Real-time autofocus system and detection system made of it

Abstract

The present application relates to the technical field of semiconductor detection, and particularly relates to a real-time automatic focusing system and a detection system formed by the same, the real-time automatic focusing system comprising a first illumination subsystem, a second illumination subsystem, a beam combination element, a first mask, a second mask, a collimating mirror group, an objective lens, a first beam splitter, a second beam splitter, a moving mechanism, a first detection subsystem and a second detection subsystem; a focusing energy signal is calculated according to imaging light energy received by the first detection subsystem and the second detection subsystem, the moving mechanism is controlled according to the focusing energy signal to adjust the position of the objective lens or a sample to be detected, and real-time focusing of the sample to be detected is realized. The present application utilizes an energy difference mode to eliminate the influence of the automatic focusing system caused by different surface pattern reflectivities of the sample to be detected and pattern etching depths, and the real-time focusing of the sample to be detected is realized by adjusting the position of the objective lens or the sample to be detected.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of semiconductor detection, and particularly relates to a real-time automatic focusing system and a detection system formed by the same. BACKGROUND

[0002] In a semiconductor detection device, a detection imaging system uses an objective lens with a large numerical aperture, and the focal depth of the objective lens is often in the sub-micron level. In order to enable the detection imaging system to perform real-time detection within the focal depth range, a real-time automatic focusing system is essential. However, the existing automatic focusing system cannot achieve stable real-time focusing on an arbitrarily specified plane within a certain range due to the influence of the reflectivity of the surface pattern of the sample to be detected and the etching depth of the pattern. SUMMARY

[0003] Therefore, the present application aims to provide a real-time automatic focusing system and a detection system formed by the same to solve the problem that the existing automatic focusing system cannot achieve stable real-time focusing on an arbitrarily specified plane within a certain range.

[0004] To achieve the above-mentioned purpose, the technical solution of the present application is as follows:

[0005] A real-time automatic focusing system, comprising a first illumination subsystem, a second illumination subsystem, a beam combining element, a first mask, a second mask, a collimating lens group, an objective lens, a first beam splitter, a second beam splitter, a moving mechanism, a first detection subsystem and a second detection subsystem; wherein the illumination beam emitted by the first illumination subsystem and the illumination beam emitted by the second illumination subsystem are incident to the beam combining element respectively, the circular spot of the first illumination subsystem and the circular spot of the second illumination subsystem are cut in half by the beam combining element, and the two half-circular spots are spliced into a complete circular spot; the spliced circular spot is collimated by the collimating lens group to illuminate the first mask, and then passes through the first beam splitter and the objective lens to reach the surface of the sample to be detected, is reflected by the sample to be detected, and then passes through the objective lens and the first beam splitter in turn to reach the second beam splitter, the reflected light after beam splitting is received by the first detection subsystem, and the transmitted light after beam splitting illuminates the second mask and is then received by the second detection subsystem; the moving mechanism is installed with the sample to be detected or with the objective lens, and the position of the sample to be detected or the objective lens is adjusted by the moving mechanism to realize real-time focusing of the sample to be detected.

[0006] Further, the collimating lens group is located in the beam combining direction of the beam combining element, and the first mask is located between the collimating lens group and the first beam splitter.

[0007] Further, the first illumination subsystem comprises a first LED light source, a first optical fiber and a first illumination lens group, the first LED light source couples the LED light emitted into the first optical fiber, and the first optical fiber outputs the light to the first illumination lens group, which irradiates one surface of the beam combining element; the second illumination subsystem comprises a second LED light source, a second optical fiber and a second illumination lens group, the second LED light source couples the LED light emitted into the second optical fiber, and the second optical fiber outputs the light to the second illumination lens group, which irradiates the other surface of the beam combining element.

[0008] Further, the end surface of the first optical fiber and the second optical fiber is engraved with a line for spot alignment.

[0009] Further, the beam combining element adopts a wedge body with a trapezoidal orthographic projection, the lower base of the wedge body faces the second detection subsystem, the oblique waist surface of the wedge body faces the first detection subsystem, the optical axis of the first detection subsystem and the optical axis of the second detection subsystem intersect at the upper base corner of the wedge body close to the first detection subsystem, and the upper base corner is 135°, a reflective film is coated on the oblique waist surface of the wedge body, and an anti-reflection film is coated on the upper base and the lower base of the wedge body; or the beam combining element adopts a reflector, the reflecting surface of the reflector faces the first detection subsystem, and the angle between the reflecting surface and the horizontal plane is 45°, and the top edge of the reflector is located at the intersection of the optical axis of the first detection subsystem and the optical axis of the second detection subsystem.

