Method for cleaning silicon wafer

Abstract

To provide a method for cleaning a silicon wafer capable of suppressing a surface defect caused by ozone water, suppressing generation of a watermark and adhesion of particles, and suppressing deterioration of surface roughness.SOLUTION: A method for cleaning a silicon wafer is applicable to single-wafer spin cleaning in which a cleaning step using hydrofluoric acid and a cleaning step using ozone water are performed in a state where the silicon wafer is rotated. The method includes: first cleaning processing in which the cleaning step using the ozone water is performed and then the cleaning step using the hydrofluoric acid is performed at a specific time interval; and second cleaning processing in which the cleaning step using the ozone water is performed without an interval after the cleaning step using the hydrofluoric acid is performed.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a method for cleaning a silicon wafer. [Background technology]

[0002] As semiconductor devices become more highly integrated and denser, it is desired that the surface of single crystal silicon wafers after mirror polishing be free of minute defects. To meet such a demand, the cleaning process after finish polishing of silicon wafers is an important process that determines the number of defects on the surface. In such a cleaning process, for example, a single-wafer spin cleaning process is used to form an oxide film using ozone water and remove the oxide film using hydrofluoric acid, and these processes are repeated one or more times, followed by spin drying.

[0003] For example, as a single-wafer spin cleaning method including a cleaning step using ozone water and a cleaning step using hydrofluoric acid, Patent Document 1 discloses a silicon wafer cleaning method in which a spin cleaning step using pure water is provided between the cleaning step using ozone water and the cleaning step using hydrofluoric acid. Patent Document 1 also describes that the flow rate of the pure water in the spin cleaning step using the pure water is 1.2 L / min or more and 2.0 L / min or less, and the wafer rotation speed is 1000 rpm or more and 1500 rpm or less.

[0004] In this cleaning method, a spin cleaning process (rinsing process) using pure water is provided between the cleaning process using ozone water and the cleaning process using hydrofluoric acid, and the coexistence of ozone water and hydrofluoric acid is prevented, thereby suppressing the deterioration of the wafer surface roughness.

[0005] Patent Document 2 discloses a method for cleaning a silicon wafer, which includes a cleaning step of supplying hydrofluoric acid to the surface of the silicon wafer while rotating the silicon wafer at a low rotation speed, a step of shaking off the hydrofluoric acid present on the surface of the silicon wafer while rotating the silicon wafer at a medium rotation speed, and then a cleaning step of supplying ozone water to the surface of the silicon wafer while rotating the silicon wafer at a high rotation speed.

[0006] In this cleaning method, after a cleaning process using hydrofluoric acid (low rotation speed: 100 rpm or less), a process of shaking off the chemical solution (medium rotation speed: 200 rpm or less) is performed without performing a cleaning process using pure water, and then a cleaning process using ozone water (high rotation speed: 500 rpm or more) is performed, thereby effectively suppressing the occurrence of watermarks and the adhesion of particles. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2015-220284 A [Patent Document 2] JP 2019-36665 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the silicon wafer cleaning method disclosed in Patent Document 1, watermarks are generated in a spin cleaning step (rinsing step) using pure water that is performed between a cleaning step using ozone water and a cleaning step using hydrofluoric acid, deteriorating the surface quality of the silicon wafer.

[0009] Furthermore, in the silicon wafer cleaning method disclosed in Patent Document 2, a process of shaking off the chemical solution (medium speed rotation: 200 rpm or less) is provided after the cleaning process using hydrofluoric acid. However, detailed experimental investigations have revealed that, for example, if a period of time (corresponding to the above-mentioned process of shaking off the hydrofluoric acid) in which no chemical solution is supplied is provided between the cleaning process using hydrofluoric acid and the cleaning process using ozone water, and the wafer rotation speed during that period is set to less than 1000 rpm, peculiar defects (surface defects caused by ozone water) occur due to the strong oxidizing power of the ozone water.

