JP6515866B2 - Evaluation method of epitaxial wafer - Google Patents

Description

  The present invention relates to a method of evaluating an epitaxial wafer on which epitaxial growth has been performed on the surface of a mirror-finished wafer.

  When epitaxial growth is applied to 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 variously called edge crown, epi crown, etc., it is called crown in the present invention. With regard to this crown, as described in Patent Document 1, it causes a decrease in yield in a photolithography process which is a process of manufacturing an electronic device such as an IC (Integrated Circuit).

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

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

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

  However, in the case of the stylus type roughness meter described in Patent Document 2 and Patent Document 3, there is a problem that it becomes a destructive inspection and causes a decrease in yield. In addition, since measurement with a 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. The crown monitoring at the time of epitaxial growth described in Patent Document 4 is not practical because there is no illustration such as a specific measurement value.

  The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide an evaluation method of an epitaxial wafer capable of nondestructively and quickly determining the height of a crown generated during epitaxial growth. To aim.

  In order to achieve the above object, the present invention is an evaluation method of an epitaxial wafer for evaluating the height of a crown formed at an edge during epitaxial growth, which is produced when manufacturing a (100) epitaxial wafer for evaluation. Prepare a (100) epitaxial wafer for preliminary test manufactured by changing manufacturing conditions based on conditions, and form the edge portion in the <100> direction for the (100) epitaxial wafer for preliminary test A preliminary test step of measuring the size of the facet and the height of the crown and determining in advance the correlation between the size of the facet and the height of the crown, and the edge in the <100> direction of the (100) epitaxial wafer for evaluation. Nondestructively measure the size of the facets formed in the part, and from the size of the facets 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.

  Thus, the size of the facet formed on the edge part of the (100) epitaxial wafer for evaluation is nondestructively measured, and the size of the facet and the crown previously obtained from the size of the facet are measured. By determining the height of the crown based on the correlation with the height, the height of the crown generated at the time of epitaxial growth can be determined nondestructively and in a short time.

  At this time, when preparing the (100) epitaxial wafer for the preliminary test in the preliminary test step, the manufacturing conditions are changed based on the manufacturing conditions when manufacturing the (100) epitaxial wafer for the evaluation. Preferably, one or more of an epitaxial growth temperature and a gas flow rate for epitaxial growth are used.

  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 measuring the size of the facets in the evaluation step, any one of a CCD, a CIS, and a laser can be used.

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

  According to the evaluation method of the epitaxial wafer of the present invention, since it is nondestructive inspection, the yield reduction of the product by the height determination of the crown generated at the time of epitaxial growth does not occur, and the time to the height determination of the crown is greatly shortened. 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. It is an enlarged image of the facet formation part of FIG. It is the figure which co-ordinated the outline of FIG. 5A. It is a figure which shows a mode that the facet of FIG. 5B was fitted with a 44 degree straight line. It is a figure which shows the relationship of the facet size and crown height which were measured in the Example. It is a figure which shows the precision of the crown height calculated | required by 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, expressions of an edge portion and a chamfered portion appear below. The chamfered portion indicates a portion on the outer periphery of the wafer which has been subjected to processing such as grinding or polishing. Further, the edge portion means the 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 the cause of a decrease in yield in the photolithography process which is a process of manufacturing an electronic device such as an IC, and the measurement of the height of the crown uses a stylus type roughness meter. It has In recent years, the thickness of the epitaxially grown epitaxial layer tends to be thin, and therefore the crown height is also low, making it difficult to accurately capture the crown apex with a stylus type roughness meter. On the other hand, there is also disclosed a manufacturing method in which the crown is monitored using a CCD at the time of epitaxial growth, and when it is judged that the flatness is deteriorated, the epitaxial growth conditions are changed.

  However, in the case of a stylus type roughness meter, it is a destructive inspection, and there is a problem that it causes a decrease in yield. In addition, since measurement with a 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. With regard to crown monitoring at the time of epitaxial growth, there are no examples such as values at the time of specific measurement, which is not practical.

