A dual-axis spectral line confocal sensor based on dual-band detection

Abstract

The present invention designs a biaxial spectral line confocal sensor based on dual-band detection, belonging to the technical field of three-dimensional surface measurement. The present invention includes: a light source assembly for providing the light radiation required for system measurement; an illumination assembly for shaping the illumination light and uniformly focusing different wavelengths at different axial positions on the measurement surface; a detection assembly for collecting the reflected light and providing an optical path conjugate to the illumination assembly to filter out the defocused wavelengths; and a spectral demodulation assembly for separating the two illumination bands and respectively recording the energy spectra containing the surface profile information of the measured sample in the two bands. The present invention combines a linear variable filter and a sub-band detection technique, solves the problems of the complex structures of the dispersion system and the spectral demodulation system and the contradiction between the spectral range and the spectral resolution of the spectral demodulation system, and realizes spectral line confocal sensing with a large measurement range and high axial resolution.

Description

Technical Field

[0001] The present invention relates to the technical field of three-dimensional surface measurement, and particularly to a dual-axis spectral line confocal sensor based on dual-band detection. Background Art

[0002] In recent years, with the breakthrough of the technology node in the integrated circuit industry, a large number of ultra-precision surface measurement devices are required in the mass production of electronic products to achieve non-contact detection of micro defects.

[0003] Spectral confocal technology is an important means for large-area sub-micron measurement. Spectral line confocal technology combines spectral confocal with laser line confocal. The slit provides line light source illumination, and the dispersion objective disperses the white light source axially. Different wavelengths are focused at different axial positions. The reflected light is focused at the detection slit through a symmetric optical path. At this time, only the wavelength that is exactly focused on the sample surface can be focused at the detection slit and pass through the detection slit. The focal spots of other wavelengths are larger than the slit size, and only a very small part of the energy can pass through the detection slit. By analyzing the spectral components of the reflected light passing through the detection slit, the surface profile of a scan line can be obtained. Although different wavelengths of light are focused at different axial positions, a complete confocal system is formed for each wavelength. Since spectral confocal technology retains the optical tomography ability of confocal measurement methods, it has a significant advantage in axial resolution compared with other surface measurement methods.

[0004] The main factor limiting the measurement accuracy of spectral confocal is the spectral resolution of the spectral demodulation system. Due to the limitation of the detector pixels, the spectral resolution of the spectral demodulation system is inversely proportional to the spectral range, and the spectral range determines the measurement range of the axial displacement. In measurement, the visible light band is generally used as much as possible, which greatly limits the resolution of the spectral demodulation system, and only the peak extraction algorithm can be used to improve the accuracy of contour positioning.

[0005] In addition, the existing spectral line confocal sensors generally have the problems of complex structures of the dispersion mirror group and the spectral demodulation system and large sizes, making it difficult to adapt to the measurement tasks in complex scenarios. Summary of the Invention

[0006] In view of the above-mentioned disadvantages of the prior art, the present invention proposes a dual-axis spectral line confocal sensor based on dual-band detection to solve the problems of insufficient spectral demodulation accuracy and complex structure in the technology.

[0007] The object of the present invention is achieved as follows:

[0008] A dual-axis spectral line confocal sensor based on dual-band detection includes: a light source assembly, an illumination assembly, a detection assembly, and a spectral demodulation assembly; wherein:

[0009] In the light source assembly, the LED light source emits broadband illumination light, which enters the fiber optic coupler, mixes and is conducted to the front of the illumination assembly.

[0010] In the illumination assembly, the broadband uniform linear illumination light emitted by the slit is dispersed into light bands evenly distributed according to wavelength by the first linear gradient filter, and then focused on different axial positions by the first dispersion objective lens. The focal lines of different wavelengths are evenly distributed on the measurement plane.

[0011] In the detection assembly, the reflected light from the surface of the sample to be measured carrying surface profile information is focused on the detection slit plane by the second dispersion objective lens symmetrically placed with the first dispersion objective lens. At this time, only the wavelength perfectly focused on the sample surface can be focused on the detection slit conjugate to the illumination slit, and the energy passing through the detection slit is the strongest. Other wavelengths are defocused, and the energy passing through the detection slit decreases according to the defocus distance.

[0012] In the spectral demodulation assembly, the collimating lens collimates the light passing through the detection slit and irradiates it on the dichroic mirror. The light is divided into two beams according to wavelength and respectively irradiated on the second linear gradient filter and the third linear gradient filter. The light passing through the second linear gradient filter and the third linear gradient filter is separated according to wavelength, and the energy spectra distributed according to wavelength are captured by the first CMOS camera placed behind the second linear gradient filter and the second CMOS camera placed behind the third linear gradient filter, obtaining the profile information of the surface of the sample to be measured.

