Buried Digit Line Access Device Airgap Capacitance Reduction
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Solution Overview
Problem
Current buried digit line (BDL) access devices in DRAM technology face high digit line-to-digit line coupling capacitances, exceeding 25%-30% of total digit line capacitance, which hampers sense margin and requires improved designs to reduce this coupling below 20% for effective sense amp operation.
Innovation Solution
The solution involves replacing metal digit lines with heavily doped Si lines and introducing air gaps between them, reducing digit line-to-digit line capacitance to 10-15% of the total capacitance through a process that includes trench formation, implantation, and sacrificial filling with polysilicon to create air gaps, thereby simplifying manufacturing and reducing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metal digit lines are used in BDL access devices, then the digit lines can conduct electricity, but the digit line-to-digit line coupling capacitance increases to 25%-30% of total digit line capacitance
Solution Approach 1:
The patent removes the metal digit line from the structure entirely, extracting the harmful metal component that causes high coupling capacitance. Instead, the invention uses heavily doped silicon regions that extend vertically through the substrate to serve as the digit line, eliminating the metal layer that was responsible for the 25%-30% coupling capacitance problem
Solution Approach 2:
The patent changes the material parameter from metal to heavily doped silicon, and changes the geometric parameter by extending the digit line vertically through the substrate rather than placing it horizontally. This parameter change reduces the coupling capacitance between adjacent digit lines from 25%-30% to below 20% of total digit line capacitance
2Ease of manufacture
If metal digit lines are used in BDL access devices, then the manufacturing process is established, but the DL-DL capacitance exceeds 20% requiring advanced sense amp schemes
Solution Approach 1:
The patent changes the digit line material from metal to heavily doped silicon and modifies the geometric configuration to vertical extension through the substrate. This parameter change reduces DL-DL capacitance to acceptable levels, enabling the use of standard sense amp schemes rather than requiring advanced or complex sense amp designs
3Reliability
If conventional BDL technology is used, then the digit lines can be buried in silicon substrate, but the total digit line capacitance remains high affecting sense margin
Solution Approach 1:
The patent extracts the metal digit line component that contributes to high total capacitance and replaces it with heavily doped silicon regions. This extraction and replacement reduces both the DL-DL coupling capacitance and the total digit line capacitance, improving sense margin without requiring additional complex compensation circuits
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 reduces digit line-to-digit line capacitance, enabling the use of advanced sense amps and improving DRAM device performance while simplifying the manufacturing process and reducing costs.
Implementation Method 1
heavily doped Si serving as digit line
Implementation Method 2
more spacer is present between the digit lines thereby reducing the DL-DL capacitance
Data Source
AI summary
An access device includes a plurality of first digit lines (DL) trenches extending along a first direction, buried digit lines between each DL trench, second and third trenches separating the digit lines, a filling material filling the digit line trenches comprising airgaps in each second trench, a plurality of word line (WL) trenches extending along a second direction, metal word lines deposited on the walls of the word line trenches, a filling material filling the word line trenches.