Optical microscope

Abstract

The utility model provides an optical microscope. The optical microscope comprises: a light source assembly configured to output monochromatic light beams of different wavelengths; the objective lens is arranged on the light path of the monochromatic light beams with different wavelengths and is configured to focus the monochromatic light beams with different wavelengths at different positions in the vertical optical axis direction; the spectrum detector is coupled with the light source assembly and is configured to collect spectrum information of the light beam focused on the surface of the to-be-detected sample; and the displacement table is configured to bear a to-be-detected sample and adjust the vertical position of the to-be-detected sample according to the spectral information, so that the surface of the to-be-detected sample is located on the focal plane of the light beam with the target wavelength, and automatic focusing is realized. According to the optical microscope provided by the utility model, the automatic focusing device which is simple in structure, light and compact is provided, so that the automatic focusing problem of the microscope can be effectively solved; the detection precision and the detection efficiency of the microscope can be improved.

Description

Technical Field

[0001] This utility model relates to the field of semiconductor detection technology, and in particular to an optical microscope. Background Technology

[0002] With the continuous advancement of semiconductor manufacturing processes, the minimum linewidth that semiconductor process equipment can etch or inspect is becoming increasingly smaller. The ever-increasing precision in inspection and measurement necessitates automated optical inspection equipment with higher optical resolution. Current microscope objectives have magnifications reaching 20x, 50x, and even higher levels. However, this increase in magnification leads to a decrease in depth of field; for example, a 20x or 50x microscope may only have a depth of field of a few micrometers. In such cases, manual focusing becomes extremely difficult and inaccurate, making autofocus an essential choice.

[0003] Existing microscope optical autofocus solutions mainly include: autofocus based on optical triangulation, autofocus based on light intensity detection, autofocus based on range measurement, and autofocus based on image algorithms. Among these, the autofocus optical path based on optical triangulation mainly consists of the visible light path of the microscope and the defocus detection path. The autofocus method based on light intensity detection utilizes the image characteristics of the point spread function (PSF). By finding the difference in the extreme values ​​of the first derivative of the fitted Gaussian function under different defocus amounts, a function curve of defocus amount versus the extreme value difference of the first derivative is plotted, thereby achieving autofocus.

[0004] Range-based autofocus is a focusing technique that achieves automatic focusing by measuring the distance between the objective lens and the sample being tested. Image algorithm-based autofocus extracts certain features from a set of out-of-focus images to determine the accuracy of focusing or to determine the focusing method and distance. Through an iterative search process, it finds the optimal focus position and continuously evaluates the degree of focus of the image until certain conditions are met or the optimal value is reached.

[0005] However, the aforementioned microscope optical autofocus schemes all have certain drawbacks. While autofocus methods based on optical triangulation and range finding offer fast focusing speeds, high efficiency, and high sensitivity, they are expensive and bulky. They are typically coaxially integrated into the optical microscope system, occupying space along the optical axis and encroaching on other auxiliary microscopic optical systems, making the entire optical microscopy system cumbersome and difficult to integrate with other detection equipment. Furthermore, the installation and calibration of these two autofocus devices are relatively complex, requiring a high level of technical skill from the operators.

[0006] Autofocus methods based on light intensity detection and those based on image algorithms are highly dependent on algorithms, requiring continuous iterative steps during the focusing process to gradually approach the optimal focus position. While these two methods are simple to implement, have low hardware requirements, and are relatively economical, their focusing speed is related to the iteration speed, sampling efficiency, and degree of defocus, typically resulting in slow focusing speed and low detection efficiency. Utility Model Content

[0007] One objective of this invention is to provide a simple, lightweight, and compact autofocus device to solve the autofocus problem of microscopes.

[0008] A further objective of this invention is to improve the detection accuracy and efficiency of microscopes, thereby increasing the production yield of semiconductor products.

