HfN Films Research Articles

Structural and interfacial properties of high- k HfO xN y gate dielectric films

The thermal stability and interfacial characteristics for hafnium oxynitride (HfO x N y ) gate dielectrics formed on Si (1 0 0) by plasma oxidation of sputtered HfN films have been investigated. X-ray diffraction results show that the crystallization temperature of nitrogen-incorporated HfO 2 films increases compared to HfO 2 films. Analyses by X-ray photoelectron spectroscopy confirm the nitrogen incorporation in the as-deposited sample and nitrogen substitution by oxygen in the annealed species. Results of FTIR characterization indicate that the growth of the interfacial SiO 2 layer is suppressed in HfO x N y films compared to HfO 2 films annealed in N 2 ambient. The growth mechanism of the interfacial layer is discussed in detail.

Barrier Characteristics of HfN Films Deposited by Using the Remote Plasma-Enhanced Atomic Layer Deposition Method

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Characterization of chemical vapor deposited HfN multilayer coatings on cemented carbide cutting tools

The present study has been carried out in order to evaluate the tribological behavior of HfN-based multilayer-coated tools used for milling. The initial results of the wear behavior of multilayer HfN coatings, during the laboratory friction and wear tests conducted at room temperature against WC as tribological pair, are reported. As part of the characterization of the mechanical properties of the coatings, Vickers microindentation tests were also carried out employing loads in the range of 0.01–10 N, in order to evaluate the composite hardness of the coating-substrate systems. Information regarding the absolute hardness of the HfN and TiCN monolayer films has been obtained employing a model recently developed by one of the authors. This information is then used in order to determine the properties of the HfN/TiCN multilayer coating. It has been found that the wear volume of the single layer HfN coatings is approximately 15 times greater than the wear volume corresponding to the HfN/TiCN for the same amount of cycles.

The effect of anisotropy on residual stress values and modification of Serruys approach to residual stress calculations for coatings such as TiN, ZrN and HfN

The residual stresses in literature on hard coatings (e.g., TiN, CrN, HfN and ZrN) are usually calculated using the mechanical elastic constants often determined by indentation technique by assuming isotropic behavior. The effect of anisotropy of the hard coatings on residual stress values such as TiN, ZrN and HfN has been documented using classical technique and Thin Film techniques (fixed incidence multiplane (FIM) Technique). Due to lack of the single crystal data, the anisotropy of coatings has been taken into account through XECs determined experimentally for ZrN, HfN and TiN films. Recently, single crystal elastic constants of the ZrN, HfN and NbN have been measured. In the light of single crystal elastic constant data, residual stresses reported in the literature were reevaluated according to Reuss, Voigt, Hill (or mixed) and Kröner models using the best fitting approach after modifying Serruys approach. The modified Serruys approach captures the anisotropic behavior of coatings such as ZrN and Zr(Hf)N. The residual stress calculations were improved and the residual stress values were significantly increased as high as 30% compared to the previously published data. The best fitting approach (modified Serruys approach) was compared to the procedure used by Perry using experimentally determined XECs.

Development of a compact angle-resolved secondary ion mass spectrometer for Ar + sputtering

A compact angle-resolved secondary ion mass spectrometer with a special geometrical configuration, composing of a differentially pumped micro-beam ion gun, a tiltable sample stage and a time-of-flight (TOF) mass spectrometer, was newly developed. This system enables the measurement of angular distribution (AD) of secondary ions, which are ejected by oblique Ar + sputtering, by a simple tilt operation of the sample stage for ejection angles ranging from 0° to 60° with keeping the ion incidence angle constant 62°±2° from the normal to the surface. Using this system, AD of secondary ions from an HfN film by 3 keV Ar +-ion bombardment was measured at room temperature. Since the yield of HfN + dimer ions was almost independent of Hf + and N + monomer ions, it was concluded that the HfN + dimer ions were generated via the “as such” direct emission process.

Integrity of copper–hafnium, hafnium nitride and multilayered amorphous-like hafnium nitride metallization under various thickness

