System and method for plasma processing

Abstract

The invention relates to a system and method for plasma processing. The system comprises a base, a gas conveying 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, and is used for generating resonance and providing uniform plasma distribution; wherein the induction coils are located in the reaction cavities and electrically connected with 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 electric appliance lengths of the induction coils is an integral multiple of the wavelength of a radio frequency signal emitted by the radio frequency power source, and three induction ring areas are formed in the reaction cavities. Compared with the prior art, the invention has the advantages of zero total magnetic moment design, improved processing efficiency, improved stability, simplified structure and the like.

Description

Technical Field

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

[0002] The present invention relates to a technical solution for plasma processing, in particular for processing applications achieved by inductive discharge. The present invention is mainly used in photoresist stripping processes in semiconductor device manufacturing. In addition, the technology of the present invention can also be widely applied to other plasma processing scenarios, such as material etching and deposition of materials such as silicon, silicon nitride, silicon dioxide, polysilicon, etc.

[0003] Plasma technology plays an important role in modern semiconductor manufacturing, and its typical applications include chemical dry etching (CDE), ion-assisted etching (IAE) and plasma-enhanced chemical vapor deposition (PECVD). These processes usually introduce radio frequency power through an induction coil to transfer energy to the working gas to excite plasma for processing tasks such as material removal, surface treatment or thin film deposition.

[0004] In many processing scenarios, neutral active species generated by plasma are used to achieve surface reactions without ion bombardment, thereby reducing the risk of damage to the substrate. However, in some processing processes, unavoidable ion bombardment can have a negative impact on material properties, such as causing interface mixing, oxide degradation, or surface morphology changes. Traditional technologies to reduce the impact of ion bombardment usually rely on increasing the distance between the plasma source and the processing chamber, or reducing the migration of charged particles through shielding structures, baffles, or grid structures, but these methods are often accompanied by other problems, such as the loss of neutral active species, reduced process efficiency and increased device complexity, potential metal ion contamination, etc. Photoresist ashing or stripping refers to the process of completely removing the photoresist layer on the substrate. Photoresist stripping can also be achieved by chemical processes. But wet chemical processes produce toxic waste. The oxygen plasma photoresist ashing process uses oxygen radicals to oxidize organic photoresists, and the byproducts are usually non-toxic COx, H 2 O gas.

[0005] In conventional plasma processing techniques, it is often difficult to effectively avoid the generation of parasitic plasma currents by using baffles, shielding structures, or increasing the spatial separation between the plasma source and the processing chamber alone. These parasitic currents usually 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 initial charged species in the electric field, these charged species will accelerate and dissociate and collide with neutral particles, thereby inducing a multiplication effect of charge concentration. If the initial charge level is high enough and the RF electric field strength is large, the charge density of the parasitic plasma may increase significantly near the wafer surface, and may even reach or exceed the plasma density in the plasma source area. This phenomenon will cause excessive ion flux to act directly on the substrate, bringing serious adverse consequences. Higher charge density may also produce a significant voltage difference between the plasma source and the processing chamber or substrate support. This voltage difference will further enhance the electric field, causing the charged particles to be accelerated and extracted from the plasma source and transferred to the substrate surface in an irregular manner, forming uneven ion-assisted etching characteristics. This will not only reduce the selectivity of the process, but may also cause local over-etching or damage to the substrate material layer.

[0006] In addition, in conventional induction discharge sources, due to the capacitive coupling between the high voltage selection of the coil and the plasma discharge, the plasma is prone to high potential fluctuations relative to the ground. This high potential fluctuation can induce high-energy ion bombardment on the substrate, leading to adverse consequences such as material mixing, surface amorphization, and contamination injection. This effect is particularly evident in the dynamic coupling caused by RF voltage changes, further exacerbating the wide variation of the energy distribution of the charged particles and making it difficult to achieve uniform control of the ion flow.

[0007] To address the above issues, some studies have attempted to introduce internal conductive shielding or electrode elements into the processing equipment downstream of the plasma source to adjust the voltage difference between the plasma source and the processing chamber. However, when the plasma potential increases significantly relative to the shielding electrode, capacitive discharge is likely to occur between the shield and the plasma source. This discharge not only causes sputtering effects and becomes a source of contamination, but also generates parasitic plasma currents, causing additional interference to the process environment. In addition, the small holes in the shielding design are usually used for gas circulation, but they increase pressure losses and induce recombination of neutral active species. In addition, the discharge phenomenon in the shielding hole may lead to a "hollow cathode effect", further reducing the stability of the system.

