TW201831992A - wafer cleaning method - Google Patents

Abstract

To provide a wafer cleaning method capable of suppressing formation of step defects due to ozonic water on a wafer. The present invention provides a wafer cleaning method, wherein cleaning solution is supplied onto the surface of the wafer while the wafer is rotating. The method includes: starting a supply of hydrofluoric acid onto the surface of the wafer, starting a supply of pure water before or at the same time as the stopping of the supply of hydrofluoric acid, starting a supply of ozonic water after the supply of the hydrofluoric acid has been stopped and before the supply of the pure water has been stopped, in order to provide a period during which the pure wafer and the ozonic water is supplied onto the surface of the wafer at the same time, the supply of the pure water is then stopped, thus only the ozonic water is supplied onto the surface of the wafer.

Description

   Cleaning method of wafer   

The present invention relates to a method for cleaning wafers, and more particularly to a method for cleaning wafers using ozone water, hydrofluoric acid, and pure water.

In the past, in the cleaning process of semiconductor wafers such as silicon wafers, ozone water or hydrofluoric acid was generally used. For example, there have been repeated ozone water washing and hydrofluoric acid washing to remove particles. In this method, an oxide film is formed on the wafer surface by washing with ozone water, and then particles and the like on the wafer surface are removed together with the oxide film by washing with hydrofluoric acid.

However, in this method, when the cleaning solution is switched, ozone water and hydrofluoric acid coexist on the wafer surface, and the formation of an oxide film caused by ozone water and an oxide film caused by hydrofluoric acid occur simultaneously on the wafer surface. Removal (etching) causes a problem that the surface roughness is deteriorated.

In addition, if the oxide film is removed with hydrofluoric acid, the bare surface of the wafer is exposed, and particles are very likely to adhere to the bare surface of the wafer. Therefore, after removing the oxide film with fluoric acid and cleaning it again with ozone water, the ozone water was repelled at the outer periphery of the wafer due to the water repellency of the bare surface of the wafer, and the ozone water could not be smoothly spread. There is a problem that particles remain on the outer periphery of the wafer.

Patent Document 1 describes a wafer cleaning method as a technique for solving this problem, and is characterized in that, in a wafer cleaning method including a cleaning procedure using ozone water and a cleaning procedure using hydrofluoric acid, There is a rotary washing program using pure water between the washing program using ozone water and the washing program using hydrofluoric acid, which is based on (1) washing program using ozone water, (2) using pure water Rotary washing procedure with water, (3) Sequence of washing procedure using hydrofluoric acid, or (1) Washing procedure using hydrofluoric acid, (2) Spin washing procedure using pure water, (3) Ozone water The cleaning method is performed in the order of the cleaning program. The flow rate of the pure water in the spin washing program using pure water is 1.2 L / min or more, and the number of rotations of the wafer is 1,000 rpm or more.

Advance technical literature

Patent Literature:

Patent Document 1: Japanese Patent Application Publication No. 2015-220284

In the technique described in Patent Document 1, the deterioration of the surface roughness of the wafer after cleaning is suppressed by avoiding the coexistence of ozone water and hydrofluoric acid, and pure water rotation is performed using a specific pure water flow rate and wafer rotation number. The cleaning allows the pure water to spread to the outer periphery of the wafer, thereby improving the particle residue in the outer periphery of the wafer after cleaning.

However, the inventors of the present application recognized that in a wafer cleaning method (hereinafter simply referred to as "rotation cleaning") in which a wafer is cleaned by supplying a cleaning solution onto the surface of the wafer while rotating the wafer, the image is like In the past, a method of repeating ozone water cleaning and fluoric acid cleaning, or a method of performing pure water cleaning between ozone water cleaning and fluoric acid cleaning, as in Patent Document 1, was used in subsequent wafer inspection procedures. The reduction of LPD (Light Point Defect) has its limitation. In the technique of Patent Document 1, it should be possible to reduce the LPD caused by particles, but there should be an LPD caused by any defect other than particles.

