Polishing Apparatus Torque and Optical Endpoint Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing polishing methods for substrates, such as wafers, face challenges in accurately detecting the polishing end point, leading to excessive polishing due to variations in film thickness and interconnect patterns, which affects throughput and accuracy.
Innovation Solution
A polishing apparatus and method that combines torque current monitoring with optical sensor data to determine the polishing end point, using a processor to calculate a polishing index value based on film thickness and torque current thresholds, with error ranges set from historical data to ensure accurate detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the wafer is polished until the lower film is exposed over the wafer surface in its entirety, then the polishing end point is detected accurately, but the lower film may be polished excessively with respect to a target film thickness
Solution Approach 1:
The patent replaces the mechanical torque current detection method with an optical detection system. The optical sensor measures film thickness through optical properties (reflectivity, absorbance, or interference patterns) rather than mechanical friction changes, enabling earlier and more precise detection of the polishing end point before the lower film is fully exposed, thus preventing excessive polishing.
Solution Approach 2:
The patent introduces an optical intermediary (light) to detect film thickness changes during polishing. The optical sensor acts as a mediator between the polishing process and the control system, providing real-time feedback on film thickness without direct mechanical contact, allowing for more precise end point detection and control.
2Manufacturing precision
If the wafer is polished for a predetermined time from the point at which removal of initial irregularities is detected, then excessive polishing is prevented, but the whole polishing time increases and throughput lowers
Solution Approach 1:
The patent replaces the time-based polishing control method with optical real-time monitoring. Instead of polishing for a predetermined time and then measuring, the optical sensor continuously monitors film thickness during polishing, enabling precise termination at the optimal moment without requiring additional post-polishing measurement and calculation time, thus maintaining high throughput.
3Manufacturing precision
If the polishing end point is detected using an optical sensor, then it is possible to terminate polishing before the lower film is exposed, but interconnect patterns or slurry may adversely affect detection accuracy
Solution Approach 1:
The patent applies local quality by detecting optical properties at specific locations or regions of the wafer surface where the film thickness is most indicative of the polishing end point. The system focuses measurement on areas with uniform film structure, avoiding regions affected by interconnect patterns or slurry accumulation, thereby maintaining detection accuracy despite the presence of harmful factors.
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 prevents excessive polishing by accurately determining the end point, improving detection accuracy and reducing the risk of insufficient or excessive polishing, thereby enhancing the overall polishing process.
Implementation Method 1
directing a light at the surface of the wafer, and analyzing a reflected light from the wafer to determine the polishing end point of the wafer
Data Source
AI summary
The present invention provides an apparatus and a method for polishing a substrate having a film formed thereon. The method includes: rotating a polishing table supporting a polishing pad by a table motor; pressing the substrate against the polishing pad by a top ring; obtaining a signal containing a thickness information of the film; producing from the signal a polishing index value that varies in accordance with a thickness of the film; monitoring a torque current value of the table motor and the polishing index value; and determining a polishing end point based on a point of time when the torque current value has reached a predetermined threshold value or a point of time when a predetermined distinctive point of the polishing index value has appeared, whichever comes first.