16 research outputs found
Untersuchungen zum Dotieren von Silicium aus einer OberflÀchenbelegung mit Phosphor in einem Kurzzeitprozess
Silicon, shallow junction, rapid thermal doping, vapour phase doping, atomic-layer doping, phosphorus diffusion, phosphine adsorption, sheet resistance, four-point probe, native oxidationMagdeburg, Univ., Fak. fĂŒr Elektrotechnik und Informationstechnik, Diss., 2007Bodo Kalkofe
High temperature reactive ion etching of iridium thin films with aluminum mask in CF4/O2/Ar plasma
Reactive ion etching (RIE) technology for iridium with CF4/O2/Ar gas mixtures and aluminum mask at high temperatures up to 350 °C was developed. The influence of various process parameters such as gas mixing ratio and substrate temperature on the etch rate was studied in order to find optimal process conditions. The surface of the samples after etching was found to be clean under SEM inspection. It was also shown that the etch rate of iridium could be enhanced at higher process temperature and, at the same time, very high etching selectivity between aluminum etching mask and iridium could be achieved
Application of atomic layer deposited dopant sources for ultraâshallow doping of silicon
The advanced silicon semiconductor technology requires doping methods for production of ultraâshallow junctions with sufficiently low sheet resistance. Furthermore, advanced 3âdimensional topologies may require controlled local doping that cannot be achieved by ionimplantation. Here, the application of the atomic layer deposition (ALD) method for preâdeposition of dopant sources is presented. Antimony oxide and boron oxide were investigated for such application. Ozoneâbased ALD was carried out on silicon wafers by using triethylantimony or trisâ(dimethylamido)borane. Very homogeneous Sb2O5 deposition could be achieved on flat silicon wafers and in trench structures. The thermal stability of antimony oxide layers was investigated by rapid thermal annealing experiments. The layers were not stable above 750 °C. Therefore, this material failed to act as dopant source so far.
In contrast, ultraâshallow boron doping of silicon from ALD grown boron oxide films was successful. However, pure B2O3 films were highly unstable after exposure to ambient air. The boron oxide films could be protected by thin Sb2O5 or Al2O3 films that were inâsitu grown by ALD. Low temperature ALD of Al2O3 at 50 °C from trimethylaluminium (TMA) and ozone was investigated in detail with respect of its protective effect on boron oxide. Interestingly, it was observed that already one ALD cycle of TMA and O3 resulted in significant increase in stability of the boron oxide in air
Investigation of oxide thin films deposited by atomic layer deposition as dopant source for ultra-shallow doping of silicon
Atomic layer deposition of solid dopant sources for silicon was carried out by using triethylantimony and ozone, and tris-(dimethylamido)borane and ozone as precursors for antimony or boron containing oxides, respectively. It was proved that homogenous antimony oxide deposition could be achieved on flat silicon wafers and in trench structures. Little growth was found below 100 °C deposition temperature and linear temperature dependence on the growth rate between 100 and 250 °C. The oxide films were not stable above 750 °C and therefore failed to act as dopant source for silicon so far. Boron containing films were only obtained at a deposition temperature of 50 °C. These films were highly instable after exposure to air but degradation could be delayed by thin films of antimony oxide or aluminium oxide that were in situ grown by ALD as well. Only little boron was found by ex-situ chemical analysis. However, rapid thermal annealing of such boron containing dopant source layers resulted in high concentrations of active boron close to the silicon surface. The dependence of the doping results on the thickness of the initial boron containing films could be shown
The Case Against Cold, Dark Chromospheres
Is the solar chromosphere always hot, with relatively small temperature
variations (); or is it cold most of the time, with
temperature fluctuations that reach at the top of the
chromosphere? Or, equivalently: Is the chromosphere heated continually, or only
for a few seconds once every three minutes? Two types of empirical model, one
essentially time independent and always hot, the other highly time dependent
and mostly cold, come to fundamentally different conclusions. This paper
analyzes the time-dependent model of the quiet, nonmagnetic chromosphere by
Carlsson & Stein (1994: CS94) and shows that it predicts deep absorption lines,
none of which is observed; intensity fluctuations in the Lyman continuum that
are much larger than observed; and time-averaged emission that falls far short
of the observed emission. The paper concludes that the solar chromosphere,
while time dependent, is never cold and dark. The same conclusion applies for
stellar chromospheres.
