An oxygen plasma cleaning method and system for in-situ removal of chamber ion contaminants

Abstract

The present application relates to a kind of oxygen plasma cleaning method and system for removing cavity ion contaminants in situ.The method first controls the pressure in the cavity below 300 mTorr, and oxygen is introduced into the cavity;Radio frequency is applied to the cavity to ionize oxygen into oxygen ions and high-energy electrons;Oxygen ions and metal ions undergo physical sputtering, causing metal ions to desorb from the surface of the cavity, while high-energy electrons and metal ions undergo neutralization reactions;Finally, the characteristic peaks of metal ions in the cavity are monitored in real time using optical emission spectroscopy, and the cleaning is completed using feedback regulation until the characteristic peaks of metal ions meet the preset conditions.Compared with the prior art, the present application has the advantages of good cleaning effect, high efficiency, environmental protection, stability and the like.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and in particular to an oxygen plasma cleaning method and system for in-situ removal of ionic contaminants from a cavity. Background Technology

[0002] In semiconductor manufacturing, cleaning is a crucial step among key processes, used to remove particles, organic matter, metal ion contaminants, and natural oxide layers from the wafer surface. The effectiveness of the cleaning process directly impacts device performance, reliability, and yield. Currently, cleaning processes are mainly divided into wet cleaning and dry cleaning. Wet cleaning primarily uses chemical solvents or deionized water (DIW) to clean wafers. Common methods include immersion and spraying. This method has the advantage of mature technology, but also has some significant drawbacks: the cleaning solutions used in wet cleaning, such as hydrofluoric acid (HF), Standard Cleaning Solution 1 (SC1), and Standard Cleaning Solution 2 (SC2), may corrode or damage device materials, especially when removing certain sensitive metals, such as aluminum (Al), copper (Cu), and iron (Fe). Wet cleaning generates a large amount of waste liquid, resulting in high treatment costs and a significant environmental impact. For metal ion contaminants on the inner walls of the cleaning chamber, wet cleaning has limited effectiveness, usually requiring disassembly of the chamber for treatment, which is complex and affects equipment efficiency.

[0003] Dry cleaning achieves surface cleaning by directly applying plasma or gas to contaminants. Compared to wet cleaning, dry cleaning is more effective at removing fine particles, organic matter, nitrides, and oxides. However, existing dry cleaning processes are mostly focused on removing organic matter or natural oxide layers, and their ability to remove metal ion contaminants is insufficient. Due to the limitations of current technology, wet cleaning is still the primary method for dealing with metal ion contaminants within chambers. However, wet cleaning faces the following challenges when handling metal ions: First, some metal ions, such as iron ions (Fe+) and copper ions (Cu+), easily form difficult-to-remove oxides in wet cleaning solutions, further adhering to the surface. Second, the complex structure of the chamber limits the coverage of the inner walls by wet cleaning, resulting in low cleaning efficiency. Furthermore, new impurities may be introduced during the cleaning process, especially in advanced nodes where high cleanliness requirements are needed, further limiting the applicability of wet cleaning.

[0004] In semiconductor manufacturing processes, particularly in photoresist stripping, metal ion contamination within the photoresist cavity can impact stripping rates and even device performance. Specifically, the growth and removal of thin metal layers inevitably leave metal ion residues within the cavity. For cavities with rising and falling ejector pins, metal ions may re-enter the cavity during the pin-raising process, altering discharge characteristics and affecting plasma stability and energy distribution. Furthermore, in a plasma environment, high-energy ions bombard the quartz surface, sputtering metal ions into the quartz, altering plasma conductivity and electric field distribution, thus affecting plasma uniformity and density. Metal ions, with their high electronegativity, form stable complexes with electron-rich groups in photoresist, such as carboxylate (COO-) and hydroxyl (OH-). Some photoresist formulations may contain complexing agents specifically designed to control metal ion concentration and prevent interference with photoresist performance. Since different foundries may use different photoresists, the impact of ions varies.

[0005] While dry cleaning shows promise for cavity cleaning, current technologies primarily focus on the chemical reactions of oxygen free radicals, particularly those generated under high pressure. Furthermore, this approach has limited effectiveness in removing metal ions. Therefore, there is an urgent need for a new, efficient, environmentally friendly, and controllable method that leverages the unique properties of plasma to efficiently remove metal ion contaminants from cavities. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art by providing an oxygen plasma cleaning method and system for in-situ removal of ionic contaminants from a cavity.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] According to one aspect of the present invention, an oxygen plasma cleaning method for in-situ removal of ionic contaminants from a cavity is provided, characterized in that the method steps include:

[0009] S1. Control the pressure inside the chamber to below 300 mTorr and introduce oxygen into the chamber;

[0010] S2. Apply radio frequency to the cavity to ionize oxygen into oxygen ions and high-energy electrons;

[0011] S3. Oxygen ions and metal ions undergo physical sputtering, causing the metal ions to desorb from the cavity surface. At the same time, high-energy electrons neutralize the metal ions. S4. The characteristic peaks of metal ions in the cavity are monitored in real time using optical emission spectroscopy. Feedback adjustment is used until the characteristic peaks of metal ions meet the preset conditions, and the cleaning is completed.

[0012] As a preferred technical solution, the pressure inside the control chamber in S1 is below 300 mTorr, specifically including a first pressure control scheme and a second pressure control scheme. The first pressure control scheme is to maintain the pressure inside the control chamber at a preset pressure value, and the preset pressure value is less than 300 mTorr. The second pressure control scheme is to select two preset pressure values ​​a and b, such that a < b ≤ 300, and control the pressure value inside the chamber to periodically switch between a and b.

[0013] As a preferred technical solution, the oxygen in S1 is high-purity oxygen, and the oxygen is introduced through a multi-point air intake method, with the oxygen flow rate ranging from 500 to 2000 sccm.

[0014] As a preferred technical solution, 10%-20% helium or nitrogen is introduced into S1 as an auxiliary gas while oxygen is introduced.

