Fabrication process for a super-self-aligned trench-gated DMOS with reduced on-resistance
First Claim
1. A method for fabricating a trench MOSFET comprising:
- forming a first mask over a surface of a body of semiconductor material, the first mask having an opening where a trench is to be located in the body;
etching the semiconductor material through the opening in the first mask to form a trench in the semiconductor body;
forming a first oxide layer in the trench, wherein forming the first oxide layer comprises;
depositing an oxide in the trench, the oxide filling at least a portion of the trench;
etching the oxide to remove the oxide from an upper portion of sidewalls of the trench and leave a bottom oxide layer on a bottom of the trench, the bottom oxide layer having a substantially flat top surface extending between the sidewalls of the trench; and
forming a sidewall oxide layer on the upper portion of the sidewalls of the trench, the sidewall oxide layer being thinner than the bottom oxide layer;
introducing a first polysilicon layer into the trench;
with the first mask in place, oxidizing an exposed surface of the first polysilicon layer to form a second oxide layer at the top of the trench, the second oxide layer extending down into the trench;
introducing dopant of a first conductivity type into the body to form a body region, a junction of the body region being at a level with the top surface of the bottom oxide layer;
removing the first mask; and
depositing a metal layer on a surface of the second oxide layer and the surface of the body.
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Abstract
A super-self-aligned (SSA) structure and manufacturing process uses a single photomasking layer to define critical features and dimensions of a trench-gated vertical power DMOSFET. The single critical mask determines the trench surface dimension, the silicon source-body mesa width between trenches, and the dimensions and location of the silicon mesa contact. The contact is self-aligned to the trench, eliminating the limitation imposed by contact-to-trench mask alignment in conventional trench DMOS devices needed to avoid process-induced gate-to-source shorts. Oxide step height above the silicon surface is also reduced avoiding metal step coverage problems. Poly gate bus step height is also reduced. Other features described include polysilicon diode formation, controlling the location of drain-body diode breakdown, reducing gate-to-drain overlap capacitance, and utilizing low-thermal budget processing techniques.
33 Citations
29 Claims
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1. A method for fabricating a trench MOSFET comprising:
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forming a first mask over a surface of a body of semiconductor material, the first mask having an opening where a trench is to be located in the body;
etching the semiconductor material through the opening in the first mask to form a trench in the semiconductor body;
forming a first oxide layer in the trench, wherein forming the first oxide layer comprises;
depositing an oxide in the trench, the oxide filling at least a portion of the trench;
etching the oxide to remove the oxide from an upper portion of sidewalls of the trench and leave a bottom oxide layer on a bottom of the trench, the bottom oxide layer having a substantially flat top surface extending between the sidewalls of the trench; and
forming a sidewall oxide layer on the upper portion of the sidewalls of the trench, the sidewall oxide layer being thinner than the bottom oxide layer;
introducing a first polysilicon layer into the trench;
with the first mask in place, oxidizing an exposed surface of the first polysilicon layer to form a second oxide layer at the top of the trench, the second oxide layer extending down into the trench;
introducing dopant of a first conductivity type into the body to form a body region, a junction of the body region being at a level with the top surface of the bottom oxide layer;
removing the first mask; and
depositing a metal layer on a surface of the second oxide layer and the surface of the body. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
oxidizing the sidewalls and the bottom of the trench; and
removing an oxide layer that results from the oxidizing.
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19. A method of fabricating a MOSFET, comprising:
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forming a trench and a mesa adjacent to the trench in a surface of a semiconductor body;
forming a first insulating layer along a wall of the trench;
forming a gate in the trench, the gate being insulated from the semiconductor body by the first insulating layer;
implanting a dopant of a first conductivity type into the mesa to form a body region;
implanting a dopant of a second conductivity type into the mesa to form a source region;
forming a second insulating layer over the mesa;
forming a mask having an opening defining an area of a contact opening to be formed in the second insulating layer;
etching the second insulating layer through the mask to form the contact opening in the second insulating layer; and
depositing a metal layer into the contact opening to form an electrical contact with the source region, the depositing being carried out at a pressure greater than atmospheric pressure. - View Dependent Claims (20, 21, 22, 23)
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24. A method of fabricating a MOSFET comprising:
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forming a trench in a surface of a semiconductor body, the trench defining a mesa;
forming a first insulating layer including a bottom layer at a bottom of the trench and a sidewall layer along a wall of the trench, wherein the bottom layer is thicker than the sidewall layer;
introducing a polysilicon layer into the trench, an exposed surface of the polysilicon layer being substantially coplanar with a surface of the semiconductor body;
oxidizing the exposed surface of the polysilicon layer to form an oxide layer at the top of the trench, the oxide layer extending down into the trench;
implanting a dopant of a first conductivity type into the mesa to form a body region with a junction at substantially the same level as a top surface of the bottom layer in the trench;
implanting a dopant of a second conductivity type into the mesa to form a source region;
forming a second insulating layer over the polysilicon layer and the mesa;
etching an opening in the second insulating layer over the mesa;
depositing a first metal layer into the opening to form an electrical contact with the source region;
planarizing the first metal layer to form a plug, a surface of the plug being coplanar with a surface of the second insulating layer; and
depositing a second metal layer over the second insulating layer and the plug. - View Dependent Claims (25, 26, 27, 28, 29)
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Specification