Oxygen plasma cleaning method and system for removing ion pollutants in cavity in situ

Abstract

The invention relates to an oxygen plasma cleaning method and system for removing ion pollutants in a cavity in situ. The method comprises the following steps: firstly, controlling the pressure in the cavity below 300mTorr, and introducing oxygen into the cavity; radio frequency is applied to the cavity, so that oxygen is ionized into oxygen ions and high-energy electrons; the oxygen ions and the metal ions are subjected to physical sputtering, so that the metal ions are desorbed from the surface of the cavity, and meanwhile, the high-energy electrons and the metal ions are subjected to neutralization reaction; and finally, metal ion characteristic peaks in the cavity are monitored in real time through the optical emission spectrum, a feedback adjustment mode is adopted till the metal ion characteristic peaks meet preset conditions, and cleaning is completed. Compared with the prior art, the device has the advantages of being good in cleaning effect, high in efficiency, environmentally friendly, stable and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor manufacturing, and particularly to an oxygen plasma cleaning method and system for in-situ removal of ionic contaminants in a chamber. Background Art

[0002] In the process of semiconductor manufacturing, the cleaning process is an important link among key processes, used to remove particles, organic substances, metal ionic contaminants, and natural oxide layers on the wafer surface. The effect of the cleaning process directly affects the performance, reliability, and yield of the device. Currently, the cleaning process is mainly divided into wet cleaning and dry cleaning. Wet cleaning mainly uses chemical solvents or deionized water (DIW) to clean the wafer. Common methods include the immersion method and the spraying method. This method has the advantages of a mature process, but also has some significant disadvantages: The cleaning liquids used in wet cleaning, such as hydrofluoric acid (HF), standard cleaning solution 1 (SC1), standard cleaning solution 2 (SC2), etc., may cause corrosion or damage to the 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, with high treatment costs and a great impact on the environment. For the metal ionic contaminants on the inner wall of the chamber, the effect of wet cleaning is limited, and usually, the chamber needs to be disassembled for treatment, with complex operations and affecting the equipment use efficiency.

[0003] Dry cleaning directly acts on the contaminants through plasma or gas to achieve surface cleaning. Compared with wet cleaning, dry cleaning has a better effect on removing fine particles, organic substances, nitrides, and oxides, but the existing dry cleaning processes mainly focus on removing organic substances or natural oxide layers, and have insufficient ability to remove metal ionic contaminants. Due to the limitations of the existing technologies, currently, for the metal ionic contaminants in the chamber, wet cleaning is still mainly relied on. However, wet cleaning faces the following challenges when dealing with metal ions: First, certain metal ions, such as iron ions (Fe+), copper ions (Cu+), are prone to form oxides that are difficult to remove in the wet cleaning liquid and further adhere to the surface. Second, the chamber structure is complex, and the coverage of the inner wall by wet cleaning is limited, resulting in low cleaning efficiency. Third, new impurities may be introduced during the cleaning process, especially in the case of high cleanliness requirements in advanced nodes, and the applicability of wet cleaning is further limited.

[0004] Take the ashing process common in semiconductor processes. Metal ion contamination in the cavity will affect the ashing rate and even the device performance. Specifically, it includes that the growth and removal of the metal thin layer will inevitably form metal ion residues in the cavity. For some cavities with lifting ejector pins at the base, with the process steps of the lifting ejector pins, metal ions may re-enter the cavity, changing the discharge characteristics and affecting the stability and energy distribution of the plasma. In addition, in the plasma environment, high-energy ions impact the quartz surface, sputtering metal ions into the quartz, changing the conductivity and electric field distribution of the plasma, thereby affecting the uniformity and density of the plasma. Metal ions have a high electronegativity and form stable complexes with electron-rich groups of the photoresist, such as carboxylate (COO-) and hydroxyl (OH-). Some photoresist formulations may contain complexing agents specifically used to control the concentration of metal ions and prevent metal ions from interfering with the performance of the photoresist. Since the photoresists used by different foundries may vary, the effects of ions are different.

[0005] Although dry cleaning has certain potential in cavity cleaning, existing technologies mostly focus on the chemical reactions of oxygen radicals, concentrating on the chemical reactions of high-pressure oxygen radicals, and the effect on the removal of metal ions is limited. Therefore, there is an urgent need for a new method that is efficient, environmentally friendly, and controllable, which can utilize the unique characteristics of the plasma to efficiently remove metal ion pollutants in the cavity. Summary of the Invention

[0006] The purpose of the present invention is to overcome the defects of the above-mentioned existing technologies and provide an oxygen plasma cleaning method and system for in-situ removal of ion pollutants in the cavity.

[0007] The purpose of the present invention can be achieved through the following technical solutions:

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

[0009] S1. Control the pressure in the cavity below 300 mTorr and introduce oxygen into the cavity;

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

[0011] S3. The oxygen ions undergo physical sputtering with the metal ions, causing the metal ions to desorb from the cavity surface. At the same time, the high-energy electrons undergo a neutralization reaction with the metal ions; S4. Use optical emission spectroscopy to monitor the characteristic peaks of metal ions in the cavity in real time, and adopt a feedback regulation method until the characteristic peaks of metal ions meet the preset conditions, and the cleaning is completed.

