Optical detection system and detection method

Abstract

According to the optical detection system and the detection method, an illumination light path and an imaging light path which share one objective lens are included, an illumination light beam transmitted along the illumination light path irradiates a to-be-detected wafer through the objective lens and is reflected by the to-be-detected wafer to form an imaging light beam, and the imaging light beam is transmitted along the imaging light path through the objective lens to be used for imaging. The illumination light beam enters in a manner that the illumination light beam is not parallel to or does not coincide with the optical axis of the objective lens, and backward reflection stray light generated by multiple times of reflection between the lenses in the objective lens is separated from an imaging light path, so that the effect of remarkably inhibiting the backward reflection stray light is achieved, and the influence of the stray light in the objective lens on imaging is eliminated.

Description

Technical Field

[0001] The present application relates to the field of semiconductor detection technology, and in particular to an optical detection system and a detection method. Background Art

[0002] In the semiconductor production process, wafer inspection is a very important part of the semiconductor manufacturing process. Effective inspection is directly related to the quality and performance of the wafer.

[0003] In some wafer inspection systems, coaxial illumination and imaging optical structures are used. The illumination light path and the imaging light path share the same objective lens. As the illumination beam passes through the objective lens, it will be reflected multiple times between the lenses inside the objective lens, generating back-reflected stray light. When the stray light enters the imaging system, it will reduce the detector signal-to-noise ratio and the contrast of the collected image, thereby affecting image recognition and wafer defect detection. Therefore, the suppression of back-reflected stray light is an important factor affecting the optical detection performance of the inspection equipment.

[0004] There are currently two main methods for suppressing back-reflected stray light from low-magnification objectives. The first is to redesign the objective, which not only has design difficulties but also increases time and price costs. The second is to reduce the brightness of the light source or reduce the light intensity by adding an attenuation plate in the optical path. Although this method can reduce back-reflected stray light to a certain extent, it also loses useful information. The third is to change the transmission direction of stray light. This method has strict requirements on the optical structure of lighting and imaging, otherwise there is a problem of incomplete elimination of stray light.

[0005] For example, patent CN205647720U discloses a video surveillance device and its shield structure, which includes a shield glass located at the opening, and the shield glass is tilted to deflect the reflected light on the surface of the lens outside the optical path. The lens optical axis of this solution is overlapped with the main optical axis of the optical path, which is more effective in eliminating stray light reflected by the external lens of the lens. However, due to the transmission effect of the shield glass, some stray light will still be transmitted along the main optical axis of the optical path, so this solution is more suitable for scenes with non-coaxial lighting and imaging, and is not applicable to coaxial lighting scenes.

[0006] For another example, patent CN221726289U discloses an eccentric stray light-free lens, which uses a specific angle setting of a beam splitter to prevent the light from irradiating the center of the object lens. The reflected stray light is deflected when propagating upward and does not reach the image sensor. The beam deflection of this solution comes from the relative position relationship between the beam shaper and the beam splitter. Due to the compact structural design, the stray light reflected by the object lens may be reflected again on the surface of the beam shaper, and some stray light will still enter the imaging optical path and cause imaging interference. Summary of the invention

[0007] In view of this, the present invention provides an optical detection system and a detection method to eliminate the influence of stray light inside the objective lens on imaging.

[0008] To solve the above problems, this application adopts the following technical solutions:

[0009] One of the purposes of the present application is to provide an optical detection system, comprising: an illumination light path and an imaging light path that share an objective lens, an illumination light beam transmitted along the illumination light path irradiating a wafer to be tested through the objective lens and reflected by the wafer to be tested to form an imaging light beam, the imaging light beam is imaged along the imaging light path through the objective lens, the illumination light beam is incident in a non-parallel or non-coincident direction with the optical axis of the objective lens and the back-reflected stray light generated inside the objective lens escapes from the imaging light path.

[0010] In some embodiments, the objective lens is tilted relative to the illumination light path so that the illumination light beam is incident in a non-parallel or non-coincident manner with the optical axis of the objective lens.

[0011] In some embodiments, there is an inclination angle between the objective lens and the incident illumination light beam, and the inclination angle needs to satisfy the relationship θ <arctan(λ / 2f*NA 3 ), wherein λ is the wavelength of the illumination light beam, f is the focal length of the objective lens, and NA is the numerical aperture of the objective lens.

