HfN Films Research Articles

A comparative study on the hardness, stress and surface free energy of HfN films grown by HIPIMS and direct-current magnetron sputtering

HfN films with rocksalt structure have been grown by high-power impulse magnetron sputtering (HIPIMS) with various duty cycles, in a comparison with direct-current magnetron sputtering (dcMS) process. Such two sputtering processes yield the quite close compositions. Increasing the duty cycle from 7.5 % to 9 % and 11 % in HIPIMS process, a compressive stress rises up from 1.5 to 1.9 and 2.1 GPa, which is much smaller than the value of 3.8 GPa from dcMS. The hardness of such low-stressed HfN films has been identified to be 25.5–25.9 GPa, which agrees well with the theoretical one of 22.5 GPa by the density functional theory without the consideration of stress. In addition, the surface free energy of 26.3–29.0 mJ/m2 has been determined in HfN films grown by HIPIMS, much lower than that of 31.5 mJ/m2 of the films grown by dcMS.

300 mm CMOS-compatible superconducting HfN and ZrN thin films for quantum applications

The rising interest in increased manufacturing maturity of quantum processing units is pushing the development of alternative superconducting materials for semiconductor fab process technology. However, these are often facing CMOS process incompatibility. In contrast to common CMOS materials, such as Al, TiN, and TaN, reports on the superconductivity of other suitable transition-metal nitrides are scarce, despite potential superiority. Here, we demonstrate fully CMOS-compatible fabrication of HfN and ZrN thin films on state-of-the-art 300 mm semiconductor process equipment, utilizing reactive DC magnetron sputtering on silicon wafers. Measurement of mechanical stress and surface roughness of the thin films demonstrates process compatibility. We investigated the materials phase and stoichiometry by structural analysis. The HfN and ZrN samples exhibit superconducting phase transitions with critical temperatures up to 5.84 and 7.32 K, critical fields of 1.73 and 6.40 T, and coherence lengths of 14 and 7 nm, respectively. A decrease in the critical temperature with decreasing film thickness indicates mesoscopic behavior due to geometric and grain-size limitations. The results promise a scalable application of HfN and ZrN in quantum computing and related fields.

Chemical Interaction of Hydrogen Radicals (H*) with Transition Metal Nitrides.

Transition metal nitrides (TMNs) are reported as protective coatings in reactive hydrogen environments. Although the permeation of H2 through TMN coatings is well reported, their reducibility in H* environments is less investigated. In this work, we categorize the interaction of H* with ambient exposed TiN, ZrN, HfN, VN, NbN, and TaN thin films at 700 °C into three classes. We find that in TiN and VN samples, H*-induced reduction was limited to the surface (≈ top 2 nm). Significant denitridation was observed in ZrN and HfN samples beneath the surface, along with an increase in the transition metal oxide (TMOx) fraction. Denitridation was observed in NbN and TaN samples as well, but the increase in the TMOx content was less than for ZrN and HfN. We propose a model in three steps: hydrogenation, formation of volatile species, and diffusion of subsurface atoms to the surface. We show that the interaction of H* with TiN, ZrN, HfN, VN, NbN, and TaN with partially oxidized surfaces can be explained using the preferred hydrogenation pathway (based on the work functions) and the thermodynamic driver for forming volatile species (NH3 and H2O; based on the change in Gibbs free energy).

Mechanical and Structural Behavior of HfN Thin Films Deposited by Direct Current and Mid-Frequency Magnetron Sputtering.

Nanocrystalline HfN thin films were deposited onto silicon substrates with direct current magnetron sputtering (dcMS) and mid-frequency magnetron sputtering (mfMS) by using hafnium metallic target with 3-inch diameter and 99.9% purity in argon/nitrogen atmosphere, under 4 different pulse frequencies and duty cycles. In order to evaluate the structural, morphological and mechanical properties, we used X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), nanoindentation tests. X-ray diffraction patterns show that films sputtered in dcMS mode have a mixed δ-HfN and HfN0.4 phases, whereas mfMS favor a single δ-HfN phase. mfMS leads to films with the higher mechanical hardness and smaller surface roughness than those of films deposited by dcMS. Hafnium nitride films with a single δ-HfN phase show the highest hardness values of 24.5 GPa while those of mixed δ-HfN and HfN0.4 phases show the lowest 18.3 GPa. In summary, the sputtering technique has a crucial role on the properties of the film and can be suitable used to adjust the structure and hardness of HfN films.