[0015] As a preferred technical solution, the power range of the radio frequency in S2 is 100-200W, its frequency is 13.56 or 27.12MHz, and its duty cycle is 0.5.

[0016] As a preferred technical solution, the specific formula for the physical sputtering and charge neutralization of oxygen ions and metal ions in cavity S3 is as follows:

[0017]

[0018] Among them, M + It is a metal ion; O is an oxygen ion; M is a metal atom; O2 is oxygen gas.

[0019] The specific formula for the neutralization reaction between high-energy electrons and metal ions in the cavity of S3 is as follows:

[0020] M + +e - →M

[0021] Among them, M + It is a metal ion; e - is a high-energy electron; M is a metal atom.

[0022] As a preferred technical solution, the preset condition in S4 is: when the intensity of the characteristic peak reaches the background value or drops to a preset percentage below the initial value, it remains stable within three consecutive preset detection cycles.

[0023] According to another aspect of the present invention, an oxygen plasma cleaning system for in-situ removal of ionic contaminants from a cavity is provided. The system operates using an oxygen plasma cleaning method for in-situ removal of ionic contaminants from a cavity as described above. The system includes a cavity, a pressure control module, a gas injection module, a radio frequency module, and a monitoring module.

[0024] The cavity's inner wall is coated with a ceramic coating, using alumina or titanium dioxide as the material, with a coating thickness of 5-30 μm. A pressure control module controls the pressure inside the cavity to be below 300 mTorr. An air injection module controls the introduction of oxygen into the cavity. A radio frequency module applies radio frequency to the cavity, ionizing the oxygen into oxygen ions and high-energy electrons. Oxygen ions physically sputter with metal ions, causing the metal ions to desorb from the cavity surface, while high-energy electrons neutralize the metal ions. A monitoring module uses optical emission spectroscopy to monitor the characteristic peaks of metal ions inside the cavity in real time.

[0025] As a preferred technical solution, the system also includes a temperature control module, which is used to control the cavity temperature at 50-200℃ during the cleaning process.

[0026] As a preferred technical solution, the system also includes a magnetic field generation module, which is used to generate a magnetic field in the cavity. The magnitude of the generated magnetic field is 20-50 mT and the direction is axial, which is used to guide the movement of metal ions.

[0027] As a preferred technical solution, the system also includes a feedback control module, which dynamically adjusts the radio frequency power, gas flow rate and cleaning time based on the characteristic peaks of metal ions in the cavity.

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

[0029] 1. In this invention, the pressure inside the chamber is controlled below 300 mTorr, and oxygen is introduced into the chamber. Radio frequency is then applied to the chamber, ionizing the oxygen into oxygen ions and high-energy electrons. The oxygen ions physically sputter with metal ions, causing the metal ions to desorb from the chamber surface. Simultaneously, the high-energy electrons neutralize the metal ions. Finally, the characteristic peaks of the metal ions inside the chamber are monitored in real time using optical emission spectroscopy, and feedback adjustment is used until the characteristic peaks meet preset conditions, completing the cleaning process. This gives it highly efficient cleaning capabilities, enabling efficient physical sputtering and charge neutralization of metal ion contaminants, significantly improving cleaning efficiency.

[0030] 2. In this invention, high-purity oxygen is used as the working gas. At the same time as oxygen is introduced, 10%-20% helium or nitrogen is introduced as an auxiliary gas. No chemical solvents are used, which avoids the problems of chemical solvents and waste liquid treatment in wet cleaning, and reduces environmental pollution and cleaning costs.

[0031] 3. In this invention, oxygen ions undergo physical sputtering and charge neutralization with metal ions, while high-energy electrons neutralize metal ions. This generates a high concentration of oxygen ions (O2+) and high-energy electrons (e-), enabling highly efficient physical sputtering and charge neutralization of metal ion contaminants, significantly improving cleaning efficiency. Furthermore, the multi-point oxygen intake ensures uniform oxygen distribution within the cavity, optimizing the plasma excitation area and enhancing cleaning effectiveness. This allows for thorough removal of contaminants from the cavity, reducing the risk of secondary contamination, eliminating the need for additional cleaning steps, and improving cleaning quality.

[0032] 4. In this invention, the characteristic peaks of metal ions within the cavity are monitored in real time using optical emission spectroscopy. Cleaning is complete when the characteristic peaks meet preset conditions. These preset conditions are a preset percentage of the characteristic peak intensity reaching the background value or falling below the initial value. This preset percentage is set according to the specific needs of the user and remains stable within three consecutive preset detection cycles. By using optical emission spectroscopy to monitor the characteristic spectrum of metal ions in real time and automatically determining the cleaning endpoint, the cleaning operation is simplified and made more intuitive, avoiding over-cleaning or under-cleaning.

[0033] 7. In this invention, the pressure within the cavity is controlled to be below 300 mTorr. Specifically, this includes a first pressure control scheme and a second pressure control scheme. The first pressure control scheme involves maintaining the pressure within the cavity at a preset pressure value, which is less than 300 mTorr. The second pressure control scheme involves selecting two preset pressure values, a and b, such that a < b ≤ 300 mTorr, and controlling the pressure within the cavity to periodically switch between these two values. Through dynamic pressure adjustment, i.e., periodically switching the pressure, the oxygen ion bombardment and electron recombination are optimized at different stages, further enhancing the cleaning effect.

[0034] 8. The radio frequency (RF) power used in this invention ranges from 100-200W, with a frequency of 13.56 or 27.12MHz and a duty cycle of 0.53. It is highly adaptable; by adjusting the RF power, frequency (13.56 or 27.12MHz), gas flow rate, and chamber pressure, it can be adapted to different equipment and process requirements. By controlling the RF power supply's duty cycle, the cleaning effect is maintained while reducing secondary sputtering of high-energy particles onto the chamber walls, thus protecting the internal structure of the equipment.

