Type of presentation: Poster

MS-8-P-2633 Field mapping in the TEM by off-axis electron holography.

Cooper D.¹, Rouveire J. L.²

¹CEA-LETI, Minatec, 17 rue des Martyrs, 38054 Grenoble, Cedex 9, France, ²CEA-INACI, Minatec, 17 rue des Martyrs, 38054 Grenoble, Cedex 9, France

david.cooper@cea.fr

In this presentation we will show how off-axis electron holography is routinely used in the semiconductor industry for mapping the presence of active dopants [1] and strain with nm-scale resolution. The need for site specifivity means that focused ion beam (FIB) milling is indispensible for the preparation of specimens. In this presentation we will discuss the problems and advantages of using the FIB for both dopant and strain mapping by electron holography.

Figure 1 shows STEM images of two different FIB-prepared fully processed semiconductor devices with and without spacers which are used to control the diffusion of dopants under the gate. The devices have been electrically tested so that the holography results can be compared to these tests and simulations. Maps of the electrostatic potential distribution arising from the presence of active dopants have been acquired by off-axis electron holography. Figure 2 shows four different boron doped pMOS devices. Device A has a wide spacer and B has a narrow spacer. The effect of the width of the spacer can be directly seen in the potential map and the active dopants have diffused underneath the gate in this case degrading the electrical properties of the device. Devices C and D show that by changing the energy and dose of the dopant implants, the electrostatic potential distribution can be tuned to provide excellent electrical properties [2].

Dark field electron holography [3] can also be used to measure the strain in the same devices. Figure 3 shows a STEM image and strain maps for the pMOS device strained using a SiN CESL. Strain maps for the inplane and growth direction are shown. Here very low values of strain are expected and dark holography can easily detect the distribution of strain under the gate. We will comapre the results obtained by dark field electron holography to other TEM-based strain mapping techniques.

[1] Rau et al. Phys Rev Lett 82, 2614 (1999)
[2] Cooper et al. Semi Science and Tech 28 125013 (2013)
[3] Hytch et al. Nature 453, 1086 (2008)

DC and thanks the ERC for the starting grant “Holoview”. These experiments were performed on the platform nanocharacterisation at Minatec (PFNC).

Fig. 1: STEM images of the pMOS devices showing the different spacer thicknesses.	Fig. 2: Electrostatic potential distributions for four different devices examined by off-axis electron holography. The spatial resolution in the potential maps is 5 nm.
Fig. 3: (a) STEM image of a pMOS device (b) strain map for the in plane and (c) growth directions. The presence of dislocations can be observed in the in plane region.