Hard Mask Wet Etching With High Nitride-Oxide Selectivity

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Solution Overview

Problem

In semiconductor lithography, removing a hard mask layer without damaging the underlying active areas is challenging due to the insufficient coverage of patterned photoresist and the need for precise pattern transfer, especially as device integration increases.

Innovation Solution

A wet etching process using an etchant with a selective etching ratio of silicon nitride to silicon oxide greater than 90, specifically phosphoric acid with Si(OH)4 concentrations between 3.95 ppm and 10 ppm, is employed to selectively remove the hard mask layer while preserving protective silicon oxide layers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If a conventional etching process is used to remove the hard mask layer, then the hard mask layer can be removed, but the active region structure will be damaged

Engineering Contradiction:

Improvehard mask layer removal precisionVSAvoiddamage to active region

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The patent modifies the chemical composition parameters of the etchant by adding Si(OH)4 to phosphoric acid, controlling the concentration within 3.95-10 ppm. This parameter change achieves a selective etching ratio greater than 90:10 between silicon nitride and silicon oxide, enabling precise removal of the hard mask layer while protecting the active region structure

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

Si(OH)4 acts as an intermediary substance added to the phosphoric acid etchant. It mediates the etching process by enhancing the selectivity between silicon nitride and silicon oxide, allowing the etchant to differentiate between the hard mask layer and the protective oxide layer, thus removing only the desired material

Inventive Principle:

Principle #24Intermediary (Mediator)

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 method effectively removes the hard mask layer without damaging the active regions, maintaining the integrity of source/drain doping regions and other active areas by adjusting the etchant's composition to prioritize silicon nitride etching over silicon oxide.

Implementation Method 1

an etchant utilized during the wet etching process has a selective etching ratio of silicon nitride to silicon oxide which is greater 90

Methodology Applied

Scientific EffectSelective etching:

Implementation Method 2

a wet etching process is performed to remove the hard mask layer and the two first spacers

Methodology Applied

Scientific EffectChemical etching:

Data Source

PatentUS12040189B2Method of removing hard mask layer

Publication Date: 2024.07.16 UNITED SEMICONDUCTOR (XIAMEN) CO LTD

AI summary

A method of removing a hard mask layer includes providing a gate. A hard mask layer covers and contacts a top surface of the gate. Two spacer structures respectively contacts two sides of the gate. Two first spacers are respectively disposed on the two spacer structures. Later, a wet etching process is performed to remove the hard mask layer and the first spacers and keep the spacer structures. An etchant is utilized in the wet etching process. A selective etching ratio of the silicon nitride to silicon oxide of the etchant is more than 90. The etchant includes Si(OH)4. A concentration of Si(OH)4. is greater than or equal to 3.95 ppm and smaller than or equal to 10 ppm.