Cleaning method of silicon wafer, manufacturing method of silicon wafer, and cleaning system of silicon wafer

Abstract

(Problem) The present invention aims to provide a method for cleaning a silicon wafer, a method for manufacturing a silicon wafer, and a silicon wafer cleaning system that can increase the uniformity of the thickness of an oxide film on a silicon wafer between wafers. (Solution) In a method for cleaning a silicon wafer, prior to the final finishing process, the oxygen concentration of the silicon wafer is acquired, and an adjustment factor is adjusted based thereon. The method for manufacturing a silicon wafer according to the present invention includes performing the above method for cleaning a silicon wafer. The silicon wafer cleaning system according to the present invention further comprises an oxygen concentration acquisition unit for acquiring the oxygen concentration of a silicon wafer and an adjustment unit for adjusting an adjustment factor based on the acquired oxygen concentration of the silicon wafer.

Description

Technology Field

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

[0002] With the recent increase in precision, multilayering, and thinning of semiconductor devices, there is a demand for thinning of various films used in semiconductor devices. For example, as a method for improving the gate characteristics of a MOS transistor, a method has been proposed in which the silicon surface is cleaned immediately before the formation of the gate oxide film, and after the silicon surface is terminated by hydrogen, a gate insulating film is formed (e.g., Patent Document 1). Prior art literature

[0003] Japanese Patent Publication No. 2000-216156 The problem to be solved

[0004] The present invention aims to provide a method for cleaning a silicon wafer, a method for manufacturing a silicon wafer, and a silicon wafer cleaning system that can increase the uniformity of the thickness of an oxide film on a silicon wafer between wafers. means of solving the problem

[0005] As a result of repeated careful consideration to solve the above problem, the inventors obtained a novel understanding that the oxygen concentration of the silicon wafer used for cleaning affects the thickness of the oxide film formed.

[0006] The present invention is based on the above understanding, and its gist is as follows.

[0007] (1) A cleaning method for a single-wafer silicon wafer comprising a final finishing process including a surface modification process for modifying the surface layer of a silicon wafer using an oxidizing agent, an etching process for etching the surface layer of the silicon wafer using an etching solution, and a rinsing process for rinsing the surface of the silicon wafer using a rinsing solution, wherein

[0008] Prior to the above final finishing process, the oxygen concentration acquisition process for acquiring the oxygen concentration of the silicon wafer is additionally included.

[0009] A method for cleaning a silicon wafer, characterized in that, in the above etching process, an adjustment factor is adjusted based on the oxygen concentration of the silicon wafer obtained by the above oxygen concentration acquisition process.

[0010] (2) In the above final finishing process, the surface modification process and the etching process are repeated multiple times, and

[0011] A cleaning method for a silicon wafer described in (1), wherein, in the etching process of the final meeting, the adjustment factor is adjusted based on the oxygen concentration of the silicon wafer obtained by the oxygen concentration acquisition process.

[0012] (3) The above adjustment factor includes at least an etching time, a method for cleaning a silicon wafer as described in (1) or (2).

[0013] (4) The above adjustment factor is only the etching time, the method for cleaning a silicon wafer described in (3).

[0014] (5) The above adjustment factor includes at least the concentration of the etching solution, a method for cleaning a silicon wafer as described in (1) or (2).

[0015] (6) A method for cleaning a silicon wafer described in (3) or (4), wherein, in the above etching process, the higher the oxygen concentration of the silicon wafer obtained by the above oxygen concentration acquisition process, the longer the etching time is.

[0016] (7) A method for cleaning a silicon wafer as described in (5), wherein, in the above etching process, the higher the oxygen concentration of the silicon wafer obtained by the above oxygen concentration acquisition process, the higher the concentration of the etching solution is.

[0017] (8) A method for cleaning a silicon wafer described in any one of (1) to (7), wherein the amount of increase in the film thickness of the silicon wafer is assumed to be a monotonically increasing function that is linear or a polynomial of degree 2 or higher of the oxygen concentration of the silicon wafer obtained by the oxygen concentration acquisition process, and the amount of adjustment of the adjustment factor to be adjusted is calculated.

[0018] (9) A method for manufacturing a silicon wafer, characterized by including the cleaning method of a silicon wafer described in any one of (1) to (8) above.

