Method for improving stability of oxide film of remote plasma source cavity

Abstract

The invention belongs to the technical field of remote plasma sources, and provides a remote plasma source cavity oxidation film stability improving method which comprises the steps that high-temperature steam hole sealing treatment is conducted on an aluminum material subjected to surface pretreatment; cutting to remove the diaspore layer on the surface; and performing mixed gas passivation on the dissociation cavity and circulating for preset times, wherein the mixed gas passivation comprises pre-passivation, hydration passivation and synergistic passivation. Firstly, high-temperature steam hole sealing is carried out on an oxide layer, then a surface diaspore layer is cut, the number of surface active sites is increased, and OH bond adsorption is facilitated; then pre-passivation, hydration passivation and synergistic passivation are carried out, and circulation is carried out for preset times, so that the stability of OH bonds is ensured, and the service life of the RPS cavity is prolonged; a random forest algorithm is used for determining the proportion of mixed gas, and the lower limit of an RPS power operation window is reduced by influencing the OH bond coverage density on the surface of an oxide film layer, so that the deposition rate requirement of an FCVD process is met.

Description

Technical Field

[0001] The present invention relates to the technical field of remote plasma sources, and particularly to a method for improving the stability of an oxide film on a remote plasma source cavity. Background Art

[0002] In the fields of semiconductor manufacturing, thin film deposition, etc., remote plasma sources have been widely used due to their advantages of generating uniform and low-damage plasmas. As one of the core components of a remote plasma source, the surface performance of the dissociation cavity has an important impact on the generation and transmission of plasmas. Aluminum materials have become commonly used materials for dissociation cavities due to their good electrical conductivity, thermal conductivity, and processing performance. However, the surface of aluminum materials is prone to reacting with moisture, oxygen, etc. in the air, resulting in surface oxidation and corrosion, thereby affecting the service life of the cavity and the plasma treatment effect. Therefore, anodizing and passivating the surface of aluminum materials to improve their surface stability and corrosion resistance has become one of the key technologies in the manufacture of remote plasma source dissociation cavities.

[0003] In the FCVD process, too fast deposition rate will lead to insufficient density of the filler on the chip surface, resulting in poor insulation effect. Therefore, it is necessary to control the deposition rate to achieve precise control of the deposited material. The deposition rate is mainly related to the output power of the remote plasma source and the composite coefficient of the anodic oxide film material. There is a linear relationship between the set output power and the deposition rate, but the remote plasma source has a minimum ignition power to meet the energy during ignition; therefore, controlling the deposition rate by adjusting the output power has limitations; at this time, the process window of the remote plasma source is determined by the composite coefficient of the anodic oxide film material.

[0004] The water vapor passivation process is a commonly used method for treating the surface of aluminum materials. Its principle is to utilize the adsorption and dissociation of water vapor on the surface of aluminum materials to form a passivation film containing hydroxyl groups (OH bonds). The formation of OH bonds is crucial for the performance of the passivation film. It not only affects the chemical stability of the passivation film but is also closely related to the adsorption capacity of the passivation film, etc.; OH bonds can adsorb active ions, reduce ion bombardment, and improve the dissociation rate of the remote plasma source. The stability and high coverage density of the OH bond layer are of great significance for ensuring the stable operation of the remote plasma source.

[0005] Due to the traditional steam passivation process only treating with high-temperature steam, OH bonds form a monolayer on the aluminum surface. The number of OH bonds is small, and the binding force with the aluminum surface is weak. Poor stability results in a low service life. At the same time, the steam passivation process relies on the rough adjustment of parameters such as temperature, pressure, and time, and has insufficient control ability over the stability and coverage density of the formation of hydroxyl groups (OH bonds). An overly high OH bond coverage density will cause the output power of the remote plasma source to be too high under the same gas flow rate and pressure during operation, which will in turn lead to an overly high deposition rate in the flowing chemical vapor deposition (FCVD) process. Therefore, it is necessary to control the OH bond coverage density to meet the process requirements. Summary of the Invention

[0006] Aiming at the defects in the prior art, the present invention provides a method for improving the stability of the oxidation film in a remote plasma source cavity to solve the problems of poor stability of OH bonds and inability to control the coverage density of OH bonds in the cavity aluminum material of the current remote plasma source through steam passivation.

[0007] In a first aspect, a method for improving the stability of the oxidation film in a remote plasma source cavity provided by the present invention includes: S1. Subject the aluminum material after surface pretreatment to high-temperature steam sealing treatment to consume the original oxide film and generate a boehmite layer. S2. Perform machining on the product obtained in S1 to remove the boehmite layer on the surface. S3. Assemble the product obtained in S2 to form a dissociation cavity, perform mixed gas passivation and cycle a preset number of times, and then perform cooling and drying; the mixed gas passivation includes pre-passivation, hydration passivation, and synergistic passivation performed in sequence. The pre-passivation is: turn on the remote plasma source, introduce an ignition gas and oxygen to form an initial oxide layer. The hydration passivation is: turn off the remote plasma source, introduce steam, and the steam is used for hydration treatment to generate OH bonds on the surface of the initial oxide layer. The synergistic passivation is: turn on the remote plasma source, and simultaneously introduce an ignition gas, an auxiliary catalytic gas, and hydrogen. The ignition gas and the auxiliary catalytic gas are used to blow away the weakened OH bonds, and hydrogen is used to generate OH bonds with the remaining oxygen atoms.

