Richard M. Silver's research while affiliated with National Institute of Standards and Technology and other places

Publications (111)

Article
Full-text available
The Hubbard model is an essential tool for understanding many-body physics in condensed matter systems. Artificial lattices of dopants in silicon are a promising method for the analog quantum simulation of extended Fermi-Hubbard Hamiltonians in the strong interaction regime. However, complex atom-based device fabrication requirements have meant emu...
Article
The doping of Si using the scanning probe hydrogen depassivation lithography technique has been shown to enable placing and positioning small numbers of P atoms with nanometer accuracy. Several groups have now used this capability to build devices that exhibit desired quantum behavior determined by their atomistic details. What remains elusive, how...
Article
The deep ultraviolet (DUV) scatterfield imaging microscopy technique enables accurate dimensional measurements of periodic nanostructures with sub-nanometer sensitivity to support semiconductor device manufacturing. A parametric sensitivity analysis for targets with uneven duty ratios is essential as the duty ratios of many periodic nanostructures...
Preprint
Full-text available
Doping of Si using the scanning probe hydrogen depassivation lithography technique has been shown to enable placing and positioning small numbers of P atoms with nanometer accuracy. Several groups have now used this capability to build devices that exhibit desired quantum behavior determined by their atomistic details. What remains elusive, however...
Preprint
The Hubbard model is one of the primary models for understanding the essential many-body physics in condensed matter systems such as Mott insulators and cuprate high-Tc superconductors. Recent advances in atomically precise fabrication in silicon using scanning tunneling microscopy (STM) have made possible atom-by-atom fabrication of single and few...
Article
Scientists have long studied the physics of highly disordered conducting systems, seeking to understand the multitude of quantum phenomena that govern how electrons move through material systems. Recently, research into silicon-based quantum computing has made disordered conducting systems, such as Si:P monolayers embedded in isotopically pure Si,...
Article
Full-text available
Atomically precise donor-based quantum devices are a promising candidate for solid-state quantum computing and analog quantum simulations. However, critical challenges in atomically precise fabrication have meant systematic, atomic scale control of the tunneling rates and tunnel coupling has not been demonstrated. Here using a room temperature grow...
Article
Full-text available
Atomically precise fabrication has an important role to play in developing atom‐based electronic devices for use in quantum information processing, quantum materials research, and quantum sensing. Atom‐by‐atom fabrication has the potential to enable precise control over tunnel coupling, exchange coupling, on‐site charging energies, and other key pr...
Article
Over the last decade, our group at the National Institute of Standards and Technology (NIST) has explored novel ways to overcome the perceived limitations of applying optical scattering and imaging in the characterization of small silicon features. As a result, we were able to both qualitatively and quantitatively characterize features that are wel...
Article
Form birefringence, where the orientation of periodic structures yields effective refractive-index differences between orthogonal polarizations, is integral to multidimensional optical data storage, is apparent for certain metamaterials, yet is also critical to the inspection of periodic devices in nanoelectronics. A traditional assumption behind f...
Preprint
Full-text available
Atomically precise donor-based quantum devices are a promising candidate for scalable solid-state quantum computing. Atomically precise design and implementation of the tunnel coupling in these devices is essential to realize gate-tunable exchange coupling, and electron spin initialization and readout. Current efforts in atomically precise lithogra...
Article
Scanning tunneling microscopy (STM) enables the fabrication of two-dimensional δ-doped structures in Si with atomistic precision, with applications from tunnel field-effect transistors to qubits. The combination of a very small contact area and the restrictive thermal budget necessary to maintain the integrity of the δ layer make developing a robus...
Article
Hydrogen atoms on a silicon surface, H-Si (100), behave as a resist that can be patterned with perfect atomic precision using a scanning tunneling microscope (STM). When a hydrogen atom is removed in this manner, the underlying silicon presents a chemically active site, commonly referred to as a dangling bond. It has been predicted that individual...
