JP2020198420A - Manufacturing method for epitaxial wafer and susceptor - Google Patents

Abstract

To provide a manufacturing method for epitaxial wafer, vapor growing a silicon epitaxial layer on a principal surface of a silicon wafer, capable of suppressing degradation in a flatness level.SOLUTION: Provided is a manufacturing method for epitaxial wafer, placing a silicon wafer on a pocket part of a susceptor and vapor growing a silicon epitaxial layer on a principal surface of the silicon wafer, the manufacturing method for epitaxial wafer using an absolute value of a second order differential of peripheral direction distribution of the pocket part of 8 μm or less as the susceptor.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for manufacturing an epitaxial wafer and a susceptor.

Silicon epitaxial wafers in which an epitaxial layer is formed on the surface of a silicon single crystal substrate (silicon wafer) by a vapor phase growth method are widely used in electronic devices. In recent years, with the miniaturization of electronic devices, improving the flatness level of epitaxial wafers has become an important issue.

Generally, when a single-wafer epitaxial wafer manufacturing apparatus is used to vapor-deposit an epitaxial layer on a polished silicon wafer, the silicon wafer is placed on a wafer mounting member called a susceptor to carry out a reaction. .. The susceptor has an edge region and has a pocket portion in the edge region that is several mm larger than the silicon wafer. By fitting the silicon wafer in this pocket, the silicon wafer can fit in a specific position even if the susceptor is rotated, and a homogeneous reaction is performed.

Japanese Unexamined Patent Publication No. 2001-3172

During the vapor phase growth of the epitaxial layer, the pocket depth of the susceptor has a great influence on the formation of the epitaxial layer, and in particular, the thickness of the epitaxial layer on the outer peripheral portion of the silicon wafer may change depending on the pocket depth. I know it. This phenomenon is considered to be due to a change in the gas flow at the outer periphery of the silicon wafer due to a change in the pocket depth of the susceptor.

If the pocket depth of the susceptor differs in the circumferential direction due to the influence of processing accuracy during manufacturing of the susceptor, the thickness of the epitaxial layer on the outer peripheral portion of the wafer changes due to the difference in the pocket depth. The film thickness becomes non-uniform, causing deterioration of the flatness level. Further, according to the investigation by the present inventor, when there is a steep local change in the circumferential distribution of the pocket depth of the susceptor, the gas flow also changes significantly locally, so that the circumferential direction of the outer peripheral portion of the wafer It was found that the film thickness non-uniformity of was more remarkable.

Conventional attention has not been paid to local steep changes in pocket depth that affect the thickness of the epitaxial layer. For example, Patent Document 1 describes a technique for improving temperature uniformity and reducing slip occurrence in a wafer surface by setting the flatness of the outer periphery of a susceptor pocket to 5 to 30 μm. There is no mention of changes in layer thickness. Further, Patent Document 1 does not specify a local steep change in the pocket depth that affects the thickness of the epitaxial layer.

The present invention has been made in view of the above problems, and is an epitaxial wafer capable of suppressing deterioration of the flatness level in a method for manufacturing an epitaxial wafer in which a silicon epitaxial layer is vapor-deposited on the main surface of the silicon wafer. It is an object of the present invention to provide a manufacturing method of. It is also an object of the present invention to provide a susceptor that can be used in such a method for manufacturing an epitaxial wafer.

In order to achieve the above object, the present invention relates to the susceptor in a method for manufacturing an epitaxial wafer in which a silicon wafer is placed in a pocket portion of the susceptor and a silicon epitaxial layer is vapor-deposited on the main surface of the silicon wafer. The present invention provides a method for manufacturing an epitaxial wafer, which comprises using a wafer having an absolute value of the second-order differential of the circumferential distribution of the depth of the pocket portion of 8 μm or less.

In this way, by manufacturing an epitaxial wafer using a susceptor having an absolute value of the second-order differential of the circumferential distribution of the depth of the pocket portion of 8 μm or less, the wafer of the susceptor is formed during the epitaxial growth of the silicon wafer. In the pocket portion on which the wafer is placed, it is possible to prevent the thickness of the epitaxial layer on the outer peripheral portion of the wafer from changing in the circumferential direction due to the influence of the depth of the susceptor pocket. As a result, it is possible to prevent the flatness level of the epitaxial wafer to be manufactured from deteriorating.

