Optical interferometry device and method

Abstract

An optical interference measurement device has a light source that generates measurement light in a continuous wavelength range, and a measurement head that is optically connected to the light source, aligns the measurement light to a measured object, and receives the measurement light reflected from the measured object. The spectrometer outputs a first spectrum of an interference result between the measurement light reflected from the first interface of the object to be measured and the measurement light reflected from at least one second interface of the object to be measured or from a reference interface to an evaluation device. The spectrometer is provided with at least one grating element which is used for enabling the measuring light guided into the spectrometer to spread in a fan shape according to the wavelength; and the first detector column is aligned with the measuring light expanded in the fan shape and consists of a plurality of detector pixels. The first spectrum is composed of a series of intensity values measured by detector pixels. And the evaluation device calculates the optical path difference between the first interface and the second interface or the reference surface through the spectrum. The optical spectrometer also has a second detector column for alignment of the measurement light spread in the fan shape, the second detector column likewise consisting of a plurality of detector pixels. The second spectrum is composed of a series of intensity values measured by the detector pixels of the second detector column. The first spectrum includes substantially the entire wavelength range at a first resolution and the second spectrum includes a portion of the wavelength range at a higher resolution.

Description

Field of the Invention

[0001] The present invention relates to an optical interferometric measuring device having a light source, a measuring head, and an optical spectrometer. The light source is configured to generate measurement light having at least a continuous wavelength range. The measuring head is optically connected to the light source and directs the measurement light onto the object to be measured, and receives the measurement light reflected from the object to be measured. The optical spectrometer outputs a first spectrum of the interference result between the measurement light reflected from a first interface of the object to be measured and the measurement light reflected from at least one second interface of the object to be measured or from a reference interface to an evaluation device. The optical spectrometer includes: at least one grating element for fanning out the measurement light introduced into the spectrometer according to wavelength; a first detector row for aligning the fanned-out measurement light, the first detector row being composed of a plurality of detector pixels. The first spectrum is composed of a series of intensity values measured by the detector pixels of the first detector row. The evaluation device is configured to calculate the optical path difference between the first interface and the second interface or the reference surface from the spectrum. The present invention also relates to an interferometric method. Background Art

[0002] In many industrial fields, for quality assurance, high-precision measurements of surface topography or layer thickness are required. For example, when manufacturing wafers (box / warpage / total thickness variation), either offline or during the manufacturing process; when manufacturing display glass or medical glass; or various high-precision manufacturing processes all require such measurements. A non-contact method well-suited for such measurements is interferometry using low-coherence light.

[0003] For this purpose, it is generally necessary to direct light in a given continuous wavelength band onto the sample to be measured and cause interference of the light reflected from two different interfaces of the object to be measured or from one interface of the object to be measured and a reference surface. With the aid of a spectrometer, this interference is analyzed according to wavelength, and advantageously, the layer thickness at the measurement point or the optical distance from the reference surface is calculated from the spectral modulation caused by the interference using the Fourier transform of the spectrum. The applicant sells such measuring devices under the name CHRocodile 2IT, for example.

[0004] Among them, the spectrum of the interference light is usually detected by a photosensitive detector, which is composed of a large number of discrete pixels. Therefore, with a given number of pixels and a given wavelength band used, each pixel detects a small range of wavelengths, and the detected spectrum is composed of a series of discrete points.

[0005] The thicker the layer measured, the more restricted the modulation of the spectrum. Therefore, there is an upper limit to the layer thickness that the detector can resolve. To measure a larger layer thickness, either the pixel density must be increased, which results in increased costs and slower readout, or a narrower wavelength band must be used, which reduces the range detected by each pixel. However, using a narrower wavelength band causes the following problem: in the case of a thinner layer, not enough modulation can be detected anymore, so that the thin layer cannot be measured. The lower limit of the measurement range is defined by the bandwidth of the spectrometer, and the upper limit is defined by the smallest resolvable bandwidth (pixel size and spot quality). This results in a fixed ratio between the lower and upper limits of the measurement range of the measuring device. Therefore, different measuring devices must be used for different applications. For a measurement object with layers of very different thicknesses present simultaneously, there may be no suitable measuring device that can detect all layers. Summary of the Invention

[0006] In view of this, an object of the present invention is to provide an interferometric measuring device with a larger ratio between the upper and lower limits of the measurement range and without significantly affecting the cost and the readout speed.

