Method for cleaning silicon wafer, method for manufacturing silicon wafer, and silicon wafer

Abstract

The method for cleaning a silicon wafer according to the present invention supplies an oxidizing agent at a position shifted from the center of the silicon wafer in the radial direction in a surface modification step. A method for manufacturing a silicon wafer according to the present invention includes a step for performing the method for cleaning the silicon wafer. When a predetermined measurement is performed on the silicon wafer according to the present invention, the difference between the maximum value and the minimum value of the thickness of the natural oxide film in the radial direction of the silicon wafer, which is obtained by normalizing the measured thickness of the natural oxide film by the maximum value, is 0.1 or less.

Description

Technical Field

[0001] The present invention relates to a method for cleaning a silicon wafer, a method for manufacturing a silicon wafer, and a silicon wafer. Background Art

[0002] An oxide film formed on the surface of a silicon wafer in an air atmosphere at room temperature or an oxide film formed by cleaning with a chemical solution is referred to as a natural oxide film or a chemical oxide film (hereinafter, referred to as a natural oxide film). The thickness of the natural oxide film is less than 1 nm (about 0.2 nm) to about 2 nm or less. The thickness of the natural oxide film formed in the normal cleaning process of a silicon wafer is (angstroms) or so. In contrast, an oxide film formed by heat treatment is called a thermal oxide film, and its thickness is 3 nm or more.

[0003] With the recent high-precision, multi-layer, and thin-type semiconductor devices, thinning of various films used in semiconductor elements is required. For example, as a method for improving the gate characteristics of a MOS transistor, a method is disclosed in which the silicon surface is cleaned immediately before forming a gate oxide film, and after making the silicon surface hydrogen-terminated, a gate insulating film is formed (for example, Patent Document 1). In order to improve the yield of the latest semiconductor devices, it is necessary to form an extremely thin silicon oxide film such as a natural oxide film uniformly and with good reproducibility in the plane (for example, Patent Document 2).

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2000-216156

[0007] Patent Document 2: Japanese Patent No. 6791454 Summary of the Invention

[0008] Technical Problem to be Solved by the Invention

[0009] An object of the present invention is to provide a method for cleaning a silicon wafer, a method for manufacturing a silicon wafer, and a silicon wafer having a more uniform natural oxide film, which can improve the uniformity of the thickness of the natural oxide film on the silicon wafer.

[0010] Solution to the Technical Problem

[0011] The main solution of the present invention is as follows.

[0012] (1) A method for cleaning a silicon wafer, which is a method for cleaning a single-piece silicon wafer, characterized in that it includes:

[0013] Surface modification step, using an oxidant to modify the surface of the silicon wafer;

[0014] Etching step, using an etching solution to etch the surface of the silicon wafer after the surface modification step; and

[0015] Rinsing step, using a rinsing solution to rinse the surface of the silicon wafer,

[0016] In the surface modification step, the oxidant is supplied at a position radially offset from the center of the silicon wafer.

[0017] Here, "supplying the oxidant at a position radially offset from the center of the silicon wafer" means that the intersection of the extension line of the extending direction of the supply pipe for supplying the oxidant and the surface of the silicon wafer is radially offset from the center of the silicon wafer, and the oxidant is supplied from the supply pipe at this position.

[0018] (2) The cleaning method of the silicon wafer according to (1) above, wherein,

[0019] The oxidant is ozone water.

[0020] (3) The cleaning method of the silicon wafer according to (1) or (2) above, wherein,

[0021] The etching solution is an aqueous hydrogen fluoride solution.

[0022] (4) The cleaning method of the silicon wafer according to (1) or (2) above, wherein,

[0023] The rinsing solution is pure water.

[0024] (5) The cleaning method of the silicon wafer according to any one of (1) to (4) above, wherein,

[0025] The position for supplying the oxidant is a position radially offset from the center of the silicon wafer within a range of 5 mm or more and 75 mm or less.

[0026] (6) The cleaning method of the silicon wafer according to (5) above, wherein,

[0027] The position for supplying the oxidant is a position radially offset from the center of the silicon wafer within a range of 15 mm or more and 20 mm or less.

