Mapping electrostatic potentials and deformation in semiconductor devices by off‐axis electron holography and other techniques

Abstract

Off‐axis electron holography can be used to measure the electrostatic and magnetic potentials in semiconductor devices with high‐sensitivity and nm‐scale resolution [1]. In this presentation we will show experimental results that have been obtained using combinations of electron holography, precession diffraction and differential phase contrast (DPC) on a range of different semiconductor devices. Deformation maps have been acquired using dark field electron holography on a variety of different device structures and these results have been compared to those obtained by precession electron diffraction (NPED). Figure 1 shows STEM images and results obtained by dark holography and NPED on a Si specimen containing 10‐nm‐thick SiGe layers with different Ge concentrations and also a recessed source and drain SiGe device. The deformation maps obtained by dark holography and shown here have a spatial resolution of 6 nm and a precision of 0.05 %. The maps obtained by precession electron diffraction have a spatial resolution of 2 nm and a precision of 0.02 %. In this presentation we will show the advantages and difficulties associated with the use of the different techniques [2]. We will also compare electron holography and DPC for dopant profiling on fully processed and electrically tested devices. Figure 2(a) and (b) shows STEM images that have been acquired from two different pMOS devices with different spacer widths. The spacers are used to prevent dopants from diffusing under the gate during the activation anneals. Figure 2(c) shows how the specimen is rotated to remove the top metal layers in the device, backside milling is then used to provide a high quality TEM specimen. Figures 2(d) and (e) show maps of the electrostatic potential in the devices that have been acquired using off‐axis electron holography. The spatial resolution in these maps is 5 nm and the difference in the potential distribution under the gate can be clearly seen. Potential profiles have been obtained from across the device and the parameters such as the electrical gate width can be measured. From the analysis of these real devices, the advantages and problems that are associated with electron holography and DPC can be discussed.