Confocal measuring device for 3D measurement of an object surface

Abstract

The invention relates to a confocal measuring device (1) for 3D measurement of an object surface (2). The measuring device (1) has a light source (4) for measuring light (5, 5A, 5B), a lens array (12) comprising a plurality of array lenses (13), a chromatic telescope (14), a multiplexer optics (11), a collimation optics (8) and a spatially resolving detection device (24). The chromatic telescope (14) images an object plane (16) into an arrangement plane (15) of the lens array (12). In the light path of the measuring light (5) from the object plane (16), the multiplexer optics (11) is arranged behind the lens array (12) at a distance of the sum of the focal length (f AL ) of the array lenses (13) and the focal length (f MO ) of the multiplexer optics (11). In the light path of the measuring light (5), a single aperture stop (10) is arranged behind the multiplexer optics (11) at a distance of the focal length (f MO ) of the multiplexer optics (11). In the light path of the measuring light (5) from the object plane (16), the collimation optics (8) is post-positioned to the aperture stop (10). In the light path of the measuring light (5, 5A, 5B) from the object plane (16), the detection device (24) is post-positioned to the collimation optics (8). A confocal measuring device is created which is simplified in its construction while at the same time having a high measuring throughput.

Description

[0001] This patent application claims the priority of German patent application DE 102020200214.2, the content of which is incorporated herein by reference. Technical Field

[0002] The present invention relates to a confocal measurement device for 3D measurement of an object surface. Background Art

[0003] Confocal measuring devices for measuring objects are known from WO 2014 / 180642 A1, DE 102005043627 A1, DE 102006007170 A1, DE 102007019267 A1, WO 2016 / 193037 A1, the paper by Zint et al. (Journal of Medical Imaging 6(3), 033502, 2019), the paper by Kim et al. (Optics Express, Vol. 21, No. 5, pp. 6286-6294, 2013), and KR 10 1 368 486 A. DE 102013016368 A1 discloses an optical microscope and a microscopic method for examining microscopic samples. DE 69729659 T2 discloses a microlens scanning device for microlithography and wide-field confocal microscopy. WO 2010 / 084478 A2 discloses a device for high-resolution microscopy and lithography using micromirrors. US Pat. No. 9,188,874 B1 discloses an imaging system with a point array for maskless lithography and parallel confocal microscopy. Summary of the Invention

[0004] The object of the present invention is to improve a confocal measuring device of the type mentioned in the introduction so that its design is simplified while achieving a high measurement throughput.

[0005] According to the invention, this object is achieved by a confocal measuring device having the features specified in claim 1 .

[0006] The multiplexer optical device (or multiplexing optical device) according to the present invention does not require the use of an aperture array that requires complex adjustment. At the same time, high spatial resolution and the possibility of parallel multi-channel measurement are provided by the lens array and the spatially resolved detection device. A single aperture diaphragm is used as a multiplexer to spatially filter all the single-channel light paths of the measurement light path starting from the object surface and assigned to the corresponding array lens. Array filtering by an aperture array that requires complex adjustment is eliminated. The multiplexer optical device can be implemented as a single multiplexer lens. The collimating optical device can be implemented as a single collimating lens. The measurement light of the light source can be coupled into the measurement light path between the chromatic telescope and the spatially resolved detection device, in particular via a polarization beam splitter. The λ / 4 plate can be part of the coupling-in optical device. The λ / 4 plate can be arranged between the polarization beam splitter and the lens array that performs the coupling-in.

[0007] The telecentric beam trajectory in the chromatic telescope according to claim 2 reduces the requirements for the positioning of the aperture of the chromatic telescope and can avoid scale errors during 3D measurements of the object surface.

[0008] The detection array according to claim 3 enables multi-channel measurement. The detection array can be implemented as a CCD array or a CMOS array.

[0009] The embodiment of the detection device according to claim 4 increases the degrees of freedom in data acquisition and data evaluation. The sub-beam paths of the measurement light can be guided separately through telescopes in order to image the detection incident plane onto the corresponding detection array. This imaging can be telecentric.