Mechanical and tribological behaviors of hard and tough TaxHf1−xN films with various Ta contents

The hardness and toughness of HfN films alloying with Ta element is crucial for their wear resistance when they are applied in the harsh environment. In this study, TaxHf1−xN (x = 0–1) thin films with various Ta contents were deposited on silicon wafer and TC4 alloy substrates by DC reactive magnetron sputtering, respectively. The relationship between structure, mechanical and tribological properties of TaxHf1−xN films was investigated. TaxHf1−xN films are presented as the solid solutions with B1-NaCl rock salt structure. As the content of tantalum increases, the grain size and residual compressive stress of TaxHf1−xN films increases firstly then decreases, while the preferred orientation transfers from (111) to (200) and then back to (111). The hardness and H/E increases initially and then decreases with the Ta contents, which is also consistent with the fracture toughness. When x is 0.58, TaxHf1−xN film shows the maximum hardness value (44 GPa), H/E (0.15), H3/E2 (1.02 GPa), fracture toughness (3.48 MPa·m1/2) and lower wear rate (5.6 × 10−6 mm3/Nm). It is found that the wear resistance of TaxHf1−xN films is directly related to the H/E and fracture toughness.

Tribological Properties Improvement of Mo-Alloyed HfN Films With a High H/E Ratio at Elevated Temperatures

Abstract In this study, the Mo-alloyed HfN films were prepared by DC-magnetron sputtering and studied their tribological properties at 25–600 °C under dry friction conditions. The relationship between H/E value and tribological properties at elevated temperature was illustrated. A single solid-solution phase was formed for all Hf-Mo-N films which with an FCC structure, and the H/E and H3/E2 values are increased. The film with x = 0.56 obtained a lower friction coefficient (0.4) and wear-rate (1.23 × 10−6 mm3/N m) at room temperature. At elevated temperature, this film maintained high structure stability, meanwhile, a dense and continuous oxide layer with lubrication was formed and tightly covered on the worn surface, that it obtained a lower coefficients of friction and better wear resistance.

Study of columnar growth, texture development and wettability of reactively sputter-deposited TiN, ZrN and HfN thin films at glancing angle incidence

In this work, TiN, ZrN and HfN thin films fabricated using glancing angle deposition (GLAD) technique are studied both experimentally and by numerical simulations. The films (~1 μm thickness) were deposited by reactive magnetron sputtering at 0.3 Pa and 300 °C on Si substrates inclined at α = 85° with respect to the target. The film morphology and crystal structure were characterized by scanning electron microscopy, atomic force microscopy and X-ray diffraction (XRD), including pole figure measurements. The wettability of these coatings was investigated using the sessile drop method with three different liquids. It is shown that TiN, ZrN and HfN films have a cubic, NaCl-type crystal structure with a [111] out-of-plane orientation and exhibit a biaxial texture. XRD pole figures reveal that the crystal habit of the grains consists of {100} facets constituting triangular-base pyramids. The films develop columnar microstructures, with typical column widths of ~100 nm. The tilt angle β of the columns is found to increase from 24.5, 31.5 to 34° for TiN, ZrN and HfN films, respectively. Atomistic computations of the growth of these nitrides at glancing angle using a kinetic Monte Carlo model reveal that the growth morphology and variation in column tilt angle is well reproduced by considering the difference in the angular distribution of the sputtered particles. This study also shows that GLAD films are hydrophilic comparatively to the same films deposited at near-normal incidence, and among the three nitrides, TiN is the more wettable coating.

Reactive sputtering for highly oriented HfN film growth on Si (100) substrate

Highly oriented cubic (100) HfN films were grown on Si (100) substrates by direct current magnetron reactive sputtering of a metallic Hf target in an Ar/N2 gas environment. The influence of N2 flow ratio on the (100) preferred orientation and crystallinity of the HfN films is investigated. X-ray diffraction shows that not only HfN but also orthorhombic HfSi2 forms in the sputtered films. Increasing the N2 flow ratio is unfavorable for the formation of HfSi2 while the deposition rate of HfN is decreased. X-ray diffraction and cross-sectional scanning transmission electron microscopy (STEM) reveal that epitaxial orthorhombic HfSi2 can form on the Si substrate, and (100) HfN is in epitaxy with the epitaxial HfSi2. As a result, a (100) oriented HfN film can grow on Si. The epitaxial relationships are shown to be HfN (100)[011¯] // HfSi2 (020)[001] // Si (100)[011¯] and HfN (100)[011¯] // HfSi2 (020)[100] // Si (100)[011¯]. Atomically resolved STEM images also show the bonding characteristics across the HfN/HfSi2 and HfSi2/Si interfaces.

