Apparatus and method for wafer bonding alignment accuracy detection

Abstract

The present application relates to a device and a method for wafer bonding alignment accuracy detection. In an embodiment of the present application, the device for wafer bonding alignment accuracy detection comprises a point light source configured to generate a light beam; a first lens configured to transmit part of incident light and reflect part of the incident light; a second lens configured to focus a mark of a wafer; and a camera configured to capture the mark of the wafer through an aperture, wherein the point light source and the camera are located on the same side of the wafer, and the first lens is configured to reflect part of the light beam towards the second lens, and after the part of the light beam is reflected at a plane where the mark is located and passes through the second lens, the part of the light beam is incident towards the aperture.

Description

Technical Field

[0001] This application generally relates to the field of semiconductor processing equipment, and more specifically, to an apparatus and method for detecting the alignment accuracy of wafer bonding. Background Technology

[0002] After wafer bonding is completed, the bonding alignment accuracy of the two wafers will be checked. During this process, the marker between the two wafers needs to be imaged. Current transmission imaging technology is mainly used for medical-related testing. If used to check the bonding alignment accuracy of wafers, reflected light from the surfaces of the two wafers and scattered light from impurities inside the wafers will reduce the imaging contrast, thus affecting the testing accuracy. Summary of the Invention

[0003] This application provides an apparatus and method for detecting wafer bonding alignment accuracy. It employs reflective imaging technology, avoiding the problems associated with transmission imaging technology. Specifically, the apparatus and method of this application utilize confocal microscopy, employing a three-dimensional scanning layered imaging method to image the marker between two wafers, thereby improving the imaging contrast and thus enhancing the detection accuracy of wafer bonding alignment.

[0004] In one aspect, this application provides an apparatus for detecting wafer bonding alignment accuracy, comprising: a point light source for generating a light beam; a first lens for transmitting a portion of the incident light and reflecting a portion of the incident light; a second lens for focusing a mark on the wafer; and a camera for capturing an image of the mark on the wafer through an aperture, wherein the point light source and the camera are located on the same side of the wafer, and the first lens is configured to reflect a portion of the light beam toward the second lens, and the portion of the light beam is reflected at the plane where the mark is located and passes through the second lens before incident toward the aperture.

[0005] According to an embodiment of this application, the point light source is either a light-emitting diode (LED) light source or a laser light source.

[0006] According to an embodiment of this application, the first lens is a semi-reflective semi-transparent lens.

[0007] According to an embodiment of this application, the second lens is an objective lens.

[0008] According to an embodiment of this application, the aperture size of the aperture is adjustable.

[0009] According to an embodiment of this application, the wafer has a first surface and a second surface, wherein the point light source and the camera are located on one side of the second surface of the wafer.

[0010] According to an embodiment of this application, the point light source, the first lens, and the second lens are located on one side of the second surface of the wafer.

[0011] According to an embodiment of this application, the marking on the wafer is located between the first surface and the second surface.

[0012] On the other hand, this application also provides a method for detecting wafer bonding alignment accuracy, comprising: providing a point light source for generating a light beam; providing a first lens for transmitting a portion of the incident light and reflecting a portion of the incident light; providing a second lens for focusing a mark on the wafer; providing a camera for photographing the mark on the wafer through an aperture; and causing the point light source to emit a light beam toward the first lens, wherein the point light source and the camera are located on the same side of the wafer, and the first lens reflects a portion of the light beam toward the second lens, and the portion of the light beam is reflected at the plane where the mark is located and passes through the second lens before incident toward the aperture.

[0013] Details of one or more embodiments of this application are set forth in the following figures and description. Other features, objectives, and advantages will become apparent from the description, figures, and claims. Attached Figure Description

[0014] The following figures are mentioned and included in the disclosure in this specification:

[0015] Figure 1 This is a schematic diagram of a system for detecting wafer bonding alignment accuracy according to some embodiments of this application;

[0016] Figure 2 yes Figure 1 A schematic diagram of the operation of the device used for wafer bonding alignment accuracy inspection;

[0017] Figure 3A This is a schematic diagram of reflective imaging according to some embodiments of this application;

[0018] Figure 3B This is a schematic diagram of transmission imaging;

[0019] Figure 4A This is a schematic diagram of a point light source according to an embodiment of this application;

[0020] Figure 4B This is a schematic diagram of a point light source according to another embodiment of this application; and

[0021] Figure 5 This is a flowchart of a method for detecting wafer bonding alignment accuracy according to some embodiments of this application.

