Chemical vapor etching method

Abstract

A chemical vapor etching method, the method comprising: before performing chemical etching, introducing hydrogen fluoride and ammonia into an etching chamber to perform chamber pretreatment, so that the adsorption and desorption of the inner wall surface of the etching chamber to the hydrogen fluoride and ammonia reaches a dynamic equilibrium, the chamber pretreatment satisfying at least one of the following conditions: the pretreatment pressure is higher than the etching pressure adopted in the chemical etching, the pretreatment hydrogen fluoride flow rate is higher than the hydrogen fluoride flow rate adopted in the chemical etching, and the pretreatment ammonia flow rate is higher than the ammonia flow rate adopted in the chemical etching; after the chamber pretreatment, performing chemical etching on a wafer having a surface with an oxidation layer to be etched at an etching pressure, a hydrogen fluoride flow rate and an ammonia flow rate. The chemical vapor etching method provided by the present application improves the consistency and stability of the chemical etching process between different etching chambers without adjusting the hardware configuration of the etching chamber.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing, and more particularly to a chemical vapor deposition method. Background Technology

[0002] In semiconductor manufacturing processes, chemical vapor deposition (CVD) is a method that uses a gas to react chemically with a solid thin film material to remove the target material. CVD is typically performed within a sealed etching chamber. By introducing a reactive gas into the chamber, the gas reacts chemically with the thin film to be etched on the wafer surface, generating volatile or sublimable solid byproducts, thereby removing the thin film material. CVD can be applied to the removal of various dielectric thin films, including silicon oxide and silicon nitride films.

[0003] In chemical vapor deposition (CVD) etching, the etching chamber, as the site of the reaction, has a significant impact on the etching process outcome due to its internal environment. An etching chamber typically includes a chamber body and a substrate within the chamber body for supporting the wafer. During etching, the reactive gases not only react with the thin film to be etched on the wafer surface but also interact with the inner wall surface of the etching chamber. For example, reactive gases may adsorb onto the inner wall surface of the etching chamber, or the chemical composition or surface state of the inner wall surface material may change during long-term processing. These factors can all affect the effective amount of gas actually participating in the wafer surface reaction within the etching chamber. With the continuous shrinking of semiconductor device feature sizes and the widespread adoption of three-dimensional device structures, increasingly higher demands are being placed on the consistency and stability of CVD processes.

[0004] Currently, the consistency and stability of chemical etching processes across different etching chambers still need to be improved. Summary of the Invention

[0005] The problem solved by the embodiments of the present invention is to provide a chemical vapor deposition method that improves the consistency and stability of chemical etching processes between different etching chambers.

[0006] To address the aforementioned problems, this invention provides a chemical vapor deposition (CVD) etching method, comprising: pre-treating an etching chamber by introducing hydrogen fluoride and ammonia gas before performing CVD, so that the adsorption and desorption of hydrogen fluoride and ammonia gas on the inner wall surface of the etching chamber reaches a dynamic equilibrium, wherein the chamber pre-treatment satisfies at least one of the following conditions: the pre-treatment pressure is higher than the etching pressure used in CVD, the pre-treatment hydrogen fluoride flow rate is higher than the hydrogen fluoride flow rate used in CVD, and the pre-treatment ammonia gas flow rate is higher than the ammonia gas flow rate used in CVD; after performing the chamber pre-treatment, performing CVD on a wafer with an oxide layer to be etched on its surface under the etching pressure, hydrogen fluoride flow rate, and ammonia gas flow rate.

[0007] Optionally, the chamber pretreatment steps include: first, introducing hydrogen fluoride and ammonia into the etching chamber at a first pretreatment pressure, wherein the first pretreatment pressure is higher than the etching pressure, and the flow rate of pretreatment hydrogen fluoride introduced into the etching chamber at the first pretreatment pressure is higher than the flow rate of hydrogen fluoride used in chemical etching, and the flow rate of pretreatment ammonia introduced into the etching chamber at the first pretreatment pressure is higher than the flow rate of ammonia used in chemical etching; then, introducing hydrogen fluoride and ammonia into the etching chamber at a second pretreatment pressure, wherein the second pretreatment pressure is lower than the first pretreatment pressure, and the flow rate of pretreatment hydrogen fluoride introduced into the etching chamber at the second pretreatment pressure is equal to the flow rate of hydrogen fluoride used in chemical etching, and the flow rate of pretreatment ammonia introduced into the etching chamber at the second pretreatment pressure is equal to the flow rate of ammonia used in chemical etching.

[0008] Optionally, the second pretreatment pressure is equal to the etching pressure.

[0009] Optionally, during the process of introducing hydrogen fluoride and ammonia into the etching chamber under the first pretreatment pressure and during the process of introducing hydrogen fluoride and ammonia into the etching chamber under the second pretreatment pressure, an inert gas is also introduced into the etching chamber.

[0010] Optional, the inert gas is argon.

[0011] Optionally, after the chemical etching is completed and before the chamber pretreatment of the next batch of wafers, the etching method may further include: introducing hydrogen fluoride and ammonia into the etching chamber for idle maintenance, maintaining a dynamic balance between the adsorption and desorption of hydrogen fluoride and ammonia on the inner wall surface of the etching chamber.

[0012] Optionally, the material of the inner wall surface of the etching chamber includes alumina; in the step of introducing hydrogen fluoride and ammonia into the etching chamber for chamber pretreatment, the hydrogen fluoride and ammonia react with the alumina on the inner wall surface to form a fluorinated layer on the inner wall surface of the etching chamber.

[0013] Optionally, the fluorinated layer may be made of aluminum ammonium fluoride.

