A wafer surface profile measuring device and a measuring method

Abstract

For the wafer surface profile measuring device and measuring method provided by the present application, a first protective glass is covered on the surface of the first detector. A part of the first interference beam reflected by the first protective glass is imaged onto the third detector after passing through the first beam splitter. The imaging information of the third detector is monitored and the surface profile measuring process of the workpiece to be measured is adjusted. The part of the light reflected by the first protective glass is effectively utilized. By imaging this part of the light and adjusting the entire surface profile measuring process according to the imaging situation, the stability and reliability of the interference measurement are ensured.

Description

Technical Field

[0001] This application relates to the technical field of semiconductor detection, and particularly to a wafer surface profile measuring device and a measuring method. Background Art

[0002] As a high-precision wafer surface profile measuring device, the Fizeau interferometer requires high system stability and illumination stability to meet the repeatability index within the nanometer level. Therefore, during the process of measuring the wafer surface profile by the Fizeau interferometer, it is necessary to monitor its working state and adjust it in a timely manner to ensure the stability and reliability of the system during the measurement process.

[0003] In addition, in the current Fizeau interferometer, for the needs of cleanliness and protection, a layer of protective glass is provided on the surface of the detector (which can be, for example, a charge coupled device (CCD)). Part of the light incident on the detector may be reflected by the protective glass, resulting in waste of the optical power of this part. How to utilize this reflected light and monitor and adjust the measurement process to ensure the system stability and reliability is particularly important. Summary of the Invention

[0004] In view of this, the present invention provides a wafer surface profile measuring device and a measuring method, which can effectively utilize part of the light reflected by the protective glass and can monitor the measurement process in real time and adjust the working state of the device in a timely manner.

[0005] To solve the above problems, the present application adopts the following technical solutions:

[0006] One of the purposes of the present application is to provide a wafer surface profile measuring device, including:

[0007] An illumination module, which is used to output a first polarized light;

[0008] A first Fizeau interferometer, which includes a first PBS beam splitter prism, a first quarter-wave plate, a first interference module and a first detector. The surface of the first detector is covered with a first protective glass. The first polarized light is incident on the upper surface of the workpiece to be measured through the first PBS beam splitter prism and the first interference module in sequence. The first interference beam formed by the beam reflected from the upper surface of the workpiece to be measured through the first interference module is imaged on the first detector through the first quarter-wave plate, the first PBS beam splitter prism and the first protective glass in sequence;

[0009] A first beam splitter is further disposed between the first PBS beam splitting prism and the first detector. A part of the first interference beam reflected by the first protective glass is imaged onto the third detector after passing through the first beam splitter, and the imaging information of the third detector is monitored to adjust the surface profile measurement process of the workpiece to be measured.

[0010] In some embodiments, a second Fizeau interferometer is further included. The second Fizeau interferometer includes a second PBS beam splitting prism, a second quarter-wave plate, a second interference module, and a second detector. The surface of the second detector is covered with a second protective glass. The illumination module is further configured to emit a second polarized light. The second polarized light is incident on the upper surface of the workpiece to be measured in sequence through the second PBS beam splitting prism and the second interference module. The second interference beam formed by the beam reflected by the upper surface of the workpiece passing through the second interference module is imaged onto the second detector in sequence through the second quarter-wave plate, the second PBS beam splitting prism, and the second protective glass. A second beam splitter is further disposed between the first PBS beam splitting prism and the second detector. A part of the second interference beam reflected by the second protective glass is imaged onto the fourth detector after passing through the second beam splitter, and the imaging information of the fourth detector is monitored to adjust the surface profile measurement process of the workpiece to be measured.

[0011] In some embodiments, the first interference module includes a first collimator and a first reference mirror. The first Fizeau interferometer further includes a first relay lens. The first polarized light passes through the first PBS beam splitting prism and then is incident on the first reference mirror through the first collimator. The first reference mirror reflects a part of the incident beam, and the other part of the beam is transmitted and then incident on the upper surface of the workpiece to be measured. The first interference beam formed by the combination of the beam reflected by the first reference mirror and the beam reflected by the upper surface of the workpiece passing through the first collimator is imaged onto the first detector in sequence through the first quarter-wave plate, the first PBS beam splitting prism, the first relay lens, and the first protective glass.

[0012] In some embodiments, the second interference module includes a second collimator and a second reference mirror. The second Fizeau interferometer further includes a second relay lens. The second polarized light passes through the second PBS beam splitting prism and then is incident on the second reference mirror through the second collimator. The second reference mirror reflects a part of the incident beam, and the other part of the beam is transmitted and then incident on the lower surface of the workpiece to be measured. The second interference beam formed by the combination of the beam reflected by the second reference mirror and the beam reflected by the lower surface of the workpiece passing through the second collimator is imaged onto the second detector in sequence through the second quarter-wave plate, the second PBS beam splitting prism, the second relay lens, and the second protective glass.

[0013] In some of these embodiments, the first detector, the second detector, the third detector, and the fourth detector include image sensors, and the image sensors include CCDs or CMOSs.

[0014] In some of these embodiments, the imaging information includes image position, interference surface profile, and image contrast, and the wafer surface profile measuring device records standard image position, interference surface profile, and image contrast.

[0015] In some of these embodiments, when the image position obtained by the third detector changes, it is determined whether the offset trajectory of the image position exceeds a set threshold compared with the standard image position. If it exceeds the set threshold, the position of the first reference mirror or the device under test is adjusted; and / or;

[0016] When the image position obtained by the fourth detector changes, it is determined whether the offset trajectory of the image position exceeds a set threshold compared with the standard image position. If it exceeds the set threshold, the position of the second reference mirror or the device under test is adjusted.

