FDSOI Back Biasing via Shallow Implant Extraction
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Solution Overview
Problem
Fully-depleted silicon-on-insulator (FDSOI) devices face challenges in efficiently back biasing due to deep well implants with large pitches, making it difficult to swap threshold voltage during logic synthesis and requiring additional area for N-well isolation rings.
Innovation Solution
Implementing shallow implants under channel regions instead of deep well implants, allowing for smaller pitches and enabling easy swapping of threshold voltage between regular and low threshold voltage devices by using N-type and P-type implants in opposite polarity wells, which simplifies bias domain grouping and ties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If deep well implants are used for back biasing in FDSOI devices, then threshold voltage control is achieved, but the pitch becomes large and area consumption increases
Solution Approach 1:
The patent extracts the biasing function from deep well implants and relocates it to shallow implants formed directly in the substrate beneath the channel region. This removes the need for deep well structures and their associated large pitches, thereby reducing area consumption while maintaining threshold voltage control capability.
Solution Approach 2:
The patent changes the implant depth parameter from deep well implants to shallow implants. By adjusting this critical parameter, the pitch is reduced and area consumption is minimized while the shallow implants still achieve effective back biasing and threshold voltage modulation in FDSOI devices.
2Reliability
If deep well implants are used for back biasing, then threshold voltage modulation is possible, but device complexity increases due to additional well ties and isolation rings
Solution Approach 1:
The patent removes the complex deep well structure and replaces it with simple shallow implants. This extraction eliminates the need for additional well ties and isolation rings, significantly reducing structural complexity while preserving threshold voltage modulation functionality through direct substrate biasing.
Solution Approach 2:
Instead of using deep well implants that extend far into the substrate, the patent inverts the approach by using shallow implants that remain close to the surface. This inverted strategy achieves the same electrical function with much simpler structures, eliminating the need for complex isolation and tying arrangements.
3Area of stationary object
If shallow implants are used under channel regions, then pitch is reduced and area is saved, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies local quality by forming shallow implants specifically in the substrate region directly beneath the channel, rather than using extensive deep well structures. This localized approach reduces the overall area while the precise localization of implants near the surface makes the manufacturing process more controllable and less demanding than deep implantation.
Data Source
AI summary
An integrated circuit includes a first device having a first threshold voltage (Vt) adjusting implant extension region having a first conductivity type and extending from a first implant rail region under an entirety of a first channel region. The first implant rail region and first Vt adjusting implant extension region are contiguous, and the first channel region is over an insulating layer and the insulating layer is over the first implant rail region and first Vt adjusting implant extension region. A second device has a second Vt adjusting implant extension region having the first conductivity type and extending from a second implant rail region under an entirety of a second channel region. The second implant rail region and second Vt adjusting implant extension region are contiguous, and the second channel region is over the insulating layer and the insulating layer is over the second implant rail region and second Vt adjusting implant extension region.