Synchronous modulation, gated and integrated 3D sensor

Abstract

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

Description

[Background technology]

[0001] One known technique for 3D optical sensing is triangulation-based phase measurement profilometry. In triangulation-based phase measurement profilometry, a spatially modulated pattern of light is projected onto an object and then observed by an imaging system from a different direction than the projection system. The three-dimensional topography of the object under inspection distorts the projected pattern as seen by the imaging system, and the 3D topography can be calculated by measuring the distortion. Triangulation-based phase measurement profilometry is well suited to high-speed industrial applications because the number of projected patterns, and therefore the number of imaging system video frames required, is small. Typically, 3 to 12 patterns and video frames are required for good performance. However, triangulation-based systems are not suitable for applications with a lateral resolution much below 2 μm, because the numerical aperture required at these resolutions increases the size of the projector and imaging system to the point where they physically interfere with each other. Furthermore, as the numerical aperture of the optical system increases, the depth of field of the system decreases, limiting such systems to a very small height range.

[0002] Confocal 3D optical sensing systems, by definition, are applicable to applications requiring high numerical apertures and lateral resolutions finer than 2 μm because the same optical system that illuminates the object also serves to collect 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 chromatic confocal. All of these techniques can provide high accuracy and large depth of field, but are relatively slow and unsuitable for many industrial applications.

[0003] White light interferometers (WLI) axially scan either the object or the reference mirror, and the peak interference at each image pixel is observed when the optical paths between the object and the reference mirror are equal. More than 100 axial positions and corresponding video frames are required to accurately measure the 3D topography of an object, making WLI slow for many industrial applications. An example of a white light interferometer is disclosed in U.S. Patent No. 5,706,085.

[0004] Conventional 3D confocal microscopes use a source aperture array to project an array of individual point light sources onto an object; the reflected light is imaged onto a detection aperture array, which is then imaged onto a camera detector. In some configurations, the same aperture array can function as both the source aperture array and the detection aperture array. The object is mechanically scanned, or the focal position is scanned axially, and the peak intensity at each pixel in the camera image is observed when the object is at best focus at that pixel. U.S. Patent No. 9,041,940 notes that 200 confocal images are conventionally required; the invention of U.S. Patent No. 9,041,940 claims to reduce that number to 20 or fewer images.

[0005] Structured illumination microscopy (SIM) projects a spatially modulated pattern of light onto an object, and the peak contrast for each point on the object during an axial scan determines the best focus and three-dimensional coordinates at that object point. Techniques have been developed to speed up SIM, but it still often requires 50 or more axial positions and video frames to accurately measure the 3D topography of an object. Examples of structured illumination microscopy are disclosed in U.S. Pat. No. 8,649,024 and U.S. Pat. No. 10,634,487.

[0006] Chromatic confocal 3D sensors encode depth via axial chromatic aberration. By measuring the peak spectral value at each pixel, 3D topography can be accurately measured. Chromatic confocal 3D sensors do not require mechanical axial scanning and can have a large depth of field. However, spectrometers that determine peak spectral values ​​typically require 64 or more pixels for a single point on the object to achieve the necessary 3D measurement accuracy. Effectively, 64 or more detector readings are required for each point on the object, again making this technology too slow for many industrial applications. An exemplary chromatic confocal 3D sensor is disclosed in U.S. Patent No. 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 temporally modulate the light source intensity. A light source pinhole aperture is positioned to be illuminated by the light source, and a variable focus lens is configured to focus illumination passing through the light source pinhole aperture onto the object. A detector pinhole aperture is configured to receive light reflected from the object, and the variable focus lens is configured to image the light reflected from the object onto the detector pinhole aperture. The detector and integrator are configured to output a measurement indicative of the total light transmitted through the detector pinhole aperture. A processor is operably coupled to the detector, integrator, and light source modulator. The processor is configured to synchronously modulate the light source intensity while causing the variable focus lens to sweep an axial focus position, and the processor is further configured to calculate the height of the point on the object based on outputs from the detector and integrator. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of an exemplary single-point 3D confocal sensor with temporal modulation, according to an embodiment disclosed herein. [Figure 2A] 1 shows an exemplary light source modulator current waveform. [Figure 2B] 1 shows an exemplary light source modulator current waveform. [Figure 2C] 1 shows an exemplary light source modulator current waveform. [Figure 2D] FIG. 10 is a schematic diagram of an alternative focal sweep according to one embodiment. [Figure 2E] FIG. 10 is a schematic diagram of an alternative focal sweep according to one embodiment. [Figure 2F] FIG. 10 is a schematic diagram of an alternative focal sweep according to one embodiment. [Figure 2G] FIG. 10 is a schematic diagram of an alternative focal sweep according to one embodiment. [Figure 2H] FIG. 10 is a schematic diagram of an alternative focal sweep according to one embodiment. [Figure 2I] FIG. 10 is a schematic diagram of an alternative focal sweep according to one embodiment. [Figure 2J] FIG. 10 is a schematic diagram of an alternative focal sweep according to one embodiment. [Figure 2K] FIG. 10 is a schematic diagram of an alternative focal sweep according to one embodiment. [Figure 2L] FIG. 10 is a schematic diagram of an alternative focal sweep according to one embodiment. [Figure 2M] FIG. 10 is a schematic diagram of an alternative focal sweep according to one embodiment. [Figure 3A] FIG. 1 is a flow diagram of a method for a 3D confocal measurement process according to one embodiment disclosed herein. [Figure 3B] FIG. 1 is a flow diagram of a method for a 3D confocal measurement process according to one embodiment disclosed herein. [Figure 4] FIG. 1 is a schematic diagram of an exemplary area-scanning 3D confocal sensor using temporal modulation according to one embodiment. [Figure 5] 1 is a flow diagram of a method for measuring a surface using a confocal 3D sensor according to one embodiment disclosed herein. [Figure 6] 1 is a schematic diagram of an exemplary 3D confocal sensor using temporal modulation according to another embodiment described herein. [Figure 7]1 is a schematic diagram of an exemplary 3D confocal sensor using temporal modulation according to another embodiment described herein. [Figure 8] 1 is a schematic diagram of an exemplary 3D confocal sensor using temporal modulation according to another embodiment described herein. [Figure 9A] Denotes a light source with a short coherence length, such as an LED or incandescent light source. [Figure 9B] Denotes a light source with a short coherence length, such as an LED or incandescent light source. [Figure 9C] Denotes a light source with a short coherence length, such as an LED or incandescent light source. [Figure 9D] Denotes a light source with a short coherence length, such as an LED or incandescent light source. [Figure 9E] The response of a conventional interferometer when using a light source with a longer coherence length (such as a multimode laser) is shown. [Figure 9F] FIG. 9E is a magnified portion of the scan showing the central portion of FIG. 9E. [Figure 9G] 10 illustrates a response / scan using a long coherence length source with a 3D confocal sensor according to one embodiment described herein. [Figure 9H] FIG. 9H is a magnified portion of the scan showing the central portion of FIG. 9G. [Figure 10] FIG. 1 is a schematic diagram of an exemplary 3D confocal sensor with temporal modulation utilizing a focusable interference objective, according to an embodiment described herein. [Figure 11] 1 is a schematic diagram of an exemplary 3D confocal sensor using temporal modulation according to another embodiment described herein. [Figure 12] 1 illustrates an exemplary SLM spatial pattern that may be used in conjunction with embodiments described herein. [Figure 13] FIG. 1 is a diagram of an exemplary 3D confocal sensor with temporal modulation that utilizes a focusable interference objective according to another embodiment described herein. [Figure 14A] 10 shows an exemplary light source modulation phase and frequency pattern for measuring double return. [Figure 14B]10 shows an exemplary light source modulation phase and frequency pattern for measuring double return. [Figure 14C] 10 shows an exemplary light source modulation phase and frequency pattern for measuring double return. [Figure 14D] 10 shows an exemplary light source modulation phase and frequency pattern for measuring double return. [Figure 14E] 10 shows an exemplary light source modulation phase and frequency pattern for measuring double return. [Figure 14F] 10 shows an exemplary light source modulation phase and frequency pattern for measuring double return. DETAILED DESCRIPTION OF THE INVENTION

