Use of light emitting chemical reactions for control of semiconductor production processes

Abstract

A low-pressure processing vessel ( 3 ) used for the production of semiconductors is provided with a light-sensitive detector ( 1 ) at a distance from the reaction site, for example in the exhaust line ( 2 ). The detector ( 1 ) is used to detect light emitted by an intermediate which relaxes or recombines with the emission of light at a characteristic wavelength, the intermediate having a long lifetime such that the detector ( 1 ) can be positioned in a relatively remote location.

1 . A method of controlling a chemical process which takes place within a low-pressure enclosure, the method comprising conducting a chemical process which produces a species that emits photons of a known wavelength or wavelength distribution by a particular chemical recombination or relaxation process, the species having a lifetime characteristic which, at the pressure of said enclosure, enables it to be detected at a significant distance from the site of the primary reaction, the method further comprising detecting said photons at said distance while rejecting other photons, and using the rate at which said photons are detected to control the process.  
   
   
       2 . A method according to  claim 1 , in which said significant distance is greater than 5 cm.  
   
   
       3 . A method according to  claim 2 , in which said significant distance is of the order of 0.5 m or more.  
   
   
       4 . A method according to  claim 1 , in which the chemical process comprises the processing of silicon with fluorine radicals, the chemical relaxation process being the combination of the silicon difluoride radical with the fluorine radical to yield electronically excited silicon trifluoride radical which subsequently returns to the ground state with the emission of a photon most probably between 380 and 650 nm.  
   
   
       5 . The method of  claim 4 , in which the silicon process is dry etching of silicon/silicon dioxide.  
   
   
       6 . The method of  claim 4 , in which the silicon process is the clean-up of silicon/Silicon Dioxide or other silicon based material deposited on the walls of the enclosure during other processing.  
   
   
       7 . The method of  claim 6 , in which the clean-up process makes use of plasma enhanced chemical vapor etch, the plasma being produced within the enclosure.  
   
   
       8 . The method of  claim 7 , in which the plasma is produced from radicals created upstream of the enclosure.  
   
   
       9 . A method according to  claim 1 , in which the photon detection is carried out in an exhaust line from the enclosure, or in a vacuum pump to which the exhaust line is connected.  
   
   
       10 . Apparatus for use in conjunction with a low-pressure enclosure serving as a reaction chamber in which takes place a chemical process which is such as to produce a species which emits photons of a known wavelength or wavelength distribution by a particular chemical recombination or relaxation process, the species having a lifetime characteristic which, at the pressure of said enclosure, enables it to be detected at a significant distance from the site of the primary reaction, the apparatus comprising a photon detector arranged at a significant distance from the primary reaction site, and means for monitoring the rate of photon detection.  
   
   
       11 . Apparatus for chemical processing, comprising a low-pressure chamber and an exhaust line extending from the chamber to a vacuum pump; the chamber defining a location in which, in use, a chemical process takes place which is such as to produce a species that emits photons of a known wavelength or wavelength distribution by a particular chemical recombination or relaxation process, the species having a lifetime characteristic which, at the pressure of said enclosure, enables it to be detected at a significant distance from the site of the primary reaction; the apparatus further comprising a photon detector arranged at a significant distance from said location, and means for monitoring the rate of photon detection.  
   
   
       12 . Apparatus according to  claim 11 , in which the photon detector is situated in the exhaust line or in the vacuum pump to which the exhaust line is it connected.  
   
   
       13 . Apparatus according to  claim 11 , in which the photon detector is provided with a light baffle to eliminate off-axis light and/or a light trap opposed to the entrance to the detector.  
   
   
       14 . Apparatus according to  claim 13 , in which the light baffle includes a number of plates having apertures which are arranged aperiodically.  
   
   
       15 . Apparatus according to  claim 14 , in which the size of the apertures are arranged to increase from one plate to another such that the apertures of smallest size are in the plate adjacent the photon detector and the apertures of largest size are in the plate furthest from the photon detector.  
   
   
       16 . Apparatus according to  claim 15 , in which the sizes and arrangement of the apertures are such that an observer located at the photon detector can only see edges of the apertures in the plate adjacent to him whilst being unable to view any edges in the apertures in the plates which are not adjacent to him.  
   
   
       17 . Apparatus according to  claim 11 , in which the photon detector is spaced at least 5 cm from said location.  
   
   
       18 . Apparatus according to  claim 17 , in which the photon detector is spaced 0.5 m or more from said location.