SAW Resonator IDT Anti-Reflection Layer for Precise Lithography
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Solution Overview
Problem
In the manufacturing of acoustic wave devices, particularly surface acoustic wave (SAW) resonators, high reflectivity of aluminum interdigital transducer (IDT) electrodes during photolithography processes leads to undesirable effects like standing waves and electrical degradation, which are challenging to mitigate with existing anti-reflection methods that react with the aluminum layer.
Innovation Solution
Incorporating a silicon-based anti-reflection layer, such as silicon oxynitride or amorphous silicon, over the IDT electrode that remains distinct from the aluminum layer, reducing reflectivity to less than 0.2 for a wavelength of 365 nanometers and maintaining minimal impact on wiring resistance, thereby allowing precise patterning without significant electrical degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If existing anti-reflection methods are used that react with the aluminum layer, then reflectivity is reduced, but electrical degradation occurs
Solution Approach 1:
A silicon-based anti-reflection layer (silicon oxynitride or amorphous silicon) is introduced as an intermediary between the photolithography light and the aluminum IDT electrode. This intermediate layer reduces light reflectivity without chemically reacting with the aluminum, thereby maintaining electrical performance while achieving the desired anti-reflection effect.
Solution Approach 2:
The silicon-based anti-reflection layer serves as a temporary, process-specific layer that performs its function during photolithography and can be removed or remains as a thin protective layer. It is a simple, easily deposited material that solves the immediate problem without long-term complications.
2Object-affected harmful factors
If a thick anti-reflection layer is used to reduce reflectivity, then reflectivity decreases, but line width control precision deteriorates
Solution Approach 1:
The patent optimizes the thickness parameter of the silicon-based anti-reflection layer to a specific range (5-15 nm for amorphous silicon, 100-120 nm for silicon oxynitride) that achieves sufficient reflectivity reduction (reflectivity ≤ 0.2) while maintaining minimal impact on photolithography line width control and electrical performance.
3Reliability
If aluminum IDT electrode is used, then electrical conductivity is high, but reflectivity during photolithography is high causing standing waves
Solution Approach 1:
The silicon-based anti-reflection layer acts as a mediator that allows the aluminum IDT electrode to maintain its high electrical conductivity while preventing excessive light reflectivity during photolithography. The anti-reflection layer absorbs or scatters incident light before it reaches the aluminum surface, eliminating standing wave issues.
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 silicon-based anti-reflection layer effectively reduces reflectivity and maintains wiring resistance, enabling precise line width control and electrical performance in SAW resonators, addressing the challenges of electrical degradation and frequency distribution issues.
Implementation Method 1
the anti-reflection layer reduces reflectivity to less than 0.2 for a wavelength of 365 nanometers
Implementation Method 2
A surface acoustic wave resonator can include an interdigital transductor electrode on a piezoelectric substrate. The surface acoustic wave resonator can generate a surface acoustic wave on a surface of the piezoelectric layer
Data Source
AI summary
Methods of manufacturing an acoustic wave device are disclosed. An anti-reflection layer can be formed over a conductive layer that is over a piezoelectric layer. The conductive layer can include aluminum, for example. The anti-reflection layer can remain distinct from the conductive layer after a heating process. A photolithography process can pattern an interdigital transducer of the acoustic wave device from one or more interdigital transducer electrode layers that include the conductive layer. The anti-reflection layer can reduce reflection from the conductive layer during the photolithography process.