Method for cleaning silicon wafers

Abstract

A method for cleaning a silicon wafer, comprising the following steps in the following order: applying hydrofluoric acid to a surface of the silicon wafer to treat the silicon wafer while it is rotated at a first speed; ceasing the application of the hydrofluoric acid and shaking off any hydrofluoric acid present on the surface of the silicon wafer without applying pure water to the surface of the silicon wafer while the silicon wafer is rotated at a second speed equal to or faster than the first speed; and applying ozonated water to the surface of the silicon wafer to treat the silicon wafer after shaking off the hydrofluoric acid from the surface while it is rotated at a third speed faster than the second speed, wherein the first speed is 100 rpm or less, the second speed is 200 rpm or less, and the third speed is 500 rpm or higher.

Description

TECHNICAL AREA

[0001] The present invention relates to a method for cleaning a silicon wafer. STATE OF THE ART

[0002] In the treatment of a water-repellent surface for a silicon wafer (semiconductor silicon wafer) using a rotary cleaning machine with single-wafer processing, an oxide layer formed on the surface of a semiconductor wafer is generally removed from the semiconductor wafer with a cleaning fluid such as hydrofluoric acid (HF) (Patent 1, Patent 2).

[0003] It was common practice to perform an oxide layer removal treatment with HF (hydrofluoric acid) at low speed, a reoxidation treatment by rinsing (with pure water or ozonated water) while increasing the rotational speed, and then switching to high rotational speed at the drying stage. A flowchart of a conventional process for cleaning a silicon wafer is shown in Fig. 6 shown. First, as in Fig. Figure 6(a) shows the oxide layer on the surface of a silicon wafer being removed with hydrofluoric acid. Then, as shown in Fig. 6(b) shows that hydrofluoric acid is substituted by pure water. Then, as in Fig. As shown in Figure 6(c), cleaning with ozonated water was carried out and an oxide layer was formed. Then, as shown in Fig. 6(d) shown, drying carried out. LIST OF REFERENCES PATENT LITERATURE Patent specification 1: Japanese unexamined patent application, publication no. 2009-272411 Patent specification 2: Japanese unexamined patent application, publication no. 2001-060576 BRIEF DESCRIPTION OF THE INVENTIONAL PROBLEM STATEMENT

[0004] Under state-of-the-art conditions, however, particles such as water spots are produced during rinsing treatment, a difference occurs in the formation rate of an oxide layer on a wafer surface in the step of forming an oxide layer with ozonated water, and particles adhere to sections where hydrophilization is delayed due to slow oxidation, thereby reducing the quality of the wafer surface.

[0005] The problems of the state of the art are discussed in more detail below. In the conventional treatment process described above, using a rotary cleaning machine with single-wafer processing, the following occurs after the oxide layer removal step with HF ( Fig. 6(a)) Water stains during treatment with pure water (treatment of substitution with pure water) of Fig. 6(b). Furthermore, at the time of ozonated water treatment ( Fig. 6(c)) the difference in the formation rate of the oxide layer on the wafer surface, due to the low rotational speed, and particles and the like adhere to parts for which hydrophilization is delayed, thereby significantly degrading the wafer quality.

[0006] The present invention was made in view of the problems described above, and one object of the present invention is to provide a method for cleaning a silicon wafer which can suppress the adhesion of water spots and particles that arise in a conventional cleaning process and improve the wafer quality. PROBLEM SOLVING

[0007] To achieve this objective, the present invention provides a method for cleaning a silicon wafer, comprising the following steps in the following sequence: applying hydrofluoric acid to a surface of the silicon wafer to treat the silicon wafer while it is rotated at a first speed; ceasing the application of the hydrofluoric acid and shaking off any hydrofluoric acid present on the surface of the silicon wafer without applying pure water to the surface of the silicon wafer while the silicon wafer is rotated at a second speed equal to or faster than the first speed; and applying ozonated water to the surface of the silicon wafer to treat the silicon wafer after shaking off the hydrofluoric acid from the surface while it is rotated at a third speed faster than the second speed.

[0008] Such a method for cleaning a silicon wafer can remove the oxide layer while preventing the formation of water spots and the adhesion of particles and the like, which occur when the oxide layer is removed with hydrofluoric acid.

[0009] In this case, the first speed is preferably 100 rpm or lower, the second speed is preferably 200 rpm or lower, and the third speed is preferably 500 rpm or higher.

