Substrate Drying via Marangoni Convection for Particle Removal
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Solution Overview
Problem
Existing substrate drying methods often result in particles from processing liquids remaining on the substrate surface after drying, which can lead to defects and water marks.
Innovation Solution
A substrate processing method involving a substrate holding step, liquid film formation, vapor atmosphere filling, thin film region formation and expansion, and Marangoni convection to remove particles by dissolving low surface tension vapors into the processing liquid, preventing particle deposition on the substrate surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If vapor of low surface tension liquid (IPA) is sprayed to the liquid film of processing liquid to form liquid film-removed region, then drying speed is improved, but particles contained in processing liquid appear on substrate surface
Solution Approach 1:
The substrate surface is divided into liquid film-removed region (where vapor is supplied) and liquid film region (where liquid film remains). This segmentation allows different regions to serve different functions: the removed region provides rapid drying, while the liquid film region prevents particle deposition through Marangoni convection.
Solution Approach 2:
The liquid film acts as an intermediary between the substrate surface and the environment. By maintaining a liquid film in specific regions, particles are trapped and removed with the liquid rather than depositing on the substrate. The vapor-liquid interface serves as a mediator that enables controlled evaporation and convection.
Solution Approach 3:
The surface tension parameter is exploited by introducing vapor of low surface tension liquid (IPA) to create surface tension gradients. This parameter change drives Marangoni convection in the liquid film, which circulates particles away from the substrate surface and prevents their deposition.
2Manufacturing precision
If vapor atmosphere is filled around liquid film and substrate is rotated to form thin film region, then particle removal is improved, but processing complexity increases
Solution Approach 1:
The substrate is rotated during the drying process to dynamically control the liquid film thickness and distribution. This rotation creates a thin film region that enhances particle removal through centrifugal force and improved vapor penetration, while the dynamic motion prevents particle settling.
Solution Approach 2:
The vapor atmosphere is maintained continuously around the liquid film throughout the drying process, ensuring sustained Marangoni convection and particle removal. The continuous vapor supply prevents particle deposition while the liquid film gradually evaporates, maintaining a clean substrate surface throughout.
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
Effectively removes particles and reduces water marks by utilizing Marangoni convection to expel particles with the processing liquid, ensuring a clean and dry substrate surface.
Implementation Method 1
a vapor atmosphere that contains vapor of a low surface tension liquid whose lower surface tension than the processing liquid is filled around the liquid film of the processing liquid... due to a difference in the low surface tension liquid in concentration based on a difference in local thickness... there occurs the Marangoni convection which flows in a direction from the thin film of the processing liquid via the boundary-close portion to the inside of the liquid film of the processing liquid
Implementation Method 2
the substrate is raised in rotational speed... the processing liquid at a portion of the liquid film is subjected to a centrifugal force resulting from rotation of the substrate, pressed and expanded outward in a radial direction. As a result, the liquid film at the portion is decreased in thickness to form a thin film of the processing liquid
Implementation Method 3
Since the vapor atmosphere is kept around an entire surface on the upper surface of the substrate, vapor of the low surface tension liquid will not undergo progressive diffusion. As a result, progressive evaporation of the low surface tension liquid contained in the thin film is reduced or prevented.
Data Source
AI summary
A substrate processing method including a vapor atmosphere filling step in which a vapor atmosphere which contains vapor of a low surface tension liquid whose lower surface tension than a processing liquid is filled around a liquid film of the processing liquid, a thin film region forming step in which, in parallel with the vapor atmosphere filling step, a substrate is rotated at a predetermined thin film region forming speed, to partially remove the processing liquid, thereby forming a thin film region on the liquid film of the processing liquid, a thin film region expanding step in which, in parallel with the vapor atmosphere filling step, the thin film region is expanded to an outer circumference of the substrate, and a thin film removing step in which the thin film is removed from the upper surface after the thin film region expanding step.