JP2003270169A - Method for evaluating octahedral void of silicon wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for evaluating an octahedral void of a silicon wafer capable of easily and accurately evaluating a size, a shape, a location and a volume and the like of an octahedral void existing in a mirror-polished silicon wafer. <P>SOLUTION: The method for evaluating an octahedral void of a silicon wafer detected as a light scattering body using a light scattering type surface inspection apparatus sequentially and repeatedly performs steps of a) detecting the light scattering body on the silicon wafer, b) forming an oxide film on the silicon wafer, and c) removing the oxide film on the silicon wafer by an acid etching treatment. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating an octahedral void in a silicon wafer, and more specifically, it uses an optical scattering type surface inspection device to detect an octahedral void present in a mirror-finished silicon wafer. , A method for evaluating an octahedral void in a silicon wafer detected as a light scatterer.

[0002]

2. Description of the Related Art Generally, a silicon wafer for semiconductor production is prepared by slicing a silicon single crystal ingot with a slicer and then subjecting it to surface treatment such as lapping, beveling, etching, polishing, cleaning, etc. The surface is clean and smooth with almost no surface defects. Then, in the above steps and finishing, the wafer under processing or the finished wafer surface is inspected by measuring the mirror surface smoothness, the existence state of microdefects, the cleanliness, etc. by using a surface inspection device or the like. Is being done.

Conventionally, in such an inspection, for example, a particle counter or the like which is a light scattering type surface inspection device is used to scatter defects such as minute voids present on the wafer surface and adhered particles such as dust. A method of detecting a body (LPD; Light Point Defect) without distinction and measuring and evaluating the body has been generally adopted. The LPD detected by this particle counter reflects both the concave shape caused by defects such as minute voids existing on the wafer surface and the convex shape caused by adhered particles such as dust.

However, in recent years, with the increasing integration of devices formed on wafers, in order to provide higher quality silicon wafers, in inspection, accurate detection and evaluation of defects affecting the device formation of wafers are performed. Has come to be required. In particular, there are many research reports that minute octahedral voids generated during pulling of a silicon single crystal cause deterioration of withstand voltage characteristics of a formed device, and it is required to reduce the octahedral voids. For that purpose, it is necessary to accurately grasp the existence state of octahedral voids in the silicon wafer.

To grasp the existence state of the octahedral void,
It is necessary to measure its size, shape, location, etc.
Many evaluation methods have been proposed. A general evaluation method is to measure a mirror-finished silicon wafer with a particle counter, and use the defect coordinates obtained by this to use an atomic force microscope (AFM) and a scanning electron microscope (S).
The shape is evaluated by EM) or the like. In addition, by using a transmission electron microscope (TEM),
It is also possible to accurately evaluate the shape of the octahedral void.

[0006]

However, among the above evaluation methods, the method using AFM, SEM, etc.
Since M, SEM, etc. are devices for performing surface analysis, voids exposed in the cross section of a silicon wafer can be evaluated even when octahedral voids are evaluated, but they are present inside the wafer. It is not possible to evaluate the voids, the state of the voids in the depth direction, and the volume of the octahedral void. In the case of the method using TEM,
Since the preparation of the evaluation sample is very complicated and difficult, it is difficult to perform a simple evaluation. As described above, according to the conventional evaluation method, it is difficult to easily and accurately evaluate the existence state of octahedral voids in the depth direction of the silicon wafer.

The present invention has been made in order to solve the above technical problems, and easily and accurately evaluates the size, shape, existing position, volume, etc. of octahedral voids existing in a mirror-finished silicon wafer. It is an object of the present invention to provide a method for evaluating an octahedral void of a silicon wafer that can be used.

