Relay system for auto-focus sensor, sensor, system and method

Abstract

The invention relates to a relay system for an automatic focusing sensor, a sensor, a system and a method. The system mainly comprises a first relay lens, a relay aperture diaphragm and a second relay lens which are sequentially arranged, the first relay lens is used for collimating light beams, the relay aperture diaphragm is located on a rear focal plane of the first relay lens or near the rear focal plane, and the relay aperture diaphragm is eccentric relative to an optical axis, has a certain size and is used for limiting a relay pupil plane light spot area; and then the light beam enters a second relay lens, and the second relay lens is used for focusing the light beam. Due to the fact that the angle of the returned light beam is controlled by the eccentric relay aperture diaphragm and then received by the detector, the influence of a sample surface pattern on the mass center of the light beam can be weakened to a great extent, the S-Curve slope does not change greatly even if the sample surface has an array pattern, and the relay system is beneficial to keeping the S-Curve slope stable.

Description

Technical Field

[0001] The present invention relates to the field of autofocus equipment, and in particular to a relay system for an autofocus sensor, an autofocus sensor, an autofocus system and an autofocus method. Background Art

[0002] The autofocus sensor is a sensor widely used in semiconductor wafer automated inspection equipment. The sensor outputs the defocus value at a high frequency, reflects the defocus information of the sample under the objective lens in real time, and feeds back to the control system to adjust the sample to the optimal focal plane of the objective lens to ensure real-time clear imaging.

[0003] Ideally, the defocus value (Defocus Value) output by the sensor should only be related to the defocus distance of the sample, that is, the relationship between the defocus value (Defocus Value) output by the sensor and the defocus distance of the sample (also known as S-Curve) is fixed in an autofocus sensor system. However, in practical applications, autofocus sensors are easily affected by the surface process of the sample being focused. For example, if the sample is a wafer, there will be multiple film layers and patterns on the surface of the wafer. Some patterns have obvious differences in reflectivity distribution, such as black and white faces, cutting paths, dense array patterns, or grooves. This causes the curve (S-Curve) of the change in the DefocusValue value to the defocus distance to deviate from the pre-calibrated curve, affecting the calculation of the defocus distance, causing inaccurate focus, and causing problems with the process adaptability of the sensor. Therefore, the stability of the S-Curve of the autofocus sensor is crucial.

[0004] The curve of the change of the sensor Defocus Value signal to the defocus distance has a linear area. The sensor signal in this area corresponds to the defocus distance one by one, which is a linear interval. The characteristics of the S-Curve can be described by slope and offset.

[0005] Autofocus sensors usually use the principle of optical triangulation. Light is incident obliquely on the sample surface. Changes in sample height will cause the light spot on the sample surface to shift. The sensitivity of the displacement as the defocus distance changes is the slope. Obviously, the slope is directly related to the incident angle of the light. In microscopic applications, the incident angle of the light is directly determined by the light spot distribution on the pupil of the objective lens, that is, the slope is determined by the light spot distribution on the pupil of the autofocus sensor. The closer the centroid of the light spot is to the edge of the pupil, the larger the light incident angle (NA) and the more sensitive the system.

[0006] Traditional autofocus sensors only pay attention to controlling the emitted light to illuminate the sample at a preset tilt angle. The return light is generally processed by default to be reflected and returned to the objective lens at a symmetrical angle, following the law of reflection. But in fact, when the light returns to the objective lens, the return angle distribution of the light will be affected by the surface pattern of the sample, such as the grating and array pattern. This is reflected on the pupil plane of the objective lens as diffraction orders of the light spot and energy redistribution. Since these orders are asymmetric with respect to the optical axis of the objective lens, the centroid of the return light spot passing through the pupil of the objective lens changes, that is, the angle of the received return light changes, so that the slope of the S-Curve fluctuates greatly with the appearance of the array pattern, and the degree of deviation fluctuates with parameters such as the period and orientation of the array pattern on the sample surface. Therefore, in the autofocus sensor, controlling the angle of the received return light is an important factor affecting the process adaptability of the sensor. Summary of the invention

[0007] Based on this, a relay system for an autofocus sensor is provided, which is beneficial for suppressing the change in the angle of the return light and maintaining a stable S-Curve slope when an array pattern appears on the sample surface.

[0008] A relay system for an autofocus sensor comprises a first relay lens, a relay aperture stop and a second relay lens which are arranged in sequence. The first relay lens is used to collimate the light beam. The relay aperture diaphragm is located between the first relay lens and the second relay lens. The relay aperture diaphragm is used to collimate the light beam. The light beam then enters the second relay lens, and the second relay lens is used to focus the light beam.

