JP3413726B2 - Wafer cleaning method - Google Patents

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 finish 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 out from a silicon single crystal ingot is subjected to a lapping process and an etching process, followed by a mirror polishing process using an abrasive for flattening the wafer surface. In general, the cleanliness of the surface of a silicon wafer directly affects the characteristics of semiconductor devices, and when the cleanliness decreases, it causes a defect in forming a device pattern and adversely affects the electrical characteristics of semiconductor devices.

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

As one of the cleaning processes, there is spin cleaning in which each wafer is rotated while rotating around its center. As the spin cleaning, the following cleaning method has been conventionally performed. . First, an oxide film is formed on the surface of the wafer by cleaning the surface of the wafer after the final polishing of 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 the particles on the wafer surface together with the oxide film. Then, the wafer surface is further washed 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 were minimized by repeatedly performing such ozone water cleaning and cleaning treatment with a hydrofluoric acid solution.

[0005]

However, in such a conventional cleaning method, since all the oxide film formed on the wafer surface by the dilute hydrofluoric acid treatment is removed, the wafer surface after the dilute hydrofluoric acid treatment is removed. It has a bare surface with no oxide film. Since the wafer surface is a hydrophobic surface, even if the particles are removed by the dilute hydrofluoric acid treatment, the particles are likely to be reattached. For this reason, there is a problem that, due to the reattachment of particles, the number of particles on the wafer surface will eventually increase even if ozone water cleaning is subsequently performed.

Further, in the conventional cleaning method, cleaning with ozone water and cleaning with dilute hydrofluoric acid solution are repeatedly performed in order to reliably remove foreign matters such as particles from the surface of the wafer, so that the cleaning process takes time. There is also.

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

[0008]

In order to achieve the above object, the invention according to claim 1 forms an oxide film consisting of a plurality of layers on the 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 the oxide film formed on the wafer surface by the hydrofluoric acid solution cleaning, leaving a layer on the wafer surface side, and a wafer surface after completion of the hydrofluoric acid solution cleaning. In contrast, 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 wafer surface on which a large amount of particles are adhered after the final polishing,
An oxide film consisting of a plurality of layers is formed by the first ozone water cleaning step, and then this oxide film layer is peeled off by the hydrofluoric acid solution cleaning step, leaving the layer on the wafer surface side. For this reason,
The surface of the wafer after cleaning with the hydrofluoric acid solution does not become a hydrophobic state, and particles are prevented from reattaching. After that, the surface of the wafer is cleaned with ozone water in the second ozone water cleaning step, so that an oxide film of high cleanliness in which particles do not remain is formed 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 due to the treatment with dilute hydrofluoric acid and particles are likely to be reattached.

Further, according to the present invention, particles are surely reduced by the series of steps of the first ozone water cleaning step, the hydrofluoric acid solution cleaning step and the second ozone water cleaning step as described above. It is not necessary to repeat washing with a hydrofluoric acid solution, which leads to shortening of the washing processing time.

The oxide film composed of a plurality of layers in the present invention means a layer having a crystal structure of silicon atoms, and the oxide film layer formed by the first ozone water washing step must be at least two layers.

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

The hydrofluoric acid solution cleaning step may be any one as long as it removes the oxide film formed on the wafer surface leaving the layer on the wafer surface side, and depending on the layer to be removed, the concentration of the hydrofluoric acid solution and the cleaning time. Can be set arbitrarily. Further, the number and ratio of oxide film layers left on the wafer surface side and the number and ratio of oxide film layers to be peeled off are not particularly limited in the present invention. For example, the oxide film layer can be configured to be peeled from the uppermost layer by about 1/3 of the whole, but the number of oxide films left on the wafer surface side is the most optimal number, and the invention according to claim 2 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 comprises:
It is characterized in that the oxide film formed on the wafer surface is peeled off, leaving only one layer on the wafer surface side.

According to the second aspect of the present invention, the hydrofluoric acid solution cleaning step peels off the oxide film formed on the wafer surface, leaving only one layer on the wafer surface side, so most of the particles floating on the oxide film are removed. Can be removed together with peeling of the oxide film, and 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 with the hydrofluoric acid solution having a concentration of about 0.5%. It is characterized by being performed.