[0014] Optionally, the oxide layer to be etched is a silicon oxide layer formed by atomic layer deposition.

[0015] Optionally, in the chamber pretreatment step, a silicon oxide wafer is placed in the etching chamber as a carrier wafer so that hydrogen fluoride and ammonia gas can chemically etch the carrier wafer.

[0016] Optionally, the number of carrier wafers etched under the first pretreatment pressure is greater than the number of carrier wafers etched under the second pretreatment pressure.

[0017] Compared with the prior art, the technical solution of the embodiments of the present invention has the following advantages: The chemical vapor deposition (CVD) etching method provided by this invention introduces hydrogen fluoride and ammonia gas into the etching chamber before chemical etching, thereby achieving a dynamic equilibrium between the adsorption and desorption of hydrogen fluoride and ammonia gas on the inner wall surface of the etching chamber. Since the chamber pretreatment satisfies at least one of the following three conditions—pretreatment pressure higher than etching pressure, pretreatment hydrogen fluoride flow rate higher than hydrogen fluoride flow rate, and pretreatment ammonia gas flow rate higher than ammonia gas flow rate—that is, the chamber pretreatment supplies hydrogen fluoride and ammonia gas to the inner wall surface of the etching chamber under process conditions stronger than chemical etching, the inner wall surfaces of different etching chambers can be uniformly pushed to a dynamic equilibrium state of adsorption and desorption within a relatively short time. When the inner wall surfaces of different etching chambers are all in this dynamic equilibrium state, the adsorption of hydrogen fluoride and ammonia on the inner wall surfaces of each etching chamber tends to be consistent. The effective reactant partial pressure on the wafer surface no longer varies due to different etching chambers, thereby eliminating the problem of inconsistent etching amounts when different etching chambers perform chemical etching on wafers with oxide layers to be etched. Then, after chamber pretreatment, chemical etching is performed uniformly with etching pressure, hydrogen fluoride flow rate, and ammonia flow rate, ensuring process consistency. Moreover, no hardware configuration adjustment of the etching chamber is required. This means that the chemical vapor deposition method provided by this invention improves the consistency and stability of chemical etching processes between different etching chambers without adjusting the hardware configuration of the etching chamber. Attached Figure Description

[0018] Figure 1 This is a flowchart of the steps corresponding to an embodiment of the chemical vapor deposition method of the present invention; Figure 2 This is a schematic diagram illustrating the evolution of the fluorination state on the inner wall surface of the etching chamber in one embodiment of the chemical vapor etching method of the present invention; Figure 3 This is a comparison diagram of etching amount under different etching pressures before and after chamber pretreatment in an embodiment of the chemical vapor deposition method of the present invention; Figure 4 This is a graph showing the trend of etching amount before and after chamber pretreatment under an etching pressure of 49 mT in one embodiment of the chemical vapor etching method of the present invention. Detailed Implementation

[0019] Currently, the consistency and stability of chemical etching processes across different etching chambers still need to be improved.

[0020] Specifically, when using hydrogen fluoride and ammonia to perform chemical vapor etching on a wafer with a silicon oxide layer on its surface, the reactive gases hydrogen fluoride and ammonia react chemically with the silicon oxide layer on the wafer surface after entering the etching chamber.

[0021] The reaction process mainly includes the following two steps: In the first step, hydrogen fluoride reacts with silicon oxide in the presence of ammonia to produce silicon tetrafluoride and water. The chemical reaction formula is as follows: SiO2+4HF+4NH3→SiF4+2H2O+4NH3; In the second step, silicon tetrafluoride further reacts with hydrogen fluoride and ammonia to produce solid ammonium fluorosilicate, as shown in the following reaction formula: SiF4 + 2HF + 2NH3 → (NH4)2SiF6.

[0022] Solid ammonium fluorosilicate is deposited on the wafer surface and can be decomposed and sublimated by heating, thereby removing the silicon oxide layer through etching. This chemical vapor deposition (CVD) process is a purely chemical reaction. As an isotropic etching process, it does not require plasma participation and therefore does not cause plasma damage to the wafer surface. It also has a very high selectivity for silicon and has increasingly important applications in advanced semiconductor manufacturing processes, such as the removal of native oxide layers and specific oxide films on wafer surfaces.

[0023] Research has revealed that in actual production processes, significant differences in etching amounts can occur between different etching chambers when performing chemical etching under the same process conditions on wafers with the same oxide layer to be etched. This indicates an inconsistency in etching amounts between etching chambers. Furthermore, within the same etching chamber, the etching amount may exhibit a trend of drift as the cumulative chemical etching time increases. For example, for silicon oxide layers formed through atomic layer deposition (ALD), under relatively high etching pressure, the etching amount difference between different etching chambers can reach approximately 50%, severely impacting product yield and process repeatability.

[0024] The reason for this is that the material on the inner wall surface of the etching chamber typically includes alumina. During chemical etching, hydrogen fluoride and ammonia not only react with the oxide layer to be etched on the wafer surface, but also gradually react with the alumina on the inner wall surface of the etching chamber, forming a fluorinated layer containing aluminum ammonium fluoride. This fluorinated layer has both adsorption and release functions for hydrogen fluoride and ammonia. During chemical etching, the fluorinated layer captures hydrogen fluoride and ammonia from the gas phase, and after chemical etching stops or when process conditions change, it may release the adsorbed hydrogen fluoride and ammonia back into the gas phase, thus acting as a buffer for hydrogen fluoride and ammonia. Due to different usage histories, different etching chambers may have different thicknesses, densities, and degrees of fluorination of the fluorinated layer on their inner wall surfaces, resulting in differences in the adsorption and release capabilities of hydrogen fluoride and ammonia. This leads to inconsistencies in the effective partial pressure of hydrogen fluoride and effective partial pressure of ammonia on the wafer surface in different etching chambers, ultimately causing inconsistencies in the amount of etching.

