MTJ Hard Mask Dimension Control for MRAM Data Retention
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Solution Overview
Problem
In semiconductor memory devices, particularly MRAM, the variation in taper angle of magnetic tunnel junction (MTJ) elements due to etching and chemical mechanical polishing processes leads to instability in magnetic properties, affecting data retention and requiring an increasing number of dummy cells, which reduces the effective chip area.
Innovation Solution
By adjusting the dimensions of the hard mask layer, specifically widening the hard mask layer in central portions of the MTJ elements and maintaining a consistent taper angle, the variation in taper and magnetic properties is controlled, reducing the need for dummy cells and stabilizing data retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the hard mask layer dimension is increased in central portions of MTJ elements, then the taper angle variation is reduced and data retention is improved, but the manufacturing process complexity increases
Solution Approach 1:
The patent applies local quality by making the hard mask layer dimension position-dependent. Specifically, the hard mask layer has a first dimension in central portions of MTJ elements and a second dimension in other portions, with the first dimension being larger than the second. This localized dimensional variation compensates for taper angle variations that occur during etching and CMP processes, thereby improving data retention without requiring complete redesign of the entire manufacturing process.
2Area of stationary object
If the number of dummy cells is reduced to increase chip area efficiency, then the effective chip area increases, but the stability of critical dimension (CD) of memory cells deteriorates
Solution Approach 1:
The patent applies parameter changes by modifying the hard mask layer dimension parameter based on position. The hard mask layer is designed with a first dimension in central portions and a second dimension in other portions, where the first dimension is larger. This parameter variation compensates for CD instability that would normally require numerous dummy cells, allowing reduction of dummy cells while maintaining manufacturing precision.
3Reliability
If the hard mask layer dimension is uniformly increased across all MTJ elements, then the taper angle is reduced, but the leakage magnetic field increases due to excessive dimension
Solution Approach 1:
The patent applies local quality by making the hard mask layer dimension position-dependent. Specifically, the hard mask layer has a first dimension in central portions of MTJ elements and a second dimension in other portions, with the first dimension being larger than the second. This localized dimensional variation compensates for taper angle variations that occur during etching and CMP processes, thereby improving data retention without requiring complete redesign of the entire manufacturing process.
Data Source
AI summary
According to one embodiment, a semiconductor memory device comprises a memory cell array. The memory cell array has a plurality of magnetic tunnel junction (MTJ) elements. Each of the MTJ elements has a first magnetic layer, a second magnetic layer and a non-magnetic layer therebetween, and a hard mask layer is arranged above the second magnetic layer. The plurality of MTJ elements have a first MTJ element having a first hard mask layer and a second MTJ element having a second hard mask layer, and a dimension of, the first hard mask layer is greater than that of the second hard mask layer.