CMP Stop Layer for Uniform MRAM Top Electrode Thickness
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Solution Overview
Problem
The fabrication of small-sized magnetoresistive random-access memory (MRAM) devices faces challenges in achieving high yield due to the disparity in top electrode thicknesses caused by photoresist consumption during plasma etching, leading to electrical opens and yield loss, especially for devices below 60 nm in size.
Innovation Solution
The introduction of a CMP stop layer and a sacrifice layer between the photoresist hard mask pattern and the top electrode, followed by a plasma etch process, ensures that the top electrode thickness remains consistent across different device sizes, allowing for easier connection with a common metal contact and eliminating electrical opens.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If photolithography and plasma etch are used to pattern MTJ devices, then device separation and patterning are achieved, but smaller size devices have less top electrode left due to photoresist consumption, resulting in non-planar surfaces and electrical opens
Solution Approach 1:
A CMP stop layer is introduced as an intermediary between the photoresist hard mask and the top electrode. This stop layer serves as a mediator that prevents direct damage to the top electrode during plasma etching while still allowing the patterning process to proceed effectively.
Solution Approach 2:
The CMP stop layer is deposited beforehand to provide preliminary protection to the top electrode before the plasma etching process begins. This preliminary action ensures that even if photoresist is consumed during etching, the top electrode remains intact and maintains uniform thickness.
2Productivity
If smaller size MTJ devices are fabricated, then device density increases, but top electrode thickness becomes non-uniform due to differential photoresist consumption, leading to yield loss
Solution Approach 1:
The CMP stop layer acts as a protective intermediary that decouples the photoresist consumption from the top electrode integrity. During plasma etching, the stop layer absorbs the differential consumption effects, ensuring that smaller devices do not suffer from excessive photoresist loss that would otherwise compromise the top electrode thickness.
Solution Approach 2:
The CMP stop layer provides beforehand cushioning or protection to the top electrode against the harmful effects of differential photoresist consumption. This protective layer ensures that even when photoresist is consumed more quickly on smaller devices, the top electrode thickness remains uniform across all device sizes.
3Manufacturing precision
If photoresist hard mask is used for patterning, then pattern transfer is achieved, but top electrode damage occurs on smaller devices, creating electrical opens
Solution Approach 1:
The CMP stop layer serves as a protective intermediary positioned between the photoresist hard mask and the top electrode. During the plasma etching process, this stop layer absorbs the harmful effects of photoresist consumption and prevents direct damage to the top electrode, thereby eliminating electrical opens while maintaining accurate pattern transfer.
4Productivity
If non-planar top surface is created by differential electrode thickness, then smaller devices are etched more aggressively, but final top metal contact cannot connect properly, resulting in open devices
Solution Approach 1:
The CMP stop layer is deposited in advance to establish a uniform reference plane before plasma etching begins. This preliminary action ensures that even though smaller devices may be etched more aggressively, the top electrode thickness remains consistent across all device sizes, creating a planar surface that facilitates proper top metal contact connection.
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 method enhances the yield of small-sized MRAM devices by maintaining uniform top electrode heights, preventing electrical opens and improving the fabrication process for sub-60 nm devices, thereby addressing the yield loss issues in existing technologies.
Implementation Method 1
plasma etch such as reactive ion etching (RIE), ion beam etching (IBE) or their combination are usually involved
Implementation Method 2
By choosing proper slurries during the following CMP process, any remaining sacrifice patterns are completely removed, stopping on the CMP stop layer
Data Source
AI summary
An array, such as an MRAM (Magnetic Random Access Memory) array formed of a multiplicity of layered thin film devices, such as MTJ (Magnetic Tunnel Junction) devices, can be simultaneously formed in a multiplicity of horizontal widths in the 60 nm range while all having top electrodes with substantially equal thicknesses and coplanar upper surfaces. This allows such a multiplicity of devices to be electrically connected by a common conductor without the possibility of electrical opens and with a resulting high yield.