On specimen tilt for electron holography of semiconductor devices

Electron holography can be successfully used for potential mapping on a nanometer scale. It relies on the fact that the phase of the electron wave is proportional to the electrostatic potential in the specimen. However, this proportionality is valid only in a kinematical condition, which is achieved by proper specimen orientation with respect to the electron beam. In this report, we examine experimentally in detail the specimen orientations of silicon devices that minimize dynamical diffraction. The tilt of the specimen from the edge-on position to a favorable orientation causes certain interfaces in the specimen to smear. We describe the smearing by a transfer function and compare it to wave transfer function of the microscope. The maximal specimen tilt alphamax that does not cause smearing greater than the resolution r of the microscope is alphamax = arctan(5.70r/t), where t is the specimen thickness.