Wafer Coating Method for Uniform Film via Annular Solvent Film
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Solution Overview
Problem
The existing coating methods for semiconductor wafers face challenges in achieving uniform distribution of the coating solution due to variations in wetting properties caused by the type of primer coating, leading to non-uniform film thickness, especially in the peripheral area of the wafer.
Innovation Solution
A coating method that forms an annular solvent liquid film in the peripheral area of the substrate and supplies the coating solution to the center while rotating at a first speed, then increases the rotational speed to spread the solution uniformly, with solvent supply continued until just before contact with the solvent liquid film, preventing non-uniform distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the solvent is supplied to a position between the center and the periphery of the wafer while rotating the wafer at a low speed, then the wetting properties of the wafer are improved and in-plane uniformity is enhanced, but when the contact angle between the primer coating and the solvent is large, the solvent cannot be kept in an annular shape and moves toward the center due to surface tension
Solution Approach 1:
The patent applies preliminary action by first forming an annular liquid film of the solvent in the peripheral area before supplying the coating solution to the center. This pre-formed annular film serves as a stable foundation that prevents the solvent from moving toward the center due to surface tension, thereby maintaining the annular shape stability while achieving uniform wetting properties across the wafer surface.
Solution Approach 2:
The patent segments the coating process into distinct steps: first forming an annular solvent liquid film in the peripheral area, then supplying the coating solution to the center, and finally spreading the coating solution by increasing rotational speed. This segmentation allows each step to be optimized independently, ensuring both annular shape stability and in-plane uniformity.
2Productivity
If the coating solution is supplied to the center of the wafer and allowed to spread by centrifugal force, then the coating film is formed on the wafer, but the degree of improvement in wetting properties differs between the center and periphery leading to non-uniform film thickness
Solution Approach 1:
The patent applies local quality by creating different liquid film configurations in different areas of the wafer: an annular solvent liquid film in the peripheral area and a central coating solution film. This local differentiation ensures that each area receives the appropriate liquid distribution, with the peripheral annular film providing uniform wetting and the central film providing efficient coating solution delivery, thereby achieving both productivity and film thickness uniformity.
3Stability of the object's composition
If the supply of the solvent is continued until just before the coating solution comes into contact with the liquid film of the solvent, then the annular liquid film shape is maintained and non-uniform distribution is prevented, but the timing control must be precise to avoid contact
Solution Approach 1:
The patent applies feedback by monitoring the position and shape of the annular liquid film during the coating process. The supply of solvent is continued until just before the coating solution comes into contact with the liquid film, with the timing controlled based on feedback from sensors that detect the film position and rotational speed, thereby maintaining the annular shape while preventing non-uniform distribution without requiring overly complex control systems.
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 ensures uniform application of the coating solution across the substrate surface, reducing the amount of coating solution used and achieving in-plane uniformity of the coating film.
Implementation Method 1
allowing the coating solution to spread on the substrate by rotating the substrate at a second rotational speed which is higher than the first rotational speed
Implementation Method 2
When wetting of the solvent to the primer coating is poor (the contact angle between the primer coating and the solvent is large), it is difficult to keep the solvent in an annular shape on the wafer after supplying the solvent to a position between the center and the periphery of the wafer
Implementation Method 3
a solvent Q that has been supplied to a peripheral portion of a wafer W may move toward the center of the wafer W due to the surface tension, and the solvent near the center of the wafer W may move toward the periphery of the wafer W due to the centrifugal force
Data Source
AI summary
There is provided a coating method which can apply a coating solution uniformly onto a substrate surface while reducing the amount of the coating solution supplied. The coating method for applying a coating solution onto a wafer includes the steps of: supplying a solvent for the coating solution onto the wafer to form an annular liquid film of the solvent in a peripheral area of the wafer; supplying the coating solution to the center of the wafer while rotating the wafer at a first rotational speed (time t1-t2); and allowing the coating solution to spread on the wafer by rotating the wafer at a second rotational speed which is higher than the first rotational speed (time t4-t5). The supply of the solvent is continued until just before the coating solution comes into contact with the liquid film of the solvent (time t0-t3).