Semiconductor device and method for manufacturing semiconductor device

Abstract

A narrow trench (2) is formed in a memory circuit region (4) and a wide trench (200) is formed in a logic circuit region (5). An oxide (3B) is formed by CVD to fill the trench (2) and planarization is performed thereon. A thin oxide film (7) is formed by thermal oxidation in an active region, and a polysilicon (15A) for gate electrode is formed and etched only in the memory circuit region (4). At this time, the polysilicon (15B) remains in a seam (6). An oxide film (11) is deposited by CVD, to play the first role of covering the seam (6) and the second role of constituting a thick oxide film together with the oxide film (7). Thus, the trenches of different widths and the oxide films of different thicknesses are formed in a semiconductor substrate, to solve the problem of burying failure which is likely to occur in a narrow trench.

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