JP2022060993A - Defect evaluation method, defect evaluation method for soi substrate, and defect evaluation method for multilayer substrate - Google Patents

Abstract

To provide a defect evaluation method capable of measuring a small defect with high sensitivity even after sticking regarding a multilayer substrate where a plurality of single crystal substrates is stuck together.SOLUTION: A defect evaluation method for evaluating, by an XRT, a defect in a multilayer substrate having a plurality of single crystal substrates where a plurality of single crystal layers is stuck together. The defect evaluation method includes: a step of preparing the multilayer substrate and determining a diffraction angle of an X ray for each of the plurality of single crystal layers in the multilayer substrate; an XRT image acquisition step of acquiring an XRT image of each of the plurality of single crystal layers in accordance with the diffraction angle of the X ray which is obtained in the step of determining the diffraction angle of the X ray, for each of the plurality of single crystal layers; and a defect in-plane generation position identification step of identifying an in-plane generation position of the defect for each of the plurality of single crystal layers from the XRT image which is obtained in the XRT image acquisition step, for each of the plurality of single crystal layers.SELECTED DRAWING: Figure 1

Description

The present invention relates to a defect evaluation method for an SOI substrate or a multilayer substrate in which a single crystal substrate is directly bonded.

Wafer bonding technology has been applied to the manufacture of 3D laminated devices and SOI wafers. When evaluating a defect existing in a wafer, the cause of the defect can be identified by inspecting it by various measurement methods before bonding, but after bonding, there is a method of identifying the defect. Limited. There is a need for a method for measuring defects caused by bonding and defects that occur after bonding.

Voids and broken wires can be detected by X-ray transmission measurement, but the accuracy is low and small defects cannot be detected. As seen in Patent Document 1, the resolution of the X-ray CT device is determined by the size of the detector, and since the CT image visualizes the difference in the transmittance of X-rays, crystal defects in Si are measured. Even if an attempt is made, defects in Si and Si cannot be detected because there is no difference in the transmittance of X-rays.

Patent Document 2 shows the XRT evaluation result of the SOI substrate. Since XRT is a method using X-ray diffraction, it is characterized by being able to detect crystal defects in Si that cannot be visualized by X-ray CT, but in Patent Document 2, it is the base that is actually evaluated by XRT. Bond wafers are not evaluated only for wafers.

Japanese Unexamined Patent Publication No. 2016-176731 Japanese Unexamined Patent Publication No. 2008-277702

With 3D laminated devices and 3D-ICs, there is no suitable method for measuring crystal defects after bonding, and although major defects such as voids and wiring shorts can be seen, it is not possible to measure dislocations and BMD between the upper and lower layers. Although it is possible with TEM, it is difficult to evaluate the entire wafer. Although defects existing before bonding can be measured before bonding, it is difficult to measure minute defects generated in the bonding process. In addition, the X-ray transmission method, which is often used to measure bonded wafers, is detected by overlapping bonded wafers, so the depth of defects is unknown, and the X-ray CT method using X-ray transmission is used. It is not possible to detect small defects on the order of microns.

Wafer bonding technology has been used as a representative of SOI substrates in the past, but in recent years, it has also been used in device processes. As a method for measuring defects of these SOI substrates and devices, there are various defect measuring methods at the stage before bonding, but there are few methods for measuring defects with high sensitivity after bonding.

The present invention has been made to solve such a problem, and by utilizing diffraction by X-rays, it is possible to perform highly sensitive measurement of small defects such as BMD and dislocations even after bonding. It is an object of the present invention to provide a defect evaluation method of an SOI substrate. Further, the present invention is not limited to the SOI substrate, and provides a defect evaluation method capable of highly sensitive measurement of small defects even after bonding a multilayer substrate in which a plurality of single crystal substrates are bonded. The purpose is.

In order to solve the above problems, the present invention provides a defect evaluation method for evaluating defects in a multilayer substrate having a plurality of single crystal layers by laminating a plurality of single crystal substrates by XRT. Then, for each of the plurality of single crystal layers in the multilayer substrate, the X of each of the plurality of single crystal layers obtained in the step of obtaining the diffraction angle of X-rays and the step of obtaining the diffraction angle of the X-rays. From the XRT image acquisition step of acquiring each XRT image of the plurality of single crystal layers according to the diffraction angle of the line, and the XRT image of each of the plurality of single crystal layers obtained in the XRT image acquisition step. Provided is a defect evaluation method comprising a defect in-plane generation position specifying step for specifying an in-plane generation position of each of the plurality of single crystal layers.

Such a defect evaluation method is not limited to the SOI substrate, and is a defect evaluation method that enables highly sensitive measurement of small defects even after bonding a multilayer substrate in which a plurality of single crystal substrates are bonded. It becomes.

Further, the present invention is a defect evaluation method for evaluating defects in an SOI substrate in which a bond wafer and a base wafer are bonded by XRT. The SOI substrate is prepared, and the bond wafer portion and the base wafer portion of the SOI substrate are evaluated. For each, an XRT image of the bond wafer portion is acquired according to the X-ray diffraction angle of the bond wafer portion obtained in the step of obtaining the X-ray diffraction angle and the step of obtaining the X-ray diffraction angle. In addition, the XRT image acquisition step of acquiring the XRT image of the base wafer portion according to the diffraction angle of the X-ray of the base wafer portion and the XRT image of the bond wafer portion obtained in the XRT image acquisition step. In-plane occurrence position specifying step of specifying the in-plane occurrence position of the defect in the bond wafer portion from the above, and specifying the in-plane occurrence position of the defect in the base wafer portion from the XRT image of the base wafer portion. Provided is a defect evaluation method for an SOI substrate, which comprises.

