Thermal Annealing and Impurities Incorporation of Electrodeposited Cobalt Thin Film

Abstract

Cobalt has recently attracted much attention as it is replacing copper in the ground rule metal level in advanced interconnects to minimize the resistivity increase in small features1. Defect-free filling of Co in small features has been demonstrated using various commercial additives2-4. Annealing has been used to further decrease and stabilize the resistivity of lines5. It is well known from copper studies that additives in electrolytes will not only be incorporated into the film as impurities but also affect the grain structures and resistivity of deposited film6, 7. Post deposition annealing has been used to further grow the grains and to influence the resistivity and reliability of lines and vias8. In this report, we use several different additives including dimethylglyoxime (DMG), sodium chloride (NaCl), and sodium 3-mercapto-1-propanesulfonate (MPS-Na) to study their individual and synergistic effects on impurity incorporation (C, N, Cl, S) in cobalt thin films. The film morphology, resistivity, crystallographic structure, and the impurity distribution were also investigated. Figures 1 (a) and (b) show the top-down SEM micrographs of two cobalt films deposited with different combinations of additives, one with 100 ppm DMG and 100 ppm MPS-Na, and the other with 100 ppm DMG and 100 ppm NaCl. A strong influence of additives on the morphology of Co films was observed. Figure 1 (c) shows the film sheet resistance change upon 300 C anneal in vacuum. The resistance decreases along the annealing time, but quickly settles within the first 2 hours except for the film deposited with a combination of the three additives (red line), 100 ppm DMG, 100 ppm NaCl, and 100 ppm MPS-Na. The later not only shows a much higher as deposited sheet resistance but also took a much longer 6 hours for the resistance to stabilize. Secondary ion mass spectroscopy (SIMS) was also used to quantify the impurities in the Co films. The resistivity change upon annealing will be discussed in detail in conjunction with the impurity and grain structure analysis. REFERENCES Gall, D., Electron mean free path in elemental metals. Journal of Applied Physics 2016, 119 (8), 085101.Rigsby, M. A.; Brogan, L. J.; Doubina, N. V.; Liu, Y.; Opocensky, E. C.; Spurlin, T. A.; Zhou, J.; Reid, J. D., Superconformal Cobalt Fill through the Use of Sacrificial Oxidants. ECS Transactions 2017, 80 (10), 767-776.Wafula, F.; Wu, J.; Branagan, S.; Suzuki, H.; Gracias, A.; van Eisden, J. In Electrolytic Cobalt Fill of Sub-5 nm Node Interconnect Features, 2018 IEEE International Interconnect Technology Conference (IITC), IEEE: 2018; pp 123-125.Kelly, J.; Chen, J.-C.; Huang, H.; Hu, C.; Liniger, E.; Patlolla, R.; Peethala, B.; Adusumilli, P.; Shobha, H.; Nogami, T. In Experimental study of nanoscale Co damascene BEOL interconnect structures, Interconnect Technology Conference/Advanced Metallization Conference (IITC/AMC), 2016 IEEE International, IEEE: 2016; pp 40-42.Kelly, J.; Kamineni, V.; Lin, X.; Pacquette, A.; Hopstaken, M.; Liang, Y.; Amanapu, H.; Peethala, B.; Jiang, L.; Demarest, J., Annealing and Impurity Effects in Co Thin Films for MOL Contact and BEOL Metallization. Journal of The Electrochemical Society 2019, 166 (1), D3100-D3109.Hau-Riege, S. P.; Thompson, C. V., In situ transmission electron microscope studies of the kinetics of abnormal grain growth in electroplated copper films. Applied Physics Letters 2000, 76 (3), 309-311.Zhang, W.; Brongersma, S.; Heylen, N.; Beyer, G.; Vandervorst, W.; Maex, K., Geometry effect on impurity incorporation and grain growth in narrow copper lines. Journal of The Electrochemical Society 2005, 152 (12), C832-C837.Ryu, C.; Kwon, K.-W.; Loke, A. L.; Lee, H.; Nogami, T.; Dubin, V. M.; Kavari, R. A.; Ray, G. W.; Wong, S. S., Microstructure and reliability of copper interconnects. IEEE transactions on electron devices 1999, 46 (6), 1113-1120. Figure 1