Growth of Si single bulk crystals with low oxygen concentrations by the noncontact crucible method using silica crucibles without Si₃N ₄ coating

A noncontact crucible method using conventional silica crucibles for reducing stress in Si bulk crystals is proposed. In this method, the Si melt used has a low-temperature region in its upper central part so that natural Si crystal growth occurs inside it. Compared with the conventional growth method, the present method has several merits such as the convex shape of the interface in the growth direction, the possibility of obtaining large ingots even with the use of a small crucible because of the growth in the large low-temperature region, and the small convection in the Si melt due to the existence of the low-temperature region. When using crucibles without Si₃N₄ coating, p-type Si single bulk crystals can grow inside the Si melt without touching the crucible wall. The single bulk crystals grown have low dislocation densities (on the order of 10³ cm^-2). The diameters of the ingots obtained using a crucible with 30 or 33 cm diameter are 21-22 cm. The surface orientation of the cross section is (100). An n-type ingot with Σ3 twin grain boundaries is grown using a crucible without Si₃N ₄ coating. The average minority carrier lifetime of a cross section is 82.8 μs for the passivated surface of an n-type wafer, which is higher than those (7.3-16.0 μs) in the case of p-type wafers. A larger temperature reduction is required for the growth using crucibles without Si ₃N₄ coating than that for the growth using crucibles with Si₃N₄ coating to obtain ingots with the same diameter. A crystal diameter, as large as 72% of the crucible diameter is obtained for the p-type single bulk crystal grown using crucibles without Si₃N ₄ coating.