Multiphase interferometer for 3D metrology

Abstract

In a system, an illumination source emits light, a first beam splitter directs a portion of the light toward a sample and another portion of the light toward a reference surface that reflects the light back to the first beam splitter to recombine with light reflected by the sample, at least one second beam splitter directs n portions of the light towards n detectors, each of the n portions of the light having a preset phase shift and n > = 2, and a processor receives an intensity of the n portions of the light. The processor calculates an interferogram envelope based on intensities measured by the n detectors as a reference surface moves between a plurality of signal collection positions.

Description

Technical Field

[0001] This invention relates to metrology systems, and more particularly, to metrology systems based on interferometry. Background Technology

[0002] The evolution of the semiconductor manufacturing industry places higher demands on yield management and, specifically, metrology and inspection systems. Critical dimensions continue to shrink, but the industry needs to reduce the time spent achieving high-yield, high-value production. Minimizing the total time from detecting a yield problem to resolving it determines a semiconductor manufacturer's return on investment.

[0003] Fabricating semiconductor devices, such as logic and memory devices, typically involves using numerous fabrication processes to process semiconductor workpieces (e.g., wafers, substrates, display panels, etc.) to form the various features and multiple layers of the semiconductor device. For example, photolithography is a semiconductor fabrication process involving transferring a pattern from a photomask onto a photoresist layer arranged on a semiconductor workpiece. Additional examples of semiconductor fabrication processes include (but are not limited to) chemical mechanical polishing (CMP), etching, deposition, and ion implantation. Multiple semiconductor devices can be fabricated as an arrangement on a single semiconductor workpiece, or the multiple semiconductor devices can be separated into individual semiconductor devices.

[0004] Inspection processes are used at various stages of semiconductor manufacturing to detect defects in the workpiece, thereby promoting higher yields and, consequently, higher profits. Inspection has always been a crucial part of manufacturing semiconductor devices such as integrated circuits (ICs). However, as the size of semiconductor devices shrinks, inspection becomes even more critical for the successful manufacture of acceptable semiconductor devices because even small defects can cause device failure. For example, as the size of semiconductor devices decreases, detecting defects in smaller sizes has become necessary because even relatively small defects can introduce undesirable aberrations into the semiconductor device.

[0005] Metrology processes are used at various stages of semiconductor manufacturing to monitor and control the process. Metrology processes differ from inspection processes in that, unlike inspection processes which detect defects on a workpiece, metrology processes are used to measure one or more characteristics of a workpiece that cannot be determined using existing inspection tools. Metrology processes can be used to measure one or more characteristics of a workpiece, allowing the performance of the process to be determined from those characteristics. For example, metrology processes can measure the dimensions (e.g., linewidth, thickness, etc.) of features formed on a workpiece during the process. Furthermore, if one or more characteristics of a workpiece are unacceptable (e.g., outside a predetermined range), the measurement of those characteristics can be used to modify one or more parameters of the process, resulting in additional workpieces manufactured through the process having acceptable characteristics.

[0006] Scanning interferometry is a common scheme for measuring the height of a sample, where light from a light source is split into two arms: a reference arm reflected by a mirror and the other arm interacting with the sample. After recombining the reflected light from the two arms on a detector, the relative lengths of the two arms can be changed by moving the mirror or the sample, and the envelope can be retrieved by recording changes in light intensity on the detector, where the maximum value of the envelope can be considered a measurement of the sample height. However, existing methods may require hundreds of thousands of measurements per scan to capture the envelope to achieve accurate measurement resolution. For example, in some cases, measurement positions less than half or a quarter of the light wavelength may be required (i.e., mirror movement). Therefore, these methods can be time-consuming and reduce system throughput.

[0007] Therefore, there is a need for an interferometric measurement method that can be used for faster and more efficient measurements. Summary of the Invention

[0008] Embodiments of this disclosure provide a system. The system may include a lighting source. The lighting source may be configured to emit light along a lighting path.

[0009] The system may further include a first beam splitter disposed in the illumination path. The first beam splitter may be configured to direct a portion of the light toward the sample and another portion of the light along a reference path. The sample may reflect the light along a collection path.

[0010] The system may further include a reference surface disposed in the reference path. The reference surface may be configured to reflect the light back to the first beam splitter for recombination with the light reflected by the sample in the collection path.

[0011] The system may further include n detectors disposed in the collection path, where n ≥ 2.

[0012] The system may further include at least one second beam splitter disposed in the collection path. The at least one second beam splitter may be configured to guide n portions of the light toward the n detectors, respectively. Each of the n portions of the light may have a preset phase shift.

[0013] The system may further include a processor that communicates electronically with the n detectors. The processor may be configured to receive the intensities of the n portions of the light, respectively, measured by the n detectors.

[0014] The reference surface can be moved between multiple signal collection locations to change the length of the reference path. The processor can be further configured to calculate the interferogram envelope based on the intensity of the n portions of the light measured by the n detectors at at least some of the multiple signal collection locations.

[0015] In some embodiments, the at least one second beam splitter may include at least one polarizing beam splitter configured to polarize at least one of the n portions of the light to have the preset phase shift.

[0016] In some embodiments, the system may further include a polarizing element disposed between the at least one second beam splitter and at least one of the n detectors. The polarizing element may be configured to polarize at least one of the n portions of the light to have the preset phase shift.

