LLDPE Bag Additive Control for Polysilicon Purity
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Solution Overview
Problem
In semiconductor applications, linear low-density polyethylene (LLDPE) bags used for storing polycrystalline silicon ingots face challenges in maintaining surface cleanliness due to additive elution, which can introduce carbon impurities into CZ silicon single crystals during production.
Innovation Solution
The use of LLDPE bags with specific concentration limits for paraffinic hydrocarbons, antioxidants, ultraviolet absorbents, and antistatic agents, where concentrations of these components in the solvent-extracted concentrates are below 300 ppmw, 10 ppmw, 5 ppmw, and 50 ppmw respectively, and double-packing with an antistatic or surfactant-containing bag to minimize surface contamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If LLDPE bags with additives (antioxidants, ultraviolet absorbents, antistatic agents) are used for storing polycrystalline silicon ingots, then the bags gain improved durability and functionality, but the additives elute onto the ingot surfaces causing carbon impurity contamination
Solution Approach 1:
The patent extracts and removes harmful additives (antioxidants, ultraviolet absorbents, antistatic agents) from the LLDPE bag material through selective extraction processes, retaining only the beneficial mechanical properties while eliminating substances that cause elution and contamination of the polycrystalline silicon ingot surfaces
Solution Approach 2:
The patent changes the chemical composition parameters of the LLDPE bag material by strictly controlling and limiting the content of specific additives to below detectable levels (e.g., antioxidants < 10 ppm, ultraviolet absorbents < 5 ppm, antistatic agents < 50 ppm), thereby transforming the material from a conventional additive-containing polymer to a high-purity semiconductor-grade packaging material
2Strength
If conventional LLDPE bags are used for packing polycrystalline silicon ingots, then the bags provide adequate mechanical protection, but the elution of low-molecular components and additives compromises the surface cleanliness required for CZ silicon single crystal production
Solution Approach 1:
The patent applies stringent parameter control by specifying maximum concentration limits for various contaminants in the LLDPE bag material, including paraffinic hydrocarbons (< 300 ppm), antioxidants (< 10 ppm), ultraviolet absorbents (< 5 ppm), and antistatic agents (< 50 ppm), ensuring the material meets semiconductor industry purity requirements while maintaining mechanical integrity
Solution Approach 2:
The patent employs single-use LLDPE bags with controlled additive content for each packaging operation, eliminating the need for repeated cleaning or sterilization processes and ensuring that no cumulative contamination occurs from multiple uses, thereby guaranteeing consistent surface cleanliness for each batch of polycrystalline silicon ingots
Data Source
AI summary
In the present invention, as a bag to store polycrystalline silicon ingots, there is used a bag in which the concentration of paraffinic hydrocarbons in a concentrate of solvent-soluble components obtained by Soxhlet extraction using acetone as a solvent is lower than 300 ppmw as a value measured by GC-MS method; the concentration of antioxidants, lower than 10 ppmw; the concentration of ultraviolet absorbents, lower than 5 ppmw; and the concentration of antistatic agents and surfactants, lower than 50 ppmw. Then, when the polycrystalline silicon ingots are packed, preferably, the polycrystalline silicon ingots are put in the storage bag; thereafter, the storage bag is sealed; further, the storage bag is put and sealed in a linear low-density polyethylene bag containing an antistatic agent or a surfactant added in the bag material.