Optical interference measurement device and method

Abstract

The present invention provides an optical interference measurement device including a light source generating measurement light over a continuous wavelength range and a measurement head optically connected to the light source, directing the measurement light toward a measurement object and receiving the measurement light reflected from the measurement object. The spectrometer outputs a first spectrum resulting from interference between the measurement light reflected from a first interface of the measurement object and the measurement light reflected from at least one second interface or reference interface of the measurement object to an evaluation device. The spectrometer includes at least one grating element for fanning out the measurement light introduced into the spectrometer according to wavelength, and a first detector array including a plurality of detector pixels onto which the fanned measurement light is directed. The first spectrum includes a series of intensity values ​​measured at the detector pixels. The evaluation device calculates the optical path difference between the first interface and the second interface or reference surface from the spectrum. The optical spectrometer further includes a second detector array onto which the fanned measurement light is directed, the second detector array also including a plurality of detector pixels. A second spectrum comprises a series of intensity values ​​measured at detector pixels of the second detector row, the first spectrum covering substantially the entire wavelength range at a first resolution and the second spectrum covering a portion of the wavelength range at a higher resolution.

Description

[Technical Field]

[0001] The present invention relates to an optical interference measurement device comprising a light source, a measurement head, and an optical spectrometer. The light source is configured to generate measurement light in at least a continuous wavelength range. The measurement head is optically connected to the light source and directs the measurement light toward a measurement object and receives the measurement light reflected from the measurement object. The optical spectrometer outputs a first spectrum of the interference result between the measurement light reflected from a first interface of the measurement object and the measurement light reflected from at least one second interface of the measurement object or 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, and a first detector array comprising a plurality of detector pixels onto which the fanned measurement light is directed. The first spectrum comprises a series of intensity values ​​measured by the detector pixels of the first detector array. 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 measurement method. [Background technology]

[0002] Many industrial sectors require highly accurate measurements of surface shapes or layer thicknesses for quality assurance purposes, e.g., offline or in-process during wafer production (box / warpage / total thickness variations), in the production of display glass or medical glass, or in various high-precision manufacturing processes. A suitable non-contact method for such measurements is interferometry using low-coherence light.

[0003] This typically involves directing light of a predetermined continuous wavelength band onto the sample to be measured, and interfering with the light reflected from two different interfaces of the measurement object, or from one interface of the measurement object and a reference surface. This interference is analyzed as a function of wavelength by a spectrometer, advantageously using a Fourier transform of the spectrum, and 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. The applicant sells such a measuring instrument, for example under the name CHRocodile 2 IT.

[0004] The spectrum of the interfering light is typically detected by a photosensitive detector consisting of a large number of discrete pixels, so that, given the number of pixels and the wavelength band used, each pixel detects a small range of wavelengths and the detected spectrum consists of a series of discrete points.

[0005] The thicker the layer being measured, the more limited the spectral modulation. Therefore, there is an upper limit to the layer thickness that a detector can resolve. To measure thicker layers, it is necessary to increase pixel density, which results in increased cost and slower readout, or to narrow the detection range of each pixel using a narrower wavelength band. However, using a narrower wavelength band results in insufficient modulation to detect thin layers, making it impossible to measure thin layers. The lower limit of the measurement range is defined by the spectrometer's bandwidth, while the upper limit is defined by the minimum resolvable bandwidth (pixel size and spot quality). As a result, the ratio between the upper and lower limits of the measurement range of a measurement instrument is constant. Therefore, different measurement instruments must be used depending on the application. For a measurement target containing layers of significantly different thicknesses, there may not be an appropriate measurement instrument that can detect all layers. Summary of the Invention

[0006] In view of this, an object of the present invention is to provide an interference measurement device in which the ratio between the upper and lower limits of the measurement range is increased without significantly affecting the cost and readout speed.

[0007] The technical solution to achieve the above-mentioned object of the present invention is as follows: the optical spectrometer includes at least one second detector row, to which the fan-shaped measurement light is directed and which comprises a plurality of detector pixels, the second spectrum being a series of intensity values ​​measured by the detector pixels of the second detector row, the first spectrum covering substantially the entire wavelength range of a first resolution, and the second spectrum covering a part of a wavelength range of a higher resolution.

