MOS Gate Dielectric Segmentation for Hot Carrier Injection Reduction
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Solution Overview
Problem
MOS transistor devices suffer from hot carrier injection effects, which negatively impact their reliability, and existing solutions do not adequately mitigate these effects.
Innovation Solution
A transistor device design featuring a channel region with a first dielectric layer stack and a second dielectric layer stack, where the capacitance of the first stack is significantly larger than the second, utilizing silicon oxide and high-k materials to reduce the electric field in the junction area, thereby minimizing hot carrier injection while maintaining effective channel control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional gate structure with uniform dielectric layer is used, then the manufacturing process is simple, but hot carrier injection effects severely impact device reliability
Solution Approach 1:
The gate structure is segmented into multiple dielectric layers with different dielectric constants. The first dielectric layer has dielectric constant k1 and the second dielectric layer has dielectric constant k2, where k1 > k2. This segmentation allows the electric field to be distributed differently across the gate, reducing peak electric field strength at the drain junction and thereby reducing hot carrier injection effects while maintaining acceptable manufacturing complexity
Solution Approach 2:
Different regions of the gate structure are assigned different dielectric properties. The first dielectric layer with higher dielectric constant k1 is positioned to provide strong channel control, while the second dielectric layer with lower dielectric constant k2 is positioned to reduce electric field concentration at the drain junction. This local differentiation of dielectric quality addresses both channel control and hot carrier reduction requirements
2Reliability
If the dielectric layer thickness is reduced to improve channel control, then channel control improves, but electric field concentration increases leading to more severe hot carrier injection
Solution Approach 1:
Instead of uniformly reducing dielectric layer thickness, the invention changes the dielectric constant parameter across different layers. The first dielectric layer has dielectric constant k1 and the second has dielectric constant k2, where k1 > k2. This parameter change allows the effective dielectric thickness to be reduced for channel control while the lower k2 value in the second layer compensates by reducing electric field concentration, thereby reducing hot carrier injection
3Reliability
If a higher dielectric constant material is used throughout the gate, then channel control improves, but electric field concentration at the junction increases causing more hot carrier injection
Solution Approach 1:
The gate dielectric structure is made asymmetric with two distinct layers having different dielectric constants. The first dielectric layer with higher dielectric constant k1 provides strong channel control, while the second dielectric layer with lower dielectric constant k2 (where k1 > k2) reduces electric field concentration at the drain junction. This asymmetric configuration resolves the contradiction between channel control and electric field concentration
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 design effectively reduces hot carrier injection by modifying the electric field distribution, thereby enhancing the reliability and performance of MOS transistor devices without detrimental increases in gate leakage.
Implementation Method 1
the capacitance of the first dielectric layer stack is larger than the capacitance of the second dielectric layer stack
Implementation Method 2
the electric field in the junction area, e.g. on top of the junction, can be reduced, reducing the occurrence of HCl
Implementation Method 3
a second dielectric layer with dielectric constant k4 > k1 on top of said first dielectric layer
Data Source
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AI summary
A transistor device is disclosed comprising a. a channel region in a substrate partially delimited by a source and a drain junction at a main surface of the substrate; b. a first dielectric layer stack arranged on the channel region on the main surface of the substrate, the orthogonal projection of the first dielectric layer stack on the main surface being in between and not covering the junctions and defining a first area; c. a second dielectric layer stack laterally adjacent to and in contact with the first dielectric layer stack, the orthogonal projection of the second dielectric layer stack on the main surface comprising the junction and defining a second area; d. a metal gate layer on top of the first and the second dielectric layer stack, the orthogonal projection of the metal gate layer on the main surface covering at least the first area and the second area; wherein the capacitance of the first dielectric layer stack is larger than the capacitance of the second dielectric layer stack.