Early Bit Line Air Gap Formation for Flash Memory
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The challenge in flash memory technology is to form uniform low resistance conductive lines, such as bit lines, in close proximity without incurring capacitive coupling issues, which affects memory operation.
Innovation Solution
The formation of air gaps between bit lines reduces bit line-to-bit line capacitance by creating dummy bit lines, followed by replacing them with actual bit lines, using a sacrificial material and etch stop layers to ensure uniform trench depth and minimize exposure to etching damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If bit lines are formed in close proximity to increase memory density, then productivity and memory capacity are improved, but capacitive coupling between bit lines increases causing harmful effects on memory operation
Solution Approach 1:
The patent extracts the dielectric material between bit lines to create air gaps, removing the harmful capacitive coupling medium while maintaining the close proximity arrangement for high density. This directly addresses the contradiction by eliminating the harmful factor (capacitive coupling) without changing the beneficial arrangement (close bit line spacing).
Solution Approach 2:
The patent introduces air gaps (porous structure) between bit lines to reduce capacitive coupling. The air gaps create a porous dielectric structure with lower permittivity than solid dielectric materials, thereby reducing the harmful capacitive effects while maintaining close bit line spacing for high memory density.
2Manufacturing precision
If etching is used to form trenches for bit lines, then manufacturing precision is improved, but exposure to etching damage degrades bit line quality
Solution Approach 1:
The patent performs the air gap formation etching before depositing the bit line metal layers. This preliminary action creates the trenches and air gaps while the sacrificial material is still in place, protecting the eventual bit lines from etching damage. The bit lines are formed later through deposition, avoiding exposure to the harmful etching process entirely.
Solution Approach 2:
The patent uses sacrificial material as an intermediary that protects the bit line locations during the air gap formation etching process. The sacrificial material occupies the bit line positions during etching, preventing etching damage to the metal layers, and is removed later to create the final air gap structure.
3Manufacturing precision
If uniform trench depth is required for consistent bit line formation, then manufacturing precision is improved, but process complexity increases
Solution Approach 1:
The patent employs an etch stop layer that automatically stops the etching process at a predetermined depth when encountered. This self-service mechanism ensures uniform trench depth across the wafer without requiring complex real-time depth monitoring or control systems. The etch stop layer performs the function of depth control inherently through its material properties and positioning.
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 improves bit line quality by reducing capacitive coupling and maintaining the integrity of conductive lines, leading to enhanced memory operation and reliability.
Implementation Method 1
patterning the second layer using a selective etch that provides an etch rate of the second layer that is substantially higher than an etch rate of the first layer
Implementation Method 2
depositing an encapsulating layer in the first trench
Implementation Method 3
performing Chemical Mechanical Polishing (CMP) to remove excess conductive line material while leaving conductive line material in the second trench
Data Source
AI summary
Dummy bit lines of are formed in a sacrificial layer at locations where bit lines are to be formed, with bit lines separated by trenches that extend through the sacrificial layer. Enclosed air gap structures are formed in the trenches between the dummy bit lines. Subsequently, the dummy bit lines are replaced with metal to form bit lines.