between the upper and lower opposing capacitor voltages is directly connected or "short-circuited" inside the resonant device, allowing the capacitor currents to cancel each other out. Therefore, without the need for additional Faraday cages, mesh plates, or baffles, the damage to the substrate under treatment by capacitor current can be effectively reduced, ensuring the electrical stability of the processing environment.

[0032] 4. In this invention, the geometric parameters and shielding distance of the induction coil meet the preset characteristic impedance requirements of the full-wavelength spiral resonator, thereby achieving intrinsic impedance optimization. The preset characteristic impedance requirement is that the characteristic impedance matches the output impedance of the RF power source. Through the design of this full-wavelength spiral resonator, conjugate matching between the signal source and the load impedance is achieved, meaning the real parts of the impedances are equal, and the imaginary parts are opposites. This design eliminates the need for additional impedance matching kits, simplifying the system structure and reducing power loss.

[0033] 5. In this invention, the full-wavelength spiral resonant device includes n reaction chambers and n induction coils. The n reaction chambers are connected in sequence, and the n induction coils are connected in series. Through the partition design, it provides characteristic control of plasma in multiple regions. The induction coils in each region can be adjusted independently to achieve a specific plasma density distribution, making the system more flexible, practical, and widely applicable.

[0034] 6. The present invention employs a full-wavelength spiral resonant device, which includes only a reaction cavity, an induction coil, and a radio frequency power source. This eliminates the need for additional matching networks, Faraday cages, and plasma distribution control components required in traditional devices, significantly simplifying the device structure, reducing manufacturing and maintenance costs, and improving the reliability and stability of the system. Attached Figure Description

[0035] Figure 1 The reaction chamber of the dry degumming machine, in which the full-wavelength spiral resonator serves as the plasma source, is described in this invention.

[0036] Figure 2 This is a schematic diagram of the enhanced plasma plane and current and voltage curves in the embodiment;

[0037] Figure 3 This is a schematic diagram of the spiral resonator in the embodiment;

[0038] Figure 4a This is a schematic diagram of the fluid simulation results of the full-wavelength resonator cavity in the embodiment;

[0039] Figure 4b This is a schematic diagram of the fluid simulation results of the half-wavelength resonator cavity in the embodiment;

[0040] Figure 5 This is a schematic diagram illustrating the relationship between slit distance and heat transfer coefficient under different air pressures in the embodiments. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0042] This application fundamentally optimizes plasma excitation through an innovative design of a full-wavelength spiral resonator. This technology achieves uniform plasma distribution by precisely matching the electrical length of the induction coil with the radio frequency, while reducing the effects of parasitic discharge and ion bombardment. Compared to traditional designs, this application eliminates the need for a matching network, directly achieving efficient energy transfer through internal impedance optimization. This effectively solves the problems of shielding losses, additional metal contamination sources, and capacitive coupling inherent in traditional technologies. This innovative design not only improves processing quality and process stability but also significantly expands its applicability, reduces costs, and meets diverse needs ranging from photoresist removal to complex material etching.

[0043] Example 1

[0044] The full-wavelength resonant spiral induction coil in this application effectively solves the shortcomings of traditional inductively coupled plasma (ICP) sources by optimizing the electrical length of the induction coil, the distribution of the induction zone, and the internal impedance balance.

[0045] The electromagnetic field distribution is optimized during the descaling process to achieve capacitor balance. Through optimized design of the induction coil's self-inductance and mutual inductance, the internal capacitor currents are mutually canceled, eliminating the risk of secondary discharge. A multi-induction zone design, with the induction coil's full-wavelength resonant design forming a central induction zone and two opposing induction zones at both ends, improves plasma uniformity through complementary magnetic fields. No matching network is required; 50Ω impedance matching is directly achieved through internal impedance optimization, eliminating the power loss caused by the matching network. Faster and more uniform heat transfer is achieved; the full-wavelength large cavity design offers superior heat transfer compared to half-height or quarter-height cavity designs. The flow rate is faster in the gap between the wafer and the substrate within the large cavity, which is more conducive to heat transfer.