[0009] Specifically, this invention provides an optical microscope, comprising: a light source assembly configured to output monochromatic light beams of different wavelengths; an objective lens disposed in the optical path of the monochromatic light beams of different wavelengths and configured to focus the monochromatic light beams of different wavelengths at different positions along the vertical optical axis; a spectral detector coupled to the light source assembly and configured to acquire spectral information of the light beam focused on the surface of the sample to be tested; and a displacement stage configured to carry the sample to be tested and adjust the vertical position of the sample to be tested according to the spectral information, so that the surface of the sample to be tested is located at the focal plane of the light beam of the target wavelength, thereby achieving automatic focusing.

[0010] Optionally, the light source assembly includes: a white light source, a beam splitter, a dispersive lens, and a beam splitter prism, wherein the white light source is configured to emit a white light beam, allowing the white light beam to pass sequentially through the beam splitter, the dispersive lens, and the beam splitter prism before being output as monochromatic beams of different wavelengths; and allowing a portion of the beam focused on the surface of the sample to be detected to pass through the objective lens, the beam splitter prism, and the dispersive lens, and then be reflected by the beam splitter and coupled into the spectral detector.

[0011] Optionally, the optical microscope also includes a drive mechanism connected to the displacement stage, configured to adjust the lifting and lowering of the displacement stage according to spectral information, thereby adjusting the vertical position of the sample to be tested.

[0012] Optionally, the short-wavelength beam, the mid-wavelength beam, and the long-wavelength beam in the monochromatic beams of different wavelengths are focused from top to bottom at different positions along the vertical optical axis, and the beam of the target wavelength is the mid-wavelength beam.

[0013] Optionally, when the beam focused on the surface of the sample to be tested is determined to be shifted to a longer wavelength based on the spectral information, the drive mechanism raises the displacement stage.

[0014] Optionally, when the beam focused on the surface of the sample to be tested is determined to be shifted to a shorter wavelength based on the spectral information, the drive mechanism lowers the displacement stage.

[0015] Optionally, the optical microscope further includes a tube lens positioned above a beam splitter prism, wherein the beam splitter prism is configured to couple coaxially with the optical path of the white light beam and the optical path of the imaging beam incident on the tube lens.

[0016] Optionally, the optical microscope also includes a camera positioned above the tube mirror so that another portion of the beam focused on the surface of the sample to be tested passes through the objective lens, beam splitter, and tube mirror before being imaged by the camera.

[0017] Optionally, the front surface of the dispersive lens facing the beam splitter is aspherical, the rear surface facing the beam splitter is conical, and the dispersive lens is configured to collimate and disperse the white light beam.

[0018] Optionally, the transmission-to-reflection ratio of the beam splitter is 7:3, and the transmission-to-reflection ratio of the beam splitter prism is 5:5.

[0019] This invention relates to an optical microscope, comprising: a light source assembly configured to output monochromatic light beams of different wavelengths; an objective lens disposed on the optical path of the monochromatic light beams of different wavelengths and configured to focus the monochromatic light beams of different wavelengths at different positions along the vertical optical axis; a spectral detector coupled to the light source assembly and configured to acquire spectral information of the light beam focused on the surface of the sample to be tested; and a displacement stage configured to support the sample to be tested and adjust the vertical position of the sample to be tested according to the spectral information, so that the surface of the sample to be tested is located at the focal plane of the light beam of the target wavelength, thereby achieving automatic focusing. By providing a simple, lightweight, and compact automatic focusing device, the automatic focusing problem of microscopes can be effectively solved.

[0020] Furthermore, the optical microscope of this invention can assist in the automatic optical microscope inspection of wafers with low-cost and high-efficiency autofocus technology, thereby improving the inspection accuracy and efficiency and increasing the production yield of semiconductor products. The principle is clear, the structure is simple and compact, and it does not rely on algorithms. At the same time, the installation, adjustment and operation are simple, the automatic alignment accuracy is high, and it can be coaxially integrated into a microscope system or set up as an independent optical path. It is simple to implement, stable and reliable.