[0017] In some embodiments, the processor may be configured to calculate the interferogram envelope based on the intensity of the n portions of the light measured by the n detectors at three or more locations in the signal collection position.

[0018] In some embodiments, the processor may be further configured to determine the height of the sample based on the maximum value of the interferogram envelope.

[0019] In some embodiments, the system may further include a motor in electronic communication with the processor. The motor may be configured to move the reference surface between the plurality of signal collection locations. The processor may be configured to control at least one of the n detectors to capture measurements at the plurality of signal collection locations.

[0020] In some embodiments, the motor may be further configured to move one or more optical components to keep the sample focused as the reference surface moves between the plurality of signal collection locations.

[0021] In some embodiments, the motor may be configured to move the reference surface at a constant speed. The processor may be configured to control the n detectors to capture measurements at different times to form the preset phase shift between each of the n portions of the light.

[0022] In some embodiments, the processor may be configured to control the n detectors to capture measurements at different signal collection locations to form the preset phase shift between each of the n portions of the light.

[0023] In some embodiments, the n detectors may be positioned such that each of the n portions of the light has the preset phase shift.

[0024] Another embodiment of this disclosure provides a method. The method may include emitting light along an illumination path using an illumination source.

[0025] The method may further include using a first beam splitter positioned in the illumination path to direct a portion of the light toward a sample. The sample may reflect the light along the collection path.

[0026] The method may further include using the first beam splitter to guide another portion of the light along a reference path. A reference surface positioned in the reference path may reflect the light back to the first beam splitter and may be recombined with the light reflected by the sample in the collection path.

[0027] The method may further include guiding n portions of the light toward n detectors using at least one second beam splitter disposed in the collection path. Each of the n portions of the light may have a preset phase shift and n ≥ 2.

[0028] The method may further include measuring the intensity of each of the n portions of the light received by the n detectors.

[0029] The method may further include moving the reference surface between multiple signal collection locations to change the length of the reference path.

[0030] The method may further include using a processor to calculate an interferogram envelope based on the intensity of the n portions of the light measured by the n detectors at at least some of the plurality of signal collection locations.

[0031] In some embodiments, the at least one second beamsplitter may include at least one polarizing beamsplitter. The method may further include using the at least one second beamsplitter to polarize at least one of the n portions of the light to have the preset phase shift.

[0032] In some embodiments, a polarizing element may be disposed between the at least one second beam splitter and at least one of the n detectors. The method may further include using the polarizing element to polarize at least one of the n portions of the light to have the preset phase shift.

[0033] In some embodiments, the method may further include moving one or more optical components to keep the sample focused as the reference surface moves between the plurality of signal collection locations.

[0034] In some embodiments, the method may further include determining the height of the sample based on the maximum value of the interferogram envelope. Attached Figure Description

[0035] For a fuller understanding of the nature and purpose of this disclosure, reference should be made to the following detailed description taken in conjunction with the accompanying drawings, wherein:

[0036] Figure 1 This is a block diagram of a system according to an embodiment of the present disclosure;

[0037] Figure 2 This is a block diagram of a system according to another embodiment of the present disclosure;

[0038] Figure 3 This is a block diagram of a system according to another embodiment of the present disclosure;

[0039] Figure 4 This is a block diagram of a system according to another embodiment of the present disclosure; and

[0040] Figure 5 This is a flowchart of a method according to an embodiment of the present disclosure. Detailed Implementation

[0041] While the claimed subject matter will be described with reference to certain embodiments, other embodiments (including those not providing all the advantages and features set forth herein) are also within the scope of this disclosure. Various structural, logical, technological, step-by-step, and electronic changes may be made without departing from the scope of this disclosure. Therefore, the scope of this disclosure is defined only by reference to the appended claims.

[0042] refer to Figures 1 to 4 Embodiments of this disclosure provide a system 100. System 100 may be associated with interferometry, 3D metrology, profile measurement, and / or characterization of optical surfaces in terms of height, single-layer or multi-layer thickness, or refractive index variations based on optical interferometry. For example, System 100 may be implemented in 3D metrology tools for automated optical inspection and re-inspection of integrated circuits, flat panel displays, or printed circuit boards. Using System 100, simultaneous or synchronous measurement of interferograms, provided the relationship between the phases of the measurements is defined, allows for relaxed requirements on mechanical scanning and stability, and measurements can be retrieved with sufficient resolution by taking significantly fewer steps in the scan.

[0043] System 100 may include an illumination source 110. Illumination source 110 may be configured to emit light along illumination path 111. Illumination source 110 is configured to emit light with a wavelength spectrum of several nanometers (e.g., 1 to 10 nm). In some embodiments, illumination source 110 may emit white light. Illumination source 110 may be configured to emit light having a center wavelength bandwidth as defined by a particular application. Illumination source 110 may include a broadband emitter, such as an LED or high-brightness lamp, and a system that allows selection of the desired bandwidth. Without loss of generality, the system may be a set (one or more) of bandpass filters, a set of edge-turn and edge-cutoff filters, or a system employing spectral dispersion through refractive or diffractive elements, selection of the desired frequency band (slit), and recombination of the transmission frequency bands into a single beam.

