Real-time automatic focusing system and detection system formed by same

Abstract

The invention relates to the technical field of semiconductor detection, in particular to a real-time automatic focusing system and a detection system formed by the same. The real-time automatic focusing system comprises a first illumination subsystem, a second illumination subsystem, a beam combining element, a first mask plate, a second mask plate, 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. A focusing energy signal is calculated according to the 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 the to-be-detected sample, and real-time focusing of the to-be-detected sample is achieved. According to the invention, an energy difference mode is utilized to eliminate the influence on the automatic focusing system due to different reflectivity of patterns on the surface of the to-be-tested sample and the etching depth of the patterns, and real-time focusing of the to-be-tested sample is realized by adjusting the position of the objective lens or the to-be-tested sample.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor detection, and in particular relates to a real-time automatic focusing system and a detection system composed of the same. Background Art

[0002] In semiconductor inspection equipment, the inspection imaging system uses an objective lens with a large numerical aperture, and the focal depth of the objective lens is often at the sub-micron level. In order to enable the inspection imaging system to perform real-time inspection within the focal depth range, a real-time autofocus system is essential. However, the existing autofocus system is affected by the different reflectivity of the surface patterns of the sample to be tested and the depth of the pattern etching, and cannot achieve stable real-time focus on any specified plane within a certain range. Summary of the invention

[0003] In view of this, the present invention aims to provide a real-time automatic focusing system and a detection system composed of the same, so as to solve the problem that the existing automatic focusing system cannot achieve stable real-time focusing on any specified plane within a certain range.

[0004] To achieve the above object, the technical solution created by the present invention is implemented as follows: A real-time autofocus system 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 beam emitted by the first illumination subsystem and the illumination beam emitted by the second illumination subsystem are respectively incident on the beam combining element, the circular light spot of the first illumination subsystem and the circular light spot of the second illumination subsystem are cut off by half by the beam combining element, and the two semicircular light spots are spliced The spliced ​​circular light spot is collimated by the collimating lens group and then illuminates the first mask, and then reaches the surface of the sample to be tested through the first beam splitter and the objective lens, and then reaches the second beam splitter through the objective lens and the first beam splitter in sequence after being reflected by the sample to be tested, and 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 then is received by the second detection subsystem; the moving mechanism is installed with the sample to be tested or with the objective lens, and the position of the sample to be tested or the objective lens is adjusted by the moving mechanism to realize real-time focusing of the sample to be tested.

[0005] Furthermore, the collimator lens group is located in the beam combining direction of the beam combining element, and the first mask is located between the collimator lens group and the first beam splitter.

[0006] Furthermore, the first lighting subsystem includes a first LED light source, a first optical fiber and a first lighting mirror group. The first LED light source couples the emitted LED light into the first optical fiber, outputs the light to the first lighting mirror group through the first optical fiber, and irradiates one surface of the beam-combining element. The second lighting subsystem includes a second LED light source, a second optical fiber and a second lighting mirror group. The second LED light source couples the emitted LED light into the second optical fiber, outputs the light to the second lighting mirror group through the second optical fiber, and irradiates another surface of the beam-combining element.

[0007] Furthermore, the end faces of the output ends of the first optical fiber and the second optical fiber are engraved with engraved lines for aligning the light spots.

[0008] Furthermore, the beam combining element adopts a wedge whose upright projection is a trapezoid, the lower base surface of the wedge faces the second detection subsystem, the slanted waist surface of the wedge 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 angle of the wedge on the side close to the first detection subsystem, and the upper base angle is 135°, a reflective film is coated on the slanted waist surface of the wedge, and anti-reflection films are coated on the upper and lower base surfaces of the wedge; or the beam combining element adopts a reflector, the reflective surface of the reflector faces the first detection subsystem, and the angle formed between the reflective 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.

