Gradient Silicon Oxynitride Encapsulation for MRAM Thermal Stability
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Solution Overview
Problem
The existing encapsulation layers in MRAM devices, such as silicon nitride, are inadequate in blocking boron diffusion and can degrade the magnetic materials during elevated temperature processes, leading to performance degradation.
Innovation Solution
A semiconductor memory structure with a magnetic tunneling junction (MTJ) stack surrounded by an encapsulation layer comprising an outer silicon oxynitride layer and an inner silicon oxynitride layer with a gradient oxygen concentration, formed by depositing a silicon-rich SiN layer and subjecting it to an oxygen plasma treatment, to reduce nitrogen damage and improve thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a stoichiometric silicon nitride (Si3N4) layer is used as an encapsulation layer, then the MTJ stack is protected from damage or contamination, but the ability to block boron diffusion is insufficient and nitrogen species can diffuse to attack magnetic materials and MgO barrier layer
Solution Approach 1:
The patent employs a composite encapsulation layer structure consisting of multiple layers with different compositions: an outer silicon oxide layer, an intermediate silicon oxynitride layer, and an inner silicon nitride layer. This composite structure combines the protective properties of silicon nitride with the boron-blocking capability of silicon oxide, while the gradient oxynitride intermediate layer provides a transition zone that prevents nitrogen species diffusion. The composite material approach resolves the contradiction by integrating multiple materials' advantages to simultaneously achieve protection and blocking functions.
Solution Approach 2:
The encapsulation layer is designed with spatially varying composition and properties: the outer silicon oxide layer provides boron diffusion blocking, the intermediate oxynitride layer provides a gradient transition to reduce nitrogen species diffusion, and the inner silicon nitride layer provides direct protection to the MTJ stack. Each layer is optimized for its specific local function, creating a gradient structure that addresses different harmful factors at different locations within the encapsulation system.
2Productivity
If elevated temperature processes such as annealing are applied, then the MRAM device manufacturing is completed, but the degradation of electrical performance worsens due to nitrogen species diffusion from the encapsulation layer
Solution Approach 1:
The encapsulation layer is designed with a preliminary gradient oxynitride intermediate layer that is formed before the elevated temperature annealing processes. This intermediate layer with its gradient composition (higher oxygen content near the MTJ stack) is prepared in advance to prevent nitrogen species diffusion during subsequent thermal processes. The preliminary structure prevents performance degradation before it can occur during manufacturing.
Solution Approach 2:
The gradient silicon oxynitride intermediate layer acts as an intermediary barrier between the silicon nitride encapsulation layer and the MTJ stack. During elevated temperature processes, this intermediate layer mediates by blocking the diffusion path of nitrogen species while allowing the thermal processing to proceed. The gradient composition creates a diffusion barrier that protects the magnetic materials and MgO barrier layer from nitrogen attack during annealing and other thermal processes.
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 gradient oxygen concentration in the encapsulation layer effectively reduces oxygen reaction with the MTJ stack, enhancing the MRAM device's thermal stability and electrical performance by blocking undesired species diffusion and maintaining high MR ratio and coercivity.
Implementation Method 1
subjecting it to an oxygen plasma treatment
Implementation Method 2
gradient oxygen concentration in the encapsulation layer effectively reduces oxygen reaction with the MTJ stack, enhancing the MRAM device's thermal stability
Implementation Method 3
the ability to block boron diffusion of the crystalline Si3N4 layer may not be satisfactory
Implementation Method 4
The MRAM device may be based on a tunneling magneto-resistance (TMR) effect wherein a stack of layers has a configuration in which two ferromagnetic layers are separated by a thin non-magnetic dielectric layer
Data Source
AI summary
A semiconductor memory structure includes a substrate, a magnetic tunneling junction (MTJ) stack disposed on the substrate, and an encapsulation layer surrounding the MTJ stack. The encapsulation layer comprises an outer silicon oxynitride layer with a composition of SiOx1Ny1 and an inner silicon oxynitride layer with a composition of SiOx2Ny2, wherein x1/y1>x2/y2.