Substrate Drying via Puddle Film and IPA Replacement
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Solution Overview
Problem
Existing substrate drying methods using low surface-tension solvents like IPA result in high consumption due to rapid replacement, leading to partial drying and watermark issues due to Marangoni convection.
Innovation Solution
A method involving a substrate processing apparatus that reduces the rotation speed to form a puddle-like liquid film, supplies low surface-tension solvent to the center of the substrate to replace the processing liquid, and expands the replaced region radially, allowing for efficient solvent use while minimizing Marangoni convection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If low surface-tension solvent is supplied in large amount to replace rinsing liquid quickly, then replacement speed is improved, but solvent consumption increases and Marangoni convection occurs causing partial drying
Solution Approach 1:
The substrate rotation speed is reduced before supplying the low surface-tension solvent, creating a thicker liquid film in advance. This preliminary action allows the solvent to replace the rinsing liquid effectively while preventing Marangoni convection and reducing solvent consumption.
Solution Approach 2:
The rotation speed parameter is changed from a constant high speed to a reduced speed during the solvent replacement phase. This parameter change thickens the liquid film, suppresses Marangoni convection, and enables efficient solvent replacement with lower consumption.
2Reliability
If rotation speed is reduced to form thicker liquid film, then Marangoni convection is suppressed, but replacement efficiency decreases
Solution Approach 1:
The substrate processing uses periodic variation in rotation speed: high speed during rinsing, then reduced speed during solvent replacement, and finally high speed for drying. This periodic action achieves both uniform liquid film formation and efficient solvent replacement.
Solution Approach 2:
The rotation speed is dynamically adjusted according to the processing stage: reduced during solvent replacement to maintain thick liquid film and prevent Marangoni convection, then increased for efficient drying. This dynamic control optimizes both film uniformity and processing efficiency.
3Productivity
If constant high rotation speed is maintained, then drying efficiency is improved, but liquid film becomes thin causing Marangoni convection and watermarks
Solution Approach 1:
The low surface-tension solvent is supplied to the central part of the substrate before high-speed drying begins. This preliminary action ensures the liquid film has sufficient thickness and solvent concentration to prevent Marangoni convection during the subsequent high-speed drying phase, maintaining surface quality.
Solution Approach 2:
The low surface-tension solvent supply continues during the transition to high-speed drying, maintaining the beneficial liquid film characteristics throughout the drying process. This continuous action ensures both high drying efficiency and watermark-free surface quality.
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 reduces the amount of low surface-tension solvent used and prevents partial drying, effectively maintaining a thicker liquid film to suppress Marangoni convection and minimize watermark formation.
Implementation Method 1
supplying a low surface-tension solvent whose surface tension is lower than that of the processing liquid to a central part of the substrate surface to form a replaced region replaced with the low surface-tension solvent in the central part of the substrate surface
Implementation Method 2
the substrate is rotated at a high speed thereafter, which removes IPA from the substrate surface and the substrate surface is dried
Implementation Method 3
the concentration of the low surface-tension solvent in a mixed part MR of the liquid film mixed with the low surface-tension solvent is increased. As a result, there occurred that the substrate surface Wf is partly dried due to the generation of Marangoni convection in the mixed part MR
Data Source
AI summary
After the rinsing processing is completed, the rotation speed of the substrate is reduced from 600 rpm to 10 rpm to form a puddle-like DIW liquid film. After the supply of DIW is stopped, the control unit waits for a predetermined time (0.5 seconds) so that the film thickness t1 of the puddle-like liquid film becomes approximately uniform. Then, IPA is discharged to a central part of the surface of the substrate at a flow rate of 100 (mL/min) for instance. By the supply of IPA, DIW is replaced with IPA at the central part of the surface of the substrate to form a replaced region. Further, after three seconds of IPA supply, the rotation speed of the substrate is accelerated from 10 rpm to 300 rpm. This causes the replaced region to expand in a radial direction of the substrate so that the entire surface of the substrate is replaced with the low surface-tension solvent.