[0010] The present invention has been made in consideration of the above problems, and provides a method for cleaning silicon wafers that can improve the quality of silicon wafers by suppressing surface defects caused by ozone water, suppressing the occurrence of watermarks and adhesion of particles, and suppressing deterioration of surface roughness (haze). [Means for solving the problem]

[0011] The silicon wafer cleaning method according to the present invention is a silicon wafer cleaning method applicable to single-wafer spin cleaning in which a cleaning step using hydrofluoric acid and a cleaning step using ozone water are performed while the silicon wafer is rotating, and is characterized by including a first cleaning process in which a cleaning step using ozone water is performed and then a cleaning step using hydrofluoric acid is performed after a specific time interval, and a second cleaning process in which after the cleaning step using hydrofluoric acid, a cleaning step using ozone water is performed without any interval.

[0012] In this case, when the second cleaning process is performed after the first cleaning process, a cleaning step using hydrofluoric acid in the first cleaning process also serves as a cleaning step using hydrofluoric acid in the second cleaning process. On the other hand, when the first cleaning process is performed after the second cleaning process, a cleaning step using ozone water in the second cleaning process also serves as a cleaning step using ozone water in the first cleaning process.

[0013] In the spin cleaning, it is preferable that the first cleaning process is performed at least once, and the second cleaning process is performed at least once.

[0014] In addition, in the silicon wafer cleaning method according to the present invention, the specific time interval is preferably 0.1 seconds or more and 1 second or less, the rotation speed of the silicon wafer at the transition timing from the cleaning step using hydrofluoric acid to the cleaning step using ozone water is preferably 1000 rpm or more, and the flow rate of hydrofluoric acid in the cleaning step using hydrofluoric acid is preferably 1 L / min or more, and the flow rate of ozone water in the cleaning step using ozone water is preferably 1 L / min or more.

[0015] By carrying out the method for cleaning silicon wafers according to the present invention, it is possible to suppress surface defects caused by ozone water, as well as the occurrence of watermarks and adhesion of particles, and to suppress deterioration of surface roughness.

[0016] In addition, the silicon wafer cleaning method according to the present invention is characterized in that a cleaning step using hydrofluoric acid is performed to remove an oxide film on the wafer surface, the wafer surface is made hydrophobic, and then a cleaning step using ozone water is performed, and the cleaning step using hydrofluoric acid is performed at least once during spin cleaning. According to the present invention, the oxide film is completely removed, and the adhesion of particles to the wafer surface can be suppressed by lifting off the abrasive and particles from the wafer surface. Effect of the Invention

[0017] According to the method for cleaning silicon wafers of the present invention, surface defects caused by ozone water can be suppressed, and the occurrence of watermarks and adhesion of particles can be suppressed, thereby suppressing deterioration of surface roughness (haze). [Brief description of the drawings]

[0018] [Figure 1]FIG. 1 is a schematic diagram showing an example of a spin cleaner capable of carrying out the silicon wafer cleaning method according to the present invention. [Diagram 2] FIG. 2 is a flow chart showing an embodiment of the method for cleaning a silicon wafer according to the present invention. [Diagram 3] FIG. 3 is a flow chart showing an embodiment of the method for cleaning a silicon wafer according to the present invention. [Figure 4] FIG. 4 is a flow chart showing a specific example of the method for cleaning a silicon wafer according to the present invention. [Diagram 5] FIG. 5 is a diagram showing the results of counting the number of surface defects caused by ozone water. [Figure 6] FIG. 6 shows the measurement results of LPD (≧19 nm LPD). [Figure 7] FIG. 7 is a diagram showing the results of measuring the surface roughness. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to these preferred embodiments.

[0020] <Spin Cleaner> First, as a premise for explaining the silicon wafer cleaning method of this embodiment, a brief overview of a single-wafer spin cleaner capable of carrying out this cleaning method will be given. Fig. 1 is a schematic diagram showing an example of a spin cleaner capable of carrying out the silicon wafer cleaning method of this embodiment, and is a schematic representation of, for example, a known single-wafer spin cleaner.

[0021] This spin cleaner 1 includes, for example, a casing 2, a rotary table 5 that is provided within the casing 2 and rotates integrally with a drive shaft 4 by the driving force of a motor (not shown) with a silicon wafer W placed on it via a holding member 3, and a supply nozzle 6 that appropriately supplies a cleaning liquid such as hydrofluoric acid, ozone water, or pure water to the surface of the silicon wafer W, and is configured to discharge waste liquid from cleaning to the bottom of the casing 2. Note that a supply nozzle 6 may be provided separately for each of the cleaning liquids, namely, hydrofluoric acid, ozone water, and pure water.