[0010] Further, an aperture is arranged in the beam combining direction of the beam combining element, two semicircular through holes for the semicircular light spots are processed on the aperture, and an opaque strip is formed between the two semicircular through holes, the center of the opaque strip coincides with the ridge space of the connection between the oblique waist surface and the upper base of the wedge body, or the center of the opaque strip coincides with the top edge of the reflector.

[0011] Further, the first detection subsystem receives the imaging light energy of the first mask plate reflected by the sample to be measured, and the second detection subsystem receives the imaging light energy of the first mask plate remaining after being blocked by the second mask plate.

[0012] Further, the focusing energy signal is calculated according to the imaging light energy received by the first detection subsystem and the imaging light energy received by the second detection subsystem, and the moving mechanism is controlled according to the focusing energy signal to adjust the position of the objective lens or the sample to be measured.

[0013] The calculation formula of the focusing energy signal E is:

[0014]

[0015] Wherein, FA is the intensity of the electric signal converted by the second mask plate in the process of focusing the illumination light emitted by the first illumination subsystem to the second detection subsystem in the automatic focusing process;

[0016] NA is the intensity of the electric signal converted by the first detection subsystem when the illumination light emitted by the first illumination subsystem is focused to the first detection subsystem without passing through the second mask during the auto-focusing operation;

[0017] Na is the intensity of the superimposed electric signal caused by the background noise during the auto-focusing operation and the dark noise of the first detection subsystem and the second detection subsystem when the illumination light emitted by the first illumination subsystem does not pass through the second mask;

[0018] FB is the intensity of the electric signal converted by the second detection subsystem when the illumination light emitted by the second illumination subsystem is focused to the second detection subsystem through the second mask during the auto-focusing operation;

[0019] NB is the intensity of the electric signal converted by the first detection subsystem when the illumination light emitted by the second illumination subsystem is focused to the first detection subsystem without passing through the second mask during the auto-focusing operation;

[0020] Nb is the intensity of the superimposed electric signal caused by the background noise during the auto-focusing operation and the dark noise of the first detection subsystem and the second detection subsystem when the illumination light emitted by the second illumination subsystem does not pass through the second mask.

[0021] Here, in the actual operation, in order to obtain FA, NA and FB, NB respectively and independently, the first illumination subsystem and the second illumination subsystem are operated alternately, that is, the first LED light source and the second LED light source need to be flashed alternately, and the flashing frequency is in the order of kilohertz.

[0022] Further, a compensation lens group is arranged between the first beam splitter and the objective lens.

[0023] Further, the first detection subsystem comprises a first converging lens and a first detector, and the reflected light after the beam splitting is received by the first detector after being converged by the first converging lens; the second detection subsystem comprises a second converging lens and a second detector, and the transmitted light after the beam splitting illuminates the second mask, and is received by the second detector after being converged by the second converging lens.

[0024] A detection system comprises the real-time auto-focusing system and the imaging system, and the imaging system comprises an imaging light source, an imaging zoom group and a camera.

[0025] Further, the imaging system further comprises a half mirror and a dichroic mirror, and the imaging light beam emitted by the imaging light source passes through the transmission of the half mirror, the reflection of the dichroic mirror and the transmission of the objective lens in sequence to reach the surface of the sample to be detected.

[0026] Compared with the prior art, the application can achieve the following beneficial effects:

[0027] (1) The present application utilizes energy difference mode to eliminate the influence of different surface pattern reflectivity and etching depth of the sample to be measured on the auto-focusing system, and realizes real-time focusing of the sample to be measured by adjusting the position of the objective lens or the sample to be measured;

[0028] (2) The present application realizes real-time focusing of different samples to be measured by adjusting the reference focus plane of the auto-focusing system through the compensation lens group;

[0029] (3) The beam combining element used in the present application can ensure that the energy of the two beams in the real-time auto-focusing system is equal, and realizes energy difference. BRIEF DESCRIPTION OF DRAWINGS