[0009] The embodiments disclosed herein include improvements to dramatically 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. In contrast to prior art confocal 3D techniques, in which, for example, 50 or more images are captured in a single focal sweep, the light source in a confocal 3D measurement system is temporally modulated synchronously with a complete focal sweep during a single detector integration period or image capture. The selected coding scheme determines the number of distinct temporal light source modulation patterns. The modulation patterns are changed between subsequent image captures and focal sweeps. The resulting image intensity from each modulation pattern and focal sweep may then be used to decode the peak focus position for each pixel in the image. For sinusoidally varying temporal modulation patterns, the light source phase is changed between subsequent image captures, and the peak focus position for every pixel in the image is calculated using a standard spatial phase shifting algorithm. In this manner, embodiments can synchronously modulate, gate, and integrate. The light source and focal point can be synchronously modulated. The pinhole aperture is a gate that transmits only light from the best focus. The detector can integrate during the entire source modulation and focus sweep.

[0010] FIG. 1 is a schematic diagram of an exemplary single-point 3D confocal sensor 22 using temporal modulation. Light from a light source 2 illuminates a source pinhole aperture 4, passes through a beam splitter 6, and is focused by a variable-focus lens 8 toward an inspected object 10. The light then reflects from the object 10, returns through the variable-focus lens 8, is reflected by the beam splitter 6, and is focused toward a detection pinhole aperture 12. Light passing through the detection pinhole 12 is collected by a detector 14 and an integrator 15. Due to the optical sectioning properties of confocal microscope systems, light transmitted through the detection pinhole 12 is maximized when the transmitted light from the pinhole aperture 4 is at best focus on the object 10. Away from best focus, most of the light reflected from the object 10 is blocked by the detection pinhole 12. The optical sectioning properties of confocal microscopes are also referred to in the literature as "confocal gating." The light source and detection pinhole aperture form a "gate" that essentially allows only light from the best focus position to pass through the detection pinhole aperture.

[0011] The light source 2 may be, but is not limited to, an LED, a laser (such as a solid-state laser), or an incandescent light source, whereby the output intensity may be temporally modulated by a light source modulator 16. The variable-focus lens 8 may be, but is not limited to, a lens that is mechanically scanned by a voice coil or linear stage. Alternatively, the variable-focus lens 8 may be a liquid lens whose 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 variable-focus lens 8.

[0012] 2A-2C show the current waveform I of the light source modulator 16 for a single frequency sinusoidal modulation pattern. src Here is an example of I src is the frequency f according to Equation 1a k where n=0, 1, 2, t is time, and I peak is the peak LED current. Peak LED current I peak The value of is selected to provide an appropriate illumination level for the object being inspected.

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[0013] The focal point modulator 18 also adjusts the focal point position Z of the variable lens 8 as shown in FIGS. 2A to 2C. foc In the example of FIG. 2A, the light detected by detector 14 is synchronized with the light source modulator 16 to sweep I src,0 Current I proportional to det The peak of Z is indicated by the vertical dashed line. foc This detected current is integrated by the integrator 15 to record the level I0. This return is the integrated signal I int In other words, the position of best focus can be seen as a function of the sinusoidal waveform I when the focus position is swept synchronously with the source modulator 16. src is encoded by the phase of

[0014] 2B, the phase of the light source modulator 16 is shifted by 2π / 3 radians, corresponding to n=1 in Equation 1. The peak detected current I det is again in best focus, I src,1 , resulting in an integral value I1. In FIG. 2C, the phase of the light source modulator 16 is shifted by 4π / 3 radians, corresponding to n=2 in Equation 1. The peak detected current I det is again in best focus, I src,2 is proportional to and gives the integral value I2. srcTo determine the phase of the beam and therefore the position of best focus, standard phase-shifting techniques from interferometry or phase-shifting profilometry, such as a technique known as ternary phase reconstruction, can be used. From a standard phase-shifting algorithm, the phase Φ, which encodes the position of best focus, is given by Equation 2. The arctangent function in Equation 2 returns values ​​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 a range of 0 to 2π. Once the phase is adjusted to a range of 0 to 2π, the time t associated with that phase can be calculated using Equation 10. The reflectivity R of the object 10 at the measurement point is given by Equation 3 and is directly proportional to the sum of the three detected peak currents with a scaling factor α. The contrast C of the received signal is given by Equation 4. Contrast differs from reflectivity (defined in Equation 3) in that reflectivity measures all light received, while contrast is a measure of the intensity of the detected sinusoid.

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[0015] Four Sinusoidal Light Source Modulation I src Other phase shifting techniques may be used, such as a four-phase technique using π / 2 radians, n (n=0, 1, 2, 3) where the phase is shifted by π / 2 radians each time n is incremented by 1. Additionally, a higher frequency sinusoidal waveform I may be used that will go through several periods as the focus is swept. src can be used to increase the sensitivity of the phase detection. This is because multiple sinusoidal waveforms I src This creates a so-called 2π ambiguity problem that can be dealt with by using frequency and phase. For example, two different frequencies can be used to create a longer synthetic wavelength and remove the 2π ambiguity.

[0016] frequency f k The wavelength of v is given by Equation 5, where v z is the velocity of the focal position change, and in MKS units, v z is m / s and f k If is in cycles / s, then λ kis m / cycle.

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[0017] Synthetically longer wavelength λ syn can be generated using wavelengths λ1 and λ2 according to Equation 6.

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[0018] When two or more frequencies are used, the closed-form solutions for phase and contrast, Equations 3 and 4, no longer apply. Because the integrated light level model includes trigonometric functions, the simplest way to estimate the object properties is an iterative least-squares solution. Several mathematical libraries provide tools for minimizing the fitting residual defined in equations such as Equation 8; for example, Matlab® (version 2022b, The MathWorks Inc.) includes the function fminsearch. Minimizing the fitting residual begins by defining the fitting residual in Equation 8.

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[0019] Here, I k,n is the image level measured for each phase n and frequency k, and I^ k,n are the estimated image levels for estimated reflectance, phase, and contrast.

