JP3255103B2 - Storage water for silicon wafers and method of storage - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to storage water and a storage method used when storing silicon wafers in water, and particularly to storage water and storage used when storing wafers immediately after polishing in water. About the method.

[0002]

2. Description of the Related Art Generally, a method for producing a semiconductor wafer includes a slicing step of slicing a single crystal ingot to obtain a thin disk-shaped wafer, and a slicing step for preventing the wafer obtained by the slicing step from cracking or chipping. A chamfering step for chamfering the outer peripheral portion, a lapping step for flattening the wafer, an etching step for removing processing distortion remaining on the chamfered and wrapped wafer, and a polishing (polishing) step for mirror-polishing the wafer surface. Then, a cleaning step of cleaning the polished wafer and removing abrasives and foreign matters adhering thereto is performed.

[0003] The above steps show the main steps, and other steps such as a heat treatment step are added or the order of the steps is changed. Storage may be required and must be performed in a manner appropriate for the state of the silicon.

For example, a wafer after the polishing step has a washing step in the next step, and may be stored in water during a waiting time before being sent to this step. This is because if the wafer is left in the air, the slurry will adhere to the slurry due to drying of the polishing slurry, and it will be difficult to remove it by washing in the next step.

[0005] In addition, when the wafer is stored in water, a surfactant may be added to the water in order to improve the ability to remove particles. In this case, in order to keep the concentration of the surfactant constant, the wafer is usually stored in a state of being immersed in pooled water (hereinafter sometimes referred to as pit water).

[0006] Generally, ultrapure water is used for the water used for storing the silicon wafer so as not to contaminate the wafer.

[0007]

It is known that when heat treatment is performed with impurities, particularly heavy metals, adsorbed on the wafer surface, the impurities have an adverse effect on the electrical characteristics of the device. For this reason, a cleaning step for removing such impurities is usually provided before the heat treatment.

Therefore, it is extremely important to grasp the contamination state in the cleaning solution and the contamination state on the silicon wafer surface and the like after the cleaning step, and these have been studied.

[0009] However, this is a case of removing the substances adhered in the process before the cleaning, and removes the contaminated material in the process before the cleaning by this cleaning or to prevent the contamination during the cleaning. This is to obtain a silicon wafer having a clean surface.

[0010] However, even if the contaminant concentration in the above-mentioned cleaning step is controlled and the cleaning is performed to obtain a silicon wafer having a clean surface, an oxide film breakdown voltage defect may occur in the final wafer.

In general, it is known that this oxide film withstand voltage defect is caused by a metal-contaminated wafer, and if the metal remains on the wafer, the withstand voltage deteriorates. Therefore,
Metal impurity analysis on the surface of the silicon wafer after cleaning was performed, and a correlation between the analysis value and the wafer having an oxide film breakdown voltage defect was performed. No remarkable difference was found between the defective wafer and the non-defective wafer. Was. That is, it was found that the defective wafer in which the oxide film breakdown voltage defect occurred was also properly cleaned, and the impurities were removed.

The present inventor has analyzed the cause of the occurrence of such a breakdown voltage failure, and as a result, it has been found that the cause of the failure lies in the method of storing the silicon wafer in the step before cleaning. In particular, when the Cu concentration of the storage water is higher than 0.01 ppb, if a silicon wafer having a hydrophobic surface immediately after polishing is stored in the water, the quality of the oxide film deteriorates when the wafer is subjected to thermal oxidation thereafter. Turned out to be significant.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a water for storing silicon wafers and a method for storing silicon wafers, which prevent contamination during storage and prevent occurrence of an oxide film withstand voltage defect. It is the main purpose.

[0014]

Means for Solving the Problems The present invention has been made to solve the above-mentioned problems, and the invention described in claim 1 of the present invention relates to a storage used for storing a silicon wafer in water. Water for use with Cu concentration of 0.01 ppb
It is storage water for silicon wafers characterized by the following.