[0022] By convention, the various features illustrated in the figures may not be drawn to scale. Therefore, for clarity, the dimensions of various features may be arbitrarily enlarged or reduced. The shapes of the components illustrated are merely exemplary and do not limit the actual shapes of the components. Furthermore, for clarity, the embodiments illustrated may be simplified. Therefore, the figures may not depict all components of a given device or apparatus. Finally, the same reference numerals may be used throughout the specification and figures to denote the same features. Detailed Implementation

[0023] To better understand the spirit of the present invention, the following description, in conjunction with some embodiments of the present invention, will provide further details.

[0024] The terms "in one embodiment" or "according to one embodiment" used in this specification do not necessarily refer to the same specific embodiment, and the terms "in other (some / some) embodiments" or "according to other (some / some) embodiments" used in this specification do not necessarily refer to different specific embodiments. The purpose is to, for example, include combinations of all or some of the exemplary embodiments. The meaning of "upper" and "lower" as used herein is not limited to the relationship directly presented in the drawings, but should include descriptions with explicit corresponding relationships, such as "left" and "right," or the opposite of "upper" and "lower." The term "connection" as used herein should be understood to encompass both "direct connection" and "connection via one or more intermediate components." The names of various components used in this specification are for illustrative purposes only and are not intended to be limiting; different manufacturers may use different names to refer to components with the same function.

[0025] Various embodiments of the invention are discussed in detail below. Although specific embodiments are discussed, it should be understood that these embodiments are for illustrative purposes only. Those skilled in the art will recognize that other components and configurations can be used without departing from the spirit and scope of the invention.

[0026] Figure 1 This is a schematic diagram of a system 100 for wafer bonding alignment accuracy detection according to some embodiments of this application.

[0027] Please see Figure 1The system 100 includes a processor 18 and a device 10 for detecting wafer bonding alignment accuracy. Before wafer bonding, a first wafer W1 has a first surface W1a and a second surface W1b opposite to the first surface W1a, and has a first mark M1 located on the first surface W1a. A second wafer W2 has a first surface W2a and a second surface W2b opposite to the first surface W2a, and has a second mark M2 located on the first surface W2a. During wafer bonding, the first mark M1 of the first wafer W1 and the second mark M2 of the second wafer W2 must be aligned with each other. Specifically, the first wafer W1 and the second wafer W2 are aligned with the first mark M1 and the second mark M2 facing each other. Therefore, after wafer bonding, the first wafer W1 and the second wafer W2, together with the first mark M1 and the second mark M2, are combined into one, and the alignment mark after wafer bonding is referred to below as "wafer mark M". The bonded wafer has a first surface W1b and a second surface W2b opposite to the first surface W1b. Furthermore, the wafer identifier M is located between the first surface W1b and the second surface W2b of the wafer.

[0028] The apparatus 10 for detecting wafer bonding alignment accuracy includes a point light source 11, a lens group 12, and a camera 16. The lens group 12 includes a first lens 121 and a second lens 122. The point light source 11 generates a light beam and emits the light beam towards the first lens 121 to detect the bonding alignment accuracy of two wafers. The first lens 121 transmits a portion of the incident light and reflects a portion of the incident light. The first lens 121 is configured to reflect a portion of the light beam toward the second lens 122, and the portion of the light beam is reflected at the plane where the marking is located and, after passing through the second lens 122, is incident toward the aperture 14.

[0029] The second lens 122 is used to focus the marking M on the wafer.

[0030] Camera 16 is used to capture images of the wafer marking M through aperture 14. The images captured by camera 16 are analyzed in processor 18. Processor 18 has related hardware and computer programs to support the analysis of the images, such as contrast analysis.

[0031] Figure 2 yes Figure 1 A schematic diagram of the operation of the device 10 for detecting wafer bonding alignment accuracy.

[0032] Please see Figure 2 Point light source 11 generates a light beam, which is incident on the first lens 121 along path P11.

