Tungsten Nitride Films Research Articles

Atomic Layer Deposition of W1.5N Barrier Films for Cu Metallization: Process and Characterization

An atomic layer deposition process to grow tungsten nitride films was established at 350°C with a pulse sequence of . The film composition was determined with Rutherford backscattering as , being a mixture of WN and phases. The growth rate was per cycle (monolayer of or WN). The films with a thickness of 16 nm showed root-mean-square roughness as low as 0.43-0.76 nm. The resistivity of the films was stable after 50 cycles at a value of . Results of four-point probe sheet resistance measurements at elevated temperature demonstrated that our films are nonreactive with Cu at least up to 500°C. Results of I-V measurements of diodes before and after heat-treatment in ambient at 400°C for 30 min confirmed excellent diffusion barrier properties of the films.

Tungsten Allylimido Complexes Cl4(RCN)W(NC3H5) as Single-Source CVD Precursors for WNxCy Thin Films. Correlation of Precursor Fragmentation to Film Properties

A mixture of the tungsten allylimido complexes Cl(4)(RCN)W(NC(3)H(5)) (3a, R = CH(3) and 3b, R = Ph) was tested as a single-source precursor for growth of tungsten nitride (WN(x)) or carbonitride (WN(x)C(y)) thin films. Films deposited from 3a,b below 550 degrees C contained amorphous beta-WN(x)C(y), while those deposited at higher temperatures were polycrystalline. Film growth rates from 3a,b ranged from 5 to 10 A/min over a temperature range of 450-650 degrees C, and the apparent activation energy for film growth was 0.15 eV. A plot of the E(a) values for deposition from Cl(4)(RCN)W(NR') [R' = Ph, (i)Pr, allyl] against the N-C imido bond strengths for the analogous amines R'NH(2) is linear, implicating cleavage of the N-C bond as the rate-determining step in film growth. The correlation of mass spectral fragmentation patterns for Cl(4)(RCN)W(NR') with film properties such as nitrogen content supports the significance of facile N-C bond cleavage in film growth.

Effects of nitrogen concentration on microstructures of WN X films synthesized by cathodic arc method

Tungsten nitride films (WN X ) were deposited by the cathodic arc method in argon–nitrogen gas mixture changing nitrogen partial pressures. When the N 2/Ar+N 2 ratios were less than 0.1, the films showed α-W with hexagonal structures. On the other hand, the crystal structure changed to cubic W 2N with the ratios between 0.1 and 0.35. When the ratios exceeded 0.35, the films were hexagonal WN. The micro-hardness of α-W, cubic W 2N and hexagonal WN phase showed approximately 13, 24 and 28 GPa, respectively. The surface roughness of WN X films were smooth with approximately 10 nm and, correspondingly, the grains are all small with 10–50 nm in size. In this paper, the changes in crystal structures of WN X were investigated as a function of nitrogen flow and their mechanical properties were studied.

MOCVD of Tungsten Nitride Films Using W ( CO ) 6 and NH 3 for Cu Diffusion Barrier

Tungsten nitride films were deposited by metalorganic chemical vapor deposition (MOCVD) using and in the growth temperature range from 250 to 500°C. The growth rate was 0.3∼193 nm/min. The film resisitivity decreased from 950 to 590 μΩ cm, and the impurity concentration of C and O both decreased from 10 to below 5% upon the temperature rise. X-ray diffraction (XRD) analysis showed that the film structure changed from an amorphous-like structure to a phase dominant polycrystalline structure with the temperature rise. Sheet resistance measurements and XRD analysis showed that the barrier of a 15 nm thickness blocked the Cu diffusion efficiently up to 600°C for 1 h annealing. © 2004 The Electrochemical Society. All rights reserved.

