Randomly Oriented Polysilicon Dummy Wafers for Thermal Furnace Durability
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Solution Overview
Problem
Current non-production wafers, such as monocrystalline silicon wafers, are limited in their durability and lifespan due to fracturing and particle issues during thermal processing, leading to inefficient thermal distribution and excessive particle generation in silicon wafer fabrication.
Innovation Solution
The use of randomly oriented polycrystalline silicon (ROPSi) wafers, grown by the Czochralski method, which are surface-treated to enhance their ruggedness and ability to withstand multiple thermal cycles without flaking, replacing traditional monocrystalline silicon wafers as buffer and dummy wafers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If monocrystalline silicon wafers are used as buffer and dummy wafers, then thermal processing can be performed, but the wafers fracture and flake during thermal cycles, leading to short lifespan and excessive particle generation
Solution Approach 1:
The patent changes the crystallographic parameter of the wafer material from monocrystalline to randomly oriented polycrystalline silicon. This parameter change fundamentally alters the material's mechanical properties, making it more resistant to fracturing and flaking during thermal processing cycles while maintaining thermal conductivity for effective buffer wafer operation
Solution Approach 2:
The patent uses randomly oriented polycrystalline silicon, which can be considered a composite microstructure composed of numerous small crystallites with random orientations. This composite structure provides both the thermal conductivity needed for buffer wafer function and the mechanical robustness to prevent fracturing and extend lifespan
2Reliability
If monocrystalline silicon wafers are used as buffer and dummy wafers, then thermal processing can be performed, but excessive particles are generated due to fracturing and flaking
Solution Approach 1:
The patent changes the crystal structure parameter from monocrystalline to randomly oriented polycrystalline, which eliminates the preferential cleavage planes present in monocrystalline silicon. This parameter change prevents the fracturing and flaking that generate particles, thereby improving particle-free operation while maintaining buffer wafer functionality
Solution Approach 2:
The patent converts what would normally be considered a disadvantage of polycrystalline silicon (random orientation) into a benefit. The random orientation eliminates directional weakness and cleavage planes, converting a potentially weak structure into one that is resistant to fracturing and particle generation during thermal processing
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
Polycrystalline silicon wafers exhibit increased durability and longer lifetimes, allowing for thicker nitride deposition without flaking, reducing particle production, and enabling more efficient thermal processing with improved uniformity and reduced need for frequent replacement.
Implementation Method 1
randomly oriented polycrystalline silicon (ROPSi), for example, grown by the Czochralski (CZ) method by drawing a seed from a silicon melt
Implementation Method 2
grown by the Czochralski (CZ) method by drawing a seed from a silicon melt
Implementation Method 3
Batch thermal processing continues to be used for several stages of fabrication of silicon integrated circuits
Implementation Method 4
deposits a layer of silicon nitride by low pressure chemical vapor deposition (LPCVD)
Data Source
AI summary
Non-production wafers of polycrystalline silicon are placed in non-production slots of a support tower for thermal processing monocrystalline silicon wafers. They may have thicknesses of 0.725 to 2 mm and be roughened on both sides. Nitride may be grown on the non-production wafers to a thickness of over 2 μm without flaking. The polycrystalline silicon is preferably randomly oriented Czochralski polysilicon grown using a randomly oriented seed, for example, CVD grown silicon. Both sides are ground to introduce sub-surface damage and then oxidized and etch cleaned. An all-silicon hot zone of a thermal furnace, for example, depositing a nitride layer, may include a silicon support tower placed within a silicon liner and supporting the polysilicon non-production wafers with silicon injector tube providing processing gas within the liner.