No abstract

Density / Prandtl-Number / Thermal Conductivity / Transport Properties / Viscosity Thermal conductivity, density, and viscosity of ethylene glycolwater mixtures have been measured. The measurements have been performed in the temperature range from -20°C to 1 8 0 T for thermal conductivity, from -10°C to 150°C for density, and from -10°C to 100°C for viscosity. Prandtl-Numbers calculated with the own experimental data and literature values of specific heat capacity are presented in dependence of temperature and concentration.

No abstract

This paper investigates the influence of film thickness, high-temperature annealing and doping by ion implantation on Young's modulus and the residual stress of LPCVD polysilicon. Films with thicknesses between 100 nm and 800 nm were deposited at with a pressure of 100 mTorr. For annealing investigations, films were annealed in a nitrogen atmosphere for 2 hours at temperatures between 600 and . The implantation doses of boron and phosphorus varied between and . This corresponds to a doping concentration of and . Young's modulus and the residual stress were determined by load-deflection measurements with suspended membranes and by the use of ultrasonic surface waves. The microstructure of the film and grain size was studied by TEM analyses and texture variations were investigated by x-ray deflection. Although Young's modulus was found to be very stable, it showed a small dependence on film thickness and annealing temperature. It varied between 151 GPa and 166 GPa. The residual stress could be strongly influenced by film thickness (-420 MPa to -295 MPa), annealing temperature (-350 MPa to -20 MPa) and ion implantation (-560 MPa to +30 MPa). The as-deposited film always showed compressive stress, a pronounced texture and a grain size of around 55 nm. Strong correlations between the variations of the elastic properties and the variations in the film thickness, annealing temperature, grain size, mass density and refractive index were found. These correlations and the observed microstructure are used to develop a model for the origin of the compressive stress and for the mechanism of stress variation. A theoretical value for Young's modulus of textured polySi was calculated and corresponds well with the measured values.

GaN layers are laterally overgrown by metalorganic chemical vapor deposition on structured Si(111) substrates in a single growth process. The substrates are structured with parallel grooves along the Si 〈1–10〉 or perpendicular to the Si 〈1–10〉 direction by standard photolithography and subsequent dry etching. Due to the anisotropic chemical dry etch process, the remaining Si ridges are underetched. The GaN layer grows nearly exclusively on the bottom of the grooves and on the top of the ridges between the grooves. These two growth fronts are completely separated from each other. As a consequence, the GaN layer growing from the ridge area between grooves can extend over the grooves. This process is similar to the so called pendeo-epitaxy process, but is completely mask free during growth and does not require any growth interruption. The improvement of the crystalline and the optical quality of the GaN layer is demonstrated by atomic force microscopy and cathodoluminescence spectroscopy.

The formation, prevention and removal of micropyramids at the {100} bottom of anisotropically etched cavities are investigated and discussed. In the case of pure KOH solutions the base of micropyramids has been found to be always rectangular or octagonal shaped. The formation is independent of the KOH supplier and the etchmask opening process. The arrangement of the rectangular based micropyramids on the {100} etch bottom depends on the etching time, etching position of the chip (vertical or horizontal) and on the oxygen content in connection with the thermal history of the wafer material. For both types of micropyramid the surface density and size increase with decreasing KOH concentration and etching temperature. Moreover the proportion of octagonal micropyramids rises in those conditions. The origin is discussed in terms of micromasking by H 2 -bubbles in connection with plateau generation and layer by layer peeling of {111} planes. Other mechanisms which are suggested in the literature are discussed. Furthermore it was exhibited that already arisen micropyramids can be removed by a short re-etching in the same etch bath in the same conditions.

No abstract

No abstract