| 摘要 |
An isolation layer of a semiconductor device and its forming method are provided to remove effectively defects such as a parasitic transistor from an isolation layer forming region using a double depth type structure. A cell region(A), a peripheral region(B) and a boundary region(C) between the cell and peripheral regions are defined on a semiconductor substrate. A first ion implantation is performed on the resultant structure to form a deep well region and a first doped region within the cell and boundary regions, respectively. A second ion implantation is performed on the resultant structure to form a shallow well region in the deep well and a second doped region in the first doped region. A first trench with a first depth(t1) is formed on the resultant structure by patterning selectively a predetermined portion between the cell and the peripheral region. A second trench with a second depth(t2) is then formed within the peripheral region alone. An insulating layer is filled in the first and the second trenche. At this time, first isolation layer with the first depth is formed within the cell region, a second isolation layer with the second depth is formed within the peripheral region, and a third isolation layer is formed within the boundary region. The third isolation layer has the first and the second depth, simultaneously.
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