[0008] The portion of the wavelength range advantageously includes less than half of the entire wavelength range.

[0009] In a preferred embodiment of the invention, the portion of the wavelength range is approximately in the middle of the entire wavelength range. It is also advantageous to select the portion so that it includes the wavelengths at which the light source emits the most light, with the advantage of maximizing the light intensity.

[0010] Depending on the specific application, it may be advantageous to select the part of the wavelength range depending on the transparency of the measurement object, in particular to select a range in which the measurement sample is particularly transparent. This is important, for example, for measurement objects made of silicon, whose transparency varies greatly in the near-infrared range. The increased transparency allows thick layers to be measured without light losses.

[0011] Another aspect to consider is the best imaging or simplest realization that can be achieved.

[0012] In a preferred embodiment of the invention, the grating element comprises two subgratings: a first subgrating that deflects the measurement light over the entire wavelength range so that it is fanned out over the length of the first detector row, and a second subgrating that deflects a portion of the wavelength range so that it is further fanned out over the length of the second detector row. The choice of two subgratings allows for particular flexibility in the design of the measurement device.

[0013] Advantageously, the subgratings form spatially separated regions of the grating element, with different portions of the measuring light beam falling on these regions. For example, the left region of the grating element can form the first subgrating, and the right region of the grating element can form the second subgrating. These two subgratings can be arranged on the same bracket, which requires separate setting options for angle adjustment.

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

[0015] In an alternative preferred embodiment of the invention, the first and second sub-gratings of the grating element have different numbers of lines, in which case the gratings are arranged with a slight tilt relative to each other.

[0016] In a preferred embodiment of the invention, the spectrometer has a single optical input end for measurement light, the beam being expanded by a collimating optical system, with the two sub-gratings each partially within the beam.

[0017] In another preferred embodiment of the present invention, the spectrometer has at least two optical inputs for measurement light that are spatially separated, in particular light having the same properties, i.e., light carrying the same interference information, passing through each of the optical inputs.

[0018] In this embodiment, the grating elements are preferably configured as continuous gratings and have different input coupling points into the spectrometer, resulting in different incidences on the grating elements and, consequently, different fan-outs at the first and second detector rows.

[0019] Advantageously, the measurement light is directed individually to the detector rows so 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 in the absence of interferometric modulation, thereby ensuring that the signal strength is approximately the same on average in each case and that no detector row is over- or under-exposed.

[0020] In a preferred embodiment of the invention, the measurement device includes a reference arm that includes a reflective reference surface from which the path length difference is measured, the reference surface representing a fixed reference point, for example for shape measurements.

[0021] Advantageously, the measuring device, more precisely the measuring head, can be moved relative to the measurement object, so that the shape or the local thickness distribution can be measured. Instead of the entire measuring head, it is also possible to scan only the measuring point, for example by using a scanning mirror.

[0022] In a preferred embodiment of the invention, all pixels of the first detector row are read out individually, and the pixels of the second detector row are read out in pairs or averaged in groups of N pixels. This has the advantage that different resolutions can be generated purely electronically. This method is faster than a method that reads out all pixels of an entire row sequentially. Instead of using two separate detector rows, the two readout methods can also be applied to the same detector row at different times.

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

[0024] Advantageously, the first spectrum covers a wider overall wavelength range than the second spectrum, and in particular the total number of data points in these two spectra is the same, i.e., wavelength range λ A ~λ D The first intensity spectrum is output, and the spacing between data points in the spectrum is Δλ1. Similarly, B ~λ C where the spacing of the data points is Δλ2, where Δλ1>Δλ2 and λ A ≦λ B ≦λ C ≦λ D and λ C -λ B <λ D -λ A is.

[0025] In accordance with 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 output together, providing a single list of values ​​to the user, possibly along with a graphical display of the spectra. This requires compensation and cancellation for values ​​within the overlap range where the two spectra provide an assessable result.

