JP2002203824A - Method for cleaning wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce particles on a wafer surface surely in a shot time. SOLUTION: A method for cleaning a wafer for cleaning the surface of a semiconductor wafer after finish polishing, comprises a first ozone water cleaning process or forming an oxide film comprising a plurality of layers by ozone water cleaning, a mechanical cleaning process for brush cleaning the wafer surface after the first ozone water cleaning process, a hydrofluoric acid solution cleaning process or exfoliating so that only one layer of a wafer surface side is left by cleaning the oxide film formed on the wafer surface with hydrofluoric acid solution, and a second ozone water cleaning process for further forming the oxide film by the ozone water cleaning to the wafer surface after finishing the hydrofluoric acid solution cleaning.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wafer cleaning method for cleaning a semiconductor wafer after final polishing, and more particularly to a wafer cleaning method using ozone water and a hydrofluoric acid solution.

[0002]

2. Description of the Related Art In general, a silicon wafer cut from a silicon single crystal ingot is subjected to a mirror polishing step using an abrasive for flattening the wafer surface after a lapping step and an etching step. In general, the cleanliness of the silicon wafer surface directly affects the characteristics of the semiconductor device. If the cleanliness is reduced, it may cause a failure in forming a device pattern or adversely affect the electrical characteristics of the semiconductor device.

[0003] The decrease in the cleanliness of the wafer substrate surface is caused not only by fine irregularities on the wafer substrate surface but also by foreign matters such as particles (fine particles) attached to the wafer substrate surface in each wafer processing step. Therefore, after the mirror polishing step, a cleaning process is performed to remove foreign substances such as particles remaining on the wafer surface.

[0004] As one of the cleaning processes, there is spin cleaning in which wafers are cleaned while rotating each wafer around its center, and the following cleaning method has been conventionally used as the spin cleaning. . First, an oxide film is formed on the wafer surface by cleaning the wafer surface after the final polishing by mirror polishing with ozone water. As a result, foreign matter such as particles attached to the wafer surface floats from the wafer surface. Next, the wafer surface is washed with a solution containing dilute hydrofluoric acid, and the oxide film formed on the wafer surface is completely peeled off, thereby removing particles on the wafer surface together with the oxide film. Then, the wafer surface is further cleaned with ozone water. As a result, a clean oxide film with few particles is formed on the wafer surface. Particles generated on the wafer surface have been minimized by repeatedly performing such cleaning treatment with ozone water and a hydrofluoric acid solution.

[0005]

However, in such a conventional cleaning method, since the oxide film formed on the wafer surface by the dilute hydrofluoric acid treatment is completely stripped off, the wafer surface after the dilute hydrofluoric acid treatment is removed. The exposed surface has no oxide film. Since the wafer surface is a hydrophobic surface, even if the particles are removed by dilute hydrofluoric acid treatment, the particles are likely to be reattached. For this reason, there is a problem in that even if the ozone water cleaning is performed thereafter, particles on the wafer surface eventually increase due to the reattachment of the particles.

In the conventional cleaning method, cleaning with ozone water and cleaning with a diluted hydrofluoric acid solution are repeatedly performed in order to reliably remove foreign substances such as particles from the wafer surface. There is also.

The present invention has been made in view of the above problems, and has as its main object to provide a wafer cleaning method capable of reliably reducing particles on a wafer surface. Another object of the present invention is to provide a wafer cleaning method capable of reliably reducing particles by a short cleaning process.

[0008]

In order to achieve the above object, according to the first aspect of the present invention, an oxide film composed of a plurality of layers is formed on a surface of a semiconductor wafer after final polishing by washing with ozone water. A first ozone water cleaning step, a hydrofluoric acid solution cleaning step of removing an oxide film formed on the wafer surface while leaving the layer on the wafer surface side, and a wafer surface after the hydrofluoric acid solution cleaning is completed A second ozone water cleaning step of further forming an oxide film by ozone water cleaning;
It is characterized by including.