[0044] System 100 may further include a first beamsplitter 120. The first beamsplitter 120 may be a polarized beamsplitter or a non-polarized beamsplitter. The first beamsplitter 120 may be positioned in illumination path 111. The first beamsplitter 120 may be configured to direct a portion of light toward sample 125 and another portion of light along reference path 131. Sample 125 may be a semiconductor workpiece (e.g., a wafer, substrate, display panel, etc.) or another object sought to be measured by system 100. Sample 125 may be positioned on stage 126. Stage 126 may be movable in a plane (i.e., perpendicular to the incident light) and / or on an axis (i.e., coaxial with the incident light) to adjust which portion of sample 125 is illuminated for measurement by system 100. As light is directed toward sample 125, it may be reflected along collection path 121. Based on the arrangement of the first beamsplitter 120 and sample 125, illumination path 111 and collection path 121 may be angled or juxtaposed. In some embodiments, the first beam splitter 120 may be placed in the collection path 121 such that light reflected by the sample 125 is transmitted back through the first beam splitter 120.

[0045] System 100 may further include a reference surface 130 for comparison with sample 125, such as a mirror or any other surface. For example, a "golden" sample may be used as reference surface 130, which may have surface features expected to match the surface features of sample 125 (i.e., the comparison will show deviations between the expected surface features of sample 125 and reference surface 130). Reference surface 130 may be positioned in reference path 131. Reference surface 130 may be configured to reflect light back to first beam splitter 120 for recombination with light reflected by sample 125 in collection path 121. In other words, illumination source 110 may separately direct light toward sample 125 and reference surface 130, and light reflected by sample 125 and reference surface 130 may be recombinated in collection path 121. Based on the arrangement of the first beam splitter 120 and the reference surface 130, the reference path 131 can be arranged such that the light reflected through the reference surface 130 can be juxtaposed with the light incident on the reference surface 130, so that the reflected light is transmitted back to the first beam splitter 120 to be recombined with the collection path 121.

[0046] The device 100 may further include n detectors 140. In some embodiments, n ≥ 2. For example, such as Figures 1 to 4 As shown, the n detectors 140 may include a first detector 140a and a second detector 140b, and in Figure 4In the process, the n detectors 140 further include a third detector 140c. The first detector 140a, the second detector 140b, and any additional detectors of the n detectors 140 can be placed in the collection path 121. Each of the n detectors 140 can be a charge-coupled device (CCD) camera or other type of detector capable of measuring the intensity of light within a wavelength range emitted by the illumination source 110.

[0047] System 100 may further include at least one second beamsplitter 150. The at least one second beamsplitter 150 may include a polarized beamsplitter or a non-polarized beamsplitter. The at least one second beamsplitter 150 may be positioned in the collection path 121. The at least one second beamsplitter 150 may be configured to direct n portions of light toward each of the n detectors 140, respectively. For example, as... Figures 1 to 4 As shown, the n portions of light may include a first portion 151a of light guided toward the first detector 140a and a second portion 151b of light guided toward the second detector 140b, and in Figure 4 In this configuration, the n portions of light further include a third portion 151c of light guided toward the third detector 140c. Additional second beamsplitters 150 disposed in the collection path 121 can be used to guide additional portions of the light toward any additional detectors of the n detectors 140. For example, for n detectors 140, there may be n-1 second beamsplitters 150. Figure 4 In the embodiment shown, there are two second beamsplitters 150a and 150b, wherein second beamsplitter 150a directs a first portion 151a of light toward a first detector 140a, and second beamsplitter 150b directs a second portion 151b of light toward a second detector 140b and a third portion 151c of light toward a third detector 140c. Each of the second beamsplitters 150a can be configured such that each of the n portions of light is a substantially equal portion of the light in the collection path 121. For example, second beamsplitter 150a can be a 33 / 66 beamsplitter, wherein approximately 1 / 3 of the light, as the first portion 151a, is directed toward the first detector 140a, and approximately 2 / 3 of the light is directed toward the second beamsplitter 150b. The second beam splitter 150b can be a 50 / 50 beam splitter, wherein approximately half of the light, as the second portion 151b, is guided toward the second detector 140b, and approximately half of the light, as the third portion 151c, is guided toward the third detector 140c. Therefore, in Figure 4In one embodiment, each of the n portions of light may be approximately one-third of the light in the collection path 121. For each additional second beamsplitter 150, a smaller fraction of the light in the collection path 121 may be separated into each of the n detectors 140. Based on the arrangement of the components of the system 100 as further described herein, each of the n portions of light may have a preset phase shift. In some embodiments, the n detectors 140 may be positioned such that each of the n portions of light has a preset phase shift to achieve the preset phase shift.

[0048] System 100 may further include processor 160. Processor 160 may include a microprocessor, microcontroller, field-programmable gate array (FPGA) or other device.

[0049] Processor 160 may be coupled to components of system 100 in any suitable manner (e.g., via one or more transmission media, which may include wired and / or wireless transmission media) so that processor 160 can receive output. Processor 160 may be configured to use the output to perform several functions. Measurement or inspection tools may receive instructions or other information from processor 160. Processor 160 may, as appropriate, communicate electronically with another inspection tool, measurement tool, or re-inspection tool (not specified) to receive additional information or send instructions.

