JP2008182203A - Heat treatment method for silicon wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat treatment method for a silicon wafer of treating the surface of the silicon wafer flattened on an atomic level by high-temperature heat treatment at 1,100°C or higher, which method reduces the surface roughness (microroughness) of the wafer into surface roughness smaller than a conventional one while maintaining a stepped terrace structure on the silicon wafer surface, and enables the stable formation of such a wafer surface. <P>SOLUTION: According to the heat treatment method for the silicon wafer of forming the stepped terrace structure on the surface of the silicon wafer, the silicon wafer is treated by heat under temperatures of 1,100°C or higher in a heat treatment furnace filled with a reducing gas or an inert gas. When a furnace interior temperature is lowered, the furnace is filled with an argon gas to create an argon gas atmosphere at the point that the furnace interior temperature is 500°C or higher, and the furnace is kept supplied with the argon gas until the silicon wafer is removed from the furnace. In this manner, the stepped terrace structure on the silicon wafer surface is maintained, and the square average roughness R<SB>ms</SB>per 3 μm×3 μm of the wafer surface is determined to be 0.06 nm or less. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a heat treatment method for obtaining a silicon wafer having a flat surface in high-temperature heat treatment of a silicon wafer.

  In the process of manufacturing a silicon wafer from a silicon single crystal ingot pulled up by the Czochralski (CZ) method, 1100 ° C. for the purpose of reducing crystal defects on the surface layer of the wafer and improving the surface roughness (microroughness). The above heat treatment is performed.

  For example, in Patent Document 1, a silicon wafer is subjected to a high temperature heat treatment at 1100 ° C. or higher for a predetermined time in an atmosphere of a reducing gas or an inert gas, and then the temperature is lowered to 850 ° C. or lower. A replacement heat treatment method is described. According to such a heat treatment method, by forming a nitride film on the surface of the wafer, it is possible to suppress the occurrence of oxide film defects caused by the wafer without increasing the surface roughness of the wafer. Has been.

  The silicon atoms on the surface of the silicon wafer were rearranged for stabilization by high-temperature heat treatment at 1100 ° C. or higher in an atmosphere of reducing gas or inert gas, and the surface of the wafer was flattened to the atomic level. It becomes a structure. In the rearrangement, a step / terrace structure is formed on the surface of the wafer.

After polishing the silicon wafer before the heat treatment, an atomic force microscope (AFM) by measured fine surface roughness (microroughness) is, R _ms (2 square average roughness) per 3 [mu] m × 3 [mu] m is 0.15 Whereas it is 0.2 nm, R _ms measured by AFM on the surface of the silicon wafer flattened as described above is about 0.1 nm.
This shows that the surface roughness can be reduced by the heat treatment as described above.

The terrace width of the step terrace structure is increased by reducing the off angle of the silicon crystal, and a clearer step terrace structure is confirmed in the AFM observation after the heat treatment.
For example, in Patent Document 2, a single crystal silicon wafer having a plane orientation (100) is sliced at an angle of 0.01 to 0.2 ° in the perpendicular <110> direction of the (001) plane, and cleaned. After that, it is described that a step-and-terrace structure can be formed by heat treatment at 600 to 1300 ° C. in an argon atmosphere.
Japanese Patent No. 3292545 JP-A-8-264401

However, in the heat treatment as described above, it has been found that the surface roughness of the silicon wafer after the heat treatment varies depending on the atmosphere. For example, when heat treatment was performed in an argon gas atmosphere, the temperature was lowered to 700 ° C., and argon was replaced with nitrogen and the furnace was discharged in a nitrogen gas atmosphere. The R _ms per 3 μm × 3 μm was about 0.07 nm. On the other hand, when the temperature was lowered to 700 ° C. after heat treatment in a hydrogen gas atmosphere and hydrogen was replaced with nitrogen and the furnace was removed in a nitrogen gas atmosphere, R _ms was about 0.1 nm.

