Pencil Pad CMP Cleaning via Variable Pivot Arm Speed
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Solution Overview
Problem
Post-CMP cleaning processes for semiconductor wafers often leave residues and contaminants that can cause surface roughness and defects in subsequent fabrication processes, such as photolithography, due to uneven cleaning across the wafer surface.
Innovation Solution
A CMP cleaning system and method utilizing a pencil pad with varying sweeping speeds and downward forces to effectively remove contaminants from semiconductor wafers, balancing clean times across different regions to prevent defects like cobalt corrosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a uniform cleaning process is applied across the wafer surface, then the simplicity of the cleaning system is maintained, but cleaning uniformity deteriorates due to varying contaminant distribution and surface topography
Solution Approach 1:
The patent applies local quality by varying the cleaning parameters (sweeping speed, downward force, pad rotation speed) across different regions of the wafer surface. The pivot arm mechanism enables different linear velocities at different radial positions, allowing tailored cleaning action for center versus edge regions, thus achieving uniform cleaning without requiring a completely different cleaning mechanism for each zone.
Solution Approach 2:
The patent implements dynamics by making the cleaning system adaptable through variable motion parameters. The pivot arm rotation combined with pad rotation creates dynamically varying cleaning conditions - the linear velocity of the pad relative to the wafer changes continuously as the pivot arm rotates, enabling the system to adapt to different contaminant types and surface conditions during a single cleaning cycle.
2Productivity
If the pencil pad moves at high speed across the wafer, then cleaning productivity is improved, but cleaning uniformity deteriorates due to insufficient contact time in high-speed zones
Solution Approach 1:
The system dynamically adjusts the effective cleaning speed through the combined rotation of the pivot arm and the pad. While the pivot arm may rotate at a relatively high speed for productivity, the simultaneous rotation of the pad at a different speed creates a variable relative velocity between the pad and wafer surface, ensuring adequate contact time in all regions while maintaining overall high productivity.
Solution Approach 2:
The periodic rotation of the pivot arm combined with continuous pad rotation creates a periodic cleaning action that systematically covers different regions of the wafer. This periodic motion ensures that each region receives appropriate cleaning attention at the right moment in the cycle, balancing speed and uniformity through rhythmic, controlled variation in contact conditions.
3Reliability
If downward force is increased to improve contaminant removal, then cleaning effectiveness is improved, but wafer surface damage risk increases
Solution Approach 1:
The patent applies local quality by varying the downward force on the pad across different regions of the wafer. The pivot arm mechanism naturally creates variations in contact pressure as it rotates, allowing higher force where needed for tough contaminants while reducing force in sensitive areas, thus achieving effective cleaning without uniform high-force damage risk.
Solution Approach 2:
The system uses dynamic force modulation through the combined motion of the pivot arm and pad rotation. The downward force is not applied statically but varies dynamically during the cleaning cycle, creating peaks and valleys in contact pressure that enhance contaminant removal during high-force phases while allowing surface recovery during lower-force phases, reducing cumulative damage risk.
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 system ensures thorough and uniform cleaning across the wafer surface, reducing the risk of defects and cobalt losses by adjusting sweeping speeds and forces, thereby enhancing the planarization and cleanliness post-CMP processes.
Implementation Method 1
During a relative movement between the brush and the wafer, the contaminants are removed from the wafer surface
Implementation Method 2
During the brush and pencil cleaning processes, various cleaning liquids may be applied to the wafer and remain on the top surface of the wafer
Data Source
AI summary
A cleaning apparatus and a method of using the cleaning apparatus are provided. The method includes first moving a pencil pad into contact with a top surface of a wafer, wherein the pencil pad is connected to a pivot arm and second moving the pivot arm in a sweeping motion from a first zone to a second zone, the first zone being closer to a center of the top surface of the wafer than the second zone, wherein the sweeping motion is controlled by a controller, the pivot arm moves at a first speed in the first zone and the pivot arm moves at a second speed in the second zone, wherein the first speed is different from the second speed.