Plasma Treated Ta, Ti, and Hf-based Diffusion Barriers for Copper Metallization System

• Main Authors: Ou Keng-Liang, 歐耿良
• Other Authors: Chou Chang-Pin
• Format: Others
• Language: en_US
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/38763350823581623724

博士 === 國立交通大學 === 機械工程系 === 91 === In this thesis, in order to promote barrier properties to apply in copper metallization, various diffusion barriers and surface treatments on deposited barrier films were prepared. The contents includes the optimum condition of Ta and TaN barrier films was set up, thermal stability of optimum condition for TaN barrier films was discussed in copper metallization, The barrier properties of CVD-Ti and TiN barrier films were discussed in thermal stability and step coverage for small trenches, various plasma treatments were performed on barrier layers to improve the thermal stability in copper metallization, and physical and electrical properties of Hf and Hf-N barrier films were also investigated. First, thermal stability of Ta barrier films with and without plasma treatments in copper metallization was discussed. Ta and TaN barrier films were comparison with plasma treated TaNx/Ta barrier films. Based on the analyses, an amorphous layer was formed on the Ta film surface with N2 plasma treatment. In addition, TaNx/Ta barrier film possessed lower resistivity and finer grains. The amorphous layer (TaNx) induced the better thermal stability and against Cu diffusion. Hence, barrier properties of TaNx/Ta films were better than that of Ta and TaN films. Secondly, various nitrogen flow ratios TaN barrier films were performed to discuss optimum conditions and thermal stability was advance discussed. Furthermore, O2 and N2 plasma treated process were also performed onto TaN barrier films. Based on the investigation, finer grains were found after TaN barrier films with O2 and N2 plasma treatments. The amorphorization phenomenon was observed on TaN(O)/TaN barriers. A thin amorphous layer was also observed on TaN surface after plasma treatments. TaN(O) and TaN(N) amorphous layers can improve barrier thermal stability. With shrinking the feature sizes of ULSI devices, physical vapor deposition for such kind of application has been replaced by chemical vapor deposition (CVD), because of the increased conformability of the film as compared with PVD films. CVD Ti and TiN layers can be deposited using TiCl4-based CVD process. Nevertheless, this process requires high-temperature (>600°C) substrates to achieve the depositions, which sometimes cause thermal damage to the deposited films and thermal diffusion of materials not suitable for devices. Moreover, deposited films are polycrystalline and provide inadequate protection because grain boundaries may presumably serve as fast diffusion paths for copper. In this paper, a low-temperature (<500°C) plasma enhanced chemical vapor deposition was used to deposit ultrathin (10 nm) Ti films. Furthermore, in-situ NH3 plasma was further employed to posttreat PECVD-Ti films. The resulted films had a multilayered amorphous Ti/TiNx structure and high thermal stability. Moreover, the effective resistivity of resulted Ti/TiNx film reduces to 122 mW-cm. Improved barrier capability against Cu diffusion is found for the Ti/TiNx barrier layer since the Cu/TiNx/Ti/n+-p junction diodes retain low leakage current densities even after annealing at 500°C for 1 hour. Ti/TiNx barrier layers present lengthened grain structures to effectively impede Cu diffusion, and thus act as much more effective barriers than conventional Ti and TiN films. Better step coverage is also observed for PECVD-Ti films deposited on small trenches defined by electron beam lithography. Finally, hafnium and hafnium nitride barriers films with lower resistivity were discussed in thermal stability. Phase transformation existed as nitrogen was incorporated with hafnium films. Various thermal stability of Hf and Hf-N barrier films was investigated.