Autofocusing apparatus and method for determining out-of-focus distance

Abstract

Provided in the present invention are an autofocusing apparatus, a method for determining an out-of-focus distance, and a storage medium. The autofocusing apparatus comprises a multi-channel light source, a first grating mask, a microscope objective lens, a first light splitting element, a second grating mask, a first multi-quadrant detector, a second multi-quadrant detector, and a processor. The multi-channel light source provides a multi-channel illumination beam. The microscope objective lens projects a first pattern generated by the multi-channel illumination beam passing through the first grating mask onto a surface of a sample under test, and collects a reflected beam generated by the surface of the sample. The first light splitting element transmits the reflected beam to a first detection optical path and a second detection optical path, respectively. The second grating mask has a second pattern different from that of the first grating mask. The first multi-quadrant detector collects a first optical signal outputted thereby. The second multi-quadrant detector collects a second optical signal transmitted by the first light splitting element to the second detection optical path. The processor determines an out-of-focus distance of the sample on the basis of the difference between the first optical signal and the second optical signal.

Description

Automatic focusing device and method for determining out-of-focus distance TECHNICAL FIELD

[0001] The present application relates to the field of wafer defect detection, and in particular to an automatic focusing device for semiconductor sample detection, a method for determining the out-of-focus distance of a semiconductor sample, and a computer-readable storage medium. BACKGROUND

[0002] In the semiconductor industry, the production process of wafers is complex and has many processes, which directly affects the final quality and performance of chips. With the continuous reduction of device size, defects occurring in the production process seriously affect chip performance. Therefore, semiconductor wafer defect detection is an indispensable link in the wafer production process. Current wafer defect detection usually uses an optical microscopic imaging system, for example, a line scan camera is used to scan the wafer during movement. However, this method cannot guarantee that the wafer is always within the focal plane range during detection, and cannot obtain a clear high-resolution wafer image, resulting in low accuracy of wafer defect detection.

[0003] In order to overcome the above-mentioned defects in the prior art, the present application provides an automatic focusing device for semiconductor sample detection, a method for determining the out-of-focus distance of a semiconductor sample, and a computer-readable storage medium, which can keep the sample to be detected within the focal plane range during detection, and realize real-time focusing of the sample to be detected during scanning, thereby further improving the accuracy and precision of wafer defect detection.

[0004] SUMMARY

[0005] The following presents a simplified summary of one or more aspects in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

[0006] In order to overcome the above-mentioned defects in the prior art, the present application provides an automatic focusing device for semiconductor sample detection, a method for determining the out-of-focus distance of a semiconductor sample, and a computer-readable storage medium, which can keep the sample to be detected within the focal plane range during detection, and realize real-time focusing of the sample to be detected during scanning, thereby further improving the accuracy and precision of wafer defect detection.

[0007] Specifically, the automatic focusing device for semiconductor sample detection according to the first aspect of the present application comprises a multi-channel light source, a first grating mask, a microscope objective, a first light splitting element, a second grating mask, a first multi-quadrant detector, a second multi-quadrant detector, and a processor. The multi-channel light source is configured to provide a multi-channel illumination beam. The first grating mask is located in a transmission path of the multi-channel illumination beam to serve as a field stop of the multi-channel illumination beam. The microscope objective is located at a rear end of the first grating mask to project a first pattern generated by the multi-channel illumination beam passing through the first grating mask onto a surface of a sample to be detected, and to collect a reflected beam generated by the surface of the sample to be detected. The first light splitting element is located at a rear end of the microscope objective to transmit the reflected beam to a first detection light path and a second detection light path, respectively. The second grating mask is located in the first detection light path and has a second pattern different from the first pattern of the first grating mask. The first multi-quadrant detector is located at a rear end of the second grating mask in the first detection light path to collect a first light signal output therefrom. The second multi-quadrant detector is located in the second detection light path to collect a second light signal transmitted from the first light splitting element to the second detection light path. The processor determines a defocus distance of the sample to be detected according to a difference between the first light signal and the second light signal.

[0008] Further, in some embodiments of the present application, the multi-channel light source is a dual-channel light source. The first multi-quadrant detector and / or the second multi-quadrant detector is a two-quadrant detector. The first pattern of the first grating mask and the second pattern of the second grating mask maintain a 1 / 4 period difference in light transmission position.

[0009] Further, in some embodiments of the present application, the first light signal comprises a first quadrant signal corresponding to a first channel of the dual-channel light source, and a second quadrant signal corresponding to a second channel of the dual-channel light source. The second light signal comprises a third quadrant signal corresponding to the first channel of the dual-channel light source, and a fourth quadrant signal corresponding to the second channel of the dual-channel light source. The step of determining the defocus distance of the sample to be detected according to the difference between the first light signal and the second light signal comprises: acquiring the first quadrant signal and the second quadrant signal via the first multi-quadrant detector; acquiring the third quadrant signal and the fourth quadrant signal via the second multi-quadrant detector; and determining the defocus distance of the sample to be detected according to a difference between a first ratio of the first quadrant signal to the third quadrant signal and a second ratio of the second quadrant signal to the fourth quadrant signal.