[0009] On the basis of the above, further, a detector is included, and the detector is located on one side of the second relay lens, and the detector is used to receive the light beam focused by the second relay lens.

[0010] An auto-focus sensor, comprising the relay system for the auto-focus sensor, It also includes an emitting light path and a returning light path. The emitting light path is provided with a plurality of optical elements. The returning light path is provided with the relay system and a detector. The detector is located on one side of the second relay lens and is used to receive the light beam focused by the second relay lens.

[0011] On the basis of the above, further, the several optical elements arranged on the emission light path include an illumination system, a field aperture, a dichroic prism and a tube lens arranged in sequence, the light beam emitted by the illumination system passes through the field aperture, the dichroic prism and the tube lens in sequence, and the first relay lens is located on one side of the dichroic prism.

[0012] On the basis of the above, further, the lighting system includes a light source, a first lens, a baffle and a second lens arranged in sequence, the first lens is used to collimate the light beam emitted by the light source, the baffle is used to block a portion of the light beam passing through the first lens, and the second lens is used to focus the light beam.

[0013] An automatic focusing system, comprising the relay system for the automatic focusing sensor, It also includes an emission light path and a return light path. The emission light path is provided with a number of optical elements. The light beam on the emission light path is reflected by the sample and then returns to the objective lens. The return light path is provided with the relay system and a detector. The detector is located on one side of the second relay lens. The detector is used to receive the light beam focused by the second relay lens.

[0014] In one embodiment, the plurality of optical elements arranged on the emission light path include an illumination system, a field aperture, a beam splitter prism and a tube lens arranged in sequence. The light beam emitted by the illumination system passes through the field aperture, the beam splitter prism and the tube lens in sequence. The first relay lens is located on one side of the beam splitter prism. The light beam emitted by the tube lens enters the objective lens after reflection. The tube lens is also used to receive the light beam returned by the objective lens.

[0015] In one embodiment, the lighting system includes a light source, a first lens, a baffle, and a second lens arranged in sequence, the first lens is used to collimate the light beam emitted by the light source, the baffle is used to block a portion of the light beam passing through the first lens, and the second lens is used to focus the light beam.

[0016] In one embodiment, a dichroic mirror or a beam splitter prism is arranged between the tube lens and the objective lens.

[0017] An autofocus method adopts the relay system for an autofocus sensor, limits the relay pupil light spot area through the relay system, suppresses the phenomenon that the light spot centroid is affected by the sample surface pattern, especially the array pattern, so as to control the angle of the return light.

[0018] The beneficial effects of this application are: 1. Since the light beam is received by the detector only after passing through, the influence of the sample surface pattern on the center of mass of the light beam can be greatly reduced. Even if the sample surface has an array pattern or other types of dense patterns, the S-Curve slope will not change significantly. The relay system of the present application is conducive to maintaining the stability of the S-Curve slope.

[0019] 2. It reduces the impact of the sample surface array pattern on the autofocus sensor signal and has the characteristics of real-time performance.

[0020] 3. After applying the relay system of the present application, the variation of the S-Curve slope corresponding to the sample with the array pattern is within 8% compared with the S-Curve slope corresponding to the sample without the pattern.

[0021] 4. The present application achieves S-Curve slope stabilization through a simple structure, and the relay system of the present application is applicable to a variety of existing autofocus sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic diagram of an embodiment of an autofocus system of the present application.

[0023] Figure 2 FIG. 4 is a schematic diagram of another embodiment of the auto-focus system of the present application.

[0024] Figure 3 The diagram is a result of a physical simulation test on the autofocus system of the present application, wherein row (a) represents the test results when there is no pattern on the sample surface, row (b) represents the test results when the sample surface has an array pattern and the relay system of the present application is not used, and only the existing autofocus system is used; row (c) represents the test results when the sample surface has an array pattern and the relay system of the present application is used.