  As a result of studying the cause of the difference in surface roughness, the present inventors have determined that this is not due to the influence of the gas atmosphere during the high-temperature heat treatment at 1100 ° C. or higher, but during the temperature drop after the high-temperature treatment. Or it discovered that it was based on the influence of the gas atmosphere substituted after temperature-fall.

  The present invention has been made on the basis of the above examination results and further improved. The surface of a silicon wafer flattened at an atomic level by high-temperature heat treatment at 1100 ° C. or higher is subjected to high-temperature heat treatment, and the silicon wafer is subjected to a furnace. By optimizing the furnace atmosphere in the temperature-falling stage until it is put out, the surface roughness (microroughness) of the wafer is reduced as compared with the conventional method while maintaining the step / terrace structure on the surface of the wafer, and An object of the present invention is to provide a silicon wafer heat treatment method capable of stably forming the surface of such a wafer.

The silicon wafer heat treatment method according to the present invention is a silicon wafer heat treatment method in which a step-and-terrace structure is formed on the surface of the silicon wafer. The silicon wafer is heated to 1100 ° C. in a heat treatment furnace in a reducing gas or inert gas atmosphere. After the heat treatment as described above, when the temperature in the furnace is lowered, the atmosphere in the furnace is changed to an argon gas, and the atmosphere of the silicon wafer is continuously introduced until the silicon wafer is discharged from the furnace. The step-and-terrace structure is maintained, and the mean square roughness R _ms per 3 μm × 3 μm is 0.06 nm or less.
Thus, with respect to the surface of the silicon wafer flattened at the atomic level by the high-temperature heat treatment at 1100 ° C. or higher, the atmosphere in the furnace from the temperature lowering stage after the high-temperature heat treatment to the furnace discharge is made argon gas, whereby the surface of the wafer The surface roughness of the wafer can be reduced as compared with the prior art while maintaining the step / terrace structure.

In the heat treatment method, it is preferable that the argon gas is continuously introduced into the furnace until at least the entire wafer placement portion of the wafer boat on which the silicon wafer is placed comes out of the furnace.
Maintaining high flatness without breaking the step / terrace structure of the silicon wafer surface by keeping the silicon wafer surface wrapped with argon gas when the temperature is lowered from 500 ° C. until the silicon wafer is unheated. be able to.

In addition, when the wafer boat is discharged from the furnace, it is preferable that the entire wafer boat is surrounded by argon gas flowing out of the furnace.
By doing in this way, the effect of maintaining the flatness of the surface of the silicon wafer can be further enhanced.

Furthermore, when the wafer boat is discharged from the furnace bottom, the flow rate of the argon gas flowing out from the opening in the furnace bottom is preferably 0.0192 m / s or more and 0.190 m / s or less.
From the viewpoint of protecting the surface of the silicon wafer exposed to the furnace with argon gas, the gas flow rate is preferably within the above range.

  As described above, according to the present invention, the surface of the silicon wafer flattened at the atomic level by the high-temperature heat treatment at 1100 ° C. or higher is obtained by the step of the wafer surface only by replacing the furnace atmosphere in the temperature-falling stage after the high-temperature heat treatment. The terrace structure can be sufficiently retained even after the furnace is removed, and as a result, the surface roughness of the wafer can be reduced as compared with the conventional one, and the surface of the wafer can be stably formed. Can do.

Hereinafter, the present invention will be described in more detail.
In the silicon wafer heat treatment method according to the present invention, first, the silicon wafer is heat-treated at 1100 ° C. or higher in a heat treatment furnace in a reducing gas or inert gas atmosphere. When the temperature is lowered after the high-temperature heat treatment step, the furnace atmosphere is made argon gas when the furnace temperature is 500 ° C. or higher. Then, the argon gas is continuously introduced into the furnace until the silicon wafer is removed from the furnace.
The present invention is intended by way of such a heat treatment process, and holds the step-terrace structure of the surface of the silicon wafer, and the R _ms per 3 [mu] m × 3 [mu] m, characterized in that so as to be less 0.06nm It is.
That is, according to the present invention, the replacement of the atmosphere in the furnace in the predetermined temperature lowering step is an efficient means for reducing the surface roughness of the silicon wafer and stably forming a more flat surface. This is based on finding something.