[0017] In some of these embodiments, when the interference surface profile obtained by the third detector changes, it is determined whether the difference between the interference surface profile and the standard interference surface profile exceeds a set threshold. When it exceeds the set threshold, the first reference mirror is replaced or maintained to ensure that the difference is within the threshold range; and / or;

[0018] When the interference surface profile obtained by the fourth detector changes, it is determined whether the difference between the interference surface profile and the standard interference surface profile exceeds a set threshold. When it exceeds the set threshold, the second reference mirror is replaced or maintained to ensure that the difference is within the threshold range.

[0019] In some of these embodiments, when the image contrast obtained by the third detector changes, it is determined whether there is attenuation or instability of the illumination based on the image contrast and the standard image contrast. When attenuation or instability occurs, the illumination light power of the illumination module is adjusted to ensure that the illumination is without attenuation or is stable; and / or;

[0020] When the image contrast obtained by the fourth detector changes, it is determined whether there is attenuation or instability of the illumination based on the image contrast and the standard image contrast. When attenuation or instability occurs, the illumination light power of the illumination module is adjusted to ensure that the illumination is without attenuation or is stable.

[0021] In some of these embodiments, a third quarter-wave plate is further disposed between the first PBS beam-splitting prism and the first relay lens. Another part of the first interference beam reflected by the first protective glass exits the optical path after passing through the first relay lens, the third quarter-wave plate, and the first PBS beam-splitting prism.

[0022] A fourth quarter-wave plate is further disposed between the second PBS beam-splitting prism and the second relay lens. Another part of the second interference beam reflected by the second protective glass exits the optical path after passing through the second relay lens, the fourth quarter-wave plate, and the second PBS beam-splitting prism.

[0023] In some of these embodiments, the fast-axis direction of the third quarter-wave plate is the same as that of the first quarter-wave plate, and the fast-axis direction of the fourth quarter-wave plate is the same as that of the second quarter-wave plate. In some of these embodiments, the fast-axis directions of the first quarter-wave plate and the second quarter-wave plate are placed at 90 degrees, and the fast-axis direction of the first quarter-wave plate forms an angle of 45° or -45° with the optical axis.

[0024] In some of these embodiments, the illumination module includes a single illumination light source, and the light beam emitted by the illumination light source is split to form a first polarized light and a second polarized light.

[0025] In some of these embodiments, the illumination module includes two illumination light sources, and the two illumination light sources respectively emit a first polarized light and a second polarized light.

[0026] The second object of the present application is to provide a measurement method for a wafer surface profile measurement device, including the following steps:

[0027] Monitor the imaging information of the third detector and adjust the surface profile measurement process of the workpiece to be measured.

[0028] In some of these embodiments, the imaging information includes image position, interference surface profile, and image contrast.

[0029] The present application adopts the above technical solutions, and the beneficial effects are as follows:

[0030] For the wafer surface profile measurement device and measurement method provided by the present application, a first protective glass is covered on the surface of the first detector. A part of the first interference beam reflected by the first protective glass is imaged onto the third detector after passing through the first beam splitter. Monitor the imaging information of the third detector and adjust the surface profile measurement process of the workpiece to be measured, effectively utilizing the part of the light reflected by the first protective glass. By imaging this part of the light and adjusting the entire surface profile measurement process according to the imaging situation, the stability and reliability of the interference measurement are ensured.

[0031] In the wafer surface profile measurement device and measurement method provided by this application, a third quarter-wave plate is arranged between the first PBS beam-splitting prism and the first relay lens, and a fourth quarter-wave plate is arranged between the second PBS beam-splitting prism and the second relay lens to prevent the light reflected by the protective glass on the opposite path from entering the interferometer on this side, filter out crosstalk, and ensure the measurement accuracy. Description of the Drawings

[0032] To more clearly illustrate the technical solutions of the embodiments of this application, the following will briefly introduce the drawings required for use in the description of the embodiments of this application or the prior art. Obviously, the following described drawings are only some embodiments of this application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0033] Figure 1 It is a schematic structural diagram of the wafer surface profile measurement device provided in Embodiment 1 of this application.

[0034] Figure 2a It is a schematic diagram of the reflected surface profile diagram detected by the third detector provided in Embodiment 1 of this application.

[0035] Figure 2b It is the image detected by the fourth detector after the lighting conditions change provided in Embodiment 1 of this application.

[0036] Figure 3 It is another schematic diagram of the optical path structure of the wafer surface profile measurement device provided in Embodiment 1 of this application. Detailed Description of the Embodiments

[0037] The following will describe in detail the embodiments of this application. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals indicate the same or similar elements or elements with the same or similar functions from beginning to end. The embodiments described below with reference to the drawings are exemplary and are intended to explain this application and should not be construed as a limitation to this application.

[0038] In the description of this application, it should be understood that the orientation or positional relationships indicated by the terms "upper", "lower", "horizontal", "inner", "outer", etc. are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to this application.

[0039] In addition, the terms "first" and "second" are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of this application, "a plurality" means two or more, unless otherwise specifically defined.

[0040] In order to make the objectives, technical solutions and advantages of this application more clear and understandable, the following further details this application in conjunction with the accompanying drawings and embodiments.

[0041] Embodiment 1

[0042] Please refer to Figure 1 , which is a schematic structural diagram of the wafer surface profile measuring device provided in Embodiment 1 of this application, including an illumination module 10 and a first Fizeau interferometer 20. The test piece provided in this application may include a wafer, or may also be other films / sheets / substrates with similar characteristics. For the convenience of description, the following details the technical solutions provided in this application with a wafer as the test piece.

[0043] The illumination module 10 is used to output a first polarized light 110.

