MEMS Sensor Double Bonding Prevents Diffusion and Reflow
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Solution Overview
Problem
The package level sealing process for MEMS sensors often results in static friction between sensing wafer and substrate components, leading to low yields and undesirable characteristics, necessitating a method that prevents diffusion and reflow phenomena during bonding.
Innovation Solution
A manufacturing method for MEMS sensors that employs polysilicon upper electrodes and a double bonding process combining anodic-bonding and eutectic-bonding to prevent diffusion and reflow phenomena, involving the formation of substrates with specific surface features and layers to facilitate bonding while minimizing defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If package level sealing process is used, then MEMS sensor can be sealed in vacuum or gaseous environment, but static friction occurs between sensing wafer and substrate components leading to low yield
Solution Approach 1:
The bonding process is divided into two separate stages: wafer-level bonding first seals individual sensors, then substrate-level bonding seals the entire array. This segmentation prevents static friction issues by establishing stable bonding interfaces before stacking, thereby maintaining both sealing quality and high yield
Solution Approach 2:
Wafer-level bonding is performed as a preliminary action before substrate stacking. This preliminary bonding creates stable interfaces and prevents static friction between components during subsequent handling and packaging, resolving the yield issue while maintaining vacuum sealing capability
2Ease of manufacture
If conventional bonding process is used, then packaging can be completed, but diffusion phenomenon and reflow phenomenon occur during bonding
Solution Approach 1:
The bonding process parameters are optimized by using anodic bonding for glass-silicon interfaces and eutectic bonding for silicon-silicon interfaces. These parameter changes prevent diffusion and reflow phenomena by controlling temperature, pressure, and time conditions specific to each material combination, achieving both ease of manufacture and high bonding precision
Solution Approach 2:
Anodic bonding serves as an intermediary process that creates stable bonding interfaces between dissimilar materials (glass and silicon). This intermediary bonding method prevents direct contact and potential diffusion between materials that would otherwise require high-temperature processing, thereby preventing diffusion and reflow phenomena
3Manufacturing precision
If polysilicon upper electrode is applied, then diffusion phenomenon and reflow phenomenon are prevented, but additional processing steps are required
Solution Approach 1:
The polysilicon upper electrode serves multiple functions: it acts as an electrical electrode, a bonding layer for eutectic bonding, and a diffusion barrier. This multi-functionality prevents diffusion and reflow phenomena while minimizing additional processing steps, as the electrode formation integrates with the bonding process rather than requiring separate dedicated layers
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 method effectively prevents diffusion and reflow phenomena during bonding, enhancing the yield and reliability of MEMS sensors by using polysilicon upper electrodes and a combination of anodic and eutectic bonding techniques.
Implementation Method 1
The first-bonding step may include anodic bonding
Implementation Method 2
the second-bonding step may include eutectic bonding
Implementation Method 3
The upper electrode may be made of polysilicon and may be formed by ion-injecting
Data Source
AI summary
A manufacturing method of a MEMS sensor includes forming a first substrate, wherein the first substrate includes a lower electrode provided at one surface thereof, forming a second substrate, wherein the second substrate includes a first concave-convex portion provided at one surface thereof, first-bonding one surface of the first substrate and one surface of the second substrate to face each other, forming a third substrate, wherein the third substrate includes an upper electrode provided at one surface thereof, second-bonding another surface of the second substrate and one surface of the third substrate to face each other, and forming an electrode line on another surface of the third substrate to be connected to the lower electrode and the upper electrode.