Low-Modulus Polyimide Passivation for Wafer Stress Reduction
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Solution Overview
Problem
Conventional polyimide passivation materials generate stress on silicon wafers, leading to delamination and warping, especially as wafers thin, and are hydrophilic, requiring complex processes and prone to moisture absorption, which can result in device failure.
Innovation Solution
Development of low modulus, hydrophobic polyimide passivation layers with a molecular weight fraction of nitrogen and oxygen less than 20%, using imide-extended bismaleimides or graft polymaleimides, which are fully imidized and photoimageable, reducing stress and moisture absorption, and suitable for thin silicon wafers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional polyimide passivation materials are used, then the passivation layer provides thermal stability and mechanical toughness, but it generates high stress on the wafer causing delamination and warping
Solution Approach 1:
The patent changes the physical and chemical parameters of the polyimide material by reducing its modulus (stiffness) while maintaining thermal stability. This is achieved through specific polyimide formulations that provide lower mechanical strength but reduced stress generation, directly resolving the contradiction between mechanical toughness and stress on the wafer
Solution Approach 2:
The patent uses composite material approaches by combining polyimide with other materials or using modified polyimide structures (such as graft polymaleimides) to achieve a balance between mechanical properties and stress characteristics, allowing the passivation layer to maintain toughness while reducing warping stress
2Reliability
If conventional polyimide passivation materials are used, then the passivation layer provides dielectric properties, but it is hydrophilic and absorbs moisture leading to device failure
Solution Approach 1:
The patent changes the chemical composition parameters of the polyimide to reduce its hydrophilicity. By modifying the molecular structure and selecting specific monomers, the passivation layer achieves lower moisture absorption while maintaining its dielectric properties, directly addressing the contradiction between reliability and moisture sensitivity
Solution Approach 2:
The patent converts the typically harmful hydrophilic nature of polyimide into a benefit by carefully controlling the degree of imidization and selecting specific chemical structures that provide optimal moisture resistance while maintaining the desired dielectric and mechanical properties
3Ease of manufacture
If conventional polyimide passivation materials are used, then the passivation layer can be patterned using lithographic process, but it requires tedious multi-step processes for via formation
Solution Approach 1:
The patent makes the polyimide passivation layer multi-functional by providing both planarization and via formation capabilities in a single material system. The photoimageable polyimide can be patterned directly during the passivation process, eliminating the need for separate via formation steps and reducing overall process complexity
4Strength
If conventional polyimide passivation materials are used, then the passivation layer protects thin films from damage, but it causes warping of thin silicon wafers upon thermal cure
Solution Approach 1:
The patent changes the thermal and mechanical parameters of the polyimide by reducing its modulus and controlling its cure characteristics. This allows the passivation layer to maintain protective capabilities while minimizing thermal stress and warping effects on thin silicon wafers during the curing process
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 new polyimide passivation layers minimize stress on thin silicon wafers, prevent warpage, and exhibit low moisture uptake, enhancing the reliability and stability of semiconductor devices.
Implementation Method 1
polyimide materials readily absorb moisture even after curing and this absorption can result in device failure
Implementation Method 2
The photomask is placed in close proximity to the polyimide layer and the assembly is irradiated by UV light
Implementation Method 3
The photomask is placed in close proximity to the polyimide layer and the assembly is irradiated by UV light sufficient to drive polymerization of the polyimide coating
Data Source
AI summary
The present invention provides polyimide polymer materials for passivating semiconductor wafers and methods for fabricating thereof. The present invention further provides a device that includes a semiconductor wafer and a passivating layer disposed on the surface of the wafer, wherein the passivating layer comprises such polyimide polymers.