[0010] The gradient filter according to claim 5 enables data evaluation as described for single-channel measurements in Kim et al., “Chromatic confocal microscopy with a novel wavelength detection method using transmittance” (Optics Express, Vol. 21, No. 5, pp. 6286-6294, 2013) or in KR 10-1368486 A. This evaluation technique can be transferred to the pixel-by-pixel channels of a detection device with a detection array, so that the individual channels can be evaluated in parallel.

[0011] The adaptation of the grid spacing / array spacing according to claim 6 optimizes the spatial resolution of the confocal measurement device. The grid spacing can be adapted so that exactly one detector pixel is assigned to each array lens. Alternatively, the grid spacing can be adapted so that multiple detector pixels are assigned to exactly one array lens.

[0012] The bandpass filter according to claim 7 can be used to limit the spectral range of the measurement light to the spectral range for which the chromatic telescope is designed. The corresponding selected spectral range can be, for example, between 400 nm and 600 nm, in particular between 400 nm and 500 nm. Instead of a bandpass filter, a combination of a spectral high-pass filter and a spectral low-pass filter can also be used. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The embodiments of the present invention are described in more detail below with reference to the accompanying drawings. In the accompanying drawings:

[0014] Figure 1 Schematically shows a confocal measurement device for 3D measurement of an object surface;

[0015] Figure 2 shows a light field diagram, wherein, in order to illustrate the effect of the grid-shaped illumination on the object to be measured, the illumination angle (NA) of the measuring light from the measuring point on the surface of the object is shown as a function of the distance x between the measuring point and the optical axis of the measuring device; and

[0016] Figure 3 Similar to Figure 1 The diagram shows another embodiment of a confocal measurement device for 3D measurement of an object surface. DETAILED DESCRIPTION

[0017] The confocal measurement device 1 is used for 3D measurement of a surface 2 of an object 3 .

[0018] The light source 4 of the measuring device 1 generates measuring light 5 . Figure 1 An exemplary single beam of measuring light 5 is shown to illustrate the optical path through measuring device 1. Light source 4 is embodied as a point light source and can be formed by the outlet end of an optical fiber. The measuring light 5 is broadband and can be, for example, white light with a wavelength between 400 nm and 750 nm. Depending on the light source or the subsequent processing of the measuring light 5, other wavelength bands in the UV, VIS, NIR, and / or IR ranges are also possible.

[0019] In order to explain the position relationship, the Cartesian xyz coordinate system is used below. Figure 1 The y-axis extends upward in the middle and is perpendicular to the optical path of the main beam of the measuring light between the light source 4 and the object 3. Figure 1 The drawing plane extends towards the viewer. The z-axis is Figure 1 The center extends to the right parallel to the direction of the main light beam between the light source 4 and the object 3.

[0020] The measuring light 5 is first collimated by a collimating lens 6, which, like the other lenses in the optical path of the measuring device 1, is positioned at the same position as the measuring lens 6 and passes through a non-polarizing beam splitter 7. Figure 1 The measuring light 5 is then focused by a focusing lens 8, resulting in a focus in a focal plane 9. An aperture stop 10 is arranged at the location of the focus on the focal plane 9, which can function as a spatial filter.

[0021] After passing through the aperture stop 10, the measuring light 5 is collimated by another collimating lens 11. The thus collimated measuring light 5 passes through a lens array 12 having a plurality of array lenses 13, which are arranged in rows and columns in the xy plane. Figure 1 Five array lenses 13 are schematically shown in FIG.

[0022] The array lens 13 is implemented as a pillow-shaped lens with a single lens size (xy extension) of 350μm×350μm. The array lenses 13 are densely arranged in the xy plane. Therefore, the distance between adjacent array lenses 13 is also 350μm. The array lenses 13 each have a focal length of 1.59mm. Therefore, one "pixel" of the lens array has a typical extension size of 350μm. Alternatively, such a pixel can also have other extension sizes in the range between 10μm and 1000μm, for example, in the range between 50μm and 500μm. The entire lens array 12 has an extension range of 10mm×10mm in the xy plane. Therefore, there are approximately 900 array lenses 13 in total. In alternative configurations of the lens array 12 , the number of array lenses 13 can also be significantly greater and can include, for example, up to 1,000, up to 5,000, up to 10,000, up to 100,000 or up to 1,000,000 array lenses 13 .

