Trench-gated MIS device having thick polysilicon insulation layer at trench bottom and method of fabricating the same
First Claim
1. A method of fabricating an MIS device comprising:
- forming a trench in a semiconductor chip comprising an N-epi layer atop an N+ substrate, the trench having a sidewall and a bottom, wherein the trench is formed in the N-epi layer and does not extend to the N+ substrate;
growing a first oxide layer on the sidewall and bottom of the trench;
depositing undoped polysilicon in the trench;
etching a portion of the undoped polysilicon to expose a portion of the first oxide layer while leaving a plug of undoped polysilicon at the bottom of the trench;
etching the exposed portion of the first oxide layer to expose a portion of a sidewall of the trench;
growing a gate oxide layer on the exposed portion of the sidewall;
growing a second oxide layer on the undoped polysilicon plug;
depositing a polysilicon layer in the trench that overflows onto a top surface of the N-epi layer, the polysilicon layer for forming a gate and is adjacent to the gate oxide and the second oxide layer; and
etching back the polysilicon layer until its top surface is approximately level with the top surface of the N-epi layer.
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Accused Products
Abstract
In a trench-gated MIS semiconductor device, a slug of undoped polysilicon is deposited at the bottom of the trench to protect the gate oxide in this area against the high electric fields that can occur in this area. The slug is formed over a thick oxide layer at the bottom of the trench. A process of fabricating the MOSFET includes the steps of growing a thick oxide layer on the sidewalls and bottom of the trench, depositing a polysilicon layer which remains undoped, etching the polysilicon layer to form the plug, etching the exposed portion of the thick oxide layer, growing a gate oxide layer and an oxide layer over the plug, and depositing and doping a polysilicon layer which serves as the gate electrode. In an alternative embodiment, the oxide layer overlying the plug is etched before the gate polysilicon is deposited such that the dopant introduced into the gate polysilicon migrates into the polysilicon plug. In this embodiment, the polysilicon plug is in electrical contact with the gate polysilicon layer and is separated from the drain by the thick oxide layer.
28 Citations
8 Claims
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1. A method of fabricating an MIS device comprising:
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forming a trench in a semiconductor chip comprising an N-epi layer atop an N+ substrate, the trench having a sidewall and a bottom, wherein the trench is formed in the N-epi layer and does not extend to the N+ substrate; growing a first oxide layer on the sidewall and bottom of the trench; depositing undoped polysilicon in the trench; etching a portion of the undoped polysilicon to expose a portion of the first oxide layer while leaving a plug of undoped polysilicon at the bottom of the trench; etching the exposed portion of the first oxide layer to expose a portion of a sidewall of the trench; growing a gate oxide layer on the exposed portion of the sidewall; growing a second oxide layer on the undoped polysilicon plug; depositing a polysilicon layer in the trench that overflows onto a top surface of the N-epi layer, the polysilicon layer for forming a gate and is adjacent to the gate oxide and the second oxide layer; and etching back the polysilicon layer until its top surface is approximately level with the top surface of the N-epi layer. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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Specification