JP2015220284A - Wafer cleaning method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wafer cleaning method that suppresses deterioration of the surface roughness of a cleaned wafer and improves the residue of particles at the outer peripheral portion of the cleaned wafer.SOLUTION: In a wafer cleaning method containing a cleaning step using ozone water and a cleaning step using hydrofluoric acid, a spin cleaning step using pure water is interposed between the cleaning step using the ozone water and the cleaning step using the hydrofluoric acid, and the cleaning process is performed in the order of (1) the cleaning step using ozone water, (2) the spin cleaning step using pure water and then (3) the cleaning step using hydrofluoric acid, or in the order of (1) the cleaning step using hydrofluoric acid, (2) the spin cleaning step using pure water and then (3) the cleaning step using ozone water. The flow rate of pure water in the spin cleaning step using the pure water is set to 1.2 L/min, and the rotational number of a wafer is set to 1,000 rpm or more.

Description

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

Conventionally, ozone water or hydrofluoric acid is generally used in a cleaning process of a semiconductor silicon wafer. For example, a method of removing particles by repeatedly performing ozone water cleaning and hydrofluoric acid cleaning has been proposed (patented). Reference 1). In such a method, an oxide film is formed on the wafer surface by ozone water cleaning, and then particles and the like on the wafer surface are removed together with the oxide film by hydrofluoric acid cleaning.
However, in such a method, ozone water and hydrofluoric acid coexist on the wafer surface when the cleaning solution is changed, and the oxide film is formed on the wafer surface by ozone water and the oxide film is removed by etching (etching). When this occurs simultaneously, there is a problem that the surface roughness deteriorates.

  Further, when the oxide film is removed with hydrofluoric acid, a wafer bear surface appears, but particles are very likely to adhere to the wafer bear surface. Therefore, after removing the oxide film with hydrofluoric acid, it is usually cleaned with pure water or ozone water. However, pure water or ozone water is repelled on the outer periphery of the wafer due to the water repellency of the wafer bear surface. There was a problem that water and ozone water did not spread, and as a result, particles remained on the outer periphery of the wafer.

JP-A-8-181137

  The present invention has been made in order to solve the above problems, and provides a wafer cleaning method that suppresses deterioration of the surface roughness of the wafer after cleaning and can improve the residual particles on the outer periphery of the wafer after cleaning. The purpose is to provide.

In order to solve the above problems, in the present invention, in a wafer cleaning method including a cleaning process using ozone water and a cleaning process using hydrofluoric acid,
By having a spin cleaning process using pure water between the cleaning process using ozone water and the cleaning process using hydrofluoric acid, (1) cleaning process using ozone water, and (2) pure water Spin cleaning step used, (3) Cleaning step using hydrofluoric acid, or (1) Cleaning step using hydrofluoric acid, (2) Spin cleaning step using pure water, (3) Using ozone water The cleaning method is performed in the order of the cleaning steps,
Provided is a method for cleaning a wafer, wherein a flow rate of pure water in a spin cleaning process using pure water is 1.2 L / min or more and a rotation speed of the wafer is 1,000 rpm or more.

With such a wafer cleaning method, the coexistence of ozone water and hydrofluoric acid is prevented by a spin cleaning process using pure water between a cleaning process using ozone water and a cleaning process using hydrofluoric acid. Deterioration of the surface roughness of the subsequent wafer can be suppressed.
Further, by performing the spin cleaning process using pure water at the flow rate and the rotational speed as described above, the pure water can be distributed to the outer periphery of the wafer without being repelled by the water-repellent surface. It is possible to improve the residual particles in the part.

  At this time, the flow rate of pure water in the spin cleaning process using the pure water is 1.2 L / min or more and 2.0 L / min or less, and the rotation speed of the wafer is 1,000 rpm or more and 1,500 rpm or less. It is preferable.

  If it is such a flow volume and rotation speed, the above effects can fully be acquired.

