Avalanche Diode Well Structure for Stable High-Voltage Clamping
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Solution Overview
Problem
High-voltage diodes in integrated circuits face reliability issues due to sensitivity to impact ionization during reverse bias operation, particularly when using shallow trench isolation (STI) structures, which lead to reduced lifetime stability under repeated breakdown stressing.
Innovation Solution
The formation of a shallow N-type well and a shallow P-type well with a thin field relief oxide structure over the PN junction, increasing the distance between the oxide/substrate interface and the breakdown region, thereby enhancing stability and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If shallow trench isolation (STI) is used to isolate SNW and SPW wells, then device isolation is achieved, but trapped charge centers form at the oxide/substrate interface reducing lifetime stability
Solution Approach 1:
The patent removes the problematic STI oxide layer from the breakdown region by using selective oxidation to create a thin field relief oxide only in specific areas, leaving the substrate interface exposed in the well space region where breakdown occurs. This extracts the harmful oxide/substrate interface from the high-field region, eliminating trapped charge center formation.
Solution Approach 2:
The patent applies different oxide thicknesses in different regions: thin field relief oxide (50-200 nm) over the SNW and SPW to prevent surface breakdown, but no oxide at the substrate interface in the well space region to eliminate trapped charges. This local differentiation of oxide quality resolves the contradiction between isolation and reliability.
2Reliability
If thin field relief oxide structure is used to increase distance from breakdown region to oxide interface, then hot carrier injection is reduced, but manufacturing complexity increases
Solution Approach 1:
The thin field relief oxide is formed before well implantation using selective oxidation. This preliminary action creates the protective oxide layer in advance, and subsequent implantation steps automatically respect this oxide mask, simplifying the overall process despite the additional oxidation step.
Solution Approach 2:
The thin field relief oxide acts as an intermediary layer that protects the substrate during fabrication while being thin enough to prevent hot carrier injection. It mediates between the need for surface protection and the need to eliminate trapped charges at the interface.
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 configuration results in a more stable and reliable avalanche diode with improved breakdown voltage stability over time, simplifying circuit design and reducing costs by replacing chains of low-voltage Zener diodes with a single avalanche diode.
Implementation Method 1
The greater distance may advantageously provide greater stability and reliability of an avalanche diode relative to an analogous STI-isolated diode
Implementation Method 2
a shallow N-type well (SNW) and a shallow P-type well (SPW) are formed adjacent each other or with a well space region between the two shallow wells to form an SNW/SPW diode that may operate as an avalanche diode
Data Source
AI summary
An integrated circuit includes a shallow P-type well (SPW) below a surface of a semiconductor substrate and a shallow N-type well (SNW) below the surface. The SPW forms an anode of a diode and the SNW forms a cathode of the diode. The SNW is spaced apart from the SPW by a well space region; and a thin field relief oxide structure lies over the well space region.