[0007] The solution of the present invention to achieve the above object is that the optical spectrometer includes at least a second detector row for aligning the fan-shaped measurement light, the second detector row is composed of a plurality of detector pixels, and the second spectrum is composed of a series of intensity values measured by the detector pixels of the second detector row, wherein the first spectrum generally includes the entire wavelength range of a first resolution, and wherein the second spectrum includes a local part of a wavelength range with a higher resolution.

[0008] Advantageously, the local part of the wavelength range includes less than half of the entire wavelength range.

[0009] In a preferred embodiment of the present invention, the local part of the wavelength range is generally in the middle of the entire wavelength range. Also advantageously, the local part is selected such that it includes the wavelength with the highest emission amount of the light source. The advantage is that the light intensity can be increased as much as possible.

[0010] Depending on the specific application, it is also advantageous to select the local part from the wavelength range according to the transparency of the measurement object, in particular to select the range where the measured sample is particularly transparent. This is of particular significance, for example, for a measurement object made of silicon, whose transparency changes strongly in the near-infrared range. Due to better transparency, thicker layers can be measured without light loss.

[0011] Another aspect to be considered is the best achievable imaging or the simplest implementation.

[0012] In a preferred embodiment of the present invention, the grating element comprises two sub-gratings. The first sub-grating deflects the measurement light over the entire wavelength range to fan out to the length of the first detector row, and the second sub-grating deflects a local part of the wavelength range to further fan out to the length of the second detector row. By selecting the two sub-gratings, the measuring device can be designed to be particularly flexible.

[0013] Advantageously, the sub-gratings are formed in spatially separated grating element regions on which different parts of the measurement beam fall. For example, the left region of the grating element can form the first sub-grating, and the right region of the grating element can form the second sub-grating. The two sub-gratings can be applied to the same support, where independent setting schemes need to be provided for the adjusted angles.

[0014] In a particularly preferred embodiment of the present invention, the first and second sub-gratings of the grating element have the same number of lines but are oriented at different spatial angles. Different diffraction orders of the sub-gratings are used and imaged onto the corresponding detector rows. The different diffraction orders result in differences in the fanning out of the wavelengths. The number of lines refers to the number of grating lines per unit length and thus determines the diffraction characteristics.

[0015] In a preferred alternative embodiment of the present invention, the first and second sub-gratings of the grating element have different numbers of lines. In this case, the gratings are arranged in a slightly relatively inclined manner.

[0016] In a preferred embodiment of the present invention, the spectrometer has a single light input for the measurement light. The light beam is expanded by collimating optics, and parts of the two sub-gratings extend into the light beam respectively.

[0017] In another preferred embodiment of the present invention, the spectrometer has at least two spatially separated light inputs for the measurement light. Specifically, light with the same characteristics, i.e., light carrying the same interference information, passes through each of the inputs.

[0018] In this embodiment, the grating element is preferably implemented as a continuous grating, and due to the different input coupling points into the spectrometer, there are differences in the incidence on the grating element, resulting in differences in the fanning out on the first and second detector rows.

[0019] Advantageously, the measurement light is separated and aligned to the detector rows such that the sum of the intensity values on the first detector row is approximately equal to the sum of the intensity values on the second detector row, especially equal in the absence of interference modulation. This ensures that the signal intensity is approximately the same on average in any case, so that no row is overexposed or underexposed.

[0020] In a preferred embodiment of the present invention, the measuring device comprises a reference arm. This reference arm includes a reflective reference surface, and the travel length difference is measured with respect to this reference surface. The reference surface represents a fixed reference point, for example, for topography measurement.

