MEMS Topped IC Stress Relief Layer Wafer Bowing
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Solution Overview
Problem
The formation of MEMS inductors on semiconductor wafers leads to significant lateral stress due to material property mismatches, causing wafer bowing, cracking, and electrical shifts, which complicates subsequent process steps and can destroy the wafer.
Innovation Solution
A stress relief layer with a high bulk elongation material, such as spin-on benzocyclobutene (BCB) or photoimagible elastomer, is introduced between the passivation layer and the MEMS devices to absorb dimensional changes and prevent stress transmission to underlying structures, reducing wafer bowing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If MEMS inductors are formed on semiconductor wafers, then integration and electrical performance are improved, but lateral stress and wafer bowing increase
Solution Approach 1:
A stress relief layer is introduced as an intermediary between the passivation layer and the MEMS inductor structure. This intermediate layer absorbs lateral stress through its high bulk elongation properties, preventing stress transmission to the underlying semiconductor wafer and circuit structures, thereby maintaining both integration benefits and wafer stability
Solution Approach 2:
The patent changes the material parameter of bulk elongation by selecting materials with exceptionally high bulk elongation (greater than 10%, preferably greater than 100%) for the stress relief layer. This parameter change enables the layer to accommodate significant dimensional changes and stress without transmitting them to the wafer, resolving the stress issue while maintaining MEMS functionality
2Device complexity
If MEMS inductors are formed on semiconductor wafers, then on-chip integration is achieved, but wafer bowing and cracking occur
Solution Approach 1:
The stress relief layer serves as a protective intermediary that decouples the stress-generating MEMS structures from the vulnerable wafer substrate. This allows on-chip integration to proceed while the stress relief layer absorbs mechanical stress, preventing wafer bowing and cracking that would otherwise occur due to material property mismatches
Solution Approach 2:
The stress relief layer is positioned beforehand between the passivation layer and MEMS structures to provide cushioning against lateral stress. This pre-positioned protective layer prevents stress accumulation and transmission that would lead to wafer deformation and failure during subsequent processing and operation
3Stability of the object's composition
If stress relief layer with high bulk elongation material is introduced, then wafer bowing is reduced, but process complexity increases
Solution Approach 1:
The patent specifies parameter ranges for bulk elongation (greater than 10%, preferably greater than 100%) and thickness (1 μm to 100 μm) for the stress relief layer material. By defining these parameters, the patent enables selection of materials and thicknesses that provide effective stress relief while maintaining compatibility with standard semiconductor processing, thus managing 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
The stress relief layer effectively reduces wafer bowing and electrical shifts, stabilizing the substrate and preventing damage, while allowing for stable formation of MEMS devices on top of integrated circuits.
Implementation Method 1
The stress relief layer is formed from a material having a maximum bulk elongation that is greater than a maximum bulk elongation of a material used to form the passivation layer
Data Source
AI summary
The bow in a wafer that results from fabricating a large number of MEMS devices on the top surface of the passivation layer of the wafer so that a MEMS device is formed over each die region is reduced by forming a stress relief layer between the passivation layer and the MEMS devices.