Multi-channel synchronous scanning optical detection system

Abstract

The multi-channel synchronous scanning optical detection system comprises a DIC light path, a PL light path, a DF light path, a bright field light source and a dark field light source. The DIC light path sequentially comprises a first camera, a polarizing beam splitter, a total reflective mirror, a DIC lens unit, a first dichroscope and a second dichroscope; the PL light path sequentially comprises a second dichroscope, a first dichroscope and a second camera; the DF light path sequentially comprises a second dichroscope and a third camera; the bright field light source irradiates the sample through part of the DIC light path; the dark-field light source directly irradiates the sample; in the working state, the sample reflects the light of the bright field light source, the reflected light returns along the DIC light path to form a first defect image, the sample receives the light of the dark field light source and excites fluorescent light, the fluorescent light forms a second defect image along the PL light path, and the light, reflected by the sample, of the dark field light source forms a third defect image along the DF light path. The multi-channel synchronous scanning optical detection system can simultaneously scan sample defects by multiple optical paths.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor detection, and particularly relates to a multi-channel synchronous scanning optical detection system. Background Art

[0002] During the wafer transfer process, defects are likely to appear on the wafer surface. Wafer defects are mainly divided into crystal defects and surface defects. Crystal defects include dislocations (such as edge dislocations, screw dislocations), microtubes, etc. These defects will change the electronic structure of the material, increase carrier scattering, resulting in an increase in the on-resistance of the device, a decrease in the breakdown voltage, and a decline in reliability. Surface defects include scratches, particle contamination, etc., which will affect the quality of epitaxial growth, increase the defect density of the epitaxial layer, and thus affect device performance. Therefore, how to effectively and comprehensively detect the defects on the wafer surface is particularly important.

[0003] Chinese Patent CN114778552A introduces a differential interference contrast imaging system with non-directional dependence achieved by secondary beam splitting. It can enable defects with relatively high parallelism to also have the characterization ability through multiple DIC polarization imaging, without causing missed detection. However, multiple polarizations in this system will lead to an increase in cost and the types of DIC defect detections are limited, and some defects (stacking faults, slip lines) cannot be detected.

[0004] When the prior art performs defect detection, in order to achieve comprehensive detection of defects, some optical systems will introduce other optical detection devices for supplementary detection, resulting in the problem of misalignment of defect images formed by multiple detection devices. For example, the wafer on the detection stage is scanned under multiple detection optical paths. After each optical path scanning is completed, due to the change of the field position, the positions of multiple detection images cannot completely coincide, and there will be deviations in the corresponding image positions. Due to the deviations of the images in each optical path, additional correction processing is required after the images are exported. In addition, some defects may be detected by two optical paths at the same time, and the same defect will have image misalignment in different optical paths. The misalignment problem will lead to inaccurate defect classification, resulting in over-detection or false killing. Eventually, due to multiple station-changing scans, the scanning efficiency of wafer defect detection is not good.

[0005] The information disclosed in this background art section is only intended to increase the understanding of the overall background of the present invention, and should not be regarded as an admission or any form of suggestion that this information constitutes the prior art already known to those of ordinary skill in the art. Summary of the Invention

[0006] The purpose of the present invention is to provide a multi-channel synchronous scanning optical detection system, which can simultaneously scan sample defects in multiple optical paths with different wavelengths and ensure that the positions of the same defect in different defect images are consistent.

[0007] To achieve the above object, the technical solution provided by a specific embodiment of the present invention is as follows: A multi-channel synchronous scanning optical detection system, which includes: a DIC optical path, a PL optical path, a DF optical path, a bright-field light source, and a dark-field light source. The DIC optical path sequentially includes a first camera, a polarization beam splitter, a total reflection mirror, a DIC lens unit, a first dichroic mirror, and a second dichroic mirror; the PL optical path sequentially includes the second dichroic mirror, the first dichroic mirror, and a second camera; the DF optical path sequentially includes the second dichroic mirror and a third camera; the bright-field light source is used to irradiate the sample through part of the DIC optical path; the dark-field light source is used to directly irradiate the sample; wherein, in the working state, the sample reflects the light of the bright-field light source, and the reflected light returns along the DIC optical path to form a first defect image, the sample receives the light of the dark-field light source and excites fluorescence, and the fluorescence forms a second defect image along the PL optical path, and the light of the dark-field light source reflected by the sample forms a third defect image along the DF optical path.

[0008] In one or more embodiments of the present invention, the DIC optical path, the PL optical path, and the DF optical path share an objective lens; the sample is placed below the objective lens.

