Lithographic method

Patent metadata

Field	Value
Publication number	US-10437154-B2
Application number	US-201715789702-A
Country	US
Kind code	B2
Filing date	Oct 20, 2017
Priority date	Jun 18, 2013
Publication date	Oct 8, 2019
Grant date	Oct 8, 2019

Abstract

A method of patterning lithographic substrates, the method comprising using a free electron laser to generate EUV radiation and delivering the EUV radiation to a lithographic apparatus which projects the EUV radiation onto lithographic substrates, wherein the method further comprises reducing fluctuations in the power of EUV radiation delivered to the lithographic substrates by using a feedback-based control loop to monitor the free electron laser and adjust operation of the free electron laser accordingly.

First claim

The invention claimed is:

1. An injector for a free electron laser, the injector comprising:
a photocathode;
a radiation output configured to emit a pulsed radiation beam and direct the pulsed radiation beam to be incident on the photocathode so as to cause the photocathode to emit a beam of electron bunches which is output from the injector, each electron bunch corresponding to a pulse of the radiation beam; and
a control apparatus configured to receive the pulsed radiation beam and substantially prevent at least one pulse of the radiation beam from being incident on the photocathode so as to interrupt the electron beam and to cause the at least one pulse of the radiation beam to have substantially no associated electron bunch in the electron beam which is output from the injector.

2. The injector of claim 1 , wherein the control apparatus is configured to interrupt the electron beam in a periodic manner.

3. The injector of claim 1 , wherein the control apparatus is configured to interrupt the electron beam so as to cause a single pulse of the radiation beam to have substantially no associated electron bunch in the electron beam which is output from the injector.

4. The injector of claim 1 , wherein the control apparatus comprises:
a Pockels cell disposed in the path of the radiation beam before the radiation beam is incident on the photocathode and wherein the Pockels cell is switchable between a first mode of operation in which the Pockels cell is configured to transmit the radiation beam without changing its polarization state and a second mode of operation in which the Pockels cell is configured to transmit the radiation beam and rotate the polarization state of the radiation beam; and
a polarizer disposed between the Pockels cell and the photocathode and in the path of the radiation beam, wherein the polarizer is configured to only transmit radiation having a given polarization state.

5. The injector of claim 4 , wherein the Pockels cell comprises an electro-optic crystal, a pair of electrodes and a voltage source and wherein the voltage source is configured to generate a potential difference between the electrodes so as to switch the Pockels cell from the first mode of operation to the second mode of operation.

6. The injector of claim 5 , wherein the Pockels cell comprises a plurality of pairs of electrodes and a plurality of voltage sources and wherein each of the plurality of voltage sources is configured to generate a potential difference between one of the plurality of pairs of electrodes so as to switch the Pockels cell from the first mode of operation to the second mode of operation.

7. The injector of claim 4 , wherein the Pockels cell is configured to rotate the polarization state of the radiation beam by about 90° when in the second mode of operation.

8. The injector of claim 7 , further comprising a second Pockels cell configured to rotate the polarization state of the radiation beam by about 90° when in the second mode of operation.

9. The injector of claim 8 , wherein the polarizer is configured to only transmit radiation having a polarization state which is orthogonal to the polarization state of the radiation beam before the radiation beam is incident on the Pockels cell.

10. The injector of claim 4 , wherein the control apparatus comprises a plurality of Pockels cells disposed in the path of the radiation beam before the radiation beam is incident on the photocathode and wherein each of the plurality of Pockels cell is switchable between a first mode of operation in which the Pockels cell is configured to transmit the radiation beam without changing its polarization state and a second mode of operation in which the Pockels cell is configured to transmit the radiation beam and rotate the polarization state of the radiation beam by less than 90° and wherein the plurality of Pockels cells are configured to apply a combined rotation of the polarization state of the radiation beam of about 90° when each of the plurality of Pockels cells are in the second mode of operation.

11. The injector of claim 4 , wherein the polarizer is configured to only transmit radiation having the polarization state of the radiation beam before the radiation beam is incident on the Pockels cell.

12. A free electron laser comprising:
an injector comprising:
a photocathode,
a radiation output configured to emit a pulsed radiation beam and direct the pulsed radiation beam to be incident on the photocathode so as to cause the photocathode to emit a beam of electron bunches which is output from the injector, each electron bunch corresponding to a pulse of the radiation beam, and
a control apparatus configured to interrupt the electron beam so as to cause at least one pulse of the radiation beam to have substantially no associated electron bunch in the electron beam which is output from the injector;

a particle accelerator configured to accelerate the electron beam output from the injector; and
an undulator configured to guide the accelerated electron beam along a periodic path so as to stimulate emission of a free electron laser radiation beam, wherein the free electron laser radiation beam comprises a series of pulses, each pulse corresponding to an electron bunch of the electron beam.

13. The free electron laser of claim 12 , wherein the control apparatus of the injector is configured to interrupt the electron beam which is output from the injector, so as to interrupt the pulses of the free electron laser radiation beam.

14. The free electron laser of claim 13 , further comprising a controller configured to control the control apparatus of the injector so as to control a number of pulses of the free electron laser radiation beam which occur in a given time period.

15. The free electron laser of claim 12 , wherein the undulator is configured to stimulate emission of an EUV free electron laser radiation beam.

16. The free electron laser of claim 15 , further comprising a sensor configured to monitor the intensity of the radiation beam and output a signal to a controller to enable feedback control.

17. A lithographic system comprising:
a radiation source comprising the free electron laser of claim 12 ; and
a lithographic apparatus.

18. The lithographic system of claim 17 , wherein the lithographic apparatus is arranged to receive a radiation beam comprising at least a portion of the free electron laser radiation beam which is output from the free electron laser of the radiation source, the lithographic apparatus comprising:
an illumination system configured to condition the radiation beam received from the radiation source;
a support structure constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam;
a substrate table constructed to hold a substrate; and
a projection system configured to project the patterned radiation beam onto a target location of the substrate.

19. The lithographic system of claim 18 , wherein the control apparatus of the injector is configured to interrupt the electron beam which is output from the injector, so as to interrupt the pulses of the free electron laser radiation beam, and so as to interrupt pulses of the radiation beam which are received by the lithographic apparatus, and so as to interrupt pulses of the patterned radiation beam which are projected onto a target location of the substrate.

20. The lithographic system of claim 19 , further comprising a controlle

Assignees

• Asml Netherlands Bv

Inventors

• Nikipelov Andrey Alexandrovich
• Frijns Olav Waldemar Vladimir
• Loopstra Erik Roelof
• Engelen Wouter Joep
• Akkermans Johannes Antonius Gerardus

Classifications

• H05H2007/041

  for beam bunching, e.g. undulators · CPC title

• H05H9/048

  Lepton LINACS · CPC title

• H05H7/18

  Cavities; Resonators {(travelling-wave tubes H01J23/18; hyperfrequency cavities in general H01P7/04, H01P7/06)} · CPC title

• H01S3/0903

  Free-electron laser · CPC title

• H01S3/0085

  Modulating the output, i.e. the laser beam is modulated outside the laser cavity · CPC title