[0021] Advantageously, the measuring device or rather the measuring head can be moved relative to the object to be measured, so that the topography or the local thickness distribution can be measured. As an alternative to the entire measuring head, for example, only the measuring points can be scanned with a scanning mirror.

[0022] In a preferred embodiment of the present invention, all the pixels of the first detector column are read individually, and the pixels of the second detector column are read pairwise or averaged in groups of N pixels. The effect is that different resolutions can be generated in a purely electronic manner. This scheme is faster compared to continuously reading and processing all the pixels of the entire column. As an alternative to using two separate detector columns, the two reading schemes can also be applied to the same detector column at different time points.

[0023] The present invention provides a method according to which the second spectrum of the interference result between the measurement light reflected from the first interface of the object to be measured and the measurement light reflected from at least one second interface or from a reference interface of the object is output to an evaluation device by a spectrometer, and the second spectrum is composed of a discrete second data series of intensity values within a wavelength range, and the number of data points per wavelength unit is greater than that of the first spectrum, and wherein according to the modulation of the spectrum, the optical path length difference is calculated by an evaluation unit from these two spectra.

[0024] Advantageously, the total wavelength range covered by the first spectrum is greater than that of the second spectrum, and specifically, the total number of data points in these two spectra is the same. That is, a first intensity spectrum with an output wavelength range of λ A –>λ D is output, where the interval between the data points of this spectrum is Δλ1. Similarly, a second intensity spectrum with an output wavelength range of λ B –>λ C is output, where the data points are spaced at Δλ2 here. Applicable: Δλ1 > Δλ2 and λ A ≤λ B ≤λ C ≤λ D and λ C –λ B <λ D –λ A .

[0025] According to a particularly preferred embodiment of the present invention, the path length differences calculated from the first spectrum and the path length differences calculated from the second spectrum are combined and centrally output. A single list of values is output to the user, optionally together with a graphical representation of the spectrum. For this purpose, the values within the overlapping range of the evaluable results provided for both spectra must be compensated and cancelled out.

[0026] With this measuring device and method, it is also possible to perform simultaneous measurements on thick samples with thin layers applied. Here, the thin layer should be read from the small measurement range and the total thickness should be read from the large measurement range. From the outside, the device appears to have only a single measurement range.

[0027] Particularly preferably, the information related to the thin layer is transmitted into the measurement result of the thick layer. For example, if the object under test involves interfaces H, J, and K, where the distance between H and J is large and the distance between J and K is relatively small. Then the low-resolution spectrum over the entire wavelength range provides the value of the layer thickness J-K, but does not provide the values of the layer thicknesses H-J and H-K. The high-resolution spectrum within the sub-range shows the interference of H-J and H-K, but these interferences cannot be distinguished or resolved separately. The average value is output. Now, the information related to the layer thickness J-K can be used to provide H-J and H-K respectively by calculating back the average value. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Further features and advantages of the present invention are described below in connection with the description of the embodiments with reference to the drawings. Among them:

[0029] Figure 1 is the measuring device of the present invention;

[0030] Figure 2 is the optical spectrometer of the measuring device of the present invention;

[0031] Figure 3 is another optical spectrometer;

[0032] Figure 4 and Figure 5 is the scheme for input coupling to the spectrometer;

[0033] Figure 6 is an exemplary measuring device with a reference arm;

[0034] Figure 7 and Figure 8 are exemplary spectra;

[0035] Figure 9 is the processing of the detector pixels. DETAILED DESCRIPTION OF THE INVENTION

[0036] Figure 1The measuring device of the present invention is shown. This measuring device includes a light source 1 that emits measuring light in a continuous wavelength band. Advantageously, it involves light in the visible range or near-infrared range, such as light with a wavelength of 960 nm - 1090 nm or 1250 nm - 1370 nm. The light source refers to known light-emitting components, such as LEDs, SLDs, etc.

[0037] Subsequently, the measuring light is guided to the measuring head 3 by means of a first optical fiber 2, and the measuring head images the measuring light onto the object 4 to be measured. One or more interfaces of the object 4 to be measured reflect the measuring light, and at least a part of the reflected light is received by the measuring head 3 again.