[0012] As a preferred technical solution, the pressure in the control cavity in S1 is below 300 mTorr, specifically including a first pressure control scheme and a second pressure control scheme. Among them, the first pressure control scheme is to keep the pressure in the control cavity 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 in the control cavity to switch periodically between a and b.

[0013] As a preferred technical solution, the oxygen in S1 is high-purity oxygen, and the oxygen is introduced by a multi-point gas inlet method, and the oxygen inlet flow rate range is 500 - 2000 sccm.

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

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

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

[0017]

[0018] Among them, M + is a metal ion; is an oxygen ion; M is a metal atom; O 2 is oxygen;

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

[0020] M + + e - → M

[0021] Among them, M + 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 that when the characteristic peak intensity reaches the background value or drops to a preset percentage lower than the initial value, and 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 removing ion contaminants in a cavity is provided. This system operates by applying an oxygen plasma cleaning method for in-situ removing ion contaminants in a cavity as described above. This system includes a cavity, a pressure control module, a gas injection module, a radio frequency module, and a monitoring module;

[0024] Among them, the inner wall of the cavity is coated with a ceramic coating. The ceramic coating material is selected from alumina or titanium oxide, and the coating thickness is 5 - 30 μm; the pressure control module is used to control the pressure in the cavity below 300 mTorr; the gas injection module is used to control the injection of oxygen into the cavity; the radio frequency module is used to apply radio frequency to the cavity to ionize oxygen into oxygen ions and high-energy electrons; the oxygen ions undergo physical sputtering with metal ions, causing the metal ions to desorb from the cavity surface, and at the same time, the high-energy electrons undergo a neutralization reaction with the metal ions; the monitoring module uses optical emission spectroscopy to monitor the characteristic peaks of metal ions in the cavity in real time.

[0025] As a preferred technical solution, the system further includes a temperature control module for controlling the temperature of the cavity at 50 - 200 °C during the cleaning process.

[0026] As a preferred technical solution, the system further includes a magnetic field generation module for generating a magnetic field in the cavity. The magnitude of the generated magnetic field is 20 - 50 mT, and the direction is axial, for guiding the movement of metal ions.

[0027] As a preferred technical solution, the system further includes a feedback control module, which dynamically adjusts the radio frequency power, gas flow rate, and cleaning time according to 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 the present invention, by controlling the pressure in the cavity below 300 mTorr, injecting oxygen into the cavity; then applying radio frequency to the cavity to ionize oxygen into oxygen ions and high-energy electrons; the oxygen ions undergo physical sputtering with metal ions, causing the metal ions to desorb from the cavity surface, and at the same time, the high-energy electrons undergo a neutralization reaction with the metal ions; finally, using optical emission spectroscopy to monitor the characteristic peaks of metal ions in the cavity in real time, and adopting a feedback adjustment method until the characteristic peaks of metal ions meet the preset conditions, the cleaning is completed. This enables it to have high cleaning ability, perform high-efficiency physical sputtering and charge neutralization reactions on metal ion contaminants, and significantly improve the cleaning efficiency.

[0030] 2. In the present invention, high-purity oxygen is used as the working gas, and while injecting oxygen, 10% - 20% helium or nitrogen is injected as the auxiliary gas. Without the use of chemical solvents, it avoids the problems of chemical solvents and waste liquid treatment in wet cleaning, reduces environmental pollution and cleaning costs.

[0031] 3. In the present invention, physical sputtering and charge neutralization occur between oxygen ions and metal ions, and a neutralization reaction occurs between high-energy electrons and metal ions. By generating a high concentration of oxygen ions (O2+) and high-energy electrons (e-), efficient physical sputtering and charge neutralization reactions are carried out on metal ion pollutants, significantly improving the cleaning efficiency. Moreover, the oxygen is introduced in a multi-point intake manner to ensure uniform distribution of oxygen in the cavity, optimize the plasma excitation region, and improve the cleaning effect. This enables the complete removal of pollutants in the cavity, reduces the risk of secondary pollution, eliminates the need for additional cleaning steps, and improves the cleaning quality.

[0032] 4. In the present invention, the characteristic peak of metal ions in the cavity is monitored in real time by using optical emission spectroscopy. When the characteristic peak of metal ions meets the preset conditions, the cleaning is completed. The preset conditions are that the peak intensity reaches the background value or drops to a preset percentage lower than the initial value. The preset percentage is set according to the specific requirements of the actual 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 judge the cleaning end point, the cleaning operation can be simplified and visualized, avoiding over-cleaning or under-cleaning.

[0033] 7. In the present invention, by controlling the pressure in the cavity below 300 mTorr, specifically including a first pressure control scheme and a second pressure control scheme. Among them, the first pressure control scheme is to control the pressure in the cavity to maintain 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 in the cavity to periodically switch between a and b. By dynamically adjusting the pressure, that is, periodically switching the pressure, the oxygen ion bombardment and electron recombination effects are optimized at different stages, further enhancing the cleaning effect.

[0034] 8. The power range of the radio frequency used in the present invention is 100 - 200 W, its frequency is 13.56 or 27.12 MHz, and its duty cycle is 0.53, which has strong applicability. By adjusting the radio frequency power, frequency (13.56 or 27.12 MHz), gas flow rate, and cavity pressure, it can adapt to different equipment and process requirements. By controlling the duty cycle of the radio frequency power supply, while maintaining the cleaning effect, the secondary sputtering of high-energy particles on the cavity wall is reduced, protecting the internal structure of the equipment.

