Berkovich Diamond Indenter Research Articles

Effects of normal load on nanotribological properties of sputtered carbon nitride films

The nanotribological properties of amorphous carbon nitride (CN x ) films of ∼380 nm thickness were investigated, in the normal (contact) load range of 2–20 mN, using a Berkovich diamond indenter. The amorphous CN x films tested in this work were grown on Si(100) substrates by reactive sputtering and energetic ion bombardment during deposition (IBD). The dependence of the friction behavior of the CN x films on normal load (NL) was investigated in terms of nanomechanical properties, deformation mode and Atomic Force Microscopy (AFM) images of scratched surfaces, and the intensity of IBD. In films sputtered without IBD, the increase of the normal load caused the coefficient of friction to decrease initially to a minimum value and, subsequently, to increase to a maximum value, after which, it remained constant. The dominant friction mechanism in the low-load range was adhesion, while both adhesion and ploughing mechanisms contributed to the friction behavior in the intermediate and high-load ranges. Elastic and plastic deformation (PD) and delamination of the amorphous CN x films occurred, depending on the normal-load ranges. On the other hand, films sputtered with high-energy IBD showed a load-dependent transition in both the scratch and the friction responses. Nanoscratching below 5 mN showed mainly elastic behavior of the film, while above 10 mN, a mixed elastic–plastic behavior was identified. Testing under a normal load of 20 mN resulted in local grooving at the film surface; however, in situ profiling of the scratch trace and AFM images showed no evidence of film failure. The increased load-carrying capacity, higher hardness and elastic response obtained with films grown with high-energy IBD, and the dominant friction mechanism at each load range illustrate the normal load dependence of the nanotribological properties of the sputtered CN x films.

Nanoindentation and atomic force microscopy measurements on reactively sputtered TiN coatings

Titanium nitride (TiN) coatings were deposited by d.c. reactive magnetron sputtering process. The films were deposited on silicon (111) substrates at various process conditions, e.g. substrate bias voltage (VB) and nitrogen partial pressure. Mechanical properties of the coatings were investigated by a nanoindentation technique. Force vs displacement curves generated during loading and unloading of a Berkovich diamond indenter were used to determine the hardness (H) and Young’s modulus (Y) of the films. Detailed investigations on the role of substrate bias and nitrogen partial pressure on the mechanical properties of the coatings are presented in this paper. Considerable improvement in the hardness was observed when negative bias voltage was increased from 100–250 V. Films deposited at |V B| = 250 V exhibited hardness as high as 3300 kg/mm2. This increase in hardness has been attributed to ion bombardment during the deposition. The ion bombardment considerably affects the microstructure of the coatings. Atomic force microscopy (AFM) of the coatings revealed fine-grained morphology for the films prepared at higher substrate bias voltage. The hardness of the coatings was found to increase with a decrease in nitrogen partial pressure.

Nano-mechano-electrochemical properties of passive titanium surfaces evaluated by in-situ nano-indentation and nano-scratching

In-situ nano-indentation and scratching tests using a pyramidal Berkovich diamond indenter were performed to examine the nano-mechano-electrochemical properties of the passivated polycrystalline titanium surfaces. There were significant differences in the load–depth curves obtained between in-situ (kept at 5 V (RHE) in solution) and ex-situ (in air) nano-indentation tests at a maximum load of L max =300 μN for the titanium surfaces passivated at 5 V (RHE) for 1 h in pH 8.4 borate solution. The hardness (9 GPa) of the passive titanium surface obtained from the in-situ load–depth curve was three or four times as large as that obtained from the ex-situ load–depth curve. The coefficient of friction for the passive titanium surface obtained from the in-situ nano-scratching was also significantly larger than from that obtained from the ex-situ nano-scratching. The large differences in hardness and coefficient of friction between in-situ and ex-situ tests were discussed from the mechano-chemical viewpoint such as the differences in repassivation rate at the film rupture sites near edge of contact area during indentation or near the front area of scratching between under potential control in solution and in air.

Characterization of interconnect interfacial adhesion by cross-sectional nanoindentation

The technique of cross-sectional nanoindentation (CSN), as applied to thin films used in microelectronic devices, is reviewed. The technique was developed to characterize interfacial adhesion of interconnect thin films. A Berkovich diamond indenter is used to initiate fracture in a silicon substrate on which multilayer thin film structures are deposited. The cracks propagate to the weakest interface in the system. Both dielectric-dielectric and metal-dielectric interfaces are studied. The technique produces a qualitative measure of interfacial adhesion for blanket and patterned thin films. Quantitative results are obtained for blanket thin films through the application of analytic and finite element modeling. Fracture energy release rates obtained with CSN are in good agreement with results obtained with the four-point bending technique.

