Segregation of Ge in B and Ge codoped Czochralski-Si crystal growth

Abstract

The segregation of Ge in B and Ge codoped Czochralski (CZ)-Si crystal growth was investigated. The concentration of Ge in heavily Ge codoped CZ-Si was measured by electron probe micro analysis (EPMA) and X-ray fluorescence spectroscopy. The effective segregation coefficient of Ge (keff) was calculated by fitting the EPMA data to the normal freezing equation, and by taking the logarithmic ratio of the Ge concentrations at the seed and tail of the ingots (top to bottom approach). The keff of Ge increased from 0.30 to 0.55, when the initial Ge concentration in the Si melt (CL(o)Ge) was increased from 3×1019 to 3×1021cm−3. To avoid cellular growth, the crystal pulling rate was decreased for heavily Ge codoped crystal growth (CL(o)Ge>3×1020cm−3). The equilibrium segregation coefficient (k0) of Ge was calculated by partitioning theory, and was smaller than the experimentally estimated keff. The variation of keff from k0 was discussed based on Ge clustering in the heavily Ge codoped crystal, which led to changes in the bonding and strain energies caused by the incorporation of Ge into Si.