An interference fringe generating element, generating apparatus, and defect detection method

Abstract

The application discloses an interference fringe generating element, a generating device and a defect detection method in the field of structured light, the generating element comprising an incident surface, the incident surface being vertically provided with a first reflecting surface and an exit surface at both ends; a second reflecting surface, one end of the second reflecting surface being connected to the first reflecting surface at an obtuse angle, and the other end being connected to the exit surface; wherein a beam splitting surface is obliquely arranged between the connection of the incident surface and the exit surface and the connection of the first reflecting surface and the second reflecting surface; the generating element designed in the application replaces the traditional structured light projection device, which utilizes the high coherence and high stability of the interference fringe, avoids the dependence of the traditional projection system on the grating and the projection device, and the pitch and direction of the fringe can be adjusted by changing the included angle of the first reflecting surface and the second reflecting surface, and the flexibility is stronger; meanwhile, the interference fringe is generated by a single element, the core elements are less, the stability is high, the maintenance is easy, and the price is lower.

Description

Technical Field

[0001] This application relates to the field of structured light technology, specifically to an interference fringe generating element, a generating device, and a defect detection method. Background Technology

[0002] Structured light is an optical technology widely used in 3D imaging and measurement. It extracts the 3D shape information of an object by projecting specific light patterns (such as stripes, dot matrix, or grid) onto the surface of the object and using a camera to capture the deformation of the pattern. Compared with traditional contact measurement methods, structured light technology is widely used in industrial inspection, robot vision, medical imaging, and virtual reality due to its non-contact, high precision, and high speed characteristics.

[0003] In the semiconductor manufacturing process, the detection of wafer defects is crucial. A fast and reliable detection method can improve product yield and production efficiency. Common wafer inspection methods include: using optical microscopes and automated optical inspection systems to examine wafer surface defects; employing scanning electron microscopes for high-resolution imaging to detect minute defects; using surface profilometers to measure height variations on the wafer surface to determine surface quality and defect conditions; and using 3D structured light to rapidly scan the wafer surface to detect depressions, bumps, and other morphological changes.

[0004] However, among the many methods for wafer inspection, 3D structured light is not a high priority, mainly because the small size of wafers requires high precision in the structured light projection stripes. The precision of the projected stripes depends on the projection period and stripe width, which in turn depend on the resolution of the projection device. In reality, whether using a projector directly or a spatial light modulator to generate stripes, limitations imposed by physical components exist. This leads to an unavoidable situation: improving stripe precision is accompanied by a significant increase in the cost of inspection equipment. Summary of the Invention

[0005] The purpose of this application is to provide an interference fringe generating element, a generating device, and a defect detection method, so as to use a more cost-effective device for the detection of defects on the wafer surface.

[0006] To achieve the above objectives, this application employs the following technical solution:

[0007] In a first aspect, this application discloses an interference fringe generating element, comprising:

[0008] An incident surface, wherein a first reflecting surface and an exiting surface are respectively perpendicularly arranged at both ends of the incident surface;

[0009] The second reflecting surface has one end connected to the first reflecting surface at an obtuse angle and the other end connected to the exiting surface; wherein a beam splitting surface is obliquely arranged between the connection between the incident surface and the exiting surface and the connection between the first reflecting surface and the second reflecting surface.

[0010] In a further embodiment of this application, an antireflection film is provided on the incident surface and the exit surface.

[0011] Secondly, this application discloses an interference fringe generating device, which includes the above-mentioned generating element, and also includes a laser, a spatial filtering system and a beam expander lens;

[0012] The spatial filtering system, the beam expander, and the generating element are arranged sequentially along the path of the light emitted by the laser, and the light transmitted through the beam expander is perpendicular to the incident surface.

[0013] In a further embodiment of this application, the spatial filtering system includes lenses spaced apart, with a pinhole between two lenses, the pinhole of which is located at the focal point of the lens on one side of the laser.

[0014] Thirdly, this application discloses a defect detection method based on the above-mentioned interference fringe generation device, which includes the following steps:

[0015] A light source is selected, and the light source enters the generating element at a preset angle. The generating element generates a first beam and a second beam that satisfy the interference condition, wherein the path difference between the first beam and the second beam is not greater than the coherence length of the light source.

