Apparatus and a method for controlling the depth of etching during alternating plasma etching of semiconductor substrates

Abstract

The present invention provides apparatus for controlling the operation of plasma etching a semiconductor substrate by an alternating etching method, the apparatus comprising: a process chamber ( 1 ) in which said substrate ( 2 ) is processed, means for generating a plasma ( 6 ); at least one first window ( 7 ) formed in a first wall ( 8 ) of said chamber ( 1 ) facing the surface ( 2 a ) to be etched of said substrate ( 2 ); at least one second window ( 10 ) formed in a second wall ( 11 ) of said chamber ( 1 ) lying in a plane different from said first wall ( 8 ); first means ( 18 ) coupled to said second window ( 10 ) to detect a light signal ( 17 ) relating to a selected wavelength emitted by said plasma ( 6 ); means ( 13, 15 ) for emitting a monochromatic light signal ( 14 ) through said first window ( 7 ) towards said surface ( 2 a ) in a direction ( 9 ) substantially perpendicular to said surface ( 2 a ) in such a manner that said incident signal ( 14 a ) is reflected on said surface ( 2 a ); second means ( 16 ) for detecting said reflected signal ( 14 b ); and transformation means ( 19 ) coupled to said first means ( 18 ) and to said second means ( 16 ) to transform the signal detected by said second means ( 16 ) as a function of the signal detected by said first means ( 18 ).

1 . A plasma etching reactor for etching a substrate by an alternating etching process, which comprises an etching portion and a deposition portion, the reactor comprising:
 a process chamber;   a plasma source to form a plasma in the process chamber;   a first detector for receiving a reflected signal reflected from the substrate which is representative of the alternating etching process;   a second detector for detecting an etch signal indicative of the etching portion of the alternating etching process; and   a controller coupled to the first and second detectors, the controller receiving simultaneously the reflected signal and the etch signal and using the etch signal to transform the reflected signal as a function of the etch signal.   
     
     
         2 . A reactor as in  claim 1  further comprising a light source for emitting a light signal towards the substrate surface in a direction substantially perpendicular to the surface, wherein the light signal is reflected from the substrate surface to be detected by the first detector. 
     
     
         3 . A reactor as in  claim 1 , wherein the second detector detects at least one of a light signal relating to a selected wavelength emitted by the plasma, and a signal associated with the presence in the plasma of a species stemming from the reaction of an etching gas with said substrate. 
     
     
         4 . A reactor as in  claim 1 , wherein the controller transforms the reflected signal, which is representative of the alternating etching process, in order to obtain a curve representative of etching steps alone. 
     
     
         5 . A reactor as in  claim 1 , wherein the transformed reflected signal provides information regarding at least one of an etch rate and an end of the alternating etching process. 
     
     
         6 . A plasma etching reactor for etching a substrate by an alternating etching process, which comprises an etching portion and a deposition portion, the reactor comprising:
 a process chamber;   a plasma source to form a plasma in the process chamber;   a monochromatic laser for sending a photon beam to the substrate in such a manner that the photon beam is reflected on the substrate surface;   a first detector for detecting the reflected signal which is representative of the alternating etching process;   a second detector for detecting an emission signal associated with the presence in the plasma of a species stemming from the reaction of an etching gas with the substrate; and   a controller coupled to the first and second detectors, the controller receiving simultaneously the reflected signal and the emission signal and using the emission signal to extract from the reflected signal a signal representative of the etching portion within the alternating etching process.   
     
     
         7 . A reactor as in  claim 6 , wherein the second detector detects plasma species of the type SiF x  or CF x . 
     
     
         8 . A reactor as in  claim 6 , wherein the controller extracting from said reflected signal those portions of the signal that correspond to the presence of said species in order to obtain a curve representative of etching steps alone. 
     
     
         9 . A reactor as in  claim 6 , wherein extracting a signal comprises retrieving a portion of the signal associated with the time that the second signal shows the etching process. 
     
     
         10 . A reactor as in  claim 6 , wherein the extracted signal provides information regarding at least one of an etch rate and an end of the etching process. 
     
     
         11 . A plasma etching reactor for etching a substrate by an alternating etching process, which comprises an etching portion using an etching gas and a deposition portion, the reactor comprising:
 a process chamber;   a plasma source to form a plasma in the process chamber;   an interferometer for sending and receiving an interferometer signal reflected from the substrate which is representative of the alternating etching process;   an emission spectrometer for receiving an emission signal associated with the presence in the plasma of a species stemming from the reaction of the etching gas with the substrate; and   a controller coupled to the interferometer and the emission spectrometer, the controller receiving simultaneously the interferometer signal and the emission signal and using the emission signal to extract from the interferometer signal a signal representative of the etching portion within the alternating etching process,   wherein extracting a signal comprises retrieving a portion of the interferometer signal associated with the time that the interferometer signal shows the etching process.   
     
     
         12 . A reactor as in  claim 11  wherein the process chamber comprises a first window formed in a first wall of the chamber facing the substrate surface to be etched, and wherein the interferometer is coupled to the first window to send and receive the interferometer signal. 
     
     
         13 . A reactor as in  claim 12  wherein the process chamber comprises a second window formed in a second wall of the chamber lying in a plane different from the first wall, and wherein the emission spectrometer is coupled to the second window to detect the emission signal. 
     
     
         14 . A reactor as in  claim 13  wherein the plane of the second window is substantially perpendicular to the plane of the first window. 
     
     
         15 . A reactor as in  claim 11  wherein the interferometer comprises at least one of a monochromatic laser, a helium-neon laser, a laser diode, and a semireflecting mirror. 
     
     
         16 . A reactor as in  claim 11  wherein the emission spectrometer detects at least one of a light signal relating to a selected wavelength emitted by the plasma, and a signal associated with the presence in the plasma of a species stemming from the reaction of the etching gas with the substrate. 
     
     
         17 . A reactor as in  claim 11  wherein the emission spectrometer detects plasma species of the type SiF x  or CF x . 
     
     
         18 . A reactor as in  claim 11  further comprising
 an etching gas source, and means for controlling the etching flow rate to govern the introduction of etching gas into the plasma source; 
 a passivation gas source, and means for controlling the passivation flow rate for governing the introduction of passivation gas into the plasma source; and 
 a control device adapted to cause the etching gas flow rate control means and the passivation gas flow rate control means to operate in alternation. 
 
     
     
         19 . A reactor as in  claim 11  wherein the controller extracting from the reflected signal those portions of the emission signal in order to obtain a curve representative of etching steps alone. 
     
     
         20 . A reactor as in  claim 11  wherein the extracted signal provides information regarding at least one of an etch rate and an end of the etching process.