A method for improving the stability of oxide films in remote plasma source chambers

Abstract

The present invention belongs to the technical field of remote plasma sources and provides a method for improving the stability of the oxide film in a remote plasma source cavity, comprising: subjecting aluminum materials that have undergone surface pretreatment to high-temperature water vapor sealing treatment; cutting to remove the diaspore layer on the surface; and subjecting the dissociation cavity to mixed gas passivation and cycling for a preset number of times, wherein the mixed gas passivation includes pre-passivation, hydration passivation, and synergistic passivation. The present invention first seals the oxide layer with high-temperature water vapor, then cuts the surface diaspore layer to increase the number of surface active sites that are conducive to OH bond adsorption; then performs pre-passivation, hydration passivation, and synergistic passivation and cycles for a preset number of times to ensure the stability of the OH bond and improve the service life of the RPS cavity; utilizes a random forest algorithm to determine the mixed gas ratio, and by affecting the OH bond coverage density on the surface of the oxide film layer, reduces the lower limit of the RPS power operation window to meet the deposition rate requirements of the FCVD process.

Description

Technical Field

[0001] The present invention relates to the technical field of remote plasma sources, and in particular to a method for improving the stability of an oxide film in 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 in generating uniform, low-damage plasma. As one of the core components of the remote plasma source, the surface properties of the dissociation chamber have an important influence on the generation and transmission of plasma. Aluminum has become a commonly used material for the dissociation chamber due to its good electrical conductivity, thermal conductivity and processing properties. However, the surface of aluminum easily reacts with moisture, oxygen, etc. in the air, resulting in surface oxidation and corrosion, which in turn affects the service life of the chamber and the plasma treatment effect. Therefore, anodizing and passivation treatment of the aluminum surface to improve its surface stability and corrosion resistance has become one of the key technologies in the manufacture of remote plasma source dissociation chambers.

[0003] In the FCVD process, an excessively fast deposition rate can lead to insufficient density of the chip surface filler, resulting in poor insulation. Therefore, the deposition rate must be controlled to achieve precise deposition control. The deposition rate is primarily related to the output power of the remote plasma source and the composite coefficient of the anodized film material. While there is a linear relationship between the set output power and the deposition rate, the remote plasma source has a minimum ignition power to meet the ignition energy requirements. Therefore, controlling the deposition rate by adjusting the output power has limitations. The process window of the remote plasma source is then determined by the composite coefficient of the anodized film material.

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

[0005] Since the traditional water vapor passivation process only uses high-temperature water vapor treatment, OH bonds form a monomolecular layer on the aluminum surface. The number of OH bonds is small, and the bonding force with the aluminum surface is weak. The poor stability leads to a short service life. At the same time, the water vapor passivation process relies on the extensive adjustment of parameters such as temperature, pressure, and time. The ability to regulate the stability and coverage density of hydroxyl groups (OH bonds) is insufficient. Excessive OH bond coverage density will cause the remote plasma source to output too high a power when running at the same gas flow and pressure, which in turn leads to an excessively high deposition rate in the flow chemical vapor deposition (FCVD) process. Therefore, the OH bond coverage density needs to be regulated to meet process requirements. Summary of the Invention

[0006] In response to the defects in the prior art, the present invention provides a method for improving the stability of the oxide film in the cavity of a remote plasma source, so as to solve the problems of poor stability of the OH bond and uncontrollable coverage density of the current cavity aluminum material of the remote plasma source through water vapor passivation.

[0007] In a first aspect, the present invention provides a method for improving the stability of an oxide film in a remote plasma source cavity, comprising:

[0008] S1. The aluminum material is subjected to a high-temperature steam sealing treatment after surface pretreatment, which consumes the original oxide film to generate a diaspore layer;

[0009] S2 S1 obtained product is cut to remove the surface of the diaspore layer;

[0010] S3. The product obtained from S2 is assembled to form a dissociation chamber, and the mixed gas passivation is performed and cycled a preset number of times, followed by cooling and drying; the mixed gas passivation includes sequential pre-passivation, hydration passivation and synergistic passivation,

[0011] The pre-passivation comprises: turning on the remote plasma source, introducing ignition gas and oxygen, and forming an initial oxide layer;

[0012] The hydration passivation comprises: turning off the remote plasma source and introducing water vapor, which is used for hydration treatment to generate OH bonds on the surface of the initial oxide layer;

[0013] The synergistic passivation is as follows: the remote plasma source is turned on, and ignition gas, auxiliary catalytic gas and hydrogen are introduced simultaneously, wherein the ignition gas and auxiliary catalytic gas are used to purge weakened OH bonds, and hydrogen is used to generate OH bonds with residual oxygen atoms.

