CMP Film Thickness Measurement Using Spectrum History Differences
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Solution Overview
Problem
Conventional chemical mechanical polishing (CMP) techniques require polishing a reference wafer in advance to determine film thickness, which is inefficient and can be inaccurate due to variations in the underlying layer thickness and light source degradation over time.
Innovation Solution
A method that creates a relative-film-thickness profile of a workpiece during polishing by directing light to irradiation points, including a reference and monitoring point, and calculating film-thickness differences based on spectrum histories, eliminating the need for pre-polishing a reference wafer and accounting for variations in the underlying layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a reference wafer is polished in advance to obtain reference spectra, then film thickness measurement can be performed, but the process becomes inefficient and time-consuming
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing expected spectrum differences for various film thickness values before the actual polishing measurement. This allows the system to directly reference pre-computed data during measurement, eliminating the need for time-consuming reference wafer polishing while maintaining measurement accuracy.
Solution Approach 2:
The patent creates a virtual reference by computing theoretical spectrum differences based on optical models and storing them as reference data. This virtual copy replaces the physical reference wafer, enabling fast measurement without the time loss associated with polishing actual reference wafers.
2Measurement precision
If conventional optical measurement is used, then film thickness can be determined, but accuracy is reduced due to variations in underlying layer thickness
Solution Approach 1:
The patent extracts and isolates the effect of the underlying layer by measuring spectrum differences between a monitoring point on the film and a reference point on the underlying layer. This separation allows the measurement system to focus only on the film thickness effect, eliminating interference from underlying layer variations and improving measurement reliability.
Solution Approach 2:
The patent introduces spectrum difference as an intermediary measurement parameter. Instead of directly measuring film thickness which is affected by underlying layer variations, the system measures the difference in reflected light spectra between monitoring and reference points, which isolates the film thickness contribution and improves accuracy.
3Measurement precision
If conventional optical measurement is used, then film thickness can be measured, but accuracy decreases due to light source quantity degradation over time
Solution Approach 1:
The patent implements feedback by continuously monitoring the reflected light spectrum and comparing it against pre-stored reference spectrum differences. The system uses this feedback to dynamically determine film thickness without relying on absolute light source intensity, compensating for light source degradation and maintaining measurement consistency over time.
Solution Approach 2:
The measurement system performs self-calibration by using the reference point on the underlying layer as an internal reference. This self-service mechanism automatically compensates for light source degradation without requiring external calibration standards or manual intervention, maintaining measurement reliability throughout the light source lifecycle.
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
Enables accurate film-thickness measurement without pre-polishing a reference wafer and reduces the impact of underlying layer variations, improving the precision and efficiency of CMP processes.
Implementation Method 1
direct light onto the workpiece and receive reflected light from the workpiece by an optical sensor head
Implementation Method 2
produce a spectrum of the reflected light from intensity of the reflected light, and determine the film thickness of the workpiece based on the spectrum of the reflected light
Data Source
AI summary
A polishing method includes: during polishing of the workpiece, creating a reference spectrum history and a monitoring spectrum history by repeatedly producing a reference spectrum and a monitoring spectrum at two points on the workpiece; calculating a plurality of reference history differences that are differences between a latest monitoring spectrum and a plurality of reference spectra in the reference spectrum history; calculating a plurality of monitoring history differences that are differences between a latest reference spectrum and a plurality of monitoring spectra in the monitoring spectrum history; calculating a film-thickness difference between a monitoring point and a reference point based on a local minimum point of a reference history difference or a monitoring history difference.