In the method for manufacturing an epitaxial wafer of the present invention, a silicon wafer having a diameter of 300 mm or more can be used.

The method for producing an epitaxial wafer of the present invention can be suitably applied to such a large-diameter silicon wafer.

Further, it is preferable that the vapor phase growth of the silicon epitaxial layer is carried out by using a single-wafer epitaxial wafer manufacturing apparatus having the susceptor.

The present invention can be suitably applied to a method for manufacturing an epitaxial wafer using such a single-wafer type epitaxial wafer manufacturing apparatus.

Further, the present invention has a pocket portion on which a silicon wafer is placed, and is a susceptor for vapor-depositing a silicon epitaxial layer on the main surface of the silicon wafer, and is a circumference of the depth of the pocket portion. Provided is a susceptor characterized in that the absolute value of the second derivative of the directional distribution is 8 μm or less.

Such a susceptor can suppress a change in the thickness of the epitaxial layer on the outer peripheral portion of the wafer in the circumferential direction due to the influence of the susceptor pocket depth. As a result, it is possible to prevent the flatness level of the epitaxial wafer to be manufactured from deteriorating.

According to the method for manufacturing an epitaxial wafer of the present invention, it is possible to prevent the thickness of the epitaxial layer on the outer peripheral portion of the wafer from changing in the circumferential direction due to the influence of the depth of the susceptor pocket. As a result, it is possible to prevent the flatness level of the epitaxial wafer to be manufactured from deteriorating. Further, the susceptor of the present invention can be used in a method for manufacturing such an epitaxial wafer.

It is a figure which shows the outline of the susceptor of this invention, (a) is a sectional view, (b) is a top view. It is a cross-sectional view which shows the positional relationship between the susceptor of this invention and a silicon wafer. It is an enlarged cross-sectional view which shows the relationship between the pocket depth of the susceptor of this invention, and a silicon wafer.

As described above, the pocket depth of the susceptor affects the thickness of the epitaxial layer on the outer periphery of the wafer. However, it was found that when the change in the circumferential direction of the pocket depth is a gradual change in the entire circumference of the susceptor, the influence on the gas flow is small and the influence on the outer peripheral portion of the wafer is limited. On the other hand, when the change in the pocket depth is a local steep change (for example, a shape like a protrusion), the gas flow changes and the degree of influence on the outer peripheral portion of the wafer becomes large. As a result of the present inventor's attempt to correlate with several indicators in order to represent a local change in pocket depth with a greater degree of influence, it was found that the correlation with the second derivative is the best.

That is, according to the present invention, in a method for manufacturing an epitaxial wafer in which a silicon wafer is placed in a pocket portion of a susceptor and a silicon epitaxial layer is vapor-deposited on the main surface of the silicon wafer, the pocket portion is used as the susceptor. This is a method for manufacturing an epitaxial wafer, which comprises using a wafer having an absolute value of the second-order differential of the circumferential distribution of depth of 8 μm or less. Here, the "depth of the pocket portion" used for calculating the absolute value of the second derivative refers to the depth on the wall surface (side wall) of the pocket portion. Further, the "second derivative" of the circumferential distribution is differentiated by an angle (rad).

Hereinafter, the present invention will be described in detail with reference to the drawings as an example of an embodiment, but the present invention is not limited thereto.

The susceptor of the present invention will be described with reference to FIGS. As shown in FIG. 1A, the susceptor 11 has a pocket portion 13. Further, as shown in FIG. 2, the silicon wafer W is placed in the pocket portion 13 of the susceptor 11. The susceptor 11 is a member for vapor-depositing a silicon epitaxial layer on the main surface of the silicon wafer W. Further, as shown in FIG. 1A, the pocket portion 13 of the susceptor 11 has a mounting surface 15 on which the silicon wafer W is mounted, and has a wall surface 17 on the outer periphery of the mounting surface 15. There is.

