Hole wall measuring device and method based on variable aperture spectral imaging

Abstract

The invention discloses a hole wall measuring device and method based on variable aperture spectral imaging, and belongs to the technical field of precision optical measurement, the device comprises a light source, a light beam collimating lens, a beam splitter prism, a pupil filter, a dispersion objective lens, a small hole, a light beam focusing lens and a camera, the beam focus lens is used for receiving the scattered beams and transmitting the beams to the camera. The axial dispersion spectrum confocal principle is adopted, the axial position is directly calculated by analyzing the characteristic wavelength of scattered light, mechanical z-axis scanning is not needed, micron-level precision measurement is achieved, the device integrates a replaceable pupil modulation mask, pupil function space distribution is optimized according to different working conditions, stray light is selectively restrained, and the measurement accuracy is improved. Therefore, the measurement stability of the low-scattering area can be improved. The device is divided into a coarse adjustment stage and a fine adjustment stage in the adjustment process, the coarse adjustment position precision is + / -0.5 mm, the fine adjustment position precision is + / -50-70 microns, and high-precision alignment and measurement reliability of the system are ensured.

Description

Technical Field

[0001] This invention belongs to the field of precision optical measurement technology, and specifically relates to a method and apparatus for non-contact, high-precision hole wall measurement. Background Technology

[0002] In the current high-end precision manufacturing field, non-destructive, high-precision measurement of the three-dimensional morphology of micron-sized apertures, deep holes, and complex vertical internal wall structures has become a key requirement for quality control and process optimization. These structures are widely found in core components such as fuel nozzles for aerospace engines, through-silicon vias (TSVs) for semiconductors, and microfluidic channels for medical devices. Their geometric accuracy directly affects fuel atomization efficiency, chip interconnect reliability, and fluid control performance. Traditional contact probe measurements are not only prone to scratching precision surfaces but also limited by probe size and contact force, making it difficult to reach the bottom of deep holes and steep sidewalls for complete measurements. Non-contact measurement technologies based on laser triangulation or ordinary machine vision, due to optical obstruction, limited depth of field, and diffraction effects, generally suffer from technical bottlenecks such as missing sidewall data and poor measurement repeatability when dealing with deep hole structures with aspect ratios >10:1 and apertures less than 100 microns, failing to meet the sub-micron precision inspection requirements of modern precision manufacturing.

[0003] Traditional focus tracking (FV) technology faces three major technical bottlenecks in the 3D topography inspection of high aspect ratio vertical micro-holes. First, in terms of measurement efficiency, FV technology, based on a point-by-point scanning mechanism, requires data acquisition point-by-point using a precision displacement stage to reconstruct the 3D contour. Single-hole measurement can take several minutes, failing to meet the efficiency requirements of industrial online inspection. Second, in terms of detection dimensions, FV technology lacks spatial parallel detection capabilities. Its sensors can only acquire information from a single point; even reconstructing a one-dimensional line contour requires mechanical scanning, which is not only inefficient but also introduces measurement errors due to vibration and temperature drift during the scanning process, affecting the stability and reliability of the data. Most critically, there is the issue of optical interference. Traditional FV technology faces inherent optical challenges when measuring vertical hole walls. The illumination beam acts simultaneously on two areas: the hole wall, nearly parallel to the light propagation direction, which generates weak scattered light for measurement; and the bottom plane of the hole, nearly perpendicular to the beam, which generates strong specular reflection light. The latter's intensity is much higher than the effective signal, and the optical path highly overlaps with the detection system. Traditional confocal pinhole systems are designed to suppress defocus background noise. However, their spatial filtering capability is severely inadequate for strong specular reflection stray light, which is almost in the same path as the effective signal. This causes the weak scattered signal from the aperture wall to be overwhelmed by the strong stray light, and the detector signal-to-noise ratio deteriorates sharply in critical areas, resulting in distorted measurement data and limiting the reliable application of this technology in precision measurements. Summary of the Invention

[0004] The present invention addresses the shortcomings of the existing technology by proposing a hole wall measurement device and method based on variable aperture spectral imaging. This device aims to achieve accurate, reliable, and micron-level three-dimensional reconstruction of hard-to-reach features such as deep holes and steep sidewalls. As a result, it can be applied to high-precision three-dimensional morphology measurement of micron-level apertures, deep holes, and complex vertical inner wall structures in core components such as aerospace fuel nozzles, semiconductor through-silicon vias, and medical device microchannels.