[0021] The above and other objects, advantages and features of this utility model will become more apparent to those skilled in the art from the following detailed description of specific embodiments of this utility model in conjunction with the accompanying drawings. Attached Figure Description

[0022] The following sections will describe some specific embodiments of the present invention in a detailed manner by way of example and not limitation, with reference to the accompanying drawings. The same reference numerals in the drawings denote the same or similar parts or components. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings:

[0023] Figure 1 This is a schematic diagram of the principle of an optical microscope according to an embodiment of the present invention. Detailed Implementation

[0024] As mentioned earlier, commonly used microscope optical autofocus solutions all have certain drawbacks. While autofocus methods based on optical triangulation and rangefinding offer fast focusing speeds, high efficiency, and high sensitivity, they are expensive and bulky. They are typically coaxially integrated into the optical microscope system, occupying space along the optical axis and encroaching on other auxiliary microscopic optical systems, making the entire optical microscopy system cumbersome and difficult to integrate with other detection equipment. Furthermore, the installation and calibration of these two types of autofocus devices are relatively complex, requiring a high level of technical skill from the operators.

[0025] Autofocus methods based on light intensity detection and those based on image algorithms are highly dependent on algorithms, requiring continuous iterative steps during the focusing process to gradually approach the optimal focus position. While these two methods are simple to implement, have low hardware requirements, and are relatively economical, their focusing speed is related to the iteration speed, sampling efficiency, and degree of defocus, typically resulting in slow focusing speed and low detection efficiency.

[0026] This embodiment provides an optical microscope with a simple, lightweight, and compact structure, which can effectively solve the problem of automatic focusing in microscopes. Figure 1 This is a schematic diagram illustrating the principle of an optical microscope according to an embodiment of the present invention. Figure 1 As shown, the optical microscope of this embodiment generally includes: a light source assembly, an objective lens 150, a spectral detector 181, and a displacement stage (not shown in the figure).

[0027] The light source assembly is configured to output monochromatic light beams of different wavelengths. Objective lenses 150 are positioned along the optical paths of these monochromatic light beams and are configured to focus the beams at different positions along the vertical optical axis. A spectrometer 181 is coupled to the light source assembly and is configured to acquire the spectral information of the light beam focused on the surface of the sample 100. A displacement stage is configured to support the sample and adjust its vertical position according to the spectral information, ensuring that the surface of the sample is located at the focal plane of the target wavelength light beam, thus achieving automatic focusing.

[0028] In one specific embodiment, the light source assembly includes: a white light source 110, a beam splitter 120, a dispersive lens 130, and a beam splitter prism 140. The white light source 110 is configured to emit a white light beam. White light in optical systems is generally considered to be a collection of visible light, typically in the wavelength range of 400 to 760 nm, which is the range of wavelengths perceptible to the human eye. White light is actually a mixture of various colors of light, such as blue, violet, red, orange, yellow, and green. These colors of light are mixed in certain proportions to form white light.

[0029] After passing through beam splitter 120, dispersive lens 130, and beam splitter prism 140 in sequence, the white light beam is output as monochromatic beams of different wavelengths. Objective lens 150 can focus the monochromatic beams of different wavelengths at different positions along the vertical optical axis. It should be noted that, because the optical devices including dispersive lens 130, beam splitter prism 140, and objective lens 150 have a relatively high refractive index for short-wavelength white light, a relatively low refractive index for long-wavelength white light, and a moderate refractive index for mid-wavelength white light, beams of different colors and frequencies will be focused at different positions along the vertical optical axis. The amount of dispersion and defocusing is positively correlated with the relative magnitude of the refractive index.

[0030] Specifically, in monochromatic light beams of different wavelengths, the short-wavelength, mid-wavelength, and long-wavelength beams are focused from top to bottom at different positions along the vertical optical axis. In a white light beam, the short-wavelength beam, such as blue-violet light, has a shorter focal length and will focus closer to the lower surface of the objective lens 150. In a white light beam, the long-wavelength beam, such as red-orange light, has a longer focal length and will focus at a greater distance from the lower surface of the objective lens 150. The mid-wavelength beam in a white light beam, such as yellow-green light, will focus at a point between these two extremes.

