Epitaxial Silicon Wafer Doping Gradient for Thermal Conductivity
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Solution Overview
Problem
Highly doped silicon substrates in semiconductor wafers exhibit poor thermal conductivity, leading to increased operating temperatures and reduced electrical performance and reliability, particularly at hot spots, and pose challenges in backside illumination applications due to limitations in material thinning and passivation.
Innovation Solution
A semiconductor wafer design featuring a lightly doped device layer, a highly doped protective layer, and a substrate with a dopant concentration gradient, where the protective layer is at least 0.5 μm thick and has a dopant concentration between 6.0×10^17 and 1.0×10^20 carriers/cm^3, providing improved thermal conductivity and resistance to device failure mechanisms while allowing for effective heat dissipation and backside illumination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a heavily-doped silicon substrate is used to provide protection against device failure mechanisms, then reliability is improved, but thermal conductivity deteriorates
Solution Approach 1:
The substrate is divided into multiple doped regions with different doping concentrations. A first doped region has a first doping concentration while a second doped region has a second doping concentration different from the first, allowing different regions to serve different functions (protection vs. heat dissipation) within the same substrate structure
Solution Approach 2:
Different regions of the substrate are given different doping concentrations tailored to their specific functional requirements. The first doped region is optimized for device failure protection while the second doped region is optimized for thermal conductivity, with each region's properties locally optimized for its intended purpose
2Reliability
If a heavily-doped silicon substrate is used, then protection against latch-up failures is improved, but heat dissipation efficiency deteriorates
Solution Approach 1:
The substrate is segmented into regions with different doping concentrations, where the first doped region provides latch-up protection and the second doped region facilitates heat dissipation, allowing both functions to coexist without compromising either
Solution Approach 2:
The doping concentration parameter is varied across different regions of the substrate. By changing the doping concentration from the first level in the first region to the second level in the second region, the substrate achieves both high reliability for latch-up protection and improved thermal conductivity for heat dissipation
3Reliability
If a lightly-doped device layer is grown on a heavily-doped substrate, then electrical performance is improved, but thermal management deteriorates
Solution Approach 1:
The substrate is divided into doped regions with different concentrations to address both electrical performance requirements (maintaining the lightly-doped device layer on heavily-doped substrate for electrical performance) and thermal management requirements (adding second doped region with different concentration for improved heat dissipation)
Solution Approach 2:
The substrate functions as a composite structure with multiple doped regions having different electrical and thermal properties. This composite doping structure allows the substrate to simultaneously provide electrical performance benefits from heavy doping while achieving thermal management benefits through regions with different doping concentrations
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 design enhances thermal conductivity by at least 5% compared to the protective layer, effectively managing heat dissipation and reducing localized heating, and enables efficient backside illumination by maintaining a smooth, passivated surface for improved image sensor performance.
Implementation Method 1
the thermal conductivity of lightly-doped silicon has been reported to be about 20% greater than heavily-doped silicon
Implementation Method 2
The substrate and the device layer are also doped with the concentration of dopant in the substrate and device layer being less than about 1×10^17 carriers/cm^3
Implementation Method 3
Epitaxial silicon layers such as these are typically grown by a chemical vapor deposition process wherein a substrate is heated while a gaseous silicon compound is passed over the wafer surface to affect pyrolysis or decomposition
Implementation Method 4
a gaseous silicon compound is passed over the wafer surface to affect pyrolysis or decomposition
Data Source
AI summary
This invention generally relates to an epitaxial silicon semiconductor wafer with increased thermal conductivity to transfer heat away from a device layer, while also having resistance to common failure mechanisms, such as latch-up failures and radiation event failures. The semiconductor wafer comprises a lightly-doped device layer, a highly-doped protective layer, and a lightly-doped substrate. The invention is also directed to a process for forming such an epitaxial silicon wafer.