[0030] The accompanying drawings, which form a part of the present application, are used to provide further understanding of the present application, and the illustrative embodiments of the present application and their description serve the purpose of explaining the present application. The accompanying drawings should not be used to limit the present application unduly. In the drawings:

[0031] Figure 1 The structure schematic diagram of the real-time auto-focusing system described in the embodiments of the present application;

[0032] Figure 2 The principle schematic diagram of the spot cutting and splicing of the beam combining element described in the embodiments of the present application;

[0033] Figure 3 The principle schematic diagram of the spot cutting and splicing of another beam combining element described in the embodiments of the present application;

[0034] Figure 4 The principle schematic diagram of the reflection pattern deviation described in the embodiments of the present application;

[0035] Figure 5 The schematic diagram of the light energy received by the second detector described in the embodiments of the present application;

[0036] Figure 6 The curve schematic diagram of the focusing energy signal described in the embodiments of the present application;

[0037] Figure 7 The principle schematic diagram of the real-time focusing realized by the movement of the compensation lens group and the objective lens described in the embodiments of the present application.

[0038] Explanation of reference signs:

[0039] First optical fiber 1, second optical fiber 2, first illumination mirror group 3, second illumination mirror group 4, beam combining element 5, first mask plate 6, first beam splitter 7, second mask plate 8, first detector 9, second detector 10, compensation mirror group 11, imaging zoom group 12, sample to be measured 13, imaging light source 14, dichroic mirror 15, camera 16, objective lens 17, collimating mirror group 18, half mirror 19, moving mechanism 20, second plane mirror 21, second beam splitter 22, first converging lens 23, second converging lens 24, first plane mirror 25, diaphragm 26, semicircular through hole 27, light blocking strip 28, ruled line 29. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and do not constitute a limitation on the present application.

[0041] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0042] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" and the like are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features limited by "first", "second" and the like can explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0043] In the description of the present application, it should be noted that unless otherwise specified and limited, the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood through specific circumstances.

[0044] The present application will be described below with reference to the accompanying drawings. Figures 1-7The invention will be described in detail with reference to the embodiments.

[0045] like Figure 1 As shown, this invention provides a real-time autofocus system, comprising: a first illumination subsystem, a second illumination subsystem, a beam combiner 5, a first mask 6, a first beam splitter 7, a second mask 8, an objective lens 17, a collimating lens group 18, a moving mechanism 20, a second beam splitter 22, a first detection subsystem, and a second detection subsystem. The illumination beams emitted by the first and second illumination subsystems are respectively incident on the beam combiner 5. The circular light spots of the first and second illumination subsystems are halved by the beam combiner 5, and the two semi-circular light spots are spliced ​​together to form a complete circular light spot. The spliced ​​circular light spot is collimated by the collimating lens group 18 and illuminates the first mask 6, then transmitted through the first beam splitter 7 and the objective lens 17 to reach the surface of the sample 13 under test, where it is reflected by the sample 13. The light is then transmitted through objective lens 17 and reflected by first beam splitter 7 to second beam splitter 22 for beam splitting. The reflected light is received by first detection subsystem, and the transmitted light illuminates second mask 8, which is then received by second detection subsystem. The first detection subsystem receives the imaging light energy reflected from first mask 6 by sample 13, while the second detection subsystem receives the remaining imaging light energy of first mask 6 after being blocked by second mask 8. Moving mechanism 20 is installed with sample 13 or objective lens 17, and the position of sample 13 or objective lens 17 is adjusted by moving mechanism 20. Focusing energy signal is calculated based on the light energy received by first and second detection subsystems, and moving mechanism 20 is controlled according to focusing energy signal to adjust the position of objective lens 17 or sample 13, thereby achieving real-time focusing of sample 13.

[0046] The moving mechanism 20 of the present invention is a displacement platform. The installation position of the moving mechanism 20 can be divided into two cases. The first case is that the objective lens 17 is mounted on the displacement platform (e.g., ...). Figure 1 As shown), the second case is to place the sample to be tested 13 on a displacement platform. By moving the displacement platform up and down, the position of the objective lens 17 or the position of the sample to be tested 13 can be adjusted, so as to achieve real-time focusing at different heights on the surface of the sample to be tested 13.