  Therefore, the present inventor has intensively studied an evaluation method of an epitaxial wafer which can determine the height of a crown generated at the time of epitaxial growth nondestructively and in a short time. As a result, the inventor noted that the crown generated at the time of 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 wafer main surface. The radial size of the facet formed in the <100> direction when epitaxial growth is applied to the (100) plane is quantified, and there is a correlation between this facet size and the crown height, and The inventors have found that it is possible to easily determine the crown height from the facet size measured nondestructively by using the present invention, and completed the present invention.

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

  FIG. 1 is a flow chart showing an example of the method for evaluating an epitaxial wafer of the present invention. Since there are steps S1 to S4 in FIG. 1, the respective steps will be described below.

  In step S1 of FIG. 1, a (100) epitaxial wafer for preliminary testing was grown by changing the epitaxial growth conditions based on the epitaxial growth conditions of the product (manufacturing conditions for manufacturing the (100) epitaxial wafer for evaluation) in advance. Prepare and measure the facet size and crown height in the <100> direction. The wafer diameter used in this step is not particularly limited, but it is preferably 100 mm to 450 mm, which can be generally manufactured. Further, the thickness of the epitaxial growth is not particularly limited, but from the viewpoint of facet growth, an epitaxial wafer having an epitaxial layer of 1 μm or more is preferable.

  The above-mentioned changing epitaxial growth conditions are preferably any one or more of an epitaxial growth temperature and a 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 the correlation to be described later is more accurate. You can get a relationship. Here, the gas flow rate for epitaxial growth can be, for example, a gas flow rate of a source gas or a carrier gas.

Further, the measuring method is not particularly limited, and for example, a stylus type roughness meter may be used as in the prior art, or a nondestructive method using a CCD as described later may be used. . Furthermore, it is also possible to use past data obtained by measurement on an epitaxial wafer manufactured and standardized under the same conditions.
The inclination angle of the facet formed in the <100> direction is known to be 44 degrees. From that, for example, it is possible to fit a 44-degree straight line with the facet surface obtained by measurement, and to make the length of the portion where they coincide the size of the facet in the present invention.

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

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

  Here, with regard to the shape of the chamfered portion, it is common to obtain an image of the wafer edge portion using a camera such as a CCD and to coordinate the obtained image. The image is shown in FIG. This FIG. 2 is an example of the edge part before the epitaxial growth process.

  FIG. 3 is a CCD image of an edge portion of a wafer obtained by epitaxially growing the wafer of FIG. This image is taken of a cross section in the <100> direction, and the flat facet 14 can be seen at the upper right of the figure.

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

  FIG. 4 is a view schematically showing a crown generated by epitaxial growth. The hatched portion in this figure is the epitaxial layer 12, and the lower part is the silicon wafer 11 which is the substrate. A raised portion around the right edge of the epitaxial layer is a crown 13. Thus, since the crown is a raised portion formed at the wafer edge in the <110> direction with respect to the plane extending from the wafer center after epitaxial growth, the crown height is a protrusion from the plane of the epitaxial layer 12 shown in FIG. It can be defined as height. Therefore, the facets formed in the <100> direction and the crowns formed in the <110> direction are located 45 ° apart on the wafer circumference.

  In step S4 of FIG. 1, from the facet size measured in step S3, the crown height is determined using the correlation between the facet size and the crown height obtained in advance in step S2. 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 crown height is determined by the worker Although it is possible to calculate and judge, it is preferable to make a judgment using a computing device in order to eliminate a worker's human error.

  If it is the evaluation method of the epitaxial wafer explained above, the size of the facet formed in the edge part of the <100> direction of the (100) epitaxial wafer for evaluation is measured nondestructively, and it is obtained in advance from the size of the facet By determining the height of the crown based on the correlation between the size of the facets stored and the height of the crown, the height of the crown generated during epitaxial growth can be determined nondestructively and in a short time.

  Hereinafter, the present invention will be more specifically described by way of examples, but the present invention is not limited thereto.

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

First, a sample wafer (a (100) epitaxial wafer for preliminary test) for determining the correlation of S2 in FIG. 1 was prepared.
The sample wafer prepared here will be described. In a sample wafer satisfying the epitaxial layer thickness standard as shown in Table 1, the epitaxial growth temperature, the gas flow rate for epitaxial growth, etc. may be slightly shaken, and as a result, the crown height changes. In view of such circumstances, six sample wafers having different crown heights were prepared by intentionally shaking the epitaxial growth temperature and the gas flow rate for epitaxial growth. By the way, at the epitaxial growth temperature, about ± 1% to the target temperature, and as the gas flow rate for the epitaxial growth, about ± 10% to the target gas flow velocity.

