TWI902575B - Concentric circular shadow moire measurement system - Google Patents

Abstract

The present invention discloses a Concentric Circular Shadow Moiré Measurement System, which includes an illumination module configured to emit light towards the wafer surface and a concentric circular grating that generates precise shadow patterns on the wafer surface. An imaging sensor captures the superimposed concentric circular shadow moiré patterns formed by the interaction of the concentric circular grating and the shadow patterns. A processing unit utilizes Fast Fourier Transform-based phase demodulation to process the captured moiré patterns and reconstruct a three-dimensional model of the wafer's surface morphology with sub-micron resolution. This Concentric Circular Shadow Moiré Measurement System achieves one-shot global measurements without mechanical scanning, eliminating geometric inaccuracies associated with displacement platforms. The concentric circular grating ensures that moiré patterns remain perpendicular to any directional surface features on the wafer, reducing inaccuracies caused by periodic surface structures with arbitrary orientations.

Description

Concentric Circle Shadow Moiré Measurement System

This invention relates to the field of optical measurement systems, and particularly to a technique for accurately measuring the surface morphology of large, unpolished semiconductor wafers. The technique combines shadow moiré patterns with a specialized grating system to achieve high-resolution three-dimensional surface morphology measurement.

In the semiconductor industry, maintaining stringent surface quality standards for semiconductor wafers is crucial. Characteristics such as flatness, warpage, and roughness significantly affect the performance and yield of semiconductor wafers. Therefore, accurate measurement and inspection of wafer surface morphology is an indispensable part of the manufacturing process.

Various optical measurement techniques have been developed and applied to evaluate the surface properties of wafers, but each method has its own unique operating principles and limitations.

Laser triangulation involves projecting a laser beam onto the wafer surface and detecting the position of the reflected beam to determine the surface morphology. This method provides high-resolution measurements, typically achieving sub-micron accuracy. However, its applicability is limited by the need to progressively scan the surface, requiring the use of long-stroke displacement platforms. This type of mechanical motion introduces geometric errors, including straightness and angular deviations, which particularly affect measurement accuracy in large-area wafer measurements.

Confocal microscopy uses point illumination and spatial filtering techniques to acquire high-resolution three-dimensional images of wafer surfaces. This technique provides submicron depth resolution, suitable for detailed surface analysis. Similar to laser triangulation, confocal microscopy relies on mechanical scanning to cover large areas, inheriting the geometric inaccuracies associated with displacement platforms.

Interferometry uses the interference of light waves to measure surface deviations with nanometer-level precision. Interferometric systems, such as those developed by Zygo, are renowned for their exceptional accuracy. However, they typically require highly reflective wafer surfaces, making them unsuitable for unpolished or non-reflective surfaces, especially in the early stages of wafer fabrication.

Structured light systems project known light patterns (such as grids or stripes) onto a wafer surface and analyze the deformation of the pattern to infer the surface morphology. Although structured light can capture large areas in a single image, its resolution is typically limited to the micrometer level, which is insufficient to meet the increasingly sophisticated demands of the semiconductor industry.

Moiré measurement techniques extract surface morphology information by overlaying two or more periodic patterns (such as gratings) to generate interference patterns. These techniques can be divided into projected moiré and shadowed moiré methods. Projected moiré involves projecting gratings onto the wafer surface and analyzing the resulting moiré fringes. Although highly sensitive to surface variations, projected moiré systems typically require complex calibration and are sensitive to alignment errors, limiting their practicality in large-scale, high-precision measurements.

In contrast, shadow moiré uses a grating placed between a light source and the wafer to project a shadow onto the wafer surface to generate a moiré pattern that encodes the morphology of the wafer surface. Shadow moiré systems have advantages due to their submicron resolution, simple setup, and simplified calibration process. However, traditional shadow moiré techniques typically use linear gratings, which align the moiré fringes in a fixed direction. This alignment can lead to measurement inaccuracies when the wafer surface has periodic structures that are not perpendicular to the grating lines (such as wire saw marks).

