Trench semiconductor device having gate oxide layer with multiple thicknesses and processes of fabricating the same
First Claim
1. A process of fabricating a trench semiconductor device comprising:
- providing a semiconductor material;
forming a trench in said semiconductor material, said trench extending from a surface of said semiconductor material into said semiconductor material;
depositing a polysilicon layer, said polysilicon layer filling said trench and overflowing said surface of said semiconductor material; and
removing a sufficient amount of said polysilicon layer such that a surface of said polysilicon layer is substantially coplanar with said surface of said semiconductor material, said removing comprising chemical-mechanical polishing.
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Accused Products
Abstract
The a trench semiconductor device such as a power MOSFET the high electric field at the corner of the trench is diminished by increasing the thickness of the gate oxide layer at the bottom of the trench. Several processes for manufacturing such devices are described. In one group of processes a directional deposition of silicon oxide is performed after the trench has been etched, yielding a thick oxide layer at the bottom of the trench. Any oxide which deposits on the walls of the trench is removed before a thin gate oxide layer is grown on the walls. The trench is then filled with polysilicon in or more stages. In a variation of the process a small amount of photoresist is deposited on the oxide at the bottom of the trench before the walls of the trench are etched. Alternatively, polysilicon can be deposited in the trench and etched back until only a portion remains at the bottom of the trench. The polysilicon is then oxidized and the trench is refilled with polysilicon. The processes can be combined, with a directional deposition of oxide being followed by a filling and oxidation of polysilicon. A process of forming a “keyhole” shaped gate electrode includes depositing polysilicon at the bottom of the trench, oxidizing the top surface of the polysilicon, etching the oxidized polysilicon, and filling the trench with polysilicon.
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Citations
5 Claims
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1. A process of fabricating a trench semiconductor device comprising:
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providing a semiconductor material;
forming a trench in said semiconductor material, said trench extending from a surface of said semiconductor material into said semiconductor material;
depositing a polysilicon layer, said polysilicon layer filling said trench and overflowing said surface of said semiconductor material; and
removing a sufficient amount of said polysilicon layer such that a surface of said polysilicon layer is substantially coplanar with said surface of said semiconductor material, said removing comprising chemical-mechanical polishing. - View Dependent Claims (2, 3, 4)
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5. A process of fabricating a trench semiconductor device comprising:
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providing a semiconductor material;
forming a trench in said semiconductor material, said trench extending from a surface of said semiconductor material into said semiconductor material;
directionally depositing a thick oxide layer on said semiconductor material, said oxide layer depositing preferentially on horizontal surfaces so as to form a first thick portion in a bottom of said trench and a second thick portion over said surface of said semiconductor material, and a thin portion on a sidewall of said trench;
removing said thin portion of said thick oxide layer from said sidewall of said trench;
growing a gate oxide layer on said sidewall of said trench depositing a first polysilicon layer, said first polysilicon layer filling said trench and overflowing said second thick portion of said thick oxide layer;
etching a sufficient amount of said first polysilicon layer such that a surface of said polysilicon layer is located inside said trench;
depositing a second polysilicon layer; and
etching a sufficient amount of said second polysilicon layer such that a surface of said second polysilicon layer is located adjacent said second thick portion of said thick oxide layer.
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Specification