Tunnel Barrier Layer Formation for MRAM
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Solution Overview
Problem
Current magnetic random-access memory (MRAM) technologies face challenges in achieving high density, low power consumption, and non-volatile properties, particularly due to issues with the tunnel barrier layer (TBL) in magnetic tunnel junction (MTJ) elements, such as poor adhesion, high pinhole density, and suboptimal stoichiometric ratios of oxygen to metal atoms, which affect the perpendicular magnetic anisotropy and tunnel magnetoresistance (TMR) ratio.
Innovation Solution
The method involves forming a tunnel barrier layer (TBL) by a sequence of DC sputter-deposition and oxygen treatment processes, ensuring good adhesion and stoichiometric integration, including a light oxygen treatment to enhance perpendicular magnetic anisotropy and a heavy oxygen treatment to increase the TMR ratio, thereby improving the performance of the MTJ stack.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional tunnel barrier layer is formed by simple sputter deposition, then the formation process is simple and fast, but the adhesion is poor and pinhole density is high
Solution Approach 1:
The tunnel barrier layer formation process is segmented into multiple distinct stages: initial sputter deposition to form the base layer, followed by oxygen plasma treatment to improve adhesion and reduce pinholes, then additional sputter deposition to achieve desired thickness, and finally annealing to optimize stoichiometry. Each stage addresses specific requirements that cannot be met by a single conventional deposition process.
Solution Approach 2:
Oxygen plasma treatment is applied as a preliminary action before completing the tunnel barrier layer formation. This preliminary oxidation step modifies the surface properties of the deposited metal layer, improving adhesion to underlying layers and reducing pinhole formation before the final layer structure is completed.
2Reliability
If the oxygen to metal atom ratio is not optimized, then the manufacturing process is simpler, but the TMR effect is reduced
Solution Approach 1:
The oxygen to metal atom ratio is precisely controlled by changing process parameters including oxygen plasma power, treatment duration, annealing temperature, and annealing atmosphere composition. These parameter adjustments optimize the stoichiometry of the tunnel barrier layer to maximize the TMR effect while maintaining manufacturing feasibility.
Solution Approach 2:
Oxygen plasma is used as a strong oxidizing environment during the formation process to accelerate oxidation of the metal layer and achieve the desired oxide stoichiometry. This controlled accelerated oxidation ensures the tunnel barrier layer has the correct oxygen content for optimal TMR performance.
3Area of moving object
If the tunnel barrier layer is made thinner to increase density, then the storage density improves, but the adhesion and electrical insulation deteriorate
Solution Approach 1:
Even at reduced thicknesses, the tunnel barrier layer maintains proper adhesion and insulation by controlling deposition parameters (power, pressure, gas flow) and applying post-deposition oxygen plasma treatment and annealing. These parameter optimizations ensure that thin layers achieve the same quality metrics as thicker layers.
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 results in a semiconductor memory structure with improved TMR ratio and reduced pinhole density, enhancing the magnetic properties and data storage capabilities of MRAM cells.
Implementation Method 1
A first metallic film is formed by a DC sputter-deposition followed by a light oxygen treatment. A second metallic oxide film is formed over the first metallic oxide film by a RF sputter-deposition
Implementation Method 2
A first metallic film is formed by a DC sputter-deposition followed by a light oxygen treatment
Data Source
AI summary
A method for forming a semiconductor memory structure is provided. The method includes following operations. An interlayer is formed over a first ferromagnetic layer, wherein forming the interlayer includes following operations. A first metal film is formed by sputtering a first target material. A first oxygen treatment is conducted to the first metal film to form a first metal oxide film. A second metal oxide film is formed over the first metal oxide film by sputtering a second target material different from the first target material. A second metal film is formed by sputtering a third target material. A second oxygen treatment is conducted to the second metal film to form a third metal oxide film.