Transistor Subfin Leakage Reduction via Backside Amorphization
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Solution Overview
Problem
Transistor architectures face significant off-state leakage due to mobile charge carriers present in the crystalline semiconductor material retained below the transistor structure, known as the subfin, which contributes to increased power consumption and reduced battery lifetimes.
Innovation Solution
The solution involves modifying the backside of the subfin by converting it into an electrically insulative amorphous material through oxygen introduction or counter-doping, reducing charge carrier transport and thereby minimizing off-state leakage. This is achieved by depositing an oxidation catalyst, implanting oxygen, or using low-temperature processes to modify the subfin without degrading the channel material or frontside structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If crystalline semiconductor material is retained below the transistor structure (subfin), then strain-based mobility enhancement is achieved, but off-state leakage current increases
Solution Approach 1:
The patent applies different material properties to different regions: the frontside subfin region under the channel maintains crystalline structure for strain, while the backside subfin region is converted to amorphous material to block carriers. This localized differentiation resolves the contradiction by preserving mobility enhancement where needed while eliminating leakage paths where harmful.
Solution Approach 2:
The subfin is segmented into functionally distinct regions: the frontside portion retains crystalline structure for strain-induced mobility, while the backside portion is transformed to amorphous material for carrier blocking. This segmentation allows simultaneous achievement of high mobility and low leakage by assigning different properties to different segments of the same structure.
2Loss of energy
If backside modification is applied to reduce off-state leakage, then power consumption is reduced, but manufacturing complexity increases
Solution Approach 1:
The patent performs backside modification after frontside transistor fabrication is complete, preparing the backside surface and applying amorphous material transformation in a preliminary manner before final device assembly. This sequencing allows the complex modification step to be added without disrupting established frontside manufacturing flows.
Solution Approach 2:
The patent uses intermediary processes such as deposition of catalyst layers (e.g., aluminum oxide) on the backside, followed by thermal treatment to induce amorphization. These intermediary steps enable controlled transformation of the subfin material without requiring complete redesign of the manufacturing ecosystem, bridging between existing processes and the new leakage-reduction capability.
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 approach effectively reduces off-state leakage in transistors, enhancing their performance and extending battery life by minimizing power consumption while maintaining strain-based mobility enhancements.
Implementation Method 1
modifying the subfin by converting it into an electrically insulative amorphous material through oxygen introduction
Implementation Method 2
converting it into an electrically insulative amorphous material
Implementation Method 3
depositing an oxidation catalyst
Implementation Method 4
modifying the subfin by converting it into an electrically insulative amorphous material through oxygen introduction
Data Source
AI summary
Integrated circuitry comprising transistor structures having a channel portion over a base portion of fin. The base portion of the fin is an insulative amorphous oxide, or a counter-doped crystalline material. Transistor structures, such as channel portions of a fin and source and drain materials may be first formed with epitaxial processes seeded by a front side of a crystalline substrate. Following front side processing, a backside of the transistor structures may be exposed and the base portion of the fin modified from the crystalline substrate composition into the amorphous oxide or counter-doped crystalline material using backside processes and low temperatures that avoid degradation to the channel material while reducing transistor off-state leakage.