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Rigorous coupled wave analysis (RCWA) is conducted on in situ spectroscopic ellipsometry data to understand profile evolution during film deposition inside nanotrenches. Lithographically patterned SiO2 nanotrenches are used as test structures. The nanotrenches are 170 nm wide at the top with a taper angle of 4.5° and are 300 nm in depth. Atomic layer deposition of ZnO is used as a model process where the thickness (cycles) of the film is varied from 0 (0 cycles) to 46 nm (300 cycles). The analysis predicts transient behavior in deposition affecting film conformality and changes to the trench taper angle. In the process, the aspect ratio varies from 2.05 at the start of the process to 6.67 at the end. The model predicts changes in the refractive index of the ZnO film as a function of thickness. The real and imaginary parts of the refractive index at a wavelength of 350 nm change from 1.81 to 2.37 and 0.25 to 0.87, respectively. Scanning electron microscopy cross sections confirm thickness at the top and bottom of the trench to within 13% of those predicted by RCWA. The experimentally measured conformality degrades as film deposition proceeds from 97.3% at 100 cycles to 91.1% at 300 cycles. These results demonstrate the potential of using RCWA for continuous and in situ monitoring of growth inside 3D nanostructures. [ABSTRACT FROM AUTHOR]

Nondestructive measurement of three-dimensional subsurface features remains one of the most difficult and unmet challenges faced during the fabrication of three-dimensional transistor architectures, especially nanosheet and nanowire based field effect transistors. The most critical fabrication step is the selective etching of silicon-germanium subsurface layers. The resulting shape and dimensions of the remaining Si(1 − x)Gex structure strongly impacts further processing steps and ultimately the electrical performance of gate-all-around transistors, thus creating the need for accurate inline metrology. In order to demonstrate the ability to characterize this etch, nanowire test structures made from Si(1 − x)Gex/Si/Si(1 − x)Gex/Si/Si(1 − x)Gex/Si multilayers have been characterized using Mueller matrix spectroscopic ellipsometry based scatterometry. Transmission electron microscopy images were used to corroborate the authors' scatterometry measurements. Here, they successfully demonstrate the ability to measure the Si(1 − x)Gex etch, providing an industrially viable technique for inline three-dimensional metrology. [ABSTRACT FROM AUTHOR]

The use of optical scattering to measure feature shape and dimensions, scatterometry, is now routine during semiconductor manufacturing. Scatterometry iteratively improves an optical model structure using simulations that are compared to experimental data from an ellipsometer. These simulations are done using the rigorous coupled wave analysis for solving Maxwell’s equations. In this article, we describe the Mueller matrix spectroscopic ellipsometry based scatterometry. Next, the rigorous coupled wave analysis for Maxwell’s equations is presented. Following this, several example measurements are described as they apply to specific process steps in the fabrication of gate-all-around (GAA) transistor structures. First, simulations of measurement sensitivity for the inner spacer etch back step of horizontal GAA transistor processing are described. Next, the simulated metrology sensitivity for sacrificial (dummy) amorphous silicon etch back step of vertical GAA transistor processing is discussed. Finally, we present the application of plasmonically active test structures for improving the sensitivity of the measurement of metal linewidths. [ABSTRACT FROM AUTHOR]