  At this time, the process time of the spin cleaning process using pure water is preferably 2 seconds or more and 10 seconds or less.

  With such a flow rate and rotation speed as described above, ozone water or hydrofluoric acid can be completely replaced with pure water in such a process time.

  At this time, it is preferable to perform the cleaning step using the ozone water and the cleaning step using the hydrofluoric acid a plurality of times.

  Thus, in the cleaning method in which the cleaning process using ozone water and the cleaning process using hydrofluoric acid are performed a plurality of times, the spin cleaning process using pure water is performed more effectively under the above-described conditions. Deterioration of the surface roughness of the wafer after cleaning can be suppressed, and the residual particles on the outer peripheral portion of the wafer after cleaning can be improved.

  Further, at this time, the cleaning process using the ozone water is performed by spin cleaning, the flow rate of the ozone water is set to 1.2 L / min to 2.0 L / min, and the rotation speed of the wafer is 1,000 rpm to 1,500 rpm. It is preferable that

  By performing the cleaning process using ozone water under such conditions, the ozone water can be distributed to the outer periphery of the wafer in the same manner as the spin cleaning process using pure water, so that the cleaning effect can be further improved. it can.

As described above, with the wafer cleaning method of the present invention, it is possible to suppress the deterioration of the surface roughness of the wafer after cleaning, and to improve the residual particles on the outer periphery of the wafer after cleaning. . Furthermore, by applying the cleaning process using ozone water and the cleaning process using hydrofluoric acid a plurality of times, the deterioration of the surface roughness of the wafer after cleaning can be more effectively suppressed. It is possible to improve the residual particles on the outer periphery of the wafer. Moreover, the cleaning effect can be further improved by performing the cleaning process using ozone water under the same conditions as the spin cleaning process using pure water.
Such a wafer cleaning method is particularly suitable for single wafer cleaning of a semiconductor silicon wafer.

It is a flowchart which shows an example of the washing | cleaning method of the wafer of this invention. It is a flowchart which shows another example of the washing | cleaning method of the wafer of this invention. It is a graph which shows the surface roughness of Example 1-1 to 1-4 and Comparative Examples 1-1 to 1-4 before and after cleaning. (A) Example 2-1, (b) Example 2-2, (c) Comparative example 2-1, (d) Comparative example 2-2, (e) In the cleaned wafer of Comparative example 2-3 It is the figure which showed the particle.

  As described above, there has been a demand for the development of a wafer cleaning method that can suppress the deterioration of the surface roughness of the wafer after cleaning, and can improve the residual particles on the outer periphery of the wafer after cleaning.

  As a result of intensive studies on the above problems, the present inventors have conducted a cleaning process using ozone water (hereinafter also referred to as ozone water cleaning) and a cleaning process using hydrofluoric acid (hereinafter also referred to as hydrofluoric acid cleaning). In a method for cleaning wafers containing ozone, a spin cleaning process using pure water between ozone water cleaning and hydrofluoric acid cleaning (hereinafter also referred to as pure water spin cleaning) prevents coexistence of ozone water and hydrofluoric acid. Deterioration of the surface roughness of the wafer after cleaning can be suppressed, and at this time, pure water can be distributed to the outer periphery of the wafer by performing pure water spin cleaning at a specific pure water flow rate and wafer rotational speed. For this reason, the inventors have found that it is possible to improve the residual particles on the outer periphery of the wafer after cleaning, and completed the present invention.

That is, the present invention provides a wafer cleaning method including a cleaning process using ozone water and a cleaning process using hydrofluoric acid.
By having a spin cleaning process using pure water between the cleaning process using ozone water and the cleaning process using hydrofluoric acid, (1) cleaning process using ozone water, and (2) pure water Spin cleaning step used, (3) Cleaning step using hydrofluoric acid, or (1) Cleaning step using hydrofluoric acid, (2) Spin cleaning step using pure water, (3) Using ozone water The cleaning method is performed in the order of the cleaning steps,
This is a wafer cleaning method in which the flow rate of pure water in the spin cleaning process using pure water is 1.2 L / min or more and the rotation speed of the wafer is 1,000 rpm or more.

  Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.

FIG. 1 is a flowchart showing an example of the wafer cleaning method of the present invention.
The wafer cleaning method of the present invention is a method of performing pure water spin cleaning between ozone water cleaning and hydrofluoric acid cleaning. For example, when ozone water cleaning and hydrofluoric acid cleaning are performed once each, FIG. Alternatively, cleaning is performed according to the flow shown in FIG.

  In the cleaning flow of FIG. 1A, first, a cleaning process (1A) using ozone water is performed, then a spin cleaning process (2A) using pure water is performed, and then a cleaning process using hydrofluoric acid ( After performing 3A), a spin cleaning process (4A) using pure water is performed, and finally a drying process (5A) is performed.

  On the other hand, in the cleaning flow of FIG. 1B, first, the cleaning step (1B) using hydrofluoric acid is performed, then the spin cleaning step (2B) using pure water is performed, and then the cleaning using ozone water is performed. After performing the step (3B), a spin cleaning step (4B) using pure water is performed, and finally a drying step (5B) is performed.

  As described above, in the wafer cleaning method of the present invention, ozone water cleaning may be performed first as shown in FIG. 1A, and then hydrofluoric acid cleaning may be performed with pure water spin cleaning interposed therebetween. As shown in (B), hydrofluoric acid cleaning may be performed first, and then ozone water cleaning may be performed with pure water spin cleaning interposed therebetween.

  Thus, by performing pure water spin cleaning between ozone water cleaning and hydrofluoric acid cleaning, ozone water or hydrofluoric acid on the wafer surface is replaced with pure water to prevent coexistence of ozone water and hydrofluoric acid. Therefore, the deterioration of the surface roughness of the wafer after cleaning can be suppressed.

In the wafer cleaning method of the present invention, the spin cleaning process using pure water between the cleaning process using ozone water and the cleaning process using hydrofluoric acid (processes (2A) and (2B) in FIG. 1). The flow rate of pure water is set to 1.2 L / min or more, and the rotation speed of the wafer is set to 1,000 rpm or more.
The flow rate of pure water is preferably 1.2 L / min or more and 2.0 L / min or less, and the rotation speed of the wafer is preferably 1,000 rpm or more and 1,500 rpm or less.

By performing pure water spin cleaning at such a flow rate and rotation speed, it is possible to spread pure water to the outer periphery of the wafer without being repelled by the water repellent surface, so that particles adhere from the air and particles on the wafer surface. Can be prevented from sticking. That is, it is possible to improve the remaining particles on the outer peripheral portion of the wafer after cleaning, and to perform more efficient cleaning.
Further, by performing pure water spin cleaning at such a flow rate and rotation speed, replacement with pure water after ozone water cleaning or hydrofluoric acid cleaning can be performed efficiently in a short time.

  If the flow rate of pure water is less than 1.2 L / min or the rotation speed of the wafer is less than 1,000 rpm, the entire surface of the wafer cannot be washed with pure water, and the wafer outer periphery cannot be washed away. A water-repellent surface appears on the surface and causes particle adhesion.

  Further, the process time of the pure water spin cleaning may be 2 seconds or more and 10 seconds or less. When performing pure water spin cleaning at the above flow rate and rotation speed, ozone water or hydrofluoric acid can be completely replaced with pure water in such a process time, thus preventing coexistence of ozone water and hydrofluoric acid. In addition, the deterioration of the surface roughness of the wafer after cleaning can be suppressed.

In the wafer cleaning method of the present invention, the cleaning process using ozone water is performed by spin cleaning, the flow rate of ozone water is 1.2 L / min or more and 2.0 L / min or less, and the rotation speed of the wafer is 1, It is preferable to set it to 000 rpm or more and 1,500 rpm or less.
By performing the ozone water cleaning under such conditions, the ozone water can be distributed to the outer periphery of the wafer in the same manner as the pure water spin cleaning described above, so that the cleaning effect can be further improved.

