Lithographic Encoder Target Thermal Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The accuracy and stability of position measurements in lithographic apparatus encoder type sensor systems are compromised due to thermal expansion and mechanical stress, particularly as the size of the encoder sensor target increases to accommodate larger substrates and increased positioning demands, requiring precise temperature control to maintain stability within milli-Kelvin ranges.
Innovation Solution
The lithographic apparatus incorporates a recess to accommodate the encoder sensor target, a gas supply to stabilize the target's temperature, movement of the substrate table to prevent localized heating, a heat shielding layer, and the use of materials with zero thermal expansion coefficients, such as Zerodur ceramic, to mitigate thermal effects and maintain position accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the encoder sensor target size is increased to accommodate larger substrates and increased positioning demands, then the positioning range and substrate handling flexibility are improved, but thermal expansion and mechanical stress effects are aggravated, deteriorating measurement accuracy
Solution Approach 1:
The patent changes the material parameter of the encoder sensor target by using materials with zero or near-zero thermal expansion coefficients (such as Zerodur ceramic, Invar, or quartz). This parameter change allows the target to maintain dimensional stability across temperature variations, resolving the contradiction between using a larger target for increased adaptability and maintaining measurement precision despite thermal effects.
2Area of stationary object
If the encoder sensor target size is increased to provide increased flexibility in substrate handling, then the ability to handle large substrates is improved, but thermal effects and mechanical tension are aggravated, making temperature stabilization more difficult
Solution Approach 1:
The patent applies parameter changes by selecting materials with zero thermal expansion coefficients for the encoder sensor target. This allows the target to maintain its dimensional parameters stable despite temperature fluctuations, enabling larger target areas to be used without proportionally increasing temperature control requirements.
Solution Approach 2:
The patent employs composite material structures, particularly combining Zerodur ceramic with other materials having complementary properties. This composite approach creates a target structure that maintains dimensional stability and thermal performance even at larger sizes, allowing increased target area without linearly increasing temperature stabilization difficulty.
3Ease of manufacture
If common encoder sensor target materials are used, then ease of manufacture is improved, but temperature stabilization requirements become extremely stringent (milli-Kelvin ranges) to achieve nanometer-level stability
Solution Approach 1:
The patent fundamentally changes the material parameter from common materials with high thermal expansion to specialized materials with zero thermal expansion coefficients. While these materials may be less common, the parameter change dramatically reduces the stringency of temperature control requirements, making the system more manufacturable and operable in practice.
Solution Approach 2:
The patent converts the harmful effect of thermal expansion into a benefit by selecting materials where thermal expansion is zero or negligible. This transforms the temperature variable from a source of error requiring extreme control into a less critical parameter, effectively converting a harmful thermal effect into a beneficial thermal stability property.
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
These measures enhance the stability and accuracy of position measurements, allowing for increased substrate handling flexibility and reduced calibration intervals, achieving nanometer-level stability and accuracy.
Implementation Method 1
Expansion of the encoder sensor target due to thermal effects caused by, for example, local heating, a gas stream, etc. may result in material expansion, mechanical tension, or other effects.
Implementation Method 2
a heat shielding layer between a stationary coil structure of a substrate table motor and the encoder sensor target
Implementation Method 3
the lithographic apparatus is configured to move the substrate table in an idle time period along a main plane of movement of the substrate table, the moving of the substrate table to prevent a localized heating of the encoder sensor target by heat from the substrate table
Implementation Method 4
the use of materials with zero thermal expansion coefficients, such as Zerodur ceramic, to mitigate thermal effects and maintain position accuracy
Data Source
AI summary
A lithographic apparatus is disclosed that includes an encoder type sensor system configured to measure a position of a substrate table of the lithographic apparatus relative to a reference structure. The encoder type sensor system includes an encoder sensor head and an encoder sensor target and the lithographic apparatus comprises a recess to accommodate the encoder sensor target.