Tungsten Word Line Structure for Fluorine Diffusion Blocking
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Solution Overview
Problem
Existing semiconductor memory devices face challenges in preventing fluorine diffusion from fluorine-containing tungsten layers, which can degrade the insulation properties of interlayer insulating films and increase electric resistance, particularly in NAND flash memory devices with numerous stacked word lines.
Innovation Solution
Incorporating a fluorine-free tungsten layer (conductivity layer 23a) between fluorine-containing tungsten layers and insulating layers to act as a diffusion barrier, reducing the risk of fluorine diffusion and maintaining low electric resistance in the stacked interconnects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fluorine-containing tungsten layers are used to improve conductivity, then electrical resistance decreases, but fluorine diffusion degrades insulation properties of interlayer insulating films
Solution Approach 1:
A fluorine-free tungsten layer is introduced as an intermediary barrier layer between the fluorine-containing tungsten layers and the interlayer insulating films. This intermediate layer prevents fluorine diffusion from the conductive tungsten layers to the insulating films, thereby maintaining insulation properties while preserving the low resistance benefits of fluorine-containing tungsten.
Solution Approach 2:
The conductive layer is segmented into multiple sub-layers with different fluorine concentrations. The structure includes a first sub conductive layer with lower fluorine concentration adjacent to the insulating film, and a second sub conductive layer with higher fluorine concentration for improved conductivity. This segmentation allows each layer to fulfill its specific function without compromising the other.
2Reliability
If fluorine concentration in tungsten layers is increased to reduce electric resistance, then conductivity improves, but risk of current leakage increases due to insulation degradation
Solution Approach 1:
The fluorine-free tungsten layer serves as a protective intermediary that shields the interlayer insulating films from fluorine exposure. This allows the fluorine-containing tungsten layers to maintain high conductivity without causing insulation degradation, thereby preventing current leakage while preserving electrical performance.
Solution Approach 2:
Different regions of the conductive structure have different fluorine concentrations optimized for their specific functions. The region adjacent to the insulating film has low fluorine concentration to prevent diffusion, while the region further from the insulating film has high fluorine concentration to maximize conductivity. This local optimization resolves the contradiction between conductivity and insulation.
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 effectively inhibits fluorine diffusion, reduces the risk of current leakage, and maintains low electric resistance in the semiconductor memory device, improving the reliability and performance of NAND flash memory devices.
Implementation Method 1
Incorporating a fluorine-free tungsten layer (conductivity layer 23a) between fluorine-containing tungsten layers and insulating layers to act as a diffusion barrier, reducing the risk of fluorine diffusion
Data Source
AI summary
A semiconductor memory device includes a first insulating layer, a first conductive layer, a first pillar, a second pillar, and a second insulating layer. The first conductive layer contains tungsten. The first conductive layer includes a first sub conductive layer and a second sub conductive layer. The first pillar and the second pillar pass through the first insulating layer and the first conductive layer. The second insulating layer divides the first insulating layer and the first conductive layer. The first sub conductive layer is in contact with the second sub conductive layer and is provided between the second sub conductive layer and the first insulating layer. A fluorine concentration in the first sub conductive layer is lower than that in the second sub conductive layer.