[0010] Further, in some embodiments of the present application, the step of determining the defocus distance of the sample to be measured according to the difference between the first ratio of the first quadrant signal to the third quadrant signal and the second ratio of the second quadrant signal to the fourth quadrant signal comprises: calculating a normalized deviation signal according to the first ratio of the first quadrant signal to the third quadrant signal and the second ratio of the second quadrant signal to the fourth quadrant signal:

[0011] wherein FocusUp is the first quadrant signal, FocusDown is the second quadrant signal, NormalUp is the third quadrant signal, and NormalDown is the fourth quadrant signal; and determining the defocus distance corresponding to the normalized deviation signal Normalized Signal according to the corresponding relationship between the normalized deviation signal and the defocus distance pre-calibrated.

[0012] Further, in some embodiments of the present application, the dual-channel light source comprises two LED light boxes and one beam-combining optical fiber. At least one LED light source is arranged in each of the two LED light boxes. The first input port of the beam-combining optical fiber is connected to the output interface of the first LED light box, and the second input port of the beam-combining optical fiber is connected to the output interface of the second LED light box. The output port of the beam-combining optical fiber is provided with two semi-circular output aperture stops. The two semi-circular output aperture stops are respectively connected to one corresponding input port and combined into a circular dual-channel aperture stop to output a circular dual-channel illumination light beam.

[0013] Further, in some embodiments of the present application, the two channels of the dual-channel light source alternately output illumination light beams for the first multi-quadrant detector to alternately collect the first quadrant signal corresponding to the first channel of the dual-channel light source and the second quadrant signal corresponding to the second channel of the dual-channel light source, and for the second multi-quadrant detector to alternately collect the third quadrant signal corresponding to the first channel of the dual-channel light source and the fourth quadrant signal corresponding to the second channel of the dual-channel light source.

[0014] Further, in some embodiments of the present application, the autofocusing device further comprises a first lens group, a second lens group, a third lens group, and / or a fourth lens group. The first lens group is located between the multi-channel light source and the first grating mask, for collecting the multi-channel illumination light beam emitted by the multi-channel light source and transmitting it to the first grating mask. The second lens group can be located between the first grating mask and the microscope objective, for projecting the first pattern generated by the multi-channel illumination light beam passing through the first grating mask to the surface of the sample to be measured via the microscope objective. In addition, the second lens group can also be located between the microscope objective and the first light splitting element, for transmitting the reflected light beam collected and output by the microscope objective to the first light splitting element. The third lens group is located between the second grating mask and the first multi-quadrant detector, for converging the superimposed pattern generated by the reflected light beam passing through the second grating mask to the detection surface of the first multi-quadrant detector. The fourth lens group is located between the first light splitting element and the second multi-quadrant detector, for converging the light splitting light beam transmitted by the first light splitting element to the second detection light path to the detection surface of the second multi-quadrant detector.

[0015] Further, in some embodiments of the present application, the output surface of the multi-channel light source is conjugate with the entrance pupil surface of the microscope objective. In addition, the multi-channel light source, the first lens group, the first grating mask, the second lens group, and the microscope objective can collectively constitute a Kohler illumination system of the multi-channel illumination light beam.

[0016] Further, in some embodiments of the present application, the autofocusing device further comprises a second light splitting element and a mirror. The second light splitting element is located between the first grating mask and the microscope objective, for bending the multi-channel illumination light beam from the first light path where the multi-channel light source and the first grating mask are located to the second light path perpendicular to the first light path, and transmitting the reflected light beam output by the microscope objective via the mirror to the first light splitting element located at the rear end of the second light path. The mirror is located between the second light splitting element and the microscope objective, for bending the multi-channel illumination light beam from the second light path to the third light path where the microscope objective is located, and reflecting the reflected light beam output by the microscope objective back to the second light splitting element, wherein the third light path is perpendicular to the second light path.

[0017] Further, in some embodiments of the present application, the autofocusing device further comprises an objective platform. The objective platform is located at the object side of the microscope objective, and is configured to carry the sample to be measured. The processor is further configured to transmit an adjusting instruction corresponding to the defocus distance of the sample to be measured to the objective platform, so as to move the sample to be measured to the object focal plane of the microscope objective via the objective platform.

