JP2017204504A - Epitaxial wafer evaluation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an epitaxial wafer evaluation method capable of determining a height of a crown generated at the time of epitaxial growth in a nondestructive manner and in a short time.SOLUTION: An epitaxial wafer evaluation method comprises: a pre-examination process of preparing a (100) epitaxial wafer for a pre-examination and measuring the size of a facet and a height of a crown which are formed on the (100) epitaxial wafer for the pre-examination at an edge part in a <100> direction; and an evaluation process of measuring the size of a facet formed on a (100) epitaxial wafer for evaluation at an edge part in the <100> direction in a nondestructive manner and calculate a height of a crown from the size of the facet based on a preliminarily calculated correlation between the size of the facet and the height of the crown.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an epitaxial wafer evaluation method in which epitaxial growth is performed on a mirror-finished wafer surface.

  When epitaxial growth is performed on the surface of a mirror-finished wafer, a bulge called a crown occurs on the outer peripheral portion of the wafer. Although this crown is called variously such as an edge crown and an epicrown, it is referred to as a crown in the present invention. As described in Patent Document 1, this crown causes a decrease in yield in a photolithography process, which is an electronic device manufacturing process such as an IC (Integrated Circuit).

  The crown has a height because it rises from the main surface of a wafer used in an IC or the like. For this height measurement, a stylus type roughness meter has been used mainly as described in Patent Document 2 and Patent Document 3. In recent years, the thickness of epitaxially grown epitaxial layers tends to become thinner as the integration of ICs and the like and the power saving progress. Therefore, the height of the crown is also lowered, and it is difficult for the stylus type roughness meter to accurately capture the crown apex.

  On the other hand, Patent Document 4 discloses a manufacturing method in which the crown is monitored using a CCD (Charge Coupled Device) during epitaxial growth, and the epitaxial growth conditions are changed when it is determined that the flatness is deteriorated.

JP 2002-353176 A JP 2012-204369 A Japanese Patent Laid-Open No. 06-112173 Japanese Patent Application Laid-Open No. 07-211652 JP 07-226349 A

  However, the stylus type roughness meter described in Patent Document 2 or Patent Document 3 has a problem that it becomes a destructive inspection and causes a decrease in yield. Moreover, since the measurement with the stylus type roughness meter is an off-line operation different from the wafer manufacturing process, there is also a problem that the manufacturing period becomes long. Regarding the crown monitoring at the time of epitaxial growth described in Patent Document 4, there is no illustration of a specific value at the time of measurement, which is not realistic.

  The present invention has been made in view of the above-mentioned problems, and provides an epitaxial wafer evaluation method capable of determining the height of a crown generated during epitaxial growth in a non-destructive manner in a short time. Objective.

  In order to achieve the above object, the present invention is an epitaxial wafer evaluation method for evaluating the height of a crown formed at an edge during epitaxial growth, and is manufactured when an (100) epitaxial wafer for evaluation is manufactured. A preliminary test (100) epitaxial wafer manufactured by changing the manufacturing conditions based on the conditions is prepared, and the preliminary test (100) epitaxial wafer is formed at the edge portion in the <100> direction. A preliminary test step of measuring a facet size and a crown height and obtaining a correlation between the facet size and a crown height in advance; and an edge in the <100> direction of the (100) epitaxial wafer for evaluation Non-destructively measuring the size of the facet formed on the part, Based on the correlation between the height of the pre-sized facet that has been determined and the crown, to provide an evaluation method of an epitaxial wafer, characterized in that it comprises an evaluation step for determining the height of the crown.

  As described above, the size of the facet formed on the edge portion in the <100> direction of the (100) epitaxial wafer for evaluation is measured nondestructively, and the facet size and the crown obtained in advance are determined from the facet size. By obtaining the height of the crown based on the correlation with the height, the height of the crown generated during epitaxial growth can be determined in a non-destructive manner in a short time.

  At this time, in the preliminary test step, when preparing the (100) epitaxial wafer for the preliminary test, the manufacturing conditions are changed based on the manufacturing conditions for manufacturing the (100) epitaxial wafer for evaluation. It is preferable to set any one or more of the epitaxial growth temperature and the gas flow rate for epitaxial growth.

  Thus, by changing any one or more of the epitaxial growth temperature and the gas flow rate for epitaxial growth, the height of the crown can be effectively changed, and a more accurate correlation can be obtained. .

