Backside Self-Aligned Contact Profile for Void-Free Metallization
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Solution Overview
Problem
As semiconductor devices scale down, frontside interconnects face increased resistance issues, particularly for power distribution, and backside power delivery poses challenges due to alignment and metallization difficulties, leading to misplacement errors and void formation in contact vias.
Innovation Solution
The implementation of a replacement contact process with a unique placeholder profile, where the dielectric placeholder is wider in the middle and tapers at both ends, allowing for self-aligned backside source/drain region contacts that improve metallization and reduce misplacement errors, enabling effective backside power delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional process flows are used for backside metallization, then the process is simple and straightforward, but voids form which increase contact resistance and degrade device performance
Solution Approach 1:
The placeholder structure is formed in advance during frontside processing, before backside metallization. This preliminary action creates a pre-defined geometric template that guides subsequent metallization steps, ensuring proper fill without voids while maintaining alignment with source/drain regions.
Solution Approach 2:
The dielectric placeholder acts as an intermediary structure between the source/drain region and the final metal contact. It provides a temporary geometric reference that facilitates accurate metallization, and is later removed to complete the contact formation process.
2Reliability
If backside power delivery is implemented to reduce resistance, then power distribution improves, but alignment precision deteriorates due to coordinate system transformations
Solution Approach 1:
The placeholder structure enables self-aligned contact formation, where the contact automatically positions itself relative to the source/drain region through the geometric relationship established during frontside processing. This self-alignment mechanism eliminates the need for complex coordinate transformations and manual alignment steps.
Solution Approach 2:
Alignment references are established in advance during frontside processing when the placeholder is formed. These pre-established references remain intact through wafer thinning and backside processing, providing continuous alignment guidance without requiring coordinate system transformations.
3Productivity
If device dimensions are scaled down to increase integration density, then device capacity improves, but interconnect resistance increases exponentially
Solution Approach 1:
The invention moves power delivery from the traditional frontside (two-dimensional planar interconnect) to the backside of the wafer, adding a third dimension (vertical separation) between power delivery and signal processing. This dimensional change allows shorter, lower-resistance power paths without compromising frontside device density.
Data Source
AI summary
Backside self-aligned contact designs using a replacement contact process with unique placeholder profile are provided. In one aspect, a semiconductor device includes: a field-effect transistor(s) on a frontside of the device; backside power rails on a backside of the device; a backside source/drain region contact connecting a given one of the backside power rails to a source/drain region of the field-effect transistor(s), and a dielectric placeholder(s) between the given backside power rail and another source/drain region of the field-effect transistor(s), where a first end of the dielectric placeholder(s) having a width W1 directly contacts the given backside power rail, a second end of the dielectric placeholder(s) having a width W2 directly contacts the other source/drain region, where W1>W2. The field-effect transistor(s) can include a stack of active layers with bottom dielectric isolation, and a gate-all-around configuration. A method of fabricating the present semiconductor devices is also provided.