The inventor of the present case investigated the LPD observed on the wafer surface after performing a conventional cleaning method (ozone water cleaning → fluoric acid cleaning → ozone water cleaning) on the polished wafer. The details of the results are described later, but as shown in FIG. 6, it can be seen that there are many round segment defects. It has been confirmed that such a step defect is different from particles considered to be a problem in Patent Document 1, and remains even after the final cleaning process after that. Furthermore, in order to investigate the cause of the formation of this step defect, the inventors of the present invention carefully observed the surface of the wafer during the spin cleaning with a high-speed camera. As a result, it was found that the following phenomena (A) and (B) occurred at the moment when switching from fluoric acid cleaning to ozone water cleaning. That is, (A) the amount of cleaning liquid on the surface of the wafer decreases in a very short period of time, and the bare silicon surface is partially exposed, (B) at the time when ozone water is first ejected (sprayed) from the nozzle, The form of the mist is released, so the fine mist adheres to the bare silicon surface, causing local oxidation. This locally oxidized part is difficult to be etched with a hydrofluoric acid treatment or an SC1 treatment in a subsequent cleaning procedure, and thus a step defect is generated in the cleaned wafer.

Therefore, the present invention has been made in view of the above problem, and an object thereof is to provide a method for cleaning a wafer, which can suppress the formation of step defects due to ozone water on a wafer.

Based on the detailed discussion as described above, the inventor of the present case explored a cleaning method. When switching from fluoric acid cleaning to ozone water cleaning, even if a fine mist is generated when the ozone water is first sprayed from the nozzle, it will not Allow fine mist to adhere to the bare silicon surface. Then come up with the method described below: the pure water supply to the wafer surface before the ozone water washing is continued after the ozone water supply has started, so that the supply period of pure water to the wafer surface and the ozone water The supply periods overlap. According to this method, when the supply of ozone water starts, a sufficient amount of pure water layer covers the entire surface of the wafer. Therefore, even if a fine mist of ozone water occurs, the fine mist will not adhere to the bare silicon surface.

The gist of the present invention completed based on the above-mentioned knowledge and insights is as follows.

(1) A method for cleaning a wafer, which is a method for cleaning a wafer by supplying a cleaning solution to a surface of the wafer while rotating the wafer, and is characterized in that the wafer is started to be cleaned. Surface supply of fluoric acid; start supply of pure water before or at the same time as stopping the supply of fluoric acid; and set to start supply of ozone water after stopping the supply of fluoric acid and before stopping the supply of pure water, The period during which pure water and ozone water are simultaneously supplied on the surface of the wafer; thereafter, the supply of the pure water is stopped, and only the ozone water is supplied on the surface of the wafer.

(2) The method for cleaning a wafer according to the above (1), on the surface of the wafer, the supply of the pure water is started before the supply of the fluoric acid is stopped, and a period for simultaneously supplying the fluoric acid and the pure water is set. .

(3) The method for cleaning a wafer as described in (2) above, after the supply of the fluoric acid is stopped on the surface of the wafer, the supply of the ozone water is started, and a period for supplying pure water is set.

(4) The wafer cleaning method according to any one of (1) to (3) above, wherein the hydrofluoric acid is discharged from the first nozzle, and the pure water and the ozone water are different from those of the first nozzle. Common nozzle spit out.

(5) The method for cleaning a wafer according to any one of (1) to (3) above, wherein the hydrofluoric acid, the pure water, and the ozone water are discharged from separate nozzles.

According to the wafer cleaning method of the present invention, it is possible to suppress formation of step defects due to ozone water on the wafer.

10‧‧‧Fluoric acid supply system

11‧‧‧The first piping

12‧‧‧The first nozzle

13‧‧‧Fluuric acid flow adjustment valve

20‧‧‧Pure water supply system

21‧‧‧ 2nd piping

22‧‧‧ Nozzle 2

23‧‧‧Pure water flow adjustment valve

30‧‧‧Ozone water supply system

31‧‧‧The third piping

32‧‧‧3rd nozzle

33‧‧‧Ozone water flow adjustment valve

40‧‧‧Pure water‧Ozone water supply system

41‧‧‧Pipe for pure water

42‧‧‧Pipe for ozone water

43‧‧‧ 4th piping

44‧‧‧ 4th nozzle

45‧‧‧Pure water flow adjustment valve

46‧‧‧Ozone water flow adjustment valve

[FIG. 1] (A), (B) is a figure which shows the structural example of the supply nozzle of the cleaning liquid used for the wafer cleaning method by one Embodiment of this invention.

