Polishing Method Using Dynamic Offset for Film Thickness Control
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Solution Overview
Problem
Conventional polishing methods using eddy current film-thickness sensors face challenges in accurately determining the polishing end point due to detection delays and varying polishing rates influenced by the thickness of the polishing pad, leading to inconsistencies in achieving the target film thickness.
Innovation Solution
A method that involves using an eddy current film-thickness sensor to determine the polishing pad thickness, calculate the polishing rate, and adjust the polishing time based on the expected amount of polishing per rotation to precisely reach the target thickness by adding an offset value to the temporary end-point film thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a predetermined offset value is added to the target thickness to account for detection delay, then the polishing process can be terminated after a fixed polishing time, but the film thickness may vary from the target thickness when polishing rate changes due to polishing pad conditions
Solution Approach 1:
The patent dynamically changes the offset value based on the thickness of the polishing pad. By measuring the polishing pad thickness and establishing a correspondence relationship between pad thickness and appropriate offset values, the system adjusts the offset parameter to match actual polishing conditions, thereby maintaining film thickness precision despite variations in polishing rate.
Solution Approach 2:
The system implements feedback by continuously monitoring the polishing pad thickness and using this information to adjust the offset value for film thickness detection. The eddy current film thickness sensor provides real-time feedback on film thickness, which is combined with the dynamically adjusted offset to determine the polishing endpoint accurately.
2Device complexity
If the eddy current film-thickness sensor obtains the film thickness signal each time the polishing table makes one rotation, then the detection system is simple, but it is not possible to obtain a polishing precision finer than the amount of polishing per one rotation
Solution Approach 1:
The patent introduces dynamic adjustment of the offset value based on polishing pad thickness measurements taken during the polishing process. This dynamic parameter adjustment enables the system to achieve higher precision without increasing the fundamental detection frequency, effectively resolving the contradiction between simple detection and fine precision control.
3Ease of manufacture
If the polishing rate is assumed to be constant, then the offset value method works adequately, but the polishing rate actually varies depending on polishing pad thickness leading to film thickness variation
Solution Approach 1:
The patent changes the parameter (offset value) based on the measured polishing pad thickness. By establishing a correspondence relationship between pad thickness and optimal offset values, the system adapts to varying polishing rates without complicating the overall process, maintaining both ease of manufacture and film thickness consistency.
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 control of the polishing process, ensuring the conductive film is polished to the target thickness by accounting for variations in polishing rates, thereby improving precision and preventing excessive polishing.
Implementation Method 1
A high-frequency alternating current is flowing in the eddy current film-thickness sensor. When the eddy current film-thickness sensor moves near the substrate, an eddy current is generated in the conductive film famed on the substrate due to an influence of the high-frequency alternating current.
Implementation Method 2
an eddy current is generated in the conductive film famed on the substrate due to an influence of the high-frequency alternating current. An impedance of an electric circuit of the eddy current film-thickness sensor varies under the influence of magnetic lines of force of the generated eddy current.
Data Source
AI summary
A polishing method includes: rotating a polishing table that supports a polishing pad; polishing a conductive film by pressing a substrate having the conductive film against the polishing pad; obtaining a film thickness signal with use of an eddy current film-thickness sensor disposed in the polishing table; determining a thickness of the polishing pad based on the film thickness signal; determining a polishing rate of the conductive film corresponding to the determined thickness of the polishing pad; calculating an expected amount of polishing of the conductive film to be polished at the determined polishing rate for a predetermined polishing time; calculating a temporary end-point film thickness by adding the expected amount of polishing to a target thickness; and terminating polishing of the conductive film when the predetermined polishing time has elapsed from a point of time when the thickness of the conductive film has reached the temporary end-point film thickness.