Method and apparatus for purifying target material for euv light source

Patent metadata

Field	Value
Publication number	US-2020015343-A1
Application number	US-201916572131-A
Country	US
Kind code	A1
Filing date	Sep 16, 2019
Priority date	Feb 29, 2016
Publication date	Jan 9, 2020
Grant date	—

Abstract

A deoxidation system for purifying target material for an EUV light source includes a furnace having a central region and a heater for heating the central region in a uniform manner. A vessel is inserted in the central region of the furnace, and a crucible is disposed within the vessel. A closure device covers an open end of the vessel to form a seal having vacuum and pressure capability. The system also includes a gas input tube, a gas exhaust tube, and a vacuum port. A gas supply network is coupled in flow communication with an end of the gas input tube and a gas supply network is coupled in flow communication with an end of the gas exhaust tube. A vacuum network is coupled in flow communication with one end of the vacuum port. A method and apparatus for purifying target material also are described.

First claim

What is claimed is:

1 - 9 . (canceled)

10 . A method, comprising:
loading a target material into a crucible, the target material to be used in a droplet generator of an extreme ultraviolet (EUV) light source; inserting the loaded crucible into a vessel and sealing the vessel; melting the target material in the loaded crucible; flowing a gas containing hydrogen over a free surface of the molten target material; allowing gas to exit the vessel while measuring a concentration of water vapor in the gas exiting the vessel; and after the measured concentration of water vapor in the gas exiting the vessel reaches a target condition, allowing the molten target material to cool.

11 . The method of claim 10 , wherein the target condition comprises the measured water vapor concentration in the gas exiting the vessel stabilizing at a minimum level

12 . The method of claim 10 , wherein the target condition indicates a predetermined concentration of oxygen in the target material.

13 . The method of claim 10 , wherein the target condition indicates a predetermined concentration of oxygen in the target material that is less than 100 times the solubility limit of oxygen in the molten target material.

14 . The method of claim 10 , wherein the target condition indicates a predetermined concentration of oxygen in the target material that is less than 10 times the solubility limit of oxygen in the molten target material.

15 . The method of claim 10 , wherein target material is high purity tin.

16 . The method of claim 10 , wherein the gas containing hydrogen is a gas mixture comprising up to 2.93 molar % of hydrogen and the balance substantially argon.

17 . The method of claim 10 , wherein the operation of melting the target material in the crucible includes:
generating a vacuum within the vessel; once an effective vacuum condition is obtained within the vessel, heating the vessel to about 500 degrees C.; and maintaining the vessel at about 500 degrees C. until the target material melts.

18 . The method of claim 10 , wherein the operation of flowing a gas containing hydrogen over a free surface of the molten target material includes:
orienting the crucible at an angle relative to a horizontal plane to increase a free surface area of the molten target material; and increasing the temperature within the vessel from about 500 degrees C. to about 750 degrees C. as the gas containing hydrogen flows over the free surface of the molten target material.

19 . The method of claim 18 , wherein the crucible is oriented at an angle of about 12 degrees relative to the horizontal plane.

20 . The method of claim 10 , wherein the operation of allowing the target material to cool includes:
turning off heaters heating the vessel while maintaining flow of the gas containing hydrogen; allowing the vessel to cool from about 750 degrees C. down to about room temperature; and after the temperature cools down to about room temperature, stopping the flow of the gas containing hydrogen and depressurizing the vessel.

21 . The method of claim 20 , wherein the operation of allowing the vessel to cool includes allowing the vessel to cool without using forced cooling.

22 . The method of claim 20 , wherein the operation of allowing the vessel to cool includes using forced cooling to cool the vessel.

23 - 30 . (canceled)

31 . A method, comprising:
loading a quantity of target material into a crucible; inserting the crucible into a vessel; sealing the vessel with a closure device having a first gas passage adapted to introduce a first gas into the crucible and a second gas passage adapted to exhaust a second gas from the vessel; melting the quantity of target material in the crucible; introducing the first gas into the crucible through the first gas passage in such a way as to cause the first gas to flow over a free surface of the molten target material, the first gas containing hydrogen; measuring a concentration of water vapor in the second gas exiting the vessel through the second gas passage; and allowing the molten target material to cool after the measured concentration of water vapor in the second gas exiting the vessel satisfies a predetermined condition.

32 . The method of claim 31 , wherein the predetermined condition comprises stabilization of the measured water vapor concentration in the second gas exiting the vessel at a minimum level

33 . The method of claim 31 , wherein the predetermined condition indicates a predetermined concentration of oxygen in the target material.

34 . The method of claim 31 , wherein the target condition indicates a predetermined concentration of oxygen in the target material that is less than 10 times the solubility limit of oxygen in the molten target material.

35 . The method of claim 31 , wherein target material is tin having a purity level exceeding 99.99%.

36 . The method of claim 31 , wherein the first gas containing hydrogen is a gas mixture comprising up to 2.93 molar % of hydrogen and the balance substantially argon.

37 . The method of claim 31 , wherein the operation of flowing the first gas containing hydrogen over a free surface of the molten target material includes:
orienting the crucible at an angle relative to a horizontal plane to increase a free surface area of the molten target material; and increasing the temperature within the vessel from about 500 degrees C. to about 750 degrees C. as the gas containing hydrogen flows over the free surface of the molten target material.

Assignees

• Asml Netherlands Bv

Inventors

• Vaschenko Georgiy
• Baumgart Peter
• Rajyaguru Chirag
• Sams Benjamin
• Ridinger Armin
• Kardokus Janine

Classifications

• F27B17/00

  Furnaces of a kind not covered by any of groups F27B1/00 - F27B15/00 (structural combinations of furnaces F27B19/02) · CPC title

• C22B9/04

  Refining by applying a vacuum · CPC title

• C22B25/08

  Refining · CPC title

• F27B17/02 Primary

  specially designed for laboratory use · CPC title

• H05G2/008 Primary

  involving an energy-carrying beam in the process of plasma generation · CPC title