[0012] In some embodiments, the tilt angle between the objective lens and the incident illumination light beam is between 0.1 and 2 degrees.

[0013] In some of the embodiments, an optical wedge is provided on the illumination optical path, and the illumination light beam is deflected by the optical wedge, so that the illumination light beam is incident in a non-parallel or non-coincident manner with the optical axis of the objective lens.

[0014] In some embodiments, the optical wedge generates a deflection angle for the incident illumination beam, and the deflection angle satisfies the following condition: Δ=2(n-1)*δ <arctan(λ / 2f*NA 3 ), n is the refractive index of the optical wedge, δ is the incident light angle, λ is the wavelength of the illumination light beam, f is the focal length of the objective lens, and NA is the numerical aperture of the objective lens.

[0015] In some embodiments, the deflection angle of the incident illumination light beam caused by the optical wedge is between 0.1 and 2 degrees.

[0016] In some of the embodiments, the magnification of the objective lens is configured to be 1.5X to 10X, and the objective lens forms retroreflected stray light through reflection by a multiple-curvature lens disposed inside.

[0017] In some embodiments, the illumination light path further includes a light source, an illumination tube lens and a spectroscopic element. The illumination light beam emitted by the light source passes through the illumination tube lens, is transmitted to the objective lens by the spectroscopic element, and then illuminates the wafer to be tested through the objective lens.

[0018] In some embodiments, the imaging optical path also includes the imaging tube lens and the detection device. The imaging light beam enters the spectroscopic element through the objective lens, is reflected by the spectroscopic element and enters the imaging tube lens, and is then converged by the imaging tube lens to form an image on the detection device. The detection device can generate an image to be tested corresponding to the wafer to be tested, and the image to be tested is used to detect and obtain defect information of the wafer to be tested.

[0019] In some embodiments, a collimating lens is further disposed between the light source and the lighting tube lens, and the lighting light beam emitted by the light source enters the lighting tube lens through the collimating lens.

[0020] In some embodiments, the optical wedge is disposed between the illumination tube lens and the beam splitter element, the illumination light beam emitted by the light source passes through the illumination tube lens, the optical wedge and the beam splitter element, and then irradiates the objective lens, and then irradiates the wafer to be tested through the objective lens.

[0021] The second object of the present application is to provide an optical detection method, comprising the following steps:

[0022] The illumination light beam emitted from the illumination light path irradiates the wafer to be tested through the objective lens, and is reflected by the wafer to be tested to form an imaging light beam; the imaging light beam is transmitted along the imaging light path through the objective lens for imaging, wherein: the illumination light beam is incident in a non-parallel or non-coincident direction with the optical axis of the objective lens, and the back-reflected stray light generated inside the objective lens deviates from the imaging light path;

[0023] Perform feature detection on the image to be tested to obtain defect information of the wafer to be tested.

[0024] This application adopts the above technical solution, and its beneficial effects are as follows:

[0025] The optical detection system and detection method provided by the present application are characterized in that the illumination light beam is incident in a non-parallel or non-coincident relationship with the optical axis of the objective lens and multiple reflections occur between the lenses inside the objective lens, resulting in the retroreflected stray light being deviated from the imaging optical path. This overcomes the problem in the existing optical detection system that the stray light enters the imaging system after the illumination light beam is incident in a parallel or coincident relationship with the optical axis of the objective lens, thereby reducing the detector signal-to-noise ratio and the contrast of the collected image, thereby affecting image recognition and wafer defect detection. This significantly suppresses the retroreflected stray light generated by light reflection from each lens inside the objective lens, eliminates the influence of the stray light inside the objective lens on imaging, and improves the imaging quality and detection accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1 is a schematic diagram of the structure of the optical detection system provided in Example 1 of the present application;

[0028] Figure 2 A schematic diagram of imaging provided by the prior art when the objective lens is not tilted;

[0029] Figure 3 The imaging diagram provided in Example 1 of the present application is when the objective lens is tilted;

[0030] Figure 4 It is a schematic diagram of the structure of the optical detection system provided in Example 2 of the present application. DETAILED DESCRIPTION

[0031] Embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, and should not be construed as limiting the present application.

[0032] In the description of the present application, it should be understood that the terms "upper", "lower", "horizontal", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0033] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0034] In order to make the objectives, technical solutions and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0035] Example 1

[0036] Please refer to 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 following details the implemented technical solution.

