Steven W. Novak

Structural and electrical properties of trimethylboron-doped silicon nanowires

Trimethylboron (TMB) was investigated as a p-type dopant source for the vapor–liquid–solid growth of boron-doped silicon nanowires (SiNWs). The boron concentration in the nanowires was measured using secondary ion mass spectrometry and results were compared for boron-doping using TMB and diborane (B2H6) sources. Boron concentrations ranging from 1×1018 to 4×1019cm−3 were obtained by varying the inlet dopant∕SiH4 gas ratio. TEM characterization revealed that the B2H6-doped SiNWs consisted of a crystalline core with a thick amorphous Si coating, while the TMB-doped SiNWs were predominantly single crystal even at high boron concentrations. The difference in structural properties was attributed to the higher thermal stability and reduced reactivity of TMB compared to B2H6. Four-point resistivity and gate-dependent conductance measurements were used to confirm p-type conductivity in the TMB-doped nanowires and to investigate the effect of dopant concentration on nanowire resistivity.

High precision measurement of obsidian hydration layers on artifacts from the Hopewell site using secondary ion mass spectrometry

Obsidian hydration dating has served as one of the chronological indicators for the Hopewell Culture earthworks (ca. 200 B.C.—A.D. 500) in central Ohio. This work presents new obsidian hydration dates developed from high precision hydration layer depth profiling using secondary ion mass spectrometry (SIMS). These data suggest that long-distance exchange in obsidian occurred throughout the Hopewell period.

Dating of hydrated obsidian surfaces by SIMS-SS

A new approach to dating ancient obsidian artifacts based on the modeling of water diffusion profiles is evaluated using multiple archaeological test cases of known age. Hydrogen profiles from hydrated obsidian surfaces have been collected by secondary ion mass spectrometry (SIMS). The H2O concentration versus depth profiles are modeled and diffusion ages have been produced. SIMS based dates for fourteen obsidian specimens of well-known age, ranging from 300-7000 years old, have been compared with radiocarbon ages. The convergence between the two dating methods is excellent and validates the new dating approach.

Cu penetration into low-k dielectric during deposition and bias-temperature stress

Cu penetration into low-k dielectrics can cause serious reliability issues in on-chip interconnect systems. Using secondary ion mass spectrometry with both front-side and back-side depth profiling strategies, Cu was found to diffuse into SiCOH low-k dielectric in a Cu/SiCOH/Si capacitor during Cu deposition. After bias-temperature stressing the capacitor at 270 °C and 2.5 MV/cm, Cu penetrates further into SiCOH, but its distribution profile is the same as that after the same temperature annealing without electrical bias, suggesting no Cu ion drift. The implication of these findings on the Cu/low-k dielectric time-dependent dielectric breakdown modeling is discussed.

Ion implantation synthesized copper oxide-based resistive memory devices

Copper oxide resistive memory layers have been synthesized by ion implantation. Devices fabricated from off-stoichiometric Cu2O exhibited unipolar switching in forward/reverse bias without a forming voltage. The on-state conduction of these devices is likely dominated by a metallic filament, which ruptures via Joule heating to transition the device to the high resistance off-state. Technology scaling was achieved by oxygen implanting copper filled vias. The resulting via-based memory devices exhibited unipolar resistive switching down to 48 nm in diameter.

Experimental Evidence of Multiple Diffusion Mechanisms in Thin-Film Cu(In,Ga)Se 2

Lattice and grain boundary diffusions of cadmium in copper indium gallium diselenide (Cu(In,Ga)Se2 or CIGS) thin films were investigated by annealing cadmium into samples of 700-nm CIGS thickness at temperatures between 250 and 300 °C. Diffusion profiles of cadmium were analyzed by dual-beam time-of-flight secondary ion mass spectroscopy (TOF-SIMS). In addition to fast cadmium grain boundary diffusion, experiments revealed cadmium diffusion profiles with two distinct lattice diffusion stages, which could be indicative of simultaneous vacancy and dissociative diffusion mechanisms.

Insights into cadmium diffusion mechanisms in two-stage diffusion profiles in solar-grade Cu(In,Ga)Se2 thin films

Cadmium diffusion experiments were performed on polished copper indium gallium diselenide (Cu(In,Ga)Se2 or CIGS) samples with resulting cadmium diffusion profiles measured by time-of-flight secondary ion mass spectroscopy. Experiments done in the annealing temperature range between 275 °C and 425 °C reveal two-stage cadmium diffusion profiles which may be indicative of multiple diffusion mechanisms. Each stage can be described by the standard solutions of Ficks second law. The slower cadmium diffusion in the first stage can be described by the Arrhenius equation D1 = 3 × 10−4 exp (− 1.53 eV/kBT) cm2 s−1, possibly representing vacancy-meditated diffusion. The faster second-stage diffusion coefficients determined in these experiments match the previously reported cadmium diffusion Arrhenius equation of D2 = 4.8 × 10−4 exp (−1.04 eV/kBT) cm2 s−1, suggesting an interstitial-based mechanism.

High mobility Ge-channel formation by localized/selective liquid phase epitaxy (LPE) using Ge+B plasma ion implantation and laser melt annealing

Localized Ge and SiGe high mobility channel material is needed for 10nm node and beyond CMOS technology. Thin direct >50% SiGe selective epi followed by oxidation for Ge condensation, 100% Ge selective epi or thermal mixing are methods that require a hard mask and epi interface defects with rough surfaces are always an issue. An alternative approach to epi is using photoresist masking as proposed by Borland et al [1] with Ge-infusion doping (dose controlled deposition), a very high dose implantation technique that leads to amorphous deposition followed by low temperature SPE of the amorphous Ge surface layer but residual interface defects remained.

Synthesis and properties of ferromagnetic nanostructures embedded within a high-quality crystalline silicon matrix via ion implantation and nanocavity assisted gettering processes

Integrating magnetic functionalities with silicon holds the promise of developing, in the most dominant semiconductor, a paradigm-shift information technology based on the manipulation and control of electron spin and charge. Here, we demonstrate an ion implantation approach enabling the synthesis of a ferromagnetic layer within a defect free Si environment by exploiting an additional implant of hydrogen in a region deep below the metal implanted layer. Upon post-implantation annealing, nanocavities created within the H-implanted region act as trapping sites for gettering the implanted metal species, resulting in the formation of metal nanoparticles in a Si region of excellent crystal quality. This is exemplified by the synthesis of magnetic nickel nanoparticles in Si implanted with H+ (range: ∼850 nm; dose: 1.5 × 1016 cm−2) and Ni+ (range: ∼60 nm; dose: 2 × 1015 cm−2). Following annealing, the H implanted regions populated with Ni nanoparticles of size (∼10–25 nm) and density (∼1011/cm2) typical of those...

Diffusion activation energy of cadmium in thin film CuInGaSe 2

Diffusivity and activation energy of cadmium in copper indium gallium diselenide (CuInGaSe2 or CIGS) thin films were investigated by annealing solar-grade SLG/Mo/CIGS/CdS samples of two different CIGS thicknesses at temperatures between 150° C and 325° C. Diffusion profiles of cadmium volume and grain boundary were investigated by dual-beam time-of-flight secondary ion mass spectroscopy. A relationship between the cadmiums volume and grain boundary diffusion coefficients and their activation energies at a given annealing temperature was established using LeClaires grain boundary diffusion model. The data also provide evidence that cadmium diffusion may be strongly modulated by a gallium gradient seen both laterally at the interface and in the bulk in solar-grade CIGS material.