[0005] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: The aperture wall measurement device based on variable aperture spectral imaging of the present invention is characterized in that it includes: a light source, a beam collimating lens, a beam splitter, a pupil filter, a dispersive objective lens, a pinhole, a beam focusing lens, and a camera arranged sequentially from the object side to the image side along the propagation of light; The light source is placed on the focal plane of the beam collimating lens; and both the light source and the beam collimating lens are located on the illumination optical axis; the beam splitter is located at the intersection of the illumination optical axis and the imaging optical axis, and the illumination optical axis is perpendicular to the imaging optical axis. A pupil filter, a dispersive objective lens, and a pinhole are sequentially arranged along the imaging optical axis on one side of the beam splitter; wherein the pinhole is located near the focal plane of the dispersive objective lens; the dispersive direction of the dispersive objective lens is consistent with the depth direction of the pinhole. On the other side of the beam splitter, the beam focusing mirror and the camera are arranged sequentially along the imaging optical axis, with the camera located on the focal plane of the beam focusing mirror. The light source emits a linear array of light beams, which are collimated into parallel light by the beam collimating lens and then incident perpendicularly on the beam splitter. The light beams are reflected at the beam splitter surface of the beam splitter at an incident angle of 45°. The reflected light is parallel to the optical axis and passes through the beam shape control of the pupil filter and the dispersion of the dispersive objective lens in sequence before finally converging on the aperture to form an illumination light path. When light shines on the inner wall of the aperture, it is scattered. Part of the scattered light carrying information about the aperture wall morphology is received by the dispersive objective lens, passes through the dispersive objective lens and the pupil filter in sequence, and is perpendicularly incident on the beam splitter prism. It is transmitted at the beam splitter surface of the beam splitter prism. The transmitted light is corrected and converged by the beam focusing lens, and finally imaged on the camera to form an imaging optical path.

[0006] The aperture wall measurement device based on variable aperture spectral imaging described in this invention is also characterized in that the pupil filter integrates a pupil modulation mask, the opening shape of which is one of the following: center blocking type, ring light-passing type, and multi-aperture distribution type. The central blocking type mask is a double-layer structure with a circular black light-blocking area covering the center of the pupil and an outer ring that allows light to pass through. It is used for small holes with a depth-to-diameter ratio greater than 10:1 and where the bottom mirror reflection is dominant. It also suppresses stray light reflected from the bottom mirror by blocking the light in the center area of ​​the pupil. The ring-shaped light-transmitting mask is a concentric ring structure with a central blocking element and an outer ring-shaped light-transmitting element. It is used for low-scattering materials with a surface roughness Ra < 0.1μm and a specular reflectivity > 85%, and for small holes where the intensity of the scattered light from the sidewalls is less than 1 / 10 to 1 / 20 of the intensity of the specular reflection at the bottom of the hole. It also retains a large-angle scattered light component with an angle > 15°. The multi-aperture distribution mask is a honeycomb structure in which multiple discrete light-transmitting holes are distributed in a ring array. It is used for small holes with an aspect ratio between 5:1 and 10:1 that need to take into account both signal strength and stray light suppression. By balancing the central blocking and the peripheral light-transmitting area, the spatial distribution of the pupil function is optimized.

[0007] Furthermore, the dispersive objective lens is composed of at least two cemented doublet lenses and a special dispersive positive lens. The dispersive objective lens has no fewer than six lenses. The axial dispersive direction of the dispersive objective lens is consistent with the depth direction of the pinhole. Light beams of different wavelengths are focused at different depths of the pinhole after being dispersed by the dispersive objective lens, so as to achieve a linear correspondence between wavelength and z-direction, where z-direction is the depth direction of the pinhole.

[0008] Furthermore, the light source is a row of point light sources arranged in a linear array to emit a broadband light beam, with the broadband spectrum ranging from 400nm to 700nm.

[0009] Furthermore, the beam focusing lens includes at least one cemented doublet lens for converging scattered beams and correcting aberrations, so that the linear light spot on the camera target surface has uniform and consistent sharpness throughout the y-direction.