[0008]

A method for evaluating octahedral voids in a silicon wafer according to the present invention is a method for scattering an octahedral void existing in a mirror-finished silicon wafer by using a light scattering surface inspection apparatus. In the method for evaluating an octahedral void of a silicon wafer to be detected as a body, a) detecting a light scatterer on the surface of the silicon wafer, b) forming an oxide film on the surface of the silicon wafer, c) surface of the silicon wafer Each of the steps of removing the oxide film by acid-based etching treatment is sequentially repeated. As described above, the oxidation and etching of the surface of the silicon wafer are repeated, and the LPD on the new wafer surface is detected and measured each time, so that the inside of the wafer is analyzed using the particle counter which is an apparatus for analyzing and measuring the surface state. It is possible to easily and accurately evaluate the size, shape, existing position, etc. of existing octahedral voids.

As one mode of the evaluation of the octahedral void, the relationship between the exposed area of the octahedral void on the silicon wafer surface and the light scattering intensity of the light scatterer is obtained in advance,
By comparing this with the light scattering intensity of the light scatterer detected in the step a), the void area of the octahedral void at each depth from the mirror-finished silicon wafer surface is evaluated. By the evaluation method described above, the void area in the plane direction of the octahedral voids existing inside the wafer can be evaluated easily and accurately.

As another aspect of the evaluation of the octahedron void, the relationship between the exposed area of the octahedron void on the silicon wafer surface and the light scattering intensity of the light scatterer is obtained in advance, and the a ) The light scattering intensity of the light scatterer detected in the step is compared to obtain the void area S corresponding to the maximum light scattering intensity.
Then, from the depth H from the time when the light scatterer is first detected to the time when it disappears, the volume V of the octahedral void is calculated by the following formula V = (1/3) · S · H (1) It can also be sought and evaluated. According to the above evaluation method, the detected and measured LPD
The volume of each octahedral void can be easily evaluated from the light scattering intensity of.

The thickness of the oxide film formed in step a) is preferably 10 to 50 nm. From the viewpoints of ensuring the uniformity of the oxide film to be formed, detecting and measuring accuracy of the size, shape, position, etc. of the octahedral void, a suitable thickness of the oxide film formed at one time is defined.

The acid-based etching treatment in the step c) is preferably carried out using hydrofluoric acid or a hydrofluoric acid / nitric acid / acetic acid mixed aqueous solution. The etching treatment for removing the oxide film is preferably a wet etching treatment using the above acidic chemical solution having isotropic etching property.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will now be described in more detail with reference to some drawings. The evaluation method according to the present invention is
When detecting an octahedral void existing in a mirror-finished silicon wafer as a light scatterer using a light scattering type surface inspection device, a) detecting the light scatterer on the surface of the silicon wafer, b) Forming an oxide film on the surface of the silicon wafer, c) removing the oxide film on the surface of the silicon wafer,
It is characterized in that each step of removing by acid-based etching treatment is sequentially repeated. That is,
In the evaluation method according to the present invention, first, a mirror-finished silicon wafer is measured with a particle counter (lower limit of detection of LPD size of about 0.06 μm), and then an oxidation heat treatment is performed. Then, the oxide film formed on this surface is removed by an acid-based etching process, and then the measurement is performed again with a particle counter. The oxidation and etching of the surface of the silicon wafer are repeated, and the LPD on the new wafer surface is detected and measured each time to evaluate the octahedral void. As a result, it is possible to easily and accurately evaluate the size, shape, existing position, etc. of the octahedral voids existing inside the wafer by using a particle counter which is an apparatus for analyzing and measuring the surface state.

Since the octahedral voids present in the silicon wafer have an octahedral shape as shown in FIG.
By repeating the process cycles of to c), the octahedral voids are exposed on the wafer surface in the state shown in FIG. More specifically, first, FIG. 2A shows a state in which the octahedral voids are not exposed on the wafer surface in the first mirror-polished silicon wafer. This silicon wafer is subjected to the above steps a) to c), and as shown in FIG. 2B, the vertices (upper vertices) of the octahedral voids are exposed on the surface, and detected and measured as LPD. Further, the octahedral voids are removed from the wafer surface as the cycle of the steps a) to c) is repeated, and the octahedral voids are transferred from the state of FIG. 2B to the state of FIG. The exposed area of voids gradually increases. Then, the exposed area of the octahedral void shifts from the state of FIG. 2C to the state of FIG. 2D after reaching the maximum, and gradually decreases until reaching the apex (lower apex) of the octahedral void.
PD disappears.