[0035] 9. The oxygen plasma cleaning system for in-situ removal of ionic contaminants from a cavity according to the present invention also includes a temperature control module for controlling the cavity temperature between 50-200°C during the cleaning process. Precise control of the cavity temperature further enhances the chemical reactivity of oxygen ions, ensures the stability of the cleaning process, prevents condensation or redeposition of contaminants on the wall surface, and extends the service life of the equipment.

[0036] 10. The oxygen plasma cleaning system for in-situ removal of ionic contaminants from a cavity according to the present invention further includes a magnetic field generation module for generating a magnetic field within the cavity. The generated magnetic field has a magnitude of 20-50 mT and an axial direction, used to guide the movement of metal ions. By adding a magnetic field device, the recombination efficiency of electrons and metal ions can be optimized, and the cleaning time can be shortened.

[0037] 11. The oxygen plasma cleaning system for in-situ removal of ionic contaminants from a cavity according to the present invention further includes a feedback control module, which dynamically adjusts the radio frequency power, gas flow rate, and cleaning time based on the characteristic peaks of metal ions in the cavity. By dynamically optimizing cleaning parameters such as gas flow rate, radio frequency power, and cavity pressure based on monitoring data, the stability and repeatability of the cleaning process can be ensured. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the steps of an oxygen plasma cleaning method for in-situ removal of ionic contaminants from a cavity, as described in this invention.

[0039] Figure 2 This is a schematic diagram illustrating the three common components of oxygen plasma and the function of each component in the embodiments.

[0040] Figure 3 This is a schematic diagram of the recombination process of pollutant metal ions and high-energy electrons after interaction in the examples;

[0041] Figure 4a This example compares oxygen ions and oxygen free radicals at a pressure of 300 mTorr.

[0042] Figure 4b This example compares oxygen ions and oxygen free radicals at a pressure of 3000 mTorr.

[0043] Figure 5 This is a flowchart of the oxygen plasma cleaning process for in-situ removal of ionic contaminants from the cavity, as shown in the embodiment. Detailed Implementation

[0044] 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.

[0045] In semiconductor manufacturing, cleaning is a crucial step among key processes, used to remove particles, organic matter, metal ion contaminants, and natural oxide layers from the wafer surface. The effectiveness of the cleaning process directly impacts device performance, reliability, and yield. Currently, cleaning processes are mainly divided into wet cleaning and dry cleaning. Wet cleaning primarily uses chemical solvents or deionized water (DIW) to clean wafers. Common methods include immersion and spraying. This method has the advantage of being a mature process, but it also has some significant drawbacks: the cleaning solutions used in wet cleaning (such as HF hydrofluoric acid, SC1, SC2, etc.) may corrode or damage device materials, especially when removing certain sensitive metals (such as Al, Cu, Fe, etc.). Wet cleaning generates a large amount of waste liquid, resulting in high treatment costs and a significant environmental impact. For metal ion contaminants on the inner walls of the cleaning chamber, wet cleaning has limited effectiveness, usually requiring disassembly of the chamber for treatment, which is complex and affects equipment efficiency.

[0046] Dry cleaning achieves surface cleaning by directly applying plasma or gas to contaminants. Compared to wet cleaning, dry cleaning is more effective at removing fine particles, organic matter, nitrides, and oxides. However, existing dry cleaning processes mainly focus on removing organic matter or natural oxide layers, and their ability to remove metal ion contaminants is insufficient. Due to the limitations of current technology, wet cleaning is still the primary method for dealing with metal ion contaminants within chambers. However, wet cleaning faces the following challenges when handling metal ions: Some metal ions (such as Fe+ and Cu+) easily form difficult-to-remove oxides in wet cleaning solutions, further adhering to the surface. The complex structure of the chamber limits the coverage of the inner walls by wet cleaning, resulting in low cleaning efficiency. New impurities may be introduced during the cleaning process, especially in advanced nodes where high cleanliness requirements are needed, further limiting the applicability of wet cleaning.

[0047] In semiconductor manufacturing processes, particularly in resist stripping, metal ion contamination within the photoresist cavity can impact stripping rates and even device performance. Specifically, the growth and removal of thin metal layers inevitably leave metal ion residues within the cavity. For cavities with rising ejector pins, metal ions may re-enter the cavity as the pins rise, altering discharge characteristics and affecting plasma stability and energy distribution. Furthermore, in a plasma environment, high-energy ions bombard the quartz surface, sputtering metal ions into the quartz, altering plasma conductivity and electric field distribution, thus affecting plasma uniformity and density. Metal ions, with their high electronegativity, form stable complexes with electron-rich groups in photoresist, such as carboxyl groups (COO-) and hydroxyl groups (OH-). Some photoresist formulations may contain complexing agents specifically designed to control metal ion concentration and prevent interference with photoresist performance. Since different factories may use different photoresists, the impact of ions varies.

[0048] While dry cleaning shows promise for cavity cleaning, current technologies primarily focus on the chemical reactions of oxygen free radicals, particularly those generated under high pressure. Furthermore, this approach has limited effectiveness in removing metal ions. Therefore, there is an urgent need for a new, efficient, environmentally friendly, and controllable method that leverages the unique properties of plasma to efficiently remove metal ion contaminants from cavities.

[0049] The purpose of this application is to provide an in-situ cleaning method based on low-pressure oxygen plasma. Through the synergistic effect of oxygen ions and high-energy electrons, it efficiently removes metal ion contaminants adhering to the inner wall of the cavity, overcoming the shortcomings of existing technologies. Through innovative process optimization, equipment design, and automated control, it solves the problem of cleaning metal ion contaminants in semiconductor manufacturing processes, possessing core advantages such as high efficiency, environmental friendliness, and wide applicability, providing a novel solution for the maintenance of semiconductor equipment at advanced nodes. The specific implementation process of this application is shown in Examples 1-3 below.

[0050] Example 1

[0051] In this embodiment, a degumming machine with a plasma chamber is used as the cleaning device, and the cleaning target is the metal ion contaminants (such as Cu+, Fe+) remaining during the degumming process.

