Karen M. Siegrist, Doctor of Philosophy, 2003
| Title of Dissertation | CHARACTERIZATION OF CONTRAST MECHANISMS OF THE PHOTOELECTRON EMISSION MICROSCOPE |
| Dissertation directed by | Professor
Ellen D. Williams Department of Physics University of Maryland, College Park |
Photoelectron emission microscopy (PEEM) is a potentially powerful technique for real-time imaging of organic, metal and semiconductor electronic devices. This non-intrusive surface-sensitive technique has primarily been used to investigate nanometer-scale surface chemistry and morphology, but its broad imaging capabilities make it well adapted for imaging of micron-scale electronic devices. This application has not yet been realized due to lack of understanding of the contrast mechanisms relevant to micron-scale imaging of devices. This work undertakes the characterization of PEEM imaging contrast and in particular, the contrast effects generated by local electric fields at the surface of a sample. Surface fields arise from a number of causes, including surface topography, junctions of different materials, charging of oxides or other insulators which are part of a sample; or potentials may be externally applied to a device under study. Such fields at the sample surface can have strong impact on the trajectories of the just-emitted, extremely low energy photoelectrons, thereby changing image intensity. We have fabricated test structures for investigating the contrast effects induced by carefully controlled contributions of the field sources mentioned above. Two sets of topographic samples, consisting of steps of varying height, were fabricated of titanium and of nickel. Samples which were topographically similar, but with the capability of biasing the topographic features in order to allow intentional variation of electric fields at the sample surface, have also been fabricated. Finally, samples with the same capability of biasing entrenched features, but without associated surface topography, were constructed. Some of the bias-capable samples were subsequently covered with oxide layers to investigate PEEM imaging of buried devices. We combined analysis of PEEM images of these test structures with numerical calculations of the sample surface field configuration and ray tracing simulations, which we have used to understand the effects of surface fields on contrast and to quantify the contrast generated. Application to the analysis of step orientation and height, magnitude of applied voltage, sample angular orientation, sample charging, and the imaging of buried interfaces are presented.