[0033] The first lens 121 transmits incident light through its transmission portion and reflects incident light along path P11f toward the second lens 122 through its reflection portion. In embodiments of this application, the first lens 121 is a semi-reflective mirror, and the second lens 122 is an objective lens.

[0034] The second lens 122 refracts the reflected light from the first lens 121 along path P12 toward the wafer marking M, so that the refracted light is focused on the wafer marking M located on the focal plane 20. In embodiments of this application, the distance between the second lens 122 and the wafer marking M is adjustable to facilitate focusing on the wafer marking M.

[0035] The focal plane 20 reflects the refracted light along path P12f toward the second lens 122. Then, the second lens 122 refracts the reflected light from the focal plane 20 along path P12r toward the first lens 121. Next, the first lens 121 reflects a portion of the refracted light from the second lens 122 toward the point light source 11 along path P21; this is known as confocal focusing. Simultaneously, the first lens 121 transmits a portion of the refracted light from the second lens 122 toward the camera 16 along path P12t through aperture 14.

[0036] On the other hand, the light beam emitted by the point light source 11 can be incident on the first lens 121 along path P21. The first lens 121 transmits the incident light and reflects it along path P12r towards the second lens 122. The second lens 122 refracts the reflected light from the first lens 121 towards the wafer marker M along path P12f, focusing the refracted light onto the wafer marker M located on the focal plane 20. The focal plane 20 reflects the refracted light towards the second lens 122 along path P12. Then, the second lens 122 refracts the reflected light from the focal plane 20 towards the first lens 121 along path P11f. Next, the first lens 121 reflects a portion of the refracted light from the second lens 122 towards the point light source 11 along path P11; simultaneously, the first lens 121 transmits a portion of the refracted light from the second lens 122 towards the camera 16 through the aperture 14 along path P21t.

[0037] If the light beam emitted by point light source 11 cannot be focused on focal plane 20, but instead falls on non-focal planes 20U or 20L as shown by the dashed lines, the transmitted light from the first lens 121 will ultimately be blocked by aperture 14 and will not be able to reach camera 16. Aperture 14 is used to control the amount of light beam passing through, and the intensity of the passing light beam can be adjusted. In the embodiments of this application, the aperture size of aperture 14 is adjustable to optimize the imaging quality of camera 16.

[0038] Figure 3A This is a schematic diagram of reflective imaging according to some embodiments of this application.

[0039] Please see Figure 3ABefore bonding the first wafer W1 and the second wafer W2, a protective layer W1f is coated on the second surface W1b of the first wafer W1. In the embodiments of this application, the point light source 11 and the camera 16 are located on one side of the second surface W2b of the second wafer W2, that is, on one side of the second surface W2b of the wafer after bonding. In addition, the point light source 11 and the lens group 12 are also located on the same side of the second surface W2b of the wafer, that is, the point light source 11, the camera 16, the first lens 121 and the second lens 122 are all located on the same side of the second surface W2b of the wafer. With this configuration, please also refer to Figure 2 Lens group 12 receives incident light from point light source 112 and focuses on the mark M located between the first surface W1b and the second surface W2b of the wafer. Lens group 12 reflects the incident light towards the portion of the mark M on the wafer. This portion of the incident light is reflected at the plane containing the mark M and then passes through lens group 12 before entering and focusing onto camera 16. During this process, the light emitted by point light source 11 is reflected at the plane containing the mark M on the wafer and does not pass through the interior of the first wafer W1, nor does it contact the protective layer W1f on the second surface W1b of the first wafer W1. This reflective imaging configuration has many advantages over transmissive imaging configurations, which will be discussed below. Figure 3B Detailed explanation.

[0040] Figure 3B This is a schematic diagram of transmission imaging, used to compare with... Figure 3A Compare with reflective imaging.

