Radiation source

Patent metadata

Field	Value
Publication number	US-9853412-B2
Application number	US-201515502462-A
Country	US
Kind code	B2
Filing date	Jul 27, 2015
Priority date	Aug 15, 2014
Publication date	Dec 26, 2017
Grant date	Dec 26, 2017

Abstract

Passage through LINACs of electron bunches in their acceleration phase is coordinated with passage through the LINACs of electron bunches in their deceleration phase. Each successive pair of electron bunches are spaced in time by a respective bunch spacing, in accordance with a repeating electron bunch sequence. The electron source provides clearing gaps in the electron bunch sequence to allow clearing of ions at the undulator. The electron source provides the clearing gaps in accordance with a clearing gap sequence such that, for each of the plurality of energy recovery LINACS, and for substantially all of the clearing gaps: for each passage of the clearing gap through the LINAC in an acceleration phase or deceleration phase the clearing gap is coordinated with a further one of the clearing gaps passing through the LINAC in a deceleration phase or acceleration phase thereby to maintain energy recovery operation of the LINAC.

First claim

The invention claimed is:

1. A method of producing extreme ultraviolet (EUV) radiation using a free electron laser (FEL), the method comprising:
directing a drive laser beam onto a cathode to generate electron bunches;
passing the electron bunches to a linear accelerator (LINAC) to accelerate the electron bunches;
passing the electron bunches along an electron bunch path through an undulator configured to generate EUV radiation; and
removing positively charged ions from the electron bunch path by applying a variation of charge or emittance of the electron bunches within a pre-determined range;
wherein the pre-determined range of charge or emittance variation is selected to restrict variation of accelerating gradients in the LINAC.

2. The method of claim 1 , wherein the pre-determined range of the variation of charge or emittance of the electron bunches is 10% or less of the charge or emittance of the electron bunches.

3. The method of claim 1 , wherein a variation is applied to both the charge and the emittance of the electron bunches.

4. The method of claim 1 , wherein the applied variation is implemented by altering the energy of laser pulses of the drive laser beam which are incident upon the cathode.

5. The method of claim 4 , wherein altering the energy of laser pulses of the drive laser beam comprises an amplification of noise associated with the drive laser.

6. The method of claim 4 , wherein a Pockels cell is used to alter the energy of pulses of the drive laser.

7. The method of claim 1 , wherein the wavefront of pulses produced by the drive laser is varied.

8. The method of claim 7 , wherein a Pockels cell is used to vary the wavefront of pulses produced by the drive laser.

9. The method of claim 1 , wherein the temperature of the cathode is varied to apply the variation of emittance of the electron bunches.

10. The method of claim 9 , wherein a laser incident on the cathode is used to vary the temperature of the cathode.

11. A free electron laser (FEL) extreme ultraviolet (EUV) radiation source comprising:
a drive laser configured to emit laser pulses;
a cathode configured to receive the laser pulses and generate electron bunches;
a linear accelerator (LINAC) configured to accelerate the electron bunches;
an undulator configured to receive the electron bunches and output an EUV radiation beam; and
an ion removal apparatus which comprises an electron bunch charge or emittance variation apparatus controlled by a control unit to vary the charge or emittance of the electron bunches within a pre-determined range, the pre-determined range being selected to remove ions from the FEL but restrict variation of accelerating gradients in the LINAC.

12. A free electron laser (FEL) extreme ultraviolet (EUV) radiation source comprising,
a linear accelerator (LINAC) configured to accelerate electron bunches;
an undulator configured to receive the electron bunches and output an EUV radiation beam; and
an RF electromagnetic wave emitter configured to provide an RF evanescent electromagnetic wave or a beating RF electromagnetic wave which extends into a beam pipe of the FEL.

13. The FEL of claim 12 , wherein the RF electromagnetic wave emitter is connected to the beam pipe on one side of an undulator module of the undulator.

14. The FEL of claim 13 , wherein extraction electrodes are provided on an opposite side of the undulator module.

15. A method of producing extreme ultraviolet (EUV) radiation using a free electron laser (FEL), the method comprising:
passing electron bunches to a linear accelerator (LINAC) to accelerate the electron bunches;
then passing the electron bunches along an electron bunch path through an undulator configured to generate EUV radiation; and
generating an RF evanescent electromagnetic wave or a beating RF electromagnetic wave which extends into a beam pipe of the FEL and which pushes the ions along the beam pipe.

16. The method of claim 15 , wherein the beam pipe into which the RF evanescent electromagnetic wave or beating RF electromagnetic wave extends is located in an undulator module.

17. The method of claim 16 , wherein the RF evanescent electromagnetic wave or beating RF electromagnetic wave provides an electrical potential which pushes ions towards an opposite end of the undulator module.

18. The method of claim 17 , wherein extraction electrodes are provided on an opposite side of the undulator module.

19. The method of claim 18 , wherein the electrical potential has a sufficiently high gradient to remove ions from the free electron laser within around 1 ms.

Assignees

• Asml Netherlands Bv

Inventors

• Nikipelov Andrey Alexandrovich
• Coenen Teis Johan
• Engelen Wouter Joep
• Brussaard Gerrit Jacobus Hendrik
• Poorter Gijsbertus Geert
• Loopstra Erik Roelof

Classifications

• H01S3/0071

  Beam steering, e.g. whereby a mirror outside the cavity is present to change the beam direction · CPC title

• H01S3/0903 Primary

  Free-electron laser · CPC title

• H01S3/1103

  Cavity dumping · CPC title

• H01S3/1024

  for pulse generation · CPC title

• H01S3/0959

  by an electron beam · CPC title