R. H. Roberts

A miniature, all-electrostatic, field emission electron column for surface analytical microscopy

The design, construction and application of a miniature, electrostatic, two-lens field emission column are presented and demonstrated. The column can provide a finely focused beam of electrons with energies ranging from 100 eV to 15 keV, with corresponding beam currents of 5 - 20 nA, onto a sample at a working distance of 10 mm. Edge resolution measurements show that the beam diameter at the sample is (at worst) at 200 eV falling to 120 nm at 5 keV.

Multi-imaging and multivariate statistics used for 3D characterization at surfaces

Several microanalytical imaging techniques—energy dispersive X-ray detection, parallel electron energy loss spectroscopy, secondary ion mass spectroscopy, photoelectron spectroscopy and XPS) and scanning Auger microscopy—have reached the stage where they are capable of producing images of a surface with a section of a spectrum in each pixel. The resulting image-spectrum is a complex data structure which requires the use of special methodologies if the data are to be interpreted effectively. Appropriate methods have been developed for Earth satellite image processing and are directly applicable to surface microanalysis. The use of scatter diagrams, interactive correlation partitioning, factor and target factor analysis and principal component analysis are outlined in this paper and their application to semiconducting, catalytic and magnetic structures is illustrated. This field of endeavour can be thought of as being the beginning of an area of study which may be called surface chemometrics.

Automatic and interactive correlation partitioning compared : Application to TiN/Ti/SiO2

A new method has been developed for the partitioning of sets of images with the objective of automatically identifying the number and locations of different regions in a material. The method is called automatic correlation partitioning and it involves the identification of clusters in the n-dimensional intensity histogram of a set of n images that are spatially registered. The method uses the peaks located in the simple intensity histograms of each image in the set to produce a list of all possible clusters in the entire data set. This list is then searched in order to find the actual clusters. The method is tested using data from a multi-imaging Auger electron microscope, which yields sets of Auger images characteristic of the spatial distributions of selected kinds of atoms in the surface of a solid. The first tests involve the use of a model sample consisting of a W overlay pattern on a Si substrate. The second tests are done on a TiN/Ti/SiO2 planar layer structure that has been ion beam bevelled to reveal a cross-section of the composition depth profile. The first set contains two images and the second set contains five images. The results of the new automatic method are compared with those obtained by the analyst working interactively with the data set to identify the clusters subjectively. Cluster analysis of the second sample reveals details of the interfacial layer chemistry not revealed by the interactive method and is consistent with published XPS depth profiling experiments reporting a titanium silicide layer at the Ti/SiO2 interface.

The application of a low energy loss electron detector in conjunction with scanning Auger microscopy: an aid to quantitative surface microscopy

The application of a low loss detector is demonstrated as a quantification aid in scanning Auger microscopy. The low loss detector collects only those electrons that have lost less than a few hundred electron volts during their passage within, and escape from the specimen. The signal thus generated originates from within a comparable information depth to that of the Auger signal and the contrast is predominantly due to the average atomic number within this information depth. Calibration of the detector using elemental standards enables rapid identification of the position of, and the local atomic number of the various phases present at the surface of the specimen. This allows rapid identification of the regions for subsequent Auger spectroscopy or imaging. The low loss detector is deemed superior to conventional secondary or backscattered electron detectors for this purpose. The methodology is demonstrated on a W/TiN/Ti/Si system of trenches and contact holes that had been back polished in order to generate a bevelled cross-section through the structure.