Wafer Polishing Vibration Control via Acceleration Differential
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Solution Overview
Problem
Conventional semiconductor wafer polishing methods generate vibrations when starting the polishing process, leading to wafer cracking and polishing cloth damage, and existing solutions complicate the apparatus structure and require costly modifications to existing facilities.
Innovation Solution
The method involves maintaining a table acceleration smaller than a work carrier acceleration when both are rotated at a predetermined number of revolutions, shifting static friction to dynamic friction early in the process, and ensuring the wafer diameter is 30% or more of the table diameter to reduce vibrations without modifying existing apparatus configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the polishing cloth and wafer are pressed against each other to start polishing, then the polishing rate and surface quality are improved, but vibrations are generated due to maximum static friction
Solution Approach 1:
The work carrier and table are rotated at predetermined speeds before the wafer is pressed against the polishing cloth. This preliminary rotation establishes dynamic motion before contact, preventing the generation of maximum static friction that causes vibrations while ensuring the polishing surfaces are already in motion for high-quality polishing.
Solution Approach 2:
The invention employs dynamic rotation of the work carrier and table before contact, converting the static friction problem into a dynamic friction scenario. By ensuring both surfaces are already rotating when contact occurs, the system operates in a dynamic state that eliminates violent vibrations while maintaining effective polishing pressure.
2Object-affected harmful factors
If the table and work carrier are rotated before pressing the polishing cloth and wafer, then vibrations are reduced, but the polishing rate decreases
Solution Approach 1:
The work carrier and table are rotated at predetermined speeds before the wafer is pressed against the polishing cloth. This preliminary rotation establishes dynamic motion before contact, preventing the generation of maximum static friction that causes vibrations while ensuring the polishing surfaces are already in motion for high-quality polishing.
3Object-affected harmful factors
If piezoelectric elements are installed to dampen vibrations, then vibrations are suppressed, but the apparatus structure becomes complicated
Solution Approach 1:
The work carrier and table are rotated at predetermined speeds before the wafer is pressed against the polishing cloth. This preliminary rotation establishes dynamic motion before contact, preventing the generation of maximum static friction that causes vibrations while ensuring the polishing surfaces are already in motion for high-quality polishing.
Solution Approach 2:
The invention replaces complex mechanical vibration damping systems (such as piezoelectric elements) with a simpler operational procedure: rotating the work carrier and table before contact. This procedural substitution eliminates the need for additional damping components while achieving the same vibration suppression effect.
4Productivity
If the area of contact and loading are increased for large-diameter wafers, then the polishing rate is improved, but frictional force and vibrations are intensified
Solution Approach 1:
The work carrier and table are rotated at predetermined speeds before the wafer is pressed against the polishing cloth. This preliminary rotation establishes dynamic motion before contact, preventing the generation of maximum static friction that causes vibrations while ensuring the polishing surfaces are already in motion for high-quality polishing.
Solution Approach 2:
The invention employs dynamic rotation of the work carrier and table before contact, converting the static friction problem into a dynamic friction scenario. By ensuring both surfaces are already rotating when contact occurs, the system operates in a dynamic state that eliminates violent vibrations while maintaining effective polishing pressure.
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 effectively prevents vibrations during the polishing process, reducing wafer cracking and polishing cloth damage while minimizing facility and maintenance costs, thus improving product yields and efficiency.
Implementation Method 1
frictional forces resulting from rotation of the work carrier 4 as well as the table 2 incurred by friction between the pressed wafer 5 and the polishing cloth 3
Implementation Method 2
a piezoelectric element is installed between bearings for a rotating shaft of a work carrier and a casing for housing the bearings
Implementation Method 3
the piezoelectric element exerts a damping force to the work carrier to attenuate the vibrations
Data Source
AI summary
In a method for polishing a semiconductor wafer by rotating a work carrier and a table while pressing the semiconductor wafer retained by the work carrier against a polishing cloth mounted on the table, at a time when the table and the work carrier both having been at rest are rotated, each at a predetermined number of revolutions, in a condition that the polishing cloth and the semiconductor wafer are pressed against each other, to thereby start polishing, a table acceleration is maintained smaller than a work carrier acceleration. By such maintaining the table acceleration smaller than the work carrier acceleration, vibrations to be generated when the polishing is started can be prevented. In the method for polishing a semiconductor wafer according to the present invention, the diameter of the semiconductor wafer is preferably defined to be 30% or more of the diameter of the table.