[0044] The first Fizeau interferometer 20 includes a first PBS beam splitter prism 210, a first quarter-wave plate 211, a first interference module, and a first detector 215. The surface of the first detector 215 is covered with a first protective glass 216. The first polarized light 110 is incident on the upper surface of the test piece successively through the first PBS beam splitter prism 210 and the first interference module. The first interference beam formed by the beam reflected from the upper surface of the test piece passing through the first interference module is then imaged on the first detector 215 successively through the first quarter-wave plate 211, the first PBS beam splitter prism 210, and the first protective glass 216, so as to obtain the surface profile characteristics of the upper surface of the test piece.

[0045] Further, the first interference module includes a first collimator 212 and a first reference mirror 213. The first Fizeau interferometer 20 further includes a first relay lens 214. The first polarized light 110 is incident on the first reference mirror 213 successively through the first PBS beam splitter prism 210, the first quarter-wave plate 211, and the first collimator 212. The first reference mirror 213 reflects a part of the incident light beam, and the other part of the light beam is transmitted and then incident on the upper surface of the test wafer 100. The first interference beam formed by the combination of the light beam reflected by the first reference mirror 213 and the light beam reflected by the upper surface of the test wafer 100 through the first collimator 212 is then imaged on the first detector 215 successively through the first quarter-wave plate 211, the first PBS beam splitter prism 210, the first relay lens 214, and the first protective glass 216.

[0046] Specifically, taking the propagation direction of the first polarized light 110 in the optical axis direction towards the device under test as the optical axis direction, after the first polarized light 110 passes through the first PBS beam splitter prism 210, the s light is reflected into the interference optical path, and after passing through the first quarter-wave plate 211 with its fast axis direction at 45° to the optical axis, it becomes left-handed circularly polarized light, and then after passing through the first collimating mirror 212, it becomes collimated light and is incident on the first reference mirror 213. The first reference mirror 213 reflects a part of the incident light beam, and the other part of the light beam is transmitted and perpendicularly incident on the upper surface of the wafer 100 under test. The first interference light beam formed by combining the light beam reflected by the first reference mirror 213 and the light beam reflected by the upper surface of the wafer 100 under test after passing through the first collimating mirror 212, after passing through the first quarter-wave plate 211 again, becomes p light, and then passes through the first PBS beam splitter prism 210 and is imaged on the first detector 215 through the first relay lens 214 and the first protective glass 216.

[0047] A first beam splitter 217 is also provided between the first PBS beam splitter prism 210 and the first detector 215. A part of the first interference light beam reflected by the first protective glass 216 is imaged on the third detector 218 after passing through the first beam splitter 217, and the imaging information of the third detector 218 is monitored to adjust the surface profile measurement process of the upper surface of the device under test.

[0048] It can be understood that in practice, for the needs of cleanliness and protection, the surface of the first detector 215 is covered with the first protective glass 216. The first protective glass 216 can reflect a part of the incident first interference light beam. When a first beam splitter is provided between the first PBS beam splitter prism 210 and the first detector 215, the part of the light beam reflected by the first protective glass 216 can be effectively utilized. A part of the first interference light beam reflected by the first protective glass 216 is imaged on the third detector 218 after passing through the first beam splitter 217. The imaging information of the third detector 218 can be monitored in real time to judge the state of the optical path, and the surface profile measurement process of the upper surface of the device under test can be adjusted in time according to the optical path state to ensure the stability and reliability of the interference measurement.

[0049] In this embodiment, the first detector 215 and the third detector 218 include image sensors, and the image sensors include CCD or CMOS.

[0050] In this embodiment, the imaging information includes image position, interference surface profile, and image contrast. The wafer surface profile measurement device records standard image position, interference surface profile, and image contrast.

[0051] It should be noted that: For the wafer surface profile measurement device provided in this embodiment, the reflected light images of the protective glass under the cavity condition (without placing the wafer) before leaving the factory and / or under the condition of calibrating the wafer (standard wafer) are imaged onto the corresponding detectors, and the image positions, image contrasts, and interference surface profiles under different conditions are recorded and saved in the configuration file. At this time, the recorded image positions, image contrasts, and interference surface profiles serve as standard reference objects. For example, record the reflected light image of the protective glass obtained by the third detector under the cavity condition before leaving the factory, and save the image position, image contrast, and interference surface profile in the configuration file; after leaving the factory and being used for a period of time, record the reflected light image of the protective glass obtained by the third detector under the cavity condition; compare the reflected light image of the protective glass after being used for a period of time with the reflected light image of the protective glass before leaving the factory to determine the monitoring information, and adjust the surface profile measurement process of the workpiece to be measured. Another example is that under the standard wafer condition, the image position, image contrast, and interference surface profile corresponding to the standard wafer with a known surface profile are saved in the configuration file as a standard reference object; after leaving the factory and being used for a period of time, record the reflected light image of the protective glass obtained by the third detector 218 under the standard wafer condition; compare the reflected light image of the protective glass after being used for a period of time with the standard reference object saved in the configuration file to determine the monitoring information, and adjust the surface profile measurement process of the workpiece to be measured.

[0052] Specifically, when the image position obtained by the third detector 218 changes, it is judged whether the offset trajectory of the image position exceeds the set threshold. If it exceeds the set threshold, the position of the first reference mirror 213 or the wafer 100 to be measured is adjusted.

[0053] Please refer to Figure 1 , when the relative positions of the first reference mirror 213 or the wafer 100 to be measured change (such as tilting), the position of the pattern reflected by the first protective glass 216 will change. According to the offset amount d, the system deviation is judged and compared with the standard image. When the surface profile deviation between the two exceeds the set threshold (that is, beyond the acceptable deviation, and the acceptable deviation is different according to different actual requirements), an alarm can be given and a reference value for adjustment can be provided. At this time, when the wafer tilts at an angle θ, the image eccentricity d of the third detector is related to the optical path L: d = θ × L. For example, the set threshold can be 0.9 to 1.1 of the standard image. The standard image can be the image saved before the device leaves the factory or the image corresponding to the standard wafer with a known surface profile as the standard image.

