Color Metrology for CMP Endpoint Thickness Measurement
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Solution Overview
Problem
Chemical mechanical polishing (CMP) processes face variations in material removal rates due to slurry distribution, polishing pad conditions, and load on the substrate, leading to inconsistencies in determining the polishing endpoint, which can result in over- or under-polishing of substrates during integrated circuit fabrication.
Innovation Solution
A metrology system utilizing a color camera and controller to capture and analyze color images of substrates, determining layer thickness by mapping pixels in a 2D or 3D color space, interpolating thickness values along a predetermined path, and resolving degeneracies to provide accurate thickness measurements for real-time control of polishing parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If chemical mechanical polishing is used for planarization, then substrate surface flatness is improved, but variations in material removal rate cause inconsistencies in polishing endpoint determination
Solution Approach 1:
The patent implements real-time optical feedback during CMP by capturing images of the substrate surface and analyzing color changes to determine polishing endpoint. The system continuously monitors the substrate during polishing and provides feedback signals to control the polishing process, enabling dynamic adjustment based on actual material removal rather than relying on predetermined time or pressure parameters.
Solution Approach 2:
The patent replaces traditional mechanical endpoint detection methods (based on time, pressure, and slurry flow control) with optical measurement systems. Instead of relying on mechanical parameters to control and detect polishing progress, the system uses optical imaging and color analysis to non-contactly measure surface changes and determine when polishing should stop.
2Ease of operation
If polishing time is used to determine endpoint, then process control is simplified, but overpolishing or underpolishing occurs due to variations in material removal rate
Solution Approach 1:
The system replaces open-loop time-based control with closed-loop feedback control using real-time optical measurements. The feedback mechanism continuously compares actual substrate surface conditions against target specifications and adjusts the polishing process accordingly, maintaining both operational simplicity and manufacturing precision.
Solution Approach 2:
The patent changes the control parameter from time-based (scalar) to optical property-based (color, reflectivity, surface topology). By measuring changes in optical parameters during polishing, the system can directly correlate measurements with material removal and endpoint conditions, achieving precise thickness control without complex mechanical parameter adjustments.
3Measurement precision
If in-situ optical monitoring is implemented, then polishing endpoint detection accuracy is improved, but system complexity increases
Solution Approach 1:
The patent introduces an intermediary image processing and analysis layer between the optical sensor and the control system. This intermediary processes raw optical images, extracts relevant features (color, texture, reflectivity), and translates them into meaningful endpoint indicators, reducing the complexity burden on both the sensing and control systems while maintaining high measurement precision.
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 allows for precise determination of substrate layer thickness, enabling improved thickness uniformity and real-time control of polishing processes, reducing variations and enhancing the accuracy of CMP operations.
Implementation Method 1
obtain a color image of the substrate... determine a thickness of the layer based on the color image data
Data Source
AI summary
A metrology system for obtaining a measurement representative of a thickness of a layer on a substrate includes a camera positioned to capture a color image of at least a portion of the substrate. A controller is configured to receive the color image from the camera, store a predetermined path in a coordinate space of at least two dimension including a first color channel and a second color channel, store a function that provides a value representative of a thickness as a function of a position on the predetermined path, determine a coordinate of a pixel in the coordinate space from color data in the color image for the pixel, determine a position of a point on the predetermined path that is closest to the coordinate of the pixel, and calculate a value representative of a thickness from the function and the position of the point on the predetermined path.