JP2010092939A - Method of cleaning semiconductor wafer, and semiconductor wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of cleaning a semiconductor wafer for appropriately removing projecting defects formed by stress operating on a surface when polishing the surface of the semiconductor wafer. <P>SOLUTION: When a silicon wafer surface 11 is subjected to slurry polishing, defects are formed, where the polished objects partially exist in a silicon wafer and the remainder rises in a projecting manner from the silicon wafer surface 11, which is oxidized by an ozone gas 2 to form a silicon oxide film 10A and an oxidation defect 12A. After that, a cleaning gas 3 is sprayed onto the silicon wafer surface 11 for etching, thus dissolving and removing oxidized defective places and oxide films. <P>COPYRIGHT: (C)2010,JPO&INPIT

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 the modified silicon has a lower etching rate than the silicon oxide film.
In order to remove this defect, it is conceivable to use a method as described in Patent Document 2. However, as described above, the etching rate of modified silicon is lower than that of silicon oxide film, so if etching is performed under the condition that the modified silicon can be removed, only defects of the modified silicon are removed and a large concave groove is formed on the surface of the semiconductor wafer. The problem of being done.
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 according to 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 and the defects to form an oxide film, and after the oxidation process, the surface of the semiconductor wafer is etched with a gas containing hydrogen fluoride to dissolve and remove the oxide film. And a vapor-phase etching process.

In the present invention, the surface and defects of the semiconductor wafer are oxidized by the gas containing ozone, so that ozone having a higher concentration can be brought into contact with the surface and defects of the semiconductor wafer as compared with the case of oxidizing by the liquid containing ozone. For this reason, defects and portions other than the defects can be oxidized at substantially the same oxidation rate, and an oxide film can be formed on the entire surface of the semiconductor wafer.
Further, after the oxidation treatment, a gas containing hydrogen fluoride is sprayed onto the surface of the semiconductor wafer, so that the oxidized defective portion and other oxide films can be etched and dissolved and removed. Therefore, the surface of the semiconductor wafer can be a substantially smooth flat surface having no defects.
Furthermore, since cleaning is performed by oxidation treatment using a gas containing ozone and vapor phase etching treatment using a gas containing hydrogen fluoride, all of the cleaning treatment can be performed in the gas phase, and the amount of deposits on the surface of the semiconductor wafer is reduced. can do.

In the semiconductor wafer cleaning method of the present invention, in the vapor phase etching process, the oxide film is preferably dissolved and removed so as to leave a predetermined film thickness portion on the back surface side of the semiconductor wafer in the oxide film.
In the present invention, the oxide film is left slightly during the vapor phase etching process, thereby preventing the unoxidized semiconductor wafer from being exposed. For this reason, it is possible to prevent exposure of the non-oxidized semiconductor wafer which is easily affected by deposits, and to prevent deposits from adhering to the surface of the semiconductor wafer after cleaning.

The semiconductor wafer of the present invention is characterized by being cleaned by the above-described semiconductor wafer cleaning method.
In the present invention, since there are very few defects and deposits on the surface of the semiconductor wafer, it is possible to eliminate the possibility that the semiconductor wafer will adversely affect the device characteristics.

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, ozone gas 2 as a gas containing ozone is injected onto the silicon wafer 1. As a result, 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, since the ozone gas 2 can be prepared at a higher concentration than the ozone aqueous solution, the oxidation treatment with the ozone gas 2 has stronger oxidizing power than the case of oxidizing with the ozone aqueous solution. For this reason, even the defect 12 which is not oxidized by the ozone aqueous solution is oxidized to become the oxidation defect 12A. A portion other than the silicon oxide film 10A in the silicon wafer 1 is referred to as a non-oxide silicon substrate 10B.