[0022] The spin cleaner 1 configured in this manner is controlled to appropriately perform the silicon wafer cleaning method of this embodiment (a cleaning step using hydrofluoric acid and a cleaning step using ozone water) described below when the silicon wafer W is set in the casing 2.

[0023] <Overview of silicon wafer cleaning methods> Next, an outline of the method for cleaning a silicon wafer according to the present embodiment will be described. Figures 2 and 3 are flow charts showing an embodiment of the method for cleaning a silicon wafer according to the present invention.

[0024] The silicon wafer cleaning method of this embodiment is a cleaning method applicable to single-wafer spin cleaning in which a cleaning step using hydrofluoric acid and a cleaning step using ozone water are performed while the silicon wafer is rotating, and an oxide film is formed on the wafer surface by the cleaning step using ozone water, and particles, watermarks, and the like on the wafer surface are removed together with the oxide film by the cleaning step using hydrofluoric acid.

[0025] The silicon wafer cleaning method of this embodiment is characterized in that, in single-wafer spin cleaning, a specific time interval is provided between a cleaning step using ozone water and a subsequent cleaning step using hydrofluoric acid, while no time interval is provided between the cleaning step using hydrofluoric acid and a subsequent cleaning step using ozone water.

[0026] That is, the silicon wafer cleaning method of this embodiment includes a first cleaning process (see FIG. 2) in which a cleaning process using ozone water is performed, and then a cleaning process using hydrofluoric acid is performed after a specific time interval, and a second cleaning process (see FIG. 3) in which a cleaning process using ozone water is performed without any time interval after the cleaning process using hydrofluoric acid. Also, in the silicon wafer cleaning method of this embodiment, the first cleaning process is performed at least once during spin cleaning, and the second cleaning process is performed at least once.

[0027] In this case, for example, when a second cleaning process is performed after a first cleaning process, a cleaning step using hydrofluoric acid in the first cleaning process also serves as a cleaning step using hydrofluoric acid in the second cleaning process. On the other hand, when a first cleaning process is performed after a second cleaning process, a cleaning step using ozone water in the second cleaning process also serves as a cleaning step using ozone water in the first cleaning process.

[0028] In addition, in the silicon wafer cleaning method of this embodiment, a cleaning step using hydrofluoric acid is performed to remove the oxide film on the wafer surface, and the wafer surface is made hydrophobic (water repellent), and then a cleaning step using ozone water is performed. This cleaning step using hydrofluoric acid is performed at least once during spin cleaning. In this embodiment, the oxide film is completely removed, and the abrasive and particles are lifted off from the wafer surface, thereby suppressing the adhesion of particles to the wafer surface.

[0029] In the silicon wafer cleaning method of this embodiment, the wafer rotation speeds in each cleaning step (cleaning step using hydrofluoric acid, cleaning step using ozone water) and in the first cleaning process at specific time intervals can be set arbitrarily within the range of 500 rpm to 1500 rpm. That is, in a series of cleaning steps, the wafer rotation speed may be always constant within the range of 500 to 1500 rpm, or spin cleaning may be performed while varying the wafer rotation speed within the range of 500 to 1500 rpm.

[0030] In the silicon wafer cleaning method of this embodiment, the cleaning time in each cleaning step is the same as that in conventional spin cleaning, specifically, the cleaning time in the cleaning step using ozone water is in the range of 5 seconds to 40 seconds, and the cleaning time in the cleaning step using hydrofluoric acid is in the range of 2 seconds to 40 seconds. The ozone concentration and hydrofluoric acid concentration are the concentrations that have been conventionally used, specifically, the ozone concentration is in the range of 5 ppm to 50 ppm, and the hydrofluoric acid concentration is in the range of 0.5 mass % to 20.0 mass %.

[0031] <Details of silicon wafer cleaning method> Next, the silicon wafer cleaning method of this embodiment will be described in more detail.

[0032] FIG. 4 is a flow chart showing a specific example of the method for cleaning a silicon wafer according to the present embodiment, and more specifically, shows a specific example in which the above-mentioned first cleaning process and second cleaning process are carried out once each.