[0008] The design of traditional spiral resonators introduces a conductive shield between the external shield and the induction coil to suppress the capacitive effect. However, this design often has difficulty in achieving reliable start-up or stable discharge, especially under low voltage conditions. In addition, unshielded sources (such as quarter-wavelength resonators) may introduce higher capacitive coupling, resulting in greater parasitic currents and plasma potential instability, thereby exacerbating the adverse effects of ion bombardment on the substrate. Therefore, in traditional induction source designs, due to the existence of capacitive coupling effects, the voltage difference between the plasma and the ground may induce irregular ion flow. This uncontrolled ion flow not only reduces process selectivity, but also causes damage to the substrate material layer and even introduces particle contamination. At the same time, the use of components such as shielding and baffles may lead to RF power loss, increase system complexity, and induce more maintenance requirements. Summary of the invention

[0009] The purpose of the present invention is to provide a system and method for plasma processing in order to overcome the defects of the prior art.

[0010] The purpose of the present invention can be achieved by the following technical solutions:

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

[0012] The pedestal is used to hold the substrate to be processed and uses a rarefied heat transfer mechanism to provide a stable temperature-controlled environment;

[0013] The gas delivery device includes a plurality of gas flow guide components for providing process gas into the reaction chamber;

[0014] The full-wavelength spiral resonance device includes n reaction chambers, n induction coils and a radio frequency power source, which are used to generate resonance and provide uniform plasma distribution; wherein the induction coil is located in the reaction chamber and electrically connected to the radio frequency power source, the n reaction chambers 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 areas are formed inside the reaction chamber, n>0, which is an integer.

[0015] As a preferred technical solution, the three induction ring areas include a central induction area and reverse induction areas at both ends; the power density of the central induction area is twice the power density of the reverse induction areas 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 passing through the reaction chamber and causing electric shock or parasitic discharge.

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

[0019] As a preferred technical solution, a cooling device is also provided in the system to maintain a stable operating temperature of the RF 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 resonator, thereby completing the intrinsic impedance optimization, wherein the preset characteristic impedance requirement is: the characteristic impedance matches the output impedance of the RF power source, and the specific formula is:

[0021]

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

[0023] As a preferred technical solution, the RF power source is also connected to a RF slider, which is slidably fixed on the induction coil. The plasma distribution in the reaction chamber is changed by changing the different positions of the RF slider on the induction coil.

[0024] According to another aspect of the present invention, a method for plasma processing is provided. The method is applied to work in a system for plasma processing as described above. In the method, a substrate to be processed is first fixedly placed on a base in a reaction chamber, and a radio frequency power source in a full-wavelength spiral resonance device provides a radio frequency frequency to an induction coil, so that the induction coil generates a resonant frequency and generates three induction ring areas inside the reaction chamber, and a gas delivery device provides gas into the reaction chamber to complete the plasma processing.

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

[0026]

[0027] Among them, 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. The present invention includes a full-wavelength spiral resonator device; the full-wavelength spiral resonator device includes n reaction chambers, n induction coils and a radio frequency power source, which are used to generate resonance and provide uniform plasma distribution; wherein the induction coil is located in the reaction chamber, electrically connected to the radio frequency power source, the n reaction chambers 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, n>0, which is an integer. The optimized design of the full-wavelength spiral resonator significantly improves the plasma excitation efficiency, so that the device can maintain stable operation within a wider process window (such as pressure from 20mTorr to 1Torr). In addition, the uniform plasma distribution combined with the current-free damage characteristics further improves the degumming rate and process yield.

[0030] 2. In the present invention, the full-wavelength spiral resonator generates three induction ring areas inside the reaction chamber through an induction coil to achieve a zero total magnetic moment design. The three induction ring areas include a central induction area and reverse induction areas at both ends, wherein the power density of the central induction area is twice the power density of the reverse induction areas at both ends. The magnetic field bias problem existing in traditional resonators is eliminated. With a quality factor of up to 2360, most of the RF energy is absorbed by the plasma, improving processing efficiency. A uniform plasma density distribution can be obtained without the need for an additional plasma distribution optimization device, thereby improving the rate consistency and long-term stability of the degumming process. The uniformity of the plasma is improved by magnetic field complementation.

