Self-aligned trench MOSFETs and methods for making the same

A method for making a semiconductor device, comprising:

• providing a semiconductor substrate with an upper surface, the substrate having a trench therein;
• providing a gate oxide layer on a bottom and sidewall of the trench;
• providing a conductive layer on a bottom and sidewall of the oxide layer, the conductive layer having an upper surface below the upper surface of the substrate;
• and
• providing a self-aligned isolation cap on the conductive layer and only within the trench by using a combination of dielectric materials with different etching rates.

A method for making a semiconductor device, comprising:

• providing a substrate with an upper surface, the substrate having a trench therein;
• providing an oxide layer on a bottom and sidewall of the trench;
• providing a conductive layer on a bottom and sidewall of the oxide layer, the conductive layer having an upper surface below the upper surface of the substrate;
• and
• providing a self-aligned isolation cap on the conductive layer within the trench by using a combination of dielectric materials with different etching rates, including providing the self-aligned isolation cap by providing a first dielectric layer having a first etching rate in the trench and on the upper substrate surface, providing a second dielectric layer having an etching rate faster than the first etching rate on the first dielectric layer, reflowing the first and second dielectric layers, and then isotropically etching until the upper substrate surface is exposed.

A method for making a semiconductor device, comprising:

• providing a semiconductor substrate with an upper surface;
• providing a nitride-containing layer on a first portion of the substrate upper surface;
• providing a trench in a second portion of the substrate, the second portion not containing the nitride-containing layer thereon;
• providing a gate oxide layer on a bottom and sidewall of the trench;
• providing a conductive layer on a bottom and sidewall of the oxide layer, the conductive layer having an upper surface below the upper surface of the substrate;
• providing a self-aligned isolation cap on the conductive layer within the trench;
• and
• removing the nitride-containing layer.

A method for making a MOSFET, comprising:

• providing a semiconductor substrate with an upper surface, the substrate having a trench therein;
• providing source and channel regions proximate the trench;
• providing a gate oxide on a bottom and sidewall of the trench;
• providing a conductive gate on a bottom and sidewall of the gate oxide, the conductive gate having an upper surface below the upper surface of the substrate;
• and
• providing a self-aligned isolation cap on the conductive gate within the trench by using a combination of dielectric materials with different etching rates.

A method for making a MOSFET, comprising:

• providing a substrate with an upper surface, the substrate having a trench therein;
• providing source and channel regions proximate the trench;
• providing a gate oxide on a bottom and sidewall of the trench;
• providing a conductive gate on a bottom and sidewall of the gate oxide, the conductive gate having an upper surface below the upper surface of the substrate;
• and
• providing a self-aligned isolation cap on the conductive gate within the trench by using a combination of dielectric materials with different etching rates, including providing the self-aligned isolation cap by providing a first dielectric layer having a first etching rate in the trench and on the upper substrate surface, providing a second dielectric layer having an etching rate faster than the first etching rate on the first dielectric layer, reflowing the first and second dielectric layers, and then isotropically etching until the upper substrate surface is exposed.

A method for making a MOSFET, comprising:

• providing a semiconductor substrate with an upper surface;
• providing source and channel regions in the substrate;
• providing a nitride-containing layer on a first portion of the substrate upper surface;
• providing a trench in a second portion of the substrate, the second portion not containing the nitride-containing layer thereon;
• providing a gate oxide on a bottom and sidewall of the trench;
• providing a conductive gate on a bottom and sidewall of the gate oxide, the conductive gate having an upper surface below the upper surface of the substrate;
• providing a self-aligned isolation cap on the conductive gate within the trench;
• and
• removing the nitride-containing layer.