Effects of Substrate Materials on Nanoindentation Tests of AlN Thin Films

ABSTRACTAluminum nitride (AlN) thin films with different thickness were synthesized by ion-beam assisted deposition on various substrates, Corning 7059 glass, fused silica, Si single crystal, and sapphire, which show the hardness ranging from 7 to 37 GPa. Effects of substrate materials on indentation-hardness of AlN films were studied by using a nanoindentation system equipped with a diamond Berkovich indenter. The maximum force applied to the films was kept at 3 mN. For the films on the Corning 7059 glass substrate, when the normalized penetration depth to the film thickness is 0.98, the film hardness is found to be about 7 GPa, which is close to the hardness of the substrate. While the normalized penetration depth is reduced to 0.11, the film hardness becomes to be about 16 GPa. On the other hand, for the films on the sapphire substrate, when the normalized penetration depth is 0.83, the film hardness is observed to be about 25 GPa, while the normalized penetration depth is reduced to 0.10, the film hardness is found to be about 15 GPa. These results reveal that when the normalized penetration depth to the film thickness is about 0.1, the hardness of the AlN film can be evaluated to be about 15 GPa without being affected by substrate materials.

Study of the mechanical properties of tetrahedral amorphous carbon films by nanoindentation and nanowear measurements

Abstract Nanoindentation and nanowear measurements, along with the associated analysis suitable for the mechanical characterization of tetrahedral amorphous carbon (ta-C) films are discussed in this paper. Films of approximately 100-nm thick were deposited on silicon substrates at room temperature in a filtered cathodic vacuum arc evaporation system with an improved S-bend filter that yields films with high values of mass density (3.2 g/cm3) and sp3 content (84–88%) when operating in a broad bias voltage range (−20 V to −350 V). Nanoindentation measurements were carried out on the films with a Berkovich diamond indenter applying loads in the 100 μN–2 mN range, leading to maximum penetration depths between 10 and 60 nm. In this measurement range, the ta-C thin-films present a basically elastic behavior with high hardness (45 GPa) and high Young's modulus (340 GPa) values. Due to the low thickness of the films and the shallow penetration depths involved in the measurement, the substrate influence must be taken into account and the area function of the indenter should be accurately calibrated for determination of both hardness and Young's modulus. Moreover, nanowear measurements were performed on the films with a sharp diamond tip using multiple scans over an area of 3 μm2, producing a progressive wear crater with well-defined depth which shows an increasing linear dependence with the number of scans. The wear resistance at nanometric scale is found to be a function of the film hardness.

Measurement of the loss tangent of low-density polyethylene with a nanoindentation technique

This paper describes experimental measurements of the linear viscoelastic behavior of the surface of low-density (LD) polyethylene in contact with a pyramidal Berkovich diamond indenter. The experiments were carried out at two different temperatures, 15.9 and 27.2 °C, between frequencies of 0.1 and 800 Hz. Using the shift of the loss tangent between the two temperatures at frequencies lower than 20 Hz and an Arrhenius equation, an activation energy of 105 ± 2 kJ/mol was obtained. This value is in good agreement with the bulk value of the a relaxation of LD polyethylene reported in the literature.

The effect of the indenter load on the nanohardness of ductile metals: An experimental study on polycrystalline work-hardened and annealed oxygen-free copper

Abstract An experimental investigation of the nanohardness of polycrystalline work-hardened and annealed oxygen-free copper (OFC) for different indenter loads is described. Nanoindentations were made using a Berkovich diamond indenter and the indenter loads used were in the range 1–100 mN. It is shown that by accurately measuring the projected contact areas of nanoindentations with an atomic force microscope the overall nanohardness behaviour of the work-hardened OFC was quite different from that of the annealed OFC. The nanohardness of the former behaved non-monotonically with increasing indenter penetration depth, whereas the nanohardness of the latter decreased monotonically with increasing indenter penetration depth. A three-stage qualitative model has been proposed to explain the nanohardness results. In the first stage, it is argued that, at low penetration depths of less than 150nm (our lowest measured depth), dislocation loops are nucleated at relatively high shear stress values of about G/75, whe...

