Megasonic Cleaning Boundary Layer Control
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Solution Overview
Problem
Megasonic cleaning processes for microelectronic substrates face limitations due to the boundary layer shielding effect, which reduces cavitation energy and cleaning efficacy, as increasing sonic frequency decreases boundary layer thickness but also decreases cavitation energy, making it difficult to effectively remove surface particles without damaging delicate features.
Innovation Solution
The use of two separate sonic waves with different frequencies, where one wave imparts cavitation energy and the other regulates the boundary layer thickness by impinging on the substrate surface from different angles, overcoming the tradeoff between boundary layer thickness and cavitation energy, thereby enhancing cleaning efficacy without inducing damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If megasonic cleaning processes use higher sonic frequencies to reduce boundary layer thickness, then boundary layer shielding effect is reduced, but cavitation energy decreases making it difficult to remove surface particles
Solution Approach 1:
The cleaning system segments the sonic frequency into two distinct components: a first frequency (e.g., 800 kHz to 2 MHz) that generates cavitation energy for particle removal, and a second frequency (e.g., 2 MHz to 5 MHz) that reduces boundary layer thickness. This segmentation allows each frequency to perform its specific function without compromising the other, resolving the trade-off between cavitation energy and boundary layer thickness.
Solution Approach 2:
The system merges two separate sonic waves of different frequencies into a single cleaning process. The first sonic wave provides cavitation energy while the second sonic wave controls boundary layer thickness, and both waves operate simultaneously in the same liquid medium to achieve enhanced cleaning efficacy without the limitations of single-frequency processes.
2Productivity
If ultrasonic cleaning processes are used to remove more particles, then cleaning efficacy is improved, but damage to substrate features increases
Solution Approach 1:
The system applies different sonic frequencies to different functional requirements: the first frequency (lower range) is optimized for generating cavitation energy to remove particles, while the second frequency (higher range) is optimized for reducing boundary layer thickness with minimal damage. This local quality assignment allows each frequency band to perform its specific function optimally, achieving effective cleaning while protecting delicate substrate features.
Solution Approach 2:
The system changes the frequency parameter of the sonic waves to resolve the contradiction. By operating at megasonic frequencies (800 kHz and above) rather than traditional ultrasonic frequencies, the system reduces cavitation energy and boundary layer thickness simultaneously, enabling effective particle removal from delicate features without the excessive damage associated with lower-frequency ultrasonic cleaning.
3Object-affected harmful factors
If single-frequency megasonic cleaning is used to minimize damage, then substrate feature protection is improved, but cleaning efficacy is insufficient due to boundary layer shielding
Solution Approach 1:
The cleaning system segments the sonic frequency spectrum into two functional components: a first frequency for cavitation energy generation and a second frequency for boundary layer thickness control. This segmentation overcomes the limitation of single-frequency processes where increasing frequency to reduce boundary layer thickness simultaneously reduces cavitation energy, thereby maintaining both substrate protection and cleaning efficacy.
Solution Approach 2:
The multifrequency megasonic system performs multiple functions simultaneously: it generates cavitation energy for particle removal, reduces boundary layer thickness to enhance cavitation effectiveness, and protects delicate substrate features from damage. This multi-functionality is achieved by combining two sonic waves of different frequencies, each contributing to different aspects of the cleaning process.
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 multifrequency approach increases the exposure of particles to cavitation energy, improving cleaning efficacy while minimizing damage to substrate features, achieving comparable or greater cleaning effectiveness than single-frequency processes without the associated damage.
Implementation Method 1
using the pressure waves to induce cavitation events proximate the substrate surface. These events can impart cavitation energy to particles attached to the surface that can remove or detach the particles.
Implementation Method 2
the second frequency f2 can regulate a thickness of a boundary layer in the liquid
Data Source
AI summary
Megasonic cleaning systems and methods of using megasonic pressure waves to impart cavitation energy proximate a surface of a microelectronic substrate are disclosed herein. In one embodiment, a megasonic cleaning system includes a process tank for containing a liquid, a support element for carrying a substrate submerged in the liquid, and first and second transducers positioned in the tank. The first transducer is further positioned and/or operated to initiate cavitation events in a bulk portion of the liquid proximate a surface of the substrate. The second transducer is further positioned and/or operated to control an interface of fluid friction between the substrate and the bulk portion of the liquid.