Measuring equipment

Abstract

According to the measuring equipment provided by the invention, based on the light path design of double Fizeau interferometers, the third quarter-wave plate is arranged between the first PBS beam splitter prism and the first protective glass, and the fourth quarter-wave plate is arranged between the second PBS beam splitter prism and the second protective glass; the first protection glass reflects part of incident light beams to the third quarter-wave plate and then reflects out of a light path after passing through the first PBS prism, and the second protection glass reflects part of incident light beams to the fourth quarter-wave plate and then reflects out of the light path after passing through the second PBS prism. Therefore, light reflected by the paired protective glass is prevented from entering the interferometer on the side, crosstalk is filtered out, and the measurement precision is ensured.

Description

Technical Field

[0001] The present application relates to the field of semiconductor detection technology, and in particular to a measuring device. Background Art

[0002] As a precision measuring instrument, the double Fizeau interferometer has a unique optical path design and strict sample preparation requirements, which enable it to perform well in various application scenarios. It is often used to measure the surface shape of optical components, evaluate the wavefront aberration of optical lenses, and detect the uniformity of optical materials. These applications are based on the high-precision measurement capability of the Fizeau interferometer, making it an indispensable measurement tool in the field of optics.

[0003] In the current double-Fizeau interferometer, for the purpose of cleanliness and protection, a layer of protective glass is provided on the surface of the detectors located on both paths. Part of the light incident on the detector on any path will be reflected by the protective glass on the same side, and when it enters the interference light path on the opposite side, it will be imaged in the detector on the opposite side, generating interference-derived fringes and forming crosstalk, which will affect the measurement accuracy. Summary of the invention

[0004] In view of this, the present invention provides a measuring device, which can prevent part of the light reflected by the protective glass from entering the opposite interference light path to improve the measurement accuracy.

[0005] To solve the above problems, this application adopts the following technical solutions: One of the purposes of this application is to provide a measuring device, comprising: An illumination module, the illumination module being configured to output a first polarized light and a second polarized light; A first interferometer, the first interferometer comprises a first PBS beam splitter prism, a first quarter wave plate, a first interference module, a third quarter wave plate 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 device to be tested through the first PBS beam splitter prism and the first interference module in sequence, the light beam reflected from the upper surface of the device to be tested forms a first interference beam through the first interference module, and then enters the first protective glass through the first quarter wave plate, the first PBS beam splitter prism and the third quarter wave plate in sequence, the first protective glass images a part of the incident first interference beam onto the first detector, and the other part of the beam is reflected to the first relay lens, and then reflects out of the light path after passing through the third quarter wave plate and the first PBS beam splitter prism in sequence; The second interferometer comprises a second PBS beam splitter prism, a second quarter wave plate, a second interference module, a fourth quarter wave plate and a second detector. The surface of the second detector is covered with a second protective glass. The second polarized light is incident on the lower surface of the device to be tested via the second PBS beam splitter prism and the second interference module in sequence. The light beam reflected from the lower surface of the device to be tested forms a second interference beam via the second interference module, and then enters the second protective glass via the second quarter wave plate, the second PBS beam splitter prism and the fourth quarter wave plate in sequence. The second protective glass images a part of the incident second interference beam onto the second detector, and another part of the beam is reflected to the second relay lens, and then reflects out of the light path after passing through the fourth quarter wave plate and the second PBS beam splitter prism in sequence.

[0006] In some embodiments, both the first interferometer and the second interferometer are Fizeau interferometers, the first interference module includes a first collimator and a first reference mirror, the first interferometer also includes a first relay lens, the first polarized light passes through the first PBS beam splitter prism and then passes through the first collimator to be incident on the first reference mirror, the first reference mirror reflects part of the incident light beam, and transmits another part of the light beam and then is incident on the upper surface of the device under test, the light beam reflected by the first reference mirror and the light beam reflected by the upper surface of the device under test are combined by the first collimator to form the first interference light beam, and then passes through the first quarter wave plate, the first PBS beam splitter prism, the third quarter wave plate, the first relay lens and the first protective glass in sequence to be imaged onto the first detector; The second interference module includes a second collimator and a second reference mirror, and the second interferometer also includes a second relay lens. The second polarized light passes through the second PBS beam splitter prism and then enters the second reference mirror through the second collimator. The second reference mirror reflects part of the incident light beam, and transmits another part of the light beam and then enters the lower surface of the device under test. The light beam reflected by the second reference mirror and the light beam reflected by the lower surface of the device under test are combined by the second collimator to form the second interference light beam, which is then imaged onto the second detector through the second quarter wave plate, the second PBS beam splitter prism, the fourth quarter wave plate, the second relay lens and the second protective glass.