[0008] As can be seen from the above technical solution, the present invention first forms a boehmite layer through high-temperature steam sealing treatment, and then performs machining on the boehmite layer, which can reduce the recombination coefficient and better adsorb OH bonds; then through mixed gas passivation, pre-passivation, hydration passivation, and synergistic passivation are performed in sequence, and OH bonds are formed on the surface of the initial oxide layer through a chemical adsorption mechanism. The OH bonds can prevent the recombination of free radicals dissociated from the remote plasma source during transportation, thereby improving the dissociation rate of the remote plasma source.

[0009] Optionally, the surface pretreatment includes degreasing, pickling, alkali washing, and water washing and drying operations carried out in sequence. Through the surface pretreatment, first, the grease and contaminants on the surface of the aluminum material are removed by degreasing and cleaning; then, the natural oxide layer is removed by pickling, and uniform roughness is formed by alkali washing to enhance the subsequent reaction activity.

[0010] Optionally, before the pre-passivation, it further includes: turning on the remote plasma source, introducing an ignition gas for ignition to clean the chamber wall. By cleaning the chamber wall after introducing the ignition gas for ignition, the residual contaminants are removed to activate the substrate surface.

[0011] Optionally, between the pre-passivation and the hydration passivation, it further includes: turning off the remote plasma source and maintaining the purge of the ignition gas for a preset time. This step can remove by-products, terminate the plasma reaction, and stabilize the reaction chamber environment, playing a role of transition and stabilization.

[0012] Optionally, between the hydration passivation and the synergistic passivation, it further includes: Turning off the remote plasma source, introducing the ignition gas for purging to remove the water vapor and by-products in the chamber and prevent impurity residues; Restarting the remote plasma source, increasing the flow rate of the ignition gas for surface reconstruction, and slightly bombarding the surface with plasma to optimize the film adhesion.

[0013] Optionally, after the synergistic passivation, it further includes: turning off the remote plasma source and introducing the ignition gas for final purging.

[0014] Optionally, during the hydration passivation, the temperature is 110 - 180 °C, the pressure is 20 ± 1 Torr, and the water vapor flow rate is 622 ± 50 sccm.

[0015] Optionally, during the synergistic passivation, the determination method of the flow rate ratio of the ignition gas, the auxiliary catalytic gas, and hydrogen includes: Respectively obtaining the importance degrees of the total flow rate of the ignition gas + auxiliary catalytic gas and the hydrogen flow rate for the OH bond coverage density and the FCVD deposition rate according to the random forest regression algorithm; Selecting the flow rate ratio of the ignition gas + auxiliary catalytic gas to hydrogen according to the importance degrees.

[0016] As can be seen from the above technical solutions, during the synergistic passivation, the importance degrees of the total flow rate of the ignition gas + auxiliary catalytic gas and the hydrogen flow rate for the OH bond coverage density and the FCVD deposition rate can be predicted by the random forest regression algorithm, and then the specific ratio is determined based on the importance degrees to ensure that the OH bond coverage density and the FCVD deposition rate can meet the established requirements.

[0017] Optionally, the importance degrees of the total flow rate of the ignition gas + auxiliary catalytic gas and the hydrogen flow rate for the OH bond coverage density are imp1 and imp2 respectively, and the importance degrees of the total flow rate of the ignition gas + auxiliary catalytic gas and the hydrogen flow rate for the FCVD deposition rate v are imp3 and imp4 respectively. The flow rate ratio is between imp1 / imp2 and imp3 / imp4.

[0018] Optionally, the preset number of cycles in step S3 is 100 times.

[0019] Adopting the above technical solution, the present application has the following beneficial effects: The present invention first forms a boehmite layer through high-temperature steam sealing treatment, and then performs cutting processing on the boehmite layer, which can reduce the recombination coefficient and better adsorb OH bonds; then through mixed gas passivation, pre-passivation, hydration passivation and synergistic passivation are carried out in sequence, and OH bonds are formed on the surface of the initial oxide layer through a chemisorption mechanism. The OH bonds can prevent the radicals dissociated from the remote plasma source from recombining during transportation, thereby improving the dissociation rate of the remote plasma source. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts do not necessarily draw according to the actual scale.

