Field Shield Structure for SOI Charge Management
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Solution Overview
Problem
Silicon-on-insulator (SOI) technology, particularly partially depleted SOI, faces damage during back-end of the line (BEOL) processing due to trapped electronic charge in the buried oxide layer, which degrades the yield and reliability of semiconductor devices.
Innovation Solution
A semiconductor structure incorporating a field shield sandwiched between upper and lower isolation layers, with a local interconnect connecting the field shield to a doped semiconductor region, shunting current away from the upper isolation layer and into the field shield to prevent electric charge buildup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current passes through the semiconductor device during BEOL charging, then the device operates normally, but trapped electronic charge builds up in the buried oxide layer degrading yield and reliability
Solution Approach 1:
A field shield layer is introduced as an intermediary conductive layer between the upper isolation layer and the buried oxide layer. This field shield acts as a mediator that captures and redirects charging current away from the BOX, preventing trapped charge accumulation while allowing normal device operation. The field shield is connected through a local interconnect to a doped semiconductor region, creating a preferential current path.
Solution Approach 2:
The field shield is positioned locally beneath the semiconductor device in the region most susceptible to charging effects. By applying this protective structure only where needed (under the device and isolation layers), the solution addresses the specific local problem of charge trapping without requiring global structural changes to the entire wafer or device architecture.
2Reliability
If a field shield is added below the semiconductor device, then trapped charge is prevented from building up in the upper isolation layer, but the device structure becomes more complex
Solution Approach 1:
The isolation structure is segmented into multiple layers: a lower isolation layer (buried oxide), a conductive field shield layer, and an upper isolation layer. This segmentation allows each layer to perform its specific function - the lower isolation provides electrical isolation, the field shield manages charging current, and the upper isolation provides additional isolation. The segmentation enables targeted charge management without redesigning the entire device structure.
Solution Approach 2:
The field shield layer serves multiple functions simultaneously: it acts as a charge sink to prevent trapped charge in the upper isolation layer, provides electrical isolation between the upper isolation and BOX, and can be integrated with existing device fabrication processes. This multi-functionality reduces the need for additional separate protective structures, thereby limiting the increase in overall device complexity.
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
The field shield effectively prevents electric charge buildup in the upper isolation layer, ensuring improved circuit yield and reliability by allowing charges to bleed into the lower isolation layer and substrate, providing a protective barrier against trapped charges.
Implementation Method 1
A local interconnect extends through the upper isolation layer and connects the field shield to a doped semiconductor region of the semiconductor device. Current that passes into the device during back-end of the line (BEOL) charging is shunted by the local interconnect away from the upper isolation layer and into the field shield.
Implementation Method 2
The field shield further functions as a protective barrier from any electric charge that is trapped within the lower isolation layer or substrate.
Data Source
AI summary
Disclosed is semiconductor structure that incorporates a field shield below a semiconductor device (e.g., a field effect transistor (FET) or a diode). The field shield is sandwiched between upper and lower isolation layers on a wafer. A local interconnect extends through the upper isolation layer and connects the field shield to a selected doped semiconductor region of the device (e.g., a source/drain region of a FET or a cathode or anode of a diode). Current that passes into the device, for example, during back-end of the line charging, is shunted by the local interconnect away from the upper isolation layer and down into the field shield. Consequently, an electric charge is not allowed to build up in the upper isolation layer but rather bleeds from the field shield into the lower isolation layer and into the substrate below. This field shield further provides a protective barrier against any electric charge that becomes trapped within the lower isolation layer or substrate