Excimer or molecular fluorine laser system with precision timing
A Master Oscillator (MO)—Power Amplifier (PA) configuration (MOPA) can be used advantageously in an excimer laser system for micro-lithography applications, where semiconductor manufacturers demand powers of 40 W or more in order to support the throughput requirements of advanced lithography scanner systems. The timing of discharges in discharge chambers of the MO and PA can be precisely controlled using a common pulser to drive the respective chambers. The timing of the discharges further can be controlled through the timing of the pre-ionization in the chambers, or through control of the reset current in the final compression stages of the pulser. A common pulser, or separate pulser circuits, also can be actively controlled in time using a feedback loop, with precision timing being achieved through control of the pre-ionization in each individual discharge chamber. Yet another system provides for real-time compensation of time delay jitter of discharge pulses in the chambers.
1. An excimer or molecular fluorine laser system, comprising:
first and second discharge chambers each being filled with a gas mixture, each of said first and second discharge chambers containing a pair of electrodes for energizing the gas mixture and outputting an optical pulse;
circuitry for providing separate, sequential excitation pulses to said first and second discharge chambers; and
a real time jitter compensation circuit, said jitter compensation circuit receiving an input corresponding to a measured laser parameter which exhibits pulse to pulse variations, said jitter compensation circuit generating a variable delay signal in response to the received input and supplying the signal to said circuitry to control the relative timing of the excitation pulses delivered to the first and second discharge chambers on a real time pulse to pulse basis, and wherein said laser parameter is selected from one or more of the voltage on a storage capacitor, a reset current and a core magnetization.
2. A laser system as recited in claim 1 , wherein the voltage on the storage capacitor is measured with a differential high voltage probe.
3. A laser system as recited in claim 1 , wherein said jitter compensation circuit includes a fast analog circuit.
4. A laser system as recited in claim 1 , wherein the circuitry includes a separate pulser for each discharge chamber.
5. A laser system as recited in claim 1 , wherein the circuitry includes a common pulser system and the compensation circuit compensates for jitter between channels of the common pulser.
6. A laser system as recited in claim 1 , further including a feedback loop to compensate for jitter caused by slower, non-pulse to pulse changes.
7. A laser system as recited in claim 6 , wherein said feedback loop monitors the delay between the excitation of the two discharges and generates a signal in response thereto that is supplied to the compensation circuit and is used in generating the variable delay signal.
8. A laser system as recited in claim 1 , wherein the first discharge chamber functions as an oscillator and the second discharge chamber functions as an amplifier to amplifier the optical pulses generated by the first discharge chamber.
9. An excimer or molecular fluorine laser system, comprising:
a master oscillator including a discharge chamber filled with a gas mixture and containing a pair of electrodes for energizing the gas mixture and outputting an optical pulse;
a power amplifier including a discharge chamber filled with a gas mixture and containing a pair of electrodes for energizing the gas mixture for amplifying the optical pulses generated by the oscillator;
circuitry for providing separate, sequential excitation pulses to said oscillator and amplifier; and
a real time jitter compensation circuit, said jitter compensation circuit receiving first inputs corresponding to a measured laser parameter which exhibits pulse to pulse variations and second inputs corresponding to slower, non-pulse to pulse variations, said jitter compensation circuit generating a variable delay signal in response to said received first and second inputs and supplying the signal to said circuitry on a real time basis to control the relative timing of the excitation pulses delivered to the oscillator and the amplifier.
10. A laser system as recited in claim 9 , wherein said laser parameter is selected from one or more of the voltage on a storage capacitor, a reset current and a core magnetization.
11. A laser system as recited in claim 9 , wherein the circuitry includes a separate pulser for the oscillator and the amplifier.
12. A laser system as recited in claim 9 , wherein the circuitry includes a common pulser system and the compensation circuit compensates for jitter between channels of the common pulser.
13. A laser system as recited in claim 6 , wherein said compensation circuit monitors the delay between the excitation of the oscillator and the amplifier and is used to generate said second inputs.