[0021] Figure 1 Shows a flowchart of a method for improving the stability of the oxidation film of a remote plasma source cavity provided by an embodiment of the present invention; Figure 2 Shows a comparison diagram of whether to execute step S2 provided by an embodiment of the present invention; Figure 3 Shows a cross-sectional SEM comparison diagram of the cavity after step S3 is completed with or without executing step S2 provided by an embodiment of the present invention; Figure 4 Shows a plan view SEM of the cavity after step S3 is completed without executing step S2 provided by an embodiment of the present invention; Figure 5 Shows a plan view SEM of the cavity after step S3 is completed with executing step S2 provided by an embodiment of the present invention; Figure 6 Shows a schematic diagram of the atomic structure of the cavity surface obtained by a method for improving the stability of the oxidation film of a remote plasma source cavity provided by an embodiment of the present invention; Figure 7Shows the flowchart for obtaining the importance degree according to the random forest regression algorithm provided by the embodiments of the present invention; Figure 8 Shows the flowchart for constructing a decision tree provided by the embodiments of the present invention; Figure 9 Shows the sorting diagram of the importance of argon + nitrogen flow rate and hydrogen flow rate for the OH bond coverage density and the FCVD deposition rate provided by the embodiments of the present invention. Detailed implementation manners

[0022] Hereinafter, embodiments of the technical solutions of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and thus are only examples and cannot be used to limit the protection scope of the present invention. It should be noted that unless otherwise specified, the technical terms or scientific terms used in this application should have the ordinary meanings understood by those skilled in the art to which the present invention belongs.

[0023] In one embodiment, as Figure 1 shown, a method for improving the stability of the oxide film in a remote plasma source cavity is provided, including: S1. Perform high-temperature steam sealing treatment on the aluminum material after surface pretreatment to consume the original oxide film and generate a boehmite layer.

[0024] Among them, the surface pretreatment includes degreasing, pickling, alkali washing, and water washing and drying operations performed in sequence.

[0025] Degreasing cleaning: Use a 50% concentration NaOH alkaline solution (or a special degreasing agent) to remove the grease and contaminants on the surface of the aluminum material.

[0026] Pickling + alkali washing activation: Pickling: Use a dilute sulfuric acid (H2SO4) or nitric acid (HNO3) solution with a concentration of 5-10% for 1-5 minutes to remove the natural oxide layer. Alkali washing: Use a 5-10% NaOH solution to etch the surface to form a uniform roughness and enhance the subsequent reaction activity.

[0027] Water washing and drying: Thoroughly rinse with deionized water and then dry to avoid residual impurities affecting the quality of the passivation layer.

[0028] The specific operation parameters of step S1 are as follows: Reaction device: Place the aluminum material in a high-pressure reaction kettle (such as a high-pressure steam reactor) and introduce high-purity water vapor.

[0029] Process parameters are temperature: 120-250 °C (commonly 180-200 °C, too high temperature may cause the formation of amorphous alumina).

[0030] Pressure: 1 - 5 MPa (corresponding to the temperature of saturated vapor pressure, precise control required). Time: 2 - 24 hours, adjusted according to the required film thickness (film thickness is usually 0.1 - 5 μm).

[0031] Reaction mechanism: The oxide film undergoes a hydrothermal reaction with water vapor: Boehmite layer (nanosheet or fibrous structure) is formed, which has dense corrosion resistance.

[0032] (1) Equation (1) is the hydration sealing reaction equation. The reaction occurs at a temperature above 80°C. During the reaction, the original oxide film is consumed, the pore walls become thinner, and the volume of the formed aluminum monohydrate oxide (boehmite) increases to block the pores.

[0033] S2. The product obtained in S1 is subjected to machining to remove the boehmite layer on the surface. Under the specific operating parameters of S1, S1 specifically involves machining and cutting off 2 μm of the hard anodized film to remove the top boehmite layer.

[0034] The free radicals generated by RPS can be lost in gas-phase reactions or reactions on the chamber surface. At low pressures, H free radicals are lost due to surface recombination; the higher the material recombination coefficient, the more easily H free radicals are lost due to surface recombination. The recombination coefficients of different materials vary greatly. Generally, metallic aluminum has a relatively high recombination coefficient (~10 -1 ), while the recombination coefficient of alumina is approximately (10 -2 ~10 -4 ), and that of aluminum hydroxide is relatively low (10 -5 ~10 -6 ). The surface recombination coefficient of the RPS chamber membrane material directly affects the deposition rate of FCVD.

[0035] The HA (hard anodized) film is formed by oxidizing and growing an aluminum cavity in a sulfuric acid electrolyte. After the pores are closed by the hydrothermal method, if the boehmite layer is not polished in step S2, Figure 2 there is still a certain thickness of boehmite layer AlO(OH) between the Al2O3 layer and Al(OH)3 in

[0036] The cross-sectional TEM images of the HA membrane before and after hydration sealing are shown in Figure 2 (a) and Figure 2 (b) respectively. Figure 2 (a) is the cross-sectional TEM image of the HA membrane before hydration sealing. The surface of the HA membrane without hydration sealing has no boehmite layer and has poor corrosion resistance; Figure 2 (b) shows that the surface of the HA membrane after hydration sealing is covered by a boehmite layer; A is the loose boehmite layer, B is the dense boehmite layer, and C is the Al2O3 layer.

[0037] In the FCVD process, H and NH generated by NH3 have a reducing effect on the HA film, increasing the surface recombination coefficient of the HA film and causing a decrease in the film deposition rate. Therefore, the direction of FCVD film development is to obtain a high density of OH bonds on the surface of the HA film to maintain a low recombination coefficient on the cavity surface.