[0010] The detection method of the aperture wall measurement device based on the aforementioned variable aperture spectral imaging according to the present invention is characterized by comprising the following steps: Step 1: Using the dispersion direction of the dispersive objective as the z-direction and the line scanning direction of the dispersive objective as the x-direction, establish the y-direction according to the right-hand coordinate system, thereby establishing a baseline, and coarsely adjust the position of the beam splitter so that the beam splitter is located at the intersection of the illumination optical axis and the imaging optical axis. Step 2: Align the illumination optical path and the imaging optical path respectively: Step 2.1: Adjust the positions of the light source and the beam collimator according to the baseline so that the collimated beam passing through the beam collimator passes through the center of the beam splitter; then fine-tune the position of the beam splitter so that the position of the beam splitter meets the accuracy requirements. Step 2.2: Adjust the confocal focus of the dispersive objective and the beam focusing lens so that the light beam scattered back by the dispersive objective can completely enter the beam focusing lens; adjust the camera position to be at the focal plane of the beam focusing lens; Step 2.3: Install the hole to be tested on the high-precision displacement stage, and adjust the high-precision displacement stage so that the hole wall is perpendicular to the plane containing the x and y directions; Step 3: Turn on the light source and preheat until the spectral output is stable; Step 4: Determine the mask on the pupil filter based on the aperture diameter, depth, aspect ratio, and scattering rate of the inner wall material of the aperture to be tested. If the aspect ratio of the aperture is greater than 10:1 and the specular reflection at the bottom of the aperture is dominant, then a center-blocking mask should be selected to block the light in the central region of the pupil and suppress stray light reflected from the specular reflection at the bottom of the aperture. If the aperture is a low-scattering material with a surface roughness Ra < 0.1μm and a specular reflectivity > 85%, and the intensity of the scattered light from the sidewalls is less than 1 / 10 to 1 / 20 of the intensity of the specular reflection from the bottom of the aperture, then a ring-shaped light-transmitting mask should be selected to retain the large-angle scattered light component with an angle > 15°. If the aspect ratio of the aperture is between 5:1 and 10:1 and both signal strength and stray light suppression need to be considered, then a multi-aperture distribution mask should be selected to balance the central blocking and the peripheral light-transmitting area. Step 5: Control the high-precision displacement stage to drive the small hole to move at a constant speed or step along the x-direction until the entire small hole is scanned. During the movement, the camera synchronously acquires the two-dimensional spectral image of the small hole at each scanning moment, thereby obtaining the complete scattering information of the hole wall region in the spectral dimension, and recording it as three-dimensional spectral data I(x, y, λ). The spatial dimension of the two-dimensional spectral image is the y-direction, and the spectral dimension is the z-direction. Each column in the two-dimensional spectral image contains a complete spectral intensity distribution curve I(λ), and the wavelength λ corresponds linearly to the z-direction.

[0011] Step 6: Analyze the spectral curve of each spatial pixel (x,y) in the three-dimensional spectral data I(x,y,λ) to calculate the morphological features at the corresponding spatial location; combine all spatial pixels and their morphological features to obtain point cloud data reflecting the three-dimensional morphology of the hole wall. Step 7: Perform surface fitting on the point cloud data to obtain a complete and continuous three-dimensional model of the hole wall, which is used to analyze the geometric parameters of the hole, including: hole diameter, hole depth, inclination and surface roughness.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention employs the spectral confocal principle based on axial dispersion, directly calculating the axial position by analyzing the characteristic wavelengths of the scattered light, thus achieving blind-zone-free, high-precision measurement of steep sidewalls. Its core advantage lies in the fact that axial positioning can be completed without relying on mechanical z-axis scanning, completely eliminating displacement transmission errors caused by traditional mechanical scanning. Simultaneously, the broadband spectrophotometer, as a necessary condition for ensuring the system's basic measurement capabilities, accuracy, and reliability, effectively guarantees spectral integrity, optimizes signal transmission efficiency, and improves the system's long-term operational stability.

[0013] 2. This invention utilizes a confocal scanning mechanism combining line illumination and line detection to upgrade single-point scanning to line scanning, achieving high-speed data acquisition of two-dimensional profiles. This design improves measurement efficiency by 1-2 orders of magnitude while avoiding cumulative errors introduced by multi-axis mechanical motion, thus meeting the throughput requirements of industrial online inspection.

[0014] 3. This invention integrates a precision pupil modulation mask at the pupil filter, and selectively suppresses stray light by optimizing the spatial distribution of the pupil function. On the one hand, it effectively filters out multiple scattering noise in deep holes, significantly improves the system signal-to-noise ratio, and enhances the measurement stability and repeatability in low scattering rate regions. On the other hand, it greatly improves the tolerance for beam incident angle, and completely overcomes the signal attenuation problem in vertical wall measurements using traditional focus tracking methods. Attached Figure Description

[0015] Figure 1 This is an overall optical path diagram of an embodiment of the present invention; Figure 2 This is a schematic diagram of the mask placed at the pupil filter in an embodiment of the present invention; Figure 3 This is a schematic diagram of the light change before and after pupil modulation in the measurement aperture wall according to an embodiment of the present invention; Figure 4 This is a schematic diagram illustrating the principle of measuring the borehole wall morphology using a dispersive objective lens according to an embodiment of the present invention. Figure 5 This is a schematic diagram of the light scanning aperture in an embodiment of the present invention, with time ranging from t1 to t3; Figure 6 This is a schematic diagram illustrating the imaging principle of a spectral camera in an embodiment of the present invention; Figure 1 Numbered components: 1-Light source; 2-Beam collimator; 3-Beam splitter; 4-Pupil filter; 5-Dispersion objective; 6-Pinhole; 7-Beam focusing lens; 8-Camera; 9-Optical axis; 10-Optical axis; x-Spot scanning direction; y-Vertical spot scanning direction; z-Aperture wall depth direction. Detailed Implementation