Such a defect evaluation method of the SOI substrate of the present invention can measure small defects such as BMD and dislocations with high sensitivity, and particularly measures defects after bonding, that is, defects generated by the influence of bonding. Can be evaluated. Moreover, it is possible to identify whether the defect is in the bond wafer portion or the base wafer portion.

Further, in the step of obtaining the X-ray diffraction angle, when the X-ray diffraction angle of the bond wafer portion and the base wafer portion is the same, the X-ray diffraction angle is changed by rotating the SOI substrate. Therefore, it is possible to obtain the diffraction angles of the X-rays that are different between the bond wafer portion and the base wafer portion.

By doing so, even if the X-ray diffraction angles of the bond wafer section and the base wafer section are the same, different X-ray diffraction angles can be obtained from different directions to easily obtain the base wafer section and the bond wafer section. Can be measured separately.

Further, in the process of specifying the in-plane occurrence position of the defect, a section topograph image is acquired at the in-plane occurrence position of the specified defect, and the position in the depth direction at the in-plane occurrence position of the defect is specified from the section topograph image. be able to.

By doing so, it is possible to obtain information on the depth of the defect, which is useful for estimating the cause of the defect and the like.

Further, the present invention is a defect evaluation method for evaluating defects in a multilayer substrate having a plurality of single crystal layers by directly laminating a plurality of single crystal substrates having a thickness of 10 μm or more by XRT, and prepares the multilayer substrate. Then, for each of the plurality of single crystal layers in the multilayer substrate, the X of each of the plurality of single crystal layers obtained in the step of obtaining the diffraction angle of X-rays and the step of obtaining the diffraction angle of the X-rays. From the XRT image acquisition step of acquiring each XRT image of the plurality of single crystal layers according to the diffraction angle of the line, and the XRT image of each of the plurality of single crystal layers obtained in the XRT image acquisition step. The present invention provides a defect evaluation method for a multilayer substrate, which comprises a defect in-plane generation position specifying step for specifying an in-plane generation position of each of the defects in the plurality of single crystal layers.

Such a defect evaluation method for a multilayer board is a defect evaluation method that enables highly sensitive measurement of small defects even after bonding a multilayer board in which a plurality of single crystal substrates are directly bonded. In particular, it is possible to measure defects for each single crystal layer, and it is also possible to identify in which layer the detected defects are generated.

Further, in the step of obtaining the diffraction angle of the X-ray, when the diffraction angle of the X-ray of at least two of the plurality of single crystal layers is the same, the diffraction of the X-ray is performed by rotating the multilayer substrate. By changing the angle, it is possible to obtain the diffraction angle of the X-ray that is different for each of the plurality of single crystal layers.

By doing so, even if the X-ray diffraction angles of two layers or three or more layers are the same, by obtaining different X-ray diffraction angles from different directions, a plurality of single crystals can be easily obtained. The crystal layer can be measured separately.

Further, in the process of specifying the in-plane occurrence position of the defect, a section topograph image is acquired at the in-plane occurrence position of the specified defect, and the position in the depth direction at the in-plane occurrence position of the defect is specified from the section topograph image. be able to.

By doing so, it is possible to obtain information on the depth of the defect, which is useful for estimating the cause of the defect and the like.

As described above, according to the present invention, even defects after bonding of SOI substrates can be measured with high sensitivity. Moreover, defects can be identified separately for the bond wafer portion and the base wafer portion. Further, since the present invention is to measure the upper layer and the lower layer of the laminated wafer separately by XRT and analyze the state of occurrence of defects, it can be applied not only to SOI substrates but also to three-dimensional laminated devices and the like. be. It can also be applied to crystals other than Si such as GaN / Si and SiC / Si. Further, even in the case of a three-dimensional device, it is possible to measure the defect for each single crystal layer, and it is also possible to specify in which layer the detected defect is generated.