[0007] In some embodiments, a first beam splitter is further arranged between the first PBS beam splitter prism and the first detector, and a portion 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, and the imaging information of the third detector is monitored and the surface measurement process of the test piece is adjusted; and / or, a second beam splitter is further arranged between the second PBS beam splitter prism and the second detector, and a portion of the second interference light 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 and the surface measurement process of the test piece is adjusted.

[0008] In some 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.

[0009] In some embodiments, the fast axis directions of the first quarter wave plate and the second quarter wave plate are arranged at 90 degrees, and the fast axis direction of the first quarter wave plate is 45° or -45° to the optical axis.

[0010] In some embodiments, the first detector, the second detector, the third detector, and the fourth detector include image sensors, and the image sensors include CCD or CMOS.

[0011] In some of the embodiments, the imaging information includes image position, interference surface type and image contrast, and the measuring device records standard image position, interference surface type and image contrast. In some embodiments, when the image position acquired by the third detector changes, it is determined whether the deviation trajectory of the image position exceeds a set threshold compared with the standard image position, and if so, the position of the first reference mirror or the piece to be tested is adjusted; and / or; when the image position acquired by the fourth detector changes, it is determined whether the deviation trajectory of the image position exceeds a set threshold compared with the standard image position, and if so, the position of the second reference mirror or the piece to be tested is adjusted.

[0012] In some embodiments, when the interference surface type obtained by the third detector changes, it is determined whether the difference between the interference surface type and the standard interference surface type exceeds a set threshold. If 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 type obtained by the fourth detector changes, it is determined whether the difference between the interference surface type and the standard interference surface type exceeds a set threshold. If it exceeds the set threshold, the second reference mirror is replaced or maintained to ensure that the difference is within the threshold range. In some embodiments, when the contrast of the image obtained by the third detector changes, it is determined whether the lighting is attenuated or unstable based on the image contrast and the standard image contrast, and when attenuation or instability occurs, the lighting light power of the lighting module is adjusted to ensure that the lighting is not attenuated or stable; and / or; when the contrast of the image obtained by the fourth detector changes, it is determined whether the lighting is attenuated or unstable based on the image contrast and the standard image contrast, and when attenuation or instability occurs, the lighting light power of the lighting module is adjusted to ensure that the lighting is not attenuated or stable.

[0013] In some embodiments, the lighting module includes a single lighting source, the light beam emitted by the lighting source is split into a first polarized light and a second polarized light, or the lighting module includes two lighting sources, the two lighting sources emit the first polarized light and the second polarized light respectively. This application adopts the above technical solution, and its beneficial effects are as follows: The measuring equipment provided by the present application is provided with a third quarter wave plate between the first PBS beam splitter prism and the first protective glass, and a fourth quarter wave plate between the second PBS beam splitter prism and the second protective glass. The first protective glass reflects part of the incident light beam to the third quarter wave plate, and then reflects the light path after passing through the first PBS beam splitter prism. The second protective glass reflects part of the incident light beam to the fourth quarter wave plate, and then reflects the light path after passing through the second PBS beam splitter prism, so as to prevent the light reflected by the protective glass on the opposite side from entering the interferometer on this side, filter out crosstalk, and ensure measurement accuracy.

[0014] In addition, the measuring equipment provided by the present application utilizes the first protective glass covering the surface of the first detector, and the portion 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, and the imaging information of the third detector is monitored and the surface measurement process of the workpiece to be measured is adjusted, thereby effectively utilizing the portion of light reflected by the first protective glass, and by imaging the portion of light and adjusting the entire surface measurement process according to the imaging situation, the stability and reliability of the interference measurement are guaranteed. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1 Schematic diagram of the optical path structure of the measuring device provided in an embodiment of the present application.

[0017] Figure 2 Schematic diagram of the optical path structure of the first Fizeau interferometer of the measuring device provided in an embodiment of the present application.

[0018] Figure 3a A schematic diagram of a reflection surface profile detected by the third detector provided in an embodiment of the present application.

[0019] Figure 3b This is an image detected by the third detector after the lighting conditions change provided in the embodiment of the present application.

[0020] Figure 4 A schematic diagram of another optical path structure of the measuring device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0021] Embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, and should not be construed as limiting the present application. In the description of the present application, it should be understood that the terms "upper", "lower", "horizontal", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present 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 understood as a limitation on the present application. In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined. In order to make the objectives, technical solutions and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0022] See also Figure 1 , is a schematic diagram of the structure of the measuring device provided in Example 1 of the present application, including an illumination module 10, a first interferometer 20 and a second interferometer 30. The device to be tested provided in the present application may include a wafer, or other films / sheets / substrates with similar characteristics. For the convenience of description, the technical solution provided in the present application is described in detail below using a wafer as the device to be tested.

