Wafer surface treatment method
Through the combination of wet oxidation, cleaning and in-situ plasma cleaning, the oxides on the wafer surface are completely removed, which solves the problems of difficulty in operation and insignificant effects in the prior art, ensuring that the wafer surface has no oxides before MOCVD, and ensuring the deposition quality.
Patent Information
- Application Number
- CN202510420110.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-03
- Publication Date
- 2025-07-04
AI Technical Summary
The prior art has problems of operation difficulties and insignificant effects when removing native oxides and free impurities on the wafer surface, especially when the wafer surface is reoxidized or the heating temperature is not suitable.
Wet oxidation and wet cleaning are combined to form stable oxides, and then unstable oxides are removed by in-situ plasma cleaning and heating, and finally surface quality inspection ensures thorough cleaning.
The wafer surface is exposed to air for several hours without new oxide formation, ensuring the deposition quality of chemical vapor deposition.
Smart Images
Figure CN120261268A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of semiconductor technology, and particularly to a method for wafer surface treatment. Background Art
[0002] Before the growth of wafers by Metal-Organic Chemical Vapor Deposition (MOCVD), it is generally necessary to remove the native oxides and some free impurities on the surface to ensure the quality of chemical vapor deposition. Taking GaAs (gallium arsenide) wafers as an example, it is necessary to remove the native oxides such as GaO (gallium oxide), Ga2O3 (gallium trioxide), As2O3 (arsenic trioxide) or As2O5 (arsenic pentoxide) on the surface and some free Ga and As atoms.
[0003] Currently, there are some problems with the methods for removing native oxides on the wafer surface in the industry. For example, when using wet cleaning to remove them, the wafer surface will be re-oxidized immediately after cleaning, so it is necessary to strictly control the waiting time, but the actual operation is rather difficult. Or, when using in-situ cleaning to remove them, the native oxides on the wafer surface will be decomposed and volatilized by heating, but the heating temperatures for the decomposition and volatilization of these native oxides are different, and the heating temperature for the decomposition and volatilization of some native oxides is too high, which also poses certain difficulties in operation, so the effect is not obvious. Summary of the Invention
[0004] The purpose of the embodiments of this application is to provide a method for wafer surface treatment, which has obvious effects in removing native oxides and free impurities on the wafer surface and is easy to operate.
[0005] On the one hand, the embodiments of this application provide a method for wafer surface treatment. The wafer includes at least a first material and a second material. After the first material is oxidized, a first oxide will be formed, and after the second material is oxidized, a second oxide will be formed. The first oxide is an oxide of a certain valence state of the first material or a composition containing multiple valence state homologous oxides of the first material, and the second oxide is an oxide of a certain valence state of the second material or a composition containing multiple valence state homologous oxides of the second material. The method includes:
[0006] Wet-oxidize the wafer surface to form a first oxide and a second oxide;
[0007] Wet-clean the wafer surface to remove the unstable components in the first oxide and the second oxide that are oxidized on the wafer surface, and only the stable components in the second oxide are left on the wafer surface;
[0008] Perform surface quality inspection on the wafer surface after wet cleaning;
[0009] Perform in-situ plasma cleaning on the wafer with qualified surface quality inspection results, and heat the wafer to remove the second oxide on the wafer surface.
[0010] Optionally, wet-oxidize the wafer surface to form a first oxide and a second oxide, including:
[0011] Place the wafer in a strong oxidant and let it stand for 20 to 30 minutes to generate a first oxide and a second oxide on the wafer surface.
[0012] Optionally, wet-clean the wafer surface to remove the unstable components in the first oxide and the second oxide that are oxidized on the wafer surface, and only the stable components in the second oxide remain on the wafer surface, including:
[0013] Clean the wafer with diluted hydrofluoric acid to remove the unstable components in the first oxide and the second oxide, and only the stable components in the second oxide remain.
[0014] Optionally, perform a surface quality inspection on the wafer surface after wet cleaning, including:
[0015] Detect oxide particles with a preset diameter on the wafer surface. When the number of detected oxide particles is less than the preset number, it is determined that the wafer surface meets the preset surface quality requirements.
[0016] Optionally, perform a surface quality inspection on the wafer surface after wet cleaning, including:
[0017] Scan the wafer surface. When a stepped platform is detected on the wafer surface and the height difference between adjacent steps is the height of a single-layer oxide lattice, and the root mean square roughness of the wafer surface meets the preset roughness, it is determined that the wafer surface meets the preset surface quality requirements.
