Polysilicon Lump Cleaning via Fluonitric Acid and Hydrogen Peroxide
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Solution Overview
Problem
Current methods for cleaning crushed polycrystalline silicon lumps, such as using fluonitric acid aqueous solutions, are insufficient in reducing surface metal impurities like tungsten and cobalt, which are contaminants from the breaking tool, and result in high etching amounts and costs, limiting the cleanliness and circuit density in semiconductor manufacturing.
Innovation Solution
A method involving a three-step washing process: initial contact with fluonitric acid, followed by an alkaline aqueous solution containing hydrogen peroxide, and a final fluonitric acid treatment, effectively reduces surface metal impurities by oxidizing and dissolving tungsten carbide and cobalt, achieving low concentrations of tungsten and cobalt on the surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If washing with fluonitric acid aqueous solution is performed to remove metal impurities, then oxide film and various metals are dissolved, but tungsten carbide contamination remains above 2 pptw due to extremely low solubility
Solution Approach 1:
The patent changes the chemical parameters of the washing solution by adding hydrogen peroxide to the fluonitric acid solution. This creates a more aggressive oxidizing environment that enables dissolution of tungsten carbide while maintaining the ability to remove other metal impurities and oxide films effectively.
Solution Approach 2:
The patent uses a composite washing solution comprising fluonitric acid and hydrogen peroxide. This composite chemical system combines the oxide-dissolving capability of fluonitric acid with the oxidizing power of hydrogen peroxide, creating a synergistic effect that removes tungsten carbide and other contaminants.
2Manufacturing precision
If etching treatment is increased to remove more metal impurities, then surface cleanliness improves, but etching amount and manufacturing costs increase
Solution Approach 1:
The patent modifies the chemical composition parameters of the washing solution by incorporating hydrogen peroxide, which enhances the removal efficiency of metal impurities. This allows achieving lower metal concentrations without proportionally increasing the etching amount, thus reducing silicon material loss.
Solution Approach 2:
The patent applies a proven washing methodology (fluonitric acid with hydrogen peroxide) that has been optimized for removing metal impurities from semiconductor substrates. By adapting this established process to polycrystalline silicon lump washing, it achieves effective contamination removal with controlled material loss.
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 achieves a surface metal concentration of 15.0 pptw or less, with tungsten and cobalt concentrations at 0.9 pptw or less, significantly improving the cleanliness and reducing defects in semiconductor wafers, while minimizing the etching amount and associated costs.
Implementation Method 1
an alkaline aqueous solution containing hydrogen peroxide... oxidizing and dissolving tungsten carbide and cobalt
Implementation Method 2
The etching treatment with the fluonitric acid aqueous solution is also applied to washing of the crushed polycrystalline silicon lumps, favorably dissolves an oxide film formed on the surface
Data Source
AI summary
[Problem] To obtain crushed polycrystalline silicon lumps from which tungsten and/or cobalt, which are derived from the material of a crushing tool and cause unavoidable contamination, have been removed to a high degree. [Solution] Provided are crushed polycrystalline silicon lumps characterized in that: the surface metal concentration is 15.0 pptw or less, preferably 7.0 to 13.0 pptw; and of the surface metal concentration, the surface tungsten concentration is 0.9 pptw or less, preferably 0.40 to 0.85 pptw, and the surface cobalt concentration is 0.3 pptw or less, preferably 0.04 to 0.08 pptw.