[0054] Specifically, when the interference surface profile obtained by the third detector changes, it is judged whether the difference between the interference surface profile and the standard interference surface profile exceeds the set threshold. When it exceeds the set threshold, the first reference mirror 213 is replaced or maintained to ensure that the difference is within the threshold range.

[0055] For example, when the first reference mirror surface profile 213 deteriorates, the interference surface profile obtained by the third detector changes. It is determined whether the difference between the interference surface profile and the standard interference surface profile exceeds a set threshold (i.e., exceeds the acceptable deviation, and the acceptable deviation varies according to actual requirements). When it exceeds the set threshold, the first reference mirror 213 is replaced or maintained to ensure that the difference is within the threshold range. For example, the set threshold can be 0.8 to 1.2 of the standard image. The standard interference surface profile can be the one saved before the device leaves the factory or the interference surface profile corresponding to a standard wafer with a known surface profile as the standard interference surface profile.

[0056] Specifically, when the image contrast obtained by the third detector changes, it is determined whether there is attenuation or instability of the illumination according to the image contrast and the standard image contrast. When there is attenuation or instability, the illumination light power of the illumination module 10 is adjusted to ensure that the illumination is without attenuation or is stable.

[0057] For example, when the illumination light power changes, the graphic contrast obtained by the third detector changes. According to the image contrast and the standard image contrast, it is determined whether there is attenuation or instability of the illumination. When there is attenuation or instability, the illumination light power of the illumination module 10 is adjusted to ensure that the illumination is without attenuation or is stable, and it is confirmed whether it can be improved. The standard image contrast can be the one saved before the device leaves the factory or the image contrast corresponding to a standard wafer with a known surface profile as the standard image contrast.

[0058] Please refer to Figure 2a and Figure 2b As shown, when the graphic contrast obtained by the third detector 218 changes, it is determined whether there is attenuation or instability of the illumination according to the image contrast and the standard image contrast, and when there is attenuation or instability, the illumination light power of the illumination module 10 is adjusted to ensure that the illumination is without attenuation or is stable.

[0059] Please refer to Figure 3 , the wafer surface profile measurement device provided by the present application further includes a second Fizeau interferometer 30. Correspondingly, the illumination module is further configured to output a second polarized light 111.

[0060] In some embodiments, the illumination module 10 includes a single illumination light source. The light beam emitted by the illumination light source is split to form a first polarized light 110 and a second polarized light 111.

[0061] In other embodiments, the illumination module 10 may further include two illumination light sources, and the two illumination light sources respectively emit a first polarized light 110 and a second polarized light 111.

[0062] Further, the second Fizeau interferometer 30 includes a second PBS beam splitter prism 310, a second quarter-wave plate 311, a second interference module, and a second detector 315. The surface of the second detector 315 is covered with a second protective glass 316. The second polarized light 111 is incident on the lower surface of the wafer to be measured through the second PBS beam splitter prism 310 and the second interference module in sequence. The second interference beam formed by the beam reflected from the lower surface of the wafer to be measured through the second interference module is imaged on the second detector 315 through the second quarter-wave plate 311, the second PBS beam splitter prism 310, and the second protective glass 316 in sequence, so as to obtain the surface profile features of the upper surface of the workpiece to be measured.

[0063] In this embodiment, the second interference module includes a second collimator 312 and a second reference mirror 313. The second Fizeau interferometer 30 further includes a second relay lens 314. The second polarized light 111 is incident on the second reference mirror 313 through the second PBS beam splitter prism 310, the second quarter-wave plate 311, and the second collimator 312 in sequence. The second reference mirror 313 reflects a part of the incident beam and transmits the other part of the beam and then incident on the lower surface of the wafer to be measured. The second interference beam formed by combining the beam reflected by the second reference mirror 313 and the beam reflected by the lower surface of the wafer to be measured through the second collimator 312 is imaged on the second detector 315 through the second quarter-wave plate 311, the second PBS beam splitter prism 310, the second relay lens 314, and the second protective glass 316 in sequence.

[0064] Specifically, the optical path of the second polarized light 111 is similar to that of the first polarized light 110. After passing through the second PBS beam splitter prism 310, the s light of the second polarized light 111 is reflected into the interference optical path and becomes right-handed circularly polarized light after passing through the second quarter-wave plate 311 with the fast axis direction at -45° to the optical axis, and then becomes collimated light after passing through the second collimator 312 and is incident on the second reference mirror 313. The second reference mirror 313 reflects a part of the incident beam and transmits the other part of the beam and then vertically incident on the lower surface of the wafer 100 to be measured. The second interference beam formed by combining the beam reflected by the second reference mirror 313 and the beam reflected by the lower surface of the wafer 100 to be measured through the second collimator 312 becomes p light after passing through the second quarter-wave plate 311 again, and then passes through the second PBS beam splitter prism 310, the second relay lens 314, and the second protective glass 316 and is imaged on the second detector 315.

[0065] Similarly, a second beam splitter 317 is further provided between the second relay lens 314 and the second detector 315. A part of the second interference beam reflected by the second protective glass 316 is imaged on the fourth detector 319 through the second beam splitter and then through the second imaging lens 318, and the imaging information of the fourth detector 319 is monitored and the surface profile measurement process of the wafer 100 to be measured is adjusted.

