Evaluation method for epitaxial substrates
The method uses LED light to detect defects and symmetry in epitaxial substrates by imaging reflected and scattered light, addressing the limitations of laser-based evaluation methods and enabling quick, non-destructive assessment of epitaxial layer symmetry.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- SHIN ETSU HANDOTAI CO LTD
- Filing Date
- 2023-02-22
- Publication Date
- 2026-06-18
AI Technical Summary
Existing methods for evaluating the crystallinity of epitaxial layers, particularly heteroepitaxial substrates, face challenges with strong absorption and directionality issues of laser light, making it difficult to detect defects and evaluate symmetry, especially in substrates with high roughness and varying lattice constants.
Irradiate the edge of the epitaxial substrate with LED light to detect reflected and scattered light in bright-field and dark-field imaging, determine defect locations, and evaluate symmetry based on the central angle between defects, using wavelengths that do not transmit through the substrate and with reduced directionality.
Enables rapid, non-destructive evaluation of epitaxial layer symmetry, even in substrates with high surface roughness or heteroepitaxial structures, by detecting defects and determining their angles, thus overcoming limitations of laser-based methods.
Smart Images
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Abstract
Description
Technical Field
[0004] ,
[0001] The present invention relates to a method for evaluating an epitaxial substrate.
Background Art
[0002] Epitaxial growth, which is one of the thin film formation technologies on a semiconductor substrate, is a technology for growing a single crystal thin film with the same plane orientation as the semiconductor substrate. Homoepitaxial growth, which forms a single crystal thin film of the same material as the substrate, and heteroepitaxial growth, which forms a single crystal thin film of a different material from the substrate, are widely known. In particular, heteroepitaxial growth requires high technical skills to grow a single crystal because the lattice constants of the semiconductor substrate and the epitaxial layer are different, and the evaluation of the crystallinity of the epitaxial layer is important. Therefore, rapid evaluation is required in the development of epitaxial growth technology. As a method for evaluating the crystallinity of a substrate, for example, Patent Document 1 discloses a technique for irradiating a laser beam onto the edge (end portion) of a semiconductor wafer and determining slips from the obtained bright field and dark field images. Further, Patent Document 2 discloses a technique for irradiating polarized parallel light onto a substrate and evaluating crystal quality (defects, strain, lattice strain).
Prior Art Documents
Patent Documents
[0003] [[ID=However, in Patent Document 1, since laser light is used as the light source, it has strong directionality and is suitable for detecting minute defects and evaluating short-wavelength components. On the other hand, if the roughness of the long-wavelength components is strong, it becomes impossible to detect reflected and scattered light even when the laser is irradiated onto the measurement surface. In addition, a single-wavelength laser may be absorbed by some materials and may not be usable for measurement. Furthermore, in Patent Document 2, transmitted light is used, and since the absorption characteristics differ depending on the transmitted light wavelength and the material, it is difficult to determine defects, and there is a problem in that it is particularly difficult to evaluate defects with high dislocation density or defect density. [Overview of the Initiative] [Problems that the invention aims to solve]
[0005] This invention has been made in view of the above-mentioned problems, and aims to provide a method for evaluating the symmetry of an epitaxial layer in an epitaxial substrate in a short time and non-destructively. [Means for solving the problem]
[0006] The present invention has been made to solve the above problems, and provides a method for evaluating an epitaxial layer in an epitaxial substrate, characterized by irradiating the edge of the epitaxial substrate with LED light, detecting the reflected light and scattered light in bright-field and dark-field, determining the location of a defect from the detected reflected light and scattered light, and evaluating the symmetry of the epitaxial layer by determining the central angle between the location of the defect and adjacent defects.
[0007] With this method, even when the roughness in the long-wavelength component is strong, reflected and scattered light can be detected by irradiating with LED light. Therefore, defects at the edges of substrates with large surface roughness can be detected and their location determined, and the central angle between adjacent defects at the edges can be determined. This allows for a quick and non-destructive evaluation of the symmetry of the epitaxial layer in an epitaxial substrate.
[0008] Furthermore, the epitaxial substrate can be a heteroepitaxial substrate obtained by heteroepitaxially growing a material different from the semiconductor substrate onto a beveled and mirror-polished semiconductor substrate. This method allows for reliable evaluation of heteroepitaxial substrates, even those with rougher surfaces (larger irregularities) than homoepitaxial substrates.
[0009] Furthermore, it is preferable that the edges of the epitaxial substrate be a region with a width of at least 1 mm, including a chamfered portion, extending from the outermost periphery of the epitaxial substrate. More preferably, the width can be 5 mm from the outermost periphery. This makes it possible to perform evaluations regardless of the semiconductor substrate processing conditions or epitaxial growth conditions.