[0018] Optionally, perform in-situ plasma cleaning on the wafer with qualified surface quality inspection and heat the wafer to remove the second oxide on the wafer surface, including:
[0019] Perform in-situ cleaning on the wafer with a mixed gas in a plasma cleaning chamber, and at the same time heat the wafer at a preset temperature to cause a chemical reaction between the mixed gas and the second oxide on the wafer surface to remove the second oxide.
[0020] Optionally, perform in-situ cleaning on the wafer with a mixed gas in a plasma cleaning chamber, and at the same time heat the wafer at a preset temperature to cause a chemical reaction between the mixed gas and the second oxide on the wafer surface to remove the second oxide, including:
[0021] Use NH3 and NF3 with a gas flow ratio of 1:4 to 1:5 or 4:1 to 5:1 as the mixed gas, and the preset temperature is 150°C to 200°C.
[0022] Optionally, NH3 and NF3 with a gas flow ratio of 1:4 to 1:5 or 4:1 to 5:1 are used as the mixed gas, and the preset temperature is 150°C to 200°C, including:
[0023] The mixed gas further includes an inert gas or hydrogen.
[0024] Optionally, the wafer with qualified surface quality is subjected to in-situ plasma cleaning, and the wafer is heated to remove the second oxide on the wafer surface. After that, the method further includes:
[0025] The wafer surface is detected a second time. When the diffraction image on the wafer surface is a dot lattice image, it is determined that the surface quality of the wafer is qualified.
[0026] In the method for wafer surface treatment provided by the embodiment of the present application, the wafer at least includes a first material and a second material. After the first material is oxidized, a first oxide is formed, and after the second material is oxidized, a second oxide is formed. The first oxide is an oxide of one valence state of the first material or a composition of multiple valence state homologous oxides containing the first material, and the second oxide is an oxide of one valence state of the second material or a composition of multiple valence state homologous oxides containing the second material; the method includes: wet-oxidizing the wafer surface to form the first oxide and the second oxide; wet-cleaning the wafer surface to remove the unstable components of the first oxide and the second oxide oxidized on the wafer surface, and only the stable components of the second oxide are left on the wafer surface; performing surface quality detection on the wafer surface after wet-cleaning; performing in-situ plasma cleaning on the wafer with qualified surface quality detection, and heating the wafer to remove the second oxide on the wafer surface. By combining wet oxidation, wet cleaning, and in-situ plasma cleaning, the oxides on the wafer surface can be effectively and thoroughly removed. After wet cleaning, the wafer surface can be exposed to the air for at least several hours without generating new oxides, so that the wafer surface can reach a state without oxides before MOCVD growth, ensuring the cleanliness of the wafer surface and thus ensuring the deposition quality of subsequent chemical vapor deposition on the wafer. Description of the Drawings
[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required to be used in the embodiments of the present application. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.
[0028] Figure 1 It is a flowchart of the method for wafer surface treatment provided in this embodiment;
[0029] Figure 2It is an AFM image of the wafer surface after multiple wet cleanings by the wafer surface treatment method provided in this embodiment;
[0030] Figure 3 It is a structural diagram of the wafer after wet cleaning by the wafer surface treatment method provided in this embodiment. Detailed implementation manners
[0031] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application.
[0032] In the description of the present application, it should be noted that the orientation or positional relationship indicated by terms such as "inside", "outside", etc. is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this application is usually placed when in use. It is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present application. In addition, terms such as "first", "second", etc. are only used for distinguishing descriptions, and cannot be understood as indicating or implying relative importance.
[0033] It should also be noted that unless otherwise clearly specified and limited, the terms "set", "connect" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific situations.
[0034] Currently, there are mainly several methods for cleaning the wafer surface in the industry:
[0035] First, wet cleaning, and solutions such as HF, HCL, NH4OH, etc. can be used. However, the wafer surface will be re-oxidized immediately after wet cleaning, so the waiting time needs to be strictly controlled, generally 15 minutes to 30 minutes. However, the loading and evacuation time of MOCVD generally far exceeds 30 minutes, so the actual operation is relatively difficult.
[0036] Second, in-situ cleaning, which can be heating or heating in a hydrogen atmosphere. When the heating exceeds 450 °C, As2O3 will decompose and volatilize, but Ga2O3 requires a high temperature of more than 1000 °C to decompose and volatilize, so the effect is not obvious either.
