| Project No. | Project Name | Responsible |
|---|---|---|
| G7 | Optical Characterization of Thin Films and Porous Materials | Prof. Dr. Dietrich R.T. ZAHN |
The Semiconductor Physics Group in the Physics Department at the Chemnitz University of Technology is specialized in the spectroscopic characterization of semiconductor interfaces and thin films. The spectroscopic information obtained is complementary to that assembled by local probes in Prof. Hietscholdīs group. Therefore strong interaction between the two groups is foreseen within this project.
The aim of our group is always to obtain a most complete picture of structural, chemical and electronic properties of interfaces and thin films. Therefore a variety of experimental tech-niques is employed ranging from surface science techniques including synchrotron radiation methods via optical spectroscopic methods to electrical characterization. For the envisaged research in this project methods based on optical spectroscopy will play a dominant role.
The following techniques are of most importance for this project: Spectroscopic Ellipsometry (SE), Raman Spectroscopy (RS), and Fourier Transform Infrared Spectroscopy (FTIRS). These optical techniques are all non-destructive and have the potential for in situ monitoring applications.
SE is a well established technique in microelectronic metrology and delivers information on layer thickness, homogeneity and roughness with sub-nanometer resolution. More sophisticated analysis of ellipsometric spectra can reveal composition, strain and anisotropies of the samples studied. We have shown in close cooperation with Prof. Gessnerīs group that SE is an excellent tool for studying porous low-k materials. SE allows not only the porosity to be determined but also can the dielectric function in the visible range be correlated with the static dielectric constant. This work shall be continued in the envisaged project. In the light of ever shrinking dimensions in electronic devices it is worth mentioning that the group has access to a worldwide unique ellipsometer working from the visible to the VUV-XUV range (photon energies 2 – 30 eV) at the synchrotron radiation light source BESSY. Sensitivity at the sub-nanometer thickness level in the VUV range was already demonstrated by us for organic molecules on silicon surfaces. The short wavelengths in the VUV-XUV range are obviously much better matched to the smallness of device structures. Scanning respectively imaging techniques are planned to be implemented within the forthcoming years and may thus become available for this project.
The information obtainable by RS includes e.g. chemical composition and reactivity, layer thickness and morphology, crystallinity, strain, size and shape of objects in the nanometer range. The group is specialized in in situ monitoring of processes such as layer growth. However, effects on samples due to other treatments like annealing can also be monitored online. Furthermore, the micro-Raman setup allows when used in a scanning mode details to be revealed at sub-micron lateral resolution. RS may thus become an important ingredient of the project for the study of polymeric materials present in electronic systems.
Last but not least FTIRS delivers information comparable to RS. While it cannot compete with RS in terms of lateral resolution its strength lies in the investigation of buried interfaces or layers. This was clearly demonstrated for the study of low temperature silicon wafer bond-ing in a joint project with Prof. Gessnerīs group. FTIRS is not only capable of revealing the thicknesses of the oxides buried at the interface of two Si wafers with high precision as judged from the comparison with HRTEM data obtained in Prof. Hietscholdīs group, but also the chemistry at the interface can be monitored during annealing of the wafer bond.
These techniques will be at the heart of the envisaged project. However, whenever needed additional spectroscopic methods such as photoemission (UPS, XPS) may be employed in order to complement the picture.
Besides the already mentioned close collaborations with the groups of Profs. Gessner and Hietschold which will be expanded within the envisaged project (G1, G8) further cooperation is in particular foreseen with project G4 (polymeric materials), G5 (investigation of layers deposited using new precursors), and G6 (correlation of mechanical properties with results from vibrational spectroscopy). Cooperation with the Chinese partners will most likely occur in projects F2, F3, F5, F6, F8, SJ2, and SJ3.