CN115307569A - A dual-axis spectral line confocal sensor based on dual-band detection - Google Patents

Abstract

The invention designs a dual-axis spectral line confocal sensor based on dual-band detection, and belongs to the technical field of three-dimensional surface type measurement. The invention comprises the following steps: a light source assembly for providing optical radiation required for system measurement; the illumination assembly is used for shaping illumination light and enabling different wavelengths to be uniformly focused on different axial positions on the measuring surface; the detection assembly is used for collecting reflected light, providing a light path conjugated with the illumination assembly and filtering out defocusing wavelength; and the spectrum demodulation component is used for separating the two illumination wave bands and respectively recording the energy spectrums of the two wave bands containing the surface profile information of the tested sample. The invention combines the linear gradient filter and the sub-band detection technology, solves the problems of complex structure of a dispersion system and a spectrum demodulation system and the contradiction between the spectrum range and the spectrum resolution of the spectrum demodulation system, and realizes the spectral line confocal sensing with large range and high axial resolution.

Description

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

technical field

The invention relates to the technical field of three-dimensional surface measurement, in particular to a dual-axis spectral line confocal sensor based on dual-band detection.

Background technique

In recent years, with the technological node breakthrough of the integrated circuit industry, a large number of ultra-precision surface measurement equipment is required in the mass production of electronic products to realize the non-contact detection of tiny defects.

Spectral confocal technology is an important means of large-area submicron measurement. Spectral line confocal technology combines spectral confocal and laser line confocal. , different wavelengths are focused at different axial positions. The reflected light is focused at the detection slit through the symmetrical optical path. At this time, only the wavelengths that are just focused on the sample surface can be focused at the detection slit and pass through the detection slit. A portion of the energy is able to pass through the detection slit. Analysis of the spectral components of the reflected light passing through the detection slit allows the surface profile to be obtained on one scan line. Although light of different wavelengths is focused at different axial positions, a complete confocal system is formed for each wavelength. Since spectral confocal technology retains the optical tomographic capabilities of confocal measurement methods, it has a significant advantage in axial resolution compared to other surface measurement methods.

The main thing that limits the accuracy of spectral confocal measurement 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 the measurement, the visible light band is generally used as much as possible, which greatly limits the resolution of the spectral demodulation system, and the accuracy of contour positioning can only be improved through the peak extraction algorithm.

In addition, the existing spectral line confocal sensors generally have the problems of complex structure and large size of the dispersion mirror group and spectral demodulation system, which are difficult to adapt to the measurement tasks of complex occasions.

Contents of the invention

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

The purpose of the present invention is achieved like this:

A dual-axis spectral line confocal sensor based on dual-band detection, including: a light source component, an illumination component, a detection component, and a spectral demodulation component; wherein:

In the light source assembly, the LED light source emits broad-spectrum illumination light, which enters the fiber coupler to mix and transmit to the front of the illumination assembly.

In the lighting assembly, the wide-spectrum uniform linear illumination light emitted by the slit is dispersed into light bands evenly distributed according to wavelength through the first linear gradient filter, and then focused on different axial positions by the first dispersion objective lens, and different wavelengths The focal line is evenly distributed on the measuring surface.

In the detection component, the reflected light on the surface of the sample to be tested carries surface profile information and is focused on the detection slit plane by the second dispersive objective lens symmetrically placed with the first dispersive objective lens. At this time, only the wavelengths that are perfectly focused on the sample surface can be focused on the illumination On the detection slit conjugated to the slit, the energy passing through the detection slit is the strongest, while other wavelengths are defocused, and the energy passing through the detection slit is weakened according to the defocus distance.

In the spectral demodulation component, the collimator lens collimates the light passing through the detection slit and irradiates it on the dichroic mirror, and divides it into two beams of light according to the wavelength and irradiates them on the second linear gradient filter and the third linear gradient filter respectively. On-chip, the light passing through the second linear gradient filter and the third linear gradient filter is separated by wavelength, the first CMOS camera is placed after the second linear gradient filter and the third linear gradient filter is placed The second CMOS camera behind the chip captures the energy spectrum distributed according to the wavelength, and obtains the profile information of the surface of the tested sample.