[0031] 3. In the present invention, the induction ring area includes a central induction area and reverse induction areas at both ends, wherein the power density of the central induction area is twice the power density of the reverse induction areas at both ends. Based on the discharge mechanism of the full-wavelength resonance, the central induction area inside the resonant device has an energy density about twice that of the side area, forming a high conductivity path. The current between the upper and lower inverted capacitor voltages is directly connected or "short-circuited" inside the resonant device, so that the capacitive currents can cancel each other out. Therefore, without the need for additional accessories such as Faraday cages, grid plates or baffles, the damage to the substrate to be processed by the capacitive current can be effectively reduced, ensuring the electrical stability of the processing environment.

[0032] 4. The geometric parameters and shielding distance of the induction coil in the present invention meet the preset characteristic impedance requirements of the full-wavelength spiral resonator, thereby completing the internal impedance optimization, wherein the preset characteristic impedance requirements are: the characteristic impedance matches the output impedance of the RF power source, and through the design of the full-wavelength spiral resonator, the conjugate matching of the signal source and the load impedance is achieved, that is, the real part of the impedance is equal, and the imaginary part is the opposite of each other. This design does not require an additional impedance matching kit, simplifies the system structure, and reduces power loss.

[0033] 5. In the present invention, the full-wavelength spiral resonance 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. The characteristic control of multi-region plasma is provided through the zoning design. Among them, the induction coils in each region can be adjusted independently to achieve a specific plasma density distribution, making the system more flexible, practical and applicable to a wide range.

[0034] 6. The present invention adopts a full-wavelength spiral resonance device, which only includes a reaction chamber, an induction coil and a radio frequency power source, eliminating the additional matching network, Faraday cage 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A reaction chamber of a dry-type adhesive stripping machine using the full-wavelength spiral resonator of the present invention as a plasma source;

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

[0037] Figure 3 Schematic diagram of a spiral resonator in an embodiment;

[0038] Figure 4a Schematic diagram of fluid simulation results of a full-wavelength resonator cavity in an embodiment;

[0039] Figure 4b Schematic diagram of fluid simulation results of a half-wavelength resonator cavity in an embodiment;

[0040] Figure 5 Schematic diagram of the relationship between the slit distance and the heat transfer coefficient under different air pressures in the embodiment. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0042] This application fundamentally optimizes the plasma excitation method through the innovative design of a full-wavelength spiral resonator. This technology achieves uniform plasma distribution by accurately matching the electrical length of the induction coil with the RF frequency, while reducing the effects of parasitic discharges and ion bombardment. Compared with traditional designs, this application does not require a matching network, and directly achieves efficient energy transmission by optimizing internal impedance, effectively solving the shielding loss, additional metal contamination sources and capacitive coupling problems in traditional technologies. This innovative design not only improves processing quality and process stability, but also significantly expands the scope of application, reduces costs, and meets diverse needs from photoresist removal to complex material etching.

[0043] Example 1

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

[0045] During the degumming process, the electromagnetic field distribution is optimized to balance the capacitance. Through the optimization design of the self-inductance and mutual inductance of the induction coil, the internal capacitance current is offset to eliminate the risk of secondary discharge. The multi-induction zone design and the full-wavelength resonance design of the induction coil form a central induction zone and reverse induction zones at both ends, and the uniformity of the plasma is improved through magnetic field complementation. No matching network is required. Through the optimization of the intrinsic impedance, 50Ω impedance matching is directly achieved, eliminating the power loss of the matching network. Faster and more uniform heat transfer, the design of the full-wavelength large cavity has more heat transfer advantages than the half-height or quarter-height cavity design. The flow rate in the gap between the wafer and the base in the large cavity is faster, which is more conducive to heat transfer.