[0016] In this embodiment, addressing the problems of low efficiency and easy obscuring of sidewall signals by reflection from the bottom mirror surface in high aspect ratio (>10:1) micro-aperture measurements using traditional focus tracking techniques, a micro-aperture wall measurement device based on variable aperture spectral imaging is proposed. This device aims to construct a dedicated micro-aperture vertical wall measurement solution by integrating a customized dispersive objective lens design, a collimation illumination architecture precisely matched to the objective lens characteristics, and a high-performance spectral imaging unit, filling a technological gap in this niche measurement field. Specifically, as... Figure 1 As shown, the device includes: a light source 1, a beam collimating lens 2, a beam splitter 3, a pupil filter 4, a dispersive objective lens 5, a pinhole 6, a beam focusing lens 7, and a camera 8, arranged sequentially from the object side to the image side along the propagation of light.

[0017] The light source 1 is placed on the focal plane of the beam collimating lens 2; a row of linearly arranged fiber optic light sources are used to emit a broadband beam covering the 400nm to 700nm wavelength range; the light source 1 and the beam collimating lens 2 are both located on the illumination optical axis 9; the beam splitter 3 is located at the intersection between the illumination optical axis 9 and the imaging optical axis 10, and the illumination optical axis 9 is perpendicular to the imaging optical axis 10.

[0018] A pupil filter 4, a dispersive objective lens 5, and a pinhole 6 are sequentially arranged along the imaging optical axis 10 on one side of the beam splitter prism 3. The pinhole 6 is located near the focal plane of the dispersive objective lens 5. The dispersive direction of the dispersive objective lens 5 is consistent with the depth direction of the pinhole 6. This design ensures a one-to-one correspondence between axial depth information and spectral dimensions.

[0019] On the other side of the beam splitter prism 3, the beam focusing mirror 7 and the camera 8 are arranged sequentially along the imaging optical axis 10. The camera 8 is located on the focal plane of the beam focusing mirror 7. The camera 8 is a line scanning hyperspectral camera with a spectral resolution of not less than 0.5 nm, which can simultaneously acquire two-dimensional information in both spatial and spectral dimensions.

[0020] Light source 1 emits a row of linear array beams, which are collimated into parallel rays by beam collimating lens 2 and then incident perpendicularly on beam splitter 3. The beams are reflected at the beam splitting surface of beam splitter 3 at an incident angle of 45°, and the reflected rays are parallel to light 10. After passing through the beam shape control of pupil filter 4 and the dispersion of dispersive objective lens 5, the beams finally converge on pinhole 6 to form an illumination light path.

[0021] After light shines on the inner wall of the small hole 6, it is scattered. Part of the scattered light carrying the topographic information of the hole wall is received by the dispersive objective lens 5, and then passes through the dispersive objective lens 5, the pupil filter 4 and is perpendicularly incident on the beam splitter prism 3. It is transmitted at the beam splitter surface of the beam splitter prism 3. The transmitted light is corrected and converged by the beam focusing lens 7, and finally imaged on the camera 8 to form the imaging optical path.

[0022] In this embodiment, the pupil filter (4) integrates a pupil modulation mask, the opening shape of which is one of the following: central blocking type, ring-shaped light-passing type, and multi-aperture distribution type; its working mechanism is based on the active modulation of the point spread function of the optical system. Traditional focus tracking technology faces a fundamental optical challenge when measuring vertical aperture walls: the illumination beam acts simultaneously on the aperture wall that is almost parallel to the light propagation direction and the aperture bottom plane that is almost perpendicular to the beam. The latter has a much higher intensity than the effective signal, and the optical path is highly overlapped with the detection system. Traditional confocal pinholes are severely inadequate in their spatial filtering capability for such strong specular reflection stray light that is almost in the same path as the effective signal. This invention solves this technical problem from the source of the optical path by integrating a replaceable pupil modulation mask at the pupil filter 4 and selecting the optimal pupil modulation strategy according to the geometric parameters and material optical properties of the aperture 6 to be measured. Figure 2 These are three typical mask shapes placed at the pupil filter 4. Figure 3 It shows a comparison of light changes before and after pupil modulation.

[0023] Center-blocking mask: Suitable for applications with a depth-to-diameter ratio greater than 10:1 and where specular reflection from the aperture bottom is dominant. This mask blocks light from the central region of the pupil, effectively suppressing strong specular stray light from the aperture bottom while retaining large-angle scattered light components from the sidewalls. Its physical essence lies in altering the spatial distribution of the pupil function, reducing the device's response to paraxial rays, and improving the collection efficiency of large-angle scattered light, thereby extracting weak but effective signals against a strong stray light background.

[0024] Annular light-transmitting mask: Suitable for applications with low scattering materials and weak sidewall signals. This mask blocks the central pupil region while allowing light to pass through the outer annular region, specifically designed to collect large-angle scattered light. Its core advantage lies in enhancing signal collection capabilities from low-scattering surfaces, overcoming the signal attenuation problem in vertical wall measurements using traditional focus-tracking methods.