[0009] Furthermore, an aperture is arranged in the beam combining direction of the beam combining element, and two semicircular through holes are processed on the aperture for the semicircular light spot to pass through, and a shading strip is formed between the two semicircular through holes. The center of the shading strip coincides with the edge space at the connection between the inclined waist surface and the upper bottom surface of the wedge, or the center of the shading strip coincides with the top edge space of the reflector.

[0010] Furthermore, the first detection subsystem receives the imaging light energy of the first mask reflected by the sample to be tested, and the second detection subsystem receives the remaining imaging light energy of the first mask after being blocked by the second mask.

[0011] Furthermore, a 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; The calculation formula of the focusing energy signal E is:

[0012] Wherein, FA is the intensity of the electrical signal converted by the illumination light emitted by the first illumination subsystem into the electrical signal after being focused by the second mask to the second detection subsystem during the autofocus operation; NA is the intensity of the electrical signal converted by the illumination light emitted by the first illumination subsystem into the first detection subsystem when the illumination light is focused to the first detection subsystem without passing through the second mask during the autofocus operation; Na is the electrical signal intensity caused by the background noise when the illumination light emitted by the first illumination subsystem is not in the autofocus operation process and the superimposed electrical signal intensity of the dark noise of the first detection subsystem and the second detection subsystem; FB is the intensity of the electrical signal converted by the illumination light emitted by the second illumination subsystem into the electrical signal after being focused by the second mask to the second detection subsystem during the autofocus operation; NB is the intensity of the electrical signal converted by the illumination light emitted by the second illumination subsystem into the electrical signal by the first detection subsystem when the illumination light is focused on the first detection subsystem without passing through the second mask during the autofocus operation; Nb is the electrical signal intensity caused by the background noise when the illumination light emitted by the second illumination subsystem is not in the auto-focusing process and the superimposed electrical signal intensity of the dark noise of the first detection subsystem and the second detection subsystem.

[0013] In the actual working process, in order to independently obtain FA, NA and FB, NB, the first lighting subsystem and the second lighting subsystem work alternately, that is, the first LED light source and the second LED light source need to flash alternately, and the flashing frequency is in the kilohertz range.

[0014] Furthermore, a compensation lens group is arranged between the first beam splitter and the objective lens.

[0015] Furthermore, the first detection subsystem includes a first converging lens and a first detector, and the split reflected light is converged by the first converging lens and received by the first detector; the second detection subsystem includes a second converging lens and a second detector, and the split transmitted light illuminates the second mask and is converged by the second converging lens and received by the second detector.

[0016] A detection system includes the above-mentioned real-time autofocus system and imaging system, the imaging system includes an imaging light source, an imaging zoom group and a camera, the imaging light beam emitted by the imaging light source reaches the surface of the sample to be tested, is reflected by the sample to be tested, and then is received by the camera through the objective lens and the imaging zoom group in sequence.

[0017] Furthermore, the imaging system also includes a half-reflecting half-mirror and a dichroic mirror. The imaging light beam emitted by the imaging light source is sequentially transmitted through the half-reflecting half-mirror, reflected by the dichroic mirror, and transmitted by the objective lens to reach the surface of the sample to be measured.

[0018] Compared with the prior art, the invention can achieve the following beneficial effects: (1) The present invention utilizes energy differential to eliminate the influence of different reflectivity of the surface pattern of the sample to be tested and the etching depth of the pattern on the autofocus system, and realizes real-time focusing of the sample to be tested by adjusting the position of the objective lens or the sample to be tested; (2) The reference focal plane of the autofocus is adjusted by the compensation lens group to achieve real-time focusing of different samples to be tested; (3) The beam combining element used in the present invention can ensure that the energy of the two beams of light is equal in the real-time autofocus system, thereby achieving energy differentiation. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings constituting part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation on the present invention. In the drawings: Figure 1 A schematic diagram of the structure of a real-time auto-focusing system according to an embodiment of the present invention; Figure 2 A schematic diagram of the principle of spot cutting and splicing by a beam combining element according to an embodiment of the present invention; Figure 3 A schematic diagram of the principle of another beam combining element for spot cutting and splicing according to an embodiment of the present invention; Figure 4 A schematic diagram of the principle of the reflection pattern shifting described in the embodiment of the present invention; Figure 5 A schematic diagram of light energy received by the second detector according to an embodiment of the present invention; Figure 6 A schematic diagram of a curve of a focusing energy signal according to an embodiment of the present invention; Figure 7 The present invention is a schematic diagram of the principle of realizing real-time focusing by cooperating with the compensation lens group and the objective lens movement described in the embodiment of the present invention.

