High Voltage Device With Non-Uniform Oxide Layer
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Solution Overview
Problem
High voltage devices, such as LDMOS transistors, face challenges in achieving high switching speed and reliability due to factors like drain-to-source on resistance (Rdson) and hot carrier-induced defects at the silicon-silicon oxide interface, which affect their performance and reliability.
Innovation Solution
A high voltage device design featuring a substrate with a recessed region, a source region, a drain region, and a gate structure with a multi-layer oxide layer, where the second part of the oxide layer is thicker than the first part, and a silicide block adjacent to the gate structure, aimed at reducing Rdson and hot carrier generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the drain-to-source on resistance (Rdson) is reduced to improve switching speed, then the switching speed increases, but the energy loss during switching increases
Solution Approach 1:
The patent applies local quality by creating a non-uniform oxide layer thickness distribution, where the oxide layer is thicker near the drain region and thinner near the source region. This localized variation in oxide thickness optimizes the electric field distribution differently in various regions, allowing reduced Rdson for faster switching while managing the energy loss through strategic field confinement
Solution Approach 2:
The patent changes the physical parameter of oxide layer thickness as a gradient rather than a uniform value. By controlling the oxide growth or deposition process to create this thickness gradient, the electric field distribution is modified to reduce hot carrier generation and optimize the trade-off between switching speed and energy loss
2Power
If hot carriers are generated at the silicon-silicon oxide interface, then the device can operate at high voltage, but defects are generated causing linear drain current (Idlin) degradation
Solution Approach 1:
The patent changes the oxide layer thickness parameter to create a gradient distribution that reduces the electric field intensity at the silicon-silicon oxide interface. This parameter modification suppresses hot carrier generation while preserving the high voltage operation capability through optimized field distribution in the drift region
Solution Approach 2:
The patent converts the potentially harmful effect of hot carriers into a beneficial outcome by using the oxide thickness gradient to control electric field distribution. The thicker oxide region acts as a field management structure that redirects and moderates the electric field, reducing harmful hot carrier injection while maintaining high voltage operation
3Ease of manufacture
If a uniform oxide layer is used between the gate structure and the substrate, then the manufacturing process is simple, but the switching speed and reliability cannot be optimized
Solution Approach 1:
The patent transitions from a uniform oxide layer to a locally varied oxide layer with different thicknesses in different regions. This local quality variation is achieved through controlled oxidation or deposition processes that create the desired thickness gradient, optimizing switching performance while remaining compatible with standard semiconductor manufacturing
Solution Approach 2:
The patent introduces dynamic optimization by creating an oxide layer structure that provides different electrical characteristics in different regions. The varying thickness creates a dynamic electric field distribution that adapts to the local requirements of the device operation, improving switching speed and reliability
Data Source
AI summary
A high voltage device may include a substrate, source and drain regions, a gate structure and an oxide layer. The substrate may include a recessed region with a recessed surface lower than a top surface of the substrate. The source and drain regions may be at least partially arranged within the substrate under the recessed surface and top surface respectively. The drain region may be positioned higher than the source region. The gate structure may include first and second portions arranged over the recessed region. The first and second portions may be nearer to the source and drain regions respectively. The oxide layer may include a first part between the first portion of the gate structure and the recessed surface, and a second part between the second portion of the gate structure and the recessed surface. The second part of the oxide layer may be thicker than the first part.