[0016] The first beam and the second beam exit the exit surface, forming an overlapping region and obtaining interference fringes;

[0017] The object to be tested is placed in the overlapping area for defect testing.

[0018] A further aspect of this application includes the formation processes of the first beam and the second beam, comprising:

[0019] The light source enters the generating element, is reflected by the beam-splitting surface, is then reflected perpendicularly by the first reflecting surface, and finally passes through the beam-splitting surface to directly form the first beam.

[0020] The light source enters the generating element, is refracted by the beam-splitting surface, reflected by the second reflecting surface, and finally reflected by the beam-splitting surface to form the second beam.

[0021] In a further embodiment of this application, the coherence length of the light source is calculated using the following formula:

[0022] ;

[0023] in, Let be the coherence length of the light source. The wavelength of the light source, The linewidth of the light source;

[0024] The path difference between the first beam and the second beam is calculated using the following formula:

[0025] ;

[0026] in, The path difference between the first beam and the second beam. The angle between the first reflecting surface and the second reflecting surface. The distance between the reflecting surface and the target position; the interference condition: .

[0027] A further aspect of this application involves adjusting the angle between the first and second reflecting surfaces to change the spacing of the interference fringes; the formula for calculating the spacing of the interference fringes is as follows:

[0028] ;

[0029] in, The spacing of the interference fringes. The wavelength of the light source, It is the angle between the first reflecting surface and the second reflecting surface.

[0030] The beneficial effects of this application are as follows:

[0031] The generating element designed in this application replaces the traditional structured light projection equipment. It utilizes the high coherence and high stability of interference fringes to avoid the dependence of traditional projection systems on gratings and projection equipment. Furthermore, the spacing and direction of the fringes can be adjusted by changing the angle between the first and second reflecting surfaces, making it more flexible. At the same time, by generating interference fringes using a single element, the structured light system has fewer core components, high stability, easy maintenance, and is also cheaper. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the interference fringe generating element structure in the embodiments of this application;

[0033] Figure 2 This is a schematic diagram of the interference fringe generation device in the embodiments of this application;

[0034] Figure 3 This is an image of the wafer illuminated by interference fringes in an embodiment of this application;

[0035] Figure 4This is a schematic diagram of the interference fringe generation process in an embodiment of this application.

[0036] Wherein: 1. Laser; 11. First beam; 12. Second beam; 2. Spatial filtering system; 21. Lens; 22. Pinhole component; 3. Beam expander; 4. Generating element; 5. Wafer sample; 41. Incident surface; 42. Beam splitting surface; 43. First reflecting surface; 44. Second reflecting surface; 45. Exit surface. Detailed Implementation

[0037] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its application or use.

[0038] Example 1

[0039] like Figure 1 As shown, this embodiment discloses an interference fringe generating element 4, which includes an incident surface 41 and a second reflecting surface 44. The incident surface 41 is perpendicularly connected to a first reflecting surface 43 and an exiting surface 45 at its two ends. One end of the second reflecting surface 44 is connected to the first reflecting surface 43 at an obtuse angle, and the other end is connected to the exiting surface 45. A beam-splitting surface 42 is obliquely arranged between the angle between the incident surface 41 and the exiting surface 45 and the angle between the first reflecting surface 43 and the second reflecting surface 44. Here, the angle between the second reflecting surface 44 and the first reflecting surface 43 is slightly greater than 90°. The following is a detailed description of each surface of the generating element 4:

[0040] The incident surface 41 is the first contact surface of the light beam, and an anti-reflection coating is deposited on this surface to improve the light transmittance;

[0041] Beam splitter 42 splits light into a reflected beam and a transmitted beam. A multilayer dielectric film design is used to reduce light loss.

[0042] The first reflecting surface 43 is perpendicular to the incident surface 41 and is coated with a reflective film, which reflects the reflected light from the beam splitting surface 42.

[0043] The second reflecting surface 44 is coated with a reflective film. The angle between the second reflecting surface 44 and the first reflecting surface 43 is θ. The two reflecting surfaces are used to make the two beams of light have an angle. The spacing between the interference fringes is controlled by controlling the size of the angle θ.

[0044] The exit surface 45 is perpendicular to the incident surface 41 and is coated with an anti-reflection film to improve the light emissivity.

