F. C. T. So

Reactive sputtering of RuO2 films

Abstract The growth rate, resistivity and intrinsic stress of RuO 2 films deposited by reactive sputtering with an O 2 Ne or an O 2 Ar gas mixture were investigated as a function of the following sputtering parameters: gas composition, gas pressure, sputtering power and substrate bias. We found that stoichiometric RuO 2 films could be obtained over a wider range of sputtering conditions in the O 2 Ne mixture than in the O 2 Ar mixture.

WNx: Properties and applications

Abstract The deposition rate, composition, resistivity, and intrinsic stress of r.f. sputter- deposited WN x films have been investigated in detail as functions of various sputtering parameters. We have also evaluated the diffusion barrier performance of WN x films in three different contact schemes to silicon and GaAs. Finally, a possible application of a Ti/WN x bilayer to the self-aligned TiSi 2 process is discussed.

WxN1−x alloys as diffusion barriers between Al and Si

Reactively sputtered tungsten nitride (WxN1–x) layers are investigated as diffusion barriers between Al overlayers and Si shallow n + -p junctions. Both amorphous W80 N20 and polycrystalline W60 N40 films were found to be very effective in preserving the integrity of the n + -p diodes for 30-min vacuum annealing up to 575 °C. Diode failure at higher temperatures is caused by localized penetration of Al into through the WxN1–x barriers. The effectiveness of the barrier decreases for polycrystalline W90 N10 and is worse for pure W.

TiAl3 formation by furnace annealing of Ti/Al bilayers and the effect of impurities

Reactions of Ti/Al couples induced by furnace annealing were investigated (at elevated temperature) using large-grained Al substrates and vacuum-evaporated bilayers of both sequences. 4 He MeV backscattering spectrometry was principally used to monitor the reactions. Profiles of oxygen impurity were obtained by elastic 16 O(alpha,alpha)16 O resonant scattering. In the range of 460–515 °C, TiAl3 forms as a laterally uniform layer at the Ti/Al interface. The thickness of this compound layer increases as (annealing time)1/2. The activation energy is 1.9–2.0±0.1 eV. For evaporated bilayers on an oxidized Si substrate, the sequence of the bilayers does not effect the growth mechanism of TiAl3 , but the growth rate of samples with the Ti on top is lower than that of samples with Al on top, that is, oxygen in Ti/Al samples can reduce the reaction rate by decreasing the pre-exponential factor. Oxygen already contained in the Ti film and oxygen from the annealing ambient are incorporated in the growing TiAl3 compound during thermal annealing. In addition, a TiAl3 layer also forms at the free Ti surface during vacuum annealing when the oxygen-containing contaminants in the ambient are minimized. So far, we succeeded in accomplishing this only for large-grained Al substrates. We conclude that the formation of the TiAl3 compound at the surface is controlled by nucleation and depends sensitively on the condition of the surface layer of the Ti film.

Properties of reactively sputtered Mo1−xOx films

Molybdenum oxide (Mo1−xOx) films were prepared by reactive rf sputtering of a Mo target in O2/Ar plasma. The dependence of film properties on various sputtering parameters is investigated. The atomic percentage of oxygen (x) in the Mo1−xOx films decreases with sputtering power and increases with the partial pressure of oxygen. Mo1−xOx films that exhibit metallic conductivities can be obtained over a wide range of sputtering conditions. The intrinsic film stress of conducting Mo1−xOx is compressive. Such M1−xOx films were shown by backscattering spectrometry to be excellent diffusion barriers between Al and Si up to 600 °C annealing for 30 min.

Chromium silicide formation by ion mixing

The formation of CrSi_2 by ion mixing was studied as a function of temperature, silicide thickness and irradiated interface. Samples were prepared by annealing evaporated couples of Cr on Si and Si on Cr at 450°C for short times to form Si/CrSi_2/Cr sandwiches. Xenon beams with energies up to 300 keV and fluences up to 8 X 10^15 cm^(-2) were used for mixing at temperatures between 20 and 300°C. Penetrating only the Cr/CrSi_2 interface at temperatures above 150°C induces further growth of the silicide as a uniform stoichiometric layer. The growth rate does not depend on the thickness of the initially formed silicide at least up to a thickness of 150 nm. The amount of growth depends linearly on the density of energy deposited at the interface. The growth is temperature dependent with an apparent activation energy of 0.2 eV. Irradiating only through the Si/CrSi_2 interface does not induce silicide growth. We conclude that the formation of CrSi_2 by ion beam mixing is an interface-limited process and that the limiting reaction occurs at the Cr/CrSi_2 interface.

