An autofocus system and thickness measurement system suitable for translucent wafers

Abstract

The application discloses an automatic focusing system and a thickness measuring system suitable for a translucent wafer, wherein the automatic focusing system comprises a translucent wafer, an objective lens to be focused, a mirror, a laser light source, a first lens, a pinhole diaphragm, a programmable liquid crystal device, a collimating lens, a second lens, a third lens, a first detector, a second detector and a motor; the precise focusing of the objective lens is realized through the detection light spots of the two detectors; the thickness measuring system comprises a translucent wafer, a dispersive objective lens, a mirror, a white light source, an achromatic lens, a pinhole diaphragm, a programmable liquid crystal device, a collimating lens, a converging lens, a slit, a lens and a detector; the mapping relationship between the lateral displacement amount on the detector and the thickness of the translucent wafer is used to realize the measurement of the unknown thickness of the translucent wafer, and the cost is low without a spectrometer.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical detection, and particularly relates to an automatic focusing system and a thickness measurement system suitable for a semi-transparent wafer. BACKGROUND

[0002] The automatic focusing system is divided into active focusing (AAF) and passive focusing (PAF) in terms of methods. The former converts focusing information into a physical quantity that can be measured, usually optical information, for focusing by using an additional light path or structure. The latter mainly relies on a digital image processing method to help complete focusing by using algorithms to perform a series of analyses directly through imaging conditions. In recent years, with the continuous improvement of computer technology, the automatic focusing technology for photography has been more inclined to the passive focusing method. Considering the needs of stability, modularity and convenience, the active focusing method is still widely used in the current industrial defect detection as an important component scheme in the automated optical inspection (AOI), and common specific applications include solder joint detection, circuit board quality detection and the like.

[0003] The semiconductor defect detection equipment has a high detection speed, needs to keep the focal plane of the optical system on the wafer surface at all times while quickly scanning the wafer surface, and thus more actively uses the focusing method. Among them, the pupil division method is the most widely used due to its low cost and high precision. Currently, WDI, MSG, Prior, Evident and other companies have developed commercial modules using this method. The specific method is that the light beam emitted by the on-axis light source is blocked by an eccentric diaphragm, the light on the side of the optical axis plane that is not blocked is collimated, and then focused on the wafer surface by the objective lens. Subsequently, the light beam is reflected by the wafer surface and propagates along the other side of the optical axis plane and is then focused on the sensor. When the focal plane of the objective lens is at different positions of the wafer reflection surface, the light spot of the returning light beam on the sensor will also change. For example, when the measured surface is located on the focal plane of the objective lens, the light spot on the sensor will be a point. When the measured surface is located above the focal plane of the objective lens, the light spot on the sensor will be a semicircle and located on the right side of the central axis of the sensor. When the measured surface is located below the focal plane of the objective lens, the light spot on the sensor will be a semicircle and located on the left side of the central axis of the sensor. The defocus amount can be judged by calculating the gray center of the light spot of the returning light beam on the sensor. However, this method is not suitable for semi-transparent wafers, and the reflection of the lower surface of the semi-transparent wafer will have a great influence on the focusing precision. SUMMARY

[0004] In view of the above, the purpose of the present application is to provide an auto-focusing system and thickness measurement system suitable for a translucent wafer, to achieve accurate focusing of an objective lens in a translucent wafer defect detection device through a designed optical path, and to measure the thickness of the translucent wafer.

[0005] To achieve the above-mentioned purpose of the application, the embodiment provides an auto-focusing system suitable for a translucent wafer, comprising: a translucent wafer, an objective lens to be focused, a mirror, a laser light source, a first lens, a pinhole diaphragm, a programmable liquid crystal device, a collimating lens, a second lens, a third lens, a first detector, a second detector, and a motor.