[0038] The returned measuring light is introduced into another optical fiber 6, which is coupled to the first optical fiber 2, for example, through an optical fiber coupler 5. Subsequently, the measuring light is introduced into the light input end 8 of a spectrometer 7 through this another optical fiber 6, where the intensity spectrum within the wavelength range is detected. This spectrum is transmitted to an evaluation device 9, and the evaluation device calculates the thickness value from the spectral data. The details of the spectrometer 7 are shown in the following figure.

[0039] Figure 2 The optical spectrometer of the measuring device of the present invention is shown. Figure 2 The shown spectrometer 7 is used as Figure 1 the optical spectrometer in the shown device.

[0040] The imaging optics is simplified and shown as a single lens here, but in any case, it can be composed of multiple optical elements, such as lenses and mirrors.

[0041] The spectrometer 7 has a light input end 8 for the measuring light to enter. Subsequently, the measuring light is collimated by a first optical device 11 and hits a grating element 12, which is composed of two diffraction gratings: sub-grating 12a and sub-grating 12b. Among them, each spatial region of the collimated light beam falls on each of the sub-gratings.

[0042] A reflection grating is shown here, but embodiments with transmission gratings are also included.

[0043] The sub-grating 12a and the sub-grating 12 are implemented in such a way that they cause different dispersions of light. This technical variant of the present invention allows for a very free selection of these two spectral ranges, because these two spectral ranges are determined by the two diffraction gratings used. In the shown embodiment, the two sub-gratings refer to diffraction gratings with the same number of lines (for example, 300 lines / mm) but arranged at different angles or orientations.

[0044] The light reflected by the grating element 12 is imaged onto the detector 14 by the focusing optical device 13. The detector 14 includes at least two detector columns 14a and 14b, and the detector columns are composed of a series of photosensitive pixels, which can convert the incident light intensity into an electrical signal. The detector can also refer to an area detector (matrix detector), and at least two columns thereof are utilized.

[0045] The principle here is described for two detector columns, but the present invention also includes corresponding implementation schemes using three columns or more columns.

[0046] The light reflected by the grating element 12a is shown as a solid line here. The sub-grating 12a is arranged and tilted in space such that the light of a certain diffraction order, for example, the second diffraction order, is imaged onto the first detector column 14a. Among them, the number of lines of the sub-grating 12a and the imaging characteristics of the focusing optical device 13 are selected such that the entire wavelength range of the measurement light is imaged in a fan-shaped manner along the length of the detector column 14a.

[0047] The light reflected by the grating element 12b is shown as a dashed line here. The sub-grating 12b is arranged and tilted in space such that the light of a diffraction order higher than the diffraction order used with the sub-grating 12a is imaged onto the second detector column 14b. For example, it refers to the fourth diffraction order. Advantageously, the sub-grating 12b is tilted not only in the splitting (transverse to the line) spatial direction relative to the sub-grating 12a, but also in the spatial direction along the line, such that the light hits other detector columns. Among them, the number of lines of the sub-grating 12b and the imaging characteristics of the focusing optical device 13 are selected such that only a local part of the wavelength range of the measurement light is imaged in a fan-shaped manner along the length of the detector column 14b. Preferably, this local part includes less than half of the entire wavelength range.

[0048] For simplifying the implementation of the device, preferably, the sub-gratings 12a and 12b have the same number of lines and only differ in orientation. However, as an alternative, the number of lines can also be different, whereby the relative spatial tilt of the sub-gratings in the splitting direction can be selected to be smaller or zero.

[0049] Among them, advantageously, the sub-gratings 12a and 12b are arranged in the light beam such that generally the same total intensity is redirected to the two detector columns 14a and 14b. That is, the interface between the sub-grating 12a and 12b is not in the middle of the light beam but is offset, such that more light falls on the sub-grating 12b.

