JP5208658B2 - Semiconductor wafer cleaning method and semiconductor wafer - Google Patents

Description

  The present invention relates to a semiconductor wafer cleaning method and a semiconductor wafer.

Conventionally, as a method for polishing a semiconductor silicon wafer using a polishing slurry, for example, a method including a primary polishing step, a secondary polishing step, and a final polishing step has been used (for example, Patent Documents). 1).
Also known is a method in which an aqueous solution containing hydrogen fluoride is sprayed onto an oxide film on the surface of a semiconductor silicon wafer to etch and remove the oxide film (see, for example, Patent Document 2).

JP 2007-73686 A JP 2006-351736 A

By the way, when performing slurry polishing as in Patent Document 1, if foreign matter is mixed in the slurry, local stress is applied to the surface of the semiconductor wafer, and altered silicon (hereinafter referred to as altered silicon) is formed. It has been confirmed that this occurs as a convex defect. Further, it has been confirmed that modified silicon has an etching rate by hydrogen fluoride higher than that of silicon and lower than that of a silicon oxide film.
In order to remove this defect, it is conceivable to use a method as described in Patent Document 2. However, because the etching rate of the modified silicon is higher than that of silicon as described above, when etching is performed under the condition that the modified silicon can be removed, only the defect of the modified silicon is removed, and a large concave groove is formed on the surface of the semiconductor wafer. Problem.
In addition, when the hydrofluoric acid is sprayed, the amount of impurities such as particles adhering to the surface of the semiconductor silicon wafer increases because the content of impurities is larger than when the gas containing hydrogen fluoride is injected. Problem.

  An object of the present invention is to provide a semiconductor wafer cleaning method and a semiconductor wafer capable of appropriately removing convex defects formed by stress acting on the surface of the semiconductor wafer when the surface is polished. is there.

  The method for cleaning a semiconductor wafer of the present invention is a method for cleaning a semiconductor wafer that removes convex defects formed by stress acting on the surface of the semiconductor wafer when the surface of the semiconductor wafer is polished. An oxidation process for oxidizing the surface of the semiconductor wafer to form an oxide film in a portion other than the defect; a liquid phase etching process for etching and removing the oxide film with a liquid containing hydrogen fluoride; and hydrogen fluoride. And a vapor phase etching process in which the defect is etched and dissolved by a gas containing gas.

According to the present invention, when the surface of the semiconductor wafer is oxidized with ozone and treated with a liquid containing hydrogen fluoride, defective portions of the modified silicon are not etched so much, and oxide films other than the defects are selectively etched. Dissolved and removed.
For this reason, by etching a portion other than the defect to increase the exposure degree of the defect, the contact area between the defect and the wafer can be reduced, and the etching rate of the defect can be increased. Since hydrogen fluoride hardly etches silicon, only modified silicon is etched, and a smooth flat surface without irregularities can be obtained.
Further, in the vapor phase etching process, the surface of the semiconductor wafer is treated with a gas containing hydrogen fluoride, so that the amount of deposits on the surface of the semiconductor wafer can be reduced compared with the case of treating with a liquid containing hydrogen fluoride. .

In the semiconductor wafer cleaning method of the present invention, it is preferable that the vapor phase etching process is performed after the oxidation process and the liquid phase etching process are repeated.
In this invention, the oxide film formation by the ozone solution and the dissolution removal of the oxide film by the liquid containing hydrogen fluoride are repeatedly performed on the surface of the semiconductor wafer. By appropriately setting the concentration of the liquid containing the oxide film, the oxide film having a predetermined thickness can be easily dissolved and removed.

The semiconductor wafer of the present invention is characterized by being cleaned by the above-described semiconductor wafer cleaning method.
In the present invention, defects and deposits generated on the surface of the semiconductor wafer due to cleaning can be extremely reduced, and the possibility that the semiconductor wafer adversely affects device characteristics can be eliminated.

A silicon wafer 1 according to this embodiment will be described with reference to FIG. FIG. 1 shows a schematic diagram of a silicon wafer in the present embodiment.
For example, when the silicon wafer surface 11 is subjected to slurry polishing, a part of the silicon wafer surface 11 of the silicon wafer 1 as a semiconductor silicon wafer exists in the silicon wafer 1 and the remaining part protrudes from the silicon wafer surface 11. A raised shape defect 12 may be formed.
The defect 12 is formed by a stress that locally concentrates due to foreign matters in the slurry and the like, and the silicon crystal structure changes to cause volume expansion.
In order to facilitate the description of the embodiment, the size of the defect 12 is expressed larger than the actual size.