[0019] (10) A stage for placing a silicon wafer, and

[0020] An oxidizing agent supply unit that supplies an oxidizing agent onto a silicon wafer placed on the above stage, and

[0021] An etching solution supply unit that supplies an etching solution onto a silicon wafer placed on the above stage, and

[0022] A cleaning system for a silicon wafer, comprising a rinse liquid supply unit that supplies a rinse liquid onto a silicon wafer placed on the above stage,

[0023] An oxygen concentration acquiring unit for acquiring the oxygen concentration of the above silicon wafer, and

[0024] A silicon wafer cleaning system characterized by additionally comprising an adjustment unit that adjusts an adjustment factor based on the oxygen concentration of the silicon wafer acquired by the oxygen concentration acquisition unit. Effects of the invention

[0025] According to the present invention, a method for cleaning a silicon wafer, a method for manufacturing a silicon wafer, and a silicon wafer cleaning system can be provided, which can increase the uniformity of the thickness of an oxide film on a silicon wafer between wafers. Brief explanation of the drawing

[0026] FIG. 1 is a flowchart of a method for cleaning a silicon wafer according to one embodiment of the present invention. Figure 2 is a diagram showing the relationship between the oxygen concentration of a silicon wafer and the increase in the thickness of an oxide film on a silicon wafer. Figure 3 is a diagram showing the relationship between etching time and the amount of reduction in the film thickness of an oxide film on a silicon wafer. Figure 4 is a diagram showing the relationship between the concentration of the etching solution and the amount of reduction in the film thickness of the oxide film on the silicon wafer. Figure 5 is a diagram showing the measurement points of oxygen concentration within the wafer surface in the embodiment. Figure 6 is a diagram showing the difference in results between the inventive example and the comparative example. FIG. 7 is a schematic diagram of a silicon wafer cleaning system according to one embodiment of the present invention. Specific details for implementing the invention

[0027] (Form for carrying out the invention)

[0028] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0029] <Silicon Wafer Cleaning Method>

[0030] FIG. 1 is a flowchart of a cleaning method for a silicon wafer (hereinafter also simply referred to as a "wafer") according to one embodiment of the present invention. The cleaning method for a silicon wafer according to this embodiment is a cleaning method for a single-wafer silicon wafer using a single-wafer spin cleaner. The cleaning method for a single-wafer silicon wafer referred to herein means a method of cleaning the wafer surface by supplying a desired chemical solution toward the wafer surface through a chemical solution supply nozzle, etc., while the wafer is rotated in a horizontal direction with the center of the wafer as the central axis.

[0031] As shown in FIG. 1, the method of the present embodiment includes a final finishing process (step S102) comprising a surface modification process (step S102-1) for modifying the surface layer of a silicon wafer (W) using an oxidizing agent, an etching process (step S102-2) for etching the surface layer of the silicon wafer (W) after the surface modification process using an etching solution, and a rinsing process (step S102-3) for rinsing the surface of the silicon wafer (W) using a rinsing solution.

[0032] Prior to Step S102, appropriately, SC-1 (Standard Clean 1) cleaning or SC-2 (Standard Clean 2) cleaning may be performed.

[0033] In the surface modification process (step S102-1), while rotating the silicon wafer (W), an oxidizing agent (ozone water in this example) is supplied to the surface of the silicon wafer (W) through an oxidizing agent supply unit (supply pipe) (3) (see FIG. 7) and brought into contact with the surface of the silicon wafer (W) to form a natural oxide film (hereinafter also simply referred to as "oxide film") on the surface of the silicon wafer (W).

[0034] It is preferable to use ozone water as the oxidizing agent. It is preferable that the concentration of the ozone water be within the range of 20 to 30 ppm. By making the concentration of the ozone water 20 ppm or higher, a natural oxide film of sufficient thickness can be formed, and on the other hand, considering the limit of ozone dissolution in water, the upper limit of the concentration is approximately 30 ppm. Here, ppm refers to the weight ratio. It is preferable that the flow rate of the ozone water be 0.5 to 1.5 L / min. It is preferable that the treatment time with ozone water be 15 to 60 seconds.

[0035] Here, the oxidizing agent (ozone water in this example) may be supplied from a position at the center (O) of the silicon wafer (W), or from a position offset in the radial direction (toward the edge of the wafer (W)) from the center (O) of the silicon wafer (W). The position at which the oxidizing agent is supplied is preferably a position offset in the radial direction from the center (O) of the silicon wafer (W) within a range of 5 mm or more and 75 mm or less, and more preferably a position offset in the radial direction from the center (O) of the silicon wafer (W) within a range of 15 mm or more and 20 mm or less.

[0036] In the etching process (step S102-2), while rotating the silicon wafer (W), an etching solution (an aqueous solution of hydrogen fluoride in this example) is supplied to the surface of the silicon wafer (W) through an etching solution supply unit (supply pipe) (4) (see FIG. 7) and brought into contact with the surface of the silicon wafer (W). Accordingly, the natural oxide film formed in the surface modification process (step S102-1) is etched. As shown in FIG. 1, the surface modification process (step S102-1) and the etching process (step S102-2) can be performed repeatedly. When the etching process (step S102-2) is performed multiple times, the amount of etching is set such that at least in the last etching process, the natural oxide film remains.

