Semiconductor nanowires are important materials for quantum transport experiments and are used in research on qubits. Extended arrays of nanowires can be grown bottom-up by Molecular Beam Epitaxy (MBE). The full process involves several steps. When fabricating nanowires, a common practice is to follow a well-established recipe and only characterize the finalized materials. If the final wires are found to be flawed, the process must be repeated with new parameters. It is therefore desirable to have a characterization method to monitor the process before and after each fabrication step. Conventional characterization techniques such as SEM are time-consuming and, in some cases, damage the samples, e.g. before and after an electron beam lithography process. Scatterometry is fast, accurate, non-destructive and is already used in the semiconductor industry. In this work, it is demonstrated that the imaging scatterometry technique is capable of monitoring the MBE fabrication process of InAs-nanowire arrays during the different process steps. Relevant parameters such as thin film thickness, hole depth, and diameter, etc., are found with nm precision for a macroscopic area in a few minutes. Using this approach, we demonstrate that errors can be caught early in the process and ultimately save resources while assuring a high quality of the final material.
Accurate scatterometry and ellipsometry characterization of non-perfect thin films and nanostructured
surfaces are challenging. Imperfections like surface roughness make the associated modelling and
inverse problem solution difficult due to the lack of knowledge about the imperfection on the surface.
Combining measurement data from several instruments increases the knowledge of non-perfect
surfaces. In this paper we investigate how to incorporate this knowledge of surface imperfection into
inverse methods used in scatterometry and ellipsometry using the Rigorous Coupled Wave Analysis.
Three classes of imperfections are examined. The imperfections are introduced as periodic structures
with a super cell periods ten times larger than the simple grating period. Two classes of imperfections
concern the grating and one class concern the substrate. It is shown that imperfections of a few
nanometers can severely change the reflective response on silicon gratings. Inverse scatterometry
analyses of gratings with imperfection using simulated data with white noise have been performed. The
results show that scatterometry is a robust technology that is able to characterize grating imperfections
provided that the imperfection class is known.
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