Stacked FET Shared Source/Drain Contact for Low-Resistance Connection
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Solution Overview
Problem
Fabricating stacked FET devices with shared source/drain contacts poses challenges such as reduced S/D volume, small contact area, and compromised silicide formation, which affect the electrical connection and efficiency of the semiconductor structure.
Innovation Solution
A semiconductor structure with a shared S/D contact that includes a recessed portion between the first and second S/D, a side portion above the recessed portion, and a top portion above the second S/D, allowing for a wider contact area and better silicide formation, enabling low-resistance connections between the FETs. This is achieved by growing a preliminary S/D, etching a recessed portion, forming a preliminary contact, and regrowing the second S/D to maintain strong electrical connections and density benefits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a deep S/D contact is formed through the top FET to reach the bottom FET, then the shared contact connection is established, but the S/D volume of the top S/D is reduced
Solution Approach 1:
The shared contact structure is segmented into three distinct portions: a recessed portion at the bottom, a side portion in the middle, and a top portion at the top. This segmentation allows each portion to serve a specific function - the recessed portion contacts the bottom S/D, the side portion contacts the lateral side of the top S/D, and the top portion provides the upper contact interface. This resolves the contradiction by maintaining full top S/D volume while still achieving reliable connection to the bottom FET through the bottom S/D.
Solution Approach 2:
The contact structure transitions from a traditional vertical deep contact approach to a multi-dimensional structure that extends laterally through the side portion. The side portion contacts the lateral side of the top S/D, adding a horizontal dimension to the contact path. This dimensional change allows the contact to reach the bottom S/D without compromising the top S/D volume, as the connection is established through lateral contact rather than vertical penetration.
2Reliability
If the shared contact area is increased for better connection, then the electrical connection improves, but the contact area with one of the S/Ds becomes small
Solution Approach 1:
Each portion of the shared contact is optimized for its specific location and function. The recessed portion is designed to contact the top surface of the bottom S/D, the side portion is configured to contact the lateral side of the top S/D, and the top portion is shaped for the upper contact interface. This local optimization ensures that each contact interface has adequate area for its specific purpose, resolving the contradiction by providing sufficient contact area at each interface rather than requiring a single large contact area.
3Ease of manufacture
If thermal treatment is applied after silicide formation to complete the process, then the fabrication is completed, but the silicide between the contact and S/Ds is compromised
Solution Approach 1:
The silicide formation is performed as a preliminary action before the thermal treatment that would compromise it. The shared contact structure is formed with silicide already in place during the recessed portion formation and side portion creation steps. By completing the critical silicide formation before the damaging thermal treatment, the invention ensures silicide integrity is maintained while still allowing subsequent fabrication steps to be completed.
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 a low-resistance, strong electrical connection between the first and second S/Ds, enhancing the efficiency and density of the semiconductor structure by maintaining a wide contact area and uncompromised silicide formation, even after thermal treatments.
Implementation Method 1
regrowing a regrown second S/D above the recessed contact
Data Source
AI summary
Embodiments herein include semiconductor structures that may include a first field-effect transistor (FET) comprising a first source/drain (S/D), a second FET comprising a second S/D squarely above the first S/D, and a shared S/D contact. The shared S/D may include a recessed portion between the first S/D and the second S/D, a side portion above the recessed portion, and a top portion above the second S/D. The side portion may contact a lateral side of the second S/D.