Pedro Rosales

High-quality spin-on glass-based oxide as a matrix for embedding HfO2 nanoparticles for metal-oxide-semiconductor capacitors

By using a low cost, simple, and reproducible spin-coating method, thin films of SOG (spin-on-glass)-based oxides with electrical characteristics resembling those of a dry thermal oxide have been obtained. The superior electrical characteristics of Metal-Oxide-Semiconductor (MOS) capacitors based on SOG-oxides come from both (1) reducing the organic content of the SOG solutions after dilution with deionized water and (2) passivation of the silicon surface by a thin chemical oxide. Fourier transform infrared spectroscopy analysis shows that the organic content in H2O-diluted SOG-oxides is reduced compared to undiluted SOG after N2 annealing. In addition, by chemically embedding HfO2 nanoparticles (np-HfO2) to these SOG-based oxides, an effective increase in the accumulation capacitance of MOS capacitors is observed and this is related to the increase in the final dielectric constant of the resulting oxide after annealing so that potential use of SOG as a glass matrix for embedding HfO2 nanoparticles and produce higher-k oxide materials is demonstrated.

Physical and electrical characteristics of atomic-layer deposition-HfO2 films deposited on Si substrates having different silanol Si-OH densities

In this work, ultrathin HfO2 films, less than 6 nm in thickness, are deposited by atomic-layer deposition (ALD) on Si substrates that have a variable density of silanol (Si-OH) chemical bonds after oxidizing the Si surface using hot H2O2. Given the surface chemistry needed for proper ALD growth of HfO2, OH-last surfaces are needed in order to react with the Hf-based precursor during half-cycle of this reaction. The later is important for proper nucleation and uniform growth of ultrathin HfO2 by ALD. Depending on the immersion time of an initially HF-last Si surface in hot H2O2, ultrathin and nonstoichiometric chemical oxides SiOx are formed presenting a variable density of Si-OH bonds which are measured after Fourier-transform infra red spectroscopy. Following SiOx formation, HfO2 is directly deposited on these surfaces by ALD using water (H2O) and tetrakis-dimethylamino-hafnium as precursors. Metal–insulator–semiconductor (MIS) capacitors are then formed using both HfO2/Si and HfO2/SiOx/Si stacked structures and their electrical characteristics are evaluated. It is found that a variable density of Si-OH chemical bonds have an impact on the physical and electrical characteristics of these MIS structures by reducing their atomic surface roughness (Rrms) and gate leakage current density (Jg), and at the same time, increasing their flat band voltage (Vfb) for the same immersion times in H2O2. Obtaining the lowest Rrms, Jg, and Vfb are possible by using intermediate H2O2 immersion times between 4 and 8 min, which is also directly related to an intermediate Si-OH bond density.In this work, ultrathin HfO2 films, less than 6 nm in thickness, are deposited by atomic-layer deposition (ALD) on Si substrates that have a variable density of silanol (Si-OH) chemical bonds after oxidizing the Si surface using hot H2O2. Given the surface chemistry needed for proper ALD growth of HfO2, OH-last surfaces are needed in order to react with the Hf-based precursor during half-cycle of this reaction. The later is important for proper nucleation and uniform growth of ultrathin HfO2 by ALD. Depending on the immersion time of an initially HF-last Si surface in hot H2O2, ultrathin and nonstoichiometric chemical oxides SiOx are formed presenting a variable density of Si-OH bonds which are measured after Fourier-transform infra red spectroscopy. Following SiOx formation, HfO2 is directly deposited on these surfaces by ALD using water (H2O) and tetrakis-dimethylamino-hafnium as precursors. Metal–insulator–semiconductor (MIS) capacitors are then formed using both HfO2/Si and HfO2/SiOx/Si stacked struct...

Thermal Oxide Grown on High Index Silicon Wafers

Even though the MOS technology was developed originally on the (0 0 1)-Si surface, some studies have shown that several MOS parameters can be optimized using other silicon orientations [1-3]. (1 1 4) and (5 5 12) Si surfaces presents a periodical surface roughness that may have technological applications [4]; however, the oxide grown on these surface orientations has not been studied. In this work we investigate the behavior of the oxide thickness in high index Si and compare it to oxides grown on standard surface orientations.

