Comparison of Ru/Ta and Ru/TaN as Barrier Stack for Copper Metallization
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0914-F09-02
Comparison of Ru/Ta and Ru/TaN as Barrier Stack for Copper Metallization Xin-Ping Qu, Jing-Jing Tan, Mi Zhou, Tao Chen, Guo-Ping Ru, and Bing-Zong Li Department of microelectronics, Fudan University, Dept. of microelectronics, 220#, Handan Road, Shanghai, 200433, China, People's Republic of
ABSTRACT The diffusion barrier properties for the ultrathin Ru/Ta and Ru/TaN bilayer as the copper diffusion barrier are compared. Cu, Ru, Ta and TaN thin films are deposited by using the ion beam sputtering technique. The experimental results show that the thermal stability of the Cu/Ru/Ta or Cu/Ru/TaN/Si structure is much more improved than that of the Cu/Ru/Si structure without the interlayer. However, the Cu/Ru/TaN/Si shows better thermal stability than the Cu/Ru/Ta/Si structure, which should be attributed to the amorphous nature of the TaN interlayer. The microstructure evolution of the Cu/Ru/Ta (TaN)/Si structure during annealing is discussed. The results show that the Ru/TaN bilayer can be a very promising diffusion barrier in the future seedless Cu interconnect technology. INTRODUCTION Ru is a promising barrier material for its potential use in seedless copper technology. It has very low sheet resistivity (~ 7µΩ⋅cm), high melting point and it allows direct copper electrodeposition on it 1-6. The latter is very attracting since it will reduce the technology complexity and the chance of poor conformance caused by relatively thick sputtered copper seed layer. It has been shown that the Ru layer adheres well to Cu. 7-8 However, the Ru layer does not adhere well to SiO2 and low dielectric constant (low k) material.9 Furthermore, thin Ru film is not a very effective diffusion barrier. It has been reported that the Ru film in the thickness of 20nm could prevent Cu diffusion until 450 oC. 1 While for 5nm Ru film capped by copper, the failure temperature is merely 300oC.4 Therefore it would be better to use Ru for the glue layer and combine Ru with some good barrier material to be the diffusion barrier for copper. Ta and TaN layers are commonly used as the diffusion barrier in the current ULSI interconnect technology. 10 In this paper, we compare the Ru/Ta and Ru/TaN bilayer as diffusion barrier for copper. EXPERIMENT N-type Si (100) wafers were used as the starting substrates. SiO2 layers in 500nm thick were thermally grown on some Si wafers. After a standard chemical cleaning followed by a diluted HF dip, the substrates were immediately loaded into the Oxford sputtering system. The purity of the Ru target and the Ta target is 99.9% while that of the Cu target is 99.99%. The Ru, Ta, TaN and Cu films were sequentially deposited on the Si and SiO2/Si substrates with the ion beam sputtering technique. The base pressure was below 5×10-5 Pa. The TaN layer was reactively sputtered by flowing N2 into Ar atmosphere with the Ar: N2 ratio at about 1:1. The sputtering rate is about 0.1Å/s. After deposition, rapid thermal annealing (RTA) or furnace annealing were carried out for these samples in high-purity N2 atmosphere. Phase
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