[0038] The HA-Enh (Enhanced Hard Anodic Oxidation) film is a cavity film that is obtained by machining and cutting 2 μm of the HA film and then passivating it with a mixed gas and water vapor process. Figure 3 (a) is the cross-sectional SEM of the ordinary cavity HA film after passivation. Figure 3 (b) is the cross-sectional SEM of the dissociated cavity HA-Enh film after passivation. Comparing Figure 3 (a) with Figure 3 (b), it can be seen that there is a boehmite layer on the top of the ordinary cavity before passivation, while the boehmite layer on the top of the HA-Enh cavity has been completely removed.

[0039] Figure 4 is the planar SEM of the ordinary cavity HA film after passivation. Figure 5 is the planar SEM of the dissociated cavity HA-Enh film after passivation. Comparing, it can be seen that the yield of the HA-Enh cavity is significantly better. The reasons include: 1. OH bonds are beneficial for more free radicals to be transported to the wafer surface instead of recombining during transportation; 2. The chemisorption effect of water vapor on the boehmite layer on the top of HA is poor, and the OH bond concentration on the surface of the passivated boehmite layer is lower than that of the passivated Al2O3 layer.

[0040] Therefore, in step S2, the hard anodic oxidation film machine is machined and cut so that the mixed gas passivation can directly act on the Al2O3 layer to better adsorb OH bonds.

[0041] S3. Assemble the product obtained in S2 to form a dissociated cavity, carry out mixed gas passivation and cycle a preset number of times, and then carry out cooling and drying.

[0042] Among them, the cooling is: natural cooling or gradient cooling (to avoid film cracking caused by thermal stress); the drying is: low-temperature drying or nitrogen purging to ensure that there is no moisture residue on the surface.

[0043] The mixed gas passivation in step S3 includes the following steps: S310. Turn on the remote plasma source, introduce the ignition gas to ignite and clean the cavity wall.

[0044] S320. Pre-passivation: Turn on the remote plasma source, introduce the ignition gas and oxygen to form an initial oxide layer. S330. Turn off the remote plasma source and maintain the ignition gas purge for a preset time.

[0045] S340. Hydration passivation: The remote plasma source is turned off, and water vapor is introduced. The water vapor is used for hydration treatment to generate OH bonds on the surface of the initial oxide layer. S350. Turn off the remote plasma source. After restoring normal pressure, introduce ignition gas for purging to thoroughly remove water vapor and by-products in the cavity and prevent impurity residues. S360. Restart the remote plasma source, increase the pressure, and increase the flow rate of the ignition gas for surface reconstruction. The plasma slightly bombards the surface to optimize the film adhesion.

[0046] S370. Synergistic passivation: The remote plasma source is turned on, the pressure is reduced, and at the same time, ignition gas, auxiliary catalytic gas, and hydrogen are introduced. Through the synergistic effect of the plasma, a long-term deep passivation reaction is achieved. The auxiliary catalytic gas is used to increase the ion bombardment energy, the ignition gas and the auxiliary catalytic gas are used to purge the weakened OH bonds, and hydrogen is used to form OH bonds with residual oxygen atoms, so that the OH bonds strongly attached to the cavity wall surface are formed synergistically to form a high-quality passivation layer and reduce the surface recombination rate.

[0047] S380. Turn off the remote plasma source, introduce ignition gas for final purging, remove the reaction gas, and cool the surface.

[0048] Based on the above steps of hybrid gas passivation, oxygen pre-passivation, hydration passivation, and synergistic passivation are introduced in stages to achieve the construction of a multi-functional layer. The RPS is only turned on in key steps, such as oxidation, activation, and film formation, to avoid damage caused by excessive ion bombardment. In steps S360 - S370, the pressure is reduced, and the low-pressure environment enhances the plasma activity and improves the film density.

[0049] Figure 6 It is a schematic diagram of the atomic structure of the cavity surface (HA-Enh film) after step S3, showing the three-layer atomic structure formed on the surface of the cavity aluminum material after the water vapor hydration reaction and the synergistic passivation process. Each layer has a unique composition and function: 1) The outermost layer - hydration layer: This layer is composed of hydrogen atoms and oxygen atoms bonded by chemical bonds to form water molecules or hydroxide ions, etc., and tightly adheres to the surface of the alumina layer. As the outermost protective barrier, the hydration layer can effectively prevent direct contact between external corrosive substances and the aluminum material surface, thus significantly enhancing the corrosion resistance of the aluminum material.

[0050] 2) The middle layer - alumina layer: Labeled as Al2O3, it is composed of aluminum atoms and oxygen atoms tightly combined. It presents a regular crystal structure, which usually has high stability and hardness. Therefore, the alumina layer can play a role in protecting the internal aluminum material and preventing its further oxidation or corrosion.

[0051] 3) Innermost layer - aluminum atom layer: It consists of neatly arranged aluminum atoms to form the basic structural part, and the alumina layer and the hydrated layer are both protective layers formed on its surface; this three-layer atomic structure not only enhances the corrosion resistance of the cavity wall but also may improve its surface hardness and wear resistance.

