Methods and apparatus for laser produced plasma EUV light source

Abstract

A system for producing EUV light using a drive laser beam to irradiate a stream of material droplets. There is included a monitoring system for monitoring at least one of drive laser beam reflection from the drive laser beam and EUV radiation pulses and producing a detector signal, the detector signal being a pulse train. There is also included an arrangement for analyzing the detector signal to ascertain whether there exists at least one satellite droplet in the stream of material droplets.

The invention claimed is: 
     
       1. A system for producing EUV light, comprising:
 a material delivery system for producing a stream of material droplets; 
 a laser system for producing a drive laser beam, the drive laser beam is configured to irradiate the material droplets at an irradiation point, wherein the laser system operates in the No Master Oscillator (NOMO) mode that is configured to cause the drive laser beam to pulse on every droplet in the stream of material droplets; 
 a monitoring system for monitoring at least one of drive laser beam reflection from the drive laser beam and EUV radiation pulses, the monitoring system producing a detector signal responsive to the monitoring of the drive laser beam reflection if the reflection from the drive laser beam is monitored or responsive to the monitoring of the EUV radiation pulses if the EUV radiation pulses are monitored, the detector signal being a pulse train wherein the stream of material droplets comprise of main droplets having a first droplet size and satellite droplets having a second droplet size smaller than the first droplet size, and wherein the material delivery system comprises arrangement to modulate a disturbance signal configured to produce the stream of material droplets at a predefined rate and wherein the main droplets represent droplets formed at the predefined rate and the satellite droplets represent droplets formed at a rate different from the predefined rate; and 
 arrangement for analyzing the detector signal to ascertain whether there exists at least one of extra pulses outside of the envelope of pulses that correspond with the irradiation of the main droplets and extra signal peaks outside of the envelope of signal peaks that correspond with the irradiation of the main droplets. 
 
     
     
       2. The system of  claim 1  wherein the laser system includes a CO 2  laser. 
     
     
       3. The system of  claim 1  wherein the arrangement for analyzing the detector signal employs a box car integration approach. 
     
     
       4. The system of  claim 1  wherein the monitoring system monitor EUV radiation pulses, the monitoring system time-stamps every EUV radiation pulse detected and the arrangement for analyzing the detector signal analyzes the intervals between pulses corresponding to the irradiation of the main droplets for the presence of the extra pulses. 
     
     
       5. The system of  claim 1  wherein the monitoring system monitors the drive laser beam reflection and wherein the detector represents an IR detector. 
     
     
       6. The system of  claim 5  wherein the drive laser beam reflection is obtained from at least one internal surface of the system for producing EUV light. 
     
     
       7. The system of  claim 1  wherein the monitoring system monitors the drive laser beam reflection. 
     
     
       8. The system of  claim 1  wherein the monitoring system monitors the EUV radiation pulses. 
     
     
       9. The system of  claim 1  wherein the arrangement for analyzing the detector signal represents a digital signal processing system. 
     
     
       10. The system of  claim 1  wherein the arrangement for analyzing the detector signal is configured to detect a signal peak that occurs outside envelopes of signal peaks representative of main droplet pulses. 
     
     
       11. A system for producing EUV light, comprising:
 a material delivery system for producing a stream of material droplets; 
 a laser system for producing a drive laser beam, the drive laser beam is configured to irradiate the material droplets at an irradiation point, wherein the laser system operates in the No Master Oscillator (NOMO) mode that is configured to cause the drive laser beam to pulse on every droplet in the stream of material droplets; 
 a detector arrangement for monitoring EUV radiation pulses, the detector producing a detector signal responsive to the monitoring of the EUV radiation pulses, the detector signal being a pulse train, wherein the stream of material droplets comprise of main droplets having a first droplet size and satellite droplets having a second droplet size smaller than the first droplet size, and wherein the material delivery system comprises arrangement to modulate a disturbance signal configured to produce the stream of material droplets at a predefined rate and wherein the main droplets represent droplets formed at the predefined rate and the satellite droplets represent droplets formed at a rate different from the predefined rate; and 
 arrangement for analyzing the detector signal to ascertain whether there exist extra pulses outside of the envelope of pulses that correspond with the irradiation of the main droplets. 
 
     
     
       12. The system of  claim 11  wherein the arrangement for analyzing the detector signal employs a reference EUV pulse train for detecting the extra pulses. 
     
     
       13. The system of  claim 11  wherein the arrangement for analyzing the detector signal employs a box car integration approach for detecting the extra pulses. 
     
     
       14. The system of  claim 11  wherein the laser system includes a CO 2  laser. 
     
     
       15. The system of  claim 11  wherein the detector arrangement time-stamps every EUV radiation pulse detected and the arrangement for analyzing the detector signal analyzes the intervals between pulses corresponding to the irradiation of the main droplets for the presence of the extra pulses. 
     
     
       16. The system of  claim 11  wherein the arrangement for analyzing the detector signal is configured to detect a signal peak that occurs outside envelopes of signal peaks representative of main droplet pulses. 
     
     
       17. A system for producing EUV light, comprising:
 a material delivery system for producing a stream of material droplets; 
 a laser system for producing a drive laser beam, the drive laser beam is configured to irradiate the material droplets at an irradiation point, wherein the laser system operates in the No Master Oscillator (NOMO) mode that is configured to cause the drive laser beam to pulse on every droplet in the stream of material droplets; 
 a detector for monitoring drive laser beam reflection from the drive laser beam, the detector producing a detector signal responsive to the monitoring of the drive laser beam reflection, the drive laser beam reflection obtained from at least one internal surface of the system for producing EUV light, the detector signal being a pulse train, wherein the stream of material droplets comprise of main droplets having a first droplet size and satellite droplets having a second droplet size smaller than the first droplet size, and wherein the material delivery system comprises arrangement to modulate a disturbance signal configured to produce the stream of material droplets at a predefined rate and wherein the main droplets represent droplets formed at the predefined rate and the satellite droplets represent droplets formed at a rate different from the predefined rate; and 
 arrangement for analyzing the detector signal to ascertain whether exist extra signal peaks outside of the envelope of signal peaks that correspond with the irradiation of the main droplets. 
 
     
     
       18. The system of  claim 17  wherein the detector includes a photo detector. 
     
     
       19. The system of  claim 17  wherein the arrangement for analyzing the detector signal employs a reference signal for detecting the extra signal peaks. 
     
     
       20. The system of  claim 17  wherein the arrangement for analyzing the detector signal employs a box car integration approach for detecting the extra signal peaks. 
     
     
       21. The system of  claim 17  wherein the laser system includes a CO 2  laser.