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[0020] Equation 1b models the integral return strength. The modeled integral return strength is I^ k,n which is the measured integral I nIn Equation 1b, R^ is the estimated reflectivity of the object, including the detector dark level and ambient light reaching the detector. The estimated signal contrast is modeled as C^0. The estimated location of the object surface is identified by the time t^0 when the focal plane sweep intersects the object surface.

[0021] A typical approach is to minimize the sum of squared residuals, calculated as S in Equation 9.

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[0022] This residual function, along with the initial parameter estimates, is fed into an iterative least squares solver to obtain best-fit estimates of R̂, Ĉ, and t̂0.

[0023] 2A to 2C show the focal position Z foc The calibration process, not shown, involves a linear sweep of the focal position Z foc Any nonlinearity in the λ / 2 as well as the exact range of the focal sweep can be accurately characterized.

[0024] Other temporal light source modulation techniques for encoding the position of best focus during a focus sweep may include, but are not limited to, Gray code, linearly rising and falling ramps, and Hamiltonian codes. Exemplary measurement coding schemes with three Hamiltonian light source modulation patterns are shown in Figures 2G-2I, and exemplary measurement coding schemes with four Hamiltonian light source modulation patterns are shown in Figures 2J-2M.

[0025] FIG. 3A is a flow diagram of a method for a 3D confocal measurement process using a phase measurement coding scheme and a sinusoidal modulation pattern, according to one embodiment disclosed herein. FIG. 3A further illustrates the measurement process of the confocal 3D sensor 22. The process begins in step 28 by the processor 20 resetting the integrator 15. The process proceeds to step 30, where the current from the detector 14 begins to be integrated by the integrator 15. Immediately after step 30, the processor 20 signals the light source modulator 16 to sinusoidally modulate the light source 2 at an initial phase and frequency in step 32, as shown in FIG. 2A, for example, while the processor 20 also signals the focus modulator 18 to begin synchronously sweeping the focal plane in step 34. Once the focus sweep is complete and the light source has passed through a predetermined number of cycles, the processor 20 signals the integrator 15 to stop integrating in step 36, and the integrated current from the detector is then read out as a voltage by the processor 20 in step 38. The voltages for each focus sweep are stored by processor 20 in step 40 before proceeding to decision block 42. In block 42, it is determined whether the last phase is complete. If not, processor 20 increments the phase and, if applicable, the next frequency in step 46. Processor 20 then resets integrator 15 in step 28, signals detector 14 to begin integrating, and signals the light source modulator with the next phase and next frequency, if applicable. This process is then repeated until processor 20 determines in step 42 that the last sweep is complete. The stored voltage corresponding to the phase of best focus for each focus sweep is retrieved in step 48, and processor 20 uses standard phase shifting techniques, such as Equation 2, to find the light source phase I corresponding to the position of best focus in step 48. srcThe time corresponding to the position of focus may then be calculated, for example, using Equation 10. The reflectance at the measurement position may be calculated using Equation 3, and the contrast may be calculated, for example, using Equation 4. In step 49, the time of best focus is converted to a calibrated height value by processor 20, taking into account the exact range of the focus sweep and any non-linearity in the focus sweep.

[0026] The measurement process can be sped up by alternating the direction of the focus sweep between each integration period to take advantage of focus retrace. Referring to Figures 2D-2F, the focus position Z foc is swept from low to high in Figure 2D. Z in Figure 2E foc The sweep direction of I is swept from high to low in Figure 2F, and from low to high in Figure 2G. To accommodate the polarity change of the sweep direction, I src, The phase of 1 is I in Figure 2B. src, 1 is time-reversed in FIG. 2E. Equation 2 can then be used to calculate the phase Φ, which encodes the position of best focus. Equation 3 is also used to calculate the reflectivity at the measurement location.

[0027] FIG. 3B is a flow diagram of a method for a 3D confocal measurement process using selectable coding patterns, according to one embodiment disclosed herein. FIG. 3B further illustrates the measurement process of the confocal 3D sensor 22. Process 220 begins in step 227 by selecting an appropriate coding scheme and light source modulation pattern, such as the coding schemes of FIGS. 2J-2M having four Hamiltonian light source patterns. Next, processor 20 resets integrator 15 in step 228. The process proceeds to step 230, where current from detector 14 begins to be integrated by integrator 15. Immediately after step 230, processor 20 signals light source modulator 16 to modulate light source 2 according to the initial modulation pattern in accordance with the selected coding scheme in step 232, while processor 20 also signals focal point modulator 18 to synchronously initiate a sweep of the focal plane in step 234, for example, as shown in FIG. 2J. Once the focus sweep and modulation pattern are complete, processor 20 signals integrator 15 to stop integrating in step 236, and the integrated current from the detector is then read as a voltage by processor 20 in step 238. The voltage for each focus sweep is stored by processor 20 in step 240 before proceeding to decision block 242. In block 242, it is determined whether the last modulation pattern is complete. If not, processor 20 increments the modulation pattern in step 246. Processor 20 then resets integrator 15 in step 228, signals detector 14 to begin integrating, and signals the light source modulator with the modulation pattern. This process is repeated until processor 20 determines in step 242 that the last sweep is complete. The stored voltage corresponding to the time of best focus for each focus sweep is retrieved in step 248, and processor 20 decodes the time corresponding to the position of best focus in step 248 according to the selected coding scheme. The reflectance is also calculated in step 248 .In step 249, the time of best focus is converted to a calibrated height value by processor 20, taking into account the exact range of the focus sweep and any non-linearity in the focus sweep.

[0028] FIG. 4 is a schematic diagram of an exemplary area-scanning 3D confocal sensor 90 using temporal modulation. Light from a light source 50 is modulated by a light source modulator 52, focused by a focusing 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 of a Nipkow disk is disclosed in U.S. Pat. No. 4,927,254. A lens 60, an aperture stop 62, and a variable-focus lens 64 form an imaging system for imaging the pinhole apertures of the Nipkow disk 58 onto an object 10. Light reflected from the object 10 is imaged onto the Nipkow disk 58 by the lens 64, the aperture stop 62, and the lens 60. The reflected light that passes through the apertures of the Nipkow disk 58 is reflected by the beam splitter 56 and imaged onto a camera detector 70 by the imaging system formed by the lens 65, the aperture stop 66, and the lens 68. Again, due to the optical sectioning properties of confocal microscopes, the transmitted reflected light passing through the pinhole aperture of the Nipkow disk 58 has a peak intensity when the point on the object is at best focus, and the intensity decreases rapidly away from best focus. The camera detector 70 can be, but is not limited to, a CMOS or CCD area array having a two-dimensional array of pixels. The variable-focus lens 64 can be, but is not limited to, a lens that is mechanically scanned by a voice coil or linear stage. Alternatively, the variable-focus lens 64 can be a liquid lens whose 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 variable-focus lens 64. The light source 50 can be, but is not limited to, an LED, solid-state laser, or incandescent light source, whereby the output intensity can be temporally modulated by the light source modulator 52.

