Jane P. Chang

Dielectric property and thermal stability of HfO2 on silicon

A stoichiometric, uniform, and amorphous hafnium oxide thin film is deposited by an atomic layer deposition process. The as-deposited hafnium oxide films showed superior electrical properties compared to zirconium oxides, including a dielectric constant of 23, a flatband voltage shift of +0.3 V, a hysteresis of 25 mV, an interfacial trap density of 1.8×1011 cm−2 eV−1, and a leakage current density several orders of magnitude lower than SiO2 at an equivalent oxide thickness of 9.3 A, suitable for metal–oxide–semiconductor device applications. The thermal stability of hafnium oxide on silicon was determined to be better than that of zirconium oxide. Post-deposition annealing in oxygen and ammonia further improved the thermal stability of HfO2 to 1000 and 1100 °C, respectively.

Kinetic study of low energy ion-enhanced polysilicon etching using Cl, Cl2, and Cl+ beam scattering

The chlorine ion-enhanced etching yield of polysilicon in the low ion energy regime was characterized as a function of Cl ion energy, ion flux, neutral-to-ion flux ratio, and the ion impingement angle by utilizing Cl+, Cl, and Cl2 beam scattering. The chlorine ionic, atomic, and molecular fluxes were controlled independently over more than an order of magnitude and at flux levels within an order of magnitude of that typically used in high density plasma processes. The etching yield increased with the increase of Cl/Cl+ flux ratio but gradually saturated at higher flux ratios as the surface became saturated with chlorine. The ion energy dependence was a linear function of (Eion1/2−Eth1/2), where the threshold energy Eth was found to be approximately 10 eV. With Cl+ ion bombardment, the etching yield of Cl was two to three times higher than that of Cl2 at higher flux ratios. The angular dependence of ion-enhanced etching yield was also measured. The etching yield was reduced by approximately 30% and 50% whe...

Profiling nitrogen in ultrathin silicon oxynitrides with angle-resolved x-ray photoelectron spectroscopy

Angle-resolved x-ray photoelectron spectroscopy (AR–XPS) is utilized in this work to accurately and nondestructively determine the nitrogen concentration and profile in ultrathin SiOxNy films. With furnace growth at 800–850 °C using nitric oxide (NO) and oxygen, 1013–1015 cm−2 of nitrogen is incorporated in the ultrathin (⩽4 nm) oxide films. Additional nitrogen can be incorporated by low energy ion (15N2) implantation. The nitrogen profile and nitrogen chemical bonding states are analyzed as a function of the depth to understand the distribution of nitrogen incorporation during the SiOxNy thermal growth process. AR–XPS is shown to yield accurate nitrogen profiles that agree well with both medium energy ion scattering and secondary ion mass spectrometry analysis. Preferential nitrogen accumulation near the SiOxNy/Si interface is observed with a NO annealing, and nitrogen is shown to bond to both silicon and oxygen in multiple distinct chemical states, whose thermal stability bears implications on the relia...

Kinetic study of low energy argon ion-enhanced plasma etching of polysilicon with atomic/molecular chlorine

Surface kinetics of ion-enhanced chlorine plasma etching in the low ion energy regime was studied by utilizing Ar+ for ion bombardment and Cl and Cl2 as reactants. The argon ion and chlorine atom (molecular) fluxes were controlled independently over more than an order of magnitude and at flux levels within an order of magnitude of that typically used in high density plasma processes. The ion-enhanced etching yield was characterized as a function of Ar ion energy, ion flux, neutral-to-ion flux ratio, and the ion incident angle. Possible reaction pathways are proposed and reduced into a two-parameter model which is useable in a profile simulator. The etching yield increases with the increase of flux ratio but gradually saturates at higher flux ratios as the ion flux limits the etching yield. The ion energy dependence was found to scale linearly with (Eion1/2−Eth1/2), where the threshold energy Eth is found to be 16 eV. The etching yield of Cl is found to be similar to that of Cl2 at flux ratios below 10, bu...

Electrical performance of Al2O3 gate dielectric films deposited by atomic layer deposition on 4H-SiC

Stoichiometric and pure Al2O3 gate dielectric films were grown on n-type 4H-SiC by a thermal atomic layer deposition process. The electrical properties of both amorphous and epitaxial Al2O3 films were studied by capacitance-voltage and current-voltage measurements of metal-oxide-semiconductor capacitors. A dielectric constant of 9 and a flatband voltage shift of +1.3V were determined. A leakage current density of 10−3A∕cm2 at 8MV∕cm was obtained for the amorphous Al2O3 films, lower than that of any high-κ gate oxide on 4H-SiC reported to date. A Fowler-Nordheim tunneling mechanism was used to determine an Al2O3∕4H-SiC barrier height of 1.58eV. Higher leakage current was obtained for the epitaxial γ-Al2O3 films, likely due to grain boundary conduction.

Active layer-incorporated, spectrally tuned Au/SiO2 core/shell nanorod-based light trapping for organic photovoltaics.