[0047] The first illumination subsystem includes a first LED light source, a first optical fiber 1, and a first illumination mirror group 3. The first LED light source couples the emitted LED light (i.e., the first illumination beam) into the first optical fiber 1, and outputs it to the first illumination mirror group 3 through the first optical fiber 1 to illuminate one surface of the beam combining element 5.

[0048] The second illumination subsystem comprises a second LED light source, a second optical fiber 2 and a second illumination lens group 4, the second LED light source couples the LED light (i.e. the second illumination light beam) emitted into the second optical fiber 2, and the second optical fiber 2 outputs the LED light to the second illumination lens group 4, and the second illumination lens group 4 illuminates the other surface of the beam combining element 5.

[0049] The LED is used to couple the light energy into the optical fiber, and the end of the optical fiber is used as the input light source of the auto-focusing system, and the design has the advantages that the angle uniformity of the input light source is ensured, the first reticle 6 is uniformly illuminated in the manner of Kohler illumination, and since the optical fiber can be customized, the end surface of the first optical fiber 1 and the end surface of the second optical fiber 2 can be marked with lines 29, and when the lines of the first optical fiber 12 are aligned with the lines 29 of the second optical fiber 2, the alignment of the two light spots is completed.

[0050] In order to avoid the influence of the surface pattern reflectivity and the pattern etching depth of the sample 13 to be measured on the auto-focusing system, the energy difference method is used, and the first illumination light path and the second illumination light path are designed, the first illumination light beam emitted by the first illumination subsystem and the second illumination light beam emitted by the second illumination subsystem are incident to the two surfaces of the beam combining element 5 respectively, the circular light spot of the first illumination light and the circular light spot of the second illumination light are cut by half by the beam combining element 5, and the remaining two half-circular light spots are spliced into a complete circular light spot.

[0051] The beam combining element 5 can adopt two structures, Figure 2 The first structure of the beam combining element 5 and the principle of light spot cutting and splicing thereof are shown, Figure 3 The second structure of the beam combining element 5 and the principle of light spot cutting and splicing thereof are shown.

[0052] As Figure 2 shown, the beam combining element 5 adopts a wedge body with an orthographic projection of a right trapezoid, realizes the cutting and splicing of the light spot, the lower base c of the wedge body faces the second illumination lens group 4, the oblique waist surface a of the wedge body faces the first illumination lens group 3, the optical axis of the first illumination lens group 3 and the optical axis of the second illumination lens group 4 intersect at the upper base corner of the wedge body close to the first illumination lens group 3, the upper base corner is the included angle between the upper base b and the oblique waist surface a, and the upper base corner is 135°.

[0053] With the edge of the junction of the inclined waist surface a and the upper bottom surface b as the demarcation line, only half of the circular light spot of the first illumination light beam is reflected by the inclined waist surface a, and the other half is left, and half of the circular light spot of the second illumination light beam is reflected by the inclined waist surface a to change the direction and does not combine with the half of the circular light spot of the first illumination light beam, and the other half transmits through the lower bottom surface c and the upper bottom surface b and combines with the half of the circular light spot of the first illumination light beam. Therefore, the circular light spot of the first illumination light beam and the circular light spot of the second illumination light beam are just cut off by half from the diameter when passing through the wedge, and only two half-circular light spots are left, and the two half-circular light spots are spliced into a complete circular light spot by the combining element 5, and the two half-circular light spots are independent of each other and do not affect each other.

[0054] In order to realize the reflection of the first illumination light beam, an LED reflection film is coated on the inclined waist surface a, and in order to realize the transmission of the second illumination light beam, an LED anti-reflection film is coated on the lower bottom surface c and the upper bottom surface b.

[0055] Since the second illumination light beam is absorbed by the LED anti-reflection film when transmitting through the LED anti-reflection film, the light intensity of the second illumination light beam is weaker than that of the first illumination light beam, in order to ensure that the energy of the second illumination light beam after transmitting through the LED anti-reflection film is the same as the energy of the first illumination light beam after being reflected by the LED reflection film, the energy of the two half-circular light spots is compensated by adjusting the light energy emitted by the second LED light source, so that the energy of the two half-circular light spots is the same.

[0056] Through the combining mode of the wedge, half of the image A formed by the first illumination light beam and half of the image B formed by the second illumination light beam can be reserved, and the energy of the first illumination light beam and the second illumination light beam in the real-time automatic focusing system is ensured to be equal, which meets the necessary condition of energy difference.