It is a flow diagram which shows the outline of the process of the defect evaluation method of the SOI substrate of this invention. It is a schematic diagram which shows an example of the XRT measurement of the SOI substrate in this invention. It is a graph which shows an example of the diffraction peak obtained from the SOI substrate in this invention. It is a schematic diagram which shows an example of the measurement of the diffraction angle of each X-ray of the bond wafer part and the base wafer part of the SOI substrate in this invention. It is a schematic diagram which shows an example of the case where the diffraction angle is measured by rotating an SOI substrate. It is a photograph which shows the XRT image of the base wafer part and the bond wafer part measured after bonding the SOI substrate of Example 1. FIG. It is a photograph which shows the section topograph image of the part where the slip dislocation occurred of Example 1. FIG. It is explanatory drawing about the section topograph image of Example 1. FIG. It is a schematic diagram which shows the relationship between the diffraction angle with respect to the diffraction plane and the diffraction angle with respect to a sample surface in a single crystal wafer. It is a graph which shows an example of the diffraction peak obtained from a single crystal wafer. It is a flow diagram which shows the outline of the process of the defect evaluation method of the multilayer board of this invention. It is a schematic diagram which shows an example of the measurement of the diffraction angle of each X-ray of the upper layer and the lower layer of the multilayer substrate in this invention. This is an example of an X-ray diffraction angle and an XRT image obtained when the thickness of each layer of the multilayer board is different and the device pattern of each layer is the same in the defect evaluation method of the multilayer board of the present invention. This is an example of an X-ray diffraction angle and an XRT image obtained when the thickness of each layer of the multilayer board is the same and the device pattern of each layer is different in the defect evaluation method of the multilayer board of the present invention. This is an example of an X-ray diffraction angle and an XRT image obtained when the thickness of each layer of the multilayer board and the device pattern of each layer are the same in the defect evaluation method of the multilayer board of the present invention. It is a measurement result of the X-ray diffraction angle of the multilayer substrate composed of the upper layer and the lower layer obtained in Example 2. 6 is an XRT image of each of the upper layer and the lower layer of the multilayer board obtained in Example 2.

XRT (X-ray Topography) is a measurement method using a diffraction phenomenon. Diffracted X-rays from a specific diffraction plane are measured two-dimensionally to visualize defects in the crystal. When the distance between the diffraction planes increases due to stress or the presence of defects and the diffraction conditions are not satisfied, contrast is created.

Here, the XRT measurement will be briefly described first. FIG. 9 shows an example of XRT measurement of a silicon single crystal wafer, which is different from the present invention. It is a schematic diagram which shows the relationship between the diffraction angle with respect to a diffraction plane and the diffraction angle (sample incident angle) with respect to a sample surface in a single crystal wafer which is a sample. As shown in the above figure, when the single crystal wafer 101 is irradiated with X-rays 104, the following equation holds if the diffraction angle (incident angle) with respect to the diffraction surface 105 is Θ.
2dsinΘ = nλ
Here, d: lattice spacing, λ: wavelength of X-rays, n: arbitrary natural number.
Assuming that the diffraction angle (sample incident angle) with respect to the surface of the single crystal wafer 101 is ω, ω = Θ when the diffraction surface 105 is parallel to the sample surface, as shown on the left side of the figure below. However, since it is unlikely that the diffraction surface 105 is completely parallel to the sample surface, ω ≠ Θ as shown on the right side of the figure below.

Since the crystal axis orientation of the epitaxial layer of the epitaxial wafer is grown by inheriting the crystal axis orientation of the substrate, there is no difference in the crystal axis orientation between the epitaxial layer and the substrate. However, in the SOI and laminated wafers, the SOI layer and the substrate do not have exactly the same crystal axis orientation, and in most cases, a deviation of about several minutes occurs. Similarly, in a wafer in which single crystal substrates are directly bonded to each other, the substrates to be bonded do not have exactly the same crystal axis orientation, and in most cases, a deviation of about several minutes occurs.

By utilizing the deviation of the crystal axis orientation by this few minutes, it is possible to separately measure the defects in the base wafer portion and the bond wafer portion after bonding. That is, if the measurement axis is aligned with the diffraction surface of the base wafer portion and the XRT image is measured, information on only the base wafer portion can be obtained, and if the conditions are adjusted to the diffraction surface of the bond wafer portion and the XRT image is measured, the bond is obtained. Information on only the wafer section can be obtained. In this way, the information of the base wafer portion and the bond wafer portion can be measured separately after the bonding, and the defects generated in the bonding can be measured. The same applies to the upper layer and the lower layer of the wafer in which the single crystal substrates are directly bonded to each other. The present inventor has found the above and completed the present invention.

Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.

<Defect evaluation method>
The present invention is a defect evaluation method for evaluating defects in a multilayer substrate having a plurality of single crystal layers by laminating a plurality of single crystal substrates by XRT. The multilayer substrate is prepared, and the defects in the multilayer substrate are evaluated. For each of the plurality of single crystal layers, the X-ray diffraction angle is adjusted to the X-ray diffraction angle of each of the plurality of single crystal layers obtained in the step of obtaining the X-ray diffraction angle and the step of obtaining the X-ray diffraction angle. From the XRT image acquisition step of acquiring each XRT image of the plurality of single crystal layers and the XRT image of each of the plurality of single crystal layers obtained in the XRT image acquisition step, the plurality of single crystal layers. It is a defect evaluation method including a defect in-plane occurrence position specifying step for specifying the in-plane occurrence position of each of the above-mentioned defects.

The defect evaluation method of the present invention can be applied to any multilayer substrate having a plurality of single crystal layers in which a plurality of single crystal substrates are bonded. Examples of such a multilayer substrate include a plurality of single crystal substrates having a thickness of 10 μm or more, such as an SOI substrate (first embodiment of the present invention) in which a bond wafer and a base wafer are bonded together, and a three-dimensional laminated device. A multilayer substrate having a plurality of single crystal layers (second embodiment of the present invention) in which the above-mentioned wafers are directly bonded is mentioned. Hereinafter, the present invention will be described in detail by exemplifying the first embodiment and the second embodiment of the present invention.