[0018] Further, the method for determining the defocus distance of the semiconductor sample according to the second aspect of the present application comprises the following steps: projecting a first pattern generated by a multi-channel illumination beam passing through a first grating mask, to the surface of the sample to be measured via a microscope objective; collecting a second light signal of a reflected light beam generated by the surface of the sample to be measured collected and output by the microscope objective, from a first output light path of a first light splitting element located at the image side of the microscope objective; collecting a first light signal of an overlapped pattern of the first pattern and a second pattern generated by the reflected light beam passing through a second grating mask, from the second grating mask located at a second output light path of the first light splitting element. The second grating mask has the second pattern; and determining the defocus distance of the sample to be measured according to the difference between the first light signal and the second light signal.

[0019] Further, the computer readable storage medium according to the third aspect of the present application has computer instructions stored thereon. When the computer instructions are executed by a processor, the method for determining the defocus distance of the semiconductor sample according to the second aspect of the present application is implemented. BRIEF DESCRIPTION OF DRAWINGS

[0020] The above features and advantages of the present application can be better understood by reading the detailed description of embodiments of the present application in conjunction with the following drawings, in which: the components are not necessarily drawn to scale, and components of similar or identical related function or features can have the same or similar reference label.

[0021] FIG. 1 shows a structural schematic diagram of an autofocusing device according to some embodiments of the present application.

[0022] FIG. 2A shows a structural schematic diagram of a first grating mask according to some embodiments of the present application.

[0023] FIG. 2B shows a structural schematic diagram of a second grating mask according to some embodiments of the present application.

[0024] FIG. 2C shows a comparison diagram of the first grating mask and the second grating mask according to some embodiments of the present application.

[0025] FIG. 3 shows a structural schematic diagram of a beam combining output head according to some embodiments of the present application.

[0026] FIG. 4 shows a structural diagram of an output aperture stop of a beam combining output head according to some embodiments of the present application.

[0027] FIG. 5 shows a flow diagram of a method for determining a defocus distance of a semiconductor sample according to some embodiments of the present application.

[0028] FIG. 6 shows a schematic diagram of an optical signal according to some embodiments of the present application.

[0029] FIG. 7A shows a schematic diagram of a light spot with a defocus distance of -4 μm according to some embodiments of the present application.

[0030] FIG. 7B shows a schematic diagram of a light spot at a focal plane according to some embodiments of the present application.

[0031] FIG. 7C shows a schematic diagram of a light spot with a defocus distance of +4 μm according to some embodiments of the present application.

[0032] FIG. 8 shows a signal curve diagram of a first multi-quadrant detector and a second multi-quadrant detector according to some embodiments of the present application.

[0033] FIG. 9 shows a deviation signal curve diagram according to some embodiments of the present application. DETAILED DESCRIPTION

[0034] The present application is described in detail below with specific reference to particular embodiments. Those of ordinary skill in the art will readily recognize that the application can be practiced with a variety of modifications and alterations of the embodiments discussed. The applications described herein are not limited to the embodiments described and illustrated, but rather, the intent is to cover all alternatives modifications and equivalents. Numerous specific details of the applications are described below with the understanding that these details are by way of example and are not intended to limit the scope of the present application. Alternative and equivalent implementations of the applications will become apparent to those of ordinary skill in the art in view of the teachings. Therefore, the full scope of the applications will be pointed out with the following claims.

[0035] In the description of the present application, it is necessary to explain that, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connecting" should be understood in a broad sense, for example, it can be fixed connection, or detachable connection, or integrally connected; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through intermediate medium, or the communication inside two elements. For those of ordinary skill in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0036] In addition, "upper", "lower", "left", "right", "top", "bottom", "horizontal", "vertical" used in the following description and shown in the drawings should be understood as the orientation of the section and related drawings. The relative terms are only for the convenience of description, and do not mean that the device described thereby needs to be manufactured or operated in a specific orientation, and therefore should not be understood as a limitation of the present application.

[0037] It can be understood that although the terms "first", "second", "third" and the like can be used herein to describe various components, regions, layers and / or parts, these components, regions, layers and / or parts should not be limited by these terms, and these terms are only used to distinguish different components, regions, layers and / or parts. Therefore, the first component, region, layer and / or part discussed below can be referred to as the second component, region, layer and / or part without departing from some embodiments of the present application.

[0038] As described above, semiconductor wafer defect detection is an indispensable link in the wafer production process. The current wafer defect detection usually adopts an optical microscopic imaging system, for example, a line scan camera is used to scan the wafer during movement. However, this method cannot guarantee that the wafer always remains within the focal plane range during detection, and cannot obtain a clear high-resolution wafer image, which has the problem of low accuracy of wafer defect detection.

[0039] In order to overcome the above-mentioned defects existing in the prior art, the present application provides an autofocus device for semiconductor sample detection, a method for determining the defocus distance of a semiconductor sample, and a computer readable storage medium, which can keep the sample to be detected within the focal plane range during detection, and is used to realize real-time focusing of the sample to be detected during scanning, so as to further improve the accuracy and precision of wafer defect detection.