[Fig. 2] (A) and (B) are diagrams showing an example of a supply sequence of a cleaning liquid when the supply nozzles of Figs. 1 (A) and (B) are used, respectively.

[FIG. 3] (A), (B) is a figure which shows the other example of a supply sequence of a washing | cleaning liquid when the supply nozzle of FIG. 1 (A), (B) is used, respectively.

FIG. 4 is a diagram showing an example of a supply sequence of a cleaning liquid in a conventional cleaning method.

FIG. 5 is a diagram showing another example of a supply sequence of a cleaning liquid in a conventional cleaning method.

[Fig. 6] An image of a step defect caused by ozone water was observed with an atomic force microscope (AFM).

The present invention relates to a method for cleaning a wafer, which is a rotary cleaning in which a cleaning solution is supplied to the surface of a wafer while the wafer is rotated. This cleaning is suitable for the polished wafer obtained by subjecting the wafer to mirror polishing treatment before the inspection.

1 (A) and 1 (B) show a configuration example of a supply nozzle of a cleaning liquid used in a method for cleaning a wafer according to an embodiment of the present invention.

FIG. 1 (A) shows a state where fluoric acid, pure water, and ozone water are discharged from individual nozzles. In this aspect, the hydrofluoric acid supply system 10 (labeled as Nz1) includes a first pipe 11, a first nozzle (exhaust port) 12 located at a tip end thereof, and a hydrofluoric acid flow adjustment valve provided in the first pipe 11. 13. Similarly, the pure water supply system 20 (labeled Nz2) includes a second pipe 21, a second nozzle 22 located at a tip end thereof, and a pure water flow adjustment valve 23 provided in the second pipe 21. Similarly, the ozone water supply system 30 (labeled Nz3) includes a third pipe 31, a third nozzle 32 located at a tip end thereof, and an ozone water flow adjustment valve 33 provided in the third pipe 31. Each of the nozzles 12, 22, and 32 is provided above the center portion of the wafer, and the cleaning liquid from each nozzle is dropped and supplied to the center portion of the wafer being rotated.

FIG. 1 (B) shows a state where pure water and ozone water are discharged from a common nozzle. In this aspect, the fluoric acid supply system 10 (labeled Nz1) is the same as that of FIG. 1 (A). The pure water and ozone water supply system 40 (labeled Nz4) includes a pure water pipe 41, an ozone water pipe 42, a fourth pipe 43 formed by the above-mentioned confluence, a fourth nozzle 44 at its tip, and a A pure water flow rate adjustment valve 45 for the pure water pipe 41 and an ozone water flow rate adjustment valve 46 provided in the ozone water pipe 42. Both the first nozzle 12 and the fourth nozzle 44 are provided above the center portion of the wafer, and the cleaning liquid from each nozzle is dropped and supplied to the center portion of the wafer being rotated.

Here, the supply sequence of the cleaning liquid in the wafer cleaning method according to the first embodiment of the present invention will be described with reference to FIGS. 2 (A) and (B). FIG. 2 (A) shows a case where the supply nozzle of FIG. 1 (A) is used, and FIG. 2 (B) shows a supply sequence using the supply nozzle of FIG. 1 (B).

As shown in FIGS. 2 (A) and (B), in this embodiment, the wafer surface is executed in sequence without interruption: a procedure of supplying only fluoric acid (1), and a procedure of simultaneously supplying fluoric acid and pure water ( 2) A procedure for supplying pure water only (3), a procedure for supplying pure water and ozone water at the same time (4), and a procedure for supplying only ozone water (5). In other words, it is as follows. First, the supply of fluoric acid is started on the wafer surface. Next, before the supply of fluoric acid is stopped, the supply of pure water is started, and a period is provided for simultaneous supply of fluoric acid and pure water on the wafer surface. Then, the supply of hydrofluoric acid was stopped. Next, before the supply of pure water is stopped, the supply of ozone water is started, and a period is set in which pure water and ozone water are simultaneously supplied on the wafer surface. Then, the supply of pure water was stopped. Finally, the supply of ozone water was stopped.