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

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

According to the second aspect of the present invention, the wafer surface is mechanically cleaned in the mechanical cleaning process after the first ozone water cleaning process and before the hydrofluoric acid solution cleaning process. Large particles are removed from the particles that have floated due to the oxide film formation. For this reason, large-sized particles do not remain due to peeling of the oxide film layer in the subsequent hydrofluoric acid solution cleaning step, and the particles can be further reduced.

The mechanical cleaning step in the present invention may be any one that mechanically cleans the wafer surface, and examples thereof include cleaning with a roll brush and cleaning with a disk brush, but are not limited thereto.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of a wafer cleaning method according to the present invention will be described in detail below with reference to the accompanying drawings. The wafer cleaning method of the present embodiment is performed by a so-called single-wafer spin cleaning method in which silicon wafers after finishing polishing processing of mirror polishing are cleaned one by one while rotating around the center thereof.

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

The first cleaning unit 2 injects a base 5 on which a wafer transferred from a polishing apparatus (not shown) is placed, a first nozzle 7 for injecting ozone water, and an injecting hydrogen fluoride solution. The second nozzle 8 and a rotation drive mechanism (not shown) for rotating the base 5 are provided. The first nozzle 7 has a concentration of 1
It is connected to an ozone water tank that stores 0 ppm of ozone water, and injects the ozone water supplied from the tank. The second nozzle 8 has a concentration 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 PVA roll brush 11, and the roll brush 11 while rotating the roll brush 11 about its axis. It comprises a moving mechanism (not shown), a pure water tank (not shown), and two third nozzles 9 for injecting pure water supplied from the pure water tank onto the wafer surface.

(Wafer Cleaning Process) Next, a wafer cleaning process by the wafer cleaning apparatus 1 configured as described above will be described. FIG. 2 is a process diagram schematically showing the state of the wafer surface by the wafer cleaning process of this embodiment in time series for each process. 2 (a) immediately after finishing polishing, FIG. 2 (b) after first ozone water cleaning, FIG. 2 (c) during roll brush cleaning, FIG. 2 (d) during hydrogen fluoride solution cleaning,
FIG. 2E shows the state of the wafer surface after the second cleaning with ozone water.

Since the wafer surface 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. 2 (a). Ozone water is jetted from the first nozzle 7 of the first cleaning unit 2 to this wafer to perform the first ozone water cleaning process (first ozone water cleaning step). The 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, as shown in FIG. 2B, an oxide film is formed on the wafer surface, and the particles on the wafer surface float on the oxide film.

Then, the wafer is moved to the second cleaning unit 3 by the robot hand 4 and placed on the base 6. And
Pure water is supplied to the wafer surface from the injection port 9. 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 (machine cleaning step). In this roll brush cleaning, the roll brush 11 is rotated at 600 rpm while rotating the wafer around its center at 30 rpm.
Rotate the shaft at rpm for 60 seconds. At this time,
As shown in (c), among the particles floating on the oxide film, large particles are removed by roll brush cleaning.

Then, the wafer is returned to the first cleaning unit 2 by the robot hand 4 and placed on the base 5. Then, about 5 ppm of hydrogen fluoride solution having a concentration of 10 ppm is supplied from the second nozzle 8.
Spraying for 2 seconds to perform a hydrogen fluoride solution cleaning treatment on the wafer surface (hydrofluoric acid solution cleaning step). As shown in FIG. 2 (d), the cleaning with the hydrogen fluoride solution causes the oxide film on the surface of the wafer to be peeled off, leaving only one silicon atom layer, so that minute particles floating on the oxide film are simultaneously removed. To be done. That is, by the hydrogen fluoride solution cleaning treatment of the present embodiment, the oxide film on the wafer surface remains without being completely peeled off, and the wafer surface does not become a hydrophobic surface. Therefore, reattachment of particles to the wafer surface is prevented.

Next, in the first cleaning unit 2, the second nozzle is cleaned with ozone water by injecting 10 ppm of ozone water from the first nozzle 7 onto the wafer surface (second ozone water cleaning step). This ozone water cleaning treatment 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 completion of the second ozone water cleaning step, the wafer surface is dried to complete the wafer cleaning.

As described above, in the wafer cleaning method of the present embodiment, the oxide film is stripped by the hydrogen fluoride solution cleaning process, leaving only one silicon atom layer on the wafer surface side, and the oxide film is not stripped completely. It is possible to prevent reattachment of particles and reliably reduce the particles.
Further, 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) Since particles can be reduced by a series of steps of the ozone water cleaning step), 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.

