Susceptor assisted microwave annealing of ion implanted silicon

149810-Thumbnail Image.png
Description
This thesis discusses the use of low temperature microwave anneal as an alternative technique to recrystallize materials damaged or amorphized due to implantation techniques. The work focuses on the annealing of high-Z doped Si wafers that are incapable of attaining

This thesis discusses the use of low temperature microwave anneal as an alternative technique to recrystallize materials damaged or amorphized due to implantation techniques. The work focuses on the annealing of high-Z doped Si wafers that are incapable of attaining high temperatures required for recrystallizing the damaged implanted layers by microwave absorption The increasing necessity for quicker and more efficient processing techniques motivates study of the use of a single frequency applicator microwave cavity along with a Fe2O3 infused SiC-alumina susceptor/applicator as an alternative post implantation process. Arsenic implanted Si samples of different dopant concentrations and implantation energies were studied pre and post microwave annealing. A set of as-implanted Si samples were also used to assess the effect of inactive dopants against presence of electrically active dopants on the recrystallization mechanisms. The extent of damage repair and Si recrystallization of the damage caused by arsenic and Si implantation of Si is determined by cross-section transmission electron microscopy and Raman spectroscopy. Dopant activation is evaluated for the As implanted Si by sheet resistance measurements. For the same, secondary ion mass spectroscopy analysis is used to compare the extent of diffusion that results from such microwave annealing with that experienced when using conventional rapid thermal annealing (RTA). Results show that compared to susceptor assisted microwave annealing, RTA caused undesired dopant diffusion. The SiC-alumina susceptor plays a predominant role in supplying heat to the Si substrate, and acts as an assistor that helps a high-Z dopant like arsenic to absorb the microwave energy using a microwave loss mechanism which is a combination of ionic and dipole losses. Comparisons of annealing of the samples were done with and without the use of the susceptor, and confirm the role played by the susceptor, since the samples donot recrystallize when the surface heating mechanism provided by the susceptor is not incorporated. Variable frequency microwave annealing was also performed over the as-implanted Si samples for durations and temperatures higher than the single frequency microwave anneal, but only partial recrystallization of the damaged layer was achieved.
Date Created
2011
Agent

Metal-oxide based transparent conductive oxides and thin film transistors for flexible electronics

149554-Thumbnail Image.png
Description
The object of this study is to investigate and improve the performance/stability of the flexible thin film transistors (TFTs) and to study the properties of metal oxide transparent conductive oxides for wide range of flexible electronic applications. Initially, a study

The object of this study is to investigate and improve the performance/stability of the flexible thin film transistors (TFTs) and to study the properties of metal oxide transparent conductive oxides for wide range of flexible electronic applications. Initially, a study has been done to improve the conductivity of ITO (indium tin oxide) films on PEN (polyethylene naphthalate) by inserting a thin layer of silver layer between two ITO layers. The multilayer with an optimum Ag mid-layer thickness, of 8 nm, exhibited excellent photopic average transmittance (~ 88 %), resistivity (~ 2.7 × 10-5 µ-cm.) and has the best Hackee figure of merit (41.0 × 10-3 Ω-1). The electrical conduction is dominated by two different scattering mechanisms depending on the thickness of the Ag mid-layer. Optical transmission is explained by scattering losses and absorption of light due to inter-band electronic transitions. A systematic study was carried out to improve the performance/stability of the TFTs on PEN. The performance and stability of a-Si:H and a-IZO (amorphous indium zinc oxide) TFTs were improved by performing a systematic low temperature (150 °C) anneals for extended times. For 96 hours annealed a-Si:H TFTs, the sub-threshold slope and off-current were reduced by a factor ~ 3 and by 2 orders of magnitude, respectively when compared to unannealed a-Si:H TFTs. For a-IZO TFTs, 48 hours of annealing is found to be the optimum time for the best performance and elevated temperature stability. These devices exhibit saturation mobility varying between 4.5-5.5 cm2/V-s, ION/IOFF ratio was 106 and a sub-threshold swing variation of 1-1.25 V/decade. An in-depth study on the mechanical and electromechanical stress response on the electrical properties of the a-IZO TFTs has also been investigated. Finally, the a-Si:H TFTs were exposed to gamma radiation to examine their radiation resistance. The interface trap density (Nit) values range from 5 to 6 × 1011 cm-2 for only electrical stress bias case. For "irradiation only" case, the Nit value increases from 5×1011 cm-2 to 2×1012 cm-2 after 3 hours of gamma radiation exposure, whereas it increases from 5×1011 cm-2 to 4×1012 cm-2 for "combined gamma and electrical stress".
Date Created
2011
Agent

Adhesion in a copper-ruthenium multilayer nano-scale structure and the use of a Miedema plot to select a diffusion barrier metal for copper metallization

149459-Thumbnail Image.png
Description
Miedema's plot is used to select the Cu/metal barrier for Cu metallization.The Cu/metal barrier system selected should have positive heat of formation (Hf) so that there is no intermixing between the two layers. In this case, Ru is chosen as

Miedema's plot is used to select the Cu/metal barrier for Cu metallization.The Cu/metal barrier system selected should have positive heat of formation (Hf) so that there is no intermixing between the two layers. In this case, Ru is chosen as a potential candidate, and then the barrier properties of sputtered Cu/Ru thin films on thermally grown SiO2 substrates are investigated by Rutherford backscattering spectrometry (RBS), X-ray diffractometry (XRD), and electrical resistivity measurement. The Cu/Ru/SiO2 samples are analyzed prior to and after vacuum annealing at various temperatures of 400, 500, and 600 oC and at different interval of times of 0.5, 1 and 2 hrs for each temperature. Backscattering analysis indicate that both the copper and ruthenium thin films are thermally stable at high temperature of 600 oC, without any interdiffusion and chemical reaction between Cu and Ru thin films. No new phase formation is observed in any of the Cu/Ru/SiO2 samples. The XRD data indicate no new phase formation in any of the annealed Cu/Ru/SiO2 samples and confirmed excellent thermal stability of Cu on Ru layer. The electrical resistivity measurement indicated that the electrical resistivity value of the copper thin films annealed at 400, 500, and 600 oC is essentially constant and the copper films are thermally stable on Ru, no reaction occurs between copper films and Ru the layer. Cu/Ru/SiO2 multilayered thin film samples have been shown to possess good mechanical strength and adhesion between the Cu and Ru layers compared to the Cu/SiO2 thin film samples. The strength evaluation is carried out under static loading conditions such as nanoindentation testing. In this study, evaluation and comparison is donebased on the dynamic deformation behavior of Cu/Ru/SiO2 and Cu/SiO2 samples under scratch loading condition as a measure of tribological properties. Finally, the deformation behavior under static and dynamic loading conditions is understood using the scanning electron microscope (SEM) and the focused ionbeam imaging microscope (FIB) for topographical and cross-sectional imaging respectively.
Date Created
2010
Agent