The advancement of semiconductor device technology has been rapid and the future development of nanoscale semiconducting devices is of significant interest for integrated computing and sensing. A key contribution to the rapid advances in semiconductor technology has been the characterisation of existing devices which has allowed an understanding of the underlying physical properties to be developed. Semiconductor technology is now pushing the nanometre lengthscale in all device dimensions, and the characterisation of these devices is proving to be extremely challenging, thus limiting the understanding and further development of these devices. Properties of nanoscale semiconductors can deviate dramatically from those of bulk material, and it is of particular interest to characterise and understand these structures.
My research uses electrons as a probe to examine semiconductor devices in electron microscopes using a range of different techniques to reveal their structure and properties. For semiconductors, determination of the electrostatic potential arising from ionised dopant atoms is key to understand and control the device properties. Electron holography is an interference technique that allows the electrostatic (and magnetic) potential to be determined to nanometre scale resolution. To improve current understanding of semiconductor devices my research has developed the technique of off-axis electron holography into a quantitative, 2-D dopant profiling technique. Although the technique is now readily applied to materials problems, the interpretation and quantification of the results is still challenging, with many problems unresolved, in particular the examination of these properties in three dimensions.
The reduction in feature sizes in many device structures has led to these structures being truly nanoscale in three-dimensions. Electron tomography is increasingly seen as an essential element of electron microscopy in the future, providing 3-D information at high resolution that is not accessible by any other means. Through the application of electron holography in combination with electron tomography, the 3-D electrostatic potential in semiconductor devices can be observed. This promises to reveal the electrostatic surface properties of such devices in addition to allowing examination of the functional doped regions in devices. Early results from the application of this technique to a simple p-n junction have revealed the 3-D electrostatic potential with nanometre-scale spatial resolution.
University of Cambridge, Device Materials
Fischione Instruments Inc.
University of Cambridge, Electron microscopy
Philips Research, Eindhoven, Device structures