Lithographic Substrate Holder Burls with DLC Release Structure
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Solution Overview
Problem
Lithographic substrate holders face challenges in releasing stress during loading while maintaining firm substrate hold during exposure, due to conflicting requirements of low friction for relaxation and high friction for stability and thermal expansion resistance.
Innovation Solution
A substrate holder with burls featuring a layer of diamond-like carbon and a recess on the distal end surfaces, optimized with additives like silicon, nitrogen, and fluorine, reduces friction during loading and increases contact area under clamping to enhance holding stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the substrate is held firmly on the substrate holder during loading, then the substrate stability is improved, but the substrate cannot release stress and distort properly
Solution Approach 1:
The substrate holder employs burls with distal end surfaces that have locally modified properties through diamond-like carbon coating and recess structures. These local modifications create regions of reduced friction specifically at the contact points between the substrate and holder, allowing stress release while maintaining overall substrate stability during exposure.
2Manufacturing precision
If the friction between burls and substrate is reduced, then the substrate can relax fully, but the substrate cannot be held firmly during exposure
Solution Approach 1:
The substrate holder system transitions from a static friction condition to a dynamic one. During loading, the diamond-like carbon coated burls provide low friction to allow substrate relaxation. During exposure, the vacuum clamping mechanism dynamically changes the interaction by creating a pressure differential that firmly holds the substrate despite the low-friction surface.
Solution Approach 2:
The system uses vacuum clamping where a pressure differential is established between the space between the substrate holder and substrate (lower pressure) and the pressure above the substrate (higher pressure). This pneumatic mechanism provides the holding force during exposure while allowing low-friction contact during loading.
3Force
If the contact area between burls and substrate is increased, then the holding force is improved, but the friction increases and prevents stress release
Solution Approach 1:
Instead of increasing the overall contact area, the invention modifies the local properties of the contact surfaces. The diamond-like carbon coating and recess structures at the distal ends of the burls create localized low-friction zones that reduce overall friction while maintaining sufficient contact area for holding force through vacuum clamping.
4Manufacturing precision
If a release structure is added to reduce friction, then the substrate can relax, but the device complexity increases
Solution Approach 1:
The substrate holder employs composite construction by coating the burl surfaces with diamond-like carbon material. This composite approach combines the structural integrity of the original burl material with the low-friction properties of the diamond-like carbon coating, achieving stress release functionality without significantly increasing device complexity.
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 release structure allows full substrate relaxation before exposure, minimizing overlay errors and providing robust clamping to resist thermal deformation and high accelerations, with reduced friction and increased stiffness compared to SiSiC holders.
Implementation Method 1
distal end surfaces of the burls are provided with a release structure configured so that the frictional force is less than would arise in the absence of the release structure
Implementation Method 2
a frictional force between the distal end of each burl and a substrate engaged therewith arises in a direction parallel to the support plane
Implementation Method 3
the release structure comprises both a layer of diamond-like carbon and a recess in the distal end surface of each burl
Implementation Method 4
In vacuum-clamping a pressure differential across the substrate is established, e.g., by connecting the space between the substrate holder and the substrate to an under-pressure that is lower than a higher pressure above the substrate
Implementation Method 5
In electrostatic clamping, electrostatic forces are used to exert a force between the substrate and the substrate holder
Implementation Method 6
the substrate absorbs energy from the projection beam during exposure and therefore heats up locally
Implementation Method 7
Such local heating can cause thermal expansion and distortion of the substrate
Data Source
Figure 1
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Figure 3~4
AI summary
A substrate holder for use in a lithographic apparatus and configured to support a substrate, the substrate holder comprising: a main body having a main body surface; and a plurality of burls projecting from the main body surface; wherein each burl has a distal end configured to engage with the substrate; the distal ends of the burls substantially conform to a support plane whereby a substrate can be supported in a substantially flat state on the burls; a frictional force between the distal end of each burl and a substrate engaged therewith arises in a direction parallel to the support plane in the event of a relative movement of the substrate and substrate holder in the direction; and distal end surfaces of the burls are provided with a release structure configured so that the frictional force is less than would arise in the absence of the release structure.