Abrasive-Free CMP Slurry for High-Rate Hard Material Polishing
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Solution Overview
Problem
Conventional chemical mechanical polishing (CMP) methods for hard materials with Vickers hardness exceeding 1,000 Kg/mm2 result in low removal rates due to the non-reactive nature of these materials, leading to significant surface and sub-surface damage, as well as long cycle times, as they require hard abrasive particles that are either ineffective or cause damage.
Innovation Solution
A CMP slurry solution comprising a per-compound oxidizer with a pH level between 2 to 5 or 8 to 11 and a buffering agent, excluding hard abrasive particles, which includes soft particles with Vickers hardness less than 300 Kg/mm2, is used to polish hard surfaces, enhancing the polishing rate and reducing damage by stabilizing the pH and catalyzing oxidation reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If hard abrasive particles (silica, alumina, diamond) are used to polish hard materials with Vickers hardness >1,000 Kg/mm2, then polishing rate is improved, but surface and sub-surface damage increases significantly
Solution Approach 1:
The patent replaces the conventional mechanical abrasion mechanism with hard particles with a chemical oxidation mechanism. The slurry uses per-compound oxidizers (such as peracetic acid, peroxymonosulfate, or permanganate) to chemically oxidize and remove material from hard surfaces (tungsten, iridium, ruthenium, diamond, GaN, SiC, AlN). This chemical mechanical polishing approach eliminates the need for hard abrasive particles, thereby achieving high polishing rates without the surface and sub-surface damage caused by mechanical abrasion.
Solution Approach 2:
The patent changes the chemical parameters of the polishing slurry by using per-compound oxidizers with specific pH levels (2-5 or 8-11) and incorporating buffering agents with buffering ratios of at least 1.5. These parameter changes enable the slurry to effectively react with chemically inert hard materials, achieving high removal rates without requiring hard abrasive particles, thus resolving the contradiction between polishing rate and surface damage.
2Object-affected harmful factors
If moderately hard particles (Mohs hardness 6-10) are used for polishing hard materials, then crystal damage is reduced, but polishing rate becomes very low requiring long cycle times
Solution Approach 1:
The patent replaces the mechanical abrasion mechanism with moderately hard particles with a chemical oxidation mechanism using per-compound oxidizers. This substitution eliminates the need for any abrasive particles (hard or moderate), achieving both low crystal damage and high polishing rates through chemical reaction with the hard material surfaces.
Solution Approach 2:
The patent employs per-compound oxidizers (peracetic acid, peroxymonosulfate, permanganate) as strong oxidizing agents to rapidly oxidize and remove material from hard surfaces. This accelerated oxidation process achieves high polishing rates without requiring abrasive particles, thereby reducing cycle time while maintaining low crystal damage.
3Productivity
If conventional CMP slurries without buffering agents are used on chemically inert hard materials, then polishing rate is low, but the process is simpler
Solution Approach 1:
The patent changes the chemical parameters of the slurry by incorporating buffering agents with buffering ratios of at least 1.5 and controlling pH levels (2-5 or 8-11). These parameter changes enable the slurry to maintain stable chemical reactivity with chemically inert hard materials throughout the polishing process, achieving high polishing rates. The buffering agents prevent pH drift that would otherwise reduce polishing effectiveness.
Solution Approach 2:
The patent uses per-compound oxidizers as strong oxidizing agents that actively react with chemically inert hard materials. The combination of strong oxidants and buffering agents creates a chemically active slurry that achieves high polishing rates on materials like tungsten, iridium, ruthenium, diamond, and GaN, overcoming the low reactivity issue without excessive complexity.
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 achieves a significant increase in polishing rates and reduces crystal damage by stabilizing the pH and catalyzing oxidation reactions, resulting in high removal rates of hard materials without the need for conventional hard abrasive particles, while maintaining surface quality with minimal subsurface damage.
Implementation Method 1
at least one per-compound oxidizer... catalyzing oxidation reactions
Implementation Method 2
at least one buffering agent... provides a buffering ratio of at least 1.5... stabilizing the pH
Data Source
AI summary
A method of CMP includes providing a slurry solution including ≥1 per-compound oxidizer in a concentration between 0.01 M and 2 M with a pH from 2 to 5 or 8 to 11, and ≥1 buffering agent which provides a buffering ratio ≥1.5 that compares an amount of a strong acid needed to reduce the pH from 9.0 to 3.0 as compared to an amount of strong acid to change the pH from 9.0 to 3.0 without the buffering agent. The slurry solution is exclusive any hard slurry particles or has only soft slurry particles that have throughout a Vickers hardness <300 Kg/mm2 or Mohs Hardness <4. The slurry solution is dispensed on a hard surface having a Vickers hardness >1,000 kg/mm2 is pressed by a polishing pad with the slurry solution in between while rotating the polishing pad relative to the hard surface.