Damascene Word Line Oxidation for 3D Memory Isolation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In three-dimensional memory arrays, forming oxide lines between word lines to ensure electrical isolation is challenging due to polysilicon residue bridges and damage to charge storage layers, leading to performance issues and increased manufacturing complexity.
Innovation Solution
A method involving the formation of silicon lines over stacked nonvolatile memory structures, followed by oxidation to create insulating surfaces in word line trenches, and subsequent etching to form word lines, which includes using damascene processes and metal silicide formation to achieve reliable electrical isolation without damaging charge storage layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If polysilicon word lines are formed prior to oxide lines, then word line structure is established, but polysilicon residue forms bridges electrically connecting neighboring word lines
Solution Approach 1:
The patent inverts the conventional process sequence by forming oxide lines first and then forming polysilicon word lines within trenches defined by the oxide lines. This reversal prevents polysilicon residue from bridging neighboring word lines, as the oxide lines are already in place to provide electrical isolation before the polysilicon deposition and etching steps occur.
Solution Approach 2:
The oxide lines are formed in advance before the polysilicon word lines are created. This preliminary formation of oxide isolation structures ensures that when polysilicon is deposited and etched to form word lines, the oxide lines are already positioned to prevent residue bridging, thereby ensuring electrical isolation is maintained throughout the subsequent processing steps.
2Reliability
If oxide lines are formed prior to polysilicon word lines, then electrical isolation structure is prepared, but oxide voids allow polysilicon residue to form bridges
Solution Approach 1:
The patent introduces a trench structure as an intermediary element between the oxide lines and polysilicon word lines. The trenches are etched through the oxide lines to create defined spaces where polysilicon word lines will be formed. This intermediary trench structure prevents polysilicon residue from creating direct bridges between oxide lines, while the oxide lines themselves remain intact and continue to provide electrical isolation.
3Ease of manufacture
If excess oxide is etched to form trenches for word lines, then word line trenches are created, but charge storage layers are damaged
Solution Approach 1:
The patent applies local quality by making the oxide etching process selective to specific regions. The etching is performed only in areas where trenches are needed for word line formation, while the oxide layers covering charge storage layers are protected from etching. This localized approach allows trench formation where required without damaging the charge storage layers in other regions.
Solution Approach 2:
The patent performs preliminary protective actions by forming the oxide lines and trenches before exposing the charge storage layers to etching processes. The oxide structures are established in advance to define the trench locations, and subsequent etching steps are confined to these predefined regions, preventing accidental damage to charge storage layers that would occur if etching were performed after charge storage layer formation.
4Manufacturing precision
If high aspect ratio trenches are etched for word lines, then word line structure is defined, but polysilicon residue cannot be completely removed
Solution Approach 1:
The patent replaces mechanical or physical removal methods with a chemical oxidation process to eliminate polysilicon residue. Instead of relying on mechanical scraping or additional etching steps that are ineffective in high aspect ratio trenches, the process uses oxidation chemistry to convert residual polysilicon into removable oxidation products, enabling complete residue removal from difficult-to-reach trench regions.
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 eliminates polysilicon residue bridges and maintains the integrity of charge storage layers, enhancing the reliability and manufacturing efficiency of three-dimensional memory devices by ensuring proper electrical isolation between word lines.
Implementation Method 1
oxidizing the silicon lines separated by the word line trenches
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The technology relates to a damascene word line for a three dimensional array of nonvolatile memory cells. Conductive lines such as silicon are formed over stacked nonvolatile memory structures. Word line trenches separate neighboring ones of the silicon lines. The silicon lines separated by the word line trenches are oxidized, making insulating surfaces in the word line trenches. Word lines are made in the word line trenches.