[0014] It can be seen from the above technical solution that the present invention first forms a diaspore layer through high-temperature water vapor sealing treatment, and then cuts the diaspore layer to 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 chemical adsorption mechanism. The OH bonds can prevent the free radicals dissociated from the remote plasma source from recombining during the transport process, thereby improving the dissociation rate of the remote plasma source.

[0015] Optionally, the surface pretreatment includes sequential degreasing, pickling, alkali cleaning, and water washing and drying. Surface pretreatment begins with degreasing to remove grease and contaminants from the aluminum surface; pickling then removes the natural oxide layer; and alkali cleaning creates a uniform roughness, enhancing subsequent reaction activity.

[0016] Optionally, before the pre-passivation, the process further includes: starting a remote plasma source, introducing an ignition gas and igniting the ignition gas to clean the cavity wall, thereby removing residual contaminants and activating the substrate surface.

[0017] Optionally, between the pre-passivation and the hydration passivation, the process further includes shutting down the remote plasma source and maintaining the ignition gas purge for a preset time. This step can remove byproducts, terminate the plasma reaction, stabilize the reaction chamber environment, and play a role in transition stabilization.

[0018] Optionally, between the hydration passivation and the synergistic passivation, the following steps are further included:

[0019] Turn off the remote plasma source and introduce ignition gas to purge the chamber to remove water vapor and byproducts to prevent impurities from remaining.

[0020] Restart the remote plasma source and increase the ignition gas flow rate to reconstruct the surface. The plasma will lightly bombard the surface to optimize the film adhesion.

[0021] Optionally, after the collaborative passivation, the method further includes: shutting down the remote plasma source and introducing an ignition gas for final purge.

[0022] Optionally, during the hydration passivation, the temperature is between 110° C. and 180° C., the pressure is 20±1 Torr, and the water vapor flow rate is 622±50 sccm.

[0023] Optionally, during the coordinated passivation, the flow ratio of the ignition gas, the auxiliary catalytic gas, and the hydrogen gas introduced may be determined by:

[0024] According to the random forest regression algorithm, the total flow rate of ignition gas + auxiliary catalytic gas and the coverage density of hydrogen flow for OH bond are obtained respectively. , the importance of FCVD deposition rate;

[0025] The flow ratio of ignition gas + auxiliary catalytic gas to hydrogen is selected according to the importance.

[0026] From the above technical solution, it can be seen that during the collaborative passivation, the random forest regression algorithm can be used to predict the total flow rate of ignition gas + auxiliary catalytic gas and the hydrogen flow rate for the OH bond coverage density. , and the importance of FCVD deposition rate, and then determine the specific ratio based on the importance to ensure that the OH bond coverage density and FCVD deposition rate can meet the established requirements.

[0027] Optionally, the total flow rate of ignition gas + auxiliary catalytic gas and hydrogen flow rate for OH bond coverage density The importance of imp1 and imp2 respectively, the importance of the total flow rate of ignition gas + auxiliary catalytic gas and hydrogen flow rate to the FCVD deposition rate v respectively, and the flow rate ratio is between imp1 / imp2 and imp3 / imp4.

[0028] Optionally, the preset number of cycles in step S3 is 100 times.

[0029] By adopting the above technical solution, this application has the following beneficial effects:

[0030] The present invention first forms a diaspore layer through high-temperature steam sealing treatment, and then cuts the diaspore layer to reduce the recombination coefficient and better adsorb OH bonds. Then, mixed gas passivation is performed, and pre-passivation, hydration passivation and synergistic passivation are performed in sequence to form OH bonds on the surface of the initial oxide layer through a chemical adsorption mechanism. The OH bonds can prevent free radicals dissociated from a remote plasma source from recombining during transportation, thereby improving the dissociation rate of the remote plasma source. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly describes the drawings required for the specific embodiments or the description of the prior art. Similar elements or parts are generally identified by similar reference numerals throughout the drawings. Elements or parts in the drawings are not necessarily drawn to scale.

[0032] Figure 1 A flow chart of a method for improving the stability of an oxide film in a remote plasma source cavity provided by an embodiment of the present invention is shown;

[0033] Figure 2 A comparison diagram showing whether step S2 is executed according to an embodiment of the present invention is shown;

[0034] Figure 3It shows the SEM comparison of the cavity cross section according to whether step S2 and step S3 are performed according to the embodiment of the present invention;

[0035] Figure 4 It shows a planar SEM image of the cavity after step S3 is completed without executing step S2 according to an embodiment of the present invention;

[0036] Figure 5 A planar SEM image of the cavity after executing step S2 and completing step S3 according to an embodiment of the present invention is shown;