  The silicon wafer to be heat-treated in the present invention is not particularly limited. For example, a silicon single crystal obtained by slicing a silicon single crystal obtained by the Czochralski (CZ) method, the floating zone (FZ) method, etc., and then mirror-finished silicon is used. Any of a wafer substrate, an epitaxial wafer, an SOI wafer, and the like may be used.

As described above, in the high-temperature heat treatment step of the present invention, the silicon wafer is heat-treated at 1100 ° C. or higher in a reducing gas or inert gas atmosphere.
Such high-temperature heat treatment is performed for the purpose of forming a step / terrace structure by reducing crystal defects on the surface layer of the silicon wafer, improving surface roughness, and the like.

In the heat treatment, an atmosphere of a reducing gas or an inert gas is used to keep the silicon wafer clean. Examples of the reducing gas include hydrogen and ammonia, and examples of the inert gas include helium, neon, and argon. These gases can be used as one or a mixture of two or more. Usually, hydrogen gas or argon gas is used.
Even before the high-temperature heat treatment, it is preferable to keep the silicon wafer in an inert gas atmosphere from the viewpoint of keeping the silicon wafer clean.

  The heat treatment temperature is preferably a high temperature from the viewpoint of reducing crystal defects of the wafer, improving the surface roughness, and the like, and is preferably performed at a high temperature of 1100 ° C. or higher as described above. This high temperature heat treatment time is preferably about 0.5 to 24 hours.

In the heat treatment method according to the present invention, after the high temperature heat treatment step, the furnace atmosphere is replaced with argon gas from a reducing gas or an inert gas when the temperature in the furnace during the temperature drop is 500 ° C. or higher.
By using argon gas, the problem that flatness deteriorates when the temperature is lowered is solved.
In this case, when the atmosphere of the high-temperature heat treatment is argon gas, the same atmosphere may be maintained even in the temperature lowering process.
In addition, although it is most preferable that it is 100% argon gas atmosphere, you may introduce | transduce gas species other than a small amount of argon gas in order to acquire another effect at the time of heat processing.

After the high-temperature heat treatment, the temperature for replacement with argon gas is set to 500 ° C. or higher.
If the temperature at the time of replacement is less than 500 ° C., it is difficult to achieve a flat surface.
Therefore, it is preferable to replace the atmosphere with argon gas at a temperature of 500 ° C. or higher. This can further reduce the deterioration of the surface roughness of the wafer flattened at the atomic level by the high-temperature heat treatment.

After the heat treatment as described above, the atmosphere in the furnace is argon gas, and then the furnace is cooled to a temperature at which the furnace can be discharged, and then the furnace is discharged. It is preferable to continue introduction.
When the silicon wafer is mounted on a wafer boat, it is preferable to continue introducing argon gas into the furnace until at least the entire wafer mounting portion of the wafer boat is out of the furnace.
In this way, the step / terrace structure of the silicon wafer surface formed during the high-temperature heat treatment by holding the silicon wafer surface so as to be enveloped with argon gas when the temperature is lowered from 500 ° C. until the silicon wafer is discharged from the furnace. It is possible to maintain high flatness without breaking.

Furthermore, it is preferable that the entire wafer boat is surrounded by argon gas flowing out of the furnace when the wafer boat is removed from the furnace.
Argon gas is easier to cling to silicon wafers than other gases. By continuing to introduce argon gas into the furnace until the wafer boat exits the opening of the furnace, the silicon gas remains for a while after the furnace exits. It remains to cover the surface of the wafer.
For this reason, by continuing to introduce the argon gas into the furnace until the wafer boat is completely out of the furnace, the entire wafer boat can be surrounded by the argon gas flowing out of the furnace. The effect of maintaining the flatness of the surface can be enhanced.