[0029] The object 10 is carried by a stage assembly 51. The stage assembly 51 may include one or more linear or rotary stages.

[0030] The timing controller 72 signals the time modulation pattern for each focus sweep to the light source modulator 52. The timing controller 72 also synchronizes the timing of the light source modulator 52 and the focus modulator 74 to sweep the focus and simultaneously temporally modulate the light source 50 during one integration period of the camera detector 70.

[0031] The Nipkow disk 58 may be designed with a pinhole pattern that follows an Archimedean spiral, and the pattern may consist of a single continuous spiral or multiple interleaved spirals. If a single spiral is used, the disk must rotate once to sample all radial distances. If there are N spirals, the disk must rotate 1 / N times to sample all radial distances. Because a focal sweep only results in a short period near best focus (when the maximum light level is returned to the detector), the pinhole pattern may be designed to sample all required radial positions over a small rotation angle. This may be achieved by utilizing a large number of spirals and alternating the radii of the pinholes within each spiral to maximize radial coverage over a short rotation angle. The geometry of the pinhole aperture may be, but is not limited to, a circle, a square, or an octagon. The geometry of the pinhole aperture may also be a thin straight line or a curve. In another embodiment, the rotating Nipkow disk 58 may be replaced by an array of linearly translated pinhole apertures. The design of the aperture pattern can be optimized to balance light throughput, axial resolution, and crosstalk from out-of-focus regions passing through adjacent apertures. Crosstalk is the background intensity I away from the position of best focus. det contribute to.

[0032] FIG. 5 is a flow diagram of a method for measuring a surface using a confocal 3D sensor according to embodiments disclosed herein. Method 300 begins in step 96 by computer 76 providing a selected coding scheme and light source modulation pattern, such as the coding scheme of FIGS. 2G-2I having three Hamiltonian light source modulation patterns, to timing controller 72. Next, camera detector 70 is reset by timing controller 72 in step 98. Method 300 proceeds to step 100, where integration for a single video frame on detector 70 begins. Immediately after step 100, timing controller 72 signals light source modulator 52 to modulate light source 50 with an initial modulation pattern in step 102, as shown in FIG. 2G, for example, while timing controller 72 also signals focus modulator 74 to synchronously begin a sweep of the focal plane in step 104. Once the focus sweep is complete and light source modulator 52 has completed the modulation pattern, timing controller 72 signals detector 70 to stop integration in step 106. The readout of the video data begins at step 108 and is transferred to memory in 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 is complete. If not, timing controller 72 increments the modulation pattern at step 116. Detector 70 is reset at step 98, and timing controller 72 signals camera detector 70 to begin integrating the next video frame at step 100. Method 300 then repeats until timing controller 72 determines at step 112 that the last sweep is complete. The stored pixel values ​​for the corresponding time of best focus for each focus sweep are retrieved at step 118, and computer 76 calculates, for all pixels of camera detector 70, the light source time I corresponding to the time of best focus at step 118. srcIn step 118, the reflectivity for all pixels is also calculated. In step 120, the time of best focus for each pixel is converted by computer 76 into a calibrated height value for each pixel, taking into account the exact range of the focus sweep and any nonlinearities in the focus sweep or optical aberrations. The calibration process of 3D confocal sensor 90 may also account for other design and manufacturing tolerances, such as field curvature across the field of view of camera detector 70. At this point, computer 76 may command stage assembly 51 to translate object 10 to a new position and begin another measurement cycle with a different field of view.

[0033] In another example, detector 70 may be a line-scan detector or a time-delay-integration (TDI) image sensor configured as a one-dimensional array of photodetectors or pixels, each of which generates a line field of view. In this example, stage assembly 51 may move continuously in a direction perpendicular to the line field of view during integration of detector 70. The speed of stage assembly 51, the integration time of detector 70, and the number of focal sweeps per measurement then affect the lateral resolution in the direction of stage movement.

[0034] FIG. 6 is a schematic diagram of an exemplary 3D confocal sensor 92 that uses time modulation similar to 3D confocal sensor 90. Like numbered elements provide the same function. The variable-focus lens 64 is replaced with a fixed lens 84 in 3D confocal sensor 92. The variable-focus lens 80 in FIG. 6 is located at or near the aperture stop 62. The variable-focus lens 80 can be, but is not limited to, a lens that is mechanically scanned by a voice coil or linear stage. Alternatively, the variable-focus lens 80 can be a liquid lens whose 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 variable-focus lens 80.

[0035] 7 is a schematic diagram of an exemplary 3D confocal sensor 91 using temporal modulation. Focal point modulators 82 synchronously sweep the position of object 10 through the focal point by moving stage assembly 51 axially of lens 84.

[0036] FIG. 8 is a schematic diagram of an exemplary 3D confocal sensor 93 that uses temporal modulation similar to that of the 3D confocal sensor 91. Like-numbered elements provide the same functions. In the 3D confocal sensor 93, the fixed lens 84 is replaced with an interference objective 69. The interference objective 69 may be, but is not limited to, a known Mirau, Michelson, or Linnik-type interferometer objective. The light source 53 may be a short-coherence length or long-coherence length light source. The light source 53 may be, but is not limited to, an LED, a superluminescent LED (SLED), a laser, or an incandescent light source, whereby the output intensity may be temporally modulated by the light source modulator 52. The focal point modulator 82 synchronously sweeps the position of the object 10 through the focal point by moving the stage assembly 51 axially of the lens 84.

[0037] During the focal sweep, individual pixels of the camera detector 70 receive a coherence interference signal from the interference objective 69 that is superimposed on the confocal response from the pinhole aperture in the Nipkow disk 58 .

[0038] Figures 9A-9D show a light source with a short coherence length, such as an LED or incandescent light source. Figure 9A shows the interference pattern of a conventional interferometer, typically referred to as a white light interferometer (WLI). Figure 9B is a magnified portion of the scan showing the central portion of Figure 9A. With conventional WLI, there are no interference ripples over most of the scan range, and a strong interference pattern, known as a correlogram, is visible over a very narrow height range defined by the coherence length of the light source. Away from best focus, the detector experiences a high background level. For sensor 93, the characteristic pixel response I det The function is the focal position Z foc9C as a function of . Figure 9D shows the same pixel response I as in Figure 9C. det , the smaller range of the focal position Z foc 9C , the background level away from best focus is much lower than the conventional WLI response shown in FIG. 9A due to the gated nature of the light source and detection pinhole apertures. This reduced background level allows the modulated return to be integrated onto the detector without adding excessive signal levels or noise. Method 30 can be used to calculate height values ​​for object 10 at each pixel location of 3D confocal sensor 93. As described in method 300, several different light source modulation frequencies can be used while sweeping the focus of object 10 with stage assembly 51. At least two frequencies can be used to find the location of the modulation envelope and the location of the correlogram peak. For example, a relatively low modulation frequency can be used to locate the confocal pinhole return, and a higher frequency can be used to find the location of the peak of the interference pattern.

