Ultrasonic Wafer Cleaning with Stable Cavitation Control
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Solution Overview
Problem
Existing methods for cleaning semiconductor wafers using ultra or mega sonic devices often result in unstable cavitation, which can damage patterned structures while being inefficient in removing fine particles, especially in 3D NAND hole structures.
Innovation Solution
The method involves controlling bubble cavitation by alternating sonic power supply settings with different powers and frequencies at specific time intervals to maintain stable cavitation, ensuring that the temperature inside the bubble reaches a critical implosion temperature and then cools down, thereby preventing damage to the wafer and enhancing particle removal efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If ultra or mega sonic power is continuously applied to clean the wafer, then particle removal efficiency is improved, but cavitation becomes unstable and damages patterned structures
Solution Approach 1:
The patent applies periodic pulsed sonic power instead of continuous power. The controller alternates between applying sonic power at a first frequency (higher particle removal efficiency) and a second frequency (lower particle removal efficiency), creating periodic action that maintains stable cavitation while preventing structure damage. This temporal modulation resolves the contradiction by distributing the mechanical stress over time.
Solution Approach 2:
The patent dynamically adjusts the sonic power frequency based on cleaning progress and cavitation stability. The system transitions from a first frequency to a second frequency, making the cleaning process adaptive rather than static. This dynamic control allows the system to optimize particle removal while preventing cavitation-induced damage to sensitive patterns.
2Productivity
If high power sonic cleaning is used to remove fine particles efficiently, then cleaning speed is improved, but cavitation becomes violent and damages the wafer structure
Solution Approach 1:
The patent uses periodic pulsing between high power (first frequency) and low power (second frequency) states. During high power phases, fine particles are removed efficiently; during low power phases, the cavitation intensity is reduced to prevent structural damage. This periodic modulation enables high cleaning speed while preserving wafer structure.
Solution Approach 2:
The patent maintains continuous cleaning action by alternating between two sonic frequencies rather than stopping. The first frequency provides aggressive particle removal, while the second frequency provides gentler cleaning that prevents damage. This continuous dual-frequency approach maintains cleaning efficacy throughout the process without interrupting the useful action.
3Object-affected harmful factors
If dilute chemicals are used to avoid side wall loss, then chemical damage is reduced, but particle removal efficiency decreases requiring mechanical force
Solution Approach 1:
The patent replaces chemical cleaning mechanisms with mechanical ultrasonic cleaning. By using controlled cavitation from pulsed sonic waves, the system achieves particle removal through mechanical means rather than chemical dissolution. This substitution allows the use of dilute chemicals (reducing side wall loss) while maintaining effective particle removal through ultrasonic mechanical action.
Solution Approach 2:
The patent changes the cleaning mechanism parameter from chemical concentration to mechanical energy frequency. Instead of increasing chemical strength to improve particle removal, the system adjusts sonic power frequency and pulse duration. This parameter change enables effective cleaning with dilute chemicals by relying on controlled mechanical cavitation energy.
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 allows for effective and damage-free ultra/mega-sonic cleaning of wafers with patterned structures by maintaining stable cavitation, increasing particle removal efficiency while minimizing damage to the wafer, even at smaller feature sizes.
Implementation Method 1
Ultra sonic or mega sonic wave will generate bubble cavitation which applies mechanical force to wafer structure
Implementation Method 2
a source of energy vibrates an elongated probe which transmits the acoustic energy into the fluid
Implementation Method 3
setting the sonic power supply with power P1 at a time interval shorter than τ1, and setting the sonic power supply with power P2 at a time interval longer than τ2... τ1 is a time interval that the temperature inside bubble raises to a critical implosion temperature; and τ2 is a time interval that the temperature inside bubble falls down to a temperature much lower than the critical implosion temperature
Data Source
AI summary
The present invention discloses a method for cleaning substrate without damaging patterned structure on the substrate using ultra/mega sonic device, comprising: applying liquid into a space between a substrate and an ultra/mega sonic device; setting an ultra/mega sonic power supply at frequency f1 and power P1 to drive said ultra/mega sonic device; after micro jet generated by bubble implosion and before said micro jet generated by bubble implosion damaging patterned structure on the substrate, setting said ultra/mega sonic power supply at frequency f2 and power P2 to drive said ultra/mega sonic device; after temperature inside bubble cooling down to a set temperature, setting said ultra/mega sonic power supply at frequency f1 and power P1 again; repeating above steps till the substrate being cleaned.