In summary, despite advancements in optical measurement techniques, several challenges remain in measuring large, unpolished semiconductor wafers. Scanning techniques such as laser triangulation, confocal microscopy, and interferometry are limited by the measurement range of each scan. Measuring large wafer surfaces requires multiple scans or stitching together data from displacement platforms, which introduces accumulated geometric errors and reduces measurement accuracy.

Furthermore, reliance on a displacement platform in the scanning system introduces potential geometric inaccuracies, including straightness and angular deviations. These errors are particularly pronounced when measuring large areas, leading to unreliable surface morphology data critical for semiconductor applications. Interferometric methods require highly reflective wafer surfaces, making them unsuitable for unpolished wafers with inherent surface roughness and non-reflective characteristics in early manufacturing stages. Additionally, while structured light technology can capture large areas in a single image, its micrometer-level resolution is insufficient for the submicrometer to nanometer-level precision required in advanced semiconductor manufacturing processes.

Traditional shadow moiré systems using linear gratings also suffer from orientation sensitivity. For example, the wafer surface obtained after a crystal pillar is diced by a wire dicing machine has periodic microstructures (dicing marks). When the alignment of these microstructures is aligned with (parallel to) the direction of the generated moiré fringes or only slightly angled, the moiré fringes may incorrectly reflect surface changes on the wafer. This error leads to inaccuracies in phase demodulation and surface morphology reconstruction, reducing the reliability of the measurement.

The limitations of existing optical measurement methods highlight the need for innovative technologies that enable high resolution, support large-area measurements, adapt to non-reflective surfaces, and reduce orientation sensitivity. Specifically, there is a need for a novel optical measurement system that utilizes advanced grating configurations and robust image processing techniques to provide accurate, high-resolution, and scalable surface morphology measurements for large, unpolished semiconductor wafers.

Meeting these requirements necessitates the development of a measurement system capable of achieving submicron to nanometer-level accuracy without relying on mechanical scanning or displacement platforms. Ideally, this system should be able to accurately measure large-area wafer surfaces in a single acquisition, thereby eliminating geometric errors associated with mechanical motion. Furthermore, the system should be able to effectively measure unpolished, non-reflective wafer surfaces and accurately reconstruct the surface morphology regardless of the periodic surface structure orientation. This invention overcomes the inherent limitations of existing methods by introducing concentric circle shadow moiré measurement technology, providing a solution with higher accuracy, reliability, and applicability in semiconductor manufacturing and other high-precision industries.

This invention provides a concentric circle shadow moiré measurement system (hereinafter referred to as the "measurement system") designed to accurately measure the surface morphology of large unpolished semiconductor wafers (hereinafter referred to as "wafers") with high precision and high resolution. The measurement system overcomes the limitations of existing optical measurement techniques and eliminates geometric inaccuracies associated with such motion by enabling one-time, full-range measurement without the need for mechanical scanning or a displacement platform.

The measurement system includes the following components: 1. Illumination module: An adjustable white light-emitting diode configured to emit coherent and stable light onto the wafer surface. Its adjustability allows for fine-tuning of light intensity and wavelength, improving measurement accuracy under various conditions. 2. Beam splitter: A planar beam splitter with a 50:50 reflectance ratio, positioned to receive light from the illumination module. It splits the emitted light into transmitted and reflected portions, directing the reflected portion towards the grating assembly to generate a shadow pattern on the wafer surface. 3. Grating assembly: Comprising concentric gratings with a specified grating period (e.g., 50 micrometers). This concentric grating design ensures that the moiré pattern always maintains a discontinuous 0-degree angle with any periodic microstructures arranged in any direction on the wafer (e.g., wafer dicing marks will only be parallel to the generated concentric moiré pattern at the dicing point (0-degree angle), while the angle at other positions is not 0 degrees), thus reducing inaccuracies caused by periodic microstructures on the surface in any direction. When illuminated, the grating assembly generates a precise shadow pattern on the wafer surface. 4. Image sensor: A high-resolution charge-coupled device camera configured to capture the overlapping shadow moiré pattern formed by the interaction between the concentric grating and the shadow pattern on the wafer surface. The image sensor captures the entire wafer surface in a single image, enabling a single measurement. 5. Processing Unit: Equipped with advanced image processing algorithms, the processing unit utilizes phase demodulation based on Fast Fourier Transform to process the captured moiré patterns. It reconstructs a three-dimensional model of the wafer surface morphology, highlighting key surface features such as warping and waviness, with sub-micron accuracy. The processing unit can also compensate for potential errors in the measurement system, such as alignment errors, phase calculation inaccuracies, and temperature-induced fluctuations.