FIG. 3 shows the relationship between the pocket depth d and the silicon wafer W when the silicon wafer W is placed on the susceptor 11. In the susceptor 11 of the present invention, the absolute value of the second derivative of the circumferential distribution of the depth d of the pocket portion 13 is 8 μm or less. FIG. 1B shows the circumferential direction C of the susceptor. As described above, as the depth of the pocket portion 13, the absolute value of the second derivative is calculated using the depth of the wall surface (side wall) 17 of the pocket portion 13. Further, the "second derivative" of the circumferential distribution is differentiated by an angle (rad).

The susceptor 11 having such an absolute value of the second derivative is manufactured by performing a process of removing a local steep change (for example, a shape like a protrusion) of the pocket depth d in the susceptor manufacturing process. Can be done.

In the method for manufacturing an epitaxial wafer of the present invention, the epitaxial wafer is manufactured by using the susceptor 11 in which the absolute value of the second derivative of the circumferential distribution of the depth d of the pocket portion 13 is 8 μm or less. That is, the silicon wafer W is placed in the pocket portion 13 of the susceptor 11, and the silicon epitaxial layer is vapor-deposited on the main surface of the silicon wafer W.

It is preferable that the vapor phase growth of the silicon epitaxial layer is carried out by using a single-wafer epitaxial wafer manufacturing apparatus having a susceptor 11. The present invention can be suitably applied to a method for manufacturing an epitaxial wafer using such a single-wafer type epitaxial wafer manufacturing apparatus.

As described above, in the present invention, in the pocket portion 13 on which the silicon wafer W is placed in the susceptor 11 that holds the silicon wafer W, the local variation in the pocket depth d is 2 of the circumferential distribution of the pocket depth d. It is a measure that can suppress the deterioration of the flatness level of the epitaxial wafer by calculating it as a derivative value and using a susceptor whose absolute value is 8 μm or less (that is, the maximum value of the absolute value is 8 μm or less). That is, the susceptor 11 of the present invention suppresses the thickness of the epitaxial layer on the outer peripheral portion of the wafer from changing in the circumferential direction due to the influence of the susceptor pocket depth d in the pocket portion 13 of the susceptor 11 in the epitaxial growth of the silicon wafer W. be able to. As a result, it is possible to prevent the flatness level of the epitaxial wafer to be manufactured from deteriorating.

In the method for manufacturing an epitaxial wafer of the present invention, a silicon wafer W having a diameter of 300 mm or more can be used. The method for producing an epitaxial wafer of the present invention can be suitably applied to such a large-diameter silicon wafer. The diameter (pocket diameter) of the pocket portion 13 of the susceptor 11 is larger than the diameter of the silicon wafer W on which the susceptor 11 is placed, but it is preferable that the diameter is appropriately matched. For example, the pocket diameter is preferably larger in the range of 5 mm or less than the diameter of the silicon wafer W. Further, when the pocket diameter is 5 mm or less larger than the diameter of the wafer, the correlation between the local change in the pocket depth d and the second derivative value is high, so that the present invention can be particularly preferably applied. ..

Regarding the pocket depth d, it is preferable that the upper surface position of the silicon wafer W when the silicon wafer W is placed on the susceptor 11 is within ± 80 μm with respect to the depth d of the pocket portion 13. That is, it is preferable that the main surface position of the silicon wafer W and the upper position of the susceptor 11 are in the range of ± 80 μm. Within such a range, the local change in the pocket depth d and the second derivative value are highly correlated, so that the present invention can be particularly preferably applied.

The absolute value of the second derivative of the circumferential distribution of the depth d of the pocket portion 13 can be measured by various measuring methods. For example, the shape of the susceptor 11 can be measured with a three-dimensional measuring machine to calculate the absolute value of the second derivative.

Hereinafter, the present invention will be further described based on examples, but these examples are exemplified and should not be construed in a limited manner.

