W. J. Varhue

Silicon dioxide films deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition

Thin films of silicon dioxide were deposited at low substrate temperatures (<375 °C) using electron cyclotron resonance plasma enhanced chemical vapor deposition. The deposition parameters studied included substrate temperature and radio frequency substrate bias. The deposited material was compared to thermally grown SiO2, through its etch rate in a buffered hydrofluoric solution, index of refraction, Fourier transform infrared spectroscopy, and Rutherford backscattering spectrometry. Through the application of rf substrate bias the deposited material properties approached that of thermally grown oxide. The feed to the substrate chamber was 40 sccm of a 2.0% silane in He. The large quantity of He in the chamber is credited with making the material more thermal‐like.

Comparison of diamond-like carbon film deposition by electron cyclotron resonance with benzene and methane

A comparative study of the deposition of diamond-like carbon films using methane or benzene in a microwave electron cyclotron resonance plasma-enhanced chemical vapor deposition system has been performed. Process variables studied were reactor pressure, applied radio frequency substrate bias, and microwave power. The plasma stream was characterized using optical emission spectroscopy and mass spectrometry. Film properties studied included optical energy gap, total hydrogen content, integrated C-H stretch absorption, index of refraction, and Raman spectra. The use of a high C/H ratio reactant such as benzene was found to be advantageous over methane in that higher deposition rates were possible and the resultant films exhibit diamond-like properties without the application of large substrate biases. Another result of this investigation was further confirmation that hard carbon films contain a significant quantity of nonbonded hydrogen [A. Grill and V. Patel, Appl. Phys. Lett. 60 (17), 2089 (1992)].

Epitaxial film thickness in the low‐temperature growth of Si(100) by plasma enhanced chemical vapor deposition

The limiting epitaxial thickness of Si films grown at a low substrate temperature by plasma enhanced chemical vapor deposition has been determined. The specific process used was electron cyclotron resonance plasma deposition. The limiting epitaxial thickness was found to decrease with the ratio of energetic ion‐to‐adatom arrivals on the substrate surface. The measured epitaxial thicknesses are similar to those obtained in previous investigations using molecular beam epitaxy. Hydrogen surface coverage does not appear to be a factor in limiting epitaxial thickness. The maximum epitaxial thickness remains to be determined for this process and substrate temperature range.

Erbium‐doped silicon films grown by plasma‐enhanced chemical‐vapor deposition

Epitaxial growth of erbium‐doped silicon films has been performed by plasma‐enhanced chemical vapor deposition using an electron‐cyclotron‐resonance source. The goal was to incorporate erbium as an optically active center (ErO6) through the use of metal‐organic dopant sources. The characteristic 1.5 μm emission was observed by photoluminescence. Chemical analysis of the film revealed, however, that the organic ligands were decomposing and contributing to the carbon contamination of the films. Analysis of the molecular flux to the substrate indicated that the metal‐organic compound used, tris(2,2,6,6‐tetramethyl‐3‐5‐heptanedionato)erbium(III), was most likely to decompose, and supply unbonded atomic erbium and not the optical active species, ErO6. Excessive carbon contamination lowered epitaxial quality and reduced the photoluminescent intensity. Photoluminescent intensity was improved by a 600 °C anneal but was strongly quenched by a 900 °C anneal. The low‐temperature anneal improved crystal quality, and ...

Low‐temperature homoepitaxial growth of Si by electron cyclotron resonance plasma enhanced chemical vapor deposition

Epitaxial Si films have been deposited at low substrate temperatures of 400 and 500 °C, by plasma enhanced chemical vapor deposition using an electron cyclotron resonance source. Samples were analyzed using Rutherford backscatter spectrometry, cross‐sectional transmission electron microscopy, and x‐ray diffraction. The ion‐to‐adatom arrival ratio was found to be an important parameter in determining epitaxial film quality. This ratio was controlled by the SiH4 feed rate, microwave power level, and shape of the magnetic field in the substrate region. Incident ion energy and ion flux were monitored with a gridded energy analyzer located at the substrate location.

