Method and apparatus for controlling droplet in extreme ultraviolet light source

1 . A lithography method in semiconductor fabrication, comprising:

generating a plurality of first drops of a target material through a first nozzle group selected from a plurality of nozzles to form a first elongated droplet, wherein an actuator is driven to generate one of the first drops for a first time period;

generating a first laser pulse to convert the first elongated droplet into a first plasma that generates a first extreme ultraviolet (EUV) radiation;

reflecting the first EUV radiation by a collector mirror; and

generating a plurality of second drops of the target material through a second nozzle group selected from the plurality of nozzles to form a second elongated droplet, wherein the actuator is driven to generate one of the second drops for a second time period, and the second time period is different than the first time period, the plurality of first drops are transmitted along an axis, the plurality of second drops are transmitted along the axis, and a longitudinal axis of the first elongated droplet and the axis has a first tilt angle therebetween, a longitudinal axis of the second elongated droplet and the axis has a second tilt angle therebetween, and the second tilt angle is different than the first tilt angle.

2 . The lithography method of claim 1 , wherein the first elongated droplet has a first length measured in the axis, the second elongated droplet has a second length measured in the axis, and the second length is different than the first length.

3 . The lithography method of claim 1 , wherein the first elongated droplet has a first length measured in a direction perpendicular to the axis, the second elongated droplet has a second length measured in the direction perpendicular to the axis, and the second length is different than the first length.

4 . The lithography method of claim 1 , further comprising:

generating a plurality of third drops of the target material through a third nozzle group selected from the plurality of nozzles to form a third elongated droplet, wherein the actuator is driven to generate one of the third drops for a third time period, and the third time period is different than the first time period.

5 . The lithography method of claim 1 , further comprising:

generating a plurality of third drops of the target material through a third nozzle group selected from the plurality of nozzles to form a third elongated droplet, wherein the actuator is driven to generate one of the third drops for a third time period, and the third time period is different than the second time period.

6 . The lithography method of claim 1 , further comprising:

generating a second laser pulse to convert the second elongated droplet into a second plasma that generates a second EUV radiation.

7 . The lithography method of claim 6 , further comprising:

reflecting the second EUV radiation by the collector mirror.

8 . A lithography method in semiconductor fabrication, comprising:

generating a plurality of first drops of a target material through a first nozzle group selected from a plurality of nozzles to form a first elongated droplet, wherein an actuator is driven to generate one of the first drops for a first time period;

generating a first laser pulse to convert the first elongated droplet into a first plasma that generates a first extreme ultraviolet (EUV) radiation;

reflecting the first EUV radiation by a collector mirror having an optical axis; and

generating a plurality of second drops of the target material through a second nozzle group selected from the plurality of nozzles to form a second elongated droplet, wherein the second elongated droplet is oblique with the optical axis of the collector mirror at a different angle than the first elongated droplet, and the actuator is driven to generate one of the second drops for a second time period, and the second time period is different than the first time period, wherein the first nozzle group includes a plurality of first nozzles arranged along a first direction, and the second nozzle group includes a plurality of second nozzles arranged along a second direction that is oblique or offset from the first direction.

9 . The lithography method of claim 8 , wherein the plurality of first drops are transmitted along an axis oblique with a longitudinal axis of the first elongated droplet.

10 . The lithography method of claim 8 , wherein the plurality of second drops are transmitted along an axis oblique with a longitudinal axis of the second elongated droplet.

11 . The lithography method of claim 8 , wherein the second elongated droplet has a different size than the first elongated droplet.

12 . The lithography method of claim 8 , further comprising:

generating a second laser pulse to convert the second elongated droplet into a second plasma that generates a second EUV radiation.

13 . The lithography method of claim 12 , further comprising:

reflecting the second EUV radiation by the collector mirror.

14 . The lithography method of claim 8 , further comprising:

generating a plurality of third drops of the target material through a third nozzle group selected from the plurality of nozzles to form a third elongated droplet, wherein the actuator is driven to generate one of the third drops for a third time period, and the third time period is different than the second time period.

15 . A lithography method in semiconductor fabrication, comprising:

generating a plurality of first drops of a target material through a first nozzle group selected from a plurality of nozzles to form a first elongated droplet, wherein an actuator is driven to generate a first one of the first drops for a first time period, and the first one, a second one, and a third one of the first drops are generated sequentially through a first one, a second one, and a third one of the nozzles of the first nozzle group;

generating a first laser pulse to convert the first elongated droplet into a first plasma that generates a first extreme ultraviolet (EUV) radiation;

reflecting the first EUV radiation by a collector mirror; and

generating a plurality of second drops of the target material through a second nozzle group selected from the plurality of nozzles to form a second elongated droplet, wherein the actuator is driven to generate one of the second drops for a second time period, and the second time period is different than the first time period, and wherein a longitudinal axis of the second elongated droplet is oblique to a longitudinal axis of the first elongated droplet.

16 . The lithography method of claim 15 , wherein a first one, a second one, and a third one of the second drops are generated sequentially through a first one, a second one, and a third one of the nozzles of the second nozzle group.

17 . The lithography method of claim 16 , wherein the first one of the first drops is generated using the first time period, and the first one of the second drops is generated using a third time period, and the third time period is different than the first time period.

18 . The lithography method of claim 15 , wherein the plurality of first drops and the plurality of second drops are transmitted along a same axis.

19 . The lithography method of claim 15 , wherein the plurality of first drops are transmitted along an axis oblique with the longitudinal axis of the first elongated droplet.

20 . The lithography method of claim 15 , further comprising:

generating a second laser pulse to convert the second elongated droplet into a second plasma that generates a second EUV radiation.