Synchronous modulation, gating and integration 3D sensor

Abstract

A confocal three-dimensional sensor (22) for measuring the height of a point on an object (10) is provided. The sensor (22) comprises a light source (2) and a light source modulator (16) configured to temporally modulate the intensity of the light source. The light source pinhole aperture (4) is positioned to be illuminated by the light source (2), and the focusable lens (8) is configured to focus illumination through the light source pinhole aperture (4) onto an object (10). The detector pinhole aperture (12) is configured to receive reflected light from the object (10), where the focusable lens (8) is configured to image reflected light from the object (10) onto the detector pinhole aperture (12). The detector (14) and integrator (15) are configured to output a measurement indicative of the total light transmitted through the detector pinhole aperture (12). A processor (20) is operably coupled to the detector (14), the integrator (15), and the light source modulator (16). The processor (20) is configured to synchronously cause the light source modulator (16) to modulate the light source intensity while causing the focusable lens (8) to sweep the axial focus position, the processor (20) being further configured to calculate a height of a point on the object (10) based on outputs from the detector (14) and the integrator (15).

Description

Background Art

[0001] A known technique for 3D optical sensing is phase measurement profilometry based on triangulation. A spatially modulated light pattern is projected onto an object in phase measurement profilometry based on triangulation and is then observed by an imaging system from a direction different from the projection system. The three-dimensional topography of the object under inspection distorts the projected pattern observed by the imaging system, and the 3D topography can be calculated by measuring the distortion. Since the number of projected patterns and thus the number of video frames of the imaging system required is low, phase measurement profilometry based on triangulation is very suitable for high-speed industrial applications. Typically, three to twelve patterns and video frames are required for good performance. However, triangulation-based systems are not suitable for applications with a lateral resolution much lower than 2 μm because at these resolutions the required numerical aperture forces the size of the projector and the imaging system to expand to the point where they physically interfere with each other. Additionally, as the numerical aperture of the optical components increases, the depth of field of the system decreases, thus limiting such systems to a very small height range.

[0002] Confocal 3D optical sensing systems are suitable for applications that require a high numerical aperture and a finer lateral resolution than 2 μm because, by definition, the same optical system that illuminates the object is also used to collect the light reflected from the object under inspection. There are many confocal 3D optical sensing techniques including white light interferometry (WLI), conventional confocal microscopy, structured illumination microscopy SIM, and color confocal. All of these techniques can provide high precision and a large depth of field, but are relatively slow, which makes them unsuitable for many industrial applications.

[0003] White light interferometry (WLI) axially scans an object or a reference mirror, and when the optical path between the object and the reference mirror is equal, a peak interference is observed at each image pixel. Typically, one hundred or more axial positions and corresponding video frames are required to accurately measure the 3D topography of the object, which makes WLI too slow for many industrial applications. An example white light interferometer is disclosed in US 5,706,085.

[0004] Conventional 3D confocal microscopes use an array of light source apertures to project an array of individual point light sources onto an object, the reflected light is imaged onto an array of detection apertures, and the array of detection apertures is then imaged onto a camera detector. In some arrangements, the same aperture array can be used as both the light source aperture array and the detection aperture array. The object is mechanically scanned or the focus position is scanned axially, and when the object is at the best focus at each pixel in the camera image, a peak intensity is observed at that pixel. US 9,041,940 states that conventionally 200 confocal images are required, and the invention of US 9,041,940 claims to reduce this number to 20 images or less.

[0005] A structured illumination microscope (SIM) projects a spatially modulated light pattern onto an object and determines an optimal focus and three-dimensional coordinates at that object point for peak contrast at each point on the object during axial scanning. Techniques for accelerating SIM have been developed, but it still often requires fifty or more axial positions and video frames to accurately measure the 3D topography of an object. Example structured illumination microscopes are disclosed in US 8,649,024 and US10,634,487.

[0006] A color confocal 3D sensor encodes depth by axial chromatic aberration. By measuring the peak spectral value at each pixel, the 3D topography can be accurately measured. The color confocal 3D sensor does not require mechanical axial scanning and can have a large depth of field. However, the spectrometer that determines the peak spectral value typically requires sixty-four or more pixels for a single point on the object to obtain the required 3D measurement accuracy. Effectively, 64 or more detector readings are required at each point on the object, again making the technique too slow for many industrial applications. An example color confocal 3D sensor is disclosed in US 9,494,529. SUMMARY OF THE INVENTION

[0007] A confocal three-dimensional sensor for measuring the height of a point on an object is provided. The sensor includes a light source and a light source modulator configured to time-modulate the intensity of the light source. A light source pinhole aperture is positioned to be illuminated by the light source, and an adjustable-focus lens is configured to focus the illumination passing through the light source pinhole aperture onto the object. A detector pinhole aperture is configured to receive reflected light from the object, wherein the adjustable-focus lens is configured to image the reflected light from the object onto the detector pinhole aperture. A detector and an integrator are configured to output a measurement value indicative of the total light transmitted through the detector pinhole aperture. A processor is operatively coupled to the detector, the integrator, and the light source modulator. The processor is configured to synchronously cause the light source modulator to modulate the intensity of the light source while causing the adjustable-focus lens to sweep an axial focus position, and the processor is further configured to calculate the height of a point on the object based on the outputs from the detector and the integrator. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a schematic diagram of an example single-point 3D confocal sensor with time modulation in accordance with embodiments disclosed herein.

[0009] Figures 2A - 2C shows an example light source modulator current waveform.

[0010] Figures 2D - 2F is a schematic diagram of an alternating focus sweep in accordance with one embodiment.

[0011] Figures 2G - 2M is a schematic diagram of an alternating focus sweep in accordance with one embodiment.

[0012] Figures 3A - 3B is a flowchart of a method of a 3D confocal measurement process according to an embodiment disclosed herein.

[0013] Figure 4 is a schematic diagram of an exemplary area-scanning 3D confocal sensor with time modulation according to an embodiment.

[0014] Figure 5 is a flowchart of a method of measuring a surface using a confocal 3D sensor according to an embodiment disclosed herein.

[0015] Figure 6 is a schematic diagram of an exemplary 3D confocal sensor with time modulation according to another embodiment described herein.

[0016] Figure 7 is a schematic diagram of an exemplary 3D confocal sensor with time modulation according to another embodiment described herein.

[0017] Figure 8 is a schematic diagram of an exemplary 3D confocal sensor with time modulation according to another embodiment described herein.

[0018] Figures 9A - 9D shows a short coherence length light source (such as an LED or incandescent light source).

[0019] Figure 9E shows the response of a conventional interferometer when using a longer coherence length light source (such as a multimode laser).

[0020] Figure 9F is a view showing Figure 9E a magnified scanned portion of the central part.

[0021] Figure 9G shows the response / scanning using a long coherence length light source with a 3D confocal sensor according to an embodiment described herein.

[0022] Figure 9H is a view showing Figure 9G a magnified scanned portion of the central part.

[0023] Figure 10 is a schematic diagram of an exemplary 3D confocal sensor with time modulation using an adjustable-focus interference objective according to an embodiment described herein.

[0024] Figure 11 is a schematic diagram of an exemplary 3D confocal sensor with time modulation according to another embodiment described herein.

[0025] Figure 12Shows an example SLM spatial pattern that can be used in conjunction with the embodiments described herein.

[0026] Figure 13 Is a schematic diagram of an example 3D confocal sensor with time modulation using an adjustable-focus interference objective according to another embodiment described herein.

