A total internal reflection wafer detection device

Abstract

The present invention discloses a total internal reflection wafer inspection device, comprising a camera, a laser, a reflective prism, a circular aperture, a support column, and a refractive cone. Upon entering the reflective prism, the laser changes its direction to be vertically upward. A circular aperture is provided on the vertically upward laser light path, blocking the center portion of the laser to form a ring-shaped laser beam. The ring-shaped laser beam is refracted by the refractive cone into the interior of the wafer to be inspected, where it undergoes total reflection. When it encounters internal defects or surface dirt on the wafer, the dirt is scattered out of the wafer and detected by the camera. The support column is located between the refractive cone and the circular aperture, and the wafer to be inspected is placed on the refractive cone. The camera is located above the wafer to be inspected. The refractive cone has a cone angle #imgabs0#, which ensures that the reflection angle #imgabs1# of the refracted light entering the wafer to be inspected is greater than the total reflection angle. Advantageously, the device of the present invention allows laser light to enter the wafer and undergo total reflection detection from the center to the outer ring of the wafer, achieving higher efficiency and detection accuracy than methods that detect from the edge of the wafer.

Description

Technical Field

[0001] The present invention relates to the field of wafer detection, and in particular to a total internal reflection wafer detection device. Background Art

[0002] Wafers in the integrated circuit manufacturing process are the foundation of chips. Internal and surface defects, as well as surface contamination, can easily lead to low chip yields and poor performance. Common non-destructive wafer defect detection methods include optical coherence tomography, confocal laser scanning microscopy, and total internal reflection microscopy. Optical coherence tomography exploits the weak coherence of the light source and can only detect samples that match the optical path length of the coherence tomography device. Confocal laser scanning microscopy offers high resolution, but the defect detection process requires point-by-point scanning and sequential imaging, resulting in low detection efficiency and time consumption, making it unsuitable for defect detection of large-aperture optical components. Furthermore, in recent years, defect or damage detection has focused on sub-surface detection, with little research focusing on in-vivo defect detection.

[0003] In the 1980s, the application of total internal reflection microscopy to detect surface defects in optical components was first proposed. It was subsequently pointed out that when using total internal reflection microscopy to inspect optical components, surface and subsurface defects can be distinguished by changing the polarization state of the incident light.

[0004] Traditional total internal reflection (TIR) inspection methods offer advantages such as simple structure, low cost, and strong adaptability. However, these methods are fixed-point inspection techniques for the surfaces or subsurfaces of small-aperture optical components and are not suitable for internal defect detection within large-aperture optical components. To address this issue, a method based on Snell's law and the angle of incidence determines the total internal reflection path of the incident light beam, and based on the different imaging positions of defects at different depths, three-dimensional positional information for internal defects within large-aperture optical components is obtained. However, this method uses a lens positioned at the edge of the sample, making it difficult to cover the entire circular wafer. Furthermore, due to processes such as glue spinning, the most susceptible areas to contamination are at the wafer edge, making it difficult to detect with these methods. Summary of the Invention

[0005] The technical problem to be solved by the present invention is: how to optimize the total internal reflection detection technology so that a larger area of circular wafer can be detected and defects can be detected.

[0006] The purpose of the present invention is to propose a total internal reflection wafer detection device, which uses a refraction cone to refract the ring laser from bottom to top, enters the interior of the wafer, and reflects outward inside the wafer through total reflection. If it encounters internal defects of the wafer or surface dirt, it will be scattered and detected by the camera.

[0007] The technical solutions adopted are as follows:

[0008] A total internal reflection wafer inspection device includes a camera, a laser, a reflecting prism, a circular aperture, a support column and a refractive cone. The laser enters the reflecting prism and changes its direction to be vertically upward. A circular aperture is set on the vertically upward laser light path to block the center part of the laser to form a ring laser. The ring laser is refracted by the refractive cone and enters the interior of the wafer to be tested. It is totally reflected inside the wafer to be tested. When it encounters internal defects of the wafer or surface dirt, it is scattered out of the wafer and detected by the camera. The support column is located between the refractive cone and the circular aperture. The wafer to be tested is placed on the refractive cone; the camera is set above the wafer to be tested; the cone angle of the refractive cone is 1 / 4. The reflection angle that causes the refraction to enter the wafer to be tested is greater than the total reflection angle;

[0009] The cone angle of the refractive cone The calculation formula is as follows:

[0010] (9)

[0011] in, is the reflection angle of the wafer to be measured, is the refractive index of air, is the refractive index of the refractive cone, is the refractive index of the wafer to be tested.