[0052] In the FCVD process, too fast deposition rate will lead to insufficient density of the fillers on the chip surface, resulting in poor insulation effect. Therefore, it is necessary to control the deposition rate at 4 - 5 nm / s to achieve precise control of the deposited materials. The deposition rate is mainly related to the output power of the remote plasma source and the film material composite coefficient. There is a linear relationship between the set output power and the deposition rate, but the remote plasma source has a minimum ignition power of 1.2 - 1.5 kW to meet the energy for ignition; therefore, controlling the deposition rate by adjusting the output power has limitations; at this time, the process window of the remote plasma source is determined by the film material composite coefficient; by precisely adjusting the OH bond density on the film material surface through passivation, the film material composite coefficient can be adjusted, thus broadening the process window and obtaining an ideal deposition rate.

[0053] H2O acts on the active sites on the Al2O3 surface through chemisorption to generate OH bonds, forming an Al(OH)3 passivation layer with a lower composite coefficient; therefore, the greater the OH bond density, the lower the deposition rate. Under the condition of setting the minimum power, ensuring a high density of OH bonds can meet the requirements of low deposition rate in the FCVD process.

[0054] During the passivation process, the formation effect of OH bonds on the inner wall surface of the remote plasma source cavity is mainly affected by step S340 and step S370; in step S340, hydrated passivation forms a monolayer of OH bond layer on the inner wall surface, forming the basic layer of OH bonds; the density of OH bonds is synergistically affected by multiple factors, mainly including water vapor flow rate, temperature, and pressure; Among them, temperature is the decisive factor, determining whether the hydration reaction can occur. High temperature can increase the movement speed of molecules, thereby increasing the collision chance between molecules and the adsorbent surface and improving the adsorption rate. When the temperature is less than 100 °C, the chemisorption reaction is extremely weak; when the temperature is between 110 - 180 °C, the reaction can proceed efficiently; when the temperature is greater than 200 °C, desorption reaction may be triggered, reducing the OH bond density.

[0055] Pressure can regulate the reaction depth. A high-pressure environment can compress gas molecules, increase the diffusion rate of water vapor, accelerate the penetration of water molecules through the pores on the surface layer of alumina, and promote the deep hydration reaction; but too high pressure (greater than 30 Torr) causes water vapor to condense on the reaction inner wall, forming liquid water, resulting in a negative limiting effect and hindering the dissociation of H2O into OH-.

[0056] From the perspective of the reaction mechanism, the reaction between water vapor and alumina is essentially a gas-solid interface reaction: Al2O3 + 3H2O → 2Al(OH)3. There are two key points in this process: one is that water molecules need to be adsorbed on the surface of the oxide layer, and the other is that the adsorbed water molecules need to be chemically bonded to alumina; when the water vapor flow rate is lower than 0.5 L / min (standard conditions), the coverage density of OH groups increases with the increase in flow rate; after exceeding 1.2 L / min, the curve flattens out. This phenomenon can be explained by surface adsorption kinetics: the relationship between the coverage density of OH bonds ( ), and the partial pressure of water vapor ( ) conforms to the Langmuir-type adsorption isotherm: (2) where K is the adsorption constant. An increase in flow rate will increase , but after reaching a certain partial pressure tends to saturate.

[0057] At low flow rates, increasing the molecular collision frequency can increase the adsorption probability. When the water vapor flow rate increases, the surface water molecule concentration rises, promoting the OH bonding reaction. However, after reaching monolayer coverage, continuing to increase the flow rate will cause physical erosion, resulting in the detachment of OH bonds, making the OH bond density stagnate or even decrease.

[0058] Therefore, the specific parameters of step S340 are: the temperature is in the range of 110~180 °C, the pressure is 20 ± 1 Torr, and the water vapor flow rate is 622 ± 50 sccm.

[0059] In the above step S340, water vapor passivation has formed initial OH bonds on the aluminum surface, but some of the bonds may be weak or unstable. Through the synergistic passivation process of step S370, it is the core control step for the density and stability of OH bonds; step S370 optimizes the quality (stability) and quantity (coverage density) of OH bonds through a purge and compensation mechanism, preparing for the final passivation layer.

[0060] Purge stage: The ignition gas and the auxiliary catalytic gas cooperate to increase the ion bombardment energy to sweep away the weakened OH bonds attached to the chamber wall to improve the stability of OH bonds; the ignition gas and the auxiliary catalytic gas form a high-speed gas flow and ion bombardment in the plasma environment and maintain it for a long time to ensure sufficient action; the low-pressure environment optimizes the plasma density, with a long ion mean free path and high bombardment energy, which is conducive to accurately removing weak bonds without damaging the substrate.

