Polishing Apparatus Torque Variation Detection
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Solution Overview
Problem
Conventional polishing apparatuses for semiconductor wafers face challenges in accurately detecting the polishing end point due to variations in phase currents of electric motors, leading to inconsistent flatness and potential short circuits or increased resistance in wiring.
Innovation Solution
The polishing apparatus incorporates a weighting unit to adjust current ratios of phase windings and a torque variation detecting unit to absorb variations in phase currents, enabling more accurate detection of torque changes and improving the determination of the polishing end point.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional polishing end point detection methods are used, then the polishing process can be automated, but the detection accuracy is insufficient due to phase current variations
Solution Approach 1:
The patent introduces a combined current signal as an intermediary that aggregates information from multiple phase currents. This combined signal serves as a mediator that filters out individual phase variations while preserving the overall torque variation information, thereby improving detection accuracy and consistency
Solution Approach 2:
The patent merges multiple phase current signals into a single combined current signal for torque variation detection. By combining the phase currents, the system achieves more reliable and accurate detection of polishing end point while reducing the impact of individual phase current variations
2Productivity
If the semiconductor wafer is insufficiently polished, then productivity is maintained, but circuit insulation is compromised causing short circuits
Solution Approach 1:
The patent implements a feedback mechanism where the combined current signal continuously monitors torque variations during polishing. This real-time feedback enables accurate detection of the polishing end point, ensuring that the wafer is polished sufficiently to maintain circuit insulation while avoiding unnecessary additional polishing that would reduce productivity
3Manufacturing precision
If the semiconductor wafer is excessively polished, then flatness is improved, but wiring cross-sectional area is reduced causing increased resistance
Solution Approach 1:
The feedback mechanism using combined current signal detects torque variations that indicate the polishing end point. This prevents excessive polishing that would otherwise continue to improve flatness at the cost of reducing wiring cross-sectional area and increasing resistance
4Device complexity
If phase current variations are not compensated, then device complexity is reduced, but torque detection accuracy deteriorates
Solution Approach 1:
The patent combines multiple phase current signals into a single combined current signal, which inherently compensates for phase variations without requiring complex compensation circuits. This merging approach maintains relatively simple device complexity while significantly improving torque variation detection accuracy
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 enhances the accuracy of polishing end point detection and improves the yield of flattened semiconductor wafers by stabilizing torque detection and reducing variations in the flattening process.
Implementation Method 1
When means for rotationally driving the turntable is an electric motor, the load torque can be measured as a current flowing into the motor
Implementation Method 2
a semiconductor wafer, as a workpiece, which is set at the top ring, is pressed against the polishing pad, so that the surface of the semiconductor wafer is polished to a flat mirror surface
Implementation Method 3
a change in the polishing friction force at the time when a different material begins to be polished with progress of the polishing. Therefore, the method is configured to detect a change in polishing friction force
Data Source
AI summary
To provide a polishing apparatus capable of more accurately determining a polishing end point. The polishing apparatus includes a turntable 12, a first electric motor 14 configured to rotationally drive the turntable, a top ring 20 configured to hold a workpiece together with the turntable, and a second electric motor 22 configured to rotationally drive the top ring. The polishing apparatus further includes a weighting unit configured to perform weighting so as to make the current ratios of the respective phases different from each other, and a torque variation detecting unit configured to detect a change in a phase current greatly weighted by the weighting unit and thereby detects a change in torque of the electric motor, the change being generated by performing the polishing.