Spin Coating Apparatus Multi-Stage Rotation Control
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Solution Overview
Problem
Conventional spin coating methods face challenges in uniformly coating large substrates due to air resistance, leading to uneven coating and high liquid usage, especially at the substrate's edges, and pre-wet liquids do not fully address these issues while increasing costs.
Innovation Solution
A spin coating apparatus and method that involves dropping a coating liquid in multiple stages with varying rotation speeds and discharge rates, using a pre-wet liquid with low viscosity and vapor pressure to improve wettability, and adjusting the drop amounts and rotation speeds to ensure uniform coating across the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the substrate is rotated at high speed to spread coating liquid, then the coating liquid spreads faster, but the coating liquid cannot reach the end portion of large substrates and uniformity deteriorates
Solution Approach 1:
The coating process is divided into multiple stages with different rotation speeds. First, the substrate is rotated at a first rotation speed to spread the coating liquid to the end portion. Then, the substrate is rotated at a second rotation speed (higher than the first) to achieve the target thickness. This segmentation allows the coating liquid to reach the edges first, then achieves uniform thickness through controlled high-speed rotation.
2Manufacturing precision
If a pre-wet liquid is used to improve wettability, then coating uniformity improves, but the cost increases and the problem is not fully solved
Solution Approach 1:
The invention changes the physical parameters of the coating liquid itself rather than introducing a separate pre-wet liquid. By adjusting the viscosity and surface tension of the coating liquid to specific ranges, the liquid naturally achieves good wettability and spreads uniformly across the substrate without requiring additional pre-wetting steps, thus maintaining coating uniformity while avoiding increased process complexity.
3Area of stationary object
If the substrate area is increased, then larger substrates can be coated, but the coating liquid cannot reach the end portion and uniformity deteriorates
Solution Approach 1:
The coating process is divided into two sequential stages: first rotating at a lower speed to ensure the coating liquid reaches the end portion of the large substrate, then increasing to a higher rotation speed to achieve uniform target thickness. This segmented approach specifically addresses the challenge of coating large-area substrates uniformly.
4Area of stationary object
If the coating liquid discharge rate is increased to coat large areas, then coverage improves, but the amount of coating liquid used increases
Solution Approach 1:
The rotation speed is dynamically adjusted during the coating process. The substrate is first rotated at a lower speed to allow the coating liquid to spread to the edges with moderate liquid usage, then the speed is increased to achieve uniform thickness. This dynamic adjustment optimizes the balance between coverage area and coating liquid consumption.
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
This approach allows for efficient use of coating liquid, achieving uniform thickness and coverage up to the substrate's edges while reducing overall liquid consumption and maintaining cost-effectiveness.
Implementation Method 1
improves the wettability by soaking the substrate with a pre-wet liquid before coating the substrate with the coating liquid
Implementation Method 2
rotating the substrate at the number of rotations for determining a thickness of the coating liquid
Data Source
AI summary
In one embodiment, a spin coating apparatus includes a coating liquid feeding module to drop a coating liquid onto a substrate, and a motor to rotate the substrate. The module drops a first drop amount of the coating liquid onto the substrate at a first discharge rate, while the motor rotates the substrate at a first number of rotations. The module drops a second drop amount of the coating liquid onto the substrate at a second discharge rate larger than the first discharge rate, while the motor rotates the substrate at a second number of rotations smaller than the first number of rotations, after the first drop amount of the coating liquid is dropped. The module discharges the coating liquid onto the substrate at a third discharge rate smaller than the second discharge rate, after the coating liquid is discharged onto the substrate at the second discharge rate.