Polishing Head Membrane Tension Control for Wafer Flatness
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Solution Overview
Problem
Conventional membrane pressurization type polishing heads experience in-plane variations in pressing force due to horizontal tension, leading to uneven polishing amounts on silicon wafers, which degrade flatness and machining accuracy.
Innovation Solution
A polishing head design where the vertical tension from the side surface part of the membrane is greater than the lateral tension from the main surface part, with a membrane support structure having a dimensional ratio of 0.75 ≤ Mh/Ph < 1 and 0.95 ≤ Md/Pd ≤ 1, ensuring a uniform pressing force distribution using a single-zone pressurization mechanism and a non-grounded retainer ring to restrict wafer movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the diameter of the inside of the membrane is set equal to or slightly smaller than the diameter of the support plate and the height of the inside of the membrane is set equal to the height of the support plate, then the membrane can be supported stably on the support plate, but the horizontal tension becomes larger than the vertical tension, causing variation in the in-plane distribution of the pressing force and increasing in-plane variation of the polishing amount
Solution Approach 1:
The patent changes the dimensional parameters of the membrane relative to the support plate. Specifically, it sets the diameter ratio (membrane inside diameter/support plate diameter) between 0.95-1.05 and the height ratio (membrane inside height/support plate height) between 0.65-0.85. These parameter changes ensure that the vertical tension component becomes dominant over the horizontal tension component, thereby uniformizing the pressing force distribution across the wafer surface while maintaining stable membrane support.
2Force
If the membrane diameter is reduced to minimize support plate contact, then the membrane tension is reduced, but the pressing force uniformity deteriorates due to increased horizontal tension relative to vertical tension
Solution Approach 1:
The patent optimizes the membrane dimensional parameters by setting the diameter ratio (Md/Pd) between 0.95-1.05 and the height ratio (Mh/Ph) between 0.65-0.85, where Md and Mh are the membrane inside diameter and height, and Pd and Ph are the support plate diameter and height. This parameter optimization ensures that the vertical tension component exceeds the horizontal tension component, achieving uniform pressing force distribution across the wafer surface while maintaining adequate membrane tension for effective polishing.
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 configuration enhances the uniformity of the polishing amount across the wafer surface, preventing membrane slack and ensuring consistent machining allowances, thereby improving the flatness and reducing variations in the polishing process.
Implementation Method 1
Such a membrane is subjected to air-pressurization to apply an elastic force to the pressing surface of the membrane facing the wafer
Implementation Method 2
subjected to air-pressurization to apply an elastic force to the pressing surface of the membrane
Implementation Method 3
mirror-finishing by CMP (Chemical Mechanical Polishing) method is performed
Data Source
AI summary
A wafer polishing apparatus is provided with a rotating platen to which a polishing pad is affixed and a polishing head that holds a wafer placed on the polishing pad while pressing the wafer. The polishing head has a membrane that contacts the upper surface of the wafer and applying a pressing force thereto and a support plate that supports the membrane. The membrane has a main surface part facing the bottom surface of the support plate and a side surface part facing the outer peripheral edge surface of the support plate. The vertical tension due to the side surface part of the membrane is larger than the lateral tension due to the main surface part of the membrane.