[0037] It is preferable that the etching solution be an aqueous solution of hydrogen fluoride. It is preferable that the concentration of the aqueous solution of hydrogen fluoride be within the range of 0.5 to 3.0 mass%. This is because sufficient etching action can be obtained by making the concentration of the aqueous solution of hydrogen fluoride 0.5 mass% or higher, while excessive etching can be suppressed by making the concentration of the aqueous solution of hydrogen fluoride 3.0 mass% or lower. It is preferable that the flow rate of the aqueous solution of hydrogen fluoride be 0.5 to 1.5 L / min. It is preferable that the treatment time with the aqueous solution of hydrogen fluoride be 1 to 10 seconds.

[0038] The etching solution (an aqueous solution of hydrogen fluoride in this example) may be supplied from the center (O) of the silicon wafer (W) (without being offset in the radial direction), and the etching solution may be supplied offset in the radial direction from the center (O) of the silicon wafer (W).

[0039] In this embodiment, as shown in FIG. 1, the surface modification process (step S102-1) and the etching process (step S102-2) are repeated a predetermined number of times (e.g., 2 to 4 times), and then proceed to the rinsing process (step S102-3) described later. In addition, the surface modification process (step S102-1) and the etching process (step S102-2) do not necessarily need to be repeated. In addition, the surface modification process (step S102-1), the etching process (step S102-2), and the rinsing process (step S102-3) may also be repeated (e.g., 2 to 4 times), including the rinsing process (step S102-3).

[0040] Next, a rinsing treatment using a rinsing liquid (rinsing process: step S102-3) is performed. In this process, while rotating the silicon wafer (W), a rinsing liquid (pure water in this example) is supplied to the surface of the silicon wafer (W) through a rinsing liquid supply unit (supply pipe) (5) (see FIG. 7) to wash away foreign matter on the surface of the silicon wafer (W).

[0041] It is preferable that the rinsing solution be pure water, and it is particularly preferable that it be DIW (Deionized Water). It is preferable that the flow rate of the pure water be 0.5 to 1.5 L / min. It is preferable that the treatment time with the pure water be 1 to 30 seconds. The pure water may be supplied from the position of the center (O) of the silicon wafer (W) (without being offset in the radial direction), or the pure water may be supplied offset in the radial direction from the position of the center (O) of the silicon wafer (W).

[0042] In steps S102-1 to S102-3, the rotational speed of the silicon wafer (W) during cleaning is preferably within the range of 100 to 500 rpm.

[0043] Herein, the cleaning method of the silicon wafer (W) of the present embodiment further includes an oxygen concentration acquisition process (step S101) for acquiring the oxygen concentration of the silicon wafer (W) (provided to the final finishing process) prior to the final finishing process (step S102), as shown in FIG. 1. In addition, when performing the aforementioned SC-1 (Standard Clean 1) cleaning or SC-2 (Standard Clean 2) cleaning, the oxygen concentration acquisition process (step S101) may be performed before these cleanings, or the oxygen concentration acquisition process (step S101) may be performed after these cleanings.

[0044] The oxygen concentration of a silicon wafer (W) can be obtained, for example, by measuring the oxygen concentration of the silicon wafer (W). This measurement can be performed using any known measuring instrument, but for example, it can be performed using a measuring instrument that uses Fourier Transform Infrared Spectroscopy (FTIR) in accordance with ASTM F121-1979. The oxygen concentration of the silicon wafer (W) can be measured for each wafer. Alternatively, the oxygen concentration of the silicon wafer (W) can be obtained by a method such as measuring the oxygen concentration of a representative wafer and calculating the oxygen concentration for other wafers using a calculation unit with a correction value. Or, if the oxygen concentration of the silicon wafer (W) is information stored in a memory unit, the oxygen concentration of the silicon wafer (W) can be obtained from the memory unit. Alternatively, if information regarding the oxygen concentration of the silicon wafer (W) is stored externally, the oxygen concentration of the silicon wafer (W) may be obtained by communicating via a communication unit. Alternatively, it may be obtained by transferring information regarding the oxygen concentration of the silicon wafer (W).

[0045] Here, in the cleaning method of the silicon wafer (W) of the present embodiment, in the etching process (step S102-2), an adjustment factor (at least one of the etching time and the concentration of the etching solution in the present embodiment) is adjusted based on the oxygen concentration of the silicon wafer (W) obtained by the oxygen concentration acquisition process (step S101). In addition, in the final finishing process (step S102), when the surface layer modification process (step S102-1) and the etching process (step 102-2) are repeated multiple times, it is preferable to adjust the adjustment factor (at least one of the etching time and the concentration of the etching solution in the present embodiment) based on the oxygen concentration of the silicon wafer (W) obtained by the oxygen concentration acquisition process (step S101) in the final etching process (step S102-2).

