Electrostatic Clamp Electrode Cutouts to Prevent Reticle Discharge
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Solution Overview
Problem
Electrostatic clamps in lithographic apparatuses experience material transfer and particle generation due to discharge mechanisms at contact points between burls and reticles, leading to damage, and backfill gases can cause reticles to lose contact, resulting in gaps and further discharge issues.
Innovation Solution
The electrostatic clamp design includes a clamp body with an electrode layer and burls, featuring cutouts in the electrode layer corresponding to burl locations to reduce electric fields, and modifications such as reducing conductive coating thickness, connecting burls for virtual grounding, or applying diamond-like carbon coatings to minimize voltage differences and prevent discharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the voltage of the electrostatic clamp is increased to offset the force from backfill gas, then the reticle maintains contact with the burls, but discharge is generated that causes damage to the reticle and clamp
Solution Approach 1:
The patent changes the electrical parameters at the contact interface by introducing a conductive coating layer on the burls. This coating modifies the voltage distribution and reduces the electric field strength at the contact points, allowing lower operating voltages that prevent discharge while maintaining sufficient clamping force to counteract backfill gas pressure.
Solution Approach 2:
The conductive coating acts as an intermediary layer between the burl and the reticle. This intermediate conductive layer facilitates gradual charge equalization and reduces the potential difference that causes discharge, while still enabling effective electrostatic clamping force transmission.
2Force
If the electrostatic clamp uses high voltage to maintain clamping force, then the reticle is held securely, but material transfer and particle generation occur due to discharge
Solution Approach 1:
The conductive coating changes the electrical parameters at the contact interface, enabling effective clamping at reduced voltages. This parameter change prevents the high-voltage discharge that causes material transfer, while maintaining sufficient electrostatic force for secure clamping through optimized field distribution.
3Reliability
If the electrostatic clamp operates with high voltage to ensure contact, then clamping effectiveness is maintained, but electric fields cause discharge at contact points
Solution Approach 1:
The conductive coating modifies the electrical parameters by distributing the electric field more uniformly across the contact surface. This reduces peak field strengths that cause discharge while maintaining the overall voltage level needed for effective clamping, thereby eliminating harmful discharge without sacrificing clamping effectiveness.
4Temperature
If backfill gas is provided at the burl-reticle interface for cooling, then thermal conduction is improved, but the gas acts as an additional force causing the reticle to lose contact with the burls
Solution Approach 1:
The conductive coating enables the system to operate at lower voltages, which reduces the electrostatic repulsion effects that amplify the backfill gas force. This allows the backfill gas to provide adequate cooling while the reduced operating parameters maintain sufficient contact force between the reticle and burls.
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 minimizes electric fields and discharge at contact points, preventing material transfer and reticle detachment, thereby reducing damage and ensuring stable clamping in lithographic processes.
Implementation Method 1
An electrostatic clamp may include an electrode at a top surface of the clamp with a plurality of burls disposed on the bottom surface of the clamp. As the clamp is energized (e.g., using a clamping voltage) and pulls the reticle in contact with the burls
Implementation Method 2
a backfill gas may be provided at the burl-reticle interface in the electrostatic clamp to facilitate with cooling of the reticle and thermal conduction
Implementation Method 3
At the moment of contact, this potential difference causes a discharge mechanism as the two potentials are equalized
Data Source
AI summary
Embodiments herein describe methods, devices, and systems for reducing an electric field at a clamp-reticle interface using an enhanced electrostatic clamp. In particular, the electrostatic clamp includes a clamp body, an electrode layer disposed on a top surface of the clamp body, and a plurality of burls that project from a bottom surface of the clamp body, wherein the electrode layer comprises a plurality of cutouts at predetermined locations that vertically correspond to locations of the plurality of burls at the bottom surface of the clamp body.