[0012] In a further preferred embodiment of the technical solution of the present invention, the laser is visible light, near infrared light or mid-infrared laser.

[0013] In a further preferred embodiment of the technical solution of the present invention, the laser is a Gaussian or flat-top beam. A flat-top beam or a Gaussian beam can obtain a higher power density, which can result in smaller loss and better detection accuracy in detecting wafer defects.

[0014] In a further preferred embodiment of the technical solution of the present invention, the sensitive wavelength of the camera is the same as the wavelength of the laser.

[0015] In a further embodiment of the technical solution of the present invention, the circular aperture is made of a transparent material, and the central blocking part of the circular aperture is made of an opaque material. The central blocking part of the circular aperture is made of an opaque material to reflect or absorb the central small-angle light and retain the light that may form total reflection.

[0016] In a further preferred embodiment of the technical solution of the present invention, the circular aperture is made of glass or resin, and the central shielding portion of the circular aperture is made of metal or plastic.

[0017] In a further preferred embodiment of the technical solution of the present invention, the diameter of the support column is less than or equal to the diameter of the central shielding portion.

[0018] In a further preferred embodiment of the technical solution of the present invention, the size of the laser covers the refraction cone, and the light emitted by the laser can be incident on the wafer at a larger angle to generate total reflection light.

[0019] In a further preferred embodiment of the technical solution of the present invention, the outer diameter of the ring laser is larger than the outer diameter of the refractive cone.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] A total internal reflection wafer detection device of the present invention enters the wafer through laser and performs total reflection detection from the center to the outer circle of the wafer. This method can reduce the loss caused by diffuse reflection of dirt in the middle area through central diffusion, and at the same time maintain a higher power density at the edge of the wafer, thereby achieving higher efficiency and higher detection accuracy than the method of detecting from the edge of the wafer. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the structure of the total internal reflection wafer detection device of the present invention (arrows indicate light paths);

[0023] Figure 2 Schematic diagram of the geometric structure of the refraction cone in the total internal reflection wafer inspection device of the present invention (arrows indicate light paths);

[0024] Figure 3 The cone angle in the total internal reflection wafer detection device of the present invention is and relationship diagram;

[0025] Figure 4 is the image captured by the camera of the embodiment, in mm;

[0026] Among them: 1-camera, 2-laser, 3-reflecting prism, 4-circular aperture, 5-support column, 6-refractive cone, 7-wafer, 8-ring laser, 9-defect, 10-dirt. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is described in detail below, but the protection scope of the present invention is not limited to the embodiments.

[0028] In order to make the content of the present invention more clear and easy to understand, the following Figure 1 -Attached Figure 4 The specific implementation methods are further described.

[0029] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0030] like Figure 1 and Figure 2 As shown, this embodiment is a total internal reflection wafer detection device, including a camera 1, a laser 2, a reflecting prism 3, a circular aperture 4, a support column 5 and a refractive cone 6. The laser 2 enters the reflecting prism 3 and changes its direction to vertically upward. A circular aperture 4 is set on the vertically upward laser light path to block the central part of the laser to form a ring laser 8. The ring laser 8 is refracted by the refractive cone 6 into the interior of the wafer 7 to be tested, and is totally reflected inside the wafer 7 to be tested. When encountering internal defects 9 of the wafer and surface dirt 10, they are scattered out of the wafer and detected by the camera 1. The support column 5 is located between the refractive cone 6 and the circular aperture 4, and the wafer 7 to be tested is placed on the refractive cone 6; the camera 1 is set above the wafer 7 to be tested; the cone angle of the refractive cone 6 The reflection angle of the refracted light into the wafer 7 to be tested is is greater than the total reflection angle.