[0037] 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 escapes from the imaging optical path 200.

[0038] 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 escapes from the imaging optical path 200.

[0039] It can be understood that in the optical detection system provided by the embodiment of the present application, 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 escapes from the imaging optical path 200. Therefore, it overcomes 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.

[0040] 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 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 L = λ / NA 2 , 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 clear imaging 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 is θ < arctan(λ / 2f*NA3 ).

[0041] Furthermore, the inclination angle between the objective lens 6 and the incident illumination light beam is between 0.1 and 2 degrees, preferably 0.5 degrees. The illumination light beam is no longer incident on the objective lens 6 vertically, but is incident on the objective lens 6 obliquely at a small angle. The illumination light beam will be reflected multiple times between the lenses inside the objective lens 6 during the process of passing through the objective lens 6. Most of the back-reflected light generated will be reflected out of the imaging light path and eventually absorbed by the light-absorbing structure, thereby significantly suppressing backscattered stray light.

[0042] Furthermore, the magnification of the objective lens 6 is configured to be 1.5X to 10X, and the objective lens 6 reflects the back-reflected stray light through the multiple curvature lenses arranged inside.

[0043] For example, if the low-power objective lens is selected with a magnification of 1.5X, focal length f = 133.33mm, numerical aperture NA = 0.06, and the central wavelength λ of the illumination source = 0.55μm, the calculated tilt angle θ<0.55 0 Therefore, the inclination angle selected in this embodiment is 0.5 degrees.

[0044] It should be noted that: this embodiment 1 is explained by calculating the tilt angle of a low-power objective lens. Although the tilt angle calculation of a high-power objective lens is also applicable, since the high-power objective lens itself is designed with the solution of eliminating retroreflected stray light in mind, and the high-power objective lens itself has a larger lens curvature, which has a greater deflection effect on stray light and can deflect stray light outside the main light path, the high-power objective lens is generally not tilted.

[0045] Furthermore, the illumination optical path 100 also includes a light source 1, a collimating lens 2, an illumination tube lens 3, a reflective device 4 and a spectroscopic element 5. The illumination light beam emitted by the light source 1 passes through the collimating lens 2, the illumination tube lens 3, and the reflective device 4, and then is transmitted to the objective lens 6 by the spectroscopic element 5, and then illuminates the wafer to be tested through the objective lens 6.

[0046] It can be understood that the illumination tube lens 3 can play various shaping roles on the illumination light beam, such as collimation, convergence, amplification, filtering, polarization, etc. In actual design, the collimating lens 2 can also be omitted according to needs.

[0047] Furthermore, the imaging optical path 200 also includes a spectroscopic element 5, an imaging tube lens 8 and a detection device 9. The imaging light beam enters the spectroscopic element 5 through the objective lens 6, and enters the imaging tube lens 8 after being reflected by the spectroscopic element 5, and then converges through the imaging tube lens 8 to form an image on the detection device 9, and finally is processed and analyzed by a computer to complete the detection of the wafer to be tested.

[0048] See also Figure 2 and Figure 3, are respectively the 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), from Figure 2 and Figure 3 It can be seen that when the objective lens is not tilted, there is back-reflected stray light in the imaging center. When the objective lens is tilted (the tilt angle is 0.5), the central stray light disappears, significantly suppressing the adverse effect of backscattered stray light on imaging.

[0049] In the optical detection system provided in Example 1 of the present application, the objective lens 6 is arranged at an angle, that is, the incident illumination light beam is incident in a non-parallel or non-coincident manner with the optical axis of the objective lens and is reflected multiple times between the lenses inside the objective lens, and the retroreflected stray light generated by the light escapes from the imaging light path. This overcomes the technical problem in the prior art that the detector signal-to-noise ratio is reduced and the contrast of the collected image is reduced due to the stray light entering the imaging system, thereby affecting image recognition and wafer defect detection. It plays a role in significantly suppressing the retroreflected stray light, thereby eliminating the influence of the stray light inside the objective lens on the imaging, and improving the imaging quality and wafer detection accuracy.

[0050] Example 2

[0051] See also Figure 4 , is a structural schematic diagram of an optical detection system provided in Example 2 of the present application. The difference from Example 1 is that an optical wedge 10 is provided on the illumination optical path 100 provided in Example 2, and the illumination light beam is deflected by the optical wedge 10 so that the illumination light beam is incident in a non-parallel or non-coincident direction with the optical axis of the objective lens 6.

