Concentration and Behavior of Carbon in Semiconductor Silicon

Abstract

The concentration of carbon in semiconductor silicon and the behavior of carbon in the fusion and crystallization of silicon have been studied by the use of charged particle activation analysis. The solubility of carbon in solid silicon has been found to be 3.5×1017 normalat./cm3 or slightly less at the melting point, and the equilibrium distribution coefficient of carbon between solid and liquid silicon has been determined to be 0.07±0.01 . Carbon content over the above solubility value has seldom been observed in silicon single crystals produced by modern industrial techniques. The content appears to depend more on the growth conditions of the single crystal than on the chemical purification method. The phase diagram of the C‐Si system in the extremely low carbon concentration range is given, together with a discussion of the kinematics of the carbon behavior in zone melting. Also, a new technique for studying the evaporation of carbon from the silicon melt is shown.

Solubilities and Equilibrium Distribution Coefficients of Oxygen and Carbon in Silicon

“…Nozaki et al 14) zone-melted silicon rods on which carbon in aqueous suspension was painted. The zone melting was carried out in a vacuum.…”

“…Durand and Duby 16) selected the carbon solubilities in solid and liquid silicon from the literatures, and the value of k C was evaluated to be 0.034 at the melting point of silicon. Other three research groups [13][14][15] experimentally measured the carbon contents in the silicon after zone melting, and the values of k C were reported in the range between 0.058 and 0.1. Since the zone melting is a dynamic process, it may be difficult to achieve the equilibrium distribution between crystal and melt especially at high temperatures, even if the zone traveling velocity is extrapolated to zero.…”

“…Since the zone melting is a dynamic process, it may be difficult to achieve the equilibrium distribution between crystal and melt especially at high temperatures, even if the zone traveling velocity is extrapolated to zero. 14,15) In addition, it was reported that carbon content in silicon was affected by the ambient atmosphere during the zone melting process.…”

“…The reported equilibrium distribution coefficients of oxygen ranged widely from 0.2 to 1.25, [4][5][6][7][8][9][10][11][12] and the values of the equilibrium distribution coefficient of carbon were reported to be less than 0.1. [13][14][15][16] The crystal-growthrelated techniques, such as the zone melting process and the CZ process, were employed to prepare the specimens for oxygen or carbon analysis in the experimental studies on the distribution. [5][6][7][8][9][10][11]14) The equilibrium distribution of oxygen or carbon between crystal and melt has been assumed in these studies.…”

“…[13][14][15][16] The crystal-growthrelated techniques, such as the zone melting process and the CZ process, were employed to prepare the specimens for oxygen or carbon analysis in the experimental studies on the distribution. [5][6][7][8][9][10][11]14) The equilibrium distribution of oxygen or carbon between crystal and melt has been assumed in these studies.…”