In addition, in the case of FIG. 2 (B), when the ozone water flow adjustment valve 46 is closed to open, and when the supply of ozone water to the wafer is started (that is, when the program (4) is started), There is a time delay due to piping remaining. Similarly, when the pure water flow rate adjusting valve 45 is opened and closed, and when the supply of pure water on the wafer is stopped (that is, the start point of the program (5)), there is a time delay due to the remaining pipe. .

Next, the supply sequence of the cleaning liquid in the wafer cleaning method according to the second embodiment of the present invention will be described with reference to FIGS. 3 (A) and (B). FIG. 3 (A) shows a case where the supply nozzle of FIG. 1 (A) is used, and FIG. 3 (B) shows a supply sequence when the supply nozzle of FIG. 1 (B) is used.

As shown in FIGS. 3 (A) and (B), in this embodiment, the wafer surface is executed in sequence without interruption: a procedure of supplying only fluoric acid (1), and a procedure of simultaneously supplying fluoric acid and pure water ( 2) Procedure (4) for supplying pure water and ozone water at the same time, and procedure (5) for supplying only ozone water. In other words, it is as follows. First, the supply of fluoric acid is started on the wafer surface. Next, before the supply of fluoric acid is stopped, the supply of pure water is started, and a period is provided for simultaneous supply of fluoric acid and pure water on the wafer surface. Then, the supply of hydrofluoric acid was stopped. At the same time, the supply of ozone water is started without stopping the supply of pure water, and a period is set for the simultaneous supply of pure water and ozone water on the wafer surface. Then, the supply of pure water was stopped. Finally, the supply of ozone water was stopped.

In addition, in the case of FIG. 3 (B), the time when the ozone water flow adjustment valve 46 is closed to open and the time when the supply of ozone water on the wafer is started (that is, the start time of the program (4)), There is a time delay due to piping remaining. Similarly, when the pure water flow rate adjusting valve 45 is opened and closed, and when the supply of pure water on the wafer is stopped (that is, the start point of the program (5)), there is a time delay due to the remaining pipe. .

The supply sequence of the cleaning liquid in the conventional cleaning method will be described with reference to Figs. 4 and 5 which are compared with the above embodiment.

In the first conventional example shown in FIG. 4, a procedure (1) for supplying only fluoric acid and a procedure (5) for supplying only ozone water are executed on the wafer surface in order without interruption. In other words, it is as follows. First, the supply of fluoric acid is started on the wafer surface. Next, the supply of fluoric acid was stopped, and the supply of ozone water was started. Finally, the supply of ozone water was stopped. In this conventional example, the nozzle configuration shown in FIG. 1 (A) is used. The supply of hydrofluoric acid is performed by the first nozzle 12 and the supply of ozone water is performed by the third nozzle 32.

In the second past example shown in FIG. 5, the procedure on the wafer surface is executed without interruption: the procedure for supplying only fluoric acid (1), the procedure for supplying pure water (3), and the procedure for supplying only ozone water ( 5). In other words, it is as follows. First, the supply of fluoric acid is started on the wafer surface. Next, while the supply of fluoric acid was stopped, the supply of pure water was started. Next, the supply of ozone water was started while the supply of pure water was stopped. Finally, the supply of ozone water was stopped. This conventional example uses the nozzle configuration of FIG. 1 (A). The supply of hydrofluoric acid is performed by the first nozzle 12, the supply of pure water is performed by the second nozzle 22, and the supply of ozone water is performed by the third nozzle 32.

The embodiment shown in Figs. 2 and 3 is compared with the conventional example shown in Figs. In the first past example shown in FIG. 4, as shown in FIG. 4, the amount of the cleaning liquid on the wafer surface decreases only in a very short period immediately after the start of the process (5), and the bare silicon surface is partially exposed. . Therefore, a fine mist of ozone water released immediately after the start of the procedure (5) adheres to the bare silicon surface, causing local oxidation. As a result, step defects are formed on the cleaned wafer surface. The same phenomenon also occurs in the second conventional example shown in FIG. 5, and step defects are formed on the wafer surface after cleaning.

