Split gate formation with high density plasma (HDP) oxide layer as inter-polysilicon insulation layer

Abstract

This invention discloses method of for manufacturing a trenched semiconductor power device with split gate filling a trench opened in a semiconductor substrate wherein the split gate is separated by an inter-poly insulation layer disposed between a top and a bottom gate segments. The method further includes a step of forming the inter-poly layer by applying a RTP process after a HDP oxide deposition process to bring an etch rate of the HDP oxide layer close to an etch rate of a thermal oxide.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The invention relates generally to the semiconductor power devices. More particularly, this invention relates to an improved and novel manufacturing process and device configuration for providing the split trench gates with high-density plasma (HDP) deposition oxide layer as the inter-poly oxide layer.[0003]2. Description of the Prior Art[0004]Conventional technologies for reducing the gate to drain capacitance Cgd in a DMOS device by employing the split trenched-gate, e.g., shielded gate trench (SGT) structure, are still confronted with technical limitations and difficulties. Specifically, trenched DMOS devices are configured with trenched gates wherein large capacitance (Cgd) between gate and drain limits the device switching speed. The capacitance is mainly generated from the electrical field coupling between the bottom of the trenched gate and the drain. In order to reduce the gate to drain capacitance, an improved ...

AI Technical Summary

Benefits of technology

[0008]Specifically, it is an object of the present invention to provide improved device configuration and manufacturing method to reduce the gate to drain capacitance while accurately control the thickness of the inter-poly layer by depositing a HDP oxide insulation layer on top of the bottom trench polysilicon then applied a controlled etch to accurately etch off a desired layer thickness of the inter-poly insulation such that the depth above the bottom trench poly can be better controlled. With this new structure and the method to fine-tune the inter-poly oxide thickness between the 2nd oxide separately, the split trench gate may be formed without compromising the integrity of gate oxide

[0009]Briefly in a preferred embodiment this invention discloses a trenched metal oxide semiconductor field effect transistor (MOSFET) cell. The trenched MOSFET cell includes a trenched gate opened from a top surface of the semiconductor substrate surrounded by a source region encompassed in a body region above a drain region disposed on a bottom surface of a substrate. The trenched gate further includes at least two mutually insulated trench-filling segments with an inter-segment insulation layer that is specially deposited to provide better planar surface characteristics and with controllable inter-segment thickness whereby trench integrity is improved. In a preferred embodiment, the inter-segment insulation is a HDP deposition layer provided with surface planar characteristics for preventing over-etching through the inter-poly layer.

Problems solved by technology

Conventional technologies for reducing the gate to drain capacitance Cgd in a DMOS device by employing the split trenched-gate, e.g., shielded gate trench (SGT) structure, are still confronted with technical limitations and difficulties.

However, as shown in FIG. 1, in the manufacturing process, a step of carrying out a wet etch of the first gate oxide often causes a problem of gate oxide weakness.

The oxide etch often extends below the top surface of the first polysilicon that have been first deposited into the bottom part of the trench thus causing the formation of an over-etching pocket.

Specifically, the sharp and thin inter-poly oxide causes early breakdown between source and gate due to the problems that 1) the dip leads to electric file concentration in the area that causes premature breakdown; and 2) the dip increases a gate-drain overlay thus the Cgd improvement is compromised.

Such technical difficulties become a problem when the conventional processes are applied.

This technical problem and performance limitation often become even more severe when the cell density is increased due to the shrinking dimension of the trench openings when form the trenched power device in the semiconductor substrate.

Images