[0037] In view of this, to solve the above problems, please refer to Figure 1As shown in the figure, an embodiment of the present application provides a method for wafer surface treatment, which is mainly applied before chemical vapor deposition of the wafer. The wafer includes at least a first material and a second material. After the first material is oxidized, a first oxide is formed, and after the second material is oxidized, a second oxide is formed. The first oxide is an oxide of a valence state of the first material or a composition of multiple valence state homologous oxides containing the first material, and the second oxide is an oxide of a valence state of the second material or a composition of multiple valence state homologous oxides containing the second material. Taking a GaAs wafer as an example, the first material is Ga, the second material is As. After the first material Ga is oxidized, GaO and Ga2O3 are formed, and after the second material As is oxidized, As2O3 and As2O5 are formed. The method includes:
[0038] Step 100: Wet-oxidize the wafer surface to form a first oxide and a second oxide.
[0039] When specifically applied to a GaAs wafer, the wafer is left standing in a strong oxidant such as hydrogen peroxide for 20 to 30 minutes to ensure that the GaAs layer on the surface of the wafer and the free Ga and As on the wafer surface are all oxidized to form GaO 、 Ga2O3, As2O3, and As2O5. Among them, the first oxide contains GaO and Ga2O3, and the second oxide contains As2O3 and As2O5.
[0040] Step 101: Wet-clean the wafer surface to remove the unstable components in the first oxide and the second oxide oxidized on the wafer surface, and only the stable components in the second oxide are left on the wafer surface.
[0041] When specifically applied to a GaAs wafer, the wafer is cleaned with diluted hydrofluoric acid to remove GaO, Ga2O3, and As2O5 in the second oxide on the wafer surface, and only As2O3 remains on the wafer surface.
[0042] When the surface of the wafer after wet cleaning is exposed to air, the second oxide (As2O3) on the surface will form a very thin film, which blocks the formation of the first oxide. This is because the hydrofluoric acid in step 101 will react with Ga to remove all the Ga on the wafer surface, and the remaining non-reactive Ga is hidden under As, forming a Ga-As-O structure, as Figure 3 shown. Since As2O3 is relatively stable, it will not spontaneously oxidize to form As2O5.
[0043] It should be noted that after step 101 wet cleaning, Ga and As on the wafer surface are not completely connected by chemical bonds, and a part of them is adsorbed by van der Waals force. Therefore, a more accurate structural diagram cannot be shown, and a simplified representation can be used: As-Ga-As-Ga---As-O, where the "---" in the middle represents the adsorption effect.
[0044] After wet cleaning, the surface of the wafer needs to be inspected to determine that a very thin As2O3 film has formed on the surface. Specifically, step 102 is performed: inspect the surface quality of the wafer surface after wet cleaning.
[0045] Inspect the oxide particles with a preset diameter on the wafer surface. When the number of detected oxide particles is less than the preset number, it is determined that the wafer surface meets the preset surface quality requirements.
[0046] For example, when the wafer is a 4-inch wafer, the number of oxide particles on the wafer surface with a diameter of more than 1 um should be less than the preset number. For example, the preset number is ten. When this requirement is met, it can be determined that the surface quality of the wafer is qualified. Specifically, a microscope dark field or a surface particle scanner can be used to inspect the oxide particles on the wafer surface.
[0047] In addition to inspecting the oxide particles on the wafer surface, on this basis, an atomic force microscope (AFM) can also be used to scan the wafer surface. When a stepped platform is detected on the wafer surface, the height difference between adjacent steps is the height of a single-layer oxide lattice, and the root mean square roughness of the wafer surface meets the preset roughness, it is determined that the wafer surface meets the preset surface quality requirements.
[0048] Among them, the single-layer oxide lattice refers to a crystal lattice with a two-dimensional planar structure formed by oxides of a single element. When applied to a GaAs wafer, it is a single-layer oxide Ga2O3 or As2O3 formed by Ga or As on the wafer surface, and its thickness is about 0.3 nanometers.
[0049] The aforementioned root mean square roughness refers to the square root of the average value of the undulation height on the wafer surface. The root mean square roughness can be obtained by statistical calculation of the discrete data of the surface height. The larger the root mean square roughness, the rougher the wafer surface.