[0035] 9. In the in-situ oxygen plasma cleaning system for removing ion pollutants in the cavity of the present invention, it further includes a temperature control module for controlling the cavity temperature at 50 - 200 °C during the cleaning process. By precisely controlling the cavity temperature, the chemical reaction activity of oxygen ions is further improved, and the stability of the cleaning process can also be ensured, preventing the condensation or re-deposition of pollutants on the wall, and extending the service life of the equipment.

[0036] 10. In the oxygen plasma cleaning system for in-situ removing ionic contaminants in the cavity of the present invention, a magnetic field generation module is further included, 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, for guiding 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. In the oxygen plasma cleaning system for in-situ removing ionic contaminants in the cavity of the present invention, a feedback control module is further included. The feedback control module dynamically adjusts the radio frequency power, gas flow rate, and cleaning time according to the characteristic peak of metal ions in the cavity. By dynamically optimizing the cleaning parameters such as gas flow rate, radio frequency power, and cavity pressure based on the monitored data, the stability and repeatability of the cleaning process can be ensured. Description of the Drawings

[0038] Figure 1 It is a schematic diagram of the steps of an oxygen plasma cleaning method for in-situ removing ionic contaminants in the cavity of the present invention;

[0039] Figure 2 It is a schematic diagram of three common components of oxygen plasma and the functions of each component in the embodiment;

[0040] Figure 3 It is a schematic diagram of the recombination process after the interaction between contaminant metal ions and high-energy electrons in the embodiment;

[0041] Figure 4a It is a comparison of oxygen ions and oxygen free radicals at a pressure of 300 mTorr in the embodiment;

[0042] Figure 4b It is a comparison of oxygen ions and oxygen free radicals at a pressure of 3000 mTorr in the embodiment;

[0043] Figure 5 It is a process flow chart of the oxygen plasma for in-situ removing ionic contaminants in the cavity in the embodiment. Detailed Embodiments

[0044] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art without making creative efforts based on the embodiments of the present invention shall fall within the protection scope of the present invention.

[0045] In the semiconductor manufacturing process, the cleaning process is an important link among key processes, which is used to remove particles, organic substances, metal ion contaminants and native oxide layers on the wafer surface. The effect of the cleaning process directly affects the performance, reliability and yield of the device. At present, the cleaning process is mainly divided into wet cleaning and dry cleaning. Wet cleaning mainly uses chemical solvents or deionized water (DIW) to clean the wafer. Common methods include the immersion method and the spraying method. This method has the advantages of a mature process, but there are also some significant disadvantages: The cleaning liquids used in wet cleaning (such as HF hydrofluoric acid, SC1, SC2, etc.) may cause corrosion or damage to the device materials, especially when removing certain sensitive metals (such as Al, Cu, Fe, etc.). Wet cleaning generates a large amount of waste liquid, with high treatment costs and a great impact on the environment. For metal ion contaminants on the inner wall of the cavity, the effect of wet cleaning is limited, and usually the cavity needs to be disassembled for treatment, which is complex in operation and affects the equipment use efficiency.

[0046] Dry cleaning directly acts on the contaminants through plasma or gas to achieve surface cleaning. Compared with wet cleaning, dry cleaning has a better effect on removing fine particles, organic substances, nitrides and oxides, but the existing dry cleaning processes mainly focus on removing organic substances or native oxide layers, and the ability to remove metal ion contaminants is insufficient. Due to the limitations of the existing technologies, currently, for metal ion contaminants in the cavity, wet cleaning is still mainly relied on. However, wet cleaning faces the following challenges when dealing with metal ions: Some metal ions (such as Fe+, Cu+) are prone to form oxides that are difficult to remove in the wet cleaning liquid and further adhere to the surface. The cavity structure is complex, and the coverage of the inner wall by wet cleaning is limited, resulting in low cleaning efficiency. New impurities may be introduced during the cleaning process, especially in the case of high cleanliness requirements at advanced nodes, and the applicability of wet cleaning is further limited.

[0047] Take the ashing process common in semiconductor manufacturing as an example. Metal ion contamination in the chamber can affect the ashing rate and even the device performance. Specifically, the growth and removal of metal thin films will inevitably result in metal ion residues in the chamber. For some chambers with lifting ejectors at the base, during the process of the ejector rising, metal ions may re-enter the chamber, changing the discharge characteristics and affecting the stability and energy distribution of the plasma. In addition, in a plasma environment, high-energy ions impact the quartz surface, sputtering metal ions into the quartz, changing the plasma conductivity and electric field distribution, and thus affecting the plasma uniformity and density. Metal ions have a high electronegativity and form stable complexes with electron-rich groups in the photoresist, such as carboxylate (COO-) and hydroxyl (OH-). Some photoresist formulations may contain complexing agents specifically used to control the concentration of metal ions and prevent metal ions from interfering with the photoresist performance. Since the photoresists used in different factories may vary, the impact of ions is also different.

