Backside Contact Enlargement Through STI Liner Recess in Nanosheet FETs
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Solution Overview
Problem
As nanosheet technology scales down, it becomes challenging to form separate backside contacts with sufficient surface contact for source/drains due to increased device density, leading to interference and reduced contact efficiency.
Innovation Solution
The method involves forming alternating layers of sacrificial layers and nanosheet channel layers, separating them into rows to create trenches, lining these trenches with a shallow trench isolation liner, and recessing the liner to create a sacrificial trench with a placeholder trench etched in the source/drain region. This allows for a wider epitaxial growth of source/drain regions and a wider backside contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If nanosheet technology is scaled down to increase device density, then the number of devices per area increases, but the surface contact area for backside contacts becomes insufficient
Solution Approach 1:
The patent extends the backside contact structure vertically by forming an enlarged contact region that penetrates through the shallow trench isolation layer to reach the source/drain region. This vertical extension in the third dimension compensates for the reduced horizontal surface area, maintaining sufficient contact area despite device scaling and increased density.
Solution Approach 2:
The enlarged backside contact structure is nested within the isolation structure, with the contact region extending through the shallow trench isolation layer and positioned within or adjacent to the source/drain region. This nested configuration allows the contact to access the source/drain region while maintaining proper device isolation.
2Area of stationary object
If devices are placed closer together to increase density, then area utilization improves, but interference between adjacent devices increases
Solution Approach 1:
The shallow trench isolation layer serves as an intermediary structure between adjacent nanosheet devices, providing electrical isolation. The enlarged backside contact carefully navigates through this isolation layer to reach the source/drain region, maintaining proper isolation between devices while enabling sufficient contact area. This mediator approach prevents interference between closely spaced devices.
3Ease of manufacture
If conventional backside contact formation is used in scaled devices, then manufacturing simplicity is maintained, but contact efficiency deteriorates
Solution Approach 1:
The contact formation process is segmented into distinct stages: forming the shallow trench isolation layer, creating the contact trench through the isolation layer, and filling with conductive material. This segmentation allows each step to be optimized independently while maintaining overall manufacturing feasibility and good contact efficiency.
Data Source
AI summary
A microelectronic structure including a first nanosheet transistor that includes a first source/drain and a second nanosheet transistor that includes a second source/drain. The first source/drain and the second source/drain are aligned along a common axis. The common axis is parallel to a gate direction. A backside width of the first source/drain and a backside width of the second source/drain are different as measured along the common axis. A bottom dielectric isolation layer located on a backside surface of the second source/drain. A backside contact located on a backside surface of the first source/drain.