Self-aligned method of fabricating terrace gate DMOS transistor
First Claim
1. A method of fabricating a terrace gate DMOS transistor comprising the steps of:
- providing a semiconductor substrate having a substrate surface containing impurities of a first conductivity type;
forming a field oxide layer on the substrate surface;
forming a first photoresist mask on the field oxide layer, thereby defining first mask protected areas and first mask exposed areas, wherein the first mask protected areas include a terrace gate area and a device gate separation area, and wherein the first mask exposed areas include a device active area;
performing an etch of the field oxide layer through the first photoresist mask within the first mask exposed area to the substrate surface;
forming a thin layer of gate oxide on the substrate surface within the device active area;
depositing a polysilicon layer;
forming a second photoresist mask on the polysilicon layer, thereby defining second mask protected areas and second mask exposed areas, wherein the second mask protected areas fully overlie the terrace gate area such that the second mask protected area is larger than the terrace gate area and overlaps the terrace gate area by a non-zero overlap distance, and wherein the second mask exposed area includes the gate separation area; and
etching the polysilicon layer so as to fully remove it within the gate separation area, thereby exposing the field oxide layer.
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Abstract
An active mask is used to etch field oxide in active areas down to an n- epitaxial substrate. After gate oxide growth, a polysilicon layer is deposited and planarized. The active mask defines the polysilicon gate critical dimension for a terrace gate DMOS structure. The edges of the polysilicon gates are self-aligned to the edges of the thick terrace gate oxide. Because no interlayer alignment is required to delineate the polysilicon gate, the design need not provide for alignment tolerance. A non-critical mask is deposited overlapping the terrace oxide. An etch back to field oxide in exposed areas is performed. An oxide-selective etch is performed to reduce the oxide thickness in source regions. Self-aligned body implantation, body contact masking and implantation, and source masking and implantation are performed. A dielectric is deposited. A source contact mask is deposited and a contact etch is performed. Source metal is deposited, and passivation layer is formed. Gate-drain capacitance caused by polysilicon gate overlap of the substrate is minimized as the overlap is minimized. Because input capacitance is reduced, switching speed is increased. This self-aligned feature also results in a smaller cell pitch dimension and higher packing density. Therefore, the specific ON resistance is reduced and current driving capacity is also greatly elevated.
135 Citations
17 Claims
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1. A method of fabricating a terrace gate DMOS transistor comprising the steps of:
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providing a semiconductor substrate having a substrate surface containing impurities of a first conductivity type; forming a field oxide layer on the substrate surface; forming a first photoresist mask on the field oxide layer, thereby defining first mask protected areas and first mask exposed areas, wherein the first mask protected areas include a terrace gate area and a device gate separation area, and wherein the first mask exposed areas include a device active area; performing an etch of the field oxide layer through the first photoresist mask within the first mask exposed area to the substrate surface; forming a thin layer of gate oxide on the substrate surface within the device active area; depositing a polysilicon layer; forming a second photoresist mask on the polysilicon layer, thereby defining second mask protected areas and second mask exposed areas, wherein the second mask protected areas fully overlie the terrace gate area such that the second mask protected area is larger than the terrace gate area and overlaps the terrace gate area by a non-zero overlap distance, and wherein the second mask exposed area includes the gate separation area; and etching the polysilicon layer so as to fully remove it within the gate separation area, thereby exposing the field oxide layer. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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Specification