When the wafer boat is discharged from the furnace bottom, the flow rate of argon gas flowing out from the opening at the furnace bottom is preferably 0.0192 m / s or more and 0.190 m / s or less.
A gas flow rate in such a range is suitable for protecting the surface of the silicon wafer exposed to the furnace with argon gas.
When the gas flow rate is less than 0.0192 m / s, a sufficient protection effect of the surface of the silicon wafer by argon gas cannot be obtained.
On the other hand, when the gas flow rate exceeds 0.190 m / s, even if the gas flow rate is increased, no further effect is observed, and there is a possibility of causing dust generation.

EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not restrict | limited by the following Example.
[Example 1]
First, mirror processing was performed on a silicon wafer obtained by slicing a silicon (100) crystal ingot having a diameter of 8 inches in the <100> direction at an off angle of 0.03 °.
The silicon wafer was placed on a wafer boat and loaded into a heat treatment furnace in an argon gas atmosphere. The inside of the furnace was replaced from an argon gas atmosphere to a hydrogen gas atmosphere at 700 ° C., the temperature was raised, and the temperature was maintained at 1100 ° C. for 1 hour to perform heat treatment.
Thereafter, the temperature was lowered, and the interior of the furnace was replaced from a hydrogen gas atmosphere to an argon gas atmosphere at 700 ° C. Then, the temperature was further lowered and argon gas was continuously introduced into the furnace until the silicon wafer was removed from the furnace.
Then, when the wafer boat on which the silicon wafer is placed is unloaded from the opening at the bottom of the furnace, the flow rate of argon gas between the opening and the wafer boat is 0.1 m / s, Furnace started.
For reference, FIG. 9 shows the flow of the atmosphere gas and temperature in the heat treatment step.
With respect to the surface of the silicon wafer after the heat treatment, the surface unevenness image and the surface roughness R _ms in the 3 μm × 3 μm region were measured by AFM.
FIG. 1 shows a surface irregularity image of a silicon wafer by AFM observation.

[Example 2]
The silicon wafer was heat-treated under the same conditions as in Example 1 except that the heat treatment temperature was changed from 1100 ° C. to 1200 ° C.
With respect to the surface of the silicon wafer after the heat treatment, the surface unevenness image and the surface roughness R _ms in the 3 μm × 3 μm region were measured by AFM.
FIG. 2 shows a surface irregularity image of the silicon wafer by AFM observation.

[Comparative Example 1]
The silicon wafer was heat-treated under the same conditions as in Example 1 except that the heat treatment temperature was changed from 1100 ° C. to 1000 ° C.
With respect to the surface of the silicon wafer after the heat treatment, the surface unevenness image and the surface roughness R _ms in the 3 μm × 3 μm region were measured by AFM.
FIG. 3 shows a surface irregularity image of a silicon wafer by AFM observation.

1 to 3, when the heat treatment temperature is 1000 ° C. (Comparative Example 1), the step / terrace structure is not formed on the surface of the silicon wafer, but when the heat treatment temperature is 1100 ° C. or 1200 ° C. ( In Examples 1 and 2, the step terrace structure was clearly confirmed.
The surface roughness R _ms is 0.158 nm when the heat treatment temperature is 1000 ° C. (Comparative Example 1), whereas it is 0.047 nm and 1200 ° C. when 1100 ° C. (Example 1) (implementation). Example 2) was 0.049 nm, and it was observed that the surface roughness decreased at 1100 ° C. or higher.

  In the photograph of FIG. 2, when the heat treatment temperature is 1100 ° C. (Example 1), the step line of the step / terrace structure is rising to the right, whereas in the photograph of FIG. 3, the heat treatment temperature is 1200. In the case of [deg.] C. (Example 2), the step line of the step / terrace structure rises to the left. This is because the direction in which the off angle is inclined slightly differs depending on the wafer.