Thus, the Cu concentration of the storage water is set to 0.01
By setting the ppb or less, it is possible to eliminate the influence of Cu ions on the silicon wafer when the silicon wafer is stored in water, and to prevent deterioration of the oxide film quality when the silicon wafer is subjected to thermal oxidation thereafter.

According to a second aspect of the present invention, there is provided storage water used for storing silicon wafers in water, wherein the Cu concentration is 0.01 ppb or less and a surfactant is added. Water for storing silicon wafers, characterized in that the water is stored.

As described above, even when the surfactant is added to the storage water, the Cu concentration in the entire storage water is reduced to 0.01 ppb.
By setting the content as described below, it is possible to prevent occurrence of an oxide film withstand voltage defect, and it is possible to improve a particle removing ability and the like by adding a surfactant to the storage water.

According to a third aspect of the present invention, there is provided a method for storing a silicon wafer in water.
A method for storing silicon wafers in water, characterized by using storage water having a Cu concentration of 0.01 ppb or less.

As described above, by storing the silicon wafer in the water using the storage water having a Cu concentration of 0.01 ppb or less, it is possible to prevent the occurrence of the sticking of the slurry or the like when the wafer is left in the air. In addition, contamination during storage can be prevented, and occurrence of oxide film breakdown voltage failure can be prevented.

Further, the invention according to claim 4 of the present invention relates to a method for storing a silicon wafer in water,
A method for storing silicon wafers in water, characterized by using storage water having a Cu concentration of 0.01 ppb or less and a surfactant added.

As described above, by using the storage water having a Cu concentration of 0.01 ppb or less and a surfactant added thereto, it is possible to prevent the occurrence of an oxide film withstand voltage failure and to prevent or remove particles from adhering. can do. In this case, it is desirable to store the wafer in a pit water state in order to keep the concentration of the added surfactant constant.

According to a fifth aspect of the present invention, there is provided a method for storing a silicon wafer in water.
Characterized in that the silicon wafer is a hydrophobic surface,
A method for storing the silicon wafer according to claim 3 or 4 in water.

The method for storing a silicon wafer in water according to the third and fourth aspects of the present invention is effective regardless of whether the surface of the silicon wafer is a hydrophilic surface or a hydrophobic surface. However, the effect is particularly remarkable when a silicon wafer which is a hydrophobic surface having no oxide film on the wafer surface is stored in water before storage in water.

Further, according to a sixth aspect of the present invention, there is provided a method for storing a silicon wafer in water.
The method for storing a silicon wafer in water according to any one of claims 3 to 5, wherein the silicon wafer is stored immediately after polishing.

The method for storing a silicon wafer in water according to the third to fifth aspects of the present invention is particularly effective when the silicon wafer, which is a hydrophobic surface immediately after polishing, is stored in water. That is, in a waiting time after the polishing step is completed in the manufacturing process of the silicon wafer and before the silicon wafer immediately after the polishing is sent to the next cleaning step, the present invention is characterized in that:
The method of storing a silicon wafer in water described in (1) can be used.

Hereinafter, the present invention will be described in more detail.
The present invention is not limited to these. The present inventor has analyzed the cause of the occurrence of the oxide film breakdown voltage failure as described above, and has found that a problem arises when a silicon wafer having a hydrophobic surface and a metal having a lower ionization tendency coexist. As a process in which such a state exists, it has been found that there is a problem, in particular, between a polishing process and a cleaning process, where a wafer immediately after polishing is temporarily stored in water before cleaning.

At this time, particularly, when the Cu concentration is 0.01 ppb
If it is higher than this, it is particularly problematic, and it has been found that the quality of the oxide film of the wafer is deteriorated. Conversely, when storage water with a Cu concentration of 0.01 ppb or less is used,
No deterioration of the oxide film quality of the wafer was detected.