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

The first embodiment of the present invention is a defect evaluation method for evaluating defects in an SOI substrate in which a bond wafer and a base wafer are bonded by XRT, in which the SOI substrate is prepared and the bond wafer portion of the SOI substrate is used. For each of the base wafer portions, the XRT of the bond wafer portion is matched with the X-ray diffraction angle of the bond wafer portion obtained in the step of obtaining the X-ray diffraction angle and the step of obtaining the X-ray diffraction angle. The XRT image acquisition step of acquiring an image and acquiring an XRT image of the base wafer portion according to the diffraction angle of the X-ray of the base wafer portion, and the bond wafer portion obtained in the XRT image acquisition step. In the defect plane, the in-plane occurrence position of the defect of the bond wafer portion is specified from the XRT image of the base wafer portion, and the in-plane occurrence position of the defect of the base wafer portion is specified from the XRT image of the base wafer portion. It is a defect evaluation method of an SOI substrate having a generation position specifying step.

Here, first, the outline of the evaluation method using the XRT measurement of the SOI substrate 1 in the present invention will be briefly described with reference to FIG. The SOI substrate 1 to be prepared is mainly composed of a bond wafer portion 2 and a base wafer portion 3, and an XRT image is obtained by using an XRT measuring device according to the diffraction angle of each of the diffraction planes 5 of the X-ray 4. Can be obtained.

However, SOI is for manufacturing a device on a bond wafer, and the bond wafer is generally made thin. Therefore, since the diffraction from the bond wafer may be very weak, it is preferable that the film thickness of the bond wafer is 10 μm or more in the present invention.

As the XRT measuring device, for example, an XRT micron manufactured by Rigaku Corporation can be used. This XRT device has a feature that cross-sectional XRT evaluation can be performed in a short time by combining a high-luminance X-ray generator and a high-sensitivity CCD.

In addition, by using this device, it is possible to measure the cross-sectional topography image (section topography image) of the wafer after bonding, and it is possible to know the distribution information in the depth direction of the defect, so that the cause of the defect can be determined. Useful for identification.

Taking an X-ray topography image (XRT image) requires a process called axis alignment. This axis alignment is a step of determining the diffraction conditions for the sample to be measured, and at this time, the inclination of the plane orientation of the sample is obtained.

In the case of a normal single crystal, as shown in FIG. 10, only two diffraction peaks, Kα1 and Kα2, can be obtained, but in the case of a bonded wafer such as an SOI substrate, as shown in FIG. 3, the base is obtained. Since two peaks of Kα1 and Kα2 are obtained from both the wafer portion and the bond wafer portion, a total of four diffraction peaks can be obtained. In this case, since the base wafer portion is usually thicker than the bond wafer portion, the one having a larger peak is the diffraction peak from the base wafer portion.

At this time, if the crystal axis orientations of the base wafer portion and the bond wafer portion are different, the diffraction peaks do not overlap, but even if the crystal axis orientations of the base wafer portion and the bond wafer portion are the same, the diffraction peaks do not overlap. As described above, since there is a slight difference in the plane orientation, the measurement can be performed separately for the base wafer portion and the bond wafer portion.

Hereinafter, the process of the defect evaluation method for the SOI substrate of the present invention will be specifically described. FIG. 1 is a flow chart showing an outline of the process of the defect evaluation method of the SOI substrate of the present invention.

First, as in step 1 of FIG. 1, an SOI substrate is prepared, and the X-ray diffraction angle is obtained for each of the bond wafer portion and the base wafer portion of the SOI substrate (step of obtaining the X-ray diffraction angle).

Here, with reference to FIG. 4, the measurement of the diffraction angle of each X-ray of the bond wafer portion 2 and the base wafer portion 3 of the SOI substrate 1 will be described in detail. As shown on the left side of the above figure, the sample incident angle of the bond wafer portion 2 is ωb, and as shown on the right side of the above figure, the sample incident angle of the base wafer portion 3 is ωa. As shown in the figure below, ωa and ωb can be obtained from the obtained four peaks. As described above, the one having a larger peak is the diffraction peak from the base wafer portion 3. Further, there are two peaks, Kα1 and Kα2, respectively, and either peak may be used, but usually the larger peak (Kα1) is used.

At this time, if the diffraction angles (sample incident angles ωa, ωb) of the X-rays 4 of the bond wafer portion 2 and the base wafer portion 3 are the same, the diffraction angle of the X-rays 4 can be changed by rotating the SOI substrate 1. can. Even when the difference in the diffraction plane is small and the peaks of the bond wafer portion 2 and the base wafer portion 3 cannot be completely separated, when the SOI substrate 1 is rotated by 90 °, a difference in crystal axis orientation may occur. FIG. 5 shows an example of measuring the diffraction angle in the case of such an SOI substrate 1. When the base wafer portion 3 and the bond wafer portion 2 are tilted as shown in the upper left figure, the crystal axis orientations of the base wafer portion 3 and the bond wafer portion 2 are the same in the YY plane (upper right figure), but the XX plane. In (lower left figure), the crystal axis orientations of the base wafer portion 3 and the bond wafer portion 2 are twisted. In this case, the difference between the base wafer portion 3 and the bond wafer portion 2 cannot be obtained even if the X-ray diffraction is measured as shown in the upper right figure, but if the X-ray diffraction is measured as shown in the lower left figure, the base wafer portion 3 is obtained. And the bond wafer section 2 can be measured separately. That is, each diffraction angle can be obtained.

