Interferometric apparatus for measuring a physical value

• US 5,757,489 A
• Filed: 08/23/1996
• Issued: 05/26/1998
• Est. Priority Date: 08/24/1995
• Status: Expired due to Term

• Current Assignee: Nikon Corporation
• Original Assignee: Nikon Corporation
• Inventors: Kawakami, Jun
• Primary Examiner(s): Font, Frank G.
• Assistant Examiner(s): MERLINO, AMANDA H
• Application Number:
  US08/703,624
• Time in Patent Office: 641 Days
• Field of Search: 356/358, 356/349
• US Class Current: 356/500
• CPC Class Codes: G01B 2290/45 Multiple detectors for detecting interferometer signals
• CPC Class Codes: G01B 2290/70 Using polarization in the interferometer
• CPC Class Codes: G01B 9/02003 using beat frequencies
• CPC Class Codes: G01B 9/02062 Active error reduction, i.e. varying with time

Abstract

The displacement of the stage of an exposure apparatus can be measured by obtaining the phase difference between a light beam reflected by a stationary mirror and a light beam reflected by a movable mirror placed on the stage. This apparatus calculates the position data of the stage at second time by using the position data of the stage at first time which is measured by using first and second frequencies, the position data of the stage at the first time which is measured by using a third frequency, and the position data of the stage at the second time which is measured by using the third frequency.

Claims

1. An apparatus for measuring displacement of an object, comprising:

at least one light source disposed to emit light beams having frequencies f₁, f₂, f₃ and f₃ '"'"', the light beams having frequencies f₃ and f₃ '"'"' having a different polarization direction;

a polarization beam splitter disposed in a pathway of the light beams having frequencies f₁, f₂, f₃ and f₃ '"'"';

a moving mirror fixed on the object, the moving mirror being irradiated with the light beams having frequencies f₁, f₂, and f₃ ;

a fixed mirror disposed to be irradiated with the light beams having frequencies f₁, f₂ and f₃ '"'"';

a plurality of photoelectric conversion elements on which light beams reflected from the fixed and moving mirrors are incident; and

a processing device connected to the photoelectric conversion elements, the processing device configured to calculate a displacement of the object based on data received from the photoelectric conversion elements.

2. An apparatus according to claim 1, wherein a number corresponding to the plurality of photoelectric conversion elements is three,

wherein the first photoelectric conversion element is arranged to receive interference light from light beams reflected by the moving mirror and, when emitted by the light source having frequencies f₁ and f₂,

wherein the second photoelectric conversion element is arranged to receive interference light from light beams reflected by the fixed mirror and, when emitted by the light source having frequencies f₁ and f₂, and wherein the third photoelectric conversion element is arranged to receive interference light from light beams reflected by the moving and fixed mirrors and, when emitted by the light source having frequencies f₃ and f₃ '"'"'.

3. An apparatus according to claim 2, wherein the processing device calculates the displacement Δ

D(tn) by using values Δ

D(f₃,tn), A, and Δ

X(t_w), where,

Δ

D(f₃,tn) is a calculated displacement determined by using the data output from the third photoelectric conversion element,

A is a constant, and Δ

X(t_w) is a displacement difference calculated by using the data output from the first and second photoelectric conversion elements.

4. An apparatus according to claim 3, wherein the processing device calculates the displacement Δ

D(tn) by using the following equation;

space="preserve" listing-type="equation">Δ

D(tn)=Δ

D(f.sub.3,tn)-Δ

X(t.sub.w).

5. An apparatus according to claim 3 wherein the processing device calculates the displacement Δ

D(tn) by using values Δ

D(f₃,tn), A, Δ

X(t_w), and Δ

M(t_w,)

where,

Δ

M(t_w) is determined by averaging a plurality of values of Δ

D(f₃,tn) multiplied by predetermined weighting functions.

6. An apparatus according to claim 5, wherein the processing device calculates the displacement Δ

D(tn) by using the following equation;

space="preserve" listing-type="equation">Δ

D(tn) Δ

D(f.sub.3,tn)-(1-A ·

Δ

X(t.sub.w)/Δ

M(t.sub.w)).

7. An apparatus for measuring displacement of an object according to claim 1, wherein the fixed mirror is configured as a corner cube prism, and

wherein the moving mirror is also configured as a corner cube prism.

8. An apparatus for measuring displacement of an object, comprising:

at least one light source disposed to emit light beams having frequencies f₁, f₂ and f₂ '"'"', the light beams having frequencies f₂ and f₂ '"'"' having a different polarization direction;

a polarization beam splitter disposed in a pathway of the light beams having frequencies f₁, f₂ and f₂ '"'"';

a moving mirror fixed on the object, the moving mirror being irradiated with the light beams having frequencies f₁ and f₂ ;

a fixed mirror disposed to be irradiated with the light beams having frequencies f₂ '"'"';

a plurality of photoelectric conversion elements on which light beams reflected from the fixed and moving mirrors are incident; and

a processing device connected to the photoelectric conversion elements, the processing device configured to calculate a displacement of the object based on data received from the photoelectric conversion elements,

wherein a number corresponding to the plurality of photoelectric conversion elements is three,

wherein the first photoelectric conversion element is arranged to receive interference light from light beams reflected by the moving mirror and, when emitted by the light source having frequencies f₁, and f₂,

wherein the second photoelectric conversion element is arranged to receive interference light from light beams reflected by the fixed mirror and, when emitted by the light source having frequencies f₁, and f₂, and

wherein the first photoelectric conversion element is arranged to receive interference light from light beams reflected by the moving and fixed mirrors and, when emitted by the light source having frequencies f₂ and f₂ '"'"'.

9. An apparatus according to claim 8, wherein the processing device calculates the displacement Δ

D(tn) by using values Δ

D(f₂,tn), A, and Δ

X(t_w),

where,

Δ

D(f₂,tn) is a calculated displacement that is determined by using the data output from the third photoelectric conversion element,

A is a constant, and

Δ

X(t_w) is a displacement difference calculated by using the data output from the first and second, photoelectric conversion elements.

10. An apparatus according to claim 9, wherein the processing device calculates the displacement Δ

D(tn) by using the following equation;

space="preserve" listing-type="equation">Δ

D(tn)=Δ

D(f.sub.2,tn)-A·

Δ

X(t.sub.w).

11. An apparatus according to claim 9, wherein the processing device calculates the displacement Δ

D(tn) by using-values Δ

D(f₂,tn), A, Δ

X(t_w), and Δ

M(t_w)

where,

Δ

M(t_w) is determined by averaging a plurality of values of Δ

D(f₂,tn) multiplied by predetermined weighting functions.

12. An apparatus according to claim 11, wherein the processing device calculates the displacement Δ

D(tn) by using the following equation;

space="preserve" listing-type="equation">Δ

D(tn)=D(f.sub.2,tn)-(1-A·

Δ

X(t.sub.w)/Δ

M(t.sub.w)).

13. An apparatus for measuring displacement of an object according to claim 8, wherein the fixed mirror is. configured as a corner cube prism, and

wherein the moving mirror is also configured as a corner cube prism.