INVESTIGATION AND CHARACTERISATION OF MIM STRUCTURES BASED ON MOCVD AND PEALD DEPOSITED Ta_2O_5 FILMS

摘要

Tantalum oxide (Ta_2O_5) is widely used for Metal-Insulator-Metal (MIM) capacitors, because of its high dielectric constant. Two deposition methods have been compared in this study: the conventional MOCVD technique and the PEALD. Ta_2O_5 layers have been characterised using ERDA, XRR and FTIR-ATR. Significant discrepancies between MOCVD and PEALD Ta_2O_5 films have been detected. MOCVD Ta_2O_5 layers contain around 10-12 % of carbon and hydrogen that arise from the incomplete decomposition of the TBTDET precursor. Even a post-treatment does not allow desorbing hydro carbonated species. We demonstrated that a temperature higher or equal to 650℃ is needed to desorb hydro carbonated branches. The porosity of MOCVD Ta_2O_5 layers is measured by XRR and is around 19 %. Material quality of Ta_2O_5 layers deposited by PEALD is better than that by MOCVD. PEALD Ta_2O_5 films have low level of hydrogen and carbon and exhibit a porosity around 6 %. Due to the improvement of material quality, PEALD capacitors exhibit two orders of magnitude lower leakage current than MOCVD capacitors.