  At this time, when the size of the facet is measured in the evaluation step, any of CCD, CIS, and laser can be used.

  When measuring the size of the facet nondestructively, any of CCD, CIS, and laser can be suitably used.

  The epitaxial wafer evaluation method of the present invention is a non-destructive inspection, so there is no reduction in product yield due to crown height judgment that occurs during epitaxial growth, and the time to crown height judgment is greatly reduced. it can.

It is a flowchart which shows an example of the evaluation method of the epitaxial wafer of this invention. It is an example of the CCD image of the edge part of the silicon wafer before epitaxial growth. It is an example of the CCD image of the edge part of the silicon wafer after epitaxial growth. It is the figure which showed typically the crown which generate | occur | produces by epitaxial growth. FIG. 4 is an enlarged image of the facet forming unit in FIG. 3. It is the figure which coordinated the outline of FIG. 5A. It is a figure which shows a mode that the facet surface of FIG. 5B was fitted with the 44-degree straight line. It is a figure which shows the relationship between the facet size measured in the Example, and crown height. It is a figure which shows the precision of the crown height calculated | required in the Example.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto. In the present specification, the expression of the edge portion and the chamfered portion will appear below. The chamfered portion indicates a portion where processing such as grinding or polishing is performed on the outer periphery of the wafer. The edge portion means a peripheral portion including the chamfered portion provided on the outer periphery of the wafer, and indicates a wider range than the chamfered portion.

  As described above, the crown is a cause of a decrease in the yield in the photolithography process, which is a process of manufacturing an electronic device such as an IC, and a stylus type roughness meter is used to measure the height of the crown. I came. In recent years, the thickness of epitaxially grown epitaxial layers tends to be reduced, and therefore the height of the crown is also lowered, making it difficult to accurately capture the crown apex with a stylus type roughness meter. On the other hand, a manufacturing method is disclosed in which the crown is monitored using a CCD during epitaxial growth, and when it is judged that the flatness has deteriorated, the epitaxial growth conditions are changed.

  However, the stylus type roughness meter has a problem that it becomes a destructive inspection and causes a decrease in yield. Moreover, since the measurement with the stylus type roughness meter is an off-line operation different from the wafer manufacturing process, there is also a problem that the manufacturing period becomes long. Regarding the crown monitoring at the time of epitaxial growth, there is no example of a specific value at the time of measurement, which is not realistic.

  In view of this, the present inventor has intensively studied an epitaxial wafer evaluation method capable of obtaining the height of a crown generated during epitaxial growth in a non-destructive manner in a short time. As a result, the present inventors pay attention to the fact that the crown generated during epitaxial growth is related to the facet formed in the chamfered portion provided on the outer periphery of the wafer as described in Patent Document 5, and is the main surface of the wafer. Quantify the radial size of the facet formed in the <100> direction when epitaxial growth is performed on the (100) plane, and there is a correlation between the facet size and the crown height, and this correlation As a result, it was found that the crown height can be easily determined from the facet size measured nondestructively, and the present invention has been completed.

  Below, the evaluation method of the epitaxial wafer of this invention is demonstrated, referring FIG.

  FIG. 1 is a flowchart showing an example of an epitaxial wafer evaluation method of the present invention. Since there are steps S1 to S4 in FIG. 1, each step will be described below.

  In step S1 of FIG. 1, a preliminary test (100) epitaxial wafer grown by changing the epitaxial growth conditions based on the product epitaxial growth conditions (manufacturing conditions for manufacturing an evaluation (100) epitaxial wafer) in advance. And measure the facet size and crown height in the <100> direction. Although the wafer diameter used at this step is not specifically limited, It is preferable that it is a wafer diameter which can be normally manufactured with 100 mm-450 mm. The epitaxial growth thickness is not particularly limited, but an epitaxial wafer having an epitaxial layer of 1 μm or more is preferable from the viewpoint of facet growth.

  It is preferable that the epitaxial growth condition to be changed is one or more of an epitaxial growth temperature and a gas flow rate for epitaxial growth. As described above, by changing any one or more of the epitaxial growth temperature and the gas flow rate for epitaxial growth, the height of the crown can be effectively changed. You can get a relationship. Here, the gas flow rate for epitaxial growth can be, for example, the gas flow rate of the source gas or carrier gas.

