Silicon Wafer Backside Seal for Epitaxial Growth
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Solution Overview
Problem
Conventional epitaxial growth processes suffer from auto-doping and irregular back-side epitaxial growth, leading to reduced breakdown voltage and uneven wafer surfaces due to dopant migration and nodule formation, which are not adequately addressed by existing mitigation techniques, especially in multiple epitaxial layer growth scenarios.
Innovation Solution
A method involving the deposition of a silicon oxide layer on all surfaces and edges of a silicon wafer, followed by the removal of the oxide from the front surface and the deposition of a poly silicon layer on the back side, which prevents auto-doping and uniform nucleation, thereby reducing nodule formation and enabling smooth epitaxial growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon oxide seal is deposited on the back side of the wafer to prevent auto-doping, then auto-doping is reduced, but the oxide seal corrodes and develops pin-hole defects during cleaning processes, causing it to fail in preventing auto-doping
Solution Approach 1:
The patent applies composite materials by combining silicon oxide and polysilicon layers to create a multi-layer seal structure. The silicon oxide layer provides the primary seal, while the polysilicon layer reinforces it and prevents corrosion and pin-hole defects that plague single-layer oxide seals during cleaning processes
Solution Approach 2:
The patent introduces a polysilicon layer as an intermediary between the silicon oxide seal and the environment during cleaning processes. This intermediate layer protects the oxide seal from direct exposure to corrosive cleaning agents, preventing degradation and maintaining seal integrity
2Manufacturing precision
If epitaxial growth is performed on the front surface of the wafer, then the desired epitaxial layer is formed, but irregular silicon nodules form on the back side due to exposure to process gases, creating an uneven wafer surface
Solution Approach 1:
The patent segments the wafer surfaces by selectively depositing seal layers only on the back side and edges, leaving the front surface exposed for epitaxial growth. This segmentation allows the front surface to receive proper epitaxial layers while the back side is protected from nodule formation
Solution Approach 2:
The polysilicon layer acts as an intermediary on the back side, providing a controlled surface that prevents uncontrolled nodule formation while allowing uniform epitaxial growth when desired
3Adaptability or versatility
If multiple epitaxial layers are grown on the wafer, then device functionality is improved, but the accumulation of auto-doping and back side nodules from multiple growth processes overwhelms conventional mitigation techniques
Solution Approach 1:
The patent applies preliminary action by depositing the silicon oxide and polysilicon seal layers on the back side before any epitaxial growth processes begin. This pre-established seal prevents auto-doping and nodule formation from accumulating across multiple epitaxial layer growth cycles
Solution Approach 2:
The multi-layer composite seal structure maintains its protective function throughout multiple epitaxial growth processes, preventing the cumulative degradation that occurs with single-layer seals or no seal
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 auto-doping and nodule formation, resulting in uniform epitaxial layers with controlled doping profiles, compatible with conventional wafer processing systems and suitable for multiple epitaxial layers and vertical trench or column formation.
Implementation Method 1
A method is provided that utilizes a seal comprising a silicon oxide layer deposited on a back side of a silicon wafer... Auto doping of the layer of epitaxial silicon is reduced when the layer of epitaxial silicon is grown on the front side of the silicon wafer with the seal in place
Implementation Method 2
deposition of a poly silicon layer on the back side, which prevents auto-doping and uniform nucleation, thereby reducing nodule formation
Implementation Method 3
Exemplary processes include chemical vapor deposition (CVD), wherein gas phase Silicon sources... are passed over a silicon substrate at a high temperature... resulting in an epitaxial growth process
Data Source
Figure 1A
Figure 1B
Figure 2A~2C
AI summary
Systems and methods for substrate wafer back side and edge cross section seals. In accordance with a first method embodiment, a silicon wafer of a first conductivity type is accessed. An epitaxial layer of the first conductivity type is grown on a front surface of the silicon wafer. The epitaxial layer is implanted to form a region of an opposite conductivity type. The growing and implanting are repeated to form a vertical column of the opposite conductivity type. The wafer may also be implanted to form a region of the opposite conductivity type vertically aligned with the vertical column.