[0037] Figure 6 A schematic diagram of the atomic structure of the cavity surface obtained by a method for improving the stability of an oxide film in a remote plasma source cavity provided by an embodiment of the present invention is shown;

[0038] Figure 7 A flowchart of obtaining importance according to a random forest regression algorithm provided by an embodiment of the present invention is shown;

[0039] Figure 8 A flowchart of building a decision tree according to an embodiment of the present invention is shown;

[0040] Figure 9 The figure shows the ranking of the importance of the argon+nitrogen flow rate and the hydrogen flow rate to the OH bond coverage density and the FCVD deposition rate provided by the embodiment of the present invention. DETAILED DESCRIPTION

[0041] The following embodiments of the technical solution 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 solution of the present invention and are therefore only examples and are not intended to limit the scope of protection of the present invention.

[0042] It should be noted that, unless otherwise specified, the technical or scientific terms used in this application should have the common meanings understood by those skilled in the art to which the present invention belongs.

[0043] In one embodiment, Figure 1 As shown, a method for improving the stability of an oxide film in a remote plasma source cavity is provided, comprising:

[0044] S1. The aluminum material that has undergone surface pretreatment is subjected to high-temperature steam sealing treatment to consume the original oxide film to generate a diaspore layer.

[0045] Among them, surface pretreatment includes degreasing, pickling, alkali cleaning and water washing and drying operations performed in sequence.

[0046] Degreasing and cleaning: Use 50% concentration of NaOH alkaline solution (or special degreasing agent) to remove grease and pollutants on the surface of aluminum.

[0047] Acid cleaning + alkali cleaning activation: Acid cleaning: Use 5-10% dilute sulfuric acid (H2SO4) or nitric acid (HNO3) solution for 1-5 minutes to remove the natural oxide layer. Alkaline cleaning: Use 5-10% NaOH solution to etch the surface to form a uniform roughness and enhance subsequent reaction activity.

[0048] Washing and drying: Rinse thoroughly with deionized water and then dry to avoid residual impurities affecting the quality of the passivation layer.

[0049] The specific operating parameters of step S1 are as follows:

[0050] Reaction device: Place the aluminum material in a high-pressure reactor (such as a high-pressure steam reactor) and introduce high-purity water vapor.

[0051] The process parameters are temperature: 120-250°C (180-200°C is commonly used, as too high a temperature may lead to the formation of amorphous aluminum oxide).

[0052] Pressure: 1-5 MPa (saturated vapor pressure corresponds to temperature and requires precise control). Time: 2-24 hours, adjusted according to the required film thickness (usually 0.1-5 μm).

[0053] Reaction mechanism: The oxide film reacts hydrothermally with water vapor to generate a diaspore layer (nanosheet or fibrous structure) with dense corrosion resistance.

[0054] (1)

[0055] Formula (1) is the hydration sealing reaction formula. The reaction is carried out at a temperature above 80°C. During the reaction, the original oxide film is consumed, thinning the pore wall. The volume of the generated monohydrated aluminum oxide (diaspore) increases and seals the pores.

[0056] S2. The product obtained in S1 is machined to remove the diaspore layer on the surface. Under the specific operating parameters of S1, S1 specifically machines and cuts off 2 μm of the hard oxide film to remove the top diaspore layer.

[0057] 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 recombination coefficient of the material, the easier it is for the H free radicals to be lost due to surface recombination. The recombination coefficients of different materials vary greatly. Generally speaking, aluminum has a higher recombination coefficient (~10 -1 ), while the composite coefficient of alumina is about (10 -2 ~10 -4 ), the composite coefficient of aluminum hydroxide is low (10 -5 ~10 -6 ), the surface composite coefficient of the film material in the RPS chamber will directly affect the deposition rate of FCVD.

[0058] The HA (hard anodized) film is formed by oxidation growth of the aluminum cavity in sulfuric acid electrolyte. After the pores are sealed by hydrothermal method, if the diaspore layer is not polished in step S2, Figure 2 There is also a certain thickness of diaspore layer AlO(OH) between the Al2O3 layer and Al(OH)3.

[0059] TEM images of the cross section of the HA membrane before and after hydration sealing, respectively. Figure 2 (a) and Figure 2 As shown in (b), Figure 2 (a) is a cross-sectional TEM image of the HA membrane before hydration sealing. The HA membrane without hydration sealing has no boehmite layer on its surface and has poor corrosion resistance. Figure 2 In (b), the surface of the HA membrane is covered with a diaspore layer after hydration sealing is completed; A is a loose diaspore layer, B is a dense diaspore layer, and C is an Al2O3 layer.

[0060] In the FCVD process, H and NH generated by NH3 have a reducing effect on the HA film, which increases the surface recombination coefficient of the HA film and causes a decrease in the film deposition rate. Therefore, how 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 is the direction of FCVD film development.

