Towards electron holography of working transistors

As semiconductor device dimensions are reduced to the deep sub-micron regime, minor departures from the designed distributions of electrostatic potentials can affect device performance dramatically. Parameter optimisation in device processing and modelling is crucial for achieving precise potential profiles. Such optimisation is not possible without comprehensive feedback from advanced characterisation techniques. The ability to acquire two- and three-dimensional measurements of potential distributions with high spatial resolution, high precision and under an applied electrical bias is therefore in great demand. The technique of off-axis electron holography in the transmission electron microscope (TEM) promises to fulfil these requirements in two dimensions and can be combined with electron tomography for three-dimensional measurements. In this dissertation, the practical challenges that are involved in the application of electron holography to the characterisation of electrostatic potentials in working MOSFETs are addressed. A novel method for the application of electrical contacts to a TEM specimen is developed and applied to a diode structure. Off-axis electron holography measurements are carried out on a pn junction using both this and an alternative geometry and compared with simulations. A semi-biased MOSFET is then characterised successfully using electron holography, suggesting that the examination of working transistors in the TEM is a realistic prospect. In order to investigate sources of error and practical challenges, the influence of diffraction contrast on electron holographic phase images is investigated. The effects of electron beam irradiation on the in-situ characterisation of electrical properties in semiconductor devices are then assessed using three complementary techniques: off-axis electron holography and measurements of electron beam induced current in the TEM and secondary electron dopant contrast in the scanning electron microscope