[0010] Furthermore, it is preferable to use LED light that includes at least two wavelengths that do not transmit through the epitaxial substrate. This allows for the measurement of materials that have absorption in specific wavelength ranges. Furthermore, by using a weakly directional LED, it is possible to evaluate epitaxial substrates that cannot be evaluated with highly directional laser light due to their strong roughness in the long-wavelength component. [Effects of the Invention]
[0011] As described above, the present invention's method for evaluating epitaxial substrates allows for the evaluation of the symmetry of the epitaxial layer in a short time and non-destructively. [Brief explanation of the drawing]
[0012] [Figure 1] This is a flowchart illustrating an example of the present invention. [Figure 2] This is a schematic diagram of the defect map in Example 1 of the present invention. [Modes for carrying out the invention]
[0013] Embodiments of the present invention will be described below, but the present invention is not limited thereto.
[0014] FIG. 1 is a flowchart showing an example of the present invention. Hereinafter, the first step and the second step shown in FIG. 1 will be described in detail. First, prepare an epitaxial substrate to be evaluated.
[0015] (First step) Next, irradiate the end portion of the epitaxial substrate with LED light having a wavelength of, for example, 615 to 645 nm, and detect the reflected light and scattered light in bright field and dark field. The end portion of the epitaxial substrate can be a region having a width of at least 1 mm including a chamfer portion from the outermost periphery of the substrate. More preferably, the width can be 5 mm from the outermost periphery. Further, the LED light can be light including at least two or more wavelengths.
[0016] Preferably, the wavelengths are different by at least 5 nm or more. Also, by making the wavelengths continuous or using emission colors with widely separated wavelength ranges, the influence of absorption can be reduced. The selected wavelength range can include at least two or more wavelengths that do not transmit through the epitaxial substrate. For example, the selected wavelength range can be 420 nm to 700 nm.
[0017] Thereby, even for a material that absorbs a specific wavelength, the reflected light and scattered light can be detected and evaluated. Also, by using LED light with weak directivity, it is possible to evaluate an epitaxial substrate that cannot be evaluated with laser light having strong directivity because the roughness of the long wavelength component is strong.
[0018] (Second step) Determine the position of the defect from the detected reflected light and scattered light. A defect map may be created based on the obtained defect coordinates.
[0019] Next, obtain the central angle with adjacent defects from the position of the detected defect and evaluate the symmetry of the epitaxial layer.
[0020] When the epitaxial growth rate has a surface orientation dependence, the epitaxial layer tends to grow in the direction where the growth rate is the highest. Therefore, the defect detected at the end of the epitaxial substrate is an epitaxial layer that has grown in an equivalent direction that is not parallel to the growth direction of the epitaxial layer. By detecting this, it is possible to evaluate the direction in which the growth rate of epitaxial growth is maximum, the rotational symmetry of the crystal grains (domains) present on the outermost surface of the epitaxial substrate, and the rotational symmetry with the central axis of the epitaxial substrate as the axis of symmetry.
[0021] In this evaluation, the end (edge part) of the epitaxial substrate is evaluated. However, the fact that it is growing on the edge part means that it is rotationally symmetric even when viewed microscopically, and it is possible to推测 that domains exist during epitaxial growth, and it is also possible to evaluate the quality of the epitaxial layer non-destructively. If the rotational symmetry is poor even when the epitaxial growth rate has a surface orientation dependence, it suggests that growth is not occurring in a specific direction, and there is a possibility that the epitaxial layer is not a single crystal.
[0022] As a result, it is possible to evaluate the symmetry of the epitaxial layer on the epitaxial substrate in a short time and non-destructively.
[0023] As described above, according to the method for evaluating an epitaxial substrate in the embodiment of the present invention, LED light is irradiated on the end of the epitaxial substrate, the reflected light and scattered light are detected in bright field and dark field, the position of the defect is determined from the detected reflected light and scattered light, and the central angle with an adjacent defect is obtained from the position of the defect to evaluate the symmetry of the epitaxial layer.
[0024] With such a method, even when the roughness of the long wavelength component is strong by irradiating LED light, the reflected light and scattered light can be detected. Therefore, the defect at the end of a substrate with a large surface roughness can be detected and the position of the defect can be determined. Since the central angle with an adjacent defect at the end is known, the symmetry of the epitaxial layer on the epitaxial substrate can be evaluated in a short time and non-destructively.
[0025] Furthermore, the epitaxial substrate can also be a heteroepitaxial substrate, which is created by heteroepitaxially growing a material different from the semiconductor substrate onto a beveled and mirror-polished semiconductor substrate. With this method, even heteroepitaxial substrates with rougher surfaces (larger irregularities) than homoepitaxial substrates can be reliably evaluated.
[0026] Furthermore, the edges of the epitaxial substrate are defined as a region with a width of at least 1 mm, including the chamfered portion, extending from the outermost edge of the epitaxial substrate. This allows for evaluation regardless of the semiconductor substrate processing conditions or epitaxial growth conditions. More preferably, the width from the outermost edge can be 5 mm.
