Dry etching method and apparatus

Abstract

An accurate dry etching technique is described that employs a flow of neutral radicals and a light beam. A dry etching apparatus 50 employs a neutral radical flow source 20 and a light beam 40 to irradiate a flow of neutral radicals 32 , so that the velocity component of the neutral radicals parallel to the surface of an object to be etched 12 is reduced, and etches anisotropically the object to be etched, while the object 12 is exposed to the radical flow 32 whose parallel velocity component is decreased. The invention reduces the problem of etching parallel to the substrate while etching perpendicular to the substrate to improve anisotropic dry etching without any adverse or damage producing effect to dielectric or semiconductor layers due to ions.

Having thus described our invention, what we claim as new and desire to secure by letters patent is:  
     
         1 . A method for dry etching comprising the steps of: 
 preparing an object to be etched;    preparing a flow of neutral radicals;    irradiating said flow of neutral radicals with a light beam so that their velocity component parallel to a surface of said object is reduced; and    exposing said flow of neutral radicals whose parallel velocity component is decreased to said object and etching said object.    
     
     
         2 . The dry etching method according to  claim 1 , wherein said step of reducing said parallel velocity component of said neutral radicals includes a step of exchanging kinetic momentum between the photons of said light beam and said neutral radicals (Doppler cooling effect) to reduce said velocity component of said neutral radicals parallel to said surface of said object to be etched.  
     
     
         3 . The dry etching method according to  claim 2 , wherein said step of preparing said object to be etched includes a step of mounting said object to be etched on a table provided in a vacuum container.  
     
     
         4 . The dry etching method according to  claim 3 , wherein said step of preparing said neutral radicals includes a step of emitting a neutral radical beam toward said object to be etched from a source of the neutral radical flow provided at a position opposite to an etching surface of said object to be etched mounted on said table.  
     
     
         5 . The dry etching method according to  claim 4 , wherein said step of irradiation with said light beam includes irradiation with a light beam traveling in a direction that is substantially perpendicular to a direction in which said radical beam is projected.  
     
     
         6 . The dry etching method according to  claim 4 , wherein said step of irradiation with said light beam includes irradiation with a light beam traveling along paths leading in at least two different directions that are substantially perpendicular to a direction in which said radical beam is projected.  
     
     
         7 . The dry etching method according to  claim 6 , wherein said two different directions diverge at an angle of 90 degrees.  
     
     
         8 . The dry etching method according to  claim 2 , wherein said light beam has a wavelength of “W+Δ, ” which is slightly greater than a wavelength of “W” that resonates when said neutral radicals have a predetermined transition level.  
     
     
         9 . The dry etching method according to  claim 1 , wherein said neutral radicals include radical fluorine atoms.  
     
     
         10 . The dry etching method according to  claim 1 , wherein said light beam is a laser beam.  
     
     
         11 . The dry etching method according to  claim 1 , wherein said object to be etched includes a semiconductor substrate.  
     
     
         12 . The dry etching method according to  claim 9 , wherein said laser beam has a light wavelength of 685.6+Δ [nm], when radical fluorine atoms are used.  
     
     
         13 . A dry etching apparatus comprising: 
 a vacuum container;    an object table provided in said vacuum container on which to mount thereon an object to be etched;    a radical flow source, located at a position opposite the surface of said object table on which said object to be etched is mounted, for emitting a flow of neutral radicals toward said object to be etched mounted on said object table; and    a light beam source, located between said object table and said radical flow source, for irradiating a light beam toward said flow of said neutral radicals emitted by said radical flow source, so that velocity component of said neutral radicals parallel to the surface of said object to be etched is negligible compared to the velocity component perpendicular to said surface.    
     
     
         14 . The dry etching apparatus according to  claim 13 , wherein a source of said radical flow is connected to said vacuum container so that a beam-shaped flow of neutral radicals is introduced to said vacuum container through an opening that is formed in said vacuum container.  
     
     
         15 . The dry etching apparatus according to  claim 14 , wherein said light beam source is connected to said vacuum container so that a light beam is introduced into said vacuum container through a transparent window that is formed in a side wall of said vacuum container.  
     
     
         16 . The dry etching apparatus according to  claim 15 , wherein said light beam source is so located that said light beam source emits a light beam traveling along a path in a direction that is substantially perpendicular to a direction in which said radical beam flow is projected.  
     
     
         17 . The dry etching apparatus according to  claim 15 , wherein said light beam source is so located that said light beam source emits a light beam traveling along paths leading in at least two different directions that are substantially perpendicular to a direction in which said radical beam flow is projected.  
     
     
         18 . The dry etching apparatus according to  claim 17 , wherein said two different directions are away from each other almost at 90 degrees.  
     
     
         19 . The dry etching apparatus according to  claim 15 , further comprising a mirror, provided inside or outside of a side wall of said vacuum container opposite to said side wall whereat said transparent window is formed, for reflecting a light beam from said light beam source to again irradiate said flow of radicals.  
     
     
         20 . The dry etching apparatus according to  claim 13 , wherein said velocity component of said radicals parallel to said surface of said object to be etched is reduced as a result of a kinetic momentum exchange between the photons of said irradiated light beam and said neutral radicals (Doppler cooling effect).  
     
     
         21 . The dry etching apparatus according to  claim 20 , wherein said light beam has a wavelength of “W+Δ, ” which is slightly greater than a wavelength of “W” that resonates when said neutral radicals have a predetermined transition level.  
     
     
         22 . The dry etching apparatus according to  claim 21 , wherein said neutral radicals include radical fluorine atoms or other halogen radicals.  
     
     
         23 . The dry etching apparatus according to one of  claims 13  to  22 , wherein said light beam source is a laser beam source.  
     
     
         24 . The dry etching apparatus according to  claim 22 , wherein said laser beam has an emission wavelength of 685.6+Δ [nm], when radical fluorine atoms are used.  
     
     
         25 . A dry etching method comprising the steps of: 
 preparing an object to be etched;    preparing a flow of neutral radicals;    irradiating said flow of neutral radicals with a light beam to impart a change in the velocity component of said neutral radicals parallel to the surface of said object to be etched; and    etching said object to be etched while said object to be etched is exposed to said flow of said neutral radicals whose parallel velocity component has been altered.    
     
     
         26 . A dry etching apparatus comprising: 
 a vacuum container;    an object table provided in said vacuum container to hold thereon an object to be etched;    a neutral radical flow source, located at a position opposite the surface of said object table on which said object to be etched is mounted, for emitting a flow of neutral radicals directed toward said object to be etched mounted on said object table; and    a light beam source, located between said object table and said neutral radicals flow source, for emitting a light beam to irradiate said flow of said neutral radicals emitted by said neutral radical flow source to impart a change in the velocity component of said neutral radicals parallel to the surface of said object to be etched.