Angled Fuel Droplet Laser Interaction for EUV Plasma Generation
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Solution Overview
Problem
Current radiation sources, such as laser-produced plasma (LPP) sources, face limitations in extending the time a fuel droplet interacts with a laser beam pulse, which affects the generation and control of plasma and subsequently the radiation output, particularly in achieving smaller feature sizes in lithographic processes.
Innovation Solution
A radiation source configuration that directs a stream of fuel droplets at an angle less than 90 degrees relative to the laser beam, allowing for increased collision time and controlled direction, thereby enhancing the generation and collection of radiation, including EUV radiation, using a collector aligned with the optical axis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If a perpendicular configuration (90° angle) is used between droplet stream and laser beam, then the device structure is simple, but the plasma generation time is limited and radiation output is reduced
Solution Approach 1:
The patent transitions from a two-dimensional perpendicular configuration to a three-dimensional angled configuration, where the droplet stream and laser beam intersect at an angle between 30° and 60° relative to the optical axis. This dimensional change allows the droplets to traverse a longer path through the laser beam, increasing plasma generation time and radiation output without significantly complicating the device structure.
2Productivity
If the angle between droplet stream and laser beam is reduced to less than 90°, then radiation output and plasma control are improved, but the device configuration becomes more complex
Solution Approach 1:
The patent optimizes the angular parameter of the droplet stream relative to the laser beam, changing it from the conventional 90° to an angle between 30° and 60° relative to the optical axis. This parameter change increases the interaction time between droplets and laser energy, thereby enhancing radiation output and plasma control while maintaining manageable device complexity through precise angular positioning.
3Productivity
If the droplet stream velocity is increased, then the productivity of the radiation source is improved, but the plasma generation time is reduced
Solution Approach 1:
The patent compensates for reduced plasma generation time at higher velocities by changing the geometric configuration from perpendicular to angled intersection. The angled configuration (30°-60° relative to optical axis) extends the effective interaction path length, allowing droplets to spend more time in the laser beam even at increased velocities, thus maintaining plasma generation time while improving overall productivity.
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 configuration increases the plasma generation time and control, leading to improved radiation output and stability, which can enhance the capability to produce smaller features in lithographic processes, such as in the manufacture of integrated circuits.
Implementation Method 1
A radiation source configured to generate radiation may include a fuel droplet generator constructed and arranged to generate a stream of droplets of fuel that are directed to a plasma generation site; a laser constructed and arranged to generate a laser beam that is directed to the plasma generation site
Implementation Method 2
The plasma may be created, for example, by directing one or more laser beam pulses at a fuel, such as droplets of a suitable material (e.g. tin), or a stream of a suitable gas or vapour, such as Xe gas or Li vapor. The resulting plasma emits radiation, e.g., EUV radiation
Implementation Method 3
a collector constructed and arranged to collect radiation generated by a plasma formed at the plasma formation site when the beam of radiation and a droplet collide, the collector being configured to reflect the radiation substantially along an optical axis of the radiation source
Data Source
AI summary
A radiation source is configured to generate radiation. The radiation source includes a fuel droplet generator constructed and arranged to generate a stream of droplets of fuel that are directed to a plasma generation site; a laser constructed and arranged to generate a laser beam that is directed to the plasma generation site, an angle between the direction of movement of the stream of droplets and the direction of the laser beam being less than about 90°; and a collector constructed and arranged to collect radiation generated by a plasma formed at the plasma formation site when the beam of radiation and a droplet collide. The collector is configured to reflect the radiation substantially along an optical axis of the radiation source. The laser beam is directed to the plasma generation site through an aperture provided in the collector.