(Gas phase etching process)
As shown in FIG. 2B, after the oxidation process, a cleaning gas 3 as a gas containing hydrogen fluoride is jetted onto the silicon wafer surface 11 to perform a gas phase etching process. Thereby, the oxidation defect 12A and the silicon oxide film 10A are etched simultaneously.
At this time, since the oxidation defect 12A is slightly higher than the silicon oxide film 10A, the etching defect 12A is etched and removed larger than the silicon oxide film 10A, so that the convex oxidation defect 12A is a planar silicon oxide film. The planar shape is substantially the same as 10A, and the entire silicon wafer surface 11 is a substantially smooth plane.
Note that it is preferable to prevent exposure of the non-oxide silicon substrate 10B by slightly leaving the oxide defects 12A and the silicon oxide film 10A during etching. Thereby, since the non-oxide silicon substrate 10B which is easily affected by the deposit is not exposed, the amount of deposit after the cleaning can be reduced.

(Effect of embodiment)
(1) In the oxidation treatment, ozone gas 2 containing ozone is sprayed onto the silicon wafer 1, so that high-concentration ozone can be brought into contact with the silicon wafer surface 11 as compared with the case where an ozone aqueous solution is sprayed.
For this reason, the defect 12 which is not oxidized by the spray of the ozone aqueous solution can be oxidized by the ozone gas 2 injection to form the oxidation defect 12A.
In addition, since the oxidation treatment in the gas phase with the ozone gas 2 is performed, the possibility of contamination due to deposits can be eliminated as compared with the oxidation treatment in the liquid phase with the ozone aqueous solution.
In the gas phase etching process, the cleaning gas 3 is injected to perform etching. In this case, since the oxidation defect 12A is slightly higher than the silicon oxide film 10A, the oxidation defect 12A is etched and removed larger than the silicon oxide film 10A, so that the convex oxidation defect 12A is removed from the planar silicon oxide film. The planar shape can be substantially the same as 10A. Therefore, the whole silicon wafer surface 11 can be made into a substantially smooth plane.
Further, since the gas phase etching process using the cleaning gas 3 is performed, the possibility of contamination due to the deposits can be eliminated as compared with the liquid phase etching process using hydrofluoric acid.

(2) During the vapor phase etching process, the oxide defects 12A and the silicon oxide film 10A are left slightly to prevent the non-oxide silicon substrate 10B from being exposed. For this reason, exposure of the non-oxide silicon substrate 10B which is easily affected by the deposits can be prevented, and deposits can be prevented from adhering to the silicon wafer surface 11 after cleaning.

(3) Since the silicon wafer surface 11 is oxidized in the gas phase by the ozone gas 2 and then subjected to the gas phase etching process by the cleaning gas 3, there is no cleaning process in the liquid phase. For this reason, it is possible to clean the surface of the silicon wafer 11 with almost no deposits.

(4) Since the silicon wafer 1 forms a substantially smooth surface shape with few deposits on the silicon wafer surface 11, it is possible to eliminate the possibility that the silicon wafer 1 adversely affects 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 this embodiment, it is assumed that the gas is oxidized by the ozone gas 2. However, the present invention is not limited to this.

  In the present embodiment, the etching is performed with the cleaning gas 3 containing hydrogen fluoride. However, the present invention is not limited to this, and the oxidation defect 12A and the silicon oxide film 10A can be etched. Any gas can be used as long as it has a high etching rate.

The best configuration for implementing the present invention has been disclosed in the above description, but 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 spraying an ozone aqueous solution 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 spraying hydrofluoric acid having a temperature of 23 ° C. and a concentration of 1 wt% on 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 spraying hydrofluoric acid having a temperature of 23 ° C. and a concentration of 1 wt% on the silicon wafer surface 11 at a flow rate of 1 liter / min for 60 seconds.

[Comparative Example 3]
The oxidation treatment was performed by injecting ozone gas 2 having a temperature of 26 ° C. and a concentration of 120 mg / m ³ onto the silicon wafer surface 11 at an injection pressure of 106 kPa for 40 seconds.
Moreover, the liquid phase etching process was performed similarly to the comparative example 2.