  A method for cleaning the silicon wafer 1 in this embodiment will be described with reference to FIG. FIG. 2 shows a schematic cross-sectional view of the silicon wafer in each step in the present embodiment.

(Oxidation treatment)
As shown in FIG. 2A, in the oxidation treatment, an ozone aqueous solution 2 as a liquid containing ozone is sprayed on the silicon wafer 1. Thereby, the silicon wafer surface 11 side of the silicon wafer 1 is oxidized by ozone to form a silicon oxide film 10A. At this time, the defect 12 made of modified silicon is hardly oxidized in the ozone aqueous solution 2, and only the portion other than the defect 12 becomes the silicon oxide film 10A. A portion other than the silicon oxide film 10A in the silicon wafer 1 is referred to as a non-oxide silicon substrate 10B.

(Liquid phase etching process)
As shown in FIG. 2B, in the liquid phase etching process, the silicon oxide film 10A is sprayed with hydrofluoric acid 3 as a liquid containing hydrogen fluoride, and the silicon oxide film 10A is dissolved and removed by a predetermined film thickness. To do.
Furthermore, after etching the silicon wafer 1, the ozone aqueous solution 2 is sprayed again to form the silicon oxide film 10A, and the process of etching the silicon oxide film 10A with hydrofluoric acid 3 is repeated to etch a predetermined film thickness. Dissolve and remove. Note that the predetermined film thickness may be dissolved and removed by one hydrofluoric acid treatment.
Since the silicon oxide film 10A has a high etching rate with the hydrofluoric acid 3 and the defects 12 are low, the silicon oxide film 10A is satisfactorily etched and removed by the hydrofluoric acid 3. However, the defects 12 are hardly etched and silicon is removed. It remains on the wafer surface 11.
That is, by the oxidation process and the etching process, the silicon oxide film 10A is selectively etched and dissolved and removed, and the defect 12 is greatly raised in a convex shape on the silicon wafer surface 11 so that the degree of exposure is increased.

(Gas phase etching process)
As shown in FIG. 2C, in the gas phase etching process, a cleaning gas 4 as a gas containing hydrogen fluoride vaporized in nitrogen gas is sprayed onto the silicon wafer surface 11. As a result, the defect 12 on the silicon wafer surface 11 and the silicon oxide film 10A are etched and removed.
In addition, since the exposure degree of the defect 12 is larger than that before the liquid phase etching process, the etching rate of the defect 12 in the vapor phase etching process is improved as compared with that before the exposure. When etching is performed until the defect 12 is completely dissolved and removed, the silicon oxide film 10A is completely dissolved and removed, and the non-oxide silicon substrate 10B is exposed on the surface.
However, since the non-oxide silicon substrate 10B is hardly etched by the cleaning gas, in this step, only the silicon oxide film 10A and the defect 12 are etched and dissolved and removed.
The silicon wafer surface 11 is exposed to the non-oxide silicon substrate 10B which is easily affected by the deposits, but the deposits adhere to the silicon wafer surface 11 because the vapor phase etching process with a small amount of deposits is performed. There is little to do.
Therefore, a smooth surface shape with few deposits from which the non-oxide substrate 10B is exposed is formed on the silicon wafer 1 through the vapor phase etching process.

(Effect of embodiment)
(1) The silicon wafer surface 11 is oxidized with ozone to form a silicon oxide film 10A on portions other than the defect 12, and the hydrofluoric acid 3 is sprayed.
Therefore, only the silicon oxide film 10A having an etching rate higher than that of the defect 12 can be selectively etched and removed by the hydrofluoric acid 3, and the degree of exposure of the defect 12 can be increased and the etching rate of the defect 12 can be increased. .
Furthermore, by spraying the cleaning gas 4 onto the surface of the silicon wafer 1 thereafter, the silicon oxide film 10A can be dissolved and removed, and twelve defects can also be etched and removed. Therefore, the surface of the silicon wafer 1 can be a substantially smooth flat surface having no defects.
Further, the non-oxide silicon substrate 10B is liable to adhere to metal and the like, but is easily contaminated. However, since the gas-phase etching process using the cleaning gas 4 is performed, there is no possibility of contamination due to the deposit compared with the liquid phase etching process using the hydrofluoric acid 3. .