Preferably, the wavelength range of the light emitted by the LED light source is λ ₁ -λ ₂ , in order to suppress the spectral inhomogeneity caused by the overlapping of different LED spectra contained in the LED light source, a notch filter can be used to suppress it.

Preferably, the optical fiber coupler may be a point fiber array, or other forms of optical waveguide devices, forming uniform line array illumination or line illumination before the illumination slit.

Preferably, said illumination slit emits broad-spectrum illumination with uniform illumination.

Preferably, the spectral range of the first linear gradient filter is λ ₁ -λ ₂ .

Preferably, the dispersion characteristic of the first linear gradient filter is k nm/mm, and there are k nm bands uniformly arranged per millimeter in the meridional direction.

Preferably, the first linear gradient filter divides the wavelength band λ ₁ to λ ₂ used for measurement into countless sub-wavelengths evenly along the sagittal direction according to the different positions of the radiation, so that the directions of light propagation of different wavelengths are different, realizing Dispersion in the sagittal direction.

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

Preferably, the optical axis of the first dispersive objective lens has a certain angle θ with the measuring surface, and the included angle θ is matched with the chromatic focal shift of the dispersive objective lens and the dispersion parameter of the linear gradient filter to ensure that light of different wavelengths is focused on The measuring plane perpendicular to the surface of the sample to be measured.

Preferably, the λ ₁ -λ ₂ band on the focal plane of the first dispersive objective lens corresponds to the axial range z ₁ -z ₂ .

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

Preferably, the second dispersive objective lens and the first dispersive objective lens are symmetrical with respect to the measurement plane, and are just focused on the wavelength of the measured sample surface passing through the second dispersive objective lens and between the illumination slit in the illumination assembly and the first dispersive objective lens The optical path of the other wavelength components is symmetrical, and the other wavelength components cannot maintain a symmetrical optical path due to defocus.

Preferably, the length of the detection slit is the same as that of the illumination slit, and the width of the detection slit is equal to or smaller than that of the illumination slit.

Preferably, the detection slit is conjugate to the illumination slit, and only the wavelengths that are just focused on the surface of the sample to be measured can be concentrated on the detection slit, and other wavelength components are projected on the detection slit due to asymmetry. It is not fully focused, the spot size is much larger than the width of the detection slit, and the light intensity through the detection slit is much smaller than the wavelength just focused on the surface of the sample to be measured, thus realizing the screening effect of the in-focus wavelength.

Preferably, the collimator 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.

Preferably, the dichroic mirror dichroic mirror acts as a beam splitter, the angle between its normal line and the optical axis of the collimator lens is 45°, and the light in the λ ₁ ~ λ' band passes through the dichroic mirror and propagates The direction remains unchanged; the light in the λ′～λ ₂ band is reflected by the dichroic mirror, and the direction leaving the dichroic mirror is perpendicular to the light beam in the λ ₁ ～λ′ band.

Preferably, the dichroic mirrors have the same transmittance/reflectance for different wavelengths, so as to ensure the consistency of the measured signal intensity.

Preferably, the spectral range of the second linear gradient filter is λ ₁ ~ λ', the light beam leaving the dichroic mirror λ ₁ ~ λ' band is irradiated on the second linear gradient filter, along the sagittal direction Dispersion, forming an energy spectrum.

Preferably, the spectral range of the third linear gradient filter is λ′～λ ₂ , the light beam leaving the dichroic mirror λ′～λ ₂ band is irradiated on the third linear gradient filter, along the sagittal direction Dispersion, forming an energy spectrum.

Preferably, the second linear gradient filter and the third linear gradient filter have the same transmittance at different wavelengths, so as to ensure the consistency of the measured signal intensity.

Preferably, the first CMOS camera records the energy spectrum passing through the second linear gradient filter in the λ ₁ -λ' band, and extracts the wavelength with the highest energy to obtain the surface profile of the sample in the axial range z ₁ -z'.

Preferably, the _second CMOS camera records the energy spectrum passing through the third linear gradient filter λ'~ _λ2 band, and extracts the wavelength with the highest energy to obtain the surface profile of the sample in the axial range z'~z2.