[0028] (7) The cleaning method of the silicon wafer according to any one of (1) to (6) above, wherein,

[0029] The oxidant is ozone water,

[0030] The etching solution is an aqueous hydrogen fluoride solution,

[0031] The concentration of the ozone water is in the range of 20 to 30 ppm, and the concentration of the hydrogen fluoride aqueous solution is in the range of 0.5 to 3.0 mass%.

[0032] (8) The method for cleaning a silicon wafer according to any one of (1) to (7) above, wherein

[0033] The rotational speed of the silicon wafer in the surface modification step, the etching step, and the rinsing step is in the range of 100 to 500 rpm.

[0034] (9) The method for cleaning a silicon wafer according to any one of (1) to (8) above, which includes the following steps:

[0035] Adjust at least any one of the position where the oxidant is supplied, the concentration of the oxidant, the concentration of the etching solution, the flow rate of the oxidant, the flow rate of the etching solution, and the rotational speed of the silicon wafer, so that the thickness of the native oxide film is measured at intervals of 29.4 mm from the center of the silicon wafer with a diameter of 300 mm by a spectroscopic ellipsometer, and the difference between the maximum value and the minimum value of the thickness of the native oxide film in the radial direction of the silicon wafer after normalizing the measured thickness of the native oxide film with the maximum value is 0.1 or less.

[0036] (10) A method for manufacturing a silicon wafer, characterized by including a step of performing the method for cleaning a silicon wafer according to any one of (1) to (9) above.

[0037] (11) A silicon wafer having a native oxide film with a thickness of 2 nm or less, wherein the silicon wafer is characterized in that

[0038] When the thickness of the native oxide film is measured at intervals of 29.4 mm from the center of the silicon wafer with a diameter of 300 mm to 147 mm by a spectroscopic ellipsometer, the difference between the maximum value and the minimum value of the thickness of the native oxide film in the radial direction of the silicon wafer after normalizing the measured thickness of the native oxide film with the maximum value is 0.1 or less.

[0039] Advantages of the Invention

[0040] According to the present invention, it is possible to provide a method for cleaning a silicon wafer, a method for manufacturing a silicon wafer, and a silicon wafer having a more uniform native oxide film, which can improve the uniformity of the thickness of the native oxide film on the silicon wafer. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a flowchart of a method for cleaning a silicon wafer according to an embodiment of the present invention.

[0042] Figure 2 It is a diagram schematically showing the positional relationship of a silicon wafer, and supply pipes for an oxidizing agent and an etching solution.

[0043] Figure 3 It is a diagram showing the measurement locations of the thickness of the native oxide film on the wafer in the examples.

[0044] Figure 4 It is a diagram showing the measurement results of the thickness of the formed native oxide film.

[0045] Figure 5 It shows Figure 4 the result of normalizing the thickness of the native oxide film in terms of the maximum value.

[0046] Figure 6 It is a diagram showing the result of comparing the uniformity of the thickness of the native oxide film based on different chemical solution types.

[0047] Figure 7 It is a diagram showing the thickness distribution of the native oxide film when changing the rotation speed of the silicon wafer during treatment with the final ozone water.

[0048] Figure 8 It shows Figure 7 the result of normalizing the thickness of the native oxide film in terms of the maximum value. Detailed implementation mode

[0049] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0050] <Method for cleaning a silicon wafer>

[0051] Figure 1 It is a flowchart of a method for cleaning a silicon wafer according to an embodiment of the present invention. Figure 2 It is a diagram schematically showing the positional relationship of a silicon wafer and supply pipes for an oxidizing agent and an etching solution.

[0052] The method for cleaning a silicon wafer in this embodiment is a method for cleaning a single - piece silicon wafer using a single - piece rotary cleaning machine. Here, the method for cleaning a single - piece silicon wafer means a method of cleaning the surface of a wafer by supplying a desired chemical solution from a chemical solution supply nozzle toward the wafer surface while rotating the wafer horizontally around the center of the wafer as the central axis. As Figure 1 shown, in the method of this embodiment, first, the surface layer of the silicon wafer W is modified using an oxidizing agent (surface layer modification step: step S101). In this step, as Figure 2As shown, while rotating the silicon wafer W, an oxidizing agent (ozone water in this example) is supplied to the surface of the silicon wafer W via the supply pipe 1 to bring it into contact with the surface of the silicon wafer W, and a native oxide film is formed on the surface of the silicon wafer W. Additionally, before step S101, SC-1 (Standard Clean 1) cleaning or SC-2 (Standard Clean 2) cleaning can also be appropriately performed.