[0045] Example 2

[0046] As attached Figure 2 As shown, this embodiment discloses an interference fringe generating device, which includes the generating element 4 from embodiment one, as well as a laser 1, a spatial filtering system 2, and a beam expander 3. The spatial filtering system 2, the beam expander 3, and the generating element 4 are arranged sequentially on the path of the light emitted by the laser 1, and the light transmitted through the beam expander 3 is perpendicular to the incident surface 41. In this embodiment, the spatial filtering system 2 can calibrate the collimation of the beam. The spatial filtering system 2 includes two lenses 21 and a pinhole component 22. The two lenses 21 are spaced apart, and the pinhole component 22 is arranged between the two lenses 21. The pinhole of the pinhole component 22 is arranged at the focal point of the lens 21 closest to the laser 1.

[0047] Example 3

[0048] As attached Figure 3 As shown, this embodiment discloses a defect detection method for an interference fringe generation device. This method uses the interference fringe generation device in Embodiment 2 above, which generates interference fringes with high contrast. The method includes the following steps: selecting a light source, here a laser 1 is used to generate the light source, the light source enters the generating element 4 perpendicularly, and generates a first beam 11 and a second beam 12 that meet the interference conditions, including that the path difference between the first beam 11 and the second beam 12 is not greater than the coherence length of the light source; the first beam 11 and the second beam 12 exit the exit surface 45, forming an overlapping area and obtaining interference fringes; the object to be tested is placed in the overlapping area for defect testing.

[0049] In some embodiments, such as Figure 4 As shown, the defect detection method for the interference fringe generation device is achieved through the following process:

[0050] Selected wavelength Line width A green semiconductor laser 1 is used as the light source, which has high coherence and stable monochromaticity to ensure that the obtained interference fringes have relatively high contrast.

[0051] The laser beam passes through a spatial filtering system 2 (a 4F system consisting of two lenses 21 and a pinhole) and a beam expander 3, generating a diameter of approximately A highly uniform parallel beam.

[0052] The beam expanded and collimated light passes through design element 4 to generate two coherent beams that satisfy the interference condition, specifically the first beam 11 and the second beam 12.

[0053] First beam 11: The light source enters the generating element 4, is reflected by the beam splitting surface 42, is then vertically reflected by the first reflecting surface 43, and finally passes through the beam splitting surface 42 to directly form the first beam 11.

[0054] The second beam 12: The light source enters the generating element 4, is refracted by the beam splitting surface 42, is reflected by the second reflecting surface 44, and finally is reflected by the beam splitting surface 42 to form the second beam 12.

[0055] The second beam 12 and the first beam 11 overlap on the target surface, forming high-contrast interference fringes, from which the spacing between the interference fringes can be obtained. :

[0056] ,

[0057] In the formula, The wavelength of the light source, The angle between the two first reflecting surfaces 43 is given. The final spacing is 6. Interference fringes are generated. By projecting the generated fringes onto the surface of the wafer sample 5 under test, 3D structured light can be used to detect defects on the wafer surface.

[0058] Figure 3 This is a result image of a specific embodiment of the invention that uses design elements to generate interference fringes. Here, the fine interference fringes are obtained by taking a picture with a camera.

[0059] In the process of using interference fringes to detect surface defects of wafer sample 5, it is also necessary to determine the placement position of wafer sample 5 to ensure that the interference fringes can be projected onto the surface of wafer sample 5 at that position.

[0060] In this embodiment, it is necessary to ensure that the path difference of the beam does not exceed the coherence length; otherwise, the interference fringes will disappear, and the wavelength will be affected. Line width The green semiconductor laser has a coherence length for:

[0061] ,

[0062] At the same time, the path difference between the two beams The calculation formula is: ,

[0063] In the formula, The angle between the first reflecting surface 43 and the second reflecting surface 44. The distance between the first reflecting surface and the target position.

[0064] The path difference between the two beams cannot exceed the coherence length, that is, the following must be satisfied: Further observation of the appearance of interference fringes can be obtained. The maximum distance is:

[0065] .

[0066] Simultaneously, the width of the interference region must be considered; only when the region is within an appropriate range can the best detection results be obtained. The width of the interference region is the width of the overlapping area of ​​the two beams, which can be approximated by the following formula: .

