Methods and apparatus for photomask processing

Abstract

Methods and apparatus leverage dielectric barrier discharge (DBD) plasma to treat samples for surface modification prior to photomask application and for photomask cleaning. In some embodiments, a method of treating a surface with AP plasma includes igniting plasma over an ignition plate where the AP plasma is formed by one or more plasma heads of an AP plasma reactor positioned above the ignition plate, monitoring characteristics of the AP plasma with an optical emission spectrometer (OES) sensor to determine if stable AP plasma is obtained and, if so, moving the AP reactor over a central opening of an assistant plate where the central opening contains a sample under treatment and where the assistant plate reduces AP plasma arcing on the sample during treatment. The AP reactor scans back and forth over the central opening of the assistant plate while maintaining stabilized AP plasma to treat the sample.

1 . An apparatus for treating a surface with plasma, comprising:
 a pedestal with a sample support area that is configured to retain a sample for plasma treatment;   an assistant plate surrounding the sample support area with a central opening configured to contain the sample;   an ignition plate adjacent to the assistant plate, the ignition plate has a solid upper surface that is configured to interact with the plasma during plasma ignition; and   a plasma reactor configured to produce the plasma and positioned above the pedestal, the plasma reactor has one or more plasma heads extending wider than the central opening of the assistant plate and is positionable over the ignition plate and the assistant plate.   
     
     
         2 . The apparatus of  claim 1 , wherein the plasma is atmospheric pressure (AP) plasma. 
     
     
         3 . The apparatus of  claim 1 , further comprising:
 an optical emission spectrometer (OES) sensor configured to monitor characteristics of the plasma.   
     
     
         4 . The apparatus of  claim 1 , further comprising:
 a controller configured to (a) ignite the plasma over the ignition plate, wherein the plasma formed by the one or more plasma heads of the plasma reactor is positioned above the ignition plate and (b) move the plasma reactor over the central opening of the assistant plate while maintaining the plasma.   
     
     
         5 . The apparatus of  claim 4 , wherein the controller is configured to monitor the plasma during treatment of the sample to determine an endpoint of the treatment based on an oxygen peak level. 
     
     
         6 . The apparatus of  claim 4 , wherein the controller is configured to scan the plasma reactor back and forth over the central opening of the assistant plate. 
     
     
         7 . The apparatus of  claim 1 , further comprising:
 a plurality of gas nozzles configured to flow one or more gases around the one or more plasma heads.   
     
     
         8 . The apparatus of  claim 1 , wherein the one or more plasma heads is positioned approximately 1 mm to approximately 2 mm above the ignition plate and above uppermost surfaces of the assistant plate. 
     
     
         9 . The apparatus of  claim 1 , wherein at least one of a plurality of plasma heads is configured to extend over at least one end of the assistant plate during plasma treatment. 
     
     
         10 . The apparatus of  claim 1 , wherein the one or more plasma heads has a central RF electrode surrounded by dielectric material with one ground electrode on each side of the central RF electrode. 
     
     
         11 . The apparatus of  claim 1 , wherein the sample is a photomask, and the apparatus is configured to modify a surface of the photomask, to remove a photoresist layer on top of the photomask, or to remove organic defects. 
     
     
         12 . A method of treating a surface with plasma, comprising:
 igniting the plasma over an ignition plate, the plasma formed by one or more plasma heads of a plasma reactor positioned above the ignition plate; and   moving the plasma reactor over a central opening of an assistant plate while maintaining the plasma, wherein the one or more plasma heads of the plasma reactor is wider than the central opening in the assistant plate.   
     
     
         13 . The method of  claim 12 , further comprising:
 monitoring the plasma to determine an endpoint of a treatment of the surface disposed in the central opening based on an oxygen peak level.   
     
     
         14 . The method of  claim 12 , further comprising:
 scanning back and forth over the central opening of the assistant plate with at least one of a plurality of plasma heads extending over the assistant plate at each end of a single scan to obtain identical plasma residence time on the surface disposed in the central opening.   
     
     
         15 . The method of  claim 12 , wherein a sample disposed in the central opening is a photomask. 
     
     
         16 . The method of  claim 15 , further comprising:
 modifying a surface of the photomask;   removing a photoresist layer on top of the photomask; or   removing organic defects.   
     
     
         17 . The method of  claim 12 , further comprising:
 flowing a gas mixture of argon gas and oxygen-based gas around an RF electrode of one or more plasma heads.   
     
     
         18 . The method of  claim 17 , further comprising:
 flowing water vapor with the gas mixture to produce hydroxyl.   
     
     
         19 . The method of  claim 12 , further comprising:
 flowing a gas mixture of argon gas and hydrogen-based forming gas around an RF electrode of one or more plasma heads.   
     
     
         20 . A non-transitory, computer readable medium having instructions stored thereon that, when executed, cause a method of treating a surface with plasma to be performed, the method comprising:
 igniting the plasma over an ignition plate, the plasma formed by one or more plasma heads of a plasma reactor positioned above the ignition plate; and   moving the plasma reactor over a central opening of an assistant plate while maintaining the plasma, wherein the one or more plasma heads of the plasma reactor is wider than the central opening in the assistant plate.