[0053] The oxidizing agent is preferably ozone water. The concentration of the ozone water is preferably in the range of 20 to 30 ppm. By setting the concentration of the ozone water to 20 ppm or more, a sufficiently thick native oxide film can be formed. On the other hand, considering the solubility limit of ozone in water, the upper limit of the concentration is around 30 ppm. Here, ppm represents the weight ratio. The flow rate of the ozone water is preferably set to 0.5 to 1.5 L / minute. The treatment time based on the ozone water is preferably set to 15 to 60 seconds.

[0054] Here, as Figure 2 shown, in the present embodiment, the oxidizing agent (ozone water in this example) is supplied at a position offset radially (towards the edge side of the wafer W) from the center O of the silicon wafer W. More specifically, the position where the oxidizing agent is supplied is preferably a position offset radially from the center O of the silicon wafer W within a range of 5 mm or more and 75 mm or less, and further preferably a position offset radially from the center O of the silicon wafer W within a range of 15 mm or more and 20 mm or less.

[0055] Next, the surface layer of the silicon wafer W is etched using an etching solution (etching step: step S102). In this process, as Figure 2 shown, while rotating the silicon wafer W, the etching solution (hydrofluoric acid aqueous solution in this example) is supplied to the surface of the silicon wafer W via the supply pipe 2 to bring it into contact with the surface of the silicon wafer W. Thereby, the native oxide film formed in the surface modification step (step S101) is etched. Additionally, in this process (in the case of performing step S102 multiple times, at least the last etching process), the etching amount is set to the extent that the native oxide film remains.

[0056] The etching solution is preferably a hydrofluoric acid aqueous solution. The concentration of the hydrofluoric acid aqueous solution is preferably in the range of 0.5 to 3.0 mass%. This is because by setting the concentration of the hydrofluoric acid aqueous solution to 0.5 mass% or more, a sufficient etching effect can be obtained. On the other hand, by setting the concentration of the hydrofluoric acid aqueous solution to 3.0 mass% or less, over-etching can be suppressed. The flow rate of the hydrofluoric acid aqueous solution is preferably set to 0.5 to 1.5 L / minute. The treatment time based on the hydrofluoric acid aqueous solution is preferably set to 1 to 10 seconds.

[0057] As Figure 2As shown, in the present embodiment, the etching solution (hydrofluoric acid aqueous solution in this example) is supplied from the position of the center O of the silicon wafer W (without radial offset). However, the etching solution may also be supplied with a radial offset from the position of the center O of the silicon wafer W.

[0058] In the present embodiment, as Figure 1 shown, after repeating the surface modification process (step S101) and the etching process (step S102) a predetermined number of times (for example, 2 to 4 times), the subsequent rinsing process (step S103) is entered. In addition, the surface modification process (step S101) and the etching process (step S102) do not necessarily need to be repeated. Moreover, it is also possible to repeat the surface modification process (step S101), the etching process (step S102), and the rinsing process (step S103) (for example, 2 to 4 times) including the rinsing process (step S103).

[0059] Next, a rinsing process using a rinsing solution (rinsing process: step S103) is performed. In this process, while rotating the silicon wafer W, the rinsing solution (pure water in this example) is supplied to the surface of the silicon wafer W via a supply pipe (not shown) different from the supply pipes 1 and 2 to rinse foreign matters on the surface of the silicon wafer W.

[0060] The rinsing solution is preferably pure water, and particularly preferably DIW (DeIonized Water). The flow rate of pure water is preferably 0.5 to 1.5 L / minute. The treatment time based on pure water is preferably 1 to 30 seconds. In the present embodiment, pure water is supplied from the position of the center O of the silicon wafer W (without radial offset). However, pure water may also be supplied with a radial offset from the position of the center O of the silicon wafer W.

[0061] In steps S101 to S103, the rotation speed of the silicon wafer W during cleaning is preferably in the range of 100 to 500 rpm.

[0062] Hereinafter, the effects of the cleaning method of the silicon wafer according to the present embodiment will be described.

