Pei-Jun Ding

Effects of the addition of small amounts of Al to copper: Corrosion, resistivity, adhesion, morphology, and diffusion

The properties of thin films of Cu with 1 at. % Al are explored. As‐deposited films of Cu(1 at. % Al) oxidize orders of magnitude more slowly than do those of pure Cu. After Cu(1 at. % Al) films are annealed in Ar at 400 °C for 30 min, very thin protective layers of aluminum oxide form on the surface. These thin oxide layers stop further oxidation of the copper. Cu(1 at. % Al) films also adhere better to SiO2 than do films of pure copper. Unlike pure Cu, films of Cu(1 at. % Al) remain microscopically smooth after anneals at temperatures up to 700 °C. In addition, Cu(1 at. % Al) films show no diffusion of Cu (as measured by Rutherford backscattering spectroscopy) into SiO2 at temperatures up to 700 °C. The addition of Al to Cu does increase its resistivity by about 2 μΩ cm per 1 at. % Al, but a possible procedure to avoid this problem is proposed.

Oxidation resistant high conductivity copper films

The properties of thin films of Cu‐doped with different percentages of Mg were investigated. It was found that as‐deposited films of Cu (2 at. % Mg) oxidize orders of magnitude more slowly than do those of pure Cu. More importantly, when Cu(2 at. % Mg) films are annealed in Ar at 400 °C for 30 min, a thin protective layer of magnesium oxide forms on the surface and completely stops further oxidation. This annealing step also reduces the resistivity of films to the value essentially the same as that of pure sputtered copper films. Films of Cu (2 at. % Mg) also adhere to SiO2 much better than do films of pure copper. Furthermore, annealing studies show that this material remains microscopically smooth and shows no diffusion into SiO2 at temperatures up to 700 °C.

Low-temperature passivation of copper by doping with Al or Mg

Abstract The doping of copper with Al and Mg is discussed as a method of passivating the exposed surface of copper films proposed for use as a conductor in microelectronics. Doping by co-deposition and by diffusion from Cu/M/SiO2 bilayers, where M = Al or Mg, is discussed. Annealing such doped films in an ambient containing small amounts of oxygen produces a thin surface barrier layer of dopant oxide which stops further oxidation. In good cases, the conductivity of these films approaches that of films of pure sputtered copper. Such doping also improves adhesion to SiO2 and stability on SiO2. Improvements in stability include both decreased roughening due to grain growth and decreased diffusion transport into SiO2.

Thermal annealing of buried Al barrier layers to passivate the surface of copper films

Annealed metallic bilayers consisting of Cu/Al/SiO2 are studied from the perspective of providing both surface passivation and diffusion barrier/adhesion promoter function for advanced copper based metallization. Upon annealing this bilayer film at 400 °C or higher, enough Al dissolves into the Cu to provide substantial oxidation resistance at the copper surface. The resistivity of these annealed films is approximately 4.5 μΩ cm. Compared to films of pure copper, these bilayer films are much more adherent to SiO2 and much more stable (both morphology and diffusion) on SiO2.

Annealing of boron‐implanted corrosion resistant copper films

Ion implantation can be used effectively to passivate copper. The effect of B ion implantation on the oxidization rate of copper is studied as a function of B energy and dose. The increase of sheet resistance associated with ion implantation damage and with the incorporation of B is studied. It is found that a post‐implantation inert gas annealing (at 400 °C for 20 min) removes the increase in sheet resistance caused by implant damage while preserving the passivation effects of the B implant.

Thermal stability of copper silicide passivation layers in copper-based multilevel interconnects

Copper thin films were exposed to a dilute silane mixture at temperatures in the range of 190–363 °C. The resulting silicide surface layers were characterized by four-point probe, Rutherford backscattering spectrometry, and x-ray diffraction. A definitive stability regime is observed in which progressively higher copper content phases exist with increasing temperature. Cu3Si, formed in silane, on annealing converts to Cu5Si and eventually to no silicide layer by a silicon diffusion reaction that in an inert ambient drives silicon into underlying copper to form a solid solution. In oxidizing ambients, a similar phenomenon occurs but now silicon also diffuses to surfaces where it oxidizes to form a self-passivating SiO2 layer on surface. These results have important implications governing integration of copper silicide as a passivation layer and silicon hydride based dielectric deposition in copper-based multilevel interconnect in ultralarge scale integration.

Investigation of the mechanism responsible for the corrosion resistance of B implanted copper

Abstract Ion implantation is an effective way to passivate copper films. The present work was designed to refine our understanding of the mechanisms which lead to this result. The oxidation of B implanted copper and copper oxide (Cu2O) was studied. It was found that the oxidation rate of Cu2O implanted with B is as low as that of copper metal implanted with B. Further, it is observed that CuO forms on the surface of both B implanted Cu and Cu2O, in contrast to the Cu2O that forms on not implanted copper. A mechanism which leads to these effects is briefly discussed.

Analysis of refractive index profile in KTiOPO4 waveguide formed by 3.0 MeV He+ implantation

Abstract The optical waveguide formation in X-cut KTiOPO 4 was achieved by single energy implantation of 3.0 MeV He + to a total dose of 2.0×10 16 ions/cm 2 at liquid nitrogen temperature. The modes were examined by the prism (LiTaO 3 ) coupling method. The analysis of the refractive index profile in the KTiOPO 4 (100) waveguide was performed based on parametrized index profile reconstruction (PIPR). We have used the TRIM (the transport of ions in matter) code to simulate the energy loss distribution. The result shows that the nuclear collision mostly influences the refractive index profile, but the peak position of the refractive index profile is shallower than that of the nuclear energy loss distribution.

The mean projected range and range straggling of Xe ions implanted in Si and Si1N1.375H0.603

Abstract Xe ions at energies from 50 to 400 keV as well as from 600, 800 and 1000 keV were implanted into Si and Si1N1.375H0.603, respectively. The mean projected ranges and range stragglings are measured by Rutherford backscattering of MeV He ions. The values obtained are compared with different calculation procedures. The results show that the maximum differences between experimental and calculated values are 11%, 14% and 7% by transport of ions in matter (TRIM), projected range algorithm (PRAL) and Wang and Shi (WS) calculation procedure based on Biersacks model, respectively. The experimental range stragglings are higher than the calculated ones for the case of 50–400 keV Xe ions implanted into amorphous Si. As for the case of 600, 800 and 1000 keV Xe implanted into Si1N1.375H0.603, the maximum differences between experimental and calculated values of the mean projected range are 25%, 26% and 15% by TRIM, PRAL and WS, respectively. Also it is observed that there are significant deviations of the experimental values from the calculated values for the range straggling.

Ion‐beam mixing of erbium into potassium titanyl phosphate by mega‐electron‐volt argon beams

A 500 A erbium (Er) film was deposited on potassium titanyl phosphate (KTiOPO4 or KTP) by electron‐beam evaporation. The doping of Er into KTP was induced by mega‐electron‐volt Ar+ with different doses. The doping amount was investigated by Rutherford backscattering of 3.0 MeV He+. The results show that the doping concentrations of Er in KTP were 2.88 and 1.88 at. % induced by 2.0 and 3.0 MeV Ar+ with the dose of 2×1016 ions/cm2 at room temperature, respectively. Perhaps the present result can provide an important approach not only for the laser and waveguide laser fabrication, but also for the high‐concentration dopants (atomic percent levels) into KTiOPO4 at room temperature.