[0027] Figures 14A - 14F Shows an example light source modulation phase and frequency pattern for measuring double echoes. Detailed Description

[0028] The embodiments disclosed herein include improvements that significantly reduce the number of confocal images required in a high-precision 3D confocal measurement system, resulting in high-speed, high-resolution, and large-depth-of-field 3D measurements. Compared to prior art confocal 3D techniques where, for example, fifty or more images are captured in a single focus sweep, the light source of the confocal 3D measurement system is synchronously modulated in time during a single detector integration period or image capture period with a full focus sweep. The selected coding scheme determines the number of different time light source modulation patterns. The modulation pattern changes between subsequent image captures and focus sweeps. Then, the resulting image intensities from each modulation pattern and focus sweep can be used to decode the peak focus position for each pixel in the image. For a sinusoidally varying time modulation pattern, the phase of the light source changes between subsequent image captures, and a standard spatial phase-shift algorithm is used to calculate the peak focus position for each pixel in the image. In this way, the embodiments can synchronously modulate, gate, and integrate. The light source and focus can be synchronously modulated. The pinhole aperture is a light gate that only allows light from the best focus to transmit through. The detector can integrate during the entire modulation of the light source and focus sweep.

[0029] Figure 1 Is a schematic diagram of an example single-point 3D confocal sensor 22 with time modulation. Light from the light source 2 irradiates the light source pinhole aperture 4, transmits through the beam splitter 6, and converges towards the object 10 to be measured through the adjustable-focus lens 8. Then, the light reflects from the object 10, returns through the adjustable-focus lens 8, is reflected by the beam splitter 6, and converges towards the detection pinhole aperture 12. The light passing through the detection pinhole 12 is collected by the detector 14 and the integrator 15. Due to the optical sectioning property of the confocal microscope system, when the transmitted light from the pinhole aperture 4 is at the best focus on the object 10, the light transmitted through the detection pinhole 12 will be maximized. Away from the best focus, most of the light reflected from the object 10 will be blocked by the detection pinhole 12. The optical sectioning property of the confocal microscope is also described in the literature as "confocal gating". The light source pinhole aperture and the detection pinhole aperture create a "gate" that essentially only allows light from the best focus position to transmit through the detection pinhole aperture.

[0030] The light source 2 can be, but is not limited to, an LED, a laser (such as a solid-state laser), or an incandescent light source, so that the output intensity can be modulated temporally by the light source modulator 16. The tunable lens 8 can be, but is not limited to, a lens mechanically scanned by a voice coil or a linear stage. Alternatively, the tunable lens 8 can be a liquid lens, where the focus is adjusted by electrostatically changing the curvature of the liquid lens surface or by using acoustic waves to change the refractive index of the tunable lens 8.

[0031] Figures 2A - 2C An example light source modulator 16 current waveform I for the single-frequency sine modulation mode is shown src . Sine-modulate I k according to Equation 1a at frequency f src , where n = 0, 1, 2, t is time, and I peak is the peak LED current. The value for the peak LED current I peak is selected to provide an appropriate illumination level for the object being inspected.

[0032]

[0033] The focus modulator 18 is also synchronized with the light source modulator 16 to sweep the focal position Z of the tunable lens 8 foc , as Figures 2A - 2C shown. In the Figure 2A example, there is a peak in the detection current I det proportional to I foc detected by the detector 14 at the Z src,0 position indicated by the vertical dashed line. This detection current is integrated by the integrator 15 to record the level I0. This echo is visible in the integrated signal I int . In other words, since the focal position is swept synchronously with the light source modulator 16, the position of the optimal focus is encoded by the phase of the sine waveform I src .

[0034] In Figure 2B , the phase of the light source modulator 16 is shifted by 2π / 3 radians, corresponding to n = 1 in Equation 1. The peak detection current I det is again at the optimal focus and is proportional to I src,1 , resulting in an integrated value I1. In Figure 2C , the phase of the light source modulator 16 is shifted by 4π / 3 radians, corresponding to n = 2 in Equation 1. The peak detection current I det is again at the optimal focus and is proportional to I src,2 , resulting in an integrated value I2. For I srcTo solve for the phase and thus obtain the position of the best focus, standard phase-shift techniques from interferometry or phase-shifting profilometry (such as the technique known as three-phase reconstruction) can be used. According to the standard phase-shift algorithm, the phase Φ encoding the position of the best focus is given by Equation 2. The arctangent function in Equation 2 returns a value between -π / 2 and π / 2, and the signs of the numerator and denominator of the equation can be used to map this phase to the range of 0 to 2π. Once the phase is adjusted to the range of 0 to 2π, Equation 10 can be used to calculate the time t associated with this phase. The reflectivity R of the object 10 at the measurement point is given by Equation 3 and is directly proportional to the sum of three detected peak currents with a scaling factor α. The contrast of the received signal C is given by Equation 4. The contrast is different from the reflectivity (defined in Equation 3), where the reflectivity measures all the light received, while the contrast is a measure of the intensity of the detected sine wave.

[0035]

[0036] Other phase-shift techniques can be used (such as the four-phase technique using four sine light sources to modulate I src ,n, where n = 0, 1, 2, 3), and whenever n is incremented by 1, the phase shifts by π / 2 radians. Additionally, a higher-frequency sine waveform I src that will experience several cycles due to the swept focus can be used to increase the sensitivity of phase detection. This gives rise to the so-called 2π ambiguity problem, which can be addressed by using multiple sine waveforms I src frequencies and phases. For example, two different frequencies can be used to create a longer synthetic wavelength and eliminate the 2π ambiguity.

[0037] For a frequency f k , the wavelength is given by Equation 5, where v z is the speed at which the focus position changes; in MKS units, if v z is in m / s and f k is in cycles / s, then λ k will be in m / cycle.

[0038]

[0039] A synthetic longer wavelength λ syn can be created from wavelengths λ1 and λ2 by Equation 6.

[0040]

[0041] If two or more frequencies are used, the closed-form solutions for phase and contrast (Equations 3 and 4) are no longer applicable. Since the integrated photoelectric level model includes trigonometric functions, the most straightforward method for estimating object characteristics is an iterative least-squares solver. Many math libraries provide tools for minimizing the fitting residuals defined in equations such as Equation 8. For example, (Release 2022b, MathWorks Inc.) includes the function fminsearch. Minimizing the fitting residuals starts with defining the fitting residuals in Equation 8.

[0042]

[0043] where I k、n is the measured image level for each phase n and frequency k, and is the estimated image level for the estimated reflectivity, phase, and contrast.

[0044]

[0045] Equation 1b models the integrated echo intensity. The modeled integrated echo intensity is identified as different from the measured integrated value I n In Equation 1b, R^ is the estimated reflectivity of the object, including the detector dark level and the ambient light reaching the detector. The estimated signal contrast is modeled as The estimated position of the object surface is identified by the time point at which the focal plane sweeps across the object surface. (the time point when the focal plane sweeps across the object surface).

[0046] A typical approach is to minimize the sum of the squared residuals, which is calculated as S in Equation 9.

[0047]

[0048] This residual function is provided to the iterative least-squares solver along with an initial parameter estimate, resulting in the best-fit estimates of R^, and .

[0049] Figures 2A - 2C shows a linear sweep of the focus position Z foc The calibration process (not shown) can accurately characterize any non-linearity of the focus position Z foc and the exact range of the focus sweep.

[0050] Other temporal light source modulation techniques that encode the position of the best focus during a focus sweep can include, but are not limited to, Gray codes, linear up ramps and linear down ramps, and Hamiltonian codes. An example measurement encoding scheme with three Hamiltonian light source modulation modes is shown in Figures 2G - 2I and an example measurement encoding scheme with four Hamiltonian light source modulation modes is shown in Figures 2J - 2M .