[0040] In some non-limiting embodiments, the above-mentioned method for determining the defocus distance of a semiconductor sample provided by the second aspect of the present application can be implemented based on the above-mentioned autofocus device for semiconductor sample detection provided by the first aspect of the present application.

[0041] For details, please refer to FIG. 1. FIG. 1 shows a structural schematic diagram of an autofocus device according to some embodiments of the present application.

[0042] In the embodiment shown in FIG. 1, the autofocusing device for semiconductor sample detection can be configured with a memory and a processor 111. The memory includes, but is not limited to, the computer readable storage medium provided in the third aspect of the present application, on which computer instructions are stored. The processor 111 is connected to the memory and is configured to execute the computer instructions stored on the memory to determine the defocus distance of the sample to be detected according to the difference between the first light signal and the second light signal, thereby implementing the method for determining the defocus distance of the semiconductor sample provided in the first aspect of the present application.

[0043] Further, the autofocusing device for semiconductor sample detection provided in the first aspect of the present application includes a multi-channel light source 101 (for example, a dual-channel LED light source), a first grating mask 102, a microscope objective 103, a first light splitting element 105, a second grating mask 108, a first multi-quadrant detector 109, and a second multi-quadrant detector 110. Here, the multi-channel light source 101 is used to provide a multi-channel illumination beam. The first grating mask 102 is located in the transmission path of the multi-channel illumination beam to serve as a field stop for the multi-channel illumination beam. The microscope objective 103 is located at the rear end of the first grating mask 102 and is used to project a first pattern generated by the multi-channel illumination beam passing through the first grating mask 102 onto the surface of the sample to be detected 104, and to collect a reflected beam generated by the surface of the sample to be detected 104. The first light splitting element 105 is located at the rear end of the microscope objective 103 and is used to transmit the reflected beam to a first detection light path 106 and a second detection light path 107, respectively. The second grating mask 108 is located in the first detection light path 106 and has a second pattern different from the first pattern of the first grating mask 102. The first multi-quadrant detector 109 is located at the rear end of the second grating mask 108 in the first detection light path 106 to collect a first light signal output therefrom. The second multi-quadrant detector 110 is located in the second detection light path 107 to collect a second light signal transmitted from the first light splitting element 105 to the second detection light path 107.

[0044] Please further refer to FIG. 2A and FIG. 2B. FIG. 2A shows a schematic diagram of the first pattern according to some embodiments of the present application. FIG. 2B shows a schematic diagram of the second pattern according to some embodiments of the present application. FIG. 2C shows a comparison diagram of the first pattern and the second pattern according to some embodiments of the present application.

[0045] As shown in FIG. 2A to FIG. 2C, the multi-channel light source 101 is a dual-channel light source. Correspondingly, the first multi-quadrant detector 109 and / or the second multi-quadrant detector 110 can be a two-quadrant detector, wherein the first pattern 21 of the first grating mask 102 and the second pattern 22 of the second grating mask 108 both have the same period of 2-5 mm, and a 1 / 4 period light transmission position difference is maintained between them.

[0046] Those skilled in the art can understand that the above-mentioned embodiment of the dual-channel light source is only some non-limiting embodiments provided by the present application, which aims to clearly show the main concept of the present application and provide some specific solutions for the public to implement, rather than to limit the protection scope of the present application.

[0047] Alternatively, in other embodiments, those skilled in the art can also choose a four-channel light source or other channel number light source. Correspondingly, the quadrant number of the above-mentioned first multi-quadrant detector 109 and / or the second multi-quadrant detector 110 does not necessarily have to be the same as the channel number of the multi-channel light source 101. For example, in some dual-channel light source embodiments, a redundant four-quadrant detector can be configured. For another example, in some redundant four-channel light source embodiments, a two-quadrant detector can also be configured to achieve the same effect of characterizing the sample defocus distance.

[0048] Please further refer to FIG. 3 and FIG. 4. FIG. 3 shows a structural schematic diagram of a beam combining output head according to some embodiments of the present application. FIG. 4 shows a structural schematic diagram of an output aperture stop of a beam combining output head according to some embodiments of the present application.

[0049] As shown in FIG. 3 and FIG. 4, the above-mentioned dual-channel light source includes two LED light boxes and a beam combining optical fiber 30. Here, at least one LED light source 31-32 is arranged in each of the two LED light boxes. The first input port of the beam combining optical fiber 30 is connected to the output interface of the first LED light box, and the second input port is connected to the output interface of the second LED light box. The light output port of the beam combining optical fiber 30 is provided with two semi-circular output aperture stops 41-42. The two semi-circular output aperture stops 41-42 are respectively connected to a corresponding input port and can be combined into a circular dual-channel aperture stop to output a circular dual-channel illumination light beam.