[0063] The present inventors have conducted in-depth research on the cause of the non-uniformity of the thickness of the natural oxide film on the silicon wafer, and as a result, it has been found that in the conventional method of supplying an oxidant (ozone water) from the position of the center 0 of the silicon wafer W, when a centrifugal force is applied in the radial direction (from the center to the edge side) due to the rotation of the silicon wafer W, the supplied oxidant (ozone water) flows in a concentrically undulating manner from the center 0 in the radial direction, thereby becoming a flow that forms a peak in the supply amount near the R / 2 point or the outer peripheral portion when the diameter is set to R, which is the cause of the non-uniformity of the thickness of the natural oxide film in the plane.

[0064] Therefore, in the present embodiment, in the single-wafer cleaning process using an oxidizing agent, an etching solution, and a rinsing solution, in the surface modification step (step S101) using the oxidizing agent, the oxidizing agent (ozone water) is supplied at a position radially offset from the center O of the silicon wafer W. Thereby, it is possible to prevent the supplied oxidizing agent (ozone water) from flowing radially in a concentric undulating manner from the center O, and thus it is possible to reduce the peak value of the supply amount of the oxidizing agent (ozone water) as described above.

[0065] Therefore, according to the cleaning method of the silicon wafer of the present embodiment, it is possible to improve the uniformity of the thickness of the natural oxide film on the silicon wafer W. The oxide film with uniform thickness formed in the cleaning process is expected to maintain uniformity in the subsequent thermal oxidation process, and thus it is expected to improve the yield in semiconductor device manufacturing.

[0066] Here, as described above, the position for supplying the oxidizing agent (ozone water) is preferably a position radially offset from the center of the silicon wafer W within a range of 5 mm or more and 75 mm or less. This is because, by radially offsetting 5 mm or more from the center of the silicon wafer W, the above-described effects can be obtained more reliably. On the other hand, by radially offsetting 75 mm or less from the center of the silicon wafer W, the supply amount of the oxidizing agent (ozone water) near the center O of the silicon wafer W will not become too small, and thus it is possible to more reliably improve the uniformity of the thickness of the natural oxide film on the silicon wafer W. For the same reason, the position for supplying the oxidizing agent (ozone water) is more preferably a position radially offset from the center O of the silicon wafer W within a range of 15 mm or more and 20 mm or less.

[0067] Here, at least any one of the position for supplying the oxidizing agent (ozone water), the concentration of the oxidizing agent (ozone water), the concentration of the etching solution (hydrofluoric acid aqueous solution), the flow rate of the oxidizing agent (ozone water), the flow rate of the etching solution (hydrofluoric acid aqueous solution), and the rotation speed of the silicon wafer W can be used as a parameter for finely adjusting the uniformity of the thickness of the natural oxide film.

[0068] That is, for example, as an index of the uniformity of the natural oxide film, the difference between the maximum value and the minimum value of the thickness of the natural oxide film in the radial direction of the silicon wafer W, which is obtained by measuring the thickness of the natural oxide film at intervals of 29.4 mm from the center of the silicon wafer W with a diameter of 300 mm using a spectroscopic ellipsometer and normalizing the measured thickness of the natural oxide film with the maximum value, is used, and the target value is set such that the difference between the maximum value and the minimum value is 0.1 or less.

[0069] Moreover, relationship data between at least any one of the position for supplying the oxidizing agent, the concentration of the oxidizing agent, the concentration of the etching solution, the flow rate of the oxidizing agent, the flow rate of the etching solution, and the rotation speed of the silicon wafer and the uniformity of the thickness of the natural oxide film (for example, the distribution of the in-plane thickness variation amount) is obtained in advance.

[0070] Based on the above-described cleaning conditions and the in-plane distribution of the thickness of the natural oxide film at present, determine the target value of the change amount (increase amount or decrease amount) of the thickness of a specified region (position) in the in-plane of the silicon wafer for achieving the above target value.

[0071] Based on the above relationship data, obtain the correction value of each of the above cleaning conditions suitable for achieving the target value of the change amount of the thickness of the specified region in the in-plane of the silicon wafer.

[0072] Moreover, after performing an adjustment to correct at least any one of the above cleaning conditions corresponding to the obtained correction value, perform the subsequent cleaning, thereby further improving the uniformity of the natural oxide film on the silicon wafer.