[0010] By adjusting each rotational speed to such a range, the formation of water spots and the adhesion of particles can be suppressed more effectively. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0011] The inventive method for cleaning a silicon wafer allows the oxide layer to be removed while preventing the formation of water spots and preventing the adhesion of particles and the like, which occur when the oxide layer is cleaned with hydrofluoric acid and the silicon wafer is cleaned. List of characters Fig. 1 a flowchart illustrating the inventive process for cleaning a silicon wafer. Fig. 2 a flowchart illustrating the conditions of the process for cleaning a silicon wafer in Examples 1 to 9. Fig. 3 a flowchart showing the conditions of the procedure for cleaning a silicon wafer in Examples 10 to 15. Fig. 4 a flowchart showing the conditions of the process for cleaning a silicon wafer in Examples 16 to 21. Fig.5 a flowchart illustrating the conditions of the process for cleaning a silicon wafer in comparative examples 1 to 3. Fig. Figure 6 shows a flowchart illustrating a conventional method for cleaning a silicon wafer. Fig. 7. A diagram showing the results of the examples and comparative examples. DESCRIPTION OF THE EXECUTION FORMS

[0012] The present invention is described in detail below as an example of an embodiment with reference to the drawings, but the present invention is not limited to these.

[0013] The present invention is a method for cleaning a silicon wafer, and first, hydrofluoric acid is applied to a surface of the silicon wafer to treat it while it is rotated at a first speed. Then, the application of the hydrofluoric acid is stopped, and the hydrofluoric acid remaining on the surface of the silicon wafer is shaken off without applying pure water to the surface of the silicon wafer while the silicon wafer is rotated at a second speed equal to or faster than the first speed. Afterward, ozonated water is applied to the surface of the silicon wafer to treat it after the hydrofluoric acid has been shaken off, while it is rotated at a third speed faster than the second speed. The inventive method for cleaning a silicon wafer comprises the foregoing steps in the described sequence.

[0014] The inventive method for cleaning a silicon wafer is described with reference to Fig. 1 described in more detail. Fig. Figure 1 is a flowchart illustrating the inventive process for cleaning a silicon wafer.

[0015] In the inventive method for cleaning a silicon wafer, a known rotary cleaning machine can be used. In the inventive method for cleaning a silicon wafer, first, as in Fig. 1(1) shown, hydrofluoric acid applied to a surface of the silicon wafer to treat the silicon wafer while it is rotated at a first rotational speed (step 1 ). An oxide layer (natural oxide layer) that is formed on the surface of the silicon wafer is removed in this step. 1The first rotation is preferably subject to a low rotational speed of 100 rpm or less. This removes particles from the wafer surface and eliminates metal contamination and the like.

[0016] Then, as in Fig. 1(2) shown, the application of hydrofluoric acid is completed, and any hydrofluoric acid on the surface of the silicon wafer is shaken off without applying pure water to the surface of the silicon wafer while the silicon wafer is rotated at a second speed (step 2Here, the second rotational speed is equal to or faster than the first. The second rotational speed is preferably a low-speed rotation (medium-speed rotation) of 200 rpm or less. An important aspect of the present invention is to avoid using pure water on a wafer whose surface has been made hydrophobic by removing the oxide layer with hydrofluoric acid. This prevents the formation of water spots on the wafer surface. It should be noted that the lower limit of the low speed is 50 rpm due to equipment limitations.

[0017] Then, as in Fig. 1(3) shown, preferably a step of increasing the rotational speed before (step 3 This reduces the rotational speed to the speed (third speed) of the ozone water treatment (step 4 ) increased, which is described below.

[0018] Then, as in Fig.1(4) shown, ozonated water applied to the surface of the silicon wafers to treat the silicon wafer while rotating at a third speed, the hydrofluoric acid having been shaken off the surface (step 4 The third rotational speed is faster than the second rotational speed. In this step 4 A reoxidation treatment of the silicon wafer surface is carried out by the action of ozonated water. The third rotational speed is preferably 500 rpm or higher. The higher the high rotational speed (third rotational speed) at the time of the acceleration step (step 1), the better. 3 ) and the ozonated water treatment step (step 4 ) is, however, due to device limitations, approximately 1500 rpm is essentially the upper limit.

[0019] After performing the ozonated water treatment, you can then proceed as described in Fig. 1(5) shown, the silicon wafer is dried (step 5The drying step can be carried out by stopping the application of ozonated water and resuming the rotation of the silicon wafer. The rotational speed is not subject to any particular restriction, but is preferably equal to or faster than the third rotational speed.