The beneficial effect of the present invention is that, because the present invention combines the linear gradient filter to realize the spectroscopic function, the structure of the illumination assembly, the detection assembly and the spectrum demodulation assembly is simplified, the optical path structure is simplified, and the shape of the spectral line confocal sensor is effectively reduced Size; using dual-band and spectral demodulation solves the contradiction between the spectral resolution and spectral range of the spectral demodulation component, realizes a spectral demodulation component with a large spectral range and high spectral resolution, and improves the axial direction of the spectral line confocal sensor Measuring range and axial resolution.

Description of drawings

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

Fig. 2 is a schematic diagram of the structure of the lighting assembly.

Fig. 3 is a schematic diagram of the structure of the spectrum demodulation component.

In Figure 1: 100-light source assembly, 110-LED light source, 120-fiber coupler, 200-illumination assembly, 210-illumination slit, 220-first linear gradient filter, 230-first dispersive objective lens, 300-detection Components, 310-detection slit, 320-second dispersive objective lens, 400-spectral demodulation component, 410-collimator lens, 420-dichroic mirror, 430-second linear gradient filter, 440-first CMOS Camera, 450-the second CMOS camera, 460-the second linear gradient filter;

In Fig. 2: 210-illumination slit, 220-the first linear gradient filter, 230-the first dispersion objective lens;

In Fig. 3: 410-collimating lens, 420-dichroic mirror, 430-the second linear gradient filter, 440-the first CMOS camera, 450-the second CMOS camera, 460-the second linear gradient filter .

Detailed ways

The implementation examples of the present invention will be described in detail below in conjunction with the accompanying drawings.

As shown in FIG. 1 to FIG. 3 , the implementation example of the present invention includes a light source component, an illumination component, a detection component, and a spectrum demodulation component.

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

In the lighting assembly (200): the lighting slit (210) has a length of 10 mm and a width of 20 μm, which is closely attached to the light output path (133) of the fiber coupler, and emits uniform and continuous linear lighting 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 dispersion objective lens (230). The spectral range of the first linear gradient filter (220) is 400nm-700nm, the dispersion characteristic is 30nm/mm, and 400nm-700nm corresponds to the 10mm long range in the meridional direction on the linear gradient filter. The light output by the illumination slit (210) completely covers this range, and does not change the propagation direction after being filtered. The first dispersive objective lens (230) uniformly focuses light of different wavelengths on the measurement surface, and performs spectral encoding on the axial displacement. Among them, 400nm～550nm corresponds to the axial displacement of 0～0.6mm; 550nm～700nm corresponds to the axial displacement of 0.6～1.2mm, realizing the axial measurement range of 1.2mm.

In the detection assembly (300): the second dispersive objective lens (320) and the first dispersive objective lens (230) are placed symmetrically with respect to the measurement plane, and the second dispersive objective lens (320) and the first dispersive objective lens (230) have exactly the same structure, and the irradiated The light on the surface of the sample to be measured returns to the second dispersive objective lens (320), and the wavelength that is just focused on the sample surface is processed by the second dispersive objective lens (320), and the propagation path is the same as that from the illumination slit (210) to the first dispersive objective lens (230). ) propagation path is completely symmetrical and can be focused on the detection slit (310) conjugated to the illumination slit (210), while the wavelengths not focused on the surface of the sample to be measured cannot be symmetrically focused on the detection slit (310) . The detection slit (310) is 10 mm long and 20 μm wide. The wavelength with the highest energy passing through the detection slit (310) is the wavelength that is just focused on the surface of the sample to be measured. ) Different positions pass different wavelengths.

