Sonic Power Control for Semiconductor Wafer Cleaning
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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 on the wafers while being inefficient in removing fine particles, especially at smaller feature sizes.
Innovation Solution
The method involves controlling bubble cavitation by varying sonic power supply settings, including power and frequency, over specific time intervals to maintain stable cavitation, ensuring that the temperature and bubble size do not exceed critical levels that could cause damage to the wafer patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If ultra or mega sonic devices are used to generate violent cavitation for particle removal, then particle removal efficiency is improved, but patterned structures on the wafer are damaged
Solution Approach 1:
The patent applies periodic pulsed sonic action instead of continuous sonic exposure. The cleaning process uses alternating cycles of sonic exposure (to generate cavitation for particle removal) and rest periods (to allow bubble collapse and prevent cumulative damage). This periodic action enables effective particle removal while limiting the duration of violent cavitation to prevent damage to fine patterned structures.
Solution Approach 2:
The patent dynamically adjusts sonic power levels during the cleaning process. By varying the sonic power in real-time based on process conditions, the system optimizes cavitation intensity for particle removal while preventing excessive power that would cause damage to delicate patterns. This dynamic control allows adaptation to different cleaning stages and wafer conditions.
2Productivity
If continuous high power sonic exposure is applied, then particle removal efficiency is improved, but bubble temperature reaches critical implosion levels causing damage
Solution Approach 1:
The patent implements periodic pulsed sonic cycles with controlled duty cycles. During the sonic exposure phase, bubbles are generated and heated; during the rest phase, bubbles collapse and temperature decreases. By controlling the pulse width and duty cycle, the system maintains cleaning effectiveness while allowing bubble temperature to return to safe levels before the next pulse, preventing critical implosion temperatures.
Solution Approach 2:
The patent incorporates rest periods between sonic pulses that serve as a cushioning mechanism. During these rest periods, the system allows bubble temperature to decrease and energy to dissipate before initiating the next sonic pulse. This beforehand cushioning prevents cumulative temperature buildup that would lead to critical implosion levels and damage to wafer structures.
3Manufacturing precision
If dilute chemicals or de-ionized water are used for cleaning, then side wall loss is reduced, but particle removal efficiency decreases
Solution Approach 1:
The patent merges mechanical cavitation cleaning with chemical cleaning in a unified process. The pulsed sonic field generates cavitation that mechanically removes particles from trenches and vias, while dilute chemicals provide chemical cleaning action. The combination of mechanical and chemical mechanisms achieves effective particle removal without requiring aggressive chemicals that would cause side wall loss.
Solution Approach 2:
The patent replaces the need for strong mechanical-chemical action with acoustic-mechanical cavitation. Instead of relying on aggressive chemicals or high mechanical stress to remove particles, the system uses ultrasonic/megasonic cavitation to generate localized mechanical forces that detach particles. This substitution enables effective cleaning with mild chemicals, preserving side walls while removing contaminants.
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 cleaning of semiconductor wafers by maintaining stable bubble cavitation, preventing violent implosions and ensuring efficient particle removal without damaging the delicate structures on the wafers.
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
a source of energy vibrates an elongated probe which transmits the acoustic energy into the fluid
Data Source
AI summary
A method for cleaning semiconductor 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; before bubble cavitation in said liquid 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. Normally, if f1=f2, then P2 is equal to zero or much less than P1; if P1=P2, then f2 is higher than f1; if the f1<f2, then, P2 can be either equal or less than P1.