Backside-Contact Diode Structure for Low-Resistance 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
The development of a two-port diode structure with one port on the frontside and another on the backside, where the frontside port is accessed through a frontside metal layer connected to a heavily doped source/drain epitaxial feature, and the backside port is accessed through a backside metal layer connected to a heavily doped semiconductor layer, reducing sheet resistance and capacitance.
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 fabricate, but the deep well is removed during backside power rail formation, compromising diode functionality
Solution Approach 1:
The diode structure is segmented into two separate ports: a frontside port with anode and cathode contacts, and a backside port with a single contact. This segmentation allows the diode to function without requiring a deep well that would be removed during backside power rail formation, thus maintaining both fabrication simplicity and device functionality.
Solution Approach 2:
The diode structure transitions from a planar configuration to a three-dimensional configuration by utilizing both the frontside and backside of the semiconductor substrate. The backside port contacts the lightly doped drift region directly, eliminating the need for a deep well and enabling compatibility with backside power rail architectures.
2Loss of energy
If backside power rails are formed, then voltage drop across power rails is reduced, but traditional frontside-only diodes lose their deep well structure, increasing contact resistance
Solution Approach 1:
The diode structure employs localized heavy doping in the form of a lightly doped drift region that is selectively contacted from the backside. This local quality change reduces the resistance at the contact interface without requiring a deep well structure, thereby maintaining low contact resistance while enabling backside power rail formation for reduced voltage drop.
3Device complexity
If both ports of the diode are on the frontside, then interconnect routing is simpler, but device integration density is limited
Solution Approach 1:
By moving one port of the diode to the backside of the substrate, the invention utilizes the third dimension (vertical depth) to increase device integration density. This allows for more compact frontside layouts and higher density integration while keeping interconnect routing manageable through the use of backside contacts.
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 configuration enhances diode compatibility with backside power rails, reduces contact resistance, and increases gate density, enabling greater device integration and improved power rail resistance.
Implementation Method 1
forming a heavily doped semiconductor layer, reducing sheet resistance and capacitance
Data Source
AI summary
A semiconductor structure includes a first semiconductor layer having an upper portion over a lower portion, a source/drain feature over the upper portion of the first semiconductor layer, a first contact structure under the lower portion of the first semiconductor layer and electrically connected to the lower portion of the first semiconductor layer. The lower portion is more heavily doped with first dopants than the upper portion. The first dopants are of a first conductivity-type. The source/drain feature includes second dopants of a second conductivity-type opposite to the first conductivity-type.