An optical detection system and method for suppressing stray light

Abstract

The optical detection system and method for suppressing stray light provided in this application include an illumination optical path and an imaging optical path sharing a common objective lens. An illumination beam transmitted along the illumination optical path illuminates the wafer under test through the objective lens and is reflected by the wafer under test to form an imaging beam. The imaging beam is transmitted along the imaging optical path through the objective lens for imaging. By arranging optical wedges in the illumination optical path, the illumination beam is incident at a non-parallel or non-coincident angle to the optical axis of the objective lens. Back-reflected stray light generated by multiple reflections between the lenses inside the objective lens is removed from the imaging optical path, which significantly suppresses back-reflected stray light and eliminates the influence of stray light inside the objective lens on imaging.

Description

[0001] This application is a divisional application of Chinese invention patent application No. 202510081189.X, filed on January 17, 2025, entitled "An Optical Detection System and Detection Method". Technical Field

[0002] This application relates to the field of semiconductor detection technology, and in particular to an optical detection system and method for suppressing stray light. Background Technology

[0003] In semiconductor manufacturing processes, wafer inspection is a crucial step, and effective inspection directly affects the quality and performance of the wafer.

[0004] In some wafer inspection systems, a coaxial illumination and imaging optical structure is used, where the illumination and imaging paths share a single objective lens. Because the illumination beam undergoes multiple reflections between the mirrors within the objective lens as it passes through, back-reflected stray light is generated. This stray light enters the imaging system, reducing the detector's signal-to-noise ratio and decreasing the contrast of the acquired image, thus affecting image recognition and wafer defect detection. Therefore, suppressing back-reflected stray light is a crucial factor affecting the optical detection performance of inspection equipment.

[0005] Currently, there are two main methods to suppress back-reflection stray light from low-magnification objectives. The first is to redesign the objective lens, which not only presents design challenges but also increases time and cost. The second is to reduce the brightness of the light source or reduce the light intensity by adding an attenuator in the optical path. Although this method can reduce back-reflection stray light to some extent, it also results in the loss of useful information. The third is to change the transmission direction of stray light. This method has strict requirements on the optical structure of illumination and imaging; otherwise, the elimination of stray light may not be thorough.

[0006] For example, patent CN205647720U discloses a video surveillance device and its protective housing structure. This housing structure includes a protective glass located at the opening, which deflects reflected light from the lens surface outside the optical path by tilting the protective glass. In this solution, the lens optical axis and the principal optical axis of the optical path are aligned, which is more effective in eliminating stray light reflected from external lens elements. However, due to the transmission effect of the protective glass, some stray light still propagates along the principal optical axis. Therefore, this solution is more suitable for scenarios where lighting and imaging are not coaxial, and is not applicable to coaxial lighting scenarios.

[0007] For example, patent CN221726289U discloses an off-center stray light-free lens. This lens utilizes a specific angle setting of the beam splitter to prevent light illumination from reaching the center of the object-side lens. The reflected stray light is deflected upwards and does not reach the image sensor. The beam deflection in this solution originates from the relative positions of the beam shaper and the beam splitter. Due to the compact design, stray light reflected from the object-side lens may be reflected again on the beam shaper surface, allowing some stray light to still enter the imaging optical path and cause imaging interference. Summary of the Invention

[0008] In view of this, the present invention provides an optical detection system and method for suppressing stray light, so as to eliminate the influence of stray light inside the objective lens on imaging.

[0009] To solve the above problems, this application adopts the following technical solution: One objective of this application is to provide an optical detection system for suppressing stray light, comprising: an illumination optical path and an imaging optical path sharing a common objective lens; an illumination beam transmitted along the illumination optical path illuminates a wafer under test through the objective lens and is reflected by the wafer under test to form an imaging beam; the imaging beam is imaged along the imaging optical path through the objective lens; an optical wedge is provided on the illumination optical path; the illumination beam is deflected by the optical wedge, causing the illumination beam to be incident non-parallel to or non-coincident to the optical axis of the objective lens, and back-reflected stray light generated inside the objective lens is removed from the imaging optical path.