[0061] HA-Enh (enhanced hard anodized) film is a cavity film that is made by machining and cutting off 2μm of HA film and then passivating it through a mixed gas and water vapor process; Figure 3 (a) is the cross-sectional SEM of the HA film in the common cavity after passivation; Figure 3 (b) is the cross-sectional SEM of the HA-Enh film in the dissociation cavity after passivation; Figure 3 (a) and Figure 3 As shown in (b), there is a diaspore layer on the top of the ordinary cavity before passivation, while the diaspore layer on the top of the HA-Enh cavity has been completely removed.

[0062] Figure 4 This is the plane SEM of the HA film in the ordinary cavity after passivation; Figure 5 This is a planar SEM image of the HA-Enh film in the dissociated cavity after passivation. The HA-Enh cavity shows significantly better yields due to the following reasons: 1. OH bonds facilitate the transport of more free radicals to the wafer surface, rather than allowing them to recombine during transport; and 2. Water vapor chemically adsorbs poorly on the diaspore layer on top of HA, resulting in a lower OH bond concentration on the surface of the passivated diaspore layer than on the Al2O3 layer.

[0063] Therefore, step S2 performs cutting processing on the hard oxide film machine so that the mixed gas passivation can directly act on the Al2O3 layer to better adsorb the OH bond.

[0064] S3. Assemble the product obtained in S2 to form a dissociation chamber, perform mixed gas passivation and cycle for a preset number of times, and then cool and dry.

[0065] Among them, cooling includes: natural cooling or gradient cooling (to avoid thermal stress causing film cracking); drying includes: low-temperature drying or nitrogen purging to ensure that there is no moisture residue on the surface.

[0066] The mixed gas passivation in step S3 includes the following steps:

[0067] S310. Turn on the remote plasma source, introduce ignition gas and ignite to clean the cavity wall.

[0068] S320. Pre-passivation: The remote plasma source is turned on, and ignition gas and oxygen are introduced to form an initial oxide layer;

[0069] S330. Turn off the remote plasma source and maintain the ignition gas purge for a preset time.

[0070] S340. Hydration passivation: The remote plasma source is turned off and water vapor is introduced. The water vapor is used for hydration treatment and forms OH bonds on the surface of the initial oxide layer.

[0071] S350. Turn off the remote plasma source, restore the pressure to normal, and then introduce the ignition gas to purge the chamber to completely remove moisture and byproducts to prevent impurities from remaining.

[0072] S360. Restart the remote plasma source, increase the pressure, and increase the ignition gas flow rate to reconstruct the surface. The plasma lightly bombards the surface to optimize the film adhesion.

[0073] S370. Synergistic passivation: The remote plasma source is turned on to reduce the pressure, and the ignition gas, auxiliary catalytic gas and hydrogen are introduced at the same time to achieve a long-term deep passivation reaction through the synergistic effect of the plasma; the auxiliary catalytic gas is used to increase the ion bombardment energy, the ignition gas and auxiliary catalytic gas are used to purge the weakened OH bonds, and the hydrogen is used to generate OH bonds with the residual oxygen atoms, so as to strengthen the OH bonds attached to the cavity wall surface, synergistically form a high-quality passivation layer, and reduce the surface recombination rate.

[0074] S380. Turn off the remote plasma source, introduce ignition gas for final purge, remove the reaction gas, and cool the surface.

[0075] Based on the above mixed gas passivation steps, oxygen pre-passivation, hydration passivation, and synergistic passivation are introduced in stages to achieve the construction of a multifunctional layer. RPS is only turned on during key steps, such as oxidation, activation, and film formation, to avoid excessive ion bombardment damage; steps S360-S370 reduce the pressure, and the low-pressure environment enhances plasma activity and improves the density of the film.

[0076] Figure 6This is a schematic diagram of the atomic structure of the cavity surface (HA-Enh film) after step S3. It shows the three-layer atomic structure formed on the cavity aluminum surface after the water vapor hydration reaction and the coordinated passivation process. Each layer has a unique composition and function:

[0077] 1) Outermost layer - Hydration layer: This layer is formed by hydrogen and oxygen atoms chemically bonded together to form water molecules or hydroxide radicals, which are tightly attached to the surface of the aluminum oxide layer. As the outermost protective barrier, the hydration layer effectively prevents external corrosive substances from directly contacting the aluminum surface, significantly enhancing the aluminum's corrosion resistance.

[0078] 2) Intermediate layer - Alumina: Labeled as Al2O3, it is composed of tightly bound aluminum and oxygen atoms. This regular crystalline structure is generally considered to be highly stable and hard. Therefore, the alumina layer protects the inner aluminum from further oxidation or corrosion.

