Bilayer Memory Cell Encapsulation for Plasma-Safe Hermetic Sealing
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Solution Overview
Problem
Chalcogenide memory cells in 3D crosspoint memory arrays face challenges with hermetic encapsulation, as existing deposition methods like PECVD and PEALD can damage the materials and result in non-ideal conformality, especially in high aspect ratio trenches, limiting the ability to protect the cells during subsequent nanofabrication steps.
Innovation Solution
A bilayer encapsulation process is employed, where a thin layer of material is deposited over the memory cell followed by a thicker layer to form a hermetic seal, using PECVD for the inner layer and PEALD for the outer layer, protecting the cell from plasma damage and improving conformality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PECVD or PEALD deposition methods are used to encapsulate chalcogenide memory cells, then hermetic encapsulation is achieved, but the memory cell materials are damaged and conformality is poor
Solution Approach 1:
The encapsulation process is segmented into multiple sequential deposition steps: first a thin layer (5-10 nm) of silicon nitride is deposited via PECVD, followed by a thicker layer (20-50 nm) of silicon nitride deposited via PEALD. This segmentation allows each layer to perform its function optimally - the first layer provides initial protection with good conformality, while the second layer provides hermetic sealing with improved conformality and reduced plasma damage.
Solution Approach 2:
The first PECVD silicon nitride layer is deposited as a preliminary protective layer before the main PEALD encapsulation layer. This preliminary layer protects the sensitive chalcogenide materials from direct exposure to the more damaging PEALD plasma, while still allowing the subsequent PEALD layer to achieve hermetic encapsulation with better conformality.
2Reliability
If a single thick layer is deposited to protect memory cells, then hermetic seal is formed, but plasma damage occurs and conformality deteriorates
Solution Approach 1:
The single thick encapsulation layer is segmented into two sequential layers with different deposition methods and thicknesses. The first layer (5-10 nm) uses PECVD with lower plasma power to minimize damage, while the second layer (20-50 nm) uses PEALD to complete the hermetic seal. This segmentation distributes the protective function across two gentler processes rather than one aggressive thick-layer deposition.
Solution Approach 2:
The first PECVD silicon nitride layer serves as a cushioning protective layer deposited beforehand to shield the sensitive chalcogenide memory cell materials from the harmful effects of the subsequent PEALD plasma. This preliminary cushioning layer absorbs the plasma damage that would otherwise directly affect the memory cell materials.
3Area of stationary object
If deposition is performed in high aspect ratio trenches, then encapsulation coverage is achieved, but conformality is non-ideal
Solution Approach 1:
The encapsulation deposition is segmented into two sequential steps with different deposition techniques. The first PECVD step provides initial conformal coverage of the high aspect ratio trench walls, and the second PEALD step improves conformality while achieving complete hermetic coverage. Each segmented step contributes to progressive improvement in conformality and coverage.
Solution Approach 2:
The deposition parameters are changed between the two layers - the first layer uses PECVD parameters optimized for initial coverage with lower plasma power, while the second layer uses PEALD parameters optimized for improved conformality and hermetic sealing. This parameter change allows optimization for different priorities in the sequential process.
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
The bilayer encapsulation effectively protects the memory cells from plasma damage and enhances conformality, allowing for the use of PEALD-deposited SiN as the outer layer, thereby improving the reliability and performance of the memory cells during nanofabrication.
Implementation Method 1
forming a first inner layer of material over the memory cell and a second outer layer of material over the first inner layer of material
Implementation Method 2
The bilayer may protect the memory cell (or other device) during subsequent nanofabrication steps
Data Source
AI summary
A memory device comprising a memory cell comprising a storage element including a phase change memory; and a bilayer formed on a first side and a second side of the memory cell, the bilayer including an inner layer comprising a first nitride and an outer layer comprising a second nitride.