Shao-Feng Ding

Cu adhesion on tantalum and ruthenium surface: Density functional theory study

This work reports a first-principles study of copper adhesion on Ta(110) and Ru(0001) surface with the density functional theory. Adsorption energy, electron density difference, and geometrical structures of Cu on pure, oxygen, and nitrogen doped Ta(110), Ru(0001) surfaces, and Ru doped Ta(110) surface were investigated. By analyzing the calculated results and the existing experimental results, it is found that although Ta has stronger chemical interaction with Cu, its larger lattice mismatch with Cu, and easy oxidation and nitridation make Ta a poorer Cu adhesion layer in comparison with Ru. The adhesion ability of Cu on Ta can be improved by doping Ru in Ta. The agglomeration of Cu on Ta or Ru is also studied. The calculation results show that Cu adsorbed on Ta(110) surface is more likely to be desorbed and agglomerated on the top of the second Cu atom layer. The substitutional oxygen O Ta in Ta will stimulate the agglomeration of Cu on the Ta surface.

Investigation of Co/TaN bilayer as Cu diffusion barrier

The diffusion barrier properties of Co/TaN bilayer as Cu adhesion layer/diffusion barrier on the Si and low k (k=2.5) substrates were investigated. The barrier was prepared by using ion-beam sputtering technique. The barrier property was investigated by sheet resistance, X-ray diffraction (XRD), and Auger electron spectroscopy (AES) and electrical measurements. No obvious Cu diffusion and agglomeration was observed after annealing at 500°C for 30 min. Results show that Co/TaN has a good potential as cost effective adhesion/diffusion stack in copper metallization.

Study of the sputtered Mo/TaN and Mo-Ta thin film as diffusion barrier for copper metallization

In this work, the properties of sputtered Mo/TaN bilayers and Mo-Ta single layer as diffusion barriers were investigated for Cu metallization. The experimental results show that the Mo(5nm)/TaN(5nm) stack can withstand annealing up to 600 °C for 30min and the Mo-Ta(5nm) alloy barrier can effectively prevent Cu diffusion after 500 °C annealing.

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

Ultrathin Al<inf>2</inf>O<inf>3</inf> films were deposited by 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 Al<inf>2</inf>O<inf>3</inf> layers with different thickness were studied after annealing. The AES, TEM and EDX results revealed that the ultrathin Al<inf>2</inf>O<inf>3</inf> films are thermally stable and have excellent Cu diffusion barrier performance. The electrical measurements of dielectric breakdown and TDDB tests further confirmed that the ultrathin Al<inf>2</inf>O<inf>3</inf> film is a potential Cu diffusion barrier in the Cu/low-k interconnects system.

Density Functional Theory Study of Cu Adhesion on Rh, Ir, Pd, Ta, Mo, Ru, Co, and Os Surfaces

In this work, first-principles calculation based on the density functional theory was applied to study Cu adhesion on the surfaces of Rh(111), Ir(111), Pd(111), Ta(110), Mo(110), Co(0001), Os(0001), and Ru(0001), on which the adsorption energy, electron density difference, and geometrical structures of Cu were investigated. The analysis of the calculated and experimental results shows that the atomic chemical interaction, surface lattice mismatch, and crystal lattice type have marked effects on Cu adhesion on glue layers. Cu atoms on all the metal surfaces studied in this work are more likely to form the fcc structure with a quasi-(111) orientation. The coupling effect of the large surface lattice mismatch and the lattice type difference between Cu and the metal surface can greatly reduce Cu adhesion ability. Among all the studied metals, Ir and Os showed comparable adhesion ability to Ru and can be considered as promising Cu glue layers for Cu interconnects.

Thermal ALD of Cu via reduction of Cu x O films for the advanced metallization in spintronic and ULSI interconnect systems

In this work, an approach for copper atomic layer deposition (ALD) via reduction of CuxO films was investigated regarding applications in ULSI interconnects, like Cu seed layers directly grown on diffusion barriers (e. g. TaN) or possible liner materials (e. g. Ru or Ni) as well as non-ferromagnetic spacer layers between ferromagnetic films in GMR sensor elements, like Ni or Co. The thermal CuxO ALD process is based on the Cu (I) β-diketonate precursor [(nBu3P)2Cu(acac)] and a mixture of water vapor and oxygen (“wet O2”) as co-reactant at temperatures between 100 and 130 °C. Highly efficient conversions of the CuxO to metallic Cu films are realized by a vapor phase treatment with formic acid (HCOOH), especially on Ru substrates. Electrochemical deposition (ECD) experiments on Cu ALD seed / Ru liner stacks in typical interconnect patterns are showing nearly perfectly filling behavior. For improving the HCOOH reduction on arbitrary substrates, a catalytic amount of Ru was successful introduced into the CuxO films during the ALD with a precursor mixture of the Cu (I) β-diketonate and an organometallic Ru precursor. Furthermore, molecular and atomic hydrogen were studied as promising alternative reducing agents.

Trapping and detrapping of oxide border traps in Al2O3 gate dielectric in MoS2 n-MOSFETs under PBTI stress

In this paper, we report the positive bias temperature instability (PBTI) effects of the back-gated MoS2 n-MOSFET with Al2O3 gate dielectric. Multilayer MoS2 was used and all measurements are carried in vacuum to avoid the electric signal contamination by the top MoS2 surface water or oxygen molecules absorption. In the stress phase, the Id-Vg curve shifts to the positive gate bias direction. In the recovery phase, the Id-Vg shifts back completely to the fresh device curve. This indicates that voltage shift is purely due to trapping or detrapping of the oxide border traps at the MoS2/Al2O3 interface and no new traps are generated during the stress time. When applying different stress voltage and measuring the Id-Vg shift, we can calculate the oxide border trap energy density Ξ(E), which has a peak value of 6×1013cm−2eV−1 at 0.035eV above EC of MoS2 conduction band.

Inhibition of enhanced Cu oxidation on ruthenium

The enhanced oxidation of Cu on Ru/diffusion barriers was observed. The in-situ X-ray diffraction results reveal that the Cu oxidation can be inhibited by doping C in either Ru adhesion layer or TaN barrier layer. The RuC/barrier becomes more robust with certain amount of C doped in Ru. ALD Cu2O on the RuC substrate was carried out and the effect of C on reduction of Cu oxide was observed.

Thermal stability of ultrathin RuC film as Cu diffusion barrier

The properties of ultrathin RuC film and RuC/TaN stack as the Cu diffusion barrier on Si substrate were studied. The results show that the thermal stability of the Cu/RuC/TaN/Si structure is better than that of the Cu/Ru/TaN/Si structure. A flush TaN layer can improve the thermal stability of RuC film and make it a more robust diffusion barrier for Cu metallization.