[0009] In one or more embodiments of the present invention, the dark-field light source is arranged on one side of the objective lens, and the light of the dark-field light source is reflected by the sample to the objective lens.

[0010] In one or more embodiments of the present invention, the first dichroic mirror is coated with a first reflection film and a first transmission film to reflect light with a wavelength above 600 nm and transmit light with a wavelength below 600 nm.

[0011] In one or more embodiments of the present invention, the first reflection film guides the fluorescence of the sample to the second camera, and the second camera is used to generate a second defect image, and the first transmission film guides the light of the bright-field light source reflected by the sample to the total reflection mirror.

[0012] In one or more embodiments of the present invention, the second dichroic mirror is coated with a second reflection film and a second transmission film to reflect light with a wavelength above 350 nm and transmit light between 300 nm and 350 nm.

[0013] In one or more embodiments of the present invention, the second reflection film guides the light of the bright-field light source reflected by the sample to the total reflection mirror, and the second transmission film guides the light of the dark-field light source reflected by the sample to the third camera.

[0014] In one or more embodiments of the present invention, a first filter is arranged between the bright-field light source and the polarization beam splitter to filter light outside the 400 - 600 nm wavelength band.

[0015] In one or more embodiments of the present invention, a second filter is disposed between the second camera and the first dichroic mirror to filter light with a wavelength below 600 nm.

[0016] In one or more embodiments of the present invention, a third filter is disposed between the third camera and the second dichroic mirror to filter light outside the wavelength range of 300 nm - 350 nm.

[0017] Compared with the prior art, in the multi-channel synchronous scanning optical detection system of the present invention, by disposing the first dichroic mirror and the second dichroic mirror between the three optical paths, light in the specified wavelength band of each optical path is reflected to the corresponding camera, so as to achieve the purpose of simultaneously scanning the sample defects in multiple optical paths, greatly improving the detection efficiency. Since the three optical paths share the first dichroic mirror and the second dichroic mirror and only one objective lens is provided, it is possible to ensure that the positions of the defect images of the same defect in each optical path are aligned without deviation, so as to intuitively reflect the defect conditions of the samples at the same position in different optical paths. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0019] Figure 1 It is a schematic diagram of a multi-channel synchronous scanning optical detection system in an embodiment of the present invention; Figure 2 It is a first schematic diagram of a multi-channel synchronous scanning optical detection system for detecting a sample in an embodiment of the present invention; Figure 3 It is a second schematic diagram of a multi-channel synchronous scanning optical detection system for detecting a sample in an embodiment of the present invention; Figure 4 It is a third schematic diagram of a multi-channel synchronous scanning optical detection system for detecting a sample in an embodiment of the present invention.

[0020] MAIN REFERENCE NUMERAL DESCRIPTION: 1 - DIC optical path, 11 - first camera, 12 - total reflection mirror, 13 - DIC lens unit, 14 - polarization beam splitter, 2 - PL optical path, 21 - second camera, 22 - first dichroic mirror, 23 - second filter, 3 - DF optical path, 31 - third camera, 32 - second dichroic mirror, 33 - third filter, 4 - bright field light source, 41 - first filter, 5 - dark field light source, 6 - objective lens, A - sample. Detailed implementation manners

[0021] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0022] The principles of several optical systems involved in the present invention are first explained as follows: DIC (Differential Interference Contrast) optical system: The light emitted by the bright-field light source becomes linearly polarized light through the polarization effect of the polarization beam splitter, enters the DIC lens unit with birefringence characteristics, is decomposed into two orthogonally vibrating polarized lights and irradiates the sample surface. Defects on the sample surface will cause an optical path difference between the two beams of light. The two beams of light with an optical path difference are reflected by the sample and then converge through the polarization beam splitter. Through the polarization analysis effect of the polarization beam splitter, the vibration directions are made consistent to produce an interference phenomenon, and thus are received by the camera.

[0023] PL (Photoluminescence) optical system: The substance absorbs the energy of the external light source and emits photons by itself after being excited. The dark-field light source provides light in the short wavelength band, and then the substance emits light in the long wavelength band. Photoluminescence can be divided into fluorescence and phosphorescence according to the delay time. Among them, fluorescence is that the substance emits photons immediately after being excited, while phosphorescence can continuously emit light for a long time, so as to achieve the detection purpose.

[0024] DF (Dark Field) optical system: The dark-field light source irradiates the sample surface at a certain angle, so that most of the light in the defect-free area is reflected out of the field of view, forming a dark background. When the light irradiates the defect part of the sample, such as particulate contaminants and cracks on the surface, due to the scattering effect of the defect on the light, part of the light will change the propagation direction and appear as a bright area against the dark background.