[0026] The measuring device and method also allow simultaneous measurements on thick samples with thin layers applied, where the thin layer must be read out from a small measuring area and the total thickness must be read out from a larger measuring area. From the outside, the device appears to have only a single measuring area.

[0027] It is particularly preferable to transfer information related to thin layers to the measurement results of thick layers. For example, in a measurement object having interfaces H, J, and K, if the distance between H and J is large and the distance between J and K is relatively small, a low-resolution spectrum over the entire wavelength range will provide the value of layer thickness JK, but not the values ​​of layer thicknesses HJ and HK. A high-resolution spectrum over a subrange will show interference between HJ and HK, but will not be able to distinguish or resolve these interferences individually. An average value is output. Currently, information related to layer thickness JK is used to provide HJ and HK, respectively, and the specific method is to recalculate the average value. [Brief explanation of the drawings]

[0028] Further features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings. [Figure 1] 1 is a measuring device according to the present invention. [Figure 2] 1 is an optical spectrometer of a measuring device according to the present invention. [Figure 3] Another optical spectrometer. [Figure 4-5] This is the form in which it is input into a spectrometer and combined. [Figure 6] 1 is an exemplary measurement device with a reference arm. [Figure 7-8] 1 is an exemplary spectrum. [Figure 9] This is processing for detector pixels. DETAILED DESCRIPTION OF THE INVENTION

[0029] 1 shows a measuring device according to the present invention. The measuring device includes a light source 1 that emits measuring light in a continuous wavelength band. Advantageously, the light is in the visible or near-infrared range, for example, with wavelengths of 960 nm to 1090 nm or 1250 nm to 1370 nm. The light source may be a known light-emitting element such as an LED or an SLD.

[0030] The measurement light is then guided to the measurement head 3 via the first optical fiber 2, and the measurement head forms an image of the measurement light on the measurement object 4. The measurement light is reflected by one or more interfaces of the measurement object 4, and at least a portion of the reflected light is received again by the measurement head 3.

[0031] The returning measurement light is introduced into another optical fiber 6, which is coupled to the first optical fiber 2, for example via an optical fiber coupler 5. The measurement light is then introduced via the other optical fiber 6 into the optical input end 8 of a spectrometer 7, which detects an intensity spectrum within a wavelength range. This spectrum is transmitted to an evaluation device 9, which calculates a thickness value from the spectral data. Details of the spectrometer 7 are shown in the following figure.

[0032] 2 shows an optical spectrometer of a measuring device according to the present invention. The spectrometer 7 shown in FIG. 2 is used as the optical spectrometer in the device shown in FIG.

[0033] Although the imaging optical system is shown here for simplicity as a single lens, it may be comprised of multiple optical elements, such as lenses and mirrors.

[0034] The spectrometer 7 has an optical input end 8 to which measurement light is input. The measurement light is then collimated by a first optical system 11 and impinges on a grating element 12, which consists of two gratings, subgrating 12a and subgrating 12b. Each spatial region of the collimated beam is contained in one of the subgratings.

[0035] Here, a reflective grating is shown, but embodiments having a transmission grating are also included.

[0036] Subgrating 12a and subgrating 12 are configured to cause different dispersions of light. In this variant of the invention, the two spectral ranges are determined by the two diffraction gratings used, allowing for great freedom in the selection of these two spectral ranges. In the embodiment shown, the two subgratings are diffraction gratings with the same number of lines (e.g., 300 lines / mm) but arranged at different angles or orientations.

[0037] The light reflected by the grating element 12 is imaged onto a detector 14 via a focusing optical system 13. The detector 14 includes at least two detector rows 14a and 14b, each consisting of a series of light-sensitive pixels that can convert the intensity of incident light into an electrical signal. The detector may also be referred to as an area detector (matrix detector) in which at least two rows are used.

[0038] Although the principles herein have been described with two detector rows, the present invention also includes corresponding implementations using three or more detector rows.

[0039] Here, the light reflected by the grating element 12a is shown by a solid line. The subgrating 12a is spatially positioned and tilted so that light of a certain diffraction order, for example the second diffraction order, is imaged onto the first detector array 14a. The line count of the subgrating 12a and the imaging characteristics of the focusing optics 13 are selected so that the entire wavelength range of the measurement light is imaged in a fan-like fashion over the length of the detector array 14a.

