Bell Jar Vacuum Drying for Polysilicon Moisture Removal
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Solution Overview
Problem
Conventional methods for cleaning the inner surface of a bell jar used in polycrystalline silicon production are inefficient in removing moisture, leading to contamination and reduced quality of the silicon produced, as moisture reacts with residual substances to form hazardous impurities.
Innovation Solution
A method involving a water washing step followed by a vacuum drying step that reduces the pressure inside the bell jar to below the vapor pressure of water, using a vacuum pump with a reachability of 200 Pa or less, and subsequent introduction of an inert gas with a dew point of -40°C or less to return the pressure to atmospheric levels, without increasing the bell jar's surface temperature, to efficiently remove moisture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional water washing method is used to clean the bell jar, then the inner surface can be cleaned, but moisture remains and causes contamination in the next batch
Solution Approach 1:
The patent applies phase transition by reducing pressure to below water's vapor pressure, causing moisture to transition from liquid to vapor state and be removed from the bell jar inner surface, preventing contamination in the next production batch
Solution Approach 2:
The patent introduces inert gas with dew point of -40°C or lower into the bell jar after vacuum drying, creating an inert atmosphere that prevents moisture re-condensation and maintains the cleaned state of the inner surface
2Productivity
If the bell jar is opened for batch production, then polycrystalline silicon can be taken out, but moisture from atmosphere adheres to the inner surface
Solution Approach 1:
The patent performs preliminary drying action by reducing pressure below water's vapor pressure after water washing and before the next batch production, proactively removing moisture that would otherwise contaminate the next batch of polycrystalline silicon
Solution Approach 2:
The patent introduces inert gas with low dew point into the bell jar to create a protective inert atmosphere that prevents atmospheric moisture from adhering to the inner surface during batch operations
3Reliability
If conventional drying methods are used, then moisture can be removed, but the process takes too long and reduces production efficiency
Solution Approach 1:
The patent utilizes phase transition by reducing pressure to below water's vapor pressure, accelerating moisture evaporation from liquid to vapor state, thereby achieving effective moisture removal in reduced time and improving production efficiency
Solution Approach 2:
The patent changes the pressure parameter to below water's vapor pressure during drying, fundamentally altering the drying conditions to achieve rapid moisture removal without extending production cycle time
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 significantly reduces the drying time, enhances the cleanliness of the bell jar's inner surface, and improves the quality of high purity polycrystalline silicon production by preventing contamination from residual substances.
Implementation Method 1
reducing pressure so that an inside of the bell jar has pressure lower than vapor pressure of water at an inner surface temperature to remove moisture
Implementation Method 2
reducing pressure so that air pressure in the bell jar is 1000 Pa or less using a vacuum pump having vacuum reachability of 200 Pa or less, and thus reducing pressure so that an inside of the bell jar has pressure lower than vapor pressure of water at an inner surface temperature to remove moisture
Data Source
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AI summary
A bell jar includes a metallic bell jar (1), and a metallic base plate (2) on which the bell jar (1) is placed, and packing (3) seals an inside of a container. To the base plate (2), a pressure gauge (4), a gas introduction line (5), and a gas discharge line (6) are connected so as to allow monitoring of internal pressure of the bell jar (1) and introduction and discharge of a gas. A vacuum pump (7) is provided in a path of the gas discharge line (6), and the vacuum pump (7) reduces internal pressure of the bell jar so as to be lower than vapor pressure of water. The vacuum pump (7) reduces the internal pressure of the bell jar so as to be lower than vapor pressure of water, thereby efficiently removing moisture, and completing drying of the bell jar in a short time.