[0025] Furthermore, as the number of wafers subjected to chemical etching in the same etching chamber accumulates, the fluoride layer gradually thickens and becomes denser. The adsorption and release of hydrogen fluoride and ammonia also gradually change, exhibiting a trend of etching amount drift over time. In particular, for silicon oxide layers formed by atomic layer deposition (ALD), the film is relatively porous, with numerous defects such as dangling bonds, hydroxyl groups, and nanopores on the microscopic surface, resulting in lower density than silicon oxide layers formed by thermal oxidation. During chemical etching, the diffusion of hydrogen fluoride and ammonia within the ALD silicon oxide layer has a more significant effect on controlling the etching rate. That is, chemical etching of ALD silicon oxide layers is more mass transfer controlled, making it more sensitive to changes in the effective partial pressure of hydrogen fluoride and ammonia. Under higher etching pressures, the inconsistency in etching amount between etching chambers and the trend of etching amount drift within the same etching chamber become more prominent.

[0026] To address the technical problem, this invention provides a chemical vapor deposition (CVD) etching method. Figure 1 This is a flowchart of the steps corresponding to an embodiment of the chemical vapor deposition method of the present invention.

[0027] Step S1: Before performing chemical etching, hydrogen fluoride and ammonia are introduced into the etching chamber for chamber pretreatment, so that the adsorption and desorption of hydrogen fluoride and ammonia on the inner wall surface of the etching chamber reach a dynamic equilibrium. The chamber pretreatment meets at least one of the following conditions: the pretreatment pressure is higher than the etching pressure used in chemical etching, the pretreatment hydrogen fluoride flow rate is higher than the hydrogen fluoride flow rate used in chemical etching, and the pretreatment ammonia flow rate is higher than the ammonia flow rate used in chemical etching. Step S2: After chamber pretreatment, chemical etching is performed on the wafer with the oxide layer to be etched on the surface under etching pressure, hydrogen fluoride flow rate and ammonia flow rate.

[0028] It should be noted that before chemical etching, hydrogen fluoride and ammonia are introduced into the etching chamber to achieve a dynamic equilibrium between the adsorption and desorption of hydrogen fluoride and ammonia on the inner wall surface of the etching chamber. Since the chamber pretreatment satisfies at least one of the following three conditions—pretreatment pressure higher than etching pressure, pretreatment hydrogen fluoride flow rate higher than hydrogen fluoride flow rate, and pretreatment ammonia flow rate higher than ammonia flow rate—that is, the chamber pretreatment supplies hydrogen fluoride and ammonia to the inner wall surface of the etching chamber under process conditions stronger than chemical etching, the inner wall surfaces of different etching chambers can be uniformly pushed to a dynamic equilibrium state of adsorption and desorption within a relatively short time. When the inner wall surfaces of different etching chambers are all in this dynamic equilibrium state, the adsorption of hydrogen fluoride and ammonia on the inner wall surfaces of each etching chamber tends to be consistent. The effective reactant partial pressure on the wafer surface no longer varies due to different etching chambers, thereby eliminating the problem of inconsistent etching amounts when different etching chambers perform chemical etching on wafers with oxide layers to be etched. Then, after chamber pretreatment, chemical etching is performed uniformly with etching pressure, hydrogen fluoride flow rate, and ammonia flow rate, ensuring process consistency. Moreover, no hardware configuration adjustment of the etching chamber is required. This means that the chemical vapor deposition method provided by this invention improves the consistency and stability of chemical etching processes between different etching chambers without adjusting the hardware configuration of the etching chamber.

[0029] To make the above-mentioned objects, features and advantages of the embodiments of the present invention more apparent and understandable, the following description is provided in conjunction with the accompanying drawings. Figures 1 to 4 Specific embodiments of the present invention will be described in detail below.

[0030] Step S1: Before performing chemical etching, hydrogen fluoride and ammonia are introduced into the etching chamber for chamber pretreatment, so that the adsorption and desorption of hydrogen fluoride and ammonia on the inner wall surface of the etching chamber reach a dynamic equilibrium. The chamber pretreatment meets at least one of the following conditions: the pretreatment pressure is higher than the etching pressure used in chemical etching, the pretreatment hydrogen fluoride flow rate is higher than the hydrogen fluoride flow rate used in chemical etching, and the pretreatment ammonia flow rate is higher than the ammonia flow rate used in chemical etching.

[0031] Specifically, by introducing hydrogen fluoride and ammonia into the etching chamber, the adsorption and desorption of hydrogen fluoride and ammonia on the inner wall surface of the etching chamber reach a dynamic equilibrium. Since the chamber pretreatment satisfies at least one of the following three conditions—pretreatment pressure higher than etching pressure, pretreatment hydrogen fluoride flow rate higher than hydrogen fluoride flow rate, and pretreatment ammonia flow rate higher than ammonia flow rate—that is, the chamber pretreatment supplies hydrogen fluoride and ammonia to the inner wall surface of the etching chamber under process conditions stronger than chemical etching, the inner wall surfaces of different etching chambers can be uniformly pushed to a dynamic equilibrium state of adsorption and desorption within a short time. When the inner wall surfaces of different etching chambers are all in this dynamic equilibrium state, the adsorption amount of hydrogen fluoride and ammonia on the inner wall surfaces of each etching chamber tends to be consistent, and the effective reactant partial pressure on the wafer surface no longer differs due to different etching chambers. This eliminates the problem of inconsistent etching amounts when performing chemical etching on wafers with oxide layers to be etched in different etching chambers.

