FDSOI Transistor Active Layer Thickness Control via Trench Etching
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Solution Overview
Problem
The formation of transistors with different channel thicknesses on a shared substrate, such as PDSOI and FDSOI transistors, is challenging due to structural anomalies at the interfaces, leading to reliability issues and high production costs in existing methods.
Innovation Solution
A method involving the formation of isolating trenches and active regions with a difference in height, allowing for simultaneous etching to control the thickness of the active layer, reducing structural anomalies and improving the reliability of FDSOI transistors by using a masking layer and dry etching techniques to taper the active layer and isolating trench, ensuring the desired thickness and rounded edges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional methods are used to form transistors with different channel thicknesses on a shared substrate, then both PDSOI and FDSOI transistors can be integrated, but structural anomalies occur at the interfaces leading to reliability issues
Solution Approach 1:
The patent applies preliminary action by forming an initial displacement (negative offset) of the isolating trench relative to the active layer before the main etching process. This pre-positioning allows the subsequent etching to create the desired positive displacement and rounded edges without directly forming the trench at the final position, thereby preventing structural anomalies at the interface between the active layer and isolating trench.
2Ease of manufacture
If conventional etching methods are used to form isolating trenches, then the manufacturing process is simple, but structural anomalies occur at the trench interfaces
Solution Approach 1:
The patent introduces a preliminary displacement step where the isolating trench is initially formed with a negative offset relative to the active layer. This preliminary positioning enables the etching process to proceed in a controlled manner, creating rounded edges and avoiding sharp interfaces that cause structural anomalies, while maintaining overall process simplicity.
Solution Approach 2:
The patent applies spheroidality by ensuring that the etching process creates rounded edges at the interface between the active layer and isolating trench, rather than sharp corners. This curvature is achieved through the controlled etching of the preliminary displacement, eliminating stress concentration points and improving interface quality without complicating the manufacturing process.
3Ease of manufacture
If the isolating trench is formed at the same level as the active layer, then the manufacturing process is straightforward, but structural anomalies and reliability issues occur
Solution Approach 1:
The patent implements preliminary action by intentionally forming the isolating trench with a negative displacement relative to the active layer surface before the final etching step. This preliminary offset allows the subsequent etching to create the desired positive displacement with rounded edges, improving reliability while keeping the manufacturing process straightforward through a systematic two-stage approach.
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 enhances the reliability of FDSOI transistors by minimizing structural anomalies and achieving the desired thickness, while maintaining a simple and cost-effective production process.
Implementation Method 1
simultaneous etching, preferably dry etching: i) of a portion of the thickness of the active layer of the second active region so as to form at least one tapered active layer
Data Source
AI summary
A method for forming an electronic device comprising a first transistor and a second transistor, from a stack of layers comprising an isolating layer surmounted on an active layer made of a semi-conductive material, the method comprising at least the following steps: Forming an isolating trench to define, in the active layer, at least one first active region and at least one second active region, said isolating trench protruding with respect to the active layer of the second active region; Forming a masking layer without covering the active layer of the second active region and without covering a portion of the isolating trench; Etching: of a portion of the thickness of the active layer of the second active region, and of at least one portion of the thickness of said portion of the isolating trench.