[0046] Under high heat transfer efficiency, higher requirements are placed on the uniformity of heat transfer. Figure 4a Schematic diagram of velocity vector of full-wavelength resonator cavity; Figure 4b Schematic diagram of the velocity vector of a half-wavelength resonator cavity; the colors in the figure represent velocity (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 lower speed, close to 0.00ms -1; Red indicates a higher speed, up to 49.76ms -1 Depend on Figure 4a , 4b From the comparison diagram, it can be seen that under the same process conditions, between the wafer and the base, the full-wavelength large cavity has a more uniform airflow distribution than the shorter half-wavelength cavity; it can be observed from the figure that the airflow in the full-wavelength cavity presents a more regular and symmetrical distribution, the streamlines are relatively smooth, and the velocity gradient changes less in the cavity, especially between the wafer and the base, the airflow uniformity is higher. In the half-wavelength cavity, due to the low height of the cavity, the fluid is limited by space, and it is easy to form a region with a large local velocity gradient, resulting in more obvious curvature and turbulence in the streamline. Especially when the airflow passes between the wafer and the base, the airflow distribution of the half-wavelength cavity is not as uniform as that of the full-wavelength cavity. Therefore, in process scenarios that require a more uniform airflow distribution between the wafer and the base, the full-wavelength cavity has more advantages.

[0047] According to the maximum power transfer theorem, maximum power transfer can be achieved when the source impedance and the load impedance are conjugate matched. This means that in order for the power on the transmission line to be absorbed by the load to the greatest extent, the output impedance of the source should be equal to the conjugate of the load impedance. Unmatched impedances can cause signal reflections, which not only reduces the efficiency of the system, but may also cause signal interference and additional noise, affecting the overall performance of the system. Impedance matching also helps prevent the Voltage Standing Wave Ratio (VSWR) from being too high due to reflected waves, which may cause damage to RF components such as amplifiers and antennas.

[0048] Using a helical resonator (HR) plasma source as an ICP source, no additional circuit elements such as resistors and capacitors are required to achieve RF resonance. Resonant modes involve the natural vibration of a circuit or system at a specific frequency. For HR plasma sources, this usually involves matching the radio frequency (RF) source with the electromagnetic properties of the helical coil (such as inductance and capacitance) to achieve the highest energy transfer efficiency at a specific radio frequency. In this mode, the natural frequency of the system is consistent with the external driving frequency, resulting in the system being able to maintain high plasma density at lower energy consumption. Another potential advantage of the HR structure compared to other ICP source structures is that the plasma distribution can be easily changed by repositioning the RF tap / slider at different locations of the helical coil. This feature provides another degree of freedom for developing plasma processes.

[0049] In this embodiment, Figure 1 The reaction chamber of the dry degumming machine is a full-wavelength helical resonator as the plasma source. Figure 1 and Figure 2 As shown, a full-wavelength resonator means that the electrical length of the coil is equal to one full wavelength of the RF 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 RF signal. This way, the coil can effectively resonate at its operating frequency. For example, for a frequency of 27.12MHz, the calculated wavelength is approximately 11.06 meters. This means that in free space, the length of one cycle of an electromagnetic wave is 11.06 meters.

[0051] Due to the self-inductance and mutual inductance of the spiral coil, the physical length required for the actual propagation path of the electromagnetic wave along the coil is reduced due to the slowing down of the electromagnetic wave. This means that in order to achieve the 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. The self-inductance effect is caused by the interaction between the magnetic field generated by the current passing through the wire and the wire itself, while the mutual inductance effect is due to the interaction between the electromagnetic fields of different parts of the coil. Therefore, the actual physical length of the spiral coil is generally shorter, depending on the comprehensive design of the coil diameter, the wire diameter, the spacing between the coils, and the material of the coil itself to ensure that the design meets the specific frequency and resonance conditions.

[0052] Apart from the initial gas breakdown, the capacitive currents generated in the ICP are generally unwanted and play a dual role in the discharge physics. Capacitive currents are necessary for the discharge ignition, but are detrimental because they create capacitance problems. Short spiral inductors, single-turn coils, spiral antennas, and traditional spiral resonators are basically capacitively unbalanced, that is, their capacitive equivalent structure is similar to the asymmetric capacitive discharge of the large area ground electrode (chamber) and the small RF electrode represented by the inductor itself. The capacitive currents from the coil can cause undesirable current flows between the plasma and the ground electrode or metal cavity. These currents not only increase energy losses, but can also cause problems such as sputtering of the cavity walls, uneven discharge, and arcing.

