Dopant Concentration Boost in Epitaxially Formed Material

Abstract

A dopant boost in the source/drain regions of a semiconductor device, such as a transistor can be provided. A semiconductor device can include a doped epitaxy of a first material having a plurality of boosting layers embedded within. The boosting layers can be of a second material different from the first material. Another device can include a source/drain feature of a transistor. The source/drain feature includes a doped source/drain material and one or more embedded distinct boosting layers. A method includes growing a boosting layer in a recess of a substrate, where the boosting layer is substantially free of dopant. The method also includes growing a layer of doped epitaxy in the recess on the boosting layer.

1 .- 20 . (canceled) 
     
     
         21 . A method, comprising:
 (a) forming a recess in a substrate;   (b) epitaxially growing a doped layer in the recess, the doped layer being doped with first dopant;   (c) epitaxially growing an undoped layer on the doped layer, the undoped layer having vacancy sites within its structure, the vacancy sites providing respective bonding locations for dopants in a subsequently formed doped layer;   (d) epitaxially growing another doped layer on the undoped layer wherein dopants in the another doped layer bond to respective vacancy sites in the undoped layer; and   repeating steps (b, (c), and (d) until the recess has been filled to a predefined extent.   
     
     
         22 . The method of  claim 21 , wherein steps (b), (c), and (d) are repeated until the recess is completely filled. 
     
     
         23 . The method of  claim 21 , wherein steps (b), (c), and (d) are repeated until the recess is partially filled and an upper portion of the recess remains unfilled, and further comprising:
 epitaxially growing an additional doped layer to fill the upper portion of the recess.   
     
     
         24 . The method of  claim 23 , wherein the doped layer, the another doped layer, and the additional doped layer comprise the same material and the same dopant. 
     
     
         25 . The method of  claim 21 , wherein the doped layer has a first crystalline structure, the undoped layer has a second crystalline structure, and the first and second crystalline structures are different. 
     
     
         26 . The method of  claim 21 , wherein the undoped layer is undoped with the first dopant, but is doped with a second dopant different than the first dopant. 
     
     
         27 . The method of  claim 21 , further comprising:
 removing respective portions of the respective undoped layers from the respective underlying doped layers.   
     
     
         28 . The method of  claim 27 , further comprising exposing the respective undoped layers to an etching process during the epitaxial growth process. 
     
     
         29 . The method of  claim 21 , overfilling the recess with the doped layers and the undoped layers. 
     
     
         30 . The method of  claim 21 , wherein the doped layer and the undoped layer are epitaxially grown in a same processing chamber. 
     
     
         31 . The method of  claim 23 , further comprising activating the first dopant within the doped layer, the another doped layer, and the additional doped layer to diffuse the first dopant into respective undoped layers. 
     
     
         32 . The method of  claim 31 , wherein a concentration of the first dopant is higher in respective undoped layers compared to respective doped layers, after the activating step. 
     
     
         33 . A method comprising:
 forming a recess in a substrate;   at least partially filling the recess with semiconductor material by repeating a pattern of epitaxially growing respective first layers doped with a first dopant species, followed by epitaxially growing respective boosting layers, substantially free of the first dopant species, until a desired portion of the recess is filled, wherein the respective boosting layers have a high concentration of unbound first dopant bonding sites relative to respective first layers; and   activating the first dopant species to diffuse from respective first layers to respective unbound first dopant bonding sites in the respective boosting layers.   
     
     
         34 . The method of  claim 33 , wherein epitaxially growing respective first layers doped with a first dopant species is performed in a first process chamber while a first dopant based vapor is being introduced into the first process chamber, and further wherein epitaxially growing respective boosting layers is performed in the first process chamber while the first dopant based vapor is being withheld from the first process chamber. 
     
     
         35 . The method of  claim 33 , wherein respective first layers are lattice mismatched to respective boosting layers. 
     
     
         36 . The method of  claim 33 , wherein a ratio of thicknesses of respective first layers to respective boosting layers is in a range of from  10 : 1  to  2 : 1 . 
     
     
         37 . The method of  claim 33  wherein respective first layers are epitaxially grown conformally on a bottom and sidewalls of the recess. 
     
     
         38 . A method comprising:
 forming a recess in a semiconductor substrate;   epitaxially growing a first layer of doped material in the recess, the doped material comprising a semiconductor material and a first dopant;   epitaxially growing a boosting layer in the recess, wherein the boosting layer has a high concentration of unbound dopant bonding sites relative to the first layer of doped material;   growing a second layer of the doped material on the boosting layer; and   activating dopants in the first layer of doped material and the second layer of the doped material to bond with unbound dopant bonding sites in the boosting layer.   
     
     
         39 . The method of  claim 38 , wherein prior to the step of activating, the boosting layer is substantially free of the first dopant. 
     
     
         40 . The method of  claim 38 , further comprising removing portions of the boosting layer during the process of epitaxially growing the boosting layer.