Effects of AlOx incorporation into atomic layer deposited Ru thin films: Applications to Cu direct plating technology

Ru-based ternary, RuAlO thin films for applications as diffusion barriers for the direct plating of Cu interconnects were grown using atomic layer deposition (ALD) by repeating super-cycles consisting of Ru and AlO_x ALD sub-cycles at 225 °C. The intermixing ratios of Ru and AlO_x in the RuAlO films were controlled by changing the total number of AlO _x ALD unit cycles at a fixed number of Ru cycles to 200. Rutherford backscattering spectrometry and secondary ion mass spectrometry showed that the Al and O content in the film increased with increasing the total number of AlO_x ALD unit cycles but the Ru content decreased. Moreover, their relative amounts in the RuAlO films had considerable effects on the performance as a Cu diffusion barrier as well as on their properties, such as resistivity, crystallinity and microstructure. The resistivity of the RuAlO film deposited with a total number of AlO_x unit cycles of 4 was ∼ 125 μδ cm, and its resistivity increased continuously with increasing the total number of AlO_x unit cycles. X-ray diffraction and electron diffraction revealed a decrease in the crystallinity and grain size of the Ru film by the incorporation of AlO_x into Ru by adding AlO_x cycles. The performance of the RuAlO films as a Cu direct-plateable diffusion barrier in terms of both the diffusion barrier performance against Cu and the interfacial adhesion energy between Cu and SiO₂ improved with increasing the amount of AlO_x in the RuAlO film. The direct plating and superfilling of Cu on RuAlO film was possible in a trench (80, 140 nm of width and 150 nm of depth) though the resistivity of the RuAlO film was as high as 210 μδ cm. It was also confirmed that the no interfacial oxide was grown when the ALD-RuAlO film was deposited on Cu surface.