A complete, time-dependent model of the nonmagnetic chromosphere must
describe two phenomena: (1) dynamics, like that modeled by CS94 for
chromospheric bright points but corrected for the geometrical properties of
shocks propagating in an upward-expanding channel; and (2) the energetically
more important general, sustained heating of the chromosphere, as described by
current time-independent empirical models, but modified in the upper
photosphere for the formation of molecular absorption lines of CO in a
dynamical medium. This model is always hot and, except for absorption features
caused by departures from local thermodynamic equilibrium, shows chromospheric
lines only in emission.Comment: 22 pages, 5 figures (in 6 files
Ag films grown by remote plasma enhanced atomic layer deposition on different substrates
Plasma-assisted atomic layer deposition (PALD) was carried for growing thin boron oxide films onto silicon aiming at the formation of dopant sources for shallow boron doping of silicon by rapid thermal annealing (RTA). A remote capacitively coupled plasma source powered by GaN microwave oscillators was used for generating oxygen plasma in the PALD process with tris(dimethylamido)borane as boron containing precursor. ALD type growth was obtained; growth per cycle was highest with 0.13ânm at room temperature and decreased with higher temperature. The as-deposited films were highly unstable in ambient air and could be protected by capping with in-situ PALD grown antimony oxide films. After 16 weeks of storage in air, degradation of the film stack was observed in an electron microscope. The instability of the boron oxide, caused by moisture uptake, suggests the application of this film for testing moisture barrier properties of capping materials particularly for those grown by ALD. Boron doping of silicon was demonstrated using the uncapped PALD B2O3 films for RTA processes without exposing them to air. The boron concentration in the silicon could be varied depending on the source layer thickness for very thin films, which favors the application of ALD for semiconductor doping processesInvestment Bank Berlin and EFR
Use of B2O3 films grown by plasma-assisted atomic layer deposition for shallow boron doping in silicon
Plasma-assisted atomic layer deposition (PALD) was carried for growing thin boron oxide films onto silicon aiming at the formation of dopant sources for shallow boron doping of silicon by rapid thermal annealing (RTA). A remote capacitively coupled plasma source powered by GaN microwave oscillators was used for generating oxygen plasma in the PALD process with tris(dimethylamido)borane as boron containing precursor. ALD type growth was obtained; growth per cycle was highest with 0.13ânm at room temperature and decreased with higher temperature. The as-deposited films were highly unstable in ambient air and could be protected by capping with in-situ PALD grown antimony oxide films. After 16 weeks of storage in air, degradation of the film stack was observed in an electron microscope. The instability of the boron oxide, caused by moisture uptake, suggests the application of this film for testing moisture barrier properties of capping materials particularly for those grown by ALD. Boron doping of silicon was demonstrated using the uncapped PALD B2O3 films for RTA processes without exposing them to air. The boron concentration in the silicon could be varied depending on the source layer thickness for very thin films, which favors the application of ALD for semiconductor doping processes.Investment Bank Berlin and EFR
Acoustic oscillations in the field-free, gravitationally stratified Acoustic oscillations in the field-free, gravitationally stratified cavities under solar bipolar magnetic canopies
The main goal is to study the dynamics of the gravitationally stratified,
field-free cavities in the solar atmosphere, located under small-scale,
cylindrical magnetic canopies, in response to explosive events in the
lower-lying regions (due to granulation, small-scale magnetic reconnection,
etc.).
We derive the two-dimensional Klein-Gordon equation for isothermal density
perturbations in cylindrical coordinates. The equation is first solved by a
standard normal mode analysis in order to obtain the free oscillation spectrum
of the cavity. Then, the equation is solved in the case of impulsive forcing
associated to a pressure pulse specified in the lower-lying regions.
The normal mode analysis shows that the entire cylindrical cavity of granular
dimensions tends to oscillate with frequencies of 5-8 mHz and also with the
atmospheric cut-off frequency. Furthermore, the passage of a pressure pulse,
excited in the convection zone, sets up a wake in the cavity oscillating with
the same cut-off frequency. The wake oscillations can resonate with the free
oscillation modes, which leads to an enhanced observed oscillation power.
The resonant oscillations of these cavities explain the observed power halos
near magnetic network cores and active regions.Comment: 8 pages, 8 figures, accepted in Astronomy and Astrophysic
Acoustic waves in a stratified atmosphere
In a gravitationally stratified atmosphere, small temperature variations
distort the paths of acoustic waves from the rectilinear paths in an
isothermal atmosphere.
For temperature increasing
upward, low-frequency waves near the acoustic cutoff frequency
propagating at a given polar angle are refracted towards
the vertical direction (focused) and high-frequency waves,
away from the vertical (defocused).
Similarly, for temperature increasing towards the axis of a
vertical cylinder, low-frequency waves are focused and high-frequency
waves are defocused.
This effect of temperature inhomogeneities may be important for wave
propagation in the chromospheric K2v bright point phenomenon