[0050] Further, in some embodiments, the outer diameters of the two input ports of the above-mentioned beam combining optical fiber 30 can be 8mm respectively, and the actual light transmission apertures are 3.5mm respectively. Correspondingly, the total outer diameter of the dual-channel aperture stop composed of the above-mentioned two semi-circular output aperture stops 41-42 can be 16mm, and the total actual light transmission aperture is 7mm, so as to fully output the dual-channel illumination light beam provided by the two LED light sources 31-32.

[0051] In this way, by using optical fiber transmission, the above-mentioned dual-channel light source provided by the present application can integrate the illumination light output by each LED light source 31-32 at a distance (for example: 1000mm or more) to the light output port of the beam combining optical fiber, and then provide the multi-channel illumination light beam required for determining the sample defocus distance to the first grating mask 102 through the beam combining optical fiber.

[0052] Those skilled in the art can understand that the above embodiment of the multi-channel illumination light coupling based on the combined fiber is only a non-limiting embodiment provided by the present application, which is intended to clearly show the main concept of the present application and provide a specific scheme for the public to implement, rather than to limit the protection scope of the present application.

[0053] Alternatively, in other embodiments, those skilled in the art can also use various light coupling forms such as converging lenses and mirrors based on the above concept to achieve the effect of integrated output of multi-channel illumination light beams.

[0054] In addition, please continue to refer to FIG. 1, the above-mentioned autofocus device for semiconductor sample detection provided by the first aspect of the present application can also include a first lens group 112, a second lens group 113, a third lens group 114 and / or a fourth lens group 115. Here, the first lens group 112 is located between the multi-channel light source 101 and the first grating mask 102, used to collect and collimate the multi-channel illumination light beams emitted by the multi-channel light source 101, and transmit them to the first grating mask 102. The second lens group 113 is located between the first grating mask 102 and the microscope objective 103, to project the first pattern generated by the multi-channel illumination light beams passing through the first grating mask 102 to the surface of the sample to be detected via the microscope objective 103. In addition, for the compact optical path system with the overlapping of the illumination light path and the reflected light path, the second lens group 113 can also be further located between the microscope objective 103 and the first light splitting element 105 at the same time, to collimate and transmit the reflected light beams collected and output by the microscope objective 103 to the first light splitting element 105. The third lens group 114 is located between the second grating mask 108 and the first multi-quadrant detector 109, used to converge the superimposed pattern of the first pattern and the second pattern generated by the reflected light beams passing through the second grating mask 108 to the detection surface of the first multi-quadrant detector 109. The fourth lens group 115 is located between the first light splitting element 105 and the second multi-quadrant detector 110, used to converge the light splitting beams transmitted by the first light splitting element 105 to the second detection light path to the detection surface of the second multi-quadrant detector 110.

[0055] Further, the output surface of the multi-channel light source 101 can be conjugate with the entrance pupil surface of the microscope objective 103. In addition, the light output surface of the multi-channel light source 101 can be located at the front focal surface of the first lens group 112, the first grating mask 102 can be located at the front focal surface of the second lens group 113, and the rear focal surface of the second lens group 113 can be located at the entrance pupil surface of the microscope objective 103, to jointly constitute a Kohler illumination system, so as to fully and uniformly irradiate the multi-channel illumination light beams output by the multi-channel light source 101 to the surface of the sample to be detected 104, so as to make the sample to be detected 104 obtain uniform and sufficient illumination and avoid glare.

[0056] In addition, in the embodiment shown in FIG. 1, the auto-focusing device for semiconductor sample detection provided by the first aspect of the present application can further optionally comprise a second light splitting element 116 and a mirror 117 for folding the optical path to achieve a compact design of the auto-focusing device. Here, the second light splitting element 116 is located between the first grating mask 102 and the microscope objective 103, and is used to bend the multi-channel illumination light beam from the first optical path 119 where the multi-channel light source 101 and the first grating mask 102 are located, to the second optical path 106 which is perpendicular to the first optical path 119, and to transmit the reflected light beam output by the microscope objective 103 via the mirror 117 to the first light splitting element 105 located at the rear end of the second optical path 106. The mirror 117 is located between the second light splitting element 116 and the microscope objective 103, and is used to bend the multi-channel illumination light beam from the second optical path 106 to the third optical path 107 where the microscope objective 103 is located, and to reflect the reflected light beam output by the microscope objective 103 back to the second light splitting element 116. Here, the third optical path 107 is perpendicular to the second optical path 106.

[0057] Further, the mirror 117 is preferably a dichroic mirror, so as to simultaneously satisfy the different light reflection requirements of the auto-focusing device in the visible light and infrared light wave bands, and the semiconductor sample detection device in the visible light and ultraviolet light wave bands, so that both can share one microscope objective to simplify the optical path structure and improve the real-time performance of switching between the semiconductor detection function and the auto-focusing function.