[0046] Hereinafter, the effects of the cleaning method of the silicon wafer (W) of the present embodiment will be explained.

[0047] As will be explained in detail in the embodiments described below, it was found that there is a relationship between the oxygen concentration of the silicon wafer (W) and the increase in the thickness of the oxide film on the silicon wafer (W) after cleaning, such that as the oxygen concentration of the silicon wafer (W) increases, the increase in the thickness of the oxide film on the silicon wafer (W) after cleaning also increases (see FIG. 2 regarding the embodiments).

[0048] On the other hand, regarding the etching time in the etching process (step S102-1) and the amount of reduction in the thickness of the oxide film on the silicon wafer (W), there is a relationship such that as the etching time increases, the amount of reduction in the thickness of the oxide film on the silicon wafer (W) also increases (see FIG. 3 regarding the example).

[0049] Likewise, regarding the concentration of the etching solution in the etching process (step S102-1) and the amount of reduction in the thickness of the oxide film on the silicon wafer (W), there is a relationship such that as the concentration of the etching solution increases, the amount of reduction in the thickness of the oxide film on the silicon wafer (W) also increases (see FIG. 4 relating to the example).

[0050] The cleaning method of a silicon wafer (W) according to the present embodiment further includes an oxygen concentration acquisition process (step S101) for acquiring the oxygen concentration of the silicon wafer (W) prior to the final finishing process (step S102), and in the etching process (step S102-2), an adjustment factor (at least one of the etching time and the concentration of the etching solution in the present embodiment) is adjusted based on the oxygen concentration of the silicon wafer (W) acquired by the oxygen concentration acquisition process (step S101).

[0051] Accordingly, in the etching process (step S102-2), the higher (lower) the oxygen concentration of the silicon wafer (W) obtained by the oxygen concentration acquisition process (step S101), the adjustment factor is adjusted accordingly (i.e., in this embodiment, at least one of the adjustments to lengthen (shorten) the etching time and the adjustment to increase (low) the concentration of the etching solution is performed), and the increase (decrease) in the amount of film thickness increase due to the high (low) oxygen concentration and, for example in this embodiment, the increase (decrease) in the amount of film thickness decrease due to at least one of the long (short) etching time and the high (low) concentration of the etching solution are offset, thereby increasing the uniformity of the oxide film thickness on the silicon wafer (W) between wafers. Afterwards, the silicon wafer (W) shipped by the product shipment process (step S103) may have the variation in oxide film thickness between wafers suppressed.

[0052] As described above, according to the cleaning method of the silicon wafer (W) of the present embodiment, the uniformity of the thickness of the oxide film on the silicon wafer (W) between wafers can be increased.

[0053] In the final finishing process (step S102), the surface modification process (step S102-1) and the etching process (step S102-2) are repeated multiple times, and in the final etching process (step S102-2), it is preferable to adjust the adjustment factor (e.g., at least one of the etching time and the concentration of the etching solution) based on the oxygen concentration of the silicon wafer (W) obtained by the oxygen concentration acquisition process (step S101). This is because the film thickness of the oxide film on the silicon wafer (W) provided to the product shipment process (step S103) depends almost entirely on the final etching process (step S102-2), so it is sufficient to perform the above adjustment in the final etching process (step S102-2).

[0054] Given the simplicity of the adjustment, it is preferable that the adjustment factor includes at least the etching time, and in particular, it is preferable that the adjustment factor is only the etching time. In this case, in the etching process (step S102-2), the concentration of the etching solution is fixed, and only the etching time is adjusted based on the oxygen concentration of the silicon wafer (W) obtained by the oxygen concentration acquisition process (step S101).

[0055] When fixing the concentration of the etching solution, for example, it is best to adopt the most standard value.

[0056] Alternatively, it is preferable that the above adjustment factor includes at least the concentration of the etching solution. The above adjustment factor may be the etching time alone. When the etching time is fixed, as an example, it is preferable to adopt the most standard value.

[0057] In addition, it is preferable to calculate the amount of adjustment of the adjustment factor to be adjusted (e.g., at least one of the etching time to be adjusted and the concentration of the etching solution to be adjusted) by assuming that the increase in film thickness of the silicon wafer (W) is a monotonically increasing function represented by a linear or polynomial of order 2 or higher with respect to the oxygen concentration of the silicon wafer (W) obtained by the oxygen concentration acquisition process (step S101). As shown in the embodiments described later, the oxygen concentration of the silicon wafer (W) and the increase in film thickness of the oxide film on the silicon wafer (W) after cleaning can be approximated by a linear relationship (see FIG. 2 regarding the embodiments), and can also be approximated using a polynomial of order 2 or higher. By using such a relationship, it is relatively easy to quantitatively calculate how much the adjustment factor (e.g., etching time or concentration of the etching solution) needs to be adjusted according to the oxygen concentration of the silicon wafer (W) obtained by the oxygen concentration acquisition process (step S101). It is desirable to express the above assumptions using, for example, an approximation based on the least squares method.

