L. J. Pilione

Stress dependence of reactively sputtered aluminum nitride thin films on sputtering parameters

Aluminum nitride thin films (∼5000 A) were deposited by reactively sputtering an aluminum target in a dc magnetron system. The stress and crystallographic orientation associated with these films were found to depend on the total sputtering pressure and the N2 partial flow rate in the sputtering mixture. A pressure range was found to exist between 3.00 and 3.75 mTorr where the film stress was in transition between compression and tension. At total sputtering pressures outside this transition range the pressure determined the type of film stress, while at total sputtering pressures within the transition range the N2 partial flow rate played an important role. Film stress was determined qualitatively by substrate curvature, while x‐ray diffraction was used to observe changes in the crystallographic orientation of the films.

Surface-enhanced Raman spectroscopy of chemical vapor deposited diamond films

By using surface‐enhanced Raman spectroscopy it was possible to clearly identify very thin diamond and amorphous carbon coatings which were not detectable by normal Raman spectroscopy. A very small amount of silver was sputtered onto the surface of thin diamond depositions. Raman spectra measured through the silver layer exhibited the 1332 cm−1 diamond line and broadbands due to other forms of carbon. Raman scattering measured through silver coatings directly on the silicon substrate revealed extremely thin layers of amorphous carbon.

Development of preferred orientation in polycrystalline AlN thin films deposited by rf sputtering system at low temperature

The development of preferred orientation in AlN thin films deposited on silica glass substrates by rf sputtering at low substrate temperature ( c -axis perpendicular to the substrate surface. At higher pressure (>15 mTorr), a spreading in the incidence angle of the arriving particles, due to gas phase collisions, favors the formation of AlN crystal twinning. A change in the preferred orientation of the films from (0001) to (10 1 1) for deposition rates above 1.8 A/s is observed.

EFFECT OF STOICHIOMETRY ON THE PHASES PRESENT IN BORON NITRIDE THIN FILMS

Boron nitride thin films were deposited by ion‐assisted evaporation and characterized by neutron depth profiling (NDP), a nondestructive method for the compositional analysis of solids. The phases present in the films were determined by infrared spectroscopy. Examination of the data presented here and comparison with the work of other authors revealed that stoichiometric or nearly stoichiometric films contained the greatest amount of the cubic phase. This led to the proposition that film stoichiometry is one of the factors that stabilize cubic boron nitride in boron nitride thin films. A shift in the position of the cubic boron nitride infrared absorption was also observed by the present authors which was related to film stoichiometry. Discussion of the various techniques commonly used to determine the stoichiometry of boron nitride thin films emphasized the need for all stoichiometry measurements to be made using the same characterization method in order for all results to be compared with confidence. Th...

Low-temperature synthesis of BaTiO3 thin films on silicon substrates by hydrothermal reaction

Crystalline BaTiO3 thin films (0.2–1 μm) of dielectric constant 450–500 have been synthesized by the hydrothermal reaction of a titanium film (∼1 μm thickness) deposited on a silicon substrate with Ba(OH)2 solution (concentration 0.4 M) in the temperature range 100–200 °C. The reaction of the silicon substrate with the Ti film was prevented by deposition of a buffer layer of amorphous TiC between the Ti film and the Si substrate. The TiC not only prevented the diffusion of Si through the Ti layer but also allowed some reaction between itself and the Ti layer so that the adherence of the films was not degraded.Crystalline BaTiO3 thin films (0.2–1 μm) of dielectric constant 450–500 have been synthesized by the hydrothermal reaction of a titanium film (∼1 μm thickness) deposited on a silicon substrate with Ba(OH)2 solution (concentration 0.4 M) in the temperature range 100–200 °C. The reaction of the silicon substrate with the Ti film was prevented by deposition of a buffer layer of amorphous TiC between the Ti film and the Si substrate. The TiC not only prevented the diffusion of Si through the Ti layer but also allowed some reaction between itself and the Ti layer so that the adherence of the films was not degraded.

Cubic boron nitride thin film deposition by unbalanced magnetron sputtering and dc pulsed substrate biasing

Boron nitride (BN) thin films were deposited by unbalanced magnetron sputtering. An asymmetric bipolar pulsed dc power supply was used to bias the substrate with a 218 kHz signal. BN was deposited at different negative bias voltages and films with over 80% of the zinc-blende cubic phase, as measured by Fourier transform infrared (FTIR) spectroscopy, were obtained. For a given set of deposition conditions a window of maximum negative bias voltage was defined inside which the cubic phase is stabilized. This negative bias voltage was used to derive the momentum imparted to the growing film per arriving boron atom, and it is shown that a threshold value for the formation of the cubic phase (cBN) is consistent with previous results using ion beam assisted deposition. Several films were deposited on aluminum nitride and diamond thin films previously deposited on crystalline silicon in order to study the effect of the substrate on the stabilization of the cBN phase. A twofold reduction in the full width at half ...

Thickness‐dependent void fraction of rf‐sputtered amorphous Ge films by spectroscopic ellipsometry

In this letter it is shown that vapor deposited thin films prepared under conditions of low adatom mobility, such as amorphous Ge films in the present study, exhibit a nonlinear decrease in void fraction, and hence an increase in density with increasing film thickness. Fractal modeling of the internal void network structure in this class of vapor deposited films shows that the void boundaries define the surfaces of growth cones and these voids are, in general, not expected to be distributed uniformly with film thickness.

CONTROL OF THE PREFERRED ORIENTATION OF ALN THIN FILMS BY COLLIMATED SPUTTERING

The effects of collimation on the crystallographic orientation of sputtered aluminum nitride thin films have been studied. The AlN films were deposited on glass at a total gas pressure of 15 mTorr using a rf-diode sputtering system. Collimators with angular widths varying from 31° to 140° were used to decrease the range of impingement angles of the flux of species sputtered and reflected from the sputtering target that arrive on the film surface. The three-dimensional crystallographic orientation of the films was studied by the x-ray pole figure method. All the AlN thin films were deposited under similar conditions, with and without collimators, and produced polycrystalline structures with the c-axis (0001) direction perpendicular to the substrate surface. A comparison of the films’ preferential orientations showed that, as the angular width of the collimator decreases, the full width at half maximum (FWHM) of the χ scan profile of the 0002 diffraction peak decreases linearly, indicating a better alignmen...

Electron emission from disordered tetrahedral carbon

Electron field-emission tests have been performed on films grown by a modified microwave plasma assisted chemical vapor deposition diamond process. This modification includes the addition of N2 and O2 during the growth stage. Characterization of these films shows the presence of a disordered tetrahedral carbon structure. Raman spectroscopy indicates a disturbance in the cubic symmetry of the lattice and x-ray diffraction indicates a disordered tetrahedral structure. Field-emission testing indicate that current densities of 0.5 mA/cm2 can be obtained for applied fields of 5–8 V/μm. The results are explained in terms of a change in the band structure and the formation of electronic states in the band gap.

Pressure dependence of the negative bias voltage for stabilization of cubic boron nitride thin films deposited by sputtering

Thin films of boron nitride were deposited by unbalanced magnetron sputtering at pressures between 0.065 and 1.32 Pa in order to study the effects of pressure and negative substrate bias on the energy of the bombarding plasma ions and subsequent stabilization of the cubic phase. It was found that the threshold bias voltage for nucleation of films with a high percentage of the cubic phase increases with the product of the pressure and sheath thickness. This trend is explained in terms of the changes in the average energy of the particles bombarding the growing film produced by pressure-dependent charge-exchange collisions in the plasma/substrate sheath. This energy modification process has predictable consequences in complex deposition processes.