[0050] After AFM scanning, a local area (a 1 um x 1 um pattern) of the wafer surface should exhibit a stepped platform structure. The width of the stepped platform is determined by the misorientation angle of the wafer (for example, a misorientation of 0.5 degrees corresponds to a stepped platform width of approximately 250 nm), and the height difference between two steps is approximately around 0.3 nm, that is, the height of a single-layer oxide lattice, and the root mean square roughness should be around 0.3 nm. Figure 2 An AFM scan image of the wafer surface after multiple cleanings is shown, and the steps can be clearly seen.
[0051] After the inspection in step 102 is qualified, step 103 can be carried out; if the inspection in step 102 is unqualified, for example, there are still a large number of oxide particles on the wafer surface, the steps 100-101 of wet oxidation and wet cleaning must be repeated until the inspection in step 102 shows that the surface quality of the wafer is qualified.
[0052] Step 103: Perform in-situ plasma cleaning on the wafer with qualified surface quality, and heat the wafer to remove the second oxide on the wafer surface.
[0053] Specifically, in the plasma cleaning chamber, use a mixed gas to perform in-situ plasma cleaning on the wafer, and at the same time heat the wafer at a preset temperature, so that the mixed gas reacts chemically with the second oxide on the wafer surface to remove the second oxide.
[0054] The mixed gas can be a mixture of NH3 and NF3 with a gas flow ratio of 1:4 to 1:5 or 4:1 to 5:1, and the preset temperature is 150°C to 200°C.
[0055] In some embodiments, the gas flow rates of NH3 and NF3 are 100 sccm to 500 sccm, the chamber pressure is 10 mTorr to 100 mTorr, the process time is 30 s to 300 s, and the heating temperature is 150°C to 200°C.
[0056] Using the plasma generated by the mixed gas to perform in-situ cleaning on the wafer surface and heating the wafer at the same time can effectively remove the second oxide As2O3 film, and then the exposed GaAs wafer surface has no oxide at all, so that the oxide on the wafer surface can be removed cleanly and thoroughly.
[0057] In the prior art, hydrogen can be used alone as the plasma gas, but the chemical activity of the hydrogen plasma state is relatively weak. Therefore, it must act directly on the wafer to work, and it mainly works through plasma bombardment rather than chemical reaction, which causes greater damage to the wafer surface and has weak control ability, which is not conducive to subsequent wafer growth.
[0058] In this application, a mixture of NH3 and NF3 is used as the plasma gas. The chemical reaction between NH3 / NF3 and GaAs is strong, and remote plasma or off-axis plasma can be used. In this way, the plasma does not act directly on the wafer, mainly using the ultra-high activity of the plasma and acting through chemical reaction. The by-products of the reaction are sublimated by heating and sucked away by the vacuum pump.
[0059] In addition, when NH3 and NF3 are mixed, the gas flow ratio is 1:4 to 1:5 or 4:1 to 5:1, and can be appropriately adjusted according to the effect of wet cleaning. NH3 can be used to improve the activity of the plasma, NF3 is used to provide a chemical reaction source, and NH3 and NF3 cooperate with each other to achieve a good cleaning effect.
[0060] Furthermore, inert gases such as N2 and Ar can be added to the mixed gas to control the chamber pressure. H2 can also be directly added. If H2 is added, the gas flow rate of the corresponding NH3 can be reduced accordingly, which is selected according to actual needs.
[0061] Step 104: Secondarily detect the surface of the wafer. When the diffraction image of the wafer surface is a dot lattice image, it is determined that the surface quality of the wafer is qualified.
[0062] Since the present application uses in-situ plasma cleaning, generally, the surface quality of the wafer can only be indirectly judged by the effect of subsequent wafer growth. It is also possible to detect the quality of the surface lattice by some special measurement means before growth to determine whether it is clean.
[0063] Specifically, a Reflection High Energy Electron Diffraction (RHEED) device can be used. The diffraction image of the lattice before and after wafer cleaning can be used to determine whether the wafer surface is clean. If there are residual oxides on the wafer surface, the formed RHEED diffraction image will have linear or circular patterns, while the RHEED image after cleaning is a pure dot lattice.
[0064] A pre-placed plasma cleaning chamber is installed before the growth chamber of MOCVD, and the two are connected by a hollow pipeline to send the cleaned wafer into the growth chamber of MOCVD for MOCVD growth.
[0065] In summary, the method for wafer surface treatment provided by the embodiments of the present application combines wet oxidation, cleaning and in-situ plasma cleaning, which can effectively and thoroughly remove the oxides on the wafer surface. After wet oxidation and cleaning, the surface of the wafer can be exposed to the air for at least several hours without generating new oxides. After in-situ plasma cleaning, the wafer surface can reach a state without oxides before MOCVD growth, ensuring the cleanliness of the wafer surface and thus ensuring the deposition quality of subsequent chemical vapor deposition of the wafer.
