Abstract
The ever-increasing complexity of semiconductor devices requires innovative three-dimensional materials characterization techniques for confined volumes. Multiple atomic force microscopy (AFM)-based methodologies, using a slice-and-measure approach have been proposed to meet this demand. They consist of scanning AFM probes that erode locally the sample’s material at a relatively high load while sensing with the secondary AFM channel, thus accessing in-depth information compared to the standard surface-limited analysis. Nonetheless, the rapid tip apex wear caused by the high forces involved, and the debris accumulation at the tip apex and inside/around the scan area, have been identified as major limitations to the accuracy and repeatability of the existing tomographic AFM sensing methods. Here we explore the use of oil as a suitable medium to overcome some of the issues such as the scan debris accumulation and the removal variability when working in air. We show how the use of oil preserves the tomographic operation while improving the efficiency in material removal for large depth sensing at a reduced debris accumulation. This is reported by comparing the results between air and oil environments, where the removal rate, depth accuracy, and tip-contamination are benchmarked. Finally, we provide the first demonstration of electrical AFM sensing using scanning spreading resistance microscopy (SSRM) in oil.
Highlights
With over 30 years of development, scanning probe microscopy (SPM) has become an important workhorse for the characterization of devices and materials in the semiconductor industry (Orji et al, 2018)
The oil remaining on the tip apex is enough to guarantee the presence of oil at the tip-sample junction while minimizing possible interference of the oil with the atomic force microscopy (AFM) laser reflection from the cantilever that can be induced by the presence of a large droplet (e.g., Figure 1A, oil pick-up step)
In the attempt to compare the impact of the scanning environment on the formation and accumulation of debris, we selected tip-sample load forces that induce a similar material removal rate from the surface as visible by the AFM images and section profiles (Figures 1B–E)
Summary
With over 30 years of development, scanning probe microscopy (SPM) has become an important workhorse for the characterization of devices and materials in the semiconductor industry (Orji et al, 2018). The pervasive introduction of three-dimensional (3D) semiconductor architectures has motivated the SPM community to explore tomographic sensing schemes for the analysis of confined volumes. These include the alternation of SPM with ion beam milling, micro blades, and wet chemical etching in combination with atomic force microscopy (AFM) sensing (Mochalov et al, 2017; Magerle, 2000; Spampinato et al, 2020). The inherent 2D nature of the SPM sensing mechanism, based on Towards 3D-SPM Tomography in Oil. GRAPHICAL ABSTRACT | SEM images of the tips and AFM images of the craters obtained after scanning in air (left) and in oil (right). The debris are efficiently removed from the tip and the crater edges in the oil environment
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