Nanosheet Power Rail Layout for Lower IR Drop and Resistance
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Solution Overview
Problem
Conventional nanosheet field effect transistor devices face challenges with high power rail resistance, increased IR drop, and electron migration, which affect circuit performance and incur additional costs due to conventional Hi-R resistors and mask requirements.
Innovation Solution
The formation of an epitaxial structure under the power rail, electrically connected to it, reduces power rail resistance and mitigates electron migration, while forming contact structures on opposite sides of the epitaxial structures to create a resistor without additional masks, thereby reducing chip area and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If conventional power rail structures are used in scaled-down integrated circuits, then chip area is reduced, but power rail resistance increases and IR drop worsens
Solution Approach 1:
The patent transitions from planar power rail structures to three-dimensional vertically-oriented nanosheet structures. Multiple nanosheets are stacked vertically to form conductive pathways that extend in the vertical dimension, effectively increasing the cross-sectional area for current flow without increasing lateral chip area. This dimensional transition resolves the contradiction by providing lower resistance paths while maintaining compact footprint.
Solution Approach 2:
The patent employs composite material structures combining different semiconductor materials with varying electrical properties. The vertically-stacked nanosheets may include materials with high carrier mobility arranged in specific configurations to optimize electrical conductivity. This composite approach enables tailored electrical characteristics that reduce power rail resistance while maintaining area efficiency.
2Ease of manufacture
If conventional Hi-R resistors are used, then resistor functionality is achieved, but additional mask costs and chip area are incurred
Solution Approach 1:
The patent makes the vertically-oriented nanosheet structures serve multiple functions: they act as both power rail conductors and as resistive elements where needed. By controlling the dimensions, material composition, and configuration of the nanosheets, the same structural motif provides both low-resistance power distribution pathways and higher-resistance functional resistors, eliminating the need for separate Hi-R resistor structures and their associated masks.
Solution Approach 2:
The patent merges the functions of power rails and resistors into a unified nanosheet-based structure. Instead of having separate power distribution networks and discrete resistor components, the vertically-stacked nanosheets simultaneously fulfill both roles depending on their specific geometric and material characteristics, thereby reducing overall device complexity and manufacturing steps.
Data Source
Figure 1
Figure 2A-1
Figure 2A-2
AI summary
A field effect transistor includes a nanosheet stack (108) and a gate structure (120), a power rail (132), first epitaxial structures (118) in the source/drain region (on the left hand side) and second epitaxial structures (118) in a boundary region of the device (on the right hand side) underneath te power rail (132). The first epitaxial structures (118 on the left hand side) are surrounded by first contact structures (122). The power rail (132) is spaced apart laterally from the gate structure and the first epitaxial structures (118), and extends in a direction perpendicular to a line connecting the source and the drain. The second epitaxial structures (118 on the right hand side) are also surrounded by a second contact structure (122), which is separated from the first contact structure by an inter layer dielectric (119). The second epitaxial structures (118) and the second contact structure (122), disposed directly beneath the power rail (132), are electrically connected to the power rail. A metal layer (126) and a via (130) electrically connect the first contact layer (122 on the left) with the second contact layer (122 on the right) and the power rail (132).