[0053] In the designed plasma discharge configuration (full wavelength, resonant), based on its special discharge mechanism, three induction toroids (corresponding to the peak positions in the current curve) are formed in the upper, middle, and lower regions. The energy of the central toroid is approximately twice that of the side toroids (superposition under the action of standing waves). The high-density plasma in the central toroid is similar to "forming a short circuit", which means that the central induction toroid (or other inductively coupled elements) provides a high-conductance path, enabling the direct connection or "short circuit" of the current flow between these two capacitively coupled voltages with opposite phases. This does not refer to a short circuit in the traditional sense that causes system failure, but rather 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 significant external circuit connections.

[0054] Due to this characteristic of the RF power distribution, the plasma first tends to form in these regions with higher energy. The central plasma toroid forms first because it is in a special position between the capacitive current and inductive coupling effects, which can optimally balance the influences of these two effects. As the RF power increases, the plasma conductivity at this position increases, enabling it to more effectively absorb and utilize RF energy, thereby triggering and maintaining a self-sustaining inductive discharge process. In other words, the central plasma toroid forms first because it can first reach sufficient conductivity under this special design to achieve self-sustaining inductive discharge, which is due to the optimal balance between the capacitive and inductive effects achieving the most efficient energy conversion and utilization.

[0055] Compared with other designs, the coil length of λ-R is at least 4 - 20 times that of any traditional induction coil (including quarter-wavelength helical resonators). This increased coil length correspondingly reduces the surface density of the capacitive current at the tube wall by 4 - 20 times, 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 can be achieved when the source impedance and the load impedance are conjugate matched. This means that in order for the power on the transmission line to be absorbed by the load to the greatest extent, the output impedance of the source should be equal to the conjugate of the load impedance. Unmatched impedances will cause signal reflections, which not only reduces the efficiency of the system, but may also cause signal interference and additional noise, affecting the overall performance of the system. Impedance matching also helps prevent excessive voltage standing wave ratio (VSWR) due to reflected waves, which may cause damage to RF components such as amplifiers and antennas. For AC, the same applies to low-frequency circuits and high-frequency circuits. When the AC circuit contains capacitive or inductive impedance, the conclusion changes, that is, the real part of the signal source and load impedance must be equal, and the imaginary part must be the opposite of each other, which is called conjugate matching. The imaginary part is the reactance, that is, the inductive reactance plus the capacitive reactance. Both inductive reactance and capacitive reactance are related to frequency. The inductive reactance is positively correlated with the frequency. When the frequency is 0, the inductive reactance is 0, and the frequency increases, the inductive reactance increases, and the inductive reactance is infinite when the frequency is infinite. The capacitive reactance is negatively correlated with the frequency. When the frequency is close to 0, the capacitive reactance is very large. As the frequency increases, the capacitive reactance becomes smaller. When the frequency is infinite, the capacitive reactance is 0. Therefore, the inductive reactance and capacitive reactance in the LC must be equal at a certain frequency. This frequency is the resonant frequency. Only at the resonant frequency are the inductive reactance and capacitive reactance equal. They are not equal at other frequencies.

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

[0058] The electrical behavior of a spiral resonator is similar to a transmission line with one end short-circuited and the other end open-circuited. Its resonant frequency is determined by the 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] Among them, α is the attenuation factor of the coil, and δ is the normalized excitation point position (the relative distance from the ground point to the excitation point). By properly 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 RF power conditions.

[0064] The helical resonator is a special transmission line whose working principle is based on the resonant characteristics of electromagnetic waves when propagating in the resonator. The realization of impedance matching depends on the following factors:

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

[0066] 2. Characteristics of full-wavelength resonance: When the physical length of the spiral resonator is equal to the wavelength of the RF signal (such as 27.12MHz corresponds to 11.06 meters), the two ends of the transmission line meet the standing wave condition and form resonance. At this time, the impedance of the input end (excitation point) is:

[0067]

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

[0069] Z in is the input impedance of the transmission line (i.e. the impedance at the excitation point). The input impedance is the equivalent impedance that the RF power source "sees" at the excitation point of the resonator, which is determined by the geometric design of the resonator, the operating frequency, and the terminal load. c is the characteristic impedance of the transmission line. The characteristic impedance is an intrinsic property of the transmission line and is determined by the geometric structure and material properties of the transmission line (such as inductance and capacitance distribution parameters). For example, for a coaxial line 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 change of phase of the radio frequency wave propagating in the transmission line, which is related to the wavelength λ and the operating frequency f (2Pi / 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 selected as an integer multiple or fraction of a specific wavelength (such as half a wavelength or a full wavelength). tan(βL) is the interaction between the propagation constant and the length of the transmission line. When βL satisfies a specific resonance condition (such as βL=nπ, where n is an integer), the input impedance Z in It is purely resistive and helps to achieve impedance matching. j is an imaginary unit used to represent the imaginary part of impedance.