[0033] In the silicon wafer cleaning method shown in Fig. 4, as the second cleaning process described above, first, a cleaning step using hydrofluoric acid is performed (step S1), and then, without any time interval, a cleaning step using ozone water is performed (step S2). Here, the oxide film is completely removed by the cleaning step using hydrofluoric acid, and the wafer surface is made hydrophobic, and then the cleaning step using ozone water is performed. In this case, the flow rate of hydrofluoric acid is set to 1 L / min or more, the flow rate of ozone water is set to 1 L / min or more, and the rotation speed of the silicon wafer at the timing of the transition from the cleaning step using hydrofluoric acid to the cleaning step using ozone water is set to 1000 rpm or more.

[0034] Here, the timing of transition from a cleaning process using hydrofluoric acid to a cleaning process using ozone water will be described in detail. For example, as a result of detailed investigations by experiments, it was found that if the cleaning process using ozone water is performed after a time interval during which no chemical solution is supplied, after the oxide film is completely removed in a cleaning process using hydrofluoric acid, a unique defect (surface defect caused by ozone water) occurs due to the strong oxidizing power of the ozone water.

[0035] Furthermore, it was found that even when a cleaning process using ozone water is started without any interval after a cleaning process using hydrofluoric acid is performed, if the wafer rotation speed at the timing of the transition is less than 1000 rpm, the strong oxidizing power of the ozone water will cause surface defects caused by the ozone water, as described above.

[0036] Therefore, in the silicon wafer cleaning method of this embodiment, in order to suppress the above-mentioned surface defects caused by ozone water, after performing the cleaning step using hydrofluoric acid (step S1), the process moves to the cleaning step using ozone water (step S2) without any time interval, and further, at the timing of the transition, the ozone water is supplied quickly and uniformly to the surface of the silicon wafer rotating at a rotation speed of 1000 rpm or more.

[0037] The cleaning process using hydrofluoric acid makes the surface of the silicon wafer water repellent, and the hydrofluoric acid is present in a thin film on the wafer surface. This hydrofluoric acid acts as a buffer against the strong oxidizing power of ozone water, thereby suppressing the occurrence of surface defects caused by ozone water.

[0038] On the other hand, even if a cleaning process using ozone water is started without a time interval after a cleaning process using hydrofluoric acid, if the wafer rotation speed at the time of the transition is slow (for example, less than 1000 rpm), the ozone water and hydrofluoric acid will coexist on the wafer surface at the time of the transition, and the formation of an oxide film by the ozone water and the removal of the oxide film by the hydrofluoric acid will occur simultaneously on the wafer surface, resulting in a deterioration in the surface roughness of the silicon wafer.

[0039] However, in the silicon wafer cleaning method of the present embodiment, the wafer surface is rendered water repellent in the cleaning process using hydrofluoric acid, and the wafer rotation speed at the timing of transition to the cleaning process using ozone water is 1000 rpm or more, so that the coexistence time of hydrofluoric acid and ozone water is short, and hydrofluoric acid is quickly replaced by ozone water, and therefore the deterioration of the surface roughness of the silicon wafer can be suppressed. That is, if the wafer rotation speed at the time of switching from hydrofluoric acid to ozone water is less than 1000 rpm, the uniform supply of ozone water to the wafer surface and the quick replacement of hydrofluoric acid with ozone water are impaired.

[0040] In the silicon wafer cleaning method of the present embodiment, the rotation speed of the silicon wafer at the transition timing from the cleaning process using hydrofluoric acid to the cleaning process using ozone water is set to 1000 rpm or more, but the wafer rotation speed of each cleaning process before and after this transition timing can be set arbitrarily within the range of 500 rpm to 1500 rpm or less, as described above. However, when the wafer rotation speed is changed during a series of cleaning processes in which the cleaning process using ozone water is performed without an interval after the cleaning process using hydrofluoric acid is performed, a time lag occurs until the rotation speed of the spin cleaner reaches the set condition, and when the rotation speed is not stable, the ozone water lands on the surface of the silicon wafer, increasing the number of watermarks and fine particles, which may deteriorate the wafer quality. In particular, when the wafer rotation speed is less than 1000 rpm at the time when the ozone water lands on the surface of the silicon wafer, the wafer quality may deteriorate. Therefore, in such a series of cleaning processes, it is preferable to keep the wafer rotation speed constant at all times. For example, if the wafer rotation speed at the transition timing is 1000 rpm, it is desirable to keep the wafer rotation speed at 1000 rpm throughout the series of cleaning steps.