[0040] Here, the light reflected by the grating element 12b is indicated by a dashed line. The subgrating 12b is spatially arranged and tilted so that light of a higher diffraction order than that used by the subgrating 12a is imaged onto the second detector row 14b. For example, the fourth diffraction order. Advantageously, the subgrating 12b is tilted not only in the spatial direction of the division (transverse to the line) relative to the subgrating 12a, but also in the spatial direction along the line, so that the light falls on another detector row. Here, the number of lines in the subgrating 12b and the imaging characteristics of the focusing optics 13 are selected so that only a portion of the wavelength range of the measurement light is imaged, fanning out over the length of the detector row 14b. Preferably, this portion includes less than half of the entire wavelength range.

[0041] To simplify the device, subgratings 12a and 12b preferably have the same number of lines and differ only in their orientation, but alternatively, the number of lines may also be different, so that the relative spatial tilt of the subgratings in the splitting direction can be chosen to be small or even zero.

[0042] Advantageously, subgratings 12a and 12b are positioned within the beam to deflect approximately the same total intensity to these two detector rows 14a and 14b, i.e., the interface between subgratings 12a and 12b is not at the center of the beam but is offset so that more light falls on subgrating 12b.

[0043] In exemplary embodiments of the invention, this portion of the wavelength range is approximately in the middle of the overall wavelength range and / or refers to the portion where light source 1 provides maximum intensity.

[0044] For example, the entire wavelength range emitted and utilized by the light source may include near-infrared light from 960 nm to 1090 nm, with the portion including 1055 nm to 1090 nm. Alternatively, the entire wavelength range emitted and utilized by the light source may include near-infrared light from 1250 nm to 1370 nm, with the portion including 1290 nm to 1320 nm. Such a wavelength range is particularly advantageous for measuring silicon or similar materials that are transparent in the near-infrared range. Depending on the application, wavelength bands in the visible range may also be considered.

[0045] For example, the entire wavelength range may be fanned out over at least substantially the entire length of the first detector row 14a, while only a portion of the wavelength range may be fanned out over the same length of the second detector row 14b. Because the two detector rows contain the same number of detector pixels, the spectrum produced from the data in the second detector row 14b will have a higher resolution per wavelength unit than the spectrum produced from the data in the first detector row 14a, although the two detector rows output the same number of data points.

[0046] The data from these two detector rows are then transmitted to an evaluation device. These two spectra are analyzed by the evaluation device. Specifically, each spectrum is corrected and Fourier transformed in a known manner to identify the modulation frequency corresponding to a certain path length difference between the reflecting surfaces. As mentioned above, when the path length difference is large (close to the upper limit of the measurement range of the instrument), the spectrum of the data from detector row 14a cannot properly resolve the modulation because the modulation is denser than the distance between the data points. On the other hand, the spectrum of the data from detector row 14b can be evaluated because the wavelength band range used here is narrow and the data points are denser. The opposite is true when the path length difference is small (close to the lower limit of the measurement range of the instrument), and the data from detector row 14a can be evaluated better. In this case, the spectrum of the data from detector row 14b does not show sufficient modulation.

[0047] That is, from these two spectra, a distinguishable optical thickness or path length difference between two surfaces can be identified, which may refer to multiple interfaces of the measurement object or a single interface of the measurement object, as well as a reference surface within the measurement device.

[0048] The resulting thickness values ​​are then compared to identify agreement within the range in which the two spectra provide assessable results. A list of the combined thickness values ​​is then output to the user. Optionally, a graphical overlay of the two spectra or the two Fourier transform spectra may be output for visual display.

[0049] FIG. 3 shows another exemplary optical spectrometer.

[0050] As an alternative to the configuration with two different sub-gratings shown in FIG. 2, only a single grating may be used, as shown in FIG. 3. Here, the grating images the diffracted measurement light of two different diffraction orders onto corresponding detector rows. To achieve a spatial offset between these two spectra, the input light must be coupled into the spectrometer via two points in space. In this variant, the ranges of these two spectra are not freely selectable as in the previous variant.

