An after etch overlay measurement on device is typically used as a reference overlay as this is what determines the final overlay. The delta between on target overlay from after develop (ADI) and this reference overlay on device after etch (AEI) is known as the metrology to device offset (MTD). As the fab overlay is controlled by a run-to-run control of ADI overlay, it is preferred to minimize the MTD. The MTD concept in overlay metrology has long been present in the industry and many ways to mitigate this problem have been adopted (such as designing overlay target at ADI that has a similarly low aberration response as the device, or dialing in a static offset between ADI and AEI overlay, etc.). As overlay margins continue to shrink, existing methods start to show gaps and are insufficient to suppress the MTD to an acceptable level on the few most critical overlay layers. In order to address this gap, we need to deploy a much wider solution space that provides an integrated design-lithography-etch solution. In order to characterize the MTD, (assuming that target design in ADI has already minimized aberration response delta between target and device), it is important to understand that there are two major components to MTD: (1) an inaccuracy in ADI overlay (metrology artifacts mostly due to the presence of target asymmetry) and (2) etch to litho offset due to any post ADI added effects such as etch induced expansion and/or stress release etc. However, the above two components are strongly coupled and traditional characterization methods have difficulty in separating their contribution to the measurement. In this technical paper we will discuss novel methods (data driven as well as model-based) to decouple these and multi-lot results will show that MTD can be further minimized compared to traditional static correction between ADI and AEI.
Advancing technology nodes in DRAM continues to drive the reduction of on-product overlay (OV) budget. This gives rise to the need for OV metrology with greater accuracy. However, the ever increasing process complexity brings additional challenges related to metrology target deformation, which could contribute to a metrology error. Typically, an accurate OV measurement involves several engineering cycles for target and recipe optimization. In particular, process optimization in either technology development (TD) phase or high volume manufacturing (HVM) phase might influence metrology performance, which requires re-optimization. Therefore, a comprehensive solution providing accuracy and process robustness hereby minimizing the cycle time is highly desirable. In this work, we report multi-wavelength µDBO enhanced with accuracy aware pixel selection as a solution for robust OV measurement against process changes as well as improved accuracy in HVM. Accuracy aware pixel selection is capable of tackling intra-target processing variations and is established on a multi-wavelength algorithm with immunity to target asymmetry impact. DRAM use cases in FEOL critical layers will be discussed in this paper. Superior robustness and accuracy will be demonstrated together with improved on-product OV performance, promising a process of record metrology solution in specific applications throughout the TD and HVM.
Metrology requirements at advanced nodes are not only tightening on specifications but also broadening in terms of flexibility needed to cover variety of product stacks. Metrology targets need to be process compatible and at the same time these targets should also be readable by the metrology system. In some cases, process conditions require a target pitch that is large compared to the wavelength used by the metrology system. Examples of these situations include for instance topography transfer or stacks with thick resist (for e.g. 3D-NAND). Traditionally overlay is extracted from the asymmetry in the positive and negative first diffraction order generated from μDBO targets. However, when the pitch is large, the targets generate multiple higher diffraction orders. Current state-of-the-art diffraction based overlay systems do not take into account the effect of these higher diffraction orders and typically only select the first diffraction order. This is done by reducing the pitch of the target, tuning the wavelength or by changing the angle of incidence of the illumination light. To address wavelength over pitch flexibility an advanced algorithm was introduced on a new metrology system in the fab, providing full flexibility in the selection of measurement wavelength and pitch. To obey the specifications on accuracy and throughput, we will present a new metrology system that is, compared to its predecessor, about 2x faster and able to measure more accurately because of the ability to measure multiple wavelengths within the same time frame.
In multi patterning processes, overlay is now entangled with CD including OPC and stochastics. This combined effect is a serious challenge for continued shrink and is driving down the allowed overlay margin to an unprecedented level. We need to do everything to improve overlay where accurate measurement and control of wafer deformation is extremely important. This requires accuracy in overlay metrology that decouples target asymmetry from wafer deformation. Multiwavelength diffraction-based overlay (DBO) is positioned for providing such accuracy while maintaining the required measurement speed. At the same time, with the increase of process complexity in advanced nodes, several new types of target asymmetries are introduced. Some of such asymmetries vary even within the target / grating area (intra-grating) and some are so severe that it impacts the center of gravity shift of the overlay target.
In this paper, we present a statistical framework for the analysis of the performance of Bag-of-Words (BOW) systems. The paper aims at establishing a better understanding of the impact of different elements of BOW systems such as the robustness of descriptors, accuracy of assignment, descriptor compression and pooling and finally decision making. We also study the impact of geometrical information on the BOW system performance and compare the results with different pooling strategies. The proposed framework can also be of interest for a security and privacy analysis of BOW systems. The experimental results on real images and descriptors confirm our theoretical findings. Notation: We use capital letters to denote scalar random variables X and X to denote vector random variables, corresponding small letters x and x to denote the realisations of scalar and vector random variables, respectively. We use X ~pX(x) or simply X ~p(x) to indicate that a random variable X is distributed according to pX(x). N(μ, σ 2X ) stands for the Gaussian distribution with mean μ and variance σ2X . B(L, Pb) denotes the binomial distribution with sequence length L and probability of success Pb. ║.║denotes the Euclidean vector norm and Q(.) stands for the Q-function. D(.║.) denotes the divergence and E{.} denotes the expectation.
KEYWORDS: Signal to noise ratio, Binary data, Lead, Databases, Data hiding, Computer programming, Reliability, Data modeling, Berkelium, Computer security
In many problems such as biometrics, multimedia search, retrieval, recommendation systems requiring privacypreserving
similarity computations and identification, some binary features are stored in the public domain or
outsourced to third parties that might raise certain privacy concerns about the original data. To avoid this
privacy leak, privacy protection is used. In most cases, privacy protection is uniformly applied to all binary
features resulting in data degradation and corresponding loss of performance. To avoid this undesirable effect
we propose a new privacy amplification technique that is based on data hiding principles and benefits from side
information about bit reliability a.k.a. soft fingerprinting. In this paper, we investigate the identification-rate vs
privacy-leak trade-off. The analysis is performed for the case of a perfect match between side information shared
between the encoder and decoder as well as for the case of partial side information.
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