Method for measuring the height map of a test surface

Abstract

A method for measuring a height map of a test surface is disclosed, the method comprising performing measurements using a multi-sensor device including a pre-scan sensor and a height measurement sensor, the test surface having varying reflectivity. The multi-sensor device further comprises one or more light sources configured to illuminate the test surface and a spatial light modulator. The spatial light modulator is positioned in an optical path between the one or more light sources and a measurement location of the multi-sensor device and is configured to modulate light emitted from at least one of the light sources. The method comprises performing measurements to determine an illumination intensity map of the test surface and performing measurements to form a height map of the test surface.

Description

Technical Field

[0001] The present invention relates to a method of measuring a height map of a test surface having large reflectivity variations using a multi-sensor device including a spatial light modulator. Background Art

[0002] EP 2977720 B1 discloses a method for measuring a high-accuracy height map of a test surface using a multi-sensor optical profiler comprising a pre-mapping sensor and a high-resolution sensor. The method comprises measuring a coarse height map using the pre-mapping sensor, subdividing the coarse height map into a plurality of sections suitable for the field of view of the high-resolution sensor, and measuring the high-accuracy height map using the high-resolution sensor by scanning the test surface through the focal range of the high-resolution sensor.

[0003] In optical profilometry techniques such as confocal, white light interferometry, focus variation, and structured illumination microscopy, a light source is used to illuminate the test surface. Typically, the illumination intensity of the light source is set relative to the signal strength of the measurement device to achieve optimal performance.

[0004] In practice, a test surface can exhibit large differences in reflectivity within a field of view of a measurement device. These differences can be the result of the test surface comprising different materials with different optical properties in the field of view, the test surface having different angles and / or high angles and / or large angle variations on the test surface, shadows on the test surface caused by features such as steps on the test surface, and glint from sharp edges or defects on the test surface. These differences in reflectivity negatively impact the measurement quality of measurements of the test surface.

[0005] In the case of large local reflectivity variations on the test surface, the illumination intensity can be set, according to methods known in the art, so that the signal intensity received by the measurement device from the high reflectivity areas of the test surface is optimized for the measurement device. In this case, the signal in darker areas (e.g., areas with lower reflectivity) will be poor because the measurement device does not receive enough light for a high-quality measurement. The illumination settings optimized for the high-reflectivity areas negatively impact the measurement quality of the darker areas.

[0006] Similarly, the illumination intensity can be set so that the measurement sensor receives an optimized light intensity from low-reflectivity areas of the test surface, resulting in high-quality images of these areas. In this case, the image quality of brighter areas (e.g., areas with higher reflectivity) will be poorer due to, for example, oversaturation of the measurement device's sensor.

[0007] This problem can be reduced by using a measurement device that combines multiple measurements with different illumination intensities. In this case, separate measurements are taken using different light intensity settings of the light source. The images obtained in these separate measurements are then combined to produce a higher-quality image of the test surface, where the effects of differences in reflectivity of the test surface are reduced. The images can be combined, for example, by replacing areas of the image that reflected too much light to allow for adequate measurement with areas obtained using images with lower light intensities.

[0008] This approach to improving image quality reduces the throughput of the measurement device, as multiple high-quality images of the test surface must be acquired. Furthermore, effects such as height drift between two consecutive measurements can introduce errors into the combined measurement, negatively impacting the performance of the measurement device when multiple measurements are required.

[0009] There is a need for improved optical microprofilometry methods for test surfaces with reflectivity variations. Summary of the Invention

[0010] Therefore, a method is provided for measuring a height map of a test surface having varying reflectivity using a multi-sensor device comprising a pre-scan sensor and a height measurement sensor,

[0011] wherein the multi-sensor device further comprises one or more light sources configured to illuminate the test surface and a spatial light modulator, wherein the spatial light modulator is placed in a light path between the one or more light sources and a measurement location of the multi-sensor device, and wherein the spatial light modulator is configured to modulate light emitted from at least one of the light sources,

[0012] The method comprises:

[0013] - placing the test surface in the measuring position of the multi-sensor device;

[0014] - illuminating the test surface using one or more of the light sources;

[0015] - using the pre-scan sensor to measure the amount of light reflected from the test surface in the field of view of the pre-scan sensor;

[0016] - determining the reflectivity of the test surface in the field of view of the pre-scan sensor based on the pre-scan sensor's measurement of the amount of reflected light;

[0017] - determining an illumination intensity map based on a determination of reflectivity in the field of view of the pre-scan sensor;

[0018] - illuminating the test surface using one or more of the light sources (e.g., other of the one or more light sources);

[0019] - modulating light emitted by one or more of the light sources using the spatial light modulator based on the illumination intensity map to produce a modulated pattern of light on the test surface; and

[0020] - measuring a height map of the test surface by means of the height measurement sensor.

