ALBERT

Notes: Many important classes of surface reactions exhibit both high heats of reaction and large, positive activation energies. In addition, many surface reactions often occur in thermally isolated environments. As a result, significant autothermic effects are possible. In part I of this article, a generalized model of these effects is presented which describes the enhancement in reaction rate as a function of activation energy, bulk temperature, and a parameter termed the characteristic temperature. Reactant concentration and reaction order effects are also considered. Part II of this work presents the application of this model to numerous experimental plasma etching data.

Notes: Part I of this paper presented a generalized model of heat effects operative during surface reactions. The enhancement in reaction rate due to autothermic effects was analyzed as a function of activation energy, bulk temperature, and a parameter termed the characteristic temperature. Application of this model to experimental plasma etching data is presented in part II of this work. Characteristic temperatures calculated from experimental data in numerous plasma etching systems agree closely with the critical characteristic temperature predicted by the heat of the reaction model. Possible reasons for this consistency are given. Further, the autothermic enhancement in the Ta-CF4/O2 etching system is accurately predicted as a function of reactant concentration by a heat of reaction model.

Notes: Thin (3–300-nm) oxides were grown on single-crystal silicon substrates at temperatures from 523 to 673 K in a low-pressure electron cyclotron resonance (ECR) oxygen plasma. Oxides were grown under floating, anodic or cathodic bias conditions, although only the oxides grown under floating or anodic bias conditions are acceptable for use as gate dielectrics in metal-oxide-semiconductor technology. Oxide thickness uniformity as measured by ellipsometry decreased with increasing oxidation time for all bias conditions. Oxidation kinetics under anodic conditions can be explained by negatively charged atomic oxygen, O−, transport limited growth. Constant current anodizations yielded three regions of growth: (1) a concentration gradient dominated regime for oxides thinner than 10 nm, (2) a field dominated regime with ohmic charged oxidant transport for oxide thickness in the range of 10 nm to approximately 100 nm, and (3) a space-charge limited regime for films thicker than approximately 100 nm. The relationship between oxide thickness (xox), overall potential drop (Vox) and ion current (ji) in the space-charge limited transport region was of the form: ji ∝ V2ox/x3ox. Transmission electron microscopy analysis of 5–60-nm-thick anodized films indicated that the silicon-silicon dioxide interface was indistinguishable from that of thermal oxides grown at 1123 K.High-frequency capacitance-voltage (C-V) and ramped bias current-voltage (I-V) studies performed on 5.4–30-nm gate thickness capacitors indicated that the as-grown ECR films had high levels of fixed oxide charge ((approximately-greater-than)1011 cm−2) and interface traps ((approximately-greater-than)1012 cm−2 eV−1). The fixed charge level could be reduced to ≈4×1010 cm−2 by a 20 min polysilicon gate activation anneal at 1123 K in nitrogen; the interface trap density at mid-band gap decreased to ≈(1–2)×1011 cm−2 eV−1 after this process. The mean breakdown strength for anodic oxides grown under optimum conditions was 10.87±0.83 MV cm−1. Electrical properties of the 5.4–8-nm gates compared well with thicker films and control dry thermal oxides of similar thicknesses.

Notes: Using a first-principles approach to the ionization rate, we re-examine some of the prejudices concerning impact ionization and offer a new view of the role of thresholds. We also discuss trends of ionization coefficients related to the energy band structure for silicon and a number of III-V compounds.

Notes: The gain saturation coefficients of tensile-strained, lattice-matched, and compressive-strained InGaAs/InGaAsP quantum-well lasers (QWLs) are calculated from intrasubband relaxation times. The intrasubband relaxation times are in turn obtained within the random-phase approximation including carrier–carrier and carrier–polar-optical phonon interactions at room temperature. The effects of strain on the band structures are included by taking into account the strain-dependent coupling among heavy-hole, light-hole, and spin-orbit split-off subbands on the basis of the multiband effective-mass theory. It is demonstrated that the gain saturation coefficient in tensile-strained QWLs is less sensitive to the amount of strain than in compressive-strained QWLs where it markedly increases with strain.