[0023] The illumination module 10 is used to output a first polarized light 110 and a second polarized light 111 .

[0024] In some embodiments, the lighting module 10 includes a single lighting light source, and a light beam emitted by the lighting light source is split into a first polarized light 110 and a second polarized light 111 .

[0025] In some other embodiments, the lighting module 10 may further include two lighting light sources, and the two lighting light sources respectively emit a first polarized light 110 and a second polarized light 111 .

[0026] The first interferometer 20 includes a first PBS beam splitter prism 210, a first quarter wave plate 211, a first interference module, a third quarter wave plate 40 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 through the first PBS beam splitter prism 210 and the first interference module in sequence. The light beam reflected from the upper surface of the test piece is formed into a first interference beam through the first interference module, and then enters the first protective glass 216 through the first quarter wave plate 211, the first PBS beam splitter prism 210 and the third quarter wave plate 40 in sequence. The first protective glass 216 images a part of the incident first interference beam onto the first detector 215, thereby obtaining the surface characteristics of the upper surface of the test piece. The other part of the beam is reflected to the third quarter wave plate 40, and then reflects out of the light path after passing through the first PBS beam splitter prism 210.

[0027] The second interferometer 30 includes a second PBS beam splitter prism 310, a second quarter wave plate 311, a second interference module, a fourth quarter wave plate 50 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 device to be tested through the second PBS beam splitter prism 310 and the second interference module in sequence. The light beam reflected by the lower surface of the device to be tested forms a second interference beam through the second interference module, and then enters the second protective glass 316 through the second quarter wave plate 311, the second PBS beam splitter prism 310 and the fourth quarter wave plate 50 in sequence. The second protective glass 316 images a part of the incident second interference beam onto the second detector 315, so as to obtain the surface characteristics of the upper surface of the device to be tested. The other part of the beam is reflected to the fourth quarter wave plate 50, and then reflects out of the light path after passing through the second PBS beam splitter prism 310.

[0028] It can be understood that the measuring device provided in this embodiment is based on the optical path design of the dual interferometer. A third quarter wave plate 40 is arranged between the first PBS beam splitter prism 210 and the first protective glass 216, and a fourth quarter wave plate 50 is arranged between the second PBS beam splitter prism 310 and the second protective glass 316. The first protective glass 216 reflects part of the incident light beam to the third quarter wave plate 40, and then reflects out of the light path after passing through the first PBS beam splitter prism 210. The second protective glass 316 reflects part of the incident light beam to the fourth quarter wave plate 50, and then reflects out of the light path after passing through the second PBS beam splitter prism 310, so as to prevent the light reflected by the protective glass on the opposite side from entering the interferometer on this side, filter out crosstalk, and ensure measurement accuracy.

[0029] The first interferometer and the second interferometer are both Fizeau interferometers, forming a first Fizeau interferometer and a second Fizeau interferometer. In other embodiments, the first interferometer and the second interferometer may also be other interferometers, such as a Mach-Zehnder interferometer, a Michelson interferometer, and the like.

[0030] In some embodiments, the first interference module includes a first collimator 212 and a first reference mirror 213, and the first interferometer also includes a first relay lens 214. The first polarized light 110 passes through the first PBS beam splitter prism 210 and then passes through the first collimator 212 to be incident on the first reference mirror 213. The first reference mirror 213 reflects part of the incident light beam, and transmits another part of the light beam and then is incident on the upper surface of the device to be tested. The light beam reflected by the first reference mirror 213 and the light beam reflected by the upper surface of the device to be tested are combined by the first collimator 212 to form a first interference light beam, which then passes through the first quarter wave plate 211, the first PBS beam splitter prism 210, and the third quarter wave plate 40 in sequence to enter the first protective glass 216. The first protective glass 216 images part of the incident first interference light beam onto the first detector 215, and the other part of the light beam is reflected to the first relay lens 214, and then passes through the third quarter wave plate 40 and the first PBS beam splitter prism 210 in sequence to reflect out of the light path.