[0051] Figure 3A is a flowchart of a method of a 3D confocal measurement process with a phase measurement encoding scheme and a sinusoidal modulation mode according to embodiments disclosed herein. Figure 3A Also shown is the measurement process of the confocal 3D sensor 22. The process starts with the processor 20 resetting the integrator 15 at step 28. The process proceeds to step 30, where the integrator 15 starts integrating the current from the detector 14. Immediately after step 30, for example, at step 32, the processor 20 signals the light source modulator 16 to sinusoidally modulate the light source 2 with an initial phase and frequency, while at step 34, the processor 20 also signals the focus modulator 18 to synchronously start sweeping the focal plane, as Figure 2A shown. When the focus sweep is complete and the light source has gone through a predetermined number of cycles, at step 36, the processor 20 signals the integrator 15 to stop integrating, and then at step 38, the processor 20 reads the integrated current from the detector as a voltage. At step 40, the processor 20 stores the voltage for each focus sweep while proceeding to the decision block 42. At block 42, it is determined whether the last phase is complete. If it is not the last sweep, then at step 46, the processor 20 increments the phase and, if applicable, increments to the next frequency. Then, the processor 20 resets the integrator 15 at step 28, signals the detector 14 to start integrating, and signals the light source modulator for the next phase and the next frequency (if applicable). Then the process is repeated until, at step 42, the processor 20 determines that the last sweep is complete. At step 48, the stored voltage corresponding to the phase of the best focus for each focus sweep is retrieved, and the processor 20 calculates the phase of the light source I src corresponding to the position of the best focus using a standard phase shift technique such as Equation 2. For example, then Equation 10 can be used to calculate the time corresponding to the focus position. For example, Equation 3 is used to calculate the reflectivity at the measurement position, and Equation 4 can be used to calculate the contrast. At step 49, taking into account the exact range of the focus sweep and any non-linearity of the focus sweep, the processor 20 converts the time of the best focus to a calibrated height value.

[0052] The measurement process can be accelerated by alternating the direction of the focus sweep between each integration period to take advantage of the focus retrace. Figures 2D - 2F ,exist Figure 2D Sweep focus position Z from low to high foc . Z foc The sweep direction is Figure 2E Sweep from high to low in Figure 2F In order to adapt to the change in the polarity of the sweep direction, I src, The phase of 1 is Figure 2E In relative to Figure 2B I src, 1 time-reversed. The phase Φ can then be calculated using Equation 2, which encodes the position of the best focus. The reflectivity at the measurement position can also be calculated using Equation 3.

[0053] Figure 3B is a flow chart of a method of a 3D confocal measurement process with selectable encoding mode according to embodiments disclosed herein. Figure 3B The measurement process of the confocal 3D sensor 22 is also shown. The process 220 begins at step 227 by selecting an appropriate encoding scheme (such as Figures 2J - 2M The coding scheme with four Hamiltonian light source modes) and the light source modulation mode are started. Then at step 228, the processor 20 resets the integrator 15. The process proceeds to step 230, where the integrator 15 begins to integrate the current from the detector 14. Immediately after step 230, for example, at step 232, the processor 20 signals the light source modulator 16 to modulate the light source 2 according to the initial modulation mode according to the selected coding scheme, and at step 234, the processor 20 also signals the focus modulator 18 to synchronously start scanning the focal plane, such as Figure 2JAs shown. When the focus sweep and modulation mode are completed, at step 236, the processor 20 signals the integrator 15 to stop integrating, and then at step 238, the processor 20 reads the integrated current from the detector as a voltage. At step 240, the processor 20 stores the voltage for each focus sweep while proceeding to decision block 242. At block 242, it is determined whether the last modulation mode is completed. If it is not the last sweep, then at step 246, the processor 20 increments the modulation mode. Then the processor 20 resets the integrator 15 at step 228, signals the detector 14 to start integrating, and signals the light source modulator for the modulation mode. Then the process is repeated until, at step 242, the processor 20 determines that the last sweep is complete. At step 248, the stored voltages corresponding to the times of the best focus for each focus sweep are retrieved, and the processor 20 decodes the times corresponding to the positions of the best focus according to the selected coding scheme at step 248. The reflectivity is also calculated at step 248. At step 249, taking into account the exact range of the focus sweep and any non-linearity of the focus sweep, the processor 20 converts the time of the best focus to a calibrated height value.

[0054] Figure 4Schematic diagram of an example area-scanning 3D confocal sensor 90 with temporal modulation. Light from a light source 50 is modulated by a light source modulator 52, collected by a condenser lens 54, transmitted through a beam splitter 56, and projected onto a Nipkow disk 58. The Nipkow disk 58 contains an array of pinhole apertures and is rotated by a motor 59. An example Nipkow disk is disclosed in US 4,927,254. A lens 60, an aperture stop 62, and a focusing lens 64 form an imaging system to image the pinhole apertures of the Nipkow disk 58 onto an object 10. Light reflected from the object 10 is imaged back onto the Nipkow disk 58 through the lens 64, the aperture stop 62, and the lens 60. The reflected light passing through the apertures of the Nipkow disk 58 is reflected from the beam splitter 56 and imaged onto a camera detector 70 through an imaging system formed by a lens 65, an aperture stop 66, and a lens 68. Similarly, due to the optical sectioning property of confocal microscopy, when a point on the object is at the best focus, the reflected light transmitted through the pinhole apertures of the Nipkow disk 58 will have a peak intensity, and away from the best focus, the intensity will rapidly decrease. The camera detector 70 can be, but is not limited to, a CMOS or CCD area array with a two-dimensional pixel array. The focusing lens 64 can be, but is not limited to, a lens mechanically scanned by a voice coil or a linear stage. Alternatively, the focusing lens 64 can be a liquid lens, where the focus is adjusted by electrostatically changing the curvature of the liquid lens surface or by changing the refractive index of the focusing lens 64 using acoustic waves. The light source 50 can be, but is not limited to, an LED, a solid-state laser, or an incandescent light source, so that the output intensity can be temporally modulated by the light source modulator 52.

[0055] The object 10 is conveyed by a stage assembly 51. The stage assembly 51 can include one or more linear or rotary stages.

[0056] A timing controller 72 signals the light source modulator 52 for the temporal modulation pattern for each focus sweep. The timing controller 72 also synchronizes the timing of the light source modulator 52 and a focus modulator 74 to sweep the focus while temporally modulating the light source 50 during one integration period of the camera detector 70.

[0057] The Nipkow disk 58 can be designed to have a pinhole pattern along Archimedean spirals, which can consist of a single continuous spiral or multiple interleaved spirals. If a single spiral is used, the disk must rotate a full turn to sample all radial distances. If there are N spirals, the disk must rotate 1 / N turns to sample all radial distances. Since the focus sweep only gets a short period close to the optimal focus (when the maximum photoelectric level returns to the detector), the pinhole pattern can be designed to sample all necessary radial positions at a small rotation angle. This can be achieved by using a very large number of spirals and by staggering the radii of the pinholes in each spiral to maximize the radial coverage at a short rotation angle. The geometry of the pinhole aperture can be, but is not limited to, circular, square, or octagonal shapes. The geometry of the pinhole aperture can also be a thin straight line or a curve. In another embodiment, the rotating Nipkow disk 58 can be replaced by an array of linearly translated pinhole apertures. The design of the aperture pattern can be optimized to balance the light flux, the axial resolution, and the crosstalk from the defocused regions passing through adjacent apertures. The crosstalk causes the background intensity I det to increase.