Cu(111) preferential orientation on thin HfN film as a diffusion barrier

We examined the effect of barrier thickness on Cu grain orientation control. We demonstrate that 5 nm thick HfN films which showed excellent barrier properties in our previous study are applicable to the underlayer for Cu grain orientation control. The strong (111)-oriented Cu layer is enhanced by using the HfN barrier with a 5 nm thickness. The obtained results bring about the compatibility of the high performance barrier with a suitable underlayer to obtain the highly-oriented Cu layer. These results are also valid for the development of barrier or underlayer materials for use in Si-LSI and three-dimensional LSI technology.

Low temperature (Ts/Tm < 0.1) epitaxial growth of HfN/MgO(001) via reactive HiPIMS with metal-ion synchronized substrate bias

Low-temperature epitaxial growth of refractory transition-metal nitride thin films by means of physical vapor deposition has been a recurring theme in advanced thin-film technology for several years. In the present study, 150-nm-thick epitaxial HfN layers are grown on MgO(001) by reactive high-power impulse magnetron sputtering (HiPIMS) with no external substrate heating. Maximum film-growth temperatures Ts due to plasma heating range from 70 to 150 °C, corresponding to Ts/Tm = 0.10–0.12 (in which Tm is the HfN melting point in K). During HiPIMS, gas and sputtered metal-ion fluxes incident at the growing film surface are separated in time due to strong gas rarefaction and the transition to a metal-ion-dominated plasma. In the present experiments, a negative bias of 100 V is applied to the substrate, either continuously during the entire deposition or synchronized with the metal-rich portion of the ion flux. Two different sputtering-gas mixtures, Ar/N2 and Kr/N2, are employed in order to probe effects associated with the noble-gas mass and ionization potential. The combination of x-ray diffraction, high-resolution reciprocal-lattice maps, and high-resolution cross-sectional transmission electron microscopy analyses establishes that all HfN films have a cube-on-cube orientational relationship with the substrate, i.e., [001]HfN||[001]MgO and (100)HfN||(100)MgO. Layers grown with a continuous substrate bias, in either Ar/N2 or Kr/N2, exhibit a relatively high mosaicity and a high concentration of trapped inert gas. In distinct contrast, layers grown in Kr/N2 with the substrate bias synchronized to the metal-ion-rich portion of HiPIMS pulses have much lower mosaicity, no measurable inert-gas incorporation, and a hardness of 25.7 GPa, in good agreement with the results for epitaxial HfN(001) layers grown at Ts = 650 °C (Ts/Tm = 0.26). The room-temperature film resistivity is 70 μΩ cm, which is 3.2–10 times lower than reported values for polycrystalline-HfN layers grown at Ts = 400 °C.

Structure and mechanical properties of hafnium nitride films deposited by direct current, mid-frequency, and high-power impulse magnetron sputtering

The structural properties of hafnium nitride films are mainly influenced by the deposition conditions, which are affected by the sputtering technique. A suitable use of the different sputtering modes allows to control the structural development of the films and thus to adjust the profile of the properties. NaCl-type hafnium nitride films were deposited using direct current magnetron sputtering (dcMS), mid-frequency magnetron sputtering (mfMS), and high-power impulse magnetron sputtering (HiPIMS). dcMS produces films with a columnar microstructure, whereas a fully-dense morphology is achieved by mfMS and HiPIMS. X-ray diffraction patterns show that films sputtered in dcMS mode have a (200) orientation, whereas mfMS and HiPIMS favor an orientation with the (111) plane parallel to the samples' surface. mfMS leads to films with the largest crystal sizes and lowest stresses, which is ascribed to recrystallization mechanisms during the film growth. Hafnium films with an overstoichiometric composition show the highest hardness values. In this context, the dcMS-Hf49.8N50.2, mfMS-Hf50.4N49.6, and HiPIMS-Hf49.0N51.0 have a hardness of 28.2 ± 2.1, 32.4 ± 3.4, and 30.4 ± 3.1 GPa, respectively. In summary, the sputtering technique has a crucial role on the properties of the film and can be suitable used to adjust the structure and hardness of HfN films.