(Examples 1 to 3)
An epitaxial wafer was manufactured in a single-wafer epitaxial wafer manufacturing apparatus. As the manufacturing conditions of the epitaxial wafer at this time, a silicon wafer having a diameter of 300 mm was used as the epitaxial growth wafer, a susceptor having a pocket diameter of 305 mm and a pocket depth of 800 μm was used, the epitaxial growth temperature was 1100 ° C., and the epitaxial layer. Epitaxy was carried out under the condition that the thickness of the wafer was 5 μm. For the production of this epitaxial wafer, three types of susceptors having different susceptor pocket depth variations were used.

The local variation in the depth of the susceptor pocket and the thickness variation of the epitaxial layer on the outer peripheral portion of the epitaxial wafer after epitaxial growth were calculated. For the local variation of the susceptor pocket depth, the second derivative value was calculated from the circumferential distribution of the pocket depth according to the index used in the present invention, and the maximum value of the absolute value was taken as D. The distribution of the pocket depth (that is, the depth on the wall surface of the pocket portion) of this susceptor was measured with a non-contact type measuring machine of an optical system (XYZAX SVA-NEX manufactured by Tokyo Seimitsu Co., Ltd.). In the distribution of the pocket depth of the susceptor, the sampling pitch of the data used for calculating the absolute value of the second derivative was set to 1 ° pitch (that is, about 0.0175 rad pitch). Regarding the thickness variation of the outer peripheral portion of the epitaxial wafer, the thickness difference of the epitaxial layer in the region having a radius of 148-145 mm on the outer peripheral portion of the wafer was calculated in the circumferential direction, and the PV (peak to valley) value thereof was taken as R.

When the local variation D of the pocket depth of the susceptor is 4.6 μm (Example 1), 6.3 μm (Example 2), and 8.0 μm (Example 3), the index R of the thickness change of the outer peripheral portion of the wafer Was 3.3 nm, 3.4 nm, and 3.9 nm, respectively, and all were 4.0 nm or less.

(Comparative Examples 1 to 3)
The epitaxial wafer was manufactured using three types of susceptors different from those of Examples 1 to 3. When the local variation D of the susceptor pocket depth is 9.8 μm (Comparative Example 1), 11.3 μm (Comparative Example 2), and 14.0 μm (Comparative Example 3), the index R of the thickness variation of the outer peripheral portion of the wafer is They were 4.8 nm, 5.0 nm, and 9.0 nm, respectively, which were larger than 4.0 nm.

Table 1 summarizes the local variation D of the susceptor pocket depths of Examples 1 to 3 and Comparative Examples 1 to 3 and the thickness change index R of the outer peripheral portion of the wafer.

As shown in Table 1, the thickness variation R of the outer peripheral portion of the epitaxial wafer is 4 nm or less in the region where the local variation D of the susceptor pocket depth is 8.0 μm or less, and the deterioration of the flatness level can be suppressed. I understood.

The present invention is not limited to the above embodiment. The above embodiment is an example, and any one having substantially the same configuration as the technical idea described in the claims of the present invention and exhibiting the same effect and effect is the present invention. It is included in the technical scope of the invention.

11 ... susceptor, 13 ... pocket, 15 ... mounting surface, 17 ... wall surface,
C ... Circumferential direction, d ... Pocket depth (pocket depth) W ... Silicon wafer.

Claims (4)

In a method for manufacturing an epitaxial wafer in which a silicon wafer is placed in a pocket portion of a susceptor and a silicon epitaxial layer is vapor-deposited on the main surface of the silicon wafer.
A method for manufacturing an epitaxial wafer, which comprises using as the susceptor an absolute value of the second derivative of the circumferential distribution of the depth of the pocket portion of 8 μm or less. The method for manufacturing an epitaxial wafer according to claim 1, wherein a silicon wafer having a diameter of 300 mm or more is used. The method for manufacturing an epitaxial wafer according to claim 1 or 2, wherein the vapor phase growth of the silicon epitaxial layer is performed using a single-wafer epitaxial wafer manufacturing apparatus having the susceptor. A susceptor for vapor-depositing a silicon epitaxial layer on the main surface of the silicon wafer, which has a pocket portion on which a silicon wafer is placed.
A susceptor characterized in that the absolute value of the second derivative of the circumferential distribution of the depth of the pocket portion is 8 μm or less.

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