[0061] Among the pre-existing OH bonds on the aluminum surface, some have relatively low bond energies, such as physically adsorbed H2O molecules or weakly bound Al-OH. These are less stable and are prone to desorption or reaction during subsequent processes. Plasma-enhanced gas flow bombardment can selectively remove these weak OH bonds and surface contaminants, such as residual carbon or impurities, leaving strongly chemically bonded OH bonds, such as Al-OH. By removing the weak bonds, the overall bond energy of the surface OH bonds increases. This is because the remaining OH bonds are more firmly bound in the aluminum oxide lattice, such as the Al-O-H structure, reducing the risk of thermal or environmentally induced desorption. The plasma also promotes surface reorganization, forming a more ordered OH layer and enhancing the passivation effect.

[0062] Compensation stage: Hydrogen reacts with residual oxygen atoms to form OH bonds, strengthening the OH bonds attached to the chamber wall surface and playing a role in compensating for the number of OH bonds. That is, the flow rate of the introduced hydrogen determines the density of the OH bonds. During the purge process, some weak OH bonds are removed, which may cause a temporary decrease in the surface OH coverage density. Hydrogen dissociates into hydrogen radicals (H•) under the plasma. These reactive species react with the aluminum surface: Al-O + H• → Al-OH. The H2 plasma promotes the surface OH bonding reaction and increases the OH bond density. A high flow rate of hydrogen ensures an adequate supply of H• to cover low-coverage areas on the surface, such as defects or edge sites, making the OH distribution more uniform. However, if an excessive amount of hydrogen is introduced, the OH bonds in the bond layer will become saturated, and physical erosion will also occur, resulting in the detachment of the OH bonds.

[0063] Regarding how to determine the flow rates of the ignition gas, auxiliary catalytic gas, and hydrogen in step S370, in one embodiment, a random forest regression algorithm is proposed to evaluate the influence of the flow rates of the ignition gas + auxiliary catalytic gas and hydrogen on the OH bond coverage density in the nitrogen-hydrogen passivation process and the FCVD deposition rate v; due to the dual randomness of random sampling and random feature selection in the random forest algorithm, that is, data sampling and feature selection suppress overfitting. It performs well on the dataset, has strong anti-noise ability and is not easily trapped in overfitting, and can adapt to high-dimensional data processing. At the same time, it can quantify the importance degree of input variables to the target value, providing a theoretical basis for feature engineering. The calculation of the variable importance E is obtained by analyzing the out-of-bag (OOB) error E: (3) where p is the number of Bootstrap samplings, represents the out-of-bag error after randomly permuting the feature , and is the original out-of-bag error. The larger the E value of a certain feature, the stronger its importance degree to the target variable.

[0064] Such as Figure 7As shown in the figure, the steps of the random forest regression prediction algorithm are as follows: Step P1: Bootstrap sampling Using the linear regression model, the approximate linear relationships between the ignition gas + auxiliary catalytic gas flow rate, hydrogen flow rate, and the OH bond coverage density , and the FCVD deposition rate v can be fitted: T subsample sets {D , D2,..., D T} are drawn with replacement from the original dataset D, and the sample size of each subset is N. The probability P(N) of each sample being selected in a single sampling is: (4) Then, the out-of-bag dataset OOB composed of the non-drawn samples is used for error estimation and feature importance analysis.

[0065] Step P2: Random feature selection As Figure 8 shown, let the total number of features be M t , for each subset D t , a regression decision tree h t (x) is constructed. When splitting nodes, m features (m ≤ M t ) are randomly selected.

[0066] The goal of node splitting in the regression tree is to minimize the mean squared error MSE. For feature j and split threshold and RR(j, s), the optimal split pair is selected as: (5) where and are the sample sets of the left and right child nodes after splitting respectively, and are the predicted values of the left and right child nodes respectively. That is, the target mean of the subset samples: (6) Step P3: Prediction result integration The average of the predictions of all decision trees is used as the final output, and ensemble learning is used to reduce the uncertainty of the prediction of a single tree. The final output is as follows: (7) where is the average result; is the prediction result of a single decision tree; T is the number of decision trees.

[0067] Step P4: Model performance evaluation metrics The root mean square error (RMSE) metric is used to quantify the OH bond coverage density respectively 、Precision of the FCVD deposition rate v: (8) Judge the coverage density of OH bonds Whether the root mean square error of the FCVD deposition rate meets the error precision requirement, and the error precision is 0.1; otherwise, return to step P1 to continue iteration until the maximum number of iterations is reached; Step P5: Feature importance evaluation and analysis Measure the feature importance by the change in the out-of-bag (OOB) error of the permuted eigenvalues. After randomly permuting the feature Xj, measure its importance degree by the change in the OOB error. If the error increases significantly after permutation, it indicates that this feature has an important impact on the model prediction. The importance degree is calculated as follows: (9) Among them, is the OOB error of the t-th tree.

[0068] Step P6: Use the predicted mean of all decision trees as the final output, and respectively fit the coverage density of OH bonds formed by the ratio combinations of each ignition gas + auxiliary catalytic gas and hydrogen flow rate 、the FCVD deposition rate v, and rank the importance of the ignition gas + auxiliary catalytic gas flow rate and hydrogen flow rate for the OH bond coverage density 、the FCVD deposition rate v; Step P7: Set the remote plasma source to an output of 1.5 kW, and select the appropriate ratio of ignition gas + auxiliary catalytic gas to hydrogen flow rate according to step P6 to ensure that while maintaining the stability and high coverage of the OH bond layer, the low deposition rate requirement of the FCVD process is met.