[Example 3]
With respect to the surface of the silicon wafer heat-treated in the same manner as in Example 2, the unevenness image and the surface roughness R _ms of the surface of the 3 μm × 3 μm region were measured by AFM.
FIG. 4 shows an uneven surface image of a silicon wafer by AFM observation.
Note that the difference between Example 2 and the result is probably due to individual differences in wafers.

[Example 4]
Heat treatment was performed under the same conditions as in Example 3 except that the atmosphere was always argon gas.
With respect to the surface of the silicon wafer after the heat treatment, the surface unevenness image and the surface roughness R _ms in the 3 μm × 3 μm region were measured by AFM.
FIG. 5 shows a surface irregularity image of a silicon wafer by AFM observation.

[Comparative Example 2]
The inside of the furnace is replaced with a nitrogen gas atmosphere from a nitrogen gas atmosphere at 700 ° C. before the temperature rise, and heat treatment is performed. After the temperature is lowered, the inside of the furnace is replaced with a nitrogen gas atmosphere from the hydrogen gas atmosphere at 700 ° C. Heat treatment was performed under the conditions of
With respect to the surface of the silicon wafer after the heat treatment, the surface unevenness image and the surface roughness R _ms in the 3 μm × 3 μm region were measured by AFM.
FIG. 6 shows a surface irregularity image of a silicon wafer by AFM observation.

[Comparative Example 3]
The inside of the furnace is replaced by a nitrogen gas atmosphere from an argon gas atmosphere at 700 ° C. before the temperature rise, and heat treatment is performed. After the temperature is lowered, the inside of the furnace is replaced by an argon gas atmosphere from the nitrogen gas atmosphere at 700 ° C. Heat treatment was performed under the conditions of
With respect to the surface of the silicon wafer after the heat treatment, the surface unevenness image and the surface roughness R _ms in the 3 μm × 3 μm region were measured by AFM.
FIG. 7 shows a surface irregularity image of a silicon wafer by AFM observation.

4 to 7, in the heat treatment under a hydrogen gas atmosphere, when the surface step / terrace structure differs greatly depending on the replacement gas, and the replacement gas is argon (Example 3), the step line becomes wavy and the replacement is performed. When the gas was nitrogen (Comparative Example 2), the step line was comb-shaped.
In addition, in the heat treatment under an argon gas atmosphere, when the replacement gas is argon (always argon) (Example 4), the step line is wavy, and when nitrogen is used (Comparative Example 3), the step line is comb-like. A step-terrace structure having a wavy intermediate shape was observed.

FIG. 8 shows a comparative graph of the surface roughness R _ms measured from the photographs of FIGS.
The surface roughness R _ms is 0.071 nm in the case of nitrogen gas substitution (Comparative Example 2) and 0.054 nm in the case of argon gas substitution (Example 3) in the heat treatment in a hydrogen gas atmosphere, In the heat treatment under an argon gas atmosphere, the case of nitrogen gas substitution (Comparative Example 3) was 0.062 nm, and the case of argon gas substitution (always argon gas) (Example 4) was 0.054 nm.
Since the shape of the step terrace differs depending on the replacement gas, the surface roughness is also different, and it was recognized that the surface roughness R _ms can be reduced to 0.06 nm or less by using argon as the replacement gas at a predetermined temperature. .
In addition, although the temperature at the time of substituting the atmosphere in a furnace at the time of temperature fall was 700 degreeC in both the said Example and the comparative example, even when it was 500 degreeC, it was confirmed that an equivalent effect is acquired. It was done.

[Example 5]
After heat treatment was performed under the same conditions as in Example 3, the temperature was lowered and the interior of the furnace was replaced from a hydrogen gas atmosphere to an argon gas atmosphere at 700 ° C.
After replacement completion, when the wafer boat in the furnace out to alter the effluent gas flow rate at the opening of the bottom portion of the furnace, were measured the surface roughness R _ms of the silicon wafer was put furnace at each gas velocity.
FIG. 10 is a graph showing the relationship between the outflow gas flow velocity at the opening at the bottom of the furnace and the surface roughness of the silicon wafer.
Note that the difference from the surface roughness values shown in the above-described Examples 1 to 4 is considered to be simply due to individual differences of wafers.

