Method for making a semiconductor device using treated photoresist as an implant mask

Abstract

Photoresist, which contains hydrogen, is patterned over a semiconductor substrate then treated with either a molecular halogen or a liquid fluorinating agent in order to improve subsequent ion implantation. Hydrogen is replaced, to whatever extent is found desirable, with the halogen. Molecular fluorine (F 2 ) has been found to be particularly effective as the molecular halogen. Molecular fluorine (F 2 ) reacts very efficiently in replacing the hydrogen and further has the benefit of continuing to penetrate into the patterned photoresist so that the entire patterned photoresist layer can have the hydrogen atoms replaced with fluorine atoms if the molecular fluorine flow is continued long enough. The resulting treated photoresist is much more resistant to penetration by implanted ions so that the photoresist can be deposited to a lesser thickness. This is beneficial in shadowing problems such as can occur in halo implants and where the patterned photoresist has a high aspect ratio.

1 . A method of making a device structure, comprising: 
 providing a semiconductor substrate;    depositing a layer of photoresist over the semiconductor substrate;    patterning the layer of photoresist to form a layer of patterned photoresist;    flowing a molecular halogen or a liquid fluorinating agent over the layer of patterned photoresist to form a layer of treated photoresist;    performing an implant using the layer of treated photoresist as a mask to the implant to form an implanted region in the semiconductor substrate; and    completing formation of the device structure, wherein the device structure includes the implanted region.    
     
     
         2 . The method of  claim 1 , wherein the molecular halogen comprises molecular fluorine (F 2 ).  
     
     
         3 . The method of  claim 1 , wherein the molecular halogen comprises one of bromine (Br 2 ), chlorine (Cl 2 ) or iodine (I 2 ).  
     
     
         4 . The method of  claim 1 , wherein flowing the molecular halogen further comprises flowing nitrogen, wherein the molecular halogen has an atomic concentration of about 1 percent.  
     
     
         5 . The method of  claim 1 , wherein flowing the molecular halogen is further characterized as being performed at a temperature below 50 degrees Celsius and above 10 degrees Celsius.  
     
     
         6 . The method of  claim 1 , wherein: 
 the layer of photoresist comprises hydrogen; and    the flowing the molecular halogen or the liquid fluorinating agent results in replacing hydrogen atoms with halogen atoms.    
     
     
         7 . The method of  claim 6 , wherein: 
 the layer of patterned photoresist has a first thickness; and    the flowing the molecular halogen or the liquid fluorinating agent results in replacing hydrogen atoms with halogen atoms to at least half of the first thickness.    
     
     
         8 . The method of  claim 7 , wherein the replacing hydrogen atoms with halogen atoms results in replacing hydrogen atoms at substantially all depth levels of the layer of patterned photoresist.  
     
     
         9 . The method of  claim 1 , wherein the implant is a halo implant.  
     
     
         10 . The method of  claim 1 , wherein the implant comprises a well implant.  
     
     
         11 . The method of  claim 1 , wherein: 
 each of the molecular halogen and the liquid fluorinating agent comprises fluorine;    the layer of treated photoresist has a top surface;    the layer of patterned photoresist comprises hydrogen; and    the flowing the molecular halogen replaces hydrogen atoms with fluorine atoms and is for controlling a profile of fluorine atoms from the top surface to control a profile of molecular weight of the patterned photoresist.    
     
     
         12 . The method of  claim 1 , wherein the molecular halogen is flowed at a pressure of at least 120 Torr.  
     
     
         13 . A method of making a device structure, comprising: 
 providing a semiconductor substrate;    depositing a layer of photoresist over the semiconductor substrate wherein the layer of photoresist comprises hydrogen;    patterning the layer of photoresist to form a layer of patterned photoresist having an exposed top surface, a bottom surface that is closest to the semiconductor substrate, and a first thickness from the exposed top surface to the bottom surface;    flowing a molecular halogen or a liquid fluorinating agent over the layer of patterned photoresist to form a layer of treated photoresist by replacing substantially all of the hydrogen from at least the exposed top surface to half of the first thickness; and    performing an implant using the layer of treated photoresist as a mask to the implant to form an implanted region in the semiconductor substrate.    
     
     
         14 . The method of  claim 13 , wherein the molecular halogen comprises molecular fluorine (F 2 ).  
     
     
         15 . The method of  claim 13 , wherein the molecular halogen comprises one of the group consisting of chlorine, fluorine, bromine, and iodine.  
     
     
         16 . The method of  claim 13 , wherein: 
 the molecular halogen comprises about 1 percent fluorine;    the molecular halogen is carried by nitrogen at a flow rate of about 1000 standard cubic centimeters per minute (SCCM); and    flowing the molecular halogen is performed at a temperature between 10 and 50 degrees Celsius.    
     
     
         17 . The method of  claim 13 , wherein the implant comprises one of a group consisting of a well implant and a halo implant.  
     
     
         18 . A method of making a device structure comprising: 
 providing a semiconductor substrate having a first region for forming N-channel transistors and a second region for forming P-channel transistors;    depositing a first layer of photoresist over the semiconductor substrate wherein the layer of photoresist comprises hydrogen;    patterning the first layer of photoresist to form a first layer of patterned photoresist over the first region, wherein the first layer of patterned photoresist has an exposed top surface, a bottom surface that is closest to the semiconductor substrate, and a first thickness from the exposed top surface to the bottom surface;    flowing a first molecular halogen over the first layer of patterned photoresist to replace substantially all of the hydrogen from the first layer of patterned photoresist from at least the exposed top surface to half of the first thickness;    performing a well implant using the first layer of patterned photoresist as a mask to an ion implant to form an N-conductivity well;    removing the first layer of patterned photoresist;    forming a gate over the N-conductivity well;    depositing a second layer of photoresist over the first region;    patterning the second layer of photoresist to form a second layer of patterned photoresist over the first region and exposing the second region;    flowing a second molecular halogen over the second layer of patterned photoresist;    performing an angled implant to form a halo region under the gate; and    forming source/drain regions in the second region substantially adjacent to the gate, wherein the device structure is a transistor.    
     
     
         19 . The method of  claim 18 , wherein the first molecular halogen and the second molecular halogen comprise molecular fluorine (F 2 ).  
     
     
         20 . The method of  claim 18 , wherein the first molecular halogen and the second molecular halogen each comprise a same or a differing one of a group consisting of chlorine, fluorine, bromine, and iodine.