[0058] An example is given regarding the case of performing linear approximation.

[0059] As can be seen from FIG. 2 relating to an embodiment, since the oxygen concentration of the silicon wafer (W) and the amount of change in the film thickness of the silicon wafer can be linearly approximated, a: slope, b: intercept, Δt: amount of change in film thickness, O i1 : One point of oxygen concentration (measurement point or estimate based on linear approximation, etc.), O i0 : O i1 One point of oxygen concentration below (measurement point or estimated value on linear approximation, etc.) (O i1 and O i0 is, 1×10 17 When standardizing by dividing into) it can be expressed by the following Equation 1.

[0060] (Equation 1)

[0061]

[0062] In addition, since the change in etching time and silicon wafer film thickness can be linearly approximated, and the change in silicon wafer film thickness and the concentration of the etching solution can be linearly approximated, c: slope (Fig. 3), d: slope (Fig. 4), T1: one point of etching time (measurement point or estimated value based on linear approximation, etc.), T0: one point of etching time (measurement point or estimated value based on linear approximation, etc.) (less than or equal to T1), Co HF : When expressed in terms of hydrofluoric acid concentration, it can be represented by the following Equation 2.

[0063] (Equation 2)

[0064]

[0065] Since it is desirable to offset these, for example, when adjusting the etching time, the following Equation 3 can be used.

[0066] (Equation 3)

[0067]

[0068] The coefficients a, b, c, and d can be obtained from experimental results (for example, as in the examples described below). Co HF It may be the setting value configured during cleaning, or Co during or before cleaning. HF The measured value may be used as the setting value. T0 is the time for etching the previous (past) wafer, and T1 is the time for etching the current (from now) wafer. O i1 is the oxygen concentration of the wafer being etched this time, and O i0 is the oxygen concentration from the previous etching. The first T0 can be determined experimentally in advance so that the wafer achieves the desired oxygen film thickness. For example, using a wafer with a known oxygen concentration, Co HF By fixing the etching time and increasing or decreasing it, the time required to achieve the desired film thickness can be determined.

[0069] Method for manufacturing silicon wafers

[0070] A method for manufacturing a silicon wafer according to one embodiment of the present invention includes performing a cleaning method for the silicon wafer of the above embodiment. For the same reasons as described in the embodiment of the silicon wafer cleaning method, the method for manufacturing a silicon wafer of the present embodiment can increase the uniformity of the thickness of the oxide film on the silicon wafer (W) between wafers.

[0071] <Silicon Wafer Cleaning System>

[0072] FIG. 7 is a schematic diagram of a silicon wafer cleaning system according to one embodiment of the present invention. As shown in FIG. 7, the silicon wafer cleaning system (1) comprises a silicon wafer cleaning device having a stage (2) on which a silicon wafer (W) is placed, an oxidizing agent supply unit (supply pipe) (3) for supplying an oxidizing agent onto the silicon wafer (W) placed on the stage (2), an etching solution supply unit (supply pipe) (4) for supplying an etching solution onto the silicon wafer (W) placed on the stage (2), and a rinse solution supply unit (supply pipe) (5) for supplying a rinse solution onto the silicon wafer (W) placed on the stage (2). The silicon wafer cleaning device can be configured similarly to a conventional configuration.

[0073] The cleaning system for a silicon wafer (W) of the present embodiment further comprises an oxygen concentration acquisition unit (6) for acquiring the oxygen concentration of the silicon wafer (W). The oxygen concentration acquisition unit (6) may be any known measuring instrument capable of acquiring the oxygen concentration of the silicon wafer (W). As an example, a measuring instrument using Fourier Transform Infrared Spectroscopy (FTIR) in accordance with ASTM F121-1979 may be used. In cases where a method is used in which the oxygen concentration of a representative wafer is measured and the oxygen concentration of other wafers is calculated by calculation using a correction value, the oxygen concentration acquisition unit (6) may be equipped with a calculation unit (e.g., any known computer) in addition to the measuring instrument. Alternatively, the oxygen concentration acquisition unit (6) may be equipped with a memory unit (e.g., memory) that stores the oxygen concentration of the silicon wafer (W). Alternatively, the oxygen concentration acquisition unit (6) may be a communication unit that acquires information on the oxygen concentration of the silicon wafer (W) from the outside.

[0074] The cleaning system for a silicon wafer (W) of the present embodiment further comprises an adjustment unit (7) that adjusts an adjustment factor (at least one of the etching time and the concentration of the etching solution in the etching process (step S102)) based on the oxygen concentration of the silicon wafer (W) obtained by the oxygen concentration acquisition unit (6).