[0051] In this embodiment, light is coupled into the spectrometer via two spatially separated inputs 8a and 8b. An implementation of these two inputs is described below in FIG. 4. The light from the two inputs 8a and 8b is collimated by an optical system 111, which may consist of multiple optical elements, and directed onto an optical diffraction grating 112. The diffracted light is then imaged onto a detector 14 by a focusing optical system 113, which may also consist of multiple optical elements. This detector embodiment corresponds to the detector described with reference to FIG. 2 and includes at least two detector rows 14a and 14b, or a matrix detector in which two rows are used. The diffraction grating shown here is a transmission grating, but in principle it could also include a reflection grating.

[0052] Input end 8a is spatially positioned relative to grating 112 and detector 14 so that light of a certain diffraction order of the grating, e.g., the third diffraction order, is imaged onto detector array 14a. The spectrometer elements are selected and positioned so that substantially the entire wavelength range of the measurement light is imaged as a fan across the length of detector array 14a.

[0053] Meanwhile, the second input end 8b is positioned a distance from the input end 8a so that light in the higher diffraction orders of the grating, e.g., the fourth diffraction order, is imaged onto the detector array 14b. Because the diffraction orders are higher, the light is more strongly fanned out, so that only a portion of the entire wavelength range is imaged across the length of the detector array.

[0054] Preferably, the input ends 8a and 8b are offset both in the spatial direction parallel to the grating lines (to image onto two different detector rows 14a and 14b) and in the spatial direction transverse to the grating lines and the optical axis (to accommodate different diffraction orders).

[0055] The principle of light incidence onto the detector array is the same as that described with respect to Figure 2. Further processing and evaluation is performed as described herein.

[0056] Although the principles herein have been described with two detector rows, the invention also includes implementations using three or more detector rows.

[0057] That is, by appropriately selecting the diffraction orders, the grating tilt angle, and the distance between the two input ends, it is possible for the two subspectra in the detector plane to have the same width or to overlap.

[0058] Another technical solution of the present invention is a combination of the technical solution of Figure 2 and the technical solution of Figure 3. There are also two sub-gratings with different orientations or characteristics, and two spaced apart optical input ends. Light from each optical input end is fanned out by the sub-gratings with different line counts and / or orientations, and each is directed to one detector row.

[0059] 4 and 5 show the configuration of the input coupled to the spectrometer 7 of FIG.

[0060] Figure 4 shows a free-beam technical solution. Light from optical fiber 6 originating from the measurement head exits optical fiber end 40 and is split into two beams by beam splitter 41, as shown here. The cube beam splitter can split the light 50 / 50 or any other ratio, preferably so that the total intensity at each of detector rows 14a and 14b is the same, as shown in Figure 2. The beam is then deflected by polarizing mirrors 42a and 42b, making the central beam parallel. The light is then further processed as described with reference to Figure 3, with the positions of input ends 8a and 8b corresponding to virtual light source points behind polarizing mirrors 42a and 42b.

[0061] Figure 5 shows an implementation using fiber optics. An optical fiber 6 extending from the measurement head is connected to two other optical fibers via an optical fiber coupler 50, and the light is split between these two optical fibers. Again, an appropriate split ratio can be selected as described above. The light then exits the ends of the optical fibers corresponding to the spectrometer inputs 8a and 8b.

[0062] FIG. 6 shows an exemplary measurement device with a reference arm. FIG. 5 corresponds to the device shown in FIG. 1 , with the addition of a reference arm 10 connected to an optical fiber coupler 5. Part of the light from the light source 1 is introduced into the reference arm 10 instead of into the measurement head 3, reflected by a reference surface 60, and then directed along the same path to the optical fiber coupler 5. There, the light from the reference arm is combined with the light from the measurement head 3 and directed into an optical fiber 6 toward the spectrometer 7. Alternatively, an embodiment may be employed in which the reference arm directs all or part of the light as a free beam without passing through an optical fiber. Specifically, in this case, a beam splitter is used instead of the optical fiber coupler.