[0052] In this embodiment, a low-pressure oxygen plasma cleaning method is applied to clean the plasma, providing a combination of innovative processes including radio frequency duty cycle optimization, dynamic pressure regulation, and magnetic field assistance. By integrating multiple processes, this cleaning method is suitable for cavity cleaning under complex process nodes. The method steps are as follows: Figure 1 As shown, it specifically includes:

[0053] S1. Adjust the chamber pressure to below 300mTorr;

[0054] S2. Introduce oxygen into the cavity at a flow rate of 500-2000 sccm;

[0055] S3. Apply radio frequency power (300-850W, frequency of 13.56MHz or 27.12MHz) to generate low-pressure oxygen plasma;

[0056] S4. Oxygen ions (O2+) and high-energy electrons (e-) react with metal ion contaminants in the cavity, causing the metal ions to desorb and be discharged from the cavity.

[0057] In this embodiment, the three common components of oxygen plasma and the schematic diagram of the function of each component are shown below. Figure 2 As shown, the plasma source includes DC, radio frequency, and microwave sources, with three components: ions, free radicals, and electrons. Ions are used for sputtering, free radicals for etching, and electrons for heating. During normal operation, taking the resist stripping process as an example, the density of free radicals is at least two orders of magnitude greater than the density of ions.

[0058] In this embodiment, during the cleaning process, oxygen ions react with metal ion contaminants through physical sputtering, reducing the metal ions to neutral metal atoms and causing them to desorb. High-energy electrons combine with the metal ions through charge neutralization, reducing their charge state and thus promoting desorption. The recombination process of contaminant metal ions after interaction with high-energy electrons is illustrated in the diagram below. Figure 3 As shown, taking an inductively coupled plasma (ICP) chamber as an example, two recombination processes occur within the chamber. Mode one involves the recombination of contaminant ions with electrons on the surface or in the central region. Mode two involves contaminant ions at a certain depth within the walls being sputtered by oxygen ions and then recombinating with electrons to form metal atoms or molecules, which are finally extracted from the chamber. Under low-pressure conditions, the generation of oxygen free radicals is suppressed, and oxygen ions and high-energy electrons dominate, improving the removal efficiency of metal ions. During the cleaning process, the chamber temperature is controlled between 50-200℃ to further enhance the chemical reactivity of oxygen ions.

[0059] The pressure within the chamber was controlled within the range of 300 mTorr. Under low pressure, the mean free path of electrons increases, their kinetic energy increases, and oxygen in the plasma mainly forms oxygen ions (O2). + The oxygen ionizes and produces high-energy electrons, while generating fewer oxygen free radicals (O). This results in less oxygen ionization (O2) under low pressure (1-5 Pa) conditions. + The concentration of high-energy electrons is relatively high, while the concentration of oxygen radicals (O) is relatively low. The mean free path of high-energy electrons is increased, and their energy is higher, enabling them to collide effectively with metal ions, leading to their reduction and desorption.

[0060] In this embodiment, a comparison is made between oxygen ions and oxygen free radicals in low-pressure and high-pressure environments, as follows: Figure 4a , Figure 4b As shown, where, Figure 4a A comparison of oxygen ions and oxygen free radicals at a pressure of 300 mTorr; wherein the pressure is 300 mTorr, the oxygen flow rate is 800 sccm, the radio frequency power is 500 W, the frequency is 27.12 MHz, and the temperature is 150 ℃. Figure 4b This comparison examines oxygen ions and oxygen free radicals at a pressure of 3000 mTorr. The pressure was 3000 mTorr, the oxygen flow rate was 10000 sccm, the radio frequency power was 500 W, the frequency was 27.12 MHz, and the temperature was 150℃. The illustration shows that under lower pressure conditions, the peak intensity of oxygen ions (≈ electrons) is higher than that of oxygen free radicals.

[0061] In this scheme, oxygen plasma is generated. In equipment with plasma chambers, such as etching machines and resist strippers, a "low-pressure oxygen plasma cleaning mode" is first preset in the equipment control system, and then parameters such as RF power, gas flow rate, and pressure are automatically adjusted according to actual needs. In equipment without plasma chambers, such as coating equipment and testing equipment, a remote plasma scheme is used. A remote plasma generator is connected externally to the equipment to generate low-pressure oxygen plasma, which is then transported into the chamber through pipelines. Oxygen ions (O2+) bombard the chamber surface, producing a physical sputtering effect that strips metal ions from the chamber surface. High-energy electrons combine with metal ions, reducing their charge and converting them into neutral metal atoms, which are then easily removed by the vacuum pump. In oxygen plasma, the composition and species concentration distribution depend on plasma parameters such as pressure, electron temperature, and collision frequency.

[0062] Under low-pressure conditions, oxygen plasma more readily generates a large number of oxygen ions and high-energy electrons, rather than oxygen free radicals. This is because under low-pressure conditions, the density of gas molecules decreases, the collision frequency between particles decreases significantly, and the mean free path of electrons, i.e., the average distance of collisions between particles, increases. This means that electrons can acquire higher kinetic energy before colliding with oxygen molecules. Due to the higher kinetic energy of the electrons, oxygen molecules are more likely to ionize rather than dissociate to form oxygen ions. The ionization threshold for this process is 12.1 eV, while the threshold for oxygen molecules to dissociate into oxygen free radicals is 5.1 eV.

[0063] Under low-pressure conditions, the probability of inelastic collisions between electrons and oxygen molecules decreases due to the reduced collision frequency. However, when electron energy is sufficiently high, collisions are more likely to trigger ionization reactions because the ionization cross-section (reaction probability) gradually increases under high-energy conditions. In low-pressure plasma, the energy distribution of electrons follows a Maxwell distribution or an approximately non-equilibrium distribution, with a higher proportion of high-energy electrons. These high-energy electrons possess energies exceeding 12.1 eV, sufficient to ionize oxygen molecules into oxygen ions. The electron energy distribution under low pressure is more "biased towards the high-energy region," meaning the high-energy tail is less likely to decrease and may even become more pronounced. Therefore, under low pressure, due to fewer collisions and higher electron kinetic energy, oxygen molecules preferentially undergo ionization reactions to generate oxygen ions, rather than simply dissociating into oxygen free radicals.

