Al-Sc Etch Stop Layer for Precise AlScN Film Patterning
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Solution Overview
Problem
The challenge in semiconductor processing is finding a CMOS-compatible metal etch stop that can effectively prevent over- or under-etching during the etching of AlScN films, which are highly resistant and difficult to etch, especially when used in conjunction with AlN and other process flows, requiring a material with low resistivity and high corrosion resistance.
Innovation Solution
The use of an Al—Sc etch stop with a strong covalent bond and low resistivity, specifically Al3Sc, which forms a robust etch stop layer that is resistant to inductively coupled plasma chlorine-based etches and can operate at elevated temperatures, allowing for precise control of etching and pattern formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If AlScN films are etched using aggressive etch processes, then etching speed improves, but underlying metal surfaces are damaged or completely etched away
Solution Approach 1:
The patent introduces SiO2 as an intermediary etch stop layer between the AlScN film and the underlying metal surface. This mediator allows the aggressive etch process to proceed at high speed while the SiO2 layer absorbs the excess etching, preventing damage to the metal surface. The SiO2 layer is specifically designed to be etched at a controlled rate that is slower than AlScN but faster than the underlying metals.
Solution Approach 2:
The SiO2 etch stop layer is deposited in advance before the AlScN film is formed. This preliminary action creates a protective buffer that will stop the etching process before it reaches the metal surface, allowing subsequent etching to proceed aggressively without risking metal surface integrity.
2Reliability
If Sc atomic percent increases in AlScN system, then material properties improve, but etching difficulty increases exponentially
Solution Approach 1:
The SiO2 etch stop layer serves as a mediator that decouples the etching difficulty of high-Sc AlScN from the underlying process. By positioning SiO2 between AlScN and the etchant, the system allows aggressive etching of AlScN (even with high Sc content) while SiO2 provides a controlled stopping point, maintaining etching efficiency despite increased material performance.
Solution Approach 2:
The patent changes the etching parameter hierarchy by introducing a third material layer with intermediate etch resistance. Instead of directly etching AlScN down to metal, the process now etches through AlScN to SiO2, then stops at SiO2. This parameter change in the film stack composition allows high-Sc AlScN to be etched efficiently with the SiO2 layer providing the necessary process window.
3Manufacturing precision
If SiO2 is used as etch stop, then over-etching margin increases, but etch stop effectiveness decreases for aggressive etch processes
Solution Approach 1:
The patent creates a composite etch stop system using SiO2 with specific properties (deposited at 300-500°C to achieve appropriate etch resistance). This composite approach combines the benefits of SiO2 as a CMOS-compatible material with tailored etch resistance properties that make it effective against aggressive AlScN etch processes, simultaneously achieving both precision and reliability.
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 Al—Sc etch stop effectively prevents over- or under-etching, maintains low resistivity, and exhibits high corrosion resistance, enabling precise etching and pattern formation, even at elevated temperatures, thus addressing the challenges of etching AlScN and AlN films while ensuring device integrity.
Implementation Method 1
The bond between Al—Sc has been shown to be a very strong covalent bond in the Al3Sc system
Implementation Method 2
the resistivity of Al+Al3Sc can be as low as 5 μΩ·cm
Implementation Method 3
Al3Sc has also been shown to be more corrosion resistant than pure Al when dipped in NaCl solutions, which can explain its resistance to inductively coupled plasma (ICP) chlorine-based etches
Data Source
AI summary
An aluminum-scandium (Al—Sc) etch stop that is both CMOS compatible and highly conductive, and a method for forming the same are disclosed. The low volatility of Sc in Cl and strong covalent bond between Al—Sc leads to an increase in resistance to NaCl corrosion and makes it difficult to dry etch in Cl-based chemistries, resulting in an excellent etch stop material, especially when used in conjunction with an overlying aluminum nitride (AlN) or aluminum scandium nitride (AlScN) piezoelectric layer. When deposited at high deposition temperatures or when subsequently annealed at >600° C., the Al—Sc has a low resistivity, enabling corresponding device operation at temperatures up to at least 500° C. While Al3Sc is the preferred composition, Al1-xScx with x between 5 and 100 atomic percent provides many of these same benefits but comes at the cost of increased electrical resistivity and etch resistance with increasing Sc content due to Sc oxidation.