[0020] Description of reference numerals: The first optical fiber 1, the second optical fiber 2, the first illumination mirror group 3, the second illumination mirror group 4, the beam combining element 5, the first mask 6, the first beam splitter 7, the second mask 8, the first detector 9, the second detector 10, the compensation mirror group 11, the imaging magnification group 12, the sample to be measured 13, the imaging light source 14, the dichroic mirror 15, the camera 16, the objective lens 17, the collimating lens group 18, the half-reflecting half-mirror 19, the moving mechanism 20, the second plane mirror 21, the second beam splitter 22, the first converging lens 23, the second converging lens 24, the first plane mirror 25, the aperture 26, the semicircular through hole 27, the shading strip 28, and the scribed line 29. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the invention more clear, the invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described here are only used to explain the invention and do not constitute a limitation of the invention.

[0022] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0023] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0024] In the description of the invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the invention can be understood according to specific circumstances.

[0025] The following will refer to Figure 1-Figure 7 The invention is described in detail with reference to the embodiments.

[0026] like Figure 1As shown, the present invention provides a real-time autofocus system, including: a first illumination subsystem, a second illumination subsystem, a beam combining element 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; wherein, the illumination light beam emitted by the first illumination subsystem and the illumination light beam emitted by the second illumination subsystem are respectively incident on the beam combining element 5, the circular light spot of the first illumination subsystem and the circular light spot of the second illumination subsystem are cut off by half by the beam combining element 5, and the two semicircular light spots are spliced ​​into a complete circular light spot; the spliced ​​circular light spot is collimated by the collimating lens group 18 to illuminate the first mask 6, and then reaches the surface of the sample to be tested 13 through transmission of the first beam splitter 7 and the objective lens 17, and is reflected by the sample to be tested 13 The light is then transmitted by the objective lens 17 and reflected by the first beam splitter 7 to reach the second beam splitter 22 for splitting. The reflected light is received by the first detection subsystem, and the transmitted light illuminates the second mask 8, and is then received by the second detection subsystem. The first detection subsystem receives the imaging light energy of the first mask 6 reflected by the sample to be tested 13, and the second detection subsystem receives the remaining imaging light energy of the first mask 6 after being blocked by the second mask 8. The moving mechanism 20 is installed with the sample to be tested 13 or with the objective lens 17, and the position of the sample to be tested 13 or the objective lens 17 is adjusted by the moving mechanism 20. The focusing energy signal is calculated according to the light energy received by the first detection subsystem and the second detection subsystem, and the moving mechanism 20 is controlled according to the focusing energy signal to adjust the position of the objective lens 17 or the sample to be tested 13 to achieve real-time focusing of the sample to be tested 13.

[0027] The mobile mechanism 20 of the present invention is a displacement platform. The installation position of the mobile mechanism 20 can be divided into two situations. The first situation is to install the objective lens 17 on the displacement platform (such as Figure 1 As shown in the figure, the second case is to carry the sample 13 to be tested on a displacement platform, and adjust the position of the objective lens 17 or the position of the sample 13 to be tested by moving the displacement platform up and down, so as to realize real-time focusing on different heights of the surface of the sample 13 to be tested.

[0028] 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 light beam) into the first optical fiber 1, and outputs the light to the first illumination mirror group 3 through the first optical fiber 1 to illuminate a surface of the beam combining element 5.

