Indirect trench sidewall doping by implantation of reflected ions

Abstract

Ion implantation (i/i) technology is employed for silicon trench sidewall doping. The aspect ratio of trenches for high Mbit DRAM is very large (depth/width≥10), so that very small glancing-angle i/i to sidewalls is necessary. In this case, reflected ions are large in number and are implanted to the opposite sidewall. It is very important to know the elemental depth profile in the opposite sidewall to understand the implantation mechanism. For the first time, we measured the depth profiles at several positions of the opposite trench sidewall by secondary-ion mass spectroscopy for arsenic and boron ion implantations. It is found that reflected ions are distributed near the facing region of the directly implanted region with smaller energies than the primary energy. These findings are compared with the simulations based on the marlowe program.