[0069] In a specific embodiment, the ignition gas is argon and the auxiliary catalytic gas is nitrogen. As Figure 9 shown, the importance degrees of the argon + nitrogen gas flow rate and hydrogen flow rate for the OH bond coverage density are 0.77 and 0.23 respectively; the importance degrees of the argon + nitrogen gas flow rate and hydrogen flow rate for the FCVD deposition rate v are 0.84 and 0.16 respectively. Therefore, the argon + nitrogen gas flow rate and hydrogen flow rate should be between (0.77 / 0.23, 0.84 / 0.16). According to the relationship between the importance degrees of the gas ratio for the OH coverage rate and deposition rate, the closer the ratio between the argon + nitrogen gas flow rate and helium flow rate is to 0.77 / 0.23, the stronger the influence on the OH coverage density and the higher the OH coverage density; if the selected gas ratio is closer to 0.84 / 0.16, the higher the control strength for the deposition rate.

[0070] Therefore, while ensuring effective cleaning of surface impurities and weakening of OH bonds, 2500 sccm of argon gas is introduced to maintain ignition and sufficient purging of weak bonds. The ratio between the gas flow rates of argon + nitrogen and hydrogen is selected to be approximately 5.0 to ensure that both the OH bond coverage density and the FCVD deposition rate meet the established requirements.

[0071] When the ignition gas is argon and the auxiliary catalytic gas is nitrogen, the specific parameters of steps S310 - S380 are shown in Table 1.

[0072] Table 1

[0073] Next, the above conclusions are verified.

[0074] The number of OH bonds per unit area is calculated by Fourier transform infrared spectroscopy. OH bonds exhibit a broad absorption peak associated with hydrogen bonding in the infrared spectrum at 3200 - 3600 cm -1 Therefore, first, the ATR - FTIR spectrum of the sample is collected to identify the characteristic peak of the OH bond near 3400 cm -1 and the absorbance A after baseline correction. Then, the number of OH bonds per unit area can be expressed as: (10) M is the molar mass, (L / (mol・cm)) is the molar extinction coefficient, is Avogadro's constant.

[0075] After that, scanning electron microscopy is used to perform SEM imaging on the cross - section of the deposited silicon wafer. The thickness of the deposited film is measured by a scale, and the FCVD deposition rate can be obtained by dividing it by the deposition time. When the flow rate ratios of argon + nitrogen gas flow and hydrogen gas flow are different, the test results are shown in Table 2.

[0076] Table 2

[0077] In this embodiment, the nitrogen gas flow rate is 175 sccm and the hydrogen gas flow rate is 525 sccm. Since the nitrogen gas flow rate is relatively low, the amount of N radicals generated is small, and the weakly attached OH bonds on the surface are purged. The number of OH bonds per square centimeter is pieces, and the deposition rate is at least 4.3 nm / s; In Comparative Examples 1 and 2, based on the HA - Enh film process, the nitrogen - hydrogen process in step 7 is modified, and 2500 sccm of argon gas is introduced: In Comparative Example 1, the nitrogen gas is increased to 325 sccm. The plasma ionization is enhanced, the concentration of N radicals increases, the ability to clean the chamber wall is enhanced, and the high nitrogen promotes the activation of reaction precursors, significantly optimizing the deposition kinetics. The number of OH bonds per square centimeter is pieces, with the highest deposition rate of 17.9 nm / s; In Comparative Example 2, the hydrogen gas was significantly increased to 750 sccm, the concentration of H radicals increased sharply, the surface reaction activity driven by hydrogen gas increased, and physical erosion occurred due to the introduction of excessive hydrogen gas, resulting in the detachment of some OH bonds, and the number of OH bonds per square centimeter decreased to pieces, with the highest deposition rate of 9.7 nm / s.

[0078] The above test results show that: under the same process conditions, the higher the nitrogen gas flow rate, the lower the OH bond coverage density, and the higher the corresponding deposition rate v; the higher the hydrogen gas flow rate, the higher the OH bond coverage density, and the lower the corresponding deposition rate v.

[0079] In summary, it can be seen that the OH bond coverage density has a regulatory effect on the deposition rate. The higher the OH bond coverage density, the more OH bonds per unit area, the higher the bombardment ionization ions that can be absorbed, the avoidance of the recombination of free radicals, and the lower the recombination rate. Then, the higher the deposition rate; therefore, controlling the gas ratio coefficient at about 5 can ensure the controllability of the deposition rate, making the OH bond coverage density not so high, capable of absorbing a certain number of free radicals, and making the deposition rate lower than the deposition rate corresponding to the set power of 1.5 kW. The ratio between the argon + nitrogen gas flow rate and the hydrogen gas flow rate determined based on the random forest regression prediction algorithm is about 5.0, which is verified.

[0080] In a specific embodiment, the number of cycles of the mixed gas passivation in step S3 is 100 times. The following verifies the number of cycles of the mixed gas passivation in step S3.

