Study of strain fields caused by crystallization of boron doped amorphous silicon using scanning transmission electron microscopy convergent beam electron diffraction method

Study of strain fields around boron doped silicon electrodes in silicon devices was carried out with scanning transmission electron microscopy convergent beam electron diffraction. Leak current, which was one of the crucial failures of this kind of structure, depends on boron concentration in the electrodes. Transmission electron microscopy and diffraction analysis showed that the electrodes consist of epitaxial phase and poly-Si phase, and the proportion of these phases depends on the boron concentration in the electrode. Strain distribution obtained with scanning transmission electron microscopy convergent beam electron diffraction revealed that the origin of the strain is volume shrinkage of the epitaxial phase in the electrode, and the poly-Si phase acts as buffer against this strain. Electron energy-loss spectroscopy analyses revealed that boron segregation occurred in samples having a higher boron concentration, and prevented epitaxial growth in the electrodes. As a result, the core of the electrode remains as poly-Si or amorphous Si and acts as strain buffer. Our analysis concluded that boron concentration in the electrodes is one of the most important factors enabling high production yield for the structure.