[0067] Considering that the defects on wafer sample 5 are at the micrometer level, the width of the interference fringes is controlled between 0.3 mm and 0.5 mm. Using the above formula, a placement range for the wafer sample can be obtained:

[0068] ; .

[0069] The wafer sample 5 to be tested can be placed within the range of 343.77mm-573.96mm from the end of the optical path to achieve a more suitable stripe projection range.

[0070] By using fine interference fringes generated by interference fringe generating elements to replace the fringes obtained by traditional projection methods, 3D structured light can be used to detect minute defects on the wafer inspection surface.

[0071] The above detection method is performed when the light source is collimated and incident from the incident surface 41. When there is an incident angle... The spacing between the new interference fringes is calculated using the following formula:

[0072] ,

[0073] in, The angle between the incident ray and the normal to the incident surface is given.

[0074] The aforementioned equipment generates stripes and uses 3D structured light to detect minute defects on the wafer's inspection surface. The stripe period and thickness are directly determined by the wavelength of the selected light source. By changing the light source, the stripe period can be rapidly altered, thereby enabling faster or more precise defect detection.

[0075] Thanks to the device's lightweight nature, different periods and widths of stripes can be obtained simply by changing the light source to a different wavelength. By switching between different wavelengths of light source to change the stripe period, multiple images can be collected, and then the surface morphology can be obtained by phase fitting. This method reduces the random errors caused by mechanical movement when acquiring images using the traditional phase-shifting method.

[0076] First, using four wavelengths, for the first beam 11... wavelength Take a picture of the stripe coordinates A total of 4 images were taken. For each stripe pattern, its format is as follows:

[0077] ,

[0078] In the formula, The background intensity (average luminance term, also called the DC component) represents the overall level of uniform illumination and surface reflection intensity from the light source. This indicates the modulation degree (amplitude term, also called fringe contrast), reflecting the sharpness of the fringes. This indicates the fringe phase, which contains information about the surface height of the object being measured.

[0079] Furthermore, the modulation phase distribution of each intensity map is extracted using a bandpass filter: ,in, This is a bandpass filter. Four phase diagrams are obtained, with a range of... arrive Periodic data, .

[0080] Furthermore, the equivalent wavelengths of the first beam 11 and the second beam 12 are calculated by combining multiple wavelengths in pairs, which is then used for phase unwrapping. , This represents the equivalent wavelength calculated from the combination of two wavelengths. Indicates the second beam 12th These equivalent wavelengths are much larger than the actual wavelengths, and are used to extend the measurement range.

[0081] Next, the phase difference method is used to obtain the phase diagram (one diagram is combined for each pair, obtained from the equivalent wavelength in the previous step). For any pair of wavelengths... The phase difference is: Its periodicity corresponds , This represents the phase difference between the corresponding phases of two sets of wavelengths. express The phase. It is also necessary to ensure that the phase diagrams are all in the same period. Inside.

[0082] This yields a detailed phase map (for a single wavelength, where the wavelength is relatively small). Coarse phase diagram (at equivalent wavelength, where the wavelength is relatively large) And the corresponding wavelength, which needs to be found to be an integer multiple. ,get This completes the unwrapping of the fine phase map, where... This indicates the fine phase of the unwrapped package.

[0083] Using a phase diagram with a larger period to guide a smaller period, calculate the difference: .

[0084] Further estimate integer period offset Divide the difference by And rounded up:

[0085] , Function: Rounds a value to the nearest integer.

[0086] The obtained integer Application to fine phase maps: .

[0087] Furthermore, this process is repeated, unwrapping layer by layer, starting with the combination with the longest equivalent wavelength and gradually guiding downwards to more refined wavelength phase maps, ultimately obtaining the most accurate and detailed unwrapped phase. The solved phase is then converted into a three-dimensional morphology for defect identification. , This represents the phase height calculated after unpacking. This represents the phase obtained after unwrapping. It is the shortest wavelength at which the final unwrapping occurs.

[0088] This method utilizes the ease of switching light sources in the device, and uses fringe patterns obtained by collecting data at different wavelengths and subtracting each pair to quickly obtain the surface and defect morphology by unwrapping layers and transitioning from large to small periods. This method is suitable for high-speed three-dimensional measurement and reduces mechanical movement.