An optional displacement platform can be included in the measurement system to adjust the distance between the grating assembly and the wafer. This adjustment changes the periodicity of the grating shadow, allowing for fine-tuning of the moiré pattern scale and adaptation to wafers of different sizes or surface properties.

The concentric circle shadow moiré measurement system in this case has the following advantages: High precision and high resolution: The system achieves sub-micron resolution, meeting the stringent precision requirements of the semiconductor industry. One-time full-area measurement: By capturing the entire wafer surface in a single image, the system eliminates the need for mechanical scanning or data stitching, avoiding geometric inaccuracies associated with displacement platforms. Orientation insensitivity: The use of concentric circle gratings ensures accurate measurement regardless of the orientation of periodic surface structures on the wafer, such as wire saw marks. Applicable to non-reflective surfaces: Unlike interferometric measurement methods that require highly reflective surfaces, this system can effectively measure unpolished, non-reflective semiconductor wafers.

While primarily designed for semiconductor wafer inspection, this measurement system's high precision makes it suitable for a variety of high-precision fields, including optics and optoelectronics, materials science, aerospace engineering, microelectronics, and biomedical engineering. It provides the detailed surface morphology data required for quality control, defect detection, and ensuring components meet stringent industry specifications.

By overcoming the limitations of existing optical measurement techniques, the concentric circle shadow moiré measurement system offers an innovative solution that improves the accuracy, reliability, and scalability of surface morphology measurements. As a key tool in industries requiring precise surface analysis, it facilitates higher manufacturing yields and the production of high-quality, defect-free components that meet the demands of next-generation technological advancements.

To make the above features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings.

This invention introduces a concentric circle shadow moiré measurement system applicable to high-precision analysis of the surface morphology of large, unpolished semiconductor wafers. This system utilizes concentric circle gratings to generate shadow moiré patterns. Unlike traditional linear grating systems, the concentric circle gratings ensure that the moiré pattern is always perpendicular to any directional surface feature (such as periodic cut marks), thereby eliminating directional measurement errors and improving the accuracy of surface morphology reconstruction. This technique can reconstruct three-dimensional surface profiles with sub-micron resolution, making it ideal for the stringent quality control requirements of the semiconductor industry.

Please refer to Figure 1, which shows a schematic diagram of the architecture of one embodiment of the concentric circle shadow moiré measurement system of the present invention. The concentric circle shadow moiré measurement system 100 (hereinafter referred to as the measurement system 100) includes an illumination module 110, a beam splitter 120, a grating assembly 130, an image sensor 140, a processing unit 150, and a displacement platform 160. The illumination module 110 serves as the light source for the measurement system 100. In this embodiment, the illumination module 110 is composed of adjustable white light-emitting diodes (LEDs) to emit a stable light beam. The adjustability of the LEDs allows for fine adjustment of the light intensity and wavelength to adapt to various measurement conditions and improve the flexibility of the measurement system 100.

The beam splitter 120 is located between the illumination module 110 and the grating assembly 130. In this embodiment, the beam splitter 120 has a 50:50 reflectance ratio and is responsible for splitting the incident beam 20 into two distinct parts: transmitted light (not shown in FIG. 1) and reflected light 22. The reflected light 22 is directed to the grating assembly 130 to produce a shadow pattern on the surface of the wafer 10. In this embodiment, the grating assembly 130 is composed of concentric circular gratings 132 (as shown in FIG. 2), and these concentric circular gratings 132 are, for example, custom-made semiconductor photomasks by Meichip Corporation. In one embodiment, the concentric circular gratings 132 consist of multiple uniformly spaced concentric circles, each concentric circle being spaced approximately λ 50 micrometers (µm) apart. This circular arrangement ensures that the shadow moiré pattern has a discontinuous 0-degree angle with any directional surface feature on wafer 10 (such as periodic dicing marks produced by the manufacturing process), regardless of its orientation. When the reflected light 22 interacts with the concentric grating 132, a precise shadow pattern is formed on the surface of wafer 10, encoding the surface morphology of wafer 10 as a moiré pattern.