[0010] In some embodiments, the optical wedge deflects the incident illumination beam at an angle that satisfies the following condition: , where n is the refractive index of the optical wedge. λ is the incident light angle, λ is the wavelength of the illumination beam, f is the focal length of the objective lens, and NA is the numerical aperture of the objective lens.

[0011] In some embodiments, the optical wedge deflects the incident illumination beam at an angle between 0.1 and 2 degrees.

[0012] In some embodiments, the magnification of the objective lens is configured to be from 1.5X to 10X, and the objective lens generates back-reflected stray light through internally arranged multiple curvature lenses.

[0013] In some embodiments, the illumination optical path further includes a light source, an illumination tube mirror, and a beam splitter. The illumination beam emitted by the light source passes through the illumination tube mirror and is then transmitted by the beam splitter to the objective lens, and then illuminates the wafer under test through the objective lens.

[0014] In some embodiments, the imaging optical path further includes the imaging tube and the detection device. The imaging beam enters the beam splitter through the objective lens, is reflected by the beam splitter, enters the imaging tube, and is then focused by the imaging tube onto the detection device. The detection device can generate a test image corresponding to the wafer under test, and the test image is used to detect and obtain defect information of the wafer under test.

[0015] In some embodiments, a collimating lens is further provided between the light source and the illumination tube mirror, and the illumination beam emitted by the light source enters the illumination tube mirror through the collimating lens.

[0016] In some embodiments, the light wedge is disposed between the illumination tube and the beam splitter. The illumination beam emitted by the light source passes through the illumination tube, the light wedge and the beam splitter to illuminate the objective lens, and then illuminates the wafer under test through the objective lens.

[0017] A second objective of this application is to provide an optical detection method, comprising the following steps: An illumination beam emitted from the illumination optical path illuminates the wafer under test through the objective lens and is reflected by the wafer under test to form an imaging beam. The imaging beam is transmitted along the imaging optical path through the objective lens for imaging, wherein: the illumination beam is deflected by the optical wedge, so that the illumination beam is not parallel or coincident with the optical axis of the objective lens, and the back-reflected stray light generated inside the objective lens leaves the imaging optical path. Feature detection is performed on the image to be tested to obtain the defect information of the wafer to be tested.

[0018] The present application adopts the above technical solution, and its beneficial effects are as follows: The optical detection system and method for suppressing stray light provided in this application, by setting an optical wedge in the illumination optical path, causes the illumination beam to be incident at a non-parallel or non-coincident angle to the optical axis of the objective lens. The back-reflected stray light generated by multiple reflections between the lenses inside the objective lens is removed from the imaging optical path. This overcomes the problem in existing optical detection systems where stray light enters the imaging system after the illumination beam is incident parallel or coincident with the optical axis of the objective lens, thereby reducing the detector signal-to-noise ratio, reducing the contrast of the acquired image, and thus affecting image recognition and wafer defect detection. This method significantly suppresses the back-reflected stray light generated by light reflection from the lenses inside the objective lens, eliminates the influence of stray light inside the objective lens on imaging, and improves imaging quality and detection accuracy. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the optical detection system provided in Embodiment 1 of this application; Figure 2 An imaging diagram provided for the prior art when the objective lens is not tilted; Figure 3 This is a schematic diagram of imaging under objective lens tilt conditions provided in Embodiment 1 of this application; Figure 4 This is a schematic diagram of the optical detection system provided in Embodiment 2 of this application. Detailed Implementation

[0021] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0022] In the description of this application, it should be understood that the terms "upper", "lower", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0023] Furthermore, the terms "first" and "second" 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. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0024] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. Example

[0025] Please see Figure 1, which is a schematic structural diagram of the optical detection system provided by the embodiment of the present application, including an illumination optical path 100 and an imaging optical path 200. The technical solutions implemented are described in detail below.

[0026] The illumination optical path 100 and the imaging optical path 200 share an objective lens 6. The illumination beam transmitted along the illumination optical path 100 irradiates the wafer to be measured through the objective lens 6 and forms an imaging beam after being reflected by the wafer to be measured. The imaging beam is transmitted along the imaging optical path 200 through the objective lens 6 for imaging. The backward reflected stray light generated by the illumination beam incident non-parallel or non-coincident with the optical axis of the objective lens 6 and reflected multiple times between the lenses inside the objective lens breaks away from the imaging optical path 200.