[0020] Based on the above procedure, which is described in Fig. By following the steps shown in 1, it is possible to prevent the formation of water spots and to clean the silicon wafer without the adhesion of particles and the like that occur when the oxide layer is removed with hydrofluoric acid.

[0021] The functions and effects of each of the inventive steps are as follows. In the hydrofluoric acid treatment of step 1Particles can be removed by removing the oxide layer at a low rotational speed (preferably 100 rpm or less), while suppressing the formation of water spots and the like. If a subsequent rinsing treatment with pure water or ozonated water is carried out at the same rotational speed as conventionally, water spots will occur. Accordingly, in the present invention, to avoid water spots and re-adhesion of particles due to the rinsing treatment, after shaking off the hydrofluoric acid chemical solution, the rotation is carried out at a low rotational speed (medium rotational speed, preferably 200 rpm or less), without in step 2 Applying pure water after removing the oxide layer with hydrofluoric acid, the step of increasing the rotational speed (preferably accelerating to 500 rpm or higher) (step 3 ) performed, and the reoxidation treatment (step 4The rinsing process is carried out with ozonated water after acceleration (preferably 500 rpm or higher). If pure water is used in the rinsing treatment, water spots will occur, and therefore, no rinsing with pure water is used in the present invention. Therefore, no rinsing with pure water is carried out in the present invention (no substitution with pure water is carried out) before the hydrofluoric acid has been shaken off after the oxide layer has been removed with hydrofluoric acid, and of course, no rinsing with pure water is carried out after the hydrofluoric acid has been shaken off. Furthermore, the above-described increase in rotational speed in step 3 and application of the ozonated water in step 4 be carried out simultaneously.

[0022] Complete removal of the oxide layer under low-speed conditions of 100 rpm or less during hydrofluoric acid treatment improves particle adhesion to the wafer surface. In the present invention, after subsequent shaking off the HF from the wafer at low speed (medium speed, preferably 200 rpm or less), the rotation is accelerated to high speed (preferably 500 rpm or higher), and the ozonated water treatment is performed at high speed. EXAMPLE

[0023] The present invention is described in more detail below with reference to examples and comparative examples; however, the present invention is not limited to these examples. (Examples 1 to 9)

[0024] A silicon wafer was purified according to the inventive flowchart described in Fig.Figure 1 shows the rotational speeds of the silicon wafer in step 1. 1 until 4 were set up so that they could access the Fig. The range of rotational speeds shown in step 2 is fulfilled. This means that one step of removing an oxide layer (step 2) 1 ) was performed at a low rotational speed of 100 rpm or less, and after a step of pouring off a chemical solution was performed at a rotational speed of 200 rpm or less (step 2 ), the process with an acceleration step (step 3 ) continued with a high rotation speed of 500 rpm or higher, a step of forming an oxide layer with ozonated water (step 4 ) was performed at a high rotation speed of 500 rpm or higher, and then the drying (step 5 ) was carried out.

[0025] The chemical solution used was hydrofluoric acid and ozonated water; pure water was not used. It should be noted that the concentration of hydrofluoric acid in step 1 The hydrofluoric acid concentration was set to 1.0% by mass, the treatment time was set to 30 seconds, and the rotational speed was set to 50 rpm at that time. Furthermore, the concentration of the ozonated water in step 4 Set to 20 ppm by mass. The duration of the ozonated water treatment in step 4 was set to 60 seconds. Drying in step 5 The test was performed for 60 seconds at 1000 rpm.

[0026] In Example 1, the first speed was set to 50 rpm, the second speed to 50 rpm, and the third speed to 500 rpm. In Examples 2 to 9, the second speed (the speed at which the chemical solution is shaken off) and the third speed (the speed during the acceleration process and oxide layer formation) were set as shown in Table 1.

[0027] The number of defects on the silicon wafer after cleaning and drying was counted and shown in Table 1. SP5, manufactured by KLA-Tencor Corporation, was used to count the defects on the silicon wafer. [Table 1] Rotational speed at which the chemical solution was shaken off (second rotational speed) (rpm) Acceleration process (third rotational speed) (rpm) Rotational speed at the time of oxide layer formation (third rotational speed) (rpm) Number of defects Example 1 50 500 500 20 Example 2 50 1000 1000 13 Example 3 50 1500 1500 12 Example 4 100 500 500 8 Example 5 100 1000 1000 9 Example 6 100 1500 1500 12 Example 7 200 500 500 22 Example 8 200 1000 1000 10 Example 9 200 1500 1500 13

