SiCN Polishing Slurry Selectivity via Ultrafine Silica
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Solution Overview
Problem
There is a need for polishing technologies that achieve high selectivity between the removal rates of silicon carbonitride (SiCN) and silicon dioxide (SiO2) thin films, while minimizing SiO2 loss, particularly in semiconductor processing where SiCN is used as an etch stop, dielectric layer, and diffusion barrier.
Innovation Solution
The development of polishing slurries using surface-modified colloidal silica particles with diameters of 35 nm or less, which are negatively charged at low pH, and include organic acids and their salts, demonstrating high SiCN/SiN removal rates and low SiO2 removal rates on both blanket and patterned test wafers, with the use of soft polishing pads to achieve high selectivity and low oxide loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional silica particle slurries are used for polishing SiCN, then SiCN removal rate is achieved, but SiO2 loss increases and selectivity between SiCN and SiO2 removal is insufficient
Solution Approach 1:
The patent modifies the particle size parameter of silica particles to 35 nm or less (ultrafine range) and adjusts the pH to low conditions (pH 2-6) with specific zeta potential ranges (-30 to -70 mV). These parameter changes enable selective removal of SiCN while minimizing SiO2 loss, achieving high selectivity between the two materials.
Solution Approach 2:
The patent uses composite slurry formulations combining ultrafine silica particles with specific organic additives (chelating agents, surfactants, or polymers) to achieve synergistic effects. This composite approach enhances SiCN removal selectivity while controlling SiO2 loss, resolving the contradiction between productivity and substance loss.
2Productivity
If higher removal rate of SiCN is achieved, then polishing efficiency improves, but selectivity between SiCN and SiO2 decreases
Solution Approach 1:
By precisely controlling multiple parameters simultaneously (particle size ≤35 nm, pH 2-6, zeta potential -30 to -70 mV, and additive concentrations), the patent achieves both high polishing efficiency and high selectivity. The ultrafine particle size combined with low pH conditions creates optimal conditions for SiCN removal while sparing SiO2.
Solution Approach 2:
The patent introduces organic additives (chelating agents, surfactants, or polymers) as intermediaries that mediate the interaction between silica particles and the film surfaces. These additives enhance the selective removal of SiCN while protecting SiO2, thereby maintaining both efficiency and precision.
3Strength
If larger silica particles are used for polishing, then mechanical removal capability increases, but surface smoothness and selectivity deteriorate
Solution Approach 1:
The patent segments the silica particles into ultrafine sizes (35 nm or less), creating numerous small particles that can effectively polish hard SiCN films while producing smooth surfaces. The segmentation into fine particles compensates for reduced individual particle strength through increased particle density and surface contact.
Solution Approach 2:
The patent changes the particle size parameter to the ultrafine range (≤35 nm) and combines it with low pH conditions and specific zeta potential ranges. This parameter change enables ultrafine particles to achieve sufficient mechanical removal capability through collective action while maintaining excellent surface smoothness and selectivity.
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 provides high removal rates for SiCN while maintaining low oxide loss, achieving selectivity ratios that enhance the polishing efficiency and surface smoothness, as evidenced by improved removal rates and surface roughness reduction.
Implementation Method 1
SiCN or SiN thin films are polished using surface-modified colloidal silica particles in a slurry at low pH
Implementation Method 2
surface-modified colloidal silica particles (which, in some embodiments are negatively-charged at low pH) show high SiCN/SiN removal rate
Implementation Method 3
the slurry further comprises an additive, an organic acid, and a salt of an organic acid. In some embodiments, the pH is adjusted with an organic acid
Implementation Method 4
surface-modified colloidal silica particles (which, in some embodiments are negatively-charged at low pH) show high SiCN/SiN removal rate and low SiO2 RR
Data Source
AI summary
A method is disclosed for polishing a wafer with a slurry. In the method, the wafer comprises at least one of silicon carbonitride (SiCN) and silicon nitride (SiN), and further comprises one or both of silicon dioxide (SiO2) and poly silicon, and a removal rate of SiCN is greater than a removal rate of poly silicon, and the removal rate of poly silicon is greater than a removal rate of SiO2, and where the slurry comprises up to about 15 wt % of surface-modified colloidal silica particles which have a primary particle size of less than about 35 nm, and the surface-modified colloidal silica particles comprise a plurality of acid moieties or salts thereof.