Spezielle Strukturbaufehler in gasdotierten Silizium-einkristallen und deren mögliche Wirkung bei der Herstellung von pn-Übergängen

Investigation and identification of special imperfections of silicon single crystals prepared by gas doping and zone floating are reported. Investigation methods used are etch technique, X-ray topography and electron beam micro-analysis. It was stated that the investigated imperfections show oxygen clusters. A possible growth process of such imperfections is discussed. In conclusion, first results of investigations on the effects of such imperfections during the formation of p–n junctions are given.     

Front Cover: Deoxygenative Intramolecular Minisci-Type Reaction to Access Fused Heterocyclic Scaffolds (Eur. J. Org. Chem. 7/2023)

Herein, we present a straightforward strategy for the synthesis of fused heterocycles through a deoxygenative, intramolecular Minisci-type reaction. This approach grants access to complex polycyclic scaffolds in three steps from readily available starting materials, such as chlorinated heteroarenes and 1,3-diols. The use of saccharide derivatives as the starting 1,3-diol motif allows for the synthesis of novel heterocyclic scaffolds with excellent diastereoselectivity and formal retention of configuration at the newly formed C−C bond.     

Resist technology for deep-etch synchrotron radiation lithography

Microstructures with characteristic dimensions down to one micrometer and structural heights of several hundred micrometers are produced by deep-etch synchrotron radiation lithography using poly-(methyl methacrylate)(PMMA) as resist. In the present paper the details of the process are described. Microstructures without defects caused by stress corrosion are produced by polymerization of a methyl methacrylate base casting resin containing 1% of a cross-linking dimethacrylate onto a metallic base plate and developing the irradiated parts in solvents with solubility parameters at the periphery of the solubility range of PMMA. In this case the structural tolerances of the microstructures are less than 0.05 μm per 100 μm structural height. Measurements of the dissolution rate and the molecular weight and calculations of the absorbed dose show that the irradiated cross-linked PMMA is only developable if the absorbed dose is greater than 1.6 kJ which yields a molecular weight MW of 14 000 g/mol.