[0057] When coating the LED reflection film and the LED anti-reflection film, a clamp is needed to fix the wedge, so that there is an uncoated film area of 0.1mm or less near the junction of the inclined waist surface a or the upper bottom surface b, which causes the energy of the two half-circular light spots to be different. In order to solve this problem, a diaphragm 26 is arranged in the combining direction of the wedge, two half-circular through holes 27 for the half-circular light spots to pass through are processed on the diaphragm 26, a relatively thin light shielding strip 28 with a width greater than 0.2mm is formed between the two half-circular through holes 27, the center of the light shielding strip 28 is coincided with the edge of the junction of the inclined waist surface a and the upper bottom surface b, and the area blocked by the light shielding strip 28 will not be combined to form an image. Taking the case that the uncoated film area is formed on the inclined waist surface a, the light shielding strip 28 can block the uncoated film area of the inclined waist surface a and the symmetrical area of the upper bottom surface b, so as to ensure that the light energy reflected by the inclined waist surface a is the same as the light energy transmitted by the upper bottom surface b.

[0058] It should be noted that the width of the light shielding strip 28 is slightly greater than twice the width of the uncoated area, and the over-wide light shielding strip 28 will affect the energy of the first and second illumination beams after passing through the diaphragm 26.

[0059] As shown in Figure 3 The beam combining element 5 is implemented by a mirror to cut and splice the light spots, the reflecting surface of the mirror faces the first illumination lens group 3, and the angle between the reflecting surface and the horizontal plane is 45°, the top edge of the mirror is located at the intersection of the optical axis of the first illumination lens group 3 and the optical axis of the second illumination lens group 4, only half of the circular light spot of the first illumination beam is reflected by the mirror to become a semicircular light spot, and the other half of the circular light spot of the second illumination beam changes the light path after being reflected by the mirror and does not participate in beam combining, and the other half forms a semicircular light spot directly combined with the semicircular light spot of the first illumination beam to form a complete circular light spot.

[0060] In order to ensure that the energy of the two semicircular light spots is exactly the same, it is also necessary to provide a diaphragm 26,

[0061] The center of the light shielding strip 28 coincides with the top edge of the mirror.

[0062] The wedge beam combining method is more conducive to adjustment than the mirror beam combining method. During adjustment, the inclination of the wedge is corrected by the second illumination lens group 4. The method is to remove the wedge and mark the position of the second illumination beam at a distance from the second illumination lens group 4, then put the wedge back, adjust the inclination angle and pitch angle of the wedge, so that the second illumination beam can still coincide with the marked second illumination beam position after passing through the wedge, then the inclination angle and pitch angle of the wedge are adjusted. The remaining only needs to be translated and rotated to the right position. The inclination angle and pitch angle of the mirror are not easy to judge whether they are suitable for the mirror beam combining method.

[0063] The first detection subsystem includes a first converging lens 23 and a first detector 9, and the reflected light after being split by the second beam splitter 22 is received by the first detector 9 after being converged by the first converging lens 23.

[0064] The second detection subsystem includes a second converging lens 24 and a second detector 10, and the transmitted light after being split by the second beam splitter 22 illuminates the second mask plate 8, and then is received by the second detector 10 after being converged by the second converging lens 24.

[0065] The first detector 9 and the second detector 10 are both power detectors, the first detector 9 receives the imaging light energy of the first mask plate 6 reflected by the sample 13 to be tested, and the second detector 10 receives the remaining imaging light energy of the first mask plate 6 after being shielded by the second mask plate 8.

[0066] The complete circular light spot is collimated by the collimating lens group 18 and uniformly illuminates the first mask plate 6. Then, it is transmitted through the first beam splitter 7 and the objective lens 17 to reach the surface of the sample 13 under test. The image formed by the first mask plate 6 on the surface of the sample 13 under test is reflected by the surface of the sample 13 under test. Then, it is transmitted through the objective lens 17 and reflected by the first beam splitter 7 to reach the second beam splitter 22 for beam splitting. The reflected light from the second beam splitter 22 is converged by the first converging lens 23 and received by the first detector 9. The transmitted light from the second beam splitter 22 illuminates the second mask plate 8. The image formed by the first mask plate 6 on the surface of the sample 13 under test will overlap onto the surface of the second mask plate 8. The remaining light beam after being blocked by the second mask plate 8 is converged by the second converging lens 24 and received by the second detector 10.

