Role of Ge and Si substrates in higher-k tetragonal phase formation and interfacial properties in cyclical atomic layer deposition-anneal Hf1−xZrxO2/Al2O3 thin film stacks

Abstract

Using a five-step atomic layer deposition (ALD)-anneal (DADA) process, with 20 ALD cycles of metalorganic precursors followed by 40 s of rapid thermal annealing at 1073 K, we have developed highly crystalline Hf1−xZrxO2 (0 ≤ x ≤ 1) thin films (<7 nm) on ∼1 nm ALD Al2O3 passivated Ge and Si substrates for applications in higher-k dielectric metal oxide semiconductor field effect transistors below 10 nm technology node. By applying synchrotron grazing incidence x-ray d-spacing maps, x-ray photoelectron spectroscopy (XPS), and angle-resolved XPS, we have identified a monoclinic to tetragonal phase transition with increasing ZrO2 content, elucidated the role of the Ge vs Si substrates in complete tetragonal phase formation (CTPF), and determined the interfacial characteristics of these technologically relevant films. The ZrO2 concentration required for CTPF is lower on Ge than on Si substrates (x ∼ 0.5 vs. x ∼ 0.86), which we attribute as arising from the growth of an ultra-thin layer of metal germanates between the Hf1−xZrxO2 and Al2O3/Ge, possibly during the first deposition and annealing cycle. Due to Ge-induced tetragonal phase stabilization, the interfacial metal germanates could act as a template for the subsequent preferential growth of the tetragonal Hf1−xZrxO2 phase following bottom-up crystallization during the DADA ALD process. We surmise that the interfacial metal germanate layer also function as a diffusion barrier limiting excessive Ge uptake into the dielectric film. An ALD Al2O3 passivation layer of thickness ≥1.5 nm is required to minimize Ge diffusion for developing highly conformal and textured HfO2 based higher-k dielectrics on Ge substrates using the DADA ALD process.