[0032] Dynamic equilibrium refers to the point during the pretreatment process where the adsorption and desorption rates of hydrogen fluoride and ammonia on the inner wall surface of the etching chamber tend to be equal, and the amount of hydrogen fluoride and ammonia adsorbed on the inner wall surface no longer changes significantly over time. When this dynamic equilibrium is reached, the amount of hydrogen fluoride and ammonia adsorbed on the inner wall surface of the etching chamber tends to a stable value. The amount of hydrogen fluoride and ammonia released from the inner wall surface back into the internal space of the etching chamber per unit time is approximately equal to the amount of hydrogen fluoride and ammonia adsorbed from the internal space of the etching chamber by the inner wall surface. The net exchange of hydrogen fluoride and ammonia between the inner wall surface of the etching chamber and the internal space of the etching chamber tends to zero, and the amount of hydrogen fluoride and ammonia actually available in the internal space of the etching chamber for participating in the chemical etching reaction on the wafer surface also tends to stabilize.

[0033] Because the chamber pretreatment satisfies at least one of the following three conditions: pretreatment pressure higher than etching pressure, pretreatment hydrogen fluoride flow rate higher than hydrogen fluoride flow rate, and pretreatment ammonia flow rate higher than ammonia flow rate, meaning that at least one of the three process parameters in chamber pretreatment is higher than the corresponding process parameters for chemical etching, it implies that the number of hydrogen fluoride and ammonia molecules contacting and reacting with the inner wall surface of the etching chamber per unit time is significantly increased compared to normal chemical etching conditions. This increases the reaction rate and degree between hydrogen fluoride and ammonia and the inner wall surface material, thereby enabling the inner wall surface of the etching chamber to complete the transformation from its initial state to a dynamic equilibrium state of adsorption and desorption in a shorter time with a reaction driving force higher than that of normal chemical etching. For different etching chambers, even if their inner wall surfaces have different initial states before chamber pretreatment, after the chamber pretreatment step, the inner wall surfaces of all etching chambers are uniformly pushed to a dynamic equilibrium state of adsorption and desorption.

[0034] In this embodiment, the chamber pretreatment step includes: firstly, introducing hydrogen fluoride and ammonia into the etching chamber at a first pretreatment pressure, wherein the first pretreatment pressure is higher than the etching pressure, and the flow rate of pretreatment hydrogen fluoride introduced into the etching chamber at the first pretreatment pressure is higher than the flow rate of hydrogen fluoride used in chemical etching, and the flow rate of pretreatment ammonia introduced into the etching chamber at the first pretreatment pressure is higher than the flow rate of ammonia used in chemical etching; then, introducing hydrogen fluoride and ammonia into the etching chamber at a second pretreatment pressure, wherein the second pretreatment pressure is lower than the first pretreatment pressure, and the flow rate of pretreatment hydrogen fluoride introduced into the etching chamber at the second pretreatment pressure is equal to the flow rate of hydrogen fluoride used in chemical etching, and the flow rate of pretreatment ammonia introduced into the etching chamber at the second pretreatment pressure is equal to the flow rate of ammonia used in chemical etching.

[0035] It should be noted that the chamber pretreatment is divided into two sequential stages. In the first stage, a pretreatment pressure higher than the etching pressure is used, along with pretreatment hydrogen fluoride and ammonia flow rates higher than those used in chemical etching. This provides a high concentration of hydrogen fluoride and ammonia to the inner wall surface of the etching chamber, accelerating the reaction rate between the hydrogen fluoride and ammonia and the material on the inner wall surface. This allows the fluorination process on the inner wall surface to proceed at a rate far exceeding that under normal chemical etching conditions, propelling the inner wall surface past the initial fluorination stage in a shorter time and rapidly approaching the dynamic equilibrium of adsorption and desorption.

[0036] It should also be noted that, after the inner wall surface has been rapidly advanced to near dynamic equilibrium in the first stage, in the second stage, hydrogen fluoride and ammonia are continued to be introduced into the etching chamber at a second pretreatment pressure lower than the first pretreatment pressure. The flow rates of pretreatment hydrogen fluoride and pretreatment ammonia introduced at the second pretreatment pressure are equal to those used in chemical etching. This provides a more moderate pressure condition compared to the first stage and is equal to the gas flow rate conditions used in chemical etching. This further adjusts and stabilizes the state formed on the inner wall surface in the first stage, making the dynamic balance of adsorption and desorption of hydrogen fluoride and ammonia on the inner wall surface more complete and stable, thus providing a stable chamber environment for subsequent formal chemical etching.

[0037] Specifically, the first pretreatment pressure is higher than the etching pressure, which is used to increase the gas phase partial pressure of hydrogen fluoride and ammonia under pressure conditions higher than those of chemical etching, thereby increasing the frequency and energy of collisions between hydrogen fluoride and ammonia molecules and the inner wall surface, thus accelerating the fluorination reaction kinetics process on the inner wall surface and shortening the time required to reach the dynamic equilibrium of adsorption and desorption.

[0038] Under the first pretreatment pressure, the pretreatment hydrogen fluoride flow rate is higher than that used in chemical etching, and the pretreatment ammonia flow rate is also higher than that used in chemical etching. This allows for a continuous supply of sufficient hydrogen fluoride and ammonia to the etching chamber with a larger gas flow rate. As a result, under the high pressure provided by the first pretreatment pressure, the inner wall surface is always in a state of sufficient supply of high-concentration reaction gases, and the rate of fluorination reaction will not be limited due to insufficient supply of reaction gases, thus further improving the effect of chamber pretreatment.