Although the cause of the poor quality of the oxide film is not clear, if Cu, especially Cu ions, are present in the storage water, they will electrochemically react with Si and precipitate, causing defects on the silicon wafer. It is thought to form. This phenomenon occurs both in a state where the surfactant is added to the storage water and in a state where the surfactant is not added, but is often observed when the surfactant is added. This is presumably because the surfactant had some effect on the form of Cu deposition, which promoted the generation of defects that degrade the oxide film quality.

In this case, Cu and the like deposited on the surface in the subsequent cleaning should be able to be removed, but defects on the surface of the silicon wafer caused by the reaction remain, which may lead to poor quality of the oxide film. It is.

Therefore, the present inventor has set the concentration of Cu to 0.0
The present invention has been completed in view of preventing the deterioration of the oxide film quality of a silicon wafer by storing the silicon wafer in water using storage water of 1 ppb or less.

That is, by reducing the Cu concentration in the storage water to 0.01 ppb or less, which causes defects on the silicon wafer, Cu ions in the storage water electrochemically react with Si and precipitate. Thus, the oxide film withstand voltage failure due to defects such as distortion of the silicon wafer surface caused by the Cu contamination can be prevented.

The storage water of the present invention does not necessarily have to be used alone, but can be used by mixing with other solutions and the like. For example, by adding and mixing a surfactant to the storage water of the present invention, the ability to remove particles can be improved. In this case, examples of the surfactant include polyoxyethylene alkylphenyl ether. Further, the storage water of the present invention and an organic solvent or the like may be mixed and used as a storage solution.

In this case, it is desirable to use the storage water in the state of pit water in order to keep the concentration of the surfactant in the storage water constant. Here, the pit water is a storage water tank used for storing silicon wafers in water, and the storage water in the water tank does not flow in or out or circulates, and the storage water is used in a fixed stationary state. Refers to the form.

The storage water of the present invention is not limited to the case where the above-mentioned surfactant is added, and may be used as storage water by mixing with another solution such as an organic solvent. This has the effect of preventing deterioration of the oxide film breakdown voltage characteristics.

The storage water and storage method of the present invention are effective regardless of whether the surface of the silicon wafer to be stored is a hydrophilic surface or a hydrophobic surface. However, since the silicon wafer which is a hydrophobic surface having no natural oxide film has an active surface and is easily contaminated, it is particularly advantageous to use the storage water and the storage method of the present invention.

Therefore, the present invention is most suitable when a silicon wafer, which is a hydrophobic surface having no natural oxide film immediately after polishing, is stored in water. For example, the polishing step and the cleaning step which are the steps of manufacturing a silicon wafer The storage water and storage method of the present invention can be used when the wafer is stored in water during the waiting time. As another application scene of the present invention, application to silicon wafers after etching or cleaning using hydrofluoric acid (HF) may be mentioned. This is because the oxide film on the surface of the silicon wafer is removed by hydrofluoric acid (HF) and becomes active, and Cu
This is because they are easily contaminated by water.

Therefore, the use of the present invention not only causes the polishing slurry to stick when left in the air during the waiting time between processes, but also causes contamination from storage water, which has been a problem in conventional underwater storage. It is possible to prevent the oxide film breakdown voltage characteristic from deteriorating.

[0038]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to examples, but the present invention is not limited to these.

[0039]

Examples of the present invention will be described below. (Example 1) As pit water, a surfactant polyoxyethylene alkyl phenyl ether was added to ultrapure water, and then copper was added to adjust the Cu ion concentration in the pit water to various concentrations from 0 to 100 ppb. A pit tank was prepared. The concentration of the surfactant was 10 vol.
1%.

Next, the natural oxide film of the mirror-finished wafer processed from the silicon single crystal grown by the Czochralski method was removed with a dilute hydrofluoric acid aqueous solution (DHF). This process is performed to remove the natural oxide film on the surface of the silicon wafer to make the silicon surface hydrophobic, and to bring the silicon wafer into the same state as the silicon wafer immediately after polishing. After this wafer was immersed in the contaminated pit water for 30 minutes, generally used RCA cleaning was performed, and then the quality of the oxide film after thermal oxidation was evaluated. Here, RCA cleaning, a standard method for cleaning a silicon wafer Kern proposed consists of three stages process to remove the oxide film and the silicon surface to the first stage in _{NH 4 OH / H 2 O 2} , 2 This is a method for cleaning a silicon wafer in which an oxide film formed in a previous stage is removed by HF at a first stage, and a heavy oxide is removed by a third stage by HCl / H ₂ O ₂ to form a natural oxide film.

