Semiconductor Wafer Sonic 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 the patterned structures on the wafers, especially at smaller feature sizes, as they fail to control mechanical force effectively and efficiently remove fine particles.
Innovation Solution
The method involves controlling bubble cavitation by adjusting sonic power supply parameters such as power and frequency at specific time intervals, monitoring the operation status of the sonic power supply to prevent damage, and maintaining stable cavitation to avoid implosion and ensure efficient particle removal without harming the wafer structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If ultra or mega sonic power is increased to remove fine particles efficiently, then particle removal efficiency is improved, but bubble cavitation becomes unstable and damages patterned structures on the wafer
Solution Approach 1:
The patent applies periodic pulsed sonic power instead of continuous power to the cleaning fluid. The sonic power is applied in cycles with specific duty ratios (e.g., 10-90%, 20-80%, 30-70%), where the power is turned on and off periodically. This periodic action allows bubbles to form and collapse gently during the off-period, preventing violent cavitation damage, while still achieving effective particle removal during the on-period. The pulsed operation maintains stable cavitation that cleans particles without damaging the wafer's patterned structures.
2Object-affected harmful factors
If dilute chemicals or de-ionized water are used to reduce side wall loss, then chemical damage is reduced, but particle removal efficiency decreases
Solution Approach 1:
The patent replaces chemical cleaning mechanisms with mechanical ultrasonic cleaning mechanisms. Instead of relying on chemical reactions to remove particles, the invention uses ultrasonic waves to generate cavitation bubbles in the cleaning fluid. These bubbles collapse and produce mechanical forces that physically remove particles from the wafer surface and from inside trenches and vias. This mechanical substitution allows the use of dilute chemicals or de-ionized water without sacrificing particle removal efficiency, thereby reducing side wall loss while maintaining effective cleaning.
3Area of stationary object
If continuous sonic power is applied to clean the wafer, then cleaning coverage is improved, but bubble temperature rises to critical levels causing violent cavitation
Solution Approach 1:
The patent implements periodic pulsed sonic power with controlled duty ratios to prevent bubble temperature from reaching critical levels. During the off-period of the pulse cycle, bubbles have time to cool down and dissipate heat to the surrounding fluid, preventing temperature accumulation. This periodic interruption of energy input maintains bubble temperatures below the critical threshold for violent cavitation, while the cumulative effect over multiple cycles still achieves comprehensive cleaning coverage across the entire wafer surface.
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 damage-free ultra or mega sonic cleaning of semiconductor wafers by maintaining stable bubble cavitation, effectively removing particles without damaging the patterned structures, even at smaller feature sizes, thereby ensuring the integrity of the wafer surfaces.
Implementation Method 1
Ultra sonic or mega sonic wave will generate bubble cavitation which applies mechanical force to the wafer structure
Implementation Method 2
a source of energy vibrates an elongated probe which transmits the acoustic energy into the fluid
Implementation Method 3
a source of energy vibrates an elongated probe which transmits the acoustic energy into the fluid
Implementation Method 4
applying liquid into a space between a semiconductor wafer and an ultra or mega sonic device
Data Source
AI summary
A method for cleaning semiconductor substrate without damaging patterned structure on the semiconductor substrate using ultra/mega sonic device comprises 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 the ultra/mega sonic device; before bubble cavitation in the liquid damaging patterned structure on the substrate, setting the ultra/mega sonic power supply at zero output; after temperature inside bubble cooling down to a set temperature, setting the ultra/mega sonic power supply at frequency f1 and power P1 again; detecting power on time at power P1 and frequency f1 and power off time separately or detecting amplitude of each waveform output by the ultra/mega sonic power supply; comparing the detected power on time with a preset time τ1, or comparing the detected power off time with a preset time τ2, or comparing detected amplitude of each waveform with a preset value, if the detected power on time is longer than the preset time τ1, or the detected power off time is shorter than the preset time τ2, or the detected amplitude of any waveform is larger than the preset value, shut down the ultra/mega sonic power supply and send out an alarm signal.