[0031] A portion of the light beam focused on the surface of the sample 100 is reflected by the beam splitter 120 after passing through the objective lens 150, the beam splitter 140, and the dispersive lens 130, and then coupled into the spectrometer 181. The spectrometer 181 is configured to acquire the spectral information of the light beam focused on the surface of the sample 100. It should be noted that, since the portion of the light beam not focused on the surface of the sample 100 is scattered and coupled into the objective lens 150 is extremely small, the center wavelength detected by the spectrometer 181 is the wavelength band of the light beam focused on the surface of the sample 100.

[0032] The displacement stage is located below the sample 100 and can adjust its vertical position according to spectral information, ensuring that the surface of the sample 100 is positioned at the focal plane of the beam of the target wavelength, thus achieving automatic focusing. The target wavelength beam can be a mid-band beam. Specifically, the vertical position of the sample 100 can be adjusted in real time based on the center wavelength and drift direction of the response of the spectral detector 181, maintaining the focus position of the microscope system in a closed loop, thereby achieving automatic focusing for optical detection.

[0033] The optical microscope in this embodiment greatly simplifies the complexity of traditional optical autofocus devices. The device is simple and stable with high focusing sensitivity. It is more practical and easier to implement in compact equipment, with excellent economy and efficiency. The overall optical components are easy to set up and adjust, and the installation and disassembly are more convenient. It has high focusing accuracy and high detection efficiency. It can be set coaxially in the optical microscope system or can be set independently in parallel outside the optical microscope.

[0034] In one specific embodiment, such as Figure 1 As shown, the optical microscope also includes a drive mechanism (not shown in the figure). The drive mechanism is connected to the displacement stage and is configured to control and adjust the lifting and lowering of the displacement stage according to the spectral information, thereby adjusting the vertical position of the sample 100 to be tested.

[0035] In one specific embodiment, the driving mechanism can be a motor, and the sample 100 to be tested can be a wafer. During assembly and calibration, the upper surface of the wafer can be positioned in the middle band of the white light spectrum, such as 532 nm. During scanning detection, due to the different heights of the wafer surface, the focused spectrum of the wafer surface will change accordingly. Based on the center wavelength and drift direction of the response of the spectral detector 181, after acquiring this signal, the driving mechanism adjusts the lifting and lowering of the displacement stage, thereby realizing the adjustment of the vertical position of the sample 100 to be tested.

[0036] As mentioned earlier, short-wavelength, mid-wavelength, and long-wavelength light beams are focused at different positions along the vertical optical axis from top to bottom. Therefore, when the light beam focused on the surface of the sample 100 is determined to be shifted towards the long-wavelength band based on spectral information, the drive mechanism raises the displacement stage. When the light beam focused on the surface of the sample 100 is determined to be shifted towards the short-wavelength band based on spectral information, the drive mechanism lowers the displacement stage. The specific distance the displacement stage is raised or lowered can be determined based on the offset of the light beam focused on the surface of the sample 100 relative to the target wavelength light beam, such as the mid-wavelength light beam, thereby allowing for accurate adjustment of the lifting distance of the displacement stage.

[0037] The following describes two specific embodiments:

[0038] When the focused beam on the wafer surface shifts towards a longer wavelength, the change in spectral composition is detected in real time on the spectral detector 181. By comparing the shift with the center wavelength, for example, 532 nm, an error signal is given, which drives the mechanism to raise the displacement stage, thereby restoring the focused beam on the wafer surface back to the center wavelength of 532 nm.

[0039] When the focused beam on the wafer surface shifts towards a shorter wavelength, the change in spectral composition is detected in real time on the spectral detector 181. By comparing the shift with the center wavelength, for example, 532 nm, an error signal in the opposite direction is given, driving the mechanism to lower the displacement stage, thereby restoring the focused beam on the wafer surface back to the center wavelength of 532 nm.

