N. D. Theodore

Improved conductivity and mechanism of carrier transport in zinc oxide with embedded silver layer

The effects of an embedded silver layer on the electrical and optical properties of zinc oxide (ZnO)/silver (Ag)/zinc oxide (ZnO) layered composite structures on polymer substrates have been investigated. We have engineered transparent conducting oxide structures with greatly improved conductivity. Optical and electrical properties are correlated with Ag thickness. Film thicknesses were determined using Rutherford backscattering spectrometry. Hall effect, four-point probe, and UV-Vis spectrophotometer analyses were used to characterize electrical and optical properties. The results show that carrier concentration, mobility, and conductivity increase with Ag thickness. Increasing Ag thickness from 8to14nm enhances sheet resistance and resistivity by six orders of magnitude. The optical transmittance of the composite structure decreases when compared to a single ZnO layer of comparable thickness. However, a composite with 12nm of Ag provides conductivity and transmittance values that are acceptable for opto...

Hydrogen plasma enhancement of boron activation in shallow junctions

The ability to activate large concentrations of boron at lower temperatures is a persistent contingency in the continual drive for device scaling in Si microelectronics. We report on our experimental observations offering evidence for enhancement of electrical activation of implanted boron dopant in the presence of atomic hydrogen in silicon. This increased electrical activity of boron at lower anneal temperature is attributed to the creation of vacancies in the boron-implanted region, lattice-relaxation caused by the presence of atomic hydrogen, and the effect of atomic hydrogen on boron-interstitial cluster formation.

The role of copper in ZnO/Cu/ZnO thin films for flexible electronics

ZnO/Cu/ZnO multilayer structures with very high conductivity have been obtained by magnetron sputtering. The Hall resistivity of the films was as low as 6.9×10−5 Ω-cm with a carrier concentration of 1.2×1022 cm−3 at the optimum copper layer thickness. The conduction mechanism has been explained in terms of metal to oxide carrier injection at low copper thickness and metal layer conduction at higher Cu thicknesses. The peak transmittance of the films is 88% and the photopic averaged transmittance is 75%. Optical transmission behavior of the films involves absorption by copper due to d-band to Fermi-surface transitions at short wavelengths and reflectance combined with scattering losses at long wavelengths. A Burstein–Moss shift in the band gap of the films is seen to take place with increase in thickness of the copper layer. The Haacke figure of merit has been calculated for the films with the best value being 8.7×10−3 Ω−1. Pole figure results reveal that the copper midlayer acts as a hindrance to (002) Zn...

Observation of interfacial void formation in bonded copper layers

Silicon wafers are bonded using copper (Cu) as the bonding medium and annealed to enhance the bonding strength at temperatures ranging from 300to400°C. The original bonding interface disappears and the Cu layers merge to form a single homogeneous layer. Cross-section transmission electron microscopy reveals a number of voids at the original bonding interface. It is observed that the size of these interfacial voids increases with bonding temperature. Thermal stress relaxation is proposed as the cause for interfacial void formation in the bonded Cu layers.

Effect of SiO2 incorporation on stability and work function of conducting MoO2

We show the incorporation of different amounts of SiO2 in conducting MoO2 results in materials that have large vacuum work functions tunable by approximately 1eV and improved thermal stability at elevated temperatures. Electrical measurements of MoSixOy∕HfO2∕SiOx∕n-Si capacitors show an approximate 5.1eV work function, suitable for p-channel metal-oxide-semiconductor devices. . Thickening of the interfacial SiOx layer was observed, however, after annealing the stack at higher temperatures in N2.

Evidence for ion irradiation induced dissociation and reconstruction of Si–H bonds in hydrogen-implanted silicon

We observe that H-related chemical bonds formed in H-implanted Si will evolve under subsequent ion irradiation. During ion irradiation hydrogen is inclined to dissociate from simple H-related defect complexes (i.e., VHx and IHx), diffuse, and attach to vacancy-type defects resulting in new platelet formation, which facilitate surface blistering after annealing, a process completely inhibited in the absence of ion irradiation. The understanding of our results provides insight into the structure and stability of hydrogen-related defects in silicon.

Susceptor assisted microwave annealing for recrystallization and dopant activation of arsenic-implanted silicon

The increasing need for quicker and more efficient processing techniques motivates the study of the use of a single frequency applicator microwave cavity, along with an alumina-coated SiC susceptor, as an alternative to current post-implantation processing. The extent of Si recrystallization and repair of the damage caused by arsenic implantation into Si is determined by cross-section transmission electron microscopy and Raman spectroscopy. Dopant activation is evaluated by sheet resistance measurements. Secondary ion mass spectroscopy is used to compare the extent of diffusion that results from such microwave annealing with that experienced when using conventional rapid thermal annealing (RTA). The results show that, compared to susceptor-assisted microwave annealing, RTA caused undesired dopant diffusion. The SiC-alumina susceptor plays a significant role in supplying heat to the Si substrate and also acts as an assistor that helps a high-Z dopant, like arsenic, to absorb the microwave energy, using a m...

Dopant Activation in Arsenic-Implanted Si by Susceptor-Assisted Low-Temperature Microwave Anneal

It is important for nanoscale transistors to have abrupt junctions, which are difficult to achieve via high-temperature anneals of implanted semiconductor layers due to undesired dopant diffusion. The use of a single-frequency microwave cavity applicator, along with a SiC-Alumina susceptor/assistor, is suggested as an alternative postimplantation process. Secondary ion mass spectroscopy analysis of microwave-annealed As-implanted Si samples show minimal diffusion, compared to rapid thermal annealed samples. Cross-sectional transmission electron microscopy and Raman spectroscopy confirm damage repair and Si recrystallization upon low-temperature microwave annealing (up to 650°C). Ion channeling and sheet resistance measurements validate dopant relocation and activation. The susceptor is used to provide surface heating to the high-atomic-number Z implanted sample to enable it to absorb microwaves and thereby recrystallize through volumetric heating.

Physical and electrical properties of nanolaminated HfO2/LaAlO3/HfO2 dielectric on Si

Because of high defectivity and poor uniformity in polycrystalline HfO2, searching for an amorphous dielectric with a high dielectric constant and good stability has become an increasingly important task for high-k gate-stack research. We show that nanolaminated HfO2∕LaAlO3∕HfO2 dielectric grown on Si not only remains amorphous after annealing in N2 at 900°C for 60s but also has an effective dielectric constant comparable to that of HfO2. Additionally, electrical characterization of the capacitors made from the laminated dielectric revealed a smaller hysteresis and improved voltage stress behavior compared to its polycrystalline HfO2 counterpart.

Prediction of transmittance spectra for transparent composite electrodes with ultra-thin metal layers

Recent interest in indium-free transparent composite-electrodes (TCEs) has motivated theoretical and experimental efforts to better understand and enhance their electrical and optical properties. Various tools have been developed to calculate the optical transmittance of multilayer thin-film structures based on the transfer-matrix method. However, the factors that affect the accuracy of these calculations have not been investigated very much. In this study, two sets of TCEs, TiO2/Au/TiO2 and TiO2/Ag/TiO2, were fabricated to study the factors that affect the accuracy of transmittance predictions. We found that the predicted transmittance can deviate significantly from measured transmittance for TCEs that have ultra-thin plasmonic metal layers. The ultrathin metal layer in the TCE is typically discontinuous. When light interacts with the metallic islands in this discontinuous layer, localized surface plasmons are generated. This causes extra light absorption, which then leads to the actual transmittance bei...