Apparatus and method for detecting an endpoint in a vapor phase etch

Abstract

Processes for the removal of a layer or region from a workpiece material by contact with a process gas in the manufacture of a microstructure are enhanced by the ability to accurately determine the endpoint of the removal step. A vapor phase etchant is used to remove a material that has been deposited on a substrate, with or without other deposited structure thereon. By creating an impedance at the exit of an etching chamber (or downstream thereof), as the vapor phase etchant passes from the etching chamber, a gaseous product of the etching reaction is monitored; and the endpoint of the removal process can be determined. The vapor phase etching process can be flow through, a combination of flow through and pulse, or recirculated back to the etching chamber

1 - 100 . (canceled)  
   
   
       101 . An apparatus for etching a sample, said apparatus comprising: 
 (a) a source of etchant gas;    (b) an etching chamber in communication with said source of etchant gas;    (c) a recirculation loop passing through said etching chamber;    (d) a pump disposed within said recirculation loop for recirculating etchant gas along said recirculation loop; and    (e) a gas analyzer for analyzing gas components within the recirculation loop.    
   
   
       102 . The apparatus in accordance with  claim 101  which said source of etchant gas comprises a source chamber.  
   
   
       103 . The apparatus in accordance with  claim 102  further comprising an expansion chamber communicating with said source chamber and with a gas source for a gas other than said etchant gas, said expansion chamber arranged for mixing gas from said source chamber with gas from said gas source.  
   
   
       104 . The apparatus in accordance with  claim 103  which said expansion chamber is in communication with said recirculation loop.  
   
   
       105 . The apparatus in accordance with  claim 101  further comprising a filter disposed within said recirculation loop, said filter being one that removes a member selected from the group consisting of byproducts or effluent from gases flowing through said recirculation loop, or particulates.  
   
   
       106 . The apparatus in accordance with  claim 101  in which said pump is a dry pump.  
   
   
       107 . The apparatus in accordance with  claim 106  in which said dry pump has no wet seals and adds no gas to said recirculation loop.  
   
   
       108 . The apparatus in accordance with  claim 107  in which said dry pump is a bellows pump.  
   
   
       109 . The apparatus in accordance with  claim 108  in which said bellows pump comprises a housing with bellows-type wall sections enclosing a hollow interior, and at least one partition disposed to divide said hollow interior into a plurality of sections.  
   
   
       110 . The apparatus in accordance with  claim 101  in which said pump is constructed to circulate etchant gas substantially continuously within said recirculation loop.  
   
   
       111 . The apparatus in accordance with  claim 103  in which said pump is defined as a first pump and said apparatus further comprises a second pump arranged to draw gases from a member selected from the group consisting of said expansion chamber, said source chamber, and said recirculation loop.  
   
   
       112 . The apparatus in accordance with  claim 103  further comprising gas flow spreading means in said source chamber for diverting incoming gas.  
   
   
       113 . The apparatus in accordance with  claim 112  in which said gas flow spreading means is a baffle.  
   
   
       114 . The apparatus in accordance with  claim 112  in which said gas flow spreading means is a perforated plate.  
   
   
       115 . The apparatus in accordance with  claim 101 , further comprising an energy source and/or electric field source at the etching chamber for forming a plasma therein.  
   
   
       116 . The apparatus in accordance with  claim 102  in which said source of etchant gas further comprises fluoride crystals retained within said source chamber.  
   
   
       117 . The apparatus in accordance with  claim 116  in which said fluoride crystals are xenon difluoride crystals.  
   
   
       118 . The apparatus in accordance with  claim 103  in which said gas source for a gas other than said etchant gas comprises a source of a gas with molar averaged molecular weight less than or equal to that of N2.  
   
   
       119 . The apparatus in accordance with  claim 118  in which said gas other than said etchant gas is a member selected from the group consisting of Ar, Ne, He and N2.  
   
   
       120 . The apparatus in accordance with  claim 103  in which said gas source for a gas other than said etchant gas comprises a plurality of gas sources, the gases from which, when mixed, yield a gaseous mixture with molar averaged molecular weight less than or equal to that of N2.  
   
   
       121 . The apparatus in accordance with  claim 120  in which said plurality of gas sources are sources of two or more members selected from the group consisting of Ar, Ne, He and N2.  
   
   
       122 . A method, comprising: 
 a) providing a sample to be etched in a chamber;    b) providing an etchant to the chamber, capable of etching the sample;    c) providing no or substantially no impedance to gas exiting the etching chamber;    d) monitoring a partial pressure of an etch product; and    e) repeating steps a) to d) except providing an increased impedance each time steps a) to d) are repeated, until an impedance is reached that allows for determining an endpoint based on monitoring the partial pressure of the etch product.    
   
   
       123 . The method of  claim 122 , wherein an impedance is reached that results in a partial pressure that begins to decrease at or near a time that the endpoint of the etch is reached.  
   
   
       124 . The method of  claim 122 , wherein an endpoint of the etch corresponds to a point where all of the material has been removed.  
   
   
       125 . The method of  claim 122 , wherein the material is silicon.  
   
   
       126 . An apparatus comprising: 
 an etching chamber;    a source of an etchant;    a gas recirculation loop for recirculating the etchant repeatedly through the etching chamber; and    a gas analyzer within the etching chamber or within the gas flow line downstream of the etching chamber.    
   
   
       127 . The apparatus of  claim 126 , wherein the gas analyzer is a spectrometer.  
   
   
       128 . The apparatus of  claim 127 , wherein the spectrometer is capable of detecting levels of fluoride etchants or fluoride etching products.  
   
   
       129 . The apparatus of  claim 126 , wherein the gas analyzer is a residual gas analyzer.  
   
   
       130 . The apparatus of  claim 126 , further comprising a semiconductor or visible light transmissive wafer held on a wafer chuck in the etching chamber.  
   
   
       131 - 135 . (canceled)