[0050] In an exemplary embodiment of the present invention, this local part of the wavelength range is generally in the middle of the entire wavelength range, and / or this local part refers to the local part where the light source 1 provides the maximum intensity.

[0051] For example, the entire wavelength range emitted and utilized by the light source includes near-infrared light in the range of 960 nm - 1090 nm, and this partial range includes 1055 nm - 1090 nm. As an alternative example, the entire wavelength range emitted and utilized by the light source includes near-infrared light in the range of 1250 nm - 1370 nm, and this partial range includes 1290 nm - 1320 nm. Such wavelength ranges are particularly advantageous for the measurement of silicon or similar materials that are transparent in the near-infrared range. Wavelength bands in the visible range can also be considered for some applications.

[0052] For example, over at least approximately the entire length of the first detector row 14a, the entire wavelength range is imaged in a fan-shaped manner, while over the same length of the second detector row, only a partial wavelength range is imaged in a fan-shaped manner. Since the two detector rows include the same number of detector pixels, the spectrum created from the data of the second detector row 14b has a higher resolution per wavelength unit than the spectrum created from the data of the first detector row 14a, where the two rows output the same number of data points.

[0053] Subsequently, the numbers of these two detector rows are transmitted to the evaluation device. These two spectra are analyzed with the aid of the evaluation device. Specifically, each spectrum is corrected and Fourier-transformed in a known manner to identify the modulation frequencies corresponding to certain path length differences between the reflecting surfaces. As described above, in the case where the path length difference is large (close to the upper limit of the measurement range of the device), the spectrum of the data from the detector row 14a can no longer resolve the modulation well because the modulation is closer than the distance between the data points. While the spectrum of the data from the detector row 14b can be evaluated because the wavelength band range used here is narrower and thus the data points are closer. The situation is just the opposite when the path length difference is small (close to the lower limit of the measurement range of the device), where the data from the detector row 14a can be better evaluated. The spectrum of the data from the detector row 14b does not show sufficient modulation in this case.

[0054] That is, the identifiable optical thickness or the path length difference between two surfaces is identified from these two spectra respectively. The surfaces can refer to multiple interfaces of the object to be measured or one interface of the object to be measured, as well as the reference surface within the measuring device.

[0055] Subsequently, the obtained thickness values are compared to identify the consistency within the range where both spectra provide evaluable results. Subsequently, a combined list of thickness values is output to the user. Optionally, a graphical overlay of the two spectra or the two Fourier-transformed spectra can be output for visual presentation.

[0056] Figure 3 Shows another exemplary optical spectrometer.

[0057] As Figure 2An alternative to the embodiment with two different sub-diffraction gratings, as shown here, can also be used Figure 3 for only a single diffraction grating as shown here. Here, the grating images the diffracted measurement light of two different diffraction orders onto corresponding detector columns. To achieve a spatial offset of the two spectra, the input light must be input-coupled into the spectrometer via two points in space. In this technical variant, the two spectral ranges cannot be freely selected as in the previous technical variant.

[0058] In this embodiment, the light is input-coupled into the spectrometer through two spatially separated input ends 8a and 8b. The implementation of these two input ends will be described below Figure 4 in. The light from the two input ends 8a and 8b is collimated by the optical device 111 and directed towards the optical diffraction grating 112, which can be composed of multiple optical elements. Subsequently, the diffracted light is imaged onto the detector 14 by the focusing optical device 113, which can be composed of multiple optical elements. The implementation of this detector corresponds to the detector described in conjunction with Figure 2 and includes at least two detector columns 14a and 14b or a matrix detector in which two of its columns are utilized. The diffraction grating shown here is a transmission grating, but in principle, it can also include a reflection grating.

[0059] Among them, the input end 8a is arranged spatially relative to the grating 112 and the detector 14 such that the light of a certain diffraction order of the grating, for example, the 3rd diffraction order, is imaged onto the detector column 14a. Among them, the elements of the spectrometer are selected and arranged such that substantially the entire wavelength range of the measurement light is imaged in a fan-shaped manner along the length of the detector column 14a.