[0039] In the second stage, the second pretreatment pressure is lower than the first pretreatment pressure. This is to avoid excessive fluorination or uneven fluorination layer structure that may result from the inner wall surface being under extreme high pressure for a long time. At the same time, it allows the inner wall surface to complete the establishment and consolidation of dynamic equilibrium under a pressure environment that is relatively close to that of subsequent chemical etching. This makes the dynamic equilibrium of adsorption and desorption established by the chamber pretreatment more suitable for the process conditions of subsequent chemical etching, reducing the risk of dynamic equilibrium being disturbed due to sudden changes in process conditions.

[0040] Under the second pretreatment pressure, the pretreatment hydrogen fluoride flow rate and pretreatment ammonia flow rate are set to be consistent with those used in chemical etching. This ensures that the final stage of chamber pretreatment is identical to the formal chemical etching in terms of process pressure and gas flow rate. This guarantees that the adsorption and desorption dynamic equilibrium established on the inner wall surface under these identical process conditions can be seamlessly connected to the subsequent chemical etching, further reducing disturbances introduced by changes in process conditions and improving the stability of the chemical etching process.

[0041] It should also be noted that under the second pretreatment pressure, the pretreatment hydrogen fluoride flow rate is equal to the hydrogen fluoride flow rate used in chemical etching, and the pretreatment ammonia flow rate is equal to the ammonia flow rate used in chemical etching. This ensures that the inner wall surface can still receive a sufficient supply of hydrogen fluoride and ammonia to achieve a stable dynamic balance. At the same time, the pretreatment hydrogen fluoride flow rate and the pretreatment ammonia flow rate help to remove the byproducts generated during the chamber pretreatment process, maintaining the purity and stability of the atmosphere inside the etching chamber.

[0042] In this embodiment, the second pretreatment pressure is equal to the etching pressure.

[0043] Specifically, when the second pretreatment pressure equals the etching pressure, the second stage of chamber pretreatment maintains the same process pressure as the subsequent chemical etching. This ensures that the pressure environment of the inner wall surface of the etching chamber during the second stage of chamber pretreatment is exactly the same as that of the subsequent chemical etching. The dynamic equilibrium of adsorption and desorption of hydrogen fluoride and ammonia established on the inner wall surface under the second pretreatment pressure directly corresponds to the pressure conditions used in chemical etching. When the subsequent chemical etching is performed under the same etching pressure, since the pressure conditions do not change, the dynamic equilibrium state of the inner wall surface will not be disturbed by pressure changes. This maximizes the maintenance and continuation of the dynamic equilibrium state established by the chamber pretreatment during chemical etching, further improving the stability of the chemical etching process.

[0044] In this embodiment, the material of the inner wall surface of the etching chamber includes aluminum oxide.

[0045] It should be noted that alumina is a commonly used material for etching the inner walls of chambers, possessing excellent corrosion resistance and mechanical strength. The chemical vapor deposition (CVD) etching method provided in this embodiment is directly applicable to etching chambers with inner wall surface materials including alumina, without requiring special coating treatment of the inner wall surface or replacement of the chamber material, thus exhibiting good process compatibility.

[0046] In this embodiment, during the step of introducing hydrogen fluoride and ammonia into the etching chamber for chamber pretreatment, the hydrogen fluoride and ammonia react with the alumina on the inner wall surface to form a fluorinated layer on the inner wall surface of the etching chamber.

[0047] Specifically, during the chamber pretreatment process, after hydrogen fluoride and ammonia are introduced into the etching chamber, the hydrogen fluoride and ammonia react with the alumina to generate compounds containing aluminum and fluorine, thereby forming a fluorinated layer on the inner wall surface.

[0048] It should be noted that the fluorinated layer is a direct product of the reaction between hydrogen fluoride and ammonia with alumina during the chamber pretreatment process. It is also the material basis for achieving the dynamic equilibrium of adsorption and desorption of hydrogen fluoride and ammonia on the inner wall surface. It is the formation of the fluorinated layer that enables the inner wall surface of the etching chamber to adsorb and release hydrogen fluoride and ammonia. When the fluorinated layer reaches the dynamic equilibrium of adsorption and desorption, the amount of hydrogen fluoride and ammonia adsorbed on the inner wall surface tends to be saturated and the net change tends to be zero, and the partial pressure of the effective reactants is stabilized.

[0049] In this embodiment, during the chamber pretreatment process, hydrogen fluoride and ammonia react with alumina on the inner wall surface. The reaction process can be represented as follows: Al₂O₃ + HF + NH₃ → (NH₄) X AlF Y + H2O Among them, (NH4) XAlF Y This refers to aluminum ammonium fluoride salts. The specific stoichiometric ratio of aluminum ammonium fluoride salts varies depending on the reaction conditions. For example, it may include one or more of (NH4)3AlF6, (NH4)2AlF5, and NH4AlF4.

[0050] Aluminum ammonium fluoride is the main component of the fluorinated layer. It is precisely because aluminum ammonium fluoride has both adsorption and desorption properties for hydrogen fluoride and ammonia that the fluorinated layer can act as a buffer for hydrogen fluoride and ammonia. When the adsorption and desorption of hydrogen fluoride and ammonia on the inner wall surface reach a dynamic equilibrium, the amount of hydrogen fluoride and ammonia released from the inner wall surface back into the etching chamber per unit time is basically equal to the amount of hydrogen fluoride and ammonia adsorbed from the inner wall surface. The amount of hydrogen fluoride and ammonia that can actually participate in the chemical etching reaction on the wafer surface in the etching chamber tends to stabilize.