[0025] As Figure 1 shown, a multi-channel synchronous scanning optical detection system in an embodiment of the present invention includes a DIC optical path 1, a PL optical path 2, a DF optical path 3, a bright-field light source 4, and a dark-field light source 5. The DIC optical path 1 sequentially includes a first camera 11, a polarization beam splitter 14, a total reflection mirror 12, a DIC lens unit 13, a first dichroic mirror 22, and a second dichroic mirror 32. The PL optical path 2 sequentially includes the second dichroic mirror 32, the first dichroic mirror 22, and a second camera 21. The DF optical path 3 sequentially includes the second dichroic mirror 32 and a third camera 31. The bright-field light source 4 is used to irradiate the sample A through part of the DIC optical path 1 (that is, without passing through the first camera 11), and the dark-field light source 5 is used to directly irradiate the sample A.

[0026] During the detection period, sample A is placed downstream of the second dichroic mirror 32, and the bright-field light source 4 and the dark-field light source 5 irradiate sample A simultaneously. In the working state, sample A reflects the light of the bright-field light source 4, and this light returns along the DIC optical path 1 to form a first defect image at the first camera 11. Sample A receives the light of the dark-field light source 5 and excites fluorescence. This fluorescence forms a second defect image at the second camera 21 along the PL optical path 2, and the light of the dark-field light source 5 reflected by sample A forms a third defect image at the third camera 31 along the DF optical path 3.

[0027] The working principle of this multi-channel synchronous scanning optical detection system is as follows: Place sample A downstream of the second dichroic mirror 32 and turn on the bright-field light source 4 and the dark-field light source 5 simultaneously. The light emitted by the bright-field light source 4 passes through the polarization beam splitter 14, reaches the total reflection mirror 12, then enters the DIC lens unit 13 and successively passes through the first dichroic mirror 22 and the second dichroic mirror 32 to reach sample A. Then this light is reflected by sample A and returns along the DIC optical path 1 to the first camera 11 to form a first defect image. The light emitted by the dark-field light source 5 causes sample A to excite fluorescence. The fluorescence passes through the second dichroic mirror 32 and is then directed to the first dichroic mirror 22, and then the first dichroic mirror 22 directs this fluorescence to the second camera 21 to form a second defect image. At the same time, the light emitted by the dark-field light source 5 is reflected by sample A to the second dichroic mirror 32, and the second dichroic mirror 32 directs this light to the third camera 31 to form a third defect image. Analyzing the first defect image, the second defect image, and the third defect image can complete the detection of sample A.

[0028] It is known in the art that a dichroic mirror is composed of multiple thin films, and the thickness and refractive index of each thin film are precisely designed. When light is incident, the light waves reflected and transmitted by each thin film will interfere due to the phase difference. Light of a specific wavelength is enhanced in the reflection or transmission direction, while light of other wavelengths is suppressed.

[0029] In the above embodiment, this multi-channel synchronous scanning optical detection system enables light of a specific wavelength band in the corresponding optical path to enter the corresponding camera by setting the first dichroic mirror 22 and the second dichroic mirror 32, effectively reflecting the defect conditions of the same position of sample A in different optical paths. Sharing the first dichroic mirror 22 and the second dichroic mirror 32 by the three optical paths can ensure that the positions of the same defect on the defect images of each optical path are consistent without deviation. In addition, the three optical paths can work simultaneously to achieve multi-optical-path simultaneous scanning of the defects of sample A, greatly improving the detection efficiency.

[0030] In one embodiment, the multi-channel synchronous scanning optical detection system further includes an objective lens 6. The DIC optical path 1, the PL optical path 2, and the DF optical path 3 share the same objective lens 6. The sample A is disposed below the objective lens 6, so that the field of view of each optical path is the same, and further, the positions of the same defect on different defect images are consistent, thereby improving the accuracy of defect detection. Preferably, the dark-field light source 5 is disposed on one side of the objective lens 6, and the light of the dark-field light source 5 is reflected by the sample A to the objective lens 6.

[0031] In order to enable the first dichroic mirror 22 and / or the second dichroic mirror 32 to more effectively transmit or reflect light of a specific wavelength, a reflection film and a transmission film can be deposited on the first dichroic mirror 22 and / or the second dichroic mirror 32, so that the three optical paths will not interfere with each other.

[0032] In one embodiment, a first filter 41 is disposed between the bright-field light source 4 and the polarization beam splitter 14 to filter out light outside the 400 - 600 nm band, so that only light in the 400 - 600 nm band can irradiate the sample A.

