Jeffrey W. Elam

Indium Oxide ALD Using Cyclopentadienyl Indium and Mixtures of H2O and O2

This study describes how In2O3 films can be prepared by ALD using alternating exposures to cyclopentadienyl indium (InCp) and combinations of H2O and O2, even though H2O and O2 are ineffective when used individually. When H2O and O2 are used together, either as a simultaneous exposure or in the sequence H2O-O2 or O2-H2O, very uniform, highly conducting In2O3 films are deposited at 1.0-1.6 Aa/cycle over large areas (12x18) at temperatures as low as 100°C. In agreement with our published mechanism, in-situ Fourier transform infrared measurements revealed that the H2O and O2 work synergistically to facilitate the In2O3 ALD. Ex-situ measurements on films prepared over the deposition temperature range 100-250°C identified a remarkable correlation between the film structure and electrical properties around an amorphous-to-crystalline phase transition near 140°C.

Growth Rate Control in ALD by Surface Functionalization: Alkyl Alcohols on Metal Oxides

In this work we explore the effect that alkyl alcohols (ROH) have on the saturation growth rate during the ALD of metal oxides. The traditional dosing sequence for metal oxide ALD is: M/O/M/O... where M is the metal precursor and O is the oxygen source. We find that by dosing organic molecules prior to dosing the metal precursor (e.g. ROH/M/O...) we can modify the surface chemistry and control the saturation growth rate. We will present results describing the effect of alkyl alcohols (R=Me, Et, iPr, and Bu) using H2O as the oxygen source and the metal precursors Ti(iPr)4 for TiO2 ALD, TMA for Al2O3 ALD, and DEZ for ZnO ALD. Furthermore, we demonstrate this effect in the ALD of doped metal oxides.

ALD-microchannel plates for cryogenic applications (Conference Presentation)

Atomic layer deposition (ALD) has enabled the development of a new technology for fabricating microchannel plates (MCPs) with improved performance that offer transformative benefits to a wide variety of applications. Incom uses a “hollow-core” process for fabricating glass capillary array (GCA) plates consisting of millions of micrometer-sized glass microchannels fused together in a regular pattern. The resistive and secondary electron emissive (SEE) functions necessary for electron amplification are applied to the GCA microchannels by ALD, which – in contrast to conventional MCP manufacturing– enables independent tuning of both resistance and SEE to maximize and customize MCP performance. nIncom is currently developing MCPs that operate at cryogenic temperatures and across wide temperature ranges. The resistive layers in both, conventional and ALD-MCPs, exhibit semiconductor-like behavior and therefore a negative thermal coefficient of resistance (TCR): when the MCP is cooled, the resistance increases, and when heated, the resistance drops. Consequently, the resistance of each MCP must be tailored for the intended operating temperature. This sensitivity to temperature changes presents a challenge for many terrestrial and space based applications. nThe resistivity of the ALD-nanocomposite material can be tuned over a wide range. The material’s (thermo-) electrical properties depend on film thickness, composition, nanostructure, and the chemical nature of the dielectric and metal components. We show how the structure-property relationships developed in this work can be used to design MCPs that operate reliably at cryogenic temperatures. We also present data on how the resistive material’s TCR characteristics can be improved to enable MCPs operating across wider temperature ranges than currently possible.

ALD Process for Dopant-Rich Films on Si

A process and experimental doping profiles for thermal Atomic Layer Deposition of boron using an AlxOy host oxide are described. Simulations for the thermal ALD of elemental phosphorus and its use are discussed for an efficient oxide doping processes. The use of recoil knock-in is illustrated by simulation. A brief summary of conformal doping approaches is included.

In Situ FTIR Characterization of Growth Inhibition in Atomic Layer Deposition Using Reversible Surface Functionalization

The layer-by-layer nature of ALD allows precise control of surface composition in the growth direction normal to the surface. However, since the density of atoms incorporated in each cycle is determined by the saturation coverage, it is harder to control the amount of material incorporated during a single ALD cycle (i.e. the lateral composition). Recently, we demonstrated an approach based on incorporating an in-situ surface functionalization step into each ALD cycle.[1] This step essentially controls the amount of reactive sites on the surface, ideally modulating the saturation coverage while maintaining the self-limiting surface chemistry. By applying this process to Al-doped ZnO ALD, we were able to increase the doping efficiency (carrier concentration per Al atom) with respect to the conventional ALD process by achieving a better spacing of the dopant.