CMP Carrier Head Acoustic Sensing for Endpoint Localization
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Solution Overview
Problem
Current chemical mechanical polishing (CMP) techniques face challenges in accurately detecting material removal and exposure of underlying layers during the polishing process, leading to difficulties in achieving precise planarization and uniformity.
Innovation Solution
An in-situ acoustic monitoring system is integrated into the carrier head of the CMP apparatus, utilizing an array of acoustic sensors to detect acoustic signals from the substrate-pad interface, allowing for real-time monitoring of layer exposure and endpoint detection through time-of-flight calculations and beamforming techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical sensors are used to monitor substrate during polishing, then real-time monitoring capability is provided, but the system complexity increases and measurement precision is limited by pad window requirements
Solution Approach 1:
The patent replaces optical sensing mechanisms with acoustic sensing mechanisms. Acoustic sensors detect mechanical vibrations and acoustic emissions generated during polishing, eliminating the need for complex optical paths, windows in the polishing pad, and associated alignment systems. This substitution maintains real-time monitoring capability while reducing system complexity and improving measurement precision through direct detection of material removal events.
Solution Approach 2:
The patent introduces acoustic waves as an intermediary medium to detect polishing events. Instead of directly observing the substrate surface with optical sensors, acoustic waves propagate through the substrate and polishing pad, carrying information about material removal and layer exposure. This intermediary approach enables monitoring without requiring direct line-of-sight or physical access to the polishing interface.
2Loss of information
If acoustic sensors are placed in the platen to monitor polishing, then monitoring capability is provided, but the ability to detect specific location events on substrate is limited
Solution Approach 1:
The patent divides the single acoustic sensing function into multiple distributed acoustic sensors positioned at different locations on the carrier head. Each sensor captures acoustic signals from its local region, enabling spatial resolution of polishing events. This segmentation transforms a single-point monitoring system into a distributed sensing network that can locate and characterize events at specific positions on the substrate surface.
Solution Approach 2:
The patent transitions from a single-dimensional (single sensor) or two-dimensional (platen-mounted sensor array) sensing approach to a three-dimensional sensing configuration with multiple sensors distributed in three-dimensional space around the substrate. This spatial distribution enables triangulation and time-difference-of-arrival calculations to precisely locate acoustic events on the substrate surface.
3Manufacturing precision
If predetermined polishing time is used for planarization, then process simplicity is maintained, but manufacturing precision of surface flatness deteriorates
Solution Approach 1:
The patent implements real-time feedback control by continuously monitoring acoustic signals during polishing and using this information to control the polishing process. When acoustic sensors detect signals indicating layer exposure or desired flatness achievement, the system automatically adjusts or terminates polishing. This closed-loop feedback replaces open-loop time-based control, significantly improving surface planarization accuracy while the automated nature of the system keeps operational complexity manageable.
Solution Approach 2:
The patent uses acoustic monitoring to detect preliminary signs of layer exposure or surface uniformity achievement before the polishing process is complete. By detecting these preliminary conditions in real-time, the system can anticipate the endpoint and adjust polishing parameters proactively, ensuring precise final surface quality rather than relying on post-process measurement and correction.
4Measurement precision
If multiple acoustic sensors are arranged in carrier head, then event location detection precision is improved, but device complexity increases
Solution Approach 1:
The patent designs the acoustic sensor array and signal processing system to perform multiple functions simultaneously: detecting acoustic events, locating events spatially, characterizing event types, and providing real-time polishing control. This multi-functionality justifies the increased device complexity by extracting maximum value from the sensor array, where the same hardware infrastructure supports diverse monitoring and control capabilities without requiring separate systems for each function.
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 solution enhances wafer-to-wafer and within-wafer polishing uniformity, enables real-time monitoring of underlying layer exposure, and improves defect detection, thereby achieving higher planarization accuracy and uniformity.
Implementation Method 1
Acoustic signals vary periodically during a polishing operation based on the interface between the substrate and the pad
Implementation Method 2
the location of a high amplitude acoustic event can be detected by the acoustic monitoring system by comparing the time the acoustic signal was received to each acoustic sensor and calculating a time-of-flight to each sensor based on the received signals
Implementation Method 3
The acoustic signal received by each acoustic sensor of the array can be shifted by a pre-determined phase based on the region of the substrate surface to be monitored. Each shifted signal is then summed to approximate the acoustic signal generated by the region of the substrate.
Data Source
AI summary
A chemical mechanical polishing apparatus, including a platen supporting a polishing pad; a carrier head to hold a surface of a substrate against the polishing pad; a motor to generate relative motion between the platen and the carrier head so as to polish an overlying layer on the substrate; an array of acoustic sensors arranged within the carrier head to receive acoustic signals from the surface of the substrate; and a controller configured to detect a position of an acoustic event on the surface of the substrate based on received acoustic signals from the array of acoustic sensors.