The characteristics of Si and SiO2 etching in HBr reactive ion etching plasmas have been studied by measuring etch rates, optical emission, scanning electron microscopy (SEM) cross-sectional analysis, and x-ray photoelectron spectroscopy (XPS). Etch rate measurements indicate that SiO2 is etched very slowly compared with Si, so that the Si/SiO2 etch selectivity may be as high as 400. Optical emission spectroscopy has been used to examine the gas phase species in the plasma, and emission from excited atomic bromine has been identified. The composition and thickness of reaction layers on silicon surfaces resulting from exposure to HBr plasmas has been obtained by XPS. It is found that the reaction layer on silicon due to HBr reactive ion etching is typically very thin, of the order of 1 monolayer thick. XPS has also been used to investigate the reaction layers on the sidewalls of etched trenches, and a thin oxidized layer has been detected for oxide-masked Si trench etching.
I n situ x-ray photoelectron spectroscopy (XPS), etch rate measurements, and optical emission spectroscopy have been used to examine the etching characteristics of tungsten in CF4/O2 reactive ion etching plasmas. It is found that the etch rate maximum of tungsten occurs at a proportion of oxygen in excess of that required to produce the maximum gas phase fluorine atom concentration, and this cannot be explained by using an etch mechanism model similar to that developed for silicon. XPS results have been used to identify tungsten oxyfluoride (WOF4) on the etched surface, and a model for tungsten etching is proposed that involves tungsten oxyfluoride as an important etch product.
Reactive ion etching of Si and SiO2 in SF6 plasmas in which the samples are mounted on a liquid-nitrogen-cooled electrode has been studied. At this temperature SF6 condenses on the electrode surface, but it is possible to maintain a plasma. Si etch anisotropy has been demonstrated at low temperature, in agreement with previous studies. Mass spectrometry and optical emission spectroscopy indicate that fluorine is the dominant species in the plasma because SF6 and SFx species are removed from the gas phase by condensation.
ASOCTM technology is based on single-mode rib waveguides formed on silicon-on-insulator wafers. Silicon waveguides have excellent properties for many applications in the 1.3 and 1.55 micron telecommunications bands that include, €or example, low loss (<0.2dB/cm) and relatively small birefringence (
Uniform arrays of approximately 57 nm diam free-standing quantum dots have been produced from GaAs/AlGaAs single quantum well material by electron-beam lithography and low damage electron cyclotron resonance plasma etching. Low-temperature (5 K) photoluminescence and photoluminescence excitation spectroscopy were used to characterize the material before and after processing into quantum dots. Clear free-exciton features of linewidth comparable to that obtained from the unprocessed material have been observed in the excitation spectra of the quantum dots. As expected for this size of dot, no significant shift in the wavelength of the luminescence was observed, however, there is an apparent enhancement of the external luminescence efficiency when the geometric fill factor is taken into account. The results also show that luminescence efficiency measurements seeking to identify and elucidate intrinsic 0D effects (i.e., those due to quantum confinement in the active region) should be performed with photoexcitation directly into the active region energy states.
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