[0048] Although dry cleaning has certain potential in chamber cleaning, existing technologies mainly focus on the chemical reactions of oxygen radicals, concentrating on the chemical reactions of high-pressure oxygen radicals, and the effect on the removal of metal ions is limited. Therefore, there is an urgent need for a new method that is efficient, environmentally friendly, and controllable, which can utilize the unique characteristics of plasma to efficiently remove metal ion contaminants in the chamber.

[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 can efficiently remove metal ion contaminants attached to the inner wall of the chamber, overcoming the deficiencies in the prior art. Through innovative process optimization, equipment design, and automation control, it solves the problem of cleaning metal ion contaminants in the semiconductor manufacturing process, and has core advantages such as high efficiency, environmental friendliness, and a wide range of applications, providing a brand-new solution for the maintenance of semiconductor equipment at advanced nodes. The specific implementation process of this application is shown in the following Examples 1-3.

[0050] Example 1

[0051] In this example, a stripping machine with a plasma chamber is used as the equipment to be cleaned, and the cleaning target is metal ion contaminants (such as Cu+ and Fe+) remaining during the ashing process.

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

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

[0054] S2. Introduce oxygen into the chamber with a gas flow rate of 500 - 2000 sccm;

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

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

[0057] In this embodiment, a schematic of the three common components of oxygen plasma and the functions of each component is as Figure 2 shown. The plasma source includes DC, RF, and microwave. Among them, the three components are ions, radicals, and electrons. The ions are used for sputtering, the radicals are used for etching, and the electrons are used for heating. During normal operation, taking the de - gluing process as an example, the density of 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 metal ions through charge neutralization, reducing their charge state, thereby promoting their desorption. A diagram of the recombination process after the interaction between contaminant metal ions and high - energy electrons is as Figure 3 shown. Taking an inductively coupled plasma (ICP) plasma chamber as an example, there are two recombination processes in the chamber. Mode 1 is the recombination of contaminant ions and electrons in the surface or intermediate region. Mode 2 is that contaminant ions with a certain depth within the wall can first be sputtered out by oxygen ions and then recombine with electrons to form metal atoms or molecules, which are finally pumped out of the chamber. Under low - pressure conditions, the generation of oxygen radicals is inhibited, and oxygen ions and high - energy electrons dominate, improving the removal efficiency of metal ions. During the cleaning process, the chamber temperature is controlled at 50 - 200 °C to further improve the chemical reactivity of oxygen ions.

[0059] Control the pressure in the chamber within the range of 300 mTorr. In a low - pressure environment, the mean free path of electrons becomes longer and their kinetic energy increases. Oxygen mainly forms oxygen ions (O 2 + ) and high - energy electrons in the plasma, while the generation of oxygen radicals (O) is less. This enables oxygen ions (O 2 +) and the concentration of high-energy electrons is relatively high, while the concentration of oxygen free radicals (O) is relatively low. The average free path of high-energy electrons increases, and their energy is higher, enabling them to effectively collide with metal ions, resulting in their reduction and desorption.

[0060] In this embodiment, a comparison of oxygen ions and oxygen free radicals in a low-pressure environment and a high-pressure environment is carried out, and the comparison is as Figure 4a , Figure 4b shown, where Figure 4a is the comparison of oxygen ions and oxygen free radicals when the pressure is 300 mTorr; where 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 °C; Figure 4b is the comparison of oxygen ions and oxygen free radicals when the pressure is 3000 mTorr, the pressure is 3000 mTorr, the oxygen flow rate is 10000 sccm, the radio frequency power is 500 W, the frequency is 27.12 MHz, and the temperature is 150 °C. Through the comparison diagram, it can be seen that under lower pressure conditions, the peak intensity of oxygen ions (≈ electrons) is higher than that of oxygen free radicals.

[0061] In this solution, oxygen plasma is generated. In equipment with a plasma chamber, such as an etcher, a degumming machine, etc., first, in the equipment control system, a "low-pressure oxygen plasma cleaning mode" is preset, and then parameters such as radio frequency power, gas flow rate, and pressure are automatically adjusted according to actual needs; in equipment without a plasma chamber, such as a coating equipment, a detection equipment, etc., a remote plasma scheme is used, that is, a remote plasma generator is connected outside the equipment to generate low-pressure oxygen plasma, which is transported into the chamber through a pipeline. Oxygen ions (O2+) impact the surface of the chamber, generating a physical sputtering effect, causing metal ions to be stripped from the surface of the chamber. High-energy electrons combine with metal ions, reducing the charge of metal ions and converting them into neutral metal atoms, which are easily discharged by the vacuum pump. In oxygen plasma, the composition of the plasma and the concentration distribution of species depend on plasma parameters such as pressure, electron temperature, and collision frequency.

[0062] Under low-pressure conditions, oxygen plasma is more likely to generate 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 average free path of electrons, that is, the average distance between particle collisions, increases. This means that electrons can obtain higher kinetic energy before colliding with oxygen molecules. Due to the high kinetic energy of electrons, oxygen molecules are more likely to be ionized rather than dissociated 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, due to the reduced collision frequency, the probability of inelastic collisions between electrons and oxygen molecules decreases. However, when the electron energy is high enough, collisions are more likely to trigger ionization reactions because the ionization cross-section (reaction probability) gradually increases under high-energy conditions. In a low-pressure plasma, the energy distribution of electrons follows a Maxwell distribution or an approximate non-equilibrium distribution, with a relatively high proportion of high-energy electrons. This part of the high-energy electrons has an energy 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", that is, the high-energy tail is not easily reduced and may even become more prominent. Therefore, under low pressure, due to fewer collisions and high electron kinetic energy, oxygen molecules preferentially undergo ionization reactions to form oxygen ions rather than simply dissociating into oxygen radicals.