In this embodiment, the image sensor 140 is a charge-coupled device (CCD) camera responsible for capturing the moiré pattern formed by the interaction between the shadow pattern formed on the surface of wafer 10 and the pattern of the concentric grating 132. In the concentric shadow moiré measurement system 100, a Basler ace U-shaped CCD camera is used because its high-resolution image capture capability is crucial for detecting subtle surface changes with sub-micron precision. The image sensor 140 is positioned behind the beam splitter 120 and captures the moiré pattern generated by the overlap between the shadow produced by the concentric grating 132 and the grating assembly 130 itself. The quality and resolution of the captured image directly affect the accuracy of subsequent surface morphology reconstruction.

Connected to the image sensor 140 is a processing unit 150, which is a computing module equipped with advanced image processing and phase demodulation algorithms. In this embodiment, the processing unit 150 performs several key functions, such as: extracting phase information from the captured moiré pattern using the Fast Fourier Transform (FFT) algorithm, compensating for system alignment, inaccurate phase calculations, and potential errors in the image sensor 140 caused by temperature fluctuations, and reconstructing a detailed three-dimensional model of the wafer surface based on the demodulated phase information.

In one embodiment, the measurement system 100 further includes a displacement platform 160 to adjust the distance between the grating assembly 130 and the wafer 10. This adjustment changes the periodicity of the shadows cast by the concentric gratings 132, allowing for fine-tuning of the moiré pattern scale to accommodate wafers 10 of different sizes or surface characteristics. Here, the displacement platform 160 enhances the flexibility and adaptability of the measurement system 100 to different measurement scenarios.

The accuracy of the concentric circle shadow moiré measurement system of this invention is based on a solid mathematical framework that establishes the relationship between the physical parameters of the measurement system and the generated moiré pattern. The basic principles governing the operation of the measurement system 100 will be explained below with reference to Figures 3A and 3B and the equations.

The light intensity distribution of the concentric grating, _IG (x, y) , captured by the image sensor 140, is described as follows: in: It refers to the background light intensity. λ is the amplitude of the beam from the concentric grating 132. λ is the period of the concentric grating 132. x and y are the horizontal and vertical distances from the center of the concentric grating 132, respectively.

The reflected light 22 passes through the concentric grating 132 and interacts with the surface of the wafer 10 to produce a grating shadow. The period of this grating shadow is... , is represented as: Where: L is the distance between the image sensor 140 and the concentric grating 132. D is the distance between the equivalent light source 140' and the image sensor 140. W(x,y) is the distance between the concentric grating 132 and the surface of the wafer 10 at point (x,y) .

The periodicity of the shadows cast by the overlapping beams. , is represented as: The above formula Substituting the values, we get the following formula:

The light intensity distribution of the shadow produced by the concentric grating 132 on the surface of wafer 10. Captured by image sensor 140, and represented as: in: It refers to the intensity of the background light in the shadow. It is the amplitude of the grating's shadow. It is the cycle of light and shadow at the overlapping points.

The composite light intensity distribution of overlapping concentric gratings 132 and shadow moiré patterns. , is represented as: in: It is the phase of the concentric grating 132. This is the phase of the grating's shadow. Expand the product terms using the trigonometric equality:

Low-frequency components, , representing the shadow moiré phase, is expressed as: Rearranging the equations to represent W(x,y) , which is the distance between the concentric grating 132 and the surface of wafer 10 at point (x,y) , we get: This mathematical framework helps to accurately reconstruct the three-dimensional surface morphology of a wafer based on captured Moiré patterns.