(2) Since the formation of the silicon oxide film 10A by the ozone aqueous solution 2 and the dissolution and removal of the silicon oxide film 10A by the hydrofluoric acid 3 are repeatedly performed on the silicon wafer surface 11, by appropriately setting the number of repetitions, The silicon oxide film 10A having a predetermined film thickness can be easily dissolved and removed.

(3) Since the silicon wafer 1 has a substantially smooth surface shape with few deposits on the silicon wafer surface 11, it is possible to eliminate the possibility of adversely affecting device characteristics.

(Modification of the embodiment)
Note that the present invention is not limited to the above embodiment, and various improvements and design changes can be made without departing from the scope of the present invention.

  That is, in the present embodiment, the ozone aqueous solution 2 and the hydrofluoric acid 3 are sprayed on the silicon wafer surface 11, but not limited to this, the silicon wafer surface 11 may be immersed in the ozone aqueous solution 2 or the hydrofluoric acid 3.

  In this embodiment, the ozone aqueous solution 2 and the hydrofluoric acid 3 are repeatedly sprayed. However, the present invention is not limited to this, and a cleaning liquid containing ammonia and hydrogen peroxide solution may be sprayed.

Although the best configuration for carrying out the present invention has been disclosed in the above description, the present invention is not limited to this. That is, the invention has been illustrated and described primarily with respect to particular embodiments, but may be configured for the above-described embodiments without departing from the scope and spirit of the invention. Various modifications can be made by those skilled in the art in terms of materials, quantity, and other detailed configurations.
Therefore, the description limited to the shape, material, etc. disclosed above is an example for easy understanding of the present invention, and does not limit the present invention. The description by the name of the member which remove | excluded the limitation of one part or all of such is included in this invention.

Examples and comparative examples for describing the effects of the present embodiment will be described.
[experimental method]
[Comparative Example 1]
The oxidation treatment was performed by dropping the ozone aqueous solution 2 having a temperature of 23 ° C. and a concentration of 15 ppm onto the silicon wafer surface 11 at a flow rate of 1 liter / min for 15 seconds.
The liquid phase etching process was performed by dropping a hydrofluoric acid 3 having a temperature of 23 ° C. and a concentration of 1% by mass onto the silicon wafer surface 11 at a flow rate of 1 liter / min for 3 seconds.

[Comparative Example 2]
The same oxidation treatment as in Comparative Example 1 was performed.
The liquid phase etching process was performed by dropping a hydrofluoric acid 3 having a temperature of 23 ° C. and a concentration of 1 mass % onto the silicon wafer surface 11 at a flow rate of 1 liter / min for 60 seconds.

[Comparative Example 3]
The same oxidation treatment and liquid phase etching treatment (3 seconds under a droplet) as in Comparative Example 1 were repeated.
Then, the liquid phase etching process (60 seconds under a droplet) similar to the comparative example 2 was performed.

[Example 1]
The same oxidation treatment and liquid phase etching treatment as in Comparative Example 1 were repeated.
Further, the gas phase etching process was performed by injecting a mixed gas containing hydrogen fluoride having a concentration of 23 g / m ^{3 in} nitrogen gas onto the silicon wafer surface 11 at an injection pressure of 101 kPa for 60 seconds as a cleaning gas 4.

[Experimental result]
FIG. 3 shows the ratio of the surface shape per unit area on the cleaned silicon wafer surface.
Referring to FIG. 3, Ridge is a defect 12 made of modified silicon on the silicon wafer surface 11, and Scratch is a defect 12 formed by etching a portion of the defect 12 on the silicon wafer surface 11. It is formed in a concave shape, and annihilation is a substantially smooth plane.
The vertical axis represents the ratio of the number of ridges changed to ridges, scratches, and disappearances, assuming that the total number of ridges immediately after polishing is 100%. On the horizontal axis, those washed by the methods of Comparative Example 1, Comparative Example 2 , Example 1 and Comparative Example 3 are shown.

Accordingly, in Comparative Example 1, about 98% is present as a ridge.
In Comparative Example 2, the liquid phase etching time is extended from 3 seconds to 60 seconds, so that the defect 12 is dissolved and the ridge is shifted to scratch. As a result, in Comparative Example 2, the ridge is about 35% and the scratch is about 60%.
In Example 1, by repeating the same oxidation process and liquid etching treatment as Comparative Example 1, the ridge embossed, further dissolve the defect 12 becomes highlighted by performing vapor phase etching for 60 seconds removed doing. As a result, the ridge is reduced to about 30% and the disappearance is about 60%.
In Comparative Example 3, the same oxidation treatment and liquid phase etching process as in Comparative Example 1 were repeated, and then the liquid phase etching process similar to that in Comparative Example 2 was further performed for 60 seconds, thereby embossing the ridge and causing defects 12 to be formed. Dissolved and removed. As a result, as in Example 1, the ridge is reduced to about 30% and the disappearance is about 60%.
From this, it was confirmed that the cleaning methods of Example 1 and Comparative Example 3 can remove ridge defects on the surface 11 of the silicon wafer, and most of them can be made into a substantially smooth plane (disappearance). .