[0021] In practice, an optimal or improved signal for a measurement sensor can be achieved by setting the light intensity such that the maximum signal intensity is just below the saturation level of the measurement sensor. Thus, for a measurement sensor that measures light reflected from a test surface, the optimal light intensity is such that the maximum signal intensity received by the sensor from light reflected from the test surface is just below the saturation level of the sensor.

[0022] This method allows for measuring a test surface with varying reflectivity by using a spatial light modulator to increase the relative light intensity in areas of the test surface with lower reflectivity and decrease the relative light intensity in areas of the test surface with higher reflectivity. This allows for a relative increase in the light intensity measured by the height measurement sensor in areas of lower reflectivity of the test surface. Similarly, this also allows for a relative decrease in the light intensity measured by the height measurement sensor in areas of higher reflectivity of the test surface.

[0023] The multi-sensor device used in the method includes a pre-scan sensor for determining the reflectivity of the surface and a measuring sensor for measuring the height of the test surface. The pre-scan sensor does not need to be a sensor capable of measuring the height of the test surface. For example, the pre-scan sensor can use a camera to determine a focused 2D image of the test surface. In another embodiment, the pre-scan sensor can determine the reflectivity or other lighting-related characteristics of the test surface based on non-imaging techniques. For example, the pre-scan sensor can utilize reflection measurement or scatter measurement. This approach may not be suitable for measuring the height of the test surface, but may be suitable for determining the surface conditions (such as reflectivity) of the test surface relevant to the current method.

[0024] A height measurement sensor is used to measure a height map of the test surface. The height measurement sensor can be a white light interferometry sensor, a focus variation sensor, or a (non-scanning) structured illumination microscope. The height measurement sensor can use a lateral scan or a point from focus technique to determine the height map. Preferably, the pre-scan sensor measures the reflectivity of the test surface faster than the height measurement sensor measures the height map of the test surface. For example, the time required to measure the height map using the height measurement sensor is twice the time required to measure the reflectivity using the pre-scan sensor.

[0025] The field of view of the height measurement sensor may be different from the field of view of the pre-scan sensor. For example, the field of view of the height measurement sensor is 0.1 x 0.1 mm 2 , while the field of view of the pre-scan sensor may be much larger, such as 1x 1mm 2 In this case, fewer pre-scans are required to determine the reflectivity of the test surface, thereby speeding up the measurement process. In this example, 100 measurements using the height measurement sensor are required to fully cover the pre-scan sensor's field of view. In another example, the pre-scan sensor's field of view can completely encompass the test surface, and the height measurement sensor's field of view can be smaller. In another example, both the pre-scan sensor's field of view and the height measurement sensor's field of view completely encompass the test surface.

[0026] The multi-sensor device also includes one or more light sources for illuminating the test surface. In a measuring microscope, there are many possible light sources and many possible light source orientations relative to the measurement setup for illuminating the test surface. For example, the wavelength of the light emitted by the light source can be adjusted to improve measurement quality depending on the test surface and sensor type used.

[0027] In an embodiment of the measuring device used in the method according to the invention, the illumination of the light source can be coaxial with the measuring axis of the height measurement sensor or the pre-scan sensor. This is suitable, for example, when the measurement is performed using the height measurement sensor as a white light interferometry sensor. Other options for the relative orientation are measurement setups in which the illumination is provided at an oblique angle relative to the measuring axis or from below the test surface (for example, from below a transparent test surface such as a lens). In another example, in which the height measurement sensor utilizes a shape from focus method, the measurement is less dependent on which illumination method is used. Similarly, if the pre-scan sensor is a simple imaging sensor, the light source during the measurement of the reflectivity of the test surface does not have to be coaxial with the pre-scan sensor.

[0028] The optimal combination of lighting and sensing methods may depend on the test surface of the sample being measured. For example, if the test surface includes steps, lighting from multiple directions can improve the performance of the measurement device because the steps are illuminated from multiple directions and the effects of shadows are minimized.

[0029] Other factors related to the illumination in the measurement device, such as the wavelength of the light, wavelength distribution, pulse frequency and / or pulse length, may also be configured to provide optimal illumination for the pre-scan sensor and / or height measurement sensor given the sample to be measured.

