Vialess Magnetic Memory Structure and Manufacturing Method
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Solution Overview
Problem
The manufacturing of magnetic random access memory (MRAM) faces challenges such as via hole etching limitations, which can result in shorted or open connections between the magnetic tunnel junction (MTJ) and the upper metal line, and requires multiple steps and thick photoresist/hard mask for fine patterning, making the process time-consuming and expensive.
Innovation Solution
A via-less method is employed where a dielectric layer protects the MTJ sidewall, and a different dielectric layer covers it, allowing direct connection of the bit line to the top electrode without a via, using specific etching processes and materials like silicon nitride and oxide to prevent shorting and ensure reliable connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If a via hole is used to connect the top electrode to the upper metal line, then the connection is established, but the memory element size must be larger than the via size, limiting further miniaturization
Solution Approach 1:
The invention extracts and eliminates the via hole structure from the memory cell architecture. By directly connecting the top electrode to the upper metal line without an intervening via hole, the patent removes the size constraint imposed by via dimensions, enabling further miniaturization of the memory cell while reducing structural complexity
Solution Approach 2:
Instead of using a via hole to bridge the gap between the top electrode and upper metal line, the invention inverts the approach by allowing the top electrode to directly contact the upper metal line. This inversion of the conventional connection method eliminates the via hole entirely, solving the miniaturization limitation
2Reliability
If the bottom of the via hole does not reach the top electrode during etching, then the top electrode is protected, but an open connection occurs between the MTJ and upper metal line
Solution Approach 1:
The invention removes the via hole structure that causes the etching depth control problem. By eliminating the via hole, there is no need to control etching depth to precisely reach the top electrode, as the top electrode directly contacts the upper metal line, thereby eliminating open connection risks
Solution Approach 2:
The patent applies protection layers to the top electrode before the etching process. This preliminary protective action ensures that even if etching conditions vary, the top electrode remains protected while the direct connection geometry ensures contact is maintained, preventing open connections
3Reliability
If the via hole etching reaches the barrier layer, then the connection to MTJ is established, but the pinned layer and free layer become shorted
Solution Approach 1:
The invention extracts and eliminates the via hole structure that causes layer shorting. By removing the via hole, there is no deep etching process that could breach the barrier layer and short the pinned and free layers, while still achieving reliable connection through direct contact geometry
Solution Approach 2:
The patent applies protection layers to the top electrode and barrier layer before etching. This preliminary protective action prevents the etching process from damaging the barrier layer and causing layer shorting, while ensuring the top electrode remains protected
4Reliability
If a thick top electrode is used to ensure via contact, then connection reliability improves, but fine patterning becomes difficult requiring thick photoresist and hard mask
Solution Approach 1:
The invention removes the via hole structure that necessitates a thick top electrode. By eliminating the via, the top electrode can be made thin while still achieving reliable connection through direct contact, thereby enabling fine patterning with thin photoresist and hard mask
Solution Approach 2:
Instead of thickening the top electrode to ensure via contact, the invention inverts the approach by eliminating the via entirely and using direct contact geometry. This allows the top electrode to remain thin, facilitating fine patterning processes
5Manufacturing precision
If multiple steps are used to build MTJ with separate via formation, then manufacturing precision is maintained, but manufacturing time and expense increase
Solution Approach 1:
The invention merges the MTJ formation and connection formation into a single integrated process. By eliminating the separate via hole formation step and using direct contact geometry, multiple manufacturing steps are combined, reducing manufacturing time and expense while maintaining precision through protection layers
Solution Approach 2:
The protection layers applied during MTJ formation serve multiple functions: they protect the top electrode during etching, ensure direct contact geometry is maintained, and prevent layer shorting. This multi-functionality eliminates the need for separate via formation steps, improving productivity
Data Source
AI summary
A method of manufacturing a magnetic memory cell, including a magnetic tunnel junction (MTJ), includes using silicon nitride layer and silicon oxide layer to form a trench for depositing copper to be employed for connecting the MTJ to other circuitry without the use of a via.