Polishing Apparatus End Point Detection via Friction Current Separation
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Solution Overview
Problem
Conventional polishing apparatuses face challenges in accurately detecting the polishing end point due to interference from sliding friction in rotary joints, leading to potential false detection of the polishing end point.
Innovation Solution
The polishing apparatus includes a current detecting unit and a friction detecting unit to differentiate between polishing friction and sliding friction, using a signal processing unit to generate a signal for accurate end point detection, which can include components like load cells, strain gauges, and displacement sensors to filter out noise and detect abnormalities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a rotary joint with seal portion is used to supply cooling water, then cooling function is improved, but sliding friction in the seal portion causes false detection of polishing end point
Solution Approach 1:
The motor current is segmented into two components: polishing friction current and sliding friction current. The polishing friction current is extracted by subtracting the sliding friction current (detected when polishing is stopped) from the total motor current, enabling accurate polishing end point detection despite the presence of the rotary joint
Solution Approach 2:
The sliding friction current characteristic is copied and stored as reference data during a calibration phase when polishing is stopped. This reference copy is then used to eliminate the sliding friction component from the total motor current during actual polishing operations
2Ease of operation
If motor current is used to detect polishing end point, then detection simplicity is improved, but sliding friction component causes false detection
Solution Approach 1:
The harmful sliding friction component is extracted and removed from the total motor current signal. By detecting and subtracting this component, the remaining signal accurately represents only the polishing friction, maintaining simplicity while improving precision
Solution Approach 2:
The system uses feedback by continuously monitoring motor current and comparing it against the stored sliding friction reference. The difference between the current signal and the reference feedback signal provides the accurate polishing end point detection criterion
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 improves the accuracy of polishing end point detection by isolating the driving load due to polishing friction from sliding friction, thereby preventing false detection and enhancing the precision of the polishing process.
Implementation Method 1
the driving load (torque) can be measured as a current flowing through the motor. Due to this, the motor current is detected by a current sensor
Implementation Method 2
sliding friction due to the rotating body and the housing arises, and the sliding friction results in driving load of the driving unit which drives the rotating body
Data Source
AI summary
A polishing apparatus includes: a polishing table 12 for holding a polishing pad; a first electric motor 14 that rotationally drives the polishing table 12; a first rotary joint 40 that has a rotating body 41 that is rotationally driven by the first electric motor 14, a housing 42 provided around the rotating body 41, and a seal portion 44 that seals between the rotating body 41 and the housing 42; a second current sensor 31 that detects a current which is correlated with driving load of the first electric motor 14; a friction detecting unit 50 that detects sliding friction in the seal portion 44 of the first rotary joint 40; and an end point detecting apparatus 60 that detects a polishing end point of the polishing target on the basis of the current and the sliding friction.