Article
Full-text available
Using photolithographically defined implant wires for electrical connections, we demonstrate measurement of a scanning tunneling microscope (STM) patterned nanoscale electronic device on Si(100). By eliminating onerous alignment and complex lithography techniques, this approach is accessible to researchers in smaller efforts who may not have access...
Article
The key building blocks for the fabrication of devices based on the deterministic placement of dopants in silicon using scanning tunneling microscopy (STM) hydrogen lithography are the formation of well-defined dopant delta-layers and the overgrowth of high quality crystalline Si. To develop these capabilities, it is of critical importance to quant...
Conference Paper
We investigate defect detectability using simulated deep-, vacuum-, and extreme-ultraviolet wavelengths. Improvements to a signal-to-noise ratio defect metric appear achievable down to λ = 47 nm.
Article
Accurate optics-based dimensional measurements of features sized well-below the diffraction limit require a thorough understanding of the illumination within the optical column and of the three-dimensional scattered fields that contain the information required for quantitative metrology. Scatterfield microscopy can pair simulations with angle-resol...
Article
Advanced hydrogen lithography techniques and low-temperature epitaxial overgrowth enable patterning of highly phosphorus-doped silicon (Si:P) monolayers (ML) with atomic precision. This approach to device fabrication has made Si:P monolayer systems a testbed for multiqubit quantum computing architectures and atomically precise 2-D superlattice desi...
Article
Widespread commercialization of proton exchange membrane fuel cells remains curbed by various manufacturing and infrastructure challenges. One such technical barrier identified by the U. S. Department of Energy is the need for high-speed, in-line process control of platinum-based catalyst layers in the membrane electrode assembly of the fuel cell....
Article
Model-based measurement techniques use experimental data and simulations of the underlying physics to extract quantitative estimates of the measurands of a specimen based upon a parametric model of that specimen. The uncertainties of these estimates are based upon not only the uncertainties in the experimental data, but also the sensitivity of that...
Article
The full 3-D scattered field above finite sets of features has been shown to contain a continuum of spatial frequency information and, with novel optical microscopy techniques and electromagnetic modeling, deep-subwavelength geometrical parameters can be determined. Similarly, by using simulations, scattering geometries and experimental conditions...
Article
Single-layer steps at Si(100) surfaces/interfaces present significant challenges to the quantitative characterization of buried dopant devices as well as the accurate imaging and relocation of fabricated quantum structures. We demonstrate the detailed spatially resolved scanning tunneling spectroscopy study across monolayer step edges on Si(100) su...
Article
Low temperature Si epitaxy has become increasingly important due to its critical role in the encapsulation and performance of buried nanoscale dopant devices. We demonstrate epitaxial growth up to nominally 25 nm, at 250 °C, with analysis at successive growth steps using STM and cross section TEM to reveal the nature and quality of the epitaxial gr...
Article
Full-text available
Quantitative optical measurements of deep sub-wavelength, three-dimensional, nanometric structures with sensitivity to sub-nanometer details address an ubiquitous measurement challenge. A Fourier domain normalization approach is used in the Fourier optical imaging code to simulate the full three-dimensional scattered light field of nominally 15 nm...
Article
Full-text available
Hybrid metrology, e.g. the combination of several measurement techniques to determine critical dimensions, is an important approach to meet the needs of semiconductor industry. A proper use of hybrid metrology may not only yield more reliable estimates for the quantitative characterization of 3-D structures but also a more realistic estimation of t...
Conference Paper
An investigation of an optical microscope tool characterization was presented for the quantitative measurements of deep sub-wavelength features using Fourier plane normalization method. The NIST 193 nm scatterfield microscope operating with an ArF Excimer laser, which has a capability of articulating the angular incident beam at the sample plane us...
Article
Full-text available
Reducing the scale of etched nanostructures below the 10 nm range eventually will require an atomic scale understanding of the entire fabrication process being used in order to maintain exquisite control over both feature size and feature density. Here, we demonstrate a method for tracking atomically resolved and controlled structures from initial...
