Silicon Nitride Etchant Composition for Stable High-Selectivity Etching
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Solution Overview
Problem
Current methods for selectively etching silicon nitride in microelectronic devices face challenges in maintaining high selectivity and stability, particularly in 3D-NAND structures, due to silica precipitation and narrow process windows, which can lead to oxide redeposition and feature damage.
Innovation Solution
An etchant composition comprising phosphoric acid, water, and specific additives such as alkylamine or silane additives is used to maintain targeted dissolved silica levels, minimizing redeposition and ensuring high selectivity in etching silicon nitride relative to silicon oxide, thereby preventing feature damage and maintaining high etch rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If concentrated phosphoric acid is used for etching silicon nitride, then etch rate is improved, but silica precipitation occurs leading to oxide redeposition
Solution Approach 1:
The patent introduces fluoride ions as an intermediary substance that mediates between the phosphoric acid etching action and the silica precipitation problem. The fluoride ions complex with silicon to form soluble fluorosilicate species, preventing silica precipitation and oxide redeposition while maintaining high etch rates. This intermediary mechanism allows the system to achieve both high productivity and process stability.
Solution Approach 2:
The patent changes the chemical parameters of the etching solution by adding fluoride-containing compounds to conventional phosphoric acid. This parameter change transforms the etching chemistry to prevent silica precipitation, thereby resolving the contradiction between maintaining high etch rates and preventing oxide redeposition. The modified composition achieves both goals simultaneously.
2Reliability
If water content is increased to control dissolved silica, then silica precipitation is reduced, but etch rate decreases
Solution Approach 1:
Fluoride ions act as an intermediary that changes the solubility characteristics of silicon species in the etching solution. By forming soluble fluorosilicate complexes, fluoride ions allow the system to maintain high dissolved silica levels without precipitation, enabling the use of higher water content formulations that provide stable silica control while preserving high etch rates.
Solution Approach 2:
The patent creates a composite etching chemistry by combining phosphoric acid, water, and fluoride-containing compounds. This composite formulation synergistically combines the benefits of high water content (stable dissolved silica) with maintained etch performance, resolving the contradiction between reliability and productivity.
3Productivity
If etching is performed in high aspect ratio structures, then device density is improved, but oxide redeposition pinches off features
Solution Approach 1:
Fluoride ions serve as a protective intermediary in high aspect ratio structure etching. By complexing with silicon and preventing silica precipitation, they eliminate the oxide redeposition that would otherwise pinch off narrow features. This enables successful etching of high aspect ratio structures while maintaining feature integrity.
Solution Approach 2:
The patent applies preliminary anti-action by adding fluoride-containing compounds to the etching solution before the etching process begins. This pre-prepared chemical environment prevents silica precipitation and oxide redeposition from occurring during the etch, thereby protecting against feature pinch-off before it can happen.
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 solution achieves high selectivity and etch rates for silicon nitride removal while minimizing silica redeposition, ensuring stable process conditions and preventing feature damage in microelectronic devices, particularly in high aspect ratio structures.
Implementation Method 1
silicon nitride can be removed from a microelectronic device surface by a wet etching process that involves exposing the substrate surface to concentrated phosphoric acid (H3PO4)
Implementation Method 2
maintain targeted dissolved silica levels, minimizing redeposition
Data Source
AI summary
The present invention relates to compositions and methods for selectively etching silicon nitride in the presence of silicon oxide, polysilicon and/or metal silicides at a high etch rate and with high selectivity. Additives are described that can be used at various dissolved silica loading windows to provide and maintain the high selective etch rate and selectivity.