Traceable localization enables accurate integration of quantum emitters and photonic structures with high yield.

In a popular integration process for quantum information technologies, localization microscopy of quantum emitters guides lithographic placement of photonic structures. However, a complex coupling of microscopy and lithography errors degrades registration accuracy, severely limiting device performance and process yield. We introduce a methodology to solve this widespread but poorly understood problem.

Sub-picoliter Traceability of Microdroplet Gravimetry and Microscopy.

Gravimetry typically lacks the resolution to measure single microdroplets, whereas microscopy is often inaccurate beyond the resolution limit. To address these issues, we advance and integrate these complementary methods, introducing simultaneous measurements of the same microdroplets, comprehensive calibrations that are independently traceable to the International System of Units (SI), and Monte-Carlo evaluations of volumetric uncertainty. We achieve sub-picoliter agreement of measurements of microdroplets in flight with volumes of approximately 70 pL, with ensemble gravimetry and optical microscopy both yielding 95% coverage intervals of ±0.

Wear comparison of critical dimension-atomic force microscopy tips.

Nanoscale wear affects the performance of atomic force microscopy (AFM)-based measurements for all applications including process control measurements and nanoelectronics characterization. As such, methods to prevent or reduce AFM tip wear is an area of active research. However, most prior work has been on conventional AFMs rather than critical dimension AFM (CD-AFM).

Detecting nanoscale contamination in semiconductor fabrication using through-focus scanning optical microscopy.

This paper reports high-throughput, light-based, through-focus scanning optical microscopy (TSOM) for detecting industrially relevant sub-50 nm tall nanoscale contaminants. Measurement parameter optimization to maximize the TSOM signal using optical simulations made it possible to detect the nanoscale contaminants. Atomic force and scanning electron microscopies were used as reference methods for comparison.

Tip on Tip Imaging and Self-Consistent Calibration for Critical Dimension Atomic Force Microscopy: Refinements and Extension to Second Lateral Axis.

One type of atomic force microscopy (AFM) used for critical dimension (CD) metrology is commonly referred to as critical dimension atomic force microscopy (CD-AFM); it uses flared tips and two-dimensional surface sensing to enable scanning of features with near-vertical sidewalls. An important consideration in this type of CD-AFM metrology is the calibration uncertainty of the tip width. Standards for traceable tip width calibration have thus been developed both by national metrology institutes (NMIs) and commercial suppliers.

Spatial dimensions in atomic force microscopy: Instruments, effects, and measurements.

Atomic force microscopes (AFMs) are commonly and broadly regarded as being capable of three-dimensional imaging. However, conventional AFMs suffer from both significant functional constraints and imaging artifacts that render them less than fully three dimensional. To date a widely accepted consensus is still lacking with respect to characterizing the spatial dimensions of various AFM measurements.

Multiple-Instrument Evaluation of the Consistency and Long Term Stability of Tip Width Calibration for Critical Dimension Atomic Force Microscopy.

Since 2004 standards for calibration of critical dimension atomic force microscope (CD-AFM) tip width have been available both commercially and through national metrology institutes (NMIs) - such as the National Institute of Standards and Technology (NIST) in the United States. There have been inter-laboratory and inter-method comparisons performed on such samples, but less attention has been paid to the long-term stability of standards and monitoring for damage, wear, or contamination. Using three different CD-AFM instruments, we have tested the consistency and long-term stability of two independent reference calibrations for CD-AFM tip width.

Comparison of line width calibration using critical dimension atomic force microscopes between PTB and NIST.

International comparisons between National Metrology Institutes (NMIs) are important to verify measurement results and the associated uncertainties. In this paper, we report a comparison of the line width calibration of a crystalline silicon line width standard, referred to as IVPS100-PTB standard, between the Physikalisch-Technische Bundesanstalt (PTB) in Germany and the National Institute of Standards and Technology (NIST) in the United States. Critical Dimension Atomic Force Microscopy (CD-AFM) was the measurement method used for this comparison.