[0006] The exit light of the laser light source is collimated through the first lens, and then passes through the pinhole diaphragm controlled by the motor to adjust the off-axis distance, so that the pinhole diaphragm serves as an off-axis light source to emit an off-axis light beam, which passes through the programmable liquid crystal device, is collimated by the collimating lens, and is incident on the mirror, which reflects the incident light to the objective lens and converges and focuses it on the translucent wafer.

[0007] When focusing on the upper surface of the translucent wafer, the reflected light passing through the upper surface of the translucent wafer is collimated by the objective lens and then reflected by the mirror to the second lens, which converges and is received by the first detector to form a light spot, while the reflected light passing through the lower surface of the translucent wafer is collimated by the objective lens and then reflected by the mirror to the third lens, which converges and is received by the second detector to form a light spot.

[0008] When focusing on the lower surface of the translucent wafer, the reflected light passing through the lower surface of the translucent wafer is collimated by the objective lens and then reflected by the mirror to the third lens, which converges and is received by the second detector to form a light spot, while the reflected light passing through the upper surface of the translucent wafer is collimated by the objective lens and then reflected by the mirror to the second lens, which converges and is received by the first detector to form a light spot.

[0009] The objective lens is adjusted by observing the light spot or the light spot to achieve focusing of the objective lens on the translucent wafer.

[0010] Preferably, the diameter of the pinhole diaphragm is 5-10 um, and the off-axis distance of the pinhole diaphragm driven by the motor is 1-3 mm.

[0011] Preferably, the focal length of the first lens, the second lens, and the third lens is 50-75 mm, and the second lens and the third lens have the same focal length.

[0012] Preferably, the programmable liquid crystal device can display a circular light-transmissible area and a non-light-transmissible area, and output an off-axis light beam after passing through the programmable liquid crystal device, and the laser light source is a laser LD with a wavelength of 660 nm or 850 nm.

[0013] To achieve the above object, the embodiment of the present application further provides a thickness measurement system suitable for a semi-transparent wafer, comprising: a semi-transparent wafer, a dispersion objective lens, a mirror, a white light source, an achromatic lens, a pinhole diaphragm, a programmable liquid crystal device, a collimating lens, a converging lens, a slit, a lens, and a detector.

[0014] The emergent light of the white light source is collimated by the achromatic lens and then is emitted as an off-axis light beam through the pinhole diaphragm as an off-axis light source. The off-axis light beam is transmitted through the programmable liquid crystal device and then is collimated by the collimating lens and is incident on the mirror. The mirror reflects the incident light to the dispersion objective lens and converges and focuses the different color light after dispersion on different depth focal planes of the semi-transparent wafer. Specifically, the long wave is focused on the lower surface of the semi-transparent wafer, and the short wave is focused on the upper surface of the semi-transparent wafer. There is a displacement amount in the lateral direction between the focal point of the long wave light beam on the lower surface and the focal point of the short wave light beam on the upper surface.

[0015] The short wave length light is reflected by the upper surface of the semi-transparent wafer and then is collimated by the dispersion objective lens. Subsequently, the light is reflected by the mirror, passes through the converging lens, and reaches the slit. The light is focused into a point at the position of the slit and is transmitted through the slit without loss. The light reflected by other surfaces is blocked by the slit. Subsequently, the light transmitted through the slit is converged on the detector after passing through the lens.

[0016] The long wave length light is reflected by the lower surface of the semi-transparent wafer and then is collimated by the dispersion objective lens. Because there is a displacement amount in the lateral direction between the light of the short wave length propagating in the semi-transparent wafer, the light is subsequently reflected by the mirror, passes through the converging lens, and reaches the slit. The light is also focused into a point at the position of the slit and has a displacement amount in the lateral direction with the converging point of the light of the short wave length. The long wave length light is subsequently transmitted through the slit without loss, and the light reflected by other surfaces is blocked by the slit. Subsequently, the light transmitted through the slit is converged on the detector after passing through the lens and has a displacement amount in the lateral direction with the converging point of the light of the short wave length on the detector.

