Ivo Raaijmakers

Reactively sputtered TiN as a diffusion barrier between Cu and Si

The properties of 100‐nm‐thick Ti55N45 and Ti45N55 films as diffusion barriers between silicon substrates and thin Cu films were studied by sheet resistance measurements, Rutherford backscattering spectrometry, Auger electron spectroscopy, secondary‐ion mass spectrometry, transmission electron microscopy, scanning electron microscopy, energy dispersive x‐ray spectroscopy, x‐ray diffractometry, and diode leakage current measurements. For unpatterned Si/titanium nitride/Cu samples, all the layers were intact and there was no indication of interdiffusion by conventional depth profiling techniques up to 700 °C for Ti55N45 and 900 °C for Ti45N55 after 30 s rapid thermal anneal in N2, respectively. Leakage current measurements did not show deterioration of diode junction (with junction depth of 0.25 and 0.30 μm) up to 650 °C for Ti55N45 and 800 °C for Ti45N55. The improvement in failure temperature of the N‐rich Ti45N55 diffusion barrier is a result of the lower defect density and a more stable feature furnishe...

The formation of an amorphous silicide by thermal reaction of sputter‐deposited Ti and Si layers

The initial reaction in amorphous Si‐Ti‐amorphous Si trilayers was investigated with Auger electron spectroscopy, transmission electron microscopy, and x‐ray diffraction. It was clearly demonstrated that at temperatures not exceeding 450 °C an amorphous Ti‐Si alloy is formed. At temperatures of 500 °C and higher, crystalline TiSi2 with the ZrSi2 (C49) structure was found. The growth kinetics of the amorphous silicide could not be described by a simple diffusion controlled process. It was shown that at 400 °C the thickness of the amorphous silicide is limited to approximately 18 nm. Since it was found that the growth of the amorphous phase is accompanied by excessive Kirkendall void formation, it is proposed that these voids eventually suppress the growth of amorphous silicide. The composition of the amorphous phase was determined to be between TiSi0.9 and TiSi1.2, i.e., close to the composition of the monosilicide.

Influence of grain size on the transformation temperature of C49 TiSi2 to C54 TiSi2

Titanium disilicide exists in two possible crystallographic structures: the C49 (ZrSi2) structure and the C54 structure. At low annealing temperatures (400–650 °C), the C49 TiSi2 phase is formed. It transforms to the C54 phase at annealing temperatures between 650–800 °C. The transformation temperature (Ttr), however, appears to be influenced by the microstructure of the C49 phase. This is concluded from the observed difference in Ttr for TiSi2 thin films with varying average grain sizes.

A comparison of the reaction of titanium with amorphous and monocrystalline silicon

This paper describes investigations into the reactions occurring between Ti and monocrystalline Si (x‐Si) or sputter‐deposited amorphous Si (a‐Si). Samples were structured so as to have the same Ti layer in contact with both crystalline and amorphous Si, and were thus ideally suited to compare the reactions in the same sample. Reactions were mainly investigated with cross‐sectional transmission electron microscopy, but also with chemical characterization techniques such as Rutherford backscattering and Auger electron spectroscopy. We demonstrated that the reaction between Ti and x‐Si or a‐Si proceeded very similarly at low temperatures (≤450 °C). In both cases an amorphous silicide layer was observed to grow. Reaction rates were found to be nearly equal, even if some impurities were present on the x‐Si surface prior to Ti deposition. One important difference was noted between the reactions, however. The reaction with a‐Si was associated with Kirkendall void formation, while these voids were absent in the ...

Nucleation and growth of titanium silicide studied by in situ annealing in a transmission electron microscope

We have studied the crystallization of sputter‐deposited amorphous Ti‐Si alloy thin films of different compositions. A versatile means of discriminating between phenomena occurring in the nucleation and subsequent growth stages was offered by in situ annealing in a transmission electron microscope. Nucleation of TiSi2 with the ZrSi2 structure was observed for all alloys studied (Ti:Si=1:2 to Ti:Si=1:3). The activation energy for nucleation was independent of composition. TiSi2 crystallites appeared to possess a rather high density of stacking faults, predominantly concentrated in the center of the crystallites. The character of these stacking faults was analyzed. The growth of TiSi2 was anisotropic in amorphous alloys up to a composition of Ti:Si=1:2.5; more silicon‐rich alloys yielded isotropic growth. The anisotropy in growth rate, and the resulting morphology of the crystallites were related to the crystal structure. The crystallization of the amorphous alloy with the composition Ti:Si=1:2 proceeded vi...

