Slanted Polyimide Openings for Thick WLP Profile Control
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Solution Overview
Problem
The challenge in semiconductor manufacturing is achieving a thicker polyimide protective layer with improved mechanical strength for wafer level packaging (WLP) and integrated fan-out (InFO) packaging, where the high absorption and low penetration of polyimide make profile control difficult, leading to insufficient under-bump metallization (UBM) adhesion and increased delamination defects.
Innovation Solution
A method involving the use of polyimide dissolved in solvents like poly(acrylic acid) and gamma-butyrolactone to form a polyimide photoresist, which is processed through a photolithographic method with increased numerical aperture, post-exposure annealing, and adjusted cross-linker dosage to create a slanted polyimide opening, enhancing UBM adhesion and coverage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If polyimide is used as a protective layer with increased thickness for improved mechanical strength, then the mechanical strength and protective capability are improved, but the profile control becomes difficult due to high absorption and low penetration
Solution Approach 1:
The patent applies parameter changes by modifying the numerical aperture (NA) of the photolithography system and adjusting annealing temperatures to control the polyimide profile. By changing these process parameters, the patent achieves improved profile control for thicker polyimide layers while maintaining mechanical strength requirements.
Solution Approach 2:
The patent performs preliminary annealing before final patterning to pre-condition the polyimide layer. This preliminary action modifies the polyimide's physical properties in advance, making it more responsive to subsequent photolithography processing and improving overall profile control.
2Ease of manufacture
If conventional photolithography is used for polyimide patterning, then the process is simple, but the under-bump metallization adhesion is insufficient and delamination defects increase
Solution Approach 1:
The patent segments the photolithography process into multiple steps with different numerical aperture settings. The first exposure uses a higher NA for better resolution and adhesion, while subsequent steps use lower NA. This segmentation allows improved UBM adhesion while maintaining process feasibility.
Solution Approach 2:
The patent employs periodic annealing cycles at different temperatures interspersed with photolithography steps. These periodic thermal treatments enhance UBM adhesion by modifying the polyimide's physical properties at critical stages, improving reliability without excessive complexity.
3Length of stationary object
If the polyimide layer is made thicker to protect scaled-down semiconductor devices, then the protective capability is improved, but the penetration and profile definition deteriorate
Solution Approach 1:
The patent introduces the numerical aperture dimension as an additional control parameter beyond simple thickness control. By adjusting NA in the photolithography process, the patent achieves profile definition control in the lateral dimension while maintaining increased thickness in the vertical dimension, effectively using dimensional leverage to resolve the contradiction.
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 slanted polyimide profile improves UBM adhesion and coverage, leading to better step coverage of metal bumps, increased uniformity, and reduced delamination defects, thereby enhancing the reliability and lifespan of WLP and InFO structures.
Implementation Method 1
exposing the photoresist to a radiation source through a photomask having a pattern
Implementation Method 2
performing a first anneal at a first temperature... performing a second anneal at a second temperature... performing a third anneal at a third temperature
Data Source
AI summary
A structure includes a controlled polyimide profile. A method for forming such a structure includes depositing, on a substrate, a photoresist containing polyimide and performing a first anneal at a first temperature. The method further includes exposing the photoresist to a radiation source through a photomask having a pattern associated with a shape of a polyimide opening. The method further includes performing a second anneal at a second temperature and removing a portion of the photoresist to form the polyimide opening. The method further includes performing a third anneal at a third temperature and cleaning the polyimide opening by ashing.