[0017] According to the mapping relationship between the displacement amount in the lateral direction on the detector and the thickness of the semi-transparent wafer and the known thickness of the semi-transparent wafer, the thickness measurement system is calibrated. Then, the unknown thickness of the semi-transparent wafer is measured by using the calibrated thickness measurement system according to the measured displacement amount in the lateral direction and the mapping relationship.

[0018] Preferably, the constrained light beam between the pinhole diaphragm and the programmable liquid crystal device has an inclination angle in the range of 0-5°.

[0019] Preferably, the slit has a slit width of 15-25 um.

[0020] Preferably, the achromatic lens has a focal length of 25-50 mm, and the collimating lens, the converging lens, and the lens each have a focal length of 50-75 mm. The lens images the size of the slit to the detector by 1:1.

[0021] Preferably, the mapping relationship between the amount of lateral displacement on the detector and the thickness of the translucent wafer is:

[0022] Suppose the wavelength range of the white light source contains λ a and λ b , the dispersive objective converges λ a and λ b at different depth positions, λ a is the wavelength of the upper surface reflection of the translucent wafer, λ b is the wavelength of the lower surface reflection of the translucent wafer, d is the thickness of the translucent wafer, and the amount of lateral displacement l between the convergence points of λ a and λ b on the detector follows the mapping relationship:

[0023]

[0024] Where f c is the focal length of the dispersive objective, f f is the focal length of the converging lens, and θ is the angle between the optical axis defined by the center of the pinhole aperture and the light-transmitting part of the programmable liquid crystal device and the optical axis defined by the white light source and the achromatic lens, so that the thickness d information is obtained from l;

[0025]

[0026] Preferably, the thickness measurement system can simultaneously measure multiple face thicknesses of the translucent wafer.

[0027] Compared with the prior art, the present application has at least the following beneficial effects:

[0028] The automatic focusing system and the thickness measurement system provided by the present application both realize precise focusing of the objective lens in the translucent wafer defect detection device by constructing a special optical path, solving the problem that the lower surface reflection of the translucent wafer will result in low focusing accuracy when the eccentric light beam method is used for focusing the translucent wafer. The special optical path is also designed to measure the thickness of the translucent wafer, without the need for a spectrometer, thereby reducing the cost of thickness measurement and improving the range of use. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only constitute some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0030] Figure 1is a structural schematic diagram of the focusing on the upper surface of the translucent wafer of the automatic focusing system suitable for the translucent wafer provided by the embodiment;

[0031] Figure 2 is a structural schematic diagram of the focusing on the lower surface of the translucent wafer of the automatic focusing system suitable for the translucent wafer provided by the embodiment;

[0032] Figure 3 is a schematic diagram of the principle of the programmable liquid crystal device provided by the embodiment;

[0033] Figure 4 is a structural schematic diagram of the automatic focusing system provided by the comparative example;

[0034] Figure 5 is a schematic diagram of the light spot when the upper surface of the pure reflective wafer is located below (a) the focal plane of the objective lens, (b) the focal plane of the objective lens, and (c) above the focal plane of the objective lens provided by the comparative example;

[0035] Figure 6 is a schematic diagram of the light spot when the upper surface of the translucent wafer is located below (a) the focal plane of the objective lens, (b) the focal plane of the objective lens, and (c) above the focal plane of the objective lens and the lower surface is located below the focal plane of the objective lens provided by the comparative example;

[0036] Figure 7 is a structural schematic diagram of the thickness measurement system suitable for the translucent wafer provided by the embodiment. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and do not limit the protection scope of the present application.

[0038] Embodiment 1

[0039] In order to solve the technical problem that the lower surface reflection of the translucent wafer will make the focusing precision not high when the eccentric light beam method is used for focusing the translucent wafer, the embodiment provides an automatic focusing system suitable for the translucent wafer, such as Figure 1As shown, the system includes a semi-transparent wafer 108, an objective lens 107 to be focused, a reflector 106, a laser light source 101, a first lens 102, an aperture stop 103, a programmable liquid crystal device 104, a collimating lens 105, a second lens 109, a third lens 111, a first detector 110, a second detector 112, and a motor 113. The laser light source 101 is a laser LD with a wavelength of 660 nm, the aperture stop 103 has a diameter of 10 μm, the motor 113 drives the aperture stop 103 at an off-axis distance of 1 mm, the focal length of the first lens 102 is generally 50 mm, the focal lengths of the second lens 109 and the third lens 111 are equal, namely 75 mm, and the second lens 109 and the third lens 111 have the same focal length.