[0039] Figure 9E shows the response of a conventional interferometer when using a longer coherence length light source (such as a multimode laser). Figure 9F is an enlarged portion of the scan showing the center of Figure 9E. With a long coherence length light source, the interference fringes are visible over a very wide range, but the peak location is difficult to determine. This is a wrapping problem common to laser-based interferometers. Using a long coherence length light source with sensor 93 results in the return shown in Figure 9G. Figure 9H is an enlarged portion of the scan showing the center of Figure 9G. The sectioning properties of the pinhole confocal system restrict the return to a small region near best focus. The correlogram peak is much easier to see in the response of sensor 93 (Figure 9G) compared to a standard interferometer (Figure 9F).

[0040] A common problem with scanning white light interferometers is the need for multiple images sampled at many focal height planes, especially over a large height range. Method 300 applied to a 3D confocal sensor 93 provides a way to overcome this limitation. When method 300 is applied to locate object 10, a first height estimate using a low-frequency temporal modulation pattern can be found in just two to three images. The low modulation frequency is not affected by interference ripple near best focus, and only the envelope is detected. This envelope detection is identical to the operating mode of sensor 90. Method 300 is then applied again using a high-frequency modulation pattern, with modulation applied only in a smaller focal sweep region near the first height estimate. Limiting illumination to a smaller scan region shortens scan time and reduces the shot noise associated with integrating background light levels and excessive background level integration.

[0041] 10 is a schematic diagram of an exemplary 3D confocal sensor 94 using time modulation that utilizes a focusable interference objective 67. The focusable interference objective 67 can be, but is not limited to, an interference objective that is mechanically scanned by a voice coil or linear stage. Alternatively, the focusable interference objective can include using acoustic waves to change the refractive index of a liquid lens element, or a lens element whose focus is adjusted by electrostatically changing the curvature of the liquid lens surface, or using acoustic waves to change the refractive index of the focusable interference objective 67. Method 300 can be used to calculate a height value of the object 10 at each pixel location of the 3D confocal sensor 94.

[0042] FIG. 11 is a schematic diagram of an exemplary 3D confocal sensor 190 using temporal modulation. The 3D confocal sensor 190 operates on the same principle as the 3D confocal sensor 90, with the functionality provided by the Nipkow disk 58 replaced by a spatial light modulator (SLM) 158. Both the Nipkow disk 58 and the spatial light modulator 158 reduce background intensity away from best focus on the pixels of the cameras 70 and 170, respectively, during a focus sweep when the measurement position of the object 10 is away from best focus. Light from the light source 150 is modulated by the light source modulator 152, collected by the collecting 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 mirror device (DMD) or a liquid crystal on silicon device (LCOS). The light then actively reflects off the pixels of the SLM 158. Lens 160, aperture stop 162, and variable-focus lens 164 form an imaging system for imaging the pixels of SLM 158 onto object 10. Light reflected from object 10 is imaged onto SLM 158 by lens 164, aperture stop 162, and lens 160. The light then actively reflects off the pixels of SLM 158, reflects off beamsplitter 163, and is then imaged onto camera 170 by the imaging system formed by lens 165, aperture stop 166, and lens 168. Spatial light modulator 158 can emulate the optical sectioning characteristics of a Nipkow disk system by utilizing a time sequence of spatial patterns similar to the spatial pattern of a Nipkow aperture array. An exemplary spatial pattern of SLM 158 is shown in FIG. 12. During a single focal sweep, the spatial pattern is rapidly switched in time to effectively emulate the sweeping aperture array of a rotating Nipkow disk. Due to the optical sectioning properties of confocal microscopes, the light actively reflected onto the SLM158 pixels has a peak intensity when the point on the object is at best focus, and the intensity decreases rapidly away from best focus.

[0043] 13 is a schematic diagram of an exemplary 3D confocal sensor 194 with temporal modulation that utilizes a variable focus interference objective lens 167. The 3D confocal sensor 194 is similar to the 3D confocal sensor 190, with the variable focus lens 164 replaced by the variable focus interference objective lens 167.

[0044] A common measurement task is estimating the thickness of a transparent layer, such as a mask layer on the surface of a printed circuit board or the thickness of photoresist on a semiconductor wafer. For a single reflective surface, a 3D confocal sensor must estimate the surface reflectivity, the height (phase of the return signal), and the contrast level of the return signal. Including a second return results in five unknowns: the reflectivity of the object, the height of both surfaces, and the contrast level of both surfaces. To solve for these five unknowns, at least five data points are required.

[0045] 14A-14F show exemplary light source modulation phase and frequency patterns for measuring double return. src is the frequency f according to Equation 1. k = 1, where n = 0, 1, 2. In Figures 14D to 14F, I src is the frequency f according to Equation 1. k = 3, where n = 0, 1, 2. In Figures 14A-14F, the focal sweep is the same and the detected current I det indicates a double return. The timing of the two peak returns is marked by the dashed lines labeled "Surface 0" and "Surface 1." This double return is int The integrals I0, I1, and I2 are visible at frequencies f k = 1. The integrals I3, I4, and I5 correspond to the measurement at frequency f k = 3. As explained, there are five unknowns, and using two modulation frequencies with three phases for each provides six measurements.

number

[0046] The integral return for each phase and frequency of a dual-return object can be modeled by Equation 7. The object reflectance estimate is R^, and the return contrast for each of the two surfaces is estimated as C^0 and C^1. The light sensed at the two focus positions is estimated as t^0 and t^1. The image of the object is captured at multiple phases n and frequencies f k Once t̂0 and t̂1 are estimated, these values ​​can be converted to phase using Equation 10 and to height using step 120 of method 300.

[0047] Because the integral light level model contains trigonometric functions, the simplest way to estimate the object properties is an iterative least-squares solution. Several mathematical libraries provide tools for minimizing the fitting residual defined in equations such as Equation 8; for example, Matlab® includes the function fminsearch. The process begins by defining the fitting residual in Equation 8:

number

[0048] One approach is to minimize the sum of squared residuals, calculated as S in Equation 9.

number

[0049] This residual function, along with the initial parameter estimates, is fed into an iterative least squares solver to obtain best fit estimates of the target reflectance, phase, and contrast.

[0050] In reality, lens blurring reduces contrast C as modulation frequency f increases. For best results, the C term in Equation 7 should be weighted by this expected frequency blurring. Fitting accuracy and robustness can be improved by including more frequencies in the image set.

[0051] As described above, temporal modulation is provided by modulating the light source. The same function can be achieved by temporally modulating the sensitivity or transmittance of other portions of the signal path. The gain of the integrator 15 in sensor 22 or the integrators that are part of the camera detectors 70 and 170 can be temporally modulated according to the same methods described to achieve the same performance. On-camera detector integrator modulation is used, for example, in time-of-flight sensors such as the Texas Instruments OPT8241.

[0052] Alternatively, the gain of the optical path can be temporally modulated by adding a ferroelectric or liquid crystal light valve to the optical path. Other means of modulating light throughput include variable absorbers and crossed polarizers. Instead of temporally modulating light source 2, light source 50, or light source 53, modulating the transparency or reflectivity of a light valve can be used.