[0050] Processor 160 can be part of various systems, including personal computer systems, graphics computers, FPGA-based boards and / or FPGA expansion boards of PCs, mainframe computer systems, workstations, network appliances, internet appliances, or other devices. Subsystems or systems may also include any suitable processor known in the art, such as parallel processors. Additionally, subsystems or systems may include platforms with high-speed processing and software as standalone tools or networking tools.

[0051] Processor 160 may be located in system 100 or another device, or otherwise be part of system 100 or another device. In examples, processor 160 may be part of a separate control unit or in a centralized quality control unit. Multiple processors 160 may be used to define multiple subsystems of system 100.

[0052] Processor 160 can be implemented in any combination of hardware, software, and firmware including a GPU. Furthermore, its functionality as described herein can be executed by a single unit or partitioned among different components, each of which can be implemented in any combination of hardware, software, and firmware. Program code or instructions for processor 160 to implement various methods and functions can be stored in a readable storage medium (e.g., memory).

[0053] If system 100 comprises more than one subsystem, then different processors 160 can be coupled to each other, enabling the transmission of images, data, information, instructions, etc., between the subsystems. For example, a subsystem can be coupled to an additional subsystem via any suitable transmission medium that can contain any suitable wired and / or wireless transmission medium known in the art. Two or more such subsystems can also be effectively coupled by sharing a computer-readable storage medium (not shown).

[0054] Processor 160 may be configured to perform several functions using the output of system 100 or other outputs. For example, processor 160 may be configured to send outputs to an electronic data storage unit or another storage medium. Processor 160 may be further configured as described herein.

[0055] Processor 160 may be configured according to any of the embodiments described herein. Processor 160 may also be configured to perform other functions or additional steps using the output of system 100 or using images or data from other sources.

[0056] Processor 160 can be communicatively coupled to any of the various components or subsystems of system 100 in any manner known in the art. Furthermore, processor 160 can be configured to receive and / or acquire data or information from other systems (e.g., test results from a testing system (e.g., a retesting tool, a remote database containing design data, and the like)) via a transmission medium that may include wired and / or wireless portions. In this manner, the transmission medium can act as a data link between processor 160 and other subsystems of system 100 or systems external to system 100. Various steps, functions, and / or operations of system 100 and the methods disclosed herein are implemented by one or more of the following: electronic circuits, logic gates, multiplexers, programmable logic devices, ASICs, analog or digital controllers / switches, microcontrollers, or computing systems. Program instructions implementing methods such as those described herein can be transmitted via or stored on a carrier medium. The carrier medium may include storage media such as read-only memory, random access memory, magnetic disk or optical disk, non-volatile memory, solid-state memory, magnetic tape, and the like. The carrier medium may include transmission media, such as wires, cables, or wireless transmission links. For example, the steps described throughout this disclosure may be performed by a single processor 160 (or computer subsystem) or alternatively by multiple processors 160 (or multiple computer subsystems). Furthermore, different subsystems of system 100 may comprise one or more computing or logic systems. Therefore, the foregoing description should not be construed as a limitation of this disclosure but is merely illustrative.

[0057] The processor 160 can communicate electronically with n detectors 140. For example, such as Figures 1 to 4As shown, the processor 160 can electronically communicate with the first detector 140a and the second detector 140b, and in Figure 4 In this embodiment, processor 160 further communicates electronically with third detector 140c. Processor 160 may be configured to receive the intensities of n portions of light measured by n detectors 140, respectively. For example, processor 160 may be configured to receive the intensities of a first portion 151a of light measured by first detector 140a, a second portion 151b of light measured by second detector 140b, a third portion 151c of light measured by third detector 140c, and any additional n portions of light received by each of the n detectors 140.

[0058] Processor 160 may electronically communicate with positioning system 135. Positioning system 135 may be configured to move reference surface 130 to change the relative length of reference path 131. For example, positioning system 135 may include motor 136 configured to move reference surface 130. In some embodiments, processor 160 may be further configured to control positioning system 135 to move sample 125 to further change the relative length of reference path 131. For example, motor 136 may electronically communicate with processor 160, and processor 160 may be configured to control motor 136 to stop moving reference surface 130 when reference surface 130 is in multiple signal collection positions, or processor 160 may be configured to control n detectors 140 to collect measurements at multiple signal collection positions while motor 136 continuously moves reference surface 130. The distance between each of the multiple signal collection positions may correspond to a fraction of the coherence length of light defined by the spectrum and numerical aperture of an imaging optics of light measured by n detectors 140. It should be understood that when the positioning system 135 moves the reference surface 130, the sample 125 and the stage 126 can remain in the same position to maintain a constant optical response of the sample 125, while changing the length of the reference path 131 to change the optical response of the reference surface 130. In some embodiments, the processor 160 may send instructions to the positioning system 135 to move optical elements (e.g., objective lens 181 and / or imaging aperture 182) in the collection path 121 to keep the relevant portion of the sample 125 in focus when scanning using the movement of the reference surface 130.

[0059] In some embodiments, the motor 136 may be configured to move the reference surface 130 at a constant speed. Therefore, the processor 160 may be configured to determine the movement of the reference surface 130 based on the time period during which the motor 136 has moved the reference surface 130 at a constant speed. By translating the reference surface 130 at a known constant speed, n detectors 140 can be triggered with the time difference between them, thereby creating a known phase shift between each of the n portions of light. The time difference may be 1 / 4 of the wavelength of the light or less.