[0066] Similarly, in practice, due to the requirements of cleanliness and protection, the surface of the second detector 315 is covered with a second protective glass 316. The second protective glass 316 can reflect a part of the incident second interference beam. When a second beam splitter 317 is provided between the second PBS beam splitting prism 310 and the second detector 315, the part of the beam reflected by the second protective glass 316 can be effectively utilized. The part of the second interference beam reflected by the second protective glass 316 forms an image on the fourth detector 319 after passing through the second beam splitter 317. The imaging information of the fourth detector can be monitored in real time and the state of the optical path can be judged. Then, according to the state of the optical path, the surface profile measurement process of the lower surface of the workpiece to be measured can be adjusted in time to ensure the stability and reliability of the interference measurement.

[0067] Furthermore, the second detector 315 and the fourth detector 319 include image sensors, and the image sensors include CCD or CMOS.

[0068] Specifically, when the image position obtained by the fourth detector 319 changes, it is judged whether the offset trajectory of the image position exceeds a set threshold. If it exceeds the set threshold, the position of the second reference mirror 313 or the wafer 100 to be measured is adjusted.

[0069] For example, when the relative position of the second reference mirror 313 or the wafer 100 to be measured changes (such as tilting), the position of the pattern reflected by the second protective glass 316 will change. According to its offset d, the system deviation is judged and compared with the standard image. When it exceeds the set threshold (that is, beyond the acceptable deviation, and the acceptable deviation is different according to different actual requirements), an alarm can be given and a reference value for adjustment can be provided. For example, the set threshold can be 0.9 - 1.1 of the standard image. The standard image can be saved before the equipment leaves the factory or the image corresponding to a standard wafer with a known surface profile can be used as the standard image.

[0070] Specifically, when the interference surface profile obtained by the fourth detector changes, it is judged whether the difference between the interference surface profile and the standard interference surface profile exceeds a set threshold. When it exceeds the set threshold, the second reference mirror 313 is replaced or maintained to ensure that the difference is within the threshold range.

[0071] For example, when the surface shape of the second reference mirror 313 deteriorates, the interference surface shape obtained by the fourth detector 319 changes. It is determined whether the difference between the interference surface shape and the standard interference surface shape exceeds a set threshold (i.e., exceeds the acceptable deviation, and the acceptable deviation varies according to actual requirements). When it exceeds the set threshold, the second reference mirror 313 is replaced or maintained to ensure that the difference is within the threshold range. For example, the set threshold can be 0.8 to 1.2 of the standard image. The standard interference surface shape can be saved before the device leaves the factory or the interference surface shape corresponding to a standard wafer with a known surface shape can be used as the standard interference surface shape.

[0072] Specifically, when the image contrast obtained by the fourth detector 319 changes, it is determined whether there is attenuation or instability of the illumination based on the image contrast and the standard image contrast. When attenuation or instability occurs, the illumination light power of the illumination module 10 is adjusted to ensure that the illumination is without attenuation or is stable.

[0073] For example, when the illumination light power changes, the graphic contrast obtained by the fourth detector 319 changes. It is determined whether there is attenuation or instability of the illumination based on the image contrast and the standard image contrast. When attenuation or instability occurs, the illumination light power of the illumination module 10 is adjusted to ensure that the illumination is without attenuation or is stable, and it is confirmed whether improvement is possible. The standard image contrast can be saved before the device leaves the factory or the image contrast corresponding to a standard wafer with a known surface shape can be used as the standard image contrast.

[0074] It can be understood that for the wafer surface shape measuring device provided in this embodiment, the first Fizeau interferometer 20 is used to measure the surface shape of one surface of the workpiece to be measured, and the second Fizeau interferometer 30 is used to measure the surface shape of the other surface of the workpiece to be measured. At the same time, a first beam splitter and a second beam splitter 317 are respectively provided to reflect a part of the light beam reflected by the first protective glass 216 and the second protective glass 316, and then the images are formed by the third detector and the fourth detector 319 respectively. The part of the light beam reflected by the protective glass is effectively utilized, and the optical path state of the corresponding surface of the workpiece to be measured is obtained by monitoring the imaging information of the third detector and the fourth detector 319, and real-time adjustment is performed according to the optical path state, thereby ensuring the stability and reliability of the interference measurement of both sides of the workpiece to be measured.

[0075] It should be noted that when the illumination light power of the above-mentioned wafer surface shape measuring device fluctuates, at this time, only the third detector needs to be set for monitoring without setting the fourth detector 319 to realize the monitoring of the illumination light power; however, for the position movement or deterioration of the reference mirror, detectors need to be set on both sides to realize the monitoring function.

[0076] In this embodiment, the fast axis direction of the first quarter-wave plate 211 is at 45° with respect to the optical axis, and the fast axis direction of the second quarter-wave plate 311 is at -45° with respect to the optical axis, that is, the fast axis directions of the first quarter-wave plate 211 and the second quarter-wave plate 311 are at 90°.

[0077] In other embodiments, it can also be set that the fast axis direction of the first quarter-wave plate 211 is at -45° with respect to the optical axis, and the fast axis direction of the second quarter-wave plate 311 is at 45° with respect to the optical axis, that is, the fast axis directions of the first quarter-wave plate 211 and the second quarter-wave plate 311 are at 90°.

[0078] It can be understood that when the fast axis direction of the first quarter-wave plate 211 is at 45° with respect to the optical axis and the fast axis direction of the second quarter-wave plate 311 is at -45° with respect to the optical axis, the right-handed polarized light of the opposite path passes through the first reference mirror 213 and the first collimating mirror 212 when the epitaxy and cavity state of the wafer under test 100, and then passes through the first quarter-wave plate 211, and will be completely blocked, thereby preventing cross-talk of the opposite path and avoiding inaccurate cavity and cavity ring tests; similarly, the left-handed polarized light of the opposite path passes through the second reference mirror 313 and the second collimating mirror 312 when the epitaxy and cavity state of the wafer under test 100, and then passes through the second quarter-wave plate 311, and will be completely blocked, thereby preventing cross-talk of the opposite path and avoiding inaccurate cavity and cavity ring tests.