[0075] According to the cleaning system (1) of the silicon wafer (W) of the present embodiment, based on the oxygen concentration of the silicon wafer (W) obtained by the oxygen concentration acquisition unit (6), the adjustment unit (7) performs adjustment of the adjustment factor as the oxygen concentration of the silicon wafer (W) increases (low) (i.e., in the present embodiment, at least one of the adjustments to lengthen (shorten) the etching time and to increase (low) the concentration of the etching solution), and the increase (decrease) in the amount of film thickness increase due to the high (low) oxygen concentration and, for example in the present embodiment, the increase (decrease) in the amount of film thickness decrease due to the long (short) etching time and the high (low) concentration of the etching solution are offset, thereby increasing the uniformity of the thickness of the oxide film on the silicon wafer (W) between wafers. After that, the silicon wafer (W) shipped by the product shipment process (step S103) may have a variation in the thickness of the oxide film between wafers suppressed.

[0076] As described above, according to the cleaning system (1) of the silicon wafer (W) of the present embodiment, the uniformity of the thickness of the oxide film on the silicon wafer (W) between wafers can be increased.

[0077] (Example)

[0078] (Example 1)

[0079] 5.8×10 17 atoms / cm³, 8.1×10⁻⁶ 17 atoms / cm³, 10.3×10⁻⁶ 17 atoms / cm³, 11.6×10⁻⁶ 17 atoms / cm³, 13.2×10⁻⁶ 17 Twenty epitaxial silicon wafers with a diameter of 300 mm and oxygen concentrations of 5 atoms / cm³ were prepared. Oxygen concentrations were measured at 31 points using FT-IR at a 5 mm pitch from the center to the periphery, and the average value was used. All of these wafers were cleaned individually under the same conditions.

[0080] The cleaning method and film thickness measurement were performed by the following method. First, a cleaning treatment was performed for 15 seconds using ozone water with an ozone concentration of 20 ppm and a wafer rotation speed of 300 rpm. Next, a cleaning treatment aimed at etching the oxide film was performed for 4 seconds using an aqueous solution of hydrogen fluoride with a concentration of 1% and a silicon wafer rotation speed of 300 rpm. At this time, the etching treatment with the aqueous solution of hydrogen fluoride was performed under conditions where the oxide film was not completely removed. Next, to form an oxide film, a cleaning treatment was performed for 30 seconds using ozone water with an ozone concentration of 20 ppm and a wafer rotation speed of 300 rpm, and this sequence of cleaning with ozone water and cleaning with the aqueous solution of hydrogen fluoride was repeated three times. Afterwards, finally, cleaning with DIW (pure water) was performed for 30 seconds. For each cleaning process, the flow rate of the chemical solution was set to 1.0 L / min. For the epitaxial silicon wafer, the supply tube was inclined from the top downward (toward the side closer to the silicon wafer) and from the radial edge of the silicon wafer toward the center, with an inclination angle of 4° in the vertical direction. The thickness of the native oxide film on the wafer was measured using a spectroscopic ellipsometer at a total of 121 measurement points spaced 29.4 mm from the center of the wafer after single-wafer cleaning (see Fig. 5).

[0081] FIG. 2 is a diagram showing the relationship between the oxygen concentration of a silicon wafer (W) and the increase in the thickness of an oxide film on the silicon wafer (W). The oxide film thickness is 5.8 × 10⁻⁶, which is the lowest oxygen concentration at the level measured this time. 17 atoms / cm³ was used as the standard, and the change compared to this was used as an indicator of film thickness. It was found that wafers with higher oxygen concentrations had thicker native oxide films. Furthermore, in the case of a linear approximation, the amount of increase was 5.8 × 10⁻⁶ oxygen concentrations 17atoms / cm³ to 13.2×10⁻⁶ 17 For wafers with atoms / cm³, it was found that the natural oxide film thickness of wafers cleaned under the same conditions increased as the oxygen concentration increased.

[0082] (Example 2)

[0083] A method for adjusting the oxygen concentration dependence of the native oxide film thickness was examined. First, the amount of change in the native oxide film thickness when the etching time in the aqueous hydrofluoric acid solution was varied was investigated. The cleaning method was the same as in Example 1. To adjust the native oxide film thickness, the etching time of the final third pass in the aqueous hydrofluoric acid solution (1 wt%) was varied to 0 seconds (no treatment), 2 seconds, 4 seconds, 6 seconds, 8 seconds, and 10 seconds, and the native oxide film thickness was measured. The wafer had an oxygen concentration of 10.3 × 10⁻⁶ 17 atoms / cm³ were prepared, and five sheets were treated at each etching time to measure the thickness of the natural oxide film. The measurement results are shown in Fig. 3. Here, the vertical axis of Fig. 3 represents the amount of thinning compared to the thickness of the natural oxide film after cleaning, with the etching time of the aqueous hydrogen fluoride solution being 0 seconds (no treatment). In the case of linear approximation, it was found that the thickness of the natural oxide film decreased (became thinner) as the etching time with the aqueous hydrogen fluoride solution (1 wt%) increased.