[0060] In some embodiments, the motor 136 may be a pulse-motion motor. The pulse-motion motor may be a stepper motor or a nanopiezoelectric motor. The analyzer that generates the motor movement pulses may also generate trigger signals for the n detectors 140 and establish a predetermined phase shift between each of the n portions of light. For example, the motor 136 may include a linear actuator using a closed-loop encoder and a servo motion controller, and the servo motion controller may generate synchronization pulses for the illumination source 110 and each of the n detectors 140. Therefore, the processor 160 may be configured to determine the movement of the reference surface 130 based on the rotation of the motor 136, and the n detectors 140 may be triggered by the positional differences between them, thereby establishing a known phase shift between each of the n portions of light.

[0061] In some embodiments, system 100 may further include a position encoder in electronic communication with processor 160. The position encoder is configured to determine when motor 136 has moved reference surface 130 to one of a plurality of signal collection positions. Therefore, processor 160 may be configured to control motor 136 to stop moving reference surface 130 and / or control n detectors 140 to capture measurements after each signal collection position has been reached. For example, electronic comparators may be used to generate trigger signals for each of the n detectors 140 based on the position of reference surface 130, and by using n such comparators, each of the n detectors 140 may be triggered at different positions, thus providing a preset phase shift between measurements.

[0062] The processor 160 can be further configured to determine the height of the sample 125 based on an interferogram envelope driven by the intensity measured by n detectors 140 at multiple signal collection locations.

[0063] Generally speaking, It is the intensity measured at each detector at mirror position z. It is the wave vector of light in the scanning direction, λ is the vacuum wavelength of light, and n is the refractive index of the propagation medium. Intensity It can be written as an envelope function Multiply by carrier fringes: , where C is a constant.

[0064] The standard way to measure interferograms is by step size. The z-scan is performed to ensure at least two measurements per fringe period. This results in a step size typically less than 100 nm. After demodulating the signal, the envelope can be retrieved by utilizing multiple measurements within each fringe period, and the maximum value of the envelope can be considered as the sample height. However, these small step sizes require tens to hundreds of thousands of measurement points to measure the sample height with sufficient resolution.

[0065] In contrast, System 100 is based on simultaneous or precise timing measurements of a small set of points that have well-defined carrier phase relationships with each other. These point sets can be used to determine local values ​​of the envelope and take distances that allow for retrieval of the envelope's shape, but do not need to follow the carrier continuously during the scan.

[0066] In this example, the n detectors 140 may include those with The first detector 140a and the second detector 140b define the phase shift (which can be constructed by any of the system arrangements and methods described herein). Therefore, the intensity measured at the first detector 140a can be... And the intensity measured at the second detector 140b can be Using these two measurements, the envelope function can be written as follows: .

[0067] Alternatively, the measurement is extended to more than two points spaced apart within a nearly constant envelope: And in a sufficiently small assumption Set of measurement points within the z range We can fit the signal to a harmonic function, for example: In this context: The envelope function will be used to search multiple regions. The signal is fitted to a common function, and its maximum value is determined at a sufficiently accurate resolution. In other words, the processor 160 can be configured to base its signal on corresponding intensity values ​​measured at at least some of the multiple signal collection locations. and Calculated The maximum value is used to determine the height of sample 125. For example, processor 160 can move 100 or more discrete steps per millimeter to trigger signal collection, but may only need some of these points to determine the interferogram function. and its maximum value.

[0068] Based on a preset phase shift between the first detector 140a and the second detector 140b, each signal collection location can provide different measurement responses at the first detector 140a and the second detector 140b. Therefore, the measurement responses at the first detector 140a and the second detector 140b can represent different data points, and it is necessary to use data points collected only at some of the multiple signal collection locations to determine the interferogram function. In some embodiments, measurements at three or more of a plurality of signal collection locations may be used to determine the interferogram function. And its maximum value. In other words, although the positioning system 135 can scan the reference surface 130 across hundreds of locations, and the first detector 140a and the second detector 140b can detect the intensity of the light received at each of these locations, measurements at only three or more of these locations can be used to determine the interferogram function. and its maximum value. Processor 160 can be configured to be based on interferogram functions. The maximum value is used to determine the height of sample 125. While this example involves the use of two detectors, n detectors 140 can include additional detectors (e.g., three or more) and are not limited to this. In such examples, each of the n portions of light can have a preset phase shift between them, so the measurement response at each of the n detectors 140 can represent different data points, and increasing the number of detectors increases the number of data points. Therefore, the use of additional detectors can further improve the determined interferogram function. The measurement fidelity and accuracy.

[0069] In some embodiments, a preset phase shift between the n detectors can be established by polarizing at least one of the n portions of light directed toward each of the n detectors 140. Different arrangements of the polarizing optics in system 100 can achieve the preset phase shift, as further described below. While an exemplary 90° preset phase shift is described, other preset phase shifts may be used and are believed to be within the scope of this disclosure.

