Ic Copper Interconnect Technology, Advanced Diffusion Barrier Layer

With continuous scaling down of the devices, the material and process of interconnect technology also require corresponding innovation. In the 32nm and beyond technology node, many issues arise due to the poor conformality caused by relative thick sputtered Ta/TaN bi-layer and seed layer. In order to decrease the resistivity of interconnect lines as well as meet the performance requirement of the device, the need of decreasing barrier and seed layer thickness has increased, and also the aspect ratio of trench and via has increased. Therefore, researches on novel diffusion barrier/seed layer materials and process have attracted great attention. There are many issues need to be studied for using novel material for diffuision barriers/adhesion layer and novel deposition process, which includes interface reaction within Cu/diffusion barrier/Si or low k system, also atomic layer deposition (ALD) process and growth mechanism, surface chemistry and low k surface pretreatment.Based on "novel material" and "novel process" for the diffusion barrier, the main contents and results of this dissertation are summaried as follows.1: Novel diffusion barrerier material - W carbidesTa/TaN bi-layer structure and Ta or TaN single layer with same total thickness are compared as diffusion barrier. The reasons for super thermal stability of Ta/TaN bi-layer structure are analysed. The microstructure evolution and the failure mechanism for Ta/TaN bi-layer diffusion barriers are proposed.W_xC_y films with different W/C ratio are prepared by co-sputtering method. The stability of different W_xC_y films as diffusion barriers is compared. The agglomeration behavior of Cu on different W_xC_y films are characterized by in-situ laser light scattering (In-situ LLS) test. The Cu agglomeration activation energys (Ea) on diffirent W_xC_y films are derived by using Kissinger equation.The effects of W carbides diffusion barriers on the twinning formation of PVD sputtered Cu films (100nm) are studied. It is found that nano-scale twinning can be formed in the Cu films deposited on the WC diffusion barrier before or after annealing process, while there is no similar result for Cu on W barrier. It reveals that the interface energy for Cu on WC is much higher than that for Cu on W and it is critical for the formation of Cu twinning. The Cu twinning formation mechanism is proposed with consideration of the whole Cu grains diffusion and rotation. The correlation between Cu twinning and Cu agglomeration is studied by stress measurement. The stress gradient caused by twinning formation affacts the vacancy concentration distribution and diffusion behavior, which will cause the voids formation after annealing process.2: Research on atomic layer deposition of TiO₂ and TaN diffusion barriersUltra thin TiO₂ films prepared by two kinds of metal-organic precursors TDMAT, Ti isopropoxide and three kinds of reactants (H₂O vapor, H₂O plasma and O₂ plasma) are studied. The atomic reaction paths are calculated by using density functional theory (DFT). The effects of precursors desorption on the TiO₂ ALD growth mode and process window are discussed. The crystallization behavior of the TiO₂ thin films with diffirent process conditions is studied. The effects of the C contents on the crystallization temperature for ultra thin TiO₂ films are analyzed.TaN films prepared by MO precursor PDMAT and two kinds reactants (NH₃ and N₂ plasma) are studied. The effects of diffirent reactants on the TaN ALD growth mode are discussed. The effects of different reactants on the stability of ALD growth TaN diffusion barriers are compared. It is revealed that the process can be optimized by using lower reactant gas vapour pressure and longer plasma exposure time.3: Novel seed/adhersion layer for Cu inteconnectRu single layer, Ru/TaN, Ru/WCN and Ru/TaCN bi-layer structure diffusion barriers prepared by physical vapor deposition are studied. The oxidation enhanced effect on Cu from under Ru layer is revealed.Plasma enhanced atomic layer deposition of Ru films prepared with MO precursor Ru(EtCp)2 and NH3 are studied. The growth mode and films properties of ALD Ru on three kinds of substrates including Si, TiN/Si and TaN/Si are compared. Results show that the surface properties of the TaN substrate are crutial to the nucleation for ALD Ru. The stability of ALD grown Ru, Ru/TiN and Ru/TaN barriers is tested. The Ru/TaN barrier can stand up annealing of 400℃/30min on Si substrate. However, results show that Cu has diffusied to the low k substrate for the ALD Ru(7nm)/ALD TaN(5nm) barriers on porous low k material (k=2.5).