[0064] After metal ions are converted into neutral particles, they are more easily removed from the chamber using methods such as airflow. This allows for further analysis of the adhesion forces between metal atoms / ions and the chamber material. In the chambers of semiconductor devices, the adhesion forces between metal atoms and ions and the chamber material (e.g., quartz, aluminum, and stainless steel) can vary significantly. The adhesion forces between metal atoms and the chamber material are influenced by three factors: physical adsorption, chemical adsorption, and the surface state of the material. Physical adsorption involves metal atoms adsorbing onto the chamber material surface through van der Waals forces or weak electromagnetic forces; this adsorption is typically weak and reversible. Chemical adsorption occurs when certain metal atoms react chemically with the chamber material to form covalent or ionic bonds. This adhesion force is stronger and difficult to reverse. For example, aluminum reacts with oxygen to form an alumina layer. The surface state of the chamber material (e.g., surface roughness and cleanliness) affects the adsorption strength of metal atoms. Clean and smooth surfaces generally have weaker adsorption forces, while rough or contaminated surfaces have stronger adsorption forces. The adhesion between metal ions and the cavity material is influenced by three factors: electrostatic adsorption, chemisorption, and interfacial potential. Electrostatic adsorption occurs when charged metal ions attract oppositely charged regions on the cavity material surface. This adsorption force is strong and directional. Chemisorption, similar to metal atoms, involves metal ions reacting with the cavity material to form strong chemical bonds. This adsorption is typically stronger because the ionic state is more reactive and readily forms chemical bonds with the material surface. Interfacial potential is determined by the formation of an electrical double layer on the cavity material surface, leading to a strong adsorption effect.

[0065] Physical adsorption (Van der Waals forces) is typically described as a weak interaction between metal atoms and the surface of the cavity material. The formulas are usually quite simple, such as the Lennard-Jones potential:

[0066]

[0067] Where U(r) is the potential energy, ∈ is the deep potential well, σ is the distance to the zero potential point, and r is the interatomic distance.

[0068] Chemisorption involves chemical bond formation and is generally more complex. It requires consideration of electron exchange or sharing between metal atoms and surface atoms. For example, the process of forming covalent or ionic bonds between atoms and the surface. However, for a quartz cavity, if some metal ions have already reacted with the cavity wall to form compounds, these metal ions can be considered consumed and will not remain inside the cavity or affect subsequent processes. Therefore, chemisorption can be temporarily disregarded in the overall adsorption process. Electrostatic adsorption, for charged metal ions, can be described by Coulomb's law:

[0069]

[0070] Where F is the electrostatic force, ∈0 is the vacuum permittivity, q1 and q2 are charges, and r is the distance between charges.

[0071] Taking copper (Cu) as an example, a rough, intuitive comparison between atomic physical adsorption and ionic electrostatic adsorption can be made through the following calculations:

[0072] First, calculate the adsorption energy of Cu atoms, i.e., the physical adsorption energy (Lennard-Jones potential function). By setting appropriate parameters, the potential well depth is obtained as r = 0.2 eV, and the distance to the zero potential point is σ = 2.5 Å. Then, calculate the adsorption energy at r = 3 Å.

[0073]

[0074] U(3)=4×0.2[0.0317-0.178]U(3)=0.8[-0.1463]U(3)=-0.117eV

[0075] Calculate Cu again + The adsorption energy of ions, i.e., the electrostatic adsorption energy, for charged Cu + For ions, the electrostatic adsorption energy is calculated using Coulomb's law. The interaction energy of the charges is negative because the attractive force lowers the system's energy.

[0076] Let the charge q1 = +1e, the surface charge q2 = -1e, and the distance r = 3A°.

[0077]

[0078] Convert it to electron volts:

[0079] 1J = 6.242 × 10 18 eVE elec = -7.68 × 10-20 J×6.242×10 18 eV / J≈-0.48eV

[0080] In terms of total adsorption energy, the physical adsorption energy of Cu atoms is relatively small, approximately -0.117 eV. + The electrostatic adsorption energy of Cu ions is relatively large, approximately -0.48 eV. 2+ The electrostatic adsorption energy of ions is greater, about -0.96 eV. Therefore, by using low-pressure, low-power oxygen plasma to generate a large number of electrons and then neutralizing the metal ions to make them neutral metal atoms, it does help to reduce the adsorption energy of these metal contaminants on the surface of the chamber, making it easier to remove them from the chamber by means of airflow and other methods.

[0081] In this scheme, the specific process includes: introducing high-purity oxygen into the cavity at a flow rate of 500-2000 sccm; applying radio frequency power (e.g., 500-1000W, frequency 13.56 or 27.12MHz) to ionize the oxygen, forming a high concentration of oxygen ions and high-energy electrons.

[0082] Under low pressure conditions, oxygen ions undergo physical sputtering and charge neutralization with metal ions, transforming the metal ions into neutral metal atoms, which then desorb from the cavity surface and are drawn away by the vacuum pump.

[0083] M + +e - →M

[0084] Among them, M + It is a metal ion; e - M represents high-energy electrons; M represents metal atoms, such as Cu, Fe, Ni, etc.

[0085] High-energy electrons possess sufficient kinetic energy under low-pressure conditions to effectively strike metal ions, accelerating their desorption. They also synergize with oxygen ions to enhance the cleaning effect. In this scheme, optical emission spectroscopy (OES) is used to monitor the spectral characteristics of oxygen ions (O2+) and metal ions (e.g., Fe+: 259.9 nm, Cu+: 324.8 nm) to determine the metal ion removal process and dynamically optimize process parameters such as gas flow rate, RF power, and cleaning time.

[0086] The cleaning process parameters are set as follows: pressure is set to 150 mTorr; oxygen flow rate is set to 850 sccm; RF power is set to 120W; frequency is set to 13.56MHz; RF duty cycle is set to 50%, i.e., the continuous power-on time per cycle is 5ms; and cleaning time is set to 8 minutes.