[0031] Specifically, the optical axis direction is taken as the propagation direction of the first polarized light 110 toward the device under test. After the first polarized light 110 passes through the first PBS beam splitter prism 210, the s light is reflected to the interference light path, and becomes left-handed circularly polarized light after passing through the first quarter-wave plate 211 placed at 45° with the optical axis in the fast axis direction, and then becomes collimated light after passing through the first collimator 212 and then enters the first reference mirror 213. The first reference mirror 213 reflects part of the incident light beam, and the other part of the light beam is transmitted and then vertically incident on the upper surface of the wafer 100 to be tested. The light beam reflected by the first reference mirror 213 and the light beam reflected by the upper surface of the wafer 100 to be tested are combined by the first collimator 212 to form a first interference light beam, which is converted into p light after passing through the first quarter wave plate 211 again, and then passes through the first PBS beam splitter prism 210 and then passes through the first relay lens 214 and the first protective glass 216 to be imaged on the first detector 215, so as to obtain the surface characteristics of the upper surface of the test piece; at the same time, the first protective glass 216 reflects part of the incident first interference light beam to the first relay lens 214, and then reflects out of the light path after passing through the third quarter wave plate 40 and the first PBS beam splitter prism 210 in sequence.

[0032] In some embodiments, the second interference module includes a second collimator 312 and a second reference mirror 313, and the second interferometer also includes a second relay lens 314. The second polarized light 111 passes through the second PBS beam splitter prism 310 and then passes through the second collimator 312 to be incident on the second reference mirror 313. The second reference mirror 313 reflects 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 device to be tested. The light beam reflected by the second reference mirror 313 and the light beam reflected by the lower surface of the device to be tested are combined by the second collimator 312 to form a second interference light beam, which then passes through the second quarter wave plate 311, the second PBS beam splitter prism 310, and the fourth quarter wave plate 50 in sequence to enter the second protective glass 316. The second protective glass 316 images part of the incident second interference light beam onto the second detector 315, and the other part of the light beam is reflected to the second relay lens 314, and then passes through the fourth quarter wave plate 50 and the second PBS beam splitter prism 310 in sequence to reflect out of the light path.

[0033] Specifically, the optical path of the second polarized light 111 is similar to that of the first polarized light 110. After the second polarized light 111 passes through the second PBS beam splitter prism 310, the s-light is reflected to the interference optical path, and becomes right-handed circularly polarized light after passing through the second quarter-wave plate 311 whose fast axis is placed at -45 degrees to the optical axis, and then becomes collimated light after passing through the second collimator 312 and then enters the second reference mirror 313. The second reference mirror 313 reflects part of the incident light beam, and the other part of the light beam is transmitted and then vertically incident on the lower surface of the wafer 100 to be tested. The light beam reflected by the second reference mirror 313 and the light beam reflected by the lower surface of the wafer 100 to be tested are combined by the second collimator 312 to form a second interference light beam, which is transformed into p light after passing through the second quarter wave plate 311 again, and then passes through the second PBS beam splitter prism 310 and then passes through the second relay lens 314 and the second protective glass 316 to be imaged on the second detector 315, so as to obtain the surface characteristics of the lower surface of the test piece; at the same time, the second protective glass 316 reflects part of the incident second interference light beam to the second relay lens 314, and then reflects out of the light path after passing through the fourth quarter wave plate 50 and the second PBS beam splitter prism 310 in sequence.

[0034] In this embodiment, the fast axis direction of the third quarter wave plate 40 is the same as that of the first quarter wave plate 211 , and the fast axis direction of the fourth quarter wave plate 50 is the same as that of the second quarter wave plate 311 .

[0035] It can be understood that a third quarter wave plate 40 is provided between the first PBS beam splitter prism 210 and the first relay lens 214. After the interference light returned by the wafer 100 to be measured and the first reference mirror 213 passes through the first PBS beam splitter prism 210, the p light is incident on the third quarter wave plate 40, forming right-handed circularly polarized light, which is imaged on the first detector 215 after passing through the first protective glass 216; the polarized light returned by the first protective glass 216 becomes s light after passing through the third quarter wave plate 40, and is reflected out of the interference system after passing through the first PBS beam splitter prism 210, thereby avoiding the crosstalk formed by the light reflected by the protective glass entering the opposite interference system, filtering out the crosstalk noise, and ensuring the measurement accuracy.

[0036] It can be understood that a fourth quarter wave plate 50 is also provided between the second PBS beam splitter prism 310 and the second relay lens 314, 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. After the interference light returned by the wafer 100 to be measured and the second reference mirror 313 passes through the second PBS beam splitter prism 310, the p light is incident on the fourth quarter wave plate 50, forming 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 after passing through the second PBS beam splitter prism 310, thereby avoiding the crosstalk formed by the light reflected by the protective glass entering the opposite interference system, filtering out the crosstalk noise, and ensuring the measurement accuracy.

[0037] In this embodiment, the fast axis direction of the first quarter wave plate 211 is 45° to the optical axis, and the fast axis direction of the second quarter wave plate 311 is −45° 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 90° to each other.