[0046] High heat transfer efficiency places higher demands on the uniformity of heat transfer. Figure 4a A schematic diagram of the cavity velocity vector of a full-wavelength resonator; Figure 4b This is a schematic diagram of the velocity vector of a half-wavelength resonator cavity; the colors in the diagram represent velocity. The color scale on the left shows the velocity values ​​corresponding to different colors, in meters per second (ms). -1 The color changes from blue to red, with blue indicating a low speed, close to 0.00ms. -1Red indicates a higher speed, reaching a maximum of 49.76ms. -1 Depend on Figure 4a , 4b The comparative illustrations show that, under the same process conditions, a full-wavelength cavity provides a more uniform airflow distribution between the wafer and substrate compared to a shorter half-wavelength cavity. The figures demonstrate that the airflow in the full-wavelength cavity exhibits a more regular and symmetrical distribution, with smoother streamlines and smaller velocity gradient variations within the cavity, particularly between the wafer and substrate, where airflow uniformity is significantly higher. In contrast, the lower height of the half-wavelength cavity restricts fluid flow, easily leading to regions with larger local velocity gradients, resulting in more pronounced streamline bending and turbulence. Especially when airflow passes between the wafer and substrate, the airflow distribution in the half-wavelength cavity is less uniform than that in the full-wavelength cavity. Therefore, in process scenarios requiring more uniform airflow distribution between the wafer and substrate, the full-wavelength cavity is more advantageous.

[0047] According to the maximum power transfer theorem, maximum power transfer is achieved when the source impedance and load impedance are conjugate matched. This means that for the power on the transmission line to be absorbed by the load to the maximum extent, the output impedance of the source should be equal to the conjugate of the load impedance. Impedance mismatch leads to signal reflection, which not only reduces system efficiency but can also cause signal interference and additional noise, affecting the overall system performance. Impedance matching also helps prevent an excessively high voltage standing wave ratio (VSWR) caused by reflected waves, which can potentially damage RF components such as amplifiers and antennas.

[0048] Using a helical resonator (HR) plasma source as an ICP source eliminates the need for additional resistors, capacitors, or other circuit components to achieve RF resonance. Resonance modes involve the natural vibration of a circuit or system at a specific frequency. For HR plasma sources, this typically involves matching the electromagnetic characteristics (such as inductance and capacitance) of the radio frequency (RF) source with those of the helical coil to achieve the highest energy transfer efficiency at a given RF frequency. In this mode, the system's natural frequency coincides with the external drive frequency, allowing the system to maintain a high plasma density with relatively low energy consumption. Another potential advantage of the HR structure compared to other ICP source structures is the ease with which the plasma distribution can be altered by repositioning the RF taps / slider at different locations on the helical coil. This capability provides another degree of freedom in developing plasma processes.

[0049] In this embodiment, Figure 1 The reaction chamber of a dry degumming machine uses a full-wavelength spiral resonator as the plasma source. For example... Figure 1 and Figure 2 As shown, a full-wavelength resonator means that the electrical length of the coil is equal to a full wavelength of the radio frequency signal. In this way, the coil can effectively resonate at its operating frequency. For example, for a frequency of 27.12 MHz, the wavelength is approximately 11.06 meters.

[0050] A full-wavelength resonator means that the electrical length of the coil should be equal to one full wavelength of the radio frequency signal. This allows the coil to effectively resonate at its operating frequency. For example, for a frequency of 27.12 MHz, the calculated wavelength is approximately 11.06 meters. This means that the length of one cycle of the electromagnetic wave in free space is 11.06 meters.

[0051] Due to the self-inductance and mutual inductance effects of a helical coil, the physical length required for an electromagnetic wave to propagate along the coil decreases as the wave speed slows down. This means that to achieve an electrical length corresponding to a specific wavelength, the physical length of the coil does not need to be equal to that wavelength in free space. Self-inductance is caused by the interaction between the magnetic field generated when current flows through a conductor and the conductor itself, while mutual inductance is caused by the interaction of electromagnetic fields between different parts of the coil. Therefore, the actual physical length of a helical coil is generally shorter, depending on the comprehensive design of the coil diameter, wire diameter, spacing between coils, and the coil material itself, to ensure that the design meets specific frequency and resonance conditions.

[0052] Aside from the initial gas breakdown, the capacitive currents generated in ICP are generally unwanted. They play a dual role in discharge physics: while necessary for discharge ignition, they are also detrimental due to the capacitive problems they create. Similar to short spiral inductors, single-turn coils, spiral antennas, and traditional spiral resonators, they are essentially capacitively unbalanced, meaning their capacitive equivalent structure resembles the asymmetric capacitive discharge of a large ground electrode (chamber) and a small RF electrode represented by the inductor itself. Capacitive currents from the coils can cause unwanted current flows between the plasma and the ground electrode or metal cavity. These currents not only increase energy loss but can also lead to problems such as cavity wall sputtering, uneven discharge, and arcing.