Article
In hybrid metrology two or more measurements of the same measurand are combined to provide a more reliable result that ideally incorporates the individual strengths of each of the measurement methods. While these multiple measurements may come from dissimilar metrology methods such as optical critical dimension microscopy (OCD) and scanning electro...
Article
Full-text available
Patterning imperfections in semiconductor device fabrication may either be noncritical [e.g., line edge roughness (LER)] or critical, such as defects that impact manufacturing yield. As the sizes of the pitches and linewidths decrease in lithography, detection of the optical scattering from killer defects may be obscured by the scattering from othe...
Article
Reducing the scale of etched nanostructures below the 10 nm range eventually will require an atomic scale understanding of the masks being used in order to maintain exquisite control over both feature size and feature density. Here, the authors demonstrate a method for tracking atomically resolved and controlled structures from initial template def...
Conference Paper
A scatterfield microscope for deep sub-wavelength semiconductor metrology using 193 nm light has been designed. In addition to accommodating the fixed numerical aperture and size of its commercial catadioptric objective lens, the illumination optics are formed to implement essential parameters necessary for angular illumination control at the sampl...
Conference Paper
We have previously introduced a new data analysis method that more thoroughly utilizes scattered optical intensity data collected during defect inspection using bright-field microscopy. This volumetric approach allows conversion of focus-resolved 2-D collected images into 3-D volumes of intensity information and also permits the use of multi-dimens...
Article
Full-text available
Optical microscopy is sensitive both to arrays of nanoscale features and to their imperfections. Optimizing scattered electromagnetic field intensities from deep sub-wavelength nanometer scale structures represents an important element of optical metrology. Current, well-established optical methods used to identify defects in semiconductor patterni...
Conference Paper
Recently, a new technique called Fourier normalization has enabled the parametric fitting of optical images with multiple or even a continuum of scattered spatial frequencies. Integral to the performance of this methodology is the characterization of the high magnification imaging microscope used in these experiments. Scatterfield microscopy techni...
Article
There has been much recent work in developing advanced optical metrology methods that use imaging optics for critical dimension measurements and defect detection. Sensitivity to nanometer-scale changes has been observed when measuring critical dimensions of subwavelength 20 nm features or when imaging defects below 15 nm using angle-resolved and fo...
Conference Paper
Experimental imaging at λ=193 nm of sub-resolved defects performed at several focus positions yields a volume of spatial and intensity data. Defects are located in a differential volume, given a reference, with up to 5x increase in sensitivity.
Conference Paper
To measure the new SEMATECH 9 nm node Intentional Defect Array (IDA) and subsequent small, complex defects, a methodology has been used to exploit the rich information content generated when simulating or acquiring several images of sub-wavelength-sized defects through best focus. These images, which are xy planes, collected using polarized illumin...
Article
Scanning probes offer a potential alternative technology pathway in practical atomic scale devices and developing atom-based dimensional standards. However, the process steps, such as atomic scale lithography and subsequent pattern transfer need considerable optimization before the technology can be utilized for manufacturing applications. Nanoscal...
Conference Paper
A new approach that involves parametric fitting of 3-D scattered field with electromagnetic simulation, Fourier domain normalization, and uncertainties analysis is presented to rigorously analyze 3-D through-focus optical images of targets that scatter a continuum of frequency components
Article
There has been much recent work in developing advanced optical metrology applications that use imaging optics for optical critical dimension (OCD) measurements, defect detection, and for potential use with in-die metrology applications. We have previously reported quantitative measurements for sub-50 nm CD dense arrays which scatter only the 0th-or...
Article
Recently, there has been significant research investigating new optical technologies for dimensional metrology of features 22 nm in critical dimension and smaller. When modeling optical measurements, a library of curves is assembled through the simulation of a multidimensional parameter space. A nonlinear regression routine described in this paper...
Article
Full-text available
For high precision applications of optical microscopes, it is critical to achieve symmetrical angular illumination intensity at the sample plane, in addition to uniform spatial irradiance achieved by Köhler illumination. A correlation between the angular illumination asymmetry and the contrast in the image of a line grating target was demonstrated...