[0029] The second illumination subsystem includes a second LED light source, a second optical fiber 2 and a second illumination mirror group 4. The second LED light source couples the emitted LED light (i.e., the second illumination light beam) into the second optical fiber 2, and outputs the light to the second illumination mirror group 4 through the second optical fiber 2 to illuminate the other surface of the beam combining element 5.

[0030] LED is used to couple light energy into the optical fiber, and the port of the optical fiber is used as the input light source of the autofocus system. The advantage of this design is to ensure the angular uniformity of the input light source, and to evenly illuminate the first mask 6 by means of Köhler illumination. Since the optical fiber can be customized, a line 29 can be made on the end face of the output end of the first optical fiber 1 and the end face of the output end of the second optical fiber 2. When the line 29 of the first optical fiber 12 is aligned with the line 29 of the second optical fiber 2, the merge alignment of the two light spots is completed.

[0031] In order to prevent the autofocus system from being affected by the different reflectivity of the surface patterns of the sample 13 to be tested and the etching depth of the patterns, the present invention adopts an energy differential method to design the first illumination light path and the second illumination light path. The first illumination light beam emitted by the first illumination subsystem and the second illumination light beam emitted by the second illumination subsystem are respectively incident on the two surfaces of the beam combining element 5. The circular spot of the first illumination light and the circular spot of the second illumination light are cut off by half by the beam combining element 5, and the remaining two semicircular spots are spliced ​​into a complete circular spot.

[0032] The beam combining element 5 can adopt two structures. Figure 2 The first structure of the beam combining element 5 and the principle of spot cutting and splicing are shown. Figure 3 The second structure of the beam combining element 5 and the principle of spot cutting and splicing thereof are shown.

[0033] like Figure 2 As shown, the beam combining element 5 adopts a wedge whose upright projection is a right-angled trapezoid to achieve cutting and splicing of light spots. The lower bottom surface c of the wedge faces the second lighting mirror group 4, and the oblique waist surface a of the wedge faces the first lighting mirror group 3. The optical axes of the first lighting mirror group 3 and the second lighting mirror group 4 intersect at the upper bottom angle of the wedge on the side close to the first lighting mirror group 3. The upper bottom angle is also the angle formed by the upper bottom surface b and the oblique waist surface a, and the upper bottom angle is 135°.

[0034] Taking the edge at the connection between the oblique waist surface a and the upper bottom surface b as the dividing line, only half of the circular light spot of the first illumination beam is reflected by the oblique waist surface a, leaving half of the circular light spot, and half of the circular light spot of the second illumination beam is reflected by the oblique waist surface a and changes direction, and is not combined with the half circular light spot of the first illumination beam, and the other half passes through the lower bottom surface c and the upper bottom surface b and is combined with the half circular light spot of the first illumination beam. Therefore, when the circular light spot of the first illumination beam and the circular light spot of the second illumination beam pass through the wedge, half of the diameter is cut off, leaving only two semicircular light spots, which are spliced ​​into a complete circular light spot by the beam combining element 5, and the two semicircular light spots are independent of each other and do not affect each other.

[0035] In order to reflect the first illumination beam, an LED reflective film is plated on the oblique waist surface a, and in order to transmit the second illumination beam, an LED anti-reflection film is plated on the lower bottom surface c and the upper bottom surface b.

[0036] Since the second illumination beam will absorb part of its energy when passing through the LED anti-reflection film, the light intensity of the second illumination beam is weaker than that of the first illumination beam. In order to ensure that the energy of the second illumination beam after passing through the LED anti-reflection film is the same as the energy of the first illumination beam after being reflected by the LED reflective film, energy compensation is performed by adjusting the light energy emitted by the second LED light source so that the energy of the two semicircular light spots is the same.

[0037] By combining the beams using the wedge, half of the image A formed by the first illumination beam and half of the image B formed by the second illumination beam can be retained, thereby ensuring that the energies of the first illumination beam and the second illumination beam are equal in the real-time autofocus system, thus satisfying the necessary conditions for energy differential.

