Query: diffaraction-based overlay metrology

Candidate papers:

abstract: In semiconductor device manufacturing, optical overlay metrology measures pattern placement between two layers in a chip with sub nm precision. Continuous improvements in overlay metrology are needed to keep up with shrinking device dimensions in modern chips. We present first overlay metrology results using a novel off axis dark field digital holographic microscopy concept that acquires multiple holograms in parallel by angular multiplexing. We show that this concept reduces the impact of source intensity fluctuations on the noise in the measured overlay. With our setup we achieved an overlay reproducibility of 0.13 nm and measurements on overlay targets with known programmed overlay values showed good linearity of R2= 0.9993. Our data show potential for significant improvement and that digital holographic microscopy is a promising technique for future overlay metrology tools.
author_names: Christos Messinis

Theodorus Thomas Marinus van Schaijk

Nitesh Pandey

Vasco T Tenner

Stefan Witte

Johannes F de Boer

Arie J den Boef
title: Diffraction based overlay metrology using angular multiplexed acquisition of dark field digital holograms.
venue: Optics express
year: 2020

abstract: 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 mDBO 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.
author_names: Simon Gijsbert Josephus Mathijssen

Herman Heijmerikx

Farzad Farhadzadeh

M J Noot

Lineke van der Sneppen

Longfei Shen

Fei Jia

Jolly Xu

Huajun Qin

Arie J den Boef

Elliott Mc Namara

Kaustuve Bhattacharyya

Chao Fang

Yaobin Feng
title: Enhancing the applications space of diffraction based overlay metrology by increasing throughput and target pitch flexibility
venue: Advanced Lithography
year: 2020

abstract: Overlay target design is an important issue in overlay metrology, whose aim is to probe the optimal overlay target to achieve good performance on measurement precision and accuracy even in the presence of process variation. In this paper, the target design problem is first formulated as a multiobjective optimization problem and then solved by the multiobjective genetic algorithm. The feasibility of the proposed method is verified based on simulations carried out on two overlay targets. The results reveal that measurements with high precision, accuracy, and process robustness could be achieved on the targets designed by the proposed method.
author_names: Yating Shi

Kuangyi Li

Xiuguo Chen

Peng Wang

Honggang Gu

Hao Jiang

Chuanwei Zhang

Shiyuan Liu
title: Multiobjective optimization for target design in diffraction based overlay metrology.
venue: Applied optics
year: 2020

abstract: In semiconductor device manufacturing, optical overlay metrology measures pattern placement between two layers in a chip with sub nm precision. Continuous improvements in overlay metrology are needed to keep up with shrinking device dimensions in modern chips. We present first overlay metrology results using a novel off axis dark field digital holographic microscopy concept that acquires multiple holograms in parallel by angular multiplexing. We show that this concept reduces the impact of source intensity fluctuations on the noise in the measured overlay. With our setup we achieved an overlay reproducibility of 0.13 nm and measurements on overlay targets with known programmed overlay values showed good linearity of R2= 0.9993. Our data show potential for significant improvement and that digital holographic microscopy is a promising technique for future overlay metrology tools. (c) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
author_names: M T

T T

R W Og Den
title: Diffraction based overlay metrology using angular multiplexed acquisition of dark field digital holograms
year: 2020

abstract: Scatterometry is an optical metrology technique, in which light scattered from a specifically designed grating stack (overlay target) is measured in the far field. Using 1D periodic overlay target designs the technique has been shown to have nanometer scale sensitivity to spatial misalignments of subsequent patterned layers, which are also known as overlay errors. However, while scatterometry is highly sensitive to overlay errors, multiple sources of systematic errors hinder its absolute accuracy. Here, we investigate how an extended version of scatterometry called Fourier scatterometry in combination with more complex overlay target designs can help addressing those challenges. To this end, we developed a statistical method, which can determine the influence of 2D overlay targets on the overlay measurement uncertainty. We study periodic and deterministic aperiodic designs as well as designs that emerged from simulated annealing optimizations. Our results suggest that current overlay target designs could be augmented by more complex 2D designs to fulfill specific purposes, such as fabrication robustness and high sensitivity over a large overlay range.
author_names: Ruslan Rohrich

Giorgio Oliveri

Stefanos Kovaios

Vasco T Tenner

Arie J den Boef

Johannes T B Overvelde

A Femius Koenderink
title: Uncertainty Estimation and Design Optimization of 2D Diffraction Based Overlay Metrology Targets
year: 2020

abstract: The current state of the art ADI overlay metrology relies on multi wavelength uDBO techniques. Combining the wavelengths results in better robustness against process effects like process induced grating asymmetries. Overlay information is extracted in the image plane by determining the intensity asymmetry in the 1st order diffraction signals of two grating pairs with an intentional shift (bias) In this paper we discuss a next evolution in DBO targets where a target is created with multiple biases. These so called cDBO (continuous bias DBO) targets have a slightly different pitch between top and bottom grating, which has the effect of having a different bias values along the grating length and are complimentary to the uDBO technology. Where for the uDBO target, the diffraction results in a uniform Intensity pattern that carries the Overlay signal, for cDBO, an oscillating intensity pattern occurs, and the Overlay information is now captured in the phase of that pattern. Phase based Overlay has an improved, intrinsic robustness over intensity based overlay and can reduce the need for multi wavelength techniques in several cases. Results on memory technology wafers confirm that the swing curve (through wavelength) behavior is indeed more stable for phase based DBO target and that for accurate Overlay, this target can be qualified with a single wavelength recipe (compared to the uDBO dual wavelength recipe) In this paper, both initial results on a Micron feasibility wafer will be shown as well as demonstrated capability in a production environment.
author_names: Masazumi Matsunobu