[0058] Figure 5 is a flowchart of a method for measuring a surface using a confocal 3D sensor according to embodiments disclosed herein. The method 300 begins in step 96 with the computer 76 providing a selected encoding scheme (such as Figures 2G - 2I an encoding scheme with three Hamiltonian light source modulation modes) and a light source modulation mode to the timing controller 72. Next, at step 98, the camera detector 70 is reset by the timing controller 72. The method 300 proceeds to step 100, where integration begins for a single video frame of the detector 70. Immediately after step 100, for example, at step 102, the timing controller 72 signals the light source modulator 52 to modulate the light source 50 with an initial modulation mode, while at step 104, the timing controller 72 also signals the focus modulator 74 to synchronously begin sweeping the focal plane, as Figure 2GAs shown. When the focus sweep is complete and the light source modulator 52 has completed the modulation pattern, at step 106, the timing controller 72 signals the detector 70 to stop integrating. The readout of the video data begins at step 108 and is transferred to the memory in the computer 76 at step 110. The process proceeds to decision block 112, where it is determined by the timing controller whether the last modulation pattern has been completed. If it is not the last sweep, at step 116, the timing controller 72 increments the modulation pattern. Then the detector 70 is reset at step 98, and then at step 100, the timing controller 72 signals the camera detector 70 to begin integrating the next video frame. Then the method 300 is repeated until, at step 112, the timing controller 72 determines that the last sweep is complete. The stored pixel values corresponding to the time of the best focus for each focus sweep are retrieved at step 118, and at step 118, the computer 76 decodes the time of the light source I src corresponding to the best focus time for all pixels of the camera detector 70. The reflectivity for all pixels is also calculated at step 118. At step 120, taking into account the exact range of the focus sweep and any non - linearities of the focus sweep or optical aberrations, the computer 76 converts the time of the best focus for each pixel to a calibrated height value for each pixel. The calibration process of the 3D confocal sensor 90 can also accommodate other design and manufacturing tolerances, such as field curvature across the field of view of the camera detector 70. At this point, the computer 76 can command the stage assembly 51 to translate the object 10 to a new position and start another measurement cycle at a different field of view.

[0059] In another example, the detector 70 can also be a line scan detector configured as a one - dimensional array of photodetectors or pixels, or a time - delay and integration (TDI) image sensor, each of which produces a line field of view. In this example, the stage assembly 51 can move continuously in a direction perpendicular to the line field of view during the integration of the detector 70. Then, the speed of the stage assembly 51, the integration time of the detector 70, and the number of focus sweeps per measurement affect the lateral resolution in the direction of stage movement.

[0060] Figure 6 is a schematic diagram of an exemplary 3D confocal sensor 92 with time modulation similar to the 3D confocal sensor 90. Elements with the same reference numerals provide the same functions. In the 3D confocal sensor 92, the adjustable focusing lens 64 has been replaced by a fixed lens 84. Figure 6The adjustable-focus lens 80 is placed at or near the aperture stop 62. The adjustable-focus lens 80 can be, but is not limited to, a lens mechanically scanned by a voice coil or a linear stage. Alternatively, the adjustable-focus lens 80 can be a liquid lens, where the focus is adjusted by electrostatically changing the curvature of the liquid lens surface or by using acoustic waves to change the refractive index of the adjustable-focus lens 80.

[0061] Figure 7 is a schematic diagram of an exemplary 3D confocal sensor 91 with time modulation. The focus modulator 82 synchronously sweeps the position of the object 10 through the focus by moving the stage assembly 51 in the axial direction of the lens 84.

[0062] Figure 8 is a schematic diagram of an exemplary 3D confocal sensor 93 with time modulation similar to the 3D confocal sensor 91. Elements with the same reference numerals provide the same functions. The fixed lens 84 has been replaced by an interference objective lens 69 in the 3D confocal sensor 93. The interference objective lens 69 can be, but is not limited to, a known Mirau, Michelson, or Linnik type interferometer objective lens. The light source 53 can be a short coherence length light source or a long coherence length light source. The light source 53 can be, but is not limited to, an LED, a superluminescent LED (SLED), a laser, or an incandescent light source, so that the output intensity can be time-modulated by the light source modulator 52. The focus modulator 82 synchronously sweeps the position of the object 10 through the focus by moving the stage assembly 51 in the axial direction of the lens 84.

[0063] Due to the interference objective lens 69, each pixel of the camera detector 70 will receive a coherent interference signal during the focus sweep, which is superimposed on the confocal response due to the pinhole aperture of the Nipkow disk 58.

[0064] Figures 9A - 9D shows a short coherence length light source (such as an LED or an incandescent light source). Figure 9A shows an interference pattern for a conventional interferometer (commonly known as a white light interferometer (WLI)). Figure 9B is a scan magnified portion showing the Figure 9A central part. For a conventional WLI over most of the scan range, there are no interference fringes, and for a very narrow height range defined by the coherence length of the light source, a strong interference pattern (known as a calibration pattern) is visible. Away from the best focus, the detector receives a high background level. For the sensor 93, the characteristic pixel response I det function is shown as a function of the focus position Z Figure 9C in foc . Figure 9D is the same pixel response I foc over a smaller range of focus positions Z Figure 9C as det . FromFigure 9C As can be seen, due to the gating characteristics of the light source and the probe pinhole aperture, the background level far from the optimal focus is much lower than that in the Figure 9A conventional WLI response shown. This reduction in background level allows the modulated echo to be integrated on the detector without adding excessive signal level or noise. Method 300 can be used for the 3D confocal sensor 93 to calculate the height value of the object 10 at each pixel position. As described in method 300, several different light source modulation frequencies can be used while sweeping the focus of the object 10 using the stage assembly 51. At least two frequencies can be used to find the position of the modulation envelope and the peak of the correlation graph. For example, a relatively low modulation frequency can be used to locate the confocal pinhole echo, and a high frequency can be used to find the peak position of the interference pattern.

[0065] Figure 9E Shows the response of a conventional interferometer when using a light source with a longer coherence length, such as a multimode laser. Figure 9F Is a magnified scan of the central part showing Figure 9E . For a light source with a long coherence length, the interference fringes are visible over a very wide range, but it is difficult to determine the peak position. This is a common wrapping problem for laser-based interferometers. Using a light source with a long coherence length with the sensor 93 gives the Figure 9G echo shown. Figure 9H Is a magnified scan of the central part showing Figure 9G . The splitting characteristics of the pinhole confocal system limit the echo to a small area near the optimal focus. Compared with a standard interferometer ( Figure 9F ), it is easier to see the peak of the calibration graph in the sensor 93 response ( Figure 9G ).

[0066] A common problem with scanning white light interferometers is the need for a large number of images sampled at many focus height planes, especially in the case of a large height range. Method 300 applied to the 3D confocal sensor 93 provides a way to overcome this limitation. Applying method 300 to find the position of the object 10, a first height estimate using a low-frequency time modulation mode can be found in as few as two or three images. The low modulation frequency is insensitive to the interference ripples near the optimal focus and only detects the envelope. This envelope detection is the same as the operating mode used for the sensor 90. Then method 300 is applied again in a high-frequency modulation mode, where the modulation is applied only in a smaller focus sweep area near the first height estimate. Limiting the illumination to a smaller scan area reduces the scan time and reduces the integration of the background photoelectric level and the shot noise associated with the integration of the excessive background level.

[0067] Figure 10FIG. 0 is a schematic diagram of an exemplary 3D confocal sensor 94 that performs time modulation using a tunable-focus interference objective 67. The tunable-focus interference objective 67 can be, but is not limited to, an interference objective that is mechanically scanned by a voice coil or a linear stage. Alternatively, the tunable-focus interference objective can include a liquid lens element, or the refractive index of the lens element is changed by using acoustic waves, where the curvature of the liquid lens surface is changed electrostatically or the refractive index of the lens element of the tunable-focus interference objective 67 is changed by using acoustic waves to adjust the focus. Method 300 can be used for the 3D confocal sensor 94 to calculate the height value of the object 10 at each pixel position.