[0060] The second input end 8b is arranged at a certain distance from the input end 8a such that the light of a higher diffraction order of the grating, for example, the 4th diffraction order, is imaged onto the detector column 14b. Since the diffraction order is higher, the light is more strongly fan-shaped, so only a part of the entire wavelength range is imaged along the length of the detector column.

[0061] Preferably, the input ends 8a and 8b are offset both in the spatial direction parallel to the grating lines (to be imaged onto two different detector columns 14a and 14b) and in the spatial direction transverse to the grating lines and the optical axis (to satisfy different diffraction orders).

[0062] The principle of the light incidence on the detector column caused is the same as that described for Figure 2 . Further processing and evaluation are implemented as described there.

[0063] The principle here is described for two detector columns, but the present invention also includes implementations using three or more columns.

[0064] That is, by appropriately selecting the diffraction order, the grating tilt angle, and the distance between the two input ends, the two sub-spectra in the detector plane can have the same width or be superimposed.

[0065] Another technical solution of the present invention is Figure 2 the technical solution of Figure 3 a hybrid solution with the technical solution of. Among them, there are two sub-gratings with different orientations or characteristics, and two spaced-apart optical input ends. The light from each input end is fan-shaped expanded by means of a sub-grating with different (number of lines and / or orientation) and is aligned with each detector column.

[0066] Figure 4 and Figure 5 show a scheme in which the input is coupled to Figure 3 the spectrometer 7.

[0067] Among them, Figure 4 shows a free beam solution. The light from the optical fiber 6 starting from the measurement head exits from the optical fiber end 40 and is split into two split beams by the beam splitter 41 shown here as. Among them, the cube beam splitter can split the beam at 50 / 50 or in any other ratio, preferably such that as Figure 2 shown, the total intensity on each of the detector columns 14a and 14b is the same. Subsequently, the light beams are turned by the deflecting mirrors 42a and 42b so that the middle light beam is parallel. Subsequently, the light is further processed as described for Figure 3 where the positions of the input ends 8a and 8b correspond to the virtual source points behind the deflecting mirrors 42a and 42b.

[0068] Figure 5 shows an implementation scheme realized as an optical fiber optical system. The optical fiber 6 starting from the measurement head is connected to another two optical fibers through the optical fiber coupler 50, and the light is split on these two optical fibers. Here, the appropriate beam splitting ratio can also be selected as described above. Subsequently, the light exits from the optical fiber ends corresponding to the spectrometer input ends 8a and 8b.

[0069] Figure 6 shows an exemplary measuring device with a reference arm. Figure 5 corresponds to Figure 1The device shown, wherein additionally there is a reference arm 10 connected to the fiber optic coupler 5. Herein, a part of the light from the light source 1 is introduced into the reference arm 10 instead of the measuring head 3, where it is reflected on the reference plane 60 and guided back to the fiber optic coupler 5 along the same path. The light from the reference arm and the light from the measuring head 3 converge there and are introduced into the optical fiber 6 in the direction of the spectrometer 7. Alternatively, an embodiment with a reference arm can also be used, which guides the light entirely or partly as a free beam instead of through an optical fiber. Specifically, in this case, a beam splitter is used instead of a fiber optic coupler.

[0070] Using the reference arm 10 enables the measurement of the height position of the object to be measured relative to a fixed reference point. If the measurement positions on the object to be measured are scanned, a topographical map can be created.

[0071] A hybrid measurement configuration can also be used, in which both the thickness of one or more layers of the object to be measured is measured (by the interference between the light reflected at different interfaces of the object to be measured), and the topography of the object to be measured relative to a fixed point is measured using the reference arm. A switchable reference arm can also be used.

[0072] Figure 7 An exemplary spectrum in the case of a large difference in travel length is shown.

[0073] The intensity signal on the detector column 14a is graphically plotted here as 70a. Thereby, the spectrum 71a is created. Correspondingly, the intensity signal on the detector column 14b is plotted as 70b, and the corresponding spectrum is 71b. As shown here, the modulation by interference is so tight that it cannot be resolved by the spectrum 71a, but can be resolved by 71b.