[0053] In the designed plasma discharge configuration (full wavelength, resonant), based on its unique discharge mechanism, three induction rings (corresponding to the peak positions in the current curve) are formed (upper, middle, and lower). The energy of the central ring is approximately twice that of the side rings (due to superposition under standing wave action). The high-density plasma in the central ring is similar to "forming a short circuit," meaning that the central induction ring (or other inductive coupling element) provides a high-conductivity path, allowing the current flow between these two opposite-phase capacitor voltages to be directly connected or "short-circuited." This does not refer to a traditional circuit short circuit causing system failure, but rather that within the plasma source, due to the high conductivity of the plasma itself, the currents generated by these two voltages can cancel each other out within the source without creating a significant external circuit connection.

[0054] Due to the characteristics of RF power distribution, plasmas tend to form first in these higher-energy regions. The central plasma ring forms first because it occupies a unique position between capacitive current and inductive coupling, an position that optimally balances the effects of these two forces. As RF power increases, the plasma conductivity at this position increases, enabling more efficient absorption and utilization of RF energy, thereby triggering and sustaining a self-supporting inductive discharge process. In other words, the central plasma ring forms first because it achieves sufficient conductivity under this specific design to realize self-sustaining inductive discharge, thanks to the optimal balance between capacitive and inductive effects that achieves the most efficient energy conversion and utilization.

[0055] Compared to other designs, the coil length of λ-R is at least 4-20 times that of any conventional induction coil (including quarter-wavelength spiral resonators). This increased coil length results in a 4-20 times reduction in the surface density of capacitive current at the tube wall, which means that for the same power, the capacitive current density at the tube wall is greatly reduced.

[0056] According to the maximum power transfer theorem, maximum power transfer is achieved when the source impedance and load impedance are conjugate matched. This means that for the power on the transmission line to be absorbed by the load to the greatest extent possible, the output impedance of the source should be equal to the conjugate of the load impedance. Impedance mismatch leads to signal reflection, which not only reduces system efficiency but can also cause signal interference and additional noise, affecting the overall system performance. Impedance matching also helps prevent excessively high voltage standing wave ratios (VSWR) caused by reflected waves, which can damage RF components such as amplifiers and antennas. This also applies to low-frequency and high-frequency circuits in AC circuits. When the AC circuit contains capacitive or inductive impedances, the conclusion changes; the real parts of the signal source and load impedances must be equal, and their imaginary parts must be opposites, a condition called conjugate matching. The imaginary part is the reactance, i.e., inductive reactance plus capacitive reactance. Both inductive and capacitive reactance are frequency-dependent. Inductive reactance is positively correlated with frequency; at 0 Hz, inductive reactance is 0, and as the frequency increases, inductive reactance increases, reaching infinity at infinite frequency. Capacitive reactance is negatively correlated with frequency. When the frequency is close to 0, the capacitive reactance is very large. As the frequency increases, the capacitive reactance decreases. When the frequency is infinite, the capacitive reactance is 0. Therefore, the inductive reactance and capacitive reactance in an LC circuit must be equal at a certain frequency, which is the resonant frequency. The inductive reactance and capacitive reactance are only equal at the resonant frequency, and are not equal at other frequencies.

[0057] A spiral resonator is a device based on radio frequency (RF) voltage amplification for gas breakdown and plasma maintenance. Its main structure includes a spiral coil, external shielding (or none), and an excitation point. It utilizes transmission line theory to achieve efficient RF energy amplification and plasma generation. During operation, one end of the spiral coil is grounded (bottom), and the other end is either unloaded or loaded (top). RF signals are injected from the excitation point, resulting in a high-voltage output.

[0058] The electrical behavior of a spiral resonator is similar to that of a transmission line with one end short-circuited and the other open-circuited. Its resonant frequency is determined by its geometric parameters and satisfies the following conditions:

[0059]

[0060] Where β is the wave number, H is the total length of the coil, and n is an integer multiple of the resonant mode.

