Polycrystalline Silicon Lump Cleaning for Copper Re-Adhesion Control
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Solution Overview
Problem
Existing methods for cleaning polycrystalline silicon crushed lumps fail to sufficiently reduce the surface concentrations of copper, iron, and zinc, which can lead to performance deterioration and reliability degradation of electronic circuits due to their high thermal diffusion rates and adhesion properties.
Innovation Solution
A cleaning process involving a first step with a hydrogen peroxide and hydrofluoric acid solution with minimal content of other acids, followed by a second step with hydrofluoric nitric acid, effectively reduces the surface concentrations of copper, iron, and zinc to 0.30 pptw, 2.00 pptw, or less, respectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If hydrofluoric acid is used for cleaning, then metal impurities are dissolved and ionized effectively, but copper re-adheres to the silicon surface due to high oxidation-reduction potential
Solution Approach 1:
The patent changes the chemical parameters of the cleaning solution by adding hydrogen peroxide to hydrofluoric acid, creating a mixed solution that alters the oxidation-reduction environment. This parameter change prevents copper re-adhesion while maintaining effective removal of other metal impurities, resolving the contradiction between general cleaning efficiency and copper-specific contamination control
Solution Approach 2:
The patent uses a composite cleaning solution combining hydrofluoric acid and hydrogen peroxide. This composite approach leverages the metal-dissolving capability of hydrofluoric acid while the hydrogen peroxide component addresses copper's high oxidation-reduction potential, achieving comprehensive cleaning without copper re-adhesion
2Ease of manufacture
If conventional cleaning methods are used, then general metal impurities are removed, but copper, iron, and zinc concentrations remain high on the surface
Solution Approach 1:
The patent modifies the cleaning solution composition by incorporating hydrogen peroxide alongside hydrofluoric acid, changing the chemical parameters to achieve superior removal of copper, iron, and zinc. This parameter enhancement maintains process simplicity while dramatically improving surface cleanliness and metal concentration reduction
Solution Approach 2:
The patent employs hydrogen peroxide as a strong oxidant in the cleaning solution. This accelerates the oxidation and removal of metal impurities including copper, iron, and zinc from the silicon surface, achieving much lower residual concentrations compared to conventional cleaning methods while keeping the process straightforward
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 produces a polycrystalline silicon crushed lump with a clean surface, significantly reducing copper to 0.30 pptw or less and iron and zinc to 2.00 pptw or less, making it suitable for producing high-purity single crystalline silicon wafers with fewer defects.
Implementation Method 1
hydrofluoric acid has a function of removing a natural oxide film on the surface of polycrystalline silicon, and metal impurities incorporated into the oxide film are also roughly removed
Implementation Method 2
hydrogen peroxide and hydrofluoric acid solution with minimal content of other acids, followed by a second step with hydrofluoric nitric acid, effectively reduces the surface concentrations of copper, iron, and zinc
Implementation Method 3
the hydrofluoric nitric acid aqueous solution used in the second cleaning treatment dissolves (etches) the surface of silicon by nitric acid, and thus contamination caused by the metal impurities on the surface of polycrystalline silicon is greatly reduced
Implementation Method 4
copper has a high oxidation-reduction potential, and thus even ionized, copper re-adheres to the surface of silicon when copper comes into contact with silicon again and is reduced
Data Source
AI summary
A polycrystalline silicon crushed lump has a surface metal concentration of 15.0 pptw or less, in which a copper concentration is 0.30 pptw or less in the surface metal concentration, and a total concentration of iron and zinc is 2.00 pptw or less in the surface metal concentration, and preferably an iron concentration is 1.25 pptw or less, and a zinc concentration is 0.75 pptw or less.