Polishing Head Retainer Ring Force Control
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Solution Overview
Problem
The existing chemical mechanical polishing (CMP) techniques for semiconductor wafers face challenges in achieving uniform polishing rates due to non-uniform pressing force distribution from retainer rings, which can lead to irregular film thickness and polishing rate variations across the wafer edge.
Innovation Solution
A polishing head system equipped with piezoelectric elements and a drive-voltage application device that allows for precise control of the pressing force on a retainer member, enabling uniform distribution of polishing rates across the wafer edge by independently applying voltages to the piezoelectric elements and measuring pressing forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a retainer ring is used to prevent wafer from coming off and control polishing rate, then wafer retention and polishing rate control are improved, but uniformity of pressing force distribution deteriorates
Solution Approach 1:
The retainer member is divided into multiple independent pressing portions (first, second, third pressing portions) arranged circumferentially. Each pressing portion can be independently controlled by separate piezoelectric actuators, allowing individual adjustment of pressing forces to compensate for non-uniform distribution and achieve uniform polishing across the wafer surface.
Solution Approach 2:
The system transitions from a static retainer ring to a dynamic pressing mechanism using piezoelectric actuators. These actuators can real-time adjust the pressing force of each retainer portion based on feedback from pressure sensors, enabling adaptive control to maintain uniform pressing force distribution despite variations in friction or wear during polishing.
2Productivity
If retainer ring presses polishing pad to control polishing rate, then polishing rate control is improved, but circumferential uniformity of polishing rate deteriorates
Solution Approach 1:
Different pressing portions of the retainer member are independently controlled to apply locally optimized pressing forces. The piezoelectric actuators and pressure sensors enable site-specific adjustment of pressing force on the polishing pad, ensuring that each circumferential region receives appropriate pressure to achieve uniform polishing rate across the entire wafer edge.
Solution Approach 2:
Pressure sensors are integrated to detect the actual pressing force applied by each retainer portion on the polishing pad. This feedback information is used by the control system to adjust the piezoelectric actuators, creating a closed-loop control system that maintains uniform pressing force distribution and ensures consistent polishing rate across the wafer circumference.
3Productivity
If retainer ring is strongly pressed against polishing pad to increase polishing pressure, then polishing rate increases, but pressing force uniformity deteriorates
Solution Approach 1:
The system uses dynamic control through piezoelectric actuators to maintain optimal pressing force levels. Rather than using a fixed strong pressing force, the system can real-time adjust each pressing portion's force to the precise level needed, preventing excessive localized pressure while maintaining overall high polishing rate through coordinated action of multiple pressing portions.
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 solution ensures precise control over the polishing rate distribution, improving the uniformity of film thickness and polishing efficiency by adjusting the pressing forces in real-time based on measured values and target profiles.
Implementation Method 1
first piezoelectric elements coupled to the retainer member; and a drive-voltage application device configured to apply voltages independently to the first piezoelectric elements
Data Source
AI summary
A polishing head system capable of precisely controlling a pressing force of a retainer member, such as a retainer ring, against a polishing pad. The polishing head system includes: a polishing head including an actuator configured to apply a pressing force to the workpiece, a retainer member arranged outside the actuator, and piezoelectric elements coupled to the retainer member; and a drive-voltage application device configured to apply voltages independently to the piezoelectric elements.