CMP Slurry for Selective Silicon Nitride Removal
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Solution Overview
Problem
Conventional chemical mechanical polishing (CMP) methods fail to achieve selective removal of silicon nitride relative to silicon oxide on patterned wafers, despite showing selectivity on blanket wafers, due to differences in removal selectivity profiles.
Innovation Solution
A CMP composition comprising a particulate abrasive, such as ceria, suspended in an aqueous carrier with a cationic polymer bearing pendant quaternized nitrogen-heteroaryl groups, which maintains a zeta potential of at least +20 mV on the abrasive particles at basic pH, ensuring selective removal of silicon nitride relative to silicon oxide.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional CMP methods use cationic abrasives at low pH to achieve high SiN removal rate, then SiN removal rate is improved, but selectivity on patterned wafers deteriorates (oxide loss increases)
Solution Approach 1:
The patent changes the pH parameter from low pH (conventional) to high pH (greater than 10, preferably greater than 11) to achieve both high SiN removal rate and high selectivity on patterned wafers. This parameter change fundamentally alters the chemical environment to enable selective SiN removal while minimizing oxide loss.
Solution Approach 2:
The patent uses a composite abrasive system consisting of ceria (CeO2) particles combined with specific additives including cationic surfactants and chelating agents. This composite formulation enhances both the removal rate and selectivity, achieving superior performance compared to conventional single-component abrasives.
2Manufacturing precision
If conventional CMP methods achieve high selectivity on blanket wafers, then selectivity is improved, but performance on patterned wafers deteriorates (different removal selectivity profile)
Solution Approach 1:
The patent changes multiple parameters simultaneously: pH (to greater than 10), abrasive type (ceria), and additive composition (cationic surfactants and chelating agents). This multi-parameter optimization ensures that the slurry performs consistently on both blanket and patterned wafers, eliminating the discrepancy between the two polishing scenarios.
3Ease of manufacture
If conventional CMP compositions use standard abrasives and additives, then ease of manufacture is improved, but ability to achieve true selective SiN removal on patterned wafers deteriorates
Solution Approach 1:
The patent employs a composite slurry formulation containing ceria abrasive particles, cationic surfactants, chelating agents, and other additives in a water-based carrier. This composite approach enables true selective SiN removal on patterned wafers while maintaining reasonable manufacturing complexity through the use of commercially available components.
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 CMP composition achieves high and selective removal of silicon nitride relative to silicon oxide on patterned wafers, mirroring performance on blanket wafers, with the cationic polymer's quaternized nitrogen-heteroaryl groups being crucial for maintaining selectivity at basic pH conditions.
Implementation Method 1
the cationic polymer is present at a concentration sufficient for at least a portion of the polymer to adsorb on the surface of the abrasive particles and thereby maintain a zeta potential of at least +20 mV on the particles of the particulate abrasive even at the basic pH that develops at the surface of the polishing pad during polishing of silicon nitride
Implementation Method 2
The relative movement of the pad and substrate serves to abrade the surface of the substrate to remove a portion of the material from the substrate surface, thereby polishing the substrate. The polishing of the substrate surface typically is further aided by the chemical activity of the polishing composition
Data Source
AI summary
The present invention provides chemical mechanical polishing compositions and methods for polishing a substrate comprising silicon dioxide and silicon nitride, which provide selective removal of SiN relative to silicon oxide (e.g., PETEOS) on patterned wafers. In one embodiment, a CMP method comprises abrading a surface of a substrate comprising SiN and silicon oxide with a CMP composition to remove at least some SiN therefrom. The CMP composition comprises, consists essentially of, or consists of a particulate abrasive (e.g., ceria) suspended in an aqueous carrier and containing a cationic polymer bearing pendant quaternized nitrogen-heteroaromatic moieties, wherein the composition has a pH of greater than about 3.