Michael Hecker

Imaging and strain analysis of nano-scale SiGe structures by tip-enhanced Raman spectroscopy.

The spatial resolution and high sensitivity of tip-enhanced Raman spectroscopy allows the characterization of surface features on a nano-scale. This technique is used to visualize silicon-based structures, which are similar in width to the transistor channels in present leading-edge CMOS devices. The reduction of the intensive far-field background signal is crucial for detecting the weak near-field contributions and requires beside a careful alignment of laser polarization and tip axis also the consideration of the crystalline sample orientation. Despite the chemical identity of the investigated sample surface, the structures can be visualized by the shift of the Raman peak positions due to the patterning induced change of the stress distribution within lines and substrate layer. From the measured peak positions the intrinsic stress within the lines is calculated and compared with results obtained by finite element modeling. The results demonstrate the capability of the tip-enhanced Raman technique for strain analysis on a sub-50nm scale.

Ptychography with multilayer Laue lenses.

Two different multilayer Laue lens designs were made with total deposition thicknesses of 48u2005µm and 53u2005µm, and focal lengths of 20.0u2005mm and 12.5u2005mm at 20.0u2005keV, respectively. From these two multilayer systems, several lenses were manufactured for one- and two-dimensional focusing. The latter is realised with a directly bonded assembly of two crossed lenses, that reduces the distance between the lenses in the beam direction to 30u2005µm and eliminates the necessity of producing different multilayer systems. Characterization of lens fabrication was performed using a laboratory X-ray microscope. Focusing properties have been investigated using ptychography.

Effects of patterning induced stress relaxation in strained SOI/SiGe layers and substrate

Local stress fields in strained silicon structures important for CMOS technology are essentially related to size effects and properties of involved materials. In the present investigation, Raman spectroscopy was utilized to analyze the stress distribution within strained silicon (sSi) and silicon-germanium (SiGe) island structures. As a result of the structuring of initially unpatterned strained films, a size-dependent relaxation of the intrinsic film stresses was obtained in agreement with model calculations. This changed stress state in the features also results in the appearance of opposing stresses in the substrate underneath the islands. Even for strained island structures on top of silicon-on-insulator (SOI) wafers, corresponding stresses in the silicon substrate underneath the oxide were detected. Within structures, the stress relaxation is more pronounced for islands on SOI substrates as compared to those on bulk silicon substrates.

Strain distribution analysis in Si/SiGe line structures for CMOS technology using Raman spectroscopy

Strained silicon underneath the field-effect transistor gate increases significantly the charge carrier mobility and thus improves the performance of leading-edge Complementary Metal Oxide Semiconductor (CMOS) devices. For better understanding of the structure-strain relationship on the nanoscale and for optimization of device structures, the measurement of the local strain state has become essential. Raman spectroscopy is used in the present investigation to analyze the strain distribution in and close to silicon/embedded silicon-germanium (SiGe) line structures in conjunction with strain modeling applying finite element analysis. Both experimental results and modeling indicate the impact of geometry on the stress state. An increase of compressive stress within the Si lines is obtained for increasing SiGe line widths and decreasing Si line widths. The stress state within the Si lines is shown to be a mixed one deviating from a pure uniaxial state. Underneath the SiGe cavities, the presence of a tensile stress was observed. To investigate a procedure to scale down the spatial resolution of the Raman measurements, tip-enhanced Raman scattering experiments have been performed on free-standing SiGe lines with 100nm line width and line distance. The results show superior resolution and strain information not attainable in conventional Raman scans.

Crack propagation and delamination analysis within the die by camera-assisted double cantilever beam technique

Crack propagation in copper-dielectric structures is an important concern regarding die failure, requiring reliable and fast characterization of crack propagation and corresponding adhesion properties. In the present investigation, a modified double cantilever beam (DCB) technique based on optical crack determination by gap opening measurement is utilized for local Gc analysis on interconnect structures for 32 nm technology node and below. In comparison to conventional DCB test set-up, a significant increase in the number of measurement points and thus in the local resolution for Gc is obtained.

The stability of C 60 and its derivatives upon handling in microsystems technologies

We investigate C<inf>60</inf>, C<inf>60</inf>(OH)<inf>24</inf>, C<inf>60</inf>(F<inf>3</inf>)<inf>12</inf>, C<inf>60</inf>Cl<inf>2</inf> and analyse the stability of these derivatives upon processing in sol-gel, spin-coating, spraying, dropping and evaporating procedures to obtain thin films for possible microsystems application. We use X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, Near Edge X-ray Absorption Fine Structure Spectroscopy (NEXAFS) to analyse the fullerene species within the films. We find fullerene molecules stable in evaporation procedure but not stable in films obtained by using fullerenes dissolved in toluene, chlorobenzene and cyclohexane. Most stable are the evaporated films of pure C<inf>60</inf>, while the soluble derivatives are less stable. The fluorine derivatives are most stable when processed by spray coating with ethanol as a solvent. Fullerol was dissolved in H<inf>2</inf>O and films are obtained by spray coating.