[0070] like Figure 3 As shown, when L = λ, tan(βL) = 0, so: 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 the gas heat transfer mainly occurring 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 with 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 platform, a floating thimble is arranged on the base, and its height is 150 um (which can be regarded as the slit spacing), that is, the value of the characteristic dimension 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 (the slit is extremely small): the term d in the denominator decreases, and the heat transfer coefficient h increases. At this time, the heat transfer efficiency is significantly improved, and the heat transfer is more concentrated. The disadvantage of a larger slit is that the rarefaction of the gas increases, and the mean free path between molecules becomes significantly larger, resulting in a decrease in heat transfer efficiency. At this time, the thermal conductivity of the gas mainly depends on the collision between molecules, rather than the direct energy exchange between the wall and the molecules.

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

[0080] The susceptor is used to carry the substrate to be processed and adopts a rarefied heat transfer mechanism to provide a stable temperature control environment; the surface of the susceptor is coated with an anti-pollution coating to reduce the risk of particle contamination.

[0081] The gas delivery device includes a plurality of gas flow guiding components for providing process gas into the reaction chamber; the gas delivery system includes a plurality of gas flow guiding components to achieve optimal uniformity of gas distribution in the chamber.

[0082] The full-wavelength spiral resonance device includes n reaction chambers, n induction coils and a radio frequency power source, which are used to generate resonance at a specific radio frequency frequency and provide uniform plasma distribution; multi-region plasma characteristic regulation is provided through a partitioned design; the induction coils in each region can be independently adjusted to achieve a specific plasma density distribution.

[0083] Among them, the induction coil is located in the reaction chamber and is electrically connected to the RF power source; the RF power source is also connected to an RF slider or RF tap, which is slidably fixed on the induction coil. The plasma distribution is controlled by adjusting the position of the RF tap to achieve flexible adaptation under different process requirements. n reaction chambers are connected in sequence, and the reaction chamber includes an internal conductive shielding layer and an external metal shielding layer. The internal conductive shielding layer is used to suppress parasitic discharge and reduce the impact of ion bombardment on the substrate. It is made of quartz material. The internal cavity of the internal conductive shielding layer is a quartz cavity, which is used to carry plasma and provide excellent light transmittance and electrical insulation performance. The external metal shielding layer is made of highly conductive material and has a cooling device to effectively dissipate heat, thereby maintaining a stable operating temperature of the RF coil and the reaction chamber; it is used to isolate RF interference and prevent stray electromagnetic fields in the external environment from affecting plasma excitation. The reaction chamber is designed as a full-wavelength structure to provide a more uniform airflow distribution and significantly reduce the energy loss caused by the capacitance current of the cavity wall. An insulating gap is set between the quartz cavity and the induction coil to prevent the RF current of the induction coil from passing through the quartz cavity to cause electric shock or parasitic discharge.

[0084] 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 RF signal emitted by the RF power source, n>0, which is an integer. The system optimizes the design parameters of the induction coil to improve the uniformity of plasma density, reduce capacitive coupling effect, and improve the efficiency of degumming. The RF power source directly provides power through the coil and achieves 50Ω impedance matching without the need for a matching network. The application method of the system is specifically as follows: first, RF power is provided to excite plasma; then, capacitive coupling is reduced by optimizing the coil length and impedance matching; finally, multiple induction ring surfaces are formed in the reaction chamber to improve the uniformity of plasma. In the process, a rarefied heat transfer mechanism is used to improve the heat transfer efficiency between the wafer and the carrier.

[0085] In this embodiment, the parasitic current can be reduced by introducing a conductive shield downstream of the plasma source; and optimizing the electromagnetic field distribution by 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 the 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] Wherein, L is the electrical length of the coil; λ = c / f is the wavelength of the RF signal; c is the speed of light in a vacuum; f is the RF frequency (27.12 MHz in this embodiment, corresponding to a wavelength of 11.06 meters); n is an integer multiple resonance mode, and in this embodiment, n = 1 is selected to achieve single wavelength resonance. By precisely controlling the physical length of the induction coil to match the wavelength of the RF signal, high-frequency losses are avoided, while ensuring the optimal resonance state of the induction coil at the operating frequency. Impedance matching is achieved intrinsically through the structural design of the coil, avoiding the power loss and complexity of the traditional matching network.

