Lamb Wave Resonator Cavity Alignment for Clean Frequency Response
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Solution Overview
Problem
Current semiconductor fabrication techniques face challenges in achieving precise alignment between cavity vias and IDT electrodes in Lamb wave filters, leading to misalignments that affect acoustic boundary conditions and resonant frequency, especially at high frequency bands above 2 GHz.
Innovation Solution
A self-alignment method is introduced that forms self-aligned vias using a dielectric hardmask or a top metal electrode as a self-aligner, eliminating the need for additional mask layers and minimizing structural complexity, allowing for precise control of overlay misalignment to less than 10 nm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If lithographic alignment is used to align cavity via and IDT electrode, then alignment precision is improved, but manufacturing complexity increases and perfect alignment cannot be achieved
Solution Approach 1:
The top IDT electrode layer serves as its own alignment reference by defining both the electrode pattern and the cavity via alignment marks. The self-aligner structure uses the electrode's own geometric features (such as finger tips or edges) as the reference for cavity via placement, eliminating the need for separate alignment marks or additional mask layers. This self-referential approach achieves sub-10nm alignment precision while simplifying the manufacturing process.
Solution Approach 2:
The patent combines the alignment reference function with the IDT electrode structure itself. Instead of using separate alignment marks or a dedicated reference layer, the electrode pattern's geometric features are directly used as the alignment reference for cavity via placement. This merging of functions eliminates additional process steps and mask layers while achieving the required alignment precision.
2Reliability
If misalignment between cavity via and IDT electrode is reduced, then acoustic boundary conditions are improved, but manufacturing complexity increases
Solution Approach 1:
The method uses the IDT electrode's own geometric features as the reference for cavity via alignment, creating a self-aligning system that automatically ensures proper acoustic boundary conditions. The self-aligner structure incorporates alignment marks that are directly derived from the electrode pattern, ensuring that cavity vias are positioned with sub-10nm precision relative to the electrode fingers, which is critical for maintaining accurate acoustic boundaries at high frequencies.
Solution Approach 2:
The patent performs alignment reference definition during the electrode formation process itself, before cavity via fabrication. By establishing the alignment reference in the electrode layer and using it to guide subsequent cavity via formation, the method ensures that alignment precision is built into the structure from the outset, rather than requiring additional alignment steps later in the process.
3Manufacturing precision
If additional mask layers are added for alignment, then alignment precision is improved, but device complexity and fabrication steps increase
Solution Approach 1:
The patent merges the alignment reference function with the IDT electrode structure, eliminating the need for separate mask layers dedicated to alignment. The electrode pattern's geometric features serve dual purposes: as the functional electrode and as the alignment reference for cavity via placement. This integration reduces the total number of mask layers and fabrication steps while maintaining sub-10nm alignment precision.
Solution Approach 2:
The IDT electrode layer performs multiple functions: it serves as the acoustic transducer element and simultaneously provides the alignment reference for cavity via placement. The self-aligner structure within the electrode layer acts as both part of the electrode pattern and as the alignment marks, eliminating the need for dedicated alignment mark layers or additional mask steps.
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 approach ensures cleaner frequency responses and enhanced frequency control by maintaining perfectly aligned IDT electrodes and cavity vias, thereby optimizing the acoustic boundary conditions and resonance frequency of the filters.
Implementation Method 1
forming a piezoelectric thin film over the first electrode
Implementation Method 2
acoustic wave filters and resonator fabrication in the advanced technology nodes
Data Source
AI summary
A method for forming a lamb acoustic wave resonator and filter and the resulting device are provided. Embodiments include forming a sacrificial layer over a substrate; forming a first electrode over the sacrificial layer; forming a piezoelectric thin film over the first electrode; forming a second electrode over the piezoelectric thin film; forming a hardmask over the second electrode; etching through the hardmask and the second electrode down to the piezoelectric thin film forming self-aligned vias; forming and patterning a photoresist layer over the self-aligned vias; etching through the photoresist layer forming cavities extending through the vias and to the sacrificial layer; and removing the sacrificial layer forming a cavity gap under the cavities and first metal electrode.