Investigation On Fabrication And Properties Of Nanosized Ta-based Barrier

With the rapid development of integrated circuit(IC) manufacture technology, the integration degree continuously increase, the feature size continuously shrinking, new metal interconnection system with low resistance metal wire and low dielectric constant medium should be developed and to take place of the traditional A1 interconnection system. For its lower resistivity, superior resistance to electro-migration and relatively lower price, Cu was considered to be the best choice to replace Al. However, Cu atoms can diffuse rapidly in Si and many dielectrics, copper and silicon can easily react and to form high resistance Cu-Si compounds, the adhesion of Cu to Si and SiO2 are too weak. These problems really decrease the reliability of IC and thus limited its application. The key solution is to add a diffusion barrier on the Cu wire surface, which can prevent Cu diffusion effectively and improve the adhesion of Cu with dielectrics. A good diffusion barrier should satisfy strict requirements such as lower resistance, as thin as possible, high thermal stability and chemical stability, not react with Cu and Si, and so on.Based on the research results at home and abroad, by using magnetron reactive co-sputtering method, N2 and Ar as react gas and working gas respectively, Ta?Ta-N?Ta-Si-N?Ta-Al-N thin films and Cu/barrier/substrate structure were fabricated. The article studied the thermal stability, structure properties and diffusion barrier ability, optimized the prepare parameters. Ternary amorphous barrier with excellent properties were successfully prepared and the failure mechanism of the barrier were researched.Firstly, the article investigated and optimized the sputtering parameters of Ta?Ta-N and Ta/Ta-N bilayer films, analyzed the diffusion barrier properties. The results showed that the sputtering Ta films winkled and fell off when the sputtering power was higher than 200W. With the Ta target sputtering power increasing, the sheet resistance decreased while the surface roughness increased. After 600?/300s rapid thermal annealing, the sheet resistance of Cu/Ta/Si increased abruptly, TaSi2 and Cu3Si appeared, which indicated that the barrier have already failed.The enlarged grain boundary after annealing provided the quick diffusion path for Cu atoms and caused the barrier to fail. Add N into the Ta film can enhance the tendency of the film to be nanocrystallize or amorphous, and at the same time, restrain the Ta-N/Si interface reaction. So, add N can improve the thermal stability and the barrier property, and with the N content increasing, the thermal stability and surface resistance increased too. The failure mechanism of Ta-N barrier was just like Ta barrier, enlarged grain boundaries after annealing were the main diffusion path for Cu atoms. For the combination of Ta films'lower resistance and good adhesion with Cu, Ta-N films'high thermal stability, the research indicated that Ta/Ta-N bilayer was the best among them. The research also indicated that the sputtered Cu films on the Ta-based barrier have an obvious{111} preferred orientation; this was benefit to improve the resistance of electro-migration.Then, based on the optimazed fabrication parameters of Ta-N films, ternary amorphous Ta-Si-N films were designed and prepared for the first time at home.The article researched the properties of Ta-Si-N films prepared with varies silicon sputtering power and N2 flow ratio in detail. The results showed that the adding silicon could surpress the crystallization of Ta nitride effectively. As the silicon content increasing, Si-N phase increased, the degree of amorphism and the surface resistance increased, too. At the same time, the adding N could also surpress the crystallization of Ta silicide. The phase diagram analysis showed that the film consisted of Ta-Si?Ta-N and Si-N. The competion among them induced the film to be amorphous. The barrier properties were closely related to the component ratio.The percentage of Silicon content greatly influenced the stability and diffusion barrier properties of Ta-Si-N films. For the samples with more silicon content, the barrier failed before it crystallized, the failure was related to the enlarged atom interval for the lots of Si atoms in the films; while for the samples with lower silicon content, the barrier failed after it crystallized, the dominating diffusion path for copper atoms was the grain boundaries and defects formed after annealing. The Ta-Si-N films in the article with the thickness of 100nm and the approximate atom ratio of 5:3:2 could keep stable even after 750?/300s thermal annealing, this films has a bright prospects to be an effective diffusion barrier for the new generation IC.The Al doped ternary Ta-A1-N films were also prepared and firstly researched as Cu diffusion barrier at home and abroad. The results showed that the as-deposited films were amorphous and with the Al content increased, the surface roughness decreased, while the sheet resistance increased abruptly. The crystalline temperature for the films with Al content at 1.7at% (Al sputtering power 100W) is very high, and the films with the thickness of 100nm can prevent copper diffusion effectively even after 800?/300s annealing, after 900?/300s thermal annealing, the films crystallized and failed, the failure was still related to the grain boundaries formed after annealing. While for the samples with Al content up to 5.5at% (Al sputtering power up to 150W), the blisters appeared on the surface after annealing at lower temperature, after annealing at higher temperature, the blisters were destroyed and caused the barrier to fail directly. By optimize the fabrication parameters and contral the Al content strictly, Ta-Al-N films with good thermal stability and good diffusion barrier ability can be getted.The research of Ta-based barrier on the Cu diffusion barrier mechanism showed that grain boundary diffusion were the main factor for its failure, the diffusion fit with the B type dynamics Model of Harrison, the diffusion coefficient can be getted by Fisher and Whipple grain boundary diffusion model. The addition of Silicon promoted the barrier to be amorphous and improved the diffusion barrier properties; the Silicon content in the film greatly influenced the barrier properties and the failure mechanism; The addition of Al atoms were also benefit for the barrier to be amorphous, at the same time, the barrier could be protected by the Al passivation layer on the surface, thus could keep stable and complete after annealing at high temperature, while the massive A1 in the films caused the blisters to form on the surface after annealing and induced the barrier to fail.