STT-MRAM Alignment Mark Trench Residual Metal Removal
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Solution Overview
Problem
Tantalum oxide by-products from the bottom electrode of spin-transfer torque magneto-resistance random access memory (STT-MRAM) devices are difficult to remove using conventional etchant gases, leading to defects in mass production.
Innovation Solution
A semiconductor memory device fabrication method that includes forming a substrate with a memory cell region and an alignment mark region, depositing a dielectric layer, creating conductive vias and an alignment mark trench, and depositing a bottom electrode metal layer that is polished to leave a residual metal stack in the trench, allowing for improved alignment and reduced defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional chlorine-based or fluorine-based etchant gas is used to remove tantalum oxide by-products, then the etching process is simple and cost-effective, but the tantalum oxide by-products are difficult to remove completely, causing serious defects in mass production
Solution Approach 1:
The patent changes the chemical composition parameter of the etchant from conventional chlorine-based or fluorine-based gases to a nitrogen trifluoride (NF3) and oxygen (O2) mixed gas system. This parameter change enables complete removal of tantalum oxide by-products while maintaining process simplicity, thereby improving reliability without significantly increasing manufacturing complexity
Solution Approach 2:
The patent employs a composite etchant system combining nitrogen trifluoride and oxygen gases. This composite approach leverages the complementary properties of both gases: NF3 provides effective etching capability while oxygen enhances the removal of tantalum oxide by-products, achieving complete clearance and eliminating defects
2Manufacturing precision
If an alignment mark (AM) is formed before the deposition of the magnetic tunnel junction (MTJ) layer and the top electrode metal layer, then alignment for subsequent MTJ layer etching is facilitated, but residual metal stacks remain in the alignment mark trench, causing alignment issues
Solution Approach 1:
The patent performs preliminary cleaning of the alignment mark trench using NF3/O2 plasma etching before subsequent deposition steps. This preliminary action removes potential residual metals that would interfere with alignment, ensuring that when the alignment mark is formed, it provides accurate alignment references without contamination-induced defects
Solution Approach 2:
The NF3/O2 plasma process acts as an intermediary treatment between metal deposition and alignment mark formation. This intermediary step effectively removes residual metals from the alignment mark trench, preventing them from interfering with the alignment function while allowing the alignment mark to be formed with high precision
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 method enables effective removal of residual metal stacks in the alignment mark trench, reducing defects and improving production yield by ensuring precise alignment and positioning of subsequent layers in STT-MRAM devices.
Implementation Method 1
A bottom electrode metal layer is formed on the memory cell region and the alignment mark region. The bottom electrode metal layer conformally covers a sidewall and a bottom surface of the alignment mark trench.
Data Source
AI summary
The disclosure provides a semiconductor memory device including a substrate having a memory cell region and an alignment mark region; a dielectric layer covering the memory cell region and the alignment mark region; conductive vias in the dielectric layer within the memory cell region; an alignment mark trench in the dielectric layer within the alignment mark region; and storage structures disposed on the conductive vias, respectively. Each of the storage structures includes a bottom electrode defined from a bottom electrode metal layer, a magnetic tunnel junction (MTJ) structure defined from an MTJ layer, and a top electrode. A residual metal stack is left in the alignment mark trench. The residual metal stack includes a portion of the bottom electrode metal layer and a portion of the MTJ layer.