Substrate Cleaning via Ultrasonic Back-Surface Cavitation
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Solution Overview
Problem
Existing substrate cleaning methods fail to effectively prevent pattern collapse during ultrasonic cleaning of the front surface while adequately cleaning the back surface, especially with fine particles, due to reduced detergency and increased costs associated with cooling processes.
Innovation Solution
A substrate cleaning method and apparatus that involves hydrophobization of the front surface patterns, forming a liquid film on the front surface, and using ultrasonic wave-applied liquid to clean the back surface, preventing cavitation-induced pattern collapse and maintaining cleaning efficacy without the need for cooling processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If ultrasonic waves are applied to clean the back surface of the substrate, then particle removal effectiveness is improved, but pattern collapse on the front surface occurs due to cavitation
Solution Approach 1:
The substrate surface is segmented into front surface (with patterns) and back surface (to be cleaned). The cleaning process is segmented into separate steps: hydrophobization of front surface patterns, formation of protective liquid film on front surface, and ultrasonic cleaning of back surface only. This segmentation allows differential treatment of different surfaces to avoid pattern damage while achieving effective cleaning.
Solution Approach 2:
A liquid film is introduced as an intermediary protective layer on the front surface patterns during ultrasonic cleaning. This liquid film acts as a mediator that absorbs and dissipates cavitation energy, preventing direct transmission of harmful ultrasonic vibrations to the patterns while allowing effective cleaning of the back surface.
2Object-affected harmful factors
If deaerated processing liquid is used for ultrasonic cleaning, then cavitation bubble generation is reduced and pattern damage is suppressed, but detergency deteriorates and fine particle removal becomes insufficient
Solution Approach 1:
Different gas saturation conditions are applied to different surfaces: the front surface is covered with a liquid film that prevents cavitation damage to patterns, while the back surface is exposed to ultrasonic wave-applied liquid with adequate dissolved gas to generate cavitation bubbles for effective fine particle removal. This local quality differentiation resolves the contradiction between pattern protection and cleaning effectiveness.
3Object-affected harmful factors
If a liquid film is formed on the front surface to protect patterns, then pattern collapse is prevented, but additional processing steps and cooling gas consumption increase running costs
Solution Approach 1:
The harmful cavitation action is extracted and directed only to the back surface where cleaning is needed, while the front surface with patterns is protected by the liquid film. This extraction approach eliminates the need for cooling gas to prevent pattern damage, as the liquid film inherently protects the patterns during back surface cleaning.
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
The method effectively prevents pattern collapse on the front surface during ultrasonic cleaning of the back surface, achieving high cleaning efficiency while reducing costs and environmental impact by eliminating the need for cooling processes.
Implementation Method 1
supplying an ultrasonic wave-applied liquid, which is obtained by applying ultrasonic waves upon a liquid, to the other principal surface
Implementation Method 2
generating micron-size air bubbles (cavitation bubbles) in the cleaning liquid. As powerful flows are created in the cleaning liquid owing to movements such as growth and collapse of cavitation bubbles
Implementation Method 3
hydrophobizing surfaces of patterns formed on one principal surface of a substrate
Implementation Method 4
forming a liquid film on the front surface of the substrate, freezes the liquid film and accordingly reinforces the patterns
Data Source
AI summary
After hydrophobization of surfaces of patterns, a liquid film of pure water or the like is formed on the surfaces of the substrate. At this stage, the liquid of the liquid film cannot be present between the patterns because of hydrophobization, and gas is present there. With the front surface of the substrate covered with the liquid film, a liquid to which ultrasonic waves are applied is supplied to the back surface of the substrate, whereby the back surface of the substrate is cleaned due to the cavitation collapse energy in the liquid caused by the ultrasonic waves. While collapse of cavitation occurs at the front surface of the substrate, the presence of the gas between the patterns prohibits collapse of cavitation between the patterns, the liquid film can prevent contamination while preventing collapse of the patterns, and the back surface of the substrate is cleaned favorably.