[0027] Furthermore, the LED light used contains at least two wavelengths that do not transmit through the epitaxial substrate. This allows for measurement even of materials that have absorption in specific wavelength ranges. Additionally, by using an LED with weak directionality, it is possible to evaluate epitaxial substrates that cannot be evaluated with highly directional laser light due to strong roughness in the long-wavelength component.
[0028] It is preferable to select two or more wavelengths within the range of 420 nm to 700 nm. Furthermore, it is preferable that they differ by at least 5 nm. In particular, a range of 615 to 645 nm is more preferable. [Examples]
[0029] The present invention will be further described below based on examples, but these examples are illustrative and should not be interpreted as limiting.
[0030] (Example 1) First, a silicon single crystal substrate with a (111) plane surface was prepared. The surface of this substrate was polished to a mirror finish.
[0031] Next, 3C-SiC was grown heteroepitaxially on a silicon single crystal substrate. For growth, a vacuum CVD apparatus was used with trimethylsilane as the source gas, and the growth was carried out at 1080°C, 5 Torr (666.61 Pa), and for 30 minutes.
[0032] Next, LED light with a wavelength of 615-645 nm was shone onto the edge of the epitaxial substrate, and the reflected and scattered light was detected using bright-field and dark-field imaging.
[0033] Next, the location of the defects was determined from the detected reflected and scattered light, and the defect map shown in Figure 2 was created.
[0034] Next, from the defect map in Figure 2, it was found that defects were detected at 60-degree intervals in 6 directions at the edges, indicating that the epitaxial substrate is 6-fold symmetrical.
[0035] Next, the surface of the epitaxial substrate was observed using a scanning electron microscope, and 3C-SiC was observed at defect locations with 6-fold symmetry.
[0036] Based on the above, it was confirmed that the epitaxial substrate is 6-fold symmetrical, and the fastest growth direction of the epitaxial layer is <111> It was confirmed to be the correct direction.
[0037] (Comparative Example 1) A laser with a wavelength of 405 nm was irradiated onto the edge of the epitaxial substrate, but the roughness of the long-wavelength component was so strong that defects could not be detected in bright-field or dark-field imaging.
[0038] As described above, Embodiment 1 of the present invention demonstrates that by irradiating the edge of an epitaxial substrate with LED light, detecting the reflected and scattered light in bright-field and dark-field imaging, determining the location of defects from the detected reflected and scattered light, and evaluating the symmetry of the epitaxial layer from the angle at which the defects are located, it is possible to detect defects at the edge of a substrate with high surface roughness, determine the location of the defects, and determine the angle at which the defects at the edge are located, thereby enabling the evaluation of the symmetry of the epitaxial layer in an epitaxial substrate in a short time and non-destructively.
[0039] The present invention encompasses the following aspects. [1]: A method for evaluating the epitaxial layer in an epitaxial substrate, The edge of the epitaxial substrate is illuminated with LED light. Reflected and scattered light are detected in bright-field and dark-field imaging. The location of the defect is determined from the detected reflected light and scattered light. A method for evaluating an epitaxial substrate, characterized by determining the central angle between adjacent defects from the location of the aforementioned defects and evaluating the symmetry of the epitaxial layer. [2]: The method for evaluating an epitaxial substrate according to [1] above, characterized in that the epitaxial substrate is a heteroepitaxial substrate obtained by heteroepitaxially growing a material different from the semiconductor substrate on a beveled and mirror-polished semiconductor substrate. [3]: The method for evaluating an epitaxial substrate according to [1] or [2] above, characterized in that the edge of the epitaxial substrate is a region with a width of at least 1 mm, including a chamfered portion, extending from the outermost periphery of the epitaxial substrate. [4]: The method for evaluating an epitaxial substrate according to any one of [1] to [3] above, characterized in that the LED light includes at least two wavelengths that do not transmit through the epitaxial substrate.
[0040] It should be noted that the present invention is not limited to the above embodiments. The above embodiments are illustrative examples, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and achieves similar effects is included within the technical scope of the present invention.
Claims
1. A method for evaluating the epitaxial layer in an epitaxial substrate, The edge of the epitaxial substrate is illuminated with LED light. Reflected and scattered light are detected in bright-field and dark-field imaging. The location of the defect is determined from the detected reflected light and scattered light. The symmetry of the epitaxial layer is evaluated by determining the central angle between adjacent defects from the location of the aforementioned defects. A method for evaluating an epitaxial substrate, characterized in that the epitaxial substrate is a heteroepitaxial substrate obtained by heteroepitaxially growing a material different from the semiconductor substrate on a beveled and mirror-polished semiconductor substrate.
2. The method for evaluating an epitaxial substrate according to claim 1, characterized in that the edge of the epitaxial substrate is a region with a width of at least 1 mm, including a chamfered portion, extending from the outermost periphery of the epitaxial substrate.
3. The method for evaluating an epitaxial substrate according to claim 1 or 2, characterized in that the LED light includes at least two wavelengths that do not transmit through the epitaxial substrate.