[0025] Figure 4 This is a result diagram of actual testing of the autofocus system of the present application, showing the S-Curve when there is no array pattern on the sample surface, the S-Curve after the sample surface has an array pattern and the relay system of the present application is applied, and the S-Curve when the sample surface has an array pattern and the relay system of the present application is not used. DETAILED DESCRIPTION

[0026] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0027] like Figure 1As shown, the first embodiment of the present application provides a relay system for an autofocus sensor, the system includes a first relay lens, a relay aperture diaphragm and a second relay lens arranged in sequence, the first relay lens is used to collimate the light beam, the relay aperture diaphragm is located between the first relay lens and the second relay lens, specifically, the relay aperture diaphragm is located at the back focal plane of the first relay lens or near the back focal plane, this plane is conjugate with the pupil plane of the objective lens, and the relay aperture diaphragm is eccentric relative to the optical axis, the size of the eccentricity is determined by the center of the spot of the returning light beam, and the diameter of the relay aperture diaphragm is determined by the width of the spot under the patternless sample. In this way, the returning light beam is limited to a small eccentric area on the relay pupil, and the light beam enters the second relay lens again, and the second relay lens is used to focus the light beam. Specifically, the focal lengths of the first relay lens and the second relay lens can be matched as required.

[0028] On the basis of the above, a detector may be arranged on one side of the second relay lens, and the detector is used to receive the light beam focused by the second relay lens.

[0029] Specifically, the above-mentioned detector can be a CMOS Sensor, a CCD Sensor, a PSD (Position Sensing Detectors) or a PD (Photodiode) and the like.

[0030] Specifically, after the light beam returning from the sample enters the relay system, it first passes through the first relay lens. After the light beam is collimated by the first relay lens, the light beam will pass through the relay aperture diaphragm, which is located at or near the back focal plane of the first relay lens. This plane is conjugate with the pupil plane of the objective lens. After the relay aperture diaphragm limits the area of ​​the light beam passing through, the light beam enters the second relay lens. After being focused by the second relay lens, the light beam hits the detector. Because the light beam has been limited to the spot area by the aperture diaphragm of the relay system before being received by the detector, even if the light spot is diffused due to the array pattern on the sample, the change of the beam centroid on the pupil plane can be suppressed to a great extent, thereby stabilizing the S-Curve.

[0031] like Figure 1 As shown, the second embodiment of the present application provides an autofocus sensor, which includes the relay system for the autofocus sensor, that is, includes the first relay lens, relay aperture stop and second relay lens. On this basis, the autofocus sensor also includes an emission light path and a return light path, the emission light path is provided with a plurality of optical elements, the return light path is provided with the relay system and a detector, the detector is located on one side of the second relay lens, and the detector is used to receive the light beam focused by the second relay lens.

[0032] On the basis of the above, further, the several optical elements arranged on the emission light path include an illumination system, a field aperture, a dichroic prism and a tube lens arranged in sequence, the light beam emitted by the illumination system passes through the field aperture, the dichroic prism and the tube lens in sequence, and the first relay lens is located on one side of the dichroic prism.

[0033] The above-mentioned field aperture is used to control the size and shape of the light spot formed by the light beam. The above-mentioned beam splitter prism is used to allow the returning light beam to enter the above-mentioned relay system of the present application.

[0034] On the basis of the above, further, Figure 2 As shown, the lighting system includes a light source, a first lens, a baffle and a second lens arranged in sequence, the first lens is used to collimate the light beam emitted by the light source, the baffle is used to block a part of the light beam passing through the first lens, and the second lens is used to focus the light beam.

[0035] The third embodiment of the present application provides an autofocus system, which includes the relay system for the autofocus sensor, that is, the first relay lens, the relay aperture stop and the second relay lens. The system also includes an emission light path and a return light path, the emission light path is provided with a plurality of optical elements, the return light path is provided with the relay system and a detector, the detector is located on one side of the second relay lens, and the detector is used to receive the light beam focused by the second relay lens.

[0036] Specifically, in this embodiment, the optical elements arranged on the emission light path include an illumination system, a field stop, a beam splitter and a tube lens arranged in sequence. The light beam emitted by the illumination system passes through the field stop, the beam splitter and the tube lens in sequence. The first relay lens is located on one side of the beam splitter. A dichroic mirror or a beam splitter is arranged between the tube lens and the objective lens. The light beam emitted by the tube lens enters the objective lens after reflection. The tube lens is also used to receive the light beam returned by the objective lens. The light beam enters the tube lens after being emitted by the objective lens and reflected.

[0037] Furthermore, the lighting system includes a light source, a first lens, a baffle and a second lens arranged in sequence, the first lens is used to collimate the light beam emitted by the light source, the baffle is used to block a portion of the light beam passing through the first lens, and the second lens is used to focus the light beam.

[0038] It can be understood that there are many implementations of the above-mentioned lighting system, which is not limited to the above-mentioned implementations.

[0039] like Figure 2As shown, the box contains the internal optical components of the autofocus sensor, and the outside of the box is the coupling dichroic mirror or beam splitter (Beam Splitter), and the microscope objective lens.