The barrier properties and failure mechanism of sputtered Hf, HfN and multilayered HfN/HfN thin films were studied for the application as a Cu diffusion barrier in metallization schemes. The barrier capability and thermal stability of Hf, HfN and HfN/HfN films were determined using X-ray diffraction (XRD), leakage current density, sheet resistance ( R s) and cross-sectional transmission electron microscopy (XTEM). The thin multi-amorphous-like HfN thin film (10 nm) possesses the best barrier capability than Hf (50 nm) and amorphous-like HfN (50 nm). Nitrogen incorporated Hf films possess better barrier performance than sputtered Hf films. The Cu/Hf/n +–p junction diodes with the Hf barrier of 50 nm thickness were able to sustain a 30-min thermal annealing at temperature up to 500 °C. Copper silicide forms after annealing. The Hf barrier fails due to the reaction of Cu and the Hf barrier, in which Cu atoms penetrate into the Si substrate after annealing at high temperature. The thermal stabilities of Cu/Hf/n +–p junction diodes are enhanced by nitrogen incorporation. Nitrogen incorporated Hf (HfN, 50 nm) diffusion barriers retained the integrity of junction diodes up to 550 °C with lower leakage current densities. Multilayered amorphous-like HfN (10 nm) barriers also retained the integrity of junction diodes up to 550 °C even if the thickness is thin. No copper–hafnium and copper silicide compounds are found. Nitrogen incorporated hafnium diffusion barrier can suppress the formation of copper–hafnium compounds and copper penetration, and thus improve the thermal stability of barrier layer. Diffusion resistance of nitrogen-incorporated Hf barrier is more effective. In all characterization techniques, nitrogen in the film, inducing the microstructure variation appears to play an important role in thermal stability and resistance against Cu diffusion. Amorphousization effects of nitrogen variation are believed to be capable of lengthening grain structures to alleviate Cu diffusion effectively. In addition, a thin multilayered amorphous-like HfN film not only has lengthening grain structures to alleviate Cu diffusion, but block and discontinue fast diffusion paths as well. Hence, a thin multilayered amorphous-like HfN/HfN barrier shows the excellent barrier property to suppress the formation of high resistance η′-(Cu,Si) compound phase to 700 °C.

Metal‐Organic CVD of Conductive and Crystalline Hafnium Nitride Films

HfN films have been deposited on Si, SiO2, and Al2O3 substrates by MOCVD using Hf(NMe2)4 and Me2NNH2 (DMHy) in the deposition temperature range 600–800 °C. The resistivity and morphology of the films strongly depends on the deposition temperature. A cubic polycrystalline and conductive HfN film deposited at 800 °C shows the lowest resistivity, of approximately 1020 μΩ·cm. The HfN film was slightly nitrogen‐rich and the film density was 12.9 g cm–3. It was found that DMHy and the high deposition temperature were important factors for the growth of good‐quality HfN films.

Angular Distribution of Sputtered Ions from HfN by Ar+ Ion Bombarment

A compact type angular-resolved secondary ion mass spectrometry was newly developed. The angular distribution (AD) of secondary ions ejected by oblique Ar+ sputtering at 62 degree from the normal to the surface was measured by a simple tilt operation of the sample stage under a special geometry of an ion gun, a sample stage and a detector. Using this system, AD of sputtered ions was measured for a HfN film sample. Ion intensities of Hf+, N+ and HfN+ decreased monotonously with an increase in the ejection angle. AD of Hf+ was identical with that of N+, implying that preferential sputtering attributed to the difference in mass and surface binding energy played a dominant role in Ar+ sputtering of HfN. Since the yield of HfN+ dimer ions was almost independent of that of Hf+ and N+ monomer ions, it was concluded that the HfN+ ions originated from a direct ejection process of clusters.

Anneal behavior of reactively sputtered HfN films

This article reports electrical and thermo-physical properties of reactively sputtered HfNx films with respect to thermal annealing. All metal nitride films were sandwiched between sputtered Si3N4 films. The resulting reduction in electrical resistivity with anneal is explained by a combination of Rutherford backscattering spectrometry and secondary ion mass spectroscopy analyses. The physical mechanisms responsible for the observed anneal behavior are discussed.

Growth and stress evolution of hafnium nitride films sputtered from a compound target

Hafnium nitride films were deposited on silicon substrates by direct sputtering a compound target in an Ar atmosphere using a radio-frequency magnetron sputtering system. X-ray diffraction, x-ray photoemission spectrum, and Rutherford backscattering spectrometry revealed the successful formation of cubic stoichiometric HfN films in a wide deposition condition range. The residual stress in stoichiometric HfN films is compressive, and depends strongly on Ar pressure and sputtering power. Unlike element metal deposition, a transition point of Ar pressure at which residual stress experiences from compressive to tensile state has not been found in stoichiometic HfN films. Although an increase in Ar pressure could lower the stress value, nitrogen enrichment was found at 2.0 Pa and much oxygen was incorporated in the film deposited at 3.0 Pa and above, which can lead to a dramatic increase in film resistivity. Shallow recoil implantation of HfN species receiving energy from fast Ar species reflected at the target surface is suggested responsible for the evolution of the stress. A possible explanation was also given for the stoichiometric composition.

