Effect of heater structure on oxygen concentration in large diameter n-type Czochralski silicon study using numerical simulation

Oxygen is the major impurity in single-crystal silicon rod derived from the growth of large-diameter n-type Czochralski (Cz) silicon, which could exert severe affects on the cell efficiency of monocrystalline silicon wafer. Reducing the concentration of oxygen in the silicon crystal could significantly improve the wafer cell efficiency. In the current work, a 2D global quasi-steady-state axisymmetric model was established based on the n-type 252 mm diameter single-crystal silicon growth process. Moreover, the effect of different heater structures on the concentration of oxygen in the hot zone, the crystal and the melt of the Cz furnace was investigated by the finite element method (FVM). It was found that the heater power was decreased by 2.22 kW after increasing the heater height from 210 mm to 300 mm. However, the average temperature of the quartz crucible was increased by 4.72 K, which contributes to the increase in the concentration of oxygen in the center of the wafer at the head of the single crystal silicon rod by 0.39 ppma. This demonstrates that increasing the heater height facilitates the reduction of the heater power consumption, but increases the oxygen concentration in the center of the wafer at the head of the monocrystalline silicon rods. The method of reducing the radiating area of the heater by increasing the slot depth was employed to reduce the heater power by 1.07 kW when adopting a heater structure with a height of 260 mm, an upper slot depth of 200 mm, and a bottom slot depth of 200 mm. The oxygen concentration of silicon wafers, which was detected by Fourier transform infrared spectroscopy, demonstrates that the oxygen concentration in the center of the head wafer was reduced by 1.324 ppma, and the average oxygen concentration of the head wafers reduced by 0.66 ppma. This study provides a theoretical basis for the design of oxygen-reducing heaters, which could be applied for the production of M10-size monocrystalline silicon wafers.