[0027] In this embodiment, the objective lens 6 is inclined relative to the illumination optical path 100, which can make the incident illumination beam enter the objective lens 6 at a certain angle, so as to ensure that the illumination beam enters non-parallel or non-coincident with the optical axis of the objective lens, so that the backward reflected stray light generated by the illumination beam reflected multiple times between the lenses inside the objective lens 6 breaks away from the imaging optical path 200.

[0028] It can be understood that for the optical detection system provided by the application of this embodiment, the illumination beam enters non-parallel or non-coincident with the optical axis of the objective lens 6 and the backward reflected stray light generated by being reflected multiple times between the lenses inside the objective lens 6 breaks away from the imaging optical path 200, thus overcoming the technical defect in the existing optical detection system that the stray light enters the imaging system due to the illumination beam entering parallel or coincident with the optical axis of the objective lens, thereby reducing the signal-to-noise ratio of the detector and the contrast of the acquired image, and further affecting image recognition and wafer defect detection. It plays a significant role in suppressing the backward reflected stray light and eliminates the influence of the stray light inside the objective lens on imaging.

[0029] It should be noted that there is an inclination angle between the objective lens 6 and the incident illumination beam, and the inclination angle needs to be strictly controlled. Otherwise, there will be a blurred area in the final imaging of the beam magnified microscopically by the objective lens 6. To make the inclined objective lens 6 still be able to present a clear image, the wafer to be measured needs to be within the depth of field of the objective lens. The formula for the depth of field of the objective lens is , where λ is the wavelength of the incident light and NA is the numerical aperture of the objective lens; due to the inclination of the objective lens 6, a height difference will be introduced in the field of view, and the height difference is H = D * tanθ, where D is the entrance pupil diameter of the objective lens 6 and θ is the inclination angle of the objective lens 6. The formula for the entrance pupil diameter of the objective lens 6 is D = 2f * NA, where f is the focal length of the objective lens. To ensure that the image is still clear after the objective lens is inclined, it is necessary to ensure that the height difference introduced by the inclination of the objective lens is less than the depth of field of the objective lens, that is, H < L. Combining the above formulas, the relationship that the inclination angle needs to satisfy can be obtained as .

[0030] Furthermore, the tilt angle between the objective lens 6 and the incident illumination beam is between 0.1 and 2 degrees, preferably 0.5 degrees. The illumination beam is no longer incident perpendicularly onto the objective lens 6, but is incident obliquely onto the objective lens 6 at a small angle. During the process of passing through the objective lens 6, the illumination beam will undergo multiple reflections between the lenses inside the objective lens 6. Most of the generated backscattered light will be reflected out of the imaging light path and eventually absorbed by the light-absorbing structure, significantly suppressing backscattered stray light.

[0031] Furthermore, the magnification of objective lens 6 is configured to be between 1.5X and 10X, and objective lens 6 generates back-reflected stray light through reflection by internally arranged multiple curvature lenses.

[0032] For example, if a low-power objective lens with a magnification of 1.5X, a focal length of f = 133.33 mm, a numerical aperture NA = 0.06, and a center wavelength of the illumination source λ = 0.55 μm is selected, then the tilt angle can be calculated. Therefore, the tilt angle selected in this embodiment is 0.5 degrees.

[0033] It should be noted that: This embodiment 1 is based on the calculation of the tilt angle of a low-magnification objective. Although the calculation of the tilt angle of a high-magnification objective is also applicable, since the high-magnification objective itself is designed with the scheme of eliminating back reflection stray light, and the high-magnification objective itself has a large lens curvature, it has a greater deflection effect on stray light, which can deflect stray light outside the main optical path. Therefore, high-magnification objectives are generally not tilted.