Realization of Sequential Epitaxial Growth of Cu/HfN Bilayered Films on (111) and (001) Si

Cu films were deposited on epitaxial HfN/Si systems using a dc magnetron sputtering system without breaking the vacuum. Crystal orientation of Cu films was investigated by X-ray diffraction (XRD) and X-ray pole figure analyses. Epitaxial growth of (111) and (110) Cu was confirmed on epitaxial (111) and (001) HfN films, respectively. Surface morphology of HfN/Si and Cu/HfN/Si systems was examined by atomic force microscopy (AFM). Both epitaxial HfN films have quite flat surfaces, in spite of the difference in their orientational planes. However, the surface roughness of (110) Cu film on (001) HfN was estimated to be half of that of (111) Cu film on (111) HfN. It is revealed that the difference in surface morphology between epitaxial (111) and (110) Cu is ascribed to the difference between factors governing the epitaxial growth at the Cu/HfN interface.

Interfacial Solid-Phase Reaction in Al/HfN/Hf/Si Contact System during Postmetallization Annealing

We investigated the sequential single-oriented growth of Al/HfN/Hf trilayered film on Si and the interfacial solid-phase reaction of a Al/HfN/Hf/Si contact system by X-ray diffraction and Auger electron spectroscopy. Since for preparing this contact system, the deposition of HfN film was carried out on a Hf/Si system at a temperature of 450°C, which is higher than the silicidation temperature of Hf3Si2 (420°C), we also confirmed whether the formation of a Hf3Si2 region with the lowest contact resistivity could be ensured at the Si interface during the deposition of HfN film. As a result of postannealing, it was revealed that the Al overlayer can be preserved at least up to 440°C and the region of Hf3Si2 phase is maintained at the Si interface up to 500°C.

Formation of hafnium nitride films by medium-energy ion-beam-assisted deposition

Hafnium nitride films were formed by evaporation of hafnium atoms from an electron beam evaporator under simultaneous nitrogen ion bombardment. The ratio of impinging ions to neutrals has been varied, in order to study its influence on elemental and phase composition. The composition of the films was studied by using Rutherford backscattering spectroscopy; their phase composition was examined by X-ray diffraction. It is shown that layers with the 1:1 stoichiometry of Hf:N can be formed under ion irradiation, although hafnium has a great affinity to oxygen. Among the nitrides known, only the cubic (B1) HfN phase is formed. No other stoichiometries were found. The texture of the HfN films is strongly influenced by the irradiation intensity and is changed from (111) over randomly oriented to (100).

Epitaxial Growth of HfN Film and Sequential Single-Oriented Growth of Al/HfN Bilayered Film on (001) and (111) Si

We have investigated epitaxial growth of HfN film and sequential single-oriented growth of Al/HfN bilayered film on (001) Si and (111) Si. Stoichiometric HfN film was prepared on Si by reactive sputtering using an ultrahigh-vacuum dc magnetron sputtering system. Orientational epitaxy and crystal structure of HfN film deposited on Si were investigated by X-ray pole figure measurement and X-ray diffraction analysis, respectively. Then, Al film was sputter-deposited on the HfN/Si system in the same sputtering chamber without breaking vacuum, and sequential single-oriented growth of Al/HfN bilayered film was examined by X-ray diffraction. It is revealed that the HfN films deposited on Si grow epitaxially with the directional relationships of HfN (001) [110] ∥Si (001) [110] and HfN (111) [002] ∥Si (111) [002], and (100) and (111) Al films also grow in a single-oriented state on epitaxial (001) and (111) HfN films.

Resistivity and structural defects of reactively sputtered TiN and HfN films

TiN and HfN thin films have been deposited by reactive r.f.-sputtering in an Ar-N 2 gas mixture under different condition of total gas pressure ( P T ) from 0.7 Pa to 5.3 Pa. Thin film X-ray diffraction studies show that the structure of the TiN films is gradually changed from TiN f.c.c. structure to amorphous with increasing P T . On the other hand, HfN f.c.c. structure with a strong (111)-preferred orientation is formed for all HfN films prepared with various P T . The resistivity of the films at room temperature ( ϱ rt ) increased with increasing P T in different ways between TiN and HfN. The films with ϱ rt ≤ 0.3 mΩm show √T dependence in conductivity at low temperature. HfN films with ϱ rt = 1.6 mΩm, the largest one measured, show an insulating behavior. The magnetoconductance Δσ(H) measurements showed that the spinorbit coupling of HfN is found to be stronger than that of TiN.

Influence of Sputtering Parameters on the Formation Process of High-Quality and Low-Resistivity HfN Thin Film

We have investigated the influence of sputtering parameters such as N2 flow ratio, applied dc power and substrate temperature on the formation process of high-quality and low-resistivity HfN film using an ultrahigh-vacuum sputtering system. The obtained film quality was evaluated using X-ray diffraction, X-ray photoelectron spectroscopy and Auger electron spectroscopy analyses. The resistivity values were measured by a four-point probe method. We found that (111) HfN and (100) HfN films with equivalent resistivity to the bulk value can be grown in a single-oriented state at the substrate temperature of 450°C on (111) Si and (001) Si, respectively. Therefore, it is revealed that impurity-free, high-quality HfN film with high crystallinity and low resistivity can be obtained at relatively low substrate temperatures, if appropriate sputtering conditions are satisfied, using an ultrahigh-vacuum sputtering system.

