DRAM Wordline Work-Function Segmentation for GIDL Reduction
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Solution Overview
Problem
Dynamic random-access memory (DRAM) devices face challenges in reducing gate-induced drain leakage (GIDL) due to high work-function materials used in word lines, which increase resistance and leakage near the source/drain area, limiting the miniaturization and density of memory cells.
Innovation Solution
The implementation of a memory device structure with a recessed metal layer comprising a first high work-function metal layer and a bulk metal layer, buried below the substrate surface, and a second low work-function metal layer on top, which reduces GIDL while maintaining low resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high work-function materials are used in word line to reduce channel impurities, then channel quality is improved, but gate induced drain leakage increases near the source/drain area
Solution Approach 1:
The word line is divided into multiple segments: a first high work-function material segment positioned over the channel region to reduce impurities, and a second low work-function material segment positioned over the source/drain region to reduce GIDL. This segmentation allows each segment to perform its specific function optimally without interfering with the other.
Solution Approach 2:
Different work-function materials are applied to different locations of the word line structure. The high work-function material is localized over the channel to improve quality, while the low work-function material is localized over the source/drain area to suppress GIDL, giving each region the specific property it needs.
2Reliability
If high work-function materials are used in word line, then channel impurities are reduced, but resistance increases
Solution Approach 1:
The word line is segmented into a first portion with high work-function material for channel region and a second portion with low work-function material for source/drain region. The low work-function segment provides a conductive path that reduces overall resistance while the high work-function segment maintains channel quality.
Solution Approach 2:
The word line structure uses a composite of two different work-function materials, combining the advantages of both: high work-function material for channel quality and low work-function material for low resistance, creating a composite structure that achieves both goals simultaneously.
3Productivity
If memory cell size is reduced to increase density, then manufacturing capacity is improved, but gate induced drain leakage becomes more significant
Solution Approach 1:
As memory cells are miniaturized, the local quality approach becomes even more critical. The low work-function material is precisely localized over the source/drain region of the scaled-down device, ensuring GIDL suppression is maintained even as overall device dimensions are reduced and density is increased.
Solution Approach 2:
The work-function parameter of the word line material is changed in specific regions to address GIDL. By modifying the work-function parameter locally over the source/drain area rather than uniformly across the entire word line, the invention enables scaling to higher densities while controlling leakage.
Data Source
AI summary
Memory devices and methods of forming memory devices are described. The memory devices comprise two work-function metal layers, where one work-function layer has a lower work-function than the other work-function layer. The low work-function layer may reduce gate-induced drain leakage current losses. Methods of forming memory devices are also described.