Katharine Dovidenko

Low temperature inorganic chemical vapor deposition of Ti–Si–N diffusion barrier liners for gigascale copper interconnect applications

A new low temperature inorganic thermal chemical vapor deposition process has been developed for the growth of titanium–silicon–nitride (Ti–Si–N) liners for diffusion barrier applications in ultralarge scale integration copper interconnect schemes. This process employs the thermal reaction of tetraiodotitanium (TiI4), tetraiodosilane (SiI4), and ammonia (NH3) as, respectively, the individual Ti, Si, and N sources. Ti–Si–N films were successfully grown over a broad range of deposition conditions, including wafer temperature, process pressure, and TiI4, SiI4, and NH3 flows ranging, respectively, from 350 to 430 °C, 0.1–1 Torr, and 2.5–8.0, 2.5–12.5, and 100–250 sccm. Film stoichiometry was tightly tailored through independent control of the Ti, Si, and N source flows. Film properties were characterized by x-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, transmission electron microscopy, scanning electron microscopy, x-ray diffraction, and four-point resistivity probe. Resulting find...

InAs quantum dot laser diodes: structure, characteristics, and temperature dependence

The influence of two monolayer (ML)-thick AlAs under- and overlayers on the formation and properties of self-assembled InAs quantum dots (QDs) has been studied using transmission electron microscopy, photoluminescence (PL) and electroluminescence. The main purpose of this work was to achieve high internal quantum efficiency of the active medium and temperature stability of the laser diodes. Single and multiple layers of 2.0-2.4ML InAs QDs with various combinations of under- and overlayers were grown on GaAs (001) substrate by molecular beam epitaxy inside a AlAs/GaAs short-period superlattice. It was found that a 2.4-ML InAs QD layer with GaAs underlayer and 2-ML AlAs overlayer exhibited the lowest QD surface density of 4.2x1010 cm-2 and the largest QD lateral size of about 19 nm as compared to the other combinations of cladding layers. This InAs QD ensemble has also shown the highest room temperature PL intensity with a peak at 1210 nm and the narrowest linewidth, 34 meV. Fabricated edge-emitting lasers using triple layers of 2.2-ML InAs QDs with AlAs overlayer demonstrated 120 A/cm2 threshold current density and 1230 nm emission wavelength at room temperature. Excited state QD lasers have shown high thermal stability of threshold current up to 130 degree(s)C.

Oxidation Kinetics and Microstructure of Wet-Oxidized MBE-Grown Short-Period AlGaAs Superlattices

Abstract : The kinetics of the wet oxidation process of MBE-grown high-Al-content AlAs/Al(0.6)Ga(0.4)As short-period superlattices (SPSLs) was investigated and compared to AlGaAs alloys and pure AlAs. We found that alloys and superlattices (SLs) have different oxidation characteristics. These differences were attributed to traces of the superlattice structure in the oxidized material. The microstructure and chemistry of SPSLs with an equivalent composition of Al(0.98)Ga(0.02)As was studied, using transmission electron microscopy, energy-dispersive x-ray spectroscopy, Rutherford backscattering, and nuclear reaction analysis for hydrogen-profiling. We also report on the mechanical stability of oxidized SPSL layers in optoelectronic device structures.

Growth and structure of epitaxial Al and Cu films on CaF2

Abstract This work explores molecular beam epitaxial growth and microstructure of thin Al and Cu films on CaF 2 /Si(111). A technique of CaF 2 growth on H-terminated Si surface is described that reduces exposure of clean Si to vacuum environment and promotes smoothness of subsequent thin metal films. Reflection high energy electron diffraction shows that epitaxial Al(111) is obtained directly on CaF 2 , and epitaxial Cu(111) is obtained on 1-nm thick Al seed layer pre-deposited on CaF 2 . Transmission electron microscopy reveals that 75-nm thick Al films have 150-nm wide grains misoriented by less than 1°. For 75-nm thick Cu, the grains are only 30 nm-wide and are misoriented by as much as ±7°. Relationship between reflection high energy electron diffraction and transmission electron microscopy results for Cu is discussed.

