Observation device, detection device, and observation method
By holding the substrate in a bent state to enhance local gradient changes, differential interference optics effectively visualize and detect cracks on substrate surfaces.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- TORAY ENG CO LTD
- Filing Date
- 2023-02-14
- Publication Date
- 2026-06-24
AI Technical Summary
Differential interference microscopes struggle to clearly visualize cracks on substrate surfaces due to subtle gradient changes that result in minimal contrast between light and dark areas, making cracks difficult to detect.
The substrate is held in a bent state using a holding part that supports the outer periphery but not the center, allowing for local gradient changes near cracks, enhancing contrast through differential interference optics.
This configuration facilitates easier visualization of cracks by generating a clear contrast between light and dark areas near cracks, improving crack detection accuracy.
Smart Images
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Abstract
Description
Technical Field
[0001] The present disclosure relates to an observation device, a detection device, and an observation method.
Background Art
[0002] For example, as shown in Patent Document 1, a method of observing the surface of a substrate using a differential interference microscope is known.
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0004] A differential interference microscope projects the surface of a substrate to obtain an image. The differential interference microscope is provided with a differential interference prism. In the differential interference microscope, the light emitted from the light source passes through the differential interference prism and is converted into two polarized lights orthogonal to each other, and a minute horizontal distance (shear) is generated between their optical paths. The two polarized lights are incident on and reflected from two different points on the surface of the substrate. The two reflected polarized lights pass through the differential interference prism again and merge into the same optical path.
[0005] When there is a gradient (height difference) between the two points where the two polarized lights are incident, the phases of the two polarized lights are shifted from each other, and the two polarized lights interfere when they merge. The interference intensity of the two polarized lights differs depending on the magnitude of the gradient between the two points where they are incident. Therefore, when there is a distribution of gradients on the surface of the substrate, contrast between light and dark occurs and irregularities are emphasized. Thus, in the differential interference microscope, minute steps on the surface of the substrate that cannot be visually recognized by a normal optical system (such as coaxial epi-illumination) are visualized.
[0006] Incidentally, even when the surface irregularities of the substrate were enhanced using a differential interference microscope, it was sometimes difficult to clearly visualize cracks formed on the substrate surface.
[0007] This disclosure has been made in view of the above, and its purpose is to make it easier to visualize cracks formed on the surface of a substrate when observing the substrate surface using differential interference optics. [Means for solving the problem]
[0008] The observation apparatus according to this disclosure is an observation apparatus for observing the surface of a substrate, comprising a holding part for holding the substrate, and a differential interference microscope for obtaining an image by projecting the surface of the substrate held by the holding part, wherein the holding part holds the substrate in a bent state.
[0009] In areas where cracks form on the surface of a substrate, the gradient usually changes subtly. However, when the substrate is not flexed, such as by holding it completely still, the change in gradient due to cracks on the substrate surface is too small. As a result, even when observing the substrate surface using a differential interference microscope, it is difficult to detect the cracks because there is little contrast between light and dark areas near them.
[0010] Therefore, the holding part holds the substrate in a bent state. By bending the substrate in this way, a local gradient change originating from the crack occurs on the surface of the substrate. As a result, when the surface of the substrate is observed using a differential interference microscope, a contrast of light and dark is more likely to occur near the crack, making the crack easier to see.
[0011] In summary, using differential interference optics to observe the surface of a substrate makes it easier to visualize cracks formed on the substrate surface.
[0012] In one embodiment, the holding portion holds the outer periphery of the substrate but does not hold the central portion of the substrate.
[0013] With this configuration, the holding part does not touch the center of the substrate, so elements and other components located in the center of the substrate can be protected.
[0014] In one embodiment, the holding portion is a table that supports the substrate from below, and a hole is made in the portion of the table corresponding to the central part of the substrate.
[0015] With this configuration, simply placing the circuit board on the table causes the central part of the board to sag (sink) downwards towards the hole in the table due to gravity, making it easy to handle.
