Towards nanometer resolution for space charge distribution measurements

The continuous reduction in size of devices, such as integrated circuits or micro-electro-mechanical systems (MEMS), results in the need to control with better and better resolution the materials involved, and in particular the electrical properties of the insulating and semiconducting parts. To measure the space charge distribution various methods exist which involve thermal diffusion or elastic propagation. However the obtained resolution is still limited to a fraction of a micron. In this paper we propose an approach applicable to these methods, for improving the resolution to the nanometer range, by using femtosecond laser pulses. We compare in each case the charge detectivity which can be expected. When a thermal or an elastic wave excitation is used, the calculated detectivity is typically two orders of magnitude better than when using an electric pulse excitation.