[0053] Alternatively, in sensors 190 and 194, SLM 158 may temporally modulate the light by actively temporally modulating the throughput on the pixels of SLM 158.

Claims

1. 1. A single point confocal sensor for measuring the height of a point on an object, said sensor comprising: A light source and a light source modulator configured to temporally modulate the light source intensity; a light source pinhole aperture positioned to be illuminated by the light source; a variable focus lens configured to focus illumination passing through the source pinhole aperture onto the object; a detector pinhole aperture configured to receive reflected light from the object, the variable-focus lens 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 processor operatively coupled to the detector, the integrator, and the light source modulator, the processor configured to cause the light source modulator to synchronously modulate a light source intensity while causing the variable-focus lens to sweep an axial focus position.

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

3. 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 variable-focus lens to sweep an axial focus position through a focus range, and the processor is configured to read and store the integrator output during the first integration period and then reset the integrator; 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 variable-focus lens to sweep an axial focus position through the focus range, and the processor is configured to read and store the integrator output during the second integration period and then reset the integrator; 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 variable-focus lens to sweep an axial focus position through the focus range, and the processor is configured to read and store the integrator output during the third integration period; 3. The single-point confocal sensor of claim 2, wherein the processor is configured to calculate a phase of the light source corresponding to a focus position based on the first, second, and third integrator outputs, and convert the phase of the light source to a height of the point on the object.

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

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

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

7. The single-point confocal sensor of claim 1 , wherein the variable focus lens is mechanically scanned by a voice coil.

8. The single-point confocal sensor of claim 1 , wherein the variable-focus lens is mechanically scanned by a linear stage.

9. The single-point confocal sensor of claim 1 , wherein the variable focus lens is a liquid lens.

10. The single-point confocal sensor of claim 9 , wherein the focus of the liquid variable-focus lens is adjusted by electrostatically varying the curvature of the liquid lens surface.

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

12. The single-point confocal sensor of claim 1 , wherein the time modulation is based on a Gray code.

13. The single point confocal sensor of claim 1 , wherein the temporal modulation is ramp based.

14. The single-point confocal sensor of claim 1 , wherein the temporal modulation is based on a Hamiltonian code.

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

16. 16. The single-point confocal sensor of claim 15, wherein the periodic function is a sinusoidal function.

17. 16. The single point confocal sensor of claim 15, wherein the periodic function has a period equal to the amount of time required for the variable focus lens to sweep the axial focus position through the focus range.

18. 1. A confocal three-dimensional sensor for measuring heights of an array of points on an object, said sensor comprising: A light source and a light source modulator configured to temporally modulate a light source intensity; a pinhole aperture array illuminated by the light source and configured to receive reflected light from the object; a variable focus lens configured to focus illumination passing through the pinhole aperture array onto the object and to image reflected light from the object onto the pinhole aperture array; a focus modulator operably coupled to the variable-focus lens, the focus modulator configured to sweep an axial focus position; an imaging system for imaging the pinhole aperture array onto a camera detector; a camera detector configured to receive reflected light from the object imaged by the variable focus lens onto the pinhole aperture array and to provide an output measurement indicative of the total transmitted light through the pinhole aperture array for each point in the array of points; a processor operably coupled to the camera detector, the processor configured to cause the light source modulator to synchronously modulate a light source intensity while causing the focus modulator to sweep an axial focus position.

19. 20. The confocal 3D sensor of claim 18, wherein the processor is further configured to calculate a height of each point in the array of points based on the output from the camera detector.

20. The processor: causing 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 a focus range during a first integration period, wherein the processor is configured to read and store video frames from the camera detector for the first integration period; causing 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 during a second integration period, wherein the processor is configured to read and store video frames from the camera detector for the second integration period; causing 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 during a third integration period, wherein the processor is configured to read and store video frames from the camera detector for the third integration period; calculating a phase of the light source corresponding to a focus position of a video frame pixel based on the first, second, and third stored video frames, and then converting the phase of the pixel to a height value; 20. The confocal three-dimensional sensor of claim 19, configured to:

21. 20. The confocal 3D sensor of claim 18, wherein the pinhole aperture array is a moving pinhole aperture array.

22. 22. The confocal 3D sensor of claim 21, wherein the moving pinhole aperture array is a rotating Nipkow disk.

23. 22. The confocal 3D sensor of claim 21, wherein the moving pinhole aperture is a reciprocating translation array.

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

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

26. 20. The confocal three-dimensional sensor of claim 18, wherein the light source is an incandescent light source.

27. 20. The confocal 3D sensor of claim 18, wherein the variable focus lens is mechanically scanned by a voice coil.

28. 20. The confocal 3D sensor of claim 18, wherein the variable focus lens is mechanically scanned by a linear stage.

29. The confocal three-dimensional sensor of claim 18 , wherein the variable focus lens is a liquid lens.

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

31. 20. The confocal 3D sensor of claim 18, wherein the focus of the variable-focus lens is adjusted by using acoustic waves to change the refractive index of the variable-focus lens.

32. 20. The confocal 3D sensor of claim 18, wherein the time modulation is based on a Gray code.

33. The confocal 3D sensor of claim 18 , wherein the temporal modulation is ramp-based.

34. The confocal 3D sensor of claim 18, wherein the temporal modulation is based on a Hamiltonian code.

35. The confocal 3D sensor of claim 18 , wherein the temporal light source modulation is a periodic function.

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

37. 36. The confocal 3D sensor of claim 35, wherein the periodic function has a period equal to the amount of time required for the variable focus lens to sweep the axial focus position through the focus range.

38. 20. The confocal three-dimensional sensor of claim 18, wherein the camera detector is a complementary metal oxide semiconductor (CMOS) area array having a two-dimensional array of pixels.

39. 20. The confocal three-dimensional sensor of claim 18, wherein the camera detector is a charge-coupled device (CCD) area array having a two-dimensional array of pixels.

40. 1. A confocal three-dimensional sensor for measuring heights of an array of points on an object, said sensor comprising: A light source and a light source modulator configured to temporally modulate a light source intensity; a pinhole aperture array illuminated by the light source and configured to receive reflected light from the object; a focal spot modulator configured to sweep an axial focal spot position; an imaging system for imaging the pinhole aperture array onto a camera detector; an interference objective configured to focus illumination passing through the pinhole aperture array onto the object and provide a coherence interference signal on the pinhole aperture array during a focal sweep; a camera detector configured to receive the coherence interference signals transmitted through the pinhole aperture array and to provide an output measurement indicative of the total transmitted light transmitted through the pinhole aperture array for each point in the array of points; a processor operably coupled to the camera detector, the processor configured to cause the light source modulator to synchronously modulate a light source intensity while causing the focus modulator to sweep an axial focus position.

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

42. The processor: causing 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 a focus range during a first integration period, wherein the processor is configured to read and store video frames from the camera detector for the first integration period; causing 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 during a second integration period, wherein the processor is configured to read and store video frames from the camera detector for the second integration period; causing 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 during a third integration period, wherein the processor is configured to read and store video frames from the camera detector for the third integration period; calculating a phase of the light source corresponding to a focus position of a video frame pixel based on the first, second, and third stored video frames, and then converting the phase of the pixel to a height value; 42. The confocal three-dimensional sensor of claim 41 configured to:

43. 41. The confocal 3D sensor of claim 40, wherein the pinhole aperture array is a moving pinhole aperture array.

