The Effects of Gas‐Phase Convection on Carbon Contamination of Czochralski‐Grown Silicon

Abstract

Measurements of carbon incorporated into a 2 in. diam Czochralski silicon crystal are compared with predictions computed using a three-step simulation: (i) the temperature field is computed throughout the melt and all solid regions of the furnace without heat transfer by gas convection; (it) the temperature and flow fields for the argon purge gas are computed with the temperatures at all solid surfaces set from the first step in the simulation; (iii) the concentrations of dilute SiO and CO in the purge gas, as well as the concentration of carbon in the melt, are computed using the temperature and flow fields computed in step (it). The concentration of carbon in the crystal is readily computed from the concentration of carbon in the melt. The predicted carbon concentrations are approximately a factor of 2 lower than the measured concentrations, with the discrepancy likely due to inaccurate thermodynamic and kinetic data. Additional simulations show that the concentration of carbon in the crystal increases with increasing gas pressure and decreases with increasing mass flux of gas through the furnace at constant pressure. Finally, convective cooling by the flowing gas is shown to be unimportant relative to radiation thereby justifying the decoupling used in the first step of the simulation.

Oxygen-transport phenomena in a small silicon Czochralski furnace

“…In their experiments, the increase of gas pressure or the decrease of gas flow rate caused a considerable increase of the oxygen concentration in the crystal. Mass-transfer characteristics in the gas phase in a Cz furnace was numerically analyzed by Bornside et al [10] in relation to the evaporation of SiO and the incorporation of carbon through the gas phase in a conventional Cz furnace, where they assumed the melt surface to be rigid and the vapor pressure of SiO on the melt surface to be constant.…”

Numerical investigation of carbon and silicon carbide contamination during the melting process of the Czochralski silicon crystal growth

“…Therefore, the dynamics of C contamination and the generation of SiC during the melting process need to be understood for controlling impurities in CZ-Si crystal growth. Most numerical studies [8][9][10] for C contamination in CZ-Si process have focused the analysis on the steady state of the diameter growth stage, using the quasi-steadystate assumption. Liu et al [11] recently addressed the generation and accumulation of C during the melting process in a CZ-Si furnace.…”

Reducing impurities of multicrystalline silicon in a unidirectional solidification furnace for solar cells

“…If the carbon concentration exceeds 1 × 10 16 atom/cm 3 , it will markedly influence the precipitation of oxygen during thermal annealing of crystals and during device processing of the wafers cut from these crystals. [2][3][4][5][6][7][8] Oxygen precipitation is known to act as intrinsic gettering sites for impurities and to affect the mechanical strength of the wafer. 2,9,10 When the concentration of carbon exceeds its solubility limit in silicon, it will precipitate to form silicon carbide (SiC) particles, which can cause severe ohmic shunts in solar cells and result in nucleation of new grains in silicon ingots.…”

“…[2][3][4][5][6][7][8] Oxygen precipitation is known to act as intrinsic gettering sites for impurities and to affect the mechanical strength of the wafer. 2,9,10 When the concentration of carbon exceeds its solubility limit in silicon, it will precipitate to form silicon carbide (SiC) particles, which can cause severe ohmic shunts in solar cells and result in nucleation of new grains in silicon ingots. 11 Carbon impurities can strongly affect the density and electrical activity of dislocations in multicrystalline silicon, 12 and oxygen impurities can cause SiO 2 precipitation, 13 dislocation, 14 and stacking faults.…”