Electrostatic chucks

Motivation

Semiconductor substrates such as Si wafers or masks for the next generation of extreme ultraviolet lithography (EUVL) are handled in a vacuum.

For nm structures and exact overlay, the reproducibility of the substrate evenness is a crucial factor, as unevenness results in structural distortions. Particles are problematic and heat input as well as thermal expansion must be taken into account.

Mechanical clamping devices (3-point suspension) cause sagging substrates, abrasion and poor heat contact.

Electrostatic “clamping” to a chuck with “zero expansion” is one alternative. With an electrical voltage between the chuck electrodes, the substrate can be held and, as required, even smoothed.

Benefits

• Substrate holder of highest evenness (< 50 nm PV for chucks for the EUVL masks) with precision manufacturing
• Thermal invariance with “zero expansion” materials
• Electrostatic forces (switchable and adjustable)
• Abrasion and particle generation are negligible
• Pin structured surface minimizes particle risk
• Lightweight design and cooling channels possible

Our work

The Fraunhofer IOF develops electrostatic chucks of the highest evenness for lithography applications. Unipolar and multipolar electrode structures are used:

• Development (CAD/FEM simulation) of next-generation wafer chucks (Si wafers with 450 mm diameter) for 22 nm node and below
• Diameter up to 12 inches
• Vacuum-compatible, non-magnetic
• Chuck materials with minimum (“zero”) thermal expansion
• Surface structuring with honeycomb or pin pattern
• In accordance with SEMI P40
• Kinematic chuck mounting
• Chuck characterization
• Integration in handling and metrology systems
• Sensor integration