Limits in crystallinity of AlN thin films produced by PE-ALD at low temperature

Abstract

Due to their physical properties, Group-III Nitrides have attracted much attention in the microelectronics industry as these materials are highly useful for the design of transducers, resonators as well as 5G and future 6G applications. In this work, we investigate the crystallographic orientation of AlN thin films deposited on Si < 111> wafers by plasma enhanced atomic layer deposition (PE-ALD) at temperatures ranging from 300 °C down to 130 °C. Our work shows a change in c-axis preferred crystalline orientation between 150 °C and 130 °C. Pole figure measurements reveal an out of plane <0001> preferred texture for AlN thin films produced by PE-ALD using deposition temperatures as low as 180 °C. From HRTEM observations, it was determined that the <0001> oriented columnar grains had an angular spread ranging from 24° to 38° when observed over a large area of 35 × 35 nm², even though no spread was observed when considering a 5 × 5 nm² region. High Resolution Transmission electron microscopy (HRTEM) EDX measurements as well as XPS profiles show a thin oxide layer at the AlN/Si<111> interface. The latter seems to be detrimental to the growth of an AlN epitaxial layer on Si<111>.