[0030] The spatial light modulator can be a digital micromirror device type, a ferroelectric liquid crystal on silicon type, or any other suitable type of spatial light modulator. The spatial light modulator is placed in the optical path between one or more light sources and the measurement position of the multi-sensor device. Light emitted by at least one of the one or more light sources used to illuminate the test surface during the measurement of the height map can be modulated by the spatial light modulator before being reflected by the test surface placed in the measurement position of the multi-sensor device. This produces a modulation pattern on the test surface. The modulation pattern allows brighter areas to receive lower light intensities and darker areas to receive higher light intensities. The modulation pattern can include different levels of light intensity, for example, several areas with different higher light intensities and several areas with different lower light intensities.

[0031] The spatial light modulator is configured to modulate light based on the illumination intensity map. The modulation pattern is used to improve the altimeter sensor's measurement of the altimeter map, thereby providing the altimeter sensor with optimal light intensity. The spatial light modulator can modulate light so that the light intensity of each pixel of the altimeter sensor is optimal. The optimal light intensity can be the light intensity that allows the altimeter sensor to operate optimally and produce the highest measurement quality.

[0032] Before taking a height measurement, a prescan is performed, where the prescan includes the following steps: placing the test surface in a measurement position; illuminating the test surface with one or more light sources; and using a prescan sensor to measure the amount of light reflected from portions of the test surface within the prescan sensor's field of view. Thus, the prescan measurement is used to obtain information about the reflectivity of the test surface by measuring the intensity of light reflected from different areas of the test surface.

[0033] Pre-scan measurements can also include measuring the location of sharp edges and defects. To counteract glint from sharp edges or defects in height measurements, it is beneficial to know the location of these features. For example, during height measurements, the effect of glint can be eliminated by using a spatial light modulator to set the relevant local illumination intensity to zero.

[0034] The light intensity information is then converted into an illumination intensity map by determining the reflectivity of a surface in the field of view of the pre-scan sensor based on the pre-scan sensor's measurement of the amount of reflected light, and determining an illumination intensity map (preferably an optimal illumination intensity map) based on the determination of the reflectivity in the field of view of the pre-scan sensor. The illumination intensity map includes information regarding a preferred modulation pattern for the test surface to allow for improved height measurement of the test surface.

[0035] The illumination intensity map can be viewed as a map of the test surface that includes information about the reflectivity of the test surface obtained from the pre-scan measurements, as well as information about the illumination settings of the light source and the settings of the spatial light modulator. The resolution of the illumination intensity map can be equal to the resolution of the height measurement sensor and / or the resolution of the pre-scan sensor. The illumination intensity map can also include additional information, such as the location of flashes or defects, information about the color of the test surface, and / or information about the material type of the test surface.

[0036] To perform height measurement, a test surface is illuminated using one or more light sources, and light emitted by a second light source of the one or more light sources is modulated using a spatial light modulator based on an illumination intensity map to produce a modulation pattern on the test surface. The height map is measured by a height measurement sensor, preferably during improved measurement conditions for the height measurement sensor.

[0037] The measurement quality may be optimal when the modulation pattern on the test surface is such that the maximum signal intensity received by the height measurement sensor is just below the saturation level of the measurement sensor. Preferably, the light reflected from the test surface during measurement of the height map has a substantially uniform intensity such that the maximum signal intensity is just below the saturation level of the measurement sensor.

[0038] By using the method according to the present invention, and in particular by modulating light with a spatial light modulator and generating a modulation pattern on the test surface according to the method according to the present invention, height measurement of a test surface is improved. High throughput can be maintained because there is no need to combine multiple height measurements with different illumination intensities. Furthermore, by using the method to modulate the light intensity to an improved value for height measurement across the field of view of the height measurement sensor and / or across the test surface, the problem of setting the light intensity relative to brighter and / or darker areas of the test surface is alleviated.

[0039] According to an embodiment of the present invention, wherein the pre-scan sensor has a larger field of view than the height measurement sensor, the method further comprises:

[0040] - subdividing the illumination intensity map into subfields, each of the subfields corresponding to a field of view of the height measurement sensor;

[0041] - illuminating a subfield of the test surface using one or more of the light sources;

[0042] - modulating light emitted by one or more of the light sources using the spatial light modulator based on the illumination intensity map to produce a modulation pattern of light on an illuminated subfield of the test surface;

[0043] - measuring a height map of the illuminated sub-field by means of the height measurement sensor;

[0044] - repeating the above three steps for each subfield of the test surface, thereby obtaining a height map of each subfield of the test surface; and

[0045] - stitching the height maps of the sub-fields to form a height map of the test surface.

[0046] The throughput of multi-sensor systems can be improved when a single prescan is combined with multiple height measurements. The prescan can measure a large portion of the test surface, while the height measurements must be performed multiple times to produce a complete height map of the test surface. In practice, this can occur when the prescan sensor has a larger field of view than the height measurement sensor.