[0013] Preferably, the wavelength range of the light emitted by the LED light source is λ 1 ~λ 2 , and in order to suppress the spectral non-uniformity caused by the overlap of different LED spectra contained in the LED light source, a notch filter can be used for suppression.

[0014] Preferably, the fiber optic coupler can be a spot fiber optic array or other forms of optical waveguide devices, forming a uniform line array illumination or line illumination in front of the illumination slit.

[0015] Preferably, the illumination slit emits broadband illumination with uniform illuminance.

[0016] Preferably, the spectral range of the first linear gradient filter is λ 1 ~λ 2 .

[0017] Preferably, the dispersion characteristic of the first linear gradient filter is k nm / mm, and the bands are evenly arranged at k nm per millimeter in the meridional direction.

[0018] Preferably, the first linear gradient filter filters the measurement band λ 1 ~λ 2It is evenly divided into countless sub - wavelengths along the sagittal direction according to different shooting positions, so that the light of different wavelengths propagates in different directions, realizing the dispersion in the sagittal direction.

[0019] Preferably, the first dispersive objective lens and the second dispersive objective lens have a large chromatic focal shift Δz, so that the focal planes of different wavelengths are at different axial depths, realizing the spectral encoding of the axial depth.

[0020] Preferably, the optical axis of the first dispersive objective lens has a certain angle θ with the measurement surface, and this angle θ is matched with the chromatic focal shift of the dispersive objective lens and the dispersion parameter of the linear - gradient filter, ensuring that the light of different wavelengths is focused on the measurement surface perpendicular to the surface of the measured sample.

[0021] Preferably, on the focal plane of the first dispersive objective lens, the axial range z 1 ~λ 2 corresponds to the wavelength band 1 ~z 2 .

[0022] Preferably, the first dispersive objective lens and the second dispersive objective lens are composed of at least one lens.

[0023] Preferably, the second dispersive objective lens and the first dispersive objective lens are symmetric about the measurement surface. The wavelength that is exactly focused on the surface of the measured sample, after passing through the second dispersive objective lens, is symmetric with the optical path between the illumination slit in the illumination component and the first dispersive objective lens. Other wavelength components cannot maintain the symmetric optical path due to defocusing.

[0024] Preferably, the detection slit has the same length as the illumination slit, and the width of the detection slit is equal to or less than the width of the illumination slit.

[0025] Preferably, the detection slit and the illumination slit are conjugate. Only the wavelength that is exactly focused on the surface of the measured sample can be focused on the detection slit. Other wavelength components, due to asymmetry, the light projected on the detection slit is not fully focused, the spot size is much larger than the width of the detection slit, and the light intensity passing through the detection slit is much smaller than that of the wavelength that is exactly focused on the surface of the measured sample, realizing the screening effect on the in - focus wavelength.

[0026] Preferably, the collimating lens is an achromatic lens, and the light of different wavelengths passing through the detection slit is shaped into parallel light after the detection lens.

[0027] Preferably, the dichroic mirror plays a beam - splitting role, and the angle between its normal and the optical axis of the collimating lens is 45°. The light in the wavelength band of λ 1 ~λ′ passes through the dichroic mirror, and the propagation direction remains unchanged; the light in the wavelength band of λ′~λ 2 is reflected by the dichroic mirror, and the direction leaving the dichroic mirror is perpendicular to the light beam in the wavelength band of λ 1 ~λ′.

[0028] Preferably, the dichroic mirror has the same transmittance / reflectance for different wavelengths to ensure the consistency of the measured signal intensity.

[0029] Preferably, the spectral range of the second linear variable filter is λ 1 ~λ′. The light beam in the λ 1 ~λ′ band leaving the dichroic mirror is irradiated on the second linear variable filter and dispersed in the sagittal direction to form an energy spectrum.

[0030] Preferably, the spectral range of the third linear variable filter is λ′~λ 2 , and the light beam in the λ′~λ 2 band leaving the dichroic mirror is irradiated on the third linear variable filter and dispersed in the sagittal direction to form an energy spectrum.

[0031] Preferably, the second linear variable filter and the third linear variable filter have the same transmittance for different wavelengths to ensure the consistency of the measured signal intensity.

[0032] Preferably, the first CMOS camera records the energy spectrum in the λ 1 ~λ′ band passing through the second linear variable filter, and extracts the wavelength with the highest energy to obtain the surface profile of the sample in the axial range z 1 ~z′.

[0033] Preferably, the second CMOS camera records the energy spectrum in the λ′~λ 2 band passing through the third linear variable filter, and extracts the wavelength with the highest energy to obtain the surface profile of the sample in the axial range z′~z 2 .