[0025] Multi-aperture distributed mask: Suitable for applications with aspect ratios between 5:1 and 10:1 where both signal strength and stray light suppression are required. This mask utilizes an optimized design of multiple discrete apertures to balance central blocking and peripheral light-passing areas, effectively suppressing stray light while ensuring sufficient signal strength.

[0026] The selected mask is fixed to the position of the pupil filter 4 by a detachable mechanism, so that the incident beam is precisely shaped and stray light is reduced from the source of the optical path. This is the essential innovation of this invention that distinguishes it from the traditional mechanical scanning method.

[0027] In this embodiment, the dispersive objective (5) is composed of at least two cemented doublet lenses and a special dispersive positive lens. The dispersive objective (5) has no less than 6 lenses. The axial dispersive direction of the dispersive objective (5) is consistent with the depth direction of the aperture (6). Light beams of different wavelengths are focused at different depths of the aperture (6) after being dispersed by the dispersive objective (5), so as to achieve a linear correspondence between wavelength and z-direction, where z-direction is the depth direction of the aperture (6).

[0028] In this embodiment, the beam focusing lens (7) includes at least one doublet lens for converging scattered beams and correcting aberrations, so that the linear light spot on the target surface of the camera (8) has uniform and consistent clarity throughout the y direction.

[0029] In this embodiment, an orthogonal coordinate system is established to describe the measurement process: the dispersion direction of the dispersive objective lens 5 is taken as the z-direction, the linear scanning direction of the dispersive objective lens 5 is taken as the x-direction, and the y-direction, along with the x and z directions, forms a right-handed coordinate system. The wall of the aperture 6 to be measured is perpendicular to the xy plane, and the depth direction is along the z-axis. This coordinate system design ensures a strict correspondence between the spectral information in the z-direction, the linear scanning information in the x-direction, and the spatial profile information in the y-direction, laying the foundation for the construction of the three-dimensional data cube I(x, y, λ).

[0030] In this embodiment, the measurement principle of the dispersive objective 5 is based on the axial dispersion spectral confocal technique. For example... Figure 4 As shown, the dispersive objective 5 produces different focusing capabilities for light of different wavelengths, causing different wavelength components in the broadband beam to be focused at different depths in the z-axis. When the beam shines on the wall of the aperture 6, the surface of the aperture wall preferentially reflects or scatters light of the wavelength corresponding to its location. This characteristic wavelength carries precise axial position information.

[0031] In this embodiment, the device directly calculates the axial position by analyzing the characteristic wavelength of the scattered light, achieving blind-zone-free and high-precision measurement of steep sidewalls. Its core advantage lies in completing axial positioning without relying on mechanical z-axis scanning, completely eliminating displacement transmission errors caused by traditional mechanical scanning. The linear correspondence between wavelength λ and axial depth z is pre-calibrated using a standard step sample block, generating a wavelength-depth calibration file, which is directly called during measurement for depth calculation.

[0032] In this embodiment, the device employs a line confocal scanning mechanism combining line illumination and line detection, which is key to achieving efficient measurement in this invention. Light source 1 emits a linear array of beams, which, after being focused by dispersive objective lens 5, form a linear illumination spot on the inner wall of aperture 6. This spot extends along the y-direction, covering a complete cross-section of the aperture wall. Line-scanning hyperspectral camera 8 simultaneously receives the scattered light from all points on this cross-section, acquiring depth information along the entire line in a single exposure, rather than the point-by-point acquisition required by traditional single-point scanning.

[0033] like Figure 5 As shown, by controlling a high-precision displacement stage to drive the small hole 6 to move at a constant speed or in steps along the x-direction, the device can complete the scanning of the entire hole wall. Compared with the point-by-point scanning mechanism of traditional focus tracking technology, the line confocal scanning mechanism of this invention improves single-point scanning to line scanning, realizing high-speed data acquisition of two-dimensional profiles, improving measurement efficiency by 1-2 orders of magnitude, and avoiding the cumulative error introduced by multi-axis mechanical motion.

[0034] In this embodiment, the optical path alignment process includes: Step 1: Using the optical platform surface and T-slot as mechanical references, establish a horizontal reference line parallel to the platform surface using a height gauge and dial indicator. Then, install and secure the adjustment bracket for the first key component, the beam splitter prism 3. Perform coarse adjustment at this point, with a positional accuracy of ±0.5mm. The goal is to make the mechanical housing outline of the beam splitter prism approximately parallel to the reference line and to reserve sufficient space for the subsequent optical path.