[0073] As a modification example of the above fine adjustment, it is also possible to perform the above fine adjustment by using an artificial intelligence method. That is, through the machine learning unit (processor) of a computer, create an artificial intelligence model in which the change amount of the thickness of the natural oxide film in a specified region (position) in the in-plane is set as an explanatory variable (input) and the correction value of at least any one of the above cleaning conditions is set as an objective variable (output) (prepare sufficient learning data required for machine learning in advance). Moreover, in the created artificial intelligence model, if the change amount of the thickness of the natural oxide film in the specified region (position) in the in-plane (corresponding to a target value such that the difference between the maximum value and the minimum value of the thickness of the natural oxide film in the radial direction of the above silicon wafer W is, for example, 0.1 or less) is input, the machine learning unit outputs the correction value of at least any one of the above cleaning conditions. Using the correction value as its output, after performing an adjustment to correct at least any one of the above cleaning conditions corresponding to the obtained correction value, perform the subsequent cleaning. In addition, as the algorithm of machine learning, any known algorithm such as a neural network can be used.

[0074] In Figure 2 In the example shown, when the direction perpendicular to the main surface of the silicon wafer is set as the vertical direction, the supply pipes 1 and 2 are inclined from above toward below (toward the side closer to the silicon wafer) and from the edge side in the radial direction of the silicon wafer toward the center. The inclination angle θ1 of the supply pipe 1 with respect to the vertical direction is not particularly limited, but can be set to 1 to 5°. The inclination angle θ2 of the supply pipe 2 with respect to the vertical direction is not particularly limited, but can be set to 1 to 5°. These supply pipes 1 and 2 do not necessarily need to be inclined with respect to the vertical direction and may also extend in the vertical direction (without inclination). Also, even when inclined in the vertical direction, the supply pipes 1 and 2 may be inclined from above toward below (toward the side closer to the silicon wafer) and from the inner side in the radial direction of the silicon wafer toward the outer side.

[0075] <Manufacturing method of silicon wafer>

[0076] A method for manufacturing a silicon wafer according to an embodiment of the present invention includes a step of performing the cleaning method of the silicon wafer according to the above embodiment. Other steps can include, as is known, an ingot pulling step, a slicing step, a grinding step, and the like. According to the method for manufacturing a silicon wafer of the present embodiment, the uniformity of the thickness of the native oxide film on the silicon wafer W can be improved.

[0077] <Silicon wafer>

[0078] A silicon wafer according to an embodiment of the present invention is a silicon wafer after performing the cleaning method of the silicon wafer according to the above embodiment, and is a silicon wafer formed with a native oxide film having a thickness of 2 nm or less. When measuring the thickness of the native oxide film at intervals of 29.4 mm from the center of a 300-mm diameter silicon wafer to 147 mm using a spectroscopic ellipsometer, the difference between the maximum and minimum values of the thickness of the native oxide film in the radial direction of the silicon wafer, with the measured thickness of the native oxide film normalized by the maximum value, is 0.1 or less. As shown in the examples described later, according to the method of the present embodiment, a silicon wafer having a more uniform thickness of the native oxide film can be obtained.

[0079] Examples

[0080] Hereinafter, examples of the present invention will be described, but the present invention is not limited to the following examples.

[0081] In this embodiment, a p-type epitaxial silicon wafer with a diameter of 300 mm (hereinafter simply referred to as a silicon wafer) was used as a sample. First, cleaning treatment was performed for 15 seconds with ozone water having an ozone concentration of 20 ppm while setting the rotation speed of the wafer to 300 rpm. Next, a cleaning treatment for etching the oxide film was performed for 4 seconds with a hydrofluoric acid aqueous solution having a concentration of 1% while setting the rotation speed of the silicon wafer to 300 rpm. The etching treatment based on the hydrofluoric acid aqueous solution at this time was set to a condition where the oxide film was not completely removed. Next, in order to form an oxide film, cleaning treatment was performed for 30 seconds with ozone water having an ozone concentration of 20 ppm while setting the rotation speed of the wafer to 300 rpm. Thus, a set of cleaning with ozone water and cleaning with a hydrofluoric acid aqueous solution was repeated 3 times. After that, cleaning with DIW (pure water) was finally performed for 30 seconds. In any cleaning treatment, the flow rate of the chemical solution was set to 1.0 L / minute. Regarding the supply pipe, it was set to be inclined from above to below (toward the side closer to the silicon wafer) and from the edge side in the radial direction of the silicon wafer toward the center with respect to the epitaxial silicon wafer, and the inclination angle with respect to the vertical direction was set to 4°. Tests were carried out under three conditions: when the position of the supply pipe during treatment with ozone water was at the center of the wafer, when it was offset by 15 mm and 20 mm respectively in the radial direction from the center of the wafer. The thickness of the native oxide film on the wafer after single-piece cleaning treatment was measured at 121 measurement points at intervals of 29.4 mm from the center of the wafer using a spectroscopic ellipsometer. In Figure 3 the measurement sites are indicated by dots.