The quality of the oxide film was evaluated by the Cu decoration method. In the Cu decoration method, when a potential is applied to a thermal oxide film in a liquid in which Cu ²⁺ is dissolved, a current flows to a portion where the oxide film is deteriorated, and Cu ²⁺ is deposited as Cu. This is an oxide film quality evaluation method used. That is, the lower the density of the precipitate, the better the oxide film quality (WJ Shannon; A Study of Dielectric Defect Dete
ction by Decorationwith Copper RCA Review.30, 43
0, 1970).

In this example, a thermal oxide film having a thickness of 25 nm was formed, an electric field of 5 MV / cm was applied thereto for 15 minutes, and the density of the deposited Cu precipitate was measured by an optical microscope to evaluate.

FIG. 1 shows the relationship between the concentration of Cu ions and the density of Cu precipitates after Cu decoration processing. Rapidly precipitates Looking at this the Cu ions is equal to or greater than 0.1ppb is more than 500pcs / cm ² is at increased 10ppb above.
It can be seen that by setting the concentration to 0.01 ppb or less according to the present invention, an oxide film quality equivalent to that of a wafer immersed in pure water without intentional contamination can be obtained.

In the above embodiment, a dilute hydrofluoric acid aqueous solution (DHF)
Although a silicon wafer from which a natural oxide film was removed was used, similar results were obtained for a silicon wafer having no oxide film, such as a silicon wafer immediately after polishing.

The present invention is not limited to the above embodiment. The above embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and has the same function and effect as that of the present invention. Within the technical scope of

For example, when the present invention is used, it is not limited to the case where the silicon wafer is temporarily used during the process of manufacturing the silicon wafer, but may be any case where the silicon wafer is stored in water. Is also applicable,
It has the above effects.

In the present invention, the Cu concentration in water is defined as
The effect is particularly great when it is contained in the form of Cu ions.
However, the present invention is not limited to this, and any form, such as a simple substance or a complex, may be used as long as it contains a component that can be ionized by stored water.

[0048]

As described above, according to the present invention, it is possible to prevent an oxide film withstand voltage defect caused by Cu contamination from storage water, which has been a problem when silicon wafers are stored in water. In particular, when the silicon wafer, which is a hydrophobic surface after the polishing step, is stored in water during a waiting time before being sent to the cleaning step, if the present invention is used, the polishing slurry when the wafer is left in the air Of the silicon wafer can be prevented from occurring, while preventing the adhesion of the silicon wafer.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the Cu ion concentration in pit water and the density of Cu precipitates after Cu decoration processing.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 21/304 H01L 21/68

Claims (6)

(57) [Claims] A storage water used for storing a silicon wafer in water, wherein the Cu concentration is 0.01 pp.
b Water for storing silicon wafers, characterized in that: 2. A storage water used for storing a silicon wafer in water, wherein the Cu concentration is 0.01 pp.
b. Water for storing silicon wafers, wherein the water content is as follows, and a surfactant is added. 3. A method for storing silicon wafers in water, comprising using water for storage having a Cu concentration of 0.01 ppb or less in water. 4. A method for storing a silicon wafer in water, comprising using a storage water having a Cu concentration of 0.01 ppb or less and a surfactant added thereto, wherein the silicon wafer is stored in water. Method. 5. The silicon wafer to be stored is a hydrophobic surface.
And storing the silicon wafer in water. 6. The method for storing a silicon wafer in water according to claim 3, wherein the silicon wafer is stored immediately after polishing.