Aqueous CMP Slurry for Selective Nitride Removal
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Solution Overview
Problem
Conventional aqueous chemical mechanical planarization (CMP) polishing compositions lack sufficient selectivity for removing silicon nitride without damaging underlying oxide layers, particularly in advanced front-end of line (FEOL) structures like self-aligned contact (SAC) capping, where high nitride removal rate with low oxide removal rate is critical to prevent electrical shorts and ensure pattern density clearance.
Innovation Solution
Aqueous CMP polishing compositions comprising colloidal silica particles, amine carboxylic acids with an isoelectric point below 5, and ethoxylated anionic surfactants, optimized to achieve a pH of 3 to 5, providing a high nitride to oxide removal rate selectivity ratio through controlled zeta potential and abrasive particle size distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional aqueous CMP polishing compositions are used, then oxide removal occurs, but nitride removal rate is insufficient and selectivity is poor
Solution Approach 1:
The patent modifies the chemical parameters of the CMP slurry by incorporating amine carboxylic acids with specific isoelectric points (pI < 5) and controlling the slurry pH to 3-5. This parameter change creates a chemical environment that selectively enhances nitride removal rate while maintaining controlled oxide removal, achieving the desired selectivity and productivity balance
Solution Approach 2:
The invention creates a composite polishing slurry system combining colloidal silica particles (abrasive component) with amine carboxylic acids (chemical component) and ethoxylated anionic surfactants (stability component). This composite formulation synergistically combines mechanical abrasion with chemical etching to achieve high nitride removal selectivity and rate
2Reliability
If high nitride removal rate is achieved, then oxide layers may be damaged, but if low oxide removal rate is maintained, then nitride removal is insufficient
Solution Approach 1:
The amine carboxylic acids exhibit local chemical reactivity that is selective to silicon nitride surfaces rather than silicon oxide surfaces. The chemical composition creates locally differentiated etching behavior where nitride regions are actively removed while oxide regions remain protected, achieving high selectivity without compromising oxide layer integrity
Solution Approach 2:
By precisely controlling the pH parameter to the 3-5 range and selecting amine carboxylic acids with specific isoelectric points below 5, the patent creates optimal chemical conditions that favor nitride removal while minimizing oxide attack. This parameter optimization ensures reliable oxide protection alongside effective nitride removal
3Manufacturing precision
If complete nitride layer clearing is performed, then oxide etching may be blocked, but if nitride removal is excessive, then electrical shorts may occur
Solution Approach 1:
The CMP process using this slurry formulation provides self-regulating feedback through the selective chemistry. As polishing progresses and nitride is removed, the underlying oxide surface becomes exposed, which has different chemical reactivity. This naturally slows further removal, preventing over-polishing and electrical shorts while ensuring complete pattern density clearance
Solution Approach 2:
The controlled pH range (3-5) and specific amine carboxylic acid selection create a chemical environment that is aggressive enough to remove nitride completely for pattern clearance but self-limiting to prevent excessive removal that would cause electrical shorts. The isoelectric point parameter of the additives is critical for achieving this precise control
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 compositions achieve a nitride to oxide removal rate selectivity ratio of 8:1 to 200:1, ensuring precise nitride removal without excessive oxide loss, thereby preventing electrical shorts and ensuring planarization of substrates in FEOL structures.
Implementation Method 1
providing a high nitride to oxide removal rate selectivity ratio through controlled zeta potential
Implementation Method 2
controlled zeta potential and abrasive particle size distribution
Implementation Method 3
ethoxylated anionic surfactants, optimized to achieve a pH of 3 to 5
Implementation Method 4
aqueous chemical mechanical planarization (CMP) polishing compositions comprising an abrasive of one or more dispersions of colloidal silica particles
Data Source
AI summary
The present invention provides aqueous chemical mechanical planarization polishing (CMP polishing) compositions comprising one or more dispersions of aqueous colloidal silica particles, preferably, spherical colloidal silica particles, one or more amine carboxylic acids having an isolectric point (pI) below 5, preferably, an acidic amino acid or a pyridine acid, and one or more ethoxylated anionic surfactants having a C6 to C10 alkyl, aryl or alkylaryl hydrophobic group, wherein the compositions have a pH of from 3 to 5. The compositions enable good silicon nitride removal and selectivity of nitride to oxide removal in polishing.