[0061] Under ideal resonance conditions, the voltage amplification factor of the resonator is:

[0062]

[0063] Where α is the coil attenuation factor, and δ is the normalized excitation point position (the relative distance from the ground point to the excitation point). By appropriately adjusting the coil length and the excitation point position, a significant voltage amplification effect can be achieved, which is especially suitable for plasma excitation under low-voltage radio frequency power conditions.

[0064] A spiral resonator is a special type of transmission line that operates based on the resonant characteristics of electromagnetic waves propagating within it. Impedance matching depends on the following factors:

[0065] 1. Characteristic impedance of a transmission line: Characteristic impedance of a spiral resonator (Z) c Z is a crucial parameter in the design, determined by coil geometry (such as number of turns, radius, and spacing) and shielding distance. By optimizing these parameters, Z... c It can approach the output impedance of an RF power supply (typically 50Ω).

[0066] 2. Characteristics of full-wavelength resonance: When the physical length of the spiral resonator is equal to the wavelength of the radio frequency signal (e.g., 27.12MHz corresponds to 11.06 meters), the two ends of the transmission line satisfy the standing wave condition, forming resonance. At this time, the impedance at the input end (excitation point) is:

[0067]

[0068] Among them, Z in It is the input impedance of the transmission line; Z c β is the characteristic impedance of the transmission line; L is the propagation constant; j is the physical length of the transmission line; and j is the imaginary unit used to represent the imaginary part of the impedance.

[0069] Z in This is the input impedance of the transmission line (i.e., the impedance at the excitation point). The input impedance is the equivalent impedance "seen" by the RF power supply at the resonator's excitation point; it is determined by the resonator's geometry, operating frequency, and terminating load. c β is the characteristic impedance of the transmission line. Characteristic impedance is an intrinsic property of the transmission line, determined by its geometry and material properties (such as inductance and capacitance distribution parameters). For example, for a coaxial or spiral resonator, it is determined by the number of turns, diameter, and shielding distance of the coil. β is the propagation constant (phase constant). It represents the rate of phase change of the radio frequency wave propagating in the transmission line and is related to the wavelength λ and the operating frequency f (2π / λ). L is the physical length of the transmission line. It represents the length of the transmission line from the excitation point to the terminal load. In resonator design, L is usually chosen as an integer multiple or fraction of a specific wavelength (such as half a wavelength or full wavelength). tan(βL) is the interaction between the propagation constant and the transmission line length. When βL satisfies a specific resonance condition (such as βL = nπ, where n is an integer), the input impedance Z... in It exhibits purely resistive properties, which helps in achieving impedance matching. j is the imaginary unit, used to represent the imaginary part of the impedance.

[0070] like Figure 3 As shown, when L = λ, tan(βL) = 0, therefore: Z in =Z cThis means that the input impedance of the spiral resonator is equal to its characteristic impedance, and it can be matched with the RF power supply without an additional impedance matching network.

[0071] Regarding rarefied heat transfer: In a narrow gap, the number of gas molecules is very small, and continuum mechanics can no longer explain the gas flow. In this case, the interaction between the gas and the rigid body plays an important role. For this rarefied gas, due to the reduction in collisions between gas particles, the heat transfer efficiency is greatly improved. In a microscale environment, the Knudsen number (comparing the mean free path of gas molecules with the characteristic length) is usually high, indicating that the gas flow is in a rarefied state. In this state, the number of collisions between gas molecules decreases, resulting in gas heat transfer mainly through the direct interaction of molecules with the surface. In a small-scale system, the surface effect becomes more significant. Due to the increase in the surface area-to-volume ratio, the interaction between gas molecules and the wall plays an important role in the heat transfer process.

[0072] The Knudsen number (usually denoted as Kn) is a dimensionless number used to describe the ratio of the mean free path of molecules in gas flow to a certain characteristic length (such as the diameter of a flow channel, the size of a particle, etc.). It is an important parameter for understanding rarefied gas dynamics and is mainly used in the fields of fluid mechanics and gas dynamics.