[0016] The detection device according to this disclosure detects cracks formed on the surface of the substrate based on the image of the surface of the substrate obtained by the observation device.
[0017] With this configuration, as described above, a contrast between light and dark areas is easily generated near cracks on the surface of the substrate, making it easier for the detection device to detect cracks based on the image of the substrate surface.
[0018] The observation method relating to this disclosure is an observation method for observing the surface of a substrate, wherein the substrate is held in a bent state, and an image is obtained by projecting the surface of the substrate using differential interference optics. [Effects of the Invention]
[0019] According to this disclosure, when observing the surface of a substrate using differential interference optics, cracks formed on the surface of the substrate become easier to visualize. [Brief explanation of the drawing]
[0020] [Figure 1] Figure 1 shows a front view of the observation device according to this embodiment. [Figure 2] Figure 2 shows the table in a plan view. [Figure 3]FIG. 3 shows the change in gradient between different regions on the surface of a substrate without cracks formed thereon. [Figure 4] FIG. 4 shows the change in gradient between different regions on the surface of a substrate with cracks formed thereon. [Figure 5] FIG. 5 shows an image obtained by projecting the surface of a substrate in a bent state onto which no crack is formed, using a differential interference microscope. [Figure 6] FIG. 6 shows an image obtained by projecting the surface of a substrate in a bent state onto which a crack is formed, using a differential interference microscope. [Figure 7] FIG. 7 shows a front view of an observation apparatus according to the prior art. [Figure 8] FIG. 8 shows the change in gradient between different regions on the surface of a substrate in the prior art. [Figure 9] FIG. 9 shows an image obtained by projecting the surface of a substrate using a differential interference microscope in the prior art.
DETAILED DESCRIPTION OF THE INVENTION
[0021] Hereinafter, an embodiment of the present disclosure will be described in detail based on the drawings. The following description of the preferred embodiments is merely exemplary in nature and is not intended to limit the present disclosure, its applications, or its uses in any way.
[0022] (Observation Apparatus) FIG. 1 shows a front view of an observation apparatus 1. The observation apparatus 1 observes the surface W1 of a substrate W. The substrate W is, for example, a semiconductor substrate. The substrate W is plate-shaped. The substrate W is circular in plan view. Cracks X are formed on the surface W1 of the substrate W. The cracks X are, for example, a general term for injuries, cracks, fissures, cracks, etc. The observation apparatus 1 includes a differential interference microscope 10 and a table 20 as a holding unit.
[0023] (Differential Interference Microscope) The differential interference microscope 10 projects an image G onto the surface W1 of the substrate W. The differential interference microscope 10 is equipped with a differential interference prism 11. In the differential interference microscope 10, light L emitted from a light source (not shown) passes through the differential interference prism 11 and is converted into two mutually orthogonal polarized light La and Lb, and a small horizontal distance (shear) is generated between their optical paths. The two polarized light La and Lb are incident on two different points Pa and Pb on the surface W1 of the substrate W and are reflected. The two reflected polarized light La and Lb pass through the differential interference prism 11 again and merge into the same optical path, reaching a photodetector (not shown).
[0024] When there is a gradient (difference in height) δ between two points Pa and Pb into which two polarized light beams La and Lb are incident, the phases of the two polarized light beams La and Lb are shifted from each other, and the two polarized light beams interfere when they meet. The interference intensity of the two polarized light beams La and Lb differs depending on the magnitude of the gradient δ between the two points Pa and Pb into which they are incident. Therefore, if there is a gradient δ distribution on the surface W1 of the substrate W, a contrast of light and dark is generated, and the unevenness is emphasized. In this way, the differential interference microscope 10 visualizes minute steps on the surface W1 of the substrate W that cannot be seen with a normal optical system (e.g., coaxial incident illumination).
[0025] (Problems with conventional technology) Figure 7 shows a front view of a prior art observation device 1'. In the prior art observation device 1', the substrate W is held as a whole by being fully supported from below by a table 20' without holes. The substrate W, fully supported by the table 20', does not flex.