[0047] To allow this method to exploit the larger field of view of the pre-scan sensor, the illumination intensity map can be cut into sub-fields, where each sub-field corresponds to the field of view of the height measurement sensor. For example, the pre-scan sensor has measured a 1x1 cm area of the test surface. 2 part, and the height measurement sensor can have 1x 1mm 2 The field of view is then compared to the 1x 1cm field of view of the test surface. 2 The part corresponds to the size of the sheet and can be cut into 100 pieces of 1x 1mm 2 This allows 100 height measurements to be taken after a single prescan, which are used to measure the height map of the prescanned sensor's field of view. Since in this case only one prescan is required instead of 100, throughput is increased.

[0048] After subdividing the illumination intensity map into subfields, each subfield of the test surface is illuminated by one of the one or more light sources. A spatial modulator then modulates the light emitted onto each subfield based on the illumination intensity map, generating a modulation pattern on the test surface. This allows the light intensity in each subfield to be optimized for the height measurement sensor during height measurements in that subfield.

[0049] After height measurements are taken in each subfield, the corresponding height maps of each subfield are stitched together to form a height map of the test surface. The stitching can be performed using known methods.

[0050] According to an embodiment, the illumination intensity map is further based on performance data of the pre-scan sensor regarding received light intensity and / or wherein the modulation pattern on the test surface is additionally based on performance data of the height measurement sensor regarding received light intensity.

[0051] This embodiment allows for compensation for inherent differences in measurement techniques between the pre-scan sensor and the height measurement sensor. Such differences may be the result of differences in the intensity of the modified light for each measurement technique and / or differences in the light sources used. Performance data can be obtained through simulated measurements, trial and error, and / or repeated use of a multi-sensor device.

[0052] In addition to the determined reflectivity of the test surface, the optimal light intensity and illumination intensity map can be determined based on additional factors. In this embodiment, the illumination intensity map is additionally based on the performance data of the pre-scan sensor regarding the received light intensity. This allows the illumination intensity map to be created based on, for example, a known bias of the pre-scan sensor.

[0053] The modulation pattern on the test surface may additionally be based on performance data of the height measurement sensor regarding the intensity of received light.

[0054] According to an embodiment, the size of the modulation pattern of the modulated light corresponds to the resolution of the altimeter sensor. This embodiment allows for optimization of light intensity for each pixel of the altimeter sensor. Therefore, the size of the modulation pattern of the light modulated by the spatial light modulator can correspond to the pixel size of the altimeter sensor. This improves image quality because it allows each pixel of the altimeter sensor to receive a signal just below the saturation level of that pixel.

[0055] According to an embodiment, the method further comprises dynamically modulating the illumination while the height measurement sensor is measuring. For example, measurements of microlenses and similar transparent and translucent objects may be best performed by not only specifying the local illumination laterally to a static setting via a spatial light modulator, but also dynamically changing the illumination as the measurement proceeds. By using this approach, the top of the microlens can be illuminated with one illumination setting, while the bottom surface of the lens is illuminated by another illumination setting. This embodiment may also be advantageous for measuring thin films, particularly where there are variations in the thickness of the film or near the edges of the film. This may further be advantageous for measuring materials where the transparency varies laterally. In another example of this embodiment, the illumination is dynamically modulated while the height measurement sensor is measuring by using strobed illumination. During strobed illumination, the test surface is illuminated using regular flashes of light emitted by one or more light sources.

[0056] According to an embodiment, the method further comprises configuring at least one of the wavelength, wavelength distribution, pulse frequency, or pulse length of the light emitted by the light source during illumination of the test surface. The configuration of the wavelength (in other words, the color of the light) can improve the efficiency of the measurement. For example, the reflectivity of the light can depend on the color of the test surface, and improved reflectivity can be achieved when the light has a color similar to that of the test surface. This further allows the use of monochromatic light with a small wavelength band as well as white light with a wide wavelength band.

[0057] Configuring the pulse frequency and / or pulse length of the light may be helpful, for example, if gated illumination is utilized during the measurement process.

[0058] According to an embodiment, the method further comprises using additional information, such as at least one of the location of sharp edges, the color of the test surface or the material type of the test surface, to determine the illumination intensity map.

[0059] Knowledge of the location of sharp edges can improve height measurements. Furthermore, the color and material type of the test surface can influence the performance of the height measurement sensor, for example through improved reflectivity or better contrast. Using this additional information can be helpful in improving the quality of the height map measurement.

[0060] According to an embodiment, the pre-scan sensor is configured to measure additional information (such as at least one of the location of sharp edges, the color of the test surface, or the material type of the test surface) to determine the illumination intensity map. Using the pre-scan to detect such information can improve the throughput of the measurement device because no additional sensors are required to obtain such information.