The concentric circle shadow moiré measurement system 100 operates through a series of coordinated steps, including the interaction between light propagation, the shadow pattern generated by the concentric circle grating 132, and advanced image processing. Referring to Figure 4, which illustrates a flowchart of one embodiment of the concentric circle shadow moiré measurement system of the present invention, the system 100 first enters a setup and calibration phase, as shown in step S105. This involves precisely aligning the illumination module 110, beam splitter 120, grating assembly 130, and image sensor 140 to ensure optimal light propagation and pattern generation. Incorrect alignment can lead to phase calculation errors and measurement inaccuracies. In one embodiment, the measurement system 100 employs a high-precision mounting bracket and adjustable fixing devices to secure the components in precise positions, allowing for fine adjustments during calibration. When adjusting the positions of the illumination module 110 and the image sensor 140, calibration standards or reference diagrams are typically used to verify the accuracy of the settings. Furthermore, temperature stabilization measures are implemented to maintain stable operating temperatures for key components (especially the CCD camera), preventing errors caused by temperature variations such as camera overheating due to long exposure times.

After calibration, the measurement process begins. As shown in step S110, the illumination module 110 emits a beam 20 towards the beam splitter 120. Then, as shown in step S120, the beam splitter 120 divides the beam 20 into transmitted light and reflected light 22. The reflected light 22 is directed towards the grating assembly 130. Next, as shown in step S130, the reflected light 22 interacts with the concentric grating 132, producing precise shadow patterns on the surface of the wafer 10. These shadow patterns overlap with the periodicity of the grating itself, generating shadow moiré patterns that encode the surface morphology of the wafer 10.

Subsequently, as shown in step S140, image sensor 140 captures overlapping shadow moiré patterns in a single high-resolution image, achieving a single global measurement of the entire wafer surface without the need for mechanical scanning or data stitching. This eliminates the geometric inaccuracies associated with displacement platforms in traditional scan-based measurement systems. Next, as shown in step S150, the captured moiré image is then processed by processing unit 150, which uses phase demodulation based on a Fast Fourier Transform algorithm to extract phase information. This phase data is then used to reconstruct a detailed three-dimensional model of the wafer 10 surface, highlighting key surface features such as warping and corrugations with sub-micron accuracy.

In an embodiment where the measurement system 100 includes a displacement platform 160, a step may also be included to adjust the distance between the grating assembly 130 and the wafer 10 to change the period size of the shadow produced by the concentric grating 132.

After capturing the moiré image, the image sensor 140 transmits the data to the processing unit 150, which uses a Fast Fourier Transform (FFT) algorithm to perform phase demodulation. The FFT algorithm decomposes the spatial moiré pattern into its constituent frequency components, facilitating the extraction of phase information. This process begins by converting the captured image to the frequency domain, isolating frequency components associated with the shadow moiré pattern. Specific frequency bands corresponding to the low-frequency moiré pattern are isolated, while high-frequency components generated by the concentric grating 132 and the overlapping of the grating shadow are filtered to reduce noise and irrelevant data.

Once the relevant frequency components are isolated, the phase information representing the shadow moiré phase is... The phase information is extracted. This phase information is crucial for determining wafer surface morphology variations. Using the established mathematical framework, cell 150 calculates the distance W(x,y) between the surface at each point (x,y) on wafer 10 and the concentric grating 132. These calculation results are summarized to construct a morphology map of the wafer surface, highlighting features such as warping, waviness, and other surface irregularities, with sub-micron accuracy.

Furthermore, the 3D surface model is visualized using specialized software, facilitating detailed analysis and quality control assessment. This visualization helps identify and quantify surface defects, ensuring that the wafer meets the stringent quality standards required for semiconductor manufacturing.

Ensuring the accuracy and reliability of the measurement system 100 involves addressing potential sources of error and implementing robust calibration procedures. The measurement system 100 employs a variety of strategies to minimize errors, including addressing alignment errors, phase calculation inaccuracies, and temperature-induced fluctuations.

Precise alignment of the illumination module 110, beam splitter 120, grating assembly 130, and image sensor 140 is crucial to preventing phase errors caused by misalignment. The measurement system 100 employs a high-precision mount and adjustable fixing devices to secure each component in precise positions, allowing for fine adjustments during calibration. A progressive alignment protocol ensures correct optical path configuration, minimizing straightness and angular deviations to avoid affecting measurement accuracy. Furthermore, accurate phase demodulation relies on the integrity of the captured moiré pattern. To mitigate phase calculation errors, the measurement system 100 uses a high-resolution CCD camera to capture detailed moiré patterns, reducing the possibility of phase misinterpretation. Additionally, a phase demodulation algorithm based on Fast Fourier Transform (FFT) improves the accuracy of phase extraction, ensuring accurate surface reconstruction.

