Silicon Nitride Wet Etching with Polysilicon Passivation
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Solution Overview
Problem
Existing methods for selectively etching silicon nitride in the presence of silicon oxide and polysilicon often result in damage to other exposed features, such as polysilicon, due to insufficient selectivity, necessitating improved compositions and methods for preferential etching.
Innovation Solution
A composition comprising sulfuric acid, water, sulfurous acid, nitric acid, and optionally formic acid is used as a passivating agent, followed by a silicon nitride etching step with phosphoric acid, enhancing selectivity and minimizing polysilicon etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional wet etching with phosphoric acid is used to remove silicon nitride, then silicon nitride etching is achieved, but polysilicon surfaces are damaged and etched
Solution Approach 1:
A passivation step is performed before the silicon nitride etching step. The passivation composition (containing sulfuric acid, sulfurous acid, and nitric acid) is applied to the substrate surface prior to etching to protect polysilicon surfaces from damage during subsequent phosphoric acid etching, thereby improving selectivity without requiring additional etch steps
Solution Approach 2:
A passivation composition acts as an intermediary layer between the phosphoric acid etchant and the polysilicon surfaces. This intermediate composition selectively protects polysilicon while allowing silicon nitride to be etched, resolving the contradiction between achieving silicon nitride removal and preventing polysilicon damage
2Productivity
If phosphoric acid concentration is increased to improve silicon nitride etching rate, then etching speed increases, but selectivity relative to polysilicon decreases
Solution Approach 1:
The invention changes the chemical parameters of the etching system by introducing a passivation composition with specific acid concentrations (sulfuric acid 20-80%, sulfurous acid 0.01-0.4%, nitric acid 0.1-10%). This parameter change enables the use of high-concentration phosphoric acid for fast etching while maintaining high selectivity through the protective passivation layer
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
The method significantly improves the selectivity of silicon nitride etching relative to polysilicon, reducing etching and roughening of polysilicon surfaces, thereby preserving device integrity.
Implementation Method 1
A method of selectively etching silicon nitride on a microelectronic device substrate... involves a passivation step and a silicon nitride etching step
Implementation Method 2
A composition comprising the reaction product of: sulfuric acid, water, sulfurous acid, nitric acid
Implementation Method 3
silicon nitride is removed from a microelectronic device surface by a wet etching process that involves exposing the substrate surface to concentrated phosphoric acid
Data Source
AI summary
Provided are compositions and methods for the wet etching of a surface of a microelectronic device substrate which contains surfaces comprising silicon nitride, silicon oxide, and polysilicon. The method of the invention involves a passivation step and a silicon nitride etching step, as more fully described below. The combination of the two steps was found to greatly improve the selectivity of the silicon nitride etching operation in the presence of polysilicon.