[0051] In this embodiment, the material of the fluorinated layer includes aluminum ammonium fluoride.

[0052] Specifically, aluminum ammonium fluoride is a fluorine-containing compound formed by the reaction of aluminum oxide in an atmosphere of hydrogen fluoride and ammonia. Aluminum ammonium fluoride exhibits excellent adsorption and desorption properties for hydrogen fluoride and ammonia, making it a key chemical substance for establishing a dynamic equilibrium between the adsorption and desorption of hydrogen fluoride and ammonia on the inner wall surface.

[0053] During the chamber pretreatment stage, hydrogen fluoride and ammonia react with alumina on the inner wall surface. The aluminum in the alumina combines with the fluorine in the hydrogen fluoride and the ammonium in the ammonia to form aluminum ammonium fluoride. The formation rate and content of aluminum ammonium fluoride depend on the pretreatment pressure, the flow rate of hydrogen fluoride, and the flow rate of ammonia. Higher pretreatment pressure and larger gas flow rates (i.e., the flow rates of hydrogen fluoride and ammonia) are conducive to the rapid formation and accumulation of aluminum ammonium fluoride, thereby accelerating the process of reaching a dynamic equilibrium between adsorption and desorption on the inner wall surface.

[0054] In this embodiment, during the chamber pretreatment step, a silicon oxide wafer is placed in the etching chamber as a carrier wafer so that hydrogen fluoride and ammonia gas can chemically etch the carrier wafer.

[0055] It should be noted that during the chamber pretreatment process, the silicon oxide wafer is placed in the etching chamber as a carrier wafer. On the one hand, the introduced hydrogen fluoride and ammonia gas participate in the fluorination reaction on the inner wall surface while also chemically etching the silicon oxide on the carrier wafer surface. This etching process consumes some hydrogen fluoride and ammonia gas, producing reaction products including silicon tetrafluoride, water, and ammonium fluorosilicate. These byproducts diffuse within the etching chamber and may come into contact with the inner wall surface, participating in the formation and regulation of the fluorinated layer on the inner wall surface. This makes the chamber pretreatment process closer to the actual chemical etching process in terms of the reaction system, thus making the dynamic equilibrium of adsorption and desorption of hydrogen fluoride and ammonia gas on the inner wall surface established by the chamber pretreatment more consistent with the process state of subsequent actual chemical etching. On the other hand, the carrier wafer is etched during the chamber pretreatment process, and as a consumable of silicon oxide, it can more realistically reflect the chamber atmosphere environment in the presence of the wafer during subsequent chemical etching compared to the chamber pretreatment of an empty cavity. This helps the dynamic equilibrium state of the inner wall surface to adapt to actual production requirements more quickly.

[0056] In this embodiment, the number of carrier wafers etched under the first pretreatment pressure is greater than the number of carrier wafers etched under the second pretreatment pressure.

[0057] Under the first pretreatment pressure, since the pressure is higher than the etching pressure, and the flow rates of pretreatment hydrogen fluoride and ammonia are both higher than those used in chemical etching, the chemical etching rate of hydrogen fluoride and ammonia on the carrier wafer is higher. Therefore, a larger number of carrier wafers are etched at this pressure, resulting in sufficient etching byproducts in the initial stage of the chamber pretreatment. These byproducts positively contribute to promoting and regulating the rapid formation of the fluorinated layer on the inner wall surface. Under the second pretreatment pressure, which is lower than the first, the chemical etching rate of hydrogen fluoride and ammonia on the carrier wafer decreases accordingly. At this pressure, a smaller number of carrier wafers are etched, primarily to maintain the reaction atmosphere within the etching chamber and further stabilize the fluorinated layer established under the first pretreatment pressure, without generating a large amount of etching byproducts.

[0058] In a specific example, the first pretreatment pressure is 120 mT (milliTorr), the flow rate of pretreatment hydrogen fluoride introduced under the first pretreatment pressure is 120 standard milliliters per minute, the flow rate of pretreatment ammonia introduced under the first pretreatment pressure is 120 standard milliliters per minute, and the number of carrier wafers etched under the first pretreatment pressure is 300 pairs.

[0059] The second pretreatment pressure is 40 mT, which is equal to the etching pressure. The flow rate of pretreatment hydrogen fluoride introduced under the second pretreatment pressure is 40 standard milliliters per minute. The flow rate of pretreatment ammonia introduced under the second pretreatment pressure is 40 standard milliliters per minute. The number of carrier wafers etched under the second pretreatment pressure is 100 pairs.

[0060] In this specific example, the first pretreatment pressure of 120 mT is significantly higher than the etching pressure of 40 mT. Simultaneously, reactive gases are supplied to the etching chamber at a flow rate of 120 standard milliliters per minute (SPM) of hydrogen fluoride and 120 standard milliliters per minute (SPM) of ammonia. This allows for a rapid reaction between the hydrogen fluoride and ammonia and the alumina on the inner wall surface, facilitating the rapid establishment of the fluoride layer on the inner wall surface during the etching of 300 pairs of carrier wafers. Subsequently, the second pretreatment pressure is reduced to 40 mTorr, equal to the etching pressure of the formal chemical etching, while maintaining a hydrogen fluoride flow rate of 40 SPM and an ammonia flow rate of 40 SPM. During the etching of 100 pairs of carrier wafers, the inner wall surface achieves dynamic equilibrium consolidation and stabilization under normal etching pressure and normal gas flow rate conditions.

