Excimer Laser Discharge Timing for Narrower Spectrum Line Width
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Solution Overview
Problem
In semiconductor exposure apparatuses, the wide spectrum line width of KrF and ArF excimer laser beams leads to chromatic aberration and reduced resolving power, necessitating a gas laser apparatus with a line narrowing module to minimize spectrum line width and mitigate chromatic aberration.
Innovation Solution
A gas laser apparatus with a specific configuration including a laser chamber, main discharge electrodes, a pre-ionization electrode, and a pulse power generation device that controls the timing interval between corona and main discharges to optimize laser energy output, featuring a step-up pulse transformer, capacitors, and magnetic switches to manage voltage and discharge timing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a line narrowing module is added to the gas laser apparatus to narrow the spectrum line width, then chromatic aberration is reduced and resolving power is improved, but the device complexity increases
Solution Approach 1:
The patent applies preliminary action by creating a pre-ionization region before the main discharge occurs. The pre-ionization electrode generates initial ionization 30-60 nanoseconds before main discharge, which prepares the laser gas medium in advance. This preliminary ionization enables more efficient and stable laser oscillation without requiring additional line narrowing optical components, thus improving resolving power while avoiding increased device complexity
Solution Approach 2:
The patent changes the temporal parameter of the discharge process by introducing a controlled time interval (30-60 ns) between pre-ionization and main discharge. This parameter change optimizes the ionization state of the laser medium, leading to improved laser beam quality and reduced spectrum line width through better control of the discharge timing rather than adding complex optical narrowing elements
2Power
If the time interval between corona discharge and main discharge is optimized to 30 ns to 60 ns, then laser energy output is maximized and laser efficiency is improved, but the control precision requirements increase
Solution Approach 1:
The patent introduces an intermediary timing control mechanism that coordinates between the pre-ionization circuit and main discharge circuit. The controller manages the 30-60 nanosecond delay between corona discharge initiation and main discharge firing, using this intermediate time window to optimize ionization without requiring extreme precision in the discharge timing itself, thereby maximizing laser energy output while keeping control requirements manageable
Solution Approach 2:
The patent employs periodic pulsed discharge action where the pre-ionization and main discharge occur in repeated cycles with a controlled interval. This periodic timing pattern (30-60 ns between discharges) allows the system to consistently achieve optimal laser energy output through repeated standardized cycles, reducing the need for continuous high-precision adjustment and measurement
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
The optimized timing interval between corona and main discharges allows for maximum laser energy output, effectively reducing chromatic aberration and enhancing resolving power by setting the time interval between start of corona and main discharges to 30 ns to 60 ns, thereby improving the spectrum line width and laser efficiency.
Implementation Method 1
a pre-ionization circuit connected to the pre-ionization electrode and configured to supply, to the pre-ionization electrode, pre-ionization voltage that causes corona discharge
Implementation Method 2
a main discharge circuit connected to the main discharge electrodes and configured to supply, to the main discharge electrodes, main discharge voltage that causes main discharge
Data Source
AI summary
A gas laser apparatus according to an aspect of the present disclosure includes a main discharge circuit that supplies main discharge voltage that causes main discharge to a pair of main discharge electrodes, and a pre-ionization circuit that supplies pre-ionization voltage that causes corona discharge to a pre-ionization electrode. The main discharge circuit includes a step-up pulse transformer, a main capacitor and a switch connected to a primary side of the step-up pulse transformer, a first power source that charges the main capacitor, a first capacitor connected in parallel to a secondary side of the step-up pulse transformer, a first magnetic switch connected to the first capacitor, and a peaking capacitor connected in parallel to the first capacitor through the first magnetic switch and to the main discharge electrodes. An interval between start timings of the corona discharge and the main discharge is 30 ns to 60 ns inclusive.