[0070] In some embodiments, at least one second beam splitter 150 may include a polarizing beam splitter, such as Figure 1 As shown in the diagram. Therefore, at least one second beamsplitter 150 can be configured to polarize at least one of the first portion 151a and the second portion 151b of light to have a preset phase shift when it separates light in the collection path 121. For example, at least one second beamsplitter 150 can be configured to polarize only one of the first portion 151a or the second portion 151b of light, while the polarization of the other portions of the light is unaffected by at least one second beamsplitter 150. Alternatively, at least one second beamsplitter 150 can be configured to polarize both the first portion 151a and the second portion 151b of light in different directions, thereby providing a preset phase shift between the two portions of light. In examples using more than two detectors, an additional second beamsplitter 150 disposed in the collection path 121 can also be a polarizing beamsplitter to polarize an additional n portions of light to another of the n detectors 140.

[0071] In some embodiments, the system may further include polarizing elements 123 disposed in the illumination path 111 between the first beam splitter 120 and the sample 125 and in the reference path 131 between the first beam splitter 120 and the reference surface 130, such as Figure 1 As shown in the diagram. The polarizing element 123 can be configured to polarize light reflected from the sample 125 and light reflected from the reference surface 130. Therefore, the light in the collection path 121 can include light in two or more polarized states to be separated by the second beam splitter 150. The polarizing element 123 can polarize the light at angles of ±22.5°, ±45°, or ±90° or any distance therebetween. Figure 1 In the embodiment shown, the polarizing element 123 includes a 45° polarizer in the illumination path 111 between the first beamsplitter 120 and the sample 125, and a 90° polarizer in the reference path 131 between the first beamsplitter 120 and the reference surface 130. In this embodiment, the first beamsplitter 120 may be a non-polarizing beamsplitter.

[0072] In some embodiments, the first beam splitter 120 may be a polarizing beam splitter, such as... Figure 2 As shown in the diagram. Therefore, the first beam splitter 120 can be configured to polarize at least one of the portion of light guided toward the sample 125 and the portion of light guided toward the reference surface 130 along the reference path 131. For example, the first beam splitter 120 can be configured to polarize only one of the portion of light guided toward the sample 125 and the portion of light guided toward the reference surface 130 along the reference path 131, while the polarization of the other portion of the light is unaffected by the first beam splitter 120. Alternatively, the first beam splitter 120 can be configured to polarize both the portion of light guided toward the sample 125 and the portion of light guided toward the reference surface 130 along the reference path 131, thereby providing a predetermined phase shift between the two portions of the light. Therefore, the light in the collection path 121 can include light in two or more polarization states based on the different polarization states of the light reflected from the sample 125 and the light reflected from the reference surface 130.

[0073] In some embodiments, the system 100 may further include a polarizing element 153 disposed between at least one of the at least one second beam splitter 150 and at least one of the n detectors 140. For example, such as Figure 2 As shown, a polarizing element 153 may be disposed between at least one second beam splitter 150 and each of the first detector 140a and the second detector 140b. The polarizing element 153 may be configured to polarize at least one of the first portion 151a and the second portion 151b of light to have a preset phase shift after the at least one second beam splitter 150 has separated the light in the collection path 121. The polarizing element 153 may polarize the light at angles of ±22.5°, ±45°, or ±90° or any distance therebetween. Figure 2In the embodiment shown, the polarizing element 153 includes a 22.5° polarizer in a first portion 151a of light between the second beamsplitter 150 and the first detector 140a, and a -22.5° polarizer in a second portion 151b of light between the second beamsplitter 150 and the second detector 140b. In this embodiment, at least one second beamsplitter 150 may be a non-polarized beamsplitter. Figure 4 In the embodiment shown, a polarizing element 153 is disposed in each of the first portion 151a, the second portion 151b, and the third portion 151c of light, such that all three portions of light have a predetermined phase shift (shown as arrows adjacent to each of the polarizing elements 153).

[0074] In some embodiments, the system 100 may further include a waveplate 124 disposed in an illumination path 111 between the first beam splitter 120 and the sample 125 and in a reference path 131 between the first beam splitter 120 and the reference surface 130. The waveplate 124 may be a quarter-wave plate or a half-wave plate. Figure 2 In the embodiment shown, wave plate 124 is a quarter wave plate.

[0075] System 100 may further include a waveplate 127 disposed in a collection path 121 between a first beam splitter 120 and at least one second beam splitter 150. Figures 1 to 4 In the embodiment shown, wave plate 127 is a quarter wave plate.

[0076] System 100 may further include an illumination optics assembly 170 disposed in an illumination path 111 between illumination source 110 and first beam splitter 120. Illumination optics assembly 170 may include one or more optical elements, such as a condenser 171, a polarizer 172, a spectral filter 173, an illumination aperture 174, and a light collector 175 disposed in a downstream order in the illumination path 111 in the direction of light emitted from illumination source 110 toward first beam splitter 120.

[0077] In some embodiments, the illumination optics assembly 170 may further include a second condenser 176 and an illumination field stop 177, which are arranged upstream of the condenser 171 and in downstream sequence in the illumination path 111, as shown below. Figure 3 As shown in the image. The addition of a second condenser 176 and an illumination field stop 177 provides Kohler illumination. Although Figure 3 Implementation examples and Figure 2 The embodiment is similar, with additional elements in the illumination optics assembly 170, but such elements can also be added to... Figure 1 Examples of this implementation are used to provide Kohler lighting. Similarly, although... Figure 4One embodiment includes additional elements in the lighting optics assembly 170 that can provide Kohler lighting, but such components may be omitted to include only [other components]. Figure 1 The optical elements shown in the embodiments.