[0028] In examples 1 to 9, where the cleaning flow of Fig.When method 2 was used, the adhesion of particles to the wafer surface was significantly improved by switching to high rotation speed of 500 rpm or higher after shaking off the chemical solution at 200 rpm or less, without rinsing with pure water after removing the oxide layer with hydrofluoric acid, and then performing treatment with ozonated water to form the oxide layer. (Comparison examples 1 to 3)

[0029] A silicon wafer was produced according to the method described in Fig. The conventional cleaning flow shown in step 6 was used. The rotational speed in each step was adjusted so that the area in the Fig. The area shown in Figure 5 was located there. In this conventional cleaning flow, the removal of the oxide layer was carried out using hydrofluoric acid at a low rotational speed of 100 rpm or less ( Fig.5(a)), and a rinsing treatment was carried out with pure water and ozonated water, while rotation at high speed (500 rpm or higher) was performed ( Fig. 5(b) and (c)). A drying process was then carried out ( Fig. 5(d)) carried out.

[0030] In comparative examples 1 to 3, the chemical solutions used were hydrofluoric acid, pure water, and ozonated water. It should be noted that the hydrofluoric acid concentration was set to 1.0% by mass, the hydrofluoric acid treatment duration was set to 30 seconds, and the rotational speed during the hydrofluoric acid treatment was set to 50 rpm, the same value as in examples 1 to 9. Furthermore, the ozonated water concentration was set to 20 ppm by mass, and the duration of the ozonated water treatment was set to 60 seconds, the same value as in examples 1 to 9. Drying was also carried out at 1000 rpm for 60 seconds, the same values ​​as in examples 1 to 9.

[0031] The rotational speed at which the chemical solution was shaken off, the rotational speed at the time of substitution with pure water, and the rotational speed at the time of oxide layer formation in comparative examples 1 to 3 were set as shown in Table 2. Since the substitution with pure water was carried out during the acceleration process, the maximum speed during the acceleration process is the same as the maximum rotational speed at the time of substitution with pure water.

[0032] As in Examples 1 through 9, the number of defects on the silicon wafer was counted after cleaning and drying and is shown in Table 2. SP5, manufactured by KLA-Tencor Corporation, was used to count the number of defects on the silicon wafer. [Table 2] Rotational speed at which the chemical solution was shaken off (rpm) Acceleration process (RPM) Rotational speed at the time of substitution with pure water (rpm) Rotational speed at the time of oxide layer formation (rpm) Number of defects Comparative example 1 200 500 500 500 152 Comparative example 2 200 1000 1000 1000 160 Comparative example 3 200 1500 1500 1500 177

[0033] Table 2 shows that many defects are present on the wafer surface in comparative examples 1 to 3. This is because, in the conventional process, significant water spots and particles adhere due to the rinsing treatment with pure water and ozonated water, which is carried out during the transition to high-speed rotation (500 rpm or higher). (Examples 10 to 15)

[0034] A silicon wafer was purified according to the inventive flowchart described in Fig. Figure 1 is shown. It should be noted that the rotational speeds of the silicon wafer in step 1 are shown. 1 until 4 were set up so that they could access the Fig. The 3-shown range of rotational speeds is fulfilled. Except that the rotational speed in step 2(the second rotational speed) has a different range, the other conditions are the same as in Examples 1 to 9. That is, the step of removing the oxide layer (step 1 ) was performed at a low rotational speed of 100 rpm or less, the step of pouring off the chemical solution (step 2 ) however, it was performed at a speed of over 200 rpm as the second speed, which differs from Examples 1 to 9. Subsequently, as shown in Examples 1 to 9, the process is accelerated with a step (step 3 ) continued at a high rotational speed of 500 rpm or above, a step of oxide layer formation (step 4 ) was carried out at a high rotation speed of 500 rpm or higher with ozonated water, and subsequently the drying (step 5). In examples 10 to 15, the second rotational speed (the speed at which the chemical solution is shaken off) and the third rotational speed (the speed at the time of the acceleration process and oxide layer formation) were set as shown in Table 3.