In contrast, in the present embodiment shown in Figs. 2 (A), (B) and 3 (A), (B), the washing process described below is performed in each program. First, in the procedure (1), the oxide film on the wafer surface is removed by etching with hydrofluoric acid. In the procedure (2), the etching of the oxide film of hydrofluoric acid is continued, and pure water is added at the same time, thereby strengthening the liquid layer on the wafer surface. In the procedure (3) shown in FIGS. 2 (A) and (B), the fluoric acid on the wafer surface is eliminated by pure water. This prevents the coexistence of ozone water and hydrofluoric acid, and suppresses deterioration of the surface roughness of the wafer. In the procedure (4), pure water is used to maintain a liquid-phase-enhanced state on the wafer surface, and an ozone film is formed on the wafer surface by ozone water. In the procedure (5), an oxide film is continuously formed on the wafer surface with ozone water.

In the sequence of FIG. 2 (A) and FIG. 3 (A), a fine mist of ozone water is generated from the third nozzle 32 at the instant when the program (4) is started. However, in FIG. 2 (A), pure water is continuously supplied with the program (3), and in FIG. 3 (A), pure water is continuously supplied with the program (2). Therefore, a sufficient amount of The pure water layer covers the entire surface of the wafer. Therefore, the fine mist of ozone water does not adhere to the bare silicon surface. As a result, it is possible to suppress the formation of the step defect of the ozone water caused by the step defect on the wafer.

According to the sequence of FIG. 2 (B) and FIG. 3 (B), the ozone water flowing through the piping 42 and the pure water flowing through the piping 41 merge, so at the moment when the ozone water is discharged from the fourth nozzle 44 (program (4) The moment it starts), fine mist does not occur at all. In addition, because there is the procedure (2) or the procedure (3), a sufficient amount of pure water layer has been covered on the entire surface of the wafer at the moment when the procedure (4) is started. Therefore, it is possible to suppress the formation of the step defect of the ozone water caused by the step defect on the wafer.

In the present invention, at the time when the supply of ozone water is started, it is important that a sufficient amount of pure water layer covers the entire surface of the wafer. Therefore, in addition to the first and second embodiments described above, the program (1), the program (3), the program (4), and the program (5) can be executed without interruption in order. That is, in the present invention, after the program (1) and the program (5), at least one of the program (2) and the program (3) is performed, and then the program (4) is performed.

From the viewpoint of suppressing the deterioration of the surface roughness of the wafer, the setting procedure (3) is preferable, that is, after the supply of hydrofluoric acid is stopped, the supply of ozone water is started, and a period for supplying only pure water is set.

The concentration of the fluoric acid supplied in the procedures (1) and (2) may be appropriately set according to the contamination level of the wafer. Although not particularly limited, it may be 0.5 to 3.0% by mass. The concentration of the ozone water supplied in the procedures (4) and (5) is not particularly limited as long as it can form an oxide film on the wafer surface, but may be 5 to 20 mass ppm. In addition, the ozone water concentration here refers to the embodiment in which pure water and ozone water are mixed with the fourth pipe 43 in FIGS. 2 (B) and 3 (B), and refers to the ozone passing through the pipe 42 before mixing. The concentration of water.

The flow rate of the fluoric acid in the program (1) and the program (2) may be appropriately set according to the pollution level of the wafer. Although not particularly limited, it may be 0.5 to 1.5 L / min. In addition, the flow rate of the pure water in the processes (2), (3), and (4) is not particularly limited as long as it is appropriately set within a range capable of forming a sufficient liquid layer, but may be 1.0 to 2.0 L / min. The flow rate of the ozone water in the procedures (4) and (5) is not particularly limited as long as it can form an oxide film on the wafer surface, but may be 1.0 to 2.0 L / min.

Although the number of rotations of the wafer in each program is not particularly limited, it may be 300 to 1000 rpm.

