CMP In-Situ Signal Processing for Accurate Endpoint Detection
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Solution Overview
Problem
Chemical mechanical polishing (CMP) processes face challenges in determining the polishing endpoint accurately due to variations in material removal rates caused by factors like slurry composition, polishing pad condition, relative speed, initial thickness, and load on the substrate, leading to non-uniformity within and between wafers.
Innovation Solution
An in-situ monitoring system, such as an eddy current monitoring system, aligns each substrate consistently to a specific angular orientation before polishing, and subtracts underlying layer noise from measured signals on a per-scan-path basis to enhance film thickness monitoring precision, using a sequence of background traces to improve endpoint detection and parameter adjustment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If polishing endpoint is determined merely as a function of polishing time, then the process is simple to control, but non-uniformity within a wafer or from wafer to wafer occurs due to variations in material removal rate
Solution Approach 1:
The patent replaces time-based endpoint control with an eddy current sensing system that uses electromagnetic fields to measure filler layer thickness in real-time. The sensing system includes a coil that generates an alternating magnetic field, inducing eddy currents in the conductive filler layer, and measures the resulting impedance changes to determine thickness without mechanical contact with the polishing surface.
Solution Approach 2:
The patent implements real-time feedback control by continuously monitoring filler layer thickness during polishing using the eddy current sensing system. The measured thickness information is fed back to the control system, which adjusts polishing parameters or triggers endpoint detection, enabling dynamic control that compensates for variations in material removal rate and achieves uniform polishing results.
2Measurement precision
If in-situ monitoring is implemented through the polishing pad using optical sensors or eddy current sensing, then thickness measurement capability is improved, but signal accuracy deteriorates due to interference from underlying layers
Solution Approach 1:
The patent extracts and removes the background signal component representing underlying layers from the total measured signal. By separating the filler layer signal from the underlying layer interference, the system obtains a clean measurement that accurately represents only the filler layer thickness, eliminating signal accuracy deterioration caused by substrate interference.
Solution Approach 2:
The patent introduces signal processing algorithms as an intermediary between the raw sensor output and the final thickness measurement. These algorithms process the complex signal containing both filler layer and underlying layer contributions, isolating the filler layer component through mathematical operations that eliminate interference from underlying structures.
3Measurement precision
If angular alignment of substrate is implemented before polishing, then measurement consistency is improved, but system complexity increases due to additional alignment procedures
Solution Approach 1:
The patent performs angular alignment of the substrate as a preliminary action before the polishing process begins. By pre-aligning the substrate to a specific angular orientation, the system ensures consistent positioning throughout polishing, which improves measurement consistency without requiring complex real-time adjustments during the polishing operation.
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 within-wafer and wafer-to-wafer uniformity by reducing noise interference, allowing for more accurate thickness calculations and improved endpoint control, thereby reducing non-uniformity.
Implementation Method 1
an eddy current sensing system may be used to induce eddy currents in a conductive layer
Implementation Method 2
The sensing system includes a coil that generates an alternating magnetic field, inducing eddy currents in the conductive filler layer
Data Source
AI summary
A technique for acquiring reference traces includes measuring an angular orientation of a calibration substrate, rotating a carrier head and a platen to respective predetermined angular positions, and bringing the calibration substrate into contact with a polishing pad on the platen. The platen and the carrier head are rotated with the calibration substrate in contact with the polishing pad. The calibration substrate is monitored by sweeping a sensor of an in-situ monitoring system across the calibration substrate to generate a sequence of reference traces with each respective reference trace of the sequence of reference traces corresponding to a respective sweep of a sequence of sweeps by the sensor, and with each reference trace including a series of signal values. The sequence of reference traces is stored and each reference trace is labelled to distinguish an order of the reference traces within the sequence.