Microstructure of reactively sputtered oxide diffusion barriers

Molybdenum oxide (Mo1-xOx) and ruthenium oxide (RuO2) films were prepared by rf reactive sputtering of Mo or Ru targets in an O2/Ar plasma. Both films exhibit metallic conductivities. The influence of the deposition parameters on the phase that forms and on the microstructure of Mo1-xOx and RuO2 films is reported. A phase transformation is observed in Mo1-xOx films subjected to heat treatment. The diffusion barrier performance of Mo1-xOx and RuO2 layers interposed between Al and Si is compared.

Amorphous NiNW film as a diffusion barrier between aluminum and silicon

The influence of nitrogen on the diffusion barrier properties of amorphous NiW films was studied. Nitrogen was introduced into the amorphous NiW film by co-sputtering nickel and tungsten in a premixed gas mixture of 90% Ar and 10% N2, resulting in the formation of amorphous Ni30N21W49 film. X-ray analysis indicates a detectable crystallization of the amorphous film after 30 min annealing in vacuum at 600°C, accompanied by the formation of W2N, but backscattering spectrometry (BS) reveals a reaction with silicon only at about 725°C. The Schottky barrier height of this amorphous film on n-Si is stable for 30 min annealing up to at least 550°C. With an aluminum overlayer, BS indicates that an amorphous Ni30N21W49 film effectively prevents the metallurgical interaction between aluminum and silicon for 30 min up to 600°C. The Schottky barrier height of that contact configuration is also stable up to at least 550°C, suggesting that amorphous NiNW films have attractive features as diffusion barriers.

Microstructure of RuO2 layer as diffusion barrier between Al and Si substrate

Abstract The microstructure of samples consisting of a 40 nm thick RuO 2 film reactively sputtered on a Si 〈 111 〉 substrate and covered with 20 nm of Al (〈 Si 〉/RuO 2 / Al) is investigated by high-resolution cross-sectional electron microscopy. The depth distributions of elements are studied by Rutherford backscattering spectrometry and electron probe microanalysis. In the as-deposited sample, the RuO 2 /Al interface is sharp, but a thin (3 nm) SiO 2 layer is observed at the 〈 Si 〉/RuO 2 interface. After annealing at temperatures ranging from 450 to 700°C for 1–6 h, that layer remains unchanged, but a crystalline compound layer forms at the RuO 2 /Al interface. No diffusion of Si and Al into RuO 2 is detectable. The possible mechanisms for the barrier characteristics are discussed. We believe that the presence of the thin SiO 2 layer and the formation of an additional compound layer is intimately related to the good barrier performance of RuO 2 .

Amorphous W-Zr films as diffusion barriers between Al and Si

Cosputtered W70Zr30 and W40Zr60 films are investigated as diffusion barriers between Aq and Si. W-Zr alloys of both compositions were determined by x-ray diffraction to crystallize at 900/sup 0/C on A1/sub 2/O/sub 3/ substrates. On Si the W-Zr alloy reacts with the substrate above 700/sup 0/C, forming a uniform, polycrystalline layer of W and Zr silicides. Despite the high crystallization temperatures, an A1 overlayer interacts with W-Zr and the Si substrate at approx. 500/sup 0/C. MeV He-backscattering spectrometry, SEM, and EDAX indicate that this reaction is laterally nonuniform with the formation of deep pits penetrating into the Si substrate. The authors believe this to be a consequence of fractures in the W-Zr layer induced by reaction with A1. Electrical measurements on shallow junction diodes with /W-Zr/Al contacts show that the device junctions were thermally stable after a 30 min annealing at 450/sup 0/C but were all shorted after heat treatments at 500/sup 0/C or above.