Polishing Apparatus Transparent Window Condensation Prevention
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Solution Overview
Problem
Condensation on the inner surface of a transparent window in a polishing pad can occur due to rapid cooling after polishing, leading to a blocked light path and reduced accuracy in film thickness measurement.
Innovation Solution
A polishing apparatus equipped with a cooling device that cools the space between the transparent window and the optical sensor head, maintaining a temperature difference to prevent condensation, and optionally includes a dehumidifying device to reduce humidity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If water is supplied onto the polishing pad to clean the polished surface, then cleaning effect is improved, but condensation occurs on the inner surface of the transparent window blocking the light path
Solution Approach 1:
The patent divides the cooling function into two distinct stages: a first cooling period during polishing and a second cooling period after polishing. This segmentation allows the system to address different thermal conditions at different times, preventing condensation while enabling effective cleaning.
Solution Approach 2:
The patent applies cooling to the transparent window before water supply begins (during the first cooling period). This preliminary cooling action reduces the temperature difference between the window and the incoming water, preventing condensation when water is supplied for cleaning.
2Temperature
If the transparent window is rapidly cooled with water after polishing, then cooling effect is improved, but condensation occurs on the inner surface of the transparent window
Solution Approach 1:
The cooling process is divided into two segmented phases: first cooling during polishing and second cooling after polishing. This prevents rapid single-stage cooling that causes condensation, while still achieving the desired cooling effect through controlled staged cooling.
Solution Approach 2:
The patent implements periodic cooling actions with distinct time periods - cooling during the polishing operation and continued cooling after polishing. This periodic approach allows temperature management that prevents condensation while maintaining cooling effectiveness.
3Productivity
If the polishing pad temperature increases due to friction during polishing, then polishing effect is improved, but condensation is likely to occur when rapidly cooled after polishing
Solution Approach 1:
The thermal management is segmented into two phases corresponding to the two operational phases: active cooling during polishing when high temperature is needed for polishing effect, and continued cooling after polishing to prevent condensation. This segmentation resolves the contradiction between needing heat for polishing and preventing condensation during cooling.
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 cooling device effectively prevents condensation on the transparent window, ensuring a clear light path and maintaining accurate film thickness measurement during and after polishing.
Implementation Method 1
the transparent window is rapidly cooled with the water after polishing of the wafer, the condensation is likely to occur on the inner surface (back surface) of the transparent window
Data Source
AI summary
A polishing apparatus capable of preventing condensation on an inner surface of a transparent window provided in a polishing pad and capable of achieving accurate measuring of a film thickness is disclosed. The polishing apparatus includes: a polishing pad having a polishing surface; a polishing head configured to press a workpiece against the polishing surface; a transparent window disposed in the polishing pad; a polishing table configured to support the polishing pad; an optical sensor head located below the transparent window and configured to direct light to the workpiece through the transparent window and receive reflected light from the workpiece through the transparent window; and a cooling device configured to cool a space between the transparent window and the optical sensor head.