[0034] The beneficial effects of the present invention are as follows. Since the present invention combines a linear variable filter to achieve the spectral splitting function, the structures of the illumination component, the detection component, and the spectral demodulation component are simplified, the optical path structure is simplified, and the external dimensions of the spectral line confocal sensor are effectively reduced; by using dual-band and spectral demodulation, the contradiction between the spectral resolution and the spectral range of the spectral demodulation component is solved, a spectral demodulation component with a large spectral range and high spectral resolution is realized, and the axial measurement range and axial resolution of the spectral line confocal sensor are improved. Description of the Drawings

[0035] Figure 1 is a schematic diagram of the structure of a dual-axis spectral line confocal sensor based on dual-band detection.

[0036] Figure 2 is a schematic diagram of the structure of the illumination component.

[0037] Figure 3 is a schematic diagram of the structure of the spectral demodulation component.

[0038] Figure 1 Among them: 100 - light source assembly, 110 - LED light source, 120 - fiber optic coupler; 200 - lighting assembly, 210 - lighting slit, 220 - first linear gradient filter, 230 - first dispersion objective; 300 - detection assembly, 310 - detection slit, 320 - second dispersion objective; 400 - spectral demodulation assembly, 410 - collimating lens, 420 - dichroic mirror, 430 - second linear gradient filter, 440 - first CMOS camera, 450 - second CMOS camera, 460 - second linear gradient filter;

[0039] Figure 2 Among them: 210 - lighting slit, 220 - first linear gradient filter, 230 - first dispersion objective;

[0040] Figure 3 Among them: 410 - collimating lens, 420 - dichroic mirror, 430 - second linear gradient filter, 440 - first CMOS camera, 450 - second CMOS camera, 460 - second linear gradient filter. Specific embodiments

[0041] The following describes the embodiments of the present invention in detail with reference to the accompanying drawings.

[0042] As Figures 1 to 3 shown, the embodiments of the present invention include a light source assembly, a lighting assembly, a detection assembly, and a spectral demodulation assembly.

[0043] In the light source assembly (100): The spectral range of the LED light source (110) is 400 nm to 700 nm. The input optical path of the fiber optic coupler (120) and the first core diameter is a multimode fiber with a core diameter of 400 μm. The output optical path of the fiber optic coupler (120) is a light guide plate, which guides the light to the front of the lighting slit (210) and realizes uniform and continuous illumination within a rectangular area of 10 mm × 1 mm.

[0044] In the illumination component (200): The illumination slit (210) has a length of 10 mm and a width of 20 μm, and is closely attached to the light output path (133) of the fiber optic coupler, emitting uniform and continuous linear illumination light. The numerical aperture of the light beam output from the illumination slit (210) is controlled between 0.1 and 0.15 to match the object-side aperture angle of the first dispersive objective (230). The spectral range of the first linear gradient filter (220) is 400 nm to 700 nm, and the dispersion characteristic is 30 nm / mm. The range corresponding to 400 nm to 700 nm on the first linear gradient filter is 10 mm long in the meridional direction. The light output from the illumination slit (210) completely covers this range and does not change the propagation direction after filtering. The first dispersive objective (230) uniformly focuses light of different wavelengths on the measurement surface and performs spectral encoding on the axial displacement. Among them, 400 nm to 550 nm corresponds to an axial displacement of 0 to 0.6 mm; 550 nm to 700 nm corresponds to an axial displacement of 0.6 to 1.2 mm, realizing an axial measurement range of 1.2 mm.

[0045] In the detection component (300): The second dispersive objective (320) is symmetrically placed with respect to the first dispersive objective (230) with respect to the measurement surface. The second dispersive objective (320) has exactly the same structure as the first dispersive objective (230). The light irradiated on the surface of the measured sample returns to the second dispersive objective (320). The propagation path of the wavelength that is exactly focused on the sample surface after being processed by the second dispersive objective (320) is completely symmetric to the propagation path from the illumination slit (210) to the first dispersive objective (230), and can be focused on the detection slit (310) conjugate to the illumination slit (210). However, the wavelength that is not focused on the surface of the measured sample cannot be symmetrically focused on the detection slit (310). The detection slit (310) has a length of 10 mm and a width of 20 μm. The wavelength with the highest energy passing through the detection slit (310) is the wavelength that is exactly focused on the surface of the measured sample. The undulation of the surface profile of the measured sample is reflected by the different wavelengths passing through different positions of the detection slit (310).