[0052] It can be understood that in the optical detection system provided by the present embodiment, an optical wedge 10 is provided on the illumination optical path 100, and the illumination light beam is deflected by the optical wedge 10 so that the illumination light beam is incident in a non-parallel or non-coincident manner with the optical axis of the objective lens 6, and the back-reflected stray light generated by multiple reflections between the lenses inside the objective lens 6 is separated from the imaging optical path 200, thereby overcoming the technical defect in the existing optical detection system that the stray light enters the imaging system due to the illumination light 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 collected image, and further affecting image recognition and wafer defect detection, and playing a role in significantly suppressing the back-reflected stray light, and eliminating the influence of the stray light inside the objective lens on imaging.

[0053] In this embodiment, the optical wedge 10 generates a deflection angle for the incident illumination light beam, and the deflection angle satisfies the following condition: Δ=2(n-1)*δ <arctan(λ / 2f*NA 3 ), where: n is the refractive index of the wedge, δ 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.

[0054] Furthermore, the deflection angle of the incident illumination light beam produced by the optical wedge is between 0.1 and 2 degrees, preferably 0.5 degrees. The illumination light beam is no longer incident vertically on the objective lens 6, but is incident obliquely on the objective lens 6 at a small angle. During the process of passing through the objective lens 6, the illumination light beam will be reflected multiple times between the lenses inside the objective lens 6. Most of the back-reflected light generated will be reflected out of the imaging light path and finally absorbed by the light-absorbing structural member, which significantly suppresses the backscattered stray light.

[0055] Furthermore, the magnification of the objective lens 6 is configured to be 1.5X to 10X, and the objective lens 6 reflects the back-reflected stray light through the multiple curvature lenses arranged inside.

[0056] For example, if the low-power objective lens is selected with a magnification of 1.5X, focal length f = 133.33mm, numerical aperture NA = 0.06, and the central wavelength of the illumination light source λ = 0.55μm, the deflection angle θ<0.55 is calculated. 0 , so the deflection angle selected in this embodiment is 0.5 degrees.

[0057] It should be noted that: this embodiment 2 is explained using a low-magnification objective lens, and it can be defined that there is a corresponding relationship between the wedge angle of the wedge mirror and the objective lens magnification. When a low-magnification objective lens is placed in the optical path, the corresponding wedge mirror is cut into the optical path. The high-magnification objective lens itself has a larger reflection angle, so it does not need to cut into the wedge mirror for cooperation when it is placed in the optical path.

[0058] Furthermore, the illumination optical path 100 also includes a light source 1, a collimating lens 2, an illumination tube lens 3, a reflective device 4, an optical wedge 10 and a spectroscopic element 5. The illumination light beam emitted by the light source 1 passes through the collimating lens 2, the illumination tube lens 3, the reflective device 4 and the optical wedge 10, and then is transmitted to the objective lens 6 by the spectroscopic element 5, and then illuminates the wafer to be tested through the objective lens 6.

[0059] It can be understood that the illumination tube lens 3 can play various shaping roles on the illumination light beam, such as collimation, convergence, amplification, filtering, polarization, etc. In actual design, the collimating lens 2 can also be omitted according to needs.

[0060] Furthermore, the imaging optical path 200 also includes an imaging tube lens 8 and a detection device 9. The imaging light beam enters the spectroscopic element 5 through the objective lens 6, and enters the imaging tube lens 8 after being reflected by the spectroscopic element 5, and then converges through the imaging tube lens 8 to form an image on the detection device 9. The detection device 9 can generate an image to be tested corresponding to the wafer to be tested. The image to be tested is used to detect and obtain defect information of the wafer to be tested, and finally the image is processed and analyzed by a computer to complete the detection of the wafer to be tested.

[0061] The optical detection system provided in Example 2 of the present application is provided with an optical wedge 10 on the illumination light path 100. The illumination light beam is deflected by the optical wedge 10 so that the illumination light beam is incident in a non-parallel or non-coincident manner with the optical axis of the objective lens 6, and the back-reflected stray light generated by multiple reflections between the lenses inside the objective lens is separated from the imaging light path, thereby overcoming the technical problem in the prior art that the detector signal-to-noise ratio is reduced and the contrast of the collected image is reduced due to the stray light entering the imaging system, thereby affecting image recognition and wafer defect detection, and playing a role in significantly suppressing the back-reflected stray light, thereby eliminating the influence of the stray light inside the objective lens on imaging, and improving the imaging quality and wafer detection accuracy; in addition, by providing the optical wedge 10 on the illumination light path 100, the operational difficulty of providing a tilted objective lens in Example 1 is improved.