Reactive pulsed laser deposition of thin molybdenum- and tungsten-nitride films

In this work reactive pulsed laser deposition of molybdenum- and tungsten-nitride thin films is investigated. Metallic targets were ablated in low-pressure (1, 10 and 100 Pa) nitrogen atmosphere by KrF excimer laser pulses (fluence ∼6.5 J/cm2). Films were deposited on silicon wafers heated to ∼25, 250 and 500 °C. The characteristics of the films strongly depend on the N2 pressure. By increasing N2 pressure, the nitrogen content increases in the films, which leads to a monotonous increase of the electrical resistivity. Deposition rate decreases at 100 Pa as indicated by Rutherford backscattering spectrometry. At this pressure, hardness of the films significantly decreases also, as shown by microhardness measurements. X-ray diffractometry shows that films crystallinity is improved by increasing the substrate temperature. In addition, atomic force microscopy (AFM) and scanning electron microscopy (SEM) were applied for visualising the film surface.

Ultra thin tungsten nitride film growth on dielectric surfaces

Ultra thin tungsten nitride film growth by chemical vapor deposition was explored on thermally grown SiO2. In situ X-ray photoelectron spectroscopy (XPS) and low energy ion scattering spectroscopy are used to establish the minimum equivalent film thickness needed to fully cover the dielectric substrate. Three-dimensional tungsten nitride growth is suggested in the initial nucleation stage by the non-linear relationship of substrate ion scattering features and the XPS-based nitride film thickness. Both higher deposition temperature and predeposition of a plasma-enhanced chemical vapor deposited tungsten nitride seed layer significantly lowers the film thickness needed to fully cover the substrate.

Ultra thin tungsten nitride film growth on dielectric surfaces

Ultra thin tungsten nitride film growth by chemical vapor deposition was explored on thermally grown SiO 2. In situ X-ray photoelectron spectroscopy (XPS) and low energy ion scattering spectroscopy are used to establish the minimum equivalent film thickness needed to fully cover the dielectric substrate. Three-dimensional tungsten nitride growth is suggested in the initial nucleation stage by the non-linear relationship of substrate ion scattering features and the XPS-based nitride film thickness. Both higher deposition temperature and predeposition of a plasma-enhanced chemical vapor deposited tungsten nitride seed layer significantly lowers the film thickness needed to fully cover the substrate.

Bias induced structural changes in tungsten nitride films deposited by unbalanced magnetron sputtering

Tungsten nitride thin films were deposited using unbalanced magnetron sputtering system. The effect of the ratio of nitrogen partial pressure to the total pressure during deposition and the substrate bias on the tungsten nitride formation has been studied. The glow discharge characteristics of the process have been studied in order to determine the deposition parameters. It is observed that nitrogen partial pressure ratio 0.4 and cathode current of 200 mA favors the formation of the W 2N films. The variation in the electrical resistivity of the films has been studied as a function of nitrogen partial pressure and substrates bias. A minimum resistivity of 406 μΩ cm is observed for tungsten nitride films prepared at −70 V bias. X-ray diffraction analysis of the films indicate the formation of β-W 2N (1 0 0) phase at the partial pressure ratio of 0.4. The effects of the bias on the structural properties were also studied at this condition. The internal stress and the particle size of the deposited films were calculated and it was found that there is no appreciable change with the applied bias voltage.

Fabry–Pérot structures for attenuated phase-shifting mask application in ArF and F2 lithography

We demonstrate a structure for an attenuated phase-shifting mask (APSM) which is based on a three-layer Fabry–Pérot structure for ArF (193 nm) and F2 (157 nm) excimer laser based lithographies. The APSM structure is composed of a metal/dielectric/metal stack. The optical characteristics of the Fabry–Pérot structure meet the following requirements: 180° phase shift, transmittance in the range of 4%–15%, reflectance of less than 10% at the exposure wavelength, and high inspection contrast at the inspection wavelength. Common dielectric and metal materials, such as chromium, tungsten, amorphous silicon, silicon dioxide, aluminum oxide, and aluminum nitride films, can be used to construct the Fabry–Pérot structure. The top metal layer can also prevent charge accumulation during electron-beam writing.

Highly Conformal Thin Films of Tungsten Nitride Prepared by Atomic Layer Deposition from a Novel Precursor

Highly uniform, smooth, and conformal coatings of tungsten nitride were synthesized by atomic layer deposition (ALD) from vapors of a novel precursor, bis(tert-butylimido)-bis(dimethylamido)tungsten, (tBuN)2(Me2N)2W, and ammonia at low substrate temperatures (250−350 °C). This tungsten precursor is a low-viscosity, noncorrosive liquid with sufficient volatility at room temperature to be a vapor source for ALD. These vapors were alternately pulsed into a heated reactor, yielding up to 0.1 nm of tungsten nitride film for every cycle, with no initial delay or induction period. The films were uniform in thickness along the 20-cm length of the deposition zone, as determined by scanning electron microscopy. Successful depositions were carried out on all substrates tested, including silicon, glass, quartz, glassy carbon, stainless steel, aluminum, gold, and copper. The films are shiny, silver-colored, and electrically conducting. All of the films showed good adhesion to the substrates, were acid-resistant, and d...

Crystallization of Reactively Sputtered Amorphous Tungsten Nitride Film

An amorphous tungsten nitride film with a 10–40 at.% nitrogen concentration was produced by reactive sputtering. The amorphous W67N33 film could be fully crystallized into a pure α-tungsten phase with equaixed grains, which had a similar resistivity to that of the sputtered pure tungsten film, by rapid thermal annealing (RTA) for 60 s at 1273 K. It was also found that the nitrogen content in the tungsten nitride films decreased significantly. This decomposition of tungsten nitride at least restrained the formation of interface reaction products such as tungsten silicide without an additional diffusion barrier layer. The RTA process of the amorphous tungsten nitrides showed the possibility of the formation of the low-resistivity pure tungsten film without a diffusion barrier.

Tungsten nitride films grown via pulsed laser deposition studied in situ by electron spectroscopies

Tungsten nitride (WNx) films were grown on silicon and glass slide substrates by laser ablating a tungsten target in molecular nitrogen ambient. By in situ Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS), the films density, elemental composition and chemical state were determined. Ex situ, the films were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Also, the transmittance and resistivity of the film on glass substrates were determined. The results show that the reaction of tungsten and nitrogen is effective; the nitrogen is integrated in the tungsten matrix changing gradually the electronic configuration, chemical states and film properties. Since with this preparation method the obtained films are of high quality, low resistivity and dense, this makes attractive to growth tungsten nitride films for technological applications.

Diffusion Barrier Deposition on a Copper Surface by Atomic Layer Deposition

Diffusion barrier materials, TiN and WN, were deposited by atomic layer deposition (ALD). The chlorine concentration of the TiN film was as low as 1.2 at.-%, and resistivity was below 200 μΩ cm. Ultra high aspect ratio (AR=85) trenches were used to assess step coverage. Tungsten nitride film, deposited from WF 6 and ammonia, was found to have high resistivity, although the residue content was low. The barrier deposition compatibility was studied using the copper surface exposed on the bottom of vias in the copper dual-damascene structure. The deposition on copper of both TiN and WN was found to be very challenging.

Effect of dc bias on the compositional ratio of WN X thin films prepared by rf-dc coupled magnetron sputtering

The effect of the dc bias on the compositional ratio, resistivity, and deposition rate for tungsten nitride (WN X ) films prepared by rf-dc coupled magnetron sputtering have been investigated in detail. The value of the film compositional ratio (N/W) is significantly decreased from 0.8 to 0.2 with increasing the target dc bias voltage. The increase of the target dc bias voltage from −100 to −500 V results in a dramatical decrease in the resistivity of WN X films. It is shown that the N/W ratio and the resistivity of WN X thin films deposited at the target dc bias voltage of −200 V are about 0.5 and 370 μΩ cm, respectively.

Structural properties and nitrogen-loss characteristics in sputtered tungsten nitride films

A combination of X-ray photoelectron spectroscopy (XPS), parallel electron energy-loss spectroscopy (PEELS), X-ray diffraction (XRD), transmission electron microscopy (TEM) and transmission electron diffraction (TED) were used to investigate structural properties and nitrogen-loss characteristics of thin WN x films prepared by reactive magnetron sputtering of tungsten in an Ar–N 2 gas mixture. XRD θ−2θ scans combined with plan-view and cross-sectional TEM showed that the as-deposited WN x films were amorphous in structure . Annealing of the as-deposited films at 600°C or above resulted in crystallization of the amorphous phases, forming either a two-phase structure consisting of W 2N and b.c.c. W or a single-phase structure of W 2N, which was related to the initial nitrogen concentration in the films. The 150-nm thick crystalline films near a stoichiometry of W 2N had a columnar microstructure with an average column width of 15–20 nm near the film surface, whereas the column grains were larger for substoichiometric films. Thermal stability and nitrogen-loss characteristics of nitride films were also studied by in situ annealing in the TEM and PEELS system. The results indicate that between 600 and 800°C the W 2N phase was stable. Nitrogen in the film started to evaporate to vacuum at approximately 820°C and was fully released after 900°C annealing.

Composition, residual stress, and structural properties of thin tungsten nitride films deposited by reactive magnetron sputtering

Thin tungsten nitride (WNx) films were produced by reactive dc magnetron sputtering of tungsten in an Ar–N2 gas mixture. The effects of the variation of nitrogen partial pressure on the composition, residual stress, and structural properties of these films as well as the influence of postdeposition annealing have been studied. The films were analyzed in situ by a cantilever beam technique, and ex situ by x-ray photoelectron spectroscopy, electron energy-loss spectroscopy, x-ray diffraction, and transmission electron microscopy (TEM). It was found that at N concentrations below 8 at. %, the films (typical 150 nm in thickness) were essentially bcc α-W. An amorphous phase was observed in the range of about 12–28 at. % N. When N concentrations reached ∼32 at. % or above, a single-phase structure of W2N was formed. Annealing of the as-deposited films resulted in crystallization of the amorphous or an improved crystallinity of the W2N structure, which was related to the N concentration. Stresses of all W and WNx films were compressive. As the N concentration was increased, the stress decreased and reached its lowest value for amorphous samples near 20 at. % N. Past this point, the compression of films rose again. These results can be ascribed to structural changes induced by the pressure-dependent variation in the average energy of particles bombarding the film during deposition. Cross-sectional TEM studies showed that all crystalline WNx films had columnar microstructures. The average column width near stoichiometry of W2N was ∼20±5 nm near the film surface.

Atomically controlled growth of tungsten and tungsten nitride using sequential surface reactions

Thin films of tungsten (W) and tungsten nitride (W 2N) were grown with atomic layer control using sequential surface reactions. Tungsten atomic layer deposition was accomplished by separating the reaction WF 6+Si 2H 6→W+2SiHF 3+2H 2 into two half-reactions. The tungsten nitride atomic layer growth was performed by dividing the reaction 2WF 6+NH 3→W 2N+3HF+9/2F 2 into two half-reactions. Successive exposure to WF 6 and Si 2H 6 (NH 3) in an ABAB… reaction sequence produced W (W 2N) deposition at substrate temperatures between 425–600 K (600–800 K). The W deposition rate was 2.5 Å/AB cycle for WF 6 and Si 2H 6 reactant exposures >800 and 3000 L, respectively. The W 2N deposition rate was also 2.5 Å/AB cycle for WF 6 and NH 3 reactant exposures >3000 and 10,000 L, respectively. Atomic force micrographs of the deposited films on Si(100) were remarkably flat indicating smooth deposition. X-ray diffraction investigations revealed that the deposited tungsten and tungsten nitride films were either amorphous or composed of very small crystalline grains. X-ray photoelectron spectroscopy demonstrated that the films contained very low impurity concentrations. The results for tungsten represent the first demonstration of atomic layer deposition (ALD) of smooth single-element films using sequential surface reactions.

Effect of oxygen on residual stress and structural properties of tungsten nitride films grown by reactive magnetron sputtering

Thin films of W–O–N were produced by reactive d.c. magnetron sputtering of tungsten in an Ar–N 2–O 2 gas mixture. The effects of oxygen incorporation on the residual stress and structural properties of these films as well as the influence of post-deposition annealing have been studied. The films were analyzed in situ by a cantilever beam technique, and ex situ by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and electron energy-loss spectroscopy (EELS). It was found that the stoichiometric W 2N films deposited under oxygen-free conditions had a high compressive stress of 1.45 GPa. The compressive stress in W–O–N films decreased significantly with an increase in the oxygen concentration and became slightly tensile for films near 10–15 at.% oxygen. These results can be ascribed to the decrease in the lattice parameter caused by incorporating small oxygen atoms in the lattice sites and the development of an amorphous network in the W–O–N films as the incorporation of oxygen was increased. By high temperature annealing the structural conversion from W 2N to W in oxygen-free films was observed using XRD and the microstructure evolution after conversion was demonstrated using cross-sectional TEM. The effect of oxygen in stabilizing the W 2N structure was also elucidated and explained on the basis of structural and thermodynamic stability.

Effect of deposition conditions on internal stresses and microstructure of reactively sputtered tungsten nitride films

A combined investigation of internal stress generation by in situ substrate curvature measurements during the growth of tungsten nitride (WN x ) thin films and of structural properties by ex situ X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and electron energy-loss spectroscopy (EELS) is reported. It was found that the properties of the deposited films not only depended on the nitrogen partial pressure in Ar–N 2 gas mixtures but also on the total sputtering-gas pressure. The stress of the films was strongly related to their microstructure, which depended mainly on the incorporation of nitrogen in the films. Annealing of as-deposited films at 600°C or above resulted in crystallization of the amorphous phases, forming either a two-phase structure consisting of W 2N and b.c.c. W or a single-phase structure of W 2N, which was related to the initial nitrogen concentration ( C N) in the films. Cross-sectional TEM studies showed that an average column width for 150-nm-thick films near stoichiometry of W 2N was ∼15 nm, whereas the column grains were larger with decreasing C N. XPS results revealed that W 2N had an ionic bonding character, W δ+–N δ−. It was also found that once the W 2N phase was formed, the density, microstructure and bonding feature were similar and insensitive to the total sputtering-gas pressure used in this study.

Atomic Layer Deposition of Tungsten Nitride Films Using Sequential Surface Reactions

Tungsten nitride films were deposited with atomic layer control using sequential surface reactions. The tungsten nitride film growth was accomplished by separating the binary reaction into two half‐reactions. Successive application of the and half‐reactions in an ABAB… sequence produced tungsten nitride deposition at substrate temperatures between 600 and 800 K. Transmission Fourier transform infrared (FTIR) spectroscopy monitored the coverage of and surface species on high surface area particles during the and half‐reactions. The FTIR spectroscopic results demonstrated that the and half‐reactions were complete and self‐limiting at temperature ≥600 K. In situ spectroscopic ellipsometry monitored the film growth on Si(100) substrates vs. temperature and reactant exposure. A tungsten nitride deposition rate of 2.55 Å/AB cycle was measured at 600–800 K for and reactant exposures ≥3000 L and 10,000 L, respectively. X‐ray photoelectron spectroscopy depth‐profiling experiments determined that the films had a stoichiometry with low C and O impurity concentrations. X‐ray diffraction investigations revealed that the tungsten nitride films were microcrystalline. Atomic force microscopy measurements of the deposited films observed remarkably flat surfaces indicating smooth film growth. These smooth tungsten nitride films deposited with atomic layer control should be useful as diffusion barriers for Cu on contact and via holes. © 2000 The Electrochemical Society. All rights reserved.