Semiconductor Substrate Fabrication with Monotonic Dopant Profiles
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Solution Overview
Problem
Existing methods for fabricating semiconductor substrates using silicon on insulator (SOI) technology face issues with dopant cross-contamination and non-monotonic dopant concentration profiles, particularly in highly doped p++ layers, which affect the quality of image sensors.
Innovation Solution
A method involving the preparation of a silicon on insulator substrate with a first semiconductor layer that is doped to create a modified layer, followed by the epitaxial growth of a second semiconductor layer with a different dopant concentration, all performed within the same fabrication device, such as an epi-reactor, to achieve improved dopant profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a highly doped substrate is used as the donor wafer in the conventional Smartcut process, then the dopant concentration in the p++ layer can be increased, but cross-contamination occurs within the production line and dopant diffusion during annealing deteriorates the substrate quality
Solution Approach 1:
The process is segmented into two independent stages: first, standard Smartcut fabrication of SOI substrates using lightly doped donor wafers; second, subsequent doping of the transferred semiconductor layer to achieve high dopant concentration. This segmentation prevents cross-contamination between differently doped wafers while eliminating dopant diffusion during Smartcut annealing, as the high doping occurs after substrate transfer.
Solution Approach 2:
The semiconductor layer is prepared with a preliminary low dopant concentration during standard Smartcut processing, then subsequently doped to the final high concentration. This preliminary action allows the substrate to be properly formed and transferred before the final doping step, avoiding contamination and diffusion issues.
2Shape
If a standard SOI substrate with a thin p- semiconductor layer is used as starting material and a further p++ layer is provided over it, then the layer structure can be obtained, but the dopant concentration cannot reach sufficient high levels and the profile is not monotonic
Solution Approach 1:
The semiconductor layer is first formed with a preliminary low dopant concentration during standard Smartcut processing, then subsequently doped to achieve the final high dopant concentration. This preliminary formation allows proper layer structure creation followed by controlled high-level doping.
Solution Approach 2:
The dopant concentration parameter is changed in two stages: first set to a low value during Smartcut layer formation, then increased to a high value in a subsequent doping step. This parameter change sequence enables both proper layer structure formation and sufficient high dopant concentration.
3Manufacturing precision
If multiple fabrication devices are used for doping and epitaxial growth, then each process can be optimized independently, but the production line complexity increases
Solution Approach 1:
The epi-reactor is designed to perform multiple functions: it can carry out both the doping process and the epitaxial growth process. This multi-functionality maintains process optimization capabilities while reducing production line complexity by eliminating the need for separate dedicated doping and epitaxial growth devices.
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 eliminates dopant cross-contamination, ensures a monotonic and higher dopant concentration profile in the p++ layer, and enhances the quality of semiconductor substrates for optoelectronic applications, particularly in image sensors, by allowing for tailored doping levels and reduced process complexity.
Implementation Method 1
doping the first semiconductor layer to thereby obtain a modified first semiconductor layer
Implementation Method 2
the second semiconductor layer can be epitaxially grown over, in particular on, the modified first semiconductor layer
Data Source
Figure 1a~1c
Figure 2a~2b
AI summary
The invention relates to a method for fabricating a semiconductor substrate comprising the steps of: providing a silicon on insulator type substrate comprising a base, an insulating layer and a first semiconductor layer, doping the first semiconductor layer to thereby obtain a modified first semiconductor layer, and providing a second semiconductor layer with a different dopant concentration than the modified first semiconductor layer over, in particular on, the modified first semiconductor layer. With this method, an improved dopant concentration profile can be achieved through the various layers which makes the substrates in particular suitable for optoelectronic applications.