Samsung Electronics Co., Ltd.

Won-saong Lee

Sang-pil Sim

A method is provided for forming a triple well of a semiconductor memory device, where a second well of a second conductive type encloses a second well of a first conductive type. A single mask is used for ion implanting the base of the enclosing well and also the entire enclosed well, which inherently avoids misalignment. Additional doping is provided to the location where the sidewalls of the enclosing well join its base. This is accomplished either by a second, deeper ion implant of the sidewalls, or by ion implanting the base at an angle and rotating it, or both. Alternately, the single mask pattern is processed between the ion implantation steps to alter its width.

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Seoul, South Korea

Won-saong Lee