[0079] It should be noted that when using a dual Fizeau interferometer, during the actual measurement of the wafer surface profile, there is a layer of protective glass on the surfaces of the first detector 215 and the second detector 315. The protective glass will reflect a small part of the p-light that passes through the corresponding PBS prism, and after passing through the PBS prism again, it enters the interference optical path and forms derivative fringes on the opposite detector, resulting in crosstalk and affecting the measurement accuracy. For example, the p-light reflected by the second protective glass 316 becomes left-handed polarized light after passing through the second quarter-wave plate 311 with a fast-axis direction of -45°. When it enters the interference optical path of the opposite side, when passing through the first quarter-wave plate 211 with a fast-axis direction of 45° that originally has an intercepting effect, it enters the opposite system, becomes p-light, passes through the first PBS beam-splitting prism 210 and is imaged on the first detector 215, thus forming derivative fringes, interfering with the interference fringes between the wafer under test and the first reference mirror 213, and affecting the measurement accuracy; for the p-light reflected by the first protective glass 216, after passing through the PBS prism again, it also enters the interference optical path, thus interfering with the interference fringes and affecting the test accuracy. In this application, a beam splitter is provided in one or both paths. For example, a first beam splitter 217 is provided between the first relay lens 214 and the first detector 215. The light reflected by the first protective glass 216 passes through the first beam splitter and then passes through the first imaging lens and is imaged on the first detector, thus avoiding the protective glass reflecting a small part of the p-light that passes through the corresponding PBS prism and then passing through the PBS prism again and entering the interference optical path, reducing the interference with the interference fringes; and effectively utilizing the light reflected by the protective glass and imaging it. By monitoring the imaging information of the third detector and / or the fourth detector, the surface profile measurement process of the wafer under test 100 is adjusted, the state of the optical path is judged, and the stability and reliability of the interference measurement are ensured.

[0080] In this embodiment, a third quarter-wave plate 40 is also provided between the first PBS beam-splitting prism 210 and the first relay lens 214. Another part of the first interference beam reflected by the first protective glass 216 is reflected out of the optical path after passing through the first relay lens 214, the third quarter-wave plate 40, and the first PBS beam-splitting prism 210.

[0081] Specifically, after the interference light returned by the wafer under test 100 and the first reference mirror 213 passes through the first PBS beam-splitting prism 210, the p-light is incident on the third quarter-wave plate 40, forms right-handed circularly polarized light, passes through the first protective glass 216 and is imaged on the first detector 215; the polarized light reflected by the first protective glass 216 becomes s-light after passing through the third quarter-wave plate 40, passes through the first PBS beam-splitting prism 210, and is reflected out of the interference system, thus avoiding the crosstalk formed by the light reflected by the protective glass entering the interference system of the opposite side, filtering out the crosstalk noise, and ensuring the measurement accuracy.

[0082] In this embodiment, a fourth quarter-wave plate 50 is further disposed between the second PBS beam-splitting prism 310 and the second relay lens 314. Another part of the second interference beam reflected by the second protective glass 316 is reflected out of the optical path after passing through the second relay lens 314, the fourth quarter-wave plate 50, and the second PBS beam-splitting prism 310.

[0083] Specifically, after the interference light returned by the wafer under test 100 and the second reference mirror 313 passes through the second PBS beam-splitting prism 310, the p-light is incident on the fourth quarter-wave plate 50 to form left-handed circularly polarized light, which is imaged on the second detector 315 after passing through the second protective glass 316; the polarized light returned by the second protective glass 316 becomes s-light after passing through the fourth quarter-wave plate 50 and is reflected out of the interference system by the second PBS beam-splitting prism 310, thereby avoiding the crosstalk caused by the light reflected by the protective glass entering the cross-path interference system, filtering out the crosstalk noise, and ensuring the measurement accuracy.

[0084] Further, the fast-axis directions of the third quarter-wave plate 40 and the first quarter-wave plate 211 are the same, and the fast-axis direction of the fourth quarter-wave plate 50 is the same as the fast-axis direction of the second quarter-wave plate 311.

[0085] For the wafer surface profile measurement device provided in this application, a first protective glass is covered on the surface of the first detector. A part of the first interference beam reflected by the first protective glass is imaged on the third detector after passing through the first beam splitter. The imaging information of the third detector is monitored and the surface profile measurement process of the workpiece under test is adjusted. The part of the light reflected by the first protective glass is effectively utilized. By imaging this part of the light and adjusting the entire surface profile measurement process according to the imaging situation, the stability and reliability of the interference measurement are ensured.

[0086] Embodiment 2

[0087] Embodiment 2 of this application provides a measurement method for a wafer surface profile measurement device, which is applied to the wafer surface profile measurement device provided in any of the above embodiments, and includes the following steps: monitoring the imaging information of the third detector and adjusting the surface profile measurement process of the wafer under test 100; and / or; monitoring the imaging information of the fourth detector 319 and adjusting the surface profile measurement process of the wafer under test 100.

[0088] In this embodiment, the imaging information includes image position, interference surface profile, and image contrast.