[0073] The Knudsen number is defined as:

[0074] Kn = λ / L

[0075] where λ is the mean free path of gas molecules, that is, the average travel distance of molecules between two consecutive collisions. L is the characteristic length in fluid flow, such as the pipe diameter or particle size. The magnitude of the Knudsen number is used to distinguish different fluid flow regions: Kn < 0.01: continuum flow region, which can be described by the traditional Navier-Stokes equations; 0.01 < Kn < 0.1: slip flow region, where the slip effect of molecules on the boundary needs to be considered. 0.1 < Kn < 10: transitional flow region, where molecular motion begins to dominate and the continuum model is no longer applicable. Kn > 10: free molecular flow region, where the interaction between molecules is much smaller than the interaction with the container boundary.

[0076] In the transitional flow region and the free molecular flow region, it belongs to the category of rarefied heat transfer. In this invention, in the reaction chamber of the machine tool, a floating thimble is arranged on the base, and its height is 150 um (which can be considered as the slit spacing), that is, the value of the characteristic size is very small. According to the calculation formula of the Knudsen number, Kn is much greater than 10, and the heat transfer between the heating plate and the wafer belongs to the category of rarefied heat transfer. In the analytical heat transfer model, the slit size d usually affects the heat transfer coefficient h in the form of the denominator. For example, in the comprehensive heat transfer formula:

[0077]

[0078] When d→0 (slit is minimal): the denominator d decreases, and the heat transfer coefficient h increases. At this point, heat transfer efficiency is significantly improved, and heat transfer is more concentrated. The disadvantage when the slit is larger is that the rarefaction of the gas increases, the mean free path between molecules increases significantly, leading to a decrease in heat transfer efficiency. In this case, the gas's thermal conductivity mainly relies on intermolecular collisions, rather than direct energy exchange between the wall and molecules.

[0079] In this embodiment, a system for plasma processing is applied, the system including: a base, a gas delivery device, and a full-wavelength spiral resonator;

[0080] The base is used to support the substrate to be processed and employs a rarefied heat transfer mechanism to provide a stable temperature control environment; the base surface is coated with an anti-fouling coating to reduce the risk of particulate contamination.

[0081] The gas delivery device includes multiple airflow guiding components for supplying process gas into the reaction chamber; the gas delivery system includes multiple airflow guiding components to achieve optimal uniformity of gas distribution within the chamber.

[0082] The full-wavelength spiral resonant device includes n reaction cavities, n induction coils, and a radio frequency power source to generate resonance at a specific radio frequency and provide a uniform plasma distribution; it provides multi-region plasma characteristic modulation through partitioned design; the induction coils of each region can be independently adjusted to achieve a specific plasma density distribution.

[0083] The system comprises an induction coil located within a reaction chamber and electrically connected to an RF power source. The RF power source is also connected to an RF slider or RF tap, which is slidably fixed to the induction coil. The plasma distribution is controlled by adjusting the position of the RF tap, allowing for flexible adaptation to different process requirements. n reaction chambers are sequentially connected. Each reaction chamber includes an internal conductive shielding layer and an external metal shielding layer. The internal conductive shielding layer, made of quartz, suppresses parasitic discharges and reduces the impact of ion bombardment on the substrate. The internal cavity of the internal conductive shielding layer, i.e., the quartz cavity, carries the plasma and provides excellent light transmittance and electrical insulation. The external metal shielding layer, made of highly conductive material, has a cooling device for effective heat dissipation, maintaining a stable operating temperature for the RF coil and reaction chamber. It also isolates RF interference and prevents stray electromagnetic fields from the external environment from affecting plasma excitation. The reaction chambers are designed with a full-wavelength structure to provide a more uniform airflow distribution and significantly reduce energy loss due to cavity wall capacitance current. An insulating gap is provided between the quartz cavity and the induction coil to prevent the RF current of the induction coil from passing through the quartz cavity and causing electric shock or parasitic discharge.

[0084] The system consists of n induction coils connected in series, where the sum of the electrical lengths of the coils is an integer multiple of the wavelength of the RF signal emitted by the RF power source (n > 0, an integer). This system optimizes the design parameters of the induction coils to improve plasma density uniformity, reduce capacitive coupling, and enhance resist removal efficiency. The RF power source provides power directly through the coils, achieving 50Ω impedance matching without a matching network. The application method of this system is as follows: first, RF power is provided to excite the plasma; then, capacitive coupling is reduced by optimizing coil lengths and impedance matching; finally, multiple induction toroidal surfaces are formed within the reaction chamber to improve plasma uniformity. During this process, a rarefied heat transfer mechanism is employed to improve the heat transfer efficiency between the wafer and the carrier.

