Vertical Transistor Memory Cell Fabrication with Self-Aligned Metal Plugs
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Solution Overview
Problem
Existing memory technologies face challenges in forming arrays of vertical transistors and memory cells, particularly in maintaining the non-volatile state of ferroelectric capacitors during read operations, as the act of reading can reverse the polarization state, requiring immediate rewriting of the memory cell.
Innovation Solution
A method is developed to form an array of vertical transistors and memory cells, involving the formation of pillars with sacrificial material, intervening layers, and conductive gate lines, followed by the creation of metal plugs and storage devices, allowing for self-aligned and efficient construction of memory cells that minimize the disruption of polarization states during read operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ferroelectric capacitor memory cells are used, then non-volatile data storage is achieved, but the act of reading the memory state reverses the polarization state requiring immediate rewriting
Solution Approach 1:
The memory cell is divided into two separate transistors: a first transistor for writing data to the ferroelectric capacitor and a second transistor for reading data from it. This segmentation allows the write and read operations to be independently controlled, enabling read operations without necessarily triggering write operations that would reverse the polarization state, thus maintaining data stability while improving read efficiency.
2Ease of manufacture
If vertical transistor arrays are formed using conventional methods, then manufacturing complexity is reduced, but manufacturing precision and alignment accuracy deteriorate
Solution Approach 1:
A sacrificial material layer is deposited and patterned before forming the vertical transistor structures. This sacrificial layer serves as a preliminary structure that defines the precise locations where metal plugs will be formed. The sacrificial material is later removed to create cavities for the metal plugs, ensuring accurate alignment without requiring complex real-time alignment processes during the main fabrication steps.
Solution Approach 2:
The sacrificial material acts as an intermediary element during fabrication. It is temporarily present to enable precise positioning of metal plugs and subsequent transistor structures, then removed after serving its alignment function. This intermediary approach simplifies the overall manufacturing process while maintaining high precision, as the sacrificial material provides a straightforward template for feature placement.
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 enables the formation of stable and efficient memory cells that maintain non-volatile states without immediate rewriting, improving the retention of data in memory arrays by reducing the impact of read operations on polarization states.
Implementation Method 1
One type of non-volatile capacitor is a ferroelectric capacitor which has ferroelectric material as at least part of the insulating material. Ferroelectric materials are characterized by having two stable polarized states and thereby can comprise programmable material of a capacitor and/or memory cell.
Implementation Method 2
Field effect transistors may also include additional structure, for example a reversibly programmable charge-storage region as part of the gate construction between the gate insulator and the conductive gate.
Data Source
AI summary
A method used in forming an array of vertical transistors comprises forming pillars individually comprising an upper source/drain region, a channel region vertically below the upper source/drain region, and sacrificial material above the upper source/drain region. Intervening material is about the sacrificial material of individual of the pillars. The intervening material and the sacrificial material comprise different compositions relative one another. Horizontally-elongated and spaced conductive gate lines are formed individually operatively aside the channel region of the individual pillars. The sacrificial material is removed to expose the upper source/drain region of the individual pillars and thereby form an opening in the intervening material directly above the upper source/drain region of the individual pillars. Metal material is formed in individual of the openings directly against the upper source/drain region of the individual pillars and atop the intervening material laterally outside of the openings. The metal material that is atop the intervening material interconnects the metal material that is in the individual openings. The metal material is removed back to have an uppermost surface that is no higher than an uppermost surface of the intervening material and to disconnect it from interconnecting the metal material that is in the individual openings and thereby form a laterally-isolated individual metal-material plug in the individual openings.