[0040] Thus, the optical microscope in this embodiment achieves automatic focusing of the optical microscopy system, improving the optical inspection efficiency of wafers and enhancing wafer production efficiency and yield. A spectral detector 181 is used to collect feedback signals, and based on the central spectrum and its offset direction, adjustment signals can be quickly and efficiently provided to achieve automatic focusing. A dispersive optical system is used to disperse and defocus the beam, thereby collecting a strong error signal. Conventional optical and optomechanical components are employed to achieve high-precision and high-efficiency optical automatic focusing.

[0041] In a preferred embodiment, the optical microscope further includes a tube lens 160, disposed above the beam splitter 140. The beam splitter 140 is configured to couple coaxially with the optical path of the white light beam entering the tube lens 160. The optical microscope also includes a camera 170, disposed above the tube lens 160, so that another portion of the light beam focused on the surface of the sample 100 is imaged by the camera 170 after passing through the objective lens 150, the beam splitter 140, and the tube lens 160.

[0042] It is important to emphasize that the front surface of the dispersive lens 130 of the optical microscope in this embodiment facing the beam splitter 120 is aspherical, while the rear surface facing the beam splitter prism 140 is conical. Furthermore, the dispersive lens 130 is configured to collimate and disperse the white light beam. In other words, the optical microscope in this embodiment does not require additional positive or negative lenses for secondary collimation or calibration; the dispersive lens 130 directly performs collimation and dispersion of the white light source 110, eliminating the need for redundant components, effectively simplifying the overall structure and reducing costs.

[0043] In one specific embodiment, the transmission-to-reflection ratio of beam splitter 120 is 7:3, and that of beam splitter prism 140 is 5:5. Placing beam splitter prism 140, instead of beam splitter 120, on the principal axis of the microscopic optical path ensures that the light path does not undergo refraction shift in the principal optical axis direction. The white light beam emitted from white light source 110 first passes through beam splitter 120 because beam splitter 120 is low-cost and easy to install, fix, and adjust. In other embodiments, beam splitter 120 can be replaced with beam splitter prism 140, but beam splitter prism 140 cannot be set as beam splitter 120; this is to effectively ensure that the light path does not undergo refraction shift in the principal optical axis direction.

[0044] In summary, the optical microscope of this embodiment includes: a light source assembly configured to output monochromatic light beams of different wavelengths; an objective lens 150 disposed in the optical path of the monochromatic light beams of different wavelengths and configured to focus the monochromatic light beams of different wavelengths at different positions in the vertical optical axis direction; a spectral detector 181 coupled to the light source assembly and configured to acquire spectral information of the light beam focused on the surface of the sample 100 to be tested; and a displacement stage configured to carry the sample to be tested and adjust the vertical position of the sample to be tested according to the spectral information so that the surface of the sample to be tested is located at the focal plane of the light beam of the target wavelength, thereby achieving automatic focusing. By providing an automatic focusing device with a simple structure and lightweight and compact design, the automatic focusing problem of the microscope can be effectively solved.

[0045] Furthermore, the optical microscope of this embodiment can assist in the automatic optical microscope inspection of wafers with low-cost and high-efficiency autofocus technology, thereby improving the inspection accuracy and efficiency and increasing the production yield of semiconductor products. The principle is clear, the structure is simple and compact, and it does not rely on algorithms. At the same time, the installation, adjustment and operation are simple, the automatic alignment accuracy is high, and it can be coaxially integrated into the microscope system or set up as an independent optical path. It is simple to implement, stable and reliable.

[0046] Those skilled in the art should understand that, unless otherwise specified, the terms "center," "longitudinal," "transverse," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "axial," "radial," "circumferential," "clockwise," and "counterclockwise" used to indicate orientation or positional relationships in the embodiments of this utility model are merely for the convenience of describing and understanding the technical solution of this utility model, and are not intended to indicate or imply that the device or component referred to must have a specific orientation, and therefore should not be construed as a limitation of this utility model.

