Electrostatic Clamp with SiC Support and Dielectric Layers
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Solution Overview
Problem
Existing electrostatic clamps in lithographic apparatuses face challenges in maintaining high accuracy and stability of object positioning due to thermal expansion issues and wear caused by uneven contact pressures, which can lead to unflatness and movement of the object over time.
Innovation Solution
An electrostatic clamp design featuring a support with burls and multiple dielectric layers surrounding an electrode, where the burls and electrode are encapsulated within these layers to maintain a stable, planar surface for object holding, using materials with low thermal expansion coefficients like SiC or Si3N4 to minimize thermal expansion-related issues and wear resistance to prevent adhesive forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional electrostatic clamp design with metal support and dielectric layer is used, then electrostatic clamping force is achieved, but thermal expansion causes unflatness and reduces positioning accuracy
Solution Approach 1:
The patent changes the material parameter of the support from traditional metal to silicon carbide (SiC), which has a significantly lower thermal expansion coefficient. This parameter change resolves the thermal expansion issue while maintaining the structural integrity and electrostatic clamping functionality.
Solution Approach 2:
The patent employs a composite structure consisting of a silicon carbide support combined with a dielectric layer and electrode. This composite material approach allows the support to resist thermal expansion while the dielectric layer provides electrical insulation and enables electrostatic clamping force generation.
2Reliability
If metal pillars are used for electrical contact, then electrical conductivity is achieved, but wear and adhesive forces reduce stability over time
Solution Approach 1:
The patent replaces the mechanical contact system (metal pillars making physical contact) with an electrostatic field-based system. The dielectric layer separates the electrode from the substrate, eliminating mechanical wear and adhesive forces while maintaining electrical conductivity through the electrostatic field.
Solution Approach 2:
The dielectric layer acts as an intermediary between the electrode and the substrate. It prevents direct mechanical contact that causes wear and adhesion, while still allowing the electrostatic field to pass through for clamping and electrical contact.
3Reliability
If thick dielectric layer is used to insulate electrode, then electrical insulation is improved, but heat transfer efficiency decreases
Solution Approach 1:
The patent optimizes the thickness parameter of the dielectric layer to achieve a balance between electrical insulation and heat transfer. The dielectric layer is made sufficiently thin to maintain good thermal contact for efficient heat transfer, while still providing adequate electrical insulation for the electrostatic clamping operation.
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 design ensures high accuracy and stability of object positioning by reducing thermal expansion-induced unflatness and wear, maintaining a stable planar surface for precise object holding and efficient heat transfer.
Implementation Method 1
An electrostatic clamp is a clamp that operates to clamp an object using electrostatic force
Implementation Method 2
The support has a peripheral portion 3 which may be 6 mm thick and a thinner, perforated central portion 5 having a thickness of approximately 3.5 mm
Data Source
AI summary
An electrostatic clamp for use in a lithographic apparatus includes burls and an electrode surrounded by an insulator and/or a dielectric material between adjacent burls. In an embodiment, two or more layers of dielectric material are provided between adjacent burls and surround an electrode provided between adjacent burls. The electrostatic clamp may be used to clamp an object to an object support in a lithographic apparatus.