[0041] 4, as the first cleaning process described above, a cleaning step using ozone water is first performed (step S2), and then, after a specific time interval (step S3), a cleaning step using hydrofluoric acid is performed (step S4). That is, an oxide film is formed by the cleaning step using ozone water, and the wafer surface is made hydrophilic, and then the cleaning step using hydrofluoric acid is performed. As described above, in the cleaning step using hydrofluoric acid, the flow rate of hydrofluoric acid is 1 L / min or more, and in the cleaning step using ozone water, the flow rate of ozone water is 1 L / min or more.

[0042] For example, when a cleaning process using ozone water is performed and then a cleaning process using hydrofluoric acid is performed, hydrofluoric acid is supplied to the wafer surface that has been hydrophilized by ozone water, and the surface roughness is worsened compared to when a cleaning process using ozone water is performed (compared to when the wafer surface is water repellent) after a cleaning process using hydrofluoric acid is performed. Therefore, in the silicon wafer cleaning method of this embodiment, a specific time interval is provided between the cleaning process using ozone water (step S2) and the subsequent cleaning process using hydrofluoric acid (step S4) (step S3). This allows hydrofluoric acid to be supplied after ozone water is discharged from the wafer surface, and therefore the deterioration of the surface roughness of the silicon wafer can be suppressed.

[0043] In addition, the specific time interval between the cleaning step using ozone water and the subsequent cleaning step using hydrofluoric acid is preferably 0.1 to 1 second. 0.1 seconds is the minimum time required to shake off the ozone water. If the specific time interval is longer than 1 second, the wafer surface will dry out, which is undesirable as it reduces the efficiency of removing particles and watermarks. In this embodiment, by providing such a specific time interval, particles and watermarks can be efficiently suppressed. EXAMPLES

[0044] Next, the method for cleaning silicon wafers according to the present invention will be further described with reference to examples, although the present invention is not limited to the following examples.

[0045] In each of the examples (Example 1 and Comparative Examples 1 to 4) described later, in the cleaning step using hydrofluoric acid (hydrofluoric acid cleaning) and the cleaning step using ozone water (ozone water cleaning), spin cleaning was performed under the following conditions. ·Hydrofluoric acid: concentration 1% by mass, flow rate 1L / min Ozone water (O 3 ): Concentration 20ppm, flow rate 1L / min DIW (ultrapure water): flow rate 1L / min, wafer rotation speed 1000rpm Drying: Wafer rotation speed 1500 rpm

[0046] The silicon wafers used were P-silicon wafers with a diameter of 300 mm, and five silicon wafers were prepared for each example (Example 1 and Comparative Examples 1 to 4). Before cleaning, the LPD (Light Point Defect) and surface roughness (haze) were measured using a KLA-Tencor "Surfscan SP5," and the wafers were of the same level.

[0047] Table 1 also shows the cleaning flow, processing time, and wafer rotation speed for each example (Example 1 and Comparative Examples 1 to 4). [Table 1]

[0048] <Example 1> Five prepared silicon wafers were cleaned using the cleaning flow shown in Table 1 (Example 1). Cleaning flow: "Ozone water 20 seconds" → "0.2 second interval" → "Hydrofluoric acid 20 seconds" → "Ozone water 20 seconds" → "0.2 second interval" → "Hydrofluoric acid 20 seconds" → "Ozone water 20 seconds" → "DIW 20 seconds" → "Drying 40 seconds"

[0049] In Example 1, the time interval between the ozone water cleaning and the subsequent hydrofluoric acid cleaning was set to 0.2 seconds. The hydrofluoric acid cleaning and the subsequent ozone water cleaning were performed without any time interval (0 seconds). The wafer rotation speed in the ozone water cleaning and hydrofluoric acid cleaning was set to 1000 rpm. The time for the first and second hydrofluoric acid cleaning was set to 20 seconds, both of which were conditions for completely removing the oxide film. Here, "completely removing the oxide film" means that the oxide film thickness at the end of the hydrofluoric acid cleaning is 0 Å. This oxide film thickness is increased to approximately 6 Å by the subsequent ozone water cleaning.

