Gas Gauge Compatible With Vacuum Environments

• US 20100309445A1
• Filed: 02/17/2009
• Published: 12/09/2010
• Est. Priority Date: 02/20/2008
• Status: Active Grant

• Current Assignee: ASML Holding NV
• Original Assignee: ASML Holding NV
• Inventors: Schultz, Geoffrey Alan
• Granted Patent: US 8,675,168 B2
• Time in Patent Office: Days
• US Class Current: 355/30
• CPC Class Codes: G01B 13/12 for measuring distance or clearance between spaced objects or spaced apertures G01B13/18 takes precedence
• CPC Class Codes: G01L 13/02 using elastically-deformable members or pistons as sensing elements
• CPC Class Codes: G03F 9/7026 Focusing
• CPC Class Codes: G03F 9/7034 Leveling
• CPC Class Codes: G03F 9/7053 Non-optical, e.g. mechanical, capacitive, using an electron beam, acoustic or thermal waves
• CPC Class Codes: G03F 9/7096 Arrangement, mounting, housing, environment, cleaning or maintenance of apparatus

Abstract

A gas gauge (100) is provided for use in a vacuum environment having a measurement gas flow channel (105). The gas gauge comprises a measurement nozzle (110) in the measurement gas flow channel (105). The measurement nozzle (110) is configured to operate at a sonically choked flow condition of a volumetric flow being sourced from a gas supply (120) coupled to the measurement gas flow channel (105). The gas gauge (100) further comprises a pressure sensor (127) operatively coupled to the measurement gas flow channel (105) downstream from the sonically choked flow condition of the volumetric flow to measure a differential pressure of the volumetric flow for providing an indication of a gap (130) between a distal end of the measurement nozzle (135) and a target surface (140) proximal thereto.

Claims

1-20. -20. (canceled)

21. A gas gauge comprising:

a measurement nozzle in a measurement gas flow channel, the measurement nozzle configured to operate at a sonically choked flow condition of a volumetric flow being sourced from a gas supply coupled to the measurement gas flow channel; and

a pressure sensor operatively coupled to the measurement gas flow channel downstream from the sonically choked flow condition of the volumetric flow to measure a differential pressure of the volumetric flow for providing an indication of a gap between a distal end of the measurement nozzle and a target surface proximal thereto.

22. The gas gauge of claim 21, further comprising:

a secondary gas flow channel comprising a secondary nozzle, the secondary nozzle operatively coupled to the pressure sensor to enable the pressure sensor to measure the differential pressure of the volumetric flow between a first pressure level of the measurement nozzle and a second pressure level of the secondary nozzle.

23. The gas gauge of claim 22, wherein the secondary nozzle is configured to perform at least one of:

limiting a range of measurement for the differential pressure that the pressure sensor to obtain, and

counteracting a variation in a constant mass flow to the measurement nozzle from the gas supply.

24. The gas gauge of claim 22, wherein the secondary gas flow channel of the gas gauge further comprises:

a second restrictor located upstream of the pressure sensor configured to depress pressure at an inlet of the secondary gas flow channel for gas flowing at a substantially constant flow rate from the gas supply, the inlet of the secondary gas flow channel being configured to receive the gas from the gas supply.

25. The gas gauge of claim 24, wherein the gas gauge is configured to operate in a vacuum environment, and is choked with a desired flow of the gas at the distal end of the measurement nozzle such that the gas supply provides a constant flow of air or Nitrogen, the secondary nozzle being configured to vent gas in the vacuum environment from the gas supply.

26. The gas gauge of claim 21, wherein a measure of an offset distance in the gap is produced based on a signal of the differential pressure from the pressure sensor and used to determine a focus position by mapping topography of a wafer.

27. The gas gauge of claim 21, wherein the measurement gas flow channel of the gas gauge further comprises:

a first restrictor located upstream of the pressure sensor and configured to depress pressure at an inlet of the measurement gas flow channel while allowing the measurement nozzle to reach the sonically choked flow condition for gas flowing at a substantially constant flow rate from the gas supply, the inlet of the measurement gas flow channel being configured to receive the gas from the gas supply.

28. The gas gauge of claim 21, wherein the gas supply and the first restrictor are configured to maintain a ratio between gas pressure directly upstream of an exit of the measurement nozzle and directly downstream of the exit of the measurement nozzle in an annulus area substantially equal to or greater than a threshold value corresponding to a maximum expected gas pressure directly downstream of the exit of the measurement nozzle.

29. The gas gauge of claim 21, wherein:

the target surface is a wafer; and

the measurement nozzle and the pressure sensor are configured to determine a best plane for an exposure step in a wafer processing by a lithography apparatus.

30. The gas gauge of claim 21, further comprising:

a sealed housing configured to enclose the measurement gas flow channel and the pressure sensor and to provide a contamination barrier in a vacuum environment.

31. A lithography apparatus, comprising:

a gas supply;

a gas gauge configured to be uses in a vacuum environment, the gas gauge comprising,

a measurement nozzle configured to operate at a sonically choked flow condition of a constant volumetric flow being supplied by the gas supply, and

a pressure sensor operatively coupled to the measurement nozzle downstream from the sonically choked flow condition of the volumetric flow and configured to measure a differential pressure of the volumetric flow to provide an indication of a gap between a distal end of the measurement nozzle and a substrate proximal thereto; and

an exposure station configured to expose the substrate to a beam of radiation comprising a pattern in its cross section.

32. The lithography apparatus of claim 31, further comprising:

a measurement station configured to measure one or more aspects of the substrate by using the gas gauge prior to exposing the substrate.

33. The lithography apparatus of claim 31, wherein the measurement nozzle and the substrate are positioned such that the gas vented from the measurement nozzle impinges on the substrate.

34. The lithography apparatus of claim 31, further comprising:

a substrate stage compartment configured to comprise a substrate stage configured to support the substrate during illumination of the substrate with a beam with a patterned cross section.

35. The lithography apparatus of claim 31, further comprising:

a lithography leveling system including the gas gauge.

36. The lithography apparatus of claim 31, further comprising:

a lithography topography mapping device that includes the gas gauge.

37. The lithography apparatus of claim 31, further comprising:

a proximity sensor for lithography that includes the gas gauge.

38. A method comprising:

using, in a vacuum environment, a gas gauge having a measurement nozzle configured to operate at a sonically choked flow condition of a constant volumetric flow being supplied by a gas supply,

measuring, using a pressure sensor, a differential pressure of the volumetric flow the pressure sensor included in the gas gauge, the pressure sensor being coupled to the measurement nozzle downstream from the sonically choked flow condition of the volumetric flow; and

producing, using the pressure sensor, an indication of a gap between a distal end of the measurement nozzle and a substrate proximal thereto determining, based on the gap, a focus position to set focus in a photolithographic exposure tool by mapping topography of a substrate in a vacuum environment.

39. The method of claim 38, further comprising:

impinging gas vented from the measurement nozzle on the substrate.

40. The method of claim 38, further comprising:

measuring one or more aspects of the substrate by using the gas gauge prior to exposing the substrate.