[0040] like Figure 3 As shown, the programmable liquid crystal device 104 can display a circular light-transmitting area 22 and a light-impermeable area 21 , and an off-axis light beam is output after passing through the programmable liquid crystal device 104 .

[0041] Specifically, the laser light source 101 emits divergent light, which is collimated into a parallel beam by the first lens 102. This parallel beam has a small divergence angle. It then passes through a pinhole diaphragm 103, where it emits a divergent light beam with a small divergence angle. This pinhole can be considered the location of a point light source. The aperture of the pinhole diaphragm 103 is offset from the optical axis of the first lens 102 and the laser light source 101 by a certain distance, so the light emitted from the pinhole can be considered an off-axis light source. The motor 113 is connected to the pinhole diaphragm 103 and can drive the pinhole diaphragm 103 to a certain distance off-axis. The off-axis light beam emitted from the pinhole remains an off-axis light beam after passing through the programmable liquid crystal device 104. This off-axis light beam is then collimated into a parallel beam by the collimating lens 105 and incident on the reflector 106, where it is reflected. This parallel light beam is incident on the right side of the optical axis and at an angle to the optical axis, and then incident on the objective lens 107, which converges the tilted parallel light beam.

[0042] In one case, when the upper surface of the translucent wafer 108 is at the focal point of the objective lens, the objective lens 107 converges the light beam and focuses it on a point on the upper surface of the translucent wafer 108. The light beam reflected from the upper surface is on the other side of the optical axis of the objective lens 107, and then collimated by the objective lens 107 again. The collimated light beam is reflected by the reflector 106, and then converged by the second lens 109, with the focal point forming a point on the first detector 110. Since the translucent wafer 108 is translucent, another part of the energy of the light beam converged by the objective lens 107 passes through the upper surface of the semi-transparent wafer 108 and is incident on the lower surface of the translucent wafer 108. Part of the energy is reflected by the lower surface of the translucent wafer 108. Since the light beam converged by the objective lens 107 converges on the upper surface of the translucent wafer 108, the light beam is a divergent light beam when it reaches the lower surface of the wafer. In addition, since the incident light beam is on one side of the optical axis of the objective lens 107 and the light beam is incident at an angle, there is a lateral offset between the convergence point of the incident light beam on the upper surface of the translucent wafer 108 and the center point of the convergent light spot on the lower surface of the translucent wafer 108. The light beam reflected by the lower surface of the translucent wafer 108 then enters the objective lens 107. Since the lower surface of the translucent wafer 108 is not at the focal point of the objective lens 107, the light beam is not a parallel light beam emitted after entering the objective lens 107. The light beam is then reflected by the reflector 106 and converged by the third lens 111. The third lens 111 and the second lens 109 have the same focal length. The light beam converged by the third lens 111 is received by the second detector 112 to form a light spot. The second detector 112 and the first detector 110 have the same lateral position. The objective lens is adjusted by observing the light spot or light point to achieve the focusing of the objective lens on the translucent wafer.