[0067] In this invention, the first mask 6 forms a conjugate surface with the surface of the sample 13 to be tested, and the surface of the sample 13 to be tested forms a conjugate surface with the second mask 8, providing conditions for real-time focusing of the sample 13 to be tested.

[0068] In this invention, the first mask 6 is disposed in the beam combining direction of the beam combining element 5, specifically located between the collimating lens group 18 and the first beam splitter 7. This avoids the need to separately set up mask plates in the first illumination subsystem and the second illumination subsystem, which saves one mask plate and simplifies the system structure, thereby reducing the need for mask plate assembly and adjustment while saving costs.

[0069] like Figure 4 As shown, when the light beam reaches different positions on the surface of the sample 13 under test, the different heights at these positions cause a shift in the reflection pattern. Here, the reflection pattern refers to the image formed by the first mask 6 on the surface of the sample 13 under test. In other words, the two semi-circular light spots, after being cut by the beam combiner 5, are imaged on the left and right sides of the pupil of the objective lens 17, respectively. The first mask 6 is imaged onto the surface of the sample 13 under test through the first beam splitter 7 and the objective lens 17, and then returns to the first beam splitter 7, and is imaged onto the surface of the second mask 8 through the second beam splitter 22. When the light beam reaches different positions on the surface of the sample 13 under test, defocusing occurs, causing the image of the first mask 6 on the second mask 8 to shift left and right.

[0070] like Figure 5 As shown, when the image of the first mask 6 on the second mask 8 shifts, the imaging light energy received by the first detector 9 and the second detector 10 will change, specifically including the following three cases:

[0071] Case 1: When the sample 13 is just in focus, the imaging light energy received by the first detector 9 and the second detector 10 is Light intensity2;

[0072] Case 2: When the sample 13 is defocused downward, the imaging light energy received by the first detector 9 and the second detector 10 is Light intensity 1;

[0073] Case 3: When the sample 13 is defocused upward, the imaging light energy received by the first detector 9 and the second detector 10 is Light intensity 3.

[0074] As shown in Figure 6 and Figure 7 , the focusing energy signal E is calculated according to the imaging light energy received by the first detector 9 and the second detector 10, and the moving mechanism 20 is controlled according to the focusing energy signal E to adjust the position of the objective lens 17 or the sample 13, so as to realize real-time focusing of the sample 13.

[0075] The calculation formula of the focusing energy signal E is as follows:

[0076]

[0077] Let the light path of the first illumination beam be A channel, and the light path of the second illumination beam be B channel, then FA is the electric signal intensity converted by the A channel through the second mask lens to the second detection subsystem during the automatic focusing process; NA is the electric signal intensity converted by the A channel without passing through the second mask lens to the first detection subsystem during the automatic focusing process; Na is the superimposed electric signal intensity of the electric signal intensity caused by the background noise during the A channel not in the automatic focusing process and the dark noise of the first detection subsystem and the second detection subsystem; FB is the electric signal intensity converted by the B channel through the second mask lens to the second detection subsystem during the automatic focusing process; NB is the electric signal intensity converted by the B channel without passing through the second mask lens to the first detection subsystem during the automatic focusing process; Nb is the superimposed electric signal intensity of the electric signal intensity caused by the background noise during the B channel not in the automatic focusing process and the dark noise of the first detection subsystem and the second detection subsystem.

[0078] Here, in the actual working process, in order to independently obtain FA, NA and FB, NB, the first illumination subsystem and the second illumination subsystem are alternately operated, that is, the first LED light source and the second LED light source need to be alternately flashed, and the flashing frequency is in the order of kilohertz.

[0079] The way of calculating the focusing energy signal E of the present application can remove the influence of the background noise and the dark noise in the detection system, and improve the calculation accuracy.

[0080] The sample 13 of the present application can be different models of wafers or other samples with different surface heights. Since the overall height of different samples 13 is different, when testing different height samples 13, the reference focus plane needs to be recalibrated.

[0081] To this end, a compensation lens group 11 is arranged between the first beam splitter 7 and the objective lens 17, and the compensation lens group 11 is used to adjust the focusing range of the real-time auto-focusing system for the sample 13, so as to adjust the reference focal plane of the sample 13 with different heights. After the reference focal plane is adjusted, the position of the objective lens 17 or the sample 13 is adjusted by controlling the moving mechanism 20, so as to realize real-time focusing of the sample 13.