Furthermore, temperature variations can affect the performance of optical components and image sensors, leading to inaccurate measurements. Measurement system 100 addresses these issues through thermal management strategies, such as incorporating cooling systems or insulation devices, to maintain stable operating temperatures for key components, particularly the CCD camera. Additionally, a temperature compensation algorithm is implemented within processing unit 150, adjusting phase calculations based on real-time temperature data to correct any temperature-induced deformation.

These error minimization strategies ensure that the concentric circle shadow moiré measurement system 100 provides consistent and reliable measurement performance under various operating conditions, maintaining high accuracy and precision.

Although a concentric grating with a period of 50 µm is used in the above embodiment, the concentric circle shadow moiré measurement system 100 can be adjusted in various embodiments to meet specific application requirements. For example, different grating periods can be used to adjust the scale of the moiré pattern to suit specific measurement resolutions or wafer sizes. For instance, a finer grating period (e.g., 25 µm) can improve the resolution of applications requiring nanometer-level precision, while a coarser period (e.g., 100 µm) is suitable for larger wafers or lower resolution requirements. Furthermore, multiple concentric gratings with different periods or orientations can be combined in the grating assembly to enable simultaneous measurement of multiple surface properties or enhance pattern complexity to improve the accuracy of phase demodulation. In other embodiments, higher-resolution image sensors or multiple cameras can be used to improve system measurement accuracy and capture more detailed moiré patterns, particularly suitable for wafers with complex surface morphologies. Additionally, the measurement system can be integrated into automated manufacturing workflows to facilitate seamless quality control. Using robotic arms or automated platforms to accurately position wafers within the measurement area increases throughput and reduces human intervention. By integrating processing units with Manufacturing Execution Systems (MES), real-time analysis and decision-making based on measurement data can be performed, improving overall manufacturing efficiency and product quality.

In summary, the concentric circle shadow moiré measurement system of this invention possesses several key advantages, making it superior to existing technologies in high-precision measurement scenarios and enhancing its effectiveness and applicability. Firstly, the concentric circle grating ensures that the moiré pattern is always perpendicular to surface features of any orientation, reducing inaccuracies caused by the periodic structure of the surface in any direction. This characteristic is particularly advantageous when measuring wafer surfaces with periodic structures such as saw cut markings. Furthermore, the concentric circle shadow moiré measurement system achieves sub-micron resolution, meeting the stringent accuracy requirements of the semiconductor industry and enabling detailed analysis of critical surface morphologies, which is crucial for quality control and defect detection.

Furthermore, unlike interferometer systems that require highly reflective surfaces, the concentric circle shadow moiré measurement system can effectively measure unpolished, non-reflective silicon wafers. This expands its applicability, especially in the early stages of wafer fabrication where surface roughness and non-reflectivity are quite common. Moreover, by achieving a one-time, full-area measurement without mechanical scanning, it avoids the geometric inaccuracies associated with displacement platforms in traditional scanning methods. This makes measurements more consistent and reliable over a large wafer area, and this design facilitates a simple calibration procedure, reduces setup complexity, and improves operational efficiency. In addition, this invention employs multiple mechanisms to address alignment errors, phase calculation inaccuracies, and temperature-induced fluctuations, ensuring consistent and reliable measurement performance under various operating conditions.

These advantages make the concentric circle shadow moiré measurement system an excellent solution for high-precision surface morphology measurement, especially suitable for applications requiring superior accuracy and reliability.

In the above embodiments, although the concentric circle shadow moiré measurement system is primarily used in semiconductor wafer inspection, its versatility and high precision open up avenues for wider application in various high-tech fields. For example, in the production of optical components such as lenses, mirrors, and optoelectronic devices, accurate surface measurement is crucial for ensuring optical performance. This measurement system can accurately measure surface morphology, ensuring that optical surfaces meet stringent specifications for flatness and curvature. In materials research and development, understanding surface morphology is key to studying material properties and behavior. This measurement system provides detailed surface characteristic data for various materials, assisting in the analysis of surface treatments, coatings, and material properties. It also assists in optimizing manufacturing processes by monitoring surface morphology changes in real time.

