Papers by Author: Thomas Stauden

Abstract: Ternary (Si_1-xC_y)Ge_x+y solid solutions were grown on Si-face 4H-SiC applying atomic layer molecular beam epitaxy at low temperatures. The grown layers consist of twinned 3C-SiC revealed by cross section electron microscopy. The germanium was incorporated on silicon lattice sites as revealed by atomic location by channeling enhanced microanalysis transmission electron microscopy studies. The Ge concentration of the grown 3C-(Si_1-xC_y)Ge_x+y heteroepitaxial layers decreases with increasing growth temperatures, but exceeds the solid solubility limit.

Abstract: Epitaxial graphene nanoribbons were fabricated and geometrically measured via scanning electron microscope in the width range of 3...45nm in a new approach. The critical dimension measurement was improved using Monte Carlo simulations for analyzing back scattering effects of the semi-insulating substrate and gaussian convolutions. Different bias powers during oxygen plasma etching allowed the identification of under-etching depths.

Abstract: Gallium oxide nanowires were grown on different substrates using a corona plasma assisted vapor phase epitaxy process and gold catalyst. It is shown that the silicon carbide pseudo substrate in combination with the plasma excitation of the gas phase supports the growth of the gallium oxide nanowires. Analyzing the orientation of the nanowires with respect to the growth surface, it is concluded that the nanowires growth proceed along the fast growth direction of gallium oxide.

Abstract: An anisotropic etching process for mesa structures using fluorinated plasma with hydrogen addition was developed in an electon cyclotron resonance setup. The evolution of the mesa morphology was studied in dependence on the gas composition, the applied bias and the pressure. The achieved side wall slope approached 90° with a negligible trenching. The aspect ratios of the fabricated structure in the developed residue free ECR plasma etching process were between 5 and 20.

Abstract: Anisotropic etching processes for mesa structure formation using fluorinated plasma atmospheres in an electron cyclotron resonance (ECR) plasma etcher were studied on Novasic substrates with 10 µm thick 3C-SiC(100) grown on Si(100). To achieve reasonable etching rates, a special gas inlet system suitable for injecting SF6 into the high density downstream Ar ECR plasma was designed. The influence of the etching mask material on the sidewall morphology was investigated. Masking materials with small grain sizes are preferable to achieve a desired shape. The evolution of the mesa form was investigated in dependence on the gas composition, the applied bias, the pressure and the composition of the gas atmosphere. The achieved sidewall slope was 84.5 deg. The aspect ratios of the fabricated structures in the developed residue free ECR plasma etching process were between 5 and 10. Mesa structures aligned to [100] and [110] directions were fabricated.

Abstract: In order to realize complex three dimensional or free standing structures on SiC substrates, an undercut, i.e. a selective isotropic etching process of SiC, is required. This was realized using an electron cyclotron resonance etching set up with pure SF6 and a SF6/Ar gas composition at elevated substrate temperatures. Above 350°C a significant lateral etch component was observed, which rose to a value of 50-70 nm/min increasing the substrate temperature up to 570°C during the etching process. Depending on substrate temperature the etching profiles and surface roughness were studied. Based on an analysis of the influence of microwave power, working pressure, bias voltage, gas flow and gas mixture on the etching behavior a novel isotropic, high selective, residue free etch process for SiC was developed, which allows for example the fabrication of piezoelectric actuated AlGaN/GaN resonators grown on SiC substrates.

Abstract: In this work nanostructures based on a 30 nm thick 3C-SiC (100) heteroepitaxially grown on Si(100) are demonstrated. They consist of free standing nanoresonators with dimensions below 50 nm. The free standing nanostructures and resonators were defined by electron beam lithography using hydrogen silsesquioxane (HSQ) as a negative tone e-beam resist acting as a selective etching mask during the anisotropic and isotropic dry etching. The influences of the proximity effect, the crystallographic orientation, the angle of exposing on the feature size are highlighted.

Abstract: Germanium modified silicon surfaces in combination with two step epitaxial growth technique consisting in conversion of the Si(100) substrate near surface region into 3C-SiC(100) followed by an epitaxial growth step allows the manipulation of the residual strain. The morphology and the residual strain in dependence on the Ge coverage are only affected by the Ge quantity and not by the growth technique. The positive effect of the Ge coverage is attributed to changes in the morphology during the conversion process, as well as to a reduced lattice and thermal mismatch between SiC and Si in consequence of alloying the near surface region of the Si substrate with Ge.

Abstract: Isotropic etching of silicon carbide was achieved using a capacitive coupled parallel plate reactor in plasma etching mode and SF6 at elevated substrate temperatures. It was observed to be remarkable at substrate temperatures above 350°C. The influence of chamber pressure, masking materials, rf-power and substrate temperature were analyzed. Thereby, 8.5° off-axis oriented 4HSiC wafers exhibit a larger vertical and lateral etching rate compared to on-axis oriented SiC wafers. Additionally, the erosion of nitrogen containing masking material results in a reduction of the etching rates.

Abstract: The influence of the growth conditions on the 3C-SiC layer quality in terms of crystallinity, morphology and residual strain was investigated. In dependence on the chosen growth conditions the stress state can be varied between inhomogeneous and homogeneous strain. For the reduction of the residual strain an alternative route for the improvement of the epitaxial growth of 3CSiC( 100) on Si(100) was developed. It consists in covering the silicon wafers with germanium prior to the carbonization step. The achieved improvement in the residual strain and crystalline quality of the grown 3C-SiC layers is comparable to SOI substrates. These beneficial effects were reached by using a Ge coverage in the range of 0.5 to 1 monolayer with respect to the silicon surface.