[0038] In other embodiments, the fast axis direction of the first quarter wave plate 211 may be -45° to the optical axis, and the fast axis direction of the second quarter wave plate 311 may be 45° to the optical axis, that is, the fast axis directions of the first quarter wave plate 211 and the second quarter wave plate 311 may be 90° to each other.

[0039] It can be understood that when the fast axis direction of the first quarter wave plate 211 is 45° to the optical axis and the fast axis direction of the second quarter wave plate 311 is -45° to the optical axis, the right-handed polarized light of the opposite path will pass through the first reference mirror 213 and the first collimator 212 from the epitaxial and cavity states of the wafer 100 to be tested, and will be completely intercepted when passing through the first quarter wave plate 211, thereby preventing crosstalk in the opposite path and avoiding inaccurate cavity and cavity ring tests; similarly, the left-handed polarized light of the opposite path will pass through the second reference mirror 313 and the second collimator 312 from the epitaxial and cavity states of the wafer 100 to be tested, and will be completely intercepted when passing through the second quarter wave plate 311, thereby preventing crosstalk in the opposite path and avoiding inaccurate cavity and cavity ring tests.

[0040] See also Figure 2 A first beam splitter 217 is also provided between the first PBS beam splitter prism 210 and the first detector 215. Part of the first interference light beam reflected by the first protective glass 216 is imaged onto the third detector 219 after passing through the first beam splitter 217 and the first imaging lens 218. The imaging information of the third detector 219 is monitored and the surface measurement process of the test piece is adjusted.

[0041] It can be understood that, in practice, for the purpose of cleanliness and protection, the surface of the first detector 215 is covered with a first protective glass 216. The first protective glass 216 can reflect part of the incident first interference light beam. When a first beam splitter 217 is arranged 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. The part of the first interference light beam reflected by the first protective glass 216 is imaged onto the third detector 219 after passing through the first beam splitter 217. The imaging information of the third detector 219 can be monitored in real time to determine the state of the optical path, and the surface measurement process of the upper surface of the workpiece to be measured can be adjusted in time according to the state of the optical path to ensure the stability and reliability of the interference measurement.

[0042] Furthermore, the first detector 215 and the third detector 219 include image sensors, and the image sensors include CCD or CMOS.

[0043] It should be noted that the wafer surface measurement equipment provided in this embodiment images the reflective pattern of the protective glass under the cavity working condition before leaving the factory (no wafer is placed) and / or the calibrated wafer (standard wafer) working condition onto the corresponding detector, and records the image position, image contrast and interference surface type under different working conditions and saves them in the configuration file. At this time, the recorded image position, image contrast and interference surface type are used as standard reference objects.

[0044] For example, the protective glass reflection image obtained by the third detector under the cavity working condition before leaving the factory is recorded, and the image position, image contrast and interference surface type image are saved in the configuration file; after leaving the factory and being used for a period of time, the protective glass reflection image obtained by the third detector under the cavity working condition is recorded; the protective glass reflection image after being used for a period of time is compared with the protective glass reflection image before leaving the factory to determine the monitoring information, and adjust the surface measurement process of the test piece. For another example, under the standard wafer working condition, the image position, image contrast and interference surface type image corresponding to the standard film of known surface type are saved in the configuration file as a standard reference object; after leaving the factory and being used for a period of time, the protective glass reflection image obtained by the third detector 219 under the standard wafer is recorded; the protective glass reflection image after being used for a period of time is compared with the standard reference object saved in the configuration file to determine the monitoring information, and adjust the surface measurement process of the test piece.

[0045] Specifically, when the position of the image acquired by the third detector 219 changes, it is determined whether the deviation trajectory of the image position exceeds a 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.

[0046] Please refer to Figure 2 When the relative position of the first reference mirror 213 or the wafer 100 to be tested changes (for example, tilts), the position of the pattern reflected by the first protective glass 216 will change. According to its offset d, the system deviation is judged and compared with the standard image. When the surface deviation of the two exceeds the set threshold (that is, exceeds the acceptable deviation, and the acceptable deviation is different for different actual needs), an alarm can be given and a reference value for adjustment can be given. At this time, when the wafer is tilted 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 0.9~1.1 of the standard image. The standard image can be saved before the equipment leaves the factory or the image corresponding to the standard film with a known surface type can be used as the standard image.

[0047] Specifically, when the interference surface pattern obtained by the third detector changes, it is determined whether the difference between the interference surface pattern and the standard interference surface pattern exceeds a set threshold. If it exceeds the set threshold, the first reference mirror 213 is replaced or maintained to ensure that the difference is within the threshold range.

