Wafer Polishing Control via F/T Value Monitoring
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Solution Overview
Problem
In single-side polishing of silicon wafers, the shape of removal at the outer periphery varies significantly throughout the life of the polishing pad due to changes in physical properties, leading to uneven edge roll-off and reduced flatness, especially near the wafer edge, making it difficult to maintain consistent wafer quality.
Innovation Solution
A method and apparatus that monitor and control the load current (mechanical polishing) and surface temperature (chemical polishing) of the polishing pad to calculate an F/T value, adjusting the rotation speed and polishing pressure in real-time to maintain a constant edge roll-off amount, thereby stabilizing the shape removal at the wafer outer periphery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If polishing is performed at constant pressure and rotation speed throughout polishing pad life, then the polishing process is simple to operate, but the shape of removal at the wafer outer periphery varies significantly leading to uneven edge roll-off
Solution Approach 1:
The patent applies dynamics by transitioning from constant polishing parameters to dynamic adjustment of rotation speed and polishing pressure based on real-time monitoring of polishing pad physical properties. The system continuously adapts parameters during the polishing pad's operational life to compensate for wear and property changes, thereby maintaining consistent wafer edge flatness while preserving operational simplicity through automated control.
Solution Approach 2:
The patent implements feedback control by monitoring the physical properties of the polishing pad (such as temperature, rotation characteristics, or removal rate) in real-time and using this information to automatically adjust polishing parameters. This closed-loop system ensures that variations in pad condition are compensated for, maintaining manufacturing precision without requiring complex manual intervention.
2Manufacturing precision
If polishing parameters are adjusted to compensate for pad wear, then wafer edge flatness is improved, but the device complexity increases due to additional monitoring and control systems
Solution Approach 1:
The patent applies self-service by enabling the polishing system to automatically monitor and adjust its own parameters without external intervention. The system uses built-in sensors and control mechanisms to detect changes in polishing pad condition and autonomously compensates for wear, thereby maintaining precision while minimizing the need for complex external monitoring equipment or manual adjustments.
Solution Approach 2:
The patent utilizes parameter changes by systematically varying polishing parameters (rotation speed, pressure, slurry flow rate) based on the operational state of the polishing pad. This approach allows the system to maintain optimal performance across the pad's entire life cycle by adapting parameters to match changing physical conditions, reducing the need for complex hardware modifications.
3Manufacturing precision
If the rotation speed of the rotating platen is increased to compensate for pad wear, then the shape of removal is maintained, but the energy consumption increases
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting multiple polishing parameters including rotation speed, polishing pressure, and potentially slurry flow rate or viscosity. This multi-parameter approach allows the system to maintain consistent shape of removal while distributing the energy compensation across multiple adjustable variables, thereby reducing the energy penalty compared to relying solely on increased rotation speed.
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 suppresses variations in wafer edge roll-off throughout the polishing pad life, ensuring consistent wafer flatness and quality by dynamically adjusting the polishing parameters based on the F/T value, thereby extending the pad life and maintaining productivity.
Implementation Method 1
measuring the temperature of a polishing cloth affixed onto the upper surface of a polishing rotating platen during machining by using a radiation thermometer
Implementation Method 2
a measurement head of an eddy current displacement sensor that measures the displacement of a rotating platen in a non-contact manner
Data Source
AI summary
A wafer polishing method of polishing one surface of a wafer by rotating a rotating platen to which a polishing pad is affixed and a pressurizing head while supplying slurry onto the rotating platen and pressurizing/holding the wafer on the polishing pad with the pressurizing head, the method including: calculating an F/T value by monitoring a load current value F of a motor for rotating the rotating platen and a surface temperature T of the polishing pad during the wafer polishing; and controlling at least one of the rotation speed of the rotating platen and the polishing pressure of the pressurizing head based on the calculated F/T value.