Grinding Thickness Measurement Probe Wear Reduction
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Solution Overview
Problem
The existing method of measuring the thickness of semiconductor wafers during grinding is prone to errors due to wear of the probe contacting the self-ground chuck table, leading to inaccurate thickness measurements and excessive grinding.
Innovation Solution
A thickness-measuring method where the reference probe is only brought into contact with the chuck table at the commencement and termination of grinding, interrupting measurement during the grinding process to minimize wear and ensuring accurate measurement by the workpiece side gauge, which continues to measure the wafer's thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the probe is brought into contact with the chuck table during grinding measurement, then thickness measurement is enabled, but the probe tip is worn away by the grinding marks on the self-ground chuck table
Solution Approach 1:
A reference block is introduced as an intermediary between the probe and the chuck table. The probe measures the reference block instead of directly contacting the chuck table, thereby eliminating direct contact wear while maintaining measurement capability. The reference block transfers the measurement function without suffering from the grinding marks on the chuck table surface.
Solution Approach 2:
The reference block serves as a copy or replica of the chuck table surface for measurement purposes. Instead of measuring the chuck table directly, the system creates a measurable copy (the reference block) that can be contacted by the probe without the harmful effects present on the original surface.
2Productivity
If the chuck table rotation speed is increased to improve productivity, then grinding efficiency increases, but probe wear accelerates due to higher circumferential velocity at the outer circumferential portion
Solution Approach 1:
The reference block acts as a mediator that decouples the probe from direct contact with the high-speed rotating chuck table. This allows the chuck table to rotate at high speeds for improved productivity while the probe remains stationary relative to the reference block, eliminating speed-related wear acceleration.
3Manufacturing precision
If continuous measurement is performed during grinding to monitor thickness in real-time, then grinding control is improved, but probe wear increases due to prolonged contact time
Solution Approach 1:
The reference block enables continuous measurement during grinding by serving as a durable intermediary surface. The probe continuously contacts the reference block (which does not wear like the chuck table) to monitor workpiece thickness in real-time, achieving both continuous control and reduced wear.
Solution Approach 2:
The measurement system discards the idea of measuring the chuck table directly and recovers the measurement function by using the reference block instead. The reference block can be easily replaced or recovered if worn, while the probe itself is protected from wear.
Data Source
AI summary
In a thickness-measuring method during a grinding process, which suppresses wear of a probe coming into contact with a chuck table subjected to self-grind and accurately grinds a workpiece, measurement of wafer thickness is performed only at the commencement and termination of grinding, and a reference probe of a reference side height gauge is separated from the upper surface of the chuck table in the practical grinding time between the commencement and termination so as to interrupt the measurement of wafer thickness, thereby significantly reducing a time of the reference probe brought into contact with the upper surface of the chuck table.