We demonstrate that incorporation of octadecyltrimethoxysilane (OTMS)-functionalized, spectrally tuned, gold/silica (Au/SiO2) core/shell nanospheres and nanorods into the active layer of an organic photovoltaic (OPV) device led to an increase in photoconversion efficiency (PCE). A silica shell layer was added onto Au core nanospheres and nanorods in order to provide an electrically insulating surface that does not interfere with carrier generation and transport inside the active layer. Functionalization of the Au/SiO2 core/shell nanoparticles with the OTMS organic ligand was then necessary to transfer the Au/SiO2 core/shell nanoparticles from an ethanol solution into an OPV polymer-compatible solvent, such as dichlorobenzene. The OTMS-functionalized Au/SiO2 core/shell nanorods and nanospheres were then incorporated into the active layers of two OPV polymer systems: a poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCB60M) OPV device and a poly[2,6-4,8-di(5-ethylhexylthienyl)benzo[1,2-b;3,4-b]dithiophene-alt-5-dibutyloctyl-3,6-bis(5-bromothiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4-dione] (PBDTT-DPP:PC60BM) OPV device. For the P3HT:PC60BM polymer with a band edge of ~700 nm, the addition of the core/shell nanorods with an aspect ratio (AR) of ~2.5 (extinction peak ~670 nm) resulted in a 7.1% improvement in PCE, while for the PBDTT-DPP:PC60BM polymer with a band edge of ~860 nm, the addition of core/shell nanorods with an AR of ~4 (extinction peak ~830 nm) resulted in a 14.4% improvement in PCE. The addition of Au/SiO2 core/shell nanospheres to the P3HT:PC60BM polymer resulted in a 2.7% improvement in PCE, while their addition to a PBDTT-DPP:PC60BM polymer resulted in a 9.1% improvement. The PCE and Jsc enhancements were consistent with external quantum efficiency (EQE) measurements, and the EQE enhancements spectrally matched the extinction spectra of Au/SiO2 nanospheres and nanorods in both OPV polymer systems.

Plasma-surface kinetics and feature profile evolution in chlorine etching of polysilicon

Chlorine-based plasma etching of polysilicon was characterized as a function of the impinging Cl+, Cl–to–Cl+ flux ratio, ion bombardment energy, ion bombardment angle, and the flux of etching by-products (SiCl2) using a multiple beam scattering apparatus. The ion-enhanced etching yield was a strong function of the neutral-to-ion flux ratio, and scaled linearly with the square root of the ion energy. The ion-enhanced etching yield was independent of the ion bombardment angle at near normal ion incidence angles, but decreased almost linearly above 40° off-normal angles. The presence of SiCl2 greatly suppressed the etching of polysilicon by either Cl+ or Cl+ with Cl. A Monte Carlo based profile simulator was constructed which incorporated the dominant reaction mechanisms of surface chlorination under ion bombardment, surface re-emission, and ion reflection. The profile evolution of patterned samples etched by Cl and Cl+ beams were simulated. Quantitatively good agreement was found between the simulated profi...

Dielectric property and conduction mechanism of ultrathin zirconium oxide films

Stoichiometric, uniform, amorphous ZrO2 films with an equivalent oxide thickness of ∼1.5 nm and a dielectric constant of ∼18 were deposited by an atomic layer controlled deposition process on silicon for potential applications in metal–oxide–semiconductor (MOS) devices. The conduction mechanism is identified as Schottky emission at low electric fields and as Poole–Frenkel emission at high electric fields. The MOS devices showed low leakage current, small hysteresis (<50 mV), and low interface state density (∼2×1011 cm−2 eV−1). Microdiffraction and high-resolution transmission electron microscopy showed a localized monoclinic phase of α-ZrO2 and an amorphous interfacial ZrSixOy layer which has a corresponding dielectric constant of 11.

Physics of high-pressure helium and argon radio-frequency plasmas

The physics of helium and argon rf discharges have been investigated in the pressure range from 50 to 760Torr. The plasma source consists of metal electrodes that are perforated to allow the gas to flow through them. Current and voltage plots were obtained at different purity levels and it was found that trace impurities do not affect the shape of the curves. The electron temperature was calculated using an energy balance on the unbound electrons. It increased with decreasing pressure from 1.1 to 2.4eV for helium and from 1.1 to 2.0 for argon. The plasma density calculated at a constant current density of 138mA∕cm2 ranged from 1.7×1011 to 9.3×1011cm−3 for helium and from 2.5×1011 to 2.4×1012cm−3 for argon, increasing with the pressure. At atmospheric pressure, the electron density of the argon plasma is 2.5 times that of the helium plasma.

Patterning and templating for nanoelectronics.

The semiconductor industry will soon be launching 32 nm complementary metal oxide semiconductor (CMOS) technology node using 193 nm lithography patterning technology to fabricate microprocessors with more than 2 billion transistors. To ensure the survival of Moores law, alternative patterning techniques that offer advantages beyond conventional top-down patterning are aggressively being explored. It is evident that most alternative patterning techniques may not offer compelling advantages to succeed conventional top-down lithography for silicon integrated circuits, but alternative approaches may well indeed offer functional advantages in realising next-generation information processing nanoarchitectures such as those based on cellular, bioinsipired, magnetic dot logic, and crossbar schemes. This paper highlights and evaluates some patterning methods from the Center on Functional Engineered Nano Architectonics in Los Angeles and discusses key benchmarking criteria with respect to CMOS scaling.