[0068] Figure 11 FIG. 1 is a schematic diagram of an exemplary 3D confocal sensor 190 having time modulation. The 3D confocal sensor 190 operates on the same principle as the 3D confocal sensor 90, where the function provided by the Nipkow disk 58 is replaced by a spatial light modulator (SLM) 158. During the focus sweep, when the measurement position of the object 10 is away from the best focus, both the Nipkow disk 58 and the spatial light modulator 158 respectively reduce the background intensity away from the best focus on the pixels of the cameras 70 and 170. The light from the light source 150 is modulated by the light source modulator 152, collected by the condenser lens 154, transmitted through the beam splitter 163, and incident on the spatial light modulator 158. The pixelated spatial light modulator 158 can be, but is not limited to, a digital micromirror device (DMD) or a liquid crystal on silicon device (LCOS). Then, the light is reflected from the pixels of the SLM 158 in the active state. The lenses 160, the aperture stop 162, and the tunable-focus lens 164 form an imaging system to image the pixels of the SLM 158 onto the object 10. The light reflected from the object 10 is imaged back onto the SLM 158 through the lens 164, the aperture stop 162, and the lens 160. Then, the light is reflected from the pixels of the SLM 158 in the active state, reflected from the beam splitter 163, and then imaged onto the camera 170 through the imaging system formed by the lens 165, the aperture stop 166, and the lens 168. The spatial light modulator 158 can simulate the optical sectioning characteristics of the Nipkow disk system by using a time series of spatial patterns similar to the spatial pattern of the Nipkow aperture array. Figure 12 FIG. 2 shows an exemplary SLM 158 spatial pattern. During a single focus sweep, the spatial pattern is switched at high speed in time to effectively simulate the sweeping aperture array of the rotating Nipkow disk. Due to the optical sectioning characteristics of the confocal microscope, when a point on the object is at the best focus, the light reflected from the pixels of the SLM 158 in the active state will have a peak intensity, and this intensity will rapidly decrease away from the best focus.

[0069] Figure 13Schematic diagram of an exemplary 3D confocal sensor 194 that uses a tunable-focus interference objective 167 for time modulation. The 3D confocal sensor 194 is similar to the 3D confocal sensor 190, where the tunable lens 164 is replaced by a tunable-focus interference objective 167.

[0070] A common measurement task is the estimation of the thickness of a transparent layer (e.g., the thickness of a mask layer on the surface of a printed circuit board or an etchant on a semiconductor wafer). For a single-reflection surface, the 3D confocal sensor must estimate the surface reflectivity, height (phase of the echo signal), and contrast level of the echo signal. Including the second echo results in five unknowns: object reflectivity, the heights of the two surfaces, and the contrast levels of the two surfaces. At least five data points are required to solve these five unknowns.

[0071] Figures 14A - 14F An exemplary light source modulation phase and frequency pattern for measuring double echoes is shown. In Figures 14A - 14C it is sinusoidally modulated I according to Equation 1 at a frequency f k = 1, where n = 0, 1, 2. In src it is sinusoidally modulated I according to Equation 1 at a frequency f Figures 14D - 14F = 3, where n = 0, 1, 2. For k the focus sweep is the same, and the detection current I src shows the double echo. The timing of the two peak echoes is marked by the dashed lines labeled "Surface 0" and "Surface 1". This double echo is visible in the integrated signal I Figures 14A - 14F . The integrated values I0, I1, I2 correspond to the measurement at a frequency f det = 1. The integrated values I3, I4, I5 correspond to the measurement at a frequency f int = 3. As described, there are five unknowns; using two modulation frequencies with three phases for each unknown provides six measurements. k = 1. The integrated values I3, I4, I5 correspond to the measurement at a frequency f k = 3. As described, there are five unknowns; using two modulation frequencies with three phases for each unknown provides six measurements.

[0072]

[0073] The integrated echo for each phase and frequency for a double-echo object can be modeled by Equation 7. The object reflectivity estimate is R^, and the echo contrast for each of the two surfaces is estimated as and The light sensed at two focus positions is estimated as and Collect images of the object with multiple phases n and frequency f k . Once and have been estimated, these values can be converted to phase using Equation 10 and to height using step 120 of method 300.

[0074] Since the integrated optoelectronic level model includes trigonometric functions, the most straightforward method for estimating object characteristics is an iterative least squares solver. Many math libraries provide tools for minimizing the fitting residuals defined in an equation such as Equation 8, e.g., including the function fminsearch. The process starts with defining the fitting residuals in Equation 8.

[0075]

[0076] One approach is to minimize the sum of the squared residuals, which is calculated as S in Equation 9.

[0077]

[0078] This residual function is provided to the iterative least squares solver along with an initial parameter estimate to obtain the best fit estimates of the target reflectivity, phase, and contrast.

[0079] In fact, lens blur will cause the contrast C to decrease as the modulation frequency f increases. To obtain the best results, the C term in Equation 7 should be weighted by this expected blur with frequency. The fitting accuracy and robustness can be improved by including more frequencies in the image set.

[0080] As described above, time modulation is provided by modulating the light source. The same functionality can be achieved by time modulating the sensitivity or transmission in other parts of the signal path. The integrator 15 in sensor 22 or the gain of the integrator as part of camera detectors 70 and 170 can be time modulated according to the same method described to achieve the same performance. For example, detector integrator modulation on the camera is used in a time-of-flight sensor such as Texas Instruments OPT8241.

[0081] Alternatively, the gain of the optical path can be time modulated by adding a ferroelectric or liquid crystal light valve in the optical path. Other devices for modulating the light flux include variable absorbers and orthogonal polarizers. Instead of time modulating the light source 2, light source 50, or light source 53, the transparency or reflectivity of the light valve can be used.

[0082] Alternatively, in sensors 190 and 194, the SLM 158 can time modulate the light by time modulating the flux of the SLM 158 pixels in the active state.

Claims

1. A single-point confocal sensor for measuring the height of a point on an object, the sensor comprising: A light source; A light source modulator configured to perform temporal modulation of the light source intensity; A light source pinhole aperture positioned to be illuminated by the light source; An adjustable-focus lens configured to focus the illumination passing through the light source pinhole aperture onto the object; A detector pinhole aperture configured to receive reflected light from the object, wherein the adjustable-focus lens is configured to image the reflected light from the object onto the detector pinhole aperture; A detector and integrator configured to output a measurement value indicative of the total light transmitted through the detector pinhole aperture; A processor operably coupled to the detector, the integrator, and the light source modulator, wherein the processor is configured to synchronously cause the light source modulator to modulate the light source intensity while causing the adjustable-focus lens to sweep an axial focus position.

2. The single-point confocal sensor according to claim 1, wherein, The processor is further configured to calculate the height of the point on the object based on the outputs from the detector and the integrator.

3. The single-point confocal sensor according to claim 2: Among them, During a first integration period, the processor is configured to control the light source modulator to modulate the light source at a first phase and a first frequency, while synchronously causing the adjustable-focus lens to sweep the axial focus position through a focus range, the processor is configured to read and store the integrator output within the first integration period, and then reset the integrator; Wherein, during a second integration period, the processor is configured to control the light source modulator to modulate the light source at a second phase and the first frequency, while synchronously causing the adjustable-focus lens to sweep the axial focus position through the focus range, the processor is configured to read and store the integrator output within the second integration period, and then reset the integrator; Wherein, during a third integration period, the processor is configured to control the light source modulator to modulate the light source at a third phase and the first frequency, while synchronously causing the adjustable-focus lens to sweep the axial focus position through the focus range, the processor is configured to read and store the integrator output within the third integration period; and Wherein the processor is configured to calculate the phase of the light source corresponding to the focus position based on the first integrator output, the second integrator output, and the third integrator output, and convert the phase of the light source to the height of the point on the object.

4. The single-point confocal sensor according to claim 1, wherein, The light source is a light-emitting diode.

5. The single-point confocal sensor according to claim 1, wherein, The light source is a laser.

6. The single-point confocal sensor according to claim 1, wherein, The light source is an incandescent light source.

7. The single-point confocal sensor according to claim 1, wherein, The adjustable-focus lens is mechanically scanned by a voice coil.

8. The single-point confocal sensor according to claim 1, wherein, The adjustable-focus lens is mechanically scanned by a linear stage.

9. The single-point confocal sensor according to claim 1, wherein, The adjustable-focus lens is a liquid lens.

10. The single-point confocal sensor according to claim 9, wherein, The focus of the liquid adjustable-focus lens is adjusted by electrostatically changing the curvature of the liquid lens surface.