[0050] <Comparative Example 1> Five prepared silicon wafers were cleaned using the cleaning flow shown in Table 1 (Comparative Example 1). "Ozone water 20 seconds" → "Hydrofluoric acid 20 seconds" → "Ozone water 20 seconds" → "Hydrofluoric acid 20 seconds" → "Ozone water 20 seconds" → "DIW 20 seconds" → "Drying 40 seconds"

[0051] In Comparative Example 1, no time interval was provided between the ozone water cleaning and the subsequent hydrofluoric acid cleaning, and between the hydrofluoric acid cleaning and the subsequent ozone water cleaning. The wafer rotation speed was 1000 rpm in the ozone water cleaning and the hydrofluoric acid cleaning. The first and second hydrofluoric acid cleaning times were 20 seconds, both of which were conditions for completely removing the oxide film.

[0052] <Comparative Example 2> Five prepared silicon wafers were cleaned using the cleaning flow shown in Table 1 (Comparative Example 2). "Ozone water 20 seconds" → "Hydrofluoric acid 20 seconds" → "Interval 0.2 seconds" → "Ozone water 20 seconds" → "Hydrofluoric acid 20 seconds" → "Interval 0.2 seconds" → "Ozone water 20 seconds" → "DIW 20 seconds" → "Drying 40 seconds" In Comparative Example 2, the ozone water cleaning and the subsequent hydrofluoric acid cleaning were performed without any time interval. The time interval between the hydrofluoric acid cleaning and the subsequent ozone water cleaning was 0.2 seconds. The wafer rotation speed in the ozone water cleaning and the hydrofluoric acid cleaning was 1000 rpm. The first and second hydrofluoric acid cleaning times were 20 seconds, both of which were conditions for completely removing the oxide film.

[0053] <Comparative Example 3> Five prepared silicon wafers were cleaned using the cleaning flow shown in Table 1 (Comparative Example 3). "Ozone water 20 seconds" → "0.2 second interval" → "Hydrofluoric acid 20 seconds" → "0.2 second interval" → "Ozone water 20 seconds" → "0.2 second interval" → "Hydrofluoric acid 20 seconds" → "0.2 second interval" → "Ozone water 20 seconds" → "DIW 20 seconds" → "Drying 40 seconds"

[0054] In Comparative Example 3, the time interval between the ozone water cleaning and the subsequent hydrofluoric acid cleaning, and between the hydrofluoric acid cleaning and the subsequent ozone water cleaning, was 0.2 seconds. The wafer rotation speed in the ozone water cleaning and the hydrofluoric acid cleaning was 1000 rpm. The time for the first and second hydrofluoric acid cleaning was 20 seconds, both of which were conditions for completely removing the oxide film.

[0055] <Comparative Example 4> Five prepared silicon wafers were cleaned using the cleaning flow shown in Table 1 (Comparative Example 4). "Ozone water 20 seconds" → "Hydrofluoric acid 20 seconds" → "Ozone water 20 seconds" → "Hydrofluoric acid 20 seconds" → "Ozone water 20 seconds" → "DIW 20 seconds" → "Drying 40 seconds"

[0056] In Comparative Example 4, no time interval was provided between the ozone water cleaning and the subsequent hydrofluoric acid cleaning, and between the hydrofluoric acid cleaning and the subsequent ozone water cleaning. The wafer rotation speed was 300 rpm in the ozone water cleaning and the hydrofluoric acid cleaning. The first and second hydrofluoric acid cleaning times were 20 seconds, both of which were conditions for completely removing the oxide film.

[0057] <Evaluation> After cleaning according to the cleaning flows of Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Example 4, the LPD and surface roughness (haze) were measured using a "Surfscan SP5" manufactured by KLA-Tencor. Then, based on the defect coordinates of LPD (≧19 nm LPD), defects were observed using a "Review-SEM G7" manufactured by AMAT, and the number of surface defects caused by ozone water was counted.

[0058] The number of surface defects caused by ozone water, ≧19 nm LPD, and surface roughness (haze) obtained are shown in FIG. 5, FIG. 6, and FIG. 7, respectively.

[0059] As shown in Fig. 5, no surface defects caused by ozone water were observed in either Example 1 or Comparative Example 1. This suggests that there was no time interval between the hydrofluoric acid cleaning and the subsequent ozone water cleaning, and that after the hydrofluoric acid cleaning, ozone water was quickly and uniformly supplied to the wafer surface at a rotation speed of 1000 rpm. In other words, it can be evaluated that in Example 1 and Comparative Example 1, the occurrence of surface defects caused by ozone water was suppressed.