[0079] 3) The innermost layer - the aluminum atomic layer: The basic structural part is composed of neatly arranged aluminum atoms, and the aluminum oxide layer and the hydration layer are 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.

[0080] In the FCVD process, an excessively fast deposition rate can lead to insufficient density of the chip surface filler, resulting in poor insulation. Therefore, the deposition rate needs to be controlled at 4-5nm / s to achieve precise deposition control. The deposition rate is mainly related to the output power of the remote plasma source and the film material recombination coefficient. The set output power has a linear relationship with the deposition rate, but the remote plasma source has a minimum ignition power of 1.2-1.5kW to meet the energy requirements during ignition. Therefore, controlling the deposition rate by adjusting the output power has limitations. In this case, the process window of the remote plasma source is determined by the recombination coefficient of the film material. By precisely adjusting the OH bond density on the film material surface through passivation, and thereby adjusting the recombination coefficient of the film material, the process window can be widened to achieve the ideal deposition rate.

[0081] H2O generates OH bonds at the active points on the Al2O3 surface through chemical adsorption, forming an Al(OH)3 passivation layer with a lower recombination coefficient. Therefore, the greater the OH bond density, the lower the deposition rate. When setting the minimum power, ensuring a high OH bond density can meet the low deposition rate requirements in the FCVD process.

[0082] 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, hydration passivation forms a monolayer of OH bonds on the inner wall surface, forming a base layer of OH bonds; the density of OH bonds is synergistically affected by multiple factors, mainly including water vapor flow rate, temperature, and pressure;

[0083] Temperature is a crucial factor in determining whether the hydration reaction can occur. High temperatures can increase the speed of molecular motion, thereby increasing the chances of collisions between molecules and the adsorbent surface and improving the adsorption rate. When the temperature is below 100°C, the chemical adsorption reaction is extremely weak; when the temperature is between 110 and 180°C, the reaction can proceed efficiently; and when the temperature is above 200°C, desorption reactions may occur, reducing the OH bond density.

[0084] Pressure can regulate the depth of the reaction. A high-pressure environment can compress gas molecules, increase the diffusion rate of water vapor, accelerate the penetration of water molecules through the surface pores of alumina, and promote deep hydration reactions. However, if the pressure is too high (greater than 30 Torr), water vapor will condense on the inner wall of the reaction to form liquid water, resulting in a negative restriction effect and hindering the dissociation of H2O into OH-.

[0085] From a reaction mechanism perspective, the reaction between water vapor and alumina is essentially a gas-solid interface reaction: Al2O3 + 3H2O → 2Al(OH)3. This process has two key points: first, water molecules need to be adsorbed on the surface of the oxide layer, and second, the adsorbed water molecules need to chemically bond with the alumina. When the water vapor flow rate is less than 0.5L / min (standard operating conditions), the OH group coverage density increases with the flow rate; after exceeding 1.2L / min, the curve tends to flatten. This phenomenon can be explained by surface adsorption dynamics: the OH bond coverage density ( ) and water vapor partial pressure ( ) is consistent with the Langmuir adsorption isotherm:

[0086] (2)

[0087] Where K is the adsorption constant. Increasing the flow rate will increase , but after reaching a certain partial pressure Tends to saturation.

[0088] Increasing the frequency of molecular collisions at low flow rates can improve the probability of adsorption. As the water vapor flow rate increases, the concentration of water molecules on the surface increases, promoting the OH bonding reaction. However, continuing to increase the flow rate after reaching a monolayer coverage will trigger physical scouring, causing the OH bonds to fall off, causing the OH bond density to stagnate or even decrease.

[0089] Therefore, the specific parameters of step S340 are: temperature between 110° C. and 180° C., pressure of 20±1 Torr, and water vapor flow rate of 622±50 sccm.

[0090] The water vapor passivation process in step S340 forms initial OH bonds on the aluminum surface, but some bonds may be weak or unstable. The coordinated passivation process in step S370 is a key step in controlling the density and stability of the OH bonds. Through a purge and compensation mechanism, step S370 optimizes the quality (stability) and quantity (coverage density) of the OH bonds, preparing for the final passivation layer.

[0091] Purge stage: The ignition gas and auxiliary catalytic gas work together to increase the ion bombardment energy to clean the weakened OH bonds attached to the cavity wall and improve the stability of the OH bonds; the ignition gas and auxiliary catalytic gas form high-speed airflow and ion bombardment in the plasma environment, maintaining it for a long time to ensure full effect; the low-pressure environment optimizes the plasma density, the ion mean free path is long, and the bombardment energy is high, which is conducive to the precise removal of weak bonds without damaging the substrate.

