Semiconductor device and method for fabricating same

Abstract

A semiconductor device includes a lower structure including a lower conductor, an upper structure having an opening exposing the lower conductor on the lower structure, and a connection structure filling the opening and connected to the lower conductor. The connection structure includes a first tungsten layer covering an inner surface of the opening and defining a recess region in the opening, and a second tungsten layer filling the recess region on the first tungsten layer. A grain size of the second tungsten layer in an upper portion of the connection structure is greater than a grain size of the second tungsten layer in a lower portion of the connection structure.

What is claimed is: 
     
         1 . A method for fabricating a semiconductor device, the method comprising:
 forming an upper structure having an opening exposing a lower conductor;   depositing a first tungsten layer covering an inner surface of the opening, the first tungsten layer defining a recess region in the opening;   performing a surface treatment process on a portion of the first tungsten layer, the first tungsten layer having a first surface treated by the surface treatment process in an upper region of the opening and a second surface not treated by the surface treatment process in a lower region of the opening; and   depositing a second tungsten layer filling the recess region, wherein sizes of tungsten grains grown from the first surface of the first tungsten layer are greater than sizes of tungsten grains grown from the second surface of the first tungsten layer.   
     
     
         2 . The method of  claim 1 , wherein a growth rate of the tungsten grains grown from the first surface is lower than a growth rate of the tungsten grains grown from the second surface when the second tungsten layer is deposited. 
     
     
         3 . The method of  claim 1 , wherein the tungsten grains of the second tungsten layer are laterally grown from sidewalls of the recess region to form an interface in a central region of the opening. 
     
     
         4 . The method of  claim 1 , wherein a depth of the recess region is greater than a half of a depth of the opening. 
     
     
         5 . The method of  claim 1 , wherein the performing of the surface treatment process comprises: performing a plasma treatment process. 
     
     
         6 . The method of  claim 1 , wherein the performing of the surface treatment process comprises: forming a metal nitride layer on a portion of a surface of the first tungsten layer.