Article
Full-text available
We present a novel optical through-focus scanning optical microscopy (TSOM) method that produces nanoscale dimensional measurement sensitivity using a conventional optical microscope. The TSOM method uses optical information from multiple focal planes for dimensional analysis. The TSOM method can be used for nanoscale dimensional and defect analysi...
Article
There has been much recent work in developing advanced optical metrology applications that use imaging optics for critical dimension measurements, defect detection and for potential use with in-die metrology. Sensitivity to nanometer scale changes has been observed when measuring critical dimensions of sub-wavelength features or when imaging defect...
Article
Smaller patterning dimensions and novel architectures are fostering research into improved methods of defect detection in semiconductor device manufacturing. This experimental study, augmented with simulation, evaluates scatterfield microscopy to enhance defect detectability on two separate 22 nm node intentional defect array wafers. Reducing the i...
Article
The semiconductor manufacturing industry is now facing serious challenges in achieving defect detection rates with acceptable throughput and accuracy. With conventional bright‐field and dark‐field inspection methods now at their limits, it has become essential to explore alternative optical methods such as angle‐resolved scatterfield microscopy,...
Article
Micrometer scale features are fabricated on Si (100) surfaces using lithographic techniques and thermally processed in an ultrahigh vacuum (UHV) environment. The process results in the formation of symmetric, step-terrace patterns with wide atomically flat regions exhibiting highly reproducible step-terrace morphology. The patterns spontaneously tr...
Article
Control of atomic morphology at the micrometer scale has been a long term challenge to enable atomically precise manufacturing. In this presentation we describe our method to pattern micrometer scale, ordered features on a Si surface with subsequent etch and high temperature processing. Following high temperature UHV processing, high quality atomic...
Article
Rapidly decreasing critical dimensions (CD) for semiconductor devices drive the study of improved methods for the detection of defects within patterned areas. As reduced CDs are being achieved through directional patterning, additional constraints and opportunities present themselves in defect metrology. This simulation and experimental study asses...
Article
Full-text available
We present an initial review of a novel through-focus scanning optical microscopy (TSOM pronounced as 'tee-som') imaging method that produces nanometer-dimensional measurement sensitivity using a conventional bright-field optical microscope. In the TSOM method a target is scanned through the focus of an optical microscope, acquiring conventional op...
Article
New techniques recently developed at the National Institute of Standards and Technology using bright-field optical tools are applied to signal-based defect analysis of features with dimensions well below the measurement wavelength. A key to this approach is engineering the illumination as a function of angle and analysis of the entire scattered fie...
Article
Resist-on-silicon sub-50-nm critical dimension targets have been investigated using a 193 nm angle-resolved scatterfield microscope (ARSM). The illumination path of this microscope allows customization of the conjugate back focal plane (CBFP) while separate collection paths permit both high-magnification and Fourier-plane imaging. Aspects of the ca...
Article
An angle-resolved scatterfield microscope (ARSM) featuring 193 nm excimer laser light was developed for measuring critical dimension (CD) and overlay of nanoscale targets as used in semiconductor metrology. The microscope is designed to have a wide and telecentric conjugate back focal plane (CBFP) and a scan module for resolving Köhler illumination...
Article
We have developed a set of techniques, referred to as scatterfield microscopy, in which the illumination is engineered at a sufficiently large Conjugate Back Focal Plane (CBFP) of the microscope. A primary advance of our new scatterfield microscope is the use of 193 nm excimer laser light. Sophisticated configurations have been implemented to allow...
Article
Full-text available
In this paper we present overlay measurement techniques that use small overlay targets for advanced semiconductor applications. We employ two different optical methods to measure overlay using modified conventional optical microscope platforms. They are scatterfield and through-focus scanning optical microscope (TSOM) imaging methods. In the TSOM m...
Article
A scatterfield microscope using 193 nm laser light was developed that utilizes angle-resolved illumination for high resolution optical metrology. An angle scan module was implemented that scans the illumination beam in angle space at the sample by linearly scanning a fiber aperture at a conjugate back focal plane. The illumination light is delivere...