[0058] Those skilled in the art can understand that the combination of optical elements shown in FIG. 1 is only a non-limiting embodiment provided by the present application, which is intended to clearly demonstrate the main concept of the present application and provide a specific scheme for the public to implement, rather than to limit the protection scope of the present application.

[0059] Optionally, in other embodiments, each lens group 112-115 can also be integrated at the output end of the front-end component and / or the input end of the rear-end component, or replaced by a curved mirror in the form, to achieve similar light condensing effect.

[0060] Alternatively, in other embodiments which do not fold the optical path or adopt other forms of optical path folding, the incident optical path of the illumination light beam incident on the image side of the microscope objective 103 can not coincide with the reflection optical path of the reflected light beam emitted from the image side of the microscope objective 103. At this time, those skilled in the art can also set a second lens group 113 in the incident optical path between the first grating mask 102 and the microscope objective 103, and in the reflection optical path between the microscope objective 103 and the first light splitting element 105, based on the above concept provided by the present application, to achieve the same light beam condensing effect.

[0061] In addition, referring back to FIG. 1, the semiconductor sample detection autofocus device provided by the first aspect of the present application can further be configured with an object platform 118. The object platform 118 is located at the object side of the microscope objective 103 and is used to carry the sample 104 to be detected. Accordingly, the processor 111 can be further configured to transmit corresponding adjustment instructions to the object platform according to the defocus distance of the sample to be detected, so as to move the sample to be detected closer to or farther away from the object plane of the microscope objective via the object platform.

[0062] The working principle of the semiconductor sample detection autofocus device will be described below in combination with some embodiments of the method for determining the defocus distance of the semiconductor sample. Those skilled in the art can understand that the embodiments of the method for determining the defocus distance of the semiconductor sample are only some non-limiting embodiments provided by the present application, which are intended to clearly demonstrate the main concept of the present application and provide some specific solutions for facilitating the public to implement, rather than to limit the overall function or overall working mode of the semiconductor sample detection autofocus device. Similarly, the semiconductor sample detection autofocus device is also only a non-limiting embodiment provided by the present application, which does not limit the execution subject or execution order of each step in the method for determining the defocus distance of the semiconductor sample.

[0063] Please refer to FIG. 1, FIG. 5 to FIG. 9. FIG. 5 shows a flowchart of the method for determining the defocus distance of the semiconductor sample according to some embodiments of the present application. FIG. 6 shows a schematic diagram of the light signal according to some embodiments of the present application. FIG. 7A shows a schematic diagram of the light spot with a defocus distance of -4 μm according to some embodiments of the present application. FIG. 7B shows a schematic diagram of the light spot at the focal plane according to some embodiments of the present application. FIG. 7C shows a schematic diagram of the light spot with a defocus distance of +4 μm according to some embodiments of the present application.

[0064] FIG. 8 shows a signal curve diagram of the first multi-quadrant detector and the second multi-quadrant detector according to some embodiments of the present application. FIG. 9 shows a deviation signal curve diagram according to some embodiments of the present application.

[0065] As shown in FIG. 1, FIG. 5-FIG. 8, in the process of auto-focusing the semiconductor sample, the processor 111 can first project the first pattern generated by the first grating mask 102 via the multi-channel light source 101, the multi-channel illumination light beam, to the surface of the sample 104 to be measured in the object side of the microscope objective 103. Then, the processor 111 can collect the second light signal of the reflected light beam generated by the surface of the sample 104 to be measured collected and output by the microscope objective 103 from the first output light path 107 of the first light splitting element 105 in the image side of the microscope objective 103. At the same time, the processor 111 can also collect the first light signal of the superimposed pattern of the first pattern and the second pattern generated by the reflected light beam passing through the second grating mask 108 from the second grating mask 108 in the second output light path 106 of the first light splitting element 105. As described above, the second grating mask 108 has a second pattern different from the first pattern.

[0066] Then, the processor 111 can determine the defocus distance of the sample to be measured according to the difference between the first light signal and the second light signal.

[0067] Specifically, the processor 111 can first acquire the first quadrant signal FocusUp and the second quadrant signal FocusDown via the first multi-quadrant detector 109, and acquire the third quadrant signal NormalUp and the fourth quadrant signal NormalDown via the second multi-quadrant detector 110.

[0068] Then, as shown in FIG. 9, the processor 111 can calculate the normalized deviation signal according to the first ratio FocusUp / NormalUp of the first quadrant signal and the third quadrant signal, and the second ratio FocusDown / NormalDown of the second quadrant signal and the fourth quadrant signal:

[0069] Wherein, FocusUp is the first quadrant signal, FocusDown is the second quadrant signal, NormalUp is the third quadrant signal, and NormalDown is the fourth quadrant signal.