[0061] According to an embodiment, the pre-scan sensor is configured to measure a light intensity range that includes both the darkest and brightest portions of the test surface. Depending on the test surface characteristics, some portions of the test surface may appear very dark or very bright relative to the rest of the test surface. Measurements taken with the pre-scan sensor can provide an understanding of these portions. To avoid having to perform multiple pre-scans due to the pre-scan sensor's inability to accurately measure very bright or very dark portions, and thereby improve the throughput of the measurement device, the pre-scan sensor is preferably configured to obtain accurate reflectance data for both dark and bright portions of the test surface.

[0062] According to an embodiment, the method further comprises using a pre-scan sensor with a large depth of field to measure the amount of light reflected by the test surface in the field of view of the pre-scan sensor. A pre-scan with a large depth of field can obtain an image of the test surface that is relatively sharp at both the upper and lower portions of the test surface. Using a pre-scan sensor with a large depth of field relaxes the requirement for strict focus on the test surface to determine surface properties such as reflectivity. This allows for faster pre-scan measurements. For example, in the case of a test surface with large height differences, if both the upper surface area and the lower surface area are sufficiently focused by the pre-scan sensor, the pre-scan measurement can be performed in a single measurement.

[0063] According to an embodiment, the pre-scan sensor is adapted to measure the height of the test surface, wherein the height measurement sensor preferably has a higher height resolution than the pre-scan sensor. This allows a rough height map of the test surface to be measured during the pre-scan. Having information about the height differences of the test surface prior to measurement, preferably at a higher resolution, can have several advantages. For example, it allows for more accurate stitching of different measurement areas, more accurate height measurements using the height measurement sensor, and faster height measurements using the height measurement sensor.

[0064] According to an embodiment, the pre-scan sensor uses a non-imaging method such as reflectometry or scatterometry to perform measurements. For example, the pre-scan sensor uses a non-imaging method such as reflectometry or scatterometry to measure the amount of reflected light or other lighting-related properties such as surface roughness or surface height. These types of pre-scan sensors operate point by point on the test surface, so in order to cover the area of the test surface, the test surface must be scanned laterally.

[0065] According to an embodiment, the height measurement sensor measures the height map using white light interferometry, non-scanning structured illumination microscopy, focus variation or lateral scanning techniques. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which like reference numerals indicate like parts, and in which:

[0067] Figure 1 A flow chart showing a method according to the present invention;

[0068] Figure 2 Showing high contrast examples of test surfaces;

[0069] Figure 3 A pre-scan sensor of a multi-sensor device is shown measuring the amount of light reflected from a test surface;

[0070] Figure 4 Shown based on Figure 3 a height measurement sensor of a multi-sensor device for measuring a height map of a test surface by performing a pre-scan measurement;

[0071] Figure 5a Show Figure 3 The field of view of the pre-scan sensor;

[0072] Figure 5b Shown based on Figure 3 a modulation pattern of the field of view of the test surface measured by the pre-scan sensor;

[0073] Figure 5cshowing the effect of the modulation pattern on the test surface; and

[0074] Figure 5d Show Figure 4 Use Figure 5b Height map of the test surface measured with the modulation pattern. DETAILED DESCRIPTION

[0075] Figure 1 A flow chart of the method according to the invention is shown, wherein the pre-scan sensor 3 has a larger field of view 10 than the height measuring sensor 4 and the illumination intensity map has been subdivided into subfields.

[0076] The blocks of the flow chart depict the steps of the method according to the invention. In a first step 100 according to the invention, a test surface 2 is placed in a measuring position of a multi-sensor device 5. The test surface 2 preferably has a large reflectivity variation, such as Figure 2 . The measurement position of the multi-sensor device 5 is, for example, positioned such that the test surface 2 can be focused by the pre-scan sensor 3 and the height measurement sensor 4. The measurement position may also include means for supporting the test surface 2 in this position, which means that the test surface 2 may be movably supported.

[0077] In a second step 110, test surface 2 is illuminated using one or more light sources 6. Illumination of test surface 2 is performed to allow pre-scan sensor 3 to measure the amount of light reflected from test surface 2 in field of view 10 of pre-scan sensor 3 in a next step 120 according to the method. Illumination of test surface 2 can be performed coaxially with the pre-scan measurement, or illumination can be performed along another axis depending on the measurement method used by the pre-scan sensor. In embodiments according to the present invention, the pre-scan measurement can be improved by configuring the illumination characteristics. For example, the wavelength of the light emitted by light source 6 can be used to improve the measurement quality depending on test surface 2 and the type of sensor used.