[0034] Furthermore, the illumination optical path 100 also includes a light source 1, a collimating lens 2, an illumination tube mirror 3, a reflector 4, and a beam splitter 5. The illumination beam emitted by the light source 1 is transmitted through the collimating lens 2, the illumination tube mirror 3, and the reflector 4, and then transmitted through the beam splitter 5 to the objective lens 6, and then illuminates the wafer under test through the objective lens 6.

[0035] It is understandable that the illumination tube lens 3 can play various shaping roles for the illumination beam, such as collimation, convergence, magnification, filtering, and polarization. In actual design, the collimating lens 2 can also be omitted as needed.

[0036] Furthermore, the imaging optical path 200 also includes a beam splitter 5, an imaging tube 8, and a detector 9. The imaging beam enters the beam splitter 5 through the objective lens 6, and is reflected by the beam splitter 5 into the imaging tube 8. The imaging tube 8 then converges the beam onto the detector 9, and finally the beam is processed and analyzed by the computer to complete the detection of the wafer under test.

[0037] Please see Figure 2 and Figure 3 These are imaging schematic diagrams of the technical solution provided by the prior art (i.e., when the objective lens is not tilted) and the technical solution provided by Example 1 (i.e., when the objective lens is tilted), respectively. Figure 2 and Figure 3 As can be seen, when the objective lens is not tilted, there is backscattered stray light at the imaging center. When the objective lens is tilted (tilt angle is 0.5), the central stray light disappears, significantly suppressing the adverse effect of backscattered stray light on imaging.

[0038] The optical inspection system provided in Embodiment 1 of this application has an objective lens 6 that is tilted. This ensures that the back-reflected stray light generated by the incident illumination beam being incident on a non-parallel or non-coincident axis with the optical axis of the objective lens and undergoing multiple reflections between the lenses inside the objective lens is removed from the imaging optical path. This overcomes the technical problem in the prior art where stray light entering the imaging system leads to a decrease in the detector signal-to-noise ratio and a reduction in the contrast of the acquired image, thereby affecting image recognition and wafer defect detection. It significantly suppresses back-reflected stray light, thereby eliminating the influence of stray light inside the objective lens on imaging and improving imaging quality and wafer inspection accuracy. Example

[0039] Please see Figure 4 This is a schematic diagram of the structure of the optical detection system provided in Embodiment 2 of this application. The difference from Embodiment 1 is that the illumination optical path 100 provided in Embodiment 2 is provided with an optical wedge 10. The illumination beam is deflected by the optical wedge 10 so that the illumination beam is not parallel or coincident with the optical axis of the objective lens 6.

[0040] It is understood that the optical inspection system provided in this embodiment has an optical wedge 10 on the illumination optical path 100. The illumination beam is deflected by the optical wedge 10, causing the illumination beam to be incident in a non-parallel or non-coincident manner with the optical axis of the objective lens 6. The back-reflected stray light generated by multiple reflections between the lenses inside the objective lens 6 leaves the imaging optical path 200. This overcomes the technical defects in existing optical inspection systems, where stray light enters the imaging system due to the illumination beam being incident in a parallel or coincident manner with the optical axis of the objective lens, thereby reducing the signal-to-noise ratio of the detector, reducing the contrast of the acquired image, and thus affecting image recognition and wafer defect detection. This system has a significant effect in suppressing back-reflected stray light and eliminates the influence of stray light inside the objective lens on imaging.

[0041] In this embodiment, the optical wedge 10 will deflect the incident illumination beam by an angle, and the deflection angle satisfies the following condition: Where: n is the refractive index of the optical wedge, λ is the incident angle, λ is the wavelength of the illumination beam, f is the focal length of the objective lens, and NA is the numerical aperture of the objective lens.

[0042] Furthermore, the deflection angle of the incident illumination beam produced by the optical wedge is between 0.1 and 2 degrees, preferably 0.5 degrees. The illumination beam is no longer incident perpendicularly onto the objective lens 6, but rather obliquely onto the objective lens 6 at a small angle. During its passage through the objective lens 6, the illumination beam undergoes multiple reflections between the mirrors inside the objective lens 6. Most of the generated backscattered light will be reflected out of the imaging optical path and ultimately absorbed by the light-absorbing structure, significantly suppressing backscattered stray light.