[0048] For example, when the surface of the first reference mirror 213 deteriorates, the interference surface obtained by the third detector 219 changes, and it is determined whether the difference between the interference surface and the standard interference surface exceeds the set threshold (that is, exceeds the acceptable deviation, and the acceptable deviation varies depending on the actual needs). 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 can be the interference surface corresponding to the standard film with a known surface shape saved before the equipment leaves the factory or used as the standard interference surface.

[0049] Specifically, when the image contrast obtained by the third detector 219 changes, it is determined whether the lighting is attenuated or unstable based on the image contrast and the standard image contrast. If attenuation or instability occurs, the lighting light power of the lighting module 10 is adjusted to ensure that the lighting is not attenuated or stable.

[0050] For example, when the illumination light power changes, the image contrast obtained by the third detector 219 changes. According to the image contrast and the standard image contrast, it is determined whether the illumination is attenuated or unstable. When attenuation or instability occurs, the illumination light power of the illumination module 10 is adjusted to ensure that the illumination is not attenuated or stable, and to confirm whether it can be improved. The standard image contrast can be saved before the device leaves the factory, or the image contrast corresponding to the standard film of the known surface type can be used as the standard image contrast.

[0051] See also Figure 3a and Figure 3b As shown, when the contrast of the pattern acquired by the third detector 219 changes, it is determined whether the lighting is attenuated or unstable based on the image contrast and the standard image contrast, and when attenuation or instability occurs, the lighting light power of the lighting module 10 is adjusted to ensure that the lighting is not attenuated or stable.

[0052] See also Figure 4 Similarly, a second beam splitter 317 is arranged between the second relay lens 314 and the second detector 315. Part of the second interference light beam reflected by the second protective glass 316 is imaged onto the fourth detector 319 through the second beam splitter 317 and then through the second imaging lens 318. The imaging information of the fourth detector 319 is monitored and the surface measurement process of the wafer 100 to be tested is adjusted.

[0053] Similarly, in practice, for the purpose 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 part of the incident second interference light beam. When a second beam splitter is provided between the second PBS beam splitter prism 310 and the second detector 315, the part of the light beam reflected by the second protective glass 316 can be effectively utilized. The part of the second interference light beam reflected by the second protective glass is imaged onto the fourth detector 319 after passing through the second beam splitter. The imaging information of the fourth detector can be monitored in real time and the state of the optical path can be determined. Then, the surface measurement process of the lower surface of the workpiece to be measured can be adjusted in time according to the state of the optical path to ensure the stability and reliability of the interference measurement.

[0054] Furthermore, the second detector 315 and the fourth detector 319 include image sensors, and the image sensors include CCD or CMOS.

[0055] Specifically, when the position of the image acquired by the fourth detector 319 changes, it is determined whether the deviation 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.

[0056] For example, when the relative position of the second reference mirror 313 or the wafer 100 to be tested changes (for example, tilts), 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, exceeds the acceptable deviation, and the acceptable deviation is different for different actual needs), an alarm can be given and a reference value for adjustment can be given. 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 the standard film of the known surface type can be used as the standard image.

[0057] Specifically, when the interference surface pattern obtained by the fourth detector changes, it is determined whether the difference between the interference surface pattern and the standard interference surface pattern exceeds a set threshold. If it exceeds the set threshold, the second reference mirror 313 is replaced or maintained to ensure that the difference is within the threshold range.

[0058] For example, when the surface of the second reference mirror 313 deteriorates, the interference surface shape obtained by the fourth detector changes, and it is determined whether the difference between the interference surface shape and the standard interference surface shape exceeds the set threshold (that is, exceeds the acceptable deviation, and the acceptable deviation varies depending on the actual needs). 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 0.8~1.2 of the standard image. The standard interference surface shape can be the interference surface shape corresponding to the standard film with a known surface shape saved before the equipment leaves the factory or used as the standard interference surface shape.

[0059] Specifically, when the image contrast obtained by the fourth detector 319 changes, it is determined whether the lighting is attenuated or unstable based on the image contrast and the standard image contrast. If attenuation or instability occurs, the lighting light power of the lighting module 10 is adjusted to ensure that the lighting is not attenuated or stable.

[0060] For example, when the illumination light power changes, the image contrast obtained by the fourth detector changes, and the illumination is judged whether it is attenuated or unstable 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 not attenuated or stable, and to confirm whether it can be improved. The standard image contrast can be saved before the device leaves the factory, or the image contrast corresponding to the standard film of the known surface type can be used as the standard image contrast.