[0061] In this embodiment, during the process of introducing hydrogen fluoride and ammonia into the etching chamber under the first pretreatment pressure and during the process of introducing hydrogen fluoride and ammonia into the etching chamber under the second pretreatment pressure, an inert gas is also introduced into the etching chamber.

[0062] While hydrogen fluoride and ammonia are introduced into the etching chamber under the first and second pretreatment pressures, an inert gas is also introduced. The inert gas does not participate in the chemical etching reaction, but it can dilute the hydrogen fluoride and ammonia, making their spatial distribution within the etching chamber more uniform. This results in a more consistent concentration of hydrogen fluoride and ammonia in contact with different areas of the inner wall surface, which helps to form a fluorinated layer of relatively uniform thickness and composition on the inner wall surface. Consequently, the dynamic balance of adsorption and desorption of hydrogen fluoride and ammonia on different areas of the inner wall surface tends to be more uniform in space. At the same time, the introduction of inert gas also helps to promote gas flow within the etching chamber, carrying away local byproducts from the inner wall surface and expelling them from the etching chamber. This prevents excessive accumulation of byproducts on the inner wall surface from affecting the quality of the fluorinated layer and the dynamic balance of adsorption and desorption.

[0063] In this embodiment, the inert gas is argon.

[0064] Argon is a commonly used inert gas with stable chemical properties and does not react with hydrogen fluoride, ammonia, or the materials on the inner wall surface.

[0065] Step S2: After chamber pretreatment, chemical etching is performed on the wafer with the oxide layer to be etched on the surface under etching pressure, hydrogen fluoride flow rate and ammonia flow rate.

[0066] After the chamber pretreatment has brought the adsorption and desorption of hydrogen fluoride and ammonia on the inner wall surface of the etching chamber to a dynamic equilibrium, the actual partial pressures of hydrogen fluoride and ammonia within the etching chamber are stable. At this point, a wafer with the oxide layer to be etched is fed into the etching chamber, or a wafer already in the etching chamber is used. Chemical etching is performed under normal etching pressure, hydrogen fluoride flow rate, and ammonia flow rate. The hydrogen fluoride and ammonia react chemically with the oxide layer to be etched on the wafer surface. The reaction process mainly includes the following two steps: In the first step, hydrogen fluoride reacts with silicon oxide in the presence of ammonia to produce silicon tetrafluoride and water. The reaction equation is as follows: SiO2+4HF+4NH3→SiF4+2H2O+4NH3; In the second step, silicon tetrafluoride further reacts with hydrogen fluoride and ammonia to produce solid ammonium fluorosilicate, as shown in the following reaction formula: SiF4 + 2HF + 2NH3 → (NH4)2SiF6.

[0067] Solid ammonium fluorosilicate is deposited on the wafer surface, and can be decomposed and sublimated by heating to complete the chemical etching of the oxide layer to be etched. Since the chamber pretreatment has brought the adsorption and desorption of hydrogen fluoride and ammonia on the inner wall surface to a dynamic equilibrium, during the chemical etching process, the inner wall surface will not produce uncontrollable net adsorption or net release of hydrogen fluoride and ammonia in the gas phase due to uneven fluorination. The effective partial pressure of hydrogen fluoride and effective partial pressure of ammonia on the wafer surface remain stable, and the inner wall surface state is consistent between different etching chambers. The effective reactant partial pressure on the wafer surface also tends to be consistent, thus ensuring the consistency and repeatability of the etching amount of different batches of wafers in different etching chambers.

[0068] In a specific example, such as Figure 3 As shown, the etching pressure used in the chemical etching process is 40 mT, the flow rate of hydrogen fluoride is 40 standard milliliters per minute, the flow rate of ammonia is 40 standard milliliters per minute, and argon gas at a flow rate of 11 standard milliliters per minute is simultaneously introduced into the etching chamber as an inert gas. Under these chemical etching conditions, the silicon oxide layer formed by atomic layer deposition is subjected to chemical vapor deposition.

[0069] Without chamber pretreatment, the etching amount of different etching chambers is basically consistent when the etching pressure is 40 mTorr. However, when the etching pressure is increased to 49 mTorr, the difference in etching amount between different etching chambers can reach about 50%, indicating a significant problem of inconsistent etching amount.

[0070] In cases where chamber pretreatment has been performed, such as Figure 4As shown, after processing 300 pairs of carrier wafers using the aforementioned first pretreatment pressure of 120 mT, hydrogen fluoride flow rate of 120 standard ml / min, and ammonia flow rate of 120 standard ml / min, followed by a second pretreatment pressure of 40 mT, hydrogen fluoride flow rate of 40 standard ml / min, and ammonia flow rate of 40 standard ml / min for 100 pairs of carrier wafers, the difference in etching amount between different etching chambers was significantly reduced to a basically consistent level at an etching pressure of 49 mTorr. Furthermore, the etching amount of chemical etching decreased from approximately 12.8 nm before chamber pretreatment to approximately 8.7 nm after chamber pretreatment, remaining stable for several consecutive days with minimal diurnal fluctuations. This means that the chamber pretreatment in the chemical vapor deposition (CVD) etching method provided by this invention can effectively solve the problem of inconsistent etching amounts between different etching chambers in CVD etching.

[0071] In this embodiment, the oxide layer to be etched is a silicon oxide layer formed by atomic layer deposition.