Notes: The decrease of the Richardson constant by more than 3 orders of magnitude in the indirect energy-gap range of composition of the GaAs/AlxGa1−xAs interface has been interpreted in the past in several ways. We present here a phenomenological model based on envelope wave functions that can describe the transmission coefficient involving two mechanisms: zero-phonon transitions due to Γ-X mixing and phonon assisted transitions. The model shows reasonable agreement with a wide range of experimental data. We conclude that a general relation for the thermionic current across heterojunctions must include phonon effects when the Al mole fraction exceeds 0.45. We also find that calculated transmission coefficients are very different from the step function used in the classical theory.

Notes: A noncontact all-optical method for surface photoacoustics is described. The surface acoustic waves (SAWs) were excited employing a KrF laser and detected with a Michelson interferometer using a 633-nm HeNe laser. Due to an active stabilization scheme developed for the interferometer a surface displacement of 0.2 A(ring) could be detected. The materials investigated included pure materials such as polycrystalline aluminum, and crystalline silicon; films of gold, silver, aluminum, iron, and nickel on fused silica; and a-Si:H on Si(100). In the case of pure materials the shape of the acoustic pulse and the phase velocity were determined. The dispersion of the SAW phase velocity observed for the film systems was used to extract information on the film thickness, density, and transverse and longitudinal sound velocity. Models for the theoretical treatment of film systems and the calculation of dispersion curves are presented.

Notes: The inability to measure pressure with accuracy at high temperature has been a hindrance to the development of simultaneous high-temperature, high-pressure experimental techniques. The results of recent laser-induced fluorescence studies at high temperature and high pressure indicate that Sm:YAG is a promising pressure calibrant with very low-temperature sensitivity. The most intense feature in the fluorescence spectrum is a doublet at 16186.5 cm−1. The Sm:YAG doublet exhibits a pressure-induced peak shift comparable to the R1 shift of ruby. However, the temperature-induced shift of the doublet is almost two orders of magnitude less than that observed for the R1 peak. Simultaneous high-pressure-temperature experiments indicate that the pressure and temperature effects on the frequency and line shape can be added linearly. An empirical model based on the linear combination of pressure dependent frequency shift and temperature dependent linewidth and intensity ratio successfully predicts the doublet line shape at simultaneous pressure and temperature. Use of the model facilitates measurement of peak position at high temperature resulting in improved accuracy and repeatability of the pressure determination. Pressure measurements at 400 °C and 40 kbar based on the Sm:YAG doublet peak position agree with the temperature-corrected ruby R1 pressure measurement to within 3 kbar. At 15 kbar and 900 °C the uncertainty in the Sm:YAG fluorescence peak wavelength is 5 cm−1 due to temperature-induced line broadening; this corresponds to an uncertainty in the pressure determination of ±2.5 kbar. The high thermal and chemical stability of YAG materials make Sm:YAG an ideal pressure calibrant for high-temperature applications. In addition the frequency and intensity of the Sm:YAG fluorescence allow simple conversion from experimental setups designed for ruby fluorescence measurement.

Notes: The pressure-induced frequency shift of the Sm:YAG Y1 peak at elevated temperature is calibrated against the temperature-corrected Raman shift of the nitrogen vibron and, at temperatures less than 673 K, the R1 shift of ruby. The results presented here indicate that pressure can be determined from the Y1 and Y2 peak frequencies, without temperature correction, from 6 to 820 K and from 1 bar to 25 GPa by using the equations: P(GPa) =−0.12204 (ωY1obs−16187.2) and P(GPa)=−0.15188 (ωY2obs−16232.2). However, pressure determinations based on Y2 are less accurate, especially at high temperature. At elevated temperature, the Sm:YAG Y1 and Y2 peak frequencies are most accurately determined by curve fitting a spectral window at least 400 cm−1 wide. The spectral range was chosen in order to include the decay of the intensity of the Lorentzian Y1 peak to a background value and incorporate a third peak at 16360 cm−1.