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This paper reviews knife-edge interferometry (KEI) capable of inspection and metrology for various engineering applications, including displacement measuring sensors for dynamic system controls and edge quality of the parts, such as cutting tools, corrosive blades, and photomask patterns. This paper includes the modeling, design, and data analysis of KEI. With the expanding market of manufacturing industries, edge topography and instrumentation technology become more and more vital to industrial manufacturing-related applications such as cutting tool wear inspection, photomask edge roughness determination, and edge corrosion propagation monitoring. Due to the limitation of measurement requirements like non-contact (photomask inspection), in-situ (cutting tool inspection), and real-time (corrosion propagation monitoring), there are only a few methods available in the market above, and those methods are based on post-processing. The KEI is capable of on-machine measurements, especially for the nanopositioning systems, providing a large working range and positioning accuracy compared with the conventional displacement sensor. This review addresses the current and future KEI technology. Here, including the theoretical approaches to KEI, this review details the data analy
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Qualitative Edge Topology Inspection and Interpretation by Enhanced Knife-Edge Interferometry
Edge topography measurement technology is vital in many engineering applications such as cutting tool inspection, photomask inspection, or corrosive wear inspection. Although those applications require high-level sharpness or smoothness of the edges to achieve their needs, there is little measurement and inspection technology available. Most of the current surface metrology and inspection technology is primarily focused on planar surface characterization [1-3], and sometimes indirect methods such as measuring the cutting force or acceleration to interpret tool wear propagation during the machining process are used [4]. This paper presents the enhanced knife-edge interferometry (KEI) that measures optical scattering behaviors that originated from the edge. KEI utilizes the optical interference of incident light and scattered light at the edge and produces the fringe patterns proportional to edge quality [5-7]. Analysis of such fringe patterns enables monitoring edge quality. We recently improved KEI performance by shaping the beam with the objective lens (4×, 10×). The incident plane wave was turned into a spherical wave by the objective lens, and the spherical wave and the diffracted wave at the edge interfered. As a result, the strong interference effect was observed, and over 3 times fringe patterns were obtained compared to the interference results of no objective case. The enhanced KEI was employed for edge quality inspection of sharp edges (razor blade), cutting tools, and photomask.
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- Award ID(s):
- 1855473
- PAR ID:
- 10334476
- Date Published:
- Journal Name:
- American Society for Precision Engineering
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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This paper presents the line-edge-roughness (LER) characterization of the photomask patterns and the lithography-printed patterns by enhanced knife edge interferometry (EKEI) that measures the interferometric fringe patterns occurring when the light is incident on the patterned edge. The LER is defined as a geometric deviation of a feature edge from an ideal sharp edge. The Fresnel number-based computational model was developed to simulate the fringe patterns according to the LER conditions. Based on the computational model, the photomask patterns containing LER features were designed and fabricated. Also, the patterns were printed on the glass wafer by photolithography. The interferometric fringe patterns of those two groups of patterns were measured and compared with the simulation results. By using the cross-correlation method, the LER effects on the fringe patterns were characterized. The simulation and experimental results showed good agreement. It showed that the amplitude of the fringe pattern decreases as the LER increases in both cases: photomask patterns and printed wafer patterns. As a result, the EKEI and its analysis methods showed the potential to be used in photomask design and pattern metrology, and inspection for advancing semiconductor manufacturing processes.more » « less
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Abstract This paper introduces a novel wafer-edge quality inspection method based on analysis of curved-edge diffractive fringe patterns, which occur when light is incident and diffracts around the wafer edge. The proposed method aims to identify various defect modes at the wafer edges, including particles, chipping, scratches, thin-film deposition, and hybrid defect cases. The diffraction patterns formed behind the wafer edge are influenced by various factors, including the edge geometry, topography, and the presence of defects. In this study, edge diffractive fringe patterns were obtained from two approaches: (1) a single photodiode collected curved-edge interferometric fringe patterns by scanning the wafer edge and (2) an imaging device coupled with an objective lens captured the fringe image. The first approach allowed the wafer apex characterization, while the second approach enabled simultaneous localization and characterization of wafer quality along two bevels and apex directions. The collected fringe patterns were analyzed by both statistical feature extraction and wavelet transform; corresponding features were also evaluated through logarithm approximation. In sum, both proposed wafer-edge inspection methods can effectively characterize various wafer-edge defect modes. Their potential lies in their applicability to online wafer metrology and inspection applications, thereby contributing to the advancement of wafer manufacturing processes.more » « less
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Line-edge roughness (LER) characterization is vital in the semiconductor industry to this day. This paper presents an EKEI (enhanced knife edge interferometry)-based system for photomask LER characterization. From the given EKEI-based system, the LER on the photomask pattern can be characterized. In this paper, the Fresnel (F) number-based geometrical optical model was developed for the LER-induced edge diffraction fringe simulation. The LER here was defined by three times the standard deviation of the edge profile on the photomask. Periodic rectangular functions were employed to characterize LER effects on the diffraction fringe patterns in simulation. The simulation-generated fringe pattern was then analyzed by cross-correlation. From the simulation result, the fringe pattern will get attenuated when adding the LER onto the line edge profile. Once the LER value increases, some of the high-order fringes vanish. A negative correlation between the similarity and the LER value was discovered. From the F number-based simulation model, the real photomask decorated with different LER values was designed and fabricated. After the photomask writing process, we used the EKEI system to scan the LER-programmed pattern for photomask LER characterization. By using the cross-correlation, the same trend was found in the experiment and simulation results. The fringe pattern from the edge was attenuated while the LER was added to the edge. The geometrical-based simulation and analysis model for photomask LER characterization was validated. From the simulation results, the fringe pattern from the edge was attenuated when adding LER on the edge. The experiment results show good agreement with the simulation ones. In sum, the proposed EKEI-based system has great potential to be utilized for on-machine photomask LER characterization and those defect inspection. The F number-based geometrical optical model also has the potential for diffraction-free pattern design and analysis.more » « less
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This paper presents a novel noncontact measurement and inspection method based on knife-edge diffraction theory for corrosive wear propagation monitoring at a sharp edge. The degree of corrosion on the sharp edge was quantitatively traced in process by knife-edge interferometry (KEI). The measurement system consists of a laser diode, an avalanche photodiode, and a linear stage for scanning. KEI utilizes the interferometric fringes projected on the measurement plane when the light is incident on a sharp edge. The corrosion propagation on sharp edges was characterized by analyzing the difference in the two interferometric fringes obtained from the control and measurement groups. By using the cross-correlation algorithm, the corrosion conditions on sharp edges were quantitatively quantified into two factors: lag and similarity for edge loss and edge roughness, respectively. The KEI sensor noise level was estimated at 0.03% in full scale. The computational approach to knife-edge diffraction was validated by experimental validation, and the computational error was evaluated at less than 1%. Two sets of razor blades for measurement and control groups were used. As a result, the lag will be increased at an edge loss ratio of 1.007/µm due to the corrosive wear, while the similarity will be decreased at a ratio of with respect to edge roughness change. Experimental results showed a good agreement with computational results.more » « less
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