| 摘要 |
In order to form a more stable silicon pillar which can be used for the formation of vertical transistors in DRAM cells, a multi-step masking process is used. In a preferred embodiment, an oxide layer and a nitride layer are used as masks to define trenches, pillars, and active areas in a substrate. Preferably, two substrate etch processes use the masks to form three levels of bulk silicon. |
