| Summary: | 博士 === 國立交通大學 === 材料科學與工程學系 === 99 === With the dimensional shrinkage of microelectronic devices, atomic layer deposition (ALD) becomes a very attractive method for the deposition of ultrathin films. Beacuse ALD can deposit uniform ultrathin thin films on substrates with high aspect ratio structures, it has been implemented in the Cu interconnect process, whcin requires diffusion barriers of high conformality and precise thickness. In addition, ALD also meets challenging requirements in many other IC processes, such as the deposition of high quality dielectrics to fabricate trench capacitors for DRAM.
We use plasma-enhanced ALD (PEALD) to deposit TaNx diffusion barriers on mesoporous SiO2 low-k dielectrics. The self-limiting nature of the surface reactions can produce uniform TaNx films of high thermal stability on the mesoporous SiO2 low-k dielectrics. However, the porous nature of the porous dielectrics leads to a difficulty for the integration of the dielectrics into Cu interconnect technology. Surface pores are penetration pathway of adverse impurities into the porous dielectrics, such as moisture uptake during cleaning and plasma species diffusion during etching. O2 and Ar plasmas were used to modify the surface of the mesoporous dielectric in a high density plasma chemical vapor deposition (HDP-CVD) system, and both of the treatments produced a densified oxide layer a few nanometer thick. The pore sealing treatment could effectively prevent metallic atoms from diffusing into the mesoporous dielectric during the PEALD process and enhance retardation of moisture uptake.
Adhesion properties of PEALD diffusion barriers with the Cu interconnect were also studied. The TaNx nitride barrier usually exhibit good diffusion barrier properties, but they often has a poor mechanical strength at the interface with the Cu layer. In the study, we used hydrogen plasma treatment and rapid thermal annealing (RTA) in hydrogen ambient to reduce the nitrogen content in the surface layer of the PEALD-TaNx barrier layer. The surface treatment greatly improved adhesion of the TaNx barrier layer with Cu and the thermal stability of the TaNx/Cu film stack.
We also deposited Ru/RuNx bilayer barriers on mesoporous SiO2 dielectrics by an in situ two-step PEALD process for the application of seedless Cu electroplating. Ru is a stable transition metal in air and has low electrical resistivity, but it has worse diffusion barrier properties than RuNx. We sequentially deposited 3.5 nm thick RuNx and 0.5 nm thick metallic Ru on the mesoporous dielectric by PEALD. The metallic Ru capping layer can retard thermal decomposition of the underlying RuNx layer and provides the barrier surface a low electrical resistance for direct Cu electroplating. The Ru/RuNx bilayer exhibits satisfactory thermal stability and electrical characteristics, and is suitable for the seedless Cu electroplating process in nanometer scale interconnect technology.
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