[0085] In this embodiment, parasitic currents can be reduced by introducing conductive shielding downstream of the plasma source and optimizing the electromagnetic field distribution through full-wavelength resonant design to eliminate capacitance imbalance.

[0086] In this embodiment, n is 1. The induction coil is designed as a full-wavelength spiral resonator. The physical length of the induction coil is adjusted by optimizing self-inductance and mutual inductance to achieve the best electromagnetic wave coupling efficiency. Its electrical length satisfies the following conditions:

[0087] L=n·λ

[0088] Where L is the electrical length of the coil; λ = c / f is the wavelength of the radio frequency signal; c is the speed of light in a vacuum; f is the radio frequency (27.12MHz in this embodiment, corresponding to a wavelength of 11.06 meters); n is an integer multiple of the resonant mode, and in this embodiment, n = 1 is chosen to achieve single-wavelength resonance. By precisely controlling the physical length of the induction coil to match the wavelength of the radio frequency signal, high-frequency losses are avoided, while ensuring the optimal resonant state of the induction coil at the operating frequency. Impedance matching is inherently achieved through the coil's structural design, avoiding the power loss and complexity of traditional matching networks.

[0089] Next, the plasma density distribution is calculated. Inside the quartz cavity, oxygen is excited by an induction coil to form plasma, the electron density of which is described by the following formula:

[0090]

[0091] Where, n e For electron density; P rf η is the input RF power (set to 2.5kW in this embodiment); η is the power transmission efficiency (optimized to 95%); A is the effective excitation area of ​​the reaction cavity; e is the electron charge constant; v ion This represents the ionization rate.

[0092] Calculation results show that, after optimization, the plasma electron density inside the quartz cavity can reach 1.2 × 10⁻⁶. 11 cm -3 This improves the photoresist removal rate.

[0093] In this embodiment, a capacitor current balance analysis is also performed. To reduce parasitic discharge caused by capacitive coupling, an intrinsic impedance balance structure is designed, whose inductive reactance and capacitive reactance satisfy the following relationship:

[0094] X L =X C

[0095] Among them, X L =2πfL is the inductive reactance, and L is the inductance of the coil; X C =1 / 2πfC is the capacitive reactance, and C is the parasitic capacitance between the coil and the quartz cavity.

[0096] In this embodiment, by adjusting the number of turns and geometric parameters of the induction coil, the RF power loss when the parasitic current is balanced is minimized, and the overall efficiency of the system is improved by about 20%.

[0097] The photoresist removal rate was calculated, and under the premise of plasma density optimization and capacitive coupling suppression, the photoresist removal rate RRR is expressed as:

[0098] R = k·n e ·σ

[0099] Where k is the reaction rate constant, which depends on the physicochemical properties of the reacting gas (oxygen); n e σ represents the plasma electron density; σ is the reaction cross section of the photoresist.

[0100] In this embodiment, the improvement is more than 30% compared to the traditional quarter-wavelength resonator.

[0101] Explanation of rarefied heat transfer within the reaction chamber: Assuming the continuously introduced oxygen is at a temperature of 20°C, after the pressure reaches 3 Torr, with a feature size of 150 micrometers for the floating pin, the Knudsen number is 0.126, belonging to the transitional flow region, not continuous flow. Similarly, when the oxygen temperature is 250°C, after 3 Torr, the Knudsen number is 0.227, also belonging to the transitional flow region, not continuous flow. Furthermore, the lower the pressure (before 3 Torr), the greater the mean free path of the gas, and the greater the Knudsen number, further deviating from continuous flow. Therefore, within the PC chamber, the flow between the wafer and the substrate is never continuous; throughout the entire operation time, it operates under rarefied heat transfer conditions.

[0102] In this embodiment, the wafer is 12 inches, 775µm thick, and has a density of 2330kg / m³. 3The specific heat capacity is 700 J / (kg·K), and the temperature is 20℃. The heat transfer between it and a hot surface maintained at 250℃ can be calculated. The relationship between the slit distance and the heat transfer coefficient of a rarefied gas under different pressures is as follows: Figure 5 As shown, the heat transfer coefficient h = 300 W / m²*K (considering the effects of heat dissipation and slit size). Based on Newton's law of cooling and the law of conservation of energy, the relationship between temperature rise and time under rarefied heat transfer conditions can be derived.