[0066] The above are only the embodiments of the present application and are not intended to limit the protection scope of the present application. For those skilled in the art, various modifications and changes can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.
Claims
1. A method for wafer surface treatment, wherein the wafer comprises at least a first material and a second material. After oxidation, the first material forms a first oxide, and the second material forms a second oxide. The first oxide is an oxide of one valence state of the first material or a composition comprising multiple valence state homologous oxides of the first material, and the second oxide is an oxide of one valence state of the second material or a composition comprising multiple valence state homologous oxides of the second material; characterized in that, The method includes: Wet-oxidizing the surface of the wafer to form the first oxide and the second oxide; Wet-cleaning the surface of the wafer to remove the unstable components in the first oxide and the second oxide oxidized on the surface of the wafer, and only the stable components in the second oxide remain on the surface of the wafer; Performing a surface quality inspection on the surface of the wafer after wet-cleaning; Performing in-situ plasma cleaning on the wafer with qualified surface quality inspection, and heating the wafer to remove the second oxide on the surface of the wafer.
2. The method for wafer surface treatment according to claim 1, characterized in that, The wet-oxidizing the surface of the wafer to form the first oxide and the second oxide includes: Placing the wafer in a strong oxidant and standing for 20 minutes to 30 minutes to generate the first oxide and the second oxide on the surface of the wafer.
3. The method for wafer surface treatment according to claim 1, characterized in that, The wet-cleaning the surface of the wafer to remove the unstable components in the first oxide and the second oxide oxidized on the surface of the wafer, and only the stable components in the second oxide remain on the surface of the wafer includes: Cleaning the wafer with diluted hydrofluoric acid to remove the unstable components in the first oxide and the second oxide, and only the stable components in the second oxide remain.
4. The method for wafer surface treatment according to any one of claims 1 to 3, characterized in that, The performing a surface quality inspection on the surface of the wafer after wet-cleaning includes: Inspecting the oxide particles with a preset diameter on the surface of the wafer. When the number of the detected oxide particles is less than a preset number, it is determined that the surface of the wafer meets the preset surface quality requirements.
5. The method for wafer surface treatment according to claim 4, characterized in that, The performing a surface quality inspection on the surface of the wafer after wet-cleaning includes: Scanning the surface of the wafer. When a stepped platform is detected on the surface of the wafer and the height difference between adjacent steps is the height of a single-layer oxide lattice, and the root mean square roughness of the surface of the wafer meets the preset roughness, it is determined that the surface of the wafer meets the preset surface quality requirements.
6. The method for wafer surface treatment according to any one of claims 1 to 3 and 5, characterized in that, The performing in-situ plasma cleaning on the wafer with qualified surface quality inspection, and heating the wafer to remove the second oxide on the surface of the wafer includes: Performing in-situ cleaning on the wafer with a mixed gas in a plasma cleaning chamber, and heating the wafer at a preset temperature at the same time, so that the mixed gas reacts chemically with the second oxide on the surface of the wafer to remove the second oxide.
7. The method for wafer surface treatment according to claim 6, wherein The performing in-situ cleaning on the wafer with a mixed gas in a plasma cleaning chamber, and heating the wafer at a preset temperature at the same time, so that the mixed gas reacts chemically with the second oxide on the surface of the wafer to remove the second oxide includes: Using NH3 and NF3 with a gas flow ratio of 1:4 to 1:5 or 4:1 to 5:1 as the mixed gas, and the preset temperature is 150°C to 200°C.
8. The method for wafer surface treatment according to claim 7, wherein The using NH3 and NF3 with a gas flow ratio of 1:4 to 1:5 or 4:1 to 5:1 as the mixed gas, and the preset temperature is 150°C to 200°C includes: The mixed gas further includes an inert gas or hydrogen.
9. The method for wafer surface treatment according to any one of claims 1 to 3, 5, 7 to 8, characterized in that, The wafers with qualified surface quality are subjected to in-situ plasma cleaning, and the wafers are heated to remove the second oxide on the surface of the wafers. After that, the method further includes: The surface of the wafer is detected for the second time. When the diffraction image on the surface of the wafer is a dot lattice image, it is determined that the surface quality of the wafer is qualified.