11. The single-point confocal sensor according to claim 1, wherein, The focus of the adjustable-focus lens is adjusted by using acoustic waves to change the refractive index of the adjustable-focus lens.

12. The single-point confocal sensor according to claim 1, wherein, The temporal modulation is based on a Gray code.

13. The single-point confocal sensor according to claim 1, wherein, The temporal modulation is based on a ramp.

14. The single-point confocal sensor according to claim 1, wherein, The temporal modulation is based on a Hamming code.

15. The single-point confocal sensor according to claim 1, wherein, The temporal light source modulation is a periodic function.

16. The single-point confocal sensor according to claim 15, wherein, The periodic function is a sine function.

17. The single-point confocal sensor according to claim 15, wherein, The period of the periodic function is equal to the amount of time required for the adjustable focus lens to sweep through the entire focus range and traverse the axial focus positions.

18. A confocal three-dimensional sensor for measuring the height of a point array on an object, the sensor comprising: A light source; A light source modulator configured to perform time modulation on the light source intensity; An array of pinhole apertures configured to be illuminated by the light source and to receive reflected light from the object; An adjustable focus lens configured to focus the illumination passing through the array of pinhole apertures onto the object and to image the reflected light from the object onto the array of pinhole apertures; A focus modulator operatively coupled to the adjustable focus lens, the focus modulator being configured to sweep through the axial focus positions; An imaging system that images the array of pinhole apertures onto a camera detector; A camera detector configured to receive the reflected light from the object imaged by the adjustable focus lens onto the array of pinhole apertures and to provide an output measurement indicative of the total transmitted light passing through the array of pinhole apertures for each point in the point array; A processor operatively coupled to the camera detector, the processor being configured to synchronously cause the light source modulator to modulate the light source intensity while causing the focus modulator to sweep through the axial focus positions.

19. The confocal three-dimensional sensor according to claim 18, wherein, The processor is further configured to calculate the height of each point in the point array based on the output from the camera detector.

20. The confocal three-dimensional sensor according to claim 19, wherein, The processor is configured to: During a first integration period, cause the light source modulator to modulate the light source at a first phase and a first frequency while synchronously causing the focus modulator to sweep through the focus range and traverse the axial focus positions, the processor being configured to read and store a video frame from the camera detector relative to the first integration period; During a second integration period, cause the light source modulator to modulate the light source at a second phase and the first frequency while synchronously causing the focus modulator to sweep through the focus range and traverse the axial focus positions, the processor being configured to read and store a video frame from the camera detector relative to the second integration period; During a third integration period, cause the light source modulator to modulate the light source at a third phase and the first frequency while synchronously causing the focus modulator to sweep through the focus range and traverse the axial focus positions, the processor being configured to read and store a video frame from the camera detector relative to the third integration period; And Calculate the phase corresponding to the light source and the focus position for the video frame pixels based on the stored first video frame, second video frame, and third video frame, and then convert the phase of the pixels to height values.

21. The confocal three-dimensional sensor according to claim 18, wherein, The array of pinhole apertures is a movable array of pinhole apertures.

22. The confocal three-dimensional sensor according to claim 21, wherein, The movable array of pinhole apertures is a rotating Nipkow disk.

23. The confocal three-dimensional sensor according to claim 21, wherein, The movable pinhole aperture position is a reciprocating translation array.

24. The confocal three-dimensional sensor according to claim 18, wherein, The light source is a light-emitting diode.

25. The confocal three-dimensional sensor according to claim 18, wherein, The light source is a laser.

26. The confocal three-dimensional sensor according to claim 18, wherein, The light source is an incandescent light source.

27. The confocal three-dimensional sensor according to claim 18, wherein The adjustable focus lens is mechanically scanned by a voice coil.

28. The confocal three-dimensional sensor according to claim 18, wherein The adjustable focus lens is mechanically scanned by a linear stage.

29. The confocal three-dimensional sensor according to claim 18, wherein, The adjustable focus lens is a liquid lens.

30. The confocal three-dimensional sensor according to claim 29, wherein, The focus of the liquid adjustable focus lens is adjusted by electrostatically changing the curvature of the liquid lens surface.

31. The confocal three-dimensional sensor according to claim 18, wherein, The focus of the tunable lens is adjusted by changing the refractive index of the tunable lens using sound waves.

32. The confocal three-dimensional sensor according to claim 18, wherein The time modulation is based on Gray code.

33. The confocal three-dimensional sensor according to claim 18, wherein, The time modulation is based on a ramp.

34. The confocal three-dimensional sensor according to claim 18, wherein, The time modulation is based on Hamming code.

35. The confocal three-dimensional sensor according to claim 18, wherein, The time light source modulation is a periodic function.

36. The confocal three-dimensional sensor according to claim 35, wherein, The periodic function is a sine function.

37. The confocal three-dimensional sensor according to claim 35, wherein The period of the periodic function is equal to the amount of time required for the tunable lens to sweep through the focal range and traverse the axial focal positions.

38. The confocal three-dimensional sensor according to claim 18, wherein, The camera detector is a complementary metal oxide semiconductor (CMOS) area array having a two-dimensional pixel array.

39. The confocal three-dimensional sensor according to claim 18, wherein, The camera detector is a charge-coupled device (CCD) area array having a two-dimensional pixel array.

40. A confocal three-dimensional sensor for measuring the height of a point array on an object, the sensor comprising: A light source; A light source modulator configured to perform time modulation on the light source intensity; A pinhole aperture array configured to be illuminated by the light source and receive reflected light from the object; A focus modulator configured to sweep through axial focal positions; An imaging system that images the pinhole aperture array onto a camera detector; An interference objective configured to focus the illumination passing through the pinhole aperture array onto the object and provide a coherent interference signal to the pinhole aperture array during the focus sweep; A camera detector configured to receive the coherent interference signal transmitted through the pinhole aperture array and provide an output measurement indicative of the total transmitted light through the pinhole aperture array for each point in the point array; A processor operably coupled to the camera detector, the processor being configured to synchronously cause the light source modulator to modulate the light source intensity while causing the focus modulator to sweep through axial focal positions.

41. The confocal three-dimensional sensor according to claim 40, wherein, The processor is further configured to calculate the height of each point in the point array based on the output from the camera detector.

42. The confocal three-dimensional sensor according to claim 41, wherein, The processor is configured to: During a first integration period, cause the light source modulator to modulate the light source at a first phase and a first frequency while synchronously causing the focus modulator to sweep through the focal range and traverse the axial focal positions, and the processor is configured to read and store a video frame from the camera detector relative to the first integration period; During a second integration period, cause the light source modulator to modulate the light source at a second phase and the first frequency while synchronously causing the focus modulator to sweep through the focal range and traverse the axial focal positions, and the processor is configured to read and store a video frame from the camera detector relative to the second integration period; During a third integration period, cause the light source modulator to modulate the light source at a third phase and the first frequency while synchronously causing the focus modulator to sweep through the focal range and traverse the axial focal positions, and the processor is configured to read and store a video frame from the camera detector relative to the third integration period; And Calculate the phase corresponding to the light source and the focus position for the video frame pixels based on the stored first video frame, second video frame, and third video frame, and then convert the phase of the pixels to height values.

43. The confocal three-dimensional sensor according to claim 40, wherein, The pinhole aperture array is a movable pinhole aperture array.

44. The confocal three-dimensional sensor according to claim 43, wherein, The moving pinhole aperture array is a rotating Nipkow disk.

45. The confocal three-dimensional sensor according to claim 43, wherein The moving pinhole aperture is a reciprocating translation array.

46. The confocal three-dimensional sensor according to claim 40, wherein, The light source is a light-emitting diode.

47. The confocal three-dimensional sensor according to claim 40, wherein, The light source is a laser.

48. The confocal three-dimensional sensor according to claim 40, wherein, The light source is an incandescent light source.