[0092] Some of the pre-existing OH bonds on the aluminum surface have low bond energies, such as physically adsorbed H₂O molecules or weakly bound Al-OH bonds. These bonds are unstable and prone to desorption or reaction during subsequent processing. Plasma-enhanced gas bombardment selectively removes these weak OH bonds and surface contaminants, such as residual carbon or impurities, leaving behind strong chemically bonded OH bonds, such as Al-OH. By removing these weak bonds, the overall bond energy of the surface OH bonds increases. This is because the remaining OH bonds are more firmly bound to the aluminum oxide lattice, such as the Al-OH 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.

[0093] During the compensation phase, hydrogen forms OH bonds with residual oxygen atoms, strengthening the OH bonds attached to the cavity wall surface and compensating for the number of OH bonds. The hydrogen flow rate determines the OH bond density. During the purge process, some weak OH bonds are removed, potentially causing a temporary decrease in the surface OH coverage density. Hydrogen dissociates into hydrogen radicals (H•) under the plasma. These active species react with the aluminum surface: Al-O + H• → Al-OH. The H2 plasma promotes surface OH bonding reactions, increasing the OH bond density. A high hydrogen flow rate ensures an ample H• supply, covering areas of low surface coverage density, such as defects or edge sites, resulting in a more uniform OH distribution. However, excessive hydrogen flow can saturate the OH bonds in the bond layer, leading to physical erosion and OH bond loss.

[0094] 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 OH bond coverage density of the ignition gas + auxiliary catalytic gas flow rate and the hydrogen flow rate in the nitrogen-hydrogen passivation process. , the FCVD deposition rate v; the random forest algorithm, due to its dual randomness of random sampling and random feature selection, i.e., data sampling and feature selection, suppress overfitting. It performs well on datasets, is highly resistant to noise, is not prone to overfitting, and is adaptable to high-dimensional data processing. It can also quantify the importance of input variables to the target value, providing a theoretical basis for feature engineering. Variable importance E is calculated by analyzing the out-of-bag (OOB) error E:

[0095] (3)

[0096] Among them, p is the number of Bootstrap sampling, Represents the feature The out-of-bag error after random permutation, is the original out-of-bag error. The larger the E value of a feature, the more important it is to the target variable.

[0097] like Figure 7 As shown, the steps of the random forest regression prediction algorithm are as follows:

[0098] Step P1: Bootstrap sampling

[0099] The linear regression model can be used to fit the relationship between the ignition gas + auxiliary catalytic gas flow rate and hydrogen flow rate and the OH bond coverage density. , the approximate linear relationship of FCVD deposition rate v:

[0100] From the original data set D, T subsample sets {D , D2,...,D T}, the sample size of each subset is N. The probability P(N) of each sample being selected in a single sampling is:

[0101] (4)

[0102] Then, the samples that are not selected constitute the out-of-bag dataset OOB, which is used for error estimation and feature importance analysis.

[0103] Step P2: Random feature selection

[0104] like Figure 8 As shown, let the total number of features be M t , for each subset D t , build a regression decision tree h t (x), randomly select m features (m≤M t ).

[0105] The goal of node splitting in a regression tree is to minimize the mean square error (MSE). For feature j and splitting threshold and RR(j, s), the optimal split pair is selected. :

[0106] (5)

[0107] in, and are the left and right child node sample sets after splitting, and are the predicted values ​​of the left and right child nodes respectively. That is, the target mean of the subset samples:

[0108] (6)

[0109] Step P3: Prediction result integration

[0110] The prediction mean of all decision trees is used as the final output, and ensemble learning is used to reduce the uncertainty of single tree prediction. The final output is as follows:

[0111] (7)

[0112] in, is the average result; is the prediction result of a single decision tree; T is the number of decision trees.

[0113] Step P4: Model performance evaluation indicators

[0114] The root mean square error (RMSE) indicator is used to quantify the OH bond coverage density. , Accuracy of FCVD deposition rate v:

[0115] (8)

[0116] Determine OH bond coverage density , whether the root mean square error of the FCVD deposition rate meets the error accuracy requirement, the error accuracy is 0.1; otherwise, return to step P1 and continue iterating until the maximum number of iterations is reached;

[0117] Step P5: Feature Importance Evaluation Analysis

[0118] The importance of a feature is measured by the change in the OOB error after permutation. After randomly permuting feature Xj, its importance is measured by the change in the out-of-bag error. If the error increases significantly after permutation, it indicates that the feature has a significant impact on the model prediction. The importance is calculated as follows:

[0119] (9)

[0120] in, is the OOB error of the t-th tree.

