Method for forming a vertical MOS transistor
First Claim
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1. A method of forming a vertical MOS transistor using a semiconductor layer, comprising:
- etching an opening in the semiconductor layer;
forming a gate dielectric in the opening that has a vertical portion that extends to a top surface of the semiconductor layer;
forming a gate in the opening having a major portion laterally adjacent to the vertical portion of the gate dielectric and an overhang portion that extends laterally over the vertical portion of the gate dielectric;
performing an implant to form a source region at the top surface of the semiconductor layer while the overhang portion is present; and
forming a third insulating layer in the opening in the semiconductor layer having the first etch characteristic; and
removing the third insulating layer using an etchant that laterally etches the first insulating layer to leave an undercut region between the first semiconductor layer and the second insulating layer prior to forming the gate dielectric.
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Abstract
A method is used to form a vertical MOS transistor. The method utilizes a semiconductor layer. An opening is etched in the semiconductor layer. A gate dielectric is formed in the opening that has a vertical portion that extends to a top surface of the first semiconductor layer. A gate is formed in the opening having a major portion laterally adjacent to the vertical portion of the gate dielectric and an overhang portion that extends laterally over the vertical portion of the gate dielectric. An implant is performed to form a source region at the top surface of the semiconductor layer while the overhang portion is present.
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Citations
18 Claims
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1. A method of forming a vertical MOS transistor using a semiconductor layer, comprising:
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etching an opening in the semiconductor layer; forming a gate dielectric in the opening that has a vertical portion that extends to a top surface of the semiconductor layer; forming a gate in the opening having a major portion laterally adjacent to the vertical portion of the gate dielectric and an overhang portion that extends laterally over the vertical portion of the gate dielectric; performing an implant to form a source region at the top surface of the semiconductor layer while the overhang portion is present; and forming a third insulating layer in the opening in the semiconductor layer having the first etch characteristic; and removing the third insulating layer using an etchant that laterally etches the first insulating layer to leave an undercut region between the first semiconductor layer and the second insulating layer prior to forming the gate dielectric. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method of forming a vertical MOS transistor using a semiconductor layer, comprising:
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etching an opening in the semiconductor layer; forming a gate dielectric in the opening that has a vertical portion that extends to a top surface of the semiconductor layer; forming a gate in the opening having a major portion laterally adjacent to the vertical portion of the gate dielectric and an overhang portion that extends laterally over the vertical portion of the gate dielectric; performing an implant to form a source region at the top surface of the semiconductor layer while the overhang portion is present; forming a first oxide layer on the semiconductor layer prior to the step of etching; forming a nitride layer on the first oxide layer, wherein the step of etching forms an opening in the first oxide layer and the nitride layer aligned to the opening in the semiconductor layer; growing a second oxide layer in the opening in the semiconductor layer; and removing the second oxide layer using an etchant that laterally etches the first oxide layer to leave an undercut region between the first oxide layer and the nitride layer prior to forming the gate dielectric; and wherein the step of forming the gate comprises depositing polysilicon in the opening in the semiconductor layer and in the undercut.
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13. A method of forming a vertical MOS transistor using a semiconductor layer, comprising:
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forming a oxide layer on the semiconductor layer; forming a nitride layer on the oxide layer; etching an opening in the semiconductor layer, the first insulating layer, and the second insulating layer; growing a second oxide layer in the opening in the semiconductor layer; removing the second oxide layer using an etchant that laterally etches the first oxide layer to leave an undercut region between the semiconductor layer and the nitride layer; forming a gate dielectric in the opening; depositing gate material in the opening, in the undercut region, and over the nitride layer whereby the gate material is present in a region of the undercut region; etching back the gate material to leave a first portion of the gate material in the opening and a second portion of the gate material in the region of the undercut region; and performing an implant to form a source region at the top surface of the semiconductor layer using the second portion of the gate material as a mask. - View Dependent Claims (14, 15, 16, 17)
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18. A method of forming a vertical MOS transistor using a semiconductor layer, comprising:
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etching an opening in the semiconductor layer; forming a gate dielectric in the opening; forming a gate having a major portion in the opening and an overhang portion that is at a higher level than a top surface of the semiconductor layer and that extends laterally over at least a portion of the gate dielectric; and performing an implant to form a source region at the top surface of the semiconductor layer using the overhang portion as a mask that reduces a depth of the implant into the gate dielectric under the overhang portion, wherein the overhang portion is formed by filling with polysilicon an undercut of an oxide layer formed on a top surface of the semiconductor layer.
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Specification