[0072] Specifically, silicon oxide layers formed by atomic layer deposition (ALD) have a lower density than those formed by thermal oxidation, exhibiting more defects, dangling bonds, and nanopores in their microstructure. Therefore, the chemical etching process of ALD is more dependent on the diffusion rate of hydrogen fluoride and ammonia within the oxide layer compared to thermal oxidation. At higher etching pressures, the difference in fluorination state on the inner wall surfaces of different etching chambers amplifies the impact on the amount of hydrogen fluoride and ammonia actually available for the wafer surface chemical etching reaction within the etching chamber. Silicon oxide layers formed by ALD, due to their mass transfer-controlled chemical etching characteristics, are particularly sensitive to changes in the amounts of hydrogen fluoride and ammonia. Therefore, chamber pretreatment significantly improves the consistency and stability of chemical etching. The chemical vapor deposition (CVD) method of this invention is applicable to silicon oxide layers formed by ALD and effectively solves the problems of inconsistent etching amounts and trend drift under higher etching pressures.

[0073] Step S3: After the chemical etching is completed and before the chamber pretreatment of the next batch of wafers, the etching method further includes: introducing hydrogen fluoride and ammonia into the etching chamber for idle maintenance, maintaining the dynamic balance of adsorption and desorption of hydrogen fluoride and ammonia on the inner wall surface of the etching chamber.

[0074] Specifically, idle maintenance is a step performed during the idle period after the chemical etching of the current batch is completed and before the chamber preprocessing of the next batch of wafers.

[0075] In actual production, there may be a certain interval between the completion of the current batch of chemical etching and the entry of the next batch of wafers into the chamber for pretreatment. During this period, hydrogen fluoride and ammonia are no longer introduced into the etching chamber, and the etching chamber may be in a vacuum or purification state. During this idle period, the fluoride layer on the inner wall surface may slowly decompose or degrade due to the lack of a hydrogen fluoride and ammonia atmosphere. For example, some aluminum ammonium fluoride salts may gradually decompose, causing the dynamic equilibrium of adsorption and desorption of hydrogen fluoride and ammonia on the fluoride layer to gradually degrade from a stable state to an unstable state. If the next batch of wafers is directly subjected to chamber pretreatment and chemical etching in this degraded state, the degradation of the dynamic equilibrium on the inner wall surface may lead to a trend of etching amount drift. This embodiment maintains idle time by introducing hydrogen fluoride and ammonia into the etching chamber during idle periods. During the idle period, the dynamic balance of adsorption and desorption of hydrogen fluoride and ammonia on the inner wall surface of the etching chamber is continuously maintained. This ensures that when the next batch of wafers enters the chamber for pretreatment, the inner wall surface is still in a dynamic balance of adsorption and desorption. As a result, the chamber pretreatment can restore the inner wall surface to a uniform dynamic balance, further ensuring the long-term process stability of multi-batch continuous chemical etching.

[0076] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A chemical vapor deposition method, characterized in that, include: Before performing chemical etching, hydrogen fluoride and ammonia are introduced into the etching chamber for chamber pretreatment to achieve a dynamic equilibrium between the adsorption and desorption of hydrogen fluoride and ammonia on the inner wall surface of the etching chamber. The material of the inner wall surface of the etching chamber includes alumina. During the chamber pretreatment step, the hydrogen fluoride and ammonia react with the alumina on the inner wall surface to form a fluorinated layer. The material of the fluorinated layer includes aluminum ammonium fluoride. The chamber pretreatment step includes: firstly, introducing hydrogen fluoride and ammonia into the etching chamber at a first pretreatment pressure higher than the etching pressure. The process involves introducing hydrogen fluoride into the etching chamber at a first pretreatment pressure, where the flow rate of pretreatment hydrogen fluoride is higher than that used in chemical etching, and the flow rate of pretreatment ammonia into the etching chamber at the first pretreatment pressure is higher than that used in chemical etching; then, hydrogen fluoride and ammonia are introduced into the etching chamber at a second pretreatment pressure, where the second pretreatment pressure is lower than the first pretreatment pressure, and the flow rate of pretreatment hydrogen fluoride into the etching chamber at the second pretreatment pressure is equal to that used in chemical etching, and the flow rate of pretreatment ammonia into the etching chamber at the second pretreatment pressure is equal to that used in chemical etching. After the chamber pretreatment is performed, the chemical etching is carried out on the wafer with the oxide layer to be etched on the surface under the etching pressure, the hydrogen fluoride flow rate and the ammonia flow rate. After the chemical etching is completed and before the chamber pretreatment of the next batch of wafers, hydrogen fluoride and ammonia are introduced into the etching chamber to maintain an idle state and maintain a dynamic balance between the adsorption and desorption of hydrogen fluoride and ammonia on the inner wall surface of the etching chamber.

2. The chemical vapor deposition method as described in claim 1, characterized in that, The second pretreatment pressure is equal to the etching pressure.

3. The chemical vapor deposition method as described in claim 1, characterized in that, During the process of introducing hydrogen fluoride and ammonia into the etching chamber under the first pretreatment pressure and during the process of introducing hydrogen fluoride and ammonia into the etching chamber under the second pretreatment pressure, an inert gas is also introduced into the etching chamber.

4. The chemical vapor deposition method as described in claim 3, characterized in that, The inert gas is argon.

5. The chemical vapor deposition method as described in claim 1, characterized in that, The oxide layer to be etched is a silicon oxide layer formed by atomic layer deposition.

6. The chemical vapor deposition method as described in claim 1, characterized in that, In the chamber pretreatment step, a silicon oxide wafer is placed in the etching chamber as a carrier wafer so that the hydrogen fluoride and the ammonia gas can chemically etch the carrier wafer.

7. The chemical vapor deposition method as described in claim 6, characterized in that, The number of carrier wafers etched under the first pretreatment pressure is greater than the number of carrier wafers etched under the second pretreatment pressure.

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