[0026] Figure 8 shows the change in gradient between two different regions R1 and R2 on the surface W1 of the substrate W in the prior art. Figure 8 shows section VIII of Figure 7. A crack X is formed on the surface W1 of the substrate W.
[0027] In the first region R1 on the left side of Figure 8, the first gradient (first height difference) δ1 between two points Pa and Pb where two polarized light beams La and Lb are incident is zero. Similarly, in the second region R2 on the right side of Figure 8, the second gradient (second height difference) δ2 between two points Pa and Pb where two polarized light beams La and Lb are incident is zero. The first region R1 and the second region R2 are separated from each other on the surface W1 of the substrate W. The first gradient δ1 in the first region R1 and the second gradient δ2 in the second region R2 are equal to each other (δ1 = δ2 = 0).
[0028] Figure 9 shows an image G' obtained by projecting the surface W1 of the substrate W using a differential interference microscope 10 in the conventional technique. Since the substrate W, which is fully supported by the table 20', does not flex, the gradient is zero in all regions of the surface W1 of the substrate W. Therefore, the image G' obtained by projecting the surface W1 of the substrate W using a differential interference microscope 10 is completely dark.
[0029] When a crack X is formed on the surface W1 of substrate W, the gradient changes subtly only in the area where the crack X is formed on the surface W1 of substrate W. However, the change in gradient due to the crack X on the surface W1 of substrate W is too small, so as shown in Figure 9, in image G', the crack X is only slightly brighter than the surrounding area and is almost invisible.
[0030] Thus, even when the surface irregularities of the substrate W1 were emphasized using the differential interference microscope 10, it was sometimes difficult to clearly visualize the cracks X formed on the surface W1 of the substrate W. In particular, it was difficult to visualize when the cracks X were thin.
[0031] In the observation apparatus 1 according to this embodiment, the following improvements have been made to make it easier to visualize cracks X formed on the surface W1 of the substrate W when observing the surface W1 of the substrate W using differential interference optics (differential interference microscope 10).
[0032] (table) Figure 2 shows a plan view of the table 20 from above. The table 20 is circular in plan view. The table 20 holds the substrate W by supporting it from below. A hole 22 is made in the central part 21 of the table 20. In other words, the table 20 is hollow.
[0033] The central portion 21 (hole 22) of the table 20 corresponds to the central portion W2 of the substrate W. That is, the central portion 21 (hole 22) of the table 20 is covered from above by the central portion W2 of the substrate W. The outer peripheral portion 23 of the table 20 corresponds to the outer peripheral portion W3 of the substrate W. That is, the outer peripheral portion 23 of the table 20 supports the outer peripheral portion W3 of the substrate W from below. The outer peripheral portion 23 of the table 20 and the outer peripheral portion W3 of the substrate W may be fixed to each other by fasteners such as adhesive tape or chucks.
[0034] Thus, the table 20 holds the outer periphery W3 of the substrate W at its outer periphery portion 23, but does not hold the central portion W2 of the substrate W at its central portion 21 (hole 22). Therefore, as shown in Figure 1, the central portion W2 of the substrate W bends (sinks) downward toward the hole 22 of the table 20 due to gravity. In other words, the table 20 holds the substrate W in a bent state. When the substrate W is in a bent state, stress is generated in the substrate W.
[0035] The differential interference microscope 10 then projects the surface W1 of the substrate W, which is held on the table 20 in a bent state, to obtain an image G. Note that in Figure 1, the amount of bending of the substrate W is depicted as larger than it actually is for clarity.
[0036] (Effect of circuit board deflection) The effect of substrate W deflection will be explained. Figure 3 shows the change in gradient between two different regions R1 and R2 on the surface W1 of substrate W where crack X is not formed. Figure 3 shows part A of Figure 1.
