Recessed Access Device Gate Height Control for DRAM
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Solution Overview
Problem
The challenge in semiconductor devices is the occurrence of gate-induced drain leakage (GIDL) due to short channel effects and varying gate heights in metal gate recessed access devices (RADs) for dynamic random access memory (DRAM), which affects data retention and performance.
Innovation Solution
A manufacturing method for a recessed access device that involves forming a trench, a gate oxide layer, and multiple gate layers with controlled etching processes to achieve uniform gate heights, including ion implantation and wet etching, to ensure consistent gate structures and prevent GIDL.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metal gate recessed access devices are used to increase data retention, then data retention is improved, but gate-induced drain leakage occurs between gate and drain
Solution Approach 1:
The patent applies different materials to different parts of the gate structure: a first gate material (e.g., metal) is used in the lower portion near the drain to prevent GIDL, while a second gate material (e.g., polysilicon) is used in the upper portion. This local differentiation allows the device to maintain high data retention while suppressing the harmful leakage effect at the critical gate-drain interface.
Solution Approach 2:
The gate structure employs a composite material approach by combining two different gate materials in a single gate electrode. The first gate material provides excellent gate control and data retention, while the second gate material suppresses GIDL. This composite structure allows simultaneous optimization of both data retention and leakage prevention that cannot be achieved with a single material.
2Speed
If shorter channel lengths are used to increase operating speed, then operating speed is improved, but short channel effects limit device performance
Solution Approach 1:
The patent changes the material parameters of the gate structure by introducing a dual-material gate configuration. The first gate material has high work function and excellent adhesion properties, while the second gate material has different electrical characteristics. This parameter change in material composition allows the device to maintain strong gate control even with shorter channel lengths, thereby preserving device performance while achieving higher operating speeds.
3Object-generated harmful factors
If multiple gate layers with different materials are formed to prevent GIDL, then GIDL is prevented, but manufacturing process complexity increases
Solution Approach 1:
The gate structure is segmented into two distinct material regions: a first gate material layer and a second gate material layer. This segmentation allows each material to be optimized for its specific function (preventing GIDL while maintaining gate control) and enables selective deposition and processing of each layer, making the complex manufacturing process more manageable through staged fabrication.
Solution Approach 2:
The patent employs preliminary actions in the manufacturing process by first forming the trench and gate oxide layer, then selectively depositing the first gate material, followed by the second gate material. Each layer is prepared and processed in a predetermined sequence with appropriate intermediate steps (such as etching exposed portions), which organizes the complex multi-material fabrication into a systematic, step-by-step process that reduces overall manufacturing complexity.
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 method effectively controls gate heights and prevents GIDL, enhancing the performance and data retention of DRAM by maintaining uniform gate structures despite varying widths, thereby improving the overall performance of semiconductor devices.
Implementation Method 1
A gate oxide layer is formed within the substrate by oxidizing an inner surface of the trench
Implementation Method 2
An ion implantation is performed to the horizontal portion to form a doped horizontal portion
Data Source
AI summary
A manufacturing method for a recessed access device includes the following operations. A trenching is formed in a substrate. A gate oxide layer is formed within the substrate by oxidizing an inner surface of the trench. A first gate layer is formed in a bottom of the trench, wherein a portion of the gate oxide layer above the first gate layer is exposed from the trench. A second gate layer is formed in the trench to cover the first gate layer and the portion of the gate oxide layer and form a recess over the first gate layer, wherein the second gate layer has a vertical portion covering the portion of the gate oxide layer and a horizontal portion having an upper surface exposed from the recess. An ion implantation is performed to the horizontal portion to form a doped horizontal portion.