Method and device for determining the heating state of a mirror in an optical system

Patent metadata

Field	Value
Publication number	US-11156922-B2
Application number	US-202017081255-A
Country	US
Kind code	B2
Filing date	Oct 27, 2020
Priority date	May 30, 2018
Publication date	Oct 26, 2021
Grant date	Oct 26, 2021

Abstract

The disclosure provides a method and to an apparatus for determining the heating state of a mirror in an optical system, in particular in a microlithographic projection exposure apparatus. A method for determining the heating state of an optical element includes: measuring values of a first temperature that the optical element has at a first position using a temperature sensor; and estimating a second temperature that the optical element has at a second position, which is located at a distance from the first position, on the basis of the measured values, wherein estimating the second temperature is accomplished while taking into account a temporal change in the previously measured values.

First claim

What is claimed is:

1. A method of estimating a temperature of an incidence surface of an optical element in a microlithographic projection exposure apparatus, the optical element comprising a substrate supporting the incidence surface, the optical element having a channel extending into the substrate from a side of the optical element facing away from the incidence surface, the channel having a channel surface located a distance from the incidence surface, the method comprising:
a) using a temperature sensor to measure values of a temperature of the channel surface, the temperature sensor being in direct contact with the channel surface; and
b) based on the values measured in a) and taking into account a temporal change in the values measured in a), estimating the temperature of the incidence surface,
wherein during use of the optical element, electromagnetic radiation impinges on the incidence surface, and
wherein estimating the temperature of the incidence surface comprises using an equation which comprises the term

p
⁡

(

∂

T
Sensor

∂
t

)

q

,

and wherein T sensor is a temperature value measured by the temperature sensor, t is time, and p and q are fit parameters.

2. The method of claim 1 , wherein the optical element is in an illumination system of the microlithographic projection exposure apparatus.

3. The method of claim 1 , wherein the channel surface faces away from the incidence surface.

4. The method of claim 1 , wherein estimating the temperature during b) comprises taking into account previously ascertained temporal changes in the values measured in a).

5. The method of claim 1 , further comprising using the temperature estimated in b) as an input signal to regulate a parameter that characterizes the optical element.

6. The method of claim 1 , further comprising using the temperature estimated in b) to control pre-heating of the optical element to at least partially compensate temporal changes in the heating state of the optical element occurring during use of the optical element.

7. The method of claim 1 , wherein the optical element is a mirror.

8. The method of claim 7 , wherein, during use of the optical element, the electromagnetic radiation that impinges on the incidence surface has an operating wavelength of less than 30 nm.

9. The method of claim 1 , wherein, during use of the optical element, the electromagnetic radiation that impinges on the incidence surface has an operating wavelength of less than 30 nm.

10. The method of claim 1 , wherein:
the channel surface faces away from the incidence surface; and
estimating the temperature during b) comprises taking into account previously ascertained temporal changes in the values measured in a).

11. A method of estimating a temperature of an incidence surface of an optical element in a microlithographic projection exposure apparatus, the optical element comprising a substrate supporting the incidence surface, the optical element having a channel extending into the substrate from a side of the optical element facing away from the incidence surface, the channel having a channel surface located a distance from the incidence surface, the method comprising:
a) using a temperature sensor to measure values of a temperature of the channel surface, the temperature sensor being in direct contact with the channel surface; and
b) based on the values measured in a) and taking into account a temporal change in the values measured in a), estimating the temperature of the incidence surface,
wherein during use of the optical element, electromagnetic radiation impinges on the incidence surface), and
wherein estimating the temperature of the incidence surface comprises using an equation which comprises the term

p
⁢

∫

-
∞

t

⁢

d
⁢

⁢

τ
⁡

(

∂

T
Sensor

∂
t

)

q

⁢

e

-

∞
⁡

(

t
-
τ

)

,

and wherein T sensor is a temperature value measured by the temperature sensor, t is time, τ is a point in time, α represents a decay constant, and p and q are fit parameters.

12. The method of claim 11 , wherein the optical element is in an illumination system of the microlithographic projection exposure apparatus.

13. The method of claim 11 , wherein the channel surface faces away from the incidence surface.

14. The method of claim 11 , wherein estimating the temperature during b) comprises taking into account previously ascertained temporal changes in the values measured in a).

15. The method of claim 11 , further comprising using the temperature estimated in b) as an input signal to regulate a parameter that characterizes the optical element.

16. The method of claim 11 , further comprising using the temperature estimated in b) to control pre-heating of the optical element to at least partially compensate temporal changes in the heating state of the optical element occurring during use of the optical element.

17. The method of claim 11 , wherein the optical element is a mirror.

18. The method of claim 17 , wherein, during use of the optical element, the electromagnetic radiation that impinges on the incidence surface has an operating wavelength of less than 30 nm.

19. The method of claim 11 , wherein, during

Assignees

• Zeiss Carl Smt Gmbh

Inventors

• De Rapper Willem Michiel
• Gruner Toralf

Classifications

• G02B17/0647

  using more than three curved mirrors (G02B17/0668, G02B17/0694 take precedence) · CPC title

• G03F7/70891 Primary

  Temperature · CPC title

• G02B5/0891

  Ultraviolet [UV] mirrors (apparatus for microlithography exposure G03F7/70; X-ray multilayer structures G21K1/06) · CPC title

• G02B17/0663

  off-axis or unobscured systems in which not all of the mirrors share a common axis of rotational symmetry, e.g. at least one of the mirrors is warped, tilted or decentered with respect to the other elements · CPC title

• G02B7/1815

  with cooling or heating systems (cooling arrangements for laser mirrors H01S3/0401) · CPC title