[0037] As shown in Figure 3, if no crack X is formed on the surface W1 of the substrate W, the first gradient (first height difference) δ1 between two points Pa and Pb where two polarized La and Lb are incident in the first region R1, and the second gradient (second height difference) δ2 between two points Pa and Pb where two polarized La and Lb are incident in the second region R2, are approximately equal to each other (δ1=δ2) and not zero (≠0).
[0038] Figure 4 shows the change in gradient between two different regions R1 and R2 on the surface W1 of the substrate W in which crack X is formed. Figure 4 shows part A of Figure 1.
[0039] As shown in Figure 4, a crack X is formed between a first region R1 and a second region R2 on the surface W1 of the substrate W. Near the crack X formed on the surface W1 of the substrate W (between the first region R1 and the second region R2), a local gradient change occurs starting from the crack X.
[0040] Therefore, when a crack X is formed between a first region R1 and a second region R2 on the surface W1 of the substrate W, the first gradient δ1 between two points Pa and Pb where two polarized La and Lb rays are incident in the first region R1 and the second gradient δ2 between two points Pa and Pb where two polarized La and Lb rays are incident in the second region R2 are different from each other (δ1 ≠ δ2).
[0041] Figure 5 shows an image G obtained by projecting the surface W1 of the substrate W using a differential interference microscope 10 when no cracks X are formed on the surface W1 of the substrate W in a bent state. Figure 5 shows the entire surface W1 of the substrate W.
[0042] When no cracks X are formed on the surface W1 of a bent substrate W, the gradient on the surface W1 of the substrate W changes smoothly, becoming larger at the outer periphery W3 and smaller at the center W2. Therefore, when no cracks X are formed on the surface W1 of a bent substrate W, the background of the image G obtained by projecting the surface W1 of the substrate W with the differential interference microscope 10 has a smooth light-dark gradient, becoming brighter at the outer periphery W3 and darker at the center W2.
[0043] Figure 6 shows an image G obtained by projecting the surface W1 of the substrate W using a differential interference microscope 10 when a crack X is formed on the surface W1 of the substrate W in a bent state. In Figure 6, as in Figure 5, the entire surface W1 of the substrate W is shown.
[0044] When a crack X is formed on the surface W1 of a bent substrate W, the gradient on the surface W1 of the substrate W changes locally near the crack X, starting from the crack X. Therefore, when a crack X is formed on the surface W1 of a bent substrate W, the image G obtained by projecting the surface W1 of the substrate W with a differential interference microscope 10 will show a contrast of light and dark (luminance) near the crack X (see part B in Figure 6).
[0045] (Detection device) Observation device 1 is connected to detection device 2 (see Figure 1). Detection device 2 detects cracks X formed on the surface W1 of the substrate W based on the image G of the surface W1 of the substrate W obtained by observation device 1. Detection device 2 includes a controller consisting of a microcontroller and a program, etc.
[0046] (Effects and Benefits) In areas where a crack X is formed on the surface W1 of substrate W, the gradient usually changes subtly. However, when the substrate W is not bent, such as by holding it completely (see Figures 7-9), the change in gradient due to the crack X on the surface W1 of substrate W is too small. Therefore, even when observing the surface W1 of substrate W using a differential interference microscope 10, it is difficult to see the crack X because a contrast between light and dark is not easily generated near the crack X.
[0047] Therefore, as shown in Figures 1 and 2, the table (holding part) 20 holds the substrate W in a bent state. By bending the substrate W in this way, as shown in Figure 4, a local gradient change originating from the crack X occurs on the surface W1 of the substrate W. As a result, when the surface W1 of the substrate W is observed using the differential interference microscope 10, as shown in Figure 6, a contrast between light and dark areas is more likely to occur near the crack X, making the crack X easier to see.
[0048] In summary, when observing the surface W1 of the substrate W using differential interference optics (differential interference microscope 10), it becomes easier to visualize cracks X formed on the surface W1 of the substrate W.
