Polysilicon Washing Apparatus with Sequential Acid Baths
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Solution Overview
Problem
Current methods for washing lump or rod-shaped polycrystalline silicon to remove impurities and spots are inefficient, leading to variations in etching reactions and re-deposition of impurities, which affects the quality of single crystal silicon production.
Innovation Solution
A washing apparatus with multiple acid baths of varying temperatures and a pure water bath system, where the polycrystalline silicon is sequentially immersed to actively remove impurities in the first bath and then gradually lower the impurity concentration in subsequent baths, using a temperature adjusting unit to maintain a stable reaction and prevent spot formation, with acid recycling to conserve chemicals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the temperature of the acid is increased to accelerate the etching reaction, then the impurity removal efficiency is improved, but the surface of the polycrystalline silicon is rapidly oxidized or dissolved, causing spot formation
Solution Approach 1:
The washing process is divided into multiple sequential acid baths (first acid bath, second acid bath, third acid bath) with progressively lower temperatures. The first bath uses higher temperature for aggressive impurity removal, while subsequent baths use lower temperatures to remove spots and perform finishing without causing rapid oxidation or dissolution.
Solution Approach 2:
The temperature parameter of the acid is systematically changed across different washing stages. The first acid bath operates at a relatively high temperature to accelerate etching and remove impurities, while the second and third acid baths operate at progressively lower temperatures to remove spots and perform final cleaning, thus preventing spot formation while maintaining impurity removal efficiency.
2Manufacturing precision
If multiple acid baths are used to remove impurities and spots, then the quality of polycrystalline silicon is improved, but the complexity of the washing apparatus increases
Solution Approach 1:
The washing apparatus is segmented into multiple independent acid baths, each with a specific function (impurity removal, spot removal, final cleaning). This segmentation allows each bath to be optimized for its specific purpose while maintaining overall system manageability and operational simplicity.
Solution Approach 2:
The acid baths are designed to automatically maintain their respective temperatures through temperature adjusting units, and the washing process follows a natural sequential flow where the polycrystalline silicon moves from one bath to the next, reducing the need for complex control mechanisms.
3Object-affected harmful factors
If the etching reaction is performed continuously to prevent oxide film formation, then spot generation is reduced, but impurities dissolved in the liquid during etching are diffused into the etchant used in subsequent processes, causing re-deposition
Solution Approach 1:
The continuous etching process is segmented into discrete acid baths separated by pure water baths. Each acid bath performs a specific etching function, and the intermediate pure water baths flush away dissolved impurities, preventing their diffusion into subsequent etching solutions and avoiding re-deposition on the polycrystalline silicon surface.
Solution Approach 2:
Pure water baths are introduced as intermediary steps between acid baths. These pure water baths serve as mediators that flush away impurities dissolved during etching, preventing them from being carried into the next acid bath where they could cause re-deposition, thus maintaining surface quality throughout the continuous washing process.
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
This approach effectively reduces impurities and spots on the polycrystalline silicon, ensuring high-quality silicon production by maintaining a stable etching reaction and reusing acid, thereby enhancing productivity and reducing chemical consumption.
Implementation Method 1
the surface of the polycrystalline silicon is washed by an etching reaction
Implementation Method 2
The temperature of the first acid bath is relatively high compared to other acid bathes, the temperatures of the acids in other acid bathes are gradually reduced
Implementation Method 3
the surface of the polycrystalline silicon may actively react with the acid
Implementation Method 4
the surface of the polycrystalline silicon is rapidly oxidized or dissolved by the chemicals used
Data Source
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AI summary
Disclosed is a polycrystalline silicon washing apparatus that sequentially immerses polycrystalline silicon into a plurality of acid baths each of which is filled with an acid to wash the polycrystalline silicon. The temperatures of the acids in the acid baths are set such that the temperature of the acid in a later acid bath of adjacent acid baths is equal to or lower than that of a former acid bath and the temperature of the acid in the last acid bath is lower than that of the acid in the first acid bath. Each of the acid baths is provided with a temperature adjusting unit that controls the temperature of the acid at a constant value.