In the evaluation method according to the present invention, the silicon wafer to be inspected is not particularly limited as long as it is an ordinary silicon wafer for semiconductors, but it is mainly a silicon single wafer pulled by the Czochralski (CZ) method. The target is a silicon wafer obtained from a crystal. Further, the silicon wafer is not limited to a prime wafer, and in addition to this, a D having a defect-free (DZ) layer formed in the vicinity of the surface is used.
Z-G wafers, hydrogen gas heat-treated wafers, epitaxial wafers, SOI wafers, etc. can be targeted.

A silicon wafer made from a single crystal pulled by the CZ method has a defect called a grown-in defect, one of which is an octahedral void considered to be a cluster of atomic vacancies. There is. If the grown-in defects are present on the surface and the surface layer of the silicon wafer that is the device forming surface, they will adversely affect the performance of the device formed on the wafer. In particular, the octahedral void causes deterioration of pressure resistance. Therefore, accurate detection and evaluation of octahedral voids existing in a silicon wafer is important in quality control in the semiconductor manufacturing process.

In the evaluation method according to the present invention, the silicon wafer to be detected has a mirror-finished surface. The LPD detection lower limit size of a particle counter or the like, which is a laser light scattering type surface inspection device, depends on the smoothness of the wafer surface. Therefore, the surface is preferably smoothed by mirror finishing. This mirror surface processing can be performed by mechanochemical polishing or the like in addition to ordinary mechanical polishing.

The evaluation method according to the present invention is carried out by detecting the LPD of the silicon wafer mirror-finished as described above by using a light scattering type surface inspection apparatus. Specifically, for the mirror-finished wafer, the LPD is detected using a particle counter, and the position, size, and number of each detected LPD are measured.
Especially as a particle counter which is a light scattering type surface inspection device, the lower detection limit of the LPD size is 0.06 μm.
A laser-light-scattering type surface inspection device of a certain degree is preferably used from the viewpoint of detection accuracy and the like.

After the LPD of the mirror-finished silicon wafer is detected and measured as described above, an oxide film is formed on the wafer surface. The thickness of the oxide film is 10 to 50 nm,
It is particularly preferable that the thickness is in the range of 10 to 20 nm from the viewpoints of ensuring the uniformity of the oxide film formed, detecting and measuring the size, shape, position and the like of the octahedral void.

The oxide film is formed, for example, by placing the wafer in a batch furnace such as a resistance heating type heat treatment furnace or a furnace such as a rapid heating / rapid cooling apparatus and mixing oxygen gas, water vapor, and oxygen gas with hydrogen gas. It is performed by heating and oxidizing treatment in an atmosphere such as a combustion gas. The heating temperature, processing time, etc. at this time are appropriately set according to the type and state of the atmospheric gas, the film thickness of the oxide film to be formed, and the like.

Next, the oxide film formed as described above is stripped and removed by an acid-based etching process.
The method of this acid-based etching treatment is not particularly limited, and may be dry etching with an acid gas such as anhydrous HF, a mixed gas of NF ₃ and NH ₃ , or wet etching with an acid chemical solution. From the viewpoint of uniform etching treatment, ease of handling, and the like, wet etching treatment using an acidic chemical solution having isotropic etching property is particularly preferable. For such etching treatment, hydrofluoric acid or a hydrofluoric acid / nitric acid / acetic acid mixed aqueous solution or the like can be preferably used.

Next, the LPD measurement is performed again on the silicon wafer from which the oxide film has been removed by the above etching process, under the same conditions as the LPD detection measurement before the oxide film formation. And a) the LPD detection measurement step as described above,
b) oxide film formation step, c) acid-based etching treatment step 1
The octahedral voids are evaluated by repeating about 10 to 40 cycles.