In the wafer cleaning method of the present invention, as shown in FIGS. 1A and 1B, a drying step (steps (5A) and (5B) in FIG. 1 is performed after cleaning with ozone water, hydrofluoric acid, and pure water). The drying step may be performed by a known method.
Further, as shown in FIGS. 1A and 1B, it is preferable to perform pure water spin cleaning immediately before the drying step (that is, the final cleaning step) (steps (4A) and (4B) in FIG. ). The pure water spin cleaning at this time may be performed under the same conditions as the pure water spin cleaning between the ozone water cleaning and the hydrofluoric acid cleaning (steps (2A) and (2B) in FIG. 1).

  In the present invention, the conditions for cleaning with ozone water are not particularly limited, and may be performed under the conditions for conventional ozone water cleaning. However, it is preferable to perform cleaning by spin cleaning using ozone water having a concentration of 10 to 60 ppm. It is preferable that the process time is 10 to 60 seconds at the above flow rate and rotation speed.

  In the present invention, hydrofluoric acid cleaning conditions are not particularly limited, and may be performed under conventional hydrofluoric acid cleaning conditions. Preferably, the hydrofluoric acid cleaning is performed by spin cleaning using 0.1 to 3.0% by mass of hydrofluoric acid. The spin cleaning conditions are preferably a flow rate of 1.0 to 2.0 L / min, a rotational speed of 100 to 1,500 rpm, and a process time of 3 to 60 seconds.

In addition, the wafer cleaning method of the present invention may perform a cleaning process using ozone water and a cleaning process using hydrofluoric acid a plurality of times.
FIG. 2 shows an example of a cleaning flow when ozone water cleaning and hydrofluoric acid cleaning are performed a plurality of times.
In the cleaning flow (C) of FIG. 2, the cleaning process (1C) using ozone water is first performed, followed by the spin cleaning process (2C) using pure water, similar to the cleaning flow of FIG. 1 (A) described above. Next, after performing a cleaning step (3C) using hydrofluoric acid, a spin cleaning step (4C) using pure water is performed. Then, it returns to the washing | cleaning process (1C) using ozone water, and repeats washing | cleaning by making (1C)->(2C)->(3C)-> (4C) into 1 cycle. After repeating this cycle a predetermined number of times, the drying step (5C) is finally performed.

In the conventional cleaning method that performs ozone water cleaning and hydrofluoric acid cleaning multiple times, the cleaning effect increases as the number of times increases, but the degree of deterioration of the surface roughness of the wafer due to cleaning and the degree of residual particles on the outer periphery of the wafer also increase. To do.
On the other hand, the cleaning method of the present invention can suppress the deterioration of the surface roughness of the wafer by pure water spin cleaning as described above and improve the residual particles on the outer periphery of the wafer. In a cleaning method in which acid cleaning is performed multiple times, by performing pure water spin cleaning between each ozone water cleaning and hydrofluoric acid cleaning under the above-described conditions, the deterioration of the surface roughness of the wafer can be more effectively suppressed. Further, it is possible to improve the residual particles on the outer periphery of the wafer.

As described above, with the wafer cleaning method of the present invention, it is possible to suppress the deterioration of the surface roughness of the wafer after cleaning, and to improve the residual particles on the outer periphery of the wafer after cleaning. . Furthermore, by applying the cleaning process using ozone water and the cleaning process using hydrofluoric acid a plurality of times, the deterioration of the surface roughness of the wafer after cleaning can be more effectively suppressed. It is possible to improve the residual particles on the outer periphery of the wafer. Moreover, the cleaning effect can be further improved by performing the cleaning process using ozone water under the same conditions as the spin cleaning process using pure water.
Such a wafer cleaning method is particularly suitable for single wafer cleaning of a semiconductor silicon wafer.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely using an Example and a comparative example, this invention is not limited to these.

