Semiconducting diamond has the potential for an order-of-magnitude increase in power handling over currently used semiconductors. This is made possible by diamond's higher thermal conductivity and a higher breakdown voltage than any other device-quality semiconductor. Diamond power devices have numerous potential applications in the power grid and in high-power high-frequency RF applications. One approach to leverage diamond's abilities is through the fabrication of field-effect transistors (FETs). The FET is made by forming a p-type surface conductive layer on the diamond surface. This is accomplished by terminating the diamond surface with hydrogen atoms and then coating the surface with a material that contains negative charges to compensate for the positive holes in the p-type layer. Impressive drain current (1.3 A mm(-1)), maximum operational voltages (> 2000 V), and frequencies of unity current gain (f(T) of 75 GHz) have been demonstrated with this surface conductance method. This surface layer, however, is not stable and FET performance degrades over time on the scale of hours to days. This paper describes an encapsulating layer with a mixed oxide, Al2O3-SiO2, which maintains the resistance of the conductive layer in the range of 1.5 to 3.5 k Omega sq(-1) by protecting the diamond surface while maintaining a stable negative charge.

Oxide etching yield has been measured directly with inductively coupled fluorocarbon plasmas. The yields measurement technique of this work can provide useful information for feature profile evolution modeling, which is essential to understand various issues in oxide etching such as reactive ion etching (RIE) lag, inverse RIE lag, etch stop, microtrenching, bowing, etc. Etching and deposition yields per ion were measured using quartz crystal microbalance (QCM) as a function of ion bombardment energy, ion-to-neutral flux ratio, and ion-impinging angle. C2HF5, C2F6, C2H4F2, and C4F8 were used for the oxide etching. Oxide etching mechanism with those gases is complex because etching and deposition are involved at the same time. In highly selective processes fluorocarbon deposition plays important role in determining etching characteristics. Two fluorocarbon deposition mechanisms are identified in this work: neutral deposition and ion-enhanced deposition. The low-energy ions are believed to enhance the deposition rates by creating active sites and fluorocarbon neutrals deposit on the active sites with higher sticking probability. A surface kinetic model is suggested to explain the ion-enhanced mechanism and shows good agreement with experimental data. Angular yield measurement shows that when fluorocarbon deposition is relatively severe, etching yield decreases significantly as the incident angle increases and deposit fluorocarbon at a high incident angle above 60°.

The "ouzo effect" enables one to create a dispersion of small droplets in a surrounding liquid phase without the use of surfactants, dispersing agents, or mechanical agitation: a phenomenon which can be of value in many disciplines. In the quantitative studies presented here, dispersions of oil droplets in water are formed by the addition of water to a solution of the oil dissolved in a solvent. This causes the oil to supersaturate and then nucleate into small droplets. The mean droplet diameter is a function only of the oil-to-solvent ratio at a given temperature. The number density of droplets formed can be controlled independently from the droplet diameter by changing the amount of water added. Smaller droplets are formed by using more hydrophilic cosolvents. The droplet size distribution is typically log-normal. The width of the distribution can be narrowed by mixing the components at an elevated temperature and then allowing the dispersion to cool.

Silicon loss during gate etch from the active region of a traditional complementary metal–oxide–semiconductor transistor is shown to take place through plasma oxidation of the silicon substrate during the overetch step. The plasma oxidation occurs by an ion-enhanced process with an activation energy of only 0.02 eV. This phenomenon is successfully modeled using the traditional Deal–Grove thermal oxidation model, with the inclusion of a depth-dependent reaction rate constant to incorporate the ion-enhancement effect. Plasma oxidation and silicon loss are reduced by using a shorter polysilicon over-etch time, lower source and bias power, lower substrate temperature, and lower O2 flow. A viable polysilicon over-etch process was developed that produced vertical gate profiles while reducing the silicon loss by 32%.

The chemistry and kinetics of alternative etching chemistries for low-k dielectric materials are explored to improve the anisotropy of the etching process and to reduce the problems associated with postetch clean-up. Etching rates, selectivities. and etching yields of Black Diamond and Coral organosilicate glasses (OSGs) have been measured, Black Diamond and Coral are etched rapidly in F-2, Cl-2, and HBr high density plasmas, and Cl-2 + HBr plasmas have been identified as a viable process chemistry with several advantages over traditional fluorocarbon plasmas. The OSG films are not spontaneously etched by F-2, Cl-2, HBr molecules, Cl, or Br atoms, however, F atoms etch the OSGs spontaneously. F, Cl, and H atoms extract a substantial amount of carbon from the films, but Cl and H do not attack the OSG oxide matrix. The Coral films are more strongly depleted of carbon after halogen plasma etching than the Black Diamond. In addition, oxygen atoms extract nearly all of the carbon and nitrogen from the OSGs, leaving a stoichiometric SiO2 layer. (C) 2002 American Vacuum Society.

The etching of polysilicon by low energy Cl2+HBr plasma beam was studied, and the etching yield as a function of composition, ion impingement energy and ion incident angle was measured. The etching yield by HBr plasma beam is slightly lower than Cl2 plasma beam. The angular dependence of etching yield by both Cl2 and HBr beam strongly suggests the mechanism of ion induced chemical etching, with highest etching yield at normal incident angle. For Cl2 beam, the etching yield almost keeps constant until the off-normal incident angle of ions increased to 45°, while for HBr beam, the etching yield starts dropping even with small off-normal angle. The angular dependence of etching yield by Cl2+HBr plasma at different composition exhibits similar trend as pure HBr. Using x-ray photoelectron spectroscopy, the coverage of Cl and Br on polysilicon surfaces after etching in Cl2+HBr plasmas was measured. The Cl coverage after etching with pure Cl2 plasma beam is about 1.4 times higher than the Br coverage after etching with pure HBr plasma beam, due to the larger size of Br atom. The instantaneous sputtering yields of polysilicon by Ar+ ions after Cl2 and HBr plasma etching are similar, indicating that the lower Br coverage is not responsible for the lower etching rate in HBr plasma. The effect of the angular dependent etching yield difference between Cl2 and HBr on feature profile evolution, as identified with Monte Carlo simulation, might contribute to the more anisotropic etching in HBr plasma.