[0031] In this embodiment, Laser 2 is a visible light, near-infrared, or mid-infrared laser. Different wavelengths are selected for different wafer materials. For example, for silicon wafers, a 2μm-6μm mid-infrared laser is selected, as the wafer has a lower absorption rate. For lithium niobate wafers, a 0.4μm-0.7μm visible light is selected, which not only has low transmittance but also provides high camera detection sensitivity and resolution.

[0032] At the same time, camera 1 is coupled with laser 2, and the sensitive wavelength of camera 1 is the same as that of the laser. For example, a 0.532nm green laser is selected, and a silicon-based CCD or CMOS is used as the camera's imaging element; a mercury cadmium telluride (MCT) or indium antimonide (InSb) CCD or CMOS is selected as the camera's imaging element.

[0033] In this embodiment, laser light 2 is a Gaussian or flat-top beam that changes direction vertically upward after reflection from reflective prism 3. The size of laser light 2 covers the refractive cone 6. After passing through reflective prism 3, the center of laser light 2 is blocked by a circular aperture 4, forming a ring shape. The blocked portion is the same size as support column 5. The circular aperture 4 is made of transparent materials such as glass and resin, while the central blocking portion is made of opaque materials such as metal and plastic.

[0034] Specifically in this embodiment, the circular aperture 4 is formed by coating a metal layer on glass to form a central shielding portion. The central shielding circular aperture is made of an opaque material to reflect or absorb the central small-angle light and retain the light that may form total reflection.

[0035] In this embodiment, the support column 5 is a structural component that connects the refractive cone 6 and the circular aperture 4. At the same time, the support column 5 is directly glued and fixed to the bottom of the refractive cone 6; the wafer 7 is placed directly between the refractive cone 6; the circular aperture 4 is placed on the top of the support column 5, and the position does not need to be fixed; the circular aperture 4 is coaxial with the reflecting prism 3.

[0036] In this embodiment, the cone angle of the refractive cone 6 is It needs to be selected according to the refractive index of the refractive cone and the wafer 7. Specifically, the cone angle The reflection angle of the refracted light into the wafer needs to be Greater than the total reflection angle.

[0037] like Figure 2 As shown, in this embodiment, the cone angle of the refractive cone 6 is The specific calculation method is as follows:

[0038] Ring laser 8 is incident vertically from bottom to top, and the refractive index of air is ; The refractive index of the refractive cone 6 is , the cone angle is ; The angle at which the laser 2 enters the refraction cone 6 is , the refraction angle in the refraction cone 6 is , the angle of entry into wafer 7 is ; The refractive index of wafer 7 is , the refraction angle in the wafer is According to the principle of total reflection, no refraction occurs in the wafer, and the refraction angle in the wafer is is equal to the reflection angle in the wafer.

[0039] According to the above relationship and Snell's law:

[0040] (1)

[0041] like Figure 2 As shown, according to the relationship between the interior angles of a triangle:

[0042] (2)

[0043] According to Snell's law:

[0044] (3)

[0045] and Need to be greater than the total reflection angle:

[0046] (4)

[0047] Combining formulas (1) and (2) we can get:

[0048] (5)

[0049] That is

[0050] (6)

[0051] After sorting:

[0052] (7)

[0053] Then from formula (3) we can get:

[0054] (8)

[0055] Substituting formula (8) into formula (7) yields:

[0056] (9)

[0057] According to formula (4), formula (9) Greater than and Determined value, so we can get The range, the cone angle within the range All meet the requirements of the present invention.

[0058] Specifically: take the refractive index of air , the refractive index of the refractive cone , the refractive index of the wafer , then according to formula (4) we can calculate ,like Figure 3 The curve shown has the minimum X-axis value. The range is ( Figure 3 Y-axis range shown) .

[0059] In order to make the reflection angle of the refraction into the wafer It should be larger than the total reflection angle and make the light beam reflect more times. Figure 3 Intermediate positions in a curve, such as a cone angle ,at this time .