[0082] The present application adjusts the position of the reference focal plane by adjusting the position of a certain lens or several lenses in the compensation lens group 11, so as to realize stable focusing on any specified plane within a certain range.

[0083] In order to reduce the volume of the real-time auto-focusing system, a first plane mirror 25 is arranged between the beam combining element 5 and the first mask 6, and a second plane mirror 21 is arranged between the first beam splitter 7 and the objective lens 17. The first plane mirror 25 and the second plane mirror 21 are used to bend the light path.

[0084] The above describes the structure and principle of the real-time auto-focusing system provided by the present application. Corresponding to the real-time auto-focusing system, the present application also provides a detection system, as shown in the figure, which comprises the real-time auto-focusing system and an imaging system. Figure 1 The imaging system comprises an imaging light source 14, an imaging zoom group 12, a dichroic mirror 15, a camera 16 and a half mirror 19. The dichroic mirror 15 and the half mirror 19 are arranged to realize the same light path for the imaging light beam of the imaging light source 14 and the illumination light beam. The imaging zoom group 12 is used to change the magnification. The imaging light beam emitted by the imaging light source 14 is transmitted by the half mirror 19, reflected by the dichroic mirror 15 and transmitted by the objective lens 17, and then reaches the surface of the sample 13. After being reflected by the surface of the sample 13, the imaging light beam is sequentially received by the camera 16 through the objective lens 17 and the imaging zoom group 12. The surface of the sample 13 is imaged by the imaging system, so as to realize detection of the surface of the sample 13.

[0085] If the imaging system is not arranged, the real-time auto-focusing system can not be provided with the half mirror 19 and the dichroic mirror 15, or the half mirror 19 and the dichroic mirror 15 can be arranged as ordinary plane mirrors.

[0086] The color of the imaging light beam emitted by the imaging light source 14 is different from the color of the illumination light beam emitted by the first LED light source and the second LED light source, and the wavelength difference is large. For example, the first LED light source and the second LED light source use infrared LEDs to emit far-infrared light beams, and the imaging light source 14 uses a deep ultraviolet light source to emit a deep ultraviolet light beam.

[0087] It should be understood that the various forms of flow shown above can be used to reorder, add, or remove steps. For example, the steps recited in the present disclosure can be performed in parallel, in series, or in a different order, as long as the desired results of the present disclosure are achieved, which is not limited herein.

[0088] The specific implementation described above does not constitute a limitation on the protection scope of the present application. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A real-time autofocus system, characterized by: The application relates to a real-time focusing system for a sample under test, which comprises a first illumination subsystem, a second illumination subsystem, a beam combining element, a first mask, a second mask, a collimating lens group, an objective lens, a first beam splitter, a second beam splitter, a moving mechanism, a first detection subsystem and a second detection subsystem; wherein the illumination light beams emitted by the first illumination subsystem and the second illumination subsystem are incident to the beam combining element respectively, the circular light spot of the first illumination subsystem and the circular light spot of the second illumination subsystem are cut by half by the beam combining element, and the two half-circular light spots are spliced into a complete circular light spot; the spliced circular light spot is collimated by the collimating lens group to illuminate the first mask, then passes through the first beam splitter and the objective lens to reach the surface of the sample under test, is reflected by the sample under test, then passes through the objective lens and the first beam splitter in sequence to reach the second beam splitter, the reflected light after beam splitting is received by the first detection subsystem, the transmitted light after beam splitting illuminates the second mask, and then is received by the second detection subsystem; the moving mechanism is installed with the sample under test or the objective lens, the position of the sample under test or the objective lens is adjusted by the moving mechanism, and real-time focusing of the sample under test is realized. The beam combining element adopts a wedge body with a trapezoidal orthographic projection, the lower bottom surface of the wedge body faces the second detection subsystem, the oblique waist surface of the wedge body faces the first detection subsystem, the optical axis of the first detection subsystem and the optical axis of the second detection subsystem intersect at the upper bottom corner of the wedge body close to the first detection subsystem, the upper bottom corner is 135 DEG, a reflecting film is coated on the oblique waist surface of the wedge body, and an anti-reflection film is coated on the upper bottom surface and the lower bottom surface of the wedge body; or the beam combining element adopts a reflecting mirror, the reflecting surface of the reflecting mirror faces the first detection subsystem, the angle between the reflecting surface and the horizontal plane is 45 DEG, and the top edge of the reflecting mirror is located at the intersection of the optical axis of the first detection subsystem and the optical axis of the second detection subsystem. The focusing energy signal is calculated according to the imaging light energy received by the first detection subsystem and the imaging light energy received by the second detection subsystem, and the moving mechanism is controlled according to the focusing energy signal to adjust the position of the objective lens or the sample under test.