[0046] In the spectral demodulation component (400): The collimating lens (410) is achromatically designed to shape the light of different wavelengths passing through the detection slit (310) into parallel light for subsequent processing. The normal of the dichroic mirror (420) forms an angle of 45° with the optical axis of the collimating lens (410). The collimated light is projected onto the dichroic mirror (420) and is split into two beams. The light with wavelengths from 400 nm to 550 nm does not change its propagation direction and irradiates on the second linear variable filter (430). The light with wavelengths from 550 nm to 700 nm is reflected by the dichroic mirror (420) and projected onto the third linear variable filter (460). The included angle between the two separated beams of light is 90°. The spectral range of the second linear variable filter (430) is 400 nm to 550 nm. To improve the spectral resolution, its dispersion characteristic is 10 nm / mm, and the effective area is 15 mm. The size of the chip of the first CMOS camera (440) is larger than 15 mm in both length and width, the number of pixels is not less than 2048, and the spectral response curve should cover the measurement spectral range. For the system integration design, the linear variable filter can be directly processed on the glass cover plate of the CMOS chip. The spectral range of the third linear variable filter (460) is 550 nm to 700 nm, the dispersion characteristic is 10 nm / mm, and the effective area is 15 mm. The requirements for the second CMOS camera (450) are the same as those for the first CMOS camera (440). At the same time, the transmittances of the second linear variable filter (440) and the third linear variable filter (460) for different wavelengths are consistent to ensure the measurement consistency. Finally, according to the energy spectra collected by the CMOS cameras, the surface profiles of the measured sample in the ranges of 0 to 0.6 mm and 0.6 to 1.2 mm can be obtained respectively. By fusing the data obtained by the two cameras, the surface profile of the measured sample in the full range of 0 to 1.2 mm can be obtained.

Claims

1. A dual-axis spectral confocal sensor based on dual-band detection, Characterized in that: It includes a light source component (100), an illumination component (200), a detection component (300), and a spectral demodulation component (400); the light source component includes an LED light source (110) and an optical fiber coupler (120), which mix and guide the light emitted by the LED light source (110) to the illumination component (200); the illumination component (200) includes an illumination slit (210), a first linear gradient filter (220), and a first dispersion objective lens (230), which uniformly project lights of different wavelengths onto the measurement surface; the detection component includes a second dispersion objective lens (320) and a detection slit (310), which are conjugated with respect to the measured surface, so that the reflected light from the measured surface is refocused at the detection slit (310), and the detection slit (310) is used to block the wavelengths that cannot be focused on the measured surface, and only allows the wavelengths that are exactly focused on the measured surface to pass through; the spectral demodulation component includes a collimating lens (410), a dichroic mirror (420), a second linear gradient filter (430), a third linear gradient filter (460), a first CMOS camera (440), and a second CMOS camera (450), which divide the light passing through the detection component into two beams according to two bands and demodulate their spectral components respectively to obtain the height information contained in the spectral energy distribution.

2. The dual-axis spectral confocal sensor based on dual-band detection according to claim 1, Characterized in that: The wavelength range of the LED light source (110) is λ 1 ~λ 2 , and the spectral distribution of the LED light source (110) is continuous and smooth.

3. The dual-axis spectral confocal sensor based on dual-band detection according to claim 1, Characterized in that: The LED light source (110) contains 1 to 2 LEDs, and the energy of each LED entering the optical fiber coupler (120) is the same, and the total spectral range covers λ1 to λ2.

4. The dual-axis spectral confocal sensor based on dual-band detection according to claim 1, Characterized in that: The illumination light emitted by the illumination slit (210) is uniform.

5. The dual-axis spectral confocal sensor based on dual-band detection according to claim 1, Characterized in that: The spectral range of the first linear gradient filter (220) is λ 1 ~λ 2 , which includes all of the spectral range emitted by the light source assembly (100).

6. The dual-axis spectral confocal sensor based on dual-band detection according to claim 1, Characterized in that: The optical axis of the first dispersion objective lens (230) forms a certain angle with the measured surface, and the axial dispersion generated matches the lateral dispersion generated by the first linear gradient filter (220), so that the focal lines of lights of different wavelengths are uniformly distributed on the measurement surface.

7. The dual-axis spectral confocal sensor based on dual-band detection according to claim 1, Characterized in that: The second dispersion objective lens (320) has the same structure as the first dispersion objective lens (230) in the illumination component.

8. The dual-axis spectral confocal sensor based on dual-band detection according to claim 1, Characterized in that: The collimating lens (410) is an achromatic lens group, and lights of different wavelengths are shaped into parallel light beams after passing through the collimating lens (410).

9. The dual-axis spectral confocal sensor based on dual-band detection according to claim 1, Characterized in that: The light wavelength range that is split by the dichroic mirror (420) and irradiated on the second linear variable filter (430) is λ 1 ~λ′, and the light wavelength range irradiated on the third linear variable filter (460) is λ′~λ 2 , the spectral range of the second linear variable filter (430) is λ1~λ′, and the spectral range of the third linear variable filter (460) is λ′~λ2.

10. A dual-axis spectral confocal sensor based on dual-band detection according to claim 1, characterized in that: The spectral responses, pixel numbers, and sizes of the first CMOS camera (440) and the second CMOS camera (450) are the same.

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