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KR-102964765-B1 - Target and algorithm for measuring overlays by modeling backscattered electrons on superimposed structures

KR102964765B1KR 102964765 B1KR102964765 B1KR 102964765B1KR-102964765-B1

Abstract

The overlay target includes a grating-over-grating structure having a bottom grating structure placed on the specimen and a top grating structure placed on the bottom grating structure. The overlay target further includes a calibration scan location that includes the bottom grating structure but not the top grating structure, and an overlay scan location that includes the top grating structure and the bottom grating structure.

Inventors

  • 구트만 나다브
  • 아체 올리버
  • 펠프스 캐리

Assignees

  • 케이엘에이 코포레이션

Dates

Publication Date
20260513
Application Date
20210630
Priority Date
20200701

Claims (20)

  1. In terms of method, A step of acquiring an overlay target and forming an acquired image using an electron beam-based output acquisition subsystem, wherein the overlay target is, A grating-over-grating structure comprising a lower grating structure and an upper grating structure disposed on the lower grating structure, A calibration scan position that includes the lower grating structure but does not include the upper grating structure, and A step of forming the acquired image, comprising an overlay scan position including the upper grating structure and the lower grating structure; and A step of measuring the overlay of the grating-over-grating structure by solving and extracting the overlay from the acquired image. Includes, The above-mentioned solving and extraction step includes a step of extracting a signal extracted from a single layer, and the above-mentioned solving and extraction step further includes a step of solving the scattering of the extracted signal, and the step of solving the scattering is A step of applying a backscattered electronic profile to the above-mentioned extracted signal; A step of determining a transfer function for the above-mentioned extracted signal; and A method comprising the step of generating a model for the scattering including the above transfer function.
  2. In paragraph 1, Step of improving the signal-to-noise ratio of the extracted signal A method that further includes.
  3. In paragraph 2, A method in which the above-mentioned improvement step includes the step of applying a design-based filter to the above-mentioned extracted signal.
  4. In paragraph 1, A method in which the parameters of the above model are optimized by using the center of symmetry or local asymmetry of the secondary electron signal, or by matching the second calibration scan location where the interaction between the backscattered electrons of a specific layer and the secondary electrons is found with the said calibration scan location.
  5. A non-transient computer-readable storage medium comprising one or more programs for executing the method of claim 1 on one or more computing devices.
  6. In the system, A stage configured to hold a specimen having an overlay target, wherein the overlay target is, A grating-over-grating structure comprising a lower grating structure disposed on the above specimen and an upper grating structure disposed on the lower grating structure, A calibration scan position that includes the lower grating structure but does not include the upper grating structure, and The stage comprising an overlay scan position including the upper grating structure and the lower grating structure; An electron beam-based output acquisition subsystem configured to measure the overlay target on the stage above; and A processor that electronically communicates with the electron beam-based output acquisition subsystem configured to measure the overlay of the grating-over-grating structure by solving and extracting the overlay from the acquired image. Includes, The above solving and extraction includes extracting a signal extracted from a single layer, and the above solving and extraction further includes solving the scattering of the extracted signal, and the scattering is, Applying a backscattered electronic profile to the above-mentioned extracted signal; Determining a transfer function for the above-mentioned extracted signal; and A system comprising generating a model for the scattering including the above transfer function.
  7. In paragraph 6, A system further comprising improving the signal-to-noise ratio of the extracted signal using the above processor.
  8. In Paragraph 7, A system in which the above improvement includes applying a design-based filter to the above extracted signal.
  9. In paragraph 6, A system in which the parameters of the above model are optimized by using the center of symmetry or local asymmetry of the secondary electron signal, or by matching the second calibration scan location where the interaction between the backscattered electrons of a specific layer and the secondary electrons is found with the said calibration scan location.
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Description

Target and algorithm for measuring overlays by modeling backscattered electrons on superimposed structures The present disclosure generally relates to semiconductor targets and measurements. With the advancement of the semiconductor manufacturing industry, the demand for yield management, particularly measurement and inspection systems, is increasing. While critical dimensions continue to shrink, the industry must shorten the time required to achieve high-yield, high-value-added production. Minimizing the total time from the detection of yield issues to their resolution determines the return on investment for semiconductor manufacturers. The inspection process is used to detect defects on wafers at various stages of semiconductor manufacturing, thereby increasing the yield of the manufacturing process and consequently boosting profits. Inspection has always been a critical part of manufacturing semiconductor devices, such as integrated circuits (ICs). However, as the dimensions of semiconductor devices decrease, inspection becomes even more critical for the successful manufacturing of acceptable semiconductor devices, as smaller defects can cause the device to fail. For example, as the dimensions of semiconductor devices decrease, it has become necessary to detect defects of reduced size, as even relatively small defects can cause unwanted aberrations in the semiconductor device. Standard marks used for electron beam overlay measurements may have separated patterns that isolate signals from different layers in a non-overlapping manner, as shown in FIG. 1 as side-by-side marks and in FIG. 2 as interleaved marks. In this case, a simple algorithm can be used to extract the location of each layer. FIGS. 3 and 4 illustrate a multilayer pattern (1) comprising a top layer (2) and a buried layer (3). In the case of a multilayer, it may not be possible to distinguish whether a secondary electron signal corresponds to a secondary electron (4) from the top layer (2), which may be denoted as SE, or to a secondary electron (5) from the buried layer (3), which may be denoted as SE2. As shown in FIG. 3, SE2 may correspond to a secondary electron (5) generated from backscattered electrons scattered from the buried layer (3). Likewise, as shown in FIG. 4, it may not be possible to determine whether a backscattered electron (BSE) signal (6 or 7) corresponds to the top layer (2) or the buried layer (3). Measuring spatially separated targets may have disadvantages. These disadvantages may include large open areas. Open areas are incompatible with microelectronic manufacturing because they increase costs. Another disadvantage is that imaging using an electron beam in an asymmetric field of view can generate beam placement distortion due to non-uniform surface charge. Additionally, separated areas may not adequately represent devices that may contain stacked layers. Previous attempts to avoid these drawbacks (i.e., to measure stacked layers where spatial separation of signals from each layer is impossible) involved modeling electron beam stacking interactions. However, complete modeling requires knowledge of the design, process steps, and tool-material interactions. In such attempts, this is performed using optical measurements, for example, optical critical dimension (OCD) applications. For electron beam overlay metrology, there is no accurate and fast measurement method. Another previous attempt involved configuring a dedicated grating-over-grating target using a specified shift. This configuration can incorporate algorithms using differential signals. Since the signal-to-noise ratio (SNR) is an order of magnitude smaller than that of spatially separated features, the required measurement time becomes longer, making these targets unsuitable for in-line production control. Therefore, an improved overlay target and a method to measure it are required. In one embodiment, the overlay target may include a grating-over-grating structure, a calibration scan location, and an overlay scan location. In another embodiment, the method may include the step of forming an acquired image by acquiring an overlay target with an electron beam-based output acquisition subsystem and measuring an overlay of a grating-over-grating structure using the acquired image. The overlay target may include a grating-over-grating structure, a calibration scan location, and an overlay scan location. Measuring an overlay of a grating-over-grating structure using the acquired image may include solving and extracting the overlay from the acquired image. In one example, a non-transient computer-readable storage medium may include one or more programs that execute steps of the method, such as acquiring an overlay target with an electron beam-based output acquisition subsystem to form an acquired image and using the acquired image to measure an overlay of a grating-over-grating structure. The steps may further include a step of solving and extracting the overlay from