Backside Metal Contact Structure for Lower-Resistance Power Rails
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Solution Overview
Problem
Existing semiconductor fabrication methods face challenges in forming metal contacts on the backside of integrated circuits (ICs) with reduced contact resistance, which hinders further scaling and performance enhancement.
Innovation Solution
A semiconductor structure with inverted V-shaped source/drain regions and backside metal contacts, combined with an epitaxial layer for electrical isolation, increases contact area and reduces resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional planar contacts are used on backside power rails, then manufacturing is simple, but contact area is insufficient leading to high resistance
Solution Approach 1:
The contact structure uses a wrapped configuration where the backside metal contact envelops the source/drain region in a U-shaped or wrapped manner, creating curved contact surfaces that increase the contact area compared to planar contacts. This curved/wrapped geometry allows the contact to engage multiple surfaces of the source/drain region, thereby reducing contact resistance while maintaining manufacturing feasibility through standard deposition and etching processes.
Solution Approach 2:
The contact structure transitions from a two-dimensional planar contact to a three-dimensional wrapped configuration. The backside metal contact extends vertically and wraps around the source/drain region, utilizing the vertical dimension to increase contact area. This dimensional transition allows the contact to engage the source/drain region from multiple angles and surfaces, significantly increasing the effective contact area and reducing contact resistance.
2Reliability
If contact area is increased to reduce resistance, then electrical performance improves, but manufacturing precision requirements increase
Solution Approach 1:
The source/drain regions are pre-formed with inverted V-shaped tops before the backside metal contact is deposited. This preliminary shaping creates a geometry that naturally guides the metal contact formation process, allowing the contact to wrap around the predetermined geometry. The pre-formed inverted V-shape ensures that subsequent contact deposition and patterning steps can achieve the desired wrapped configuration with standard manufacturing tolerances, reducing the precision requirements compared to forming the contact geometry in a single step.
3Productivity
If backside power rails are implemented for scaling, then logic connection density improves, but contact resistance becomes a limiting factor
Solution Approach 1:
The wrapped backside metal contact uses curved geometry to maximize contact area with the source/drain regions, thereby reducing contact resistance. This curved contact configuration enables effective power delivery to densely packed logic connections on the backside, allowing the backside power rail architecture to achieve both high connection density and low contact resistance, thus resolving the limiting factor in backside scaling.
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 proposed structure enhances contact area and reduces device resistance, improving performance and reliability of backside power delivery in ICs.
Implementation Method 1
a first epitaxial layer in contact with a top portion of at least another source/drain region adjacent to the at least one source/drain region for electrically isolating the at least another source/drain region from the backside power rail
Data Source
AI summary
A semiconductor structure having a backside contact structure with increased contact area includes a plurality of source/drain regions within a field effect transistor, each of the plurality of source/drain regions includes a top portion having an inverted V-shaped area. A backside power rail is electrically connected to at least one source/drain region through a backside metal contact. The backside metal contact wraps around a top portion of the at least one source/drain region. A tip of the top portion of the plurality of source/drain regions points towards the backside power rail with the top portion of the at least one source/drain region being in electric contact with the backside metal contact. A first epitaxial layer is in contact with a top portion of at least another source/drain region adjacent to the at least one source/drain region for electrically isolating the at least another source/drain region from the backside power rail.