In the following examples and comparative examples, the following wafers, hydrofluoric acid, and ozone water were used.
Wafer: 300 mm in diameter, P ^- type <100> silicon wafer, hydrofluoric acid: concentration 0.5% by mass
Ozone water: concentration 10ppm

In the following examples and comparative examples, ozone water cleaning and hydrofluoric acid cleaning were performed by spin cleaning under the following conditions.
Ozone water cleaning conditions: flow rate 1.5 L / min, rotation speed 1,000 rpm, process time 20 seconds Hydrofluoric acid cleaning conditions: flow rate 1.5 L / min, rotation speed 1,000 rpm, process time 30 seconds

[Wafer surface roughness]
Example 1
Four wafers were prepared (Examples 1-1 to 1-4), and the wafer was cleaned according to the following cleaning flow 1-1. In the pure water cleaning step, cleaning was performed under the following condition of pure water spin cleaning condition 1.
Cleaning flow 1-1: {ozone water → pure water → hydrofluoric acid → pure water} × 3 → drying Pure water spin cleaning condition 1: flow rate 1.5 L / min, rotation speed 1,300 rpm, process time 3 seconds at each wafer Table 1 shows the results of measuring the surface roughness before cleaning and the surface roughness after cleaning with Surfscan SP3 manufactured by KLA-Tencor.

(Comparative Example 1)
Four wafers were prepared (Comparative Examples 1-1 to 1-4), and the wafer was cleaned according to the following cleaning flow 1-2. In the pure water cleaning step, cleaning was performed under the condition of pure water spin cleaning condition 1 as in Example 1.
Cleaning flow 1-2: {ozone water → hydrofluoric acid} × 3 → pure water → drying Table 2 shows the results of measuring the surface roughness before cleaning and the surface roughness after cleaning in the same manner as in Example 1. Shown in

  Moreover, what summarized the result of Table 1 and Table 2 in the graph is shown in FIG. As shown in Table 1, Table 2, and FIG. 3, in Examples 1-1 to 1-4 in which pure water spin cleaning was performed between ozone water cleaning and hydrofluoric acid cleaning, ozone water cleaning and hydrofluoric acid cleaning were performed. Compared with Comparative Examples 1-1 to 1-4 in which no pure water spin cleaning was performed during this period, deterioration of the surface roughness of the wafer after cleaning was suppressed.

[Particles on the wafer surface]
(Example 2-1)
The wafer was cleaned according to the following cleaning flow 2. In the pure water cleaning step, cleaning was performed under the following pure water spin cleaning condition 2a.
Cleaning flow 2: Ozone water → pure water → hydrofluoric acid → pure water → drying Pure water spin cleaning condition 2a: flow rate 1.5 L / min, rotation speed 1,300 rpm, process time 2 seconds Particles on the wafer surface after cleaning FIG. 4 (a) shows the result of measurement with Surfscan SP3 manufactured by KLA-Tencor.

(Example 2-2)
The wafer was washed along the washing flow 2 in the same manner as in Example 2-1. In the pure water cleaning step, cleaning was performed under the following pure water spin cleaning condition 2b.
Pure water spin cleaning condition 2b: flow rate 1.2 L / min, rotation speed 1,000 rpm, process time 2 seconds Particles on the wafer surface after cleaning were measured in the same manner as in Example 2-1, and the results are shown in FIG. ).

(Comparative Example 2-1)
The wafer was washed along the washing flow 2 in the same manner as in Example 2-1. In the pure water cleaning step, cleaning was performed under the following pure water spin cleaning condition 2c.
Pure water spin cleaning condition 2c: flow rate 1.0 L / min, rotation speed 1,000 rpm, process time 2 seconds Particles on the wafer surface after cleaning were measured in the same manner as in Example 2-1, and the results are shown in FIG. ).