[0081] Table 3

[0082] Table 3 changes the preset number of passivation cycles in the passivation process of the mixed gas in S3. Comparative Examples 3 and 4 are both based on the HA-Enh film process. In Comparative Example 3, the number of cycles of the passivation process is reduced from 100 times to 50 times, and the deposition rate decays from 17.9 nm / s to 10.3 nm / s. And after using for 4553 h, the deposition rate further decays, and the decline exceeds 5% of the deposition rate. Therefore, it is determined that the RPS cavity has reached the service life and needs to be replaced; as can be seen from Table 3, the number of cycles of the passivation process has an impact on the stability of OH bonds. Too few cycles result in low adhesion of OH bonds. Under the repeated purging of the passivation process, fewer strong bonds are left, causing the stability of OH bonds to decrease, and the service life of RPS also decays.

[0083] Comparative Example 4 increased the number of cycles of the passivation process from 100 to 150 times. The deposition rate decreased from 17.9 nm / s to 17.7 nm / s, and the service life of the cavity decreased from 5412 h in Comparative Example 1 to 5325 h. It can be seen that after the mixed gas passivation process exceeds a certain number of cycles, the number of strong bonds on the inner wall surface of the cavity reaches a saturated state. Excessive number of cycles has little effect, and the influence on the stability of OH bonds is also small.

[0084] The above embodiments are only used to introduce the technical solutions of the present application in detail. However, the description of the above embodiments is only for helping to understand the method of the embodiments of the present invention, and should not be construed as a limitation of the embodiments of the present invention. Any changes or substitutions that can be easily thought of by those skilled in the art should be covered within the protection scope of the embodiments of the present invention.

Claims

1. A method for improving the stability of the oxide film in a remote plasma source cavity, characterized in that, Including: S1. Subject the surface-pretreated aluminum material to high-temperature steam sealing treatment to consume the original oxide film and generate a boehmite layer. S2. Perform cutting on the product obtained in S1 to remove the boehmite layer on the surface. S3. Assemble the product obtained in S2 to form a dissociation cavity, perform mixed gas passivation and cycle a preset number of times, and then perform cooling and drying; the mixed gas passivation includes pre-passivation, hydration passivation, and synergistic passivation performed in sequence. The pre-passivation is as follows: Turn on the remote plasma source, introduce an ignition gas and oxygen to form an initial oxide layer. The hydration passivation is as follows: Turn off the remote plasma source, introduce steam for hydration treatment to generate OH bonds on the surface of the initial oxide layer. The synergistic passivation is as follows: Turn on the remote plasma source, and simultaneously introduce an ignition gas, an auxiliary catalytic gas, and hydrogen. The ignition gas and the auxiliary catalytic gas blow the weakened OH bonds, and hydrogen and residual oxygen atoms generate OH bonds.

2. The method according to claim 1, wherein The surface pretreatment includes degreasing, pickling, alkali washing, and water washing and drying operations performed in sequence.

3. The method according to claim 2, wherein Before the pre-passivation, it also includes: Turn on the remote plasma source, introduce the ignition gas to ignite for cleaning the cavity wall.

4. The method according to claim 2, wherein Between the pre-passivation and the hydration passivation, it also includes: Turn off the remote plasma source and maintain the ignition gas purge for a preset time.

5. The method according to claim 4, characterized in that, Between the hydration passivation and the synergistic passivation, it also includes: Turn off the remote plasma source, introduce the ignition gas for purging to remove water vapor and by-products in the cavity. Restart the remote plasma source and increase the flow rate of the ignition gas for surface reconstruction.

6. The method according to claim 5, characterized in that, After the synergistic passivation, it also includes: Turn off the remote plasma source, introduce the ignition gas for final purge.

7. The method according to claim 1, characterized in that During the hydration passivation, the temperature is 110 - 180 °C, the pressure is 20 ± 1 Torr, and the steam flow rate is 622 ± 50 sccm.

8. The method according to claim 1, characterized in that, During the synergistic passivation, the method for determining the flow rate ratio of the introduced ignition gas, auxiliary catalytic gas, and hydrogen includes: Obtain the importance degrees of the total flow rate of the ignition gas + auxiliary catalytic gas and the hydrogen flow rate for the OH bond coverage density respectively according to the random forest regression algorithm , and the FCVD deposition rate v; Select the flow rate ratio of the ignition gas + auxiliary catalytic gas to hydrogen according to the importance degree.

9. The method according to claim 8, wherein Importance degrees of the total flow rate of ignition gas + auxiliary catalytic gas and hydrogen flow rate for the OH bond coverage density are imp1 and imp2 respectively, and importance degrees of the total flow rate of ignition gas + auxiliary catalytic gas and hydrogen flow rate for the FCVD deposition rate v are imp3 and imp4 respectively. The flow rate ratio of the total flow rate of ignition gas + auxiliary catalytic gas to hydrogen flow rate is between imp1 / imp2 and imp3 / imp4.

10. The method according to claim 1, wherein The preset number of cycles in step S3 is 100 times.

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