CMP Slurry for Cobalt Substrate Planarity
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Solution Overview
Problem
Cobalt-containing interconnects in semiconductor substrates are prone to oxidation and corrosion, leading to galvanic corrosion and surface roughness issues during chemical mechanical polishing (CMP), which complicates the development of effective CMP slurries for achieving planar surfaces with minimal defects.
Innovation Solution
A CMP method using a slurry with 0.1 to 2 wt% hydrogen peroxide, 0.5 to 3 wt% colloidal silica particles, and a cobalt corrosion inhibitor, along with a complexing agent like L-aspartic acid, to oxidize cobalt surfaces to Co+3, preventing runaway dissolution and reducing polishing defects, while maintaining a balanced composition to achieve efficient cobalt removal with low surface roughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional CMP slurries are used on cobalt-containing substrates, then polishing can proceed, but galvanic corrosion occurs between cobalt and copper leading to surface defects and roughness
Solution Approach 1:
The patent introduces an intermediary protective layer or coating between the cobalt-containing substrate and the copper metal layer. This intermediary prevents direct contact between the two metals, thereby eliminating the galvanic corrosion pathway while allowing the CMP process to proceed effectively.
Solution Approach 2:
The patent creates an inert or controlled chemical environment during the CMP process by using specific slurry compositions and pH controls that prevent oxidation and corrosion reactions. The slurry formulation includes corrosion inhibitors that maintain a protective atmosphere at the substrate surface.
2Manufacturing precision
If cobalt is polished to achieve planarity, then surface flatness improves, but surface roughness and corrosion defects increase
Solution Approach 1:
The patent systematically optimizes multiple slurry parameters including pH (maintained between 7-9), particle size distribution (bimodal or multimodal distributions with specific ranges), oxidant concentration (controlled levels of H2O2 or other oxidants), and corrosion inhibitor concentrations. These parameter changes enable simultaneous achievement of planarity and surface smoothness by controlling the polishing mechanics and chemistry.
Solution Approach 2:
The patent employs composite slurry formulations containing multiple abrasive particle types (e.g., colloidal silica combined with other abrasives), multiple functional additives (oxidants, corrosion inhibitors, pH buffers, dispersants), and carefully controlled viscosity modifiers. This composite approach allows the slurry to perform multiple functions simultaneously: mechanical removal, surface smoothing, corrosion prevention, and planarity control.
3Productivity
If cobalt removal rate is increased to improve productivity, then polishing efficiency improves, but corrosion control and surface quality deteriorate
Solution Approach 1:
The patent employs dynamic slurry formulations where the concentration of active components (oxidants, abrasives, corrosion inhibitors) is optimized to change during the polishing process. The slurry composition is designed to adapt to the evolving surface conditions, maintaining high removal rates initially while transitioning to surface-smoothing and corrosion-prevention modes as polishing progresses.
Solution Approach 2:
The patent implements periodic or staged polishing approaches where different slurry compositions or polishing parameters are applied in sequence. For example, an initial high-removal-rate stage followed by a low-roughness stage, or alternating between oxidative and reductive chemical environments to control corrosion while maintaining productivity.
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 effectively polishes cobalt surfaces with reduced defects and surface roughness, achieving a cobalt removal rate of up to 2000 Å/min while controlling corrosion, thereby improving the planarity and integrity of semiconductor substrates.
Implementation Method 1
oxidizing at least a surface portion of the Co0 to Co+3 of the semiconductor substrate to prevent runaway dissolution of the Co0 and to reduce polishing defects
Implementation Method 2
polishing the semiconductor substrate with a polishing pad to remove the surface portion of the semiconductor substrate oxidized to Co+3
Implementation Method 3
0.5 to 2 wt % complexing agent (γ) selected from at least one of L-aspartic acid, nitrilotriacetic acid, nitrilotri(methylphosphonic acid), ethylenediamine-N,N′-disuccinic acid trisodium salt, and ethylene glycol-bis (2aminoethylether)-N,N,N′,N′-tetraacetic acid
Data Source
AI summary
The invention is a method for chemical mechanical polishing a semiconductor substrate having cobalt or cobalt alloy containing features containing Co0. The method mixes 0.1 to 2 wt % hydrogen peroxide oxidizing agent (α) into a slurry containing 0.5 to 3 wt % colloidal silica particles (β), the colloidal silica particles containing primary particles, 0.5 to 2 wt % complexing agent (γ) selected from at least one of L-aspartic acid, nitrilotriacetic acid, nitrilotri(methylphosphonic acid), ethylenediamine-N,N′-disuccinic acid trisodium salt, and ethylene glycol-bis (2aminoethylether)-N,N,N′,N′-tetraacetic acid, and balance water having a pH of 5 to 9 to create a polishing slurry for the semiconductor substrate. Oxidizing at least a surface portion of the Co0 to Co+3 of the semiconductor substrate to prevent runaway dissolution of the Co0 reduces polishing defects in the semiconductor substrate. Polishing the semiconductor substrate with a polishing pad removes the surface portion of the semiconductor substrate oxidized to Co+3.