[0041] Please see Figure 3B The transmissive imaging device 30 includes a point light source 31, lenses 320, 321, 322, and a camera 36. Lens 320 is an aspherical lens, and lens 321 is an objective lens. The point light source 31, lenses 320 and 321 are located on one side of the second surface W1b of the first wafer W1, i.e., one side of the first surface W1b of the bonded wafer; while the camera 36 and lens 322 are located on one side of the second surface W2b of the second wafer W2, i.e., one side of the second surface W2b of the bonded wafer. The transmissive imaging device 30 operates as follows: lens 320 receives incident light from the point light source 31 and generates a collimated beam that enters lens 321. Lens 321 focuses on the marker M located between the first surface W1b and the second surface W2b of the wafer. Then, light penetrating the second surface W2b of the wafer passes through lens 322 and is focused onto the camera 36. Because the point light source 31 and the camera 36 are located on different sides of the wafer, the light emitted by the point light source 31 must pass through the protective layer W1f, the interior of the first wafer W1, and the interior of the second wafer W2 before reaching the camera 36. Using the transmission imaging device 30 for detecting the bonding alignment accuracy of the wafer has the following disadvantages:

[0042] First, a wafer contains a considerable number of components, conductive layers, and insulating layers. When incident light penetrates the wafer, the components and conductive layers cause reflected light, and impurities within the wafer cause scattered light. This reflected and scattered light attenuates the light energy of the incident light, reducing image contrast and thus affecting detection accuracy.

[0043] Secondly, the transmittance of incident light decreases after it penetrates the protective layer W1f. Therefore, the protective layer W1f also attenuates the light energy of the incident light, thereby reducing imaging contrast and detection accuracy.

[0044] Secondly, before operation, the relative positions of the point light source 31, lens 320, and lens 321 in the transmission imaging device 30 must be adjusted to ensure they are coaxial. This adjustment involves fine-tuning the position of the point light source 31 along the X, Y, and Z axes, which is quite challenging. Deviations in the relative positions of the point light source 31, lens 320, and lens 321 will also reduce the imaging contrast, thus affecting the detection accuracy.

[0045] To compensate for the attenuation of incident light energy, the transmissive imaging device 30 needs to consider using light with a longer wavelength, but this is not easy in the application of infrared light in the point light source 31. On the other hand, the transmissive imaging device 30 needs to consider using a high-quality camera, which would increase the detection cost.

[0046] The apparatus and method for detecting wafer bonding alignment accuracy in this application employs reflective imaging technology. The light emitted by the point light source 11 is reflected at the plane where the wafer marker M is located, and does not pass through the protective layer W1f or the interior of the first wafer W1, thus avoiding the problems associated with transmission imaging technology. Furthermore, the relative positions of the point light source 11 and the lens group 12 do not require precise adjustment, thus eliminating the complex pre-processing required by apparatus 30 for transmission imaging. The detection accuracy of apparatus 30 for transmission imaging is approximately 25 to 30 nanometers (nm), while the detection accuracy of the reflective imaging apparatus and method of this application is approximately 10 to 15 nanometers (nm). Compared to apparatus 30 for transmission imaging, the reflective imaging apparatus and method of this application can detect smaller wafer bonding misalignments, significantly outperforming apparatus 30 for transmission imaging.

[0047] Figure 4A This is a schematic diagram of a point light source 11 according to an embodiment of this application.

[0048] Please see Figure 4AThe point light source 11 includes a light-emitting diode (LED) light source 41, a first beam splitter 411, and a second beam splitter 412. In embodiments of this application, the first beam splitter 411 and the second beam splitter 412 are convex lenses with the same or similar optical characteristics. In embodiments of this application, the LED light source 41 is approximately 20 mm away from the first beam splitter 411, the first beam splitter 411 is approximately 10 mm away from the second beam splitter 412, and the second beam splitter 412 is approximately 20 mm away from the converging point f1. These distances can be adjusted according to the size of the detection area.

[0049] In the embodiments of this application, a light homogenizer can be installed behind the light-emitting diode light source 41 to make the emitted light from the light-emitting diode light source 41 more uniform.

[0050] Figure 4B This is a schematic diagram of a point light source 11 according to another embodiment of this application.

[0051] Please see Figure 4B The point light source 11 includes a laser light source 45 and a beam splitter 452. In this embodiment, the laser light source 45 uses infrared light as the light source. In this embodiment, the beam splitter 452 is a convex lens. In this embodiment, the laser light source 45 and the beam splitter 452 are approximately 30 mm apart, and the beam splitter 452 is approximately 20 mm apart from the converging point f2. These distances can be adjusted according to the size of the detection area.

[0052] Figure 5 This is a flowchart of a method for detecting wafer bonding alignment accuracy according to some embodiments of this application.