Etching yields of silicon in F-2, Cl-2, Br-2, and HBr high density plasmas have been measured as a function of ion bombardment energy, ion bombardment angle, and plasma composition. This information contributes to a database of experimental values needed for feature profile evolution modeling. For all plasma chemistries, the etching yield increases approximately with the square root of ion energy. Pure Cl-2 and pure HBr plasmas have very similar etching yields. Silicon etching rates are lower in HBr plasmas than in Cl-2 plasmas due to lower ion fluxes, not lower etching yields. The dependence of the etching yield on ion bombardment angle is significantly different for Cl-2 and HBr plasmas. The etching yield in Cl-2 plasmas decreases rapidly for ion angles above 60 degrees (measured from the surface normal), which results in significant ion scattering from the sidewalls, and may cause the sidewall bowing and microtrenching seen when patterning polysilicon with Cl-2 plasmas. The etching yield in HBr plasmas decreases more gradually with the ion angle, resulting in less ion reflection from the feature sidewalls and may explain the much less pronounced sidewall bowing and microtrenching typically seen when patterning polysilicon with HBr plasmas. HBr plasmas have higher etching yields than Br-2 plasmas due to the ability of H atoms to increase the surface coverage and penetrate farther into the silicon lattice. As the temperature of the silicon increases, the etching yield in HBr plasmas decreases, due to the reduced surface coverage by adsorbed Br and H atoms. (C) 2001 American Vacuum Society.

The etching chemistry of benzocyclobutene (BCB) low-k dielectric films was studied in a high density plasma etcher using F2+O2 and Cl2+O2 plasmas. The etching rate in F2+O2 plasmas exceeded 1.2 μm/min with selectivity over oxide and nitride of 16 and 32, respectively. The etching rate in Cl2+O2 plasmas exceeded 0.6 μm/min with selectivity over oxide and nitride of 40 and 80, respectively. BCB films do not etch in pure Cl2 or pure O2 plasmas without ion bombardment, but etching rates of 1000 Å/min were observed using F2 plasmas without ion bombardment. The ion flux in F2+O2 plasmas is primarily O2+ and O+, whereas in Cl2+O2 the dominant ion is ClO+. BCB etching yields in F2+O2 plasmas were measured with a plasma beam/quartz crystal microbalance system. The etching yields suggest that the neutral fluxes and surface chemistry control the etching rates under these conditions, not the ion flux. Using x-ray photoelectron spectroscopy, it was determined that oxygen plasmas preferentially remove the carbon content of BCB, leaving behind a silicon oxide surface. Chlorine plasmas preferentially remove the silicon, leaving behind a carbon surface. F2+O2 plasmas etch BCB through a fluorocarbon film layer, the thickness of which increases with increasing fluorine concentration in the plasma.

Experimental results in a low temperature, low power density rf plasma reactor show that C2F6 can be decomposed by plasma reaction with oxygen, but CF4, an undesirable byproduct, is produced. Previously, it had been shown in a high temperature, high power density microwave reactor that C2F6 can be decomposed without CF4 formation. Calculations show that low temperature neutral species kinetics favor the formation of CF4 over COF2, while the opposite is true at high temperature. Further, a high degree of feedstock dissociation such as that observed in high density plasma reactors is predicted to lead to very little CF4 formation. Calculations show that adding hydrogen, water, or hydrocarbons to the C2F6+O2 mixture should reduce the power necessary for abatement, and will reduce CF4 formation. Hydrogen is predicted to getter atomic fluorine to form thermodynamically stable HF, and thus prevent perfluorocompound reformation.

An electron beam generated plasma reactor is used to decompose low concentrations of ethyl chloride (EC) and vinyl chloride (VC) in atmospheric pressure air streams. The energy requirements for 90% decomposition of each compound are reported as a function of inlet concentration. VC decomposition is enhanced by chlorine radical reactions. Both the EC and VC reactions seem to be inhibited by electron scavenging decomposition products. A simple analytic expression is used for fitting decomposition data where inhibition effects are important.

An electron beam generated plasma reactor is used to decompose low concentrations (100–3000 ppm) of 1,1-dichloroethane and 1,1-dichloroethene in atmospheric pressure air streams. The energy requirements for 90% and 99% decomposition of each compound are reported as a function of inlet concentration. Dichloroethene decomposition is enhanced by a chlorine radical propagated chain reaction. The chain length of the dichloroethene reaction is estimated to increase with dichloroethene concentration from 10 at 100 ppm initial dichloroethene concentration to 30 at 3000 ppm. Both the dichloroethane and dichloroethene reactions seem to be inhibited by electron scavenging decomposition products. A simple analytic expression is proposed for fitting decomposition data where inhibition effects are important and simple first order kinetics are not observed.

Pseudo-first-order reaction rate constants for the decomposition of carbon tetrachloride, trichloroethane, trichlorethylene, dichloroethane, dichloroethene, ethyl chloride and vinyl chloride were determined experimentally in an electron beam generated plasma reactor. The chlorinated ethylenes and ethanes were decomposed in a dry-air based attachment-dominated plasma. The experimental results agree well a simple, steady-state calculation used to predict the active species concentrations in the plasma and the overall pseudo-first-order reaction rate constants. Dissociative electron attachment is the dominant mechanism of decomposition of the chlorinated molecules, though oxygen radical reactions play a role as well.