[Comparative Example 4]
After heat treatment was performed under the same conditions as in Example 3, the temperature was lowered and the interior of the furnace was replaced from a hydrogen gas atmosphere to a nitrogen gas atmosphere at 700 ° C.
After replacement completion, when the wafer boat in the furnace out to alter the effluent gas flow rate at the opening of the bottom portion of the furnace, were measured the surface roughness R _ms of the silicon wafer was put furnace at each gas velocity.
FIG. 10 is a graph showing the relationship between the outflow gas flow velocity at the opening at the bottom of the furnace and the surface roughness of the silicon wafer, together with Example 5.

  From the graph shown in FIG. 10, the flatness of the surface of the silicon wafer is maintained in the furnace atmosphere when the silicon wafer is discharged from the argon gas (Example 5) rather than the nitrogen gas (Comparative Example 4). It has also been found that it is preferable to continue introducing argon gas into the furnace until the silicon wafer exits the furnace.

  In the above examples and comparative examples, in order to more clearly show the effect of reducing the surface roughness and the difference in the surface structure, a silicon wafer sliced at an off angle as small as 0.03 ° was used. It is not limited to the size of the off angle, and even when the off angle is increased, the effect of reducing the surface roughness of the silicon wafer can be obtained.

2 is an AFM image photograph of the surface (3 μm × 3 μm) of a silicon wafer according to Example 1. 4 is an AFM image photograph of the surface (3 μm × 3 μm) of a silicon wafer according to Example 2. 6 is an AFM image photograph of the surface (3 μm × 3 μm) of a silicon wafer according to Comparative Example 1. 4 is an AFM image photograph of the surface (3 μm × 3 μm) of a silicon wafer according to Example 3. 6 is an AFM image photograph of the surface (3 μm × 3 μm) of a silicon wafer according to Example 4. 5 is an AFM image photograph of the surface (3 μm × 3 μm) of a silicon wafer according to Comparative Example 2. 6 is an AFM image photograph of the surface (3 μm × 3 μm) of a silicon wafer according to Comparative Example 3. It is a graph of the surface roughness R _ms of AFM micrograph of Figure 4-7. It is a flowchart for demonstrating the heat treatment process in an Example. Relationship between the outflow gas flow rate at the opening at the bottom of the furnace and the surface roughness of the silicon wafer in the case where the atmosphere in the furnace at the time of taking out the silicon wafer is argon gas (Example 5) and the case of nitrogen gas (Comparative Example 4) It is the graph which showed.

Claims (4)

In a silicon wafer heat treatment method in which a step-and-terrace structure is formed on the surface of a silicon wafer, the silicon wafer is heat-treated at 1100 ° C. or more in a heat treatment furnace in a reducing gas or inert gas atmosphere, and the temperature inside the furnace is lowered when the temperature is lowered. Is maintained at a step terrace structure on the surface of the silicon wafer by continuously introducing the argon gas into the furnace until the silicon wafer is discharged from the furnace at a stage of 500 ° C. or higher. A method for heat treatment of a silicon wafer, characterized in that a mean square roughness R _ms per 3 μm × 3 μm is 0.06 nm or less.   2. The method for heat-treating a silicon wafer according to claim 1, wherein the argon gas is continuously introduced into the furnace until at least the entire wafer mounting portion of the wafer boat on which the silicon wafer is mounted comes out of the furnace.   3. The silicon wafer heat treatment method according to claim 2, wherein when the wafer boat is unloaded, the entire wafer boat is surrounded by argon gas flowing out of the furnace.   The flow rate of argon gas flowing out from the opening of the bottom of the furnace when the wafer boat is unloaded from the bottom of the furnace is 0.0192 m / s or more and 0.190 m / s or less. Heat treatment method for silicon wafer.

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