R. A. Roy

Filtered arc deposition of amorphous diamond

A cathodic arc with beam filter is employed for the deposition of hydrogen‐free amorphous carbon films. A linear filter is used to prevent macroparticles and nonionized carbon atoms from reaching the substrate. The deposited films are characterized by their optical and mechanical behavior. Depending on the deposition conditions, optical band gaps in the range 2.1–2.4 eV are measured. Mechanical properties are investigated using the nanoindentation method and are shown to approach those of natural diamond. To our knowledge, the data obtained thus far reveal these films to be more diamondlike than those prepared using any other method for the deposition of nonhydrogenated amorphous diamond.

Properties of amorphous diamond films prepared by a filtered cathodic arc

Amorphous diamond films have been prepared by filtered cathodic arc deposition of carbon. The filtered arc is well suited for the growth of amorphous diamond, as it provides carbon ions with optimum kinetic energies at practical deposition rates. These films contain no hydrogen and are therefore structurally different from diamond‐like carbon films generated by plasma chemical vapor deposition. Diamond‐type bonding of carbon is quantitatively determined by electron energy loss spectroscopy, as an sp3 content up to 83% is measured. Data on the macroscopic properties are provided by optical transmittance, ellipsometry, Rutherford backscattering, elastic recoil scattering, and resistivity measurements. The films exhibit high optical transparency and an optical gap of 2.4 eV. Trends in the optical gap and refractive index as a function of deposition energy are consistent with semiconductor theory and indicates a change in the average bond length.

Processing of La1.8Sr0.2CuO4 and YBa2Cu3O7 superconducting thin films by dual‐ion‐beam sputtering

High quality La1.8Sr0.2CuO4 and YBa2Cu3O7 superconducting thin films, with zero resistance at 88 K, have been made by dual‐ion‐beam sputtering of metal and oxide targets at elevated temperatures. The films are about 1.0 μm thick and are single phase after annealing. The substrates investigated are Nd‐YAP, MgO, SrF2, Si, CaF2, ZrO2‐9% Y2O3, BaF2, Al2O3, and SrTiO3. Characterization of the films was carried out using Rutherford backscattering spectroscopy, resistivity measurements, transmission electron microscopy, x‐ray diffraction, and secondary ion mass spectroscopy. Substrate/film interaction was observed in every case. This generally involves diffusion of the substrate into the film, which is accompanied by, for example, the replacement of Ba by Sr in the YBa2Cu2O7 structure, in the case of SrTiO3 substrate. The best substrates were those that did not significantly diffuse into the film and which did not react chemically with the film. In general, the superconducting transition temperature is found to ...

In situ x‐ray diffraction analysis of the C49–C54 titanium silicide phase transformation in narrow lines

The transformation of titanium silicide from the C49 to the C54 structure was studied using x‐ray diffraction of samples containing arrays of narrow lines of preformed C49 TiSi2. Using a synchrotron x‐ray source, diffraction patterns were collected at 1.5–2 °C intervals during sample heating at rates of 3 or 20 °C/s to temperatures of 1000–1100 °C. The results show a monotonic increase in the C54 transition temperature by as much as 180 °C with a decreasing linewidth from 1.0 to 0.1 μm. Also observed is a monotonic increase in (040) preferred orientation of the C54 phase with decreasing linewidth. The results demonstrate the power of in situ x‐ray diffraction of narrow line arrays as a tool to study finite size effects in thin‐film reactions.

Low temperature formation of C54–TiSi2 using titanium alloys

We demonstrate that the temperature at which the C49 TiSi2 phase transforms to the C54 TiSi2 phase can be lowered more than 100 °C by alloying Ti with small amounts of Mo, Ta, or Nb. Titanium alloy blanket films, containing from 1 to 20 at. % Mo, Ta, or Nb were deposited onto undoped polycrystalline Si substrates. The temperature at which the C49–C54 transformation occurs during annealing at constant ramp rate was determined by in situ sheet resistance and x-ray diffraction measurements. Tantalum and niobium additions reduce the transformation temperature without causing a large increase in resistivity of the resulting C54 TiSi2 phase, while Mo additions lead to a large increase in resistivity. Titanium tantalum alloys were also used to form C54 TiSi2 on isolated regions of arsenic doped Si(100) and polycrystalline Si having linewidths ranging from 0.13 to 0.56 μm. The C54 phase transformation temperature was lowered by over 100 °C for both the blanket and fine line samples. As the concentration of Mo, Ta...

