CMP Thickness Profiling With In-Situ Eddy Current Calibration
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing chemical mechanical polishing (CMP) methods struggle to accurately determine the polishing endpoint due to variations in slurry composition, polishing pad condition, relative speed, initial thickness, and load, leading to non-uniformity within and between wafers, especially when underlying doped semiconductor wafers contribute inconsistently to eddy current signals.
Innovation Solution
An in-situ monitoring system calculates an adjusted target thickness profile by accounting for the contributions from underlying layers and doped substrates, using eddy current sensors to generate accurate thickness measurements by fitting functions to signal values and adjusting target values based on known starting and initial target profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If in-situ monitoring is used to detect polishing endpoint, then real-time thickness measurement capability is improved, but measurement precision deteriorates due to inconsistent contributions from underlying doped semiconductor layers to eddy current signals
Solution Approach 1:
The patent introduces an intermediary calibration process using a calibration substrate with known layer structures. This calibration substrate serves as a mediator to establish a reference relationship between eddy current signals and actual thickness values, allowing the system to account for contributions from underlying layers without directly measuring them during production polishing.
Solution Approach 2:
The system performs preliminary calibration measurements on a calibration substrate before actual production polishing. This preliminary action establishes baseline signal characteristics and thickness relationships that are stored for use during subsequent production runs, enabling accurate thickness measurement without real-time complexity.
2Manufacturing precision
If polishing process parameters are kept constant, then process stability is improved, but manufacturing precision deteriorates due to variations in material removal rate caused by slurry composition, pad condition, and load variations
Solution Approach 1:
The patent implements a feedback control system where in-situ thickness measurements are continuously monitored during polishing. The measured thickness values are compared against target values, and polishing parameters (such as pad pressure or polishing time) are adjusted in real-time to compensate for variations in material removal rate, ensuring uniform thickness across wafers despite process variations.
Solution Approach 2:
The system transitions from static, pre-determined polishing parameters to dynamic, real-time parameter adjustment. Polishing process parameters are continuously adapted based on actual thickness measurements, allowing the system to respond to varying material removal rates caused by slurry composition changes, pad wear, or load variations.
3Manufacturing precision
If polishing time is used as the sole endpoint criterion, then ease of operation is improved, but manufacturing precision deteriorates due to non-uniformity from variable material removal rates
Solution Approach 1:
The patent replaces the simple time-based endpoint detection with an electrical measurement system using eddy current sensors. Instead of relying on mechanical timing and manual intervention, the system uses electrical signals to continuously monitor thickness and automatically determine endpoint, maintaining ease of operation while dramatically improving thickness uniformity.
Solution Approach 2:
The polishing system performs self-monitoring and self-adjustment through integrated eddy current sensors that continuously measure thickness during polishing. The system automatically determines when the polishing endpoint is reached without external intervention, combining the simplicity of automated operation with high precision thickness control.
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 the accuracy of thickness calculations, reduces wafer-to-wafer and within-wafer non-uniformity, and improves control of the polishing process by compensating for inconsistent underlayer contributions, ensuring precise endpoint detection and uniformity.
Implementation Method 1
One monitoring technique is to induce an eddy current in the conductive layer and detect the change in the eddy current as the conductive layer is removed.
Data Source
AI summary
A method of determining a starting thickness profile for a conductive layer on a substrate includes monitoring a calibration substrate during polishing to generate a sequence of first traces, detecting exposure of an underlying layer, and continuing to monitor the calibration substrate after exposure to generate a second trace. The second trace is subtracted from each first trace to generate a sequence of modified traces. For each zone on the substrate, a portion of the modified first trace corresponding to the zone is converted into a thickness value for the zone, thereby providing a plurality of sequences of thickness values. For each respective zone a function is fit to the sequence of thickness values for the respective zone thereby providing a plurality of fit functions, and a starting thickness profile for the conductive layer at a start of polishing using the plurality of fit functions.