[0087] In this embodiment, the cavity is first prepared by starting the vacuum pump, adjusting the cavity pressure in the degumming machine to 150 mTorr, and continuously introducing high-purity oxygen at a flow rate of 850 sccm.

[0088] Then, plasma excitation is performed, the radio frequency power supply is turned on, the power is set to 120W and the frequency is 13.56MHz, and the duty cycle is adjusted to 50% through the control system, that is, the radio frequency power supply works continuously for 5ms in every 10ms cycle and is turned off for the rest of the time.

[0089] In this embodiment, under duty cycle control, the plasma generation process is periodically interrupted, maintaining a stable oxygen ion concentration and reducing secondary sputtering of high-energy particles (such as high-energy electrons and oxygen ions) onto the cavity walls. Oxygen ions react with metal ions as follows:

[0090]

[0091] Among them, M + It is a metal ion; O is an oxygen ion; M is a metal atom; O2 is oxygen gas.

[0092] The desorbed metal atoms are removed by a vacuum pump.

[0093] In this embodiment, monitoring and endpoint determination are performed by real-time monitoring of the characteristic peak intensity of Cu (324.8nm) using optical emission spectroscopy. When the characteristic peak intensity drops to the background level or drops to a preset percentage below the initial value, and remains stable within three consecutive preset detection cycles, the cleaning is stopped.

[0094] In this embodiment, the preset percentage is set as a threshold based on the specific needs of the actual user.

[0095] In summary, the cleaning method described in this solution achieves a metal ion contaminant removal rate of over 97% within the cavity, with no obvious splash marks on the cavity wall.

[0096] Example 2

[0097] This solution employs automated control for low-pressure plasma cleaning, suitable for various equipment with or without plasma chambers, including etching machines, resist strippers, resist coating equipment, and high-temperature reaction chambers. The control process is as follows: First, the cleaning program is initiated, setting the target pressure below 300 mTorr, and setting the RF power and gas flow rate. Then, the characteristic spectra of oxygen ions and metal ions are monitored in real time using an optical emission spectroscopy detection device. Next, based on the spectral analysis results, the cleaning parameters are automatically adjusted via a feedback control module. When the characteristic spectral intensity reaches the cleaning endpoint set value, the cleaning program is automatically terminated.

[0098] In this scheme, the interaction efficiency between electrons and metal ions is enhanced by optimizing the distribution of the radio frequency electric field, thereby increasing the desorption rate of metal ions. By adjusting the duty cycle of the radio frequency power supply, secondary sputtering of high-energy particles onto the cavity wall is reduced while maintaining the oxygen ion concentration. The sheath thickness is controlled by adjusting the frequency and power of the radio frequency electric field within the cavity, optimizing the bombardment efficiency of oxygen ions on the contaminant surface. The frequency of the radio frequency electric field can be dynamically switched between 13.56MHz and 27.12MHz to accommodate different types of metal ion contaminants. The cleaning efficiency is further optimized by periodically changing the cavity pressure, alternating between oxygen ion bombardment and contaminant removal under different pressure conditions. The periodic variation range of the cavity pressure is 50-300 mTorr, with each cycle lasting 1-5 seconds to enhance the dynamic cleaning effect. Finally, the characteristic peak values ​​of oxygen ions and metal ions are monitored in real time based on optical emission spectra, and the gas flow rate, radio frequency power, and cavity pressure are automatically adjusted through a feedback control system to achieve the optimal cleaning effect.

[0099] When the characteristic peak meets the preset conditions, the cleaning stops. The preset conditions are the characteristic peak intensity reaching the background value or decreasing to a preset percentage below the initial value, and remaining stable within three consecutive preset detection cycles.

[0100] In this embodiment, the preset percentage is set as a threshold based on the specific needs of the actual user.

[0101] In this embodiment, the cleaning equipment is an etching machine with a magnetic field-assisted device; the object to be cleaned is the metal ion contaminants (such as Ni+, Al+) deposited on the inner wall of the cavity during the etching process; the specific process parameters for the cleaning process include: pressure set to 100 mTorr; oxygen flow rate set to 600 sccm; radio frequency power set to 150 W; radio frequency set to 27.12 MHz; magnetic field strength set to 20 mT; and cleaning time set to 12 minutes.

[0102] Table 1 Comparison of Metal Ion Contaminant Content in the Cavity Before and After Cleaning

[0103]

[0104]

[0105] In this embodiment, during the cleaning process, the cavity is first prepared by adjusting the initial pressure inside the etching machine cavity to 100 mTorr and continuously introducing oxygen at a flow rate of 600 sccm. Then, plasma excitation is performed with the aid of a magnetic field. The radio frequency power supply is activated, set to a power of 150 W and a frequency of 27.12 MHz, to excite the oxygen inside the cavity to form plasma. Simultaneously, the magnetic field assist device is activated, applying an axial magnetic field of 20 mT to guide the movement of metal ions and enhance their recombination probability with high-energy electrons. During the cleaning process, in the magnetic field-assisted plasma cleaning process, oxygen ions remove metal ions through physical bombardment, while high-energy electrons reduce the metal ions to neutral atoms through charge neutralization. The reduced metal atoms are then discharged through a vacuum pump. Monitoring and endpoint determination are performed throughout the process. The characteristic peak intensity of nickel (Ni) (341.5 nm) is monitored in real time using an OES (Optical Image Steering) system. When the peak intensity drops below 10% of the initial value, the cleaning process automatically stops.

[0106] In this embodiment, as shown in Table 1, where C001 represents before cleaning and C002 represents after cleaning, it can be seen from the table that the content of metal ion contaminants in the cavity decreases after cleaning for 5 minutes under these conditions.

[0107] In summary, this solution can achieve a metal ion contaminant removal rate of over 98%, and the magnetic field effectively improves the recombination efficiency of metal ions and electrons, significantly shortening the cleaning time.