[0040] Specifically, the light source is a laser diode or LED light source. The light source is used to emit a light beam, which is collimated by a first lens and then blocked by a baffle to block half of the light spot. Then, the light beam is converged by a second lens to form a light spot, which can be circular or long. At the same time, the size and shape of the light spot are controlled by the field aperture. The light beam then passes through a beam splitter prism (BeamSplitter) and enters the tube lens. After emitting from the tube lens, it is reflected by a dichroic mirror or a beam splitter prism (Beam Splitter) and enters the objective lens. The light beam is converged by the objective lens and irradiates the sample surface. The reflected or scattered light beam from the sample surface enters the objective lens again, and enters the tube lens after being reflected by a dichroic mirror or a beam splitter. The light beam emitted from the tube lens is turned 90° by the beam splitter and enters the first relay lens of the relay system. The relay aperture diaphragm is located at or near the back focal plane of the first relay lens. This surface is conjugate with the pupil surface of the objective lens. The relay aperture diaphragm is eccentric relative to the optical axis and has a certain size. The spot area on this surface is limited. The light beam enters the second relay lens again. After being focused by the second relay lens, the spot hits the detector. Since the received light beam is limited by the aperture diaphragm of the relay system, even if the array pattern on the sample causes the spot to spread, the change of the beam centroid on the pupil surface can be suppressed to a great extent, stabilizing the S-Curve.

[0041] It should be noted that in the present application, after the light beam emitted from the autofocus sensor is reflected by the sample surface with an array pattern, diffraction orders are generated. When the pattern period is very small or very dense, the -1 order in the ±1 order will not be collected by the objective lens, and the +1 order will enter the objective lens, which will cause a change in the energy distribution of the pupil surface, causing a change in the triangulation angle in the return light path, and the S-Curve slope changes accordingly. However, since the present application is provided with a relay system, the relay system can introduce a relay surface of the pupil surface, and on this surface, the spot area passing through is limited by an eccentric aperture diaphragm, thereby suppressing the change in the centroid of the pupil surface spot, thereby controlling the angle of the return light. Therefore, the present application can stabilize the S-Curve so that it will not change significantly due to the array pattern on the sample surface.

[0042] The fourth embodiment of the present application provides an autofocus method, which uses the relay system for the autofocus sensor to limit the area of ​​the light beam returned by the sample on the pupil surface through the relay system. The sample surface is provided with an array pattern.

[0043] Specifically, the above method of the present application reduces the sensitivity of the auto-focus sensor signal to the array pattern on the sample surface, and improves the accuracy of the auto-focus sensor in detecting the defocus position.

[0044] The present application has conducted simulation experiments, and the simulation experiment results are described in detail below.

[0045] The scheme used in the simulation experiment is the above-mentioned autofocus system of the present application, which includes the relay system for the autofocus sensor, which includes a first relay lens, a relay aperture diaphragm and a second relay lens arranged in sequence, the first relay lens is used to collimate the light beam, the relay aperture diaphragm is located at the back focal plane of the first relay lens or near the back focal plane, this plane is conjugate with the pupil plane of the objective lens, the relay aperture diaphragm is eccentric relative to the optical axis, has a certain size, and is used to limit the area of ​​the light beam passing through, and then the light beam enters the second relay lens, and the second relay lens is used to focus the light beam. It also includes an emission light path and a return light path, a plurality of optical elements are arranged on the emission light path, the return light path is provided with the relay system and a detector, the detector is located on one side of the second relay lens, the detector is used to receive the light beam focused by the second relay lens, the light beam emitted by the tube lens enters the objective lens after reflection, and the tube lens is also used to receive the light beam returned by the objective lens. The optical elements arranged on the emission light path include an illumination system, a field stop, a beam splitter and a tube lens arranged in sequence. The light beam emitted by the illumination system passes through the field stop, the beam splitter and the tube lens in sequence. The first relay lens is located on one side of the beam splitter. The illumination system includes a light source, a first lens, a baffle and a second lens arranged in sequence. The first lens is used to collimate the light beam emitted by the light source, the baffle is used to block a part of the light beam passing through the first lens, and the second lens is used to focus the light beam. A dichroic mirror or a beam splitter is arranged between the tube lens and the objective lens.

[0046] like Figure 3 As shown, physical simulation shows that the relay system of the present application has a significant effect on stabilizing the triangulation slope.

[0047] In general, the calibrated S-Curve is obtained without a pattern (light sheet), for example Figure 3 The slope of row (a) in the graph is 20.19.