In the spectrum demodulation component (400): the collimator lens (410) is designed achromatically, and the light of different wavelengths passing through the detection slit (310) is shaped into parallel light, which is convenient for subsequent processing. The included angle between the normal line of the dichroic mirror (420) and the optical axis of the collimating lens (410) is 45°, and the collimated light projected onto the dichroic mirror (420) is divided into two beams, and the light of 400nm-550nm is not Change the propagation direction, illuminate on the second linear gradient filter (430), the light of 550nm～700nm is reflected by the dichroic mirror (420), and project on the third linear gradient filter (460), the two beams are separated The included angle of light is 90°. The second linear gradient filter (430) has a spectral range of 400nm to 550nm. In order to improve the spectral resolution, the dispersion characteristic is 10nm/mm, and the effective area is 15mm; the chip size of the first CMOS camera (440) is greater than 15mm in length and width, The pixels shall not be less than 2048 points, and the spectral response curve shall cover the measured spectral range. Designed for system integration, the linear gradient filter can be directly processed on the glass cover of the CMOS chip. The spectral range of the third linear gradient filter (460) is 550nm-700nm, the dispersion characteristic is 10nm/mm, and the effective area is 15mm; the second CMOS camera (450) has the same requirements as the first CMOS camera (440). At the same time, the second linear gradient filter (440) and the third linear gradient filter (460) have the same transmittance for different wavelengths, so as to ensure measurement consistency. Finally, according to the energy spectrum collected by the CMOS camera, the surface profile of the tested sample in the range of 0-0.6mm and 0.6-1.2mm can be obtained respectively. Measure the surface profile of the sample.

Claims (10)

1. A dual-band detection-based dual-axis spectroscopic confocal sensor, characterized in that the device comprises: the device comprises a light source assembly (100), an illumination assembly (200), a detection assembly (300) and a spectrum demodulation assembly (400);

the light source assembly comprises an LED light source (110), a fiber coupler (120) for mixing and guiding the light emitted by the LED light source (110) to the illumination assembly (200);

the illumination assembly (200) comprises an illumination slit (210), a first linear gradient filter (220) and a first dispersive objective lens (230), and light with different wavelengths is uniformly projected on a measuring surface;

the detection assembly comprises a second dispersive objective lens (320) and a detection slit (310), the second dispersive objective lens and the detection slit are arranged in a conjugate mode relative to the measured surface, the reflected light of the measured surface is focused at the detection slit (310) again, the detection slit (310) is used for blocking the wavelength which cannot be focused on the measured surface and only allowing the wavelength which is just focused on the measured surface to pass through;

the spectrum demodulation component comprises 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), and light passing through the detection component is divided into two beams according to two wave bands to demodulate the spectrum components of the light respectively, so that height information contained in the spectrum energy distribution is obtained.

2. The light source module (100) according to claim 1, characterized in that the wavelength range of the LED light source (110) is λ |) ₁ ～λ ₂ The spectral distribution of the LED light source (110) is continuous and smooth.

3. The LED light source (110) of the light source module (100) according to claim 1, comprising 1 to 2 LEDs, each LED having the same energy entering the fiber coupler (120), the sum of the spectral ranges covering λ £ ₁ ～λ ₂ 。

4. The illumination assembly (200) of claim 1, wherein the illumination slit (210) emits uniform illumination.

5. The lighting assembly (200) according to claim 1, wherein the spectral range of the first linear graded filter (220) is λ ₁ ～λ ₂ The spectral range emitted by the light source assembly (100) is entirely included.

6. The illumination assembly (200) of claim 1, wherein the first dispersive objective (230) has an optical axis at an angle to the surface being measured and produces an axial dispersion that matches the lateral dispersion produced by the first linear graded filter (220) so that the focal lines of different wavelengths of light are evenly distributed over the measurement surface.

7. A detection assembly (300) according to claim 1, characterized in that the second dispersive objective (320) is structurally identical to the first dispersive objective (230) in the illumination assembly.

8. The spectral demodulation assembly (400) of claim 1, wherein the collimating lens (410) is an achromatic lens set, and light of different wavelengths passes through the collimating lens (410) and is shaped into parallel beams.

9. The spectral demodulation assembly (400) of claim 1, wherein the range of light wavelengths split by the dichroic mirror (420) and impinging on the second linear graded filter (430) is λ ₁ λ ', the wavelength range of the light irradiated on the third linear gradation filter (460) is λ' λ ₂ The spectral range of the second linear graded filter (430) is lambda ₁ λ ', the spectral range of the third linear graded filter (460) is λ'. About λ ₂ 。

10. The spectral demodulation assembly (400) of claim 1, wherein the spectral response and the number of pixels, the size of the first CMOS camera (440), the second CMOS camera (450) are the same.

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