Silicon Substrate Gettering via Phosphorus and Carbon Doping
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Solution Overview
Problem
Existing silicon substrates for solid-state imaging devices face challenges with heavy metal contamination, leading to deteriorated device characteristics and increased manufacturing costs due to methods like intrinsic and extrinsic gettering, which require complex heat treatments and can result in reduced gettering capability and device defects.
Innovation Solution
A silicon substrate with specific phosphorus and carbon doping levels, grown by the CZ method, incorporating an n+ epitaxial layer and an n epitaxial layer, along with a carbon concentration and oxygen concentration optimized to form gettering sinks, preventing heavy metal segregation and improving gettering capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If intrinsic gettering method is used to prevent heavy metal contamination, then gettering capability is improved, but manufacturing cost increases due to multi-stage heat treatment processes
Solution Approach 1:
The patent applies preliminary action by forming oxygen precipitates through heat treatment before epitaxial growth, creating gettering sinks in advance that will capture heavy metals during subsequent manufacturing processes. This pre-formed structure eliminates the need for complex multi-stage heat treatments during device fabrication, reducing manufacturing costs while maintaining high gettering capability.
2Reliability
If ion implantation method is used to reduce white spots, then electrical characteristics are improved, but device characteristics deteriorate due to heavy metal segregation on photodiode
Solution Approach 1:
The patent applies local quality by creating non-uniform phosphorus concentration distribution with distinct n+ and n regions. The n+ epitaxial layer with high phosphorus concentration (1.0×10^18 to 1.0×10^20 atoms/cm³) serves as a phosphorus getter that captures heavy metals, while the n epitaxial layer with lower phosphorus concentration (1.0×10^16 to 1.0×10^18 atoms/cm³) maintains low dark current. This spatial differentiation of doping concentrations allows simultaneous achievement of electrical characteristic improvement and heavy metal segregation prevention.
3Speed
If n+ epitaxial layer is formed to improve device speed, then high speed operation is achieved, but heavy metal contaminates the photodiode portion causing characteristic deterioration
Solution Approach 1:
The patent introduces an intermediary mechanism by forming an n epitaxial layer with moderate phosphorus concentration between the n+ substrate and the photodiode region. This intermediate layer acts as a buffer that prevents heavy metals from reaching the photodiode while still allowing the n+ epitaxial layer to provide high-speed operation. The graded phosphorus concentration profile serves as a transition zone that mediates between the conflicting requirements of speed and contamination prevention.
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
The optimized silicon substrate effectively reduces heavy metal contamination, maintains high gettering capability, and lowers manufacturing costs by forming gettering sinks that prevent defects in solid-state imaging devices, thereby enhancing device yield and reliability.
Implementation Method 1
a single crystal silicon that is doped with phosphorus (P) and is grown by a CZ method
Implementation Method 2
a carbon concentration that is greater than or equal to 1.0×10^16 atoms/cm³ and less than or equal to 1.6×10^17 atoms/cm³
Implementation Method 3
an initial oxygen concentration that is greater than or equal to 1.4×10^18 atoms/cm³ and less than or equal to 1.6×10^18 atoms/cm³
Data Source
AI summary
A silicon substrate is manufactured from a single crystal silicon that is doped with phosphorus (P) and is grown by a CZ method to have a predetermined carbon concentration and a predetermined initial oxygen concentration. An n+ epitaxial layer or an n+ implantation layer that is doped with phosphorus (P) at a predetermined concentration or more is formed on the silicon substrate. An n epitaxial layer that is doped with phosphorus (P) at a predetermined concentration is formed on the n+ layer.