Photosensitive Polyimide Films for Low-Stress Wafer Patterning
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional polyimide materials used in semiconductor packaging face challenges such as high cure temperatures, post-cure shrinkage, and residual stress, which are detrimental for advanced 3D integration applications where silicon wafers need to be thinned, requiring materials with low cure temperature and low shrinkage to minimize stress on fragile wafers.
Innovation Solution
Development of photosensitive compositions comprising fully imidized polyimide polymers with a weight average molecular weight between 20,000 to 70,000 Daltons, combined with solubility switching compounds and photoinitiators, that form films with high dissolution rates in cyclopentanone, allowing for precise patterning and minimal stress on wafers during the packaging process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional polyimide materials are used, then good mechanical and thermal properties are achieved, but high cure temperatures and high post-cure shrinkage cause residual stress and wafer bowing
Solution Approach 1:
The patent modifies the molecular weight parameter of polyimide polymers to a specific range (20,000-70,000 Daltons) and incorporates solubility switching compounds that change solubility characteristics upon exposure. These parameter changes enable the material to achieve both good mechanical properties and low residual stress through reduced post-cure shrinkage
Solution Approach 2:
The invention creates a composite photosensitive composition combining polyimide polymer, solubility switching compound, and photoinitiator. This composite material integrates the mechanical strength of polyimide with the low-shrinkage characteristics enabled by the solubility switching mechanism, resolving the contradiction between strength and stress
2Strength
If polyimide molecular weight is increased to achieve acceptable mechanical properties, then mechanical strength is improved, but solubility in developer decreases and lithographic performance deteriorates
Solution Approach 1:
The solubility switching compound acts as an intermediary that decouples the relationship between molecular weight and solubility. It provides a solubility control mechanism independent of polymer chain length, allowing high molecular weight polymers to maintain both mechanical strength and lithographic processability
Solution Approach 2:
The invention changes the solubility parameter through the solubility switching compound rather than relying on molecular weight control. This enables independent optimization of mechanical properties (through molecular weight) and lithographic performance (through solubility switching)
3Productivity
If silicon wafers are thinned to 20 μm for vertical integration, then device density is improved, but wafer fragility increases and excessive residual stress becomes catastrophic
Solution Approach 1:
The photosensitive composition is designed with preliminary anti-action against residual stress generation. By incorporating solubility switching compounds that minimize post-cure shrinkage, the material preemptively counteracts the stress that would otherwise damage thinned wafers, enabling safe processing of 20 μm thinned substrates
4Stability of the object's composition
If high cure temperature is used for polyimide curing, then complete imidization is achieved, but thermal stress and energy consumption increase
Solution Approach 1:
The invention changes the cure temperature parameter from conventional high temperatures (>350°C) to lower temperatures by incorporating solubility switching compounds and photoinitiators. This enables complete imidization at reduced thermal energy input, lowering both energy consumption and thermal stress on thinned wafers
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 solution provides photosensitive compositions and films with excellent lithographic and mechanical properties, enabling efficient patterning and reducing residual stress on thinned silicon wafers, thus meeting the requirements for advanced semiconductor packaging in 3D integration.
Implementation Method 1
The composition includes at least one photoinitiator and, upon exposure to ultraviolet light, the photoinitiator initiates a free radical reaction
Implementation Method 2
The composition includes at least one solubility switching compound and, upon exposure to ultraviolet light, the photoinitiator initiates a free radical reaction that results in a loss of solubility of the film in a developer
Data Source
AI summary
This disclosure relates to a photosensitive composition that includes at least one fully imidized polyimide polymer having a weight average molecular weight in the range of about 20,000 Daltons to about 70,000 Daltons; at least one solubility switching compound; at least one photoinitiator; and at least one solvent. The composition is capable of forming a film or a dry film having a dissolution rate of greater than about 0.15 micron/second using cyclopentanone as a developer.