[0108] Example 3

[0109] In this solution, a device suitable for low-pressure oxygen plasma cleaning is used for cleaning. The system includes a vacuum chamber, a gas supply module, an RF power supply module, and a vacuum pump.

[0110] In this design, the inner wall of the vacuum chamber is coated with a low-adhesion ceramic coating to prevent the redeposition of residual metal ions or oxides during cleaning, reducing secondary contamination. The coating material is selected from alumina or titanium dioxide, with a thickness of 5-30 μm to ensure corrosion resistance and low particle adhesion. The vacuum chamber is equipped with a pressure regulating device; a remote plasma input terminal is located within the chamber to introduce remotely generated low-pressure oxygen plasma. A gas supply module is used to introduce oxygen and control the gas flow rate; a dynamic gas distribution system is equipped to ensure uniform oxygen distribution within the chamber through multi-point gas intake, optimizing the spatial uniformity of the plasma; the flow rate at each intake point can be independently adjusted to optimize oxygen distribution according to the chamber geometry. The gas supply module is equipped with a gas mixing device to add small amounts of argon or nitrogen as needed and control the gas flow rate to optimize plasma generation. A radio frequency power module is used to generate radio frequency power to excite oxygen to form plasma; a pulse power control system is installed within the device to excite oxygen through a pulsed electric field, enhancing the reaction efficiency of oxygen ions with metal ions while reducing damage to the chamber wall. By adjusting the frequency and power of the radio frequency electric field within the chamber, the sheath thickness is controlled, thus optimizing the bombardment efficiency of oxygen ions on the contaminant surface. The radio frequency power module operates at 13.56MHz or 27.12MHz, with an adjustable power range of 300-850W. A vacuum pump maintains a low-pressure state within the chamber and removes contaminants. The device is also equipped with a high-efficiency vacuum pumping system, which optimizes the pumping rate to reduce the recombination probability of metal ions with gas molecules within the chamber, thereby improving contaminant removal efficiency.

[0111] In this solution, for equipment without a plasma chamber, a suitable cleaning module is provided. This module includes a remote plasma generator, a gas delivery pipeline, and a control system. The remote plasma generator generates low-pressure oxygen plasma; the gas delivery pipeline delivers the plasma to the cleaning area of ​​the target equipment; and the control system adjusts the plasma generation parameters and cleaning time. The remote plasma generator can operate independently of the main equipment and seamlessly connect to the target equipment via an interface module.

[0112] In this solution, the equipment also includes a monitoring system, which comprises an optical emission spectroscopy module, a data analysis module, and a feedback control module. The optical emission spectroscopy detection device is used to monitor the characteristic spectra of oxygen ions and metal ions in real time. The data analysis module analyzes changes in the intensity of the characteristic spectra to determine the progress of the cleaning process. The feedback control module dynamically adjusts the RF power, gas flow rate, and cleaning time based on the monitoring results. The characteristic spectra of metal ions include common metal categories in the later stages of semiconductor manufacturing processes, such as Cu (324.8 nm), Fe (259.9 nm), and Ni (341.5 nm). The cleaning endpoint is automatically determined when the intensity of the characteristic spectra decreases to a set threshold.

[0113] In this embodiment, the cleaning equipment is a reaction chamber with a temperature control system; the cleaning target is complex metal ion contaminants (such as Fe+, Cu+) within the chamber; specific cleaning process parameters include: the pressure cycle is set to switch between 50 mTorr and 300 mTorr; the oxygen flow rate is set to 30 sccm; the radio frequency power is set to 180W and the frequency is set to 27.12MHz; the chamber temperature is controlled at 80℃; the duration of each pressure cycle is set to 4 seconds, with 2 seconds for the high-pressure stage and 2 seconds for the low-pressure stage; the total cleaning time is set to 10 minutes.

[0114] In this embodiment, the temperature control system monitors the cavity temperature in real time using a temperature sensor on the inner wall of the cavity, and controls the cavity temperature within the range of 50-200℃ through heating or cooling devices to ensure the stability of the cleaning process. The temperature control device includes a far-infrared heating module and a cooling circulating water system to precisely regulate the cavity temperature and prevent contaminants from condensing or redepositing on the cavity wall.

[0115] In this embodiment, the cleaning process applied to the equipment is as follows: Figure 5 As shown, the specific process includes the cleaning preparation stage, the cleaning process stage, and the cleaning completion stage.

[0116] During the cleaning preparation phase, system startup, gas introduction, and radio frequency power excitation are performed sequentially. During the cleaning process, plasma generation begins first. Under low pressure, oxygen is ionized to form plasma, generating oxygen ions and high-energy electrons as the main reactants. This is followed by physical and chemical reactions. Oxygen ions physically bombard the cavity, reacting with metal ion contaminants on the cavity surface via sputtering. This sputtering causes the metal ions to desorb from the cavity surface. Simultaneously, high-energy electron recombination occurs, with high-energy electrons neutralizing the metal ions. The neutralized metal atoms are more easily removed from the cavity by vacuum extraction. Dynamic process parameters are controlled during the cleaning process, allowing for dynamic pressure adjustment. In the relatively high-pressure phase, the oxygen ion concentration and chemical reaction rate are increased; in the relatively low-pressure phase, the electron free path is increased, enhancing the proportion of high-energy electrons. The pressure switching cycle is 4-6 seconds. Magnetic field assistance can also be used. If the cavity is equipped with a magnetic field device, magnetic field-assisted cleaning is activated, using an axial magnetic field of 20-50 mT to guide the movement of metal ions and improve the recombination efficiency between metal ions and electrons. Real-time monitoring using optical emission spectroscopy is also employed during the cleaning process. During the final cleaning stage, the cleaning endpoint is determined based on OES monitoring data. When the intensity of the metal ion characteristic peak continuously decreases to the set threshold and remains stable within 3 consecutive monitoring cycles, the cleaning process ends. At this point, cleaning is stopped, the RF power supply is turned off to stop plasma excitation, the oxygen flow control system is turned off to stop gas supply, and the vacuum pump is turned off to restore the chamber pressure to atmospheric pressure or a pressure level suitable for subsequent processes.

