SOI Substrate Diode Formation via Buried Insulator Window
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Solution Overview
Problem
In SOI semiconductor devices, the formation of substrate diodes is challenging due to issues such as non-ideal diode characteristics, heat dissipation problems, and variability in diode behavior caused by complex processing steps and materials like nickel silicide, which affect the accuracy of thermal sensing and overall device performance.
Innovation Solution
The substrate diode is formed prior to patterning gate electrodes, with openings created through isolation structures and filled with conductive materials like silicon or carbon to decouple diode characteristics from transistor elements, allowing for high-temperature processing without compromising diode behavior, and using semiconductor materials for contact elements to reduce material system influences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If substrate diodes are formed in the crystalline substrate material using conventional implantation processes, then the diode structure can be integrated with transistor elements, but the diode characteristics become non-ideal and highly variable due to overlap with transistor PN junctions and nickel silicide formation
Solution Approach 1:
The substrate window region is segmented as a separate functional area distinct from the transistor active regions. The diode anode is formed in the substrate through the buried insulating layer in this segmented region, while transistor cathodes are formed in the device layer above, spatially separating diode and transistor formation processes to prevent characteristic interference
Solution Approach 2:
The diode anode formation is extracted from the conventional implantation process used for transistor drain/source regions. Instead of forming diodes through substrate implantation that overlaps with transistor PN junctions, the invention forms diode anodes separately through the buried insulating layer into the substrate, removing the harmful overlap with transistor elements
2Ease of manufacture
If high energy implantation is used to form the substrate diode, then the diode can be formed in the crystalline substrate, but the implantation-induced damage and subsequent annealing affect both the diode and transistor characteristics, increasing variability
Solution Approach 1:
The substrate window opening is formed preliminarily through the buried insulating layer before diode anode implantation. This preliminary action defines a precise implantation region that is spatially separated from transistor active areas, allowing subsequent implantation and annealing processes to affect the diode and transistors differently, reducing characteristic variability
Solution Approach 2:
Different regions of the substrate receive different treatments: the substrate window region receives high energy implantation for diode anode formation, while the transistor active regions receive standard drain/source implantation. This local differentiation allows each structure to be optimized independently, improving manufacturing precision for both diodes and transistors
3Reliability
If nickel silicide is formed in the substrate diode contact regions to improve conductivity, then the contact resistance is reduced, but the nickel diffusion into the PN junction deteriorates the diode characteristic uniformity
Solution Approach 1:
The nickel silicide formation is extracted from the diode contact regions and applied only to transistor drain and source regions. By removing nickel silicide formation from the diode area, the harmful nickel diffusion into the diode PN junction is eliminated, preserving diode characteristic uniformity while still providing low contact resistance for transistors through nickel silicide
4Object-affected harmful factors
If the body of SOI transistors is not connected to a specified reference potential, then the SOI architecture provides reduced parasitic capacitance, but the body potential floats due to accumulated minority charge carriers, affecting device performance
Solution Approach 1:
A dedicated substrate contact structure serves as an intermediary element that provides a stable reference potential to the transistor bodies through the buried insulating layer. This intermediary substrate contact, formed through the substrate window, acts as a potential reference that stabilizes the floating body potential while maintaining the SOI architecture's low parasitic capacitance benefits
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 approach provides superior uniformity and stability of diode behavior, reduces complexity in interlayer dielectric formation, and enhances device performance by decoupling diode characteristics from transistor elements, improving thermal sensing accuracy and overall device reliability.
Implementation Method 1
The openings are filled with a conductive material, such as silicon, silicon/germanium, carbon or the like
Data Source
AI summary
A substrate diode of an SOI device may be formed on the basis of contact regions in an early manufacturing stage, i.e., prior to patterning gate electrode structures of transistors, thereby imparting superior stability to the sensitive diode regions, such as the PN junction. In some illustrative embodiments, only one additional deposition step may be required compared to conventional strategies, thereby providing a very efficient overall process flow.