44. 44. The confocal 3D sensor of claim 43, wherein the moving pinhole aperture array is a rotating Nipkow disk.

45. 44. The confocal 3D sensor of claim 43, wherein the moving pinhole aperture is a reciprocating translation array.

46. 41. The confocal three-dimensional sensor of claim 40, wherein the light source is a light emitting diode.

47. 41. The confocal three-dimensional sensor of claim 40, wherein the light source is a laser.

48. 41. The confocal three-dimensional sensor of claim 40, wherein the light source is an incandescent light source.

49. 41. The confocal 3D sensor of claim 40, wherein the time modulation is based on a Gray code.

50. 41. The confocal 3D sensor of claim 40, wherein the temporal modulation is ramp-based.

51. 41. The confocal 3D sensor of claim 40, wherein the time modulation is based on a Hamiltonian code.

52. 41. The confocal 3D sensor of claim 40, wherein the temporal light source modulation is a periodic function.

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

54. 53. The confocal 3D sensor of claim 52, wherein the periodic function has a period equal to the amount of time required for the variable focus lens to sweep the axial focus position through the focus range.

55. 41. The confocal three-dimensional sensor of claim 40, wherein the camera detector is a complementary metal oxide semiconductor (CMOS) area array having a two-dimensional array of pixels.

56. 41. The confocal three-dimensional sensor of claim 40, wherein the camera detector is a charge-coupled device (CCD) area array having a two-dimensional array of pixels.

57. 41. The confocal three-dimensional sensor of claim 40, wherein the interference objective lens is a variable focus interference objective lens.

58. 1. A confocal three-dimensional sensor for measuring heights of an array of points on an object, said sensor comprising: A light source and a light source modulator configured to temporally modulate a light source intensity; a spatial light modulator illuminated by the light source and configured to receive light reflected from the object; a variable focus lens configured to focus illumination gated by the spatial light modulator onto the object and to image light reflected from the object onto the spatial light modulator; a focus modulator operably coupled to the variable-focus lens, the focus modulator configured to sweep an axial focus position; an imaging system for imaging the spatial light modulator onto a camera detector; a camera detector configured to receive reflected light from the object imaged onto the spatial light modulator by the variable focus lens and to provide an output measurement indicative of the total light gated by the spatial light modulator for each point in the array of points; a processor operably coupled to the camera detector, the processor configured to cause the light source modulator to synchronously modulate a light source intensity while causing the focus modulator to sweep an axial focus position.

59. 59. The confocal three-dimensional sensor of claim 58, wherein the processor is further configured to calculate a height of each point in the array of points based on the output from the camera detector.

60. The processor: causing 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 a focus range during a first integration period, wherein the processor is configured to read and store video frames from the camera detector for the first integration period; causing 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 during a second integration period, wherein the processor is configured to read and store video frames from the camera detector for the second integration period; causing 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 during a third integration period, wherein the processor is configured to read and store video frames from the camera detector for the third integration period; calculating a phase of the light source corresponding to a focus position of a video frame pixel based on the first, second, and third stored video frames, and then converting the phase of the pixel to a height value; 60. The confocal three-dimensional sensor of claim 59 configured to:

61. 59. The confocal three-dimensional sensor of claim 58, wherein the light source is a light emitting diode.

62. 59. The confocal three-dimensional sensor of claim 58, wherein the light source is a laser.

63. 59. The confocal three-dimensional sensor of claim 58, wherein the light source is an incandescent light source.

64. 59. The confocal three-dimensional sensor of claim 58, wherein the variable focus lens is mechanically scanned by a voice coil.

65. 59. The confocal 3D sensor of claim 58, wherein the variable focus lens is mechanically scanned by a linear stage.

66. 59. The confocal three-dimensional sensor of claim 58, wherein the variable focus lens is a liquid lens.

67. 67. The confocal three-dimensional sensor of claim 66, wherein the focus of the liquid variable-focus lens is adjusted by electrostatically varying the curvature of the liquid lens surface.

68. 59. The confocal three-dimensional sensor of claim 58, wherein the focus of the variable-focus lens is adjusted by using acoustic waves to change the refractive index of the variable-focus lens.

69. 59. The confocal three-dimensional sensor of claim 58, wherein the time modulation is based on a Gray code.

70. 59. The confocal three-dimensional sensor of claim 58, wherein the time modulation is lamp-based.

71. 59. The confocal three-dimensional sensor of claim 58, wherein the time modulation is based on a Hamiltonian code.

72. 59. The confocal three-dimensional sensor of claim 58, wherein the temporal light source modulation is a periodic function.

73. 73. The confocal three-dimensional sensor of claim 72, wherein the periodic function is a sine function.

74. 73. The confocal 3D sensor of claim 72, wherein the periodic function has a period equal to the amount of time required for the variable focus lens to sweep the axial focus position through the focus range.

75. 59. The confocal three-dimensional sensor of claim 58, wherein the camera detector is a complementary metal oxide semiconductor (CMOS) area array having a two-dimensional array of pixels.

76. 59. The confocal three-dimensional sensor of claim 58, wherein the camera detector is a charge-coupled device (CCD) area array having a two-dimensional array of pixels.

77. 59. The confocal 3D sensor of claim 58, wherein the spatial light modulator is a pixelated spatial light modulator.

78. 59. The confocal three-dimensional sensor of claim 58, wherein the spatial light modulator is a digital mirror device (DMD).

79. 59. The confocal three-dimensional sensor of claim 58, wherein the spatial light modulator is a silicon device (LCOS).

80. 1. A single point confocal sensor for measuring the height of a point on an object, said sensor comprising: A light source and a light source modulator configured to temporally modulate the light source intensity; a lens configured to focus illumination passing therethrough onto the object; a light source pinhole aperture positioned to be illuminated by the light source; a focal point modulator configured to generate relative motion between the object and a 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 indicative of the total light transmitted through the detector pinhole aperture; a processor operably coupled to the detector, the light source modulator, and the focus modulator, the processor configured to cause the light source modulator to synchronously modulate a light source intensity while causing the focus modulator to sweep an axial focus position.

81. 81. A single point confocal sensor as claimed in claim 80, wherein the processor is further configured to calculate a height of the point on the object based on outputs from the detector and integrator.

82. 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 focus modulator to sweep an axial focus position through a focus range, and the processor is configured to read and store the detector output during the first integration period and then reset the detector; 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, and the processor is configured to read and store the detector output during the second integration period and then reset the detector; 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, and the processor is configured to read and store the detector output during the third integration period; 82. The single-point confocal sensor of claim 81, wherein the processor is configured to calculate a phase of the light source corresponding to a focus position based on the first, second, and third detector outputs, and convert the phase of the light source to a height of the point on the object.

83. 81. A single point confocal sensor as described in claim 80, wherein the light source is a light emitting diode.

