Wafer-Cleaning Brush Break-In Using Megasonic Debris Removal
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Solution Overview
Problem
Current wafer-cleaning brushes, especially post-CMP cleaning brushes, often have ions, liquid-borne particles, and trace metals on their surfaces, which can be defect sources during inline wafer processing, and the breaking-in process is time-consuming and inefficient, requiring multiple dummy wafers.
Innovation Solution
A method involving passing a wafer with a polished and unpolished side between a pair of rotating cylindrical brushes with protrusions, using a cleaning solution and washboards to remove debris, and applying megasonic waves and gases to enhance cleaning, while the brushes are rotated and alternately contacted with washboards to remove contaminants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional breaking-in process is used for new wafer-cleaning brushes, then the brushes can be prepared for use, but the process is time-consuming and requires hundreds of dummy wafers
Solution Approach 1:
The patent replaces the conventional mechanical breaking-in process (rubbing brushes against each other using dummy wafers) with an ultrasonic cleaning system. The ultrasonic waves generate cavitation bubbles that mechanically implode to remove contaminants from the brush surface, achieving the same cleaning objective through a different physical mechanism that is significantly faster and more efficient.
Solution Approach 2:
The patent utilizes the phase transition of liquid to gas through ultrasonic cavitation. High-frequency ultrasonic waves create microscopic bubbles in the cleaning solution that rapidly form and collapse, generating localized high-pressure shocks that dislodge contaminants from the brush surface without requiring prolonged mechanical contact.
2Productivity
If conventional cleaning methods are used, then the process is simple, but the cleaning effectiveness is insufficient and leaves ions, particles, and trace metals on brush surfaces
Solution Approach 1:
The patent introduces an ultrasonic cleaning bath as an intermediary system between the brush and the cleaning solution. This intermediary device generates ultrasonic waves that propagate through the liquid, creating cavitation effects that enhance the cleaning action. The ultrasonic field acts as a mediator that transfers energy to the brush surface through the liquid medium, achieving superior cleaning without direct mechanical contact.
Solution Approach 2:
The patent applies high-frequency mechanical vibrations through ultrasonic waves to the cleaning solution and brush assembly. These vibrations create intense localized mechanical stresses through cavitation and micro-streaming, which effectively remove stubborn contaminants, ions, and trace metals from the brush surface that conventional static or low-energy cleaning methods cannot eliminate.
3Reliability
If brushes are not thoroughly cleaned, then the process is faster, but ions and trace metals remain as defect sources during inline wafer processing
Solution Approach 1:
The patent replaces simple mechanical rubbing with ultrasonic cavitation to achieve thorough cleaning. The ultrasonic field penetrates deep into the brush structure, dislodging embedded contaminants that mechanical methods miss. This substitution maintains process simplicity from the user perspective while dramatically improving cleaning effectiveness and wafer quality outcomes.
Solution Approach 2:
The patent changes the energy parameters of the cleaning process by introducing high-frequency ultrasonic vibrations (typically 20-100 kHz). This parameter change transforms the cleaning mechanism from low-energy mechanical contact to high-energy cavitation, enabling the removal of stubborn contaminants while maintaining operational simplicity through automated ultrasonic cleaning systems.
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 method significantly speeds up the brush breaking-in and cleaning process, improves cleanliness, and prolongs brush life by effectively removing contaminants and enhancing mechanical agitation.
Implementation Method 1
applying megasonic waves and gases to enhance cleaning
Implementation Method 2
applying megasonic waves and gases to enhance cleaning
Implementation Method 3
enhancing mechanical agitation
Implementation Method 4
a pair of rotating cylindrical brushes with protrusions
Data Source
AI summary
A method of cleaning wafer-cleaning brushes includes passing a wafer having a first polished main side and an opposing unpolished backside between a pair of substantially cylindrical shaped wafer-cleaning brushes are rotated about an axial direction of the brushes while passing the wafer between the pair of wafer-cleaning brushes. A cleaning solution is applied to the brushes while passing the wafer between the pair of wafer-cleaning brushes. While passing between the pair of brushes, the first polished main side of the wafer faces a first direction, the first direction is an opposite direction to which a polished side of a production wafer faces during a subsequent polished wafer cleaning operation. The substantially cylindrical shaped wafer-cleaning brushes include a plurality of protrusions on an external surface of the brushes, and the brushes contact the wafer at least a portion of time the wafer is passing between the pair of brushes.