[0089] It should be noted that: The wafer surface profile measuring device provided in this embodiment forms an image of the reflection pattern of the protective glass under the cavity condition (without placing a wafer) before leaving the factory and / or under the condition of calibrating the wafer (standard wafer) on the corresponding detector, and records the image position, image contrast, and interference surface profile under different conditions and saves them in the configuration file. At this time, the recorded image position, image contrast, and interference surface profile are used as the standard reference object. For example, record the reflection pattern of the protective glass obtained by the third detector under the cavity condition before leaving the factory, and save the image position, image contrast, and interference surface profile in the configuration file; after leaving the factory and being used for a period of time, record the reflection pattern of the protective glass obtained by the third detector under the cavity condition; compare the reflection pattern of the protective glass after being used for a period of time with the reflection pattern of the protective glass before leaving the factory to determine the monitoring information, and adjust the surface profile measurement process of the workpiece to be measured. Another example is that under the standard wafer condition, save the image position, image contrast, and interference surface profile corresponding to the standard wafer with a known surface profile in the configuration file as the standard reference object; after leaving the factory and being used for a period of time, record the reflection pattern of the protective glass obtained by the third detector 218 under the standard wafer condition; compare the reflection pattern of the protective glass after being used for a period of time with the standard reference object saved in the configuration file to determine the monitoring information, and adjust the surface profile measurement process of the workpiece to be measured.

[0090] Specifically, when the image position obtained by the third detector 218 changes, determine whether the offset trajectory of the image position exceeds the set threshold. If it exceeds the set threshold, adjust the position of the first reference mirror 213 or the wafer to be measured 100.

[0091] Please refer to Figure 1 , when the relative position of the first reference mirror 213 or the wafer to be measured 100 changes (such as tilting), the position of the pattern reflected by the first protective glass 216 will change. According to its offset d, determine the system deviation and compare it with the standard image. When the surface profile deviation between the two exceeds the set threshold (that is, beyond the acceptable deviation, and the acceptable deviation is different according to different actual requirements), an alarm can be given and a reference value for adjustment can be provided. At this time, when the wafer tilts at an angle θ, the image eccentricity d of the third detector is related to the optical path L: d = θ × L. For example, the set threshold can be 0.9 to 1.1 of the standard image. The standard image can be the one saved before the device leaves the factory or the image corresponding to the standard wafer with a known surface profile as the standard image.

[0092] Specifically, when the interference surface profile obtained by the third detector changes, determine whether the difference between the interference surface profile and the standard interference surface profile exceeds the set threshold. When it exceeds the set threshold, replace or maintain the first reference mirror 213 to ensure that the difference is within the threshold range.

[0093] For example, when the first reference mirror surface type 213 deteriorates, the interference surface type obtained by the third detector changes. It is judged whether the difference between the interference surface type and the standard interference surface type exceeds a set threshold (that is, exceeds the acceptable deviation, and the acceptable deviation varies according to different actual requirements). When it exceeds the set threshold, the first reference mirror 213 is replaced or maintained to ensure that the difference is within the threshold range. For example, the set threshold can be 0.8 - 1.2 of the standard image. The standard interference surface type can be the one saved before the device leaves the factory or the interference surface type corresponding to the standard wafer with a known surface type is used as the standard interference surface type.

[0094] Specifically, when the image contrast obtained by the third detector changes, it is judged whether there is attenuation or instability of the illumination according to the image contrast and the standard image contrast. When attenuation or instability occurs, the illumination light power of the illumination module 10 is adjusted to ensure that the illumination is without attenuation or is stable.

[0095] For example, when the illumination light power changes, the graphic contrast obtained by the third detector changes. According to the image contrast and the standard image contrast, it is judged whether there is attenuation or instability of the illumination. When attenuation or instability occurs, the illumination light power of the illumination module 10 is adjusted to ensure that the illumination is without attenuation or is stable, and it is confirmed whether improvement can be made. The standard image contrast can be the one saved before the device leaves the factory or the image contrast corresponding to the standard wafer with a known surface type is used as the standard image contrast.

[0096] Please refer to Figure 2a and Figure 2b As shown, when the graphic contrast obtained by the third detector 218 changes, it is judged whether there is attenuation or instability of the illumination according to the image contrast and the standard image contrast. When attenuation or instability occurs, the illumination light power of the illumination module 10 is adjusted to ensure that the illumination is without attenuation or is stable.

[0097] In the wafer surface type measurement method based on a dual Fizeau interferometer provided by this application, a first protective glass is covered on the surface of the first detector. A part of the first interference light beam reflected by the first protective glass is imaged onto the third detector after passing through the first beam splitter. The imaging information of the third detector is monitored and the surface type measurement process of the workpiece to be measured is adjusted, effectively utilizing a part of the light reflected by the first protective glass. By imaging this part of the light and adjusting the entire surface type measurement process according to the imaging situation, the stability and reliability of the interference measurement are ensured.

[0098] The above are only preferred embodiments of the present application, and only specifically describe the technical principles of the present application. These descriptions are only for explaining the principles of the present application and cannot be interpreted as limiting the scope of protection of the present application in any way. Based on the explanation here, any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application, and other specific implementation methods of the present application that can be associated with the technicians in this field without creative work, should be included in the scope of protection of the present application.

Claims

1. A wafer surface profile measuring device, characterized in that, Comprising: A lighting module for outputting a first polarized light; A first Fizeau interferometer, which includes a first PBS beam splitter prism, a first quarter-wave plate, a first interference module, and a first detector. The surface of the first detector is covered with a first protective glass. The first polarized light is incident on the upper surface of the workpiece to be measured successively through the first PBS beam splitter prism and the first interference module. The first interference beam formed by the beam reflected from the upper surface of the workpiece through the first interference module is imaged onto the first detector successively through the first quarter-wave plate, the first PBS beam splitter prism, and the first protective glass; A first beam splitter is further provided between the first PBS beam splitter prism and the first detector. A part of the first interference beam reflected by the first protective glass is imaged onto a third detector through the first beam splitter, and the imaging information of the third detector is monitored to adjust the surface profile measurement process of the workpiece to be measured; The imaging information includes image position, interference surface profile, and image contrast. The wafer surface profile measuring device records standard image position, interference surface profile, and image contrast.