The step of detecting and measuring the LPD on the wafer surface by using the particle counter is, specifically, the LP measurement for each depth from the first silicon wafer surface (mirror-finished surface).
The position (plane coordinates) of D on the wafer surface is specified and the light scattering intensity is measured. This makes it possible to accurately evaluate the depth position of the LPD from the mirror-finished surface, the size and position of the LPD on the wafer surface, and the like.

In the case of the LPD detected at the same position (planar coordinates) on the wafer surface, when the light scattering intensity thereof gradually increases, reaches the maximum, then decreases again, and finally disappears,
This is identified as an octahedral void detected and measured by following the course shown in FIG. In this case, LP
The depth at the time when D is first detected (depth from the mirror-finished surface of the wafer) is the upper vertex position of this octahedral void. In addition, the depth at the time when the LPD disappears is the lower vertex position of this octahedral void. Thereby, the vertical length and the depth position of the octahedral void can be obtained. As described above, according to the evaluation method of the present invention, it is possible to accurately evaluate only the octahedral void by distinguishing it from the convex shape LPD formed by surface-attached particles such as dust.

Further, the correlation between the exposed area of the octahedral void on the surface of the silicon wafer and the light scattering intensity of the LPD is obtained in advance, and the detected and measured LPD is added to this.
It is possible to evaluate the void area of the octahedral void at each depth from the mirror-finished surface of the wafer by comparing the light-scattering intensities.

FIG. 4 is a diagram showing the relationship between the exposed area of the octahedral void on the silicon wafer surface and the light scattering intensity of the LPD. As shown in FIG. 4, the relationship between the exposed area of the octahedral void and the light scattering intensity of the LPD is
It can be shown by a cubic approximation curve. From this correlation, the void area of the octahedral void at each depth from the mirror-finished surface of the wafer can be obtained by detecting and measuring the light scattering intensity of LPD. Thus, not only in the depth direction but also in the plane direction, more accurate information can be obtained, and the void area in the plane direction of the octahedral voids existing inside the wafer can be easily and accurately evaluated. .

From the relationship between the exposed area of the octahedral void on the silicon wafer surface and the light scattering intensity of the light scatterer as shown in FIG. 4, the void corresponding to the maximum light scattering intensity of the LPD detected and measured. The area S is obtained. Then, as described above, the depth H from the time when the LPD is first detected to the time when it disappears corresponds to the height from the upper apex to the lower apex of the octahedral void, that is, the vertical length of the octahedral void. . Therefore, the void area S and LP
From the depth H from the time when D is first detected to the time when it disappears, the volume V of the octahedral void is obtained by the following formula V = (1/3) · S · H (1). As described above, according to the above-described evaluation method, the volume of each octahedral void can be easily evaluated from the detected and measured light scattering intensity of LPD.

As described above, in the octahedral void evaluation method according to the present invention, the depth position, void area, and volume of octahedral voids existing in a silicon wafer can be easily evaluated. It is useful for simple and highly accurate inspection for quality control of silicon wafers in the manufacturing process.

The void evaluation method by detecting the LPD as described above can be applied to not only octahedral voids but also irregular voids, and various defects other than defects (COP) caused by adhered particles. Can also be evaluated.

[0030]

EXAMPLES The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited by the following examples. [Embodiment] First, a laser light scattering type particle counter (SFS6200: manufactured by Tencor, resolution 0.001 μm) is applied to a mirror-finished 8-inch P-Type silicon wafer.
Was used to detect LPD, and the size and position of the detected LPD were measured. Next, this wafer is
The wafer was heated at 0 ° C. for 5 minutes in an oxygen atmosphere to form an oxide film having a thickness of 40 nm on the wafer surface. Then, the oxide film was removed by acid-based etching treatment using 1% hydrofluoric acid. Each of the steps of the LPD detection measurement, oxide film formation, and acid-based etching treatment was sequentially repeated to perform 15 cycles.

