Thermal stability of Ta-Si-N and Nb-Si-N as barriers against Cu diffusion

초록

The barrier properties of Ta-Si-N and Nb-Si-N was investigated using X-ray diffration and AES depth profiling particularly focussing the effect of the N2/Ar gas flow ratio of reactive sputter deposition process on the barrier properties of Ta-Si-N. Ta-Si-N fails at 900℃ when it is in contact with Cu. while Ta and TaN fail at 600 and 650℃, respectively. The optimum N2/Ar flow ratio in the sputter deposition of Ta-Si-N which offers the best barrier property is 15%. The Ta-Si-N barrier fails by migration of Cu through the Ta-Si-N layer to the Ta-Si-N/Si interface and reaction of Cu with Si to form copper silicides. The crystallization temperature of Ta-SiN in the Cu/Ta-Si-N/Si sample is higher than 900℃. Therefore, the failure of Ta-Si-N at 900℃ is not directly related to the crystallization of Ta-Si-N. The N2/Ar gas flow ratio for the sputtering deposition of the Nb-Si-N film with the highest thermal stability was found to be 5%. The Nb-Si-N film failed at 700℃. The failure mechanism of the Nb-Si-N is as follows: Cu atoms move to the Nb-Si-N interface through the Nb-Si-N film and react with Si atoms in the Si substrate resulting in the formation of Cu3Si at the Nb-Si-N/Si interface.