[0061] It can be understood that the measuring equipment provided in this embodiment uses the first interferometer 20 to perform surface measurement on one of the surfaces of the workpiece to be measured, and uses the second interferometer 30 to perform surface measurement on the other surface of the workpiece to be measured, and at the same time, the first beam splitter 217 and the second beam splitter 317 are respectively set to reflect the partial light beam reflected by the first protective glass 216 and the second protective glass 316, and then image them through the third detector and the fourth detector respectively, thereby effectively utilizing the partial light beam reflected by the protective glass, and obtaining the optical path state of the corresponding surface of the workpiece to be measured by monitoring the imaging information of the third detector 219 and the fourth detector 319, and adjusting in real time according to the optical path state, thereby ensuring the stability and reliability of the interference measurement of the two sides of the workpiece to be measured.

[0062] It should be noted that: when the illumination light power of the above-mentioned measuring equipment fluctuates, it is only necessary to set up the third detector 219 for monitoring without setting up the fourth detector 319, so as to realize the monitoring of the illumination light power; however, if the position of the reference mirror moves or deteriorates, it is necessary to set up detectors on both sides to realize the monitoring function.

[0063] It can be understood that the measurement equipment provided in this embodiment adopts a double Fizeau interferometer. In the actual wafer surface measurement process, there is a layer of protective glass on the surface 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, pass through the PBS prism again, enter the interference light path, and form derivative fringes on the opposite detector, forming crosstalk, which affects the measurement accuracy. For example, the p-light returned by the second protective glass 316 becomes left-handed polarized light after passing through the second quarter-wave plate 311 in the fast axis direction of -45°, and when it enters the opposite interference light path, it passes through the first quarter-wave plate 211 in the fast axis direction of 45° that originally intercepts, and enters the opposite system, becoming p-light that passes through the first PBS beam splitter prism 210 and is imaged on the first detector 215, thereby forming derivative fringes, interfering with the interference fringes of the wafer to be tested and the first reference mirror 213, affecting the measurement accuracy; and the p-light returned by the first protective glass 216 passes through the PBS prism again and also enters the interference light path, thereby interfering with the interference fringes and affecting the test accuracy; the present application sets a beam splitter in one or both of the paths. For example, a second beam splitter 317 is arranged between the second relay lens 314 and the second detector 315. The light reflected by the second protective glass 316 passes through the second beam splitter 317 and then passes through the second imaging lens 318 to be imaged onto the fourth detector 319, thereby avoiding the protective glass reflecting a small part of the p-light that passes through the corresponding PBS prism and enters the interference light path again through the PBS prism, thereby reducing the interference with the interference fringes; and effectively utilizes the light returned by the protective glass and performs imaging, and adjusts the surface measurement process of the wafer 100 to be measured by monitoring the imaging information of the third detector 219 and / or the fourth detector 319, judges the state of the light path, and ensures the stability and reliability of the interference measurement.

[0064] The measuring equipment provided by the present application is provided with a third quarter wave plate between the first PBS beam splitter prism and the first protective glass, and a fourth quarter wave plate between the second PBS beam splitter prism and the second protective glass. The first protective glass reflects part of the incident light beam to the third quarter wave plate, and then reflects the light path after passing through the first PBS beam splitter prism. The second protective glass reflects part of the incident light beam to the fourth quarter wave plate, and then reflects the light path after passing through the second PBS beam splitter prism, so as to prevent the light reflected by the protective glass on the opposite side from entering the interferometer on this side, filter out crosstalk, and ensure measurement accuracy.

[0065] 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 measuring device, characterized in that: include: An illumination module, the illumination module being configured to output a first polarized light and a second polarized light; A first interferometer, the first interferometer comprises a first PBS beam splitter prism, a first quarter wave plate, a first interference module, a third quarter wave plate 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 device to be tested via the first PBS beam splitter prism and the first interference module in sequence, the light beam reflected from the upper surface of the device to be tested forms a first interference beam via the first interference module, and then enters the first protective glass via the first quarter wave plate, the first PBS beam splitter prism and the third quarter wave plate in sequence, the first protective glass images a part of the incident first interference beam onto the first detector, and another part of the beam is reflected to the third quarter wave plate, and then reflects out of the light path after passing through the first PBS beam splitter prism; The second interferometer comprises a second PBS beam splitter prism, a second quarter wave plate, a second interference module, a fourth quarter wave plate and a second detector. The surface of the second detector is covered with a second protective glass. The second polarized light is incident on the lower surface of the device to be tested via the second PBS beam splitter prism and the second interference module in sequence. The light beam reflected from the lower surface of the device to be tested forms a second interference beam via the second interference module, and then enters the second protective glass via the second quarter wave plate, the second PBS beam splitter prism and the fourth quarter wave plate in sequence. The second protective glass images a part of the incident second interference beam onto the second detector, and another part of the beam is reflected to the fourth quarter wave plate, and then reflects out of the light path after passing through the second PBS beam splitter prism.

