Polishing Head Assembly With Radial Stiffness Control for Wafer Flatness
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Solution Overview
Problem
Existing polishing heads fail to match the thickness variation profile of double side polished wafers, resulting in uneven final polishing and suboptimal flatness of semiconductor wafers.
Innovation Solution
The polishing head assembly features a cap and template with varying thickness along the radius, modulating stiffness and contact pressure profiles to achieve a smooth domed removal profile, using a template support and adjustable pressure distribution to control material removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional polishing head with uniform thickness is used, then the structure is simple and easy to manufacture, but the removal profile does not match the thickness variation profile of double side polished wafers, resulting in uneven final polishing
Solution Approach 1:
The template is designed with non-uniform thickness distribution, where the thickness varies along the radial direction from the center to the edge. This local variation in thickness allows different regions of the template to provide different support characteristics, enabling the polishing head to match the thickness variation profile of double side polished wafers and achieve uniform material removal across the wafer surface.
Solution Approach 2:
The template thickness parameter is changed from a uniform value to a variable value that depends on the radial position. By adjusting the thickness parameter radially, the polishing head can control the contact pressure distribution and removal profile to match the desired wafer thickness variation profile, improving final polishing flatness.
2Strength
If the template thickness is increased to improve support stiffness, then the structural strength is improved, but the contact pressure distribution becomes less adaptable to match wafer thickness variations
Solution Approach 1:
Instead of using a uniformly thick template, the design employs local quality by varying the thickness at different radial positions. The template is thicker at certain regions and thinner at others, allowing each region to provide appropriate support stiffness for matching the local wafer thickness variation profile, thereby achieving both structural strength and removal profile matching.
3Manufacturing precision
If the polishing head is designed to match smooth dome-type thickness variation profile, then the final wafer flatness is improved, but the device complexity increases due to variable thickness template
Solution Approach 1:
The template thickness parameter is systematically varied according to a predetermined profile that matches the smooth dome-type thickness variation of double side polished wafers. By defining the thickness as a function of radial position, the template can be manufactured to provide the desired removal profile, improving wafer flatness while maintaining manufacturability through controlled parameter variation.
Data Source
AI summary
Polishing head assemblies for single side polishing of silicon wafers. The polishing head assemblies may include a template having a step at the edge of the template and/or a template support disposed between the template and the floor of the cap of the polishing head assembly. Some polishing head assemblies may include a cap having a thinner floor.