SiON MTJ Encapsulation for Sidewall Protection During Annealing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Magnetic tunnel junctions (MTJs) in MRAM and spin-torque MRAM devices are susceptible to sidewall damage during etching and deposition processes, especially under high temperature annealing conditions, which affects the magnetoresistive ratio and integration into CMOS technology for sub-100 nm device sizes.
Innovation Solution
A silicon oxynitride (SiON) encapsulation layer is conformally deposited using plasma-enhanced chemical vapor deposition (PECVD) with a controlled nitrous oxide (N2O):silane flow rate ratio to minimize exposure to reactive species, followed by a second encapsulation layer to completely fill gaps and a chemical mechanical polish to ensure top surfaces are coplanar with MTJ nanopillars.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional encapsulation layer is deposited to electrically isolate MTJs, then electrical isolation is achieved, but sidewall damage occurs during deposition and high temperature annealing
Solution Approach 1:
A silicon oxynitride (SiON) layer is deposited as an intermediary protective layer between the MTJ sidewalls and the subsequent encapsulation layer. This SiON layer acts as a mediator that protects the MTJ sidewalls from chemical and physical damage during the deposition of the encapsulation layer and during high temperature annealing processes, while still allowing the encapsulation layer to provide electrical isolation.
Solution Approach 2:
The silicon oxynitride protective layer is deposited before the main encapsulation layer to preemptively protect the MTJ sidewalls. This preliminary protective action ensures that when the encapsulation layer deposition and subsequent high temperature annealing (around 400°C for 30 minutes) occur, the MTJ sidewalls are already shielded from harmful effects.
2Temperature
If the encapsulation layer is deposited to protect MTJ sidewalls during high temperature annealing, then thermal stability is improved, but the magnetoresistive ratio may be affected by sidewall damage from deposition processes
Solution Approach 1:
The silicon oxynitride layer serves as a protective intermediary that is deposited under controlled conditions to minimize sidewall damage. This protective layer allows subsequent high temperature annealing (around 400°C for 30 minutes) to proceed without damaging the MTJ sidewalls, thereby maintaining the magnetoresistive ratio while achieving thermal stability.
Solution Approach 2:
The deposition parameters of the silicon oxynitride layer are carefully controlled, including the N2O:silane flow rate ratio, to optimize both the protective capability and the minimal impact on the magnetoresistive ratio. By adjusting these parameters, the protective layer provides thermal stability during annealing while minimizing sidewall damage that would affect the magnetoresistive ratio.
3Reliability
If a conformal encapsulation layer is deposited to electrically isolate adjacent MTJs, then electrical isolation is achieved, but gap filling may be insufficient for sub-100 nm device sizes
Solution Approach 1:
The encapsulation process is segmented into multiple steps: first depositing a silicon oxynitride protective layer, then depositing the main encapsulation layer. This segmentation allows each layer to serve its specific function - the SiON layer provides protection and initial gap filling, while the subsequent encapsulation layer provides complete electrical isolation and gap filling for sub-100 nm device sizes.
Solution Approach 2:
The silicon oxynitride layer acts as an intermediary that partially fills gaps and provides a foundation for the subsequent encapsulation layer. This intermediate structure ensures that when the final encapsulation layer is deposited, complete gap filling and electrical isolation are achieved for closely spaced sub-100 nm MTJ devices.
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 solution significantly improves the magnetoresistive ratio by reducing sidewall damage and providing thermal stability, dielectric, and moisture resistance, enhancing the performance of MTJ nanopillars in MRAM devices integrated into CMOS technology.
Implementation Method 1
a first encapsulation layer that is silicon oxynitride (SiOXNY), where x and y are both>0, is conformally deposited on the substrate and on the plurality of MTJ nanopillars and their sidewalls to partially fill the gaps by a plasma enhanced CVD (PECVD) method
Data Source
AI summary
A plasma enhanced chemical vapor deposition (PECVD) method is disclosed for forming a SiON encapsulation layer on a magnetic tunnel junction (MTJ) sidewall that minimizes attack on the MTJ sidewall during the PECVD or subsequent processes. The PECVD method provides a higher magnetoresistive ratio for the MTJ than conventional methods after a 400° C. anneal. In one embodiment, the SiON encapsulation layer is deposited using a N2O:silane flow rate ratio of at least 1:1 but less than 15:1. A N2O plasma treatment may be performed immediately following the PECVD to ensure there is no residual silane in the SiON encapsulation layer. In another embodiment, a first (lower) SiON sub-layer has a greater Si content than a second (upper) SiON sub-layer. A second encapsulation layer is formed on the SiON encapsulation layer so that the encapsulation layers completely fill the gaps between adjacent MTJs.