[0048] The closer the S-Curve obtained under different patterns is to the S-Curve under the light sheet, the better the process adaptability of the autofocus sensor.

[0049] Figure 3The (b) row shows that the array pattern significantly affects the pupil spot. The pupil has multiple diffraction orders and has a significant impact on the S-Curve. The slope drops significantly to 17.6.

[0050] Figure 3 The (c) row shows the pupil spot after the relay system of the present application is adopted, and the slope of the S-Curve is close to the slope under the light sheet, which is 20.16.

[0051] pass Figure 3 It can be seen that the relay system of the present application can effectively stabilize the slope of the S-Curve in theory.

[0052] Furthermore, Figure 4 The measured data of the influence of the relay system of the present application on the S-Curve is shown.

[0053] from Figure 4 It can be seen that after relaying using the relay system of the present application, even if the sample surface has a periodic pattern, that is, an array pattern, its S-Curve is very close to the S-Curve in the case of no pattern. However, if the sample surface has a periodic pattern and the relay system of the present application is not used, the S-Curve will deviate significantly from the S-Curve in the case of no pattern. This result is consistent with the simulation prediction. A stable S-Curve is conducive to calibrating the correct S-Curve and ultimately reflects the correct defocus position.

[0054] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A relay system for an autofocus sensor, characterized in that: comprising a first relay lens, a relay aperture stop and a second relay lens arranged in sequence, The first relay lens is used to collimate the light beam. The relay aperture diaphragm is located between the first relay lens and the second relay lens. The relay aperture diaphragm is eccentric to the optical axis and has a certain size. It is used to limit the return light beam area on the surface. Then the light beam enters the second relay lens, and the second relay lens is used to focus the light beam.

2. The relay system for an auto-focus sensor according to claim 1, characterized in that: The device also includes a detector, which is located at one side of the second relay lens and is used to receive the light beam focused by the second relay lens.

3. An autofocus sensor, characterized in that comprising the relay system for an autofocus sensor as claimed in claim 1, It also includes an emitting light path and a returning light path. The emitting light path is provided with a plurality of optical elements. The returning light path is provided with the relay system and a detector. The detector is located on one side of the second relay lens and is used to receive the light beam focused by the second relay lens.

4. The autofocus sensor according to claim 3, characterized in that: The optical elements arranged on the emission light path include an illumination system, a field diaphragm, a beam splitter prism and a tube lens arranged in sequence. The light beam emitted by the illumination system passes through the field diaphragm, the beam splitter prism and the tube lens in sequence. The first relay lens is located on one side of the beam splitter prism.

5. The autofocus sensor according to claim 4, characterized in that: The lighting system includes a light source, a first lens, a baffle and a second lens which are arranged in sequence. The first lens is used to collimate the light beam emitted by the light source, the baffle is used to block a part of the light beam passing through the first lens, and the second lens is used to focus the light beam.

6. An autofocus system, characterized in that, comprising the relay system for an autofocus sensor as claimed in claim 1, It also includes an emission light path and a return light path. The emission light path is provided with a plurality of optical elements. The return light path is provided with the relay system and a detector. The detector is located on one side of the second relay lens. The detector is used to receive the light beam focused by the second relay lens. The light beam on the emission light path enters the objective lens after reflection.

7. The automatic focusing system according to claim 6, characterized in that: The plurality of optical elements arranged on the emission light path include an illumination system, a field diaphragm, a beam splitter prism and a tube lens arranged in sequence. The light beam emitted by the illumination system passes through the field diaphragm, the beam splitter prism and the tube lens in sequence. The first relay lens is located on one side of the beam splitter prism. The light beam emitted by the tube lens enters the objective lens after reflection. The tube lens is also used to receive the light beam returned by the objective lens.

8. The automatic focusing system according to claim 7, characterized in that: The lighting system includes a light source, a first lens, a baffle and a second lens which are arranged in sequence. The first lens is used to collimate the light beam emitted by the light source, the baffle is used to block a part of the light beam passing through the first lens, and the second lens is used to focus the light beam.

9. The automatic focusing system according to claim 7, characterized in that: A dichroic mirror or a beam splitter prism is arranged between the tube lens and the objective lens.

10. An automatic focusing method, characterized in that: The relay system for an autofocus sensor as described in claim 1 is used to limit the relay pupil light spot area through the relay system, thereby suppressing the phenomenon that the light spot centroid is affected by the sample surface pattern, especially the array pattern, so as to control the angle of the returning light.

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