Apparatus and method for in-situ chamber cleaning in a compound semiconductor etching system

Abstract

This invention consists of an apparatus and method of permitting automatic, in-situ cleaning of the process chamber and condensation trap of the vacuum pumping system used for etching Gallium Arsenide and other materials producing toxic and condensable etching by-products. This automated cleaning greatly reduces the danger of human exposure to the toxic materials and by-products of the etching. There are two key features. First, the process chamber and condensation trap are designed so that all components are vacuum-sealed to each other (or may be purged with inert gas) such that during wafer processing gas phase species from the process environment cannot condense in narrow spaces between components in the chamber. The surfaces of all parts that come in contact with, and may react to, enchant byproducts, process gases, or any cleaning liquid, are covered with nickel, or Teflon or other highly chemically inert coating. The second feature is that a liquid cleaning cold wall condensation trap is used to capture etching byproducts. The reactor and trap are cleaned separately or simultaneously by injecting water, with or without, liquid cleaner(s) into the process chamber through a set of injection holes. Said liquid cleaner may contain acidic, caustic or other reagents. The wet cleaning step dissolves or converts to soluble form any arsenic (or other toxic) compounds condensed in the process chamber or trap. In addition the flushing action of the liquids aids in the dislodging and removal of any insoluble or low soluble deposits. Liquid cleaning is typically followed with a heated air or nitrogen flow to evaporate any remaining liquid. Said cleaning process may have multiple steps. In a typical clean sequence the chamber and trap are flushed with water-based cleaning compounds that may be acidic or basic. This may be followed by a water-based rinse to rinse away all condensates or remnant compounds from the etching process. The next step may be a rinse with an alcohol or non-aqueous liquid with higher vapor pressure to scavenge or drive out remaining water. And finally, the system may be purged with a drying gas such as nitrogen to remove remnant traces of liquid. The result of such flushing is the virtually complete removal of traces of arsenic and its compounds from the system so as to greatly improve the safety of any ensuing manual chamber clean or replacement of parts. This cleaning process also maintains a more consistent process environment for process stability and reduces particulate that can affect yield.

1 . A plasma etching or deposition system comprising a process chamber, electrodes, vacuum lines with shutoff valves, a valve system to inject cleaning fluid(s) and a valve system to drain fluids from the chamber to be cleaned.  
   
   
       2 . A plasma etching or deposition system comprising a process chamber, electrodes, vacuum lines with shutoff valves making connection to a cold trap for condensation pumping, a valve system to inject cleaning fluid(s) and a valve system to drain fluids from cold traps and pumping lines to be cleaned.  
   
   
       3 . A system as in  claim 1  where an additional valve is used to allow liquids to be drained off by a valve open to the room, or catch pan, in order to prevent liquid from reaching the seals of a vacuum valve when the system is under vacuum in order to prevent virtual water or liquid leaks into the process chamber or vacuum system.  
   
   
       4 . A system as in  claim 2  where valves are used to allow liquids to be drained off by a valve open to the room, or catch pan, in order to prevent liquid from reaching the seals of a vacuum valve when the system is under vacuum in order to prevent virtual water or liquid leaks into the process chamber or vacuum system.  
   
   
       5 . A system as in  claim 1  where liquid(s) are used for cleaning that comprises a water shield to prevent liquids from entering small spaces that would be difficult to dry.  
   
   
       6 . A system as in  claim 2  where liquid(s) are used for cleaning that comprises a water shield to prevent liquids from entering small spaces that would be difficult to dry.  
   
   
       7 . A system as in  claim 1  where plumbing lines, chamber bottoms, and trap surfaces are all made to be non-horizontal to facilitate good drainage and prevent puddling.  
   
   
       8 . A system as in  claim 1  where plumbing lines, chamber bottoms, and trap surfaces are all made to be non-horizontal to facilitate good drainage and prevent puddling.  
   
   
       9 . A system as in  claim 1  where the liquid cleaner consists of water and water based chemicals followed by solvents such as alcohol that help remove water from the chamber.