[0078] Pre-scan measurement 120 for measuring the amount of light reflected from test surface 2 utilizes pre-scan sensor 3. Pre-scan sensor 3 need not be a sensor capable of measuring the height of test surface 2. Pre-scan sensor 3 is preferably optimized for measuring the intensity of light reflected from test surface 2. Pre-scan sensor 3 can be a focused 2D image of test surface 2 using a camera. In another embodiment, pre-scan sensor 3 can utilize reflectometry or scatterometry to determine reflectivity.

[0079] After taking the pre-scan measurement 120, the reflectivity of the test surface 2 in the field of view 10 of the pre-scan sensor 3 is determined 130. Due to various factors, such as the presence of steps and sharp edges or variations in material type, the reflectivity of the test surface 2 may vary significantly across the field of view 10 of the pre-scan sensor 3. The reflectivity of the test surface 2 may be determined based on the amount of light received by the pre-scan sensor 3 and the amount of light emitted by the one or more light sources 6. The reflectivity of the test surface 2 may be lower in areas 12 that appear darker in the pre-scan measurement than in areas 13 that appear lighter in the pre-scan measurement. In situations where the field of view 10 of the pre-scan sensor 3 is insufficient to adequately measure the test surface 2, multiple pre-scans may be taken to determine the reflectivity of the test surface 2.

[0080] Based on the determination of the reflectivity in the field of view 10 of the pre-scan sensor 3, an illumination intensity map 140 is determined. The illumination intensity map includes information regarding the preferred illumination settings for height measurement. This information may include the settings of the spatial light modulator 7, one or more light sources 6, the location of defects, steps, or flashes, and other relevant information. The illumination map also includes information regarding the preferred modulation pattern 9 to be projected onto the test surface 2 to allow for improved height measurement of the test surface 2 using the height measurement sensor 4.

[0081] The resolution of the illumination intensity map may be equal to the resolution of the height measurement sensor 4 and / or the resolution of the pre-scan sensor 3 .

[0082] The illumination intensity map is subdivided 150 into subfields, each subfield corresponding to the field of view 11 of the height measurement sensor 4. Preferably, the illumination intensity map is subdivided into subfields such that the subfields fully cover the illumination intensity map. In a subsequent step, the height measurement sensor 4 performs a height measurement in each subfield.

[0083] When pre-scanning is combined with multiple height measurements, the throughput of the multi-sensor device 5 can be improved. The pre-scan sensor 3 can measure a large portion of the test surface 2, while the height measurement must be performed multiple times to measure the height of the test surface 2. Figure 1 In practice, this may be the case when the pre-scan sensor 3 has a larger field of view 10 than the height measurement sensor 4. In order to maximize the throughput of the multi-sensor device 5, the number of sub-fields is preferably kept to a minimum while covering the illumination intensity map.

[0084] Before taking 180 height measurements in the subfields, the subfields are illuminated 160 using one or more light sources 6. A spatial light modulator 7 is used 170 to modulate the light emitted by the one or more light sources 6 to produce a modulation pattern 9 of light on the illuminated subfields of the test surface 2 based on the illumination intensity map.

[0085] Modulation pattern 9 is used to improve the height measurement sensor 4 Figure 1The spatial light modulator 7 can modulate the light so that the light intensity of each pixel of the height measurement sensor 4 can be optimized.

[0086] The height of the 180° illuminated subfield is measured using the height measurement sensor 4. Figure 1 The illuminated subfields are illuminated by one or more light sources 6, which are modulated by a spatial light modulator 7 to allow for improved height Figure 1 The measured modulation pattern 9.

[0087] Steps 160, 170 and 180 are repeated for each subfield of the illumination intensity map. In this way, the height of each subfield is measured. Figure 1 To obtain the height of the test surface 2 Figure 1 , the height corresponding to the subfield Figure 1 Splice 190 to form the height of the test surface 2 Figure 1 The splicing can be performed by known methods.

[0088] Figure 2 A high contrast example of test surface 2 is shown. Figure 2 The test surface 2 is a chrome-on-glass sample, wherein two squares on the test surface 2 are formed of chrome 14 and two squares on the test surface 2 are formed of glass 15. The reflectivity index of chrome is approximately 90%, and the reflectivity index of glass is approximately 4%.

[0089] Configuring the light source 6 to provide an illumination intensity that allows for improved height measurement of the chrome 14 does not allow for height measurement of the glass 15, since the light reflected by the glass 15 will not be sufficient to provide a signal in the height measurement sensor 4. The result is that Figure 2 The image shown, in which the glass 15 appears as dark squares.