Next, as in step 2 of FIG. 1, an XRT image of the bond wafer portion is acquired according to the X-ray diffraction angle of the bond wafer portion obtained in the step of obtaining the X-ray diffraction angle, and the base wafer is obtained. The XRT image of the base wafer part is acquired according to the diffraction angle of the X-ray of the part. That is, XRT measurement is performed according to the diffraction angles of the X-rays of the bond wafer portion and the base wafer portion, and each XRT image is acquired (XRT image acquisition step).

The substrate is set in the XRT measuring device, and X-ray irradiation is performed with ωa obtained in step 1 to acquire an XRT image, and then X-ray irradiation is performed with ωb to acquire an XRT image.

In this way, the XRT image of only the bond wafer portion can be acquired by matching the measurement conditions of the XRT measuring device with the X-ray diffraction angle of the bond wafer portion, and the X-ray diffraction of the base wafer portion can be obtained. It is possible to acquire an XRT image of only the base wafer portion by measuring according to the measurement conditions according to the angle. As a result, in the next step 3, the defect of the bond wafer portion and the defect of the base wafer portion can be observed separately.

Finally, as in step 3 of FIG. 1, the in-plane occurrence position of the defect of the bond wafer portion is specified from the XRT image of the bond wafer portion obtained in the XRT image acquisition step, and the XRT image of the base wafer portion is used. The in-plane occurrence position of the defect in the base wafer portion is specified (defect in-plane occurrence position identification process).

That is, the acquired XRT image is usually taken from the front and back surfaces (main surface) of the substrate, and the position where the defect occurs in the surface of the main surface is visually confirmed and specified.

At this time, by acquiring the section topograph image at the in-plane occurrence position of the specified defect, the position in the depth direction at the in-plane occurrence position of the defect can be specified. By specifying the position of the defect in the depth direction, it is possible to obtain information such as to what depth the defect has reached or where it originated, and it is possible to find out the cause of the defect.

As described above, according to the defect evaluation method of the SOI substrate of the present invention, small defects such as BMD and dislocations can be measured with high sensitivity, and defects after bonding can also be measured and evaluated. Moreover, it is possible to identify whether the defect is in the bond wafer portion or the base wafer portion.

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

The second embodiment of the present invention is a defect evaluation method for evaluating defects in a multilayer substrate having a plurality of single crystal layers by directly laminating a plurality of single crystal substrates having a thickness of 10 μm or more by XRT. The plurality of single crystal layers obtained in the steps of preparing a multilayer substrate and determining the X-ray diffraction angle for each of the plurality of single crystal layers in the multilayer substrate and the step of determining the X-ray diffraction angle. An XRT image acquisition step of acquiring each XRT image of the plurality of single crystal layers according to the diffraction angle of each of the X-rays, and a respective of the plurality of single crystal layers obtained in the XRT image acquisition step. It is a defect evaluation method of a multilayer substrate having a defect in-plane generation position specifying step for specifying an in-plane generation position of each of the defects in the plurality of single crystal layers from the XRT image.

In the defect evaluation method of the multilayer substrate of the present invention, a multilayer substrate having a plurality of single crystal layers in which a plurality of single crystal substrates having a thickness of 10 μm or more are directly bonded is used. Since the single crystal substrate is directly bonded to each other (that is, without interposing a layer other than the single crystal layer), the multilayer substrate is an SOI substrate in which _two SiO substrates are sandwiched between a base wafer and a bond wafer. (The first embodiment of the present invention) is different. The SiO ₂ layer is generally amorphous. Since X-ray diffraction does not occur in amorphous, the defect evaluation method of the present invention can be applied without distinguishing between a directly bonded wafer and an SOI wafer. At this time, if the thickness of one directly bonded single crystal substrate is 10 μm or more, a high-intensity diffraction peak can be obtained.

The defect evaluation method for a multilayer substrate of the present invention is used for a multilayer device in which a large number of wafers having 5 or more layers are directly bonded, as well as 2 to 4 layers, if the patterns formed on the single crystal substrate (wafer) are different. Is adaptable without any problems. On the other hand, in a multi-layer device in which the same pattern is formed and bonded on a wafer, even if the thickness of the bonded substrates is different, the X-ray diffraction peaks tend to overlap as the number of bonded substrates increases, so it is more precise. From the viewpoint of performing a good evaluation, it is preferable to apply up to about 4 layers as an upper limit.

As described above, the XRT measuring device is preferably an XRT micron manufactured by Rigaku. This XRT device has a feature that cross-sectional XRT evaluation can be performed in a short time by combining a high-luminance X-ray generator and a high-sensitivity CCD.

Even with an XRT measuring device other than this device, it is possible to measure each single crystal layer. However, since XRT micron can easily measure the cross-sectional topograph, it is possible to specify the distribution information in the depth direction of the defect, which is useful for identifying the cause of the defect.

Taking an X-ray topography image requires a process called axis alignment. This axis alignment is a step of determining the diffraction conditions for the sample to be measured, and at this time, the inclination of the plane orientation of the sample is obtained.

