Silicon Epitaxial Wafer Carbon Diffusion Control
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Solution Overview
Problem
The variation in carbon dopant concentration in silicon substrates affects the diffusion distance of elements in the intermediate epitaxial layer, leading to inconsistencies in the p/n boundary position, which is critical for device performance, especially in thin device forming regions of semiconductor devices like solid-state image sensors.
Innovation Solution
A silicon epitaxial wafer structure is developed with a second intermediate epitaxial layer between the silicon substrate and the first intermediate epitaxial layer, with a thickness ranging from 0.5 μm to 2 μm, to control carbon diffusion and maintain a consistent p/n boundary position during thermal processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon substrate with carbon dopant is used to achieve intrinsic gettering capability, then the IG capability is improved, but the diffusion distance of elements in the intermediate epitaxial layer varies, leading to inconsistent p/n boundary position
Solution Approach 1:
The intermediate epitaxial layer is divided into two separate layers: a first intermediate epitaxial layer and a second intermediate epitaxial layer. The second layer is positioned between the silicon substrate and the first layer to specifically manage carbon diffusion, while the first layer maintains the p/n boundary. This segmentation allows independent control of carbon diffusion and dopant diffusion processes, resolving the contradiction between maintaining gettering capability and ensuring boundary position consistency.
Solution Approach 2:
The second intermediate epitaxial layer acts as an intermediary layer between the carbon-doped silicon substrate and the first intermediate epitaxial layer. This intermediary structure controls and limits carbon diffusion into the first layer, preventing carbon from reaching the p/n boundary region. Meanwhile, it allows the dopant diffusion process to proceed normally in the first layer, thus maintaining both gettering capability and boundary position consistency.
2Productivity
If the thickness of the intermediate epitaxial layer is reduced to accommodate thin device forming regions, then the device integration is improved, but the variation in p/n boundary position becomes more significant
Solution Approach 1:
By segmenting the intermediate epitaxial layer into two distinct layers with different functions and thicknesses, the invention enables the overall intermediate region to be made thinner while maintaining adequate carbon diffusion control. The second layer (closer to substrate) can be very thin to limit carbon diffusion, while the first layer (closer to device region) provides the necessary dopant diffusion space, allowing thin device forming regions without compromising boundary position control.
Solution Approach 2:
Different regions of the intermediate epitaxial structure are given different qualities: the second intermediate layer has properties optimized for carbon diffusion control (positioned near the carbon-doped substrate), while the first intermediate layer has properties optimized for dopant diffusion and p/n boundary formation. This local differentiation allows the structure to simultaneously support thin device regions and precise boundary positioning.
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 ensures that the p/n boundary remains stable and consistent, preventing variations in device performance and reducing production costs by adjusting the second intermediate epitaxial layer thickness based on carbon concentration and substrate position, thereby enhancing the reliability of semiconductor devices.
Implementation Method 1
The variation in carbon dopant concentration in silicon substrates affects the diffusion distance of elements in the intermediate epitaxial layer
Implementation Method 2
forming a first intermediate epitaxial layer that is doped with a dopant and disposed on the silicon substrate; stacking an epitaxial layer on the first intermediate epitaxial layer
Data Source
AI summary
A silicon epitaxial wafer including: a second intermediate epitaxial layer on a silicon substrate produced by being cut from a silicon single crystal ingot grown by the CZ method so as to have a carbon concentration ranging from 3×1016 to 2×1017 atoms/cm3, a first intermediate epitaxial layer doped with a dopant, and an epitaxial layer of a device forming region stacked on the first intermediate epitaxial layer, and to a method of producing this wafer. Also providing an industrially excellent silicon epitaxial wafer that is produced with a silicon substrate doped with carbon and used as a semiconductor device substrate such as a memory, a logic, or a solid-state image sensor, and a method of producing this silicon epitaxial wafer.