Olaf Baake

Nondestructive and Nonpreparative Chemical Nanometrology of Internal Material Interfaces at Tunable High Information Depths

Improvement in the performance of functional nanoscaled devices involves novel materials, more complex structures, and advanced technological processes. The transitions to heavier elements and to thicker layers restrict access to the chemical and physical characterization of the internal material interfaces. Conventional nondestructive characterization techniques such as X-ray photoelectron spectroscopy suffer from sensitivity and quantification restrictions whereas destructive techniques such as ion mass spectrometry may modify the chemical properties of internal interfaces. Thus, novel methods providing sufficient sensitivity, reliable quantification, and high information depths to reveal interfacial parameters are needed for R&D challenges on the nanoscale. Measurement strategies adapted to nanoscaled samples enable the combination of Near-Edge X-ray Absorption Fine Structure and Grazing Incidence X-ray Fluorescence to allow for chemical nanometrology of internal material interfaces. Their validation has been performed at nanolayered model structures consisting of a silicon substrate, a physically vapor deposited Ni metal layer, and, on top, a chemically vapor deposited B(x)C(y)N(z) light element layer.

An apparatus for in situ spectroscopy of radiation damage of polymers by bombardment with high-energy heavy ions.

A new target station providing Fourier transform infrared (FT-IR) spectroscopy and residual gas analysis (RGA) for in situ observation of ion-induced changes in polymers has been installed at the GSI Helmholtz Centre for Heavy Ion Research. The installations as well as first in situ measurements at room temperature are presented here. A foil of polyimide Kapton HN(®) was irradiated with 1.1 GeV Au ions. During irradiation several in situ FT-IR spectra were recorded. Simultaneously outgassing degradation products were detected with the RGA. In the IR spectra nearly all bands decrease due to the degradation of the molecular structure. In the region from 3000 to 2700 cm(-1) vibration bands of saturated hydrocarbons not reported in literature so far became visible. The outgassing experiments show a mixture of C(2)H(4), CO, and N(2) as the main outgassing components of polyimide. The ability to combine both analytical methods and the opportunity to measure a whole fluence series within a single experiment show the efficiency of the new setup.

Synthesis and Characterization of (Na0.5K0.5)NbO3 (NKN) Thin Films Formed by a Diol-based Sol-gel Process

Lead-free (Na 0.5 K 0.5 )NbO 3 (NKN) thin films were fabricated by spin coating on Pt/Ti/SiO 2 /Si substrates by a diol-based sol-gel process. Na-acetate, K-acetate, Nb-pentaethoxide and 1,3 propanediol were used to prepare the NKN precursor solution. Thermal analysis showed two characteristic temperatures of 360 and 600 °C. Based on these temperatures, a heat treatment program with pyrolysis at 360 °C and calcination at 600 °C after every layer was used. To avoid inhomogeneities and secondary phases, an excess of sodium and potassium was necessary. To evaluate the proper excess amount of sodium and potassium secondary ion mass spectrometry (SIMS) lateral element maps and X-ray diffraction (XRD) patterns were recorded. An excess amount of 20% led to homogeneous distribution of the elements and to single phase perovskite NKN films with random crystal orientation. Scanning electron microscopy (SEM) images showed a pore free surface with 100 nm grains. The leakage current measurements showed a current of 1×10 −3 A/cm 2 at 150 kV/cm.

Nondestructive characterization of nanoscale layered samples

Multilayered samples consisting of Al, Co and Ni nanolayers were produced by MBE and characterized nondestructively by means of SRXRF, μ-XRF, WDXRF, RBS, XRR, and destructively with SIMS. The main aims were to identify the elements, to determine their purity and their sequence, and also to examine the roughness, density, homogeneity and thickness of each layer. Most of these important properties could be determined by XRF methods, e.g., on commercial devices. For the thickness, it was found that all of the results obtained via XRR, RBS, SIMS and various XRF methods (SRXRF, μ-XRF, WDXRF) agreed with each other within the limits of uncertainty, and a constant deviation from the presets used in the MBE production method was observed. Some serious preliminary discrepancies in the results from the XRF methods were examined, but all deviations could be explained by introducing various corrections into the evaluation methods and/or redetermining some fundamental parameters.

Speciation of BCxNy films grown by PECVD with trimethylborazine precursor

Films of BCxNy were produced in a plasma-enhanced chemical vapor deposition process using trimethylborazine as precursor and with H2, He, N2, and NH3, respectively, as auxiliary gas. These films deposited on Si(100) wafers or fused quartz glass substrates were characterized chemically by X-ray photoelectron spectroscopy and by synchrotron radiation-based total-reflection X-ray fluorescence combined with near-edge X-ray absorption fine structure. Independent of the auxiliary gas, the B–N bonds are dominating. Furthermore, B–C and N–C bonds were identified. Oxygen, present in the bulk (in contrast to the surface layer of some nanometers, where molecular oxygen and/or water are absorbed) as an impurity, is bonded to boron or to carbon, respectively. The relation of boron and nitrogen changes with the character of the auxiliary gas: cB/cN ≈ 4:3 (for H2 and He) and cB/cN ≈ 1 (for N2 or NH3). Furthermore, physical properties such as the refractive index and the optical band-gap energy were determined.

Analytical characterization of BCxNy films generated by LPCVD with triethylamine borane

Triethylamine borane (TEAB) and He, N2 or NH3 were applied as additional reaction gases in the production of BCxNy layers by low-pressure chemical vapor deposition (LPCVD). These layers were deposited on Si(100) wafers and characterized chemically by X-ray photoelectron spectroscopy (XPS) and synchrotron radiation-based total-reflection X-ray fluorescence analysis combined with near-edge X-ray absorption fine-structure spectroscopy (TXRF-NEXAFS). The composition of the material produced without NH3 was found to be dominated by B–C bonds with the stoichiometric formula B2C3N. B–N bonds with the formula B2CN3 were preferred when NH3 was added. A first attempt was made to compare the results obtained by applying trimethylamine borane and TEAB as single-source precursors.