[0062] Example 3

[0063] Embodiment 3 of the present application further provides an optical detection method, comprising the following steps: an illumination light beam emitted from an illumination light path illuminates a wafer to be tested via an objective lens and is reflected by the wafer to be tested to form an imaging light beam, the imaging light beam is transmitted along the imaging light path via the objective lens for imaging, wherein: the illumination light beam is incident in a non-parallel or non-overlapping direction with the optical axis of the objective lens and the retroreflected stray light generated inside the objective lens escapes from the imaging light path; feature detection is performed on the image to be tested to obtain defect information of the wafer to be tested.

[0064] In some embodiments, the objective lens is tilted relative to the illumination light path so that the illumination light beam is incident in a non-parallel or non-coincident direction with the optical axis of the objective lens.

[0065] In the present embodiment, the objective lens is arranged at an inclination relative to the illumination light path, that is, the incident illumination light beam enters the objective lens at a certain angle, thereby ensuring that the illumination light beam is incident in a non-parallel or non-coincident manner with the optical axis of the objective lens, so that the back-reflected stray light generated by multiple reflections of the illumination light beam between the lenses inside the objective lens deviates from the imaging light path, thereby overcoming the technical defect in the existing optical detection system that the stray light enters the imaging system due to the illumination light beam being incident in parallel or coincident with the optical axis of the objective lens, thereby reducing the detector signal-to-noise ratio and the contrast of the collected image, thereby affecting image recognition and wafer defect detection, and playing a role in significantly suppressing back-reflected stray light, and eliminating the influence of the stray light inside the objective lens on imaging.

[0066] It should be noted that there is a tilt angle between the objective lens 6 and the incident illumination beam, and the tilt angle needs to be strictly controlled, otherwise the objective lens will eventually have a blurred area in the image. To make the image of the tilted objective lens clear, the wafer to be tested needs to be within the depth of field of the objective lens, where the depth of field calculation formula of the objective lens is L = λ / NA 2, 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 clear imaging 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 θ < arctan(λ / 2f * NA 3 ).

[0067] 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 is no longer incident perpendicularly on the objective lens, but obliquely incident on 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 components, significantly suppressing the backward scattered stray light.

[0068] 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 the multi-curvature lens arranged inside.

[0069] 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 is incident non-parallel or non-coincident with the optical axis of the objective lens.

[0070] 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 is incident 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 being incident 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 eliminating the influence of the stray light inside the objective lens on imaging.

[0071] In this embodiment, the prism will generate a deflection angle for the incident illumination beam, and the deflection angle satisfies the following conditions: Δ = 2(n - 1) * δ < arctan(λ / 2f * NA 3 ), where: n is the refractive index of the prism, δ 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.

[0072] Furthermore, the deflection angle of the incident illumination light beam produced by the optical wedge is between 0.1 and 2 degrees, preferably 0.5 degrees. The illumination light beam is no longer incident vertically on the objective lens 6, but is incident obliquely on the objective lens 6 at a small angle. During the process of passing through the objective lens 6, the illumination light beam will be reflected multiple times between the lenses inside the objective lens 6. Most of the back-reflected light generated will be reflected out of the imaging light path and finally absorbed by the light-absorbing structural member, which significantly suppresses the backscattered stray light.

[0073] The optical detection method provided by the present application is that the illumination light beam is incident in a non-parallel or non-coincident relationship with the optical axis of the objective lens and is reflected multiple times between the lenses inside the objective lens, resulting in the back-reflected stray light being deviated from the imaging optical path. This overcomes the problem in the existing optical detection system that the stray light enters the imaging system after the illumination light beam is incident in a parallel or coincident relationship with the optical axis of the objective lens, thereby reducing the detector signal-to-noise ratio and the contrast of the collected image, thereby affecting image recognition and wafer defect detection. It plays a role in significantly suppressing the back-reflected stray light, eliminating the influence of the stray light inside the objective lens on the imaging, and improving the imaging quality and detection accuracy.