[0064] After turning metal ions into neutral particles, it is easier to remove them from the chamber by means such as gas flow, and further analyze the magnitude of the adhesion force between metal atoms / ions and the chamber material. In the chamber of a semiconductor device, the adhesion forces between metal atoms and metal ions and the chamber material (such as quartz, aluminum, and stainless steel) can be significantly different. The adhesion force between metal atoms and the chamber material includes the effects of physical adsorption, chemical adsorption, and the surface state of the material. Among them, physical adsorption is that metal atoms are adsorbed on the surface of the chamber material through van der Waals forces or weak electromagnetic forces, and this adsorption is usually weak and reversible. Chemical adsorption is that some metal atoms can react with the chamber material to form covalent bonds or ionic bonds. This adhesion force is strong and difficult to reverse. For example, aluminum reacts with oxygen to form an aluminum oxide layer. The surface state of the material is that the surface state of the chamber material (such as surface roughness and cleanliness) affects the adsorption strength of metal atoms. A clean and smooth surface usually has a weak adsorption force, while a rough or contaminated surface has a strong adsorption force. The adhesion force between metal ions and the chamber material includes the effects of electrostatic adsorption, chemical adsorption, and interfacial potential; among them, electrostatic adsorption is that metal ions are charged and can undergo electrostatic attraction with regions on the surface of the chamber material with opposite charges. This adsorption force is strong and has a clear direction. Chemical adsorption is similar to that of metal atoms, and metal ions may also react with the chamber material to form strong chemical bonds. This adsorption is usually stronger because the ionic state is more reactive and easily forms chemical bonds with the material surface. Interfacial potential is that ions form a double-layer structure on the surface of the chamber material, resulting in a strong adsorption effect.

[0065] Among them, physical adsorption (Van der Waals forces) is usually described as the weak interaction between metal atoms and the surface of the chamber material. The formula is usually relatively simple, such as the Lennard-Jones potential function:

[0066]

[0067] Among them, U(r) is the potential energy, ∈ is the depth of the potential well, σ is the distance of the zero-potential point, and r is the interatomic distance.

[0068] Chemical adsorption involves the formation of chemical bonds and is usually more complex. The electron exchange or sharing between metal atoms and surface atoms needs to be considered. For example, the process of covalent bond or ionic bond formation between atoms and the surface. However, for a quartz cavity, if some metal ions have reacted with the cavity wall to form compounds, these metal ions can be regarded as having been consumed and will not stay inside the cavity and affect the subsequent process. Therefore, chemical adsorption can be temporarily ignored in the overall adsorption process. For charged metal ions, the electrostatic adsorption force can be described by Coulomb's law:

[0069]

[0070] Among them, F is the electrostatic force, ∈ 0 is the vacuum permittivity, q 1 and q 2 are the charges, and r is the distance between the charges.

[0071] Then, taking Cu as an example, the comparison between atomic physical adsorption and ionic electrostatic adsorption can be roughly and intuitively compared through the following calculations:

[0072] First, calculate the adsorption energy of Cu atoms, that is, the physical adsorption energy (Lennard-Jones potential function). Set reasonable parameters to calculate the adsorption energy of Cu atoms and obtain the potential well depth ∈ = 0.2 eV and the distance of the zero-potential point σ = 2.5 Å. 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) = -0.117 eV

[0075] Then calculate the adsorption energy of Cu + ions, that is, the electrostatic adsorption energy. For charged Cu + ions, use Coulomb's law to calculate the electrostatic adsorption energy. The interaction energy of the charges is negative because the attraction reduces the energy of the system.

[0076] Set the charge q1 = +1e, the surface charge q2 = -1e, and the distance r = 3 Å.

[0077]

[0078] Convert it to electron volts:

[0079] 1 J = 6.242×1018 eVE elec = -7.68×10 -20 J×6.242×10 18 eV / J ≈ -0.48 eV

[0080] Comparing the total adsorption energies, the physical adsorption energy of Cu atoms is relatively small, about -0.117 eV, and that of Cu + ions is relatively large, about -0.48 eV. The electrostatic adsorption energy of Cu 2+ ions is even larger, about -0.96 eV. Therefore, generating a large number of electrons using low-pressure and low-power oxygen plasma and then neutralizing metal ions to make them into neutral metal atoms can indeed help reduce the adsorption energy of these metal pollutants on the cavity surface, making it easier to remove them from the chamber by means such as gas flow.

[0081] In this solution, the specific process includes: introducing high-purity oxygen into the cavity, with a flow rate range of 500 - 2000 sccm. Applying radio frequency power (for example, a power of 500 - 1000 W and a frequency of 13.56 or 27.12 MHz) to ionize oxygen to form 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, converting metal ions into neutral metal atoms, which desorb from the cavity surface and are pumped away by the vacuum pump:

[0083] M + + e - → M

[0084] where M + is a metal ion; e - is a high-energy electron; M is a metal atom, such as Cu, Fe, Ni, etc.