[0038] When coating the LED reflective film and the LED anti-reflection film, a clamp is required to fix the wedge so that there is an uncoated area within 0.1mm near the intersection of the bevel surface a or the upper bottom surface b, resulting in different energies of the two semicircular light spots. In order to solve this problem, the present invention sets an aperture 26 in the beam combining direction of the wedge, processes two semicircular through holes 27 on the aperture 26 for the semicircular light spots to pass through, and forms a thinner shading strip 28 with a width greater than 0.2mm between the two semicircular through holes 27. The center of the shading strip 28 coincides with the ridge space at the connection between the bevel surface a and the upper bottom surface b, and the area blocked by the shading strip 28 will not be combined for imaging. Taking the uncoated area formed on the bevel surface a as an example, the shading strip 28 can block both the uncoated area of ​​the bevel surface a and the area of ​​the upper bottom surface b that is symmetrical to the uncoated area, thereby ensuring that the light energy reflected by the bevel surface a is the same as the light energy transmitted by the upper bottom surface b.

[0039] It should be noted that the width of the shading strip 28 only needs to be slightly larger than twice the width of the uncoated area. An overly wide shading strip 28 will affect the energy of the first illumination light beam and the second illumination light beam after passing through the aperture 26 .

[0040] like Figure 3As shown, the beam combining element 5 uses a reflector to achieve cutting and splicing of light spots. The reflective surface of the reflector faces the first lighting mirror group 3, and the angle between the reflective surface and the horizontal plane is 45°. The top edge of the reflector is located at the intersection of the optical axis of the first lighting mirror group 3 and the optical axis of the second lighting mirror group 4. Only half of the circular light spot of the first lighting beam is reflected by the reflector and becomes a semicircular light spot. Half of the circular light spot of the second lighting beam is reflected by the reflector and changes the optical path without participating in beam combining, and the other half forms a semicircular light spot which is directly combined with the semicircular light spot of the first lighting beam to form a completed circular light spot.

[0041] In order to ensure that the energy of the two semicircular light spots is exactly the same, it is also necessary to set an aperture 26. The center of the light shielding strip 28 coincides with the top edge space of the reflector.

[0042] Compared with the beam combining method using a reflector, the beam combining method using a wedge is more conducive to installation and adjustment. During the installation and adjustment process, the tilt of the wedge is corrected by the second lighting mirror group 4. The method is to take away the wedge and calibrate the position of the second lighting beam at a distance from the second lighting mirror group 4, then put the wedge, adjust the tilt angle and pitch angle of the wedge, so that the second lighting beam can still coincide with the calibrated second lighting beam position after passing through the wedge. The tilt angle and pitch angle of the wedge are adjusted, and the rest is to translate and rotate the wedge into place. However, it is not easy to judge whether the tilt angle and pitch angle of the reflector are appropriate in the beam combining method using a reflector.

[0043] The first detection subsystem includes a first converging lens 23 and a first detector 9 . The reflected light split by the second beam splitter 22 is converged by the first converging lens 23 and then received by the first detector 9 .

[0044] The second detection subsystem includes a second converging lens 24 and a second detector 10 . The transmitted light split by the second beam splitter 22 illuminates the second mask 8 , and then is converged by the second converging lens 24 and received by the second detector 10 .

[0045] 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 6 reflected by the sample 13 to be tested, and the second detector 10 receives the remaining imaging light energy of the first mask 6 after being blocked by the second mask 8 .

[0046] The complete circular light spot is collimated by the collimating lens group 18 to evenly illuminate the first mask 6, and then reaches the surface of the sample to be tested 13 through the transmission of the first beam splitter 7 and the transmission of the objective lens 17 in sequence. The image formed by the first mask 6 on the surface of the sample to be tested 13 is reflected by the surface of the sample to be tested 13, and then reaches the second beam splitter 22 for beam splitting through the transmission of the objective lens 17 and the reflection of the first beam splitter 7 in sequence. The reflected light of the second beam splitter 22 is converged by the first converging lens 23 and received by the first detector 9. The transmitted light of the second beam splitter 22 illuminates the second mask 8. The image formed by the first mask 6 on the surface of the sample to be tested 13 will overlap on the surface of the second mask 8. The remaining light beam blocked by the second mask 8 is converged by the second converging lens 24 and received by the second detector 10.