[0033] The propagation path of light in the DIC optical path 1 is as follows: The light emitted by the bright-field light source 4 is filtered by the first filter 41 and reaches the polarization beam splitter 14, and then is reflected by the total reflection mirror 12 into the DIC lens unit 13, and sequentially passes through the first dichroic mirror 22 and the second dichroic mirror 32 and irradiates the surface of the sample A. Two beams of light with an optical path difference are reflected by the sample A and return along the original path, and then sequentially pass through the second dichroic mirror 32, the first dichroic mirror 22, and the DIC lens unit 13, and then converge through the polarization beam splitter 14. The polarization analyzing effect of the polarization beam splitter 14 makes the vibration directions consistent to generate an interference phenomenon, and finally is received by the first camera 11 to form a first defect image.

[0034] In one embodiment, the propagation path of light in the PL optical path 2 is as follows: The dark-field light source 5 irradiates the surface of the sample A, so that the sample A is excited to generate excitation light (fluorescence). The excitation light is reflected by the second dichroic mirror 32 to the first dichroic mirror 22. Among them, the excitation light is basically all reflected at the first dichroic mirror 22 and will not pass through the first dichroic mirror 22. Preferably, the first dichroic mirror 22 is coated with a first reflection film and a first transmission film to reflect light with a wavelength above 600 nm and transmit light with a wavelength below 600 nm. The first reflection film guides the fluorescence of the sample A to the second camera 21, and the first transmission film guides the light of the bright-field light source 4 reflected by the sample A to the total reflection mirror 12.

[0035] The principle of fluorescence emission of Sample A is as follows: Taking a wafer as an example, when the wafer is irradiated with a dark-field light source 5 whose energy is greater than the bandgap of the wafer, after the photons in the light are absorbed by the wafer, electrons jump from the valence band to the conduction band, forming electron-hole pairs. After the electrons are captured by the defect energy levels, they undergo transitions and emit fluorescence of a specific wavelength.

[0036] Furthermore, a second filter 23 is provided between the second camera 21 and the first dichroic mirror 22 to filter the light with a wavelength below 600 nm.

[0037] Therefore, when the excitation light is reflected to the second filter 23, except for the excitation light, other lights will be blocked by the second filter 23 from passing through. The second camera 21 receives the excitation light and generates a second defect image. In addition, the second filter 23 can be replaced according to the excitation light wavelength of different defects to adapt to different detection requirements.

[0038] In an embodiment, the propagation path of light in the DF optical path is as follows: The dark-field light source 5 irradiates the surface of Sample A at a certain angle. Due to the scattering effect of the defects of Sample A on the light, part of the light will change its propagation direction and enter the third camera 31 through the second dichroic mirror 32.

[0039] Among them, the second dichroic mirror 32 is coated with a second reflective film and a second transmissive film to reflect the light with a wavelength above 350 nm and transmit the light between 300 nm and 350 nm. The second reflective film guides the light of the bright-field light source 4 reflected by Sample A to the total reflection mirror 12, and the second transmissive film guides the light of the dark-field light source 5 reflected by Sample A to the third camera 31.

[0040] Furthermore, a third filter 33 is provided between the third camera 31 and the second dichroic mirror 32 to filter the light outside the wavelength range of 300 nm - 350 nm.

[0041] Figures 2-4 Shows the display conditions of different defects of the wafer under different optical paths.

[0042] As Figure 2 shown, the second defect image in the PL optical path 2 shows a triangular defect. This type of defect shows various dark triangles extending along the diagonal direction when the emission wavelength of the sample is greater than 650 nm. Since the DIC optical path 1 uses the optical path difference of light to detect defects, the first defect image in the DIC optical path 1 can only determine that there is a depression here and cannot see the triangular defect. The third defect image in the DF optical path 3 can only see the bright spot and cannot see the triangular defect.

[0043] As Figure 3As shown, a particulate defect is shown in the third defect image of the DF optical path 3. Due to the rough surface of this defect, the DF optical path 3 receives more scattered light from the defect, so it appears as a bright spot. The first defect image of the DIC optical path 1 is pit-like, and the particulate defect cannot be seen due to the detection characteristics of the DIC optical path 1. The second defect image of the PL optical path 2 appears completely black, and the particulate defect cannot be seen because this defect does not produce energy level transitions and cannot emit fluorescence. Therefore, this defect cannot be detected by the PL optical path 2.