[0085] High-energy electrons have sufficient kinetic energy under low-pressure conditions, can effectively hit metal ions, accelerate their desorption, and cooperate with oxygen ions to enhance the cleaning effect. In this solution, optical emission spectroscopy (OES) is also used to monitor the spectral characteristics of oxygen ions (O2+) and metal ions (such as Fe+: 259.9 nm, Cu+: 324.8 nm) to judge the removal process of metal ions and dynamically optimize process parameters such as gas flow rate, radio frequency power, and cleaning time.

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

[0087] In this embodiment, first, the chamber is prepared, that is, the vacuum pump is started, the chamber pressure in the degumming machine is adjusted to 150 mTorr, and high-purity oxygen is continuously introduced at a flow rate of 850 sccm.

[0088] Then, plasma excitation is carried out. The RF power supply is started, the power is set at 120 W, the frequency is set at 13.56 MHz, and the duty cycle is adjusted to 50% through the control system, that is, the RF power supply works continuously for 5 ms in each 10-ms cycle and is turned off for the rest of the time.

[0089] In this embodiment, under the duty cycle control, the generation process of the plasma is periodically interrupted, so that the oxygen ion concentration remains stable, and at the same time, the secondary sputtering of high-energy particles (such as high-energy electrons and oxygen ions) on the chamber wall is reduced. The following reactions occur between oxygen ions and metal ions:

[0090]

[0091] where M + is a metal ion; is an oxygen ion; M is a metal atom; O 2 is oxygen.

[0092] The desorbed metal atoms are discharged through the vacuum pump.

[0093] In this embodiment, monitoring and endpoint judgment are carried out. The characteristic peak intensity of Cu (324.8 nm) is monitored in real time through optical emission spectroscopy. When the characteristic peak intensity drops to the background level or drops to a preset percentage lower than 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 according to the specific needs of the actual user.

[0095] In summary, the cleaning method of this solution enables the removal rate of metal ion pollutants in the chamber to reach more than 97%, and there are no obvious sputtering marks on the chamber wall.

[0096] Embodiment 2

[0097] In this solution, automated control is applied for low-pressure plasma cleaning, which is applicable to various devices with or without plasma chambers, including etching machines, resist strippers, spin coaters, and high-temperature reaction chambers, etc. The control process is as follows: First, start the cleaning program, set the target pressure below 300 mTorr, and set the RF power and gas flow rate; then, use an optical emission spectroscopy detection device to monitor the characteristic spectra of oxygen ions and metal ions in real time; next, according to the spectral analysis results, automatically adjust the cleaning parameters through a feedback control module; when the intensity of the characteristic spectrum reaches the set value of the cleaning end point, automatically terminate the cleaning program.

[0098] In this solution, by optimizing the distribution of the RF electric field, the interaction efficiency between electrons and metal ions is enhanced, and the desorption rate of metal ions is increased. By adjusting the duty cycle of the RF power supply, while maintaining the oxygen ion concentration, the secondary sputtering of high-energy particles on the chamber wall is reduced. By adjusting the frequency and power of the RF electric field in the chamber, the sheath thickness is controlled, and the bombardment efficiency of oxygen ions on the surface of pollutants is optimized. The frequency of the RF electric field can be dynamically switched between 13.56 MHz and 27.12 MHz to adapt to different types of metal ion pollutants; by periodically changing the chamber pressure, oxygen ion bombardment and pollutant removal are alternately carried out under different pressure conditions to further optimize the cleaning efficiency. The periodic change range of the chamber pressure is 50 - 300 mTorr, and the time of each cycle is controlled within 1 - 5 seconds to enhance the dynamic cleaning effect. Finally, based on the optical emission spectroscopy, the characteristic peaks of oxygen ions and metal ions are monitored in real time, and the gas flow rate, RF power, and chamber pressure are automatically adjusted through a feedback control system to achieve the optimal cleaning effect.

[0099] When the characteristic peak meets the preset conditions, stop the cleaning. Among them, the preset conditions are that the intensity of the characteristic peak reaches the background value or drops to a preset percentage lower than the initial value and remains stable within three consecutive preset detection cycles.

[0100] In this embodiment, the preset percentage sets the threshold according to the specific requirements of the actual user.

[0101] In this embodiment, the cleaning device is an etching machine with a magnetic field assist device; the cleaning object is metal ion pollutants (such as Ni+, Al+) deposited on the inner wall of the chamber during the etching process; the specific settings of the process parameters during the cleaning process include: the pressure is set to 100 mTorr; the oxygen flow rate is set to 600 sccm; the RF power is set to 150 W, and the RF frequency is set to 27.12 MHz; the magnetic field intensity is set to 20 mT; the cleaning time is set to 12 minutes.

