(A) study on the plasma-enhanced atomic layer deposition of TaN thin films

Abstract

Until this day, a variety of metals have been used for the Cu diffusion barrier and such diffusion barriers deposited using a physical vapor deposition (PVD) technique. But the device scaling is being gradually smaller and demanded barrier thickness thinner. Hence, the existing techniques arrive at a limit. To overcome this situation, many researches have been done. As a result of studies, nitrides and silicon nitrides of Ta, Ti, and W are considered to the candidate materials of diffusion barrier. In these candidates, Ta-N has many outstanding advantages as high melting point (2669℃), good adhesion property with low-k materials and no compound between Cu and Ta, Cu and N, comparing to the others. At the same time atomic layer deposition (ALD) method is suggested the solution of the step coverage problem in PVD and high impurity concentrations in chemical vapor deposition (CVD) technique because ALD has superior conformailty and improved thickness controllability. In this paper, the characteristics of Ta-N thin films deposited by plasma-enhanced atomic layer deposition (PEALD) using metal-halide precursor $TaF_5$ and $N_2/H_2/Ar$ mixed gas plasma described. The film thickness/cycle saturated at 0.41Å/cycle, when the source pulse time exceeds 1.5 s. The resistivity of films was 600 uΩ-cm and films grown to (111) direction. The film composition was determined using ERD-TOF, RBS and AES. The N/Ta ratio of thin films was 1.17 and fluorine (F) and hydrogen (H) did not exist as much as detectable. As plasma time is increasing, the thickness/cycle and resistivity of Ta-N thin films were not saturated but gradually heightened and the N/Ta ratio of films increased from 1.17 to 1.34. Thus, there were two possibilities about the reason of the increasing of thickness/cycle and resistivity. First thing was the increment of precursor adsorption rate and another one is the formation of $Ta_3N_5$ phase. Since $Ta_3N_5$ has high resistivity and low density relatively to the T...