MEMS Sacrificial Layer Planarization via Conductive Reflow
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Solution Overview
Problem
MEMS devices face challenges in achieving repeatable and consistent capacitance due to non-uniform shapes of movable plates, which are often caused by insufficient planarity of sacrificial layers used in their fabrication.
Innovation Solution
The method involves depositing a sacrificial layer over a substrate, followed by conductive heating to allow the sacrificial layer to reflow and become planarized, ensuring the movable plate is formed on a uniform surface, and then removing the sacrificial layer to create a cavity for the movable plate to move within.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If sacrificial material is deposited to form the movable plate cavity, then the cavity structure is formed, but the sacrificial material surface becomes non-planar with high height difference
Solution Approach 1:
The patent applies thermal energy to change the physical state of the sacrificial material from solid to liquid phase, enabling it to flow and redistribute. By controlling the temperature parameter, the material transitions through phase change to achieve surface planarization, then solidifies to maintain the planar shape. This parameter-based approach directly addresses the height uniformity issue without requiring additional mechanical planarization steps.
2Manufacturing precision
If the sacrificial layer is heated to reflow and planarize, then surface planarity is improved, but the heating process must be carefully controlled to avoid damaging other structures
Solution Approach 1:
The patent implements selective heating by applying thermal energy locally to the sacrificial material region while protecting surrounding structures. The heating process is spatially differentiated, with the sacrificial layer receiving sufficient thermal energy for reflow while adjacent sensitive structures are shielded or heated to lower temperatures. This local quality approach enables planarization without causing thermal damage to other device components.
3Ease of manufacture
If the movable plate is formed on a non-planar sacrificial layer, then fabrication is simpler, but device-to-device repeatability and capacitance consistency deteriorate
Solution Approach 1:
The patent performs planarization of the sacrificial layer before depositing the movable plate material. By预先 (in advance) creating a planar surface on the sacrificial layer, the subsequent movable plate formation occurs on a uniform substrate, ensuring consistent thickness and electrical properties across devices. This preliminary action eliminates the need for complex post-fabrication adjustments while maintaining high device repeatability and capacitance consistency.
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 the formation of a substantially planar movable plate, enhancing device repeatability and performance by maintaining consistent capacitance levels across MEMS devices.
Implementation Method 1
conduction heating the substrate and sacrificial layer to reflow the sacrificial layer and substantially planarized the sacrificial layer
Implementation Method 2
conduction heating the substrate and sacrificial layer to reflow the sacrificial layer and substantially planarized the sacrificial layer
Data Source
AI summary
The present invention generally relates to a method of fabricating a MEMS device. In the MEMS device, a movable plate is disposed within a cavity such that the movable plate is movable within the cavity. To form the cavity, sacrificial material may be deposited and then the material of the movable plate is deposited thereover. The sacrificial material is removed to free the mov able plate to move within the cavity. The sacrificial material, once deposited, may not be sufficiently planar because the height difference between the lowest point and the highest point of the sacrificial material may be quite high. To ensure the movable plate is sufficiently planar, the planarity of the sacrificial material should be maximized. To maximize the surface planarity of the sacrificial material, the sacrificial material may be deposited and then conductive heated to permit the sacrificial material to reflow and thus, be planarized.