Substrate Cleaning Method for Hydrophobic Wafer Drying
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Solution Overview
Problem
Existing substrate cleaning methods for semiconductor wafers and flat panel displays face challenges in preventing particle formation due to hydrophobic surfaces, particularly when using hydrofluoric acid, as rinsing liquids can rebound and leave watermarks or droplets, leading to contamination.
Innovation Solution
A substrate cleaning method involving controlled rotational speed reduction, liquid supply from the center to the periphery, and inert gas drying from the center to the periphery using a slit nozzle, ensuring uniform drying and minimizing particle formation on hydrophobic surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the wafer is spun at high speed during drying, then centrifugal force can remove rinsing liquid effectively, but rinsing liquid rebounds from the chamber and adheres to dried parts causing particles
Solution Approach 1:
The patent applies preliminary action by performing the drying process at reduced rotational speed before increasing speed. The method first dries the wafer at a first rotational speed (lower than cleaning speed), then increases to a second rotational speed for final drying. This preliminary low-speed drying prevents liquid rebound and particle generation while still achieving effective drying through controlled centrifugal force.
2Manufacturing precision
If the wafer is cleaned using hydrofluoric acid, then cleaning effectiveness is improved, but the front surface becomes hydrophobic causing rinsing liquid to shake off prematurely and create watermarks
Solution Approach 1:
The patent applies dynamics by dynamically adjusting the rotational speed during the drying process. The method transitions from a first rotational speed to a second rotational speed, and further to a third rotational speed, optimizing the centrifugal force at each stage. This dynamic speed adjustment ensures uniform drying across the wafer surface regardless of hydrophobicity, preventing watermark formation while maintaining cleaning effectiveness.
3Speed
If high speed rotation is used during drying, then liquid removal is accelerated, but liquid drops remain at the wafer center causing particle generation
Solution Approach 1:
The patent applies preliminary action by first drying the wafer at a lower first rotational speed, which allows uniform liquid removal across the surface including the center region. Only after this preliminary drying is complete does the method increase to higher rotational speeds for final drying. This sequential approach prevents liquid drop retention at the center while still achieving rapid liquid removal.
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 effectively reduces particle formation and contamination by ensuring uniform drying and preventing liquid rebound, even on substrates with hydrophobic areas, enhancing the cleaning process for various substrates with hydrophobic patterns.
Implementation Method 1
the rinsing liquid in the periphery of the wafer may be shaken off in a short period by centrifugal force
Implementation Method 2
supplying a gas towards the substrate while rotating the substrate at a higher rotational speed than the second rotational speed
Data Source
AI summary
A substrate cleaning method including rotating a substrate at least for a period, supplying a liquid to the front surface of the substrate and cleaning the substrate, and drying the substrate is provided. Said drying of the substrate includes: reducing a rotational speed of the substrate to a first rotational speed lower than a rotational speed for cleaning the substrate; starting to move a liquid supply position from approximately the center of the substrate towards a peripheral portion when the rotational speed of the substrate is reduced down to the first rotational speed; stopping liquid supply when the second rotational speed lower than the first rotational speed is reached; increasing the rotational speed from the second rotational speed; and supplying a gas towards the substrate while rotating the substrate at a higher rotational speed than the second rotational speed.