CMP Optical Sensor Cleaning for Film Thickness Accuracy
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Solution Overview
Problem
Chemical mechanical polishing (CMP) processes face challenges in accurately measuring film thickness due to the influence of polishing liquids, which affect the intensity of reflected light and lead to discrepancies in calculated film thickness.
Innovation Solution
A polishing method and apparatus that incorporates a cleaning liquid nozzle to remove polishing liquid from the optical sensor head's target position, ensuring accurate film thickness measurement by supplying cleaning liquid upstream of the polishing head and intermittently synchronizing with the polishing table's rotation, and optionally using a gas nozzle to further remove polishing liquid.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If polishing liquid is supplied onto the polishing pad during CMP, then polishing performance is improved, but the intensity of reflected light from the workpiece decreases, leading to inaccurate film thickness measurement
Solution Approach 1:
The polishing pad surface is segmented into different functional zones: a polishing region where polishing liquid is supplied for effective material removal, and a measurement region where polishing liquid is excluded to ensure accurate optical measurements. This spatial segmentation allows both polishing performance and measurement accuracy to be achieved simultaneously in different areas of the same system.
Solution Approach 2:
A non-conductive insulating layer is introduced as an intermediary between the conductive polishing pad and the conductive polishing liquid. This insulating layer prevents direct contact between the polishing liquid and the polishing pad's conductive surface, thereby blocking the polishing liquid from reaching the optical measurement area while maintaining effective polishing in the polishing region.
2Productivity
If polishing liquid flow rate is increased or polishing liquid concentration is increased, then polishing efficiency is improved, but the reflected light intensity decreases significantly, causing large deviations in calculated film thickness
Solution Approach 1:
The polishing pad is functionally segmented into a polishing zone that receives high flow rate polishing liquid for efficient material removal, and a measurement zone that remains free of polishing liquid to ensure consistent optical reflection characteristics. This allows the system to operate at high polishing efficiency while maintaining measurement accuracy.
Solution Approach 2:
The non-conductive insulating layer acts as a mediator that prevents polishing liquid from reaching the optical measurement area regardless of polishing liquid flow rate or concentration. This intermediary layer decouples the polishing efficiency parameters from the measurement accuracy, allowing both to be optimized independently.
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 reduces the impact of polishing liquid on reflected light, allowing for precise film thickness determination during the CMP process.
Implementation Method 1
directing light from an optical sensor head onto the workpiece and receiving reflected light from the workpiece by the optical sensor head
Data Source
AI summary
A polishing method that can reduce influence of polishing liquid (e.g., slurry) on measuring of a film thickness of a workpiece and can achieve accurate measuring of the film thickness is disclosed. The polishing method includes pressing the workpiece against a polishing pad by a polishing head while polishing liquid is present on the polishing pad to polish the workpiece; during polishing of the workpiece, directing light from an optical sensor head onto the workpiece and receiving reflected light from the workpiece by the optical sensor head, the optical sensor head being disposed in the polishing table; determining a film thickness of the workpiece based on a spectrum of the reflected light; and during polishing of the workpiece, supplying cleaning liquid from a cleaning nozzle to a target position which is located just above the optical sensor head.