SAW IDT Anti-Reflection Layer for Low-Reflectivity Lithography
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Solution Overview
Problem
In the manufacturing of 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 conventional anti-reflection films 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 and has a thickness optimized to reduce reflectivity to less than 0.2 for a wavelength of 365 nanometers, thereby minimizing electrical degradation and maintaining wiring resistance similar to structures without anti-reflection layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional anti-reflection films are used over aluminum IDT electrodes, then reflectivity is reduced, but electrical degradation occurs due to chemical reaction between the film and aluminum layer
Solution Approach 1:
The patent introduces silicon oxynitride as an intermediary anti-reflection layer that mediates between the aluminum IDT electrode and the photolithography process. This material reduces light reflectivity during patterning while remaining chemically inert to aluminum, thus preventing the electrical degradation that occurs with conventional organic anti-reflection films.
Solution Approach 2:
The patent changes the material parameter of the anti-reflection layer from organic compounds to silicon oxynitride, and optimizes its thickness parameter (5nm-15nm for amorphous silicon, 100nm-120nm for silicon oxynitride) to achieve the desired reflectivity reduction while maintaining electrical integrity of the aluminum electrode.
2Reliability
If no anti-reflection layer is used, then wiring resistance remains low, but standing waves and electrical degradation occur during photolithography
Solution Approach 1:
The silicon-based anti-reflection layer is applied in advance to the aluminum IDT electrode before photolithography to preemptively counteract the standing wave effect. By reducing reflectivity beforehand, the layer prevents the harmful interference patterns that would otherwise cause electrical degradation during the patterning process.
3Object-affected harmful factors
If anti-reflection layer thickness is increased, then reflectivity is reduced, but wiring resistance increases due to material contribution
Solution Approach 1:
The patent optimizes the thickness parameter of the silicon-based anti-reflection layer to achieve the minimum necessary value that provides sufficient reflectivity reduction while minimizing the layer's contribution to wiring resistance. The specified thickness ranges (5nm-15nm for amorphous silicon, 100nm-120nm for silicon oxynitride) represent this optimized balance.
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, allowing for precise patterning of IDT electrodes with desired line widths without significant electrical degradation, thus improving the manufacturing process and performance of SAW resonators.
Implementation Method 1
an anti-reflection layer positioned over the conductive layer. The anti-reflection layer includes silicon. The anti-reflection layer has a thickness that together with the material causes reflectivity of the acoustic wave device to be less than or equal to 0.2 for light having a wavelength of 365 nanometers
Data Source
AI summary
An acoustic wave device is disclosed. The acoustic wave device includes a piezoelectric layer, an interdigital transducer electrode positioned over the piezoelectric layer, and an anti-refection layer over a conductive layer of the interdigital transducer electrode. The conductive layer can include aluminum, for example. The anti-reflection layer can include silicon. The anti-reflection layer can be free from a material of the interdigital transducer electrode. The acoustic wave device can further include a temperature compensation layer positioned over the anti-reflection layer in certain embodiments.