According to the first aspect of the present invention, the surface of the wafer on which a large amount of the particles after the final polishing adhere is attached to the surface of the wafer.
An oxide film composed of a plurality of layers is formed by a first ozone water cleaning step, and thereafter, the oxide film layer is peeled off by a hydrofluoric acid solution cleaning step except for a layer on the wafer surface side. For this reason,
The surface of the wafer after the cleaning with the hydrofluoric acid solution does not become hydrophobic, so that reattachment of particles is prevented. Thereafter, the wafer surface is cleaned with ozone water in the second ozone water cleaning step, thereby forming a high-purity oxide film with no particles remaining on the wafer surface. Therefore, according to the present invention, it is possible to surely reduce the number of particles as compared with the conventional wafer cleaning method in which the surface of the wafer becomes a hydrophobic surface by the dilute hydrofluoric acid treatment and the particles are likely to adhere again.

Further, in the present invention, particles are reliably reduced by a series of the first ozone water cleaning step, the hydrofluoric acid solution cleaning step, and the second ozone water cleaning step. It is not necessary to repeat the hydrofluoric acid solution cleaning many times, which leads to shortening of the cleaning processing time.

In the present invention, the oxide film comprising a plurality of layers means a layer having a crystal structure of silicon atoms, and it is necessary that at least two oxide films are formed in the first ozone water cleaning step.

The first ozone water cleaning step only needs to form an oxide film composed of a plurality of layers on the wafer surface, and the concentration of ozone water and the cleaning time for this can be arbitrarily determined.

The hydrofluoric acid solution cleaning step may be any as long as the oxide film formed on the wafer surface is peeled off while leaving the layer on the wafer surface side. The concentration of the hydrofluoric acid solution and the cleaning time are determined according to the layer to be peeled off. Can be arbitrarily determined. Further, the number and ratio of the oxide film layers left on the wafer surface side and the number and ratio of the oxide film layers to be separated are not particularly limited in the present invention. For example, the oxide film layer can be configured to be peeled off from the uppermost layer by about 1/3 of the whole, but the number of oxide film layers left on the wafer surface side is determined to be the most optimum. Is mentioned.

According to a second aspect of the present invention, in the wafer cleaning method according to the first aspect, the hydrofluoric acid solution cleaning step includes:
The oxide film formed on the wafer surface is peeled off while leaving only one layer on the wafer surface side.

According to the second aspect of the present invention, since the hydrofluoric acid solution cleaning step removes the oxide film formed on the wafer surface except for one layer on the wafer surface side, most of the particles floating on the oxide film Can be removed together with the removal of the oxide film, and the particles can be further reduced.

According to a third aspect of the present invention, in the wafer cleaning method according to the first or second aspect, the hydrofluoric acid solution cleaning step is a cleaning process for about 5 seconds using the hydrofluoric acid solution having a concentration of about 0.5%. Is performed.

The invention according to claim 3 is a preferred embodiment of the hydrofluoric acid solution washing step. As a result of experiments performed by the present inventor in various patterns, the hydrofluoric acid solution having a concentration of about 0.5% was used for about 5 seconds. When the cleaning process is performed, the effect of reducing the particles is most apparent.

According to a fourth aspect of the present invention, there is provided the wafer cleaning method according to any one of the first to third aspects, wherein
The method further includes a mechanical cleaning step of mechanically cleaning the wafer surface after the ozone water cleaning step and before the hydrofluoric acid solution cleaning step.

According to the second aspect of the present invention, in the mechanical cleaning step after the completion of the first ozone water cleaning step and before the hydrofluoric acid solution cleaning step, the wafer surface is subjected to the mechanical cleaning processing, thereby performing the first ozone water cleaning step. Large particles are removed from the particles levitated by the formation of the oxide film. Therefore, in the subsequent hydrofluoric acid solution cleaning step, the oxide film layer is peeled off, so that large-sized particles do not remain, and the particles can be further reduced.

