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Method for protecting EUV source optical windows at room temperature from metal vapor deposition

IP.com Disclosure Number: IPCOM000132111D
Publication Date: 2005-Dec-01
Document File: 3 page(s) / 32K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for protecting extreme ultraviolet (EUV) source optical windows at room temperature from metal vapor deposition. Benefits include improved functionality and improved performance.

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Method for protecting EUV source optical windows at room temperature from metal vapor deposition

Disclosed is a method for protecting extreme ultraviolet (EUV) source optical windows at room temperature from metal vapor deposition. Benefits include improved functionality and improved performance.

Background

              Conventionally, xenon (Xe) is the leading element for the production of EUV photons. Its vapor quickly contaminates optical elements at the boundaries of the source chamber.

      No solution exists in the EUV community for preventing contamination. Theoretically, heating the windows to avoid condensation might work but would require high temperature compatibility for the window materials and may be impossible in practice.

General description

      The disclosed method protects EUV source optical windows at room temperature from metal vapor deposition. The optical window is located at the cooled end of a tube that has a strong temperature differential. Metal vapor, particularly lithium (Li) or tin (Sn) condenses on the cooled end but stays active in generating EUV photons on the heated end. The optical windows do not require heating to high temperature to stay clean.

      The key elements of the disclosed method include:

•             Active metal vapor is confined to the heated side of the tube.

•             Optical windows remain clean and cool without metal condensation.

•             The windows stay clean at room temperature.

•             Light source active metal material is conserved by the vapor condensation and flow-back process in the tube.

Advantages

              The disclosed method provides advantages, including:
•             Improved functionality due to enabling the usage of low temperature window materials

•             Improved functionality due to providing optical windows that remain transmissive at room temperatures
•             Improved performance due to approximately doubling the output of the source fuel by using Li or Sn

Detailed description

      The disclosed method includes a tube, which is essentially a heat pipe that is open at the hot end and closed with a window at the cold end. The tube has the following features (see Figure 1):

•             Tube made of a corrosion-resistant material, such as stainless steel

•             Coils at one end of the tube for heating

•             Heatsink or liquid-cooled condenser coils for removal of heat

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