In the case of a normal single crystal, as shown in FIG. 12 (left), only two diffraction peaks, Kα1 and Kα2, can be obtained, but in the case of a directly bonded wafer of a two-layer single crystal substrate, FIG. As shown in (right), a total of four diffraction peaks can be obtained from both the upper layer and the lower layer.

At this time, if the crystal axis orientations of the upper and lower wafers are different, for example, if the upper layer is (100) and the lower layer is (111), the diffraction peaks do not overlap, but the crystal axis orientations of the upper layer and the lower layer are different. For example, even when both the upper and lower layers are (100) wafers, the measurement can be performed separately for the upper layer and the lower layer because there is a slight inclination. The XRT displays the intensity of the diffracted X-rays as a contrast with respect to the axisd crystal. If the axis is aligned to either the upper layer or the lower layer, defect information can be obtained only for the diffracted surface that has been centered, so that crystal defect information of the upper layer or the lower layer alone can be obtained.

At this time, whether the obtained peak is a peak from the upper layer or a peak from the lower layer can be determined if the thickness of the wafer is known. Further, even if the thickness of the wafer of each layer is the same, if the upper layer and the lower layer are chips having different patterns, it is possible to determine whether the upper layer or the lower layer is from the XRT image.

When two diffraction peaks are obtained by measuring a two-layer device, the diffraction peak intensity depends on the amount of diffraction from each crystal, so the diffraction peak intensity from the thick layer is high, and the diffraction peak from the thin layer. The strength is low. Therefore, in the case of a two-layer device in which wafers having different thicknesses are directly bonded, the layer to be measured can be easily identified from the height of the diffraction peak intensity.

Even when wafers of almost the same thickness are bonded together, if the device has different patterns, for example, if the upper layer is a memory and the lower layer is a logic, the image obtained by XRT is a memory pattern. It is XRT information from the upper memory portion, and if a logic pattern is seen, it is an XRT image from the lower logic portion.

Even in the case of three layers, four layers, or more, defect evaluation can be performed for each layer in the same manner. If the thickness of each layer is different and the diffraction intensity is different, it is possible to determine which layer the diffraction peak is from. It is possible to determine whether it is an XRT image from a wafer.

In the case of a three-layer device in which three substrates having a thickness of 20, 100, and 500 μm are directly bonded together, as shown in FIG. 13, three diffraction peaks are obtained in the axis alignment process of the XRT. Of these, the highest peak is the peak from the substrate having a thickness of 500 μm, the next highest peak is the peak from the substrate having a thickness of 100 μm, and the smallest peak is the peak from the substrate having a thickness of 20 μm. The XRT image obtained by setting the highest peak as the diffraction condition is an XRT image from a substrate having a thickness of 500 μm, and the image obtained by adjusting the diffraction conditions to the second highest peak and the third highest peak is It is an XRT image from a substrate having a thickness of 100 μm and a substrate having a thickness of 20 μm.

When three substrates having the same thickness but different device patterns are bonded together, diffraction peaks having the same height are obtained as shown in FIG. 14, and it is not possible to distinguish which layer is due to which diffraction peak. .. In that case, as shown in FIG. 14, by matching the diffraction conditions to each of the three peaks, obtaining an XRT image, and comparing the three device patterns with the XRT image, which layer the peak and the XRT image are from? To determine. If the device patterns are different in this way, it is possible to determine the substrate of the diffraction peak obtained from the characteristics of each device pattern.

Further, even when three substrates having the same thickness and device pattern are bonded together, diffraction peaks corresponding to each layer can be obtained as shown in FIG. 15, and each diffraction peak is centered to each layer. XRT image can be obtained. This makes it possible to evaluate defects for each single crystal layer after bonding. In this case, it is not possible to directly determine from the measurement result which layer of the device each XRT image specifically reflects.

That is, in the present invention, even when wafers having exactly the same crystal axis orientation are directly bonded, if the thickness is different, it is possible to specify the number of layers measured from the diffraction peak, and the thickness is also the same. Even so, if the pattern of the formed device is different, it is possible to specify the number of layers to be measured from the difference in the diffraction pattern. Therefore, in the defect evaluation method of the multilayer board of the present invention, it is preferable that the thickness of each layer or the device pattern of the multilayer board is different from the viewpoint of performing more precise defect evaluation.

Hereinafter, the process of the defect evaluation method for the multilayer board of the present invention will be specifically described. FIG. 11 is a flow chart showing an outline of the process of the defect evaluation method for the multilayer board of the present invention.

First, as in step 1 of FIG. 11, a multilayer substrate is prepared, and the diffraction angle of X-rays is obtained for each of the plurality of single crystal layers in the multilayer substrate (step of obtaining the diffraction angle of X-rays).

The measurement of the diffraction angle in step 1 can be performed in the same manner as in the first embodiment. When the thickness of each of the plurality of single crystal layers in the multilayer substrate is different, the thicker layer exhibits higher diffraction peak intensity.

Further, as in the first embodiment, when the diffraction angles of the X-rays of at least two of the plurality of single crystal layers are the same, the diffraction angles of the X-rays are changed by rotating the multilayer substrate to change the diffraction angles of the plurality of single crystals. Different X-ray diffraction angles can be obtained for each layer.