A comparative study of the emitter formation of a c-si solar cell using gas and spin on dopant sources

In this work, a comparative study for the n-type emitter formation in the fabrication of simple structures of crystalline silicon (c-Si) solar cells is reported. Gas and spin on dopant sources were employed in the pn junction formation of the solar cells in order to compare their performance. Phosphine (PH3) was used as n-type gas for phosphorus diffusion while the Filmtronics Spin-On Dopant SOD-P905 was used as n-type liquid source. From the results, we observed that there was a small discrepancy in the open circuit voltage, short circuit current and fill factor of the two processes, with similar efficiency. These results suggest that SOD-P905 can be used to produce low-cost silicon solar cells. Also in order to improve the efficiency of the SOD solar cells, a wet surface texturization stage was incorporated in the fabrication process.

Study of the spin on dopant technique as alternative for the fabrication of c-Si solar cells

In this work is reported a simple fabrication process of crystalline silicon (c-Si) solar cells using a n-type liquid source (Spin-On-Dopant, SOD) for the solar cell emitter formation. The solar cells were fabricated on p-type (5-15 Ωcm), (100), low cost Czochralski (Cz) silicon wafers and were textured using a solution based on potassium hydroxide (KOH). The efficiency reached in this work was of 14 % in a solar cell of 100 mm2. Despite the efficiency reported in this work is still lower than that achieved in high efficiency c-Si solar cells, it is important to stress that the simplicity of the fabrication process, the use of low cost CZ wafers and the use of SOD instead of doping gases (PH3 or POCL3), made this work interesting for a low cost and industrially compatible fabrication process of solar cells.

Amorphous, Polymorphous, and Microcrystalline Silicon Thin Films Deposited by Plasma at Low Temperatures

The present chapter is devoted to the study of amorphous (a-Si:H), polymorphous (pmSi:H), and microcrystalline (μc-Si:H) silicon, deposited by the plasma-enhanced chemical vapor deposition (PECVD) technique at low temperatures. We have studied the main deposition parameters that have strong influence on the optical, electrical, and structur‐ al properties of the polymorphous and microcrystalline materials. Our results reveal the key deposition conditions for obtained films with optical and electrical characteristics, which are suitable for applications on thin-film solar cells and semiconductor devices.

Evaluation of interface-states density for MOSFETs fabricated on high-index (114) silicon surfaces

Metal-oxide-semiconductor field-effect transistor (MOSFET) devices were fabricated on high-index silicon (114) surfaces and their threshold voltage (Vth) and interface-states density (Dit) parameters were both evaluated for the first time. Even though MOSFET devices aligned at 0°, 30°, 60° and 90° off the equivalent [110] direction present two closely related average Vth values, Dit evaluation shows that for all channel orientations (0°, 30°, 60° and 90°), this high-index silicon (114) surface develops a high-quality interface with SiO₂ in which few electrons are trapped so that Dit as low as 10¹⁰ cm^-2eV^-1 can be obtained.

Performance of a MOHOS-type memory using np-HfO 2 and variable tunneling oxide thickness

We use HfO2 nanoparticles (np-HfO2 embedded in a spin-on glass SOG oxide matrix) as a charge trapping layer CTL in metal/oxide/high-k/oxide/silicon (MOHOS)-memories. This CTL is then deposited on ultra-thin layers of chemical oxide SiOx ≤2nm. Depending on the SiOx thickness, a trade-off in writing/erasing and data retention time characteristics is obtained.

Progressive-degradation and breakdown of W-La 2 O 3 MOS structures after constant voltage stress

In this paper, we report the progressive electrical degradation and consequent breakdown (both soft and hard-breakdown regimes) of thin W-La2O3 stacked films deposited on silicon substrates and their influence on the electrical characteristics of metal-oxide-semiconductor (MOS) devices. Initial electrical degradation of the MOS devices results in an increase of the gate oxide leakage current (mostly known as Stress-Induced Leakage-Current, SILC), with the devices practical effect being a monotonous shift in threshold voltage (¿Vth) after constant voltage stressing. Following the initial degradation of the gate oxide, both soft and hard-breakdown modes are detected and their influence on the electrical characteristics of the MOS devices are also obtained and compared.

Reliability characteristics of W-La 2 O 3 structures compared with those of HfO 2 -based gate oxides

In this paper, we report and compare the reliability results obtained for W-La2O3 gated Metal-Oxide-Semiconductor (MOS) devices with those of HfO2-based systems reported in literature. Reliability issues like stress-induced leakage current (SILC), interface-states generation (Dit), threshold voltage shift (DeltaVth) and time to breakdown (tbd) were compared and analyzed for both dielectrics in order to obtain a more specific assessment of their resistance to electrical degradation and breakdown.