Method of controlling exposure

• US 5,965,308 A
• Filed: 03/29/1996
• Issued: 10/12/1999
• Est. Priority Date: 11/17/1995
• Status: Expired due to Fees

• Current Assignee: Nikon Corporation
• Original Assignee: Nikon Corporation
• Inventors: Ozawa, Ken
• Primary Examiner(s): Young, Christopher G.
• Application Number:
  US08/624,087
• Time in Patent Office: 1,292 Days
• Field of Search: 355/67, 355/68, 355/69, 355/71, 250/559.11, 250/492.23, 430/30
• US Class Current: 430/30
• CPC Class Codes: G03F 7/70058 Mask illumination systems
• CPC Class Codes: G03F 7/70558 Dose control, i.e. achievement of a desired dose

Abstract

The exposure quantity with respect to a wafer is correctly measured under each illumination condition even when illumination conditions are changed over. Under each of conditions where the σ value (coherence factor) of an illumination optical system is set to various values including its small, standard, and large values, a correlation data between the output (E) of a reference illuminance meter and the output (I) of an integrator sensor is obtained. With respect to the correlation data for the respective σ values, approximate lines (24A, 24B, 24C, etc) are determined by the method of least squares and then gradients of these lines are stored as correlation coefficients (α). Under the illumination condition corresponding to each σ value, the output (I) of the integrator sensor is divided by its corresponding correlation coefficient (α) so as to compute the exposure energy on the image surface.

Claims

1. A method of controlling exposure in which an object on a stage is exposed to light with a desired exposure quantity, said method comprising the steps of:

selecting an aperture size of an aperture stop which can vary said aperture size;

detecting a part of light passed through said aperture stop by a photodetector;

calibrating an output of said photodetector based on the aperture size of said aperture stop;

detecting a part of light on said stage by an illuminance meter; and

storing a correlation function between an output of said photodetector and an output of said illuminance meter corresponding to each aperture size of said aperture stop, wherein said correlation function is;

space="preserve" listing-type="equation">I=α

(I)E

wherein I is the output of said photodetector, α

(I) is a high-order function which corresponds to the aperture size and depends on the output I, and E is the output of said illuminance meter.

2. A method according to claim 1, further comprising the step of:

varying an extinction ratio of light based on the aperture size of said aperture stop.

3. A method according to claim 1, wherein said light contains pulse light in response to input of a trigger signal, said input of the trigger signal satisfies the following expression:

space="preserve" listing-type="equation">t≧

α

(I)P/I

wherein t is a number of trigger signals and P is said desired exposure quantity.

4. A method according to claim 1, further comprising the step of:

emitting a plurality of secondary light sources from said light.

5. A method of illuminating with exposure illumination light under which the pattern of a mask is transferred onto a photosensitive substrate, said method comprising:

receiving a luminous flux separated from said illumination light and outputting a signal of the luminous flux;

calculating an exposure quantity of said illumination light on said substrate based on said signal of the luminous flux; and

storing correlation values for computing the exposure quantity on said substrate from said signal, said correlation values corresponding to each of a plurality of illumination conditions in said exposure illumination light, wherein a correlation function is;

space="preserve" listing-type="equation">I=α

(I)E

wherein I is said signal of the luminous flux, α

(I) is a high-order function which corresponds to the illumination condition, and E is an exposure energy on said photosensitive substrate.

6. A method according to claim 5, wherein said plurality of illumination conditions include a plurality of aperture sizes of said aperture stop.

7. A method according to claim 5, wherein said illumination light contains pulse light in response to input of a trigger signal, said input of the trigger signal satisfies the following expression:

space="preserve" listing-type="equation">t≧

α

(I)P/I

wherein t is a number of trigger signals and P is a desired exposure quantity.

8. A method of illuminating with exposure illumination light under which the pattern of said mask is transferred onto a photosensitive substrate, said method comprising:

receiving a luminous flux separated from said illumination light and outputting a signal of the luminous flux;

calculating an exposure quantity of said illumination light on said substrate based on said signal of the luminous flux; and

storing correlation coefficients or correlation maps for computing the exposure quantity on said substrate from said signal, said correlation coefficients or correlation maps corresponding to each of a plurality of illumination conditions in said exposure illumination light, wherein a correlation function is;

space="preserve" listing-type="equation">I=α

(I)E

wherein I is said signal of the luminous flux, α

(I) is a high-order function which corresponds to the illumination condition, and E is an exposure energy on said photosensitive substrate.

9. A method according to claim 8, wherein said plurality of illumination conditions include a plurality of aperture sizes of said aperture stop.

10. A method according to claim 8, wherein said illumination light contains pulse light in response to input of a trigger signal, said input of the trigger signal satisfies the following expression:

space="preserve" listing-type="equation">t≧

α

(I)P/I

wherein t is a number of trigger signals and P is a desired exposure quantity.