49. The confocal three-dimensional sensor according to claim 40, wherein, The time modulation is based on a Gray code.

50. The confocal three-dimensional sensor according to claim 40, wherein, The time modulation is based on a ramp.

51. The confocal three-dimensional sensor according to claim 40, wherein, The time modulation is based on a Hamming code.

52. The confocal three-dimensional sensor according to claim 40, wherein, The time light source modulation is a periodic function.

53. The confocal three-dimensional sensor according to claim 52, wherein, The periodic function is a sine function.

54. The confocal three-dimensional sensor according to claim 52, wherein, The period of the periodic function is equal to the amount of time required for the focusing lens to traverse the focal range and sweep the axial focal position.

55. The confocal three-dimensional sensor according to claim 40, wherein, The camera detector is a complementary metal-oxide-semiconductor (CMOS) area array with a two-dimensional pixel array.

56. The confocal three-dimensional sensor according to claim 40, wherein, The camera detector is a charge-coupled device (CCD) area array with a two-dimensional pixel array.

57. The confocal three-dimensional sensor according to claim 40, wherein, The interference objective lens is a tunable focus interference objective lens.

58. A confocal three-dimensional sensor for measuring the height of a point array on an object, the sensor comprising: A light source; A light source modulator configured to perform time modulation on the light source intensity; A spatial light modulator configured to be illuminated by the light source and receive reflected light from the object; A tunable focus lens configured to focus the illumination gated by the spatial light modulator onto the object and image the reflected light from the object onto the spatial light modulator; A focus modulator operably coupled to the tunable focus lens, the focus modulator being configured to sweep the axial focal position; An imaging system that images the spatial light modulator onto a camera detector; A camera detector configured to receive the reflected light from the object imaged by the tunable focus lens onto the spatial light modulator and provide an output measurement indicating the total light gated by the spatial light modulator for each point in the point array; A processor operably coupled to the camera detector, the processor being configured to synchronously cause the light source modulator to modulate the light source intensity while causing the focus modulator to sweep the axial focal position.

59. The confocal three-dimensional sensor according to claim 59, wherein, The processor is further configured to calculate the height of each point in the point array based on the output from the camera detector.

60. The confocal three-dimensional sensor according to claim 60, wherein, The processor is configured to: During a first integration period, cause the light source modulator to modulate the light source with a first phase and a first frequency, while synchronously causing the focus modulator to traverse the focal range and sweep the axial focal position, and the processor is configured to read and store a video frame from the camera detector relative to the first integration period; During a second integration period, cause the light source modulator to modulate the light source with a second phase and the first frequency, while synchronously causing the focus modulator to traverse the focal range and sweep the axial focal position, and the processor is configured to read and store a video frame from the camera detector relative to the second integration period; During a third integration period, cause the light source modulator to modulate the light source with a third phase and the first frequency, while synchronously causing the focus modulator to traverse the focal range and sweep the axial focal position, and the processor is configured to read and store a video frame from the camera detector relative to the third integration period; And Calculate the phase corresponding to the light source and the focal point position for the video frame pixels based on the stored first video frame, second video frame, and third video frame, and then convert the phase of the pixels into height values.

61. The confocal three-dimensional sensor according to claim 59, wherein, The light source is a light-emitting diode.

62. The confocal three-dimensional sensor according to claim 59, wherein, The light source is a laser.

63. The confocal three-dimensional sensor according to claim 59, wherein, The light source is an incandescent light source.

64. The confocal three-dimensional sensor according to claim 59, wherein, The adjustable focus lens is mechanically scanned by a voice coil.

65. The confocal three-dimensional sensor according to claim 59, wherein, The adjustable focus lens is mechanically scanned by a linear stage.

66. The confocal three-dimensional sensor according to claim 59, wherein, The adjustable focus lens is a liquid lens.

67. The confocal three-dimensional sensor according to claim 67, wherein, Adjust the focus of the liquid adjustable focus lens by electrostatically changing the curvature of the liquid lens surface.

68. The confocal three-dimensional sensor according to claim 59, wherein, Adjust the focus of the adjustable focus lens by using sound waves to change the refractive index of the adjustable focus lens.

69. The confocal three-dimensional sensor according to claim 59, wherein, The time modulation is based on a Gray code.

70. The confocal three-dimensional sensor according to claim 59, wherein, The time modulation is based on a ramp.

71. The confocal three-dimensional sensor according to claim 59, wherein, The time modulation is based on a Hamming code.

72. The confocal three-dimensional sensor according to claim 59, wherein, The time light source modulation is a periodic function.

73. The confocal three-dimensional sensor according to claim 73, wherein, The periodic function is a sine function.

74. The confocal three-dimensional sensor according to claim 73, wherein, The period of the periodic function is equal to the amount of time required for the adjustable focus lens to sweep the axial focal position through the focal range.

75. The confocal three-dimensional sensor according to claim 59, wherein, The camera detector is a complementary metal-oxide-semiconductor (CMOS) area array with a two-dimensional pixel array.

76. The confocal three-dimensional sensor according to claim 59, wherein, The camera detector is a charge-coupled device (CCD) area array with a two-dimensional pixel array.

77. The confocal three-dimensional sensor according to claim 59, wherein, The spatial light modulator is a pixelated spatial light modulator.

78. The confocal three-dimensional sensor according to claim 59, wherein, The spatial light modulator is a digital micromirror device (DMD).

79. The confocal three-dimensional sensor according to claim 59, wherein, The spatial light modulator is a liquid crystal on silicon (LCOS) device.

80. A single-point confocal sensor for measuring the height of a point on an object, the sensor comprising: A light source; A light source modulator configured to perform time modulation on the light source intensity; A lens configured to focus the illumination passing through it onto the object; A light source pinhole aperture positioned to be illuminated by the light source; A focus modulator configured to generate relative movement between the object and the single-point confocal three-dimensional sensor; A detector pinhole aperture configured to receive reflected light from the object; A detector and integrator configured to output a measurement value indicating the total light transmitted through the detector pinhole aperture; A processor operably coupled to the detector, the light source modulator, and the focus modulator, wherein the processor is configured to synchronously cause the light source modulator to modulate the light source intensity while causing the focus modulator to sweep the axial focal position.

81. The single-point confocal sensor according to claim 81, wherein The processor is further configured to calculate the height of the point on the object based on the output from the detector and integrator.

82. The single-point confocal sensor according to claim 82: Among them, During a first integration period, the processor is configured to control the light source modulator to modulate the light source with a first phase and a first frequency, while synchronously causing the focus modulator to sweep the axial focal position through the focal range. The processor is configured to read and store the detector output within the first integration period, and then reset the detector; Wherein, during a second integration period, the processor is configured to control the light source modulator to modulate the light source at a second phase and a first frequency, while synchronously causing the focus modulator to sweep an axial focus position through the focus range, the processor is configured to read and store the detector output within the second integration period, and then reset the detector; Wherein, during a third integration period, the processor is configured to control the light source modulator to modulate the light source at a third phase and a first frequency, while synchronously causing the focus modulator to sweep an axial focus position through the focus range, the processor is configured to read and store the detector output within the third integration period; and Wherein the processor is configured to calculate a phase of the light source corresponding to the focus position based on the first detector output, the second detector output, and the third detector output, and convert the phase of the light source into a height of a point on the object.

83. The single-point confocal sensor according to claim 81, wherein, The light source is a light-emitting diode.

84. The single-point confocal sensor according to claim 81, wherein, The light source is a laser.

85. The single-point confocal sensor according to claim 81, wherein, The light source is an incandescent light source.

86. The single-point confocal sensor according to claim 81, wherein, The focus modulator is operatively coupled to a mobile stage assembly.

