Polyimide Wafer Coating for Cu RDL Edge Uniformity
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Solution Overview
Problem
In semiconductor manufacturing, aluminum (Al) metallization layers are prone to stress, cracks, and electro-migration issues, which can lead to short circuits and device failure, especially under high temperatures or current surges, necessitating the development of alternative materials and processes for reliable copper (Cu) redistribution layers (RDLs).
Innovation Solution
A low viscosity polyimide photoresist composition, including tetraethylene glycol dimethacrylate, is used to form a spiral dispense pattern that improves edge coating and gap fill capabilities, allowing for higher rotation speeds and shorter spin times, thereby reducing stress and enhancing the reliability of Cu RDLs by modifying the coating process and recipe.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional photoresist coating processes are used, then the coating process is simple, but the edge thickness uniformity is poor and gap fill capability is insufficient
Solution Approach 1:
The patent implements a multi-stage spin coating process with dynamically changing rotation speeds. The process transitions through different phases: initial high-speed rotation for rapid dispensing and spreading, intermediate speed for edge coating, and final high-speed rotation for thickness uniformity. This dynamic speed adjustment optimizes both edge thickness uniformity and gap fill capability without requiring additional equipment
Solution Approach 2:
The coating process employs periodic action through multiple spin stages with specific duration and speed parameters. Each stage serves a distinct purpose: the first stage dispenses and spreads the photoresist, the second stage coats the edges, and the third stage ensures uniform thickness. This periodic multi-stage approach achieves superior manufacturing precision while maintaining process simplicity
2Productivity
If higher rotation speeds are used during spin coating, then productivity increases, but coating uniformity deteriorates
Solution Approach 1:
The patent resolves the contradiction between productivity and coating uniformity by implementing dynamic speed adjustment across three stages. The process uses high initial speed for rapid coating (productivity), reduces speed for edge uniformity, then increases speed again for final thickness control. This dynamic approach achieves both high productivity and superior coating uniformity that cannot be obtained with constant speed operation
3Ease of manufacture
If aluminum metallization layers are used, then the manufacturing process is established, but stress, cracks, and electro-migration issues occur leading to device failure
Solution Approach 1:
The patent addresses the reliability issues of aluminum metallization by changing the material parameter from aluminum to copper for the redistribution layer. This material substitution eliminates stress, cracks, and electro-migration problems while maintaining compatibility with established manufacturing processes. The polyimide photoresist system is optimized to support copper RDL formation, achieving both ease of manufacture and improved device reliability
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 modified polyimide photoresist composition effectively reduces uneven edge thickness and improves the reliability of Cu RDLs by enhancing gap fill and stress migration properties, preventing potential voids and cracks, and maintaining the total volume of polyimide used, thus ensuring consistent and reliable semiconductor device manufacturing.
Implementation Method 1
A first photoresist pattern is dispensed to form a polyimide layer... rotating the wafer at a first speed... rotating the wafer at a second speed lower than the first speed... rotating the wafer at a third speed higher than the first speed
Implementation Method 2
dispensing a polyimide photoresist composition... to form an inner circle... moving at least one of the nozzle or the wafer in a lateral direction to form a first portion of a spiral arm
Data Source
AI summary
A semiconductor device comprises a metallization layer, a passivation layer disposed above the metallization layer, a copper redistribution layer disposed on the passivation layer, a second passivation layer disposed on the copper redistribution layer, and a polyimide layer disposed over the second passivation layer. The polyimide layer and the second passivation layer include a continuous gap there-through that exposes a portion of the copper redistribution layer.