[0043] Another case, such as Figure 2As shown, when the lower surface of the semi-transparent wafer 108 is on the focal point of the objective lens 107. At this time, the convergent light beam of the objective lens 107 is focused on the upper surface of the semi-transparent wafer 108 as a light spot. The light beam reflected by the upper surface of the semi-transparent wafer 108 is on the other side of the optical axis of the objective lens 107, and then collimated by the objective lens 107 again. The collimated light beam is reflected by the mirror 106, and then converges by the second lens 109, and a light spot is formed on the first detector 110. Since the semi-transparent wafer 108 is semi-transparent, another part of the convergent light beam of the objective lens 107 transmits through the upper surface of the semi-transparent wafer 108, and is incident on the lower surface of the semi-transparent wafer 108. Since the lower surface of the semi-transparent wafer 108 is on the focal point of the objective lens 107, a convergent point is formed on the lower surface of the semi-transparent wafer 108. A part of the light beam is reflected by the lower surface of the semi-transparent wafer 108. In addition, since the incident light beam is on the side of the optical axis of the objective lens 107 and the light beam is obliquely incident, the convergent light spot on the upper surface of the semi-transparent wafer 108 and the convergent point on the lower surface of the semi-transparent wafer 108 are laterally offset. The light beam reflected by the lower surface of the semi-transparent wafer 108 then enters the objective lens 107. Since the lower surface of the semi-transparent wafer 108 is on the focal point of the objective lens 107, the light beam entering the objective lens 107 is emitted as a parallel light beam. The light beam is then reflected by the mirror 106, and then converges by the third lens 111. The third lens 111 and the second lens 109 have the same focal length. The light beam converging by the third lens 111 is received by the second detector 112. The second detector 112 and the first detector 110 have the same lateral position. The second detector 112 receives a light spot. The objective lens is adjusted by observing the light spot or the light spot, so as to realize the focusing of the objective lens on the semi-transparent wafer.

[0044] Comparative Example 1

[0045] An autofocus system as shown in Figure 4 is provided as a comparative example. In the comparative example, a laser light source 201 emits a divergent light beam, and then the light beam passes through a light barrier 202. The light barrier 202 is arranged on the side of the optical axis, and blocks half of the light beam. Only the light beam on the other side of the optical axis can pass through the light barrier 202, and then the light beam passes through a collimating lens 203 to become a parallel light beam. The parallel light beam then continues to propagate along the other side of the optical axis, and then enters an objective lens 205 after being reflected by a mirror 204. The light beam is then convergent by the objective lens 205. The upper surface of a wafer 206 is arranged on the focal point of the objective lens 205, and thus a convergent point is formed on the upper surface of the wafer 206. The light beam reflected by the upper surface of the wafer 206 propagates along the other side of the optical axis, and then is collimated by the objective lens 205. The collimated light beam is then reflected by the mirror 204 again, and then converges by the collimating lens 204 again. The light beam converging by the collimating lens 204 is then reflected by a mirror 207, and converges on a detector 208.

[0046] The above is the case where the wafer 206 is a pure reflective wafer, and the wafer 206 is exactly on the focal plane of the objective lens. At this time, the light spot on the detector 208 is exactly a point, as shown in Figure 5Fig. 3 shows the light spot on the wafer when the focal plane of the objective is above the wafer 208. The light spot on the wafer is a circle, and the light spot on the detector 208 is a semi-circle on the right side of the detector 208. Figure 5 Fig. 4 shows the light spot on the wafer when the focal plane of the objective is below the wafer 208. The light spot on the wafer is a circle, and the light spot on the detector 208 is a semi-circle on the left side of the detector 208. Figure 5 Fig. 5 shows the light spot on the wafer when the focal plane of the objective is below the wafer 208. The light spot on the wafer is a circle, and the light spot on the detector 208 is a semi-circle on the left side of the detector 208.

[0047] When the wafer 208 is a translucent wafer, the light spot is very complex. As shown in Fig. 6, when the upper surface of the wafer 208 is below the focal plane of the objective, the light spot on the wafer is a circle, and the light spot on the detector 208 is a semi-circle on the right side of the detector 208. Figure 6 As shown in Fig. 7, when the upper surface of the wafer 208 is below the focal plane of the objective, the light spot on the wafer is a circle, and the light spot on the detector 208 is a semi-circle on the right side of the detector 208. Figure 6 As shown in Fig. 8, when the upper surface of the wafer 208 is below the focal plane of the objective, the light spot on the wafer is a circle, and the light spot on the detector 208 is a semi-circle on the right side of the detector 208. Figure 6 As shown in Fig. 9, when the upper surface of the wafer 208 is below the focal plane of the objective, the light spot on the wafer is a circle, and the light spot on the detector 208 is a semi-circle on the right side of the detector 208. Figure 6 As shown in Fig. 10, when the upper surface of the wafer 208 is below the focal plane of the objective, the light spot on the wafer is a circle, and the light spot on the detector 208 is a semi-circle on the right side of the detector 208.

