Isotropic Etching of Oxide and Nitride Layers in SONOS Structures

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Solution Overview

Problem

Conventional methods for manufacturing silicon-oxide-nitride-oxide-silicon (SONOS) structures in non-volatile static random access memory (nvSRAM) result in unwanted residual material layers during dry etching, leading to increased STI structure width, reduced effective area, and substrate damage due to over-etching, affecting device performance.

Innovation Solution

A method involving a single isotropic etching process is used to remove the redundant fence by patterning the oxide and nitride layers, with careful control to minimize damage to the thin bottom oxide layer, employing a patterned photoresist mask and specific etching gases like NF3 and He to achieve selective etching.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If additional isotropic etching process or anisotropic etching process is added to remove the redundant fence, then the redundant fence is removed, but the bottom oxide layer suffers from twice over-etching causing substrate damage

Engineering Contradiction:

Improveremoval of redundant fenceVSAvoidsubstrate damage from over-etching

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The patent applies preliminary action by performing the etching process in a specific sequence: first etching the nitride layer to remove the redundant fence, then etching the oxide layer. This preliminary removal of the nitride layer prevents it from protecting the substrate during subsequent oxide layer etching, thereby eliminating the need for a second etching process that would cause over-etching damage.

Inventive Principle:

Principle #10Preliminary action

2Productivity

If conventional dry etching is used to etch top oxide layer and nitride layer, then the layers are etched, but sidewalls of STI structure have unwanted residual material layer forming redundant fence

Engineering Contradiction:

Improveetching efficiencyVSAvoidcleanliness of STI sidewalls

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The patent applies segmentation by dividing the etching process into two distinct stages: first etching the nitride layer with selective removal of sidewall residues, then etching the oxide layer. This segmentation allows each layer to be processed with optimized parameters, preventing the formation of redundant fences on STI sidewalls while maintaining etching efficiency.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent employs periodic action through a two-step etching sequence with different etching conditions for the nitride layer and oxide layer. The first etching step removes nitride material and cleans STI sidewalls, followed by a second step for oxide layer removal. This periodic alternation of etching conditions ensures clean sidewalls without redundant material accumulation.

Inventive Principle:

Principle #19Periodic action

3Manufacturing precision

If additional etching process is added to remove redundant fence, then the redundant fence is removed, but the process complexity increases

Engineering Contradiction:

Improveremoval of redundant fenceVSAvoidnumber of etching processes

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent applies merging by combining the removal of redundant fence with the primary etching objective into a single integrated process sequence. The selective etching of the nitride layer simultaneously achieves pattern transfer and redundant fence removal, eliminating the need for separate corrective etching steps and reducing overall process complexity.

Inventive Principle:

Principle #5Merging (Combining)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach effectively removes the redundant fence without damaging the substrate, maintaining the integrity of the bottom oxide layer and enhancing the performance of the manufactured device by maintaining the effective area and electrical properties.

Implementation Method 1

performing an isotropic etching process by using an etching mask unmasking the isolating structure, and thereby removing the unmasked portion of the second oxide layer and the unmasked portion of the nitride layer

Methodology Applied

Scientific EffectIsotropic etching:

Implementation Method 2

employing a patterned photoresist mask and specific etching gases like NF3 and He to achieve selective etching

Methodology Applied

Scientific EffectChemical Vapour Deposition: Chemical Vapour Deposition

Data Source

PatentUS8034690B2Method of etching oxide layer and nitride layer

Publication Date: 2011.10.11 UNITED MICROELECTRONICS CORP

AI summary

An exemplary method of etching an oxide layer and a nitride layer is provided. In particular, a substrate is provided. A surface of the substrate has an isolating structure projecting therefrom. A first oxide layer, a nitride layer and a second oxide layer are sequentially provided on the surface of the substrate, wherein the first oxide layer is uncovered on the isolating structure, the nitride layer is formed overlying the first oxide layer, and the second oxide layer is formed overlying the nitride layer. An isotropic etching process is performed by using an etching mask unmasking the isolating structure, and thereby removing the unmasked portion of the second oxide layer and the unmasked portion of the nitride layer and further exposing sidewalls of the isolating structure. The unmasked portion of the first oxide layer generally is partially removed due to over-etching.