Therefore, the concentric circle shadow moiré measurement system of this invention represents a major advancement in optical surface morphology measurement technology. By integrating concentric gratings within a shadow moiré framework, this measurement system achieves high-precision, one-time, full-range measurement of large, unpolished semiconductor wafers, overcoming the shortcomings of traditional scanning and interferometer methods. Furthermore, this invention not only meets the immediate needs of semiconductor wafer inspection, but also provides an effective and reliable tool for maintaining and improving quality standards in various high-tech fields as industries continuously push the boundaries of technological and manufacturing precision.

Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art may make some modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

10: Wafer; 20: Beam; 22: Reflected light; λ: Period of concentric grating ; _λS : Period of grating shadow; L : Distance between image sensor and concentric grating ; D : Distance between equivalent light source and image sensor; W(x,y) : Distance between concentric grating and wafer surface at point (x,y) ; 100: Concentric shadow moiré measurement system; 110: Illumination module; 120: Beam splitter; 130: Grating assembly; 132: Concentric grating; 140: Image sensor; 140': Equivalent light source; 150: Processing unit; 160: Displacement platform; S110~S150: Flowchart symbols

Figure 1 shows a schematic diagram of the architecture of one embodiment of the concentric circle shadow moiré measurement system of the present invention. Figure 2 shows a schematic diagram of the structure of one embodiment of the concentric circle grating of the present invention. Figure 3A shows a schematic diagram of the optical path of the concentric circle shadow moiré measurement system of Figure 1, and Figure 3B shows a schematic diagram of the equivalent architecture of the concentric circle shadow moiré measurement system of Figure 1. Figure 4 shows a flowchart of the operation of one embodiment of the concentric circle shadow moiré measurement system of the present invention.

10: Wafers

20: Beam

22: Reflected light

100: Concentric Circle Shadow Moiré Measurement System

110: Lighting Module

120: Spectrometer

130: Raster assembly

140: Image Sensor

150: Processing Unit

160: Displacement Platform

Claims (9)

A concentric circle shadow moiré measurement system includes: an illumination module configured to emit light onto a surface of an object; a grating assembly including a concentric circle grating having a specified grating period, the grating assembly being positioned to receive the light emitted from the illumination module and generate a shadow pattern on the surface of the object; an image sensor configured to capture an overlapping shadow moiré pattern formed by the interaction of the concentric circle grating with the shadow pattern on the surface of the object; and a processing unit configured to process the captured moiré pattern using phase demodulation processing based on fast Fourier transform to reconstruct a three-dimensional model of the wafer surface morphology. The concentric circle shadow moiré measurement system as described in claim 1, wherein the illumination module includes an adjustable white light emitting diode. The concentric circle shadow moiré measurement system as described in claim 1 further includes a beam splitter configured to receive light from the illumination module and split the light into a transmitted and a reflected portion, and the grating assembly is positioned to receive light from the portion reflected by the beam splitter. The concentric circle shadow moiré measurement system as described in claim 1, wherein the beam splitter divides the light into transmitted and reflected parts in a 50:50 ratio. The concentric circle shadow moiré measurement system as described in claim 1, wherein the period of the concentric circle grating is 50 micrometers. The concentric circle shadow moiré measurement system as described in claim 1, wherein the image sensor is a charge-coupled device camera. The concentric circle shadow moiré measurement system as described in claim 1 is configured to capture the entire wafer surface in a single image without mechanical scanning or displacement of the wafer or system components. The concentric circle shadow moiré measurement system as described in claim 1 further includes a displacement platform configured to adjust the distance between the grating assembly and the wafer to change the periodicity of the grating shadow. The concentric circle shadow moiré measurement system as described in claim 1, wherein the processing unit is further configured to compensate for alignment errors, phase calculation inaccuracies, and temperature-induced fluctuations when processing the captured moiré pattern.