Article
Full-text available
This article describes how an uncertainty analysis may be performed on a scatterometry measurement. A method is outlined for propagating uncertainties through a least-squares regression. The method includes the propagation of the measurement noise as well as estimates of systematic effects in the measurement. Since there may be correlations between...
Article
Full-text available
We present a novel optical technique that produces nanometer dimensional measurement sensitivity using a conventional bright-field optical microscope, by analyzing through-focus scanning-optical-microscope images obtained at different focus positions. In principle, this technique can be used to identify which dimension is changing between two nanos...
Article
Full-text available
We present a new optical technique for dimensional analysis of sub 100 nm sized targets by analyzing through-focus images obtained using a conventional bright-field optical microscope. We present a method to create through-focus image maps (TFIM) using optical images, which we believe unique for a given target. Based on this we present a library ma...
Article
Full-text available
We present a detailed experimental study of a new through-focus technique to measure critical dimension linewidth with nanometer sensitivity using a bright field optical microscope. This method relies on analyzing intensity gradients in optical images at different focus positions, here defined as the focus metric (FM) signature. The contrast of an...
Article
Full-text available
We demonstrate optical critical dimension measurement of lines in silicon grating targets using back focal plane scatterfield micros- copy. In this technique, angle-resolved diffraction signatures are ob- tained from grating targets by imaging the back focal plane of a bright- field microscope that has been modified to allow selection of the angula...
Article
Full-text available
We have developed a set of techniques, referred to as scatterfield microscopy, in which the illumination is engineered in combination with appropriately designed metrology targets to extend the limits of image-based optical metrology. Previously we reported results from samples with sub-50-nm-sized features having pitches larger than the convention...
Article
This paper is a comprehensive summary and analysis of a SEMATECH funded project to study the limits of optical critical dimension scatterometry (OCD). The project was focused on two primary elements: 1) the comparison, stability, and validity of industry models and 2) a comprehensive analysis of process stacks to evaluate the ultimate sensitivity a...
Article
Patterns of lines and trenches with nominal linewidths of 50 nm have been proposed for use as an overlay target appropriate for placement inside the patterned wafer die. The National Institute of Standards and Technology (NIST) Scatterfield Targets feature groupings of eight lines and/or trenches which are not resolvable using visible-wavelength br...
Article
Dependence of Köhler factor 2 (KF 2: angular homogeneity) and Köhler factor 3 (KF 3: wavefront homogeneity) on the intensity profile of line target was investigated for an optical system designed for high-resolution optical metrology using ArF excimer laser of a wavelength of 193 nm. The intensity profiles for the isolated and multiple lines of 60...
Article
In this paper, we have extended the kinetic Monte Carlo simulation method to study the etching dynamics of Si (111) surfaces in NH4F on a time-resolved basis. We have examined the step-flow dynamics of Si (111) etching using various simulation window sizes for a variety of miscut angles and miscut orientations as well as other parameters which affe...
Article
Super-resolution in optical microscopy has been pursued historically through different methods, e.g., dark-field, phase contrast, and oblique illumination, etc. For each type of microscopy, the ultimate resolution available is dependent upon the amount of a priori knowledge the observer has about the object. The metrology of photolithographically p...
Article
The semiconductor industry has exploited productivity improvements through aggressive feature size reduction for over four decades. While enormous effort has been expended in developing the optical lithography tools to print ever finer features, significant advances have also been required to measure the printed features. In this article we will di...
Article
Full-text available
In this paper we present recent developments in optical microscope image analysis using both, best focus optical image as well as those images conventionally considered out of focus for metrology applications. Depending on the type of analysis, considerable information can be deduced with the additional use of the out of focus optical images. One m...
Article
Uniform sample illumination via Kohler illumination is achieved by establishing a pair of conjugate focal planes; a light source is focused onto the condenser lens back focal plane while the image of the field aperture is focused at the plane of the specimen. Placement accuracy of these elements along the optical axis will determine the quality of...