The mechanical cleaning step in the present invention may be any method that mechanically cleans the wafer surface, and includes, for example, cleaning with a roll brush and cleaning with a disk brush, but is not limited thereto.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a wafer cleaning method according to the present invention will be described below in detail with reference to the accompanying drawings. The wafer cleaning method according to the present embodiment is performed by a so-called single-wafer spin cleaning method in which the silicon wafers after the finish polishing process of the mirror polishing are cleaned one by one while being rotated around the center thereof.

(Configuration of Wafer Cleaning Apparatus) FIG. 1 is a schematic configuration diagram of a wafer cleaning apparatus of the present embodiment. As shown in FIG. 1, a wafer cleaning apparatus 1 of the present embodiment includes a transfer path 10 for a silicon wafer from a polishing apparatus and a surface of a transferred silicon wafer on an ozone (O ₃ ) water or a hydrogen fluoride (HF). A) a first cleaning unit 2 for supplying and cleaning a solution, and a second cleaning unit 3 for mechanically cleaning the wafer with a roll brush 11.
And a robot hand 4 for transferring a wafer between the first cleaning unit 2 and the second cleaning unit 3.

The first cleaning unit 2 mounts a base 5 on which a wafer conveyed from a polishing apparatus (not shown) is mounted, a first nozzle 7 for injecting ozone water, and injects a hydrogen fluoride solution. It comprises a second nozzle 8 and a rotation drive mechanism (not shown) for rotating the base 5. The first nozzle 7 has a density of 1
It is connected to an ozone water tank storing 0 ppm ozone water, and is configured to inject ozone water supplied from the tank. The second nozzle 8 has a density of 0.5%
Is connected to a hydrogen fluoride solution tank storing the hydrogen fluoride solution, and the hydrogen fluoride solution supplied from the tank is injected.

The second cleaning unit 3 performs a roll brush cleaning process, and moves the base 6 on which the wafer is placed, the roll brush 11 made of PVA, and the roll brush 11 while rotating the roll brush 11 around the axis. It comprises a moving mechanism (not shown), a pure water tank (not shown), and two third nozzles 9 for spraying pure water supplied from the pure water tank onto the wafer surface.

(Wafer Cleaning Process) Next, a description will be given of a wafer cleaning process performed by the wafer cleaning apparatus 1 configured as described above. FIG. 2 is a process diagram schematically showing the state of the wafer surface by the wafer cleaning process of this embodiment in a time series for each process. FIG. 2A shows a state immediately after finishing polishing, FIG. 2B shows a state after the first ozone water cleaning, FIG. 2C shows a state during the roll brush cleaning, FIG.
FIG. 2E shows the state of the wafer surface after the second ozone water cleaning.

Since the surface of the wafer transferred to the first cleaning unit 2 after the finish polishing is a hydrophobic surface, a large number of particles are firmly attached as shown in FIG. 2A. Ozone water is jetted from the first nozzle 7 of the first cleaning unit 2 to the wafer to perform a first ozone water cleaning process (first ozone water cleaning step). This first ozone water cleaning step is performed by supplying ozone water having a concentration of 10 ppm to the wafer surface at a flow rate of 1 L / min for 90 seconds while rotating the wafer around the center at a rotation speed of 100 rpm. As a result, an oxide film is formed on the wafer surface as shown in FIG. 2B, and particles on the wafer surface float on the oxide film.

Next, the wafer is moved to the second cleaning section 3 by the robot hand 4 and placed on the base 6. And
Pure water is supplied from the injection port 9 to the wafer surface. While performing such pure water cleaning, the roll brush 11 is rotated around its axis by a drive mechanism to move on the wafer surface, and a roll brush cleaning process is performed (mechanical cleaning process). In this roll brush cleaning, the roll brush 11 is rotated at a rotational speed of 600 while rotating the wafer around its center at a rotational speed of 30 rpm.
The rotation is performed at 60 rpm for 60 seconds. At this time, FIG.
As shown in (c), the large particles among the particles floating on the oxide film are removed by the roll brush cleaning.