[0078] System 100 may further include a collection optics assembly 180 disposed in a collection path 121 between a first beam splitter 120 and at least one second beam splitter 150. The collection optics assembly 180 may include an objective lens 181, an imaging aperture 182, and a barrel lens 183 arranged in a downstream order in the collection path 121 in the direction of the recombinated light reflected by the sample 125 and the reference surface 130 toward the second beam splitter 150.

[0079] Using system 100, the height of sample 125 can be determined using a small number of points (e.g., three or more) within the envelope, reducing the total number of measurements by 10 to 100 times compared to existing systems. n detectors 140 are synchronized using detector-based time delay triggering, positional differences of the reference surface 130, or a preset phase shift of the polarization difference between the light received by each detector, such that the detectors provide several pairs of measurement points to determine the interferogram envelope function using only a few measurements and to calculate the maximum value of the envelope corresponding to the height of sample 125. This efficiency allows for increased throughput while maintaining accuracy for precise measurements.

[0080] Embodiments of this disclosure provide method 200. (See also...) Figure 5 Method 200 may include the following steps.

[0081] At step 210, the illumination source emits light along the illumination path. The illumination source may be configured to emit light with a wavelength spectrum selected based on a specific measurement application. For example, the wavelength spectrum may be a few nanometers (e.g., 1 to 10 nm). In some embodiments, the illumination source may emit white light. The illumination source may be configured to emit light with a center wavelength bandwidth as defined by a specific application. The illumination source may include a broadband emitter, such as an LED or a high-brightness lamp, and a system that allows selection of the desired bandwidth. Without loss of generality, the system may be a set (one or more) of bandpass filters, a set of edge-turn and edge-cutoff filters, or a system employing spectral dispersion through refraction or diffraction elements, selection of the desired frequency band (slit), and recombination of the transmission frequency bands into a single beam.

[0082] At step 220, a first beamsplitter positioned in the illumination path directs a portion of the light toward the sample, and the sample reflects the light along the collection path. The sample may be a semiconductor workpiece (e.g., a wafer, substrate, display panel, etc.) or another object to be measured. Depending on the arrangement of the first beamsplitter and the sample, the illumination path and the collection path may be angled or juxtaposed. In some embodiments, the first beamsplitter may be positioned in the collection path such that light reflected from the sample is transmitted back through the first beamsplitter.

[0083] At step 230, the first beamsplitter guides another portion of the light along the reference path, and a reference surface positioned in the reference path reflects the light back to the first beamsplitter and recombines it with the light reflected by the sample in the collection path. The reference surface can be a mirror or any surface used for comparison with the sample. For example, a "standard" sample can be used as the reference surface, which may have surface features expected to match the surface features of the sample (i.e., the comparison will show deviations between the sample and the expected surface features of the reference surface). Based on the arrangement of the first beamsplitter and the reference surface, the reference path can be arranged such that the light reflected through the reference surface is juxtaposed with the light incident on the reference surface, such that the reflected light is transmitted back to the first beamsplitter for recombination with the collection path.

[0084] At step 240, at least one second beam splitter disposed in the collection path directs n portions of light toward n detectors. Each of the n portions of light has a preset phase shift. In some embodiments, the n detectors may be positioned such that each of the n portions of light has a preset phase shift. In other embodiments, optical components may polarize at least one of the n portions of light to form the preset phase shift.

[0085] At step 250, n detectors measure the intensity of n portions of the light. Each of the n detectors may be a charge-coupled device (CCD) camera or other type of detector capable of measuring the intensity of light within a wavelength range emitted by an illumination source. Each of the n detectors may capture the measurements at slightly different times to induce a preset phase shift. Alternatively, each of the n detectors may capture the measurements simultaneously, but receive polarized light with a preset phase shift.

[0086] At step 260, the reference surface moves between multiple signal collection locations to change the length of the reference path. For example, a positioning system may be configured to move the reference surface between multiple signal collection locations. The positioning system may include a motor configured to move a reference mirror to perform measurements at each of the multiple signal collection locations. The distance between each of the multiple signal collection locations may correspond to a fraction of the coherence length of light defined by the spectrum and numerical aperture of an imaging optics of light measured by each of n detectors. In some embodiments, the reference surface may be moved to 100 or more signal collection locations to perform measurements. Based on a preset phase shift between the n detectors, each signal collection location may provide a different measurement response at the n detectors. Therefore, the measurement responses at the n detectors may represent different data points, and the interferogram envelope needs to be determined using only some of the data points collected at the multiple signal collection locations.

[0087] At step 270, the processor calculates the interferogram envelope based on the intensity of n portions of light measured by n detectors at at least some of the multiple signal collection locations. For example, the processor may generate the interferogram envelope based on measurements by n detectors at three or more of the signal collection locations, and the maximum value of the interferogram envelope may be used to determine the height of the sample.

