CBED rocking curves of low-order reflections from doped silicon

Institute of Multidisciplinary Research for Advanced Materials, Tohoku University* Fujitsu Ltd.**
â—‹Kenji Tsuda* Hajime Mitsuishi* Masami Terauchi* Kazuo Kawamura**

Determination of strain distributions in devices with a nanometer-scale spatial resolution has become a crucial issue in semiconductor technologies. Lattice strains of semiconductor devices have been investigated using higher-order Laue zone (HOLZ) line patterns in convergent-beam electron diffraction (CBED) disks. We report here another promising way to detect strains using CBED rocking curves of low-order reflections.

Terauchi et al. found anomalously high intensities in rocking curves of CBED patterns of the 004 reflection for arsenic-doped silicon with doping concentration of less than 1 at.% [Terauchi et al.: J. Electron Microsc. 52 (2003) 441]. Such high intensities can never be expected from scattering power of the doped As atoms of less than 1 at.%. In order to clarify the origin of the anomalous intensities, CBED rocking curves of low-order reflections have been investigated with various doping amounts, ion-implantation conditions and specimen preparation methods, using an energy-filter transmission electron microscope. Simulations of CBED patterns were performed using models with different types of strains based on dynamical diffraction theories. Kato's statistical dynamical theory for X-ray diffraction [Kato: Acta Cryst. A36 (1980) 763.] was first applied to electron diffraction.

As a result of these analyses, it has been revealed that the anomalously high intensities in the rocking curves are reproduced by two types of strains: (i) statistically-distributed local strains and (ii) lattice bending caused by strain relaxation in thin TEM lamella. Both types of the strains originate from doped atoms, interstitial atoms and clusters induced by ion implantation. Thus the CBED rocking curves of low-order reflections can be used as a new probe to detect strains.