Next, the wafer is returned to the first cleaning unit 2 by the robot hand 4 and placed on the base 5. Then, a hydrogen fluoride solution having a concentration of 10 ppm is supplied from the second nozzle 8 for about 5 hours.
By spraying for 2 seconds, the wafer surface is subjected to a hydrogen fluoride solution cleaning process (a hydrofluoric acid solution cleaning step). As shown in FIG. 2D, the oxide film on the wafer surface is peeled off by the hydrogen fluoride solution cleaning, leaving only one layer of silicon atoms, thereby removing minute particles floating on the oxide film at the same time. Is done. That is, the oxide film on the wafer surface remains in a state in which the oxide film on the wafer surface is not completely removed by the hydrogen fluoride solution cleaning processing of the present embodiment, and the wafer surface does not become a hydrophobic surface. This prevents the particles from re-adhering to the wafer surface.

Next, in the first cleaning section 2, a second ozone water cleaning is performed by injecting 10 ppm ozone water from the first nozzle 7 onto the wafer surface (second ozone water cleaning step). This ozone water cleaning process is performed for 30 seconds. As a result, as shown in FIG. 2E, a clean oxide film is formed on the wafer surface. After the second ozone water cleaning step, the wafer surface is dried to complete the wafer cleaning.

As described above, according to the wafer cleaning method of the present embodiment, the oxide film is peeled off by the hydrogen fluoride solution cleaning process while leaving only one silicon atom layer on the wafer surface side, and the oxide film is not completely peeled off. Reattachment of particles is prevented, and particles can be reliably reduced.
In addition, the first ozone water cleaning (first ozone water cleaning step), the roll brush cleaning (mechanical cleaning step), the hydrogen fluoride solution cleaning (hydrofluoric acid solution cleaning step), and the second ozone water cleaning (second cleaning step) Particles can be reduced by a series of steps of the ozone water cleaning step), so that it is not necessary to repeat the ozone water cleaning and the hydrofluoric acid solution cleaning many times, and the cleaning processing time is shortened.

Incidentally, in the wafer cleaning method of this embodiment, 1
Second ozone water cleaning (first ozone water cleaning step), roll brush cleaning (mechanical cleaning step), hydrogen fluoride solution cleaning (hydrofluoric acid solution cleaning step), and second ozone water cleaning (second ozone water cleaning) Steps) may be performed in this order, a step of pure water cleaning and a step of disk brush cleaning with cathode water may be included between the roll brush cleaning step and the hydrogen fluoride solution cleaning step, and the second ozone water cleaning. After completion of the process, a process such as pure water cleaning, disk cleaning with pure water, megasonic cleaning with pure water, or the like may be performed, and then the process may be shifted to a drying process.

Further, in the wafer cleaning method of the present embodiment,
Although the concentration of the hydrogen fluoride solution used in the hydrogen fluoride solution cleaning step is 10 ppm, and the cleaning time is 5 seconds,
If the oxide film on the wafer surface is not completely removed,
Arbitrary concentration and washing time can be adopted.

[0033]

[Example 1] (1) Cleaning process The following process A was performed on a silicon wafer after final polishing.
And the process B. Process A: [1] → [2] → [3] → [4] → [6] →
[7] Process B: [1] → [2] → [3] → [4] → [5] →
[6] → [7] Here, [1] ozone water cleaning (first ozone water cleaning step) [2] roll brush cleaning (mechanical cleaning step) [3] pure water cleaning [4] hydrogen fluoride solution cleaning (Hydrofluoric acid solution washing step) [5] Ozone water washing (second ozone water washing step) [6] Pure water washing [7] Drying treatment.

