Bottom Dielectric Isolation for Nanosheet Devices
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Solution Overview
Problem
Current full bottom dielectric isolation processing schemes in nanosheet containing devices cause source/drain epitaxy issues for both long and short channel devices, leading to missing epi defects and degraded epitaxy growth.
Innovation Solution
A semiconductor structure with a bottom dielectric isolation structure formed after source/drain structures, featuring a first portion beneath each nanosheet stack and a second portion in a single diffusion break point trench, ensuring high quality epitaxy for both long and short channel devices by preventing substrate leakage and maintaining epitaxial integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If full bottom dielectric isolation processing is performed before source/drain epitaxy, then substrate leakage is shut-off, but source/drain epitaxy quality is degraded causing missing epi defects and un-merged structures
Solution Approach 1:
The patent performs source/drain epitaxy growth before forming the bottom dielectric isolation structure. This preliminary action allows high-quality epitaxial growth to occur on the substrate before the dielectric isolation is introduced, avoiding the degradation that would result from performing isolation first. The epitaxy is grown while the substrate surface is still accessible and in optimal condition.
Solution Approach 2:
The patent inverts the conventional processing sequence by performing source/drain epitaxy before bottom dielectric isolation instead of after. This reversal of the traditional process order resolves the contradiction by ensuring that epitaxy quality is not compromised by the presence of the dielectric isolation structure during the epitaxial growth phase.
2Reliability
If full bottom dielectric isolation is formed early in processing, then substrate leakage is prevented, but contact structures miss landing on source/drain epitaxy layers
Solution Approach 1:
The patent performs source/drain epitaxy and contact structure formation before creating the bottom dielectric isolation. This preliminary sequencing ensures that contact structures are precisely aligned with the source/drain epitaxy layers while the substrate geometry is still accessible, before the dielectric isolation is formed that would otherwise cause misalignment.
3Reliability
If bottom dielectric isolation is formed before source/drain epitaxy, then leakage is shut-off, but epitaxial merger happens prematurely degrading lower nanosheet quality
Solution Approach 1:
The patent inverts the conventional process order by forming source/drain epitaxy structures before creating the bottom dielectric isolation. This inversion prevents premature epitaxial merger that would occur if isolation were formed first, allowing each nanosheet to receive high-quality epitaxial material deposition before the dielectric barrier is introduced that would restrict subsequent growth.
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 solution provides high quality source/drain structures with no missing epi defects and massive epi stacking faults, enhancing epitaxial growth and contact structure accuracy for nanosheet containing devices.
Implementation Method 1
full bottom dielectric isolation is needed to shut-off the substrate leakage path
Implementation Method 2
an epitaxial source/drain structure is formed on the epitaxial semiconductor buffer layer
Data Source
AI summary
A semiconductor structure is provided that includes nanosheet containing devices having a bottom dielectric isolation structure and high quality source/drain (S/D) structures. In the present application, the bottom dielectric isolation structure is formed after the S/D structures to ensure high quality epitaxy for both long channel and short channel nanosheet containing devices. The bottom dielectric isolation structure of the present application has a first portion that is located beneath each nanosheet stack and a second portion that is located in a single diffusion break point trench.