Characterization of WF6/N2/H2 plasma enhanced chemical vapor deposited WxN films as barriers for Cu metallization

Abstract

Low temperature plasma-assisted chemical vapor deposition of tantalum nitride from tantalum pentabromide for copper metallization W x N is a promising candidate as a barrier material for Cu metallization. In this work, we report the characterization of W x N films deposited by plasma enhanced chemical vapor deposition using WF 6 /N 2 /H 2 gas mixtures. The films are analyzed by Rutherford backscattering spectrometry, Auger electron spectroscopy, atomic force microscopy, x-ray diffraction, transmission electron microscopy, differential scanning calorimetry, and sheet resistance combined with thickness measurements. The diffusion barrier properties are studied by using Cu-gate metal-oxidesemiconductor capacitors and subjecting to either bias-temperature stress ͑BTS͒ of 2 MV/cm at 250°C or thermal anneal up to 700°C, and evaluated by capacitance-voltage measurement. It is found that the as-deposited films with W/N ratios from 2-19 have an ''amorphous-like'' nature.Study of the initial growth shows that the W x N films form by nucleation and grow through coalescence, and the films exhibit a granular structure. The transformation from the amorphous-like structure to crystalline phase͑s͒ depends on the film stoichiometry. For the W/Nϳ2 films, there are two transformations starting at 497 and 578°C ͑at a heating rate of 10°C/min͒, corresponding to the formation of the W 2 N phase and to the further growth of the phase together with the formation of a small amount of ␣-W, respectively. The corresponding activation energies are 2.20 and 2.98 eV. For the W/Nϳ3 films, there is only one transformation ͑to the W 2 Nϩ␣-W͒ starting at 601°C and with an activation energy of 2.94 eV. The resistivity is found to be insensitive to the film stoichiometry when the film has an amorphous-like nature, but shows a larger decrease for W richer films upon annealing at 500°C. Moreover, for W/Nϳ2 and 3 films, the resistivities are largely determined by the film thickness, from about 200 ⍀ cm for the 120 nm films to 310-350 ⍀ cm for the 10 nm films. BTS results reveal that 10 nm of the W/Nϳ3 barrier shows no sign of degradation at least up to 105 h. By contrast, it is found that the initial barrier degradation occurs by annealing at 600°C and above. This is probably due to the formation of ␣-W grains in the W x N barrier at these temperatures.

Zirconium-Doped Tantalum Oxide Gate Dielectric Films Integrated with Molybdenum, Molybdenum Nitride, and Tungsten Nitride Gate Electrodes

“…The resistivity of the WN film is insensitive to the N content if it is amorphous, but the resistivity increases drastically with the N content when it is in crystal form. 19 However, the WN films in Fig. 2c, either as-deposited or after annealing, were polycrystalline and their resistivities were dependent on the N concentration in the film.…”

“…16 It was also reported that WN could be deposited as an amorphous-like film by plasma-enhanced chemical vapor deposition ͑PECVD͒ if an appropriate W/N ratio was obtained, i.e., 2-19. 19 However, in this study, the as-deposited WN film has a cubic crystal structure, as shown in the inset of Fig. 2c.…”

Effect of NH3 thermal treatment on an atomic layer deposited on tungsten films and formation of W–B–N

“…This indicates that the film has an amorphous structure both as deposited or post 700°C annealed. 2,29 This suggests that the film formation mechanism of ALD is different from that of CVD. 16 The spectra from other annealing temperatures, 400-600°C, have identical XRD spectra.…”

Growth of Ternary WCxNy Thin Films from a Single‐source Precursor, W(NtBu)2(NEt2)2

“…Tungsten nitride films have been proposed to be a good barrier layer to prevent inter-diffusion of Al or Cu and Si during subsequent high-temperature annealing processes. [1][2][3][4] Alternatively, chemical nitridation of tungsten metal and reduction of WCl 6 , WF 6 , and WO 3 by NH 3 at high temperatures have been employed. [5][6] Unlike many other transition metal nitrides, thin films of tungsten nitride are rarely grown by metal-organic chemical vapor deposition (MOCVD).…”