[0070] Then, the processor 111 can determine the defocus distance corresponding to the normalized deviation signal Normalized Signal according to the corresponding relationship between the normalized deviation signal and the defocus distance calibrated in advance.

[0071] Those skilled in the art can understand that the above implementation of calibrating and calculating the out-of-focus distance by normalizing the deviation signal is only a preferred solution for adapting the light source, grating mask and other elements with various optical parameters. Alternatively, in other embodiments, those skilled in the art can also individually calibrate the correspondence between the ratio difference FocusUp / NormalUp-FocusDown / NormalDown and the out-of-focus distance for each specific auto-focusing device to achieve the technical effect of determining the out-of-focus distance.

[0072] Further, the processor 111 can transmit corresponding adjustment instructions to the object platform 118 according to the out-of-focus distance of the sample 104 to be tested, so as to move the sample 104 to be tested to the object focal plane of the objective lens 103 by the object platform 118.

[0073] Further, in some embodiments, the two channels of the above-mentioned dual-channel light source can preferably output the illumination beams alternately, so as to alternately collect the first-quadrant signal FocusUp of the first channel of the dual-channel light source and the second-quadrant signal FocusDown of the second channel of the dual-channel light source by the first multi-quadrant detector 109, and alternately collect the third-quadrant signal NormalUp of the first channel of the dual-channel light source and the fourth-quadrant signal NormalDown of the second channel of the dual-channel light source by the second multi-quadrant detector 110. In this way, the present application can effectively avoid the mutual interference of the illumination beams of the two output channels, so as to further improve the detection accuracy of the out-of-focus distance.

[0074] In summary, the above-mentioned auto-focusing device for semiconductor sample detection, the method for determining the out-of-focus distance of a semiconductor sample and the computer readable storage medium provided by the present application can all keep the sample to be tested within the focal plane range during the detection process, so as to realize the real-time focusing of the sample to be tested during the scanning process, and further improve the accuracy and precision of wafer defect detection.

[0075] Although the above methods are illustrated and described as a series of acts for simplicity of explanation, it should be understood and appreciated that the methods are not limited by the order of acts, as some acts can occur in different orders and / or concurrently with other acts from that shown and described herein or in other acts not shown and described herein that are understood by those skilled in the art.

[0076] The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other variations without departing from the spirit or scope of the disclosure. Thus, the disclosure is not intended to be limited to the examples described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An autofocus device for semiconductor sample inspection, characterized by, The application relates to a method for measuring the defocus distance of a sample, comprising the following steps: a multi-channel light source is used to provide a multi-channel illumination light beam; a first grating mask is arranged in the transmission path of the multi-channel illumination light beam to serve as a field stop of the multi-channel illumination light beam; a microscope objective is arranged at the rear end of the first grating mask to project a first pattern generated by the first grating mask on the surface of the sample to be measured and collect a reflected light beam generated by the surface of the sample to be measured; a first light splitting element is arranged at the rear end of the microscope objective to transmit the reflected light beam to a first detection light path and a second detection light path respectively; a second grating mask is arranged in the first detection light path and has a second pattern different from the first grating mask; a first multi-quadrant detector is arranged at the rear end of the second grating mask in the first detection light path to collect a first light signal output by the first multi-quadrant detector; a second multi-quadrant detector is arranged in the second detection light path to collect a second light signal transmitted by the first light splitting element to the second detection light path; and a processor is used to determine the defocus distance of the sample to be measured according to the difference between the first light signal and the second light signal. The multi-channel light source is a double-channel light source, the first multi-quadrant detector and / or the second multi-quadrant detector is a two-quadrant detector, and the first pattern of the first grating mask and the second pattern of the second grating mask maintain a 1 / 4 period light transmission position difference.

2. The autofocus device of claim 1, wherein The first light signal comprises a first quadrant signal corresponding to a first channel of the double-channel light source and a second quadrant signal corresponding to a second channel of the double-channel light source, the second light signal comprises a third quadrant signal corresponding to the first channel of the double-channel light source and a fourth quadrant signal corresponding to the second channel of the double-channel light source, and the step of determining the defocus distance of the sample to be measured according to the difference between the first light signal and the second light signal comprises the following steps:

3. The autofocus device of claim 2, wherein the first quadrant signal and the second quadrant signal are acquired via the first multi-quadrant detector; the third quadrant signal and the fourth quadrant signal are acquired via the second multi-quadrant detector; and the defocus distance of the sample to be measured is determined according to the difference between a first ratio of the first quadrant signal and the third quadrant signal and a second ratio of the second quadrant signal and the fourth quadrant signal. The step of determining the defocus distance of the sample to be measured according to the difference between the first ratio of the first quadrant signal and the third quadrant signal and the second ratio of the second quadrant signal and the fourth quadrant signal comprises the following steps:

