Edge Contact Gripper Roller Mechanism for Wafer Seating
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Solution Overview
Problem
Conventional edge contact grippers for handling semiconductor wafers or substrates often experience 'gripper lock up' due to increased friction caused by contamination buildup, which prevents proper seating of the substrate on the end effector.
Innovation Solution
The implementation of a substrate transporter with an edge contact gripper featuring a roller arrangement at the active contact point, which reduces frictional resistance and eliminates lock up issues by using a rotatable coupling member to urge the substrate against rest pads, ensuring proper seating without interference from fiducial features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a flat slide surface is used at the pusher tip to contact the substrate edge, then the substrate can be clamped against hard stops, but friction buildup from contamination causes gripper lock up and prevents proper substrate seating
Solution Approach 1:
The pusher tip is changed from a flat surface to a spherical surface with a radius of curvature of 0.020 to 0.050 inches. This curved surface reduces the contact area with the substrate edge from a line contact to a point contact, significantly reducing frictional resistance and preventing gripper lock up caused by contamination buildup.
Solution Approach 2:
The geometric parameter of the pusher tip is changed from flat (zero curvature) to spherical (positive curvature with specific radius). This parameter change transforms the contact mechanics from high-friction line contact to low-friction point contact, eliminating the harmful effect of contamination-induced friction.
2Ease of operation
If the pusher extends to clamp the substrate, then the substrate is secured against hard stops, but high friction prevents the substrate from rolling along the hard stop to complete seating
Solution Approach 1:
The spherical pusher tip reduces frictional resistance during the substrate rolling phase. The point contact geometry minimizes the force required for the substrate to roll along the hard stop, enabling easy completion of substrate seating while maintaining effective clamping force.
3Reliability
If contamination builds up on the flat slide surface, then friction increases and changes force direction, but the gripper locks up and stops substrate movement
Solution Approach 1:
The spherical pusher tip minimizes the contact area between the pusher and substrate edge, reducing the amount of contamination that can accumulate. The point contact geometry ensures that even with contamination present, the frictional force remains insufficient to cause gripper lock up, maintaining operational consistency.
Solution Approach 2:
The invention accepts that contamination will occur but designs the spherical contact surface such that the reduced contact area makes contamination less effective at generating locking friction. The geometry itself converts the potential harm of contamination into a benign condition where friction remains low enough to allow substrate seating.
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 solution effectively prevents gripper lock up and ensures reliable seating of substrates by minimizing frictional resistance, allowing for smooth operation even with contamination, and accommodating substrates with alignment fiducials.
Implementation Method 1
The coefficient of friction between the edge of the substrate and the flat side surface of the pusher... the force can be decomposed into a component normal to the edge of the substrate and the flat side of the pusher at the point of contact, and a frictional component tangential to the edge of the substrate
Data Source
AI summary
An apparatus for gripping a substrate on its peripheral edge including a substrate support having proximate and distal ends, at least one distal rest pad disposed at the distal end, the at least one distal rest pad includes a back stop portion and is configured to support the peripheral edge of the substrate, at least one proximate rest pad disposed at the proximate end, the at least one proximate rest pad being configured to support the peripheral edge of the substrate, and an active contact member assembly disposed at the proximate end, the active contact member assembly including a pusher member, a contact member and a rotatable coupling member that are reciprocably movable towards the distal end for urging the substrate against the back stop portion, the contact member being rotatably secured to the pusher member and free to rotate about an axis of the rotatable coupling member.