[0063] The height position of the object can be measured relative to a fixed reference point using the reference arm 10. By scanning the measurement points on the object, a topographical map can be created.

[0064] A combined measurement configuration may be employed in which the thickness of one or more layers of the measurement object is measured (by interference between light reflected at different interfaces of the measurement object) and the shape of the measurement object relative to a fixed point is measured by a reference arm. A turnable reference arm may also be employed.

[0065] FIG. 7 shows an example spectrum for a large path length difference.

[0066] Here, the intensity signal on detector row 14a is shown graphically as 70a. From this, spectrum 71a is produced. Correspondingly, the intensity signal on detector row 14b is shown as 70b, with the corresponding spectrum 71b. As can be seen, the interference modulation is so dense that it cannot be resolved by spectrum 71a, but can be resolved by spectrum 71b.

[0067] FIG. 8 shows an example spectrum for small path length differences.

[0068] The detector signal and spectrum correspond to FIG. 7, where the modulation can be better resolved by spectrum 71a.

[0069] FIG. 9 shows a schematic diagram of the processing of detector pixels in another optical measurement device.

[0070] Instead of physically fanning out the measurement light with a spectrometer, as shown in the previous figure, the spectral resolution and number of data points can also be set electronically. This allows the use of a single switchable detector row, although implementations with two detector rows simultaneously providing different resolutions may also be employed.

[0071] This is the basis for so-called "pixel binning", which allows adjacent pixels of a detector row to be read out in groups.

[0072] A line detector is used that allows pixels to be read out together by binning. This allows, for example, a detector originally having 2048 pixels to use only 1024 pixels (two binned pixels combined) for faster processing. At the same time, the detector can read out 2048 unbinned pixels, but only half of them are used for faster processing as well. It is also possible to read out only a portion of the pixels, for example pixels 512 to 1536. Advantageously, a portion of the column is read out. This results in two readout positions that can be performed faster and, above all, in the same way in downstream processing.

[0073] The device can be switched between small and large measurement ranges during operation by pixel binning without changing the signal processing within the device, allowing devices with large measurement ranges to be realized even when computer resources are limited.

[0074] The entire spectral range is imaged onto the detector over the entire length of the column. The spot size of the optical image on the detector must be less than or equal to the pixel size of the detector (the size of an unbinned pixel).

[0075] By binning or ignoring half of the pixels, two spectral ranges and two measurement ranges can be evaluated in further processing using the same optical configuration (and the same light source) and software.

[0076] The entire spectral range of the light source is imaged onto the detector array. In the first mode, all pixels can be read out individually, but half of the pixels are still unused. The unused pixels must be adjacent, i.e. they form a geometric block. A small spectral range is therefore read out efficiently. This allows large path length differences to be measured. In the second mode, adjacent pixels are read out in pairs. Due to the entire spectral range, small path length differences can be measured with the interferometric instrument. Both modes can be used without any changes to further processing in the controller.

[0077] Advantageously, the modes are switched depending on the specific properties of the object being measured. It is also possible to switch between modes continuously and rapidly in order to measure different path length differences almost simultaneously.

[0078] A first mode is shown schematically as M1 in Figure 9, in which all pixels of the detector row are read out and transmitted to the evaluation device 9. A second mode is shown as M2, in which pixels are read out in pairs and the sum or average value of each pair is transmitted to the evaluation device 9. An alternative second mode is shown as M3, in which pixels are read out in groups of four instead of in pairs, and can also be generally summarized as groups of N pixels.

[0079] The example above can also be used with two columns (again, there is only one light source and one spectrometer, but the spectrum is split over two or more columns as above, but the fan-out in the two columns is the same). Therefore, modes 1 and 2 can be used separately, or possibly in parallel.

[0080] Other alternative technical solutions not shown in the drawings can also be considered.

[0081] In this implementation, the detector consists of only one row, but the optical system has a variable focal length. Therefore, the spectral width imaged onto the detector is variable. This technical solution is complex and cannot simultaneously detect two spectral ranges / resolutions, but it can work with fewer detector rows.