[0035] Step 2: Align the illumination optical path and the imaging optical path respectively: Step 2.1: Install the light source 1 and beam collimator 2. Do not install the beam splitter prism yet; temporarily place a shearing interferometer or beam analyzer in front of the light source. Fine-tune the relative position of the beam collimator 2 and the light source 1 until the emitted beam is high-quality parallel light, detectable by the absence of significant changes in beam size over long distances. Place the beam splitter prism 3 back into the optical path. Place a white screen with crosshairs at the exit of the beam splitter's transmission path. Finely adjust the pitch and deflection of the beam splitter prism 3 so that the center of the collimated beam's spot coincides with the center of the crosshairs on the white screen, with a fine-tuning accuracy of ±50-70 μm. This ensures that the illumination beam passes precisely through the geometric center of the beam splitter prism and the beam-splitting film.

[0036] Step 2.2: Install the dispersive objective 5 along the reflected light path of the beam splitter prism 3. Temporarily place a highly scattering frosted glass or a special scattering plate as a "template" at the focal plane of the dispersive objective to simulate the scattering of the beam on the wall of the pinhole 6. At the other end of the reflected light path of the beam splitter prism, install the beam focusing lens 7 and the line-scan hyperspectral camera 8. Fine-tune the up / down, left / right, and pitch angles of the dispersive objective 5 and the beam focusing lens 7, while simultaneously observing the spot image acquired by the camera 8. Unlike traditional single-point confocal systems that only pursue a single brightest focal point, the goal of this invention is to ensure that the linear spot on the camera target surface has uniform and consistent clarity throughout the entire y-direction. This ensures the consistency of axial dispersion calibration across the entire profile in subsequent line-scan measurements, laying the foundation for acquiring depth information for a single line at once.

[0037] Step 2.3: Remove the sample plate, install the small hole 6 to be measured on the precision displacement stage, and move it to the depth of field range of the dispersive objective lens. Perform a test scan to observe whether the camera can receive clear spectral signals from different depths of the hole wall. At this point, the optical path alignment process is complete, and the device enters the measurable state.

[0038] Step 3: Turn on light source 1 and preheat until the spectral output is stable; start the control and analysis device and load the pre-calibrated wavelength-depth correspondence curve; install the small hole 6 to be measured on the high-precision displacement stage and use a plane standard or hole edge of known height for zero-position calibration.

[0039] Step 4: Based on the aperture diameter, depth, aspect ratio, and scattering rate of the inner wall material of the aperture 6 to be tested, determine the mask on the pupil filter 4: If the aspect ratio of aperture 6 is greater than 10:1 and the specular reflection at the bottom of the aperture is dominant, then a center-blocking mask should be selected to block the light in the central region of the pupil and suppress stray light reflected from the specular reflection at the bottom of the aperture. If the aperture 6 is a low-scattering material with a surface roughness Ra < 0.1μm and a specular reflectivity > 85%, and the intensity of the scattered light from the sidewall is less than 1 / 10 to 1 / 20 of the specular reflection intensity at the bottom of the aperture 6, then a ring-shaped light-transmitting mask should be selected to retain the large-angle scattered light component with an angle > 15°. If the aspect ratio of aperture 6 is between 5:1 and 10:1 and both signal strength and stray light suppression need to be considered, then a multi-aperture distribution mask should be selected to balance the central blocking and the peripheral light-transmitting area. Step 5: Control the high-precision displacement stage to drive the small hole 6 to move at a constant speed or step along the x-direction until the entire small hole 6 is scanned. During the movement, the camera 8 synchronously acquires the two-dimensional spectral image of the small hole 6 at each scanning moment, thereby obtaining the complete scattering information of the hole wall region in the spectral dimension, and recording it as three-dimensional spectral data I(x, y, λ). The spatial dimension of the two-dimensional spectral image is the y-direction, and the spectral dimension is the z-direction. Each column in the two-dimensional spectral image contains a complete spectral intensity distribution curve I(λ), and the wavelength λ corresponds linearly to the z-direction.

[0040] Step 6: Analyze the spectral curve of each spatial pixel (x,y) in the three-dimensional spectral data I(x,y,λ) to calculate the morphological features at the corresponding spatial location; combine all spatial pixels and their morphological features to obtain point cloud data reflecting the three-dimensional morphology of the hole wall. Step 7: Perform surface fitting on the point cloud data to obtain a complete and continuous three-dimensional model of the hole wall, which is used to analyze the geometric parameters of the hole 6, including: hole diameter, hole depth, inclination and surface roughness.

[0041] In this embodiment, as Figure 6As shown, the imaging of camera 6 is based on the principle of spectral dispersion. The scattered beam, after passing through the dispersive objective lens 5 and the beam-splitting prism 3, is converged to the camera target surface by the beam-focusing lens 7. The camera internally contains a beam-splitting element and a matrix detector, which spatially separates light of different wavelengths, forming a two-dimensional image in the spectral dimension (z-axis) and the spatial dimension (y-axis). A high-spectral-resolution camera is selected, with a spectral resolution of no less than 0.5 nm, to ensure micrometer-level accuracy in the z-axis direction. The camera requires pre-calibration, including wavelength calibration using multicolor light sources and geometric distortion correction using a standard grid plate, to ensure measurement accuracy.