Low temperature MOCVD of advanced barrier layers for the microelectronics industry

Abstract Metalorganic chemical vapor deposition (MOCVD) of TiN thin films at low temperatures and low pressures using tetrakis(diethylamino) titanium (TDEAT) and NH3 is described. Conformal TiN films, having layer resistivities as low as 200 μΩ·cm, densities close to those of sputtered films, and low impurity contents can be obtained with this chemistry. These TiN films can be applied as adhesion layers for chemical-vapor-deposited W, or as barrier layers between Si and Al. Rapid thermal anneal (RTA) of MOCVD-TiN and physical-vapor-deposited (PVD) Ti/MOCVD-TiN bi-layers is described. RTA at temperatures of 600 to 800°C is shown to lead to formation of a TiSi2/TiN bi-layer on Si substrates, just as with completely sputter-deposited Ti/TiN bi-layers. Low contact resistance to p+-Si is demonstrated with PVD-Ti/MOCVD-TiN bi-layers. It is demonstrated that thermal decomposition of TDEAT (i.e. without NH3 as the coreactant) leads to films having better conformality. But, the resistivity and impurity content of the material produced by thermal decomposition of TDEAT is too high for them to be good candidates for barrier and adhesion layers.

Energy distribution of negative O− and OH− ions emitted from YBaCuO and iron garnet targets by dc and rf magnetron sputtering

Energy‐dispersive mass spectrometry has been used to analyze the energy distribution of O− and OH− species ejected from YBaCuO and iron‐garnet targets by Ar+, Kr+, and Xe+ bombardment in H2‐ and in O2‐doped dc and rf magnetron plasmas at 0.05–4.2 Pa pressure. The orifice of the plasma monitor was at 70 mm from the erosion groove underneath the plasma ring. The energy spectra of O− and OH− ions are found to exhibit two major peaks: a sharp one at typically 20 eV termed A and a sharp (dc case) or broad (rf case) peak termed B at higher energies. Peak‐A ions may be formed near the edge of the cathode sheath by electron attachment to sputtered neutral oxygen atoms accelerated in the remaining potential gradient of the sheath. Peak‐B ions are shown to be accelerated from the target surface to kinetic energies given by the potential gradient across the cathode sheath. In the case of rf magnetron plasmas the total flux of O− and OH− ions associated with the peak B steeply increases with pressure up to ∼0.6 Pa fo...

TiSi2 strap formation by Ti–amorphous‐Si reaction

This report describes the formation of a TiSi2 strap in combination with the self‐aligned titanium silicide (salicide) technology. The TiSi2 strap is formed by reaction of amorphous silicon (a‐Si) with the underlying Ti layer. It was determined that sputter deposition of the Ti and a‐Si had to be done in one deposition cycle, otherwise interface contamination would prevent the Ti–a‐Si reaction and give rise to extensive silicon diffusion from the active areas. Since TiSi2 straps are formed over diffusion areas as well as over oxide surfaces, the influence of the substrate on the Ti/a‐Si reaction was determined. It was found that for straps deposited on oxide substrate the properties of the silicide layer formed were determined by the Ti/a‐Si atomic ratio. A titanium‐rich strap resulted in a high‐resistivity silicide layer due to TiSi compound formation. Stoichiometric straps formed low‐resistivity TiSi2 layers with a thin‐TiN top layer and silicon‐rich straps also resulted in a low‐resistivity TiSi2 layer...

Microstructure and barrier properties of reactively sputtered Ti-W nitride

The materials properties of Ti-W, sputter deposited in pure Ar, and Ti-W-N deposited in Ar-N2 mixtures containing up to 50% N2 have been reported. Films with N contents between 0 and 45 at.% have been produced. The W/Ti ratio in the nitrided alloy has been varied from that corresponding to pure W, to that of pure Ti. The metastable ter-nary phase diagram Ti-W-N was composed from data presented in this paper and lit-erature data. For low N contents (up to about 20 at.%) the film consists of a metastable solid solution of N in bcc Ti-W. For high N contents (from about 35 to 45 at.%). We observed the film to consist of an fcc ternary Ti-W nitride. The barrier performance was evaluated in an Al-Cu metallization to TiSi2/Si contacts by Auger electron spectroscopy and junction leakage measurements. In clean sputtering environments, we need to cre-ate the ternary nitride to form a reliable barrier. Adding some N to “stuff” the grain boundaries of the bcc phase, or contaminating the Ti-W surface by an exposure to at-mosphere, was found to be less effective in producing a reliable barrier.

Crystallization of amorphous Ti‐Si alloy thin films: Microstructure and resistivity

Cosputtered amorphous thin films consisting of Ti and Si were crystallized to the C49 TiSi2 phase at temperatures of about 390 °C. Prolonged annealing of the crystalline C49 TiSi2 phase at higher temperatures resulted in a gradual decrease in resistivity. We investigated the changes in microstructure which were associated with this slow decrease of the resistivity of the C49 phase. In situ resistivity and Hall‐effect measurements, electron microscopy, and x‐ray diffraction were used. It was demonstrated that the slow decrease in resistivity of the crystalline C49 phase was associated with a decreasing stacking fault density (typically 2×106 cm−1) and a decreasing density of point defects. The presence of point defects was found to be related to stoichiometry deviations. Polymorphous crystallization of a slightly Si‐rich sample was found to result in a supersaturated solid solution of Si in C49 TiSi2. It was proposed that the phase field of the C49 phase is significantly wider than that of the equilibrium ...