[0053] Please see Figure 5 In operation 51, a point light source is provided to generate a light beam.

[0054] In operation 52, a first lens is provided for transmitting incident light from the portion and reflecting incident light from the portion.

[0055] In operation 53, a second lens is provided for focusing the markings on the wafer.

[0056] In operation 54, a camera is provided for photographing the markings on the wafer through an aperture, the camera and the point light source being located on the same side of the wafer.

[0057] In operation 55, the point light source emits a beam of light toward the first lens.

[0058] In operation 56, the first lens reflects the light beam of the portion of the second lens, and the portion of the light beam is reflected at the plane where the mark is located and passes through the second lens before incident on the aperture.

[0059] Compared to transmissive imaging devices or methods, the device and method for detecting wafer bonding alignment accuracy in this application are based on reflective imaging technology. They utilize confocal imaging to eliminate image noise caused by reflections from various wafer surfaces and scattering from impurities within the wafer, thus improving imaging contrast and detection accuracy. Furthermore, the device and method for detecting wafer bonding alignment accuracy in this application can detect even minute wafer bonding misalignments, allowing for wafer compensation based on image comparison results to improve alignment accuracy.

[0060] The description herein is provided to enable those skilled in the art to make or use the invention. Various modifications to the invention will readily be apparent to those skilled in the art, and the general principles defined herein can be applied to other variations without departing from the spirit or scope of the invention. Therefore, the invention is not limited to the examples and designs described herein, but is given the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An apparatus for detecting wafer bonding alignment accuracy, comprising: A point light source for generating a light beam, wherein the light beam is incident toward a first lens; The first lens is a semi-reflective lens that reflects incident light toward the second lens and transmits refracted light from the second lens toward the camera through an aperture. The second lens is used to refract reflected light from the first lens toward the marking on the wafer, so that the refracted light is focused on the marking on the wafer located on the focal plane, and to refract reflected light from the focal plane toward the first lens; The aperture stop, located between the camera and the first lens, is used to block transmitted light from the first lens that falls on the off-focal plane from reaching the camera; and The camera is used to photograph the markings on the wafer through the aperture.

2. The apparatus according to claim 1, wherein the point light source comprises a light-emitting diode light source, a first beam splitter, and a second beam splitter, wherein, Both the first and second beam splitters are convex lenses. The light-emitting diode light source is 20 mm away from the first beam splitter, the first beam splitter is 10 mm away from the second beam splitter, and the focal length of the second beam splitter is 20 mm.

3. The device according to claim 2, wherein a light-diffusing tube is provided behind the light-emitting diode light source.

4. The apparatus according to claim 1, wherein the point light source comprises a laser light source and a third beam splitter, wherein, The laser source emits infrared light, the third beam splitter is a convex lens, the laser source is 30 mm away from the third beam splitter, and the focal length of the third beam splitter is 20 mm.

5. The apparatus of claim 1, wherein the second lens is an objective lens and the distance between the second lens and the marking on the wafer is adjustable.

6. The apparatus according to claim 1, wherein the aperture size of the aperture is adjustable.

7. The apparatus of claim 1, wherein the wafer has a first surface and a second surface, the first surface is coated with a protective layer, and the point light source and the camera are located on one side of the second surface of the wafer.

8. The apparatus of claim 7, wherein the point light source, the semi-reflective lens, and the second lens are located on one side of the second surface of the wafer.

9. The apparatus of claim 7, wherein the marking of the wafer is located between the first surface and the second surface.

10. A system for detecting wafer bonding alignment accuracy, comprising: The apparatus for detecting wafer bonding alignment accuracy according to any one of claims 1 to 9; as well as A processor for analyzing images captured by the device's camera.

11. The system of claim 10, wherein the analysis includes contrast analysis.

12. A method for detecting wafer bonding alignment accuracy, comprising: The point light source of the device for wafer bonding alignment accuracy detection as described in any one of claims 1 to 9 emits a light beam toward the semi-reflective lens of the device; as well as The camera of the device takes a picture of the markings on the wafer through the aperture of the device.

13. The method of claim 12, further comprising: The images captured by the camera of the device are analyzed.

14. The method of claim 13, wherein the analysis includes contrast analysis.

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