(2) Cleaning Conditions The cleaning conditions in each of the above steps [1], [2], [4] and [5] are as follows. [1] Ozone water cleaning (first ozone water cleaning step) Ozone water concentration: 10 ppm Cleaning time: 90 seconds [2] Roll brush cleaning (mechanical cleaning step) Cleaning time: 60 seconds [4] Hydrogen fluoride solution cleaning ( Hydrofluoric acid solution cleaning step) Concentration of hydrogen fluoride solution: 0.5% Cleaning time: 5 seconds [5] Ozone water cleaning (second ozone water cleaning step) Ozone water concentration: 10 ppm Cleaning time: 30 seconds

(3) Result A Process A and Process B
After performing each of the above processes, the number of particles of 80 nm or more remaining on the wafer surface was measured, and the following results were obtained. Process A: Number of particles (80 nm or more): 980 Process B: Number of particles (80 nm or more): 370

(4) Comparative example The following processes C, D, E, G and H are used as comparative examples.
[4] Table 1 shows the number of particles having a size of 80 nm or more when the cleaning was performed under different conditions of the hydrogen fluoride solution.

[0037]

[Table 1]

(5) Evaluation As can be seen from the above, according to the present embodiment, the number of particles of 80 nm or more on the wafer surface is extremely reduced as compared with the comparative example.

Example 2 (1) Cleaning Process The silicon wafer after finish polishing was spin-cleaned in the following order. [1] Ozone water cleaning (first ozone water cleaning process) [2] Roll brush cleaning (mechanical cleaning process) [3] Disk brush cleaning with cathode water [4] Pure water cleaning [5] Hydrogen fluoride solution cleaning ( Hydrofluoric acid solution cleaning process) [6] Ozone water cleaning (second ozone water cleaning process) [7] Disc brush cleaning with pure water [8] Megasonic cleaning with pure water [9] Pure water cleaning [10] Drying treatment

(2) Cleaning Conditions The cleaning conditions are the same as in the first embodiment.

(3) Implementation Results Number of particles after completion of all processes (80 nm or more):
59 As can be seen from the result, the number of particles could be almost removed.

[0042]

As described above, according to the present invention,
There is an effect that particles can be surely reduced without causing particles to re-adhere. Also, there is no need to repeat the ozone water cleaning and hydrofluoric acid solution cleaning many times,
This has the effect of shortening the cleaning processing time.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a wafer cleaning apparatus of the present embodiment.

FIG. 2 is a process diagram schematically showing a state of a wafer surface by a wafer cleaning process of the embodiment in a time series for each process.

[Explanation of symbols]

 1: Cleaning device 2: First cleaning unit 3: Second cleaning unit 4: Robot hand 5, 6: Base 7: First nozzle 8: Second nozzle 9: Third nozzle 10: Transport path 11: Roll brush W : Silicon wafer P: Particle O: Oxide film

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Junichi Matsuzaki 555-1, Nakanoya, Annaka-shi, Gunma Inside the Super Silicon Research Laboratories (72) Inventor Kenro Hayashi 555-1, Nakanoya, Annaka-shi, Gunma F-term in the Super Silicon Laboratories, Inc. (reference) 5F043 AA31 BB27 DD30 EE07 EE08 EE35 GG10

Claims (4)

[Claims] A first ozone water cleaning step of forming an oxide film composed of a plurality of layers by ozone water cleaning on the surface of the semiconductor wafer after the final polishing; and a hydrofluoric acid solution cleaning formed on the wafer surface. A hydrofluoric acid solution cleaning step of removing the oxide film left while leaving the layer on the wafer surface side; and a second ozone water cleaning step of forming an oxide film on the wafer surface after the completion of the hydrofluoric acid solution cleaning by ozone water cleaning. A wafer cleaning method comprising: 2. The wafer cleaning method according to claim 1, wherein the hydrofluoric acid solution cleaning step is to peel off an oxide film formed on the wafer surface while leaving only one layer on the wafer surface side. . 3. The hydrofluoric acid solution washing step is performed at a concentration of about 0.
3. The wafer cleaning method according to claim 1, wherein a cleaning process is performed for about 5 seconds with the 5% hydrofluoric acid solution. 4. The method according to claim 1, further comprising a mechanical cleaning step of mechanically cleaning the wafer surface after the first ozone water cleaning step and before the hydrofluoric acid solution cleaning step.
4. The method for cleaning a wafer according to any one of items 3 to 3.