Method of forming a MOS transistor

A method of forming a MOS transistor, comprising:

• providing a substrate having a gate thereon, a source region and a drain region therein with a channel region under the gate therebetween;
• pre-amorphizing the source region and the drain region to form amorphized regions;
• performing a first ion implantation to implant a first dopant in the source region and the drain region to form a first doped region;
• forming at least a spacer on the sidewalls of the gate;
• performing a second ion implantation to implant a second dopant in the source region and the drain region to form a second doped region;
• annealing the source region and the drain region to activate the first dopant, regrow the amorphized regions to a substantially crystalline form, and form a junction profile;
• and
• performing a co-implantation process, after pre-amorphizing the source region and the drain region and before annealing the source region and the drain region, to implant a carbon co-implant in the source region and the drain region, wherein the carbon co-implant is from a precursor comprising CO or CO2.