2. The measuring device according to claim 1, characterized in that The first interferometer and the second interferometer are both Fizeau interferometers, the first interference module includes a first collimator and a first reference mirror, the first interferometer also includes a first relay lens, the first polarized light passes through the first PBS beam splitter prism and then passes through the first collimator to be incident on the first reference mirror, the first reference mirror reflects 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 device to be tested, the light beam reflected by the first reference mirror and the light beam reflected by the upper surface of the device to be tested are combined by the first collimator to form the first interference light beam, which then passes through the first quarter wave plate, the first PBS beam splitter prism, the third quarter wave plate, the first relay lens and the first protective glass in sequence, the first protective glass images part of the incident first interference light beam onto the first detector, and the other part of the light beam is reflected to the first relay lens, and then passes through the third quarter wave plate and the first PBS beam splitter prism in sequence and reflects out of the light path; The second interference module includes a second collimator and a second reference mirror, and the second interferometer also includes a second relay lens. The second polarized light passes through the second PBS beam splitter prism and then enters the second reference mirror through the second collimator. The second reference mirror reflects part of the incident light beam, and transmits the other part of the light beam and then enters the lower surface of the device under test. The light beam reflected by the second reference mirror and the light beam reflected by the lower surface of the device under test are combined by the second collimator to form the second interference light beam, which then passes through the second quarter wave plate, the second PBS beam splitter prism, the fourth quarter wave plate, the second relay lens and the second protective glass in sequence. The second protective glass images part of the incident second interference light beam onto the second detector, and the other part of the light beam is reflected to the second relay lens, and then passes through the fourth quarter wave plate and the second PBS beam splitter prism in sequence and then reflects out of the light path.

3. The measuring device according to claim 2, characterized in that A first beam splitter is further arranged between the first PBS beam splitter prism and the first detector, and a portion of the first interference light beam reflected by the first protective glass is imaged onto a third detector after passing through the first beam splitter, and the imaging information of the third detector is monitored and the surface measurement process of the piece to be tested is adjusted; and / or, a second beam splitter is further arranged between the second PBS beam splitter prism and the second detector, and a portion of the second interference light beam reflected by the second protective glass is imaged onto a fourth detector after passing through the second beam splitter, and the imaging information of the fourth detector is monitored and the surface measurement process of the piece to be tested is adjusted.

4. The measuring device according to claim 1 or 2, characterized in that 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.

5. The measuring device according to claim 1 or 2, characterized in that The fast axis directions of the first quarter wave plate and the second quarter wave plate are arranged at 90 degrees, and the fast axis direction of the first quarter wave plate is 45 degrees or -45 degrees to the optical axis.

6. The measuring device according to claim 3, characterized in that The first detector, the second detector, the third detector and the fourth detector include image sensors, and the image sensors include CCD or CMOS.

7. The measuring device according to claim 6, characterized in that The imaging information includes image position, interference surface type and image contrast, and the measuring device records the standard image position, interference surface type and image contrast.

8. The measuring device according to claim 7, characterized in that When the image position acquired by the third detector changes, it is determined whether the deviation trajectory of the image position exceeds a set threshold compared with the standard image position, and if so, the position of the first reference mirror or the piece to be tested is adjusted; and / or; when the image position acquired by the fourth detector changes, it is determined whether the deviation trajectory of the image position exceeds a set threshold compared with the standard image position, and if so, the position of the second reference mirror or the piece to be tested is adjusted.

9. The measuring device according to claim 7, characterized in that When the interference surface type obtained by the third detector changes, it is determined whether the difference between the interference surface type and the standard interference surface type exceeds a set threshold. If 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 type obtained by the fourth detector changes, it is determined whether the difference between the interference surface type and the standard interference surface type exceeds a set threshold. If it exceeds the set threshold, the second reference mirror is replaced or maintained to ensure that the difference is within the threshold range.

10. The measuring device according to claim 7, characterized in that When the contrast of the image acquired by the third detector changes, it is judged whether the lighting is attenuated or unstable based on the image contrast and the standard image contrast, and when attenuation or instability occurs, the lighting light power of the lighting module is adjusted to ensure that the lighting is not attenuated or stable; and / or; when the contrast of the image acquired by the fourth detector changes, it is judged whether the lighting is attenuated or unstable based on the image contrast and the standard image contrast, and when attenuation or instability occurs, the lighting light power of the lighting module is adjusted to ensure that the lighting is not attenuated or stable.

11. The measuring device according to claim 1, characterized in that The lighting module includes a single lighting light source, and the light beam emitted by the lighting light source is split to form a first polarized light and a second polarized light; or the lighting module includes two lighting light sources, and the two lighting light sources emit the first polarized light and the second polarized light respectively.

Images