[0048] Embodiment 3

[0049] To solve the technical problem of high cost and limited use caused by the introduction of a spectrometer in the thickness measurement of a translucent wafer, the embodiment provides a thickness measurement system suitable for a translucent wafer, as shown in Fig. 11. Figure 7The system is shown in FIG. 1, which includes a semi-transparent wafer 308, a dispersive objective 307, a mirror 306, a white light source 301, an achromatic lens 302, a pinhole diaphragm 303, a programmable liquid crystal device 304, a collimating lens 305, a converging lens 309, a slit 310, a lens 311, and a detector 312. The angle of the light beam between the pinhole diaphragm 303 and the programmable liquid crystal device 304 is within 5°. The slit 310 has a width of 15 um. The achromatic lens 302 has a focal length of 25 mm, and the collimating lens 305, the converging lens 309, and the lens 311 each have a focal length of 50 mm. The lens 311 images the slit 310 to the detector 312 with a magnification of 1:1.

[0050] Specifically, the white light source 301 is a white light LED, which emits a divergent light beam. The divergent light beam is collimated by the achromatic lens 302 into a parallel light beam with a small divergence angle. The parallel light beam then passes through the pinhole diaphragm 303. The light beam passing through the pinhole diaphragm 303 is emitted from a small hole with a small divergence angle. The small hole can be regarded as a point light source. The small hole of the pinhole diaphragm 303 is offset from the optical axis of the achromatic lens 302 and the white light source 301 by a certain distance, and thus the light emitted from the small hole can be regarded as an off-axis light source. The light beam emitted from the small hole then passes through the programmable liquid crystal device 304, which is shown in FIG. 2. Figure 2 The programmable liquid crystal device 304 can display a circular light-transmissive region 22 and a light-non-transmissive region 21. The light beam passing through the programmable liquid crystal device 304 is an off-axis light beam, where the axis is the optical axis defined by the white light source 301 and the achromatic lens 302. The off-axis light beam is collimated into a parallel light beam by the collimating lens 305, reflected by the mirror 306, and incident on the dispersive objective 307 at a certain angle with respect to the optical axis on the right side of the optical axis. The dispersive objective 307 separates the incident white light and focuses different color lights at different depths, as shown in FIG. 3. Figure 7 Because the incident light beam is inclined, the long-wavelength and the short-wavelength have a displacement in the lateral direction.

[0051] Specific short wavelength light is reflected by the upper surface of the semi-transparent wafer 308, collimated by the dispersion objective 307 again, reflected by the mirror 306, and then focused by the converging lens 309 to the slit. The light beam is focused to a point at the slit position and passes through the slit without loss. The light reflected by other surfaces is blocked by the slit. Then the light beam is focused on the detector 312 by the lens 311. The long wavelength light is reflected by the lower surface, collimated by the dispersion objective 307 again, because there is a lateral displacement amount in the semi-transparent material compared with the short wavelength light, reflected by the mirror 306, and then focused by the converging lens 309 to the slit. The light beam is focused to a point at the slit position and there is a lateral displacement amount compared with the short wavelength light. The light beam then passes through the slit without loss. The light reflected by other surfaces is blocked by the slit. Then the light beam is focused on the detector 312 by the lens 311 and there is a lateral displacement amount compared with the short wavelength light on the detector 312.

