Growth Strategies for Crystalline Oxides on Silicon by ALD

Featuring Brian G. Willis, Ph.D.
Assistant Professor, Chemical Engineering
University of Delaware

Location:  Donald Bren Hall (DBH) Room 1500

Abstract:
The growth of the semiconductor industry over the past 40 years has been enabled by a combination of device miniaturization and the implementation of new materials.  As the industry races toward the impending limits of device miniaturization, new materials will be critical to extend innovation in semiconductor technology.  One promising avenue is to integrate complex oxides with silicon devices through the heteroepitaxy of crystalline oxides on semiconductors.  The integration of crystalline oxides with semiconductors may enable new device structures that harness the useful functional properties of oxide materials.  These useful properties include ferroelectricity, piezoelectricity, and many others.  In addition, the crystalline oxides are of interest for applications as high-k dielectrics for transistor or memory devices.        

The integration of oxides with semiconductors is a challenging materials engineering problem due to the differences in crystal structure and chemical bonding between the covalent bonded semiconductor and the ionic bonded oxide layer.  Presently, the successful heteroepitaxy of crystalline oxides on semiconductors has only been achieved using molecular beam epitaxy (MBE).  While MBE methods have advantages in terms of the precise control of the growth process, their disadvantages include high capital and operating costs, and growth rates are considerably lower than standard manufacturing practice.  A more cost effective method to grow epitaxial oxides would be a significant advance for the practical implementation of these useful materials. 

This talk will present research strategies for the use of metal-organic compounds to grow crystalline oxides using chemical vapor deposition or atomic layer deposition.  The critical objectives are to control the composition and structure of an interface layer that is less than one nanometer thick.  Using surface chemistry methods including ultra-high vacuum scanning tunneling microscopy along with Hafnium and Strontium compounds as model systems, we present several strategies for a chemical approach to oxide heteroepitaxy.  It will be shown that direct reaction of the common β-diketonate precursors with the semiconductor surface is unlikely to be a successful strategy due to adverse surface reactions of the organic components associated with these compounds.  A second approach is to use a water-templated Si(100)-2x1 surface to form an atomically abrupt semiconductor/metal-oxide interface.  It is shown that abrupt interfaces can be achieved, but forming an ordered two dimensional surface requires a more detailed understanding of the adsorption kinetics of H2O(g).  Lastly, it is shown that the most promising approach is to use alkaline earth metal-oxide layers grown by ALD with a catalytic oxide desorption step.  It will be demonstrated that the results are comparable to MBE data and that the ALD approach is promising as an alternative method for the growth of crystalline oxides.

About the Speaker:
Willis is an assistant professor of chemical engineering at the University of Delaware.  He received his B.S. degree from Northwestern University and his Ph.D. from the Massachusetts Institute of Technology, both in chemical engineering.  Prior to joining the University of Delaware, he was a member of technical staff at Bell Laboratories, Lucent Technologies where he worked on issues related to copper metallization.  Willis’ research is focused on surface chemistry aspects of technologically important materials including electronic materials, sensors, and energy.  His current work includes a focus on scanning tunneling microscopy (STM) and tunneling spectroscopy to investigate surface reaction processes.  His research is partially supported by a National Science Foundation Faculty Early Career Development (CAREER) Award.