84. 81. The single point confocal sensor of claim 80, wherein the light source is a laser.

85. 81. A single point confocal sensor as described in claim 80, wherein the light source is an incandescent light source.

86. 81. The single point confocal sensor of claim 80, wherein the focal modulator is operably coupled to a motion stage assembly.

87. 81. A single point confocal sensor as claimed in claim 80, wherein the time modulation is based on a Gray code.

88. 81. A single point confocal sensor as described in claim 80, wherein the temporal modulation is ramp based.

89. 81. The single point confocal sensor of claim 80, wherein the temporal modulation is based on a Hamiltonian code.

90. 81. A single point confocal sensor as described in claim 80, wherein the temporal light source modulation is a periodic function.

91. 91. A single-point confocal sensor as claimed in claim 90, wherein the periodic function is a sine function.

92. 91. The single point confocal sensor of claim 90, wherein the periodic function has a period equal to the amount of time required for the variable focus lens to sweep the axial focus position through the focus range.

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

94. 94. The confocal three-dimensional sensor of claim 93, wherein the processor is further configured to calculate a height of each point in the array of points based on the output from the camera detector.

95. The processor: causing 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 a focus range during a first integration period, wherein the processor is configured to read and store video frames from the camera detector for the first integration period; causing 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 during a second integration period, wherein the processor is configured to read and store video frames from the camera detector for the second integration period; causing 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 during a third integration period, wherein the processor is configured to read and store video frames from the camera detector for the third integration period; calculating a phase of the light source corresponding to a focus position of a video frame pixel based on the first, second, and third stored video frames, and then converting the phase of the pixel to a height value; 95. The confocal three-dimensional sensor of claim 94 configured to:

96. 94. The confocal three-dimensional sensor of claim 93, wherein the light source is a light emitting diode.

97. 94. The confocal three-dimensional sensor of claim 93, wherein the light source is a laser.

98. 94. The confocal three-dimensional sensor of claim 93, wherein the light source is an incandescent light source.

99. 94. The confocal three-dimensional sensor of claim 93, wherein the time modulation is based on a Gray code.

100. 94. The confocal three-dimensional sensor of claim 93, wherein the time modulation is ramp-based.

101. 94. The confocal three-dimensional sensor of claim 93, wherein the time modulation is based on a Hamiltonian code.

102. 94. The confocal three-dimensional sensor of claim 93, wherein the temporal light source modulation is a periodic function.

103. 103. The confocal three-dimensional sensor of claim 102, wherein the periodic function is a sine function.

104. 103. The confocal 3D sensor of claim 102, wherein the periodic function has a period equal to the amount of time required for the variable focus lens to sweep the axial focus position through the focus range.

105. 94. The confocal three-dimensional sensor of claim 93, wherein the camera detector is a complementary metal oxide semiconductor (CMOS) area array having a two-dimensional array of pixels.

106. 94. The confocal three-dimensional sensor of claim 93, wherein the camera detector is a charge-coupled device (CCD) area array having a two-dimensional array of pixels.

107. 1. A confocal three-dimensional sensor for measuring heights of an array of points on an object, said sensor comprising: A light source and a light source modulator configured to temporally modulate a light source intensity; a spatial light modulator illuminated by the light source and configured to receive light reflected from the object; a focal spot modulator configured to sweep an axial focal spot position; an imaging system for imaging the spatial light modulator onto a camera detector; an interference objective configured to focus illumination gated by the spatial light modulator onto the object and provide a coherence interference signal on the spatial light modulator during a focus sweep; a camera detector configured to receive the coherence interference signal gated by the spatial light modulator and to provide an output measurement indicative of total reflected light by the spatial light modulator for each point in the array of points; a processor operably coupled to the camera detector, the processor configured to cause the light source modulator to synchronously modulate a light source intensity while causing the focus modulator to sweep an axial focus position.

108. 108. A confocal three-dimensional sensor as described in claim 107, wherein the processor is further configured to calculate a height of each point in the array of points based on the output from the camera detector.

109. 108. The confocal three-dimensional sensor of claim 107, wherein the light source is a light emitting diode.

110. 108. The confocal three-dimensional sensor of claim 107, wherein the light source is a laser.

111. 108. A confocal three-dimensional sensor as described in claim 107, wherein the time modulation is based on a Gray code.

112. 108. The confocal three-dimensional sensor of claim 107, wherein the time modulation is based on a lamp.

113. 108. The confocal three-dimensional sensor of claim 107, wherein the time modulation is based on a Hamiltonian code.

114. 108. The confocal three-dimensional sensor of claim 107, wherein the temporal light source modulation is a periodic function.

115. 108. The confocal three-dimensional sensor of claim 107, wherein the periodic function is a sine function.

116. 1. A single point confocal sensor for measuring the height of a point on an object, said sensor comprising: A light source and a light source pinhole aperture positioned to be illuminated by the light source; a variable focus lens configured to focus illumination passing through the source pinhole aperture onto the object; a detector pinhole aperture configured to receive reflected light from the object, the variable-focus lens 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 temporally modulate at least one of the light source, the light reflected by the object, an integrator gain, and a detector gain; a processor operatively coupled to the detector, the integrator, and the light source modulator, the processor configured to synchronously temporally modulate the light source modulator while causing the variable-focus lens to sweep an axial focus position.

117. 1. A confocal three-dimensional sensor for measuring heights of an array of points on an object, said sensor comprising: A light source and a pinhole aperture array illuminated by the light source and configured to receive reflected light from the object; a variable focus lens configured to focus illumination passing through the pinhole aperture array onto the object and to image reflected light from the object onto the pinhole aperture array; a focus modulator operably coupled to the variable-focus lens, the focus modulator configured to sweep an axial focus position; an imaging system for imaging the pinhole aperture array onto a camera detector; a camera detector configured to receive reflected light from the object imaged by the variable focus lens onto the pinhole aperture array and to provide an output measurement indicative of the total transmitted light through the pinhole aperture array for each point in the array of points; a light source modulator configured to temporally modulate at least one of the light source, the light reflected from the object, an integrator gain, and a detector gain; a processor operably coupled to the camera detector, the processor configured to synchronously temporally modulate the light source modulator while causing the focal modulator to sweep an axial focal position.

118. 1. A confocal three-dimensional sensor for measuring heights of an array of points on an object, said sensor comprising: A light source and a pinhole aperture array illuminated by the light source and configured to receive reflected light from the object; a focal spot modulator configured to sweep an axial focal spot position; an imaging system for imaging the pinhole aperture array onto a camera detector; an interference objective configured to focus illumination passing through the pinhole aperture array onto the object and provide a coherence interference signal on the pinhole aperture array during a focal sweep; a camera detector configured to receive the coherence interference signals transmitted through the pinhole aperture array and to provide an output measurement indicative of the total transmitted light transmitted through the pinhole aperture array for each point in the array of points; a light source modulator configured to temporally modulate at least one of the light source, the light reflected from the object, an integrator gain, and a detector gain; a processor operably coupled to the camera detector, the processor configured to synchronously temporally modulate the light source modulator while causing the focal modulator to sweep an axial focal position.

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