Preserving the seed layer on sti edge and improving the epitaxial growth

Abstract

A method of forming self-aligned STI regions extending over portions of a Si substrate to enable the subsequent formation of epitaxially grown embedded S/D regions without using a lithography mask and the resulting device are provided. Embodiments include forming a STI etch mask with laterally separated openings over a Si substrate; forming shallow trenches into the Si substrate through the openings; forming first through fourth oxide spacers on opposite sidewalls of the shallow trenches and the openings; forming a deep STI trench between the first and second oxide spacers and between the third and fourth oxide spacers down into the Si substrate; forming a STI oxide layer over the first through fourth oxide spacers and a portion of the STI etch mask, the STI oxide layer filling the deep STI trenches; and planarizing the STI oxide layer down to the portion of the STI etch mask.

What is claimed is: 
     
         1 . A method comprising:
 forming a shallow trench isolation (STI) etch mask over a silicon (Si) substrate, the STI etch mask having laterally separated openings on opposite sides of the Si substrate;   forming shallow trenches in a portion of the Si substrate through the openings;   forming first, second, third, and fourth oxide spacers on opposite sidewalls of the shallow trenches and the openings;   forming a deep STI trench between the first and second oxide spacers and between the third and fourth oxide spacers down through a portion of the Si substrate;   forming a STI oxide layer over the first, second, third, and fourth oxide spacers and a portion of the STI etch mask, the STI oxide layer filling the deep STI trenches; and   planarizing the STI oxide layer down to the portion of the STI etch mask.   
     
     
         2 . The method according to  claim 1 , comprising forming the STI etch mask of nitride. 
     
     
         3 . The method according to  claim 1 , comprising forming the STI etch mask to a thickness of 10 nanometer (nm) to 100 nm. 
     
     
         4 . The method according to  claim 1 , comprising forming the openings with a width of 20 nm to 200 nm. 
     
     
         5 . The method according to  claim 1 , comprising forming the first, second, third, and fourth oxide spacers by:
 forming an oxide layer along the sidewalls of the shallow trenches; and   etching the oxide layer down to the Si substrate along a pair of opposite sidewalls.   
     
     
         6 . The method according to  claim 1 , comprising forming each of the first, second, third, and fourth oxide spacers with a width of 5 nm to 100 nm. 
     
     
         7 . The method according to  claim 1 , comprising forming the deep STI trenches by:
 removing the STI etch mask except adjacent to the first oxide spacer, but opposite the second oxide spacer; between the second and third oxide spacers; and adjacent to the fourth oxide spacer, but opposite the third oxide spacer, the portion of the STI etch mask remaining;   etching the substrate between the first and second oxide spacers and between the third and fourth oxide spacers to a depth of 100 nm to 500 nm; and   etching opposite sidewalls of the deep STI trenches at a 70° to 90° angle.   
     
     
         8 . A transistor device comprising:
 a silicon (Si) substrate;   a gate structure formed on the Si substrate;   shallow trench isolation (STI) structures formed in the Si substrate on opposite sides of the gate structure;   seed layer protection structures formed over the Si substrate on opposite sides of the gate structure; and   epitaxial structures formed in the Si substrate under the seed protection structure and the gate structure, the epitaxial structures formed on opposite sides of the gate structure.   
     
     
         9 . The device according to  claim 8 , wherein the seed protection structure is formed as part of the STI structure. 
     
     
         10 . The device according to  claim 8 , wherein the seed protection structure is formed as a nitride spacer material layer over the STI structure and extending over a portion of the Si substrate. 
     
     
         11 . The device according to  claim 8 , wherein the epitaxial structure is formed in a box-shaped, sigma-shaped, or ball-shaped cavity in the Si substrate. 
     
     
         12 . The device according to  claim 8 , wherein the epitaxial structure is formed higher than the seed protection structure. 
     
     
         13 . The device according to  claim 8 , wherein no intervening layer is present between the single spacer nitride material layer and the STI structures. 
     
     
         14 . The device according to  claim 13 , wherein no intervening layer is present between the single spacer nitride material layer and the substrate. 
     
     
         15 . A method comprising:
 forming a shallow trench isolation (STI) etch mask over a silicon (Si) substrate, the STI etch mask having laterally separated openings on opposite sides of the Si substrate;   forming shallow trenches in a portion of the Si substrate through the openings;   forming first, second, third, and fourth oxide spacers on opposite sidewalls of the shallow trenches and the openings;   forming a deep STI trench between the first and second oxide spacers and between the third and fourth oxide spacers down through a portion of the Si substrate, the deep STI trench formed by:
 removing the STI etch mask except adjacent to the first oxide spacer, but opposite the second oxide spacer; between the second and third oxide spacers; and adjacent to the fourth oxide spacer, but opposite the third oxide spacer, the portion of the STI etch mask remaining; 
 etching the substrate between the first and second oxide spacers and between the third and fourth oxide spacers; and 
 etching opposite sidewalls of the deep STI trenches; 
   forming a STI oxide layer over the first, second, third, and fourth oxide spacers and a portion of the STI etch mask, the STI oxide layer filling the deep STI trenches; and   planarizing the STI oxide layer down to the portion of the STI etch mask.   
     
     
         16 . The method according to  claim 15 , comprising:
 etching the substrate between the first and second oxide spacers and between the third and fourth oxide spacers to a depth of 100 nm to 500 nm.   
     
     
         17 . The method according to  claim 15 , comprising:
 etching opposite sidewalls of the deep STI trenches at a 70° to 90° angle.   
     
     
         18 . The method according to  claim 15 , comprising forming the STI etch mask of nitride. 
     
     
         19 . The method according to  claim 1 , comprising forming the first, second, third, and fourth oxide spacers by forming an oxide layer along the sidewalls of the shallow trenches 
     
     
         20 . The method according to  claim 19 , further comprising etching the oxide layer down to the Si substrate along a pair of opposite sidewalls.