FIG. 4 shows the relative amount of deposits adhering to the silicon wafer surface after cleaning.
Referring to FIG. 4, the vertical axis represents the ratio when the amount of deposits (metal particles, etc.) adhering to the silicon wafer surface 11 in an example in which the cleaning of Comparative Example 2 is performed is 100%.
According to this, the amount of adhering material for Comparative Example 3 increases as in Comparative Example 2, whereas the amount of adhering material for Comparative Example 1 and Example 1 is 20% or less of Comparative Example 2. It was found that the amount of deposits was very large when the liquid phase etching process was performed for a long time.
From this, it was found that the cleaning of the silicon wafer 1 is preferable to the vapor phase etching process rather than the liquid phase etching process.

FIG. 5 shows (A) the particle size after cleaning when the particle size of the defective portion before cleaning is 60 nm or more, and (B) cleaning when the particle size of the defective portion before cleaning is 35 to 60 nm. The later particle size is shown.
Referring to FIG. 5, the horizontal axis indicates the particle size of the defective portion before cleaning, and the vertical axis indicates the particle size of the defective portion after cleaning.
According to this, it can be seen that in both FIGS. 5A and 5B, the particle size of the defective portion after cleaning becomes smaller in the order of Example 1 (Comparative Example 3 is also equivalent), Comparative Example 2 and Comparative Example 1. . From this, it can be seen that the ability to remove or reduce the defective portion is high in the order of Example 1 (Comparative Example 3 is equivalent), Comparative Example 2 and Comparative Example 1. Therefore, it was confirmed that the cleaning method of Example 1 was most preferable in view of the amount of deposits, defect removal, and the like.

  Since the cleaning method of the present invention is a cleaning method for removing defects on the surface of a semiconductor wafer, it can be used in a semiconductor wafer cleaning apparatus.

It is a schematic diagram of the silicon wafer in embodiment of this invention, (A) is a perspective view, (B) is sectional drawing. It is typical sectional drawing of the silicon wafer of each process in the said embodiment, (A) is after an oxidation process, (B) is after an oxidation etching process, (C) shows after a liquid phase etching process. The graph which shows the ratio of the various surface shapes per unit area in the silicon wafer surface after washing | cleaning in the Example of this invention. The graph which shows the quantity of the deposit | attachment adhering to the silicon wafer surface after the washing | cleaning in the said Example by a relative ratio. It is a graph which shows the particle size of the defect location before and behind washing | cleaning in the said Example, (A) is the particle size of the defect location before washing | cleaning, when (B) is the particle size of the defect location before washing | cleaning being 35 nm or more. The case of ˜60 nm is shown.

Explanation of symbols

1 ... Silicon wafer (semiconductor wafer, semiconductor silicon wafer)
2. Ozone aqueous solution (liquid containing ozone)
3 ... Hydrofluoric acid (liquid containing hydrogen fluoride)
4 ... Cleaning gas (gas containing hydrogen fluoride)
10A ... Silicon oxide film (oxide film)
10B ... Non-oxide silicon substrate 11 ... Silicon wafer surface (surface)
12 ... Defects

Claims (3)

A method for cleaning a semiconductor wafer, which removes convex defects formed by stress acting on the surface when the surface of the semiconductor wafer is polished,
An oxidation treatment that oxidizes the surface of the semiconductor wafer with a liquid containing ozone to form an oxide film on a portion other than the defect;
A liquid phase etching process in which the oxide film is etched and removed with a liquid containing hydrogen fluoride; and
A gas phase etching process in which the defect is etched and dissolved by a gas containing hydrogen fluoride; and
A method for cleaning a semiconductor wafer, comprising: A method for cleaning a semiconductor wafer according to claim 1,
A method of cleaning a semiconductor wafer, wherein the vapor phase etching process is performed after the oxidation process and the liquid phase etching process are repeated. A semiconductor wafer, which has been cleaned by the semiconductor wafer cleaning method according to claim 1.

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