[0102] Table 1 Comparison table of the content of metal ion pollutants in the chamber before and after cleaning

[0103]

[0104]

[0105] In this embodiment, during cleaning, first, the chamber is prepared. The initial pressure in the etching machine chamber is adjusted to 100 mTorr, and oxygen is continuously introduced at a flow rate of 600 sccm. Then, it is excited by plasma and a magnetic field is set for assistance. The radio frequency power supply is started, and the power is set to 150 W and the frequency is 27.12 MHz to excite the oxygen in the chamber to form plasma. At the same time, the magnetic field assistance device is started, and an axial magnetic field of 20 mT is applied to guide the movement of metal ions and enhance the probability of their recombination with high-energy electrons. During the cleaning process, in the plasma cleaning process assisted by the magnetic field, oxygen ions remove metal ions through physical bombardment, while high-energy electrons neutralize the charge to reduce metal ions to neutral atoms, and the reduced metal atoms are discharged through the vacuum pump. During the process, monitoring and endpoint judgment are carried out. The characteristic peak intensity of nickel Ni (341.5 nm) is monitored in real time by OES. When the peak intensity drops to less than 10% of the initial value, the cleaning is automatically stopped.

[0106] In this embodiment, as shown in Table 1, where C001 is before cleaning and C002 is after cleaning. It can be seen from the table that after cleaning for 5 minutes under this condition, the content of metal ion pollutants in the chamber decreases.

[0107] In summary, this solution can make the removal rate of metal ion pollutants reach more than 98%. The magnetic field effectively improves the recombination efficiency of metal ions and electrons, and significantly shortens the cleaning time.

[0108] Embodiment 3

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

[0110] In this solution, the inner cavity wall of the vacuum chamber is coated with a ceramic coating with low adhesion to prevent the re-deposition of residual metal ions or oxides during the cleaning process and reduce secondary contamination. The coating material is selected from alumina or titanium oxide, and the coating thickness is 5 - 30 μm to ensure the corrosion resistance and low particle adhesion of the coating. The vacuum chamber is equipped with a pressure regulating device; a remote plasma input end is provided inside the chamber for introducing the low-pressure oxygen plasma generated remotely into the chamber. The gas supply module is used to introduce oxygen and control the gas flow rate; it is equipped with a dynamic gas distribution system to ensure the uniform distribution of oxygen in the chamber through multi-point gas inlet mode and optimize the spatial uniformity of the plasma. The flow rate of each gas inlet point can be independently adjusted to optimize the oxygen distribution according to the chamber geometry. A gas mixing device is equipped in the gas supply module, which can add a small amount of argon or nitrogen as needed and control the gas flow rate to optimize the generation of the plasma. The radio frequency power module is used to generate radio frequency power to excite oxygen to form plasma; a pulse power control system is set inside the device to excite oxygen through a pulsed electric field, enhance the reaction efficiency between oxygen ions and metal ions, and reduce the damage to the chamber wall at the same time. By adjusting the frequency and power of the radio frequency electric field in the chamber, the sheath thickness is controlled to optimize the bombardment efficiency of oxygen ions on the surface of contaminants. The frequency of the radio frequency power module is 13.56 MHz or 27.12 MHz, and the adjustable range of the radio frequency power is 300 - 850 W. The vacuum pump is used to maintain the low-pressure state of the chamber and discharge contaminants. The device is also equipped with an efficient vacuum pumping system to reduce the recombination probability of metal ions and gas molecules in the chamber by optimizing the pumping rate and improve the discharge efficiency of contaminants.

[0111] In this solution, for the equipment without a plasma chamber, a cleaning module suitable for it is equipped. This module includes a remote plasma generator, a gas delivery pipeline, and a control system; among them, the remote plasma generator is used to generate low-pressure oxygen plasma; the gas delivery pipeline is used to deliver the plasma to the cleaning area of the target equipment; the control system is used to adjust the generation parameters of the plasma and the cleaning time. The remote plasma generator can operate independently of the main equipment and is seamlessly connected to the target equipment through an interface module.

[0112] In this solution, the equipment is also equipped with a monitoring system, which includes an optical emission spectrum, a data analysis module, and a feedback control module; among them, the optical emission spectrum detection device is used to monitor the characteristic spectra of oxygen ions and metal ions in real time; the data analysis module is used to analyze the change of the characteristic spectrum intensity to judge the progress of the cleaning process; the feedback control module is used to dynamically adjust the radio frequency power, gas flow rate, and cleaning time according to the monitoring results. The characteristic spectra of metal ions include common metal categories such as Cu(324.8 nm), Fe(259.9 nm), and Ni(341.5 nm) in the back-end of semiconductor process manufacturing. The cleaning end point is automatically judged when the characteristic spectrum intensity drops to a set threshold.

[0113] In this embodiment, the cleaning device is a reaction chamber with a temperature control system; the object to be cleaned is complex metal ion contaminants (such as Fe+ and Cu+) in the chamber; the 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 180 W, and the frequency is set to 27.12 MHz; the chamber temperature is controlled at 80 °C; each pressure cycle time is set to 4 seconds, including 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 chamber temperature in real time through a temperature sensor on the inner wall of the chamber, and controls the chamber temperature within the range of 50 - 200 °C through a heating or cooling device 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 adjust the chamber temperature and prevent the condensation or redeposition of contaminants on the chamber wall surface.