Phase formation and microstructure changes in tantalum thin films induced by bias sputtering

The effects of argon‐ion bombardment on the structure and properties of sputtered tantalum films have been studied. Applied substrate bias voltage was used to control the bombardment energy in a hollow‐cathode‐enhanced low‐pressure magnetron sputtering system. The films were characterized by x‐ray diffraction, electrical measurements, Rutherford backscattering spectrometry, and stress measurements. The findings concerning the effects of negative substrate bias on film resistivity and structure run counter to earlier work. In particular, as opposed to results found in many early studies, which primarily involved higher‐pressure discharges, at zero bias voltage the films have low resistivity and contain the bcc phase. Increasing the bias to −100 V, increases the resistivity dramatically, and induces formation of β‐Ta, with no significant change in film impurity levels. The difference from earlier work is attributed to the lower relative impurity flux, as well as more energetic substrate bombardment in low‐p...

Processing of La/sub 1. 8/Sr/sub 0. 2/CuO/sub 4/ and YBa/sub 2/Cu/sub 3/O/sub 7/ superconducting thin films by dual-ion-beam sputtering

High quality La1.8Sr0.2CuO4 and YBa2Cu3O7 superconducting thin films, with zero resistance at 88 K, have been made by dual‐ion‐beam sputtering of metal and oxide targets at elevated temperatures. The films are about 1.0 μm thick and are single phase after annealing. The substrates investigated are Nd‐YAP, MgO, SrF2, Si, CaF2, ZrO2‐9% Y2O3, BaF2, Al2O3, and SrTiO3. Characterization of the films was carried out using Rutherford backscattering spectroscopy, resistivity measurements, transmission electron microscopy, x‐ray diffraction, and secondary ion mass spectroscopy. Substrate/film interaction was observed in every case. This generally involves diffusion of the substrate into the film, which is accompanied by, for example, the replacement of Ba by Sr in the YBa2Cu2O7 structure, in the case of SrTiO3 substrate. The best substrates were those that did not significantly diffuse into the film and which did not react chemically with the film. In general, the superconducting transition temperature is found to ...

Thin‐film Bi‐Sr‐Ca‐Cu‐O high‐temperature superconductors using pulsed laser evaporation from sintered disks

Films of the high‐temperature superconductor in the Bi‐Sr‐Ca‐Cu‐O system were deposited by pulsed laser evaporation from a ceramic disk. Films deposited onto (100) MgO show x‐ray diffraction patterns characteristic of c‐axis textured Bi2(Sr,Ca,Bi)3Cu2Ox phase following annealing for 10 min at 850 °C in 20% O2‐80% N2. These textured films have zero resistance at 78 K and show resistance drops near 110 K. The effects of the annealing environment on the electrical and structural properties are presented.

Ferroelectric Film Synthesis, Past and Present: A Select Review

A review of the history of ferroelectric (FE) thin film synthesis is given covering the period of the 1960s to the present. Early methods, materials and applications are discussed. An assessment of the recent upsurge in activity takes note of current targeted applications, including nonvolatile memory, piezoelectric actuators, capacitors, and electro-optic devices. Focus is placed on similarities and differences in the most common film deposition processes. Comparison of microstructure and composition variation seen in films deposited by sputtering, laser ablation, and solution deposition is made. More detailed understanding of process-microstructure relations is stressed as necessary for film property control. Also discussed are the roles of substrate interactions and interface layers in thin film growth.

Study of C49‐TiSi2 and C54‐TiSi2 formation on doped polycrystalline silicon using in situ resistance measurements during annealing

In situ resistance versus temperature or time for reactions between 32 and 57.5 nm of titanium and undoped or doped polycrystalline silicon (boron, arsenic, or phosphorus, 7.9×1019–3.0×1020/cm3) has been measured and no clear correlation was found between the activation energy for the formation of the industrially important low‐resistance C54‐TiSi2 phase and its formation temperature. It is also demonstrated that with certain moderate doping levels typical of complementary metal‐oxide‐semiconductor manufacturing, boron or phosphorus‐doped polycrystalline silicon can delay the formation of C54‐TiSi2 more than arsenic‐doped polycrystalline silicon. Finally, by using in situ resistance measurements, it is demonstrated that the ‘‘two‐step’’ thermal annealing process similar to a salicide process requires less thermal annealing time at high temperatures to form C54‐TiSi2 than a single ‘‘one‐step’’ thermal anneal at the same temperature.