Ultrasonic distance sensors

• US 7,391,676 B2
• Filed: 12/22/2004
• Issued: 06/24/2008
• Est. Priority Date: 12/22/2004
• Status: Expired due to Fees

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: Venema, Willem Jurrianus, Bruinsma, Anastasius Jacobus Anicetus
• Primary Examiner(s): Lobo; Ian J
• Application Number:
  US11/018,926
• Publication Number:
  US 20060133209A1
• Time in Patent Office: 1,280 Days
• Field of Search: 367/99, 367/908, 735/97, 736/27, 736/29, 736/43, 736/55, 736/57, 732/90.V
• US Class Current: 367/99
• CPC Class Codes: G01S 15/101 Particularities of the measurement of distance G01S15/12, G01S15/14, and G01S15/18 take precedence
• CPC Class Codes: G01S 15/88 Sonar systems specially adapted for specific applications seismic or acoustic prospecting or detecting G01V1/00
• CPC Class Codes: G01S 2007/52014 involving a reference reflector integrated in the sensor or transducer configuration
• CPC Class Codes: G01S 7/52004 Means for monitoring or calibrating short-range imaging G01S7/5205
• CPC Class Codes: G01S 7/52006 with provision for compensating the effects of temperature

Abstract

A lithographic apparatus comprises an illumination system, a support constructed to support a patterning device, and a projection system. In pixel grid imaging, a large number of small optical spots are imaged onto the substrate surface using a micro-lens array (MLA). The z position of the MLA is adjustable in order to focus the spots on the substrate surface and/or to compensate for differences in height of the substrate surface. The focusing adjustment is based on an output of an ultrasonic distance sensor provided in the vicinity of the substrate surface.

Claims

1. A lithographic apparatus comprising:

an illumination system that conditions a radiation beam;

a support that supports a patterning device, the patterning device pattering the beam;

a projection system that projects the patterned beam onto a target portion of a substrate; and

an ultrasonic distance sensor that monitors a height of a surface of the substrate, the sensor comprising,

an ultrasonic emitter system that emits a first transmitted beam towards the substrate surface and a second transmitted beam,

an ultrasonic receiver system that receives a first reflected beam produced by reflection of the first transmitted beam from the substrate surface and a second reflected beam produced by reflection of the second transmitted beam, and

a signal processor that processes signals received from the ultrasonic emitter system and the ultrasonic receiver system indicative of time differences between the emission and the receipt of the transmitted and reflected beams in order to monitor the height of the substrate surface.

2. The sensor of claim 1, wherein the ultrasonic emitter system comprises:

a first transducer that emits the first transmitted beam; and

a second transducer that emits the second transmitted beam.

3. The sensor of claim 2, wherein the ultrasonic receiver system comprises:

the first transducer that receives the first reflected beam; and

the second transducer that receives the second reflected beam.

4. The sensor of claim 2, wherein the first and second transducers are located, such that paths of the first and second transmitted beams are adjacent and substantially parallel to one another.

5. The sensor of claim 2, wherein the first and second transducers are located, such that paths of the first and second transmitted beams are mutually transverse to one another.

6. The sensor of claim 2, wherein:

the first and second transducers are located a known distance apart; and

the signal processor determines a distance of the substrate surface from the sensor from the relationship between, the time difference between emission of the first transmitted beam and receipt of the first reflected beam reflected from the substrate surface, the time difference between emission of the second transmitted beam and receipt of the second reflected beam reflected from the substrate surface, and the known distance apart of the first and second transducers.

7. The sensor of claim 6, wherein the signal processor comprises:

a calibration arrangement that determines a distance separating the first and second transducers by monitoring the time differences between the emission of the second transmitted beam and the receipt of the beam reflected from the substrate surface for two different height positions of the second transducer that are a known distance apart.

8. The sensor of claim 1, wherein the ultrasonic emitter system comprises:

a single transducer that emits both the first transmitted beam and the second transmitted beam.

9. The sensor of claim 8, wherein the ultrasonic receiver system comprises:

the single transducer that receives both the first reflected beam and the second reflected beam.

10. The sensor of claim 1, wherein:

a reference surface is located at a known distance from the sensor that reflects the second transmitted beam; and

the signal processor determines a distance of the substrate surface from the sensor from the relationship between, the time difference between emission of the first transmitted beam and receipt of the first reflected beam reflected from the substrate surface, the time difference between emission of the second transmitted beam and receipt of the second reflected beam reflected from the reference surface, and the known distance of the reference surface from the sensor.

11. The sensor of claim 1, wherein the ultrasonic emitter system emits the first and second transmitted beams in as ultrasonic pulses.

12. A method of monitoring a height of a substrate surface, comprising:

emitting a first ultrasonic transmitted beam towards the substrate surface;

emitting a second ultrasonic transmitted beam;

receiving a first reflected beam produced by reflection of the first transmitted beam from the substrate surface;

receiving a second reflected beam produced by reflection of the second transmitted beam; and

processing signals indicative of time differences between the emission and the receipt of the transmitted and reflected beams in order to monitor the height of the substrate surface.

13. The method of claim 12, further comprising:

emitting the first transmitted beam from a first transducer; and

emitting the second transmitted beam from a second transducer.

14. The method of claim 13, further comprising:

receiving the first reflected beam at the first transducer; and

receiving the second reflected beam at the second transducer.

15. The method of claim 13, further comprising:

positioning the first and second transducers a known distance apart; and

determining a distance of the substrate surface from the sensor a relationship between a time difference between emission of the first transmitted beam and receipt of the first reflected beam reflected from the substrate surface and a time difference between emission of the second transmitted beam and receipt of the second reflected beam reflected from the substrate surface and from the known distance apart of the first and second transducers.

16. The method of claim 15, further comprising:

a calibration step that determines the distance apart of the first and second transducers by monitoring the time differences between the emission of the second transmitted beam and the receipt of the second reflected beam reflected from the substrate surface for two different height positions of the second transducer that are a known distance apart.

17. The method of claim 12, wherein the paths of the first and second transmitted beams are adjacent and substantially parallel to one another.

18. The method of claim 12, wherein the paths of the first and second transmitted beams are mutually transverse to one another.

19. The method of claim 12, further comprising:

using a single transducer to emit both the first transmitted beam and the second transmitted beam.

20. The method of claim 19, further comprising:

receiving the first reflected beam and the second reflected beam using the single transducer.

21. The method of claim 12, further comprising:

positioning a reference surface at a known distance from the sensor to reflect the second transmitted beam; and

determining a distance of the substrate surface from the sensor from a relationship between a time difference between emission of the first transmitted beam and receipt of the first reflected beam reflected from the substrate surface and a time difference between emission of the second transmitted beam and receipt of the second reflected beam reflected from the reference surface and from the known distance of the reference surface from the sensor.