[0047] In the present 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 subsequent real-time focusing of the sample 13 to be tested.

[0048] In the present invention, the first mask 6 is arranged in the beam combining direction of the beam combining element 5, specifically at a position between the collimating lens group 18 and the first beam splitter 7. This can avoid setting masks in the first illumination subsystem and the second illumination subsystem respectively, thereby saving a mask and simplifying the system structure, thereby saving costs and reducing the mask adjustment once.

[0049] like Figure 4 As shown, when the light beam reaches different positions on the surface of the sample 13 to be tested, the reflection pattern will be offset due to the different heights of the different positions on the surface. The reflection pattern here refers to the image of the first mask 6 on the surface of the sample 13 to be tested. In other words, the two semicircular light spots cut by the beam combining element 5 are imaged on the left and right sides of the pupil of the objective lens 17 respectively. The first mask 6 is imaged on the surface of the sample 13 to be tested through the first beam splitter 7 and the objective lens 17, and then returns to the first beam splitter 7 along the original path, and is imaged on 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 to be tested, defocusing will occur, thereby causing the image of the first mask 6 on the second mask 8 to be offset to the left and right.

[0050] like Figure 5 As shown, when the imaging of the first mask 6 on the second mask 8 is offset, the imaging light energy received by the first detector 9 and the second detector 10 will change, specifically including the following three situations: Case ①: When the sample 13 to be tested is just in focus, the imaging light energy received by the first detector 9 and the second detector 10 is Light intensity 2; Case ②: When the sample 13 to be tested is defocused downward, the imaging light energy received by the first detector 9 and the second detector 10 is Light intensity 1; Case ③: When the sample 13 to be tested is defocused upward, the imaging light energy received by the first detector 9 and the second detector 10 is Light intensity 3.

[0051] like Figure 6 and Figure 7 As shown, 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 to be tested 13 to achieve real-time focusing of the sample to be tested 13.

[0052] The calculation formula of the focusing energy signal E is as follows:

[0053] Assume that the optical path of the first illumination beam is channel A, and the optical path of the second illumination beam is channel B, then FA is the electrical signal intensity converted from channel A to the second detection subsystem after being focused through the second mask during the autofocus operation; NA is the electrical signal intensity converted from channel A to the first detection subsystem without passing through the second mask during the autofocus operation; Na is the electrical signal intensity caused by background noise when channel A is not in the autofocus operation and the superimposed electrical signal intensity of the dark noise of the first detection subsystem and the second detection subsystem; FB is the electrical signal intensity converted from channel B to the second detection subsystem after being focused through the second mask during the autofocus operation; NB is the electrical signal intensity converted from channel B to the first detection subsystem without passing through the second mask during the autofocus operation; Nb is the electrical signal intensity caused by background noise when channel B is not in the autofocus operation and the superimposed electrical signal intensity of the dark noise of the first detection subsystem and the second detection subsystem.

[0054] In the actual working process, in order to independently obtain FA, NA and FB, NB, the first lighting subsystem and the second lighting subsystem work alternately, that is, the first LED light source and the second LED light source need to flash alternately, and the flashing frequency is in the kilohertz range.

[0055] The method of calculating the focusing energy signal E of the present invention can remove the influence of background noise and dark noise in the detection system and improve the calculation accuracy.

[0056] The test samples 13 of the present invention may be wafers of different models or other samples with different surface heights. Since the overall heights of different test samples 13 are different, when testing test samples 13 of different heights, the reference focal plane needs to be recalibrated.