2. The real-time autofocus system of claim 1, wherein: The collimating lens group is located on the beam combining direction of the beam combining element, and the first mask is located between the collimating lens group and the first beam splitter.

3. The real-time autofocus system of claim 1, wherein: The first illumination subsystem comprises a first LED light source, a first optical fiber and a first illumination lens group, the LED light emitted by the first LED light source is coupled into the first optical fiber, is output to the first illumination lens group through the first optical fiber, and irradiates one surface of the beam combining element; The second illumination subsystem comprises a second LED light source, a second optical fiber and a second illumination lens group, the LED light emitted by the second LED light source is coupled into the second optical fiber, is output to the second illumination lens group through the second optical fiber, and irradiates the other surface of the beam combining element.

4. The real-time autofocus system of claim 3, wherein: End faces of the output ends of the first optical fiber and the second optical fiber are engraved with engraved lines for light spot alignment.

5. The real-time autofocus system of claim 1, wherein: A diaphragm is arranged on the beam combining direction of the beam combining element, two half-circular through holes for the half-circular light spots to pass through are processed on the diaphragm, an opaque strip is formed between the two half-circular through holes, the center of the opaque strip is coincident with the ridge space of the connection position of the oblique waist surface and the upper bottom surface of the wedge body, or the center of the opaque strip is coincident with the top edge space of the reflecting mirror.

6. The real-time autofocus system of claim 1, wherein: The first detection subsystem receives the imaging light energy reflected by the first mask plate of the sample to be measured, and the second detection subsystem receives the imaging light energy remaining after the first mask plate is shielded by the second mask plate.

7. The real-time autofocus system of claim 6, wherein: The calculation formula of the focusing energy signal E is: FA is the intensity of the electric signal converted by the second mask plate in the automatic focusing process of the illumination light emitted by the first illumination subsystem; NA is the intensity of the electric signal converted by the first detection subsystem in the automatic focusing process of the illumination light emitted by the first illumination subsystem without passing through the second mask plate; Na is the superimposed electric signal intensity of the electric signal intensity caused by the background noise in the automatic focusing process of the illumination light emitted by the first illumination subsystem and the dark noise of the first detection subsystem and the second detection subsystem; FB is the intensity of the electric signal converted by the second detection subsystem in the automatic focusing process of the illumination light emitted by the second illumination subsystem passing through the second mask plate; NB is the intensity of the electric signal converted by the first detection subsystem in the automatic focusing process of the illumination light emitted by the second illumination subsystem without passing through the second mask plate; Nb is the superimposed electric signal intensity of the electric signal intensity caused by the background noise in the automatic focusing process of the illumination light emitted by the second illumination subsystem and the dark noise of the first detection subsystem and the second detection subsystem.

8. The real-time autofocus system of claim 1, wherein: A compensation lens group is arranged between the first beam splitter and the objective lens.

9. The real-time autofocus system of claim 1, wherein: The first detection subsystem includes a first converging lens and a first detector, and the reflected light after beam splitting is received by the first detector after converging by the first converging lens; the second detection subsystem includes a second converging lens and a second detector, and the transmitted light after beam splitting illuminates the second mask plate, and is received by the second detector after converging by the second converging lens.

10. A detection system characterized by: The imaging system includes an imaging light source, an imaging variable magnification group, and a camera, and the imaging light beam emitted by the imaging light source reaches the surface of the sample to be measured, is reflected by the sample to be measured, and is then received by the camera through the objective lens and the imaging variable magnification group.

11. The detection system of claim 10, wherein: The imaging system further includes a half mirror and a dichroic mirror, and the imaging light beam emitted by the imaging light source reaches the surface of the sample to be measured through the transmission of the half mirror, the reflection of the dichroic mirror, and the transmission of the objective lens.

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