Characteristics of Cobalt Thin Films Deposited by Very High Frequency Plasma Enhanced Atomic Layer Deposition (60 and 100 MHz) Using Cobaltocene (Co(Cp)₂)/NH₃.

In this study, cobalt films were deposited by plasma enhanced atomic layer deposition (PEALD) with cobaltocene (Co(Cp)₂) using two different very high frequency (VHF) NH₃ plasmas (60 MHz, 100 MHz), and the effect of different frequencies of VHF on the characteristics of NH₃ plasmas and the properties of cobalt films were investigated. It is found that the higher frequency showed the higher plasma density at the same input power and, the NH radicals, which are required to remove the ligands of the cobalt precursor during the plasma exposure step in the ALD cycle, were higher at 100 MHz than those at 60 MHz. The RMS surface roughness and carbon impurity percentage of the deposited cobalt films were lower at the higher frequency possibly indicating denser films due to more active surface reactions at the higher frequency. As a result, it is expected that the cobalt thin films deposited by the higher VHF PEALD will improve the characteristics of deposited thin films.