[0057] To this end, a compensation lens group 11 is provided between the first beam splitter 7 and the objective lens 17, and the compensation lens group 11 is used to implement the real-time automatic focusing system to adjust the focusing range of the sample to be tested 13, thereby implementing the adjustment of the reference focal plane of the sample to be tested 13 at different heights. After adjusting the reference focal plane, the position of the objective lens 17 or the sample to be tested 13 is adjusted by controlling the moving mechanism 20 to implement real-time focusing of the sample to be tested 13.

[0058] The present invention 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, thereby achieving stable focusing on any specified plane within a certain range.

[0059] In order to reduce the volume of the real-time autofocus system, a first plane mirror 25 is arranged between the beam combining element 5 and the first mask plate 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 play the role of folding the light path.

[0060] The above content describes in detail the structure and principle of the real-time automatic focusing system provided by the present invention. Corresponding to the real-time automatic focusing system, the present invention also provides a detection system, such as Figure 1 As shown, the detection system includes the above-mentioned real-time autofocus system and imaging system, and the imaging system includes an imaging light source 14, an imaging magnification group 12, a dichroic mirror 15, a camera 16 and a half-reflecting half-mirror 19. The dichroic mirror 15 and the half-reflecting half-mirror 19 are arranged to realize that the imaging light beam of the imaging light source 14 and the illumination light beam have the same optical path. The imaging magnification group 12 is used to change the magnification. The imaging light beam emitted by the imaging light source 14 reaches the surface of the sample to be tested 13 through the transmission of the half-reflecting half-mirror 19, the reflection of the dichroic mirror 15, and the transmission of the objective lens 17. After being reflected by the surface of the sample to be tested 13, it is received by the objective lens 17 and the imaging magnification group 12 in sequence by the camera 16. The surface of the sample to be tested 13 is imaged by the imaging system to realize the detection of the surface of the sample to be tested 13.

[0061] If the imaging system is not provided, the real-time autofocus system may not provide the half-reflecting half-mirror 19 and the dichroic mirror 15, or the half-reflecting half-mirror 19 and the dichroic mirror 15 may be provided as ordinary plane mirrors.

[0062] 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 relatively 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.

[0063] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the disclosure of the present invention can be performed in parallel, sequentially or in different orders, as long as the desired results of the technical solution disclosed in the present invention can be achieved, and this document does not limit this.

[0064] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A real-time autofocus system, characterized in that: The invention 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 beam emitted by the first illumination subsystem and the illumination beam emitted by the second illumination subsystem are respectively incident on the beam combining element, the circular light spot of the first illumination subsystem and the circular light spot of the second illumination subsystem are cut off by half by the beam combining element, and the two semicircular 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, and then reaches the surface of the sample to be tested through the first beam splitter and the objective lens, and is reflected by the sample to be tested and then reaches the second beam splitter through the objective lens and the first beam splitter in sequence, 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 to be tested or with the objective lens, and the position of the sample to be tested or the objective lens is adjusted by the moving mechanism to realize real-time focusing of the sample to be tested.

2. The real-time auto-focus system according to claim 1, characterized in that: The collimator lens group is located in the beam combining direction of the beam combining element, and the first mask is located between the collimator lens group and the first beam splitter.

3. The real-time auto-focus system according to claim 1, characterized in that: The first illumination subsystem includes a first LED light source, a first optical fiber and a first illumination mirror group. The first LED light source couples the emitted LED light into the first optical fiber, outputs the light to the first illumination mirror group through the first optical fiber, and irradiates a surface of the beam combining element. The second illumination subsystem includes a second LED light source, a second optical fiber and a second illumination mirror group. The second LED light source couples the emitted LED light into the second optical fiber, outputs the light to the second illumination mirror group through the second optical fiber, and irradiates the other surface of the beam combining element.

4. The real-time auto-focus system according to claim 3, characterized in that: The end faces of the output ends of the first optical fiber and the second optical fiber are engraved with lines for aligning the light spots.

