Immersion Lithography Photomask Sensor Gap Control
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Solution Overview
Problem
In immersion lithography, achieving a precise and consistent gap between the substrate and photomask is challenging due to issues like sticking, contamination, and variability in photoresist thickness, which affects the sharpness of corners/edges in photoresist structures and optical transmission efficiency.
Innovation Solution
An immersion lithography system with sensors to monitor the electric field and determine the thickness of the liquid layer or distance between substrates, using a controller to adjust the gap and maintain a desired range, and an adjustable mechanism to apply a selectable force to ensure a clean and uniform fluid gap.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the substrate is placed very close to the photomask to achieve sharp corners/edges, then the manufacturing precision is improved, but the risk of photoresist sticking to the mask and contamination increases
Solution Approach 1:
A liquid medium (water or glycol) is introduced as an intermediary between the substrate and photomask, enabling close spacing for sharp edges while preventing direct contact that causes sticking and contamination. The liquid fills the gap and acts as a barrier layer.
Solution Approach 2:
The mechanical contact-based spacing system is replaced with a liquid-filled gap system. Instead of relying on mechanical spacers or direct contact, the liquid medium maintains the precise gap distance while preventing adhesion and contamination.
2Reliability
If direct contact between substrate and photomask is avoided to prevent sticking, then the reliability is improved, but the manufacturing precision of corners/edges deteriorates
Solution Approach 1:
The liquid medium serves as an intermediary that enables close spacing without direct contact. It maintains the precise gap needed for sharp edges while preventing the sticking problem that occurs with direct contact.
Solution Approach 2:
The physical state of the gap is changed from air/vacuum to liquid-filled. This parameter change allows the system to achieve both close spacing (for precision) and non-contact (for reliability) simultaneously, as the liquid provides both gap maintenance and anti-adhesion properties.
3Manufacturing precision
If sensors and control mechanisms are added to monitor and adjust the gap, then the manufacturing precision is improved, but the device complexity increases
Solution Approach 1:
Sensors are integrated into the photomask substrate to detect the presence and thickness of the liquid layer. This feedback information is used by a controller to adjust the substrate position, maintaining the optimal gap distance through closed-loop control.
Solution Approach 2:
The photomask substrate serves multiple functions: it acts as both the optical mask and as a platform for mounting sensors. This integration reduces overall system complexity by combining multiple functions into a single component.
4Manufacturing precision
If the gap distance is reduced to improve edge sharpness, then the manufacturing precision is improved, but the susceptibility to contamination and sticking increases
Solution Approach 1:
The liquid medium acts as a protective intermediary layer that fills the small gap distance. It prevents direct contact between surfaces (reducing sticking) and blocks contamination from entering the gap, while allowing the gap to remain small enough for sharp edge formation.
Solution Approach 2:
The liquid medium creates a controlled, inert environment within the gap that protects against contamination from the external environment. The liquid barrier prevents dust and impurities from reaching the critical interface between substrate and photomask.
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 ensures precise control over the gap distance, reducing contamination and achieving sharper photoresist edges, thereby enhancing optical transmission efficiency and reproducibility in waveguiding structures.
Implementation Method 1
receiving, from the at least one sensor, information indicative of an electric field proximate to the at least one sensor
Data Source
AI summary
The present application relates to contact immersion lithography systems and methods of their use. An example immersion lithography system includes a photomask substrate and at least one sensor disposed along a surface of the photomask substrate. The immersion lithography system also includes a controller having at least one processor and a memory. The at least one processor is configured to execute program instructions stored in the memory so as to carry out operations. The operations include receiving, from the at least one sensor, information indicative of an electric field proximate to the at least one sensor. The operations also include determining, based on the received information, at least one of: a thickness of a liquid layer adjacent to the photomask substrate or a distance to a further substrate adjacent to the photomask substrate.