[0089] Then, the plasma density distribution is calculated. In the quartz chamber, oxygen is excited by the induction coil to form plasma, and its electron density is described by the following formula:

[0090]

[0091] Among them, n e is the electron density; P rf is the input RF power (set to 2.5 kW in this embodiment); η is the power transmission efficiency (95% after optimization); A is the effective excitation area of ​​the reaction chamber; e is the electron charge constant; v ion is the ionization speed.

[0092] The calculation results show that after the optimized design, the plasma electron density in the quartz chamber can reach 1.2×10 11 cm -3 , improving the photoresist removal rate.

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

[0094] X L =X C

[0095] Among them, X L =2πfL is the inductive reactance, L is the inductance value 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 radio frequency power loss when the parasitic current is balanced is minimized, and the overall efficiency of the system is improved by about 20%.

[0097] And calculate the stripping rate. 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 reaction gas (oxygen); n e is the plasma electron density; σ is the reaction cross section of the photoresist.

[0100] In this embodiment, the performance is improved by more than 30% compared with the conventional quarter-wavelength resonator.

[0101] Explanation of rarefied heat transfer in the reaction chamber: Assuming that the temperature of the continuously introduced oxygen is 20°, after the pressure reaches 3 Torr, the characteristic size floating ejector pin is 150 microns, and the Knudsen number at this time is 0.126, which belongs to the transition flow area, not the continuous flow; when the oxygen temperature is 250℃, after 3 Torr, the Knudsen number is 0.227, which also belongs to the transition flow area, not the continuous flow; and the lower the pressure (the stage before 3 Torr), the greater the mean free path of the gas, the greater the Knudsen number, and it is not a continuous flow. Therefore, in the PC chamber, the wafer and the base are not in the category of continuous flow, and are in the condition of rarefied heat exchange during the entire operation time.

[0102] In this embodiment, for a 12-inch wafer, a thickness of 775 μm, and a density of 2330 kg / m 3, the specific heat capacity is 700 J / (kg·K), the temperature is 20°C, and the heat transfer between it and the hot surface maintained at 250°C can be calculated. The relationship between the slit distance and the heat transfer coefficient of rarefied gas at different pressures is as follows Figure 5 As shown, the heat transfer coefficient h = 300 W / m2*K (considering the influence of heat dissipation and slit size). According to Newton's cooling law and energy conservation equation, the relationship between temperature rise and time under rarefied heat exchange conditions can be derived.

[0103] Newton's law of cooling is:

[0104] Q = hAΔT;

[0105] Where Q is the heat transfer rate in W; h is the heat transfer coefficient in W / m 2 K; A is the heat exchange surface area, in m 2 ; ΔT is the temperature difference between the object and the environment, in K.

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

[0107] mc*dT / dt=hAΔT

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

[0109] In the first 10 seconds, at intervals of 1 second, the temperature of the wafer rises as follows: 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 the heat transfer rate is very fast.

[0110] In summary, the optimized design of the full-wavelength spiral resonator significantly improves the plasma excitation efficiency, allowing the device to maintain stable operation within a wide process window (such as pressure from 20mTorr to 1Torr). In addition, the uniform plasma distribution combined with the current-free damage characteristics further improves the degumming rate and process yield.

[0111] Example 2

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

[0113] The base is used to carry the substrate to be processed and adopts a rarefied heat transfer mechanism to provide a stable temperature control environment;

[0114] The gas delivery device includes a plurality of gas flow guide components for providing process gas into the reaction chamber;

[0115] The full-wavelength spiral resonance device includes n reaction chambers, n induction coils and a radio frequency power source, which are used to generate resonance and provide uniform plasma distribution; wherein the induction coil is located in the reaction chamber and is electrically connected to the radio frequency power source, the n reaction chambers 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, and n>0 is an integer.

