Reticle Sub-field Thermal Control via Gas Pressure Modulation
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Solution Overview
Problem
In lithographic apparatuses, reticle heating leads to non-uniform temperature distributions, causing deformation and increasing overlay errors due to conventional uniform reticle backside cooling methods that over-cool unused areas.
Innovation Solution
A clamp with spatially arranged gas distribution features, thermoelectric devices, heating wires, and infrared heaters, along with a temperature controller, is used to modulate gas pressure and heat flux distributions to selectively control the temperature of reticle sub-fields, ensuring uniform temperature distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a uniform reticle backside cooling system is used, then the cooling coverage is comprehensive, but it causes over-cooling of unused areas leading to temperature non-uniformities and reticle deformation
Solution Approach 1:
The reticle backside cooling system is divided into multiple independently controllable cooling zones corresponding to different sub-fields. Each zone has its own cooling channels and control valves, allowing selective cooling of only those areas currently being exposed, preventing over-cooling of unused areas and maintaining temperature uniformity across the entire reticle
Solution Approach 2:
The cooling system dynamically adjusts the cooling activation status based on the current exposure pattern. Control valves switch cooling channels on or off in real-time according to which sub-fields are being exposed, transforming a static uniform cooling system into a dynamic adaptive system that matches the actual heat generation patterns
2Adaptability or versatility
If conventional uniform cooling is applied, then the system complexity is low, but it cannot selectively control temperature of sub-fields leading to thermal deformation
Solution Approach 1:
The cooling system is segmented into multiple independently controllable zones with separate gas supply channels and control valves for each zone. This segmentation enables selective temperature control of different sub-fields while maintaining a relatively simple overall structure based on modular repetition of cooling units
Solution Approach 2:
A gas pressure controller acts as an intermediary device that regulates gas flow to individual cooling zones through control valves. This intermediary control mechanism enables selective temperature control without requiring complex direct control systems for each cooling channel, simplifying the overall control architecture
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 overlay errors by maintaining uniform temperature across the reticle, minimizing thermal deformations and improving precision in lithographic processes.
Implementation Method 1
a gas pressure controller configured to individually control a gas flow rate through each of the plurality of gas distribution features to spatially modulate a gas pressure distribution in a space between the clamp and the object
Implementation Method 2
a plurality of thermoelectric devices embedded in the clamp and arranged in an array form. Each of the plurality of thermoelectric devices is configured to locally control a temperature of a corresponding region of the clamp
Implementation Method 3
a plurality of heating wires embedded in the clamp and arranged in a patterned array. Each heating wire forms a sub-circuit configured to locally heat a corresponding region of the clamp
Implementation Method 4
a plurality of infrared heaters each configured to emit an infrared beam to a sub-field of a frontside of the object to locally heat the sub-field of the object
Data Source
AI summary
An apparatus for reticle sub-field thermal control in a lithography system is disclosed. The apparatus includes a clamp configured to fix an object. The clamp includes a plurality of gas distribution features that are spatially arranged in a pattern. The apparatus further includes a gas pressure controller configured to individually control a gas flow rate through each of the plurality of gas distribution features to spatially modulate a gas pressure distribution in a space between the clamp and the object. The gas distribution features include a plurality of trenches or holes arranged in an array form.