[0074] The above are only preferred embodiments of the present application, and only specifically describe the technical principles of the present application. These descriptions are only for explaining the principles of the present application and cannot be interpreted as limiting the scope of protection of the present application in any way. Based on the explanation here, any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application, and other specific implementation methods of the present application that can be associated with the technicians in this field without creative work, should be included in the scope of protection of the present application.

Claims

1. An optical detection system, characterized in that: include: The illumination optical path and the imaging optical path share the same objective lens; The illumination light beam transmitted along the illumination light path irradiates the wafer to be tested through the objective lens and is reflected by the wafer to be tested to form an imaging light beam, and the imaging light beam is transmitted along the imaging light path through the objective lens for imaging; The illumination light beam is incident in a non-parallel or non-coincident relationship with the optical axis of the objective lens, and the back-reflected stray light generated inside the objective lens deviates from the imaging light path.

2. The optical detection system according to claim 1, characterized in that: The objective lens is arranged at an angle relative to the illumination light path, so that the illumination light beam is incident in a non-parallel or non-coincident relationship with the optical axis of the objective lens.

3. The optical detection system according to claim 2, characterized in that: There is an inclination angle between the objective lens and the incident illumination light beam, and the inclination angle needs to satisfy the relationship θ <arctan(λ / 2f*NA 3 ); Wherein, λ is the wavelength of the illumination light beam, f is the focal length of the objective lens, and NA is the numerical aperture of the objective lens.

4. The optical detection system according to claim 3, characterized in that: The inclination angle between the objective lens and the incident illumination light beam is between 0.1 and 2 degrees.

5. The optical detection system according to claim 1, characterized in that: An optical wedge is arranged on the illumination optical path, and the illumination light beam is deflected by the optical wedge, so that the illumination light beam is incident in a non-parallel or non-coincident direction with the optical axis of the objective lens.

6. The optical detection system according to claim 5, characterized in that: The optical wedge will generate a deflection angle for the incident illumination light beam, and the deflection angle satisfies the following condition: Δ=2(n-1)*δ <arctan(λ / 2f*NA 3 ), n is the refractive index of the optical wedge, δ is the incident light angle, λ is the wavelength of the illumination light beam, f is the focal length of the objective lens, and NA is the numerical aperture of the objective lens.

7. The optical detection system according to claim 6, characterized in that: The deflection angle of the incident illumination light beam caused by the optical wedge is between 0.1 and 2 degrees.

8. The optical detection system according to claim 1, characterized in that: The magnification of the objective lens is configured to be 1.5X to 10X, and the objective lens forms retroreflected stray light through reflection by a multiple curvature lens disposed inside.

9. The optical detection system according to claim 5, characterized in that: The illumination light path also includes a light source, an illumination tube lens and a beam splitter. The light source emits the illumination light beam which is then transmitted to the objective lens by the beam splitter and then illuminates the wafer to be tested through the objective lens.

10. The optical detection system according to claim 9, characterized in that: The imaging optical path also includes the imaging tube lens and the detection device. The imaging light beam enters the beam splitter through the objective lens, is reflected by the beam splitter and enters the imaging tube lens, and is then converged by the imaging tube lens to form an image on the detection device. The detection device can generate an image to be tested corresponding to the wafer to be tested, and the image to be tested is used to detect and obtain defect information of the wafer to be tested.

11. The optical detection system according to claim 9, characterized in that: A collimating lens is also arranged between the light source and the lighting tube lens, and the lighting light beam emitted by the light source enters the lighting tube lens through the collimating lens.

12. The optical detection system according to claim 9, characterized in that: The optical wedge is arranged between the illumination tube lens and the beam splitter element. The illumination light beam emitted by the light source is irradiated to the objective lens after passing through the illumination tube lens, the optical wedge and the beam splitter element, and then irradiates the wafer to be tested through the objective lens.

13. An optical detection method, using the optical detection system according to any one of claims 1 to 12, characterized in that: The steps include: The illumination light beam emitted from the illumination light path illuminates the wafer to be tested through the objective lens, and is reflected by the wafer to be tested to form an imaging light beam; The imaging light beam is transmitted along the imaging light path through the objective lens for imaging, and the image to be measured is acquired; wherein the illumination light beam is incident in a non-parallel or non-coincident manner with the optical axis of the objective lens, and the back-reflected stray light generated inside the objective lens deviates from the imaging light path; Perform feature detection on the image to be tested to obtain defect information of the wafer to be tested.

Images