[0052] Thus, there is a mapping relationship between the lateral displacement amount on the detector and the thickness of the semi-transparent wafer. The thickness measurement system is calibrated according to the mapping relationship and the known thickness of the semi-transparent wafer. Then the unknown thickness of the semi-transparent wafer is measured according to the measured lateral displacement amount and the mapping relationship by using the calibrated thickness measurement system. The system can not only measure the thickness of two surfaces, but also measure the thickness of multiple surfaces.

[0053] Specifically, it is assumed that the wavelength range of the white light source contains λ a and λ b , the dispersion objective converges λ a and λ b at different depth positions, λ a is the wavelength of the light reflected by the upper surface of the semi-transparent wafer, λ b is the wavelength of the light reflected by the lower surface of the semi-transparent wafer, d is the thickness of the semi-transparent wafer, and the lateral displacement amount l between the converging points of λ a and λ b on the detector follows the following mapping relationship:

[0054]

[0055] where f c is the focal length of the dispersion objective, f f is the focal length of the converging lens, and θ is the inclination angle of the optical axis determined by the pinhole aperture and the light transmission part of the programmable liquid crystal device and the optical axis determined by the white light source and the achromatic lens. Then the thickness d information is obtained from l.

[0056]

[0057] The thickness measurement system provided by the embodiment does not need an additional dispersion spectrometer compared with the existing structure using a dispersion objective to make depth measurement, is more cost-effective, and can measure the thickness of multiple layers at the same time without moving the objective.

[0058] The above detailed description of the specific embodiments has described the technical solutions and beneficial effects of the present application. It should be understood that the above description is only the most preferred embodiment of the present application and is not intended to limit the present application. Any modifications, supplements, and equivalent replacements made within the principle range of the present application should be included in the protection range of the present application.

Claims

1. An auto-focusing system suitable for a translucent wafer, characterized by, The device comprises a semi-transparent wafer, an objective lens to be focused, a mirror, a laser light source, a first lens, a pinhole diaphragm, a programmable liquid crystal device, a collimating lens, a second lens, a third lens, a first detector, a second detector, and a motor; The laser light source is collimated by the first lens, and then passes through the pinhole diaphragm which is controlled by the motor to adjust the off-axis distance, so that the pinhole diaphragm emits an off-axis light beam as an off-axis light source. The off-axis light beam passes through the programmable liquid crystal device, is collimated by the collimating lens, and is incident on the mirror. The mirror reflects the incident light to the objective lens and focuses it on the semi-transparent wafer; When focusing on the upper surface of the semi-transparent wafer, the reflected light passing through the upper surface of the semi-transparent wafer is collimated by the objective lens, and then reflected by the mirror to the second lens. The light is focused by the second lens and received by the first detector to form a light spot. At the same time, the reflected light passing through the lower surface of the semi-transparent wafer is collimated by the objective lens, and then reflected by the mirror to the third lens. The light is focused by the third lens and received by the second detector to form a light spot. When focusing on the lower surface of the semi-transparent wafer, the reflected light passing through the lower surface of the semi-transparent wafer is collimated by the objective lens, and then reflected by the mirror to the third lens. The light is focused by the third lens and received by the second detector to form a light spot. At the same time, the reflected light passing through the upper surface of the semi-transparent wafer is collimated by the objective lens, and then reflected by the mirror to the second lens. The light is focused by the second lens and received by the first detector to form a light spot. The objective lens is adjusted by observing the light spot or the light spot to realize the focusing of the objective lens on the semi-transparent wafer.

2. The auto-focusing system suitable for a translucent wafer according to claim 1, wherein, The diameter of the pinhole diaphragm is 5-10 um, and the off-axis distance of the pinhole diaphragm driven by the motor is 1-3 mm.

3. The auto-focusing system suitable for translucent wafers according to claim 1, wherein, The focal length of the first lens, the second lens, and the third lens is 50-75 mm, and the second lens and the third lens have the same focal length.

