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 properties of basic devices needed for solid state quantum computing and analog quantum simulation. Using hydrogen-based scanning probe lithography, individual dopant atoms are deterministically placed relative to atomically aligned contacts and gates to build single electron transistors, single atom transistors, and gate-controlled quantum sensing devices. The key steps required to fabricate and demonstrate the essential building blocks needed for spin selective initialization/readout, and coherent quantum manipulation are described.
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 is then used to identify an optimum set of parameters that yields the closest experiment-to-theory agreement. However, parametric correlation, measurement noise, and model inaccuracy all lead to measurement uncertainty in the fitting process for optical critical dimension measurements. To improve the optical measurements, other techniques such as atomic force microscopy and scanning electronic microscopy can also be used to provide supplemental a priori information. In this paper, a Bayesian statistical approach is proposed to allow the combination of different measurement techniques that are based on different physical measurements. The effect of this hybrid metrology approach will be shown to reduce the uncertainties of the parameter estimators.
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 the various parameters determined by the measurement, a method is described for visualizing the uncertainty in the extracted profile. The analysis is performed for a 120 nm pitch grating, consisting of photoresist lines 120 nm high, 45 nm critical dimension, and 88 • side wall angle, measured with a spectroscopic rotating compensator ellipsometer. The results suggest that, while scatterometry is very precise, there are a number of sources of systematic errors that limit its absolute accuracy. Addressing those systematic errors may significantly improve scatterometry measurements in the future.
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 conventional Rayleigh resolution criterion, which resulted in images having edge contrast and elements of conventional imaging. In this paper we extend these methods to targets composed of features much denser than the conventional Rayleigh resolution criterion. For these applications, a new approach is presented that uses a combination of zero-order optical response and edge-based imaging. The approach is, however, more general and a more comprehensive set of analyses using theoretical methods is presented. This analysis gives a direct measure of the ultimate size and density of features that can be measured with these optical techniques. We present both experimental results and optical simulations using different electromagnetic scattering packages to evaluate the ultimate sensitivity and extensibility of these techniques.
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