Further, the measuring method is not particularly limited, and for example, a stylus type roughness meter may be used as in the conventional case, or a nondestructive method using a CCD or the like as described later may be used. . Furthermore, past data obtained by actual measurement on an epitaxial wafer manufactured and standard under the same conditions can also be used.
The inclination angle of the facet formed in the <100> direction has been found to be 44 degrees. Therefore, for example, a facet surface obtained by measurement and a straight line of 44 degrees are fitted, and the length of the portion where they match can be set as the facet size in the present invention.

  In step S2 in FIG. 1, the correlation between the facet size and the crown height obtained in step S1 is obtained in advance. In this step, when the thickness of the epitaxial layer varies depending on the type, it is preferable to obtain the correlation between the facet size and the crown height for each type.

  In step S3 of FIG. 1, the facet size of the product (evaluation (100) epitaxial wafer) is measured nondestructively. This measurement is preferably performed by, for example, a pre-shipment inspection. In this pre-shipment inspection, the flatness inspection of the wafer main surface after epitaxial growth, the particle inspection on the wafer main surface, the shape inspection of the edge portion, and the scratch inspection are performed.

  Here, as for the shape of the chamfered portion, it is common to acquire an image of the wafer edge portion using a camera such as a CCD and to coordinate it. The image is shown in FIG. FIG. 2 shows an example of an edge portion before the epitaxial growth process.

  FIG. 3 is a CCD image of the edge portion of the wafer obtained by epitaxial growth on the wafer of FIG. This image is taken of a cross section in the <100> direction, and a flat facet 14 can be confirmed in the upper right of the figure.

  Regarding the shape of the edge portion, there is a method of acquiring a two-dimensional or three-dimensional image or coordinates by laser measurement in addition to acquiring an image by a CCD or CIS (CMOS Image Sensor).

  FIG. 4 is a diagram schematically showing a crown generated by epitaxial growth. The hatched portion in this figure is the epitaxial layer 12, and below that is a silicon wafer 11 that serves as a substrate. A portion of the epitaxial layer that rises around the right edge is a crown 13. As described above, the crown is a raised portion formed at the wafer edge portion in the <110> direction with respect to a plane extending from the wafer center after the epitaxial growth, and thus the crown height is raised from the plane of the epitaxial layer 12 shown in FIG. Can be defined as height. Therefore, the facet surface formed in the <100> direction and the crown formed in the <110> direction are located at 45 ° apart on the wafer circumference.

  In step S4 in FIG. 1, the crown height is determined from the facet size measured in step S3, using the correlation between the facet size determined in advance in step S2 and the crown height. Specifically, for example, by inputting the facet size of the evaluation (100) epitaxial wafer measured in step S3 into the correlation equation obtained from the correlation obtained in step S2, the height of the crown is determined by the operator. However, in order to eliminate human error of the operator, it is preferable to use an arithmetic device.

  If it is the evaluation method of the epitaxial wafer demonstrated above, the size of the facet formed in the edge part of <100> direction of the (100) epitaxial wafer for evaluation will be measured nondestructively, and it calculates | requires beforehand from the size of a facet By obtaining the height of the crown based on the correlation between the facet size and the height of the crown, the height of the crown generated during epitaxial growth can be determined in a non-destructive manner in a short time.

  EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated more concretely, this invention is not limited to these.

(Example)
In this example, the standard of the substrate wafer and the epitaxial layer thickness shown in Table 1 was adopted.

First, a sample wafer ((100) epitaxial wafer for preliminary test) for obtaining the correlation of S2 in FIG. 1 was prepared.
The sample wafer prepared here will be described. A sample wafer that satisfies the epitaxial layer thickness specifications as shown in Table 1 may fluctuate slightly in the epitaxial growth temperature, the gas flow rate for epitaxial growth, and the like, and as a result, the crown height changes. In view of such circumstances, six sample wafers were prepared in which the crown height was changed by deliberately changing the epitaxial growth temperature and the gas flow rate for epitaxial growth. Incidentally, the epitaxial growth temperature was varied about ± 1% relative to the target temperature, and the gas flow rate for epitaxial growth was varied about ± 10% relative to the target gas flow rate.