[0084] (Example 3)

[0085] Next, the change in native oxide film thickness when the concentration of the aqueous hydrogen fluoride solution was varied was investigated. The cleaning method was the same as in Examples 1 and 2. To adjust the native oxide film thickness, the concentration of the final third aqueous hydrogen fluoride solution was varied to 0 wt% (no treatment), 1 wt%, and 3 wt%, and etching was performed for 2 and 6 seconds, after which the native oxide film thickness was measured. The wafer had an oxygen concentration of 10.3 × 10⁻⁶ 17atoms / cm³ were prepared, and five sheets were treated at each etching time to measure the thickness of the natural oxide film. The measurement results are shown in Fig. 4. Here, the vertical axis of Fig. 4 represents the amount of thinning compared to the natural oxide film thickness after cleaning, with the concentration of the aqueous hydrogen fluoride solution set to 0 wt% (no treatment). It was found that the concentration of the aqueous hydrogen fluoride solution and the amount of reduction in the natural oxide film thickness were in a proportional relationship regardless of the etching time.

[0086] (Example 4)

[0087] To verify the native oxide film thickness under conventional conditions, a wafer with a known oxygen concentration was cleaned using the same method as in Examples 1 to 3, and subsequently, the native oxide film thickness was measured. In this experiment, the data used in Example 1 was also utilized, with an oxygen concentration of 5.8 × 10⁻⁶ 17 atoms / cm³ to 13.2×10⁻⁶ 17 A total of 340 wafers were used between atoms / cm³.

[0088] (Example 5)

[0089] In the prior art, since it was known that the natural oxide film thickness changes depending on the oxygen concentration (see Fig. 6), a method for aligning the natural oxide film thickness was considered by taking into account the trend of the relationship between the film thickness and the oxygen concentration. For example, when the oxygen concentration is 12.0 × 10 17 A wafer of atoms / cm³ of 10.0×10 17 In the case where the thickness of the natural oxide film is to be the same as atoms / cm³, when the conditions are a=0.10, b=0.00, c=0.20, d=2, CoHF=1wt%, and To=10s, applying Equation 3 results in an etching time of 10.5s.

[0090] In FIG. 6, when cleaning is performed continuously, the film thickness difference between the first wafer and the second wafer after cleaning is plotted using the first wafer and the second wafer during cleaning. The film thickness difference is plotted in the same way for subsequent cleaning. In the cleaning method before control (conventional), when using 0 as the reference, the film thickness difference deviates from the reference value (0) and the deviation is large. On the other hand, in the cleaning method that has been adjusted, the film thickness difference from the reference value (0) can be reduced and the deviation is also reduced.

[0091] Although embodiments and examples of the present invention have been described above, the present invention is not limited in any way to the above embodiments and examples.

[0092] For example, the relationship between the oxygen concentration of the silicon wafer (W) and the increase in the thickness of the oxide film on the silicon wafer (W) is not limited to a linear representation, and various approximation formulas can be used. Such approximation formulas may include polynomials of degree 2 or higher, exponential functions, logarithmic relationships, etc. Furthermore, although the least squares method was exemplified for the approximation, other approximations may also be used.

[0093] In addition, in the above embodiments, etching time and the concentration of the etching solution were exemplified as adjustment factors, but they are not limited thereto. The temperature during the etching process (typically, the higher the temperature, the greater the amount of etching and the thinning of the oxide film) or the rotation speed of the silicon wafer (W) during cleaning (typically, the higher the rotation speed, the greater the amount of etching and the thinning of the oxide film) may be used, and one or more of these may be used in combination with the etching time or the concentration of the etching solution, or both the etching time and the concentration of the etching solution. In addition, various adjustment factors that affect the thickness of the oxide film may be used individually or in combination with other adjustment factors.