[0115] In this embodiment, the cleaning process flow applied to this device is as Figure 5 shown, and its specific process includes a cleaning preparation stage, a cleaning process stage, and a cleaning end stage;

[0116] In the cleaning preparation stage, system startup, gas introduction, and radio frequency power source excitation are carried out in sequence. During the cleaning process, plasma generation is first performed. Under low-pressure conditions, oxygen is ionized to form plasma, generating main reactants oxygen ions and high-energy electrons. Then, physical and chemical reactions occur. The physical bombardment of oxygen ions, that is, the sputtering reaction occurs between oxygen ions and metal ion contaminants on the chamber surface. The sputtering effect causes metal ions to desorb from the chamber surface. At the same time, the high-energy electron recombination effect occurs, that is, the high-energy electrons and metal ions undergo a neutralization reaction. The neutralized neutral metal atoms are more easily evacuated from the chamber by pumping. During the cleaning process, dynamic process parameter control is carried out. The pressure can be dynamically adjusted to increase the oxygen ion concentration and chemical reaction rate in the relatively high-pressure stage, and increase the electron mean free path and the proportion of high-energy electrons in the relatively low-pressure stage. The pressure switching cycle is 4 - 6 s. At the same time, magnetic field assistance can be carried out. If the chamber is equipped with a magnetic field device, magnetic field-assisted cleaning is started, and the axial magnetic field of 20 - 50 mT is used to guide the movement of metal ions to improve the recombination efficiency of metal ions and electrons. During the cleaning process, optical emission spectroscopy is also used for real-time monitoring. In the cleaning end stage, based on the OES monitoring data, the cleaning end point is judged. When the intensity of the metal ion characteristic peak continuously drops to the set threshold and remains stable within 3 consecutive monitoring cycles, the cleaning process ends. At this time, the cleaning is stopped, the radio frequency power supply is turned off to stop plasma excitation; the oxygen flow control system is turned off to stop gas supply; 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, during the cleaning process, the chamber is first prepared. The chamber temperature control system is set to stabilize the chamber temperature at 80 °C. The initial pressure is adjusted to 300 mTorr by a vacuum pump, and high-purity oxygen is continuously introduced at a flow rate of 850 sccm. Then, dynamic pressure regulation is carried out. During the cleaning process, the pressure control system is used to periodically switch between 300 mTorr and 50 mTorr: the high-pressure stage is 300 mTorr, with a duration of 2 seconds, which can increase the concentration of oxygen ions and enhance the physical bombardment efficiency with pollutants. The low-pressure stage is 50 mTorr, with a duration of 2 seconds, which can extend the electron mean free path, increase the proportion of high-energy electrons, and enhance the reduction efficiency of pollutants.

[0118] In this embodiment, the combination of dynamic pressure and the temperature control system makes the cleaning process more efficient. Oxygen ions and high-energy electrons act on metal ion pollutants alternately, and the generated neutral metal atoms are discharged through the vacuum pump. The characteristic peak intensity of iron Fe(259.9 nm) is detected by optical emission spectroscopy. When the peak intensity does not change significantly for three consecutive pressure cycles, the cleaning is completed.

[0119] In summary, the dynamic pressure regulation of this solution combined with the temperature control system significantly improves the cleaning efficiency, and the removal rate of complex metal ion pollutants reaches more than 99%.

[0120] As described above, the above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. An oxygen plasma cleaning method for in-situ removal of cavity ion contaminants, characterized in that: The method steps include: S1. Control the pressure in the chamber below 300 mTorr and introduce oxygen into the chamber; S2, applying radio frequency to the chamber to ionize oxygen into oxygen ions and high-energy electrons; S3, oxygen ions and metal ions are physically sputtered, so that the metal ions are desorbed from the cavity surface, and high-energy electrons react with the metal ions to neutralize; S4. Use optical emission spectroscopy to monitor the characteristic peak of metal ions in the cavity in real time, and use feedback adjustment until the characteristic peak of metal ions meets the preset conditions, and the cleaning is completed.

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

3. The oxygen plasma cleaning method for in-situ removal of cavity ion contaminants according to claim 1, characterized in that: The oxygen in S1 is high-purity oxygen, and the oxygen is introduced by a multi-point intake method. The oxygen flow rate range is 500-2000sccm. When the oxygen is introduced, 10%-20% helium or nitrogen is introduced as an auxiliary gas.

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

5.

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

6. The oxygen plasma cleaning method for in-situ removal of cavity ion contaminants according to claim 1, characterized in that: The preset condition in S4 is: the characteristic peak intensity reaches the background value or drops 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 cavity ion contaminants, characterized in that: The system works by applying an oxygen plasma cleaning method for in-situ removal of cavity ion contaminants as described in any one of claims 1 to 6, and the system comprises 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, the ceramic coating material is selected from aluminum oxide or titanium oxide, and the coating thickness is 5-30 μm; The pressure control module is used to control the pressure in the cavity to be below 300mTorr; 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 to ionize oxygen into oxygen ions and high-energy electrons; the oxygen ions and metal ions undergo physical sputtering and charge neutralization to convert the metal ions into metal atoms, so that the metal ions are desorbed from the cavity surface; the high-energy electrons and metal ions undergo a neutralization reaction 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 chamber ion contaminants according to claim 7, characterized in that: The system also includes a temperature control module for controlling the chamber temperature at 50-200° C. during the cleaning process.

9. The oxygen plasma cleaning system for in-situ removal of cavity ion contaminants according to claim 7, characterized in that: The system also includes a magnetic field generating 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.

10. The oxygen plasma cleaning system for in-situ removal of cavity ion contaminants 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 according to the characteristic peaks of metal ions in the cavity.

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