Transparent Liquid Filling for Optical Path Stabilization in CMP
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Solution Overview
Problem
The optical film-thickness measuring system in chemical mechanical polishing (CMP) apparatuses faces inaccuracies due to liquid, such as polishing liquid or pure water, penetrating into the space between the transparent window and the optical sensor head, causing light scattering or intensity changes, especially with bubbles present, which prevents accurate film thickness measurement.
Innovation Solution
A polishing apparatus with a transparent liquid filling method that evacuates the space between the transparent window and the optical sensor head to create negative pressure, followed by filling it with a transparent liquid, such as pure water, to stabilize the optical path and ensure accurate film thickness measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If liquid is supplied onto the polishing pad for dressing and cleaning, then the polishing pad can be cleaned and dressed, but liquid may penetrate into the polishing pad and enter the space between the optical sensor head and transparent window, causing light scattering and preventing accurate film thickness measurement
Solution Approach 1:
The polishing pad is divided into a polishing region and a transparent window region, with the transparent window acting as a barrier to prevent liquid from reaching the optical sensor head. This segmentation allows cleaning functions while protecting the measurement system.
Solution Approach 2:
A transparent window is introduced as an intermediary element between the polishing pad surface and the optical sensor head. This window allows light transmission for measurement while blocking liquid penetration to the sensor space.
2Adaptability or versatility
If bubbles are present in the liquid in the space, then the liquid may change the intensity of the reflected light, but accurate measuring of the film thickness is prevented
Solution Approach 1:
The space between the transparent window and optical sensor head is evacuated to remove air and bubbles before introducing the transparent liquid. This preliminary action ensures the optical path is free from scattering elements that would affect measurement accuracy.
Solution Approach 2:
The space is filled with an inert transparent liquid that does not scatter light or contain bubbles, creating a stable optical environment. This inert liquid medium maintains consistent light transmission for accurate measurements.
3Device complexity
If the space between the transparent window and optical sensor head is left empty, then the structure is simple, but the optical path is unstable due to liquid penetration and bubble formation
Solution Approach 1:
A transparent liquid is introduced as a mediator to fill the space between the transparent window and optical sensor head. This liquid stabilizes the optical path by preventing air bubbles and maintaining consistent light transmission, while the space itself remains a simple structural element.
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
The transparent liquid filling method provides a stable optical path, allowing for precise film thickness measurement by removing moisture and dust and maintaining light transmission, thus enhancing the accuracy of the optical film-thickness measuring system.
Implementation Method 1
a space formed between the transparent window and the optical sensor head being filled with a transparent liquid
Data Source
AI summary
A polishing apparatus is disclosed. The polishing apparatus can stabilize an optical path in a space between a transparent window of a polishing pad and an optical sensor head, thereby achieving accurate measuring of a film thickness of a workpiece. polishing apparatus includes: a polishing pad having a transparent window configured to allow light to pass therethrough; a polishing table supporting the polishing pad; a polishing head configured to press a workpiece against the polishing pad; and an optical film-thickness measuring system having an optical sensor head disposed below the transparent window, a space formed between the transparent window and the optical sensor head being filled with a transparent liquid.