Accurate determination of the mechanical properties of thin aluminum films deposited on sapphire flats using nanoindentations

Nanoindentations using a Berkovich diamond indenter have been made on 1, 2, and 5 μm thick 99.99% purity polycrystalline aluminum films thermally evaporated in vacuum on to 2 mm thick R-cut polished sapphire flats. The projected contact areas of the residual indentations were estimated from the unloading load-displacement curves, and some of the indentations were imaged with an atomic force microscope (AFM). It was found that a large majority of indents showed material pileup, and the projected areas of these indents, as measured with the AFM, were up to 50% greater than those calculated from the unloading curves. This discrepancy between the calculated and directly measured indentation areas has a strong influence on the derived values of Young's modulus and hardness of the aluminum films. Using a new analytical model, Young's modulus of the aluminum films has been determined to be in the range of 50–70 GPa, independent of the relative indentation depth. The composite nanohardness of the 1 and 2 μm thick films was found to have a load-independent value of 1 GPa, whereas the composite nanohardness of the 5 μm film decreased from 1 to 0.7 Gpa with increasing indenter penetration. Finally, it has been suggested that in order to improve the accuracy with which the mechanical properties of thin films or bulk specimens can be determined by nanoindentation techniques, the projected contact areas should be measured by direct methods, such as atomic force microscopy.

Mechanical and fracture toughness studies of amorphous SiC–N hard coatings using nanoindentation

a: SiC x – N y films were deposited on Si(111) and sapphire substrates at ambient temperatures by reactive magnetron sputtering of SiC in a mixed Ar/N2 discharge. Nanoindentation was used to characterize the mechanical (hardness and elastic modulus) and fracture (toughness) properties. A conventional sharp Berkovich diamond indenter (three-sided pyramid) was used to assess the mechanical properties. The hardness and elastic modulus slightly increased from 23 and 220 GPa to 27 and 270 GPa with incorporation of N2 (up to 4.4%). The fracture toughness (Kc) was characterized by replacing the aforementioned indenter with a cube corner indenter, which also is trigonal but has the geometry of a cube corner with a smaller angle between the axis of symmetry and a face. The purpose of the switch was to reduce the much higher cracking thresholds associated with the Berkovich and Vickers indenters. The smaller volume of thin films requires this reduction for reliability. The nucleation and propagation of median-radial indentation cracks was made feasible by the cube corner geometrically displacing more volume than the Berkovich under similar loads. A substrate fracture toughness effect was observed dependent upon indenter penetration depth. Fracture toughness was relatively constant (≈3.1 MPa√m) from 19 (threshold load) to 40 mN; however, loads ⩾50 mN resulted in a decrease to ≈2.4 MPa√m since the greater penetration depths approaching the sapphire substrate played a role. The structure, composition, and bonding of the films were qualitatively and quantitatively assessed by x-ray diffraction, energy dispersive x-ray spectroscopy, and micro-Raman spectroscopy, respectively, and subsequently correlated to the overall film properties.

Nanowear/nanomechanical testing and the role of stress in sputtered CNx overcoats

a: C–N x films were deposited on Si(111) wafers at ambient temperatures by reactive magnetron sputtering of C in a mixed Ar/N2 discharge. The hardness (H) and elastic modulus (E) were assessed via nanoindentation using a Berkovich diamond indenter. The nitrogenated films exhibited increased hardness and elastic moduli values compared to the amorphous carbonated films, i.e., 25 and 240 GPa to 16 and 160 GPa, respectively. A sphere-on-flat (magnetic tape) wear tester was used to assess wear scar volume losses as a function of wear time. All films were in a state of compression (intrinsic and thermal stress). The bonding, composition, and structure of the films for all the deposition conditions were assessed by micro-Raman spectroscopy, energy dispersive x-ray spectroscopy (EDX), and x-ray diffraction (XRD), respectively, and subsequently correlated to overall film properties.

Adhesion assessment of silicon carbide, carbon, and carbon nitride ultrathin overcoats by nanoscratch techniques

This paper presents experimental results for adhesion assessment of 20 nm ultrathin SiC, amorphous carbon and carbon nitride films deposited on silicon (111) substrates by sputtering. In the experiment, the ultrathin overcoats were scratched by a face-forward Berkovich diamond indenter with a continuous depth sensing nanoscratch system. Experimental results indicate that the nanoscratch system has very good sensitivity for detecting ultrathin overcoat cracking, delamination, and brittle fracture caused by scratching. A well-defined critical load for each film was determined by the nanoscratch techniques. The highest critical load (800 μN) is found for the CN film and the lowest (500 μN) is for SiC. Scanning electron microscopy (SEM) investigations to the surface damage of the samples reveal that the SiC overcoat was damaged more severely than other films due to its brittle fracture. The adhesion properties of the three films tested in this work are best in carbon nitride, followed by amorphous carbon and then silicon carbide.