EXAFS study on yttrium oxide thin films deposited by RF plasma enhanced MOCVD under the influence of varying RF self-bias

Abstract

• Local structure and surface morphology of Y 2 O 3 thin films deposited by RF plasma MOCVD at different RF self-bias level investigated by EXAFS and AFM. • Bond length and oxygen coordination changes with bias. • Films are nanostructured with structural distortion at higher bias. • Surface morphology of films changes with bias. • Changes observed in local structural parameters are correlated with observed properties of films. • EXAFS study on Y 2 O 3 films deposited under different RF self-bias levels is not been reported so far. Extended X-ray absorption fine structure (EXAFS) and atomic force microscopy (AFM) studies are carried out on yttrium oxide (Y 2 O 3 ) thin films deposited by radio frequency plasma assisted metalorganic chemical vapor deposition (MOCVD) process at different RF self-bias (−50 V to −175 V with a step of −25 V) on silicon substrates. A (2,2,6,6-tetramethyl-3,5-heptanedionate) yttrium (commonly known as Y(thd) 3 ) precursor is used in a plasma of argon and oxygen gases at a substrate temperature of 350 °C for deposition. To gain profound understanding about influence of RF self-bias on the properties of the deposited Y 2 O 3 thin films, the films are characterized by EXAFS and AFM measurements. From the EXAFS measurements it is observed that oxygen co-ordination is high for the film deposited at the lowest self bias (−50 V) which is due to presence of higher amount of hydroxyl group in the sample. Oxygen coordination however decrease to lower values for the films deposited at self bias of −75 V. Y O bond length decreases gradually with increase in self bias indicating reduction in hydroxyl content. However there is reduction in bond length for the film deposited at −100 V as compared to other films resulting from structural changes. The disorder factor obtained from EXAFS measurement increases for films deposited at voltages beyond −125 V due to degradation in crystallinity of the films caused by increased bombardment by incident ions. From AFM measurements, it is observed that the surface morphology of the films also change with self bias. The root mean square roughness value and the entropy factor are found to be low for films deposited at lower bias values and increase for films deposited at bias voltages above −100 V.