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This report provides a summary of stakeholder responses to the Request for Information (RFI) titled “Incentives, Infrastructure, and Research and Development Needs To Support a Strong Domestic Semiconductor Industry,” issued by the U.S. Department of Commerce, with the assistance of the National Institute of Standards and Technology (NIST).

This paper reports on an investigation to determine whether through-focus scanning optical microscopy (TSOM) is applicable to micrometer-scale through-silicon via (TSV) reveal metrology. TSOM has shown promise as an alternative inspection and dimensional metrology technique for FinFETs and defects. In this paper TSOM measurements were simulated using 546 nm light and applied to copper TSV reveal pillars with height in the 3 μm to 5 μm range and diameter of 5 μm. Simulation results, combined with white light interferometric profilometry, are used in an attempt to correlate TSOM image features to variations in TSV height, diameter, and sidewall angle (SWA). Simulations illustrate the sensitivity of Differential TSOM Images (DTI’s) using the metric of Optical Intensity Range (OIR), for 5 μm diameter and 5 μm height TSV Cu reveal structures, for variation of SWA (Δ = 2°, OIR = 2.35), height (Δ = 20 nm, OIR = 0.28), and diameter (Δ = 40 nm, OIR = 0.57), compared to an OIR noise floor of 0.01. In addition, white light interferometric profilometry reference data is obtained on multiple TSV reveal structures in adjacent die, and averages calculated for each die’s SWA, height, and diameter. TSOM images are obtained on individual TSV’s within each set, with DTI’s obtained by comparing TSV’s from adjacent die. The TSOM DTI’s are compared to average profilometry data from identical die to determine whether there are correlations between DTI and profilometry data. However, with several significant TSV reveal features not accounted for in the simulation model, it is difficult to draw conclusions comparing profilometry measurements to TSOM DTI’s when such features generate strong optical interactions. Thus, even for similar DTI images there are no discernible correlations to SWA, diameter, or height evident in the profilometry data. The use of a more controlled set of test structures may be advantageous in correlating TSOM to optical images.

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 method a target is scanned through the focus of an optical microscope, simultaneously acquiring optical images at different focal positions. The TSOM images are constructed using the through- focus optical images. Overlay analysis is then performed using the TSOM images. In the scatterfield method, a small aperture is scanned at the conjugate back focal plane of an optical microscope. This enables angle-resolved scatte rometry on a high-magnification optical platform. We also present evaluation of optical constants using the scatterfield method. Keywords : Overlay, Scatterfield, Scatterometry, TSOM , In-chip, Through-focus, Optical constants

Many scanning probe microscopes (SPMs), such as the scanning tunneling microscope (STM) and atomic force microscope (AFM), 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 applied to the AFM images to determine and quantify the hysteresis. This method requires both trace and retrace profiles to be recorded. With a window imposed on each of the profiles, cross correlation are calculated between the data inside two windows to find corresponding pixel pairs on two different profiles but the same physical positions along the fast scanning direction. This method is applied to the image distorted by the hysteresis attempting to correct the distortion.

Image stitching is a technique that combines two or more images to form one composite image, which provides a field of view that the originals cannot. It has been widely used in photography, medical imaging, and computer vision and graphics. For such applications, the emphasis is on the appearance of the composite image from a rendering perspective and not on performing measurements using the composite image. The potential use of image stitching in dimensional metrology is a relatively less explored field. In our experiment, a linewidth structure with nearly vertical sidewalls is imaged by an atomic force microscope (AFM) using a multi‐walled carbon nanotube tip. Since the nanotube is mounted at an angle with respect to the surface, the resulting image of such a structure exhibits significant probe‐related distortion on one side but very little on the other. If the sample is rotated by 180°, then both sidewalls can be accurately imaged. The two images can be stitched together to form a composite image in which both sidewalls are minimally distorted. Our paper describes AFM linewidth measurements using a composite image developed by manually stitching two individual images. The results are compared with measurements taken with critical‐dimension AFM (CD‐AFM), which is capable of measuring structures with near‐vertical sidewalls. The challenge is to perform the stitching well enough that the composite image can be used for linewidth metrology. Our preliminary results on two different structures show agreement between image stitching and CD‐AFM.

A key requirement for nanomanufacturing is maintaining acceptable traceability of measurements performed to determine size. Given that properties and functionality at the nanoscale are governed by absolute size, maintaining the traceability of dimensional measurements of nanoscale devices is crucial to the success of nanomanufacturing. There are various strategies for introducing traceability into the nanomanufacturing environment. Some involve first principles, but most entail the use of calibrated artifacts. In an environment where different types of products are manufactured, it is challenging to maintain traceability across different products mix. In this paper, we present some of the work we have done in developing methods to track the traceability of dimensional measurements performed in a wafer fabrication facility. We combine the concepts of reference measurement system, measurement assurance, and metrological timelines to ensure that traceability is maintained through a series of measurements that involve different instruments and product mixes, spanning a four-year period. We show how to use knowledge of process-induced and instrument systematic errors, among others, to ensure that the traceability of the measurements is maintained.

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. This method requires both trace and retrace profiles to be recorded. With a window imposed on each of the profiles, correlations are implemented between the data inside two windows to find corresponding pixel pairs on two different profiles but the same physical positions along the fast scanning axis (x). The x-distances between pixel pairs are calculated and then a simple correction scheme is applied to reduce the distortion.