[0060] On the other hand, in Comparative Examples 2 and 3, a time interval was provided between the hydrofluoric acid cleaning and the subsequent ozone water cleaning, and as a result, surface defects caused by ozone water were observed. Furthermore, in Comparative Example 4, the wafer rotation speed (wafer rotation speed at the transition timing) in the ozone water cleaning and hydrofluoric acid cleaning was set to 300 rpm, and as a result, surface defects caused by ozone water were observed. This is believed to be because the oxide film was completely removed by the hydrofluoric acid cleaning, and then quick and uniform oxidation was not performed by the ozone water cleaning.

[0061] Furthermore, as shown in FIG. 6, in Example 1 and Comparative Example 1, no time interval was provided between the hydrofluoric acid cleaning and the subsequent ozone water cleaning, and after the hydrofluoric acid cleaning, ozone water was quickly and uniformly supplied to the wafer surface at a rotation speed of 1000 rpm, thereby suppressing the occurrence of surface defects caused by ozone water, and thus the value of ≧19 nm LPD was better than in Comparative Examples 2, 3, and 4.

[0062] 7, the surface roughness (haze) was better in Example 1 and Comparative Example 3 than in Comparative Examples 2, 4, and 5. This is believed to be because a time interval (0.2 seconds) was provided between the ozone water cleaning and the subsequent hydrofluoric acid cleaning, and the ozone water was discharged from the wafer surface before the hydrofluoric acid was supplied, thereby suppressing the deterioration of the surface roughness.

[0063] The evaluation results of the number of surface defects caused by the above-mentioned ozone water, ≧19 nm LPD, and surface roughness for each example (Example 1 and Comparative Examples 1 to 4) are shown in Table 2. From these results, it can be evaluated that the silicon wafer cleaned with the cleaning flow of Example 1 is of the highest quality.

[0064] [Table 2] [Explanation of symbols]

[0065] 1 Spin Cleaner 2 Casing 3 Retaining member 4 Drive shaft 5 Rotating table 6 Supply Nozzle

Claims

1. A method for cleaning silicon wafers that is applicable to single-wafer spin cleaning, in which a cleaning step using hydrofluoric acid and a cleaning step using ozone water are performed while the silicon wafer is rotating, comprising: A first cleaning process in which a cleaning step using ozone water is performed, and then a cleaning step using hydrofluoric acid is performed after a specific time interval; a second cleaning process in which a cleaning process using ozone water is performed immediately after the cleaning process using hydrofluoric acid; Including, 1. A method for cleaning a silicon wafer, comprising:

2. In a case where the second cleaning process is performed after the first cleaning process, a cleaning step using hydrofluoric acid in the first cleaning process also serves as a cleaning step using hydrofluoric acid in the second cleaning process; In a case where the first cleaning process is performed after the second cleaning process, a cleaning step using ozone water in the second cleaning process also serves as a cleaning step using ozone water in the first cleaning process.

2. The method for cleaning a silicon wafer according to claim 1,

3. In the spin cleaning, carrying out said first washing treatment at least once; Also, the second cleaning treatment is carried out at least once.

2. The method for cleaning a silicon wafer according to claim 1,

4. The specific time interval is 0.1 seconds or more and 1 second or less.

2. The method for cleaning a silicon wafer according to claim 1,

5. The rotation speed of the silicon wafer at the timing of transition from the cleaning process using hydrofluoric acid to the cleaning process using ozone water is set to 1000 rpm or more.

2. The method for cleaning a silicon wafer according to claim 1,

6. The flow rate of hydrofluoric acid in the cleaning process using hydrofluoric acid is set to 1 L / min or more, and the flow rate of ozone water in the cleaning process using ozone water is set to 1 L / min or more.

2. The method for cleaning a silicon wafer according to claim 1,

7. A cleaning step using hydrofluoric acid is performed to remove an oxide film on the wafer surface, and the wafer surface is made hydrophobic. Then, a cleaning step using ozone water is performed, and the cleaning step using hydrofluoric acid is performed at least once during spin cleaning.

7. The method for cleaning a silicon wafer according to claim 1, wherein the silicon wafer is immersed in a water-repellent solution.

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