Self-Aligned Back-Plane Contacts in FDSOI Devices
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Solution Overview
Problem
The formation of back-plane and well contacts in fully depleted silicon on insulator (FDSOI) devices faces challenges such as high process complexity, defects, and yield issues due to topography and the need for shallow or deep trench isolation, which increases costs and variability.
Innovation Solution
The use of self-aligned contacts with insulating spacers to isolate the back-plane and well contacts from the gate structure, allowing for a smaller footprint and reduced process complexity, replacing traditional shallow trench isolation with low-k spacers and enabling contact formation before or after gate structure formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional shallow or deep trench isolation structures are used for back-plane and well contacts, then contact isolation is achieved, but process complexity and manufacturing cost increase
Solution Approach 1:
The patent extracts the isolation function from the traditional trench isolation structure and assigns it to a separate insulating spacer layer. This spacer layer is formed independently and then positioned to provide isolation, separating the isolation function from the contact formation process itself, thereby reducing overall process complexity while maintaining reliable contact isolation.
Solution Approach 2:
The patent introduces an insulating spacer layer as an intermediary element between the back-plane/well contacts and the gate structure. This spacer acts as a mediator that provides the necessary electrical isolation without requiring complex trench isolation processes, simplifying the manufacturing steps while ensuring proper contact isolation.
2Reliability
If traditional trench isolation structures are used for back-plane and well contacts, then contact isolation is achieved, but manufacturing cost increases
Solution Approach 1:
The patent employs a relatively simple insulating spacer layer instead of complex trench isolation structures. This spacer layer can be formed using standard deposition techniques and serves its isolation purpose effectively, representing a more cost-effective approach compared to the material-intensive and process-intensive trench isolation methods.
Solution Approach 2:
The patent changes the approach from three-dimensional trench structures to a two-dimensional spacer layer, fundamentally altering the geometric parameters of the isolation structure. This parameter change from volumetric trench isolation to planar spacer isolation reduces manufacturing complexity and cost while maintaining the essential isolation function.
3Reliability
If contacts are formed with minimum footprint of one Rx island, then contact area is sufficient, but device footprint increases
Solution Approach 1:
The patent utilizes the vertical dimension by forming contacts that extend through multiple layers (from the top surface down to the back-plane and well regions). This vertical extension allows sufficient contact area to be achieved within a smaller horizontal footprint, effectively using the third dimension to resolve the area conflict.
Solution Approach 2:
The patent implements a nested contact structure where multiple contact regions are vertically stacked and interconnected. The back-plane contact, well contacts, and gate structure are nested in a vertical arrangement, allowing each contact to have adequate area while the overall device footprint remains compact due to the vertical integration.
Data Source
AI summary
The present disclosure generally relates to semiconductor structures and, more particularly, to self-aligned back-plane and well contacts for a fully depleted silicon on insulator device and methods of manufacture. The structure includes a back-plane, a p-well and an n-well formed within a bulk substrate; a contact extending from each of the back-plane, the p-well and the n-well; a gate structure formed above the back-plane, the p-well and the n-well; and an insulating spacer isolating the contact of the back-plane from the gate structure.