[0116] In this embodiment, n is 2. That is, by connecting two half-wavelength degumming cavities in series, a degumming device of a full-wavelength spiral resonator is formed. This scheme utilizes two half-wavelength resonant structures to optimize the distribution of electromagnetic waves, and realizes efficient plasma excitation and uniform photoresist removal. First, the substrate to be processed is fixedly placed on a base in the reaction chamber, and the radio frequency power source in the full-wavelength spiral resonator device provides radio frequency frequency to the induction coil, so that the induction coil generates three induction ring areas inside the reaction chamber, and the gas delivery device provides gas to the reaction chamber to complete the plasma treatment. The three induction ring areas include a central induction area and reverse induction areas at both ends, wherein the power density of the central induction area is twice the power density of the reverse induction areas at both ends.

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

[0118] L = λ / 2 = c / 2f

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

[0120] In this embodiment, two half-wavelength cavities are connected in series through an induction coil to form a full-wavelength resonator, and the total length is:

[0121] L total =L 1 +L 2 =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 =P 1 +P 2

[0124] Among them, P rf is the total RF power (set to 5kW); P 1 and P 2are the powers of two half-wavelength cavities respectively. In this embodiment, P 1 =P 2 =2.5kW). The number of turns, diameter and material selection of the induction coil are optimized to ensure uniform power distribution in the two cavities and efficient transmission of RF energy.

[0125] In this embodiment, through the series design, the plasma density distribution in the two sections of the cavity is more uniform. The electron density formula is:

[0126]

[0127] A total =A 1 +A 2

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

[0129] The experimental results show that the electron density of the two cavities reaches 1.1×10 11 cm -3 , the deviation is less than 3%.

[0130] In summary, a system for plasma processing in this embodiment has good resonance performance, and two half-wavelength cavities achieve higher resonance efficiency under full-wavelength conditions, avoiding the unevenness problem caused by concentrated power density in traditional single-cavity designs. Its modular design allows the two cavities to work independently, but achieves full-wavelength optimization in series mode, which is easy to maintain and upgrade. In addition, its low-loss operation and series design significantly reduce parasitic discharge and electromagnetic wave interference, and improve system stability.

[0131] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A system for plasma processing, characterized in that include: a pedestal, a gas delivery device, and a full-wavelength helical resonator; The base is used to carry the substrate to be processed and adopts a rarefied heat transfer mechanism to provide a stable temperature control environment; The gas delivery device includes a plurality of gas flow guide components for providing process gas into the reaction chamber; The full-wavelength spiral resonance device includes n reaction chambers, n induction coils and a radio frequency power source, which are used to generate resonance and provide uniform plasma distribution; wherein the induction coil is located in the reaction chamber and is electrically connected to the radio frequency power source, the n reaction chambers 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 areas are formed inside the reaction chamber, and n>0 is an integer.

2. A system for plasma processing according to claim 1, characterized in that: The three induction ring areas include a central induction area and reverse induction areas at both ends; the power density of the central induction area is twice the power density of the reverse induction areas at both ends.

3. A 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.

4. A system for plasma processing according to claim 3, 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 passing through the reaction chamber to cause electric shock or parasitic discharge.

5. A system for plasma processing according to claim 1, characterized in that: The surface of the base is coated with an anti-pollution coating to avoid particle contamination.

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

7. A system for plasma processing according to claim 1, characterized in that: The geometric parameters and shielding distance of the induction coil meet the preset characteristic impedance requirements of the full-wavelength spiral resonator, thereby completing the intrinsic impedance optimization, wherein the preset characteristic impedance requirement is: the characteristic impedance matches the output impedance of the RF power source, and the specific formula is: Among them, Z in is the input impedance of the induction coil; Z c is the characteristic impedance of the induction coil; β is the propagation constant; L is the electrical length of the induction coil; j is the imaginary unit used to represent the imaginary part of the impedance.

8. 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. The plasma distribution in the reaction chamber can be changed by changing different positions of the radio frequency slider on the induction coil.

9. A method for plasma treatment, characterized in that The method is applied to work in a system for plasma processing as described in any one of claims 1 to 8. In the method, the substrate to be processed is first fixedly placed on a base in a reaction chamber, and an RF power source in a full-wavelength spiral resonator provides an RF frequency to an induction coil, so that the induction coil generates a resonant frequency and generates three induction ring areas inside the reaction chamber, and a gas delivery device provides gas into the reaction chamber to complete plasma processing.

10. A method for plasma treatment according to claim 9, 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: Among them, 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.

Images