(Comparative Example 2-2)
The wafer was washed along the washing flow 2 in the same manner as in Example 2-1. In the pure water cleaning step, cleaning was performed under the following pure water spin cleaning condition 2d.
Pure water spin cleaning condition 2d: flow rate 1.2 L / min, rotation speed 800 rpm, process time 2 seconds Particles on the wafer surface after cleaning were measured in the same manner as in Example 2-1, and the result is shown in FIG. Show.

(Comparative Example 2-3)
The wafer was washed along the washing flow 2 in the same manner as in Example 2-1. In the pure water cleaning step, cleaning was performed under the following pure water spin cleaning condition 2e.
Pure water spin cleaning condition 2e: flow rate 1.2 L / min, rotation speed 300 rpm, process time 2 seconds Particles on the wafer surface after cleaning were measured in the same manner as in Example 2-1, and the results are shown in FIG. Show.

  As shown in FIG. 4, Example 2-1 (FIG. 4A) in which pure water spin cleaning was performed under the conditions of a flow rate of 1.5 L / min and a rotation speed of 1,300 rpm, and a flow rate of 1.2 L / min. In Example 2-2 (FIG. 4B) in which pure water spin cleaning was performed under the condition of a rotational speed of 1,000 rpm, there was little crowding of particles on the outer periphery of the wafer.

On the other hand, in Comparative Example 2-1 (FIG. 4C) with a flow rate of less than 1.2 L / min, the pure water does not reach the outer periphery of the wafer due to the insufficient flow rate of pure water. There was a crowd.
Further, in Comparative Example 2-2 (FIG. 4 (d)) and Comparative Example 2-3 (FIG. 4 (e)) in which the rotation speed of the wafer is less than 1,000 rpm, pure water is repelled on the outer peripheral portion of the wafer. As a result, pure water did not spread and particles were concentrated on the outer periphery of the wafer.

  Similarly, when the cleaning flow is “hydrofluoric acid → pure water → ozone water → pure water → dry”, the flow rate of pure water in the pure water spin cleaning is less than 1.2 L / min, or the rotational speed of the wafer is When the speed was less than 1,000 rpm, particles were densely gathered on the outer periphery of the wafer.

  From the above, it has been clarified that the wafer cleaning method of the present invention can suppress the deterioration of the surface roughness of the wafer after cleaning, and can improve the residual particles on the outer periphery of the wafer after cleaning.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

Claims (5)

In a wafer cleaning method including a cleaning process using ozone water and a cleaning process using hydrofluoric acid,
By having a spin cleaning process using pure water between the cleaning process using ozone water and the cleaning process using hydrofluoric acid, (1) cleaning process using ozone water, and (2) pure water Spin cleaning step used, (3) Cleaning step using hydrofluoric acid, or (1) Cleaning step using hydrofluoric acid, (2) Spin cleaning step using pure water, (3) Using ozone water The cleaning method is performed in the order of the cleaning steps,
A method for cleaning a wafer, wherein a flow rate of pure water in a spin cleaning step using pure water is 1.2 L / min or more and a rotational speed of the wafer is 1,000 rpm or more.   The flow rate of pure water in the spin cleaning process using pure water is 1.2 L / min or more and 2.0 L / min or less, and the rotation speed of the wafer is 1,000 rpm or more and 1,500 rpm or less. The method for cleaning a wafer according to claim 1.   3. The wafer cleaning method according to claim 1, wherein a process time of the spin cleaning process using the pure water is 2 seconds or more and 10 seconds or less.   The method for cleaning a wafer according to any one of claims 1 to 3, wherein the cleaning step using the ozone water and the cleaning step using the hydrofluoric acid are performed a plurality of times.   The cleaning step using the ozone water is performed by spin cleaning, the flow rate of the ozone water is set to 1.2 L / min to 2.0 L / min, and the rotation speed of the wafer is set to 1,000 rpm to 1,500 rpm. The wafer cleaning method according to claim 1, wherein the wafer is cleaned.

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