4. The autofocus device of claim 3, wherein wherein FocusUp is the first quadrant signal, FocusDown is the second quadrant signal, NormalUp is the third quadrant signal, and NormalDown is the fourth quadrant signal; and calculating a normalized deviation signal from a first ratio of the first-quadrant signal to the third-quadrant signal, and a second ratio of the second-quadrant signal to the fourth-quadrant signal: the defocus distance corresponding to the normalized deviation signal Normalized Signal is determined according to the corresponding relationship between the normalized deviation signal and the defocus distance in advance. The double-channel light source comprises:

5. The autofocus device of claim 2, wherein, two LED light boxes, wherein at least one LED light source is arranged in each LED light box; and ​ The combined fiber, wherein the first light inlet of the combined fiber is connected to the output interface of the first LED light box, the second light inlet of the combined fiber is connected to the output interface of the second LED light box, and the light outlet of the combined fiber is provided with two semi-circular output aperture diaphragms, the two semi-circular output aperture diaphragms are respectively connected to a corresponding light inlet, and are combined into a circular double-channel aperture diaphragm to output a circular double-channel illumination light beam.

6. The auto-focusing apparatus of claim 2, wherein The two channels of the double-channel light source alternately output illumination light beams for the first multi-quadrant detector to alternately collect a first-quadrant signal corresponding to a first channel of the double-channel light source and a second-quadrant signal corresponding to a second channel of the double-channel light source, and for the second multi-quadrant detector to alternately collect a third-quadrant signal corresponding to the first channel of the double-channel light source and a fourth-quadrant signal corresponding to the second channel of the double-channel light source.

7. The autofocus device of claim 1, wherein, Further comprising: A first lens group located between the multi-channel light source and the first grating mask, for collecting the multi-channel illumination light beam emitted by the multi-channel light source and transmitting it to the first grating mask; And / or A second lens group located between the first grating mask and the microscope objective, for projecting the first pattern generated by the multi-channel illumination light beam passing through the first grating mask onto the surface of the sample to be measured via the microscope objective, and / or located between the microscope objective and the first light splitting element, for transmitting the reflected light beam collected and output by the microscope objective to the first light splitting element; And / or A third lens group located between the second grating mask and the first multi-quadrant detector, for converging the superimposed pattern generated by the reflected light beam passing through the second grating mask to the detection surface of the first multi-quadrant detector; And / or A fourth lens group located between the first light splitting element and the second multi-quadrant detector, for converging the light splitting beam transmitted by the first light splitting element to the second detection light path to the detection surface of the second multi-quadrant detector.

8. The autofocus device of claim 7, wherein, The output surface of the multi-channel light source is conjugate to the entrance pupil surface of the microscope objective, and / or The multi-channel light source, the first lens group, the first grating mask, the second lens group, and the microscope objective together form a Kohler illumination system of the multi-channel illumination light beam.

9. The autofocus device of claim 1, wherein, Further comprising: A second light splitting element located between the first grating mask and the microscope objective, for bending the multi-channel illumination light beam from the first light path where the multi-channel light source and the first grating mask are located to a second light path perpendicular to the first light path, and transmitting the reflected light beam output by the microscope objective via a mirror to the first light splitting element located at the rear end of the second light path; and The mirror is located between the second light splitting element and the microscope objective, for bending the multi-channel illumination light beam from the second light path to a third light path where the microscope objective is located, and reflecting the reflected light beam output by the microscope objective back to the second light splitting element, wherein the third light path is perpendicular to the second light path. Further comprising:

10. The autofocus device of claim 1, wherein, ​ A sample stage is located at an object side of the microscope objective and configured to hold the sample to be measured. The processor is further configured to transmit an adjustment instruction to the sample stage according to the defocus distance of the sample to be measured, so as to move the sample to be measured to the focal plane of the microscope objective via the sample stage.

11. A method of determining the defocus distance of a semiconductor sample, characterized by, The method comprises the following steps: projecting a first pattern generated by a first grating mask from a multi-channel illumination beam onto the surface of the sample to be measured via the microscope objective; collecting a second optical signal of a reflected light beam generated by the surface of the sample to be measured from a first output light path of a first light splitting element located at an image side of the microscope objective, wherein the reflected light beam is collected and output by the microscope objective; collecting a first optical signal of an overlaid pattern of the first pattern and a second pattern generated by the reflected light beam passing through a second grating mask from a second output light path of the second grating mask, wherein the second grating mask has the second pattern; and determining the defocus distance of the sample to be measured according to a difference between the first optical signal and the second optical signal. The computer instructions, when executed by the processor, implement the method for determining the defocus distance of the semiconductor sample according to claim 11.

12. A computer readable storage medium having stored thereon computer instructions, wherein, ​

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