5. The real-time auto-focus system according to claim 1, characterized in that: The beam combining element adopts a wedge whose upright projection is a trapezoid, the lower base surface of the wedge faces the second detection subsystem, the slanted waist surface of the wedge 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 angle of the wedge on the side close to the first detection subsystem, and the upper base angle is 135°, a reflective film is coated on the slanted waist surface of the wedge, and anti-reflection films are coated on the upper and lower base surfaces of the wedge; or the beam combining element adopts a reflector, the reflective surface of the reflector faces the first detection subsystem, and the angle between the reflective 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.

6. The real-time auto-focus system according to claim 5, characterized in that: An aperture is arranged in the beam combining direction of the beam combining element, and two semicircular through holes are processed on the aperture for semicircular light spots to pass through, and a shading strip is formed between the two semicircular through holes. The center of the shading strip coincides with the edge space at the connection between the oblique waist surface and the upper bottom surface of the wedge, or the center of the shading strip coincides with the top edge space of the reflector.

7. The real-time auto-focus system according to claim 1, characterized in that: The first detection subsystem receives the imaging light energy of the first mask reflected by the sample to be tested, and the second detection subsystem receives the remaining imaging light energy of the first mask after being blocked by the second mask.

8. The real-time auto-focus system according to claim 7, characterized in that: Calculating a focusing energy signal according to the imaging light energy received by the first detection subsystem and the imaging light energy received by the second detection subsystem, and controlling the moving mechanism according to the focusing energy signal to adjust the position of the objective lens or the sample to be measured; The calculation formula of the focusing energy signal E is: Wherein, FA is the intensity of the electrical signal converted by the illumination light emitted by the first illumination subsystem into the electrical signal after being focused by the second mask to the second detection subsystem during the autofocus operation; NA is the intensity of the electrical signal converted by the illumination light emitted by the first illumination subsystem into the first detection subsystem when the illumination light is focused to the first detection subsystem without passing through the second mask during the autofocus operation; Na is the electrical signal intensity caused by the background noise when the illumination light emitted by the first illumination subsystem is not in the autofocus operation process and the superimposed electrical signal intensity of the dark noise of the first detection subsystem and the second detection subsystem; FB is the intensity of the electrical signal converted by the illumination light emitted by the second illumination subsystem into the electrical signal after being focused by the second mask to the second detection subsystem during the autofocus operation; NB is the intensity of the electrical signal converted by the illumination light emitted by the second illumination subsystem into the electrical signal by the first detection subsystem when the illumination light is focused on the first detection subsystem without passing through the second mask during the autofocus operation; Nb is the electrical signal intensity caused by the background noise when the illumination light emitted by the second illumination subsystem is not in the auto-focusing process and the superimposed electrical signal intensity of the dark noise of the first detection subsystem and the second detection subsystem.

9. The real-time auto-focus system according to claim 1, characterized in that: A compensation lens group is arranged between the first beam splitter and the objective lens.

10. The real-time auto-focus system according to claim 1, characterized in that: The first detection subsystem includes a first converging lens and a first detector. The split reflected light is converged by the first converging lens and received by the first detector. The second detection subsystem includes a second converging lens and a second detector. The split transmitted light illuminates the second mask and is converged by the second converging lens and received by the second detector.

11. A detection system, characterized in that: The invention comprises an imaging system and the real-time autofocus system according to any one of claims 1 to 10, wherein the imaging system comprises an imaging light source, an imaging zoom group and a camera, wherein an imaging light beam emitted by the imaging light source reaches the surface of a sample to be tested, is reflected by the sample to be tested, and then is received by the camera through an objective lens and an imaging zoom group in sequence.

12. The detection system according to claim 11, characterized in that: The imaging system also includes a half-reflecting half-mirror and a dichroic mirror. The imaging light beam emitted by the imaging light source is sequentially transmitted through the half-reflecting half-mirror, reflected by the dichroic mirror, and transmitted by the objective lens to reach the surface of the sample to be measured.

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