# Ultrathin Monatomic Antimony Films by Sacrificial Atomic Layer Deposition for Phase Change Memory

## TL;DR

A new method deposits ultrathin antimony films with high uniformity and smoothness, enabling faster and more reliable phase change memory devices.

## Contribution

A sacrificial atomic layer deposition technique enables conformal and ultra-smooth antimony films for nanoscale electronics.

## Key findings

- Ultrathin Sb films with <1 nm roughness and wafer-scale uniformity are achieved using s-ALD.
- Phase change memory devices with 5 nm Sb films show ultrafast switching and low variability.
- The s-ALD process enables epitaxial growth of Sb films with aligned crystal structures.

## Abstract

Antimony (Sb) is an intriguing material for advanced electronics, with thickness‐dependent properties at the nanoscale offering new functionalities. However, conventional methods for depositing Sb thin films cannot produce continuous ultrathin films with conformality in complex nanoscale structures. This study introduces a novel sacrificial atomic layer deposition (s‐ALD) approach that overcomes these limitations by using chemical substitution between the antimony precursor and the pre‐deposited Sb2Te3. The structural similarity between Sb2Te3 and Sb enables local epitaxial growth of a uniform, (00l)‐oriented Sb film with exceptional surface smoothness (root‐mean‐squared roughness << 1 nm) at a 4‐nm thickness. Highly pure Sb films with excellent wafer‐scale uniformity and conformality are achieved on high‐aspect‐ratio structures. The mechanism involves substitution reactions driven by the preferential Te‐(CH3)3Si bonding, along with enhanced atomic diffusion through the aligned crystal structure. Phase change memory devices using 5‐nm‐thick s‐ALD Sb films demonstrate ultrafast switching with femtosecond laser pulses (≈220 fs) with high device‐to‐device uniformity (coefficient of variation < 5 %) and ultralow drift coefficients (0.0013 for the on state and 0.0073 for the off state). This s‐ALD technique offers a promising pathway for depositing ultrathin, uniform Sb films, enabling full utilization of Sb's unique nanoscale properties.

A three‐step sacrificial atomic layer deposition (s‐ALD) process enables wafer‐scale growth of ultrathin and uniform antimony (Sb) thin films. An ultrathin (≈4 nm) Sb film is uniformly deposited with its characteristic bilayer structure (Sb‐Sb) aligned along the substrate. The excellent surface coverage of the s‐ALD allows facile electrical conduction even in the few‐nanometer thickness range.