Cobalt CMP Slurry with Dual Chelators for Corrosion Control
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Solution Overview
Problem
Current CMP technologies for cobalt interconnects face challenges in achieving high removal rates without causing corrosion, as existing slurries for copper or tungsten cannot be used effectively for cobalt, leading to high defect counts and galvanic corrosion issues.
Innovation Solution
A CMP composition comprising colloidal silica, dual amino acid chelators (glycine and alanine), and optional additives like corrosion inhibitors and oxidizing agents, optimized for pH between 2.0 and 8.5, to achieve high and tunable cobalt film removal rates while minimizing static etch rates and galvanic corrosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If existing slurries for copper or tungsten polishing are used on cobalt, then polishing can proceed, but cobalt dissolution occurs leading to high defect counts
Solution Approach 1:
The patent changes the chemical parameters of the slurry by adjusting pH to alkaline conditions (pH 10-12) and selecting specific chelating agents that form stable complexes with cobalt ions. This parameter modification prevents cobalt dissolution while maintaining high removal rates, resolving the contradiction between productivity and reliability.
Solution Approach 2:
The patent introduces chelating agents as intermediaries that bind to cobalt ions during polishing. These chelators act as mediators between the abrasive and cobalt surface, enabling material removal through controlled complexation rather than direct dissolution, thus preventing defects while maintaining productivity.
2Productivity
If chemically aggressive slurry compositions are used to achieve high removal rates, then polishing efficiency increases, but corrosion defects are introduced
Solution Approach 1:
The patent transforms the slurry from chemically aggressive to chemically selective by changing pH to alkaline conditions and selecting specific chelating agents. This parameter change enables high removal rates through controlled complexation rather than uncontrolled corrosion, eliminating the contradiction between productivity and corrosion resistance.
Solution Approach 2:
The patent converts the naturally high reactivity of cobalt, which causes dissolution and defects, into a beneficial property by using chelating agents that selectively complex with cobalt ions. This controlled complexation harnesses cobalt's reactivity to achieve high removal rates while preventing harmful corrosion, turning the harmful factor into a benefit.
3Loss of time
If high removal rates are required for cobalt interconnect polishing, then polishing time decreases, but existing slurries cause cobalt dissolution and defects
Solution Approach 1:
The patent changes the chemical environment to alkaline pH (10-12) and introduces specific chelating agents that enable fast, controlled removal of cobalt. This parameter modification allows achieving high removal rates in reduced time without the cobalt dissolution problems that plague conventional slurries, simultaneously improving both time efficiency and reliability.
4Ease of operation
If conventional polishing slurries are used on cobalt, then polishing can be performed, but galvanic corrosion occurs at the Co/Cu interface
Solution Approach 1:
The patent changes the pH to alkaline conditions (10-12) and selects chelating agents that preferentially complex with cobalt over copper. This parameter modification creates a chemically selective environment that prevents galvanic corrosion at the Co/Cu interface while maintaining ease of polishing operation.
Solution Approach 2:
The patent introduces chelating agents as selective intermediaries that bind to cobalt ions but not copper ions. These intermediaries act as protective mediators at the Co/Cu interface, preventing the galvanic corrosion that would otherwise occur during polishing, thus maintaining both processability and corrosion resistance.
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 cobalt film removal rates, low static etch rates for corrosion protection, and selective removal of cobalt versus dielectric and barrier films, effectively minimizing galvanic corrosion at the Co/Cu interface.
Implementation Method 1
dual chelators such as glycine and alanine
Implementation Method 2
oxidizing agents
Implementation Method 3
colloidal silica as an abrasive
Data Source
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Figure 3(a)
AI summary
Chemical mechanical polishing (CMP) compositions, methods and systems for polishing cobalt or cobalt-containing substrates are provided. Dual, or at least two chelators are used in the CMP polishing compositions as complexing agents for achieving the unique synergetic effects to afford high, tunable Co removal rates, and low static etch rates on Co film surface for efficient Co corrosion protection during CMP process. The cobalt chemical mechanical polishing compositions also provide very high selectivity for Co film removal vs. removal of other barrier layers, such as Ta, TaN, Ti, and TiN, and dielectric film, such as TEOS, SiNx, low-k, and ultra low-k films.