[0035] The number of defects on the silicon wafer was counted after cleaning and drying as in Examples 1 to 9 and is shown in Table 3. [Table 3] Rotational speed at which the chemical solution was shaken off (second rotational speed) (rpm) Acceleration process (third rotational speed) (rpm) Rotational speed at the time of oxide layer formation (third rotational speed) (rpm) Number of defects Example 10 300 500 500 51 Example 11 300 1000 1000 50 Example 12 300 1500 1500 54 Example 13 400 500 500 70 Example 14 800 1000 1000 76 Example 15 1200 1500 1500 64

[0036] As can be seen from Table 3, the number of defects increases when the process of shaking off the chemical solution is carried out faster than 200 rpm, but there are fewer defects compared to the conventional method (comparative example). 1 until 3 ). (Examples 16 to 21)

[0037] A silicon wafer was purified according to the inventive flowchart described in Fig.Figure 1 is shown. It should be noted that the rotational speeds of the silicon wafer in step 1 are shown. 1 until 4 were set up so that they could access the Fig. The speed range shown in step 4 must be met. With the exception that the speeds in step 4 are... 3 and step 4 If the areas differ, the other conditions are the same as in Examples 1 to 9. That is, the step of removing the oxide layer (step 1 ) was performed at a low rotational speed of 100 rpm or less and the step of pouring off the chemical solution (step 2 ) was carried out at a rotational speed of 200 rpm or less. Subsequently, unlike in Examples 1 to 9, the process was accelerated with a step (step 3 ) continued at a speed of less than 500 rpm, a step of forming an oxide layer with ozone water (step 4) was performed at a speed of less than 500 rpm, and then drying was carried out (step 5 ). In examples 16 to 21, the second rotational speed (the speed at which the chemical solution is shaken off) and the third rotational speed (the speed at the time of the acceleration process and oxide layer formation) were set as shown in Table 4.

[0038] The number of defects on the silicon wafer was counted after cleaning and drying as in Examples 1 to 9 and is shown in Table 4. [Table 4] Rotational speed at which the chemical solution was shaken off (second rotational speed) (rpm) Acceleration process (RPM) Rotational speed at the time of oxide layer formation (third rotational speed) (rpm) Number of defects Example 16 50 50 200 45 Example 17 50 100 300 51 Example 18 50 400 400 42 Example 19 200 50 250 57 Example 20 200 100 300 61 Example 21 200 400 400 55

[0039] As can be seen from Table 4, the number of defects increases in Examples 16 to 21 compared to Examples 1 to 9. This is because, when acceleration and ozonated water treatment are performed at less than 500 rpm after shaking off the chemical solution, the rate of oxide layer formation becomes uneven, and particles adhere to parts where oxidation with ozonated water is delayed. However, the number of defects decreased in Examples 16 to 21 compared to the comparison examples 1 to 3.If the acceleration process is slower than the process of shaking off the chemical solution, no acceleration process takes place and the speed is reduced, and therefore the oxide layer formation with ozonated water begins at a speed that is lower than the rotational speed at the time of oxide layer formation, which causes an uneven rate of oxide layer formation due to insufficient rotational speed, thus causing particle adhesion.

[0040] Fig. Figure 7 shows a diagram summarizing the number of defects in examples 1 to 21 and comparison examples 1 to 3. As shown from Fig.As can be seen in Figure 7, the number of defects in Examples 1 to 21 is small compared to Comparative Examples 1 to 3, which means that the advantage of the present invention has been achieved. In particular, the number of defects in Examples 1 to 9 is remarkably small. As described, after delaminating the oxide layer with hydrofluoric acid, the process of draining the hydrofluoric acid was carried out at a low (medium) speed of 200 rpm or less, without releasing a chemical solution such as a rinse, and then the speed was increased to 500 rpm or higher, and then the treatment for oxide layer formation was carried out with ozonated water, and in this way the best effect was achieved.

[0041] It should be noted that the present invention is not limited to the embodiments described above. The embodiments are merely examples, and all examples that exhibit essentially the same features and demonstrate the same functions and effects as the technical concepts disclosed in the claims of the present invention are included within the technical scope of the present invention. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2009272411

[0003] JP 2001060576

[0003]

Claims

[1] Method for cleaning a silicon wafer, comprising the following steps in the following order: Applying hydrofluoric acid to a surface of the silicon wafer to treat the silicon wafer while it is being rotated at a first rotation speed, Terminating the application of hydrofluoric acid and shaking off any hydrofluoric acid present on the surface of the silicon wafer, without applying pure water to the surface of the silicon wafer, while the silicon wafer is rotated at a second speed equal to or faster than the first speed, and Applying ozonated water to the surface of the silicon wafer to treat the silicon wafer after shaking off the hydrofluoric acid from the surface while it is rotated at a third speed that is faster than the second speed. [2] Method for purifying a silicon wafer according to claim 1, wherein the first speed is 100 rpm or lower, the second speed is 200 rpm or lower, and The third speed is 500 rpm or higher.