van den Pj Peter Oever

a-Si:H∕c-Si heterointerface formation and epitaxial growth studied by real time optical probes

The deposition of amorphous and epitaxial silicon thin films on H-terminated Si(100) has been studied in real time by the simultaneous application of spectroscopic ellipsometry, attenuated total reflection infrared spectroscopy, and optical second-harmonic generation. The morphology development of the films could be monitored nonintrusively in terms of critical point resonances and H bonding resolving the abruptness of the film-substrate interface and providing a clear distinction between direct heterointerface formation, nanometer-level epitaxial growth, and epitaxial breakdown.

Density and production of NH and NH2 in an Ar–NH3 expanding plasma jet

The densities of NH and NH2 radicals in an Ar–NH3 plasma jet created by the expanding thermal plasma source were investigated for various source-operating conditions such as plasma current and NH3 flow. The radicals were measured by cavity ringdown absorption spectroscopy using the (0,0) band of the AΠ3←XΣ−3 transition for NH and the (0,9,0)-(0,0,0) band of the AA12←XB12 transition for NH2. For NH, a kinetic gas temperature and rotational temperature of 1750±100 and 1920±100K were found, respectively. The measurements revealed typical densities of 2.5×1012cm−3 for the NH radical and 3.5×1012cm−3 for the NH2 radical. From the combination of the data with ion density and NH3 consumption measurements in the plasma as well as from a simple one-dimensional plug down model, the key production reactions for NH and NH2 are discussed.The densities of NH and NH2 radicals in an Ar–NH3 plasma jet created by the expanding thermal plasma source were investigated for various source-operating conditions such as plasma current and NH3 flow. The radicals were measured by cavity ringdown absorption spectroscopy using the (0,0) band of the AΠ3←XΣ−3 transition for NH and the (0,9,0)-(0,0,0) band of the AA12←XB12 transition for NH2. For NH, a kinetic gas temperature and rotational temperature of 1750±100 and 1920±100K were found, respectively. The measurements revealed typical densities of 2.5×1012cm−3 for the NH radical and 3.5×1012cm−3 for the NH2 radical. From the combination of the data with ion density and NH3 consumption measurements in the plasma as well as from a simple one-dimensional plug down model, the key production reactions for NH and NH2 are discussed.

Real time spectroscopic ellipsometry on ultrathin (<50Å) hydrogenated amorphous silicon films on Si(100) and GaAs(100)

Real time spectroscopic ellipsometry was used to determine the time evolution of the dielectric function, bulk thickness, and surface roughness during hot-wire chemical vapor deposition of hydrogenated amorphous silicon (a-Si:H). The amorphous silicon films were deposited on native-oxide-covered c-Si(100) and GaAs(100) substrates at temperatures in the range from 70to350°C. Data analysis by a three layer optical model, consisting of substrate, bulk, and surface roughness layer, revealed that the dielectric function of the a-Si:H film changes in the initial growth regime (d<50A), which can be attributed to a higher optical band gap for films with a smaller thickness. It is argued that the origin of this higher band gap lies most likely in quantum confinement effects of the electron wave function in the ultrathin film, with possibly a small contribution of a higher hydrogen content in the ultrathin film. In addition, we show that the trends in surface roughness and bulk thickness are only marginally affecte...

Downstream ion and radical densities in an Ar-NH3 plasma generated by the expanding thermal plasma technique

A full characterization of the Ar–NH3 expanding thermal plasma source applied in industrial processes for high-rate silicon nitride deposition is presented in terms of absolute densities of reactive species such as ions and radicals. The ion composition of the plasma was identified by mass spectrometry, while absolute ion density information was obtained by Langmuir probe measurements. N radicals were detected by threshold ionization mass spectrometry, whereas NH and NH2 radicals were measured by cavity ringdown spectroscopy. It was found that the ion density decreases from 1013 cm−3 in a pure Ar plasma to 1010–1011 cm−3 when NH3 is injected, with ArH+, , , and being the most abundant ions. The densities of N and NH both saturate at a level of 3 × 1012 cm−3 at NH3 flows above 3 sccs while the density of NH2 increases linearly with the NH3 flow and reaches a level of 4 × 1012 cm−3. When the plasma source current is increased, the densities of N and NH increase linearly, while the NH2 density remains approximately constant. Furthermore, it is revealed that most of the consumed NH3 is converted into N2 and H2 in the plasma.

Radial cataphoresis in a low-pressure neon-mercury positive column

The process of radial cataphoresis is investigated in the positive column of a low-pressure neon-mercury discharge. The emission spectrum and the electric field are measured for several discharge tube diameters, neon pressures, mercury pressures and electric currents. From the results of these measurements, the current from which the emission spectrum of the lamp starts to contain a significant amount of neon radiation is determined. At this critical current, the mercury density profile in the tube is assumed to be significantly depleted due to the process of radial cataphoresis. The measured trends in the critical current are compared to an approximate discharge model.

A Real-Time Study of the a-Si:H/c-Si Interface Formation using Ellipsometry, Infrared Spectroscopy, and Second Harmonic Generation

The formation of the c-Si/a-Si:H interface has been studied in real time during the deposition of a-Si:H on H-terminated c-Si using hot-wire CVD. Several optical diagnostics were used simultaneously: spectroscopic ellipsometry revealing information about the film morphology during the initial stage of growth; attenuated total reflection infrared spectroscopy yielding the H-bonding configuration and depth profile; and optical second harmonic generation providing insight into c-Si and a-Si:H interface and surface states. In this paper these techniques are introduced and initial results are presented

The a-Si:H growth mechanism : temperature study of the SiH3 surface reactivity and the surface silicon hydride composition during film growth

We report on two experimental studies carried out to reveal insight into the interaction of SiH3 radicals with the a-Si:H surface as assumed essential in the a-Si:H growth mechanism. The surface reaction probability β of SiH3 on the a-Si:H has been investigated by spectroscopic means as a function of the substrate temperature (50 - 450 °C) using the time-resolved cavity ringdown technique. The silicon hydrides -SiHx on the a-Si:H surface during deposition have been studied by the combination of in situ attenuated total reflection infrared spectroscopy and argon ion-induced desorption of surface hydrogen. For SiH3 dominated plasma conditions, it is found that the surface reactivity of SiH3 is independent of the substrate temperature with β = 0.30±0.03 whereas the silicon hydride composition on the a-Si:H surface changes drastically for increasing substrate temperature (from -SiH3 to = SiH2 to ≡SiH). The implications of these observations for the a-Si:H growth mechanism are addressed.