Patent Number: 
Section: claims

1. An extreme ultraviolet (EUV) radiation source, comprising:a target droplet generator configured to generate target droplets;a first laser source configured to generate pre-pulses that heat the target droplets to produce target plumes;a second laser source configured to generate main pulses that heat the target plumes to produce plasma emitting EUV radiation;a controller configured to adjust at least one parameter of the first and second laser sources comprising a delay between one of the pre-pulses and a corresponding one of the main pulses, and positions of the pre-pulses in a Y direction that is different from an X direction along which the target droplets travel;an energy detector configured to monitor an energy of the EUV radiation and record the parameters of the first and second laser sources with which the energy of the EUV radiation is maximized;a first laser beam generator and a second laser beam generator configured to generate first and second laser beams, respectively, that are directed onto a travel path of the target plumes, wherein the first and second laser beams are substantially parallel; anda laser beam monitor configured to receive the first and second laser beams reflected by the target plumes to determine a real-time velocity of the target plumes in their traveling path. 2. The EUV radiation source as claimed in claim 1, wherein one of the main pulses heats the target plumes produced by the corresponding one of the pre-pulses. 3. The EUV radiation source as claimed in claim 1, wherein a range for tuning the delay is 100 ns (nanoseconds), and an amount in each adjustment for tuning the delay is 10 ns. 4. The EUV radiation source as claimed in claim 1, wherein the Y direction is perpendicular to the X direction. 5. The EUV radiation source as claimed in claim 1, wherein a range for tuning each of the positions is 6 μm, and an amount in each adjustment for tuning each of the positions is 1 μm. 6. The EUV radiation source as claimed in claim 1, wherein the energy detector records the energy of the EUV radiation at an initial time period of each EUV burst. 7. The EUV radiation source as claimed in claim 1, wherein the controller is configured to adjust the delay between the one of the pre-pulses and the corresponding one of the main pulses according to the real-time velocity of the target plumes in its traveling path. 8. The EUV radiation source as claimed in claim 1, wherein the pre-pulses heat the target droplets along a Z direction and the Y direction is substantially perpendicular to both the X direction and the Z direction. 9. The EUV radiation source as claimed in claim 6, wherein the initial time period is the earliest 5% of the entire time period of the each EUV burst. 10. An extreme ultraviolet (EUV) lithography system, comprising:a radiation source, wherein the radiation source comprises:a target droplet generator configured to generate target droplets;a first laser source configured to generate pre-pulses that heat the target droplets to produce target plumes;a second laser source configured to generate main pulses that heat the target plumes to produce plasma emitting EUV radiation;a controller configured to adjust at least one parameter of the first and second laser sources comprising a delay between one of the pre-pulses and a corresponding one of the main pulses, and positions of the pre-pulses in a Y direction that is different from an X direction along which the target droplets travel;an energy detector configured to monitor an energy of the EUV radiation and record the parameters of the first and second laser sources with which the energy of the EUV radiation is maximized;a collector configured to collect and reflect the EUV radiation;a mask stage configured to secure an EUV mask;a wafer stage configured to secure a semiconductor wafer;one or more optical modules configured to direct the EUV radiation from the radiation source to image an integrated circuit (IC) pattern defined on the EUV mask onto the semiconductor wafer;a first laser beam generator and a second laser beam generator configured to generate first and second laser beams, respectively, that are directed onto a travel path of the target plumes, wherein the first and second laser beams are substantially parallel; anda laser beam monitor configured to receive the first and second laser beams reflected by the target plumes to determine a real-time velocity of the target plumes in their traveling path. 11. The EUV lithography system as claimed in claim 10, wherein one of the main pulses heats the target plumes produced by the corresponding one of the pre-pulses. 12. The EUV lithography system as claimed in claim 10, wherein a range for tuning the delay is 100 ns (nanoseconds), and an amount in each adjustment for tuning the delay is 10 ns. 13. The EUV lithography system as claimed in claim 10, wherein the Y direction is perpendicular to the X direction. 14. The EUV lithography system as claimed in claim 10, wherein a range for tuning each of the positions is 6 μm, and an amount in each adjustment for tuning each of the positions is 1 μm. 15. The EUV lithography system as claimed in claim 10, wherein the energy detector monitors the energy of the EUV radiation at an initial time period of each EUV burst. 16. A method for extreme ultraviolet (EUV) lithography, the method comprising:generating a target droplet;producing a target plume by heating the target droplet with a pre-pulse generated by a first laser source;producing EUV-radiating plasma by heating the target plume with a main pulse generated by a second laser source;adjusting at least one parameter of the first and second laser sources comprising a delay between the pre-pulse and the main pulse, and a position of the pre-pulse in a Y direction that is different from an X direction along which the target droplet travel;monitoring an energy of the EUV radiation and recording the parameters of the first and second laser sources with which the energy of the EUV radiation is maximized;generating first and second laser beams that are directed onto a travel path of the target plume, wherein the first and second laser beams are substantially parallel; andreceiving the first and second laser beams reflected by the target plume to determine a real-time velocity of the target plume in its traveling path. 17. The method as claimed in claim 16, wherein a range for tuning the delay is 100 ns (nanoseconds), and an amount in each adjustment for tuning the delay is 10 ns. 18. The method as claimed in claim 16, wherein a range for tuning the position is 6 μm, and an amount in each adjustment for tuning the position is 1 μm. 19. The method as claimed in claim 16, wherein a mean value of the energy of the EUV radiation of each EUV burst is monitored and recorded. 20. The method as claimed in claim 16, wherein the energy of the EUV radiation at an initial time period of each EUV burst is monitored and recorded, and the initial time period is the earliest 5% of the entire time period of the each EUV burst.