[0023] The lens array 12 can be manufactured using the technology disclosed in the papers by Gissibl et al. (Nature Photonics, Vol. 10, pp. 554-561, 2016, and Nature Communications, 7: 11763, DOI: 10.1038 / necomms11763).

[0024] Hyperchromic objective 14 , which is arranged downstream of lens array 12 in the beam path of measurement light 5 , as an example of a chromatic telescope, images arrangement plane 15 of array lenses 13 of lens array 12 into object plane 16 , in which surface 2 of object 3 is arranged.

[0025] The components of the chromatic telescope 14 are two telescope lenses 17, 18 and a telecentric stop 19 located therebetween. The telecentric stop is arranged in a pupil plane 19a of the chromatic telescope 14.

[0026] The focal length of the hyperchromatic objective 14 is strongly dependent on the wavelength of the measuring light 5. For the prior art of corresponding hyperchromatic objectives and hyperchromatic lenses, see the article in the journal Optolines, issue 23, 2010, pages 14-17.

[0027] The measurement light reflected from the surface 2 passes through the hyperchromatic objective 14 and the lens array 12, and then through the collimating lens 11, which acts as a focusing lens. Then, the portion of the measurement light 5 that is allowed to pass is selected by the aperture stop 10 based on the height of the structure of the object 3 on the surface 2 and the corresponding wavelength of the measurement light 5.

[0028] The lens array 12, the aperture stop 10 and the lens 11 therebetween are components of an aperture stop multiplexer 20. The lens 11 of the aperture stop multiplexer 20 is a multiplexer optical device. The multiplexer optical device 11 is arranged at a focal length f of the array lens 13. AL and the focal length f of the multiplexer optics 11 itself MO It is not necessary to follow this sum distance relationship exactly, but it is allowed to be at a focal length f AL 、f MO There is a deviation of, for example, 20% between the sum and the distance of the multiplexer optics 11 from the lens array 12. The multiplexer optics 11 is arranged after the lens array 12 in the beam path of the measurement light 5 from the surface 2 of the object 3, i.e., from the object plane 16.

[0029] The beam path in the chromatic telescope 14 is telecentric. The main beams from an object point on the surface 2 of the object 3 therefore run parallel to one another between the object plane 16 and the lens 18. The same applies to the path of the main beams between the telescope lens 17 and the lens array 12.

[0030] The aperture stop 10 is in turn arranged downstream of the multiplexer optics at a focal length f of the multiplexer optics 11. MO distance.

[0031] The lens 8 between the beam splitter 7 and the aperture stop 10 is a collimating optical component which is arranged downstream of the aperture stop 10 in the beam path of the measuring light 5 coming from the object plane 16 .

[0032] The aperture stop 10 serves as a multiplexer for spatially filtering all the beam paths of the measuring light beam path that are assigned to the individual channels of the corresponding array lens 13. Spatial filtering in the form of an aperture stop array that must be adjusted in a complex manner is eliminated.

[0033] The measurement light 5, which has been reflected by the beam splitter 7 and allowed to pass through the aperture stop 10, is guided by a folding mirror 21 and a further non-polarizing beam splitter 22 and is split by the beam splitter 22 into two measurement photon beams 5A and 5B. Depending on the design of the optical path in the measuring device 1, the folding mirror 21 can also be omitted. The measurement photon beam 5A reflected by the beam splitter 22 is incident on a first detector array 23 of a spatially resolving detection device 24. The measurement photon beam 5B, which has been allowed to pass through the beam splitter 22, first passes through a linear filter 25 and then is incident on a further detector array 26 of the detection device 24.

[0034] The detection device 24 is arranged downstream of the collimating optics, ie, the lens 8 , in the beam path of the measuring light 5 coming from the object plane 16 .

[0035] The light source 4 , the lenses 6 and 8 and the beam splitter 7 therebetween are components of an illumination device 27 of the measuring device 1 .

[0036] The pixel resolution of the detector pixels of the detection arrays 23 and 26 is adapted to the array arrangement of the array lenses 13 of the lens array, so that one array lens 13 is respectively assigned to one detector pixel. The grid pitch of the array lenses 13 of the lens array 12 is therefore adapted to the grid pitch of the detector pixels of the detector arrays 23 and 26.