[0117] In this embodiment, the cleaning process begins with chamber preparation, where a chamber temperature control system is set up to stabilize the chamber temperature at 80°C. An initial pressure of 300 mTorr is adjusted using a vacuum pump, and high-purity oxygen is continuously introduced at a flow rate of 850 sccm. Dynamic pressure regulation is then implemented, periodically switching between 300 mTorr and 50 mTorr during the cleaning process: the high-pressure phase is 300 mTorr for 2 seconds, increasing the oxygen ion concentration and enhancing the physical bombardment efficiency with contaminants; the low-pressure phase is 50 mTorr for 2 seconds, extending the electron free path, increasing the proportion of high-energy electrons, and enhancing the reduction efficiency of contaminants.

[0118] In this embodiment, dynamic pressure combined with a temperature control system makes the cleaning process more efficient. Oxygen ions and high-energy electrons interact alternately with metal ion contaminants, and the generated neutral metal atoms are discharged through a vacuum pump. The characteristic peak intensity of iron (Fe, 259.9 nm) is detected by optical emission spectroscopy, and cleaning ends when the peak intensity shows no significant change for three consecutive pressure cycles.

[0119] In summary, the dynamic pressure regulation combined with the temperature control system in this solution significantly improves cleaning efficiency, achieving a removal rate of over 99% for complex metal ion contaminants.

[0120] 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. An oxygen plasma cleaning method for in-situ removal of ionic contaminants from a cavity, characterized in that, The method steps include: S1. Control the pressure inside the chamber to below 300 mTorr and introduce oxygen into the chamber; S2. Apply radio frequency to the cavity to ionize oxygen into oxygen ions and high-energy electrons; S3. Oxygen ions and metal ions undergo physical sputtering, causing the metal ions to desorb from the cavity surface. At the same time, high-energy electrons neutralize the metal ions. S4. Use optical emission spectroscopy to monitor the characteristic peaks of metal ions in the cavity in real time, and use feedback adjustment until the characteristic peaks of metal ions meet the preset conditions, and the cleaning is completed.

2. The oxygen plasma cleaning method for in-situ removal of ionic contaminants from a cavity according to claim 1, characterized in that, The control chamber pressure in S1 is kept below 300 mTorr, specifically including a first pressure control scheme and a second pressure control scheme. The first pressure control scheme is to maintain the chamber pressure at a preset pressure value, which is less than 300 mTorr. The second pressure control scheme is to select two preset pressure values ​​a and b, such that a < b ≤ 300, and control the chamber pressure value to periodically switch between the two pressure values ​​a and b.

3. The oxygen plasma cleaning method for in-situ removal of ionic contaminants from a cavity according to claim 1, characterized in that, The oxygen in S1 is high-purity oxygen. The oxygen is introduced through a multi-point inlet method, and the oxygen flow rate ranges from 500 to 2000 sccm. At the same time as the oxygen is introduced, 10% to 20% helium or nitrogen is introduced as an auxiliary gas.

4. The oxygen plasma cleaning method for in-situ removal of ionic contaminants from a cavity according to claim 1, characterized in that, The power range of the radio frequency in S2 is 100-200W, its frequency is 13.56 or 27.12MHz, and its duty cycle is 0.

5.

5. The oxygen plasma cleaning method for in-situ removal of ionic contaminants from a cavity according to claim 1, characterized in that, The specific formula for the physical sputtering and charge neutralization of oxygen ions and metal ions in the cavity of S3 is as follows: Among them, M + It is a metal ion; O is an oxygen ion; M is a metal atom; O2 is oxygen gas. The specific formula for the neutralization reaction between high-energy electrons and metal ions in the cavity of S3 is as follows: M + +e - →M Among them, M + It is a metal ion; e - is a high-energy electron; M is a metal atom.

6. The oxygen plasma cleaning method for in-situ removal of ionic contaminants from a cavity according to claim 1, characterized in that, The preset condition in S4 is: the characteristic peak intensity drops to the background value or decreases to a preset percentage below the initial value, and remains stable within three consecutive preset detection cycles.

7. An oxygen plasma cleaning system for in-situ removal of ionic contaminants from a cavity, characterized in that, The system operates using an oxygen plasma cleaning method for in-situ removal of ionic contaminants from a cavity as described in any one of claims 1-6. The system includes a cavity, a pressure control module, a gas injection module, a radio frequency module, and a monitoring module. The inner wall of the cavity is coated with a ceramic coating, and the ceramic coating material is selected from alumina or titanium oxide, with a coating thickness of 5-30μm. The pressure control module is used to control the pressure inside the cavity to be below 300 mTorr; The gas injection module is used to control the introduction of oxygen into the cavity; The radio frequency module is used to apply radio frequency to the cavity, causing oxygen to ionize into oxygen ions and high-energy electrons; the oxygen ions undergo physical sputtering and charge neutralization with the metal ions, converting the metal ions into metal atoms, so that the metal ions desorb from the cavity surface; the high-energy electrons undergo a neutralization reaction with the metal ions to accelerate the desorption process of the metal ions. The monitoring module uses optical emission spectroscopy to monitor the characteristic peaks of metal ions in the cavity in real time.

8. The oxygen plasma cleaning system for in-situ removal of ionic contaminants from a cavity according to claim 7, characterized in that, The system also includes a temperature control module for controlling the cavity temperature between 50-200°C during the cleaning process.

9. The oxygen plasma cleaning system for in-situ removal of ionic contaminants from a cavity according to claim 7, characterized in that, The system also includes a magnetic field generation module, which generates a magnetic field within the cavity. The magnitude of the generated magnetic field is 20-50 mT, and its direction is axial, which is used to guide the movement of metal ions.

10. An oxygen plasma cleaning system for in-situ removal of ionic contaminants from a cavity according to claim 7, characterized in that, The system also includes a feedback control module, which dynamically adjusts the radio frequency power, gas flow rate, and cleaning time based on the characteristic peaks of metal ions in the cavity.

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