[0044] As Figure 4 shown, the second defect image of the PL optical path 2 shows a stacking fault defect. The first defect image of the DIC optical path 1 appears completely black, and the stacking fault defect cannot be seen. The third defect image of the DF optical path 3 also appears completely black, and the stacking fault defect cannot be seen. Only the PL optical path 2 can detect this defect. Therefore, there are no defect images in the DIC optical path 1 and the DF optical path 3.

[0045] As can be seen from the above, different defects will present different forms under different optical paths, and some defects can only be detected by some optical paths. Through this multi-channel synchronous scanning optical detection system, defects can be effectively detected.

[0046] In this multi-channel synchronous scanning optical detection system, since the three optical paths share the first dichroic mirror 22 and the second dichroic mirror 32 and the field of view of the same objective lens 6, the first defect image, the second defect image, and the third defect image obtained are all generated based on the same position. The characteristics of the same defect under different image optical paths can further realize the identification and classification of defects and avoid misdetection of defect classification. By synchronously comparing these three defect images, defects can be accurately identified and classified.

[0047] In summary, the multi-channel synchronous scanning optical detection system of the present invention arranges the first dichroic mirror 22 and the second dichroic mirror 32 between the three optical paths, so that the light of a specific wavelength band of each optical path reaches the corresponding camera, thereby achieving the purpose of simultaneously scanning the defects of the sample A by multiple optical paths and greatly improving the detection efficiency. Since the three optical paths share the first dichroic mirror 22 and the second dichroic mirror 32 and only one objective lens 6 is provided, it can be ensured that the positions of the defect images of the same defect in each optical path are aligned without deviation, so as to directly reflect the defect conditions of the sample A at the same position under different optical paths.

[0048] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be embraced within the present invention. Any reference signs in the claims should not be construed as limiting the claims involved.

[0049] In addition, it should be understood that although this specification is described in terms of embodiments, not every embodiment only contains an independent technical solution. This narrative manner of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A multi-channel synchronous scanning optical detection system, characterized in that: include: The DIC optical path includes, in sequence, a first camera, a polarization beam splitter, a total reflection mirror, a DIC lens unit, a first dichroic mirror, and a second dichroic mirror; A PL optical path, comprising in sequence the second dichroic mirror, the first dichroic mirror and a second camera; a DF optical path, comprising the second dichroic mirror and the third camera in sequence; a bright field light source, used to illuminate the sample through a portion of the DIC light path; as well as A dark field light source, used to directly illuminate the sample; In which, in the working state, the sample reflects the light of the bright field light source, and the reflected light returns along the DIC optical path to form a first defect image, the sample receives the light of the dark field light source and excites fluorescence, and the fluorescence forms a second defect image along the PL optical path, and the light of the dark field light source reflected by the sample forms a third defect image along the DF optical path.

2. The multi-channel synchronous scanning optical detection system according to claim 1, characterized in that: The device also includes an objective lens; the sample is placed under the objective lens.

3. The multi-channel synchronous scanning optical detection system according to claim 2, characterized in that: The dark field light source is arranged at one side of the objective lens, and the light of the dark field light source is reflected by the sample to the objective lens.

4. The multi-channel synchronous scanning optical detection system according to claim 1, characterized in that: The first dichroic mirror is coated with a first reflective film and a first transmissive film to reflect light above the 600nm band and transmit light below the 600nm band.

5. The multi-channel synchronous scanning optical detection system according to claim 4, characterized in that: The first reflective film guides the fluorescence of the sample to the second camera, and the second camera is used to generate a second defect image. The first transmissive film guides the light of the bright field light source reflected by the sample to the total reflection mirror.

6. The multi-channel synchronous scanning optical detection system according to claim 1, characterized in that: The second dichroic mirror is coated with a second reflective film and a second transmissive film to reflect light above the 350nm wavelength band and transmit light between the 300nm-350nm wavelength band.

7. The multi-channel synchronous scanning optical detection system according to claim 6, characterized in that: The second reflective film guides the light of the bright field light source reflected by the sample to the total reflection mirror, and the second transmissive film guides the light of the dark field light source reflected by the sample to the third camera.

8. The multi-channel synchronous scanning optical detection system according to claim 7, characterized in that: A first filter is arranged between the bright field light source and the polarization beam splitter to filter light outside the 400-600nm band.

9. The multi-channel synchronous scanning optical detection system according to claim 1, characterized in that: A second filter is disposed between the second camera and the first dichroic mirror to filter light below the 600nm band.

10. The multi-channel synchronous scanning optical detection system according to claim 1, characterized in that: A third filter is arranged between the third camera and the second dichroic mirror to filter light outside the 300nm-350nm band.

Images