Site-specific cross-sectioning of carbon nanotube-to-metal junctions for high spatial resolution chemical and structural analysis

In this study, we have demonstrated successful site-specific cross-sectioning of carbon-nanotube - metal junctions which provided samples suitable for high resolution transmission electron microscopy and electron energy loss spectroscopy. For the cross-sectioning, we have suggested a modified technique based on combination of the Focused Ion Beam (FIB) lift-out and the conventional Ar + ion milling techniques. Electron-transparent cross-sections of multiwall carbon nanotubes showing no significant surface amorphization or Ga contamination (typical artifacts of conventional FIB lift-out technique) were obtained. High-resolution transmission electron microscopy and electron energy loss spectroscopy of a multi-wall carbon nanotube cross-section have been carried out.

Physical Properties and Diffusion Characteristics of CVD-Grown TiSiN Films

TiSiN films grown by chemical vapor deposition were characterized to evaluate the properties relevant to the application as a diffusion barrier in Cu-based interconnects. The films were grown using TiI 4 + SiI 4 + NH 3 + H 2 chemistry at substrate temperature, 370°C, and SiI 4 - to-TiI 4 precursor flow rate ratio of 30. The combined results from x-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) revealed that the bulk of Ti 32 Si 21 N 42 films were predominantly consisted of a mixture of cubic TiN and amorphous SiN x phases. The specific electrical resistivity of the films was about 2000 μΩcm which is a few times higher than that of sputtered TiSiN films having similar composition and thicknesses. The 40 nm-thick barrier appeared to be thermally stable against Cu diffusion at the annealing temperatures up to 550°C. Breakdown of this diffusion barrier occurred at 600°C and was accompanied by the formation of Cu3Si protrusions at the TiSiN/Si interface.

InAs Quantum Dots in AlAs/GaAs Short Period Superlattices: Structure, Optical Characteristics and Laser Diodes

Abstract : The influence of two monolayer - thick AlAs under- and overlayers on the formation and properties of self-assembled InAs quantum dots (QDs) has been studied using transmission electron microscopy (TEM) and photoluminescence (PL). Single sheets of InAs QDs were grown inside a 2 ML/8 ML AlAs/GaAs short-period superlattice with various combinations of under- and overlayers. It was found that 2.4 ML InAs QDs with GaAs underlayer and 2 ML AlAs overlayer exhibited the lowest QD surface density of 4.2 x 10(exp 10)/sq cm and the largest QD lateral size of about 19 nm as compared to the other combinations of cladding layers. This InAs QD ensemble has also shown the highest room temperature PL intensity with a peak at 1210 mn and the narrowest linewidth, 34 meV. Fabricated edge-emitting lasers using triple layers of InAs QDs with AlAs overlayer demonstrated 120 A/sq cm threshold current density and 1230 nm emission wavelength at room temperature. Excited state QD lasers have shown high thermal stability of threshold current up to 130 deg C.

Thin Epitaxial Al and Cu Films Grown on CaF2/Si(111)

The ability to grow single-crystalline Al and Cu films is of significance for several areas of materials research, such as the resistivity size effect in thin metal films, electromigration failure of interconnects, and magneto-resistance studies. Here, we explore the microstructure and resistivity of thin Al and Cu films grown on CaF 2 /Si(111). A three-step technique of CaF 2 growth is described that permits deposition under imperfect vacuum conditions and promotes smoothness of subsequent thin metal films. Reflection high-energy electron diffraction shows that epitaxial Al(111) is obtained directly on CaF 2 , while epitaxial Cu(111) is obtained only by growing on a 1 nm thick Al seed layer pre-deposited on CaF 2 . Transmission electron microscopy reveals that 75 nm thick Al films have 150 nm wide sub-grains misoriented by less than 1 degree. For 75 nm thick Cu, the grains are only 30 nm wide and are misoriented by as much as 10 degrees. Room temperature resistivity measurements of the 10-300 nm thick Al films agree with the Fuchs-Sondheimer model in which conduction electrons scatter totally diffusely at the film interfaces. For 50-1000 nm thick Cu films, the resistivity size effect is substantially greater than the prediction of this model, which may be explained in terms of grain boundary scattering.