  First, shape measurement of the chamfered portion of the sample wafer was performed using VisEdge CV 350 manufactured by KLA-Tencor. In the present apparatus, an image shown in FIG. 2 or 3 can be acquired by the CCD. Here, FIG. 5A is an enlarged view of the facet formation portion of FIG. 3, and FIG. 5B is a diagram in which the outline of FIG. The X position indicates the distance from the radial center of the wafer, and the Y position indicates the thickness of the wafer. This coordinateization was performed using a KLA-Tencor VisEdge CV 350.

  Next, FIG. 6 shows how a 44-degree straight line is fitted to the contour of FIG. 5B in consideration of the fact that the facet formed in the <100> direction is known to be 44 degrees. It is a thing.

  Here, the length of the portion where the contour and the fitted straight line coincide is taken as the facet size. With regard to the facet size, an arithmetic unit was prepared separately, and digitization was achieved by simple image processing.

  The crown height of the prepared sample wafer is measured using the above-described stylus type roughness meter, and the crown height of the epitaxial wafer for the preliminary test is measured 10 times, except for the lower five values among them. The averaged value was taken as the representative value. Incidentally, Surfcom-1400D manufactured by Tokyo Seimitsu Co., Ltd. was used as a stylus-type roughness meter.

  The above is the measurement of the facet size and crown height shown in S1 of FIG.

  FIG. 7 is a graph obtained from the measured values of the facet size and the crown height in the present embodiment, and is the correlation shown in S2 of FIG. It has been found for the first time by the present inventors that such correlation can be obtained. However, since FIG. 7 shows the correlation of the epitaxial wafers satisfying the standards of Table 1, the manufacturing conditions are different in the case of the epitaxial wafers of the 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 nondestructive measurement of the facet size shown in S3 of FIG. 1 was carried out for the product concerned, and as shown in S4 of FIG. 1, from the measured facet size, based on the correlation of FIG. I asked. This is the series of flows of the present invention shown in FIG.

  Further, for verification, the crown height obtained in step S4 of FIG. 1 and 20 pieces of the product are respectively measured 10 times with the above-mentioned stylus type roughness meter, and averaging is performed except for 5 low values among them. The crown height was compared.

  FIG. 8 is a histogram of a value obtained by subtracting an actual value measured with the above-described stylus type roughness meter from the crown height obtained in the step S4 of FIG. 1 for the above 20 products. 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 was within ± several%, It has been found that the evaluation method according to the present invention enables determination with high accuracy. In addition, the height of the actual evaluation target crown can be evaluated nondestructively in a simple manner and in a short time.

  The present invention is not limited to the above embodiment. The above embodiment is an exemplification, and it has substantially the same configuration as the technical idea described in the claims of the present invention, and any one having the same function and effect can be used. It is included in the technical scope of the invention.

11 silicon wafer 12 epitaxial layer 13 crown
14: Facet surface.

Claims (3)

An epitaxial wafer evaluation method for evaluating the height of a crown formed at an edge during epitaxial growth, comprising:
Prepare a (100) epitaxial wafer for preliminary test manufactured by changing the manufacturing conditions based on the manufacturing conditions when manufacturing a (100) epitaxial wafer for evaluation, and (100) epitaxial for the preliminary test Pre-testing step of measuring the size of the facet formed on the edge portion in the <100> direction and the height of the crown and determining the correlation between the size of the facet and the height of the crown in advance for the wafer;
Nondestructively measure the size of the facet formed at the edge part in the <100> direction of the (100) epitaxial wafer for evaluation, and from the size of the facet, the previously determined size of the facet and the height of the crown And evaluating the height of the crown based on the correlation with the height.   In preparing the (100) epitaxial wafer for the preliminary test in the preliminary test step, the epitaxial growth temperature is changed based on the manufacturing conditions when producing the (100) epitaxial wafer for evaluation. 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 method for evaluating an epitaxial wafer according to claim 1 or 2, wherein the size of the facets is measured in the evaluation step, using one of a CCD, a CIS, and a laser.