Ultra shallow junction fabrication in future ultra large scaled integrated (ULSI) technology is one of the difficult challenges in device manufacturing. Low energy ion implantation is hte most widely used technique at present to form ultra shallow junction but research has been to overcome its limitations such as crystal damage. In this research paper, thermal diffusion from spin-on dopant (SOD) into silicon has been studied in order to form shallow junction. This study was done by simulation using TSUPREM-4 from Synopsys Inc to determine the junction depth and the sheet resistance in order to fulfill the ITRS requirements. Ultra shallow junction which is defined to be less than 30 nm in depth has been obtained through this simulation using this easy and simple spin-on dopant technique. This economical spon-on dopant (SOD) technique has been proven as one promising method for shallow junction formation in future generations.