CMP Profile Control Using Eddy Current Endpoint Detection
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Solution Overview
Problem
Existing chemical mechanical polishing (CMP) processes face challenges in achieving uniformity when polishing stacks of conductive layers on substrates, particularly in detecting the exposure of underlying layers and adjusting polishing parameters in real-time to maintain consistent layer thickness across the substrate.
Innovation Solution
An in-situ eddy current monitoring system is used to measure thickness and conductivity of conductive layers, enabling real-time adjustments of polishing parameters through a first and second control algorithm, which adapt to the detection of underlying layer exposure, using a Preston matrix and window logic to optimize pressure and rate adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional CMP processes are used without real-time monitoring, then the polishing process is simpler to operate, but the within-wafer uniformity and thickness control are poor
Solution Approach 1:
The system employs in-situ eddy current monitoring to continuously measure conductive layer thickness during polishing and feeds this information back to the controller. The controller compares real-time measurements with target thickness values and dynamically adjusts polishing parameters (downforce, platen speed, carrier head speed) to maintain uniform thickness across the wafer, resolving the contradiction between precision and complexity through closed-loop control.
Solution Approach 2:
The patent replaces traditional mechanical endpoint detection methods with eddy current sensing technology. The eddy current sensor non-contactively measures the thickness of conductive layers by detecting changes in electrical conductivity as layers are removed during polishing, eliminating the need for complex mechanical measurement systems while improving measurement precision and real-time control capability.
2Manufacturing precision
If real-time polishing parameter adjustments are implemented, then the thickness uniformity improves, but the control system complexity increases
Solution Approach 1:
The system dynamically adjusts polishing parameters during the polishing process based on real-time eddy current measurements. The controller modifies downforce, platen rotational speed, and carrier head speed on-the-fly to compensate for thickness variations across different regions of the wafer, transforming a static polishing process into a dynamic, adaptive system that maintains consistent thickness despite variations in material properties and tool wear.
Solution Approach 2:
The patent changes multiple polishing parameters (applied downforce, platen speed, carrier head speed) in response to real-time thickness measurements. By adjusting these parameters dynamically based on eddy current sensor feedback, the system optimizes polishing rate and uniformity across the wafer surface, resolving the contradiction between precision and complexity through multi-parameter control.
3Reliability
If multiple control algorithms are used for different time periods, then the response to layer exposure improves, but the algorithm complexity increases
Solution Approach 1:
The system implements a multi-phase control strategy where preliminary control algorithms operate during the initial polishing stage, and upon detecting layer exposure through eddy current signal changes, the controller transitions to different control algorithms optimized for post-exposure polishing. This preliminary action approach ensures reliable layer exposure detection while managing algorithm complexity through phased control strategies.
Solution Approach 2:
The patent employs periodic switching between different control algorithms based on detected polishing stages. The controller continuously monitors eddy current signals to detect layer exposure events and periodically transitions between control modes (e.g., from constant speed control to adaptive downforce control), improving reliability through stage-appropriate algorithms while maintaining manageable complexity through systematic mode switching.
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 improves within-wafer non-uniformity by ensuring that both target and control zones reach the desired thickness simultaneously, enhancing polishing uniformity and efficiency.
Implementation Method 1
an eddy current sensing system may be used to induce eddy currents in a conductive region on the substrate to determine parameters such as the local thickness of the conductive region
Data Source
AI summary
During polishing of a stack of adjacent conductive layers on a substrate, an in-situ eddy current monitoring system measures sequence of characterizing values. A polishing rate is repeatedly calculated from the sequence of characterizing values repeatedly, one or more adjustments for one or more polishing parameters are repeatedly calculated based on a current polishing rate using a first control algorithm for an initial time period, a change in the polishing rate that meets at least one first predetermined criterion that indicates exposure of the underlying conductive layer is detected, and one or more adjustments for one or more polishing parameters are calculated based on the polishing rate using a different second control algorithm for a subsequent time period after detecting the change in the polishing rate.