Method of controlling a radiation source and lithographic apparatus comprising the radiation source

Patent metadata

Field	Value
Publication number	US-9645510-B2
Application number	US-201414787738-A
Country	US
Kind code	B2
Filing date	Apr 16, 2014
Priority date	May 20, 2013
Publication date	May 9, 2017
Grant date	May 9, 2017

Abstract

A method of selecting a periodic modulation to be applied to a variable of a radiation source, wherein the source delivers radiation for projection onto a substrate and wherein there is relative motion between the substrate and the radiation at a scan speed, the method including: for a set of system parameters and for a position on the substrate, calculating a quantity, the quantity being a measure of the contribution to an energy dose delivered to the position that arises from the modulation being applied to the variable of the source, wherein the contribution to the energy dose is calculated as a convolution of: a profile of radiation, and a contribution to an irradiance of radiation delivered by the source; and selecting a modulation frequency at which the quantity for the set of system parameters and the position on the substrate satisfies a certain criteria.

First claim

The invention claimed is:

1. A method of selecting a periodic modulation to be applied to a variable of a radiation source, wherein the radiation source is operable to deliver radiation to a lithographic apparatus for projection as a band of radiation onto a substrate and wherein the lithographic apparatus is operable to provide relative motion between the substrate and the radiation at a scan speed, the method comprising:
for a set of system parameters and for a position on the substrate, calculating a quantity, the quantity being a measure of the contribution to an energy dose delivered to the position that arises from the modulation being applied to the variable of the radiation source, wherein the contribution to the energy dose is calculated as a convolution of: a profile of the band of radiation, and a contribution to an irradiance of radiation delivered by the radiation source; and
selecting a frequency value of the modulation at which the quantity for the set of system parameters and the position on the substrate satisfies a certain criteria.

2. The method as claimed in claim 1 , wherein the modulation is applied to an amplitude of an output power or irradiance of the radiation source.

3. The method as claimed in claim 1 , wherein the radiation source has a variable that can be varied so as to vary an output power or irradiance of the radiation source and wherein the modulation is applied to the variable.

4. The method as claimed in claim 1 , wherein the system parameters comprise a time taken for the band of radiation to sweep past a position on the substrate or a time taken for a position on the substrate to sweep past the band of radiation.

5. The method as claimed in claim 1 , wherein the system parameters comprise a size and shape of the profile of the band of radiation.

6. The method as claimed in claim 1 , wherein the system parameters comprise the scan speed.

7. The method as claimed in claim 1 , wherein the system parameters comprise a phase of the modulation.

8. The method as claimed in claim 1 , wherein the radiation produced by the radiation source is a pulsed radiation beam having a pulse frequency and wherein the system parameters comprise (i) the pulse frequency, (ii) a phase of the pulsed radiation beam, (iii) the number of pulses that contribute to an energy dose, (iv) a ratio of the scan speed to the pulse frequency, or (v) any combination selected from (i)-(iv).

9. The method as claimed in claim 1 , wherein the quantity is the amplitude of a modulation in the energy dose received by the point on the substrate expressed as a percentage of an average energy dose.

10. The method as claimed in claim 1 , wherein the quantity is proportional to the ratio of the contribution to an energy dose delivered to the position on the substrate that arises from the modulation to an energy dose that would be delivered to the position on the substrate if no modulation had been applied.

11. The method as claimed in claim 1 , wherein the quantity is normalized by the amplitude of the modulation that is applied to a variable of the radiation source.

12. The method as claimed in claim 1 , wherein the criteria requires the quantity to be below a certain threshold.

13. The method as claimed in claim 1 , wherein the criteria requires the frequency of the modulation to be at a local minimum of the quantity or within a particular amount thereof.

14. The method as claimed in claim 1 , wherein the modulation is applied to the variable of the radiation source while the band of radiation beam is being projected onto the substrate.

15. The method as claimed in claim 1 , further comprising using the modulation that is applied to the variable of the radiation source to calibrate a lithographic apparatus.

16. The method as claimed in claim 15 , wherein the calibration of the lithographic apparatus comprises measuring an irradiance of a radiation beam and comparing this to the value of the variable of a radiation source to which the modulation is applied.

17. The method as claimed in claim 16 , wherein the irradiance of the beam of radiation is parameterized as a polynomial function of the variable of the radiation source and calibration of the lithographic apparatus involves determination of a value of a parameter of the polynomial function.

18. The method as claimed in claim 17 , wherein the frequency of the modulation is chosen so that aliasing effects have a negligible effect on the determination of the parameter.

19. A method comprising:
measuring irradiance of a radiation beam produced by a radiation source, the radiation source having a variable that can be varied so as to vary the output power or irradiance of the radiation source, wherein a periodic modulation is applied to the variable;
determining a relationship between the variable and the measured irradiance of the radiation beam;
controlling the value of the variable according to the determined relationship in order to control the irradiance of the radiation beam;
using a patterning device to impart the radiation beam with a pattern in its cross-section; and
projecting the patterned radiation beam onto a target portion of a substrate as a band of radiation,
wherein the frequency of the periodic modulation is selected according to claim 1 .

20. A lithographic apparatus comprising:
a controller configured to output a control signal to a radiation source, wherein the control signal controls the value of a variable of the radiation source and wherein a modulation is applied to the control signal;
a radiation sensor configured to measure the irradiance of a radiation beam produced by the radiation source;
a substrate table configured to hold a substrate; and
a projection system configured to project the radiation beam as a band of radiation onto a target portion of the substrate,
wherein the controller is further configured to:
calculate a relationship between the variable of the radiation source and the irradiance of the radiation beam, wherein the calculation comprises, for a set of system parameters and for a position on the substrate, calculation of a quantity, the quantity being a measure of the contribution to an energy dose delivered to the position that arises from the modulation being applied, wherein the contribution to the energy dose is calculated as a convolution of: a profile of the band of radiation, and a contribution to an irradiance of radiation delivered by the radiation source, and
control the control signal according to the calculated relationship in order to control the irradiance of the radiation beam, wherein the control comprises selection of a frequency value for the modulation at which the quantity for the set of system parameters and the position on the substrate satisfies a certain criteria.

Assignees

• Asml Netherlands Bv

Inventors

• Op 'T Root Wilhelmus Patrick Elisabeth Maria
• Bommer Adrianus Leonardus Gertrudus
• De Jong Robert
• Everts Frank
• Godfried Herman Philip
• Stolk Roland Pieter
• Van Der Veen Paul

Classifications

• G03F7/70558 Primary

  Dose control, i.e. achievement of a desired dose · CPC title

• H01S3/225

  comprising an excimer or exciplex · CPC title

• H01S3/104

  in gas lasers · CPC title

• G03F7/70516

  Calibration of components of the microlithographic apparatus, e.g. light sources, addressable masks or detectors · CPC title

• G03F7/70025

  by lasers · CPC title