MRAM Pillar Redeposition Control via Dielectric Sleeve
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Solution Overview
Problem
Metallic redeposition during the etching process of Magnetic Tunnel Junction (MTJ) memory devices in semiconductor Back-End-Of-Line (BEOL) memories can short the magnetic layers, making the devices inoperable due to redeposition material coating the sidewalls of the memory element.
Innovation Solution
The implementation of methods and structures to reduce metallic redeposition on MTJ barrier layer sidewalls, including forming metal studs on top of MTJ landing pads, patterning MTJ and bottom electrodes separately, dividing the etching process into phases, and using a hard mask with a dielectric sleeve to protect the sidewalls from redeposition material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional lithography and dry etching process are used to fabricate MTJ memory device, then the manufacturing process is simple and efficient, but metallic redeposition material coats the patterned pillar sidewalls causing electrical shorting
Solution Approach 1:
A dielectric layer is introduced as an intermediary material between the metal layers and etching environment. This dielectric layer prevents direct contact between the metallic redeposition material and the MTJ barrier layer sidewalls, thereby preventing electrical shorting while allowing the conventional etching process to continue
Solution Approach 2:
The dielectric layer is deposited in advance before the etching process to preemptively protect the sidewalls from redeposition. This preliminary protective action prevents the harmful effect of metallic redeposition before it can occur during the etching process
2Manufacturing precision
If ion milling or high biased reactive ion etching is used to etch MTJ layers, then the etching process is effective in removing material mechanically, but the mechanically etched material is easily redeposited on sidewalls
Solution Approach 1:
The dielectric layer serves as a mediator that intercepts the mechanically etched material during ion milling or high biased reactive ion etching, preventing its redeposition on the sidewalls while allowing the etching process to proceed effectively
Solution Approach 2:
The harmful redeposition material is extracted from the problematic location (sidewalls) by being trapped in the dielectric layer, separating it from the MTJ barrier layer and preventing electrical shorting
3Ease of manufacture
If the bottom electrode layer is etched away completely, then the landing pad metal is exposed to etching ambient, but the exposed metal can be sputtered out and redeposited on sidewall
Solution Approach 1:
The dielectric layer acts as a protective intermediary that remains on the sidewalls even after the bottom electrode is etched away, preventing the sputtered metal from redepositing on the sidewalls while allowing complete etching of the bottom electrode layer
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
Prevents electrical shorting of the magnetic layers by minimizing exposure of metal surfaces to the etching ambient, ensuring a smooth surface for patterning, and effectively protecting the sidewalls from redeposition material, thereby maintaining the functionality of the memory devices.
Implementation Method 1
A first embodiment forms metal studs on top of the MTJ landing pads in a dielectric layer that otherwise covers the exposed metal surfaces on the wafer to prevent exposing the metal to the MTJ etching ambient
Implementation Method 2
The MTJ layers and bottom electrode are etched conventionally with ion milling or high biased reactive ion etching where elements are mainly removed mechanically
Implementation Method 3
After the bottom electrode layer is etched away, previously deposited metal in the MTJ landing pad and peripheral circuits is exposed to the etching ambient and can be sputtered out and redeposited on the sidewall
Implementation Method 4
The metal studs provide the electrical connection between the bottom electrodes and the landing pads
Data Source
AI summary
Methods and structures are described to reduce metallic redeposition material in the memory cells, such as MTJ cells, during pillar etching. One embodiment forms metal studs on top of the landing pads in a dielectric layer that otherwise covers the exposed metal surfaces on the wafer. Another embodiment patterns the MTJ and bottom electrode separately. The bottom electrode mask then covers metal under the bottom electrode. Another embodiment divides the pillar etching process into two phases. The first phase etches down to the lower magnetic layer, then the sidewalls of the barrier layer are covered with a dielectric material which is then vertically etched. The second phase of the etching then patterns the remaining layers. Another embodiment uses a hard mask above the top electrode to etch the MTJ pillar until near the end point of the bottom electrode, deposits a dielectric, then vertically etches the remaining bottom electrode.