Evaluation of carbon nanotube probes in critical dimension atomic force microscopes.

The decreasing size of semiconductor features and the increasing structural complexity of advanced devices have placed continuously greater demands on manufacturing metrology, arising both from the measurement challenges of smaller feature sizes and the growing requirement to characterize structures in more than just a single critical dimension. For scanning electron microscopy, this has resulted in increasing sophistication of imaging models. For critical dimension atomic force microscopes (CD-AFMs), this has resulted in the need for smaller and more complex tips.

Lateral Tip Control Effects in CD-AFM Metrology: The Large Tip Limit.

Sidewall sensing in critical dimension atomic force microscopes (CD-AFMs) usually involves continuous lateral dithering of the tip or the use of a control algorithm and fast response piezo actuator to position the tip in a manner that resembles touch-triggering of coordinate measuring machine (CMM) probes. All methods of tip position control, however, induce an effective tip width that may deviate from the actual geometrical tip width. Understanding the influence and dependence of the effective tip width on the dither settings and lateral stiffness of the tip can improve the measurement accuracy and uncertainty estimation for CD-AFM measurements.

Deep-subwavelength Nanometric Image Reconstruction using Fourier Domain Optical Normalization.

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 sized structures, accurately replicating the light field as a function of the focus position. Using the full three-dimensional light field, nanometer scale details such as a 2 nm thin conformal oxide and nanometer topography are rigorously fitted for features less than 1/30 of the wavelength in size.

Tip characterization method using multi-feature characterizer for CD-AFM.

In atomic force microscopy (AFM) metrology, the tip is a key source of uncertainty. Images taken with an AFM show a change in feature width and shape that depends on tip geometry. This geometric dilation is more pronounced when measuring features with high aspect ratios, and makes it difficult to obtain absolute dimensions.

A moving window correlation method to reduce the distortion of scanning probe microscope images.

Many scanning probe microscopes such as the scanning tunneling microscope and atomic force microscope use piezoelectric actuators operating in open loop for generating the scans of the surfaces. However, nonlinearities mainly caused by hysteresis and drift of piezoelectric actuators reduce the positioning accuracy and produce distorted images. A moving window correlation method is proposed in this paper to determine and quantify the hysteresis.

Three-dimensional image correction of tilted samples through coordinate transformation.

In scanned probe measurements of micrometer- or nanometer-scale lines, it is nearly impossible to maintain the sample in a perfectly level position, and even a small amount of tilt can contribute to the accuracy of the result of the measure such as linewidth or step height. The current practice in image processing to deal with this problem is to conduct a line-by-line analysis to find the best fit of the substrate profile and subtract this background from all data points, thus describing 3D plane turns as a series of lines and processing them in succession in the x- or y-direction. In this paper a coordinate transformation method is proposed.

Linewidth measurement technique using through-focus optical images.

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 optical image of a structured target, where a particular structure is repeated several times, varies greatly as it is moved through-focus if the spacing between the structures is such that the scattered field from the features interferes.

Computational models of a nano probe tip for static behaviors.

It is difficult to predict the measurement bias arising from the compliance of the atomic force microscope (AFM) probe. The issue becomes particularly important in this situation where nanometer uncertainties are sought for measurements with dimensional probes composed of flexible carbon nanotubes mounted on AFM cantilevers. We have developed a finite element model for simulating the mechanical behavior of AFM cantilevers with carbon nanotubes attached.

RM 8111: Development of a Prototype Linewidth Standard.

Staffs of the Semiconductor Electronics Division, the Information Technology Laboratory, and the Precision Engineering Laboratory at NIST, have developed a new generation of prototype Single-Crystal CD (Critical Dimension) Reference (SCCDRM) Materials with the designation RM 8111. Their intended use is calibrating metrology instruments that are used in semiconductor manufacturing. Each reference material is configured as a 10 mm × 11 mm silicon test-structure chip that is mounted in a 200 mm silicon carrier wafer.