Investigation of ultra-thin Al<inf>2</inf>O<inf>3</inf> film as Cu diffusion barrier on low-k (k=2.5) dielectrics

Abstract

Ultra thin Al 2 O 3 films were deposited by plasma enhanced atomic layer deposition (PEALD) as Cu diffusion barrier on low-k (k=2.5) material. The thermal stability and electrical properties of the Cu/low-k system with Ta, Ta/Al 2 O 3 and Ru/Ta layers with different thickness were compared after annealing. The TEM and EDX results reveal that the ultrathin Al 2 O 3 films are thermally stable and have excellent Cu diffusion barrier performance. The I-V and TDDB electrical measurements further confirm that the ultra thin Al 2 O 3 film is a potential Cu diffusion barrier in copper/low k interconnect.Corresponding Author:Xin-Ping Qu, Professor, With the continuing scaling down of the line pitch in very large scale integrated circuits, ultrathin Cu diffusion barriers are necessary to mitigate the increase in the effective resistivity of the Cu interconnects due to grain boundary scattering and interface scattering. Conformal deposition of thin films in high aspect ratio trenches using traditional physical vapor deposition (PVD) Systematic study of ALD oxide films as Cu diffusion barrier on the low-k dielectric has been rarely reported. In this work, ultra thin Al 2 O 3 films were deposited by plasma enhanced atomic layer deposition (PEALD) together with Ta adhesion layer, its properties as a Cu diffusion barrier on the low k dielectric (k=2.5) were studied.The low k films (Novellus CORAL, k=2.5) were deposited on the 12" p-type Si wafers with a thickness of 220 nm. The wafers were cut into small pieces and then were cleaned in an ultrasonic cleaner with 2-propanol solution before loading to the loadlock chamber. After in-situ annealing at 250 ° C for 20 minutes in the high vacuum ALD chamber, 11 or 21 cycles (~1.2 Å/cycle) Al 2 O 3 films were grown by plasma enhanced atomic layer deposition (PEALD) using trimethylaluminium (TMA) and remote O 2 plasma (200W) as precursors. The growth temperature was 250° C. After deposition, samples were taken out and sent into a PVD chamber. The details of the ALD growth can be seen elsewhere. [7] Then the Cu(50 nm)/Ta(5 nm) film stacks were deposited by DC magnetron sputtering. The thin Ta film was used as a glue layer to promote adhesion between the Cu and Al 2 O 3 barrier layers. To form the patterned metal-insulatorsemiconductor (MIS) structures, a shadow mask was used when depositing the Cu/Ta stacks. For comparison, the Cu/Ta stack was also directly deposited onto the low k substrates. A Ti(40 nm)/Pt(30 nm) bi-layer was deposited as backside electrode by sputtering. Furnace annealing was conducted in the N 2 atmosphere at 400 °C for 30 minutes. After annealing, energy dispersive X-ray (EDX) transmission electron microscope (TEM), time-dependent dielectric breakdown (TDDB), and dielectric breakdown measurements were used to characterize the thermal stability and electrical reliability of the Cu/barrier/low k/Si system. The capacitance-voltage (C-V) measurements were carried out using an HP 4192A impedance analyzer to evaluate the effective k value of the system. The XTE...