[0043] Furthermore, the magnification of objective lens 6 is configured to be between 1.5X and 10X, and objective lens 6 generates back-reflected stray light through reflection by internally arranged multiple curvature lenses.

[0044] For example, if a low-power objective lens with a magnification of 1.5X, a focal length of f = 133.33 mm, a numerical aperture NA = 0.06, and a center wavelength of the illumination source λ = 0.55 μm is selected, then the deflection angle can be calculated. Therefore, the deflection angle selected in this embodiment is 0.5 degrees.

[0045] It should be noted that: This embodiment 2 uses a low-magnification objective lens as an example, which can limit the wedge angle of the wedge lens to have a corresponding relationship with the objective lens magnification. When a certain low-magnification objective lens is placed in the optical path, the corresponding wedge lens is cut into the optical path. The high-magnification objective lens itself has a larger reflection angle, so it does not need to be cut into the wedge lens for cooperation when it is placed in the optical path.

[0046] Furthermore, the illumination optical path 100 also includes a light source 1, a collimating lens 2, an illumination tube mirror 3, a reflector 4, an optical wedge 10, and a beam splitter 5. The illumination beam emitted by the light source 1 passes through the collimating lens 2, the illumination tube mirror 3, the reflector 4, and the optical wedge 10, and is then transmitted to the objective lens 6 by the beam splitter 5, and then illuminates the wafer under test through the objective lens 6.

[0047] It is understandable that the illumination tube lens 3 can play various shaping roles for the illumination beam, such as collimation, convergence, magnification, filtering, and polarization. In actual design, the collimating lens 2 can also be omitted as needed.

[0048] Furthermore, the imaging optical path 200 also includes an imaging tube 8 and a detector 9. The imaging beam enters the beam splitter 5 through the objective lens 6, and is reflected by the beam splitter 5 into the imaging tube 8. The imaging tube 8 then converges the beam onto the detector 9. The detector 9 can generate a test image corresponding to the wafer under test. The test image is used to detect the defect information of the wafer under test. Finally, the wafer under test is processed and analyzed by a computer to complete the detection of the wafer under test.

[0049] The optical inspection system provided in Embodiment 2 of this application has an optical wedge 10 on the illumination optical path 100. The illumination beam is deflected by the optical wedge 10, causing the illumination beam to be incident on a non-parallel or non-coincident optical axis with the objective lens 6. The back-reflected stray light generated by multiple reflections between the lenses inside the objective lens leaves the imaging optical path. This overcomes the technical problem in the prior art where stray light entering the imaging system leads to a decrease in the detector signal-to-noise ratio and a reduction in the contrast of the acquired image, which in turn affects image recognition and wafer defect detection. It plays a significant role in suppressing back-reflected stray light, thereby eliminating the influence of stray light inside the objective lens on imaging and improving imaging quality and wafer inspection accuracy. In addition, setting the optical wedge 10 on the illumination optical path 100 improves the operational difficulty of setting the tilted objective lens in Embodiment 1. Example

[0050] Embodiment 3 of this application also provides an optical inspection method, including the following steps: an illumination beam emitted from the illumination optical path illuminates the wafer under test through an objective lens and is reflected by the wafer under test to form an imaging beam; the imaging beam is transmitted along the imaging optical path through the objective lens for imaging, wherein: the illumination beam is incident on the objective lens in a manner that is not parallel or coincident with the optical axis of the objective lens and back-reflected stray light generated inside the objective lens leaves the imaging optical path; feature detection is performed on the image under test to obtain defect information of the wafer under test.

[0051] In some embodiments, the objective lens is tilted relative to the illumination optical path such that the illumination beam is incident on a direction that is not parallel to or coincides with the optical axis of the objective lens.