[0121] Step P6: Using the predicted mean of all decision trees as the final output, the OH bond coverage density formed by each combination of ignition gas + auxiliary catalytic gas and hydrogen flow ratio is fitted. , FCVD deposition rate v, and the ignition gas + auxiliary catalytic gas flow rate, hydrogen flow rate for OH bond coverage density , rank the importance of FCVD deposition rate v;

[0122] Step P7: Set the remote plasma source to 1.5kW output and select the appropriate ignition gas + auxiliary catalytic gas and hydrogen flow ratio according to step P6 to ensure that the low deposition rate requirements of the FCVD process are met while maintaining the stability and high coverage of the OH bond layer.

[0123] In a specific embodiment, the ignition gas is argon and the auxiliary catalytic gas is nitrogen. Figure 9 As shown, the argon + nitrogen gas flow rate and hydrogen flow rate have an impact on the OH bond coverage density. The importance of argon + nitrogen gas flow rate and hydrogen gas flow rate for FCVD deposition rate v are 0.77 and 0.23, respectively; the importance of argon + nitrogen gas flow rate and hydrogen gas flow rate for 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). Based on the importance relationship between the gas ratio and OH coverage and deposition rate, the closer the ratio of argon + nitrogen gas flow rate to helium flow rate is to 0.77 / 0.23, the stronger the influence on OH coverage density and the higher the OH coverage density; if the gas ratio is closer to 0.84 / 0.16, the stronger the control over deposition rate.

[0124] Therefore, while ensuring effective cleaning of surface impurities and weakened OH bonds, 2500 sccm of argon is introduced to maintain ignition and be sufficient to purge weak bonds. The ratio between the argon + nitrogen gas flow rate and the hydrogen flow rate is selected to be approximately 5.0 to ensure that the OH bond coverage density and FCVD deposition rate meet the established requirements.

[0125] When the ignition gas is argon and the auxiliary catalytic gas is nitrogen, the specific parameters of steps S310 to S380 are shown in Table 1.

[0126] Table 1

[0127]

[0128] The above conclusions are verified below.

[0129] The number of OH bonds per unit area was calculated by Fourier transform infrared spectroscopy. OH bonds appear as 3200-3600 cm in infrared spectra. -1 The broad absorption peak of hydrogen bonding; therefore, the ATR-FTIR spectrum of the sample was first collected to identify the peak at 3400 cm -1 The absorbance A after the nearby OH bond characteristic peak and baseline correction; then, the number of OH bonds per unit area can be expressed as:

[0130] (10)

[0131] M is the molar mass, (L / (mol・cm)) is the molar absorption coefficient, is Avogadro's constant.

[0132] A scanning electron microscope (SEM) was then used to image the cross-section of the deposited silicon wafer. The film thickness was measured using a ruler and divided by the deposition time to obtain the FCVD deposition rate. Table 2 shows the test results for different ratios of argon + nitrogen and hydrogen flow rates.

[0133] Table 2

[0134]

[0135] In this embodiment, the nitrogen flow rate is 175 sccm and the hydrogen flow rate is 525 sccm. The nitrogen flow rate is low, the amount of N free radicals generated is small, and the OH bonds attached to the surface are weakened. The number of OH bonds per square centimeter is The lowest deposition rate is 4.3 nm / s.

[0136] Comparative Examples 1 and 2 are based on the HA-Enh film process, and the nitrogen-hydrogen process in step 7 is modified to introduce 2500 sccm of argon:

[0137] In comparative example 1, the nitrogen gas is increased to 325 sccm, the plasma ionization is enhanced, the N radical concentration is increased, the ability to clean the cavity wall is enhanced, the high nitrogen gas promotes the activation of the reaction precursor, the deposition kinetics is significantly optimized, and the number of OH bonds per square centimeter is The maximum deposition rate is 17.9 nm / s;

[0138] In comparative example 2, the hydrogen was greatly increased to 750 sccm, the H radical concentration increased sharply, the hydrogen-driven surface reaction activity increased, and the excessive hydrogen introduced caused physical scouring, resulting in the shedding of some OH bonds, and the number of OH bonds per square centimeter decreased to The maximum deposition rate is 9.7nm / s.

[0139] The above test results show that: under the same process conditions, the higher the nitrogen flow rate, the higher the OH bond coverage density. The lower the hydrogen flow rate, the higher the corresponding deposition rate v; the higher the hydrogen flow rate, the higher the OH bond coverage density The higher it is, the lower the corresponding deposition rate v is.

[0140] In summary, the OH bond coverage density regulates the deposition rate. The higher the OH bond coverage density, the more OH bonds there are per unit area, and the more bombarding ionized ions can be absorbed, preventing free radical recombination. The lower the recombination rate, the higher the deposition rate. Therefore, controlling the gas ratio coefficient to around 5 ensures controllable deposition rate, reducing the OH bond coverage density to a certain level, allowing for the absorption of a certain number of free radicals, resulting in a deposition rate lower than that corresponding to the set power of 1.5 kW. This was verified by the ratio of argon + nitrogen flow rate to hydrogen flow rate of approximately 5.0, as determined by the random forest regression prediction algorithm.

