CMP Endpoint Detection via Spectral Normalization
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Solution Overview
Problem
Chemical mechanical polishing (CMP) processes face challenges in determining the polishing endpoint due to variations in material removal rates caused by initial thickness, slurry composition, polishing pad condition, and load on the substrate, leading to inaccurate endpoint detection.
Innovation Solution
A normalization method is introduced, where a base spectrum is measured before polishing and used to normalize in-situ spectra during the process, allowing for accurate comparison to reference spectra and determining the polishing endpoint or adjusting the polishing rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If optical monitoring is used to detect polishing endpoint, then real-time feedback is obtained, but measurement precision deteriorates due to noise from underlayer variations
Solution Approach 1:
The patent introduces a reference spectrum as an intermediary to mediate between the measured spectrum and the underlying layer variations. By comparing the measured spectrum against a reference spectrum obtained under known conditions, the system can isolate and eliminate noise components caused by underlayer variations, thereby improving measurement precision while maintaining reliable endpoint detection
Solution Approach 2:
The patent changes the parameter of spectrum comparison by introducing spectral normalization and reference-based comparison methods. Instead of directly comparing raw measured spectra, the system transforms the spectra by dividing by reference spectra or applying normalization factors, which removes the influence of underlayer variations and enhances the precision of thickness and endpoint measurements
2Ease of operation
If polishing time is used to determine endpoint, then process is simple to control, but manufacturing precision deteriorates due to material removal rate variations
Solution Approach 1:
The patent implements real-time optical feedback during the polishing process. The in-situ optical monitoring system continuously measures the thickness of the outermost layer and provides feedback signals that indicate when the polishing endpoint is reached. This feedback mechanism allows the system to automatically terminate polishing at the precise moment the target thickness is achieved, eliminating the need for fixed-time polishing and ensuring high manufacturing precision regardless of material removal rate variations
Solution Approach 2:
The patent replaces the mechanical/time-based endpoint determination method with an optical measurement system. Instead of relying on pre-calculated polishing times based on assumed material removal rates, the system uses optical spectra analysis to directly measure the physical thickness of the layer in real-time, substituting mechanical control with optical sensing for precise endpoint detection
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 method improves the accuracy of endpoint detection by filtering noise from variations in underlying layer thickness and refractive index, enabling precise tracking of the outermost layer thickness during polishing.
Implementation Method 1
a spectrum measured in-situ, e.g., during a polishing process of CMP, is compared to a library of reference spectra
Implementation Method 2
The measured base spectrum is used to normalize each measured spectra obtained during polishing
Data Source
AI summary
A method of controlling polishing includes storing a base spectrum, the base spectrum being a spectrum of light reflected from a substrate after deposition of a deposited dielectric layers overlying a metallic layer or semiconductor wafer and before deposition of a non-metallic layer over the plurality of deposited dielectric layer. After deposition of the non-metallic layer and during polishing of the non-metallic layer on the substrate, measurements of a sequence of raw spectra of light reflected the substrate during polishing are received from an in-situ optical monitoring system. Each raw spectrum is normalized to generate a sequence of normalized spectra using the raw spectrum and the base spectrum. At least one of a polishing endpoint or an adjustment for a polishing rate is determined based on at least one normalized predetermined spectrum from the sequence of normalized spectra.