Among the measurement results obtained as a result, as a representative, FIG. 3 shows the relationship between the light scattering intensity of the LPD detected on the same plane coordinate for three points and the depth from the mirror-polished surface of the wafer. In FIG. 3, at each point, the difference between the depths at the beginning and the end of the plot is the vertical length (depth from the time when the LPD is first detected to the time when the LPD disappears) H of the octahedral void, and Vertical length H of face body voids 1, 2, 3
Was found to be 140, 100 and 120 μm in that order.

It was also found that the light scattering intensity of the LPD changed with the change of the area of the octahedral void exposed on the wafer surface. For the octahedron voids 1, 2, and 3, the void area S corresponding to the maximum light-scattering intensity of each LPD detected and the longitudinal length of the octahedron void (LPD is detected first, in contrast to FIG. The volume V of the octahedron void was obtained from the depth H from the point of time of disappearance to the point of disappearance H by the equation (1). As a result, the volume of each octahedral void is as follows: 1 is 708200 nm ³ , 2 is 359900 nm ³ ,
3 was 523200 nm ³ .

[0033]

As described above, according to the evaluation method of the present invention, not only the surface of the mirror-finished silicon wafer but also the size, shape, and position of the octahedral voids existing inside the wafer can be easily calculated. And it can be evaluated accurately. That is, the depth position, area, and volume of the octahedral void existing in the silicon wafer can be easily evaluated. Therefore, the evaluation method according to the present invention is useful for a simple and highly accurate inspection for quality control of a silicon wafer in a semiconductor manufacturing process, and eventually contributes to providing a high quality silicon wafer. is there.

[Brief description of drawings]

FIG. 1 is a perspective view schematically showing a three-dimensional shape of octahedral voids existing in a silicon wafer.

FIG. 2 is a cross-sectional view schematically showing the progress of a state in which octahedral voids are exposed on the surface of a silicon wafer in order from (a) to (d) by repeating oxide film formation and acid-based etching treatment steps. Is.

FIG. 3 is a diagram showing the relationship between the depth position of the LPD of an octahedral void detected in the same plane coordinates and the light scattering intensity in the example.

FIG. 4 is a diagram showing the relationship between the exposed area of an octahedral void on the surface of a silicon wafer and the light scattering intensity of LPD.

Claims (5)

[Claims] 1. A method for evaluating an octahedral void in a silicon wafer, wherein an octahedral void existing in a mirror-finished silicon wafer is detected as a light scatterer by using a light-scattering surface inspection apparatus, wherein: a) the silicon The steps of detecting light scatterers on the wafer surface, b) forming an oxide film on the silicon wafer surface, and c) removing the oxide film on the silicon wafer surface by an acid-based etching process are sequentially repeated. A method for evaluating an octahedral void in a silicon wafer, which is characterized by being performed. 2. The relationship between the exposed area of the octahedral void on the surface of the silicon wafer and the light scattering intensity of the light scatterer is obtained in advance, and the light scattering intensity of the light scatterer detected in the step a) is calculated in advance. 2. The method for evaluating an octahedral void according to claim 1, wherein the void area of the octahedral void at each depth from the surface of the mirror-finished silicon wafer is evaluated by comparing the above. 3. The relationship between the exposed area of the octahedral void on the surface of the silicon wafer and the light scattering intensity of the light scatterer is obtained in advance, and the light scattering intensity of the light scatterer detected in step a) is obtained. The void area S corresponding to the maximum light-scattering intensity is determined by comparing the above-mentioned void area S and the depth H from the time when the light scatterer is first detected to the time when the light scatterer disappears. The octahedral void evaluation method according to claim 1, wherein the volume V of the octahedral void is obtained and evaluated by (1/3) · S · H (1). 4. The octahedral void of a silicon wafer according to claim 1, wherein the oxide film formed in step b) has a thickness of 10 to 50 nm. Evaluation methods. 5. The acid-based etching treatment in the step c) is performed using hydrofluoric acid or a mixed aqueous solution of hydrofluoric acid / nitric acid / acetic acid.
8. A method for evaluating an octahedral void in a silicon wafer according to any one of 1 to 4 above.