Digit Line Formation for Horizontal DRAM Access Devices
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Solution Overview
Problem
As design rules shrink, there is a challenge in forming digit lines for DRAM arrays with limited semiconductor space, requiring innovative methods for digit line formation that improve isolation, reduce capacitance, and allow for complex three-dimensional structures while maintaining low contact resistance.
Innovation Solution
The method involves forming layers of dielectric and semiconductor materials in a vertical stack, creating horizontal openings, gas phase doping, and converting high doped semiconductor material to a conductive form, which allows for highly conformal digit line formation with better isolation from body contact lines, reducing capacitance and dopant diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional digit line formation methods are used in shrinking design rules, then manufacturing process remains simple, but isolation between digit lines and body contact lines deteriorates, resulting in increased capacitance
Solution Approach 1:
The patent segments the digit line formation process into distinct stages: forming openings through alternating dielectric and semiconductor layers, selectively doping semiconductor regions, and converting doped regions to conductive material. This segmentation enables better isolation between digit lines and body contact lines by creating separate formation pathways, reducing capacitance while managing process complexity through systematic breakdown of the fabrication steps.
Solution Approach 2:
The patent applies local quality by selectively doping specific semiconductor regions through horizontally extended openings while leaving other regions undoped or differently doped. This localized doping approach, combined with selective conversion to conductive material, creates regions of different electrical properties within the same structure, improving isolation characteristics without requiring complete process redesign.
2Adaptability or versatility
If horizontally oriented access devices are used with vertically oriented access lines, then three-dimensional integration is improved, but digit line formation complexity increases
Solution Approach 1:
The patent transitions from conventional planar digit line formation to three-dimensional formation by extending digit lines horizontally through vertically stacked layers. The method forms openings that extend in a first horizontal direction through alternating dielectric and semiconductor layers, then converts selected semiconductor regions to conductive material. This dimensional transition enables better integration with vertically oriented access lines while managing complexity through systematic layer-by-layer processing.
Solution Approach 2:
The patent implements nesting by forming digit line structures within the existing vertical stack of dielectric and semiconductor layers. The horizontally extending openings and converted conductive regions are nested within the pre-formed vertical layer structure, allowing three-dimensional integration without requiring complete restructuring of the device architecture.
3Manufacturing precision
If gas phase doping and material conversion are used, then doping uniformity is improved, but process time increases
Solution Approach 1:
The patent replaces conventional solid-phase or liquid-phase doping methods with gas phase doping, which provides superior doping uniformity through vapor-phase impurity distribution. The gas phase process allows impurities to diffuse uniformly throughout the semiconductor region. The subsequent conversion of doped semiconductor material to conductive material further enhances electrical properties. While these processes add time, they significantly improve manufacturing precision and device performance.
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 enables better body bias control, improved access device channel control, and uniform doping, resulting in lower digit line capacitance and reduced complexity in forming digit lines within complex three-dimensional structures.
Implementation Method 1
gas phase doping a dopant on a top surface of the low doped semiconductor material in the horizontal opening to form a source/drain region
Implementation Method 2
converting the remaining high doped semiconductor material to a conductive material having a different characteristic from the remaining high doped semiconductor material
Data Source
AI summary
Systems, methods, and apparatuses are provided for digit line formation for horizontally oriented access devices. One example method includes forming layers of a first dielectric material, a low doped semiconductor material, and a second dielectric material, in repeating iterations vertically to form a vertical stack, forming a vertical opening in the vertical stack, selectively etching the second dielectric material to form a horizontal opening in the second dielectric material, gas phase doping a dopant on a top surface of the low doped semiconductor material in the horizontal opening to form a source/drain region, forming a high doped semiconductor material in the horizontal opening, selectively etching the high doped semiconductor material formed in the horizontal opening such that a portion of the high doped semiconductor material remains, and converting the remaining high doped semiconductor material to a conductive material having a different characteristic from the remaining high doped semiconductor material.