Toshiharu Nishiyama

Michio Inoue

Richard T Housley

Cornel Bozdog

Justin Frederick L Lim

Brian Watson

Jason Reece

Steve McCandless

Olger Victor Zwier

Maurits van der Schaar

Murat Bozkurt

Masudur al Arif

Elliott McNamara

Pieter Kapel

Alan Khan

S Strom

Paul Jonathan Turner

P A Olson

Ewoud van West
title: Novel diffraction based overlay metrology utilizing phase based overlay for improved robustness
venue: Advanced Lithography
year: 2021

abstract: As 3D NAND devices increase memory density by adding layers, scaling and increasing bits per cell, new overlay (OVL) metrology challenges arise. On product overlay (OPO) may decrease for critical thick layers such as thick deck to deck alignment, whereas high aspect ratio (Z axis) structures introduce stress, tilt and deformation that require accurate and robust OVL measurements. Advanced imaging metrology (AIM(r) targets, that consist of two side byside periodic gratings in the previous and current layers, are typically used to measure OVL with Imaging Based Overlay (IBO) metrology systems. In this paper, we present a new approach that utilizes the Talbot effect in AIM to produce multiple contrast planes along the Z axis, which enables a common focus position for both layers at a similar focus plane, resulting in improved measurement robustness. We will present Talbot effect theory, target design steps by metrology target design (MTD) simulator, actual measurement results on an advanced 3D NAND device and conclusions for such targets.
author_names: Brian Watson

Shlomit Katz

Richard T Housley

Kar Wui Thong

Nikhil Aditya Kumar Roy

Yoav Grauer

Diana Shapirov

Raviv Yohanan

Greg Gray

Yonglei Li

Daniel Chalom
title: Robustness improvement in imaging based overlay metrology for high topography layers by Talbot targets
venue: Advanced Lithography
year: 2021

abstract: On product overlay (OPO) challenges continue to be yield limiters for most advanced technology nodes, requiring new and innovative metrology solutions. In this paper we will cover an approach to boost accuracy and robustness to process variation in imaging based overlay (IBO) metrology by leveraging optimized measurement conditions per alignment layer. Results apply to both DUV and EUV lithography for advanced Logic, DRAM, 3D NAND and emerging memory devices. Such an approach fuses multi signal information including Color Per Layer (CPL) and focus per layer. This approach with supporting algorithms strives to identify and address sources of measurement inaccuracy to enable tight OPO, improve accuracy stability and reduce overlay (OVL) residual error within the wafer and across lots. In this paper, we will present a theoretical overview, supporting simulations and measured data for multiple technology segments. Lastly, a discussion about next steps and future development will take place.
author_names: Shlomit Katz

Yoav Grauer

Raviv Yohanan

Xiaolei Liu

Daria Negri

Anna Golotsvan
title: Accuracy enhancement in imaging based overlay metrology by optimizing measurement conditions per layer
venue: Advanced Lithography
year: 2021

abstract: Digital holographic microscopy allows access to the complex electric field, enabling computational propagation of light. This enables computational corrections for lens aberrations, which remove the requirement for antireflective coatings on the lens and enable imaging over a wide spectral range. This makes digital holographic microscopy an interesting candidate for overlay metrology on semiconductor wafers. We show that a single holographic image contains all data that is required for computing the overlay, by using a source with a limited coherence length and incoherently adding multiple measurements on a camera. As an additional benefit we show that such parallel acquisition improves the reproducibility of the experiment by eliminating noise sources that are common to the two measurements that typically constitute a single overlay measurement.
author_names: Theodorus Thomas Marinus van Schaijk

Christos Messinis

Nitesh Pandey

Vasco T Tenner

Armand Koolen

S Witte

Johannes F de Boer

Arie J den Boef
title: Fast and robust diffraction based overlay metrology using dark field digital holographic microscopy
venue: Optical Metrology
year: 2021

abstract: Optical overlay metrology has been adopted for years as baseline for overlay control in semiconductor manufacturing. More stringent overlay budget for securing good product yield has been required as device dimension shrinkage. For effective and tight overlay control, the traditional optical overlay metrology has faced two primary challenges of increasing the measurement accuracy and minimizing the measurement variance between overlay mark in scribe lane and in die device pattern. Overlay mark asymmetry is one of the general factors to induce optical overlay metrology error. While 3D NAND deep etch processes would induce within wafer mark asymmetry which worsens measurement robustness of optical overlay metrology. Accurately determining on product overlay (OPO) errors at both after develop inspection (ADI) and after etch inspection (AEI) is also desirable in 3D NAND process for applying non zero offset (NZO) at photo exposure. To address the measurement robustness of optical overlay metrology in 3D NAND process, also for accurately bridging the scribe lane based optical overlay metrology to OPO metrology, a complementary overlay metrology by high voltage scanning electron microscope (HV SEM) was adopted as the reference metrology for optimizing the optical measurement condition on scribe lane targets. In this paper, the measurement accuracy of imaging based overlay (IBO) target under various optical conditions was calibrated by HV SEM. HV SEM can measure both the scribe lane and in device targets via capturing buried structures, and it was employed to bridge the measurement results from IBO and in device target. Then the optimal optical metrology can be decided for both ADI and AEI to facilitate effective advance process control (APC) and NZO purpose.
author_names: Yu-Lin Liu

Li-Ting Chang

Chi-Hao Huang

Mars Yang

Elvis Yang

T H Yang

K C Chen
title: Imaging based overlay metrology optimized by HV SEM in 3D NAND process
venue: Advanced Lithography
year: 2021