[0074] Figure 8 An exemplary spectrum in the case of a small difference in travel length is shown.

[0075] The detector signal and spectrum correspond to Figure 7 , where the modulation can be better resolved by the spectrum 71a here.

[0076] Figure 9 The processing of detector pixels in another optical measurement device is schematically shown.

[0077] As an alternative to the physical fan-shaped spreading of the measurement light in the spectrometer, as shown in the previous figures, the resolution of the spectrum and the number of data points can also be set electronically. In this way, a single switchable detector column can be used. However, an implementation with two detector columns that simultaneously provide different resolutions can also be used.

[0078] It is based on the so-called "pixel merging", which enables grouped reading of multiple adjacent pixels in a detector column.

[0079] Use a column detector that can read pixels by merging them together. Thus, in a detector that originally has 2048 pixels, only 1024 pixels can be used for further rapid processing (two merged pixels together). At the same time, in the detector, it should be possible to read 2048 unmerged pixels, but only half of them are used for the same rapid further processing. It is also possible to read only a part of the pixels, such as pixels 512 to 1536. Advantageously, read a local part of a column. This results in two reading positions that are faster in downstream processing and mainly can operate in the same way.

[0080] During operation, the device can switch between a small measurement range and a large measurement range through pixel merging, and the signal processing in the device does not need to be changed. This can also achieve a device with a large measurement range under the condition of limited computer resources.

[0081] Image the entire spectral range on the entire column length of the detector. The spot size of the optical imaging on the detector should be less than or equal to the pixel size of the detector (the size of unmerged pixels).

[0082] By merging or ignoring half of the pixels, two spectral ranges and two measurement ranges can be evaluated in the same optical structure (the light source is also the same) and in the further processing using software.

[0083] The entire spectral range of the light source is imaged onto the detector column. In the first mode, all pixels can be read separately, but half of the pixels will not be used further. The unused pixels must be adjacent, that is, form a geometric block. Thus, a smaller spectral range is read efficiently. This enables measurement of a larger travel length difference. In the second mode, adjacent pixels are read in pairs. Since the spectral range is complete, a smaller travel length difference can be measured in an interferometric device. Both modes can be used, and the further processing in the controller does not need to be changed.

[0084] Advantageously, switch between modes according to the specific nature of the object to be measured. It is also possible to continuously and rapidly switch back and forth between modes to measure different travel length differences almost simultaneously.

[0085] The first mode is in Figure 9is schematically shown as M1: All pixels of the detector column are read and transferred to the evaluation device 9. The second mode is shown as M2: Here, the pixels are read in pairs, and the sum or average value of each pair is transferred to the evaluation device 9. The second mode of the alternative is shown as M3: Here, the pixels are read in groups of 4 instead of in pairs. It can also be generally summarized as the grouping of N pixels.

[0086] The above example can also be carried out on two columns (similarly there is only one light source and one spectrometer, but the spectrum is divided into two columns or more columns as described above, but the fan-out on the two columns is the same. Therefore, modes 1 and 2 can be applied separately or in parallel as the case may be.

[0087] Other alternative solutions not shown in the drawings can also be considered:

[0088] An implementation where the detector only includes one column, but the focal length of the optical device is variable. Therefore, the spectral width imaged on the detector is variable. This solution has a complex structure and cannot detect two spectral ranges / resolutions simultaneously, but it can work with fewer detector columns.

[0089] It is also possible to use only one grating, but the angle of the grating is adjustable, so that it is possible to switch between different grating orders. Similarly, a solution according to Figure 3 the principle can be adopted, but for example, switching is carried out between the input ends through an optical fiber switch.