[0060] The present invention will be further described below with reference to examples.

[0061] The wafer 7 to be measured is a lithium niobate wafer with a thickness of 0.5 mm and a diameter of 6 inches (15.24 cm). The refractive index is Lithium niobate is transparent in the visible light band, so Laser 2 uses a 532nm green laser, generated by frequency doubling a solid-state laser, with an average power of approximately 10mW. Camera 1 uses a silicon-based CCD, such as the AX251AM-U3 camera. The appropriate lens and distance from the wafer are selected so that the entire wafer is within the field of view.

[0062] The refractive cone 6 is made of quartz glass with a refractive index of According to formulas (4) and (9), the cone angle is calculated The value range is . Select the cone angle The diameter of the lower base of the refractive cone is 10 mm, the height is 15 mm, and the diameter of the upper plane is 24 mm.

[0063] A metal cylinder with a diameter of 10 mm is used as the support column 5 and is connected to the bottom surface of the refractive cone by gluing.

[0064] The laser light 2 is expanded to a diameter of 24 mm by a reflecting prism 3 and shaped into a ring-shaped laser beam with an inner diameter of 10 mm by a circular aperture 4 .

[0065] The above-mentioned annular laser beam is coupled into the interior of the lithium niobate wafer through the refraction cone 6, and the reflection angle is , it is totally reflected inside the wafer, from the center to the edge. When the totally reflected light encounters internal defects 9 or surface dirt 10, it is scattered and captured by the camera. Figure 4 shown.

[0066] The above embodiments are only for illustrating the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A total internal reflection wafer detection device, characterized in that: The invention comprises a camera (1), a laser (2), a reflecting prism (3), a circular aperture (4), a supporting column (5) and a refractive cone (6). The laser (2) changes its direction to be vertically upward after entering the reflecting prism (3). A circular aperture (4) of an annular laser is formed by setting a shielded laser center portion on the vertically upward laser light path. The annular laser (8) is refracted by the refractive cone (6) into the interior of the wafer (7) to be tested and is totally reflected inside the wafer (7) to be tested. When encountering internal defects of the wafer and dirt on the surface, the light is scattered out of the wafer and detected by the camera (1). The supporting column (5) is located between the refractive cone (6) and the circular aperture (4). The wafer (7) to be tested is placed on the refractive cone (6). The camera (1) is arranged above the wafer (7) to be tested. The cone angle of the refractive cone (6) is 0. The reflection angle that causes the refraction to enter the wafer (7) to be tested is greater than the total reflection angle; The cone angle of the refractive cone (6) The calculation formula is as follows: （9） in, is the reflection angle of the refracted light entering the wafer (7) to be tested, is the refractive index of air, is the refractive index of the refractive cone (6), is the refractive index of the wafer (7) to be tested.

2. The total internal reflection wafer detection device according to claim 1, characterized in that: The laser (2) is a visible light or near infrared or mid infrared laser.

3. The total internal reflection wafer detection device according to claim 2, characterized in that: The laser (2) is a Gaussian or flat-top beam.

4. The total internal reflection wafer detection device according to claim 2, characterized in that: The camera (1) is sensitive to the same wavelength as the laser (2).

5. The total internal reflection wafer detection device according to claim 1, characterized in that: The circular aperture (4) is made of a transparent material, and the central shielding portion of the circular aperture (4) is made of an opaque material.

6. The total internal reflection wafer detection device according to claim 5, characterized in that: The circular aperture (4) is made of glass or resin, and the central shielding portion of the circular aperture (4) is made of metal or plastic.

7. The total internal reflection wafer inspection device according to claim 5, characterized in that: The diameter of the support column (5) is less than or equal to the diameter of the central shielding portion.

8. The total internal reflection wafer detection device according to claim 5, characterized in that: The size of the laser light (2) covers the refraction cone (6).

9. The total internal reflection wafer detection device according to claim 8, characterized in that: The outer diameter of the ring laser (8) is greater than the outer diameter of the refractive cone (6).

Images