[0049] The table (holding portion) 20 holds the outer periphery W3 of the substrate W with its outer periphery portion 23, while not holding the central portion W2 of the substrate W with its central portion 21 (hole 22). As a result, the table 20 does not touch the central portion W2 of the substrate W, thus protecting elements (for example, circuit patterns provided on a semiconductor substrate) located in the central portion W2 of the substrate W.
[0050] By simply placing the substrate W on a table 20 with a hole 22 in its central part 21, the central part W2 of the substrate W will bend (sink) downward toward the hole 22 in the table 20 due to gravity, making it easy to handle.
[0051] As described above, a contrast between light and dark areas is easily generated near the crack X on the surface W1 of the substrate W, making it easier for the detection device 2 to detect the crack X based on the image G of the surface W1 of the substrate W.
[0052] (Other embodiments) Although this disclosure has been described above with reference to preferred embodiments, this description is not limiting, and various modifications are, of course, possible.
[0053] A projection may be provided on the central portion 21 of the table (holding portion) 20, which does not have a hole 22, and the central portion W2 of the substrate W may be placed on the projection, thereby supporting the central portion W2 of the substrate W from below. In other words, the table (holding portion) 20 may hold the central portion W2 of the substrate W, but not hold the outer periphery portion W3 of the substrate W. In this case, the outer periphery portion W3 of the substrate W will bend downward due to gravity.
[0054] The holding portion 20 is not limited to a table. The holding portion 20 may be, for example, a chuck that grips the outer periphery W3 of the substrate W. The holding portion 20 may also cantilever support one end of the substrate W.
[0055] In order to properly flex the substrate W, it is preferable that the holding portion 20 deliberately refrain from holding at least a portion of the substrate W. The substrate W may bend due to external forces other than gravity. For example, the substrate W may bend due to an upward external force (by being pulled upward).
[0056] The substrate W is not limited to a semiconductor substrate, but may also be a glass substrate, a metal substrate, a resin substrate, etc. The substrate W is not limited to a circular shape, but may also be a polygonal shape, for example.
[0057] The observation method according to this disclosure is an observation method for observing the surface W1 of a substrate W, wherein an image G is obtained by projecting the surface W1 of the substrate W using differential interference optics while holding the substrate W in a bent state. In this observation method, the substrate W may be held in a bent state manually. [Industrial applicability]
[0058] This disclosure is extremely useful and highly industrially applicable, as it can be applied to observation devices, detection devices, and observation methods. [Explanation of symbols]
[0059] W board W1 surface W2 Central Section W3 Outer perimeter X Crack G statue L light La polarization Lb Polarization δ gradient δ1 First gradient δ2 Second gradient 1. Observation device 2. Detection device 10 Differential Interference Microscope 11 Differential Interference Prism 20 Table (holding part) 21 Central part 22 holes 23 Outer area
Claims
1. A detection device for detecting cracks formed on the surface of a substrate based on an image of the substrate surface, A holding portion for holding the substrate, The system includes a differential interference microscope that projects the surface of the substrate held in the holding part to obtain the image, The holding part holds the substrate in a state where it is bent in the thickness direction, The detection device detects the crack based on the brightness-dark contrast in the image, which corresponds to a local gradient change that occurs on the surface starting from the crack due to the substrate bending in the thickness direction by the holding part.
2. A detection device according to claim 1, The holding portion is a detection device that holds the outer periphery of the substrate but does not hold the central part of the substrate.
3. A detection device according to claim 2, The holding part is a table that supports the substrate from below. A detection device having a hole drilled in the portion of the substrate in the table that corresponds to the central part.
4. A detection method for detecting cracks formed on the surface of a substrate based on an image of the substrate surface, While holding the substrate in a state of bending in the thickness direction, the surface of the substrate is projected by differential interference optics to obtain the image. A detection method for detecting a crack based on the brightness-dark contrast in an image that corresponds to a local gradient change that occurs on the surface starting from the crack due to the substrate bending in the thickness direction.