<i>In Situ</i> ALD-TEM System to Study Atomic Nucleation Phenomena - Enabled by Ultrathin Large Aspect Ratio Free-Standing Shell Structures

Abstract

Today, Atomic Layer Deposition (ALD) sets the limits for achieving nanometer precision of thin, yet almost dense films. However, the initial growth process, determining possible film thinness, is poorly understood. A better understanding can be obtained with the help of in-situ characterization during film growth with high spatial and chemical resolution. Transmission Electron microscopy (TEM) would be a suitable and widely available technique to accomplish this objective. However, standard instruments have differing vacuum requirements than those necessary for ALD. During ALD, TEM detectors could be damaged as they are being exposed to corrosive volatile chemical compounds. Here we present a dedicated TEM holder design, where ALD deposition occurs inside a microchip containing a large area cavity surrounded by thin film Al2O3 membranes. These membranes act as windows for TEM characterization while decoupling the ALD process from the TEM environment. The microchip consists of longitudinal large overhang shell structures, themselves made by ALD and etched in an HF vapor etch processes. The set-up, which includes controlled heating, was tailored to ALD requirements, and passed a vacuum-pressure test. Post-mortem inspection of film growth on a silicon sample chip demonstrates the successful formation of an ALD Al2O3 film with 40 nm thickness inside the cavity. These results demonstrate the potential of the system to enable a range of experiments on growth phenomena that may lead to even thinner films and better control of interfaces than previously possible.