[0052] In this embodiment, the objective lens is tilted relative to the illumination optical path, so that the incident illumination beam enters the objective lens at a certain angle. This ensures that the illumination beam is not parallel or coincident with the optical axis of the objective lens, causing back-reflected stray light generated by multiple reflections between the lenses inside the objective lens to escape from the imaging optical path. This overcomes the technical defects in existing optical inspection systems, where stray light enters the imaging system due to the illumination beam being parallel or coincident with the optical axis of the objective lens, thereby reducing the detector signal-to-noise ratio, reducing the contrast of the acquired image, and thus affecting image recognition and wafer defect detection. This significantly suppresses back-reflected stray light and eliminates the influence of stray light inside the objective lens on imaging.

[0053] It should be noted that there is a tilt angle between objective lens 6 and the incident illumination beam. This tilt angle needs to be strictly controlled; otherwise, the objective lens will ultimately produce a blurry image. To ensure a clear image from the tilted objective lens, the wafer under test needs to be within the depth of field of the objective lens. The formula for calculating the depth of field of the objective lens is as follows: , where λ is the wavelength of the incident light and NA is the numerical aperture of the objective lens; due to the tilt of the objective lens, a height difference will be introduced in the field of view, and the height difference is H = D * tanθ, where D is the entrance pupil diameter of the objective lens and θ is the tilt angle of the objective lens. The formula for calculating the entrance pupil diameter of the objective lens is D = 2f * NA, where f is the focal length of the objective lens. To ensure that the image remains clear after the objective lens is tilted, it is necessary to ensure that the height difference introduced by the tilt of the objective lens is less than the depth of field of the objective lens, that is, H < L. Combining the above formulas, the relationship that the tilt angle needs to satisfy can be obtained as .

[0054] Furthermore, the tilt angle between the objective lens and the incident illumination beam is between 0.1 and 2 degrees, preferably 0.5 degrees. The illumination beam no longer enters the objective lens perpendicularly, but obliquely enters the objective lens at a small angle. During the process of passing through the objective lens, the illumination beam will undergo multiple reflections between the lenses inside the objective lens. Most of the generated backward reflected light will be reflected out of the imaging optical path and finally absorbed by the light-absorbing structural member, significantly suppressing the backward scattered stray light.

[0055] Furthermore, the magnification of the objective lens 6 is configured to be 1.5X to 10X, and the objective lens 6 forms backward reflected stray light through the reflection of multiple curvature lenses provided inside.

[0056] In some other embodiments, a prism is further provided on the illumination optical path, and the illumination beam is deflected by the prism so that the illumination beam enters the objective lens non-parallel or non-coincident with the optical axis of the objective lens.

[0057] It can be understood that in this embodiment, a prism is provided on the illumination optical path, and the illumination beam is deflected by the prism so that the illumination beam enters the objective lens non-parallel or non-coincident with the optical axis of the objective lens, and the backward reflected stray light generated by multiple reflections between the lenses inside the objective lens is separated from the imaging optical path, thereby overcoming the technical defect in the existing optical detection system that the stray light enters the imaging system due to the illumination beam entering the objective lens parallel or coincident with the optical axis of the objective lens, thereby reducing the signal-to-noise ratio of the detector, reducing the contrast of the acquired image, and further affecting image recognition and wafer defect detection. It plays a role in significantly suppressing the backward reflected stray light and eliminates the influence of the internal stray light of the objective lens on imaging.

[0058] In this embodiment, the prism will generate a deflection angle for the incident illumination beam, and the deflection angle satisfies the following conditions: , where: n is the refractive index of the prism, is the incident light angle, λ is the wavelength of the illumination beam, f is the focal length of the objective lens, and NA is the numerical aperture of the objective lens.

[0059] Furthermore, the deflection angle of the incident illumination beam produced by the optical wedge is between 0.1 and 2 degrees, preferably 0.5 degrees. The illumination beam is no longer incident perpendicularly onto the objective lens 6, but rather obliquely onto the objective lens 6 at a small angle. During its passage through the objective lens 6, the illumination beam undergoes multiple reflections between the mirrors inside the objective lens 6. Most of the generated backscattered light will be reflected out of the imaging optical path and ultimately absorbed by the light-absorbing structure, significantly suppressing backscattered stray light.