87. The single-point confocal sensor according to claim 81, wherein, The time modulation is based on a Gray code.

88. The single-point confocal sensor according to claim 81, wherein, The time modulation is based on a ramp.

89. The single-point confocal sensor according to claim 81, wherein, The time modulation is based on a Hamming code.

90. The single-point confocal sensor according to claim 81, wherein, The time light source modulation is a periodic function.

91. The single-point confocal sensor according to claim 91, wherein, The periodic function is a sine function.

92. The single-point confocal sensor according to claim 91, wherein, A period of the periodic function is equal to an amount of time required for a tunable lens to sweep an axial focus position through the focus range.

93. A confocal three-dimensional sensor for measuring heights of a point array on an object, the sensor comprising: A light source; A light source modulator configured to perform time modulation on a light source intensity; A pinhole aperture array configured to be illuminated by the light source and receive reflected light from the object; A lens configured to focus illumination passing through the pinhole aperture array onto the object; A focus modulator configured to generate relative movement between the object and the confocal three-dimensional sensor; A camera detector configured to receive reflected light from the object imaged by the lens onto the pinhole aperture array and provide an output for each point in the point array; A processor operatively coupled to the light source modulator, the focus modulator, and the camera detector, the processor being configured to synchronously cause the light source modulator to modulate the light source intensity while causing the focus modulator to sweep an axial focus position.

94. The confocal three-dimensional sensor according to claim 94, wherein, The processor is further configured to calculate a height of each point in the point array based on an output from the camera detector.

95. The confocal three-dimensional sensor according to claim 95, wherein, The processor is configured to: During a first integration period, cause the light source modulator to modulate the light source at a first phase and a first frequency, while synchronously causing the focus modulator to sweep an axial focus position through the focus range, the processor being configured to read and store a video frame from the camera detector relative to the first integration period; During a second integration period, the light source modulator modulates the light source at a second phase and a first frequency, while synchronously causing the focus modulator to sweep an axial focus position through the focus range, and the processor is configured to read and store video frames from the camera detector relative to the second integration period; During a third integration period, the light source modulator modulates the light source at a third phase and a first frequency, while synchronously causing the focus modulator to sweep an axial focus position through the focus range, and the processor is configured to read and store video frames from the camera detector relative to the third integration period; And Calculate, for video frame pixels, a phase corresponding to the light source and the focus position based on the stored first, second, and third video frames, and then convert the phase of the pixels to height values.

96. The confocal three-dimensional sensor according to claim 94, wherein, The light source is a light-emitting diode.

97. The confocal three-dimensional sensor according to claim 94, wherein, The light source is a laser.

98. The confocal three-dimensional sensor according to claim 94, wherein, The light source is an incandescent light source.

99. The confocal three-dimensional sensor according to claim 94, wherein, The time modulation is based on a Gray code.

100. The confocal three-dimensional sensor according to claim 94, wherein, The time modulation is based on a ramp.

101. The confocal three-dimensional sensor according to claim 94, wherein, The time modulation is based on a Hamming code.

102. The confocal three-dimensional sensor according to claim 94, wherein, The time light source modulation is a periodic function.

103. The confocal three-dimensional sensor according to claim 103, wherein, The periodic function is a sine function.

104. The confocal three-dimensional sensor according to claim 103, wherein, The period of the periodic function is equal to the amount of time required for the tunable focus lens to sweep an axial focus position through the focus range.

105. The confocal three-dimensional sensor according to claim 94, wherein, The camera detector is a complementary metal oxide semiconductor (CMOS) area array having a two-dimensional pixel array.

106. The confocal three-dimensional sensor according to claim 94, wherein, The camera detector is a charge-coupled device (CCD) area array having a two-dimensional pixel array.

107. A confocal three-dimensional sensor for measuring the height of a point array on an object, the sensor comprising: A light source; A light source modulator configured to perform time modulation on the light source intensity; A spatial light modulator configured to be illuminated by the light source and receive reflected light from the object; A focus modulator configured to sweep an axial focus position; An imaging system that images the spatial light modulator onto a camera detector; An interference objective configured to focus the illumination gated by the spatial light modulator onto the object and provide a coherent interference signal to the spatial light modulator during focus sweeping; A camera detector configured to receive the coherent interference signal gated by the spatial light modulator and provide an output measurement indicating the total reflected light of the spatial light modulator for each point in the point array; A processor operably coupled to the camera detector, the processor being configured to synchronously cause the light source modulator to modulate the light source intensity while causing the focus modulator to sweep an axial focus position.

108. The confocal three-dimensional sensor according to claim 108, wherein, The processor is further configured to calculate the height of each point in the point array based on the output from the camera detector.

109. The confocal three-dimensional sensor according to claim 108, wherein, The light source is a light-emitting diode.

110. The confocal three-dimensional sensor according to claim 108, wherein, The light source is a laser.

111. The confocal three-dimensional sensor according to claim 108, wherein, The time modulation is based on a Gray code.

112. The confocal three-dimensional sensor according to claim 108, wherein, The time modulation is based on a ramp.

113. The confocal three-dimensional sensor according to claim 108, wherein, The time modulation is based on a Hamming code.

114. The confocal three-dimensional sensor according to claim 108, wherein, The time light source modulation is a periodic function.

115. The confocal three-dimensional sensor according to claim 108, wherein, The periodic function is a sine function.

116. A single-point confocal sensor for measuring the height of a point on an object, the sensor comprising: A light source; A light source pinhole aperture positioned to be illuminated by the light source; A tunable-focus lens configured to focus illumination passing through the light source pinhole aperture onto the object; A detector pinhole aperture configured to receive reflected light from the object, wherein the tunable-focus lens is configured to image the reflected light from the object onto the detector pinhole aperture; A detector and integrator configured to output a measurement indicative of the total light transmitted through the detector pinhole aperture; A light source modulator configured to perform temporal modulation on at least one of the light source, the light reflected from the object, the integrator gain, and the detector gain; A processor operatively coupled to the detector, the integrator, and the light source modulator, wherein the processor is configured to synchronously modulate the light source modulator in time while sweeping the axial focus position of the tunable-focus lens.

117. A confocal three-dimensional sensor for measuring the height of a point array on an object, the sensor comprising: A light source; An array of pinhole apertures configured to be illuminated by the light source and to receive reflected light from the object; A tunable-focus lens configured to focus illumination passing through the array of pinhole apertures onto the object and to image the reflected light from the object onto the array of pinhole apertures; A focus modulator operatively coupled to the tunable-focus lens, the focus modulator being configured to sweep the axial focus position; An imaging system that images the array of pinhole apertures onto a camera detector; A camera detector configured to receive the reflected light from the object imaged by the tunable-focus lens onto the array of pinhole apertures and to provide an output measurement indicative of the total transmitted light through the array of pinhole apertures for each point in the point array; A light source modulator configured to perform temporal modulation on at least one of the light source, the light reflected from the object, the integrator gain, and the detector gain; And A processor operatively coupled to the camera detector, the processor being configured to synchronously modulate the light source modulator in time while sweeping the axial focus position of the focus modulator.

118. A confocal three-dimensional sensor for measuring the height of a point array on an object, the sensor comprising: A light source; An array of pinhole apertures configured to be illuminated by the light source and to receive reflected light from the object; A focus modulator configured to sweep the axial focus position; An imaging system that images the array of pinhole apertures onto a camera detector; An interference objective configured to focus illumination passing through the array of pinhole apertures onto the object and to provide a coherent interference signal to the array of pinhole apertures during focus sweeping; A camera detector configured to receive the coherent interference signal transmitted through the array of pinhole apertures and to provide an output measurement indicative of the total transmitted light through the array of pinhole apertures for each point in the point array; A light source modulator configured to perform temporal modulation on at least one of the light source, the light reflected from the object, the integrator gain, and the detector gain; And A processor, operably coupled to the camera detector, the processor being configured to synchronously modulate the light source modulator in time while sweeping an axial focus position with the focus modulator.

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