[0047] The terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first," "second," etc., may explicitly or implicitly include at least one of that feature, that is, include one or more of that feature. In the description of this utility model, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified. When a feature "includes or contains" one or more of the features it encompasses, unless otherwise specifically described, this indicates that other features are not excluded and may be further included.

[0048] Unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art should be able to understand the specific meaning of the above terms in this utility model according to the specific circumstances.

[0049] Furthermore, in the description of this embodiment, "above" or "below" the second feature can include direct contact between the first and second features, or it can include contact between the first and second features through another feature between them. That is, in the description of this embodiment, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," or "below" of the second feature can mean the first feature is directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0050] In the description of this embodiment, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this utility model. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0051] Therefore, those skilled in the art should recognize that although many exemplary embodiments of the present invention have been shown and described in detail herein, many other variations or modifications conforming to the principles of the present invention can be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the present invention. Thus, the scope of the present invention should be understood and recognized as covering all such other variations or modifications.

Claims

1. An optical microscope, characterized in that, include: The light source assembly is configured to output monochromatic light beams of different wavelengths; An objective lens is positioned in the optical path of the monochromatic light beams of different wavelengths and configured to focus the monochromatic light beams of different wavelengths at different positions along the vertical optical axis. A spectral detector, coupled to the light source assembly, is configured to acquire spectral information of a light beam focused on the surface of the sample to be tested; as well as A displacement stage is configured to carry the sample to be tested and adjust the vertical position of the sample to be tested according to the spectral information so that the surface of the sample to be tested is located at the focal plane of the light beam of the target wavelength, thereby achieving automatic focusing.

2. The optical microscope according to claim 1, characterized in that, The light source assembly includes: a white light source, a beam splitter, a dispersive lens, and a beam splitter prism. The white light source is configured to emit a white light beam, allowing the white light beam to pass sequentially through the beam splitter, the dispersive lens, and the beam splitter prism before being output as monochromatic beams of different wavelengths; and allowing a portion of the beam focused on the surface of the sample to be detected to pass through the objective lens, the beam splitter prism, and the dispersive lens before being reflected by the beam splitter and coupled into the spectral detector.

3. The optical microscope according to claim 1, characterized in that, Also includes: A drive mechanism, connected to the displacement stage, is configured to adjust the lifting and lowering of the displacement stage according to the spectral information, thereby adjusting the vertical position of the sample to be tested.

4. The optical microscope according to claim 3, characterized in that, Among the monochromatic light beams of different wavelengths, the short-wavelength beam, the mid-wavelength beam, and the long-wavelength beam are focused from top to bottom at different positions along the vertical optical axis. The beam of the target wavelength is the beam of the intermediate band.

5. The optical microscope according to claim 4, characterized in that, When the light beam focused on the surface of the sample to be tested is determined to be shifted to a longer wavelength range based on the spectral information, the driving mechanism raises the displacement stage.

6. The optical microscope according to claim 5, characterized in that, When the light beam focused on the surface of the sample to be tested is determined to be shifted to a shorter wavelength based on the spectral information, the driving mechanism lowers the displacement stage.

7. The optical microscope according to claim 2, characterized in that, Also includes: The tube mirror is positioned above the beam splitter, and The beam splitter is configured to achieve coaxial coupling between the optical path of the white light beam and the optical path of the imaging beam incident on the tube.

8. The optical microscope according to claim 7, characterized in that, Also includes: A camera is positioned above the tube mirror so that another portion of the light beam focused on the surface of the sample to be tested passes through the objective lens, the beam splitter, and the tube mirror before being imaged by the camera.

9. The optical microscope according to claim 2, characterized in that, The front surface of the dispersive lens facing the beam splitter is aspherical, and the rear surface facing the beam splitter is conical. The dispersive lens is configured to collimate and disperse the white light beam.

10. The optical microscope according to claim 2, characterized in that, The transmission-to-reflection ratio of the beam splitter is 7:3, and the transmission-to-reflection ratio of the beam splitter prism is 5:5.

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