Reduction of impurity sources in Si crystal growth system with electron gun beam heating

Abstract

A new series of experiments was conducted to determine the source of impurities in the process of silicon crystal growth with electron beam heating. A gas-dynamic window was placed between the electron gun and growth chamber. Also positively-charged traps were placed along the crucible to reduce the number of electrons hitting the chamber and the crucible. Five experiments were conducted: two with the window, two with charge traps, and one with both the window and charge traps. The analysis of obtained samples showed that the gas-dynamic window decreases the content of Al, Cu, Fe, Cr and O₂, and the trap, used in the experiments, decreases the content of Fe, Cr and Cu in residues of the melt. The content of all impurities, except Al, is close to the goal level. Al impurities come only from the gun, but the gas-dynamic window cannot eliminate them completely. It seems that Al impurities come either as neutral atoms carried by the gas or as positively charged ions. To reduce these impurities, a separation of the Al flow from the beam by the magnetic field is proposed.