[0037] Furthermore, a central control device 28 is part of the measuring device 1 , which is signal-connected to the detector arrays 23 , 26 and the light source 4 in a manner not shown.

[0038] Figure 2 The spatial resolution effect of the aperture stop multiplexer 20 with the lens array 12 and the aperture stop 10 is shown abstractly. The measurement light field is shown as a two-dimensional function. In the dimension x, i.e. on the x-axis, the corresponding measurement points or object points of the object 3 (from which the measurement light 5 originates) and the central optical axis oA of the measurement light beam path (see Figure 1 ) distance. Figure 2 The illumination angle or beam angle of the corresponding measuring light beam from the object point is shown on the graph axis "NA" perpendicular thereto.

[0039] The light field of the focused illumination point FBP is shown perpendicularly to the x-axis, i.e. spatially localized, at the positions of the object points, which correspond to the respective positions of the array lenses 13 of the lens array 12. Due to the focusing of the focused illumination points FBP, these illumination points each have only one x-coordinate, but have a beam angle bandwidth, so that the focused illumination point FBP covers a bandwidth between the values ​​-NA0 and +NA0 in the angular dimension NA.

[0040] In addition, Figure 2 The defocused illumination point DBP is shown in FIG. Figure 2 The x / NA light field diagram of φ appears as a shear line, ie a line extending obliquely. In the x dimension, each defocused illumination point DBP has a distribution over the total distance of x0, for example from -x0 / 2 to +x0 / 2.

[0041] By selecting the distances between the array lenses 13 of the lens array 12, it is ensured that the defocused illumination points DBP do not overlap in the x-dimension, so that no crosstalk occurs between the individual channels of the beam path of the lens array 12. Therefore, in the case of spatially resolved measurements using the detection device 24, the respective measured light signal can be assigned to exactly one object point, corresponding to the spatial resolution of the lens array 12.

[0042] The color-dependent intensity ratio of the measurement results of the two detection arrays 23 and 26 can be evaluated to determine the structure of the surface 2, as is known, for example, from the article "Chromatic confocal microscopy with a novel wavelength detection method using transmittance" by Kim et al., Optics Express, Vol. 21, No. 5, pp. 6286-6294, 2013, or from KR 10-1368486 A. The single-channel evaluation described there can be performed separately for each pixel of the detection arrays 23, 26 of the detection device 24, so that spatially resolved measurement results of the structural measurement of the surface 2 can be determined in parallel.

[0043] The following is based on Figure 3 A further embodiment of a confocal measuring device 31 is described, which can be used for 3D measurement of object surfaces instead of the measuring device 1 .

[0044] The above is combined with the confocal measurement device 1 and in particular with Figure 1 and Figure 2 Components and functions as well as measuring methods that have already been explained have the same reference numerals and will not be discussed again in detail.

[0045] In the measuring device 31, the measuring light 5 is coupled into the measuring and detection light path via a polarization beam splitter 32, which is arranged in the light path between the collimating lens 11 and the lens array 12. For example, perpendicular to Figure 3 Drawing of the plane polarized measurement light 5 in accordance with Figure 3 In the arrangement of , the light 5 reaches the polarization beam splitter 32 from below and is initially reflected to the right by the polarization beam splitter toward the lens array 12. To polarize the measurement light 5, a polarizer 33 for the measurement light 5 is arranged in the optical path between the light source 4 and the polarization beam splitter 32. The polarizer 33 is implemented as a linear polarization filter. A 90° deflection mirror 34 is arranged in the optical path between the polarizer 33 and the polarization beam splitter. A spectral bandpass filter 35 is arranged in the optical path upstream of the polarizer 33. This spectral bandpass filter limits the spectral range of the measurement light 5 to the spectral range for which the hyperchromatic objective 14 of the measuring device 31 is designed.

