LDMOS Transistor CHC Reliability via Rotated Substrate and STI Oxide
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Solution Overview
Problem
LDMOS transistors in integrated circuits face reliability issues due to channel hot carriers (CHC) that degrade the gate dielectric and increase turn-on voltage over time, leading to potential circuit failure, as they switch high voltages and generate hot carriers that overcome the substrate/gate dielectric barrier.
Innovation Solution
Improving LDMOS transistor reliability by growing a second STI liner oxide and building the transistor on a rotated substrate, which reduces the peak electric field and subsequent CHC generation through corner rounding, allowing for enhanced oxidation and reduced hot carrier injection into the gate dielectric.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If LDMOS transistors are used to switch high voltages, then high voltage switching capability is achieved, but channel hot carriers are generated that degrade the gate dielectric and increase turn-on voltage over time
Solution Approach 1:
The patent applies corner rounding to the STI-gate dielectric interface, transforming sharp corners into curved surfaces. This curvature reduces the peak electric field concentration at the interface, thereby reducing hot carrier generation and improving transistor reliability while maintaining high voltage switching capability
Solution Approach 2:
The patent changes the geometric parameters of the STI structure by rounding the corners at the interface with the gate dielectric. This parameter change modifies the electric field distribution, reducing peak field strength and subsequently reducing hot carrier injection into the gate dielectric, which extends transistor lifetime
2Ease of manufacture
If a single STI liner oxide is grown, then basic isolation is achieved, but corner rounding is insufficient to reduce peak electric field and hot carrier generation
Solution Approach 1:
The patent segments the STI liner oxide formation into two distinct oxidation steps. The first oxidation provides baseline isolation, while the second oxidation specifically targets corner rounding. This segmentation allows each step to be optimized for its specific function, achieving both ease of manufacture and improved reliability
Solution Approach 2:
The first STI liner oxidation is performed as a preliminary action before the second oxidation step. This preliminary oxidation establishes the baseline isolation structure, which is then further processed by the second oxidation to achieve the desired corner rounding and electric field reduction
3Ease of manufacture
If the substrate is not rotated, then standard fabrication alignment is maintained, but corner rounding effect is insufficient to achieve adequate CHC lifetime improvement
Solution Approach 1:
The patent introduces asymmetry by rotating the substrate 45 degrees relative to the standard fabrication alignment. This asymmetric orientation maximizes the corner rounding effect during the second oxidation step, creating more effective electric field reduction and significantly improving CHC lifetime while remaining compatible with standard fabrication processes
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 significantly extends the channel hot carrier lifetime of LDMOS transistors, with a 30-fold increase in 20V LDNMOS transistor lifetime, and when combined with two-step liner oxidation, achieves a 66-fold improvement over single-step oxidation on a non-rotated substrate, enhancing transistor performance and reliability.
Implementation Method 1
growing a second STI liner oxide
Implementation Method 2
the acceleration of electrons in the channel is increased resulting in the generation of channel hot carriers (CHC). These hot carriers may have sufficient energy to overcome the substrate/gate dielectric barrier and maybe injected into or through the gate dielectric
Data Source
AI summary
An integrated circuit on a rotated substrate with an LDMOS transistor. A method of enhancing the CHC performance of an LDMOS transistor by growing a second STI liner oxide. A method of enhancing the CHC performance of an LDMOS transistor building the LDMOS transistor on a rotated substrate and growing a second STI liner oxide.