[0090] If the light source 6 is configured to provide an illumination intensity that allows an improved height measurement of the glass 15 , the chrome 14 will reflect too much light and the height measurement sensor 4 will not emit a signal due to oversaturation. Figure 2 This possibility is not shown.

[0091] Figure 3 Prescan sensor 3 of multi-sensor device 5 is shown, configured to measure the amount of light reflected from test surface 2. Test surface 2 has a regular contour. Prescan sensor 3's field of view 10 shows test surface 2 including darker areas 12 and lighter areas 13. Darker areas 12 are spherical surfaces regularly placed on test surface 2. Due to the curvature of the spherical surface, light reflects away from prescan sensor 3 near the sphere's equator. These areas appear darker. The sphere's poles and background reflect light back toward prescan sensor 3. These areas appear lighter.

[0092] The device comprises a light source 6 for illuminating the test surface 2 in the measurement position. The device also comprises several lenses 17 for directing the light emitted by the light source 6 and reflected by the test surface. A beam splitter 16 is positioned to allow the light from the light source 6 to be coaxial with the reflected light captured by the pre-scan sensor 3.

[0093] The pre-scan sensor 3 is configured to measure a range of light intensities including darker areas 12 and lighter areas 13. As can be seen from the figure, there is a sharp contrast between the brightest and darkest areas. By using the measurements of the pre-scan sensor 3, detailed knowledge of the reflectivity in these areas can be obtained.

[0094] As can be seen from the figure, the field of view 10 of the pre-scan sensor 3 is smaller than the surface of the test surface 2. Therefore, preferably, the pre-scan sensor 3 performs multiple measurements to collect information related to the reflectivity of the test surface 2. The multiple fields of view 10 obtained in these multiple measurements can be stitched together to create a reflectivity map of the entire test surface 2.

[0095] Figure 4 Shown based on Figure 3 Pre-scan measurement to measure the height of the test surface 2 Figure 1 The multi-sensor device 5 includes a height measurement sensor 4. The device includes a light source 6 for illuminating a test surface 2. Light emitted by the light source 6 travels toward the test surface 2 through a plurality of lenses 17, interacts with a spatial light modulator 7, and is redirected by a mirror 18 and a beam splitter 16.

[0096] exist Figure 4 The size of the field of view 11 of the height measurement sensor 4 is approximately equal to Figure 3 The size of the field of view 10 of the pre-scan sensor 3.

[0097] The light reflected from the test surface 2 travels coaxially towards the height measurement sensor 4 .

[0098] The spatial light modulator 7 used by the multi-sensor device 5 can be a digital micromirror device type, a ferroelectric liquid crystal on silicon type, or any other suitable type of spatial light modulator 7. As can be seen from the figure, the spatial light modulator 7 is placed in the optical path 8 between one or more light sources 6 and the measurement position of the multi-sensor device 5.

[0099] The light emitted by the light source 6 is modulated by the spatial light modulator 7 before being reflected by the test surface 2 placed in the measuring position of the multi-sensor device 5. This produces a spatial light modulator 7 on the test surface. Figure 5bThe modulation pattern 9 is visible in FIG. The modulation pattern 9 allows brighter areas to receive lower light intensities and darker areas to receive higher light intensities. The modulation pattern may include nine different levels of light intensity, for example, several areas with different higher light intensities and several areas with different lower light intensities.

[0100] The spatial light modulator 7 is used to modulate the light based on the illumination intensity map. The modulation pattern 9 is used to improve the height measurement sensor 4 to measure the height. Figure 1 The spatial light modulator 7 can modulate the light so that the light intensity of each pixel of the height measurement sensor can be optimized.

[0101] Figure 5a Show Figure 3 The field of view 10 of the pre-scan sensor 3, Figure 5b Shown based on Figure 3 the modulation pattern 9 of the field of view of the test surface 2 measured by the pre-scan sensor 3, Figure 5c shows the effect of the modulation pattern 9 on the test surface, and Figure 5d Show Figure 4 Use Figure 5b The height of the test surface measured by the modulation pattern 9 Figure 1 .

[0102] Figure 5a 、 5b , 5c and 5d all correspond to or show the same area of the test surface 2. Figure 5a The field of view 10 of the pre-scan sensor 3 is shown. Figure 5b A corresponding modulation pattern 9 based on an illumination diagram according to the invention is shown. Figure 5c Shown in use Figure 5b The field of view 11 of the height measurement sensor 4 when the modulation pattern 9 illuminates the test surface 2 is shown. Figure 5d The height obtained by using the method of the present invention is shown Figure 1 .