[0089] However, the traditional four-step phase-shift method for image acquisition introduces random errors due to the mechanical structure, which are difficult to avoid directly. But with this device, multiple sets of phase-shift images at different wavelengths can be quickly obtained. After obtaining the results, the multiple sets of data are fitted to reduce the impact of random errors, thereby obtaining more accurate defect measurement results.

[0090] After determining the wavelengths, four phase-shifted images are taken for each wavelength. The principle is that the fringe phase is changed each time. That is, by controlling the interference fringe generating element designed above through a device, it is moved multiple times along the optical axis, with each movement representing 1 / 4 of a fringe cycle, to obtain: .

[0091] Furthermore, the phase diagram corresponding to each wavelength is calculated: .

[0092] Calculation adjustment system Quality assessment: .

[0093] Based on the modulation index, the weight corresponding to each wavelength is obtained, and the weighted average phase diagram is calculated. :

[0094] ;

[0095] in, This represents the weight of each phase graph during the weighted calculation. This represents the total number of phase maps obtained before weighted calculation.

[0096] Finally, the three-dimensional height is obtained to obtain the surface and defect morphology. , This represents the average wavelength.

[0097] In the description of this application, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0098] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art will understand the specific meaning of the above terms in this application based on the specific circumstances.

Claims

1. A method for detecting defects in an interference fringe generation device, characterized in that, include: An interference fringe generating device includes a generating element (4), a laser (1), a spatial filtering system (2), and a beam expander (3). The generating element (4) includes An incident surface (41) is provided with a first reflecting surface (43) and an exiting surface (45) respectively at its two ends. A second reflecting surface (44) is connected at one end to the first reflecting surface (43) at an obtuse angle, and at the other end to the exiting surface (45); a beam splitting surface (42) is provided between the connection between the incident surface (41) and the exiting surface (45) and the connection between the first reflecting surface (43) and the second reflecting surface (44). The spatial filtering system (2), the beam expander (3), and the generating element (4) are arranged sequentially on the path of the light emitted by the laser (1), and the light transmitted through the beam expander (3) is perpendicular to the incident surface (41). The method includes selecting a light source, the light source entering the generating element (4), and generating a first beam (11) and a second beam (12) that satisfy interference conditions through the generating element (4), the interference conditions including that the path difference between the first beam (11) and the second beam (12) is not greater than the coherence length of the light source; The formation processes of the first beam (11) and the second beam (12) include: The light source enters the generating element (4), is reflected by the beam splitting surface (42), is then vertically reflected by the first reflecting surface (43), and finally forms the first beam (11) after passing through the beam splitting surface (42). The light source enters the generating element (4), is refracted by the beam splitting surface (42), is reflected by the second reflecting surface (44), and finally is reflected by the beam splitting surface (42) to form the second beam (12). The first beam (11) and the second beam (12) exit the exit surface (45), forming an overlapping region and obtaining interference fringes; The test object is placed in the overlapping area for defect testing, and the test object is a wafer sample.

2. The defect detection method of the interference fringe generating device according to claim 1, characterized in that, An anti-reflection membrane is provided on the incident surface (41) and the exit surface (45).

3. The defect detection method of the interference fringe generating device according to claim 1, characterized in that, The spatial filtering system (2) includes lenses (21) spaced apart, with a pinhole (22) between the two lenses (21), and the pinhole of the pinhole (22) is arranged on the focal point of the lens (21) located on one side of the laser (1).

4. The defect detection method of the interference fringe generating device according to claim 1, characterized in that, The coherence length of the light source is calculated using the following formula: ； in, Let be the coherence length of the light source. The wavelength of the light source, The linewidth of the light source; The path difference between the first beam (11) and the second beam (12) is calculated using the following formula: ； in, The path difference between the first beam (11) and the second beam (12) The angle between the first reflecting surface (43) and the second reflecting surface (44) is... The distance between the reflecting surface and the target position is; the interference condition is... .

5. The defect detection method of the interference fringe generating device according to claim 1, characterized in that, Adjust the angle between the first reflecting surface (43) and the second reflecting surface (44) to change the spacing of the interference fringes; the formula for calculating the spacing of the interference fringes is as follows: ； in, The spacing of the interference fringes. The wavelength of the light source, The angle between the first reflecting surface (43) and the second reflecting surface (44) is denoted by .

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