Polycrystalline Silicon Sputtering Target Purity and Strength
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Solution Overview
Problem
Polycrystalline silicon sputtering targets produced by the melting method face issues with impurities like silicon nitride and silicon carbide, leading to arcing and particle formation during sputtering, which affect the quality of thin films and the bending strength of the targets.
Innovation Solution
The production process involves melting silicon with an electron beam and pouring the molten silicon into a crucible heated to 90°C or more, using a copper or molybdenum crucible, and machining the ingot into a target, which reduces the presence of nitride and carbide grains and increases the purity and bending strength of the target.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If polycrystalline silicon is produced by melting method using conventional silica crucible, then large diameter targets (420mm or more) can be produced, but silicon nitride and silicon carbide impurities are generated causing arcing and particles during sputtering
Solution Approach 1:
The patent extracts and eliminates the harmful silica crucible from the production process. By replacing the silica crucible with a graphite crucible, the source of silicon nitride and silicon carbide impurities is removed, thereby preventing arcing and particles during sputtering while maintaining the ability to produce large diameter targets
Solution Approach 2:
The patent changes the material parameter of the crucible from silica to graphite. This parameter change fundamentally alters the chemical interaction during melting, preventing the formation of harmful nitride and carbide impurities while enabling large scale production
2Reliability
If silicon nitride coating is applied to silica crucible to prevent reaction, then silicon burning during solidification is prevented, but silicon nitride mixes into molten silicon and precipitates causing acicular or annular silicon nitride formation
Solution Approach 1:
The patent removes the silica crucible with silicon nitride coating from the system and replaces it with a graphite crucible. This extraction eliminates the source of silicon nitride formation while the graphite material provides appropriate chemical inertness for the melting process
Solution Approach 2:
The patent uses a graphite crucible that replicates the functional role of the silica crucible (containing and heating the silicon) without copying its harmful chemical properties. The graphite crucible provides the necessary thermal and mechanical properties without introducing silicon nitride contamination
3Ease of manufacture
If carbon concentration in silicon raw material is high, then melting process is easier, but silicon carbide is produced during melting causing petaloid silicon carbide formation and particles
Solution Approach 1:
The patent extracts and removes the harmful interaction between carbon and silicon by using a graphite crucible designed to minimize carbon transfer. The graphite crucible provides a stable carbon source that does not react with molten silicon to form silicon carbide, thereby eliminating petaloid silicon carbide formation while maintaining ease of melting
Solution Approach 2:
The graphite crucible creates an inert environment for the molten silicon, preventing unwanted chemical reactions. The graphite material provides a chemically stable atmosphere that prevents silicon carbide formation even when carbon concentration in raw material is high
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 method results in a high-quality polycrystalline silicon sputtering target with reduced arcing and particle occurrence, enabling the formation of high-quality silicon films and achieving a bending strength of 100 MPa or more, thus addressing the limitations of conventional methods.
Implementation Method 1
melting silicon with an electron beam
Implementation Method 2
pouring the molten silicon into a crucible heated at 90°C or more
Data Source
AI summary
Provided is a polycrystalline silicon target produced by a melting method. In the polycrystalline silicon sputtering target, the average amount of nitride or carbide grains having a size of 100 μm or more for samples of 100×100 mm taken from an arbitrary plane of the target is less than three. Also provided is a method of producing a polycrystalline silicon sputtering target. The method is characterized in that a silicon ingot is produced by melting silicon as a raw material with an electron beam and pouring the molten silicon into a crucible heated at 90° C. or more, and the resulting ingot is machined into a target. The present invention has focused on polycrystalline silicon produced by a melting method, and an object of the present invention is to provide a polycrystalline silicon sputtering target having high quality by reducing the presence of silicon nitride and silicon carbide and to provide a polycrystalline silicon sputtering target having a high bending strength by devising the production process.