[0082] Figure 4 is a graph showing the measurement results of the thickness of the formed native oxide film. As Figure 4 shown, an oxide film of about was formed on the wafer. Figure 5 is a graph showing the result of normalizing the thickness of the native oxide film in Figure 4 by the maximum value. Figure 4 、 Figure 5 The horizontal axis of Figure 5 represents the measurement site (mm) represented by the radial distance from the center of the wafer and the radial distance of the supply pipe from the center of the wafer (mm). Figure 5 The vertical axis represents the value obtained by normalizing the thickness of the native oxide film by the maximum value. It can be said that the lower the standard deviation of the in-plane distribution of the thickness of the native oxide film, the higher the in-plane distribution uniformity. From this, it can be known that compared with the case where the position of the supply pipe for ozone water is at the center position of the wafer, when the position of the supply pipe for ozone water is offset in the radial direction of the wafer, the uniformity of the thickness of the native oxide film in the plane of the silicon wafer becomes higher.

[0083] Regarding Figure 5, the relationship between the standard deviation of the thickness of the oxide film in the radial direction of the wafer and the difference between the maximum value and the minimum value is shown in Table 1 below. From Table 1, it can be seen that regarding the radial direction of the wafer, by shifting the position of the ozone water supply pipe along the radial direction of the wafer, the values of the standard deviation and the difference between the maximum value and the minimum value become smaller, that is, the uniformity of the thickness of the oxide film in the plane of the silicon wafer becomes higher. And, compared with the case where the distance from the center in the circumferential direction of the wafer is 20 mm, the case where the distance from the center in the circumferential direction of the wafer is 15 mm is at the same level.

[0084] [Table 1]

[0085] Distance of the supply pipe from the center of the wafer (mm) Standard deviation Maximum - Minimum 0 0.03 0.13 15 0.02 0.07 20 0.02 0.08

[0086] As described in the description of the embodiment, by using the difference between the maximum value and the minimum value of the thickness of the natural oxide film in the plane of the wafer as an index, the cleaning conditions of the silicon wafer can also be adjusted. It is considered that, for example, when the difference between the maximum value and the minimum value of the thickness of the natural oxide film of the silicon wafer cleaned under a certain cleaning condition is 0.1 or more, the in-plane distribution of the natural oxide film is confirmed. When the thickness of the natural oxide film is relatively thick near the R / 2 (where the diameter is set as R) or the outer peripheral part of the silicon wafer, as the cleaning condition to be adjusted, for example, by reducing the rotation speed of the silicon wafer during the final ozone water treatment, the uniformity of the thickness of the natural oxide film can be improved.

[0087] Next, the difference in the effect of shifting the supply position from the center of the wafer according to the different supplied liquid medicines was verified. Figure 6 It is a diagram showing the results of comparing the uniformity of the thickness of the natural oxide film based on different liquid medicine types. The existing example is the result when ozone water, hydrofluoric acid aqueous solution, and pure water are all supplied from the center of the wafer. The inventive example is the result when ozone water is shifted 20 mm along the radial direction from the center of the wafer and hydrofluoric acid aqueous solution and pure water are supplied from the center of the wafer. The comparative example is the result when hydrofluoric acid aqueous solution is shifted 20 mm from the center of the wafer and ozone water and pure water are supplied from the center of the wafer. When these are compared, it can be seen that the uniformity of the thickness of the natural oxide film in the inventive example is good compared with the existing example and the comparative example. That is, when the supply position of ozone water is shifted along the radial direction from the center of the silicon wafer, good results are obtained. Although the detailed mechanism is not clear yet, the present inventors believe that the change in the liquid film caused by splashing water generated when spraying liquid medicines such as ozone water will affect the deviation of the reaction rate of the liquid medicine in the radial direction of the wafer. And, the present inventors believe that the natural oxide film is not uniformly removed or formed by the treatment of ozone water and hydrofluoric acid aqueous solution, but the uniformity of the oxide film is ensured by the balance of the two liquid medicines.