[0094] In addition, in the above embodiments and examples, an example using a formula was shown for adjusting an adjustment factor (at least one of the etching time and the concentration of the etching solution in the above examples) based on the oxygen concentration of the silicon wafer (W) obtained in the etching process (step S102-2), but this is not limited to this case. For example, in the case of etching time or the concentration of the etching solution, if there is a sufficient amount of data to perform machine learning, the explanatory variables (inputs) include at least the oxygen concentration of the silicon wafer (W), the etching time in the etching process (step S102-2), and the concentration of the etching solution, and the target variables (outputs) include at least the film thickness of the oxide film on the silicon wafer (W), and thus an artificial intelligence model is created by machine learning, and when the oxygen concentration of the silicon wafer (W), the etching time, and the concentration of the etching solution are input into the artificial intelligence model, the film thickness of the oxide film on the silicon wafer (W) can be output. As an example, if the concentration of the etching solution is input as a fixed value (e.g., commonly used), the oxygen concentration of the acquired silicon wafer (W) is input as a fixed value, and 10 to 1,000 candidate etching times (from past data, etc.) are input, 10 to 1,000 film thickness values ​​of the oxide film on the silicon wafer (W) are obtained as outputs. Among such outputs, the input corresponding to the film thickness value closest to the target value can be set as the etching time value to be adjusted. When adjusting only the concentration of the etching solution, it is preferable to perform the same processing by fixing the etching time and varying the concentration of the etching solution; when adjusting both the etching time and the concentration of the etching solution, it is preferable to perform the same processing by varying the combination of the etching time and the concentration of the etching solution. Such a machine learning model can be any known one, but as an example, a neural network can be used. The same applies to other adjustment factors.

[0095] For example, even if there is not enough data for machine learning, if there is a certain amount of data, data regarding the thickness of the oxide film on the silicon wafer (W), the oxygen concentration of the silicon wafer (W), the etching time, and the concentration of the etching solution can be obtained by mapping, and by adopting the etching time and the concentration of the etching solution in the mapping that correspond to the acquired oxygen concentration of the silicon wafer (W) and the desired thickness of the oxide film on the silicon wafer (W), at least one of the etching time and the concentration of the etching solution can be adjusted. The same applies to other adjustment factors. In addition, various modifications or changes are possible. Explanation of the symbols

[0096] 1 : Silicon Wafer Cleaning System 2 : Stage 3 : Oxidizer supply section (supply pipe) 4 : Etching solution supply section (supply pipe) 5 : Rinse liquid supply unit (supply pipe) 6 : Oxygen concentration acquisition unit 7 : Adjustment Department W: Silicon wafer

Claims

Claim 1 A cleaning method for a single-wafer silicon wafer comprising a final finishing process including a surface modification process for modifying the surface layer of a silicon wafer using an oxidizing agent, an etching process for etching the surface layer of the silicon wafer using an etching solution, and a rinsing process for rinsing the surface of the silicon wafer using a rinsing solution, wherein, prior to the final finishing process, the method further comprises an oxygen concentration acquisition process for acquiring the oxygen concentration of the silicon wafer, and wherein, in the etching process, an adjustment factor is adjusted based on the oxygen concentration of the silicon wafer acquired by the oxygen concentration acquisition process. Claim 2 A method for cleaning a silicon wafer according to claim 1, wherein in the final finishing process, the surface modification process and the etching process are repeated multiple times, and in the final etching process, the adjustment factor is adjusted based on the oxygen concentration of the silicon wafer obtained by the oxygen concentration acquisition process. Claim 3 A method for cleaning a silicon wafer according to claim 1 or 2, wherein the adjustment factor comprises at least an etching time. Claim 4 In paragraph 3, the above adjustment factor is only the etching time, a method for cleaning a silicon wafer. Claim 5 A method for cleaning a silicon wafer according to claim 1 or 2, wherein the adjustment factor comprises at least the concentration of the etching solution. Claim 6 A method for cleaning a silicon wafer according to claim 3, wherein, in the etching process, the higher the oxygen concentration of the silicon wafer obtained by the oxygen concentration acquisition process, the longer the etching time is adjusted. Claim 7 A method for cleaning a silicon wafer according to claim 5, wherein, in the etching process, the higher the oxygen concentration of the silicon wafer obtained by the oxygen concentration acquisition process, the higher the concentration of the etching solution is adjusted. Claim 8 A method for cleaning a silicon wafer according to claim 1 or 2, wherein the amount of increase in film thickness of the silicon wafer is assumed to be a monotonically increasing function represented by a linear or polynomial of degree 2 or higher of the oxygen concentration of the silicon wafer obtained by the oxygen concentration acquisition process, and the amount of adjustment of the adjustment factor to be adjusted is calculated. Claim 9 A method for manufacturing a silicon wafer, characterized by including performing a cleaning method of a silicon wafer as described in claim 1 or 2. Claim 10 A cleaning system for a silicon wafer comprising a stage for placing a silicon wafer, an oxidizing agent supply unit for supplying an oxidizing agent onto a silicon wafer placed on the stage, an etching solution supply unit for supplying an etching solution onto a silicon wafer placed on the stage, and a rinsing solution supply unit for supplying a rinsing solution onto a silicon wafer placed on the stage, wherein the cleaning system for a silicon wafer further comprises an oxygen concentration acquisition unit for acquiring an oxygen concentration of the silicon wafer and an adjustment unit for adjusting an adjustment factor in an etching process based on the oxygen concentration of the silicon wafer acquired by the oxygen concentration acquisition unit.

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