[0141] In a specific embodiment, the number of cycles of the mixed gas passivation in step S3 is 100. The number of cycles of the mixed gas passivation in step S3 is verified below.

[0142] Table 3

[0143]

[0144] Table 3 changes the preset number of passivation cycles in the passivation process of the S3 mixed gas. Comparative Examples 3 and 4 are both based on the HA-Enh film process. Comparative Example 3 reduces the number of passivation process cycles from 100 to 50, and the deposition rate decays from 17.9 nm / s to 10.3 nm / s. Moreover, the deposition rate further decays after 4553 hours of use, and the drop exceeds 5% of the deposition rate. Therefore, it is determined that the RPS chamber has reached the end of its service life and needs to be replaced. As can be seen from Table 3, the number of passivation process cycles affects the stability of the OH bond. Too few cycles result in lower OH bond adhesion. Under repeated purges in the passivation process, fewer strong bonds are left, resulting in reduced stability of the OH bond and a decay in the service life of the RPS.

[0145] In Comparative Example 4, the number of passivation cycles was increased from 100 to 150, and the deposition rate decreased from 17.9 nm / s to 17.7 nm / s. The chamber life also decreased from 5412 hours in Comparative Example 1 to 5325 hours. This indicates that after a certain number of mixed gas passivation cycles, the number of strong bonds on the chamber's inner wall surface reaches saturation. Exceeding the number of cycles has little effect and has little impact on the stability of the OH bonds.

[0146] The above embodiments are merely provided to provide a detailed description of the technical solutions of the present application. However, the descriptions of the above embodiments are intended only to facilitate understanding of the methods of the embodiments of the present invention and should not be construed as limiting the embodiments of the present invention. Any changes or substitutions that can be readily conceived by a person skilled in the art should fall within the scope of protection of the embodiments of the present invention.

Claims

1. A method for improving the stability of an oxide film in a remote plasma source cavity, characterized in that: include: S1. The aluminum material is subjected to a high-temperature steam sealing treatment after surface pretreatment, which consumes the original oxide film to generate a diaspore layer; S2 S1 obtained product is cut to remove the surface of the diaspore layer; S3. The product obtained in S2 is assembled to form a dissociation chamber, and the mixed gas passivation is performed and cycled a preset number of times, followed by cooling and drying; the mixed gas passivation includes pre-passivation, hydration passivation and synergistic passivation performed sequentially, The pre-passivation comprises: turning on the remote plasma source, introducing ignition gas and oxygen to form an initial oxide layer; The hydration passivation comprises: turning off the remote plasma source, introducing water vapor for hydration treatment, and generating OH bonds on the surface of the initial oxide layer; The synergistic passivation is as follows: the remote plasma source is turned on, and the ignition gas, the auxiliary catalytic gas and the hydrogen are introduced simultaneously, the ignition gas and the auxiliary catalytic gas purge the weakened OH bonds, and the hydrogen and the residual oxygen atoms generate OH bonds.

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

3. The method according to claim 2, characterized in that Before the pre-passivation, the process also includes: starting a remote plasma source, introducing an ignition gas and igniting the ignition gas to clean the cavity wall.

4. The method according to claim 2, characterized in that Between the pre-passivation and the hydration passivation, the method further includes: turning off the remote plasma source and maintaining 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 and introduce ignition gas to purge and remove water vapor and byproducts in the chamber; Restart the remote plasma source and increase the ignition gas flow rate for surface reconstruction.

6. The method according to claim 5, characterized in that After the collaborative passivation, the method further includes: closing the remote plasma source and introducing ignition gas for final purge.

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

8. The method according to claim 1, characterized in that During the coordinated passivation, the flow ratio of the ignition gas, the auxiliary catalytic gas, and the hydrogen gas is determined by: According to the random forest regression algorithm, the total flow rate of ignition gas + auxiliary catalytic gas and the coverage density of hydrogen flow for OH bond are obtained respectively. , the importance of FCVD deposition rate v; The flow ratio of ignition gas + auxiliary catalytic gas to hydrogen is selected according to the importance.

9. The method according to claim 8, characterized in that Total flow of ignition gas + auxiliary catalytic gas and hydrogen flow rate for OH bond coverage density The importance of are imp1 and imp2 respectively, the importance of the total flow rate of ignition gas + auxiliary catalytic gas and hydrogen flow rate to the FCVD deposition rate v are imp3 and imp4 respectively, and 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, characterized in that The preset number of cycles in step S3 is 100 times.

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