[0103] from Figure 5b As can be seen, the modulation pattern 9 ensures that a relatively low light intensity reaches Figure 5a The result can be seen in Figure 5c As can be seen from the figure, the light intensity on the sphere is Figure 5a By using this modulation pattern 9 , the height measurement sensor 4 can accurately measure the height of the test surface 2 without being hindered by oversaturation or too little light.

Claims

1. A method for measuring a height map of a test surface having varying reflectivity, said method comprising: performing the measurement using a multi-sensor device comprising a pre-scan sensor and a height measurement sensor; in, The multi-sensor device further comprises one or more light sources configured to illuminate the test surface and a spatial light modulator, wherein the spatial light modulator is placed in a light path between the one or more light sources and a measurement location of the multi-sensor device, and wherein the spatial light modulator is configured to modulate light emitted from at least one of the light sources, The method comprises: - placing the test surface in the measuring position of the multi-sensor device; - illuminating the test surface using one or more of the light sources; - using the pre-scan sensor to measure the amount of light reflected from the test surface in the field of view of the pre-scan sensor; - determining the reflectivity of the test surface in the field of view of the pre-scan sensor based on the pre-scan sensor's measurement of the amount of reflected light; - determining an illumination intensity map based on a determination of reflectivity in the field of view of the pre-scan sensor; - illuminating the test surface using one or more of the light sources; - modulating light emitted by one or more of the light sources using the spatial light modulator based on the illumination intensity map to produce a modulated pattern of light on the test surface; and - measuring a height map of the test surface by means of the height measurement sensor, wherein the pre-scan sensor has a larger field of view than the height measurement sensor, and wherein the method further comprises: - subdividing the illumination intensity map into subfields, each of the subfields corresponding to a field of view of the height measurement sensor; - illuminating a subfield of the test surface using one or more of the light sources; - modulating light emitted by one or more of the light sources using the spatial light modulator based on the illumination intensity map to produce a modulation pattern of light on an illuminated subfield of the test surface; - measuring a height map of the illuminated sub-field by means of the height measurement sensor; - repeating the above three steps for each subfield of the test surface, thereby obtaining a height map of each subfield of the test surface; and - stitching the height maps of the sub-fields to form a height map of the test surface.

2. The method for measuring a height map according to claim 1, wherein: The illumination intensity map is further based on performance data of the pre-scan sensor with respect to received light intensity, and / or wherein the modulation pattern on the test surface is additionally based on performance data of the height measurement sensor with respect to received light intensity.

3. The method for measuring a height map according to claim 1, wherein: The size of the modulation pattern on the test surface corresponds to a measurement resolution of the height measurement sensor.

4. The method for measuring a height map according to claim 1, wherein: The method also includes dynamically modulating illumination while the height measurement sensor is measuring.

5. The method for measuring a height map according to claim 1, wherein: The method also includes configuring at least one of a wavelength, a wavelength distribution, a pulse frequency, or a pulse duration of light emitted by the light source during illumination of the test surface.

6. The method for measuring a height map according to claim 1, wherein: The method further comprises using additional information to determine the lighting intensity map.

7. The method for measuring a height map according to claim 6, wherein: The pre-scan sensor is configured to measure the additional information to determine the lighting intensity map.

8. The method for measuring a height map according to claim 1, wherein: The pre-scan sensor is configured to measure a range of light intensities that includes the darkest and lightest portions of the test surface.

9. The method for measuring a height map according to claim 1, wherein: The method includes using a pre-scan sensor with a large depth of field to measure the amount of light reflected by the test surface in the field of view of the pre-scan sensor.

10. The method for measuring a height map according to claim 1, wherein: The pre-scan sensor is adapted to measure the height of the test surface.

11. The method for measuring a height map according to claim 1, wherein: The pre-scan sensor uses a non-imaging method to make measurements.

12. The method for measuring a height map according to claim 1, wherein: The height measurement sensor measures the height map using white light interferometry, non-scanning structured illumination microscopy, focus variation, or lateral scanning techniques.

13. The method for measuring a height map according to claim 1, wherein: One or more of the light sources used to illuminate the test surface is another of the one or more light sources than the light source used for the pre-scan sensor measurements.

14. The method for measuring a height map according to claim 6, wherein: The additional information is at least one of a location of a sharp edge, a color of the test surface, and a material type of the test surface.

15. The method for measuring a height map according to claim 7, wherein: The additional information is at least one of a location of a sharp edge, a color of the test surface, and a material type of the test surface.

16. The method for measuring a height map according to claim 10, wherein: The height measurement sensor has a higher height resolution than the pre-scan sensor.

17. The method for measuring a height map according to claim 11, wherein: The non-imaging method is reflectometry or scatterometry.

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