Enhanced capacitive property of HfN film electrode by plasma etching for supercapacitors

Transition metal nitrides (TMN) films, fabricated by physical vapor deposition (PVD), have attracted much attention in supercapacitor electrode applications due to their high conductivity, easily-controlled composition, high structural and chemical stability, and good cycling life, which are promising candidates for flexible thin-film supercapacitors and on-chip micro-supercapacitors. The main drawback of the PVD-TMN film electrodes is that they have relatively dense structure and smooth surface, which limits their specific surface area and capacitive performance of the supercapacitors. In this work, a novel strategy was employed to modify the surface morphology of TMN films by plasma etching technology. HfN films with high conductivity were chosen to be deposited by reactive DC magnetron sputtering, followed by plasma etching using Ar and Kr gases. Effects of plasma etching on the microstructure, surface morphology and electrochemical properties of the HfN films were investigated. The results indicated that plasma etching significantly changed the surface morphology and enhanced specific capacitance of the HfN films.

Growth of HfN thin films by reactive high power impulse magnetron sputtering

Thin hafnium nitride films were grown on SiO2 by reactive high power impulse magnetron sputtering (HiPIMS) and reactive direct current magnetron sputtering (dcMS). The conditions during growth were kept similar and the film properties were compared as growth temperature, nitrogen flow rate, and in the case of HiPIMS, duty cycle were independently varied. The films were characterized with grazing incidence X-ray diffraction (GIXRD), X-ray reflection (XRR) and X-ray stress analysis (XSA). HiPIMS growth had a lower growth rate for all grown films, but the films surfaces were smoother. The film density of HiPIMS deposited films grown at low duty cycle was comparable to dcMS grown films. Increasing the duty cycle increased the density of the HiPIMS grown films almost to the bulk density of HfN as well as increasing the growth rate, while the surface roughness did not change significantly. The HiPIMS grown films had large compressive stress while the dcMS grown films had some tensile stress. The dcMS grown films exhibit larger grains than HiPIMS grown films. The grain size of HiPIMS grown films decreases with increasing nitrogen flow rate, while the dcMS grain size increased with increasing nitrogen flow rate. This work shows that duty cycle during HiPIMS growth of HfN films has a significant effect on the film density and growth rate while other film properties seem mostly unaffected.

Si Surface Orientation Dependence on the Electrical Characteristics of HfN Gate Insulator with sub-0.5 nm EOT Formed by ECR Plasma Sputtering

ABSTRACTThis paper investigated the silicon substrate orientation dependence on the electrical properties of high-κ HfN gate insulator formed by electron-cyclotron-resonance (ECR) plasma sputtering. The effect of N2/4.9%H2 forming-gas annealing (FGA) was studied. By using N2/4.9%H2 FGA at 500°C for 20 min, the interfacial layer (IL) formation was not formed and led to the zero-interface layer (ZIL). The EOTs of 0.47 and 0.51 nm with leakage current of 1.1 and 1.4 A/cm2 (@VFB -1 V) were obtained on p-Si(100) and p-Si(110), respectively. The density of interface states (Dit) with the order of 1011 cm-2eV-1 was obtained on both p-Si(100) and p-Si(110). This suggests that the direct deposition of HfN film with ZIL prevented the degradation of electrical characteristics on the p-Si(100) and p-Si(110) substrate in comparison to the case of oxide-based hafnium gate insulator.

MECHANICAL AND TRIBOLOGICAL BEHAVIOR OF VN AND HfN FILMS DEPOSITED VIA REACTIVE MAGNETRON SPUTTERING

HfN and VN thin films were deposited onto silicon and 4140 steel substrates with r.f. reactive magnetron sputtering by using Hf and V metallic targets with 4-inch diameter and 99.9% purity in argon/nitrogen atmosphere, applying a substrate temperature of 250°C and a pressure of 1.2 × 10-3 mbar. In order to evaluate the structural, chemical, morphological, mechanical and tribological properties, we used X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), atomic force microscopy (AFM), scanning electron microscopy (SEM), nanoindentation, pin-on-disc and scratch tests. Film structure determined by XRD showed that FCC ( NaCl -type) films are formed in both the cases by δ- HfN and δ- VN phases. Hardness and elastic modulus values obtained for both the films were 21 and 224 GPa for the HfN film and 19 and 205 GPa for the VN film, respectively. Additionally, the films showed low friction coefficient of 0.44 for HfN and 0.62 for VN when these films were evaluated against 100 Cr 6 steel, and finally the critical load was found at 41 N for the HfN film and 34 N for the VN film.

