Etching Solution Recycling System for Silicon Nitride Selectivity

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Solution Overview

Problem

The existing methods for wet chemical etching of silicon nitride layers face challenges in selectively etching silicon nitride relative to silicon oxide, as the etching solution's silicate concentration increases, leading to reduced etching rates and particle formation that can hinder semiconductor processing.

Innovation Solution

A wafer etching apparatus with a spectrophotometry real-time monitoring system and etching solution recycling system is employed to monitor and control silicate concentration, using a seed crystal to precipitate silicates and recirculate the etching solution, thereby maintaining optimal etching selectivity and reducing the need for fresh phosphoric acid.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If wet chemical etching uses phosphoric acid to remove silicon nitride layer, then silicon nitride etching is achieved, but silicate concentration increases and inhibits subsequent silicon oxide etching

Engineering Contradiction:

Improvesilicon nitride etching rateVSAvoidetching selectivity

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent implements a recirculation system that continuously pumps etching solution from the etching tank through a settling tank, removes accumulated silicates via seed crystals, and returns the purified solution to the etching tank. This recovery process maintains etching solution performance over extended periods, preventing selectivity degradation while sustaining high etching rates.

Inventive Principle:

Principle #34Discarding and recovering

Solution Approach 2:

The system employs a spectrophotometry real-time monitoring system that continuously measures silicate concentration in the etching solution and provides feedback to the recirculation control. This enables dynamic adjustment of the recirculation rate and timing of seed crystal addition, optimizing the balance between maintaining etching rate and preventing selectivity loss.

Inventive Principle:

Principle #23Feedback

2Duration of action of moving object

If silicate concentration in etching solution increases, then silicon nitride etching continues, but particle formation occurs that hinders semiconductor processing

Engineering Contradiction:

Improveetching solution lifespanVSAvoidparticle formation

Core Design Contradiction:

Duration of action of moving objectVSObject-generated harmful factors

Solution Approach 1:

The patent introduces seed crystals (such as silicon carbide or silicon oxide particles) into the etching solution that act as nucleation sites for silicate precipitation. The harmful silicate byproduct that causes particle formation is converted into a beneficial process: silicates precipitate onto the seed crystals in a controlled manner, preventing random particle formation while maintaining solution effectiveness.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The settling tank serves as an intermediary component between the etching tank and the recirculation system. It provides a separate environment where silicate precipitation and particle removal occur without interfering with the primary etching process, allowing continuous particle-free solution to be returned to the etching tank.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Productivity

If fresh phosphoric acid is continuously added to maintain etching rate, then silicon nitride etching efficiency is maintained, but cost and complexity increase

Engineering Contradiction:

Improveetching efficiencyVSAvoidchemical management system

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The recirculation system enables continuous reuse of the etching solution by constantly circulating it through the settling tank for silicate removal. This continuous regeneration process eliminates the need for periodic solution replacement or continuous fresh acid addition, maintaining etching efficiency while simplifying chemical management.

Inventive Principle:

Principle #20Continuity of useful action

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 manages silicate concentration, maintaining controlled etching selectivity and reducing particle formation, thereby improving the efficiency and yield of silicon nitride etching processes in semiconductor manufacturing.

Implementation Method 1

at least one seed crystal is provided into the settling tank to reduce a silicate concentration in the etching solution

Methodology Applied

Scientific EffectPrecipitation: Precipitation

Implementation Method 2

A wafer etching apparatus with a spectrophotometry real-time monitoring system

Methodology Applied

Scientific EffectAbsorption Spectroscopy: Absorption Spectroscopy

Data Source

PatentUS11229856B2Etching solution recycling system and method for wafer etching apparatus

Publication Date: 2022.01.25 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

An etching solution recycling system for a wafer etching apparatus is provided. The etching solution recycling system includes a settling tank, a seed provider, and a fluid control unit. The settling tank is connected to an etching tank of the wafer etching apparatus and configured to receive an etching solution from the etching tank. The seed provider is configured to provide at least one seed crystal into the settling tank to reduce the silicate concentration in the etching solution in the settling tank. The fluid control unit is configured to deliver the etching solution in the settling tank back into the etching tank.