Polishing Head Inner Ring Downforce Control
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Solution Overview
Problem
Conventional chemical mechanical polishing (CMP) systems face challenges in uniformly polishing the surface of substrates due to pad flexing and rebound, leading to uneven film thickness and reduced die yield, particularly at the edge regions of the substrate.
Innovation Solution
The use of localized downforce control actuators applied to an inner ring of the carrier head to counteract pad flex and rebound, ensuring uniform polishing by adjusting the downforce at discrete locations, such as the trailing and leading edges, to maintain consistent film thickness across the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional CMP systems use a rotating polishing pad with uniform downforce, then the polishing process is simple and efficient, but the pad flexes and rebounds causing uneven film thickness particularly at edge regions
Solution Approach 1:
The carrier head is divided into multiple independent downforce control zones, each with its own actuator that can independently adjust the polishing pressure applied to different regions of the substrate. This segmentation allows localized compensation for pad flex and rebound effects at edge regions while maintaining overall polishing efficiency.
Solution Approach 2:
Different regions of the carrier head are equipped with different downforce characteristics - edge regions have adjustable actuators that can apply localized downforce to counteract pad rebound, while central regions maintain uniform pressure. This local differentiation addresses the specific problem of edge non-uniformity without over-complicating the entire system.
2Productivity
If the polishing pad is rotated at high speed to increase productivity, then polishing efficiency improves, but pad flex and rebound effects are amplified leading to greater film non-uniformity
Solution Approach 1:
The system incorporates sensors that monitor film thickness and polishing pressure in real-time, providing feedback to the downforce control actuators. This feedback loop allows the system to dynamically adjust downforce at different carrier head regions to compensate for pad flex and rebound effects that occur at high rotation speeds, maintaining film uniformity while preserving high productivity.
Solution Approach 2:
The downforce control actuators are designed to dynamically adjust polishing pressure during the polishing process, adapting to the varying pad flex and rebound conditions that occur at different rotation speeds. This dynamic adjustment capability allows the system to maintain precision across a range of productivity levels.
3Manufacturing precision
If the carrier head applies high downforce to prevent pad rebound, then film uniformity improves, but lateral forces increase causing substrate displacement and edge non-uniformity
Solution Approach 1:
The downforce is segmented into multiple independently controlled zones rather than applied uniformly across the entire substrate. This allows vertical pressure to be optimized for preventing pad rebound at specific regions (such as edge regions) while minimizing lateral forces that could cause substrate displacement, thereby maintaining both film uniformity and positioning stability.
Data Source
AI summary
Exemplary carrier heads for a chemical mechanical polishing apparatus may include a carrier body. The carrier heads may include a substrate mounting surface coupled with the carrier body. The carrier heads may include an inner ring that is sized and shaped to circumferentially surround a peripheral edge of a substrate positioned against the substrate mounting surface. The inner ring may be characterized by a first surface that faces the carrier body and a second surface opposite the first surface. The carrier heads may include at least one downforce control actuator disposed above the first surface of the inner ring at a discrete position about a circumference of the inner ring.