[0088] Using method 200, the height of a sample can be determined using a small number of points (e.g., three or more) within the envelope, reducing the total number of measurements by 10 to 100 times compared to existing systems. n detectors are synchronized using detector-based time delay triggering, reference surface position differences, or a preset phase shift via the polarization difference between the light received by each detector, such that the n detectors provide a set of measurement points to determine the interferogram envelope using only a few measurements and to calculate the maximum value of the envelope corresponding to the sample height. This efficiency allows for increased throughput while maintaining accuracy for precise measurements.

[0089] Although this disclosure has been described with respect to one or more specific embodiments, it will be understood that other embodiments of this disclosure may be made without departing from the scope of this disclosure. Therefore, this disclosure is to be considered limited only by the appended claims and their reasonable interpretation.

Claims

1. A system comprising: A lighting source configured to emit light along a lighting path; A first beam splitter is disposed in the illumination path and configured to direct a portion of the light toward the sample and another portion of the light along a reference path, wherein the sample reflects the light along a collection path; A reference surface, which is disposed in the reference path and configured to reflect the light back to the first beam splitter to recombine with the light reflected by the sample in the collection path; n detectors are placed in the collection path, where n ≥ 2; At least one second beam splitter is disposed in the collection path and configured to guide n portions of the light toward the n detectors, each of the n portions of the light having a predetermined phase shift; and A processor that communicates electronically with the n detectors, the processor being configured to receive the intensities of the n portions of the light as measured by the n detectors, respectively; The reference surface is movable between multiple signal collection locations to change the length of the reference path, and the processor is further configured to calculate the interferogram envelope based on the intensity of the n portions of the light measured by the n detectors at at least some of the multiple signal collection locations.

2. The system of claim 1, wherein the at least one second beam splitter comprises at least one polarizing beam splitter configured to polarize at least one of the n portions of the light to have the preset phase shift.

3. The system of claim 1, further comprising a polarizing element disposed between the at least one second beam splitter and at least one of the n detectors, wherein the polarizing element is configured to polarize at least one of the n portions of the light to have the preset phase shift.

4. The system of claim 1, wherein the processor is configured to calculate the interferogram envelope based on the intensity of the n portions of the light measured by the n detectors at three or more locations in the signal collection position.

5. The system of claim 1, wherein the processor is further configured to determine the height of the sample based on the maximum value of the interferogram envelope.

6. The system of claim 1, further comprising a motor electronically communicating with the processor and configured to move the reference surface between the plurality of signal collection locations, wherein the processor is configured to control at least one of the n detectors to capture measurements at the plurality of signal collection locations.

7. The system of claim 6, wherein the motor is further configured to move one or more optical components to keep the sample focused as the reference surface moves between the plurality of signal collection locations.

8. The system of claim 6, wherein the motor is configured to move the reference surface at a constant speed, and the processor is configured to control the n detectors to capture measurements at different times to form the preset phase shift between each of the n portions of the light.

9. The system of claim 6, wherein the processor is configured to control the n detectors to capture measurements at different signal collection locations to form the preset phase shift between each of the n portions of the light.

10. The system of claim 1, wherein the n detectors are positioned such that each of the n portions of the light has the preset phase shift.

11. A method comprising: Use a lighting source to emit light along the lighting path; A portion of the light is directed toward a sample using a first beam splitter positioned in the illumination path, wherein the sample reflects the light along the collection path; The first beam splitter guides another portion of the light along a reference path, wherein a reference surface placed in the reference path reflects the light back to the first beam splitter and recombines it with the light reflected by the sample in the collection path; The light is directed toward n detectors by at least one second beam splitter placed in the collection path, wherein each of the n portions of the light has a preset phase shift and n ≥ 2; The intensity of each of the n portions of the light received by the n detectors is measured respectively; The reference surface is moved between multiple signal collection locations to change the length of the reference path; and The processor calculates the interferogram envelope based on the intensity of the n portions of the light measured by the n detectors at at least some of the plurality of signal collection locations.

12. The method of claim 11, wherein the at least one second beamsplitter comprises at least one polarizing beamsplitter, and the method further comprises: The light is polarized by the at least one second beam splitter to have the preset phase shift, at least one of the n portions of the light.

13. The method of claim 11, wherein the polarizing element is disposed between the at least one second beam splitter and at least one of the n detectors, and the method further comprises: The polarizing element is used to polarize at least one of the n portions of the light to have the preset phase shift.

14. The method of claim 11, wherein the processor is configured to calculate the interferogram envelope based on the intensity of the n portions of the light measured by the n detectors at three or more locations in the signal collection position.

15. The method of claim 11, wherein the processor is configured to control at least one of the n detectors to capture measurements at the plurality of signal collection locations.

16. The method of claim 11, further comprising: One or more optical components are moved to keep the sample focused as the reference surface moves between the multiple signal collection locations.

17. The method of claim 11, wherein the processor is configured to control the n detectors to capture measurements at different times to form the preset phase shift between the n portions of the light.

18. The method of claim 11, wherein the processor is configured to control the n detectors to capture measurements at different signal collection locations to form the preset phase shift between the n portions of the light.

19. The method of claim 11, wherein the n detectors are positioned such that each of the n portions of the light has the preset phase shift.

20. The method of claim 11, further comprising: The height of the sample is determined based on the maximum value of the interferogram envelope.

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