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) Process) in this order, and may include a process of cleaning with pure water or a disc brush with cathode water between the roll brush cleaning process and the hydrogen fluoride solution cleaning process, and the second ozone water cleaning process. After completion of the steps, steps such as pure water cleaning, disk cleaning with pure water, megasonic cleaning with pure water, and the like may be performed and then the drying step may be performed.

Further, in the wafer cleaning method of this 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 peeled off,
It is possible to adopt any concentration and washing time.

[0033]

EXAMPLES [Example 1] (1) Process of cleaning treatment The following process A was applied to a silicon wafer after finish polishing.
And the treatment of Process B was performed. Process A: [1] → [2] → [3] → [4] → [6] →
[7] Process B: [1] → [2] → [3] → [4] → [5] →
[6] → [7] Where, [1] Ozone water cleaning (first ozone water cleaning process) [2] Roll brush cleaning (mechanical cleaning process) [3] Pure water cleaning [4] Hydrogen fluoride solution cleaning (Hydrofluoric acid solution cleaning process) [5] Ozone water cleaning (second ozone water cleaning process) [6] Pure water cleaning [7] Drying process.

(2) Cleaning conditions The cleaning conditions in each of the steps [1], [2], [4], and [5] are as follows. [1] Ozone water cleaning (first ozone water cleaning process) Ozone water concentration: 10 ppm Cleaning time: 90 seconds [2] Roll brush cleaning (mechanical cleaning process) Cleaning time: 60 seconds [4] Hydrogen fluoride solution cleaning ( Hydrofluoric acid solution cleaning step) Hydrogen fluoride solution concentration: 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) Execution Result Process A and Process B
After performing each of the above processes, the number of particles of 80 nm or more remaining on the surface of the wafer 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) Proportionality As a proportionality, the following processes C, D, E, G and H are
[4] Table 1 shows the number of particles having a particle size of 80 nm or more when the conditions of the hydrogen fluoride solution cleaning are changed and the cleaning is performed.

[0037]

[Table 1]

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

Example 2 (1) Process of Cleaning Treatment The silicon wafer after final 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 washing conditions are the same as in Example 1.

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

[0042]

As described above, according to the present invention,
There is an effect that the number of particles can be surely reduced without causing reattachment of particles. Also, it is not necessary to repeat ozone water cleaning and hydrofluoric acid solution cleaning many times,
This has the effect of shortening the cleaning processing time.

[Brief description of drawings]

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

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

[Explanation of symbols]

1: Cleaning device 2: First cleaning section 3: Second cleaning section 4: Robot hand 5,6: Base 7: No. 1 nozzle 8: Second nozzle 9: No. 3 nozzle 10: Transport path 11: Roll brush W: Silicon wafer P: Particle O: oxide film

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenro Hayashi 1 555 Nakanoya, Annaka-shi, Gunma Inside the Super Silicon Research Institute (56) References JP-A-3-228328 (JP, A) JP-A 11-251275 (JP, A) JP-A-8-153698 (JP, A) JP-A-11-111661 (JP, A) JP-A-2001-53050 (JP, A) (58) Fields investigated (Int.Cl . ⁷ , DB name) H01L 21/304 H01L 21/308

Claims (4)

(57) [Claims] 1. A first ozone water cleaning step of forming an oxide film consisting of a plurality of layers on the surface of a semiconductor wafer after finish polishing by cleaning with ozone water, and a hydrofluoric acid solution cleaning process to form a wafer surface on the wafer surface. And a hydrofluoric acid solution cleaning step for removing the oxide film leaving a layer on the wafer surface side, and a second ozone water cleaning step for further forming an oxide film on the wafer surface after the cleaning with the hydrofluoric acid solution by ozone water cleaning. A method for cleaning a wafer, comprising: 2. The wafer cleaning method according to claim 1, wherein in the hydrofluoric acid solution cleaning step, the oxide film formed on the wafer surface is peeled off leaving only one layer on the wafer surface side. . 3. The hydrofluoric acid solution washing step has a concentration of about 0.
3. The wafer cleaning method according to claim 1, wherein the cleaning process is performed with the 5% hydrofluoric acid solution for about 5 seconds. 4. 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 is further included.
4. The wafer cleaning method according to any one of 3 to 3.