Backside-Contact Diode Structure for Backside Power Rails
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Solution Overview
Problem
Conventional semiconductor fabrication methods are inadequate for forming diodes compatible with backside power rails, as traditional two-port diodes with both ports on the frontside are compromised when forming backside power rails, leading to issues with contact resistance and diode compatibility.
Innovation Solution
A two-port diode design is implemented with one port on the frontside and another on the backside, featuring a heavily doped source/drain epitaxial feature, a well, and a heavily doped semiconductor layer to reduce sheet resistance, accessed through frontside and backside metal layers and contacts, respectively, allowing for integration with backside power rails and contacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traditional two-port diodes with both ports on the frontside are used, then the diode structure is simple to manufacture, but the deep well may be removed during the process of forming backside power rails, compromising diode functionality
Solution Approach 1:
The diode structure is segmented into two separate ports: one port remains on the frontside while the other port is formed on the backside. This segmentation allows the diode to function without requiring a deep well that would interfere with backside power rail formation, thus resolving the conflict between manufacturing simplicity and device functionality.
Solution Approach 2:
The diode structure transitions from a planar configuration (both ports on frontside) to a three-dimensional configuration with ports on opposite sides of the substrate. This dimensional change eliminates the need for deep wells while maintaining diode functionality and enabling integration with backside power rails.
2Loss of energy
If power rails are moved to the backside of the ICs, then voltage drop across the power rails is reduced, but traditional diodes with both ports on the frontside become incompatible
Solution Approach 1:
The diode is segmented into frontside and backside ports, allowing one port to remain on the frontside while the other is formed on the backside near the power rails. This enables the diode to function effectively with the relocated power rails while maintaining electrical connectivity through the substrate.
Solution Approach 2:
The substrate acts as an intermediary medium, providing electrical connectivity between the frontside port and the backside port of the diode. This intermediary structure enables the diode to bridge the frontside circuitry with the backside power rails without requiring deep wells or complex interconnections.
3Reliability
If a heavily doped semiconductor layer is added to reduce sheet resistance, then contact resistance is reduced, but the device structure becomes more complex
Solution Approach 1:
A heavily doped semiconductor layer is added locally at the backside contact region where low sheet resistance is critical for reducing contact resistance. This localized modification improves electrical connectivity without significantly increasing the overall device complexity, as the doping is confined to a specific region rather than the entire structure.
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
This design enhances diode compatibility with backside power rails, reduces contact resistance, and increases gate density, enabling greater device integration and improved performance in semiconductor devices.
Implementation Method 1
The interface between the well and the backside contact is a heavily doped semiconductor layer, for reducing the sheet resistance of the interface
Data Source
AI summary
A method includes providing a first semiconductor layer at a frontside of a structure; implanting first dopants of a first conductivity-type into the first semiconductor layer, resulting in a doped layer in the first semiconductor layer; forming a stack of semiconductor layers over the first semiconductor layer; patterning the stack of semiconductor layers and the first semiconductor layer into fins; forming an isolation structure adjacent to a lower portion of the fins; etching the stack of semiconductor layers to form a source/drain trench over the first semiconductor layer; forming a source/drain feature in the source/drain trench, wherein the source/drain feature is doped with second dopants of a second conductivity-type opposite to the first conductivity-type; forming a contact hole at a backside of the structure, wherein the contact hole exposes the doped layer in the first semiconductor layer; and forming a first contact structure in the contact hole.