Next, as in step 2 of FIG. 11, each XRT of the plurality of single crystal layers is matched with the diffraction angles of the X-rays of the plurality of single crystal layers obtained in the step of obtaining the diffraction angle of the X-rays. Acquire an image (XRT image acquisition process).

Finally, as in step 3 of FIG. 11, the in-plane generation position of each defect of the plurality of single crystal layers is specified from each XRT image of the plurality of single crystal layers obtained in the XRT image acquisition step (. Defect in-plane occurrence position identification process). At this time, since the device pattern of each single crystal layer is projected on the obtained XRT image, even if the thickness of each single crystal layer is the same, if the device pattern is different, which layer from the shape of this pattern It is possible to identify whether it is.

At this time, by acquiring the section topograph image at the in-plane occurrence position of the specified defect, the position in the depth direction at the in-plane occurrence position of the defect can be specified. By specifying the position of the defect in the depth direction, it is possible to obtain information such as to what depth the defect has reached or where it originated, and it is possible to find out the cause of the defect.

As described above, the defect evaluation method for the multilayer board of the present invention enables highly sensitive measurement of small defects even after bonding a multilayer board in which a plurality of single crystal substrates are directly bonded. It is a defect evaluation method. In particular, it is possible to measure defects for each single crystal layer, and it is also possible to identify in which layer the detected defects are generated.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

(Example 1)
The following SOI substrate, which is obtained by bonding a base wafer and a bond wafer and performing heat treatment, is prepared, and the evaluation method of the present invention is carried out. The presence / absence, position, etc. of slip dislocations due to the above heat treatment are evaluated.
Base wafer: P type, (100), diameter 300 mm, thickness 775 μm
Bond wafer: P type, (100), diameter 300 mm, thickness 30 μm

In this SOI substrate, the bond wafer of (100) is bonded on the base wafer of (100). The notch orientation is also <110>, which is the same orientation. That is, the crystal axis orientations of the base wafer portion and the bond wafer portion are almost the same. However, when actually measured, there was a slight difference in the crystal axis orientation, and it was possible to obtain the difference between the base wafer section and the bond wafer section.

First, in order to obtain the diffraction conditions, the measurement diffraction surface was set to (220), and the X-ray sample incident angle ω was changed in the range of −75 ° to −90 ° for measurement. As a result, the diffraction angle of the base wafer portion was −79.479 °, and the diffraction angle of the bond wafer portion was −79.625 °.

An XRT micron manufactured by Rigaku Co., Ltd. was used for the measurement of the XRT image. Only the bond wafer part is measured by adjusting the measurement conditions to the angle of the diffracted X-rays from the bond wafer part, and similarly, the measurement conditions are adjusted to the angle of the diffracted X-rays from the base wafer part. We also measured only the base wafer part.

FIG. 6 shows an XRT image of the base wafer portion and an XRT image of the bond wafer portion measured after bonding.

As a result of measuring the X-ray diffraction conditions for each of the base wafer part and the bond wafer part, concentric contrast due to BMD can be seen in the base wafer part in the left figure, and the thickness is caused in the bond wafer part in the right figure. Contrast was visible and defects could be investigated independently. As a result, slip dislocations were confirmed in the broken line.

Since the slip dislocations of this sample occur in both the bond wafer part and the base wafer part, it is judged that the occurrence position is at the interface.

Furthermore, taking advantage of the feature of XRT micron that can take a section topograph image in a short time, the section topograph image of only the base wafer part and the section topograph image of only the bond wafer part confirm how far the slip dislocation reaches each wafer. bottom. By measuring the section topograph image according to the X-ray diffraction conditions of the base wafer part and the bond wafer part, it is possible to obtain defect depth information, and it is possible to obtain information on the depth of defects. It is possible to obtain information such as whether it is generated from the department. FIG. 7 shows a section topograph image (cross-sectional view) of the portion where the slip dislocation has occurred. The upper figure shows the base wafer part, and the lower figure shows the bond wafer part. Each left figure shows a cross-sectional view of the part of the broken line part shown in each right figure. The method of acquiring such a section topograph image will be described in detail.

FIG. 8 is an explanatory diagram of the section topograph image. Specify the depth to obtain the cross section. Here, as an example, as shown in the left figure (the same image as the upper right figure of FIG. 7), the depth of about 1/3 from the surface of the base wafer portion (interface with the bond wafer portion) (blank dashed line portion). Specified to display a cross section at the position. The cross-sectional view obtained thereby is the right figure (the same image as the upper left figure of FIG. 7).

As a result of acquiring a plurality of section topograph images and specifying the positions of the slip dislocations in the depth direction in this way, it was confirmed that the slip dislocations were generated from the interface as expected.

In addition to this, the above-mentioned defects (slip dislocations) could not be confirmed in the XRT images of the bond wafer and the base wafer before bonding, which were acquired in advance. It was confirmed that it was formed after bonding.

As described above, the defect evaluation method for the SOI substrate of the present invention is highly sensitive and has high sensitivity even for small defects such as dislocations generated due to the influence of bonding and subsequent heat treatment, and the bond wafer portion and the base wafer portion. Can be measured and evaluated separately.