[0046] The aperture 36 located in the optical path between the polarization beam splitter 32 and the lens array 12 is implemented as a field aperture for the measurement light 5 and defines the illuminated area on the input area of ​​the lens array 12. A λ / 4 plate 37 is arranged in the optical path of the measurement light 5 between the polarization beam splitter 32 and the aperture 36. After passing through the λ / 4 plate 37 twice, the measurement light 5 is initially perpendicular to the field aperture. Figure 3 The drawing plane polarized measurement light 5 is parallel to Figure 3 The drawing plane is polarized, and therefore in Figure 3 , passes through polarization beam splitter 32 from right to left. The subsequent beam path, through collimating lens 11 serving as a focusing lens, aperture stop 10, and focusing lens 8 serving as a collimating lens, corresponds to the beam path described above in conjunction with measuring device 1. In the detection beam path of measuring light 5 after lens 8, it first passes through a further aperture stop 38, which defines a plane 39 to be imaged. This plane is optically conjugate to the arrangement plane 40 of lens array 12. Lenses 8 and 11 thus image plane 39 onto plane 40, with this image being telecentric. The image between planes 39 and 12 produced by lenses 8 and 11 is telecentric.

[0047] The detection beam path of the measuring light 5 first passes through an additional focusing lens 41 after the aperture 38 and then passes through a non-polarizing beam splitter 42. The measuring photon beam 5B reflected by the non-polarizing beam splitter first passes through a linear color filter 25 and then through a collimating lens 43 before reaching the detector array 26. The measuring photon beam 5B allowed to pass by the non-polarizing beam splitter 42 first passes through a collimating lens 44 and then reaches the detector array 23. The lens pairs 41, 43 and the lens pairs 41, 44 are telescopes that ensure that the incident plane 39 is imaged, in particular telecentrically, onto the arrangement plane of the detection arrays 26, 23.

[0048] The illumination plane is spaced apart from the arrangement plane 15 or 40 by the focal length of the array lens 13. Figure 3 45 is indicated in the figure. This plane 45 is the illumination plane of the lens array 12. This plane 45 is imaged onto the object plane 16 by the chromatic objective 14.

[0049] By means of Figure 3 The spatial extent of the light source 4 can be variably adjusted by presetting parameters implemented by fibers or apertures (not shown).

Claims

1. A confocal measuring device (1; 31) for 3D measurement of an object surface (2), the confocal measuring device comprising: - a light source (4) for measuring light (5), - a lens array (12) having a plurality of array lenses (13), a chromatic telescope (14) which images the object plane (16) into the arrangement plane (15) of the lens array (12), - a multiplexer optical device (11) arranged in the optical path of the measurement light (5) coming from the object plane (16) after the lens array (12) and at a distance from the lens array of the focal length (f AL ) and the focal length (f MO ), a single aperture stop (10) arranged in the beam path of the measuring light (5) coming from the object plane (16) after the multiplexer optics (11) at a distance from the multiplexer optics (11) of the focal length (f MO ), - collimating optics (8) arranged downstream of the aperture stop (10) in the beam path of the measuring light (5) coming from the object plane (16), a spatially resolving detection device (24) arranged downstream of the collimating optics (8) in the beam path of the measuring light (5) coming from the object plane (16), - a beam splitter (7) arranged between the light source (4) and the single aperture stop (10); - having another beam splitter (22) for splitting the measuring light (5) into two measuring photon beams, wherein a first measuring photon beam (5A) of the two measuring photon beams is incident on a first detector array (23), and a second measuring photon beam (5B) of the two measuring photon beams is incident on another detector array (26); in, A multiplexer optical device (11) is arranged between the lens array (12) and the single aperture stop (10); The single aperture stop (10) is used as a multiplexer to spatially filter all single-channel optical paths of the measuring light path assigned to the corresponding array lens (13).

2. The confocal measurement device according to claim 1, characterized in that The beam path of the measuring light (5) in the chromatic telescope (14) is telecentric.

3. The confocal measurement device according to claim 1 or 2, characterized in that: The detection device (24) has at least one detector array with detector pixels.

4. The confocal measurement device according to claim 1, characterized in that At least one gradient filter (25) is provided in one of the two sub-beam paths of the detection device (24).

5. The confocal measurement device according to claim 3, characterized in that The grid pitch of the array lenses (13) of the lens array (12) is adapted to the grid pitch of the detector pixels of the at least one detector array.

6. The confocal measurement device according to claim 1 or 2, characterized in that: A spectral bandpass filter (35) is provided for limiting the spectral range of the measurement light.

Images