Registration mark within an overlap of dopant regions

Abstract

A first mark, in a double-well integrated circuit technology, is formed by a first etching of a first mask layer on top of an ONO stack. After a first well is doped, a second etching occurs at the first etching sites in the uppermost layer of oxide of the ONO stack forming a first alignment artifact. A second mask layer is applied after removing the first mask layer. A second well doping occurs at second mask layer etching sites to maintain clearance between the two wells within active areas and provide an overlap of the two wells in a frame area. At the first alignment artifact in the overlap of the two wells, further etchings remove remaining layers of the ONO stack and remove silicon from the upper most layer of the semiconductor forming a second registration mark, which may be covered by a protective layer.

1 . A method of fabricating a device with an alignment feature, the method comprising: 
 applying at least one protective layer onto an uppermost surface of a substrate;    applying a first photoresist on the at least one protective layer;    patterning a plurality of first openings in the first photoresist;    doping the substrate with a first dopant substantially within the plurality of first openings;    removing the first photoresist;    applying a second photoresist on the at least one protective layer;    patterning second openings in the second photoresist;    doping the substrate with a second dopant substantially within the second openings;    aligning the second openings with the plurality of first openings so as to form an overlap region of the second dopant with the first dopant; and    etching a registration mark recess through both the at least one protective layer and a first portion of an upper layer of the substrate in the overlap region so as to form a registration mark.    
   
   
       2 . The method of  claim 1  further comprising: etching a registration mark artifact in an uppermost portion of the at least one protective layer within each of the plurality of first openings.  
   
   
       3 . The method of  claim 1  further comprising: 
 removing the second photoresist and the at least one protective layer; and    applying a further at least one protective layer onto the surface of the substrate and over the registration mark.    
   
   
       4 . The method of  claim 1  further comprising: 
 applying an ONO stack on to the surface of the substrate.    
   
   
       5 . The method of  claim 1  further comprising: 
 removing the second photoresist and the at least one protective layer;    applying a third photoresist on the substrate;    aligning a pattern of dopant windows in the third photoresist, the alignment being relative to the registration mark; and    doping the substrate with a third dopant.    
   
   
       6 . A method of fabricating a double-well device with an alignment feature, the method comprising: 
 applying a first layer of oxide, a layer of silicon nitride, and a second layer of oxide onto an uppermost surface of a substrate;    patterning a plurality of first openings in a first photoresist on an uppermost surface of the second layer of oxide;    doping the substrate with a first dopant substantially within the plurality of first openings forming a first dopant region;    removing the first photoresist;    patterning second openings in a second photoresist on an uppermost surface of the device;    doping the substrate with a second dopant substantially within the second openings forming a second dopant region;    aligning the second openings with the plurality of first openings so as to form an overlap region of the second dopant region with the first dopant region; and    etching a registration mark recess through the silicon nitride layer, the first oxide layer, the second layer of oxide, and a first portion of the upper layer of the substrate in the overlap region so as to form a registration mark.    
   
   
       7 . The method of  claim 6  further comprising: etching a registration mark artifact in the second layer of oxide within each of the plurality of first openings.  
   
   
       8 . The method of  claim 6  further comprising: 
 removing the first layer of oxide, the layer of silicon nitride, and the second layer of oxide; and    applying a third oxide layer over the uppermost surface of a substrate and over the registration mark.    
   
   
       9 . The method of  claim 6  further comprising: 
 removing the first layer of oxide, the layer of silicon nitride, and the second layer of oxide;    applying a third photoresist on the substrate;    aligning a pattern of dopant windows in the third photoresist, the alignment being relative to the registration mark; and    doping the substrate with a third dopant.