[0042] In summary, the hole wall measurement device of this invention adopts the spectral confocal principle based on axial dispersion. It directly calculates the axial position by analyzing the characteristic wavelength of the scattered light, achieving one-time hole measurement in the z-axis without the need for mechanical z-axis scanning, thus eliminating displacement transmission errors. The device employs a line confocal scanning mechanism combining line illumination and line detection, upgrading single-point scanning to line scanning, enabling high-speed data acquisition of two-dimensional profiles, and improving measurement efficiency by 1-2 orders of magnitude. The core innovation lies in the integration of a precision pupil modulation mask at the pupil filter. Through different mask strategies such as center blocking, ring-through, and multi-aperture distribution, it selectively suppresses multiple scattering noise and specular reflection stray light within deep holes, improving the system's signal-to-noise ratio and enhancing measurement stability and repeatability in low-scattering regions, addressing various operating conditions such as high aspect ratio holes dominated by specular reflection at the bottom, weak signals from low-scattering polished metal sidewalls, and moderate aspect ratio holes requiring a balance between intensity and stray light suppression. This improves the system's signal-to-noise ratio and enhances measurement stability and repeatability in low-scattering regions.

Claims

1. A variable-aperture spectral imaging-based borehole wall measurement device, comprising: The application relates to a light path device for a small aperture imaging system. The device comprises a light source (1), a beam collimator (2), a light splitting prism (3), a pupil filter (4), a dispersion objective (5), a small aperture (6), a beam focusing mirror (7) and a camera (8) arranged in sequence along the light path from the object side to the image side. The light source (1) is arranged on the focal plane of the beam collimator (2), and the light source (1) and the beam collimator (2) are located on the illumination optical axis (9); the light splitting prism (3) is located at the intersection between the illumination optical axis (9) and the imaging optical axis (10), and the illumination optical axis (9) is perpendicular to the imaging optical axis (10). The pupil filter (4), the dispersion objective (5) and the small aperture (6) are arranged in sequence along the imaging optical axis (10) on one side of the light splitting prism (3); the small aperture (6) is located near the focal plane of the dispersion objective (5); the dispersion direction of the dispersion objective (5) is consistent with the hole depth direction of the small aperture (6). The beam focusing mirror (7) and the camera (8) are arranged in sequence along the imaging optical axis (10) on the other side of the light splitting prism (3), and the camera (8) is located on the focal plane of the beam focusing mirror (7). The light source (1) emits a linear array of light beams, which are collimated by the beam collimator (2) into parallel light rays, then vertically incident on the light splitting prism (3) and reflected at an incident angle of 45 degrees on the light splitting surface of the light splitting prism (3), and the reflected light rays are parallel to the optical axis (10), then pass through the beam shape control of the pupil filter (4) and the dispersion of the dispersion objective (5), and finally converge on the small aperture (6) to form an illumination light path. After the light rays are scattered on the inner wall of the small aperture (6), part of the scattered light rays carrying the hole wall topography information are received by the dispersion objective (5), then pass through the dispersion objective (5), the pupil filter (4) and are vertically incident on the light splitting prism (3), are transmitted on the light splitting surface of the light splitting prism (3), then pass through the correction and convergence of the beam focusing mirror (7) and finally are imaged on the camera (8) to form an imaging light path.

2. The variable-aperture spectral imaging-based borewall measurement apparatus of claim 1, wherein, The pupil filter (4) is integrated with a pupil modulation mask, and the opening shape of the mask is one of a center blocking type, a ring bandpass light type and a multi-aperture distribution type. The center blocking type mask is a double-layer structure with a circular black light shielding area covering the center of the pupil and an outer ring light transmission, is used for a small aperture (6) with a high depth ratio greater than 10:1 and a mirror reflection on the hole bottom as the main part, and can inhibit the stray light of the mirror reflection on the hole bottom by blocking the light rays in the center of the pupil. The ring bandpass light type mask is a concentric ring structure with a center blocking and a peripheral ring bandpass light, is used for a small aperture (6) with a surface roughness Ra < 0.1 mu m, a mirror reflectivity > 85% and a side wall scattering light intensity lower than 1 / 10 to 1 / 20 of the mirror reflection intensity on the hole bottom, and can retain the large-angle scattering light component with an angle > 15 degrees. The mask of the multi-aperture distribution type is a honeycomb structure in which a plurality of discrete light holes are distributed in a ring array, and is used for a small hole (6) with a depth-width ratio between 5:1 and 10:1 and needing to balance signal strength and stray light suppression, and realizes the optimization of the spatial distribution of the pupil function by balancing the central blocking and the peripheral light transmission area.