[0103] Newton's law of cooling is:

[0104] Q = hAΔT;

[0105] Where Q is the heat transfer rate, measured in W; and h is the heat transfer coefficient, measured in W / m³. 2 K; A is the heat exchange surface area, in m². 2 ΔT is the temperature difference between an object and its environment, measured in Kelvin (K).

[0106] The energy conservation equation is used to calculate the temperature change of the silicon wafer over time. The energy conservation equation is:

[0107] mc*dT / dt=hAΔT

[0108] Where m is the mass of the silicon wafer in kg; calculated to be 132g; c is the specific heat capacity of the silicon wafer in J / kg·K; dT / dt is the rate of temperature change over time; hAΔT represents the heat received by the silicon wafer.

[0109] In the first 10 seconds, the temperature rise of the wafer was as follows, with 1-second intervals: 20°, 106.9°, 161.0°, 194.6°, 215.6°, 228.6°, 236.7°, 241.7°, 244.8°, 246.8°, 248°. It can be seen that its heat transfer rate is very fast.

[0110] In summary, the optimized design of the full-wavelength spiral resonator significantly improves plasma excitation efficiency, enabling the device to maintain stable operation over a wide process window (e.g., pressure from 20 mTorr to 1 Torr). Furthermore, the uniform plasma distribution combined with the current-damage-free characteristics further enhances the resist removal rate and process yield.

[0111] Example 2

[0112] In this embodiment, it includes: a base, a gas delivery device, and a full-wavelength spiral resonant device;

[0113] The base is used to support the substrate to be processed and employs a rarefied heat transfer mechanism to provide a stable temperature control environment.

[0114] The gas delivery device includes multiple airflow guiding components for supplying process gas into the reaction chamber;

[0115] The full-wavelength spiral resonant device includes n reaction cavities, n induction coils, and a radio frequency power source, used to generate resonance and provide a uniform plasma distribution; wherein, the induction coils are located in the reaction cavities and electrically connected to the radio frequency power source, the n reaction cavities are connected in sequence, the n induction coils are connected in series, and the sum of the electrical lengths of the induction coils is an integer multiple of the wavelength of the radio frequency signal emitted by the radio frequency power source, where n>0 and is an integer.

[0116] In this embodiment, n is 2. That is, a photoresist removal device is formed by connecting two half-wavelength photoresist removal cavities in series to create a full-wavelength spiral resonator. This scheme utilizes a two-segment half-wavelength resonant structure to optimize electromagnetic wave distribution, achieving efficient plasma excitation and uniform photoresist removal. First, the substrate to be processed is fixedly placed on a base in the reaction cavity. The radio frequency power source in the full-wavelength spiral resonator provides radio frequency to the induction coil, causing the induction coil to generate three induction ring regions inside the reaction cavity. Gas is then supplied to the reaction cavity by a gas delivery device to complete the plasma treatment. The three induction ring regions include a central induction region and two opposing induction regions at both ends. The power density of the central induction region is twice that of the opposing induction regions at both ends.

[0117] In this embodiment, the electrical length L of each cavity is set to half the wavelength of the radio frequency signal:

[0118] L=λ / 2=c / 2f

[0119] Where λ is the wavelength; c is the speed of light in a vacuum; and f is the radio frequency (27.12MHz in this embodiment, corresponding to L=5.53m).

[0120] In this embodiment, two half-wavelength cavities are connected in series via induction coils to form a full-wavelength resonator, with a total length of:

[0121] L total =L1+L2=λ

[0122] Each half-wavelength cavity is powered by an independent induction coil, but a unified resonant frequency is achieved through a series circuit. The power distribution formula is:

[0123] P rf =P1+P2

[0124] Among them, P rf The total RF power is set to 5kW; P1 and P2 are the power of the two half-wavelength cavities, respectively (in this embodiment, P1 = P2 = 2.5kW). The number of turns, diameter, and material selection of the induction coil have been optimized to ensure uniform power distribution in the two cavities and efficient RF energy transfer.

[0125] In this embodiment, the plasma density distribution within the two cavities is more uniform through a series design. The electron density formula is:

[0126]

[0127] A total =A1+A2

[0128] Among them, A total The total effective area of ​​the two cavities is denoted as ; other parameters are the same as in Example 1.

[0129] Experimental results show that the electron density in both cavities reaches 1.1 × 10⁻⁶. 11 cm -3 The deviation is less than 3%.

