BAW Circuit Planarization Using HDP CVD Instead of CMP
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Solution Overview
Problem
Existing methods for planarizing BAW resonators, such as CMP and etch-back, suffer from defects like 'dishing' and poor control over pit size and shape, leading to undesirable acoustic modes and increased costs.
Innovation Solution
A unique patterning and etching scheme using a sacrificial layer with high-density plasma chemical vapor deposition (HDP CVD) to control the shape and planarity of the acoustic mirror structure, eliminating the need for CMP and etch-stop layers and mitigating defect pits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If chemical mechanical polishing (CMP) is used to reduce topography, then planarity is improved, but manufacturing cost increases and dishing defects occur that reduce overall planarity
Solution Approach 1:
The patent extracts and removes the problematic high acoustic impedance layer (tungsten) selectively using etch-back process, eliminating the need for CMP while achieving the desired planarity. The sacrificial layer is also removed to reveal the underlying structure, solving both planarity and cost issues simultaneously.
Solution Approach 2:
Instead of using CMP to mechanically polish down the topography, the patent inverts the approach by using selective etching to remove material precisely where needed, achieving planarity through chemical removal rather than mechanical polishing.
2Manufacturing precision
If chemical mechanical polishing (CMP) is used to reduce topography, then planarity is improved, but dishing defects occur that propagate undesirable acoustic modes
Solution Approach 1:
The patent replaces the mechanical CMP process with a chemical etching process. The etch-back method uses chemical reactions to remove material selectively, avoiding the mechanical forces that cause dishing defects while achieving the desired planar surface for optimal acoustic performance.
3Ease of manufacture
If etch-back method is used to reduce topography, then manufacturing cost is reduced, but control over pit size and shape at edges is poor
Solution Approach 1:
The patent introduces a sacrificial layer as an intermediary element that facilitates precise control during the etch-back process. This sacrificial layer acts as a mask and structural guide, enabling better control over the size and shape of pits formed at the edges of the patterned high acoustic impedance layer, while still maintaining the cost advantages of the etch-back method.
4Ease of manufacture
If etch-back method is used to reduce topography, then manufacturing cost is reduced, but etch-stop layer is required to prevent over-etching
Solution Approach 1:
The patent employs a self-service mechanism where the sacrificial layer itself serves as the etch-stop mechanism. The sacrificial layer is designed to be selectively removable, providing automatic protection against over-etching of the underlying low acoustic impedance layer, thereby eliminating the need for separate etch-stop layers and reducing process complexity.
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 achieves nearly planar structures with improved control over the acoustic mirror shape, reducing defects and costs while maintaining optimal acoustic wave reflection in BAW resonators.
Implementation Method 1
high-density plasma chemical vapor deposition (HDP CVD) to control the shape and planarity
Implementation Method 2
high-density plasma chemical vapor deposition (HDP CVD)
Implementation Method 3
A unique patterning and etching scheme using a sacrificial layer
Data Source
AI summary
Planarization methods for maintaining planar surfaces in the fabrication of such devices as BAW devices and capacitors on a planar or planarized substrate are described. In accordance with the method, a metal layer is deposited and patterned, and an oxide layer is deposited using a high density plasma chemical vapor deposition (HDP CVD) process to a thickness equal to the thickness of the metal layer. The HDP CVD process provides an oxide layer on the patterned metal tapering upward from the edge of the patterned metal layer. Then, after masking and etching the oxide layer from the patterned metal layer, the patterned metal layer and surrounding oxide layer form a substantially planar layer, interrupted by small remaining oxide protrusions at the edges of the patterned layer. These small remaining oxide protrusions may be too small to significantly disturb the flatness of a further oxide or other layer or they may be further mitigated by the application of another HDP CVD oxide film.