2. The wafer surface profile measuring device according to claim 1, wherein It further includes a second Fizeau interferometer, which includes a second PBS beam splitter prism, a second quarter-wave plate, a second interference module, and a second detector. The surface of the second detector is covered with a second protective glass. The lighting module is further used for emitting a second polarized light. The second polarized light is incident on the upper surface of the workpiece to be measured successively through the second PBS beam splitter prism and the second interference module. The second interference beam formed by the beam reflected from the upper surface of the workpiece through the second interference module is imaged onto the second detector successively through the second quarter-wave plate, the second PBS beam splitter prism, and the second protective glass.

3. The wafer surface profile measuring device according to claim 2, characterized in that, A second beam splitter is further provided between the second PBS beam splitter prism and the second detector. A part of the second interference beam reflected by the second protective glass is imaged onto a fourth detector through the second beam splitter, and the imaging information of the fourth detector is monitored to adjust the surface profile measurement process of the workpiece to be measured.

4. The wafer surface profile measuring device according to claim 3, wherein, The first interference module includes a first collimator and a first reference mirror. The first Fizeau interferometer further includes a first relay lens. The first polarized light passes through the first PBS beam splitter prism and then is incident on the first reference mirror through the first collimator. The first reference mirror reflects a part of the incident beam, and the other part of the beam is transmitted and then incident on the upper surface of the workpiece to be measured. The first interference beam formed by the combination of the beam reflected by the first reference mirror and the beam reflected by the upper surface of the workpiece through the first collimator is imaged onto the first detector successively through the first quarter-wave plate, the first PBS beam splitter prism, the first relay lens, and the first protective glass; The second interference module includes a second collimator and a second reference mirror. The second Fizeau interferometer further includes a second relay lens. The second polarized light is incident on the second reference mirror through the second PBS beam splitter prism and then through the second collimator. The second reference mirror reflects a part of the incident light beam, and the other part of the light beam is transmitted and then incident on the lower surface of the test piece. The second interference light beam formed by combining the light beam reflected by the second reference mirror and the light beam reflected by the lower surface of the test piece through the second collimator is then sequentially imaged on the second detector through the second quarter-wave plate, the second PBS beam splitter prism, the second relay lens, and the second protective glass.

5. The wafer surface profile measuring device according to claim 4, characterized in that, The first detector, the second detector, the third detector, and the fourth detector include image sensors, and the image sensors include CCDs or CMOSs.

6. The wafer surface profile measuring device according to claim 5, wherein, When the image position obtained by the third detector changes, it is judged whether the offset trajectory of the image position exceeds a set threshold compared with the standard image position. If it exceeds the set threshold, the position of the first reference mirror or the test piece is adjusted; and / or; when the image position obtained by the fourth detector changes, it is judged whether the offset trajectory of the image position exceeds a set threshold compared with the standard image position. If it exceeds the set threshold, the position of the second reference mirror or the test piece is adjusted.

7. The wafer surface profile measuring device according to claim 5, characterized in that, When the interference surface shape obtained by the third detector changes, it is judged whether the difference between the interference surface shape and the standard interference surface shape exceeds a set threshold. When it exceeds the set threshold, the first reference mirror is replaced or maintained to ensure that the difference is within the threshold range; and / or; when the interference surface shape obtained by the fourth detector changes, it is judged whether the difference between the interference surface shape and the standard interference surface shape exceeds a set threshold. When it exceeds the set threshold, the second reference mirror is replaced or maintained to ensure that the difference is within the threshold range.

8. The wafer surface profile measuring device according to claim 5, wherein When the image contrast obtained by the third detector changes, it is judged whether there is attenuation or instability of the illumination according to the image contrast and the standard image contrast. When attenuation or instability occurs, the illumination light power of the illumination module is adjusted to ensure that the illumination is non-attenuated or stable; and / or; when the image contrast obtained by the fourth detector changes, it is judged whether there is attenuation or instability of the illumination according to the image contrast and the standard image contrast. When attenuation or instability occurs, the illumination light power of the illumination module is adjusted to ensure that the illumination is non-attenuated or stable.

9. The wafer surface profile measuring device according to claim 4, wherein, A third quarter-wave plate is further arranged between the first PBS beam splitter prism and the first relay lens. The other part of the first interference light beam reflected by the first protective glass is reflected out of the optical path through the first relay lens, the third quarter-wave plate, and the first PBS beam splitter prism. A fourth quarter-wave plate is further disposed between the second PBS beam splitting prism and the second relay lens, and another part of the second interference beam reflected by the second protective glass is reflected out of the optical path after passing through the second relay lens, the fourth quarter-wave plate, and the second PBS beam splitting prism.

10. The wafer surface profile measuring device according to claim 9, characterized in that, The fast axis directions of the third quarter-wave plate and the first quarter-wave plate are the same, and the fast axis direction of the fourth quarter-wave plate is the same as that of the second quarter-wave plate.

11. The wafer surface profile measuring device according to claim 2, wherein, The fast axis directions of the first quarter-wave plate and the second quarter-wave plate are placed at 90 degrees, and the fast axis direction of the first quarter-wave plate forms an angle of 45° or -45° with the optical axis.

12. The wafer surface profile measurement device according to claim 1, characterized in that, The illumination module includes a single illumination light source, and the beam emitted by the illumination light source is split into a first polarized light and a second polarized light, or the illumination module includes two illumination light sources, and the two illumination light sources respectively emit a first polarized light and a second polarized light.

13. A measuring method of a wafer surface shape measuring device as described in claim 1, characterized in that, It includes the following steps: Monitor the imaging information of the third detector and adjust the surface shape measurement process of the workpiece to be measured.

Images