[0082] Only one grating may be used, but the angle of the grating may be adjustable, allowing for switching between different grating sequences.Technical solutions based on the principle of Figure 3 may also be employed, but with switching between input ends, for example, by means of a fiber optic switch.

Claims

1. a light source configured to generate measurement light in at least a continuous range of wavelengths; a measurement head optically connected to the light source, directing measurement light toward the measurement object and receiving measurement light reflected from the measurement object; an optical spectrometer that outputs to an evaluation device a first spectrum of an interference result between the measurement light reflected from the first interface of the measurement object and the measurement light reflected from at least one second interface or a reference interface of the measurement object; The optical spectrometer comprises: at least one grating element for fanning out the measurement light introduced into the spectrometer according to wavelength; a first detector array onto which the fanned measurement light is directed and which comprises a plurality of detector pixels; the first spectrum comprises a series of intensity values ​​measured at detector pixels of the first detector row; the evaluation device is an optical interference measurement device configured to calculate an optical path difference between the first interface and the second interface or a reference surface from the spectrum, the optical spectrometer includes at least one second detector row toward which the fanned measurement light is directed and which comprises a plurality of detector pixels, the second spectrum comprising a series of intensity values ​​measured at the detector pixels of the second detector row; the first spectrum includes substantially the entire wavelength range at a first resolution; The second spectrum includes a portion of the wavelength range with higher resolution.

2. 2. The measurement device of claim 1, wherein the grating element includes two subgratings: a first subgrating that deflects measurement light for the entire wavelength range so that it fans out over the length of the first detector row, and a second subgrating that further deflects a portion of the wavelength range so that it fans out over the length of the second detector row.

3. 3. The measuring device of claim 2, wherein the subgratings form spatially separated regions of the grating element, different portions of the beam of measuring light falling on said regions.

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

5. 4. The measuring device according to claim 2, wherein the first and second sub-gratings of the grating element have different numbers of lines.

6. 6. The measuring device according to claim 1, wherein the spectrometer has a single optical input end for the measuring light.

7. 6. The measuring device according to claim 1, wherein the spectrometer has at least two optical inputs for the measuring light, which are spatially separated.

8. 8. The measurement device of claim 7, wherein light having the same characteristics is incident through each of the optical input ends of the spectrometer.

9. 9. The measuring device according to claim 1, wherein the measuring light is directed individually to the detector rows so that the sum of the intensity values ​​on the first detector row and the sum of the intensity values ​​on the second detector row are approximately equal, in particular in the absence of interferometric modulation.

10. Measuring device according to any one of claims 1 to 9, characterized in that it comprises a reference arm, in particular an onable reference arm.

11. 2. The measurement device of claim 1, wherein all pixels of the first detector row are read out individually and the pixels of the second detector row are read out in pairs or averaged in groups of N pixels.

12. The measurement head directs light in a continuous wavelength band onto the object to be measured. inputting light reflected from the measurement object via the measurement head and / or light reflected from a reference surface into a spectrometer; outputting, by the spectrometer, a first spectrum of an interference result between the measurement light reflected from the first interface of the measurement object and the measurement light reflected from at least one second interface or a reference interface of the measurement object to an evaluation device; 1. An optical interferometry method, wherein the first spectrum comprises a discrete data sequence of intensity values ​​within a wavelength range, outputting, by the spectrometer, a second spectrum of the interference result between the measurement light reflected from the first interface of the measurement object and the measurement light reflected from at least one second interface or reference interface of the measurement object to an evaluation device; the second spectrum comprises a second discrete data series of intensity values ​​within a wavelength range, the second spectrum having a greater number of data points per wavelength unit than the first spectrum; 10. A method for measuring optical interference, characterized in that an optical path length difference is calculated from the two spectra by an evaluation unit based on the modulation of the spectra.

13. 13. The method of claim 12, wherein the first spectrum covers a wider overall wavelength range than the second spectrum, and specifically, the total number of data points in the two spectra is the same.

14. 14. The method according to claim 12, wherein the path length difference calculated from the first spectrum and the path length difference calculated from the second spectrum are integrated and output together.

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