Postdeposition relaxation of internal stress in sputter-grown thin films caused by ion bombardment

A hitherto unreported postdeposition method of relaxing ultrahigh internal stresses prevailing in sputter-grown thin films is the subject of the present research. A significant reduction of stress has been confirmed by x-ray diffraction and independent substrate deflection measurements for HfN films treated with Si+ ions of various energies (450 keV, 500 keV, and 1.1 MeV). The particular sequence of the performed experiments has allowed us to deduce the most likely scenario of the resulting stress relaxation. We argue that the observed reduction of internal stress had been caused by structural changes, namely the transport of interstitial defects occurring within the thermal spikes induced by ion bombardment and an increase in vacancy concentration. Simple theoretical considerations proved that the existence of an amorphous silicon interlayer formed right under the HfN film during the bombardment cannot be the cause of the observed stress relaxation. The employed Auger electron spectroscopy, transmission electron microscopy, and x-ray diffraction technique confirmed that the ion bombardment did not seriously affect either the composition, dislocation structure, or texture of nitride films. The relative softening of HfN after ion bombardment was found to be caused by amorphization of the substrate directly under the film. The penetration of incident particles deeper than predicted by a numerical simulation was attributed to a distinct crystallographic texture determined experimentally for HfN films. It was confirmed that modification with Si+ ions does not affect the resistivity of HfN films.

Nano-indentation of ion-beam modified HfN/Si system: Identification of the amorphized inter-layer

The work aims to clarify the considerable softening registered for the HfN/Si system after its bombardment with energetic ions ( E=1, 2.5 and 5 MeV, fluence=10 14 Au ++cm −2). The mechanical properties of the virgin and ion-modified films were characterized using the depth-sensing indentation experiments performed under maximum indentation load ranging from 2 to 50 mN. The surface deformation in the vicinity of the contact with a triangular indenter was modeled by the finite element simulation of the axisymmetric-indenter penetration into the hard-film/soft-substrate system. The applied approach allowed us to attribute the observed difference in hardness of virgin and ion-treated samples to the structural changes which have been induced in the silicon substrate by bombarding ions. The calculated results led us to the conclusion that bombardment with energetic Au-ions resulted in formation of the inter-layer of amorphous silicon, right under HfN film. The present work aims to prove that the depth-sensing experiments supplemented by the finite-element calculations provide a new, powerful method of characterizing the multilayer structures.

Amorphization of the silicon substrate and stress-relaxation in HfN films bombarded with Au ions

Abstract Sputter-deposited HfN films were exposed (after their growth) to a mono-energetic Au-ion beam ( E =1, 2.5 and 5 MeV, fluence=10 14 cm −2 ). This treatment resulted in a significant reduction of high internal stresses which arise in transition metal nitride films during the deposition process. The structural changes induced in the ion modified HfN-film/silicon-substrate system were studied by means of scanning and transition electron microscopy. The latter reveals that bombardment with energetic Au ions does not affect either the dislocation arrangement or the crystal structure of HfN films, but causes an amorphization of those parts of the silicon substrate located directly under the top nitride film. The registered stress release is ascribed to a transport of defects within thermal spikes induced by the applied ion treatment, since the amorphous layer is the thicker the smaller the observed stress reduction. Energy considerations of the stress-relaxation process in a multilayer system are used to estimate the possible influence of the amorphization of the substrate on the reduction of intrinsic stresses prevailing in HfN films.

Post-deposition reduction of internal stress in thin films: The case of HfN coatings bombarded with Au ions

Abstract The post-deposition bombardment of reactively sputtered HfN thin films with energetic (1, 2.5 and 5 MeV) gold ions to a fluence of 10 14 cm −2 resulted in a considerable reduction of high internal stresses which were estimated from the measurements of the surface curvature. The higher the energy of the gold species the lower degree of relaxation was registered. The observed phenomena are attributed here to the transport of the interstitial defects within the thermal spikes induced by bombarding HfN with Au ions. An alternative explanation of stress-reduction caused by an increase in vacancy concentration is also presented. Significant softening of HfN films after ion-beam treatment was registered by the high accuracy depth-sensing indentation method and attributed to the formation of an inter-layer of amorphous silicon, directly under the film. A structural analysis has been carried out using thin film X-ray diffraction. Nitride film resistivity was found to be slightly enhanced by bombardment with Au ions.