Semiconductor transistor having a stressed channel

Abstract

A process is described for manufacturing an improved PMOS semiconductor transistor. Recesses are etched into a layer of epitaxial silicon. Source and drain films are deposited in the recesses. The source and drain films are made of an alloy of silicon and germanium. The alloy is epitaxially deposited on the layer of silicon. The alloy thus has a lattice having the same structure as the structure of the lattice of the layer of silicon. However, due to the inclusion of the germanium, the lattice of the alloy has a larger spacing than the spacing of the lattice of the layer of silicon. The larger spacing creates a stress in a channel of the transistor between the source and drain films. The stress increases I DSAT and I DLIN of the transistor. An NMOS transistor can be manufactured in a similar manner by including carbon instead of germanium, thereby creating a tensile stress.

1 . A semiconductor transistor comprising: 
 a layer having source and drain recesses formed therein with a channel between the source and drain recesses, and being made of a semiconductor material having a first lattice with a first structure and a first spacing;    a source and a drain formed in the source and drain recesses respectively, at least one of the source and the drain being made of a film material which:    (a) includes a dopant selected from one of a p-dopant and an n-dopant; and    (b) is formed epitaxially on the semiconductor material so as to have a second lattice having a second structure which is the same as the first structure, the second lattice having a second spacing which differs from the first spacing;    a gate dielectric layer on the channel; and    a conductive gate electrode on the gate dielectric layer.    
   
   
       2 . The semiconductor transistor of  claim 1  wherein: 
 (a) if the dopant is a p-dopant, the second spacing is larger than the first spacing; and    (b) if the dopant is an n-dopant, the second spacing is smaller than the first spacing.    
   
   
       3 . The semiconductor transistor of  claim 1  wherein the difference between the first spacing and the second spacing creates a stress in the channel.  
   
   
       4 . The semiconductor transistor of  claim 1  wherein the second material includes the semiconductor material and an additive, the difference between the first spacing and the second spacing being due to the additive.  
   
   
       5 . The semiconductor transistor of  claim 4  wherein the semiconductor material is silicon and the additive is selected from one of germanium and carbon.  
   
   
       6 . The semiconductor transistor of  claim 5  wherein the additive is germanium.  
   
   
       7 . The semiconductor transistor of  claim 6  wherein the germanium comprises between 1 and 20 atomic percent of the silicon and the germanium of the film material.  
   
   
       8 . The semiconductor transistor of  claim 7  wherein the germanium comprises approximately 15 atomic percent of the silicon and the germanium of the film material.  
   
   
       9 . The semiconductor transistor of  claim 4 , further comprising: 
 tip regions formed between the source and the drain with the channel between the tip regions, the tip regions being formed by implanting of dopants and excluding the additive.    
   
   
       10 . The semiconductor transistor of  claim 9  wherein: 
 (a) if the dopant of the film material is a p-dopant, the dopants of the tip regions are p-dopants; and    (b) if the dopant of the film material is an n-dopant, the dopants of the tip regions are n-dopants.    
   
   
       11 . The semiconductor transistor of  claim 1  wherein the dopant comprises at least 0.5×10 20 /cm 3  of the film material.  
   
   
       12 . The semiconductor transistor of  claim 11  wherein the film material has a resistivity of less than 1.1 mOhm-cm.  
   
   
       13 . The semiconductor transistor of  claim 1  wherein the source and drain have a depth into the layer and are spaced by a width from one another, a ratio of the depth to the width being at least 0.12.  
   
   
       14 . The semiconductor transistor of  claim 13  wherein the ratio is at least 0.15.  
   
   
       15 . The semiconductor transistor of  claim 14  wherein the ratio is at least 0.2.  
   
   
       16 . The semiconductor transistor of  claim 15  wherein the ratio is at least 0.35.  
   
   
       17 . The semiconductor transistor of  claim 16  wherein the ratio is approximately 92/215.  
   
   
       18 . A semiconductor transistor comprising: 
 a layer having source and drain recesses formed therein with a channel between the source and drain recesses and being made of a semiconductor material having a first lattice with a first structure and a first spacing;    a source and a drain formed in the source and drain recesses respectively, at least one of the source and the drain being made of film material which:    (a) includes a dopant selected from one of a p-dopant and an n-dopant; and    (b) is formed epitaxially on the semiconductor material so as to have a second lattice having a second structure which is the same as the first structure; and 
 (i) if the dopant is a p-dopant, the second lattice has a second spacing which is larger than the first spacing, so that a compressive stress is created between the source and the drain in the channels; and  
 (ii) if the dopant is an n-dopant, the second lattice has a second spacing which is smaller than the first spacing, so that a tensile stress is created between the source and the drain in the channel;  
   a gate dielectric layer on the channel; and    a conductive gate electrode on the gate dielectric layer.    
   
   
       19 . The semiconductor transistor of  claim 18  wherein the film material includes the semiconductor material and an additive, wherein: 
 (a) if the dopant is a p-dopant, the second spacing is larger than the first spacing due to the additive; and    (b) if the dopant is an n-dopant, the second spacing is smaller than the first spacing due to the additive.    
   
   
       20 . The semiconductor transistor of  claim 19  wherein: 
 (a) if the dopant is a p-dopant, the additive is germanium; and    (b) if the dopant is an n-dopant, the additive is carbon.    
   
   
       21 . A semiconductor transistor comprising: 
 a layer having source and drain recesses formed therein with a channel between the source and drain recesses, the layer being made of a semiconductor material;    a source and a drain formed in the source and drain recesses respectively, the source and the drain being made of a film material which includes a dopant selected from one of a p-dopant and an n-dopant, the source and the drain having a depth into the layer and being spaced by a width from one another, a ratio between the depth and the width being at least 0.12;    a gate dielectric layer on the channel; and    a conductive gate electrode on the gate dielectric layer.    
   
   
       22 . The semiconductor transistor of  claim 21  wherein the ratio is at least 0.35.  
   
   
       23 . The semiconductor transistor of  claim 21  wherein the depth is at least 80 nm.  
   
   
       24 . The semiconductor transistor of  claim 21  wherein the width is less than 220 nm.  
   
   
       25 . A method of forming a transistor comprising: 
 forming a gate dielectric layer on a layer of semiconductor material;    forming a gate electrode on the gate dielectric layer;    implanting dopants into the layer of semiconductor material to form doped tip regions in the layer with a channel between the tip regions;    etching the layer to form source and drain recesses in the layer with the tip regions between the recesses; and    filling the source and drain recesses with a source and a drain respectively.    
   
   
       26 . The method of  claim 25  wherein at least one of the source and the drain is made of a film material which: 
 (a) includes a dopant selected from one of a p-dopant and an n-dopant; and    (b) is formed epitaxially on the semiconductor materials.    
   
   
       27 . The method of  claim 25  wherein the source and drain have a depth into the layer and are spaced by a width from one another, a ratio of the depth to the width being at least 0.12.