Multi-step Substrate Rotation for Uniform Resist Coating
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Solution Overview
Problem
Conventional resist coating methods for semiconductor wafers result in irregular distribution and drying of resist solutions due to high rotation speeds, leading to coating mottles and non-uniform film thickness, especially when applying small amounts of coating solution.
Innovation Solution
A multi-step coating treatment method involving sequential changes in rotation speed of the substrate, starting with high speed, then decelerating to 1500-2000 rpm, further decelerating, and finally accelerating again, while continuously supplying the coating solution to the center, ensuring concentric diffusion and uniform film thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the substrate is rotated at high speed in the first step, then the coating solution is quickly distributed across the substrate, but the coating solution dries and fluidity decreases leading to irregular diffusion and coating mottles
Solution Approach 1:
The coating process is divided into four distinct steps with different rotation speeds: first step (high speed for initial distribution), second step (decelerated speed to maintain fluidity), third step (further decelerated speed for continued diffusion), and fourth step (accelerated speed for final uniformity). This segmentation allows each step to optimize for its specific function, preventing premature drying while achieving uniform coating
Solution Approach 2:
The rotation speed is dynamically adjusted throughout the coating process rather than maintaining a constant speed. The system transitions from high speed to decelerated speeds and then accelerates again, adapting the rotational dynamics to the evolving state of the coating solution to prevent drying and ensure uniform diffusion
2Manufacturing precision
If the supply amount of coating solution is reduced, then the coating precision is improved, but the coating solution becomes insufficient for uniform diffusion
Solution Approach 1:
The coating solution supply is maintained continuously from the first step through the middle of the third step, ensuring that sufficient coating solution is available throughout the diffusion process. This continuous supply compensates for the reduced total amount by ensuring optimal availability during critical diffusion phases
3Manufacturing precision
If the rotation speed is decelerated to maintain fluidity, then the coating uniformity is improved, but the diffusion speed decreases
Solution Approach 1:
The rotation speed follows a periodic pattern: high speed initially for rapid distribution, then decelerated phases for fluidity maintenance, and finally accelerated phase for enhanced diffusion. This periodic variation in rotational speed balances the competing requirements of diffusion speed and coating uniformity
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 method allows for uniform application of a small amount of coating solution without causing mottles, reducing the supply amount needed and achieving consistent film thickness across the substrate.
Implementation Method 1
diffusing the resist solution on the wafer by a centrifugal force
Data Source
AI summary
A substrate is rotated at a first rotation number (first step). The rotation of the substrate is decelerated to 1500 rpm that is a second rotation number and the substrate is rotated at the second rotation number for 0.5 seconds (second step). The rotation of the substrate is further decelerated to a third rotation number and the substrate is rotated at the third rotation number (third step). The rotation of the substrate is accelerated to a fourth rotation number and the substrate is rotated at the fourth rotation number (fourth step). A resist solution is continuously supplied to a center portion of the substrate from a middle of the first step to a middle of the third step.