The thickness of the chalcogenide ovonic threshold switching (OTS) layer is one of the most critical parameters for the switch-only memory (SOM) process control. Traditionally, the OTS thickness and composition were measured by XRF using the amounts of Ge, As, and Se. Still, XRF has a few limitations in delivering the required performance, especially for products with multilayer memory architecture. For these products, x-ray fluorescence (XRF) signals overlap and cannot be used to measure the thickness of each layer. In the current paper, we have studied three new alternative approaches for measurements of the OTS thickness on-cell: Spectral Interferometry, Raman spectroscopy, and Hybrid Machine Learning technique. The first method, Spectral interferometry with the Vertical Traveling Scatterometry approach (VTS), allowed OCD modeling of the top of the structure by blocking the complex underlayers and measuring only the top OTS thickness on all targets, including within the chip. The second method, Raman spectroscopy, demonstrated oncell dimensional capabilities with an excellent correlation of the Ge-Se, As-Se, and Ge-Ge bonds of Raman active chalcogenide to TEM OTS thickness values. Finally, the third method used Raman parameters calibrated with TEM as a reference thickness for the ML solution using the VTS spectra on-cell. This ML method is fast, model-free, and requires minimal TEM samples for setup. All three methods have demonstrated capability for on-cell measurements and HVM process control.
Devices based on 2D material channels require high-quality monolayer material. However, although the value of many laboratory metrology techniques has been demonstrated on small coupons, the development of inline characterization of 2D material layers grown on full 300mm wafers is still missing. In this work, we evaluate and combine different inline metrologies to characterize at wafer level the thickness and the morphology of tungsten disulfide (WS2) layers grown on full 300mm wafers. Combining the results from the different techniques allows us to reveal the morphology and the thickness of the WS2 layers as well as their uniformity across the 300 mm wafers for different growth conditions.
In-line Raman spectroscopy for compositional and strain metrology throughout front-end-of-line (FEOL) manufacturing of next-generation gate-all-around nanosheet field-effect transistors is presented. Thin and alternating layers of fully strained pseudomorphic Si(1 − x)Gex and Si were grown epitaxially on a Si substrate and subsequently patterned. Intentional strain variations were introduced by changing the Ge content (x = 0.25, 0.35, 0.50). Polarization-dependent in-line Raman spectroscopy was employed to characterize and quantify the strain evolution of Si and Si(1 − x)Gex nanosheets throughout FEOL processing by focusing on the analysis of Si-Si and Si-Ge optical phonon modes. To evaluate the accuracy of the Raman metrology results, strain reference data were acquired by non-destructive high-resolution x-ray diffraction and from destructive lattice deformation maps using precession electron diffraction. It was found that the germanium-alloy composition as well as Si and Si(1 − x)Gex strain obtained by Raman spectroscopy are in very good agreement with reference metrology and follow trends of previously published simulations.
In-line Raman spectroscopy for compositional and strain metrology throughout front-end-of-line manufacturing of next generation stacked gate-all-around nanosheet field-effect transistors is presented. Thin and alternating layers of fully strained pseudomorphic Si(1-x)Gex and Si were grown epitaxially on a Si substrate and subsequently patterned. Intentional strain variations were introduced by changing the Ge content (x = 0.25, 0,35, 0.50). Polarization-dependent in-line Raman spectroscopy was employed to characterize and quantify the strain evolution of Si and Si(1-x)Gex nanosheets throughout front-end-of-line processing by focusing on the analysis of Si-Si and Si-Ge optical phonon modes. To evaluate the accuracy of the Raman metrology results, strain reference data were acquired by non-destructive high-resolution x-ray diffraction and from destructive lattice deformation maps using precession electron diffraction. It was found that the germanium-alloy composition as well as Si and Si(1-x)Gex strain obtained by Raman spectroscopy are in excellent agreement with reference metrology and follow trends of previously published simulations.
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