Immersion Lithography Thermal Control via Evaporation Synchronization
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Solution Overview
Problem
Lithographic apparatuses with immersion liquid systems face issues with liquid evaporation leading to energy loss, temperature fluctuations, and subsequent errors in pattern exposure due to evaporation occurring between the liquid confinement system and the substrate, on the substrate surface, in exhaust channels, and between the substrate holder and table, causing thermal and refractive index variations.
Innovation Solution
A system that includes a liquid supply system, a liquid confinement structure, and a substrate table displacement system, along with a liquid evaporation or condensation controller that synchronizes evaporation or condensation techniques with a timetable to control the net rate of energy loss, using methods such as heating, condensation principles, adsorption principles, and phase change materials to maintain thermal equilibrium.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If liquid is supplied to fill the space between the projection system and substrate, then imaging resolution is improved due to shorter wavelength in liquid, but energy loss through evaporation increases causing temperature fluctuations and exposure errors
Solution Approach 1:
The patent converts the harmful effect of evaporation (energy loss, temperature drop) into a beneficial control mechanism by actively managing evaporation and condensation cycles. The system uses controlled evaporation followed by condensation to transfer heat back to the substrate, transforming the previously harmful thermal fluctuations into a controllable thermal management strategy that maintains imaging precision while accepting some evaporative loss.
Solution Approach 2:
The system dynamically changes physical parameters (temperature, humidity, liquid flow rate) to optimize the balance between maintaining liquid immersion for high-resolution imaging and managing evaporative energy loss. By adjusting these parameters in real-time based on detected thermal conditions, the system maintains optimal imaging resolution while minimizing net energy loss.
2Reliability
If liquid confinement system is used to limit liquid to localized area, then turbulence and acceleration issues are reduced, but evaporation occurs at multiple locations (between confinement system and substrate, on substrate surface, in exhaust channels, between substrate holder and table) increasing total energy loss
Solution Approach 1:
The patent divides the liquid immersion system into multiple segmented zones (between projection system and substrate, on substrate surface, in exhaust channels, between substrate holder and table), each with its own evaporation control strategy. This segmentation allows targeted management of evaporation at each location, reducing total energy loss by addressing each zone's specific thermal characteristics rather than treating the entire system uniformly.
Solution Approach 2:
The system introduces intermediary elements (exhaust channels, substrate holder design features, liquid confinement structures) that mediate between the liquid immersion zone and the ambient environment. These intermediaries control where and how evaporation occurs, directing it to manageable locations while maintaining the liquid immersion benefits for high-resolution imaging.
3Productivity
If substrate is scanned through liquid during exposure, then pattern transfer is achieved, but liquid must be accelerated with substrate requiring additional power and causing turbulence
Solution Approach 1:
The system performs preliminary action by pre-positioning and pre-conditioning the liquid in the immersion zone before substrate scanning begins. The liquid is already in place and thermally conditioned, eliminating the need to accelerate large volumes of liquid during scanning. This reduces the power required for substrate table acceleration and minimizes turbulence, while maintaining high productivity through efficient pattern transfer.
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
This approach effectively reduces energy loss and maintains thermal stability, minimizing overlay errors and focus distortions by controlling evaporation and condensation rates, thereby ensuring consistent pattern exposure.
Implementation Method 1
liquid evaporation or condensation controller arranged to control a net rate of energy lost through evaporation or condensation of liquid supplied by the liquid supply system
Implementation Method 2
liquid evaporation or condensation controller arranged to control a net rate of energy lost through evaporation or condensation of liquid supplied by the liquid supply system
Implementation Method 3
maintains thermal equilibrium
Implementation Method 4
immerse the substrate in the lithographic projection apparatus in a liquid having a relatively high refractive index, e.g. water, so as to fill a space between the final element of the projection system and the substrate. The point of this is to enable imaging of smaller features since the exposure radiation will have a shorter wavelength in the liquid.
Data Source
AI summary
Methods and apparatus for maintaining the thermal equilibrium of a substrate and an immersion lithographic apparatus are disclosed using or having a timetable comprising information regarding the position, speed and/or acceleration of the substrate; and an evaporation controller and/or condensation controller acting to decrease localized evaporation and/or increase localized condensation in response to the information in the timetable. Evaporation of liquid from the surface of the substrate cools it down, while condensing liquid on its bottom surface heats the substrate locally.