[Example 1]
The same oxidation treatment as in Comparative Example 1 was performed.
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 3.

[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%. The abscissa indicates those cleaned by the methods of Comparative Example 1, Comparative Example 2, and Example 1.

  Thus, in Comparative Example 1, about 98% remains as ridges. In Comparative Example 2, the liquid phase etching time is extended from 3 seconds to 60 seconds, so that the defect 12 becomes concave and the ridge shifts to scratch. As a result, in Comparative Example 2, the ridge is about 35% and the scratch is about 60%.

In Example 1 and Comparative Example 3, the silicon wafer surface 11 is oxidized with ozone gas 2 to form a silicon oxide film 10A and an oxide defect 12A, and then a gas phase etching process is performed to form the silicon oxide film 10A and the oxide defect. 12A is dissolved and removed by etching. As a result, it was found that there was a transition from ridge to extinction without generation of scratches.
In addition, since the silicon oxide film 10A and the oxidation defects 12A are formed by the high-concentration ozone gas 2, it has been found that most of the ridge has been extinguished by the vapor phase etching process.
From this, it was confirmed that the cleaning methods of Example 1 and Comparative Example 3 can remove the ridges on the silicon wafer surface 11, and most of the ridges can be made into a substantially smooth plane.

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, since the amount of deposits in Comparative Example 1 was 20% or less of Comparative Example 2, it was found that the amount of deposits was extremely increased when liquid phase etching was performed for a long time.
Moreover, the comparative example 3 was substantially equivalent to the amount of deposits of the comparative example 2. From this, it was found that the amount of deposits is greatly influenced by the processing time of the liquid phase etching process.
On the other hand, in Example 1, since both the oxidation process and the gas phase etching process are processes in the gas phase, the amount of deposits is very small, which is only about 9% of Comparative Example 2.
From this, it was found that the cleaning of the silicon wafer 1 is more preferably the vapor phase etching cleaning than the liquid phase etching cleaning.

FIG. 5 shows the particle size after cleaning when (A) the particle size of LPD (Light Point Defect) before and after cleaning is 60 nm or more, and (B) the particle size of LPD before and after cleaning is 35 to 60 nm. The particle size after washing in the case 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 the particle size of the defective portion after cleaning becomes smaller in the order of Example 1 (Comparative Example 3 is equivalent), Comparative Example 2 and Comparative Example 1 in both FIGS. It was. Therefore, it turned out that the capability which can remove or reduce a defect location in the order of Example 1 (comparative example 3 is equivalent), comparative example 2, and comparative example 1 is high.
In addition, since the particle size after washing in Example 1 (comparative example 3 is equivalent) compared to Comparative Examples 1 and 2 is significantly reduced, the cleaning method in Example 1 (equal to Comparative Example 3) is It was confirmed that it has excellent defect removal ability.
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) shows after an oxidation process, (B) shows after a liquid phase etching process. The graph which shows the ratio of the various surface shape 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 LPD (Light Point Defect) before and behind the washing | cleaning in the said Example, (A) is the particle size of LPD before washing | cleaning, when the particle size of LPD before washing | cleaning is 60 nm or more. Shows the case of 35-60 nm.

Explanation of symbols

1 ... Silicon wafer (semiconductor wafer, semiconductor silicon wafer)
2 ... Ozone gas (gas containing ozone)
3. 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 for oxidizing the surface of the semiconductor wafer and the defects with a gas containing ozone to form an oxide film;
After the oxidation treatment, a gas phase etching treatment for dissolving and removing the oxide film by etching the surface of the semiconductor wafer with a gas containing hydrogen fluoride,
A method for cleaning a semiconductor wafer, comprising: A method for cleaning a semiconductor wafer according to claim 1,
In the vapor phase etching process, the oxide film is dissolved and removed so as to leave a predetermined film thickness portion of the oxide film on the back surface side of the semiconductor wafer.   A semiconductor wafer cleaned by the semiconductor wafer cleaning method according to claim 1.

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