Raman scattering and the π-orbitals in amorphous carbon films

We report a Raman study of amorphous carbon films grown by different techniques. We compare Raman line shapes, depolarization ratios, and excitation profiles obtained from samples grown by rf‐plasma deposition or sputtering as opposed to arc‐evaporated carbon films. We find that all features of the Raman spectra are closer to results from crystalline graphite for samples deposited with an electron cyclotron resonance plasma using either a hydrocarbon gas source or a graphite sputtering target. This is surprising in view of the much larger optical band gap of these samples and also in view of recent e‐2e scattering results which suggest that the π orbitals are more graphitelike in arc‐evaporated carbon films. We offer a possible explanation of this paradox based on a reinterpretation of the optical properties of amorphous carbon which takes into account the special characteristics of the electronic states derived from π orbitals.

Growth of Er‐doped silicon using metalorganics by plasma‐enhanced chemical vapor deposition

Epitaxial growth of Er‐doped silicon films has been performed by plasma‐enhanced chemical vapor deposition at low temperature (430 °C) using an electron cyclotron resonance source. The goal was to incorporate an optically active center, erbium surrounded by nitrogen, through the use of the metalorganic compound tris (bis trimethyl silyl amido) erbium. Films were analyzed by Rutherford backscattering spectrometry, secondary ion mass spectroscopy, and high resolution x‐ray diffraction. The characteristic 1.54 μm emission was observed by photoluminescence spectroscopy. Previous attempts to incorporate the complex (ErO6) using tris (2,2,6,6‐tetramethyl‐ 3,5‐heptanedionato) erbium (III) indicated that excessive carbon contamination lowered epitaxial quality and reduced photoluminescent intensity. In this study, chemical analysis of the films also revealed a large carbon concentration, however, the effect on epitaxial quality was much less destructive. A factorial design experiment was performed whose analysis ...

Control of ruthenium oxide nanorod length in reactive sputtering

Ruthenium oxide nanorods have been grown on Si wafer substrates under a variety of pre-existing surface conditions by reactive radio frequency sputtering in an electron cyclotron resonant plasma process. Nanorod formation by this method is fast relative to that observed in other processes reported in the literature, with nucleation being the rate determining step. Growth in the axial direction is limited by the availability of ruthenium precursors which competes with their consumption in the lateral growth of the nanorods. The availability of Ru precursors at the top of the nanorods can be controlled by surface diffusion and therefore substrate temperature. The ultimate length of the nanorods is determined by the mole fraction of oxygen used in the reactor ambient through the production of mobile Ru hyperoxide precursors. The results of this investigation show the way to develop a process for producing a high density field of nanorods with a specified length.

Structural evolution and characterization of heteroepitaxial GaSb thin films on Si(111) substrates

This paper describes the structural evolution and characterization of heteroepitaxial GaSb thin films on Si(111) substrates. The growth process used a combination of atomic sources which included the rf sputtering of Sb and the thermal effusion of Ga. The formation of crystalline GaSb thin films required that initially a monolayer thick Sb buffer layer be applied directly to a clean H-passivated Si(111) substrate surface. The resulting film was characterized by high resolution x-ray diffraction, Rutherford backscattering spectrometry, transmission electron microscopy, secondary ion mass spectroscopy, and atomic force microscopy (AFM). The AFM images were taken from the material after several periods of growth to determine the evolution of crystal structure with thickness. Atomic force microscopy images of the film surface showed that the heteroepitaxial layers were formed via the Stranski-Krastanov growth mechanism. This result is consistent with the heteroepitaxial growth of systems representing large di...

Radiative melting of crystalline ruthenium oxide nanorods

In this investigation, crystalline ruthenium oxide square nanorods have been observed via scanning electron microscopy (SEM) to melt at significantly lower temperatures than the melting temperature of bulk ruthenium oxide (1200 °C) at a measured substrate temperature of only 180 °C. The heating and subsequent melting of these nanorods occurs as a result of the combined effects of enhanced infrared (IR) absorption by the surface plasmon resonance and the inability of the nanorods to radiate at long wavelengths. This can result in the transfer of energy from a lower temperature body to a higher temperature body. This observation does not violate any thermodynamic laws as the entropy of the system is reduced with the concurrent input of energy.