[0130] In summary, the plasma processing system in this embodiment exhibits excellent resonant performance. The two half-wavelength cavities achieve higher resonant efficiency across the entire wavelength range, avoiding the non-uniformity issues caused by concentrated power density in traditional single-cavity designs. Its modular design allows the two cavities to operate independently, while achieving full-wavelength optimization in series mode, facilitating maintenance and upgrades. Furthermore, its low-loss operation and series design significantly reduce parasitic discharge and electromagnetic interference, enhancing system stability.

[0131] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A system for plasma processing, characterized in that, include: Base, gas delivery device, and full-wavelength spiral resonator; The base is used to support the substrate to be processed. A floating pin is provided on the base. The height of the floating pin is 150um, so that a slit gap is formed between the substrate to be processed and the base. Under the process pressure of the reaction chamber, the Knudsen number Kn of the gas flow in the gap is greater than 10, thereby adopting a rarefied heat transfer mechanism to provide a stable temperature control environment. The gas delivery device includes multiple airflow guiding components for supplying process gas into the reaction chamber; The full-wavelength spiral resonant device includes n reaction cavities, n induction coils, and a radio frequency power source, used to generate resonance and provide a uniform plasma distribution; wherein, the induction coils are located in the reaction cavities and electrically connected to the radio frequency power source, the n reaction cavities are connected in sequence, the n induction coils are connected in series, the sum of the electrical lengths of the induction coils is an integer multiple of the wavelength of the radio frequency signal emitted by the radio frequency power source, and three induction ring regions are formed inside the reaction cavities, where n>0 is an integer; The three sensing ring regions include a central sensing region and two reverse sensing regions at both ends; the power density of the central sensing region is twice the power density of the two reverse sensing regions at both ends. The geometric parameters and shielding distance of the induction coil meet the preset characteristic impedance requirements of the full-wavelength spiral resonant device, thereby achieving intrinsic impedance optimization. The preset characteristic impedance requirement is that the characteristic impedance matches the output impedance of the RF power source, and its specific formula is: in, Z in It is the input impedance of the induction coil; Z c It is the characteristic impedance of the induction coil; β It is the propagation constant; L It is the electrical length of the induction coil; j It is the imaginary unit, used to represent the imaginary part of impedance.

2. The system for plasma processing according to claim 1, characterized in that, The reaction chamber includes an internal conductive shielding layer and an external metal shielding layer. The internal conductive shielding layer is made of quartz material to suppress parasitic discharge and reduce the impact of ion bombardment on the substrate. The external metal shielding layer is made of conductive material. The external metal shielding layer is used to isolate radio frequency interference and prevent stray electromagnetic fields in the external environment from affecting plasma excitation.

3. The system for plasma processing according to claim 2, characterized in that, An insulating gap is provided between the internal conductive shielding layer and the induction coil to prevent the radio frequency current of the induction coil from causing electric shock or parasitic discharge through the reaction cavity.

4. A system for plasma processing according to claim 1, characterized in that, The base surface is coated with an anti-fouling coating to avoid particulate contamination.

5. A system for plasma processing according to claim 1, characterized in that, The system is also equipped with a cooling device to maintain a stable operating temperature for the radio frequency coil and the reaction chamber.

6. A system for plasma processing according to claim 1, characterized in that, The radio frequency power source is also connected to a radio frequency slider, which is slidably fixed on the induction coil. By changing the different positions of the radio frequency slider on the induction coil, the plasma distribution in the reaction chamber can be changed.

7. A method for plasma processing, characterized in that, The method is applied to a plasma processing system as described in any one of claims 1-6. In the method, the substrate to be processed is first fixedly placed on a base in the reaction chamber. The radio frequency power source in the full-wavelength spiral resonant device provides radio frequency to the induction coil, so that the induction coil generates a resonant frequency and generates three induction ring regions inside the reaction chamber. Gas is supplied to the reaction chamber by a gas delivery device to complete the plasma processing.

8. A method for plasma processing according to claim 7, characterized in that, The resonant frequency generated by the induction coil is determined by the geometric parameters of the induction coil and satisfies the following conditions: in, Wave number; This is the total length of the induction coil; It is an integer, and an integer multiple of the resonant mode; It is the propagation speed of electromagnetic waves. This is the resonant frequency.

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