Lithographic apparatus and method

Patent metadata

Field	Value
Publication number	US-10627724-B2
Application number	US-201615759358-A
Country	US
Kind code	B2
Filing date	Aug 23, 2016
Priority date	Sep 23, 2015
Publication date	Apr 21, 2020
Grant date	Apr 21, 2020

Abstract

A method of controlling output of a radiation source, the method including: periodically monitoring an output energy of the radiation source; determining a difference between a reference energy signal and the monitored output energy; determining a feedback value; determining a desired output energy of the radiation source for a subsequent time period; and controlling an input parameter of the radiation source in dependence on the determined desired output energy during the subsequent time period. If the magnitude of the determined difference between the monitored output energy of the radiation source and the reference energy signal exceeds a threshold value: the determined difference does not contribute to the feedback value; and the determined difference is spread over the subsequent time period according to a reference energy signal adjustment profile and the reference energy signal adjustment profile is added to the reference energy signal for the subsequent time period.

First claim

The invention claimed is:

1. A method of controlling an output of a radiation source, the method comprising:
periodically monitoring an output energy of the radiation source;
determining a difference between a reference energy signal and the monitored output energy of the radiation source;
determining a feedback value, the feedback value being dependent on the determined difference between the reference energy signal and the monitored output energy for a preceding time period;
determining a desired output energy of the radiation source for a subsequent time period, the desired output energy being a combination of the reference energy signal and the feedback value;
controlling an input parameter of the radiation source in dependence on the determined desired output energy during the subsequent time period;
spreading a certain determined difference between the monitored output energy of the radiation source and the reference energy signal over a particular subsequent time period according to a reference energy signal adjustment profile; and
for that particular subsequent time period during which the determined difference between the monitored output energy of the radiation source and the reference energy signal does not contribute to the feedback value, altering the reference energy signal for the subsequent time period such that the reference energy signal adjustment profile is added to or subtracted from the reference energy signal for the subsequent time period.

2. The method of claim 1 , wherein the length of the subsequent time period over which the determined difference between the monitored output energy of the radiation source and the reference energy signal is added to or subtracted from the reference energy is dependent on the magnitude of the determined difference between the monitored output energy of the radiation source and the reference energy signal.

3. The method of claim 1 , wherein a shape of the reference energy signal adjustment profile is dependent on the magnitude of the determined difference between the monitored output energy of the radiation source and the reference energy signal.

4. The method of claim 1 , wherein the reference energy signal adjustment profile is a constant profile such that the determined difference between the monitored output energy of the radiation source and the reference energy signal is spread evenly over the subsequent time period.

5. The method of claim 1 , wherein the reference energy signal adjustment profile is a linear profile such that a fraction of the determined difference between the monitored output energy of the radiation source and the reference energy signal that is added to or subtracted from the reference energy signal decreases linearly with time during the subsequent time period.

6. The method of claim 1 , wherein the reference energy signal adjustment profile is a maximized constant profile wherein the reference energy signal is increased to a maximum value for a first portion of the subsequent time period and decreases to a smaller value for a second portion of the subsequent time period.

7. The method of claim 1 , comprising evaluating the magnitude of the determined difference between the monitored output energy of the radiation source and the reference energy signal against a threshold value, wherein the threshold value is chosen such that the magnitude of the determined difference between the monitored output energy of the radiation source and the reference energy signal exceeds the threshold value responsive to the determined difference between the monitored output energy of the radiation source and the reference energy signal giving rise to a value of the input parameter of the radiation source outside of its operational range.

8. The method of claim 1 , comprising evaluating the magnitude of the determined difference between the monitored output energy of the radiation source and the reference energy signal against a threshold value, wherein the threshold value is chosen such that the magnitude of the determined difference between the monitored output energy of the radiation source and the reference energy signal will not exceed the threshold value responsive to the determined difference between the monitored output energy of the radiation source and the reference energy signal being less than a typical amplitude of noise on a signal indicative of the monitored output energy of the radiation source.

9. The method of claim 1 , comprising evaluating the magnitude of the determined difference between the monitored output energy of the radiation source and the reference energy signal against a threshold value, wherein the threshold value is equal to or more than 25% of the reference energy.

10. The method of claim 1 , wherein the feedback value is determined such that the desired output energy for the subsequent time period at least partially compensates for a difference between the reference energy and the monitored output energy over the preceding time period.

11. The method of claim 1 , wherein controlling the input parameter of the radiation source in dependence on the determined desired output energy during the subsequent time period comprises:
calculating a value for the input parameter of the radiation source using a relationship, and
controlling the radiation source using the calculated input parameter.

12. The method of claim 1 , wherein the radiation source is a gas laser comprising a pair of discharge conductors across which a voltage is applied and the input parameter of the radiation source comprises the voltage applied across the pair of discharge conductors.

13. The method of claim 1 , wherein controlling the input parameter of the radiation source in dependence on the determined desired energy during the subsequent time period further comprises limiting the one or more parameters to an allowed operational range.

14. A lithography method comprising:
providing a radiation beam using a radiation source;
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;
wherein an output power of the radiation source is controlled using the method of claim 1 .

15. The lithography method of claim 14 , wherein the power of the radiation beam is controlled so as to ensure that one or more parts of the target portion receive a desired dose of radiation.

16. A method of controlling an output of a radiation source, the method comprising:
periodically monitoring an energy of the radiation source;
determining a difference between a reference energy signal and the monitored energy of the radiation source;
determining a desired energy of the radiation source for a subsequent time period, wherein the determination of the desired energy is dependent on the magnitude of the determined difference between the monitored energy of the radiation source and the reference energy signal; and
controlling an input parameter of the radiation source in dependence on the determined desired energy during the subsequent time period,
wherein, for a period of time, the determined difference between the monitored energy of the radiation source and the reference energy signal does not cross a threshold value and the determination of the desired energy is according to a first operational mode, which first operational mode involves control of the input parameter based on the determined desired energy, and
wherein, for another period of time, the determined difference between the monitored energy of the radiation source and the refere

Assignees

• Asml Netherlands Bv
• Cymer LLC

Inventors

• Everts Frank
• Op 'T Root Wilhelmus Patrick Elisabeth Maria
• Godfried Herman Philip
• Thornes Joshua Jon
• O'Brien Kevin Michael
• Saanen Leon Pieter Paul
• Aggarwal Tanuj

Classifications

• G03F7/70525

  Controlling normal operating mode, e.g. matching different apparatus, remote control or prediction of failure · CPC title

• G03F7/70066

  Size and form of the illuminated area in the mask plane, e.g. reticle masking blades or blinds · CPC title

• G03F7/70008

  Production of exposure light, i.e. light sources · CPC title

• G03F7/70558 Primary

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

• G03F7/70533

  Controlling abnormal operating mode, e.g. taking account of waiting time, decision to rework or rework flow · CPC title