Claims

1. An optical interferometric measuring device having a light source, a measuring head, and an optical spectrometer, wherein the light source is configured to generate measurement light at least in a continuous wavelength range, and wherein the measuring head is optically connected to the light source and directs the measurement light onto the object to be measured and receives the measurement light reflected from the object to be measured, wherein the optical spectrometer outputs a first spectrum of the interference result between the measurement light reflected from a first interface of the object to be measured and the measurement light reflected from at least one second interface of the object to be measured or from a reference interface to an evaluation device, and the optical spectrometer comprises: - at least one grating element for fan - unfolding the measurement light introduced into the spectrometer according to wavelength, - a first detector row for aligning the fan - unfolded measurement light, the first detector row being composed of a plurality of detector pixels, wherein the first spectrum is composed of a series of intensity values measured by the detector pixels of the first detector row, wherein the evaluation device is configured to calculate the optical path difference between the first interface and the second interface or the reference surface from the spectrum, characterized in that, the optical spectrometer comprises at least one second detector row for aligning the fan - unfolded measurement light, the second detector row being composed of a plurality of detector pixels, and a second spectrum is composed of a series of intensity values measured by the detector pixels of the second detector row, wherein the first spectrum generally comprises the entire wavelength range with a first resolution, and wherein the second spectrum comprises a portion of the wavelength range with a higher resolution.

2. The measuring device according to claim 1, characterized in that, The grating element comprises two sub - gratings, the first sub - grating deflects the measurement light of the entire wavelength range to fan - unfold it to the length of the first detector row, and the second sub - grating deflects the portion of the wavelength range to further fan - unfold it to the length of the second detector row.

3. The measuring device according to claim 2, characterized in that, The sub - gratings form spatially separated regions of the grating element on which different parts of the measurement beam fall.

4. The measuring device according to claim 2 or 3, characterized in that, The first and second sub - gratings of the grating element have the same number of lines but are oriented at different spatial angles.

5. The measuring device according to claim 2 or 3, characterized in that The first and second sub - gratings of the grating element have different numbers of lines.

6. The measuring device according to any one of the above claims, characterized in that, The spectrometer has a single light input for the measurement light.

7. The measuring device according to any one of claims 1 to 5, characterized in that The spectrometer has at least two spatially separated light inputs for the measurement light.

8. The measuring device according to claim 7, characterized in that, Light with the same characteristics enters through each of the light inputs of the spectrometer.

9. The measuring device according to any one of the preceding claims, characterized in that, The measurement light is directed onto the detector rows such that the sum of the intensity values on the first detector row is approximately equal to the sum of the intensity values on the second detector row, particularly equal in the absence of interference modulation.

10. The measuring device according to any one of the above claims, characterized in that, The measuring device includes a reference arm, particularly a switchable reference arm.

11. The measuring device according to claim 1, characterized in that, All pixels of the first detector row are read individually, and the pixels of the second detector row are read pairwise or averaged in groups of N pixels.

12. An optical interferometric method, wherein light in a continuous wavelength band is directed onto the object to be measured by means of a measuring head, and the light reflected from the object to be measured via the measuring head and / or from a reference surface is input into a spectrometer, The spectrometer outputs a first spectrum of the interference result between the measurement light reflected from the first interface of the object under test and the measurement light reflected from at least one second interface of the object under test or from a reference interface to an evaluation device, wherein the first spectrum is composed of a discrete data series of intensity values within a wavelength range, characterized in that, the spectrometer outputs a second spectrum of the interference result between the measurement light reflected from the first interface of the object under test and the measurement light reflected from at least one second interface of the object under test or from a reference interface to an evaluation device, wherein the second spectrum is composed of a discrete second data series of intensity values within a wavelength range, and the number of data points per wavelength unit is greater than that of the first spectrum and wherein, based on the modulation of the spectrum, an optical path length difference is calculated from the two spectra by an evaluation unit.

13. The method according to claim 12, characterized in that, The total wavelength range covered by the first spectrum is greater than that of the second spectrum, and specifically, the total number of data points in the two spectra is the same.

14. The method according to claim 12 or 13, wherein the travel length difference calculated from the first spectrum and the travel length difference calculated from the second spectrum are combined and output in a concentrated manner.

Images