3. The variable-aperture spectral imaging-based borewall measurement apparatus of claim 1, wherein, The dispersion objective lens (5) is composed of at least two doublet lenses and a special dispersion positive lens, the number of lenses of the dispersion objective lens (5) is not less than 6, the axial dispersion direction of the dispersion objective lens (5) is consistent with the hole depth direction of the small hole (6), and the light beams of different wavelengths are focused on different depths of the small hole (6) after dispersion through the dispersion objective lens (5), so as to realize the linear correspondence between wavelength and z direction, wherein the z direction is the depth direction of the small hole (6).

4. The variable-aperture spectral imaging-based borewall measurement apparatus of claim 1, wherein, The light source (1) adopts a point light source arranged in a line array, which is used to emit a wide spectrum light beam, and the wide spectrum range is 400nm to 700nm.

5. The variable-aperture spectral imaging-based borewall measurement apparatus of claim 1, wherein, The light beam focusing lens (7) at least includes a doublet lens, which is used to converge the scattered light beam and correct aberration, so that the linear light spot on the target surface of the camera (8) has uniform and consistent clarity in the entire y direction.

6. A detection method based on the variable-aperture spectral imaging-based borehole wall measurement device of claim 1, characterized by, The method comprises the following steps: Step 1, taking the dispersion direction of the dispersion objective lens (5) as the z direction and the line scanning direction of the dispersion objective lens (5) as the x direction, thereby establishing the y direction according to the right-hand coordinate system, thereby establishing the reference line, and coarsely adjusting the position of the light splitting prism (3) so that the light splitting prism (3) is located at the intersection of the illumination optical axis (9) and the imaging optical axis (10); Step 2, respectively aligning the illumination light path and the imaging light path: Step 2.1, adjusting the positions of the light source (1) and the light beam collimation lens (2) according to the reference line, so that the collimated light beam passing through the light beam collimation lens (2) passes through the center of the light splitting prism (3); then finely adjusting the position of the light splitting prism (3) so that the position of the light splitting prism (3) meets the accuracy requirement; Step 2.2, co-focusing the dispersion objective lens (5) and the light beam focusing lens (7), so that the light beam scattered back through the dispersion objective lens (5) can completely enter the light beam focusing lens (7); adjusting the position of the camera (8) to be at the focal plane of the light beam focusing lens (7); Step 2.3, installing the small hole (6) to be measured on the high-precision displacement table, and adjusting the high-precision displacement table so that the hole wall of the small hole (6) is perpendicular to the plane in which the x direction and the y direction lie; Step 3, turning on the light source (1) and preheating until the spectral output is stable; Step 4, determining the mask on the pupil filter (4) according to the aperture, hole depth, depth-diameter ratio and inner wall material scattering rate of the small hole (6) to be measured: If the high-depth-diameter ratio of the small hole (6) is greater than 10:1 and the hole bottom mirror reflection is dominant, a central blocking type mask is selected to block the light in the central area of the pupil and suppress the stray light of the hole bottom mirror reflection; If the small hole (6) is a low scattering material with surface roughness Ra < 0.1 μm, mirror reflectivity > 85%, and the side wall scattering light intensity is lower than 1 / 10 to 1 / 20 of the hole bottom mirror reflection intensity, then a ring bandpass light type mask is selected to retain the large angle scattering light component with an angle > 15°; If the aspect ratio of the small hole (6) is between 5:1-10:1 and both signal intensity and stray light suppression need to be considered, then a multi-aperture distribution type mask is selected to balance the central blocking and peripheral light transmission area; Step 5, control the high-precision displacement table to drive the small hole (6) to move uniformly or stepwise along the x direction until the entire small hole (6) is scanned, and in the process of movement, the camera (8) synchronously collects the two-dimensional spectral image of the small hole (6) at each scanning time, so as to obtain the complete scattering information of the hole wall region of the small hole (6) in the spectral dimension, and record it as three-dimensional spectral data I(x, y,λ), wherein the spatial dimension of the two-dimensional spectral image is the y direction, and the spectral dimension is the z direction; each column in the two-dimensional spectral image contains a complete spectral intensity distribution curve I(λ), and the wavelength λ linearly corresponds to the z direction. Step 6, analyze the spectral curve of each spatial pixel point (x, y) in the three-dimensional spectral data I(x, y,λ) for calculating the topographic features at the corresponding spatial position; after combining all spatial pixel points and their topographic features, point cloud data reflecting the three-dimensional topography of the hole wall is obtained; Step 7, surface fitting is performed on the point cloud data, so as to obtain a complete and continuous hole wall three-dimensional model, which is used for analyzing the geometric parameters of the small hole (6), including: hole diameter, hole depth, inclination and surface roughness.

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