MEMS Multi-Material Metallization for Substrate Warping
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing MEMS fabrication methods face challenges with substrate warping and voiding when using secondary metals for multi-layer structures, particularly in large or laterally extensive microstructures, due to the stress caused by plating secondary metals across the entire substrate, and the reliance on time-consuming photolithography processes.
Innovation Solution
A method involving the deposition of a first sacrificial secondary metal in a thin layer and a second sacrificial secondary metal in a thick layer around the primary metal structure, both covering the entire substrate, to provide mechanical support during machining and etching, while avoiding substrate warping and voiding, using a plating bath with specific additives for superfilling to enhance structural stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If secondary metal is plated across the entire substrate to provide mechanical support during machining, then structural stability is improved, but substrate warping occurs due to plating stress
Solution Approach 1:
The secondary metal layer is segmented into two distinct layers: a first secondary metal layer providing mechanical support during machining, and a second secondary metal layer applied afterward to restore planarity. This segmentation allows each layer to have specialized functions, resolving the conflict between needing support during machining and maintaining substrate planarity.
Solution Approach 2:
The first secondary metal layer is applied preliminarily before machining to provide the necessary mechanical support and structural stability during the machining process. This preliminary action prevents substrate warping during machining, and subsequent planarity restoration is performed as a separate corrective step.
2Manufacturing precision
If photoresist is used to pattern secondary metal during multi-layer fabrication, then manufacturing precision is improved, but process time increases due to repeated photolithography steps
Solution Approach 1:
The patent extracts and eliminates the photolithography step from the secondary metal patterning process. Instead of using photoresist and mask-based patterning, the secondary metal layers are applied as complete layers and then selectively removed in targeted areas, taking out the time-consuming photolithography工序 while maintaining the ability to create precise patterns.
Solution Approach 2:
The approach is inverted from the conventional method: instead of using photolithography to define where secondary metal should be present, the patent applies secondary metal everywhere and then uses selective removal to define the final pattern. This inversion eliminates photolithography while achieving the same patterning result.
3Strength
If thick secondary metal layers are used to support large microstructures, then mechanical strength is improved, but substrate warping increases due to plating stress
Solution Approach 1:
The thick secondary metal structure is segmented into two functional layers: a first thick layer providing the necessary mechanical strength and support during machining, and a second layer applied afterward to counterbalance plating stress and restore substrate planarity. This segmentation allows the structure to have both strength and geometric stability.
Solution Approach 2:
The patent uses a composite structure of two different secondary metal layers, each with potentially different material properties. The first layer is optimized for mechanical strength and support, while the second layer is optimized for stress compensation and planarity restoration, creating a composite system that achieves both strength and geometric stability.
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 allows for the fabrication of multi-layered MEMS structures without substrate warping, with improved mechanical support and reduced voiding, enabling the creation of large microstructures over a single substrate at a lower cost and with reduced complexity in the deposition process.
Implementation Method 1
a first sacrificial secondary metal is electroplated in a thin layer around the primary metal structure and over the entire surface of the substrate; a second sacrificial secondary metal is electroplated in a thick layer around the first sacrificial secondary metal
Implementation Method 2
using a plating bath with specific additives for superfilling to prevent voiding
Implementation Method 3
etching away the first and second sacrificial secondary metals from the machined primary metal structure
Data Source
AI summary
Processes are provided herein for the fabrication of MEMS utilizing both a primary metal that is integrated into the final MEMS structure and two or more sacrificial secondary metals that provide structural support for the primary metal component during machining. A first secondary metal is thinly plated around the primary metal and over the entire surface of the substrate without using photolithography. A second secondary metal, is then thickly plated over the deposited first secondary metal without using photolithography. Additionally, techniques are disclosed to increase the deposition rate of the first secondary metal between primary metal features in order to prevent voiding and thus enhance structural support of the primary metal during machining.