4. The auto-focusing system suitable for translucent wafers according to claim 1, wherein, The programmable liquid crystal device can display a circular light-transmissible area and a non-light-transmissible area. The off-axis light beam is outputted after passing through the programmable liquid crystal device. The laser light source is a laser LD with a wavelength of 660 nm or 850 nm.

5. A thickness measurement system for semi-transparent wafers, characterized in that: The device comprises a semi-transparent wafer, a dispersive objective lens, a mirror, a white light source, an achromatic lens, a pinhole diaphragm, a programmable liquid crystal device, a collimating lens, a converging lens, a slit, a lens, and a detector; The white light source is collimated by the achromatic lens, and then passes through the pinhole diaphragm as an off-axis light source to emit an off-axis light beam. The off-axis light beam passes through the programmable liquid crystal device, is collimated by the collimating lens, and is incident on the mirror. The mirror reflects the incident light to the dispersive objective lens and focuses the dispersed light beams of different colors on different depth focal planes of the semi-transparent wafer. Specifically, the long-wave light is focused on the lower surface of the semi-transparent wafer, and the short-wave light is focused on the upper surface of the semi-transparent wafer. There is a displacement between the focal point of the long-wave light on the lower surface and the focal point of the short-wave light on the upper surface in the lateral direction. The short-wavelength light reflected by the upper surface of the semi-transparent wafer is collimated by the dispersive objective lens again, is reflected by the mirror, passes through the converging lens, and reaches the slit. The light is focused into a point at the position of the slit and passes through the slit without loss. The light reflected by other surfaces is blocked by the slit. Subsequently, the light passing through the slit is focused on the detector after passing through the lens. The long wavelength light is reflected by the lower surface of the semi-transparent wafer, collimated by the dispersion objective again, and then reflected by the mirror and the converging lens to the slit. The long wavelength light is focused to a point at the slit, and there is a lateral displacement between the long wavelength light and the short wavelength light. The long wavelength light passes through the slit without loss, and the light reflected by other surfaces is blocked by the slit. Then the light passing through the slit is converged on the detector by the lens, and there is a lateral displacement between the long wavelength light and the short wavelength light on the detector. According to the mapping relationship between the lateral displacement on the detector and the thickness of the semi-transparent wafer, and the known thickness of the semi-transparent wafer, the thickness measurement system is calibrated. Then the unknown thickness of the semi-transparent wafer is measured according to the measured lateral displacement and the mapping relationship.

6. The thickness measurement system suitable for a translucent wafer according to claim 5, wherein The angle of the light beam between the pinhole aperture and the programmable liquid crystal device is in the range of 0-5°.

7. The thickness measurement system suitable for a translucent wafer according to claim 5, wherein The slit width is 15-25 um.

8. The thickness measurement system suitable for a translucent wafer according to claim 5, wherein, The focal length of the achromatic lens is 25-50 mm, and the focal lengths of the collimating lens, the converging lens and the lens are all 50-75 mm. The lens images the slit to the detector with a size ratio of 1:

1.

9. The thickness measurement system suitable for a translucent wafer according to claim 5, wherein, The mapping relationship between the lateral displacement on the detector and the thickness of the semi-transparent wafer is: Assume that the wavelength range of the white light source contains λ a and λ b , the dispersive objective converges λ a and λ b at different depth positions, λ a is the wavelength of the reflected light on the upper surface of the translucent wafer, λ b is the wavelength of the reflected light on the lower surface of the translucent wafer, d is the thickness of the translucent wafer, and the lateral displacement l between the convergence points of λ a and λ b on the detector follows the mapping relationship: where f c is the focal length of the dispersing objective, f f is the focal length of the converging lens, and θ is the angle of inclination of the optical axis defined by the center of the pinhole aperture and the light-transmitting portion of the programmable liquid crystal device with the optical axis defined by the white light source and the achromatic lens, then the thickness d information is obtained from l; 10. The thickness measurement system suitable for a translucent wafer according to claim 5, wherein, The system can measure the thickness of multiple surfaces of the semi-transparent wafer simultaneously.

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