[0060] The optical inspection method provided in this application eliminates back-reflected stray light generated by the illumination beam being incident on the objective lens in a manner that is not parallel to or coincident with the optical axis of the objective lens, and undergoing multiple reflections between the lenses inside the objective lens. This overcomes the problem in existing optical inspection systems where stray light enters the imaging system after the illumination beam is incident on the objective lens in a manner that is parallel to or coincident with the optical axis of the objective lens. This reduces the signal-to-noise ratio of the detector, decreases the contrast of the acquired image, and consequently affects image recognition and wafer defect detection. The method significantly suppresses back-reflected stray light, eliminates the influence of stray light inside the objective lens on imaging, and improves imaging quality and inspection accuracy.

[0061] The above are merely preferred embodiments of this application, and only specifically describe the technical principles of this application. These descriptions are only for explaining the principles of this application and should not be construed as limiting the scope of protection of this application in any way. Based on this explanation, any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application, as well as other specific embodiments of this application that can be conceived by those skilled in the art without creative effort, should be included within the scope of protection of this application.

Claims

1. An optical detection system for suppressing stray light, characterized in that, include: They share the same illumination and imaging optical paths for a single objective lens; An illumination beam transmitted along the illumination optical path illuminates the wafer under test through the objective lens and is reflected by the wafer under test to form an imaging beam. The imaging beam is transmitted along the imaging optical path through the objective lens for imaging. The illumination optical path is provided with an optical wedge, and the illumination beam is deflected by the optical wedge, so that the illumination beam is incident on a non-parallel or non-coincident optical axis with the objective lens, and the back-reflected stray light generated inside the objective lens leaves the imaging optical path.

2. The optical inspection system as described in claim 1, characterized in that, The optical wedge will deflect the incident illumination beam by an angle, and the deflection angle satisfies the following condition: , where n is the refractive index of the optical wedge. λ is the incident light angle, λ is the wavelength of the illumination beam, f is the focal length of the objective lens, and NA is the numerical aperture of the objective lens.

3. The optical inspection system as described in claim 2, characterized in that, The deflection angle of the incident illumination beam produced by the optical wedge is between 0.1 and 2 degrees.

4. The optical inspection system as described in claim 1, characterized in that, The magnification of the objective lens is configured to be between 1.5X and 10X, and the objective lens generates back-reflected stray light through reflection by internally arranged multiple curvature lenses.

5. The optical inspection system as described in claim 1, characterized in that, The illumination optical path also includes a light source, an illumination tube mirror, and a beam splitter. The illumination beam emitted by the light source passes through the illumination tube mirror and is then transmitted by the beam splitter to the objective lens, and then illuminates the wafer under test through the objective lens.

6. The optical inspection system as described in claim 5, characterized in that, The imaging optical path also includes the imaging tube and the detector. The imaging beam enters the beam splitter through the objective lens, is reflected by the beam splitter and enters the imaging tube, and is then focused by the imaging tube to form an image on the detector. The detection device can generate a test image corresponding to the wafer under test, and the test image is used to detect and obtain the defect information of the wafer under test.

7. The optical inspection system as described in claim 5, characterized in that, A collimating lens is also provided between the light source and the illumination tube mirror, and the illumination beam emitted by the light source enters the illumination tube mirror through the collimating lens.

8. The optical inspection system as described in claim 5, characterized in that, The light wedge is disposed between the illumination tube and the beam splitter. The illumination beam emitted by the light source passes through the illumination tube, the light wedge and the beam splitter and then illuminates the objective lens, which in turn illuminates the wafer under test.

9. An optical detection method, employing the optical detection system as described in any one of claims 1-8, characterized in that, Includes the following steps: The illumination beam emitted from the illumination optical path illuminates the wafer under test through the objective lens, and is reflected by the wafer under test to form an imaging beam; The imaging beam is transmitted along the imaging optical path through the objective lens for imaging and to acquire the image to be tested; wherein, the illumination beam is deflected by the optical wedge, so that the illumination beam is incident on a non-parallel or non-coincident optical axis with the objective lens, and the back-reflected stray light generated inside the objective lens leaves the imaging optical path. Feature detection is performed on the image to be tested to obtain the defect information of the wafer to be tested.

Images