(Example 2)
According to the present invention, XRT measurement was performed on a wafer in which two wafers having a pattern conforming to a device were directly stacked and bonded together. The thickness of the upper layer is 100 μm, the thickness of the lower layer is 200 μm, and both the upper layer and the lower layer are substrates having a crystal plane orientation (100).

The diffraction condition was (220) transmission, and the axis was set around ω = -80 degrees, which is the diffraction condition. As a result, as shown in FIG. 16, two Kα1 lines, -79.585 degrees and -79.402 degrees, were found. Then, it was determined that the peak at −79.585 ° C with a large intensity ratio was from the thick lower layer of 200 μm, and the peak at −79.402 ° C. with a small intensity ratio was from the thin upper layer.

Next, FIG. 17 shows the results of XRT measurement of the lower layer with the angle set to −79.585 degrees and the upper layer with the angle set to −79.402 degrees. The left figure is an XRT image of the lower layer wafer, and the right figure is an XRT image of the upper layer wafer. In this way, it was possible to measure the defects of the upper and lower wafers separately after bonding. In this case, it was found that the upper substrate had a defect along the scribe line at the position indicated by the arrow in the right figure.

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 having the same effect and effect is the present invention. It is included in the technical scope of the invention.

1 ... SOI substrate, 2 ... Bond wafer part, 3 ... Base wafer part,
4, 104 ... X-ray, 5, 105 ... Diffractive surface, 101 ... Single crystal wafer.

Claims (7)

It is a defect evaluation method for evaluating defects in a multilayer substrate having a plurality of single crystal layers by laminating a plurality of single crystal substrates by XRT.
A step of preparing the multilayer board and obtaining an X-ray diffraction angle for each of the plurality of single crystal layers in the multilayer board.
An XRT image acquisition step of acquiring an XRT image of each of the plurality of single crystal layers according to the diffraction angle of each of the plurality of single crystal layers obtained in the step of obtaining the diffraction angle of the X-rays. When,
From the XRT image of each of the plurality of single crystal layers obtained in the XRT image acquisition step, the defect in-plane generation position specifying step of specifying the in-plane generation position of each of the defects of the plurality of single crystal layers. A defect evaluation method characterized by having. It is a defect evaluation method that evaluates defects in the SOI substrate with bonded wafers and base wafers by XRT.
A process of preparing the SOI substrate and obtaining an X-ray diffraction angle for each of the bond wafer portion and the base wafer portion of the SOI substrate.
An XRT image of the bond wafer portion is acquired according to the X-ray diffraction angle of the bond wafer portion obtained in the step of obtaining the diffraction angle of the X-ray, and the diffraction of the X-ray of the base wafer portion. An XRT image acquisition process for acquiring an XRT image of the base wafer portion according to an angle,
The in-plane generation position of the defect of the bond wafer portion is specified from the XRT image of the bond wafer portion obtained in the XRT image acquisition step, and the base wafer portion is obtained from the XRT image of the base wafer portion. A defect evaluation method for an SOI substrate, which comprises a defect in-plane generation position specifying step for specifying the in-plane generation position of the defect. In the step of obtaining the diffraction angle of the X-ray, when the diffraction angle of the X-ray of the bond wafer portion and the base wafer portion is the same, the diffraction angle of the X-ray is changed by rotating the SOI substrate. The defect evaluation method for an SOI substrate according to claim 2, wherein the X-ray diffraction angles different between the bond wafer portion and the base wafer portion are obtained. In the process of specifying the in-plane occurrence position of the defect, a section topograph image is acquired at the in-plane occurrence position of the specified defect, and the position in the depth direction at the in-plane occurrence position of the defect is specified from the section topograph image. The defect evaluation method for an SOI substrate according to claim 2 or 3, which is characterized by the above-mentioned method. It is a defect evaluation method for evaluating defects in a multilayer substrate having a plurality of single crystal layers by directly bonding a plurality of single crystal substrates having a thickness of 10 μm or more by XRT.
A step of preparing the multilayer board and obtaining an X-ray diffraction angle for each of the plurality of single crystal layers in the multilayer board.
An XRT image acquisition step of acquiring an XRT image of each of the plurality of single crystal layers according to the diffraction angle of the X-rays of the plurality of single crystal layers obtained in the step of obtaining the diffraction angle of the X-rays. When,
From the XRT image of each of the plurality of single crystal layers obtained in the XRT image acquisition step, the defect in-plane generation position specifying step of specifying the in-plane generation position of each of the defects of the plurality of single crystal layers. A defect evaluation method for a multilayer substrate, which comprises. In the step of obtaining the diffraction angle of the X-ray, when the diffraction angle of the X-ray of at least two of the plurality of single crystal layers is the same, the diffraction angle of the X-ray is determined by rotating the multilayer substrate. The defect evaluation method for a multilayer substrate according to claim 5, wherein a different diffraction angle of the X-ray is obtained for each of the plurality of single crystal layers. In the process of specifying the in-plane occurrence position of the defect, a section topograph image is acquired at the in-plane occurrence position of the specified defect, and the position in the depth direction at the in-plane occurrence position of the defect is specified from the section topograph image. The defect evaluation method for a multilayer substrate according to claim 5 or 6, which is characterized by the above-mentioned method.

Images