11. An exposure method for exposing a substrate by illuminating a pattern of a mask with exposure light and projecting an image of said pattern onto said substrate via a projection optical system, said method comprising the steps of:

using a reference photodetector among a plurality of exposure apparatuses to detect energy of said exposure light on an image surface side of said projection optical system under a plurality of illumination conditions; and

determining exposure quantity control data corresponding to said plurality of illumination conditions respectively on the basis of a result of detection by said reference photodetector.

12. An exposure method according to claim 11, further comprising the step of detecting energy of a portion of said exposure light by a second detector other than said reference photodetector and closer to a light source than said reference photodetector, when said exposure light is detected by said reference photodetector, and

wherein said step of determining said exposure quantity control data comprises determining said exposure quantity control data on the basis of a result of detection by said second detector and the result of detection by said reference photodetector.

13. An exposure method according to claim 12, wherein said exposure quantity control data includes correlated data in relation to the result of detection by said second detector and the result of detection by said reference photodetector.

14. An exposure method according to claim 11, further comprising the steps of:

detecting energy of a portion of said exposure light by a second detector an optical path of said exposure light, and

controlling an integrated exposure quantity on said substrate on the basis of a result of detection by said second detector and said exposure quality control data.

15. An exposure method according to claim 14, wherein said step of controlling said integrated exposure quantity comprises the operations of monitoring an integrated value of said exposure light irradiating said substrate in an optical path of said exposure light and controlling the irradiation of said exposure light to said substrate on the basis of said integrated value and a preset exposure quantity to said substrate.

16. An exposure method according to claim 15, wherein said step of controlling said integrated exposure quantity comprises cutoff control of said exposure light.

17. An exposure method according to claim 11, wherein said exposure quantity control data is used to obtain interchangeability of exposure quantity to said substrate between said plurality of exposure apparatuses among which said reference photodetector is used.

18. An exposure method according to claim 11, wherein said reference photodetector is disposed detachably on a substrate stage for holding said substrate.

19. An exposure method according to claim 11, wherein said plurality of illumination conditions includes a difference in distribution state of said exposure light in a predetermined plane in an optical path of said exposure light.

20. An exposure method according to claim 19, wherein the difference in distribution state of said exposure light in said predetermined plane includes a large difference of a stop in said predetermined plane.

21. An exposure method according to claim 11, wherein said exposure light is pulse light, and further comprising the step of controlling emission of said pulse light on the basis of said exposure quantity control data.

22. An exposure method for exposing a substrate by illuminating a pattern of a mask with exposure light and projecting an image of said pattern onto said substrate via a projection optical system, said method comprising the steps of:

obtaining first exposure quantity control data by using a reference illuminance meter to detect energy of said exposure light on an image surface side of said projection optical system under a first illumination condition;

obtaining a first signal outputted from a photodetector disposed on a stage for holding said substrate when energy of said exposure light is detected by said photodetector under the first illumination condition;

obtaining a second signal outputted from said photodetector when the energy of said exposure light is detected by said photodetector under a second illumination condition differing from the first illumination condition; and

obtaining second exposure quantity control data under the second illumination condition on the basis of said first exposure quantity control data, said first signal and said second signal.

23. An exposure method according to claim 22, further comprising the step of:

detecting energy of a portion of said exposure light under said first and said second illumination conditions by a second detector other than said reference illuminance meter and said photodetector, said second detector being disposed closer to a light source that provides said exposure light than said reference illuminance meter and said photodetector, and wherein

said first exposure quantity control data includes correlated data in relation to a result of detection by said second detector and the result of detection by said reference illuminance meter, and

said second exposure quantity control data includes correlated data in relation to the result of detection by said second detector and the energy of said exposure light on said substrate.

24. An exposure method according to claim 23, wherein said second exposure quantity control data is obtained on the basis of said first exposure quantity control data, the ratio of the result of detection by said second detector under the first illumination condition to said first signal, and the ratio of the result of detection by said second detector under the second illumination condition to said second signal.

25. An exposure method according to claim 22, further comprising the steps of:

controlling an integrated exposure quantity to said substrate under the first illumination condition on the basis of said first exposure quantity control data; and

controlling an integrated exposure quantity to said substrate under the second illumination condition on the basis of said second exposure quantity control data.

26. An exposure method according to claim 22, wherein said photodetector detects energy of a portion of exposure light irradiating said stage.

27. An exposure method according to claim 22, wherein said photodetector detects said exposure light via a pinhole.

28. An exposure method according to claim 27, wherein said reference illuminance meter is disposed detachably on said stage.

29. An exposure method according to claim 28, wherein said reference illuminance meter is used among a plurality of exposure apparatuses and obtains interchangeability of exposure quantity to said substrate between said plurality of exposure apparatuses on the basis of said first exposure quantity control data and said second exposure quantity control data.

30. An exposure method according to claim 22, wherein exposure light is pulse light, and further comprising a step of controlling the emission of said pulse light on the basis of said first exposure quantity control data and said second exposure quantity control data.