Monitoring the high aspect ratio etch profiles in state-of-the-art three-dimensional NAND memory fabrication processes has pushed metrology technologies to new limits. Here, we discuss how a mid-infrared ellipsometric measurement can yield angstrom level discrimination in critical dimension changes of memory channel hole (CH) profiles across such a memory chip. Using finite-difference time-domain and rigorous coupled-wave analysis simulations, we demonstrate how dispersion mitigated mid-infrared beam penetration into these memory structures permits parameter decorrelation and the measurement of the full CH profile.
A novel mid-infrared critical dimension (IRCD) metrology has been developed on a platform suitable for fab production. Compared to traditional optical critical dimension (OCD) technology based on ultraviolet, visible, and near-IR light, the IRCD system exploits unique optical properties of common semiconductor fab materials in the mid-infrared to enable accurate measurements of high-aspect-ratio etched features. In this paper, we will show two examples of critical dry etch steps in 3D NAND channel formation module of an advanced node that require nondestructive process control: (1) channel hole active area etch and (2) amorphous carbon hardmask etch. In the first example, we take advantage of the absorption bands of silicon dioxide and silicon nitride to get accurate CD measurements at different depths, resulting in high-fidelity z-profile metrology of the channel – key to guiding process development and accelerated learning for 3D NAND device manufacturing. In the second example, the most common amorphous carbon hardmask materials for advanced 3D NAND nodes are opaque in the traditional OCD wavelength range; however, in the mid-infrared, there is light penetration and hence spectral sensitivity to dimensional parameters including sub-surface features. We show successful detection of intentional process skews and as well accurate bottom CD measurements of the hardmask.
Semiconductor quantum dots provide a platform for studying and exploiting individual electron spins as they
interact with a complex solid state environment. Colloidal nanocrystal quantum dots are of particular interest
for potential applications, because they can achieve sufficient confinement to operate at room temperature with
relatively robust electron spin coherence. The strong confinement in these nanostructures leads to significant
effects caused by mixing of valence subbands and variation in particle size and shape. These effects influence
the processes of carrier spin initialization and detection. We have performed ensemble time-resolved Faraday
rotation experiments as well as single-dot photoluminescence excitation measurements to study how the strong
quantum confinement affects the spin physics in these systems. Single dot PLE measurements reveal mechanisms
of transition broadening that are relevant at room temperature, including thermal broadening and spectral
diffusion due to mobile charges in the surrounding environment. We find that the mixing of valence subbands
in the confined hole states largely determines the efficiency of optical spin pumping and Faraday-rotation-based
spin detection. By studying these effects, we take a step towards controlling and exploiting spin coherence in
this flexible room temperature platform.
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