Memory Array Staircase Liner Conversion for Dense Word Line Contacts
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Solution Overview
Problem
The challenge in memory device manufacturing is the inadequate formation of lateral sub-treads in word line contacts, which limits the increase in the quantity of word line contacts per unit area, leading to increased area consumption.
Innovation Solution
A method involving the use of a liner material, initially polysilicon, which is doped and then converted to tungsten, allowing for the formation of two lateral sub-treads on the staircase architecture of word line contacts, reducing the area consumed by these contacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If traditional staircase architecture is used for word line contacts, then the manufacturing process is simpler, but the quantity of word line contacts per unit area is limited and area consumption increases
Solution Approach 1:
The patent divides each tread of the staircase into multiple lateral sub-treads, creating segmented contact surfaces. This segmentation allows multiple word line contacts to be formed on a single tread level, thereby increasing the quantity of word line contacts per unit area without requiring additional vertical levels or expanding the overall footprint of the contact structure.
Solution Approach 2:
The patent introduces lateral sub-treads that extend in the lateral dimension rather than only in the vertical direction. By utilizing the lateral dimension for additional contact surfaces, the design increases contact density without proportionally increasing the vertical height or lateral footprint, effectively reducing area consumption per contact.
2Area of stationary object
If lateral sub-treads are formed to increase contact density, then area consumption is reduced, but the manufacturing process becomes more complex and requires additional process steps
Solution Approach 1:
The patent changes the material parameter of the liner from uniform polysilicon to a composite structure with a tungsten portion and a polysilicon portion. This parameter change enables selective etching where the polysilicon portion can be removed to expose sub-treads while the tungsten portion remains to maintain structural integrity. The material transformation simplifies the manufacturing process by eliminating gap filling steps and reducing the number of lithography operations required.
Solution Approach 2:
The patent introduces a liner structure with distinct material portions that acts as an intermediary between the staircase architecture and the final contact formation. The liner's differentiated material composition (tungsten vs. polysilicon) serves as a mediator that enables selective removal processes, allowing sub-treads to be exposed without requiring complex direct patterning of the contact holes themselves.
3Strength
If a thicker liner is used to maintain structural integrity, then mechanical strength is improved, but the ability to form thin sub-treads and increase contact density is reduced
Solution Approach 1:
The patent applies local quality by creating different material portions within the liner at different locations. The tungsten portion is placed where structural support is needed, while the polysilicon portion is placed where selective removal is desired to expose sub-treads. This local differentiation allows the liner to be thin overall while maintaining structural integrity in critical areas and enabling sub-tread formation in other areas.
Solution Approach 2:
The patent uses composite materials by combining tungsten and polysilicon within the same liner structure. This composite approach allows the liner to exhibit both the structural strength of tungsten in critical regions and the etch-selectivity of polysilicon in regions intended for removal, thereby achieving both mechanical integrity and manufacturability of thin sub-treads simultaneously.
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 a thinner liner and eliminates the need for additional process steps, such as gap filling, while effectively increasing the number of word line contacts per unit area.
Implementation Method 1
A liner is deposited within a cavity... doping a first portion of the liner; converting a second portion of the liner into a second liner material based at least in part on doping the first portion
Data Source
AI summary
Methods, systems, and devices for staircase formation in a memory array are described. A liner composed of a first liner material may be deposited on a tread and a first portion of the liner may be doped. After doping the first portion of the liner, a second portion of the liner may be converted into a second liner material using a chemical process. After converting the second portion of the liner into the second liner material, the first portion of the liner material may be removed so that a subsequent removal process can expose a first sub-tread. After exposing the first sub-tread, the second portion of the liner may be removed so that a second sub-tread is exposed.