  First, the shape measurement of the chamfered portion of the sample wafer was performed using a VisEdge CV350 manufactured by KLA-Tencor. In this apparatus, the images shown in FIGS. 2 and 3 can be obtained by the CCD. Here, FIG. 5A is an enlarged view of the facet forming portion of FIG. 3, and FIG. 5B is a coordinated representation of the contour of FIG. 5A. The X position indicates the distance from the center in the radial direction of the wafer, and the Y position indicates the thickness of the wafer. Up to this coordinate processing was performed using a VisEdge CV350 manufactured by KLA-Tencor.

  Next, FIG. 6 shows a state where a straight line of 44 degrees is fitted to the contour of FIG. 5B in consideration of the fact that the facet surface formed in the <100> direction is found to be 44 degrees. Is.

  Here, the length of the matching portion between the contour line and the fitted straight line is the facet size. Regarding the facet size, a separate computing device was prepared and quantified by simple image processing.

  For the measurement of the crown height of the prepared sample wafer, the above-mentioned stylus type roughness meter is used, and the crown height of the epitaxial wafer for preliminary test is measured 10 times, except for the low value of 5 points. Averaged values were used as representative values. Incidentally, Surfcom-1400D manufactured by Tokyo Seimitsu was used as the stylus type roughness meter.

  This is the actual measurement of the facet size and crown height shown in S1 of FIG.

  FIG. 7 is a graph obtained from the actual measurement values of the facet size and the crown height in the present embodiment, and shows the correlation indicated by S2 in FIG. It was first found by the present inventor that such a correlation was obtained. However, since FIG. 7 shows the correlation of epitaxial wafers satisfying the standards shown in Table 1, the manufacturing conditions differ in the case of epitaxial wafers of other standards, so it is necessary to separately obtain the correlation.

  Next, 20 epitaxial wafer products having the standards shown in Table 1 were prepared. The non-destructive measurement of the facet size shown in S3 of FIG. 1 is performed on the product, and the crown height is calculated from the measured facet size based on the correlation of FIG. 7 as shown in S4 of FIG. Asked. This is the series of the flow of the present invention shown in FIG.

  For further verification, the crown height obtained in step S4 in FIG. 1 and the 20 products are measured 10 times with the aforementioned stylus-type roughness meter, and averaged except for the low value of 5 points. The crown height was compared.

  FIG. 8 is a histogram showing the value obtained by subtracting the actual measurement value measured with the stylus type roughness meter from the crown height obtained in step S4 of FIG. is there. Since the average value of the crown height of this product was 129 nm, from FIG. 8, the difference between the judgment value evaluated in the present invention and the actually measured value by the stylus type roughness meter is within ± several%, It was found that the evaluation method according to the present invention can make a determination with high accuracy. In addition, the height of the actual crown to be evaluated can be evaluated non-destructively and easily in a short time.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

11 ... Silicon wafer, 12 ... Epitaxial layer, 13 ... Crown,
14 ... Faceted surface.

Claims (3)

An epitaxial wafer evaluation method for evaluating the height of a crown formed at an edge during epitaxial growth,
A preliminary test (100) epitaxial wafer manufactured by changing the manufacturing conditions based on the manufacturing conditions when manufacturing the (100) epitaxial wafer for evaluation is prepared, and the (100) epitaxial for the preliminary test is prepared. A preliminary test step of measuring a facet size and a crown height formed at an edge portion in a <100> direction for a wafer, and obtaining a correlation between the facet size and a crown height in advance;
The size of the facet formed at the edge portion in the <100> direction of the (100) epitaxial wafer for evaluation is measured nondestructively. From the size of the facet, the facet size determined in advance and the height of the crown are measured. An evaluation method for an epitaxial wafer, comprising: an evaluation step for obtaining a height of a crown based on a correlation with the wafer.   In the preliminary test step, when preparing the (100) epitaxial wafer for the preliminary test, the manufacturing conditions to be changed on the basis of the manufacturing conditions for manufacturing the (100) epitaxial wafer for evaluation are changed to the epitaxial growth temperature. The method for evaluating an epitaxial wafer according to claim 1, wherein any one or more of gas flow rates for epitaxial growth are used.   The epitaxial wafer evaluation method according to claim 1, wherein when the size of the facet is measured in the evaluation step, any one of CCD, CIS, and laser is used.