Recessed Access Device Gate Oxide Thickness Optimization
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Solution Overview
Problem
Metal gate recessed access devices (RADs) face gate induced drain leakage (GIDL) issues due to high electric fields between the gate layer and source/drain region, which can be mitigated by thicker gate oxide layers but result in reduced drive current and control over the gate layer.
Innovation Solution
A recessed access device structure with a trench in the substrate, featuring a gate oxide layer with a connection portion of greater thickness than other portions, positioned between the gate layer and source/drain region, to reduce GIDL without compromising gate control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a thicker gate oxide layer is used to reduce GIDL, then GIDL is minimized, but drive current is reduced and gate control ability deteriorates
Solution Approach 1:
The gate oxide layer is designed with non-uniform thickness, having a first thickness in the first region and a second thickness in the second region. This local quality variation allows the oxide layer to provide enhanced GIDL protection in regions where it is thicker while maintaining adequate drive current in regions where it is thinner, thus resolving the contradiction between reducing GIDL and maintaining drive current.
Solution Approach 2:
The gate oxide layer is segmented into different thickness regions (first region with first thickness, second region with second thickness) along the trench. This segmentation enables different functional zones within the same gate oxide layer, allowing simultaneous optimization of GIDL suppression and drive current characteristics in different spatial locations.
2Object-affected harmful factors
If a thicker gate oxide layer is used to reduce GIDL, then GIDL is minimized, but control over the gate layer deteriorates
Solution Approach 1:
The gate oxide layer thickness is locally optimized with a first thickness in the first region and a second thickness in the second region. This local quality approach allows the structure to provide enhanced GIDL protection where needed while preserving gate control ability in other regions, thus resolving the contradiction between minimizing GIDL and maintaining ease of gate operation.
Solution Approach 2:
The gate oxide layer is divided into segmented thickness regions, enabling different portions to serve different functions: one portion optimized for GIDL suppression and another portion optimized for maintaining gate control, thereby resolving the contradiction between these two requirements.
Data Source
AI summary
A method of manufacturing a recessed access device includes the following operations. A first trench is formed in a substrate. A first gate oxide layer is formed on an inner surface of the first trench. A sacrificial layer is formed in a bottom of the first trench, in which a portion of the first gate oxide layer above the sacrificial layer is exposed from the first trench. The portion of the first gate oxide layer is removed to expose a sidewall of the first trench. The sidewall of the first trench is oxidized to form a second gate oxide layer within the substrate, in which the second gate oxide layer is in contact with the first gate oxide layer. The sacrificial layer is removed to form a second trench.