The processing time of each program may be appropriately set according to the contamination level of the wafer. Although not particularly limited, the processing time of the program (1) is preferably 10 to 60 seconds, and the processing time of the program (2) is preferably 5 seconds or less. The processing time of the program (3) is preferably 10 seconds or less, the processing time of the program (4) is preferably 0.5 to 2 seconds, and the processing time of the program (5) is preferably 10 to 30 seconds.

The silicon single crystal wafer (300 mm in diameter) after mirror polishing was subjected to spin cleaning using various cleaning solutions. In the comparative example and the invention example 1,2, each of the spin-washing procedures was performed without interruption as shown in Table 1. In Table 1, "○" indicates that the corresponding cleaning procedure has been performed, and "×" indicates that it has not been performed.

The conditions of each washing procedure are as follows. The number of rotations of the wafer in each cleaning procedure was 500 rpm.

Fluoric acid cleaning program (HF)

Fluoric acid concentration: 1.0% by mass

Flow: 0.8L / min

Processing time: 10 seconds

Fluoric acid, pure water washing procedure (HF / DIW)

Fluoric acid concentration: 1.0% by mass

Fluoric acid flow: 0.8L / min

Pure water flow: 1.2L / min

Processing time: 3 seconds

Pure water washing program (DIW)

Pure water flow: 1.2L / min

Processing time: 10 seconds

Pure water and ozone water washing program (DIW / O ₃ W)

Ozone water concentration: 15 mass ppm

Pure water flow: 1.2L / min

Ozone water flow: 1.2L / min

Processing time: 1 second

Ozone water washing program (O ₃ W)

Ozone water concentration: 15 mass ppm

Flow: 1.2L / min

Processing time: 20 seconds

At each level, six wafers were cleaned in the order described above and spin-dried. After that, the wafers are subjected to a regular spin-rinsing of each wafer as a final rinse, and then spin-dried. Then, the surface of each wafer was measured in a DCO mode using a laser particle counter (KLA-Tencor, SP-3), and the number of LPDs having a size of 26 nm or more was determined. Table 1 shows the average number of LPDs at each level.

As can be seen from Table 1, compared with the comparative example, the number of LPDs in the inventive examples 1 and 2 can be reduced. In addition, when observing the place where the LPD was detected in the comparative example with an atomic force microscope (AFM), a plurality of step defects (approximately 3 to 12 μm in diameter and 0.05 to 0.24 nm in height) were observed as shown in FIG. 6. Cylindrical defects). On the other hand, when observing all positions detected as LPD in Invention Examples 1 and 2 with AFM, no such step defect was observed.

[Industrial possibilities]

According to the wafer cleaning method of the present invention, it is possible to suppress formation of step defects due to ozone water on the wafer.

Claims (5)

    A wafer cleaning method is a wafer cleaning method in which a cleaning liquid is supplied to the surface of the wafer while the wafer is rotated, and is characterized in that: Supply of fluoric acid; start the supply of pure water before or at the same time as stopping the supply of fluoric acid; start the supply of ozone water before stopping the supply of fluoric acid and before stopping the supply of pure water; The period during which pure water and ozone water are simultaneously supplied on a circular surface; thereafter, the supply of the pure water is stopped, and only ozone water is supplied to the wafer surface.         According to the method for cleaning a wafer described in item 1 of the scope of patent application, on the surface of the wafer, the supply of the pure water is started before the supply of the fluoric acid is stopped, and a period for simultaneously supplying the fluoric acid and the pure water is set.         According to the method for cleaning a wafer described in the second item of the patent application scope, after the supply of the hydrofluoric acid is stopped on the surface of the wafer, the supply of the ozone water is started, and a period for supplying pure water is set.         According to the method for cleaning a wafer described in any one of claims 1 to 3, the hydrofluoric acid is discharged from the first nozzle, and the pure water and the ozone water are from a common nozzle different from the first nozzle. Spit it out.         According to the wafer cleaning method described in any one of claims 1 to 3, the hydrofluoric acid, the pure water, and the ozone water are respectively discharged from individual nozzles.