Study on Oxygen Control of Large Diameter N-type Monocrystalline Silicon with Large Thermal Field

Reduction of oxygen concentration in 300 mm diameter n-type Czochralski silicon crystal growth using an optimized heating zone with dual side-heaters

“…For instance, installing an insulation ring below the side heater is demonstrated to be able to lower the oxygen concentration by 0.67 ppma, since it can prevent some of the thermal radiation from the side heater to the bottom of the silica crucible. 7 However, this method would induce a problem where the longitudinal temperature of the silicon melt (above and below the insulation ring) varies a lot. In addition, the longitudinal temperature gradient of the silicon melt cannot be adjusted very well by a single side heater.…”

“…In our previous work, it has been demonstrated by numerical simulations and on-site experiments that the comprehensive application of oxygen control techniques can further reduce the oxygen concentration at the crystal head of a 275 mm diameter n-type RCz-Si crystal to lower than 12 ppma in the conventional heating zone structure. 7 After the further modification in the production process recently, it has been found that the 275 mm diameter n-type RCz-Si crystal with an oxygen concentration of 11.262 ppma can be grown even without the insulation ring. However, it is difficult to further reduce the oxygen concentrations below 11 ppma, as shown in Fig.…”

“…As listed in the Introduction section above, the techniques for oxygen control mainly include: (1) a higher argon gas flow which can cause a faster rate of volatiles (SiO) released from the surface of the silicon melt, (2) a low furnace pressure which is beneficial to accelerate the evaporation of SiO in an argon atmosphere, (3) an optimized heating zone structure for narrowing the heating zone which can lower the temperature and hence, the dissolution rate of the silica crucible, and (4) a modified rotation rate of the crucible and crystal to suppress the incorporation of oxygen into the silicon melt. 7,8,32,33 For instance, Zhou et al also applied dual side heaters to modify the temperature distribution in the silicon melt, during which the growth of an 8′′ p-type Cz-Si crystal with an oxygen concentration of 10–15 ppma is realized. 10 However, they haven't explored the effects of dual-heater configurations on the temperature and oxygen concentration distribution of the silicon melt.…”

“…Several available methods have been tried in the silicon crystal growth process, including heating zone and growth condition optimization, such as the installation of a heat shield, the applications of a higher argon gas flow or magnetic field, the optimization of the heater structure, and so on. 7–11 Based on the above techniques, the oxygen concentration in Cz-Si has been reduced from 20 ppma to 15 ppma. However, to realize the goal of “higher conversion efficiency and lower cost”, the development direction of Cz-Si has turned to larger diameter and n-type crystals since n-type Cz-Si solar cells are recognized to obtain the potential of higher conversion efficiency than p-type ones.…”