[0088] Next, verification was also carried out on changing the rotation speed of the silicon wafer at the time of finally supplying ozone water when the supply position of the ozone water was fixed at 15 mm from the center of the wafer. Regarding the rotation speed, it was set to 100 rpm, 150 rpm, 200 rpm, and 300 rpm. Figure 7 It is a diagram showing the thickness distribution of the native oxide film when changing the rotation speed of the silicon wafer during treatment with the final ozone water. It can be seen that by reducing the rotation speed at the time of finally supplying ozone water, a better in-plane distribution of the thickness of the native oxide film can be obtained.

[0089] Figure 8 It is a diagram showing Figure 7 the result of normalizing the thickness of the native oxide film in Figure 8 by the maximum value. And regarding

[0090] [Table 2]

[0091] Rotation speed Standard deviation Maximum - Minimum POR 0.02 0.13 100 rpm 0.02 0.07 150 rpm 0.01 0.05 200 rpm 0.01 0.06

[0092] Description of reference numerals

[0093] 1 - supply pipe, 2 - supply pipe.

Claims

1. A cleaning method for a silicon wafer, which is a cleaning method for a single-piece silicon wafer. The cleaning method for the silicon wafer is characterized by comprising: A surface modification step of modifying the surface layer of the silicon wafer using an oxidant; An etching step of etching the surface layer of the silicon wafer after the surface modification step using an etching solution; And A rinsing step of rinsing the surface of the silicon wafer using a rinsing solution, In the surface modification step, the oxidant is supplied at a position radially offset from the center of the silicon wafer.

2. The cleaning method for a silicon wafer according to claim 1, wherein The oxidant is ozone water.

3. The cleaning method for a silicon wafer according to claim 1 or 2, wherein The etching solution is an aqueous hydrogen fluoride solution.

4. The cleaning method for a silicon wafer according to claim 1 or 2, wherein The rinsing solution is pure water.

5. The cleaning method for a silicon wafer according to claim 1 or 2, wherein The position where the oxidant is supplied is a position radially offset from the center of the silicon wafer within a range of 5 mm or more and 75 mm or less.

6. The cleaning method for a silicon wafer according to claim 5, wherein The position where the oxidant is supplied is a position radially offset from the center of the silicon wafer within a range of 15 mm or more and 20 mm or less.

7. The cleaning method for a silicon wafer according to claim 1 or 2, wherein The oxidant is ozone water, The etching solution is an aqueous hydrogen fluoride solution, The concentration of the ozone water is within the range of 20 to 30 ppm, and the concentration of the aqueous hydrogen fluoride solution is within the range of 0.5 to 3.0 mass%.

8. The cleaning method for a silicon wafer according to claim 7, wherein The rotation speed of the silicon wafer in the surface modification step, the etching step, and the rinsing step is within the range of 100 to 500 rpm.

9. The cleaning method for a silicon wafer according to claim 1 or 2, which comprises the following steps: Adjust at least any one of the position where the oxidant is supplied, the concentration of the oxidant, the concentration of the etching solution, the flow rate of the oxidant, the flow rate of the etching solution, and the rotation speed of the silicon wafer, so that the thickness of the native oxide film is measured at intervals of 29.4 mm from the center of the silicon wafer with a diameter of 300 mm by a spectroscopic ellipsometer, and the difference between the maximum value and the minimum value of the thickness of the native oxide film in the radial direction of the silicon wafer, after normalizing the measured thickness of the native oxide film with the maximum value, becomes 0.1 or less.

10. A method for manufacturing a silicon wafer, characterized in that, Comprises the step of performing the cleaning method for a silicon wafer according to claim 1 or 2.

11. A silicon wafer, which is formed with a native oxide film having a thickness of 2 nm or less. The silicon wafer is characterized in that When the thickness of the native oxide film is measured at intervals of 29.4 mm from the center of the silicon wafer with a diameter of 300 mm to 147 mm by a spectroscopic ellipsometer, the difference between the maximum value and the minimum value of the thickness of the native oxide film in the radial direction of the silicon wafer, after normalizing the measured thickness of the native oxide film with the maximum value, is 0.1 or less.

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