Anisotropic high-k deposition for gate-last processing of metal-oxide-semiconductor field-effect transistor utilizing electron-cyclotron-resonance plasma sputtering

A high-k/metal gate structure has been investigated for application to state-of-the-art metal-oxide-semiconductor field-effect transistors. In the high-k/metal gate structure, the 32-nm technology node was realized by using the high-k-last, metal-last integration process. We investigated anisotropic deposition for 3-dimensional gate structures on Si substrates utilizing electron-cyclotron-resonance plasma sputtering to reduce parasitic capacitance. Anisotropic HfN film deposition was realized and the deposition thickness on the side wall was reduced with decreasing sputtering gas pressure, from 0.15 to 0.06Pa, corresponding to Ar/N2 flow ratios of 20/1 and 5/1sccm. The HfSiON gate insulator formed from the anisotropically deposited HfN film showed an equivalent-oxide-thickness of 2.1nm and a gate leakage of 3.1×10−6A/cm2 @VFB-1.0.

Effect of Deposition Temperature on the Characteristics of HfN<SUB><I>x</I></SUB> Thin Films Prepared by Plasma Assisted Cyclic Chemical Vapor Deposition

This study examined the resistivity, composition and crystallinity of chemically-vapor-deposited HfN(x) films deposited using tetrakis(dimethylamido)hafnium and plasma activated hydrogen as a function of the deposition temperature. The film growth rate (thickness/cycle) ranged from 0.09-0.15 nm/cycle depending on the deposition temperature. The deposition rate was initially insensitive to the substrate temperature at 150-200 degrees C but increased significantly at higher temperatures. The carbon impurities in the films were in the range of approximately 17 to 18 at% and formed Hf-C bonds. All the deposited films were polycrystalline, regardless of the deposition conditions, with a (111) preferred orientation. High substrate temperatures tended to yield films with low resistivity that was relatively constant at temperatures above 225 degrees C.

?Characteristics of HfN Films Deposited by Remote Plasma-enhanced Atomic Layer Deposition

?Characteristics of HfN Films Deposited by Remote Plasma-enhanced Atomic Layer Deposition

Effects of substrate bias and nitrogen flow ratio on the resistivity, composition, crystal structure, and reflectance of reactively sputtered hafnium-nitride film

Hf-N films were sputtered in an Ar + N 2 atmosphere, with different substrate biases (0 to −200 V) at various nitrogen flow ratios (N 2% = 0–5%). The resistivity, composition, crystal structure, and reflectance of Hf-N films were examined. The resistivity of Hf-N films deposited at 0% nitrogen flow ratio decreases with increasing substrate bias. In addition, the resistivity of −200 V biased Hf-N films increases to a limited extent with increasing nitrogen flow ratio, whereas the resistivity of zero- and −100 V biased films increases abruptly with an increasing nitrogen flow ratio of up to 5%. The zero- and −100 V biased Hf-N films display a hafnium oxide phase when film is deposited at a 5% N 2 flow ratio, while Hf-N films deposited at −200 V bias show a HfN phase. The reflectance of zero- and −100 V biased films deposited at 5% N 2 flow ratio shows a significant interference hump in the visible region. In addition, the reflectance edge of Hf-N films is related to the density of the conduction electron. The connection among resistivity, composition, crystal structure, and reflectance and how they are influenced by the substrate bias and nitrogen flow ratio is discussed.

Influence of N 2 flow ratio on the properties of hafnium nitride thin films prepared by DC magnetron sputtering

Hafnium nitride (Hf-N) thin films were deposited on fused silica at different N 2 flow ratio (N 2/N 2 + Ar) using a reactive DC magnetron sputtering system. A gradual evolution in the composition of the films from Hf 3N 2, HfN, to higher nitrides was found through X-ray diffraction (XRD). Films of Hf 3N 2 and HfN show positive temperature coefficients of resistivity, while higher nitride has a negative one. Highly oriented growth of (